A DecADe After the emergency

Transcription

© WWF-SA/Peter Chadwick
A Decade After the Emergency: The Proceedings of the 4th
Linefish Symposium
Colin Attwood, Tony Booth, Sven Kerwath, Bruce Mann, Sean Marr,
Jorisna Bonthuys, John Duncan and Warren Potts (Editors)
Marine Technical report title: WWF South Africa Report Series - 2013/Marine/001
Acknowledgements:
This work would not have been possible without the generous
contributions of a scientists. These contributions are
acknowledged within the various papers.
Key Funders:
Charl van Der Merwe Trust
Two Oceans Aquarium
Key Partners:
Department of Agriculture, Forestry and Fisheries (DAFF)
University of Cape Town (UCT)
Citation: Attwood C, Booth T, Kerwath S, Mann B, Marr
S, Duncan J, Bonthuys J & Potts W. (eds) 2013. A Decade
After the Emergency: The Proceedings of the 4th Linefish
Symposium. WWF South Africa Report Series - 2013/
Marine/001
Published in December 2013 by WWF-World Wide Fund
For Nature (Formerly World Wildlife Fund), Cape Town,
South Africa. Any reproduction in full or in part must mention
the title and credit the above-mentioned publisher as the
copyright owner.
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page 2 | A Decade After the Emergency: The Proceedings of the 4th Linefish Symposium
A Decade After the Emergency:
The Proceedings of the 4th Linefish Symposium
Held at Geelbek, West Coast National Park, Langebaan
16th to 20th April 2012
Edited by
Colin Attwood (Marine Research Institute, University of Cape Town)
Tony Booth (Department of Icthyology & Fisheries Science, Rhodes University)
Sven Kerwath ( Department of Agriculture, Forestry & Fisheries)
Bruce Mann (Oceanographic Research Institute)
Sean Marr (Biological Sciences Department, University of Cape Town)
Warren Potts (Department of Icthyology & Fisheries Science, Rhodes University)
Jorisna Bonthuys (WWF-SA)
John Duncan (WWF-SA)
A Decade After the Emergency: The Proceedings of the 4th Linefish Symposium | page 3
Executive Summary
The fourth Marine Linefish Symposium held at Geelbek in the West Coast National Park, from
the 16th to the 20th April 2012, was attended by 71 delegates representing a variety of academic
institutions and government agencies. Linefish symposia have been held approximately
every decade, hosted by the National Marine Linefish Research Group, a productive and
ever-changing group of fishery scientists who work on species caught by the linefishery. This
symposium broke with the tradition, by not inviting fishing and industry representatives, and
not inviting papers from managers. For reasons related to the number of emerging scientists
and the disharmony emanating from rights allocation issues, it was deemed preferable to
focus solely on science. Nevertheless, of the 36 contributed papers (including four poster
presentations), not one failed to address an important management problem.
The linefishery is a collective term for a variety of unrelated fish species, united only by their
representation in the catches of linefishers, which themselves form a diverse group. Many such
fishes are also targets of other fisheries, but the linefishery retains the Pariah status among
fisheries in South Africa. Any discourse on linefish almost certainly alludes to over-exploitation,
poor control and socio-economic hardships, yet this is South Africa’s oldest commercial fishery
still in existence. Two likely reasons include (i) the diversity and low productivity of fishes,
which has failed to attract sufficient funds for the management of any one species, and (ii) the
low information content of CPUE data, which troubles conventional assessment approaches.
The linefishery is in a rebuilding phase, following the legal emergency declared in 2000, and
one of the most important themes of the symposium was an assessment of the effects of the
regulations which followed. A renewed focus on assessment resulted in a number of important
contributions, some of which, for the first time, have shown a recovery of some linefish species,
and an arrest of a century-long downward spiral.
Technological advances, and particularly the use of telemetry to study fish behaviour, resulted in
another batch of contributions, which were as facinating as they were relevant to management.
Never before have we got to know fish at such a personal level, nor can we easily comprehend
their amazing journeys.
Other contributions were based on genetic studies, examing stock structure and origins, tradedynamics, user conflict and social research. Oral presentation are reproduced here in non-peerreviewed papers, mostly condensed to 4000 words.
The symposium itself produced lively discussions and a healthy (and often frank) exchange of
opinions. Proceedings were wrapped up by summaries from Dr Kim Prochazka and Mr Dennis
Fredericks, both of the Department of Agriculture, Forestry and Fisheries, who praised the
standard of the research but also made no attempt to hide the socio-economic challenges that
have yet to be addressed.
Much gratitude is owed to the WWF and the Two Oceans Aquarium who funded the symposium,
and to WWF who funded the publication.
Foreword by Rob Tarr
Scientific Manager, Fisheries Branch, Department of Agriculture, Forestry and Fisheries (DAFF)
With a coastline of over 3000 kilometres, a sunny climate, and two oceans supporting a vast
array of marine species, it is no surprise that the South African Linefishery is both highly
active and highly productive. This productivity was recognised early, dating back to the mid1600s from early Dutch colonists. Already, by the mid 1800s, there was an active boat-based
linefishery. Yet, despite the productivity of our oceans, history has shown that the linefish
resource was not able to match the high off-take from the many users, be they commercial,
recreational or subsistence. As a result, and after sustained pressure from the research
community who provided evidence of stock collapse and unsustainable harvests, an emergency
was declared in 2000 by the then Minister of Environmental Affairs and Tourism, and the
recreational linefishing regulations were revised in 2001.
The South African Linefishery is now facing severe challenges from new sectors. An expanding
“Interim Relief” group that has been in existence for seven years, offers challenges in terms
of increased effort, as well as the difficulty of data gathering and compliance. In addition
the government’s new policy on Small Scale Fisheries is generating great interest among
prospective linefishers, who are hoping for new access rights, which in terms of the policy, will
be community based.
It is therefore imperative that there be a solid base of scientific evidence from which to derive
the advice that will be required to ensure that the threatened linefish resource is not further
weakened by unsustainable expansion of fisher effort.
In that regard, the content of this publication is welcomed, and timely. The purpose and theme
of this Symposium, which was held in April 2012 at Geelbek, Langebaan, was to assess the
effect of the major reductions in fishing effort that were imposed on the linefishery after the
declaration of an Emergency, and contributions were invited that would report on this. As a
result, we now have numerous papers covering the challenging area of stock assessment, as
well as many others reporting on movement and genetic studies. This is an important aspect
of resource management given the need to understand both stock delineation as well as the
potential benefits of marine protected areas. The important area of socio-economic research is
also reported on here, and this generated welcome and lively debate among the contributors
to the symposium. The equally important areas of fish biology as well as some long-term
monitoring studies are also reported on.
I am sure that the contents of this publication will provide a solid foundation for future advice
to our fishery managers. And we hope, therefore, that this fishery might continue for many
more centuries, to provide recreational, subsistence and commercial benefits to the people of
South Africa.
Table of Contents
Proceedings of the Linefish Symposium
Executive Summary
Foreword Background to the theme: A decade after the emergency
Session 1 - Fish Stock Assesment: Chair Tony Booth
3
4
5
9
15
The National Marine Linefish System: The largest geo-referenced marine dataset in the world
15
Model-based standardization of multispecies catch and effort data from the South African linefishery
22
Session 2 – Fish Biology Studies: Chair Bruce Mann
35
The biology and fisheries of king mackerel (Scomberomorus commerson) in the south west Indian Ocean
35
The effects of barotrauma on five South African line caught fishes
44
Preliminary results of the life history of red stumpnose (Chrysoblephus gibbiceps) an endemic seabream.
56
Preliminary findings on the reproductive characteristics of yellowtail (Seriola lalandi) in South African waters
60
Session 3 – Fish Movement Studies: Chair Paul Cowley
65
Movement patterns and genetic stock structure of an estuarine-dependent, overexploited fish species, white steenbras Lithognathus lithognathus (Teleostei: Sparidae) 65
Fish movements in the Pondoland Marine Protected Area: balancing conservation and fisheries enhancement
70
A review of the Oceanographic Research Institute’s (ORI) Voluntary Tagging Project: 27 years down the line
81
Session 4 – Fish Stock Assessment: Chair Henning Winker
89
Assessment of five South African linefish species with biomass production models
89
Long-term changes in a surf zone fish community associated with the linefish collapse
in the Eastern Cape, South Africa
103
The Kosi Bay fishtrap catches, impacts and management
108
Session 5 – Monitoring: Chair Colin Attwood
115
Monitoring the recovery of a previously exploited surf-zone habitat in the St Lucia Marine Reserve using a no-take sanctuary area as a benchmark
115
Status of chondrichthyans in False Bay
128
Attempts to contribute to a better understanding of the mortality of linefish due to recreational angling
139
Session 6 – Socio-Economic Research: Chair John Duncan
145
The recreational and subsistence linefisheries in the Knysna and Swartvlei Estuaries – some concerns and management challenges
145
Enactments, Disconcertments and Dialogues: Regarding marine social-ecological systems
through the lens of relational ontologies
160
Trade dynamics of South African Linefish
173
Session 7 – Fish Distribution and Stock Delineation: Chair Meaghan McCord
185
Movement behaviour and genetic stock delineation of a coastal reef fish species, poenskop, Cymatoceps nasutus (Teleostei: Sparidae)
185
Are changing water temperatures in the Benguela about to alter the evolutionary history
of our Argyrosomus fishes?
194
Identification of a warming hotspot in the northern Benguela, and the possible effects of this on Argyrosomus coronus 201
Session 8 – Fish Movement Studies: Chair Tor Næsje
207
The genetic stock structure of Slinger (Chrysoblephus puniceus) in the South West Indian Ocean 207
Does the restricted movement paradigm apply to the estuarine-dependent spotted grunter Pomadasys commersonnii?
212
Spatio-temporal dynamics of fish and fisheries in the Breede River estuary, South Africa
218
Patterns and volumes of commercial and recreational harvest of white stumpnose in Saldanha Bay: an assessment of the fishery
224
Notes on the spatio-temporal behavior of the smoothhound sharks of Langebaan Lagoon 232
Session 9 – Fish Stock Assessment: Chair Sven Kerwath
241
A comparison of the commercial and recreational sectors in the Port Alfred linefishery and their response to management changes between 1985 and 2008
241
An assessment of the shorefishery for largespot pompano, Trachinotus botla, in KwaZulu-Natal, South Africa
242
Standardization of the Catch per Unit Effort for albacore (Thunnus alalunga) for the South African tuna-pole (baitboat) fleet for the time series 1999-2010
253
Session 10 – Miscellaneous: Chair Chris Wilke
260
Variation in shore-angler effort on the South African coast 1994 -2011
260
Baited Remote Underwater Video (BRUV) in the Stilbaai Marine Protected Area: a survey of reef fish with an assessment of monitoring requirements
261
Competition between line and trawl fisheries on the Cape south coast
Poster Contribution
267
278
Shore-based recreational angling catches and catch per unit effort adjacent to Agulhas and West Coast National Parks
278
Background to the theme: A decade after the
emergency
Colin G. Attwood
Associate Professor
Marine Research Institute, Zoology Department, University of Cape Town
It gives me pleasure as chairman of the National Linefish Research Group to introduce the
proceedings of the 4th Linefish Symposium, held at Geelbek from the 16th to 20th April 2012.
The National Linefish Research Group represents a remarkably cohesive, co-operative and
productive group of scientists - a group that, despite succession (I believe that only Bruce Mann
has attended all four symposia), has been in existence for almost 30 years. Scattered across the
country, the linefish scientists are employed at a variety of government research institutions,
museums and centres of higher education. This diversity is part of the strength of linefish
research. But whereas the scientists are a productive group, the same cannot be said of the fish.
Linefish research is a remarkably difficult subject to describe, partly because it is so varied in
scope and partly because of the diversity of linefish itself. In the words of Lees (1969):’...the
inshore fishermen provides the variety but not the bulk of the nation’s fish diet’. This time the
diversity is the Archilles heel of the fishery, as I will try to explain in the following paragraphs.
You would have noticed that Microsoft’s spell-checker puts a red line under the term ‘linefish’.
Is it trying to tell us that there is no such thing? Linefish, which make up at least 10% of our
marine fish diversity, are scattered across the taxonomic spectrum, and occupy every habitat
on the continental shelf, and some beyond. It would be very difficult to gain consensus on a list.
And just as an aside, is it appropriate to define fish according to the methods we use to harvest
them? There is some precedent in the word ‘game’, which, although still in use, has transcended
its origin.
I thought I might tackle the problem of linefish definition empirically. I got hold of
comprehensive data sets of fish catches, covering over 500 species, and eight fisheries and
conducted a similarity analysis among the species on the basis of their fractional contribution
to each South African fishery. I expected to get a clear ordination of species from which I could
identify the targets of each method, but the exercise served only to emphasis the extent of
overlap (Figure 1). Silver kob for example are caught in trek nets, by shore anglers, in trawls, yet
we think of it as a commercial handline species. Several species are drawn to the centre of the
ordination, not being exclusively targeted by any single fishery. This pattern makes it difficult
to isolate causes of fish declines for many species, it complicates stock assessments and allows
fishers plenty of scope to blame ‘others’.
At least I know what linefishing refers to. But even here I had a moment of insecurity when
paging through an authoritative text book on fisheries (Jennings et al. 2002). Is it possible
that Simon Jennings forgot about linefishing in his chapter on fishing methods employed
throughout the world? His discourse covers every commercial fishing method imaginable from
trawling to fishing with cormorants, but no mention of handlines and hook and bait fishing.
Perhaps linefishing is an anachronism. After all, Gilchrist and his successor, von Bonde, strongly
encouraged South African fishers to progress beyond their primitive ways, and embrace the
industrial-scale methods of trawling and purse-seining, and trammel and set-nets. Von Bonde
(1933), had this to say [my inserts]:
‘During the last few years considerable advances have been made in the types of craft [referring
largely to the installation of engines] employed in the inshore [line] fisheries, but the actual
fishing methods have not kept pace with these improvements, and in fact the inshore fishermen
of today still practise the methods utilized by their forbears about a century ago.’
In the ensuing 80 years the craft have continued to improve, and yet the basic elements of the
linefishing method have remained: manually operated lines, day-trips, no cold storage, no value
added production, and, critically, no bargaining power on the part of the fishers. Without the
ability to slowly release their product on the market, fishers are exposed to catch fluctuations
and the vagaries of supply and demand.
Figure 1. A multi-dimensional scaling plot of similarity among fish species on the basis of their
representation in catches of different fisheries. Colour code for symbols: Silver=Silver kob,
Amber=longfin tuna, Turqoise=anchovy, Brown=Mini kob, Majenta=spotted grunter, light
grey=galjoen
Gilchrist and Von Bonde played a major role in developing the trawl fisheries, but they never
succeeded in diminishing enthusiasm for linefishing. In fact, Scott’s descriptions of the trawl
grounds (Scott 1949) and the linefish grounds (Scott 1951) at the end of WWII would almost
suffice today. Why did the linefishing method remain virtually unchanged in South Africa,
whereas other countries turned to longlines, gillnets and pots to fish rocky grounds? The answer
is possibly the lack of suitable harbours for larger vessels.
I mention this bit of history, not to attempt to resolve the claims of linefisher’s, but to
contemplate why our oldest and least altered fishery should find itself in such a parlous
state. What are the reasons that linefish feature negatively in any discussion on fisheries
sustainability in South Africa? Most articles, scientific and popular, give the impression that
it is the typical combination of life-history traits that render linefish unproductive - high
longevity, hermaphroditism, territoriality etc. But given the high diversity and degree of
taxonomic distinctiveness among linefish, this cannot be the ultimate cause. A more plausible
explanation lies in the economics of the fishery. From the earliest 1900’s, the linefishery was
cast in the primitive role, with the real resources being directed at more lucrative operations
and industrial-scale activities. On a species-by-species comparison, the two hakes generate
easily one hundred times greater revenue than the top linefish species. Despite this, the effort
dedicated to the study of the biology of the harvested fishes themselves is not inequitable. In
fact, our biological knowledge of hake is rather disappointing, and certainly well behind that
of many linefish species, but hake’s post-EEZ recovery rates as a rare success in Africa and the
world. In contrast, the majority of linefish are believed to be over-exploited. I can only conclude
that the skewed revenue allocation has disadvantaged the linefishery at the level of management
and compliance.
Although I believe that the best efforts were made under the circumstances, I must report that
assessments of linefish species to date have been unreliable. Most commonly, spawner biomass
per recruit (SB/R) models were used to calculate the likely impact of fishing mortality rates,
measured from size-distributions, as a percentage drop in SB/R. These declines were frequently
over 90%. The SB/R statistics have been incorrectly taken to assume that stocks are depleted to
these levels. I am aware that Griffiths (2000) reported a correlation between SB/R depletions
and biomass (B/Bk,) depletion, but the two metrics refer to very different quantities. If I were
to hazard a guess, I would say that the SB/R estimates were optimistic, judging from the likely
biases in the estimation of fishing mortality rates.
In many cases low SB/R estimates were confirmed qualitatively by other sources of information,
and these successfully formed the motivation for the much-quoted (and misquoted) emergency
in the linefishery in 2000. The primary aim of the emergency was to enable a substantial
reduction in effort in the commercial fishery. Nominally the reduction was a 70% removal of
boats, although the effective reduction was probably lower, as the more efficient boats remained.
Politicians are regularly lambasted for their reluctance to act effectively in fisheries, even
when signs of stock depletion are clear. Not this time. In Valli Moosa we had a Minister who
responded decisively. The scale of the intervention was unprecedented among fisheries globally.
But I have to ask - now twelve years later - why has no attempt been made to assess the impact
of the reduction? For a stock assessment scientist, the cut should have been a gift. The contrast
in the time series is precisely what is needed to test the response of the resource.
Was it because we had not been collecting data? No. On the contrary, the National Marine
Linefish System (NMLS) is a massive, continuous and comprehensive set of catch records dating
back to 1985. In fact, it has been rated as the largest geo-referenced set of biological data in the
world! Are South Africans hopeless at stock assessment? Again not. South African universities
have produced and continue to produce very capable stock assessment scientists, many of whom
ply their trade in the USA, the UK, Arabia, the Antipodes and the FAO, where they are highly
regarded.
The answer is more technical. Firstly, it is not useful to repeat per-recruit estimates. An
assumption of the per-recruit model is that there is no inter-annual trend in recruitment, yet
this is exactly what we hoped would happen by eliminating 70% of the fishing boats. What perrecruit models amount to is a method of assessment that only works when nothing changes.
This is unfortunate, as SB/R is the one model that many linefish biologists (who are happier at
sea than in front of a PC) have mastered. Fitting age-structured production models is now the
industry standard, but for most of us this is close to voodoo. Production models rely on an index
of abundance, which in the context of the linefishery is almost certainly catch-per-unit-effort
(CPUE). The abundant CPUE data in the NMLS are low on information content. With so many
species in the linefishery, and no indication of targeting, how does one apportion the effort
among the species? Does a zero catch for species X imply no fish, or no attempt at catching that
species. A brave attempt at solving this problem appears in these proceedings.
One change to the management of all fisheries since the last linefish symposium has been the
introduction and profound influence of eco-labelling. Eco-labels, such as the South African
Seafood Initiative (SASSI) and the Marine Stewardship Council have appropriately brought
public opinion into the fisheries management arena, and have adjusted the relationship between
the fishers and the government regulator. It is no longer sufficient for fishing enterprises to
satisfy the law - both the regulator and the fishers need to satisfy public opinion if the products
are to maintain market share. In South Africa, scientists are being consulted to provide SASSI
with linefish assessments at the level of the stock and - to be blunt - this eco-labelling agency has
done so with greater urgency and rigour than the government regulator up until now.
The information content of CPUE data itself is imperilled by the very restrictions we put on
fishers. Bag and size limits by their very action will reduce the catch rate (the pessimist will say it
has no effect at all), but such reductions have no relation to stock size. To date such effects have
not played an important role in our thinking on regulation, but this may need to change with a
renewed focus on CPUE.
The severity of depletion of some species has resulted in complete closure of fisheries, such
as the seventy-four. Closing fisheries: is it sensible, considering the need to maintain a data
stream? Red steenbras is the latest to be shut. A quote from Biden provides some motivation for
protecting red steenbras: “It is difficult to account for the present scarcity - the few hundreds,
as compared with the thousands of twenty years ago.....” He wrote this in 1930. Considering
that the real pressure on this species escalated from the 1970’s when ski-boats proliferated
(Penney et al. 1989), and that the species has disappeared from much of its coastal range, this
drastic step would seem to be necessary. But I have to ask how we now propose to monitor a
recovery if the catches are outlawed. Whereas ski-boat anglers maintain that unintentional
catches of seventy-four are now common place (hinting at a recovery since the ban on that
species), scientific surveys are too few and too small (i.e. it is too expensive) to detect a recovery.
What alternatives can we offer? The preliminary trials with Baited Underwater Videos featured
in these proceedings may offer hope.
Marine protected areas (MPAs) are a theme that ran through many presentation at the
symposium. Whereas other fisheries rely heavily on total allowable catch (TAC) or effort
control, the linefishery in its recreational, subsistence and commercial guises, needs MPAs
to maintain a critical level of spawner biomass. Linefish scientists find ample evidence to
support this method of fishery control, but debates rage with traditional stock assessment
modellers and social scientists. The stock assessors (e.g. Walters et al. 2007) theorise that
fisheries are more efficiently managed by way of quota management (but can it be practical and
economically viable in the linefishery?), while the sociologists highlight the unfairness in the
system. MPAs, if carelessly designed, may bring unnecessary hardship to some communities
(Hilborn et al. 2004). I will leave it to those groups of scientists to show me a better system
- until then we should regard our twenty or so coastal MPAs as the backbone of linefish
sustainability. Conservation is far from an exact science. I am reminded of Pinchot’s adaptation
of the utilitarian principle of conservation: ‘ the greatest good to the greatest number - and
that for the longest time.’ Fortunately, the overlap of objectives of fisheries management and
biodiversity protection are increasingly being recognised (Rice et al 2012).
The success or otherwise of MPAs has driven research into fish movement and behaviour.
Whereas the conventional tagging methods continue to provide useful data on fish behaviour,
it is the telemetry contributions which provide exciting and novel insights. Never before have
we got to know fish on a such a personal level. The day-to-day behaviour of fish in relation
to environmental cues sheds light on the rôle of climate change in fishery dynamics. Several
telemetry studies are included in these proceedings.
The theme of the symposium - A decade after the emergency -was intended to highlight the
most recent attempts by members of the linefish working group to fit age-structured production
models and to spark a discussion on the possible recovery of the linefishery. (As a personal
aside: having been involved in linefish research for over 20 years, I would regard my career as
something of a failure if we were not able to turn around the fortunes of South Africa’s most
iconic fishes and the fishermen who depend on them.) More broadly, the symposium aimed
to discuss recent trends across all habitats, with respect to effort and population sizes, and to
highlight novel research approaches and technology, including genetics, telemetry and a new
angle on sociological research. The latter takes most linefish biologists well outside their comfort
zones, but I see a real need to engage on these issues. After digesting this volume, I am sure you
will agree with me that linefish research in South Africa is as strong as ever.
A comparison between the 3rd and 4th Symposia shows an interesting shift in the subject of
papers, much of which was driven by new technology (Table 1). The decision to eliminate
management contributions was not easy, but was necessitated on the grounds that the number
of researchers had grown, and that young scientists needed a platform to expose their work.
Whereas managers were invited to participate in discussions, it was decided to keep the focus
on science rather than on management. Allocation disputes in the fishery have escalated and
diversified, and the management issues related to these problems in all likelihood would have
swamped the scientific debates. It was felt that these issues were best left for more appropriate
fora. But as you will see, there is barely a paper in these proceedings which is not directly
applied to a management problem.
It remains for me to thank WWF-South Africa and the Two Oceans Aquarium, who sponsored
this symposium and the publication of the proceedings, in equal measure. We are most
fortunate for the interest shown by these organisations.
Table 1. Breakdown of contributions by subject, in the 3rd and 4th Linefish Symposium
Subject
3rd
4th
Stock assessment
2
8
Monitoring
3
7
Fish Biology
1
4
Socio-economic
0
4
Fish movement & distribution
5
11
Surveys
9
0
Marine protected areas
4
1
Management
9
1
Ecosystem
1
0
Research prioritisation
1
0
Total
35
36
References
Biden CL 1930. Sea-angling fishes of the Cape. London: Oxford University Press.
Griffiths MH 2000. Long-term trends in catch and effort of commercial linefish off South Africa’s
Cape Province: snapshots of the 20th century. South African Journal of Marine Science 22:
81-110.
Hilborn R, Stokes K, Maguire J-J, Smith T, Botsford LW, Mangel M, Orensanz L, Parma A, Rice
J, Bell J, Cochrane K, Garcia S, Hall SJ, Kirkwood GP, Sainsbury K, Stefansson G, Walters C.
2004. When can marine protected areas improve fisheries management? Ocean and Coastal
Management 47(3-4): 197-205.
Jennings S, Kaiser MJ, Reynolds, JD 2001. Marine fisheries ecology. Malden: Blackwell Publishing.
Lees R 1969. Fishing for fortunes. the story of the fishing industry in southern Africa and the men
who made it. Cape Town: Purnell.
Penney AJ, Buxton CD, Garratt PA and Smale MJ 1989. The commercial linefishery. In: Payne AIL,
Crawford MJ (eds), Oceans of life of southern Africa. Cape Town: Vlaeberg. pp 214-229.
Rice J, Mokness E, Attwood C, Brown SK, Dahle G, Gjerde KM, Grefsrud ES, Kenchington R, Kleiven
AR, McConney P, Ngoile MAK, Næsje TF, Olsen E, Olsen EM, Sanders J, Sharma C, Vestergaard
O, Westlund L (2012) The role of MPAs in reconciling fisheries management with conservation
of biological diversity. Ocean and Coastal Management 69: 217-230.
Scott P 1949. Otter trawl fisheries of South Africa. Geographical Review, 39(4): 529-551.
Scott P 1951. Inshore fisheries of South Africa. Economic Geography 27(2): 123-147.
Solano-Fernández S, Attwood CG, Chalmers R, Clark BM, Cowley PD, Fairweather T, Fennessy
ST, Götz A, Harrison TD, Kerwath SE, Lamberth SJ, Mann BQ, Smale MJ, Swart L (2012)
Assessment of the effectiveness of South Africa’s marine protected areas at representing
ichthyofaunal communities. Environmental Conservation 39(3): 259-270.
Von Bonde C 1933. Report of the Fisheries and Marine Biological Survey for the year ending
December, 1932. 10: 32-84.
Walters CJ, Hilborn R and Parrish R 2007. An equilibrium model for predicting the efficacy of
marine protected areas in coastal environments. Canadian Journal of Fisheries and Aquatic
Science 64: 1009-1018.
Session 1 - Fish Stock Assesment: Chair Tony Booth
The National Marine Linefish System: The largest georeferenced marine dataset in the world
SE Kerwath1,2 , H Winker1, and CG Attwood1
1
Zoology Department, University of Cape Town, Private Bag Rondebosch 7700, South Africa.
2
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, South
Africa.
Introduction
‘Linefishery’ is a South African term for a cluster of multi-species, multi-user fisheries in
the country that target marine or estuarine organisms by means of hand-lines or rod and
reels (i.e. longline fishing is not included). The National Marine Linefish System (NMLS), a
database housed by the Linefish Section of the Fisheries Research Division of the Department
of Agriculture Forestry and Fisheries (DAFF), is the primary repository for all data related to
the South African Linefishery, which includes recreational angling, commercial boat-based
linefishing and, to a certain point in time, squid jigging. A recently published book on the results
of the ‘Census of Marine Life’ mega-project (McIntyre 2010) lists the NMLS with 2.7 million
records as the largest dataset available within the Ocean Biographic Information System (OBIS),
with the Sir Alistair Hardy Foundation zooplankton database a distant second (1.3 million
records) and all listed European and North American initiatives far behind. On individual
species level, the NMLS entries of Cape snoek, Thyrsites atun, makes it the most recorded
organism ahead of the Arctic fulmar, a seabird, and the common dab, a pleuronectiform fish
abundant in northern European waters. Although there might be bigger datasets of marine
organisms not made available to the Census of Marine Life, the NMLS compares well with
international datasets from some of the most renowned marine biological research centres
in the world, a fact that is not widely recognised, even to people familiar with this system.
The purpose of this contribution is therefore to: (1) re-introduce this database to the wider
community of fisheries and marine biological scientists, fisheries managers and stakeholders,
(2) provide a brief inventory of the data collected thus far, (3) discuss challenges associated with
the NMLS, in particular with regard to data validity, accessibility and spatial integrity, and (4)
provide an outlook into the future of this initiative.
History
South Africa has a long history of systematic recording of fisheries related data. In 1896,
John Dow Fisher Gilchrist was appointed as the Government Marine Biologist at the Cape of
Good Hope. Professor Gilchrist started recording landings of trawl and linefish catches from
harbours around the Cape of Good Hope in addition to recording of survey data collected
during experimental trawling and linefishing from a research vessel. These surveys were
continued by his successor Dr. Cecil Von Bonde, but this data stream ends during World War
II. New initiatives to collect linefish related data were initiated in the seventies at two different
institutes, the Oceanographic Research Institute (ORI) in Durban and the Sea Fisheries
Research Institute (SFRI) in Cape Town. Whereas ORI was collecting catch and effort data
from recreational shore and boat anglers, sourced mainly from voluntarily submitted catch
cards and angler interviews, the SFRI focused on commercial catches recorded in the form of
daily landings from fisheries harbours (in the tradition of Gilchrist); dealer returns, and from
voluntarily submitted catch return forms from some commercial fishers operating in more
remote areas with little or no harbour infrastructure, such as Struisbay and Port Alfred (Penney
A Decade After the Emergency: The Proceedings of the 4th Linefish Symposium| page 15
1994). According to Andrew Penney, the head of the linefish research section at the SFRI in
the 1980s, the NMLS initiative was born when ORI approached SFRI for funding to cope with
the ever growing administrative requirements for the collection of recreational angler data,
which, at the time, already included data from shore angling patrols carried out by the Natal
Parks Board. After much deliberation between the two institutes the SFRI as a governmental
organization assumed full responsibility for administration and collection of linefish related
data. In 1983, the linefish research section was established at the SFRI and the development
of the NMLS was initiated. In 1985 the linefishery was formally recognized and catch returns
where made mandatory for commercial fishers.
The NMLS data was stored with dumb terminals in a hierarchical INFOS database with
programs were written in COBOL on a mini computer (MV10000) installed in some SFRI’s
offices at the Foretrust building. ORI retained the collection and capture of recreational angler
data under contract. ORI captured their data on an HP9825 (small device with limited memory
and space). The SFRI then installed a mini computer (DG30) with limited capacity with dumb
terminals in a computer room at ORI, where the data was stored in the INFOS database
using the SFRI programs. The SFRI maintained a staff complement at the ORI office and the
data was downloaded onto a floppy disk and dispatched to Cape Town on a weekly basis, and
uploaded into the NMLS at the SFRI. Later, a Diginet line was installed and the ORI office could
directly connect to the SFRI. In the 1990s, the yellowtail and the tuna pole dataset were added
and the first summary reports were developed, to fulfil reporting requirements to ICCAT. In
1995 the NuTek project was initiated to transfer all data and programs (not only the NMLS)
off the MV10000 as this computer was not Y2K compliant. Sybase was used as the backend
database server which the front end application was written in Delphi. The development of
the NMLS on Sybase was completed in 2001. The NMLS programs were written for a client/
server configuration and consist of two units; the Linefish_data and Linefish_reports. The
Linefish_data was developed for the capturing of data whereas the Linefish_ module was
designeds to extract the information. In 2004, a further upgrade to the data systems, the Marine
Administration SysTem (MAST) application, was initiated at the SFRI, now called Marine
and Coastal Management. MAST is a web-based application written in Java with Oracle as
the database backend. The original vision was that MAST integrates all information related to
fishing rights ranging from catches to levy declarations. Due to various constraints in budget,
skills, commitment and buy-in, not all the catch systems (NMLS is one of them) have been
transferred to MAST such that, at present, the NMLS being still run on the now outdated Sybase
system with little development since a decade ago. Since 2007, the commercial catch data and
the observer data have been exported to MS access format to facilitate analyses and reporting.
Inventory of data
By the end of 2011, the NMLS contained more than 5 million individual records of species per
boat or per shore angler day. The data can be categorised into several different data series (Table
1). Most of the data were collected from 1985 onwards; however some data such as yellowtail
size frequencies go back to the 1970s.
Although data were consistently recorded for the last 26 years, data volumes fluctuate
considerably between years and between categories (Fig. 1). Commercial catch returns dropped
considerably with the state of environmental emergency in the linefishery in 2000, which lead
to a drastic reduction in effort. The drop in voluntary, recreational catch reporting around the
same time is more difficult to explain but might be related to uncertainty regarding the changing
fisheries management measures at the time. The shore patrol data from KZN has increased
considerably, whereas the dealer and harbour return data streams have almost ceased, mainly due
to the voluntary nature of these reports and a reduction in communication between research and
compliance staff at the Department of Agriculture, Forestry and Fisheries (DAFF), which has been
subjected to considerable restructuring and is currently split between two national departments.
Observer data, length frequency data and biological data appear to be cyclic. These can be
explained by the existence of national surveys and national observer programmes which are often
run for limited time periods. At the time of the writing of this article, the last linefish observer
programme ended in March 2011 with no further observer programmes planned.
Table 1: A summary of data stored on the National Marine Linefish database. Note that number of
records is expressed as number of individual species recorded per day per boat or per shore angler.
For the length frequency and biological data, data for individual fish are recorded (i.e. length).
Data type
No. of records (Species per day per boat or shore angler)
Commercial catch returns
Harbour returns
Dealer returns
Recreational angling
Observers
Length frequencies
Biological data
3,333,971
108,776
78,483
1,257,177
87,594
505,440
16,875
Figure 1: Volumes of data recorded per year from the development of the National Marine
Linefish System in 1985 to end of 2011, expressed in number of species per day per boat, or
shore angler.
Challenges
Since the inception of the NMLS, there has been criticism and scepticism of the system from a
number of different sectors. Scepticism regarding the validity of the data has been expressed
(Penny 1994): ” …one of the main criticisms ... of the NLMS … is that much of the data captured
are incorrect, or greatly under- or over-reported by fishermen…”. Penney further observed
that “…criticism of the NMLS … always escalates sharply whenever data are used in support of
unpopular management measures…”. Now, almost 20 years after Penney’s observations, little
has changed regarding these perceptions, but recent developments have provided confidence in
the validity of the data increasing researchers leverage to convince the stakeholders of the validity
of specific data streams. The commercial data returns which represent the largest, and in many
respect the most important dataset within the system, have been mandatory since 1985 and
represent log book entries of catches per species per day. Although the reported catch is essentially
an estimate by the skipper, it is thought to be accurate within 10% as the weight of a full bin of fish
is known. The validity and the accuracy of the data can be assessed by comparing these to data
recorded from linefish observer programmes, which provide an independent recording of catch
returns for a subset of linefish boat outings. The comparison of a subset of data from 2011, 800
species/day records from a cross-section of species, slinger, kob, carpenter, hottentot, geelbek
and santer revealed little difference between reported and observed catch returns with a mean
percent error of 5.76% (Fig. 2). The distribution of the differences in reported to observed catches
was symmetrical around zero (median=0), indicating no systematic over- or under-reporting.
Furthermore, the total catch between the observer and the skipper estimates only differed by 8%,
confirming the perceived accuracy of the catch reporting. Although this analysis is preliminary,
as it does not contain any information of nil-reporting or species-specific bias, the results are
encouraging and should strengthen the confidence in the reported data.
Another criticism that has persisted since Andrew Penney’s time is that NMLS data is not
easily assessable. However, in 1994 Anesh Govender, a linefish scientist then working at ORI,
remarked: “The fact that the raw data can be downloaded as a sequential file to a PC means
that the researcher … can quite easily parse the data. Then extracts and computations can
quite easily [be] done on PC.” Govender’s remark demonstrates the main issue with assessing
the NMLS: retrieving the data from the database. While output summaries are available for
common reporting requirements, the system in its current format does not allow for customised
queries and the raw data has to be extracted and manipulated prior to in-depth analyses.
Whereas this does not a a challenge to most fisheries modellers, such as Govender, many
biological scientists have not been trained to manipulate large, complex datasets. For the NMLS,
this problem is exacerbated by the absence of continuous metadata recording and up to date
documentation. However, requests for access to NMLS data are as frequent today as they were
in 1994 (1- 4 /month). Moreover, since 2008, the NMLS has been exported into a more user
friendly Microsoft Access database, allowing the users to construct their own queries.
Relative Frequency
Difference between reported and observed catches (kg)
Figure 2: Relative frequency of differences between observed and reported catches for 800 catch
return records in 2011. Data from five species from all three management zones were included.
Spatial integrity
The MS-Access format also allows for a direct connection to Geographical Information System
software such as ArcView and ArcGIS. However, the system of recording catch location in the NMLS
does not allow for direct plotting in GIS as it does not include geographical coordinates. Fishing
locations are captured according to a shore code and a distance offshore. In 2010 these codes were
translated into a 5X5 nautical mile grid system identical to the one used by the demersal research
section. The positions were assigned to the grid blocks by first determining a latitude and longitude
for every offshore distance associated with a shore locality by getting a bearing approximately
perpendicular to the shoreline at the point of the shore locality. These points, along the bearings
were then linked to the respective grid-blocks that they fell within (Fig. 3).
Figure 3: The geo-referencing of the shore code-offshore distance system into the linefish grid,
a 5X5 nautical mile grid system.
Whereas this system has been shown to be sufficient for tested positions within the first 10
nm from shore in areas where the coastline is relatively straight, it might not work as well
in case of offshore positions and within large bays such as Algoa Bay. It is anticipated that
inaccuracies in the assignment of known fishing positions to geographical coordinates will be
discovered and rectified once the system is used more widely by the linefish research fraternity.
The geo-referencing of the NMLS codes constitutes the first tool to visualize this dataset. Here
we provide two examples, the distribution of species diversity in the catch (Fig. 4) and the
distribution of total catch weight (Fig. 5).
Conclusions
The National Marine Linefish System has clearly been the single most important data source
for linefish related research over the past two and a half decades. A quick search of citations
using Google scholar reveals that more than 200 published papers have made use of NMLS
data. Moreover, the NMLS forms the basis of most linefish related fisheries management
recommendations, and countless management reports and working group documents are in
one way or another based on information stored on the NMLS. The NMLS has undergone many
changes during the 26 years of its existence. Fortunately, thanks to the dedicated staff of the
Linefish research section of DAFF and their ORI counterparts, the standards of data validation
and controls and the upkeep of the development of the system with technological advances
have largely been maintained through many challenges, including change of government
departments, funding and skill shortages and a lack of interest by decision makers.
Figure 4: Distribution of species richness in the catch of the commercial linefishery plotted on
the linefish grid. The light green represents 1-5 species, the darkest green 50-97 species.
Figure 5: Distribution of total catch weight for linefish plotted on the linefish grid.
Acknowledgements
We wish to thank Christopher Wilke and Marileen De Wet for providing invaluable information
and insights on the early years of National Marine Linefish System.
References
McIntyre AD. 2010. Life in the world’s oceans : diversity, distribution, and abundance. In: Van den
Berghe E, Stocks KI. Grassle JF (eds.), Data integration: The Ocean Biogeographic Information
System. Wiley-Blackwell, Chichester; Ames, Iowa. pp 333-353.
Penney AJ. 1994. An assessment of the National Marine Linefish System. Sea Fisheries Institute
Internal Report No. 128, Cape Town.
Model-based standardization of multispecies catch
and effort data from the South African linefishery
H Winker1, SE Kerwath2,1, CG Attwood1
MA-RE Institute, Zoology Department, University of Cape Town, South Africa.
2
Department of Agriculture, Forestry and Fisheries, Cape Town, South Africa.
1
Introduction
In South Africa, the boat-based commercial ‘linefishery’ provides an example of a multispecies fishery, in which more than 200 fish species are caught by handline or rod and reel
over a large geographical range (Solano-Fernàndez et al. 2012). In the late 1990’s, decreases
in catches and spawner-biomass per-recruit assessments indicated alarming states for many
linefish stocks, which subsequently lead to the declaration of a state of emergency in this fishery
in 2000, followed by a significant, forced reduction in commercial effort. To date, a decade
later, quantitative assessments of the impact of these management interventions, which were
designed to allow the stocks to recover, are overdue.
Fisheries-dependent catch and effort data represent one of the most important data sources
used as a measure of abundance in many stock assessments (Quinn and Deriso 1999),
particularly in coastal multi-species fisheries or stocks with large spatial distributions for which
it is not economically feasible to collect sufficient fisheries-independent data. In South Africa,
mandatory catch and effort returns from the boat-based commercial linefishery have been
captured in the National Marine Linefish System (NMLS) since 1985. This database system was
developed to archive and analyse recreational and commercial linefishing data and is hosted by
the Department of Agriculture, Forestry and Fisheries (DAFF). The raw data from the NMLS
should be used cautiously because changes in spatial and temporal effort allocation, and fishing
behaviour, result in time-varying catchabilty that need to be accounted for in analyses using this
data (Maunder and Punt 2004).
In particular, the adjustment for fishing behaviour can be a challenging task within a multispecies context because the available catch information may reflect a variety of alternative
fishing tactics associated with different target species, even within a single fishing trip (Stephens
and MacCall 2004; Palmer et al. 2009). Here, the term ‘fishing tactic’ (FT) is defined as a
sequence of decisions made a skipper at sea, which may involve choices of gear, fishing ground
and habitat-type (Marchal et al. 2006), while the term ‘targeting tactic’ denotes a particular
choice associated with one or more target species. The choice of FT can be complex and may
be influenced by the preference of the skipper, market conditions, fisheries regulations and the
population dynamics of the various stocks targeted by the fishery (Hilborn and Walters 1992;
Pelletier and Ferraris 2000). As a particular targeting tactic allocates effort towards a target
species or species-complex, it also alters the catchability (i.e. fraction of biomass/abundance
caught per unit effort) of other species. The use of CPUE as an index of abundance assumes that
catchability for the species under assessment is constant and, therefore, critically relies on the
ability to standardize for effects that impact on catchability other than abundance (Maunder
and Punt 2004). Consequently, ignoring the effect of heterogeneous FTs in the standardization
process may result in severely biased abundance indices and subsequent misinterpretation of
the resource status.
In this paper, we apply Generalized Additive Models (GAMs) to standardize the CPUE for two
commercially important linefish species, carpenter (Argyrozona argyrozona) and silver kob
(Argyrosomus inodorous), for spatial and temporal dynamics in effort allocation and fishing
behaviour. Specifically, we explore two approaches to adjust for the heterogeneity of targeting
strategies in this multispecies handline fishery.
Material and Methods
Theoretical basis for standardizing across fishing tactics
The idea of standardizing for multi-species targeting is to remove from the total variation in
the CPUE data that component which is attributed to the direction of targeting. A common
assumption of multi-species standardization approaches is that information on the direction
of targeting can be found in the species composition of the catch (Pelletier and Ferraris 2000;
Carvalho et al. 2010). From the mix of species in the catch (not the quantity of catch), a model
can be used to estimate the degree to which a particular species was targeted. It follows that
some combinations of species will tend to co-occur in catches, whereas others will be negatively
correlated (they may be allopatric or be susceptible to alternative gear types), and yet others will
show very little correlation, either positive or negative.
A simple four-species assemblage is used to illustrate the concept (Fig.1). Consider data from
three separate fishing trips, collected on the same day: x, y and z. Although the CPUE of a
particular target species T varies among them, the abundance of species T is common on
the day, so the source of variation in CPUE is attributed to targeting, for which the species
composition, illustrated in the pies, holds information (Fig. 1b). Catch data are used to cluster
fishing trips on the basis of their similarity in catch composition (Pelletier and Ferraris, 2000;
Deporte et al. 2012).
Several targeting clusters are identified and coded. Each record in the CPUE data base is assigned
a fishing tactic code. A Generalized Linear Model (GLM) or GAM will attempt to remove some of
the variation in the raw CPUE data by treating these clusters as categorical covariates (Carvalho
et al. 2010). This is termed the ‘Clustering Fishing Tactics’ method (CFT). If the species under
assessment features strongly within a certain fishing tactic, the estimated coefficient for this factor
will be high. If it is a rarity in the fishing tactic, the coefficient will be low. In this way, targeting
variation is removed, leaving the year effect to reflect real abundance trends.
A relatively novel method is to replace the categorical factors with a small number of continuous
principle component scores (PCs), derived from a Principle Component Analysis (PCA) of
the catch composition data (Fig. 1 c). The number of PC-axes are selected on the basis that
they represent the majority of the variation in species composition. Each CPUE record is
assigned PC scores, and these are used as continuous, rather than categorical, variables in the
standardization model. This is termed the ‘Direct Principle Component’ method (DPC).
It is important to ensure that the targeting predictors (fishing tactics or PC scores) contain
information on targeting only and not on the abundance of the species under assessment. Some
confounding (between targeting and abundance) will occur, but the extent will be reduced by
using proportions in defining targeting tactics, and not absolute CPUE. Further elimination of
abundance information can be achieved by transforming the proportions (square- or fourthroot) to down-weight the effect of abundance and to promote the information in species
representation, i.e. to ensure that rare species are not ‘lost’.
Fishery data
Commercial catch and effort data for the period from 1985 to 2010 were extracted from the
NMLS database. The raw data comprised mandatory daily catch returns (kg) per species per
boat day as estimated by the skipper, vessel number, crew number, hours on sea, the date and
catch location. The reported catch location, initially provided as a shore position and a distance
offshore, is referenced to the midpoints of 5 × 5 nautical mile latitude and longitude gridcells. For the analyses, we first subset the dataset into three regions along the South African
south coast (Fig. 2): (i) south-west (SW), (ii) south-central (SC) and (iii) south-east (SE),
containing a total of 404,646, 200,584 and 441,793 daily catch returns, respectively. These
three regions cover the fishing grounds of carpenter and silver kob and were selected to reflect
the geographical division of the fishery and the targeted stocks, and to account for geographical
differences in species composition and targeting. Data were eliminated from the analyses for
several reasons: Records were rejected because information about crew size and hours at sea
was missing. Time at sea was restricted to a maximum of 12 hours and crew size to 12 fishers.
These two cut-offs were chosen to remove the impact of freezer vessels on the expected CPUE.
Data aggregation
All boat trips for the same month, vessel number, and grid-cell were combined into a single
record and species-specific CPUE was expressed as average catch (kg) per boat day (trip). The
reason for combining information from different boat trips in this way was because of concerns
that temporal and spatial autocorrelation caused by boats that consecutively fished a particular
grid-cell over several days may result in overestimated precision of the model results and
subsequently violate the assumption of independence of data (Dobby et al. 2008). The source
of fishing tactic information in the catch composition of each record was therefore not the
individual fishing trip, but rather the choices of fishing techniques (e.g. bait, tackle), habitattype and one or more target species, as made by the skipper of a particular vessel for a particular
month and fishing ground. The numbers of records included in the final datasets were 97,295
for SW, 36,658 for SC and 58,566 for SE.
Figure 1: Conceptual graphs illustrating the CFT and DPC methods when applied to a
hypothetical four-species hand-line fishery. The target species T occurs together with species
A, overlaps randomly with species B, and occupies different habitat to species C, leading
to positive, no and negative correlations in catch per unit effort (CPUE), respectively (a).
Information on the strength of targeting directed at species T in three concurrent fishing
trips labelled x, y and z, is contained in the catch composition of the trips, represented as pies
(b), which form the basis of clusters in the CFT method. The DPC method utilises the same
information represented in two principal component scores (c). The vector influence of each
species on the ordination of the three fishing trips corresponds to the non-linear relationship
between CPUE of species T and the PC scores.
Adjusting for targeted effort
Two approaches were explored to derive variables as predictors for fishing tactics, hereafter
referred to as ‘Clustering Fishing Tactics’ (CFT) and ‘Direct PCA’ approach (DPC).
The CFT approach has been used in recent years to identify fishing tactics from commercial
data by applying clustering techniques to catch composition records (Pelletier and Ferraris
2000; Deporte et al. 2012). The first step entails applying a Principle Component Analysis (PCA)
to a multidimensional catch composition matrix to obtain a smaller number of informative
components, with most the variation in the data explained by the first few axes of the PCAtransformed data (Pelletier and Ferraris 2000; Deporte et al. 2012). For this purpose, a data
matrix comprising CPUE records for each species was constructed for each region. The data
were converted into relative proportions by weight and then square-root transformed to allow
less dominant target species to contribute to the similarity among catch compositions. To
eliminate noise from the data, data matrixes were restricted to the species under assessment and
those species or species groups that contributed at least 1% to the total landings per region. This
resulted in the selection of fourteen, nine and thirteen species for the SW, SC and SE regions,
respectively (Table 1). All PCA-axes were retained for the cluster analysis (Pelletier and Ferraris,
2000). To identify clusters of fishing tactics, we selected the non-hierarchical clustering method
CLARA (Kaufman and Rousseeuw 1990; Struyf et al. 1996), which provides a reasonably
straightforward way for clustering large datasets.
Figure 2. Fishing regions along the coast, with bubble plots illustrating the model-predicted
spatial distribution of standardized CPUE for (a) carpenter and (b) silver kob during 2010 along
the South African coastline.
The CLARA method is an extension for large datasets of the ‘Partitioning Around Medoids’
(PAM) method (Kaufman and Rousseeuw 1990), where medoids are objects within a cluster
for which the average dissimilarity to the remaining objects in the cluster is minimal. As the
PAM method is restricted to applications for small data matrixes, the CLARA algorithm was
subsequently designed to apply PAM clustering to a number of data subsets of a fixed size
within a large matrix. The CLARA analysis was based on 100 data subsets, each comprising 250
records. The optimal number of clusters was selected by way of iterative maximization of the
‘Average Silhouette Width’ (ASW), which can be used as a measure of within-cluster tightness
and among cluster separation (Punzón et al. 2010).
Table 1: List of species and groups of fishes, including abbrivations, that were included in
Principle Component Analyses (PCAs) for the south-west (SW), south-central (SC) and southeast coast (SE) along of South Africa. SW: n = 14, SC: n = 9; SE: n = 13
Classification and species
Common name
Regions
Species code
Caragidae
Seriola lalandi
yellowtail
SW
YLTL
Gempylidae
Thyrsites atun
snoek
SW
SNOK
Merlucciidae
Merluccius sp.
hakes
S, SE
HAKE
Ophidiidae
Genypterus capensis
kingklip
S
KKLP
Pomatomidae
Pomatomus saltatrix
elf
SW, SE
ELF
Sciaenidae
Argyrosomus inodorus
silver kob
SW, S, SE
KOB
Atractoscion aequidens
geelbek
SW, S, SE
GLBK
Scombridae
Scomber japonicus
mackerel
SW, S, SE
MCKR
Sparidae
Argyrozona argyrozona
carpenter
SW, S, SE
CRPN
Cheimerius nufar
santer
S, SE
SNTR
Chrysoblephus cristiceps
dageraad
SE
DGRD
Chrysoblephus gibbiceps
red stumpnose
SW, SE
RSTM
Chrysoblephus laticeps
roman
SW, S, SE
ROMN
Pachymetopon blochii
hottentot
SW
HTTN
Petrus rupestris
red steenbras
SE
RDST
Pterogymnus laniarius
panga
SW,SE
PANG
Rhabdosargus globiceps
white stumpnose
SW
WSTM
Spondyliosoma emarginatum
steentjie
SW
STNT
Elasmobranchii
sharks
SW, S, SE
SHRK
For the iterative determination of the optimal cluster number, we assumed a range from 2 to 25
clusters to be sufficient to describe the possible combinations of different targeting tactics. In
the last step, the identified fishing tactic clusters for each catch composition record, were aligned
with the original dataset and treated as categorical variable in the GAM (Carvalho et al. 2010).
The DPC approach, proposed by MacNeil et al. (2009), used the first- and second- PC-axes
directly as predictor variable in a Generalized Linear Model (GLM) to model the effect of
variations in long-line catch composition on expected shark depredation rates. Making direct
use of the first n PC-axes as covariates appears appealing as it omits multiple steps involved in
the clustering approach. This approach has, however, not been tested for CPUE standardization
and it could be questioned whether GLMs are appropriate for the potentially non-linear
relationships between CPUE and PC covariates. The alternative would be to first test this
approach using a GAM framework. Therefore, we followed the same steps described above
for the PCA of the catch composition matrix, but directly related the first four PC-axes to the
records in the original datasets as covariates for the GAM analysis.
Modelling
The application of GLMs and GAMs has been the most frequently employed modelling
approach used to standardise CPUE (Maunder and Punt 2004). The GAM class of models is a
semi-parametric extension of the GLM and provides increased flexibility for modelling nonlinear relationship between CPUE and continuous predictor variables. GAMs have proved to
be particularly useful for incorporating spatial effects and other nonlinear relationships into
the CPUE standardization process (Bigelow et al. 2002; Su et al. 2011) and were therefore
considered as the most suitable framework for this study.
As carpenter and silver kob represent major target species along the three south coast regions,
it was deemed extremely difficult to objectively distinguish between fishing trips where either
species were targeted but no catch was made (‘true zeros’) and those trips where zero catches
were caused by non-targeted effort (‘false zeros’). To avoid zero-inflation caused by ‘false zero’
catches, we excluded trips with zero CPUE values for the species under assessment from the
standardization datasets such that only records that indicated at least partial targeting of the
species under assessment were used.
Because frequency distributions of positive CPUE data were considerably right-skewed, we
considered the log-normal distribution an adequate statistical error model to account for the
variability in the data. Accordingly, we first normalised the CPUE response by the natural
logarithm transformation, ln(CPUE), a common procedure in CPUE standardization (Quinn and
Deriso 1999).
Predictor variables considered in the model included year, month, latitude (lat) and longitude
(long), crew size (crew) and mean hours spent at sea per record (hours). Although it is common
practice to include vessel name or type as a covariate in the standardization (Punt et al. 2000;
Glazer and Butterworth 2002; Battaile and Quinn 2004), this could not be done here because
linefishers have the habit of using the same name and number for different boats, changing
boat names, and even physically changing the boats themselves, without these changes being
reflected in the available information.
The full GAMs for each region and species were formulated for the CFT as:
(1)
and DPC as:
(2),
where ε is the error term with ε ~ N(0, σ2) , and s() denotes the smoother functions. A cyclic
cubic regression spline was chosen to smooth the month predictor, while smoothing of other
continuous variables was realized by thin plate regression spline functions (Wood 2006).
Model selection
Covariates for each GAM were first evaluated based on minimizations of the model deviance
and Aikake’s information criterion (AIC) using a forward stepwise selection procedure.
Acknowledging that inferences of significance are based on the assumption of independence of
data, which rarely holds true for fisheries-dependent catch and effort time series (Glazer and
Butterworth 2002), we additionally conducted 10-fold bootstrap cross-validations (BCV; Efron
and Tibshirani 1993) to determine the set of covariates included in the final models (Hinton and
Maunder 2003; Maunder and Punt 2004). As a measure of predictive power, we calculated the
average prediction error (PEboot) based on 200 BCV runs.
Standardized abundance indices and confidence intervals
Annual standardized CPUE was calculated by setting all covariates other than ‘year’ to
standardized conditions X0. The choices made were such that one standard unit of effort
denotes an average boat trip with eight crew members who spent eight hours on sea, fished in
the 5 × 5 grid and during the month with the highest effort frequencies and directly targeted the
species under assessment. A bias-corrected natural estimate for the expected yearly mean CPUE
for the vector of standardized covariates X0 was then calculated as:
(7),
where
is standardized, model-predicted mean ln(CPUE) for year y and
model standard deviation (residual standard error).
is the estimated
Confidence intervals for expected yearly CPUE values were estimated by applying a nonparametric bootstrapping procedure (Efron and Tibshirani 1986).
Results
Covariates for targeted effort
The first four PC-axes, which were retained for GAM analysis according to the DPC method,
explained the majority of the dissimilarity in catch composition, accumulating 62.7%, 87.8% and
70.1% for SW, SC and SE, respectively.
For the CFT approach, different numbers of clusters were tested iteratively by applying CLARA
analyses to the PCA-transformed data matrixes. The optimum numbers of clusters were 13 for
SW, 22 for SC and 24 SE, with corresponding ASW values of 0.46, 0.49 and 0.33, respectively
(Fig. 3). Differentiations between the maximum ASW and the next highest ASW values were
clearest for SW and SE, whereas groups of two and 21 to 24 clusters produced relatively similar
ASW values for SC (Fig. 3).
Fig. 3. Average Silhouette Width (ASW) obtained for different number of clusters of
the 1985 -2010 time series of the boat-based south African linefish fleet operating along the (a)
south-west coast, (b) south coast and (c) south-east coast .
Model selection
The results of GAMs fitted to three subsets of covariates for each species and region (Table 2): (1)
subsets comprising the initial covariates year, month, latitude and longitude, crew size and hours
spent at sea, but no adjustment for FTs (no-FT), (2) the initial set of covariates and FTs used as
categorical variable (CFT) and (3) the initial set of covariates and the covariates PC1 – PC4 (DPC).
In all cases, all covariates considered in the GAMs were found to explain a highly significant
amount of the variation in the data (p < 0.001) and resulted in reductions of the AIC and average
prediction error (PEboot). The variation explained by the no-FT GAMs ranged from 12% for
silver kob CPUE in SE to 33% for carpenter CPUE in SE. The no-FT GAMs fitted to carpenter
CPUE had consistently higher R2 values (0.25 – 0.33) than those fitted to silver kob CPUE (R2 =
0.12 – 0.23). This could be attributed mainly to the larger amount of variation explained by catch
position (lat-long interaction). Compared to silver kob, spatially standardized CPUE of carpenter
revealed a stronger CPUE gradient increasing from inshore to offshore, with highest standardized
CPUE values expected for the offshore areas of the central Agulhas Bank in SC (Fig.1).
In all instances, both the CFT and the DPC approaches resulted in substantial reductions of the
model deviance (represented by higher R2 values), lower AIC and lower PEboot compared to
the no-FT option (Table 2). The DPC consistently provided the best fit to the data, shown by the
AIC and R2 values, and the superior predictive power given the lower PEboot averages obtained
from bootstrap cross-validations (Table 2). In general, these results gave statistical evidence
in favour of the DPC approach. Residual plots and quantile-quantile plots confirmed that the
assumed log-normal error model was justified.
Table 2. Summary statistics of log-normal GAMs fitted to carpenter and silver kob CPUE data
from three fishing regions along the South African coast. Res. df: Residual degrees of freedom.
Species
Region
Model
Res. d.f.
AIC
R2
PEboot
Carpenter
south-west
no-FS
13988
43347
0.27
1.28
(n = 14,043)
CFT
13981
39041
0.46
0.94
DPC
13955
38563
0.48
0.91
South
no-FS
5317
17730
0.25
1.59
(n = 5,368)
CFT
5305
16323
0.43
1.23
DPC
5286
11038
0.79
0.46
south-east
no-FS
19116
59260
0.33
1.28
(n = 19,171)
CFT
19644
53433
0.50
0.95
DPC
19111
43746
0.70
0.57
Silver kob
south-west
no-FS
23644
70822
0.13
1.16
(n = 23,699)
CFT
23638
65706
0.30
0.94
DPC
23611
61927
0.41
0.80
South
no-FS
23361
69949
0.23
1.16
(n = 23,468)
CFT
23350
58562
0.53
0.71
DPC
23329
53765
0.61
0.58
south-east
no-FS
18705
54340
0.12
1.18
(n = 18,757)
CFT
18698
48614
0.36
0.80
DPC
19635
42955
0.52
0.61
Trends in CPUE
Nominal CPUE (geometric mean) and standardized CPUE indices predicted based on the noFT, CFT and DPC GAMs all showed an increase in CPUE in most recent years (Fig. 4). The four
CPUE indices were normalized to their means for the period 1985 to 2000 (i.e. the period prior
to the forced effort reduction) to facilitate comparisons among CPUE indices. The standardized
CPUE indices diverged markedly from the nominal CPUE for carpenter in SW (Fig. 4 a) and in
SE (Fig. 4 c), with the standardized indices implying more conservative predictions of CPUE
increase compared to the nominal CPUE. With the exception of these two cases, the no-FT
CPUE indices closely resembled the nominal CPUE.
Generally the trends in normalized CPUE indices were fairly insensitive to the choice between
the CFT and the DPC GAMs. The most notable difference between the two CPUE indices was
that the DPC CPUE trend increased earlier and more consistent in SC from 1997 onwards,
whereas the CFT CPUE trend showed little changes until 2008 and a slightly more rapid
increase thereafter (Fig. 4 b). Year-to-year variations in standardized CPUE indices based on the
CFT and DPC tended to be less extreme than in the nominal CPUE indices (Fig. 4).
Declines in total landings of silver kob and carpenter were not uniform and generally began
prior to the forced effort reduction in 2000, which may indicate that both species were overexploited at the time (Fig. 5). Total landings were typically at minimum during the period 2002
– 2005. The standardized CPUE indices based on the DPC approach showed positive responses
in CPUE for both species as total landings decreased; with lower 95% C.I.s well above the mean
from the period before 2000. Strongest increases in standardized CPUE indices were observed
in SE, while SW showed slower increases for both species (Fig. 5).
Figure 4. Relative trends in carpenter (a) – (c) and silver kop (d) – (f) CPUE (1985 – 2010)
comparing the nominal CPUE with the standardized CPUE based on either including spline fits
of the first four PC scores (PCA) or a factor for fishing tactics (FT) for the south-west (upper
panel), south-central (middle panel) and south-east coast (lower panel) . Note that CPUE values
for carpenter and silver kob are adjusted for the changes in minimum size limits in 2005
Discussion
In this contribution, we introduced the DPC method, a novel approach for standardizing multispecies catch and effort data. We evaluated its performance in comparison to the CFT approach,
implemented following and adapting the methods of Pelletier and Ferraris (2000), Carvalho
et al. (2010) and Deporte et al. (2012). Our results showed that both approaches removed
substantial variation from the CPUE data, but that the DPC approach clearly outperformed the
CFT approach (AIC, deviance explained, and results from 10-fold bootstrap cross-validations).
While the CFT approach has the merit in that it provides more detailed insights into the fishery,
it involves the implementation of a fairly complex analytical framework, including multiple
steps, which can often be associated with elements of subjectivity (Deporte et al. 2012). By
comparison, the DPC approach represents the more direct approach, is less time-consuming
and subjective and therefore considerably easier to implement into the routine CPUE
standardization.
Figure 5. Standardized CPUE indices (solid line) with 95% confidence intervals (dashed lines)
and total reported landings by the South African hand-line fishery (open circles) for carpenter
(a) – (c) and silver kob (d) – (f) from the south-west (upper panel), south-central (middle panel)
and south-east coast (lower panel).
We used species composition in the catches as the basis for the two standardization methods
(Pelletier and Ferraris 2000; Carvalho et al. 2010) rather than CPUE values of selected nontarget species. Untransformed CPUE should be avoided when using a catch composition
matrix to prevent the predictor variable from including abundance information. Although
species composition is to some extent related to the dependent variable CPUE, it does not hold
direct information about the magnitude of the catch. The inclusion of PC-axes as covariates
in the standardization model is defendable on the grounds that other covariates explained
a substantial fraction of the variation (Battaile and Quinn 2004). While the non-linear
relationship between CPUE and the first four PC-axes was significant, the variation explained by
the remaining covariates indicated that the PCA-transformed catch composition data contained
additional information to that contained in the response variable CPUE. The separation of
targeting and abundance information was achieved by standardizing to proportions and then
root (root)-transforming. The effect of these actions was to shift the source of information
away from raw abundance and towards species composition. The most extreme form of
transformation, presence-absence, could have achieved the dissociation more decisively
(Stephens and MacCall 2004), but weighting all species equally may preclude a realistic
determination of the partitioning of targeted effort. In addition, there is risk of introducing noise
associated with rare and inconsequential species.
The South African linefishery over the last three decades has provided a substantial data set to
test the performance of standardization models. Based on evidence of severe over-exploitation
for many linefish species, the number of boats operating in the linefishery was drastically
reduced by 70% in 2000, although the resulting reduction in effort was likely to be smaller
because boats with poor performance were preferentially excluded. This intervention should
have resulted in strong recovery signals across several depleted species. Part of the recovery
sequence was likely to have included shifts in targets, as species recovered and market demands
altered. Such concurrent change in targeting and abundance should be evident as a divergence
in nominal and standardized CPUE. Indeed, it would not be possible to evaluate the impact of
the effort cut accurately, without being able to account for shifts in targeting.
Conclusions
Further tests and validations of the method might be advisable using data sets for which the
direction of targeting was independently known and recorded such as those described by Palmer
et al. (2009). It is difficult to imagine that the method could be adequately tested by way of
simulation, given the need to replicate trends in many species and to realistically reproduce
spatial and temporal trends in species associations, and species-catchability for particular
targeting tactics.
The development of a standardization method to account for the effect of targeting has the
potential to unlock a wealth of useful information in the linefishery catch records. The data
series used in this analysis comprised of over two million catch and effort records of which 17
species account for 95% of the volume of catches, never before used for a stock assessment.
These standardization methods outlined in this paper are therefore likely to be applied routinely
to other fishery data sets. We anticipate that there is scope for applying the DPC method of
standardization to other multi-species fisheries, including longline and trawl fisheries.
Acknowledgements
We wish to thank the members of the Linefish Scientific Working Group and in particular Prof
Tony Booth for providing valuable input for this study. This work was funded by the Responsible
Fisheries Programme of WWF-SA, the Department of Agriculture, Forestry and Fisheries and
the Ma-Re BASICS programme of the University of Cape Town.
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Session 2 – Fish Biology Studies: Chair Bruce Mann
The biology and fisheries of king mackerel (Scomberomorus commerson) in the south west Indian Ocean
B. Lee and B. Q. Mann
Oceanographic Research Institute, PO Box 10712, Marine parade, Durban, 4056.
Introduction
The South West Indian Ocean Fisheries Projects (SWIOFP) is a collaborative program between
nine countries. The program involves the development of a regional ecosystem-based fisheries
data collection system and assessment initiative for transboundary shared and migrating
fisheries resources (van der Elst et al. 2009).
The king mackerel, Scomberomorus commerson belongs to the family Scombridae (Mackerels,
tunas, bonitos), subfamily: Scombrinae. It is widely distributed throughout the Indo-Pacific
regions from South Africa and the Red Sea to south-east Asia, North to China and Japan and
South to Australia (Collette and Nauen 1983). Within the South West Indian Ocean (SWIO)
region S. commerson occurs from KwaZulu-Natal northwards through Mozambique, Tanzania
and Kenya, and around the islands of Madagascar and Comoros. It is an epipelagic species,
occurring from the edge of the continental shelf to shallow coastal waters where it is found along
drop-offs, gently sloping reefs and lagoon waters from 10 – 70 m (Grandcourt et al. 2005).
This species is targeted throughout its range by commercial, artisanal, and recreational fisheries.
On the East Coast of Africa, where it is a prized market fish, king mackerel is primarily caught
by trolling lures or dead bait such as pilchards, or live bait using rod and line (Govender 1992,
Siddeek 1996). Off South Africa, S. commerson is also actively pursued by spearfishermen. King
mackerel are also caught in artisanal beach seines and gill nets along much of the east coast of
Africa and Madagascar (WIOFISH 2008).
The total reported catch of S. commerson in the West Indian Ocean (FAO statistical area 51) was
just over 70 000 tonnes, taken by around 17 countries (FAO 2005). Catch data for two countries
(South Africa and Mozambique) within the SWIO region indicate a total catch of 883 tonnes,
with 77%, 21% and 13% of this being attributed to artisanal, industrial and the recreational
fisheries sectors respectively (Table 1) (WIOFISH, 2008).
Apart from the work of Govender (1992) in KwaZulu-Natal, little is known about the biology
and population dynamics of S. commerson within the SWIO region with the majority of studies
of this species being limited to areas within the Arabian Sea, the Persian Gulf, the coast of
India and Australia. It is therefore uncertain to what extent S. commerson stocks are separated
throughout the SWIO region.
Tagging experiments off Australia have shown that S. commerson is a coastal migrant that
undertakes seasonal north-south migrations as well an onshore-offshore spawning migration
(McPherson 1981). Local feeding southward migrations from Mozambique into South African
waters during summer have also been reported (Govender 1992).
Comparisons of population trends and the biology of S. commerson at various sites in the SWIO
could be used to determine the extent of feeding and reproductive movements off eastern Africa,
and thus the extent to which this species is shared between SWIOFP countries. This information
is a prerequisite for the development of local, sub-regional and regional management strategies.
This study is currently underway and is being conducted by the Oceanographic Research
Institute
Aim and Objectives
The aim of this study is to evaluate the fishery and biology of S. commerson in the South West
Indian Ocean and identify the data gaps required for its effective management. Field based
biological data collection will focus on a sub-region of the SWIO including the coast of KwaZuluNatal, South Africa and potentially Mozambique and Tanzania (Zanzibar).
Specific objectives:
1. To evaluate historical catch and effort data of S. commerson from countries within the
SWIO region to determine species distribution and trends in abundance over time.
2. To improve the understanding of the biology of S. commerson in terms of its age and growth
and reproduction within the sampled area.
3. To investigate the feeding biology of S. commerson in KwaZulu-Natal.
4. To determine the exploitation levels and stock status of S. commserson within the
sampled area.
Table 1: Summary of line fishery catch data for S. commerson in KwaZulu-Natal, South Africa
and Mozambique (data from WIOFISH 2011)
Fishery
Catch rate
(2007-2010)
% S. commerson
catch
composition
Area
Mozambique Sport, ski-boat
12.8kg/boat/day
36
Maputo and Inhaca
Mozambique Recreational,
ski-boat
9.375 kg/boat/
day
14
Ponta do Ouro
Mozambique Shore
0.9kg/man day
Unknown
Ponta do Ouro
Mozambique commercial, Line
270kg/boat/day
19
Sofala Bank, Southern
Region
Mozambique Artisanal, Line
12.6 kg/boat/day 4
Entire Coastline
South Africa Recreational, skiboat
15 kg/boat/day
KZN coastline
South Africa Recreational,
fishing kayak
2.98 kg/man trip 34
KZN coastline
South Africa Recreational,
jet-ski
2.8 kg/man trip
KZN coastline
12.4
18
General Methods
Study Area
The study area includes the maritime zones of two of the nine nations that fall within the South
West Indian Ocean Fisheries Projects (SWIOFP) area: namely KwaZulu-Natal (KZN), South
Africa and Mozambique. A retrospective analysis of historical catch and effort data will cover the
coastline of KZN and Mozambique (where data are available). To date the biological sampling
area has included waters of KZN and southern Mozambique between Port Edward in the South
and Beira, Mozambique in the north (Fig. 1).
Figure 1: Map displaying the area of the coastline where biological sampling of king mackerel
has been undertaken, including key sampling sites.
Data Capture
Historical data
A retrospective analysis is planned to analyze historical catch and effort records for the S.
commerson fisheries throughout the sample area to evaluate trends in CPUE. These data will be
obtained from a number of databases including:
•
•
•
•
•
The National Marine Linefish System (NMLS) recreational data
The Boat Launch Site Monitoring System (BLSMS) recreational data
Mozambique recreational catch and effort data (IIP)
Mozambique artisanal catch and effort data (IIP)
Mozambique semi-commercial catch and effort data (IIP)
The ORI tagging database is expected to provide biological information for age validation and
movements of king mackerel within the study area.
Field sampling
To date sampling has been undertaken on a monthly basis between April 2011 and March 2012.
Data were collected from recreational fisherman through sampling at boat launch sites and fish
markets across the study area. Additionally, samples were collected at angling and spearfishing
tournaments to enable the collection of large quantities of data over a short time period.
Information recorded during sampling included the date of capture, the landing site, region of
capture, and the gear and method of capture. Biological data was collected from a target sample
of at least 30 fish per month from a representative size range. However, due to the seasonal
nature of S. commerson in KwaZulu-Natal, this was not always possible. Total length and fork
length (FL) was recorded to the nearest millimetre using a measuring board. Whole wet weight
was measured with an electronic balance and recorded to the nearest gram.
Fish were sexed and the stage of reproductive maturity determined using a macroscopic staging
system (Table 2). The maturity stages were based on keys described by Mackie and Lewis (2001),
Grandcourt et al. (2005) and Claereboudt et al. (2005) and modified for this study. Gonads were
dissected out and subsequently weighed to the nearest 0.01 gram using an electronic balance. A
sub-set of 36 gonads (three per macroscopic stage for males and females) were dissected out and
preserved for histological macroscopic stage validation. Stomachs were removed, cut open and
the contents preserved in 10% formalin for future analysis. A visual estimation of percent stomach
fullness was recorded. The sagittal otoliths were extracted, cleaned in freshwater, dried with paper
towel and stored in labelled envelopes in preparation for ageing.
Voluntary support from fishers was gathered by widely advertising the project through a range
of media including fishing magazines, oral presentations at club meetings and competitions,
interviews, phone conversations, emails and face to face meetings.
Morphological Relationships
The relationship between length (FL) and weight (TW) will be estimated for all fish combined
and males and females separately using a linear regression analysis. The relationship between
length and weight can best be represented by the power curve equation W = aLb which will be
transformed into a linear form by the use of natural logarithms as Ln W = ln q + b (ln L). Model
parameters will be estimated using Solver by minimizing the residual sum-of-squares function
in Microsoft Excel (2010).
Reproduction
The mean size at 50% sexual maturity will be estimated for both sexes by fitting the logistic
function to the proportion of mature fish in 5 cm size categories. Mean monthly gonado-somatic
indices (GSI) will be calculated for each sex by expressing the gonad weight as a proportion of
the total body weight. The timing of spawning will be calculated by plotting the mean monthly
GSI against the sample period. Sex ratios will be calculated for the entire sample as well as for
individual size classes.
Table 2: Macroscopic criteria used for assessing stages of reproductive development in S.
commerson.
Development Stage
Description
Male
I
Juvenile
Gonads too small to distinguish between testes or ovaries.
II
Inactive /
Immature
Testes are small and straplike with a smooth appearance and opaque,
ivory or bone colour. No sperm is present.
III
Developing
Testes are small, opaque and straplike. Sperm is extruded when
squeezed. Central tissue often browner then bone or ivory coloured
peripheral tissue. Testes may occasionally be tinged in red.
IV
Mature
Testes are large, opaque, and ivory in colour. Exterior dorsal
blood vessels are large and small blood vessels are usually present.
Internally, sperm can be squeezed from the central sperm sinus.
V
Ripe
Testes opaque, swollen and with large exterior blood vessels. Sperm is
released with little or no pressure on the abdomen or when the testes
are cut.
VI
Spent
Testes are short, dark-reddish brown and have a bruised appearance.
A small amount of residual sperm may be present, but usually no
sperm is released. Wall flaccid and rich in blood vessels.
Female
I
Juvenile
Gonads too small to distinguish between testes or ovaries.
II
Inactive /
Immature
Ovary is glassy, translucent pink, small and with compact wall. Ovaries
may be opaque pink, flattened, flaccid and inconspicuous in larger
fish. Oocytes not visible to the human eye resulting in smooth, uniform
appearance.
III
Developing
Ovaries becoming progressively rounder and firmer as the gonad
wall contracts and thickens and the ovarian tissue develops. Colour
typically semi-translucent rose, pink or ivory, although often red.
Small eggs visible.
IV
Mature
Early in this stage, the ovaries appear semi-translucent and speckled.
As more oocytes develop, ovaries become large, round and opaque
with prominent blood vessels. Opaque oocytes are visible through the
gonad wall and the colour is typically pale yellow or apricot.
V
Ripe
Ovaries are very large and swollen. Colour is apricot to peach with
a prominent network of external blood vessels. The presence of
translucent, hydrated oocytes gives the ovaries a distinctive speckled
or granular appearance through the thin gonad wall. Eggs released
when pressure is applied to the abdoment and may be present in the
ovarian lumen.
VI
Spent
Gonad flaccid and dark in colour. Few residual eggs may be present
Preliminary Results
To date a total of 439 fish have been sampled, ranging in size from 525 mm to 1410 mm fork
length (males) and 490 to 1615 mm fork length (females).
Length-weight Relationship
The length-weight relationship provided a good fit to length and weight data for males, females
and the combined sexes (Table 3).
Table 3: Estimates of the parameters describing the length-weight relationship for male, female
and combined sexes of S. commerson
A
b
R2
Standard
Deviation
N
Combined
0.347 x 10-5
3.182
0.976
0.109
398
Females
0.353 x 10
3.178
0.973
0.113
230
Males
0.308 x 10
3.210
0.977
0.098
163
-5
-5
Reproduction
The mean size at 50% sexual maturity was 656 mm FL for males and 871 mm FL for females.
The gonado-somatic index for both males and females increased rapidly between June and
September with peak spawning most likely occurring between September and October (Fig
2). The increase in GSI coincides with the reduction in CPUE of S. commerson in KZN waters.
This indicates that spawning is unlikely to occur in South African waters and that the return
migration to South Africa is most likely a post-spawning feeding migration (Fig 3).
Figure 2: Mean monthly gonado-somatic indices for male (n = 158) and female (n = 227) S.
commerson along the KwaZulu-Natal and southern Mozambique coast.
Biological parameters
There was a female bias in the overall male to female sex ratio of 1: 1.38. Males dominated
the catch numbers in the size classes below 80 cm FL (Male: Female - 1:0.6), while females
displayed a greater frequency in the larger size classes (1:3.6) (Fig 4). As a result, the average
length of males (847 mm FL) was less than that of females (959 mm FL).
Discussion
The estimated size at 50% sexual maturity for males and females, respectively (656 and 872
mm FL), is similar to the estimated size at maturity of 628 (Males) and 809 mm FL (Females)
given by Mackie et al. (2004) off the west coast of Australia. S. commerson females were found
to mature at 790 mm FL on the east coast of Australia and at 800 mm FL for the northern stock
(McPherson 1993). Grandcourt et al. (2005) estimated the size at 50% sexual maturity off the
Sultanate of Oman at 728 mm FL for males and 863 mm FL for females. In the northern Indian
Ocean the mean size at 50% sexual maturity was estimated at 750 mm FL by Devaraj (1983).
The values estimated in this study thus compare favourably with those from other regions. They
are however slightly lower than the estimates of 1096 mm FL calculated for combined males and
females off the KZN coast by (Govender 1992).
Figure 3: Monthly catch per unit effort (number of fish per angler hour) along the KwaZuluNatal coastline based on BLSMS recreational ski-boat data.
Figure 4: Length frequency distribution by sex of S. commerson sampled off KwaZulu-Natal
and southern Mozambique between April 2011 and March 2012
The period during which peak gonado-somatic indices were attained suggest a single spawning
period from September to January (ie. over the spring and summer months). This is similar
to the results of McPherson (1993) and Mackie et al. (2005) that revealed a single spawning
season in October and November off the east and west coasts of Australia (Spring – Summer).
In northern Australia, S. commerson spawning was much more protracted, occurring between
August and ending March. The reproductive activity of S. commerson in waters off the Sultinate
of Oman also peaked in the spring and summer months between April and August (Grandcourt
et al, 2005; Claereboudt et al. 2005). The results of Govender (1992) indicated that spawning
occurs over a protracted period from November – March. His study did postulate that the main
spawning of S. commerson occurred off Mozambique, after which the females migrate south
into KZN.
There was a female bias in the overall sex ratio (1:1.38). This is comparable to the female bias
observed by Govender (1992) in KwaZulu-Natal of 1:1.81. Sex ratios of S. commerson in the
Sultanate of Oman (Grandcourt et al. 2005; Claereboudt et al. 2005) as well as the east coast
of Australia (Tobin and Mapleston 2001) all displayed an overall female bias. In this study, fish
below 800 mm FL displayed a male bias (1:0.6). Sex ratio was therefore heavily biased towards
females in the size classes above 800 mm FL (1:3.6). The female bias observed in these catches
can either be a result from real differences in the actual sex ratio in the fish stock or from a
bias introduced in the samples as a result of the fishing methods used. Furthermore, there is
evidence that the males and females migrate separately off the east coast of Australia (Lester et
al. 2001).
The shape of a length frequency distribution is governed by recruitment, growth, mortality and
sampling bias (King 1995). In S. commerson it would be expected that the length frequency
distribution would display multiple mode peaks due to the species’ rapid growth rates. A minor
mode peak was evident for small males between 600 and 650 mm FL. This modal length class
would be expected to be the faster growers of the first cohort being recruited into the fishery.
The main modal class at 800 mm (males) and 900 mm FL (females) indicates the first length
class that has been fully recruited into the fishery. A similar pattern is evident in the length
composition of catches on the east coast of Australia where an initial minor modal length class is
apparent at 75 cm FL. This is followed by a major modal length class at 85 cm (males) and 95 cm
FL (females) (Tobin and Mapleston 2004).
Conclusions and expected outcomes
This project is only halfway through its expected duration and as such the preliminary results
presented are subject to change. Furthermore much statistical analysis and further objectives
are still to be achieved prior to the completion of the study. Further outcomes of the project still
to be achieved include:
•
•
•
•
•
•
•
A more detailed statistical analysis of the reproductive biology of S. commerson within
KwaZulu-Natal and Southern Mozambique.
A detailed overview of biological characteristics of S. commerson within the study area
ie. length composition of catches, age composition of catches, mortality estimates and sex
composition of catches.
A detailed age and growth analysis of S. commerson within the study area.
A detailed feeding study on S. commerson within KwaZulu-Natal.
A per-recruit stock assessment of S. commerson within KwaZulu-Natal and Southern
Mozambique.
An analysis of historical catch and effort trends of S. commerson within the study area to
evaluate trends in CPUE.
The implications that these data have on the management of the fishery and
recommendations for the effective management of the S. commerson fishery on a national,
sub-regional and/or regional basis.
References
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Southern Africa. Struik Publishers, Cape Town.
Claereboudt MR, McIlwain JL, Al-Oufi HS, Ambu-Ali AA. 2005. Patterns of reproduction and
spawning of the kingfish (Scomberomorus commerson, Lacepede) in the coastal water of the
Sultanate of Oman. Fisheries Research 73: 273-282.
Collette BB, Nauen, CE. 1983. FAO Species Catalogue. Vol. 2. Scombrids of the world. An annotated
and illustrated catalogue of Tunas, Mackerels, Bonitos and related species known to date. FAO
Fish. Synopsis, 125 (2) 137.
Devaraj, M. 1983. Maturity, spawning and fecundity of the king seer, Scomberomorus commerson
(Lacepede), in the seas around the Indian peninsula. Indian Journal of Fisheries 30: 203-230.
FAO Fisheries Department. 2005. Review of the state of the world marine fishery resources 2005:
Marine resources – Western Indian Ocean, 2002. FIRMS Reports. In: Fishery Resources
Monitoring System (FIRMS) [online]. Rome. Updated 18 July 2006.
Govender A. 1992. Biology and population dynamics of the king mackerel (Scomberomorus
commerson, (Lacepede, 1800) off the coast of Natal. MSc. Thesis. Oceanographic Research
Institute. University of Natal.
Grandcourt EM, Al Abdessalaam TZ, Francis F, Al Shamsi AT. 2005. Preliminary assessment of
the biology and fishery for the narrow-barred Spanish mackerel, Scomberomorus commerson
(Lacepede), in the southern Arabian Gulf. Fisheries Research 76: 277-290.
King M. 1995. Fisheries Biology Assessment and Management. Blackwell Science Ltd. London
Lester RJG, Thompson C, Moss H, Barker SC. 2001. Movement and stock structure of narrowbarred Spanish mackerel as indicated by parasites. Journal of Fish Biology 59: 833-842.
Mackie M, Lewis PD. 2001. Assessment of gonad staging systems and other methods used in
the study of the reproductive biology of narrow-barred Spanish mackerel, Scomberomorus
commerson, in Western Australia. Fisheries Research Report No. 136, Department of Fisheries,
Western Australia.
Mackie MC, Lewis PD, Graughan DJ, Newman SJ. 2005. Variability in spawning frequency
and reproductive development of the narrow-barred Spanish mackerel (Scomberomorus
commerson) along the west coast of Australia. Fishery Bulletin 103: 344-354
McPherson GR. 1981. Preliminary report: investigations of Spanish mackerel, Scomberomorus
commerson in Queensland waters. In: Grant, C. J., Walter, D. G. (Eds.), Northern Pelagic
Fish Seminar. Darwin, Northern Territory, 20-21 January. Australian Government Publishing
Service, Canbera, pp. 51-58.
McPherson GR. 1993. Reproductive biology of the narrow barred Spanish mackerel (Scomberomorus
commerson Lacepede, 18000 in Queensland waters. Asian Fisheries Science 6: 169-182.
Siddeek MSM. 1996. Review of fisheries biology of Scomberomorus and Acanthocybium species
in the Western Indian Ocean (FAO Area 51). Department of fisheries science and technology,
College of Agriculture. Sultan Qaboos University. Sultanate of Oman.
Tobin A, Mapleston A. 2004. Exploitation dynamics and biological characteristics of the
Queensland east coast Spanish mackerel (Scomberomorus commerson) fishery. CRC Reef
Research Centre Technical Report No 51, CRC Reef Research Centre, Townsville
Van der Elst RP, Groeneveld JC, Baloi AP, Marsac F, Katonda KI, Ruwa RK, Lane WL. 2009. Nine
nations, one ocean: A benchmark appraisal of the South West Indian Ocean Fisheries Project
(2008-2012). Ocean and Coastal Management 52: 258-267
WIOFISH. 2008. Western Indian Ocean Fisheries Database: A catalogue of small-scale fisheries
The effects of barotrauma on five South African line
caught fishes
CG Wilke1 , SE Kerwath1,2 and A Götz3
1
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay, 8012, South
Africa.
2 Zoology Department, University of Cape Town, Private Bag Rondebosch 7700, South Africa.
3
South African Environmental Observation Network, Elwandle Node, Private bag 1015,
Grahamstown, South Africa.
Abstract
The effects of barotrauma on five commercially important line caught species, roman
Chrysoblephus laticeps, hottentot Pachymetopon blochii, santer Cheimerius nufar, carpenter
Argyrozona argyrozona and silver kob Argyrosomus inodorus, were investigated. A
classification for the signs of barotrauma was developed and internal and external signs of
barotrauma across fishing depths and species were compared. Immediate post-release survival
was investigated during a catch and release experiment. The short-term survival of red roman
was observed in submerged cages using SCUBA over a period of 24 hours. The healing of
ruptured swimbladders of hottentot and carpenter was examined over a period of several
months in a tank experiment.
Introduction
Management measures in the South African linefishery include input controls such as
closed seasons and output controls such as bag and minimum size limits and a full no-take
moratorium on two species (seventy-four Polysteganus undulosus and brindle bass Epinephelus
lanceolatus). The inclusion of red steenbras Petrus rupestris under the full no-take moratorium
is presently receiving attention. There is, however, concern that these management measures
might be ineffective based on anecdotal information that suggests that post-release mortality for
line caught species is unacceptably high.
Minimum size- and bag- limits are usually determined by applying stock assessment models
that equate the total fishing mortality to the total reported catch only (Woodward and Griffin
2003), but post-release effects are seldom taken into account. Most of the line caught fish
species are susceptible to barotrauma, a condition caused by the rapid reduction in hydrostatic
pressure while ascending to the surface during capture. Catch and release has several potentially
negative effects on the biological processes that contribute to the survival of a fish on individual
and on population level. Apart from immediate and delayed mortality these include retardation
in growth, alteration of behaviour, reduced fitness and reproductive capacity (Arlinghaus et al.
2007). These effects are caused by a combination of stress and injury associated with damage by
fishing gear i.e. hook penetration during capture, barotraumas and poor handling and failure to
re-submerge after release (Brown et al. 2010).
The signs of barotrauma as a result of decompression have been documented for many marine
and freshwater species around the world. Externally visible signs of barotrauma have been
reported after capture from depths as shallow as 3.5 m (Shasteen and Sheehan 1997), and
included distension of the body cavity area, exophthalmia (bulging eyes), protrusions of the
inverted alimentary canal into the buccal cavity, through the gills or out of the cloaca, protrusion
of gonads from the cloaca and subcutaneous gas bubbles between fin rays and in the tissues
around the eyes. These signs are concomitant with a number of internal injuries ranging from
overexpansion or rupture of the swimbladder and the resultant pressurisation and displacement
of internal organs to rupturing of blood vessels and kidneys as a result of the formation of gas
bubbles in the circulatory system. Studies on the symptoms and effects of barotrauma over
the last decade indicate that these are species specific and dependent on a number of external
factors including capture depth.
In this study we examined the effects of capture on a number of South African line caught
species with an emphasis on barotrauma. We describe the barotrauma related conditions of
five commonly caught South African fishes, four sparids and one sciaenid. Furthermore, we
examined intraspecific differences in external barotrauma signs and the effect of the different
barotrauma related conditions and their severity on immediate post-release survival. In
addition, short-term release effects on roman Chrysoblephus laticeps, were studied by returning
fishes to capture depth inside cages, and medium-term recovery of barotraumatised hottentot
Pachymetopon blochii and carpenter Argyrozona argyrozona with emphasis on the repair of
the swimbladder, was studied in a tank experiment.
Capture
Fishes were captured on commercial line fish tackle in scientifically controlled angling
experiments. The hooks ranged between 4/0 and 6/0 in size with the barbs pressed flat to allow
for easy hook extraction after capture. The angling operation was conducted off the west and
south Cape coasts of South Africa from the RV Sardinops, and from a 5.5 m power boat between
2003 and 2007 with 314 angling stations occupied and 5320 fish captured representing seven
species sampled. Hottentot were targeted between Dassen Island and False Bay whilst roman
and carpenter were captured in False Bay and on the western Agulhas Bank adjacent to Struis
Bay and inshore off Goukamma marine reserve on the south coast. Santer, Cheimerius nufar,
were capturedmainly on the western Agulhas Bank adjacent to the De Hoop marine reserve.
Kob, Argyrosomus inodorus, was captured from the centre of their distributional range adjacent
to Stilbaai on the eastern Agulhas Bank. Information recorded for each angling station included
start and end time of angling activity, water depth, surface water temperature and on selected
stations a temperature profile throughout the water column. Each fish was identified to species
level and measured to the nearest millimetre fork length. Measuring was undertaken by lifting
the fish, whilst still attached to the line, onto a measure board thereby avoiding additional
handling of the fish. The fish was restrained by holding over the head area, avoiding increased
pressure over the body cavity, and measured. The assessment of external barotrauma signs was
conducted prior to removing the fish from the hook to exclude handling as a factor influencing
the condition of the fish. External signs of barotrauma were categorised according to the affected
body area and a degree of severity in three categories: no visible sign, mild and severe (Table
1). A subset of the fishes was culled immediately by thrusting a sharpened spike directly into
the brain after the measurement. The barbless hook was then removed and fish were dissected,
sexed and examined for internal signs of barotrauma, specifically damage to the swimbladder.
Table 1: Categories of external signs of barotrauma
Affected area
Mild
Severe
Mouth
Stomach inverted in
buccal cavity
Stomach inverted and protruding from mouth;
stomach protruding from mouth deflated but
impaled on teeth; liver or intestine in buccal cavity
or mouth (as a result of being forced through
stomach)
Eyes
Gas bubbles around
eye orbit
Eyes bulging (exophthalmia)
Gills
N/A
Stomach protruding through gills distended
or deflated but stuck to gill rakers; intestines
protruding from side of gills(hooked on gill
rakers); liver forced out and protruding through
side of gills
Cloaca
Cloaca distended
Ovary protruding and ruptured; protrusion of
intestine sometimes with spleen exposed
Skin
N/A
Gas bubbles
aggregating in tissue
between rays or spines
of the fins (dorsal,
caudal, pectoral,
pelvic or anal fins);
gas bubbles venting
from body tissue
mostly centred over
the swimbladder area
of the body cavity
causing scales to lift
Immediate discard effects
To observe discard effects, a subset of fishes was immediately released into a floating,
bottomless ring-net (Fig. 1) that was deployed next to the research vessel. The ring was 3.1 m
in diameter constructed from two separate rings of 22 mm outside diameter synthetic flexible
water piping (polycop pipe) used in the plumbing industry. Floatation was provided by 15
moulded foam buoys with a buoyancy of 2.4 kg each slipped onto one of the rings of polycop
piping. The second ring was attached by whipping it with nylon braided string to the first
ring thereby adding rigidity to the structure and preventing the floats from moving round the
circumference. Buoys were drilled to accept a 60 cm length of polycop piping which passed
through the buoy at 90 degrees to the perimeter ring providing a rigid upright that protruded
above water level. Two cross pieces, connected by 90o plumbing connectors to the uprights at
the eight and four, and ten and two o-clock positions ensured rigidity of the structure. Pilchard
netting of one meter width was attached to the perimeter of the structure with nylon braided
string. The netting was weighted with lead weights at the bottom and attached to the uprights at
the top thus forming a skirt around the structure which protruded 50 cm below the floating ring
and 50 cm above the water level. This prevented the fish from washing out of the structure and
kept them captive for observation until they could overcome any residual buoyancy and swim
down through the ring-net.
Figure 1: The ring-net through which fish were returned when monitoring immediate postrelease survival.
The response of fish returned into the ring-net was monitored and the duration that each
individual fish floated at the surface before successfully re-submerging was recorded with a stop
watch. Floating fish that failed to re-submerge and fishes that did not show any signs of life were
retrieved and dissected.
A limited number of fish were deliberately not returned via the ring-net allowing those that
floated to drift away from the vessel in order to monitor incidental predation by birds and Cape
fur seals Arctocephalus pusillus pusillus.
Short-term post-release effects
To study the short-term (24 hour) post-release effects 50 captured roman were individually
transferred into cages and returned to depth of capture after the effects of barotrauma were
classified into three severity codes based on a progressively increasing suite of symptoms (Table
2). Observations were categorized according to four classification codes based on the appearance
and response of the fish (Table 2). The cages were cylindrical in form with a diameter of 100 cm
and a height of 68 cm and constructed of 12 mm stainless steel rod (Fig. 2).
The upper and lower rings were connected by six equally spaced uprights attached around the
circumference. The construction was such that the cage could be collapsed to the thickness of
the two rings for easy transport and storage especially for deployment from the 5.5 m power
boat. Each upright could swivel at the ring attachment point and had an articulating joint at
their midpoint to pivot inwards towards the centre of the cylinder allowing the upper and lower
rings of the cage to collapse together. The articulated joints were locked when the uprights were
fully extended via a spring operated tube that slipped over the joint thereby holding it rigid.
Cages were covered in pilchard netting with an entrance provided on the upper ring of the
cage. The entrance was a quarter segment of the upper ring with the pilchard netting extended
as a sock, allowing for the entrance to be secured by tying off the netting once the fish was
introduced. A weighted stainless ring of the same size which was threaded through the netting
prior to the welding of the ring was attached to the base of the cage with cable ties to provide
stability when deployed. During trials, roman in the cage became stressed if they did not have a
place to hide away from external threats such as the approach of a predator or diver. A slatted
plastic crate of 41 x 33 x 31 cm in size was covered with pilchard netting and attached to the floor
of the cage. An entrance hole was made on the side of the plastic crate facing the centre of the
cage thus forming a hideaway. Each cage had a unique number attached for identification and a
surface buoy was attached by a line to mark its position on the bottom. Details of the fish were
linked to the individual cage number prior to deployment. The cages were then deployed to the
original capture depth and allowed to settle to the seafloor. The fish were assessed during two
observation dives 2-4 hours and 22-24 hours after they had been re-submerged.
Figure 2: The cages for redeployment of fish to depth of capture.
Table 2: Descriptive codes used by divers to describe the condition of red roman
(Chrysoblephus laticpes) in the cage experiment.
Code
Description
1
Fish was able to swim normally or able to maintain and hold position.
2
Fish lacked buoyancy control, swimming in a head up position or swam in short
bursts falling to the floor of the cage to rest whilst remaining upright, but lolling
from side to side.
3
Fish was seriously compromised, lying on its side on the bottom of the cage and did
not respond to the approach of the diver
4
Fish was dead
A depth range was between 14 and 24 m was maintained for the ten cages so that the divers did
not have to undertake decompression stops. In order to provide a control group, comprising
eight fish were monitored in cages after being captured at depth with hook and line by the divers
sitting on the sea bed. Observations by the divers specifically addressed the ability of the fish to
control their buoyancy by swimming normally and maintaining an upright position when at rest
as well as responsiveness to the presence of the diver. Any obvious external injuries were also
noted. The observed response of the fish was recorded on a scale of one to four ranging between
normal swimming activities to dead, respectively (Table 3).
Table 3: Description of the observation and severity codes for the categorisation of the
symptoms of barotrauma.
Key to severity code
Key to observation code
1 = Distended cavity + any other symptom at level of 1
1 = Fish swims normally
2 = Single symptom > 1 or two symptoms at level of 1
2 = Buoyancy control problem
3 = Combination of symptoms adding up to > 2
3 = Seriously compromised; lying
on side
Controls caught at depth no symptoms
4 = Fish dead
Medium-term repair of the swimbladder
To assess the medium-term effects of barotrauma, just over 100 hottentot and 30 carpenter were
captured from the RV Sardinops at 30 to 40 m depth and 70 to 80 m depth, respectively. These
depths were chosen because 100% of the dissected fish caught beyond these depths had ruptured
swimbladders. The fish were immediately placed in an onboard open circulating holding tank (Fig.
3) transported back to Cape Town and transferred to holding tanks in the Sea Point Aquarium.
These laboratory holding tanks were 7,500 litre capacity polyethylene circular tanks of two-meter
diameter and a height of 1.2 m covered with pilchard netting (Fig. 3). Water flow was via an open
circulating seawater system. A total of 95 hottentot survived transportation and were divided into
batches and placed into three tanks whilst 17 surviving carpenter were held in one tank. Hottentot
were then culled in batches of seven to ten at a time at approximately weekly intervals over a
period of 180 days after capture. Due to the limited number of carpenter available a batch of seven
and a final batch of ten were culled after 21 and 41 days, respectively. All fish were dissected to
detect barotrauma related injuries. The swimbladders were carefully examined for signs of rupture
and the status of their repair was noted.
Figure 3: The onboard holding tank and the holding tanks in the Sea Point Aquarium.
Results
General
The majority of fishes (86%) exhibited at least one external symptom of barotrauma apart from
a distended ventral area (Fig. 4), but there were differences in the occurrence of symptoms
related to the different body areas and differences between species (Table 3). The most common
symptoms were related to the mouth area, with the inverted stomach protruding into and
from the mouth. Often the gas trapped behind the alimentary canal was released when the fish
punctured the stomach lining with its teeth. This occurred with the species that had very sharp
canines such as carpenter and santer whilst roman with blunter canines seldom penetrated the
protruding stomach.
Figure 4: The external barotrauma symptoms related to the mouth, cloaca and gill areas of
the fish.
The second most commonly occurring symptom was related to a distension of the cloaca and
protrusion of the intestine and in severe cases other organs such as gonads and spleen as most
commonly observed in hottentot. Symptoms related to the eyes, epidermis and gills were less
common. Exophthalmia and subcutaneous bubbles in the tissues around the lens affected
roman, carpenter and kob whereas subcutaneous bubbles between the finrays were observed
only in roman and carpenter. These two species were also affected by a condition that caused gas
venting from the skin, lifting the scales along the dorsal flanks. Symptoms related to the gill area
were infrequent and only observed in carpenter and kob (Fig. 4). However, these were always
severe as the inverted alimentary canal had been pushed through the gills and usually hooked on
the gill rakers. Gill related symptoms of barotrauma always lead to mortality.
Table 4: Occurrence of different symptoms (%) of external barotrauma for five species of line
caught fish.
Species
Symptoms
Mouth
Gills
Eyes
Cloaca
Epidermis
Cheimerius nufar (n = )
94
87
0
0
7
0
Chrysoblephus laticeps (n = )
99
78
0
2
23
7
Argyrozona argyrozona (n = )
79
75
3
3
10
1
Pachymetopon blochii (n = )
82
03
0
0
79
0
Argyrosomus inodorus (n = )
99
96
1
1
1
0
Dissections revealed that the swimbladder had ruptured in most of the captured fishes (88%),
even when they exhibited no external symptom other than a slightly distended ventral area
(74%). Again there were slight differences among species (Table 5). Apart from swimbladder
damage, frothy blood and haemorrhaging of liver and kidney were frequently observed (Fig.
5). Occasionally stomachs were found in the early stages of inversion with the stomach looking
like a rolled sock but still contained in the visceral cavity (Fig. 5). Swimbladder rupture was
influenced significantly by depth (Fig. 6).
Figure 5: Internal symptoms of barotraumas related to the swimbladder and other organs.
Table 5: Occurrence of ruptured swimbladders (%) in five species of line caught fishes as
fraction of total number caught per species.
Species
Swimbladder rupture Swimbladder rupture without
external symptoms
Cheimerius nufar
96
92
98
74
85
62
83
74
98
100
Total
88
74
Figure 6: Occurrence of ruptured swimbladders in five species of line caught fishes by depth.
Immediate discard effects
The majority of fishes that were discarded (73%) managed to leave the surface immediately
after being returned into the water. The remainder of the fish struggled to overcome the positive
buoyancy caused by the gas within their bodies and floated on the surface. Species exhibited
different abilities to re-submerge with roman being most and santer least prone to floating
(Table 6). Consequently, mortality rates as a result of failure to re-submerge varied among
species. The probability of submerging successfully decreased with floating time. Less than ten
percent of fish that floated for more than five minutes left the surface. Predation by birds was
commonly observed and accounted for up to 42% of the mortalities of floating fishes. Most bird
attacks were directed at the gill area and resulted in the death of fishes even if they were far too
large to be carried away by the birds. In three instances, floating fishes were eaten by Cape fur
seals, a species commonly regarded as pests by commercial linefishermen on the southern and
western coasts of South Africa.
Table 6: Response (%) of five species immediately returned to the water after capture.
Species
Floating
Predation
Mortality
Mortality of
floaters
Mortality by
predation
Cheimerius nufar
19
2
5
27
36
49
7
20
42
36
Argyrozona argyrozona 25
2
5
19
42
20
0
1
5
0
Short-term post-release effects
A total of 17% of the fish categorised into barotrauma severity scale 1 died after 2-4 hours and
31% by the end of the experiment (Table 7, 8). In contrast only 12.5% of the fish categorised in
barotrauma severity scale 2 died and 16.7% by the end of the experiment. All fish categorised in
barotraumas severity scale 3, did not recover and remained in that state for the duration of the
24 hour experiment. These fish would have likely succumbed to predators if not protected by the
confines of the cage. The eight control fish that were captured in situ showed normal responses
for the full period of the observations and were in no way compromised.
Table 7: Survival (by severity code) of captured red roman (Chrysoblephus laticeps) returned
to depth after 2-4 hours.
Severity code Sample size 1
2
3
4
1
30
62.07
13.79
6.90
17.24
2
18
81.25
0.00
6.25
12.50
3
2
0.00
0.00
100.00
0.00
Total
50
Controls
8
100.00
0.00
0.00
0.00
Table 8: Survival (%) of red roman (Chrysoblephus laticeps) with different barotrauma
symptoms 18-24 hours after release of roman returned to depth by observation and severity codes.
Severity code
Sample size 1
2
3
4
1
30
51.72
17.24
0.00
31.03
2
18
72.22
5.56
5.56
16.67
3
2
0.00
0.00
100.00
0.00
Controls
8
100.00
0.00
0.00
0.00
Overall 14.9% of the fish (excluding those that were severely compromised (severity scale 3))
died within 2-4 hours and 24.5% after 24 hours. These results suggest that mortality rates can
be significant in fish that only display mild symptoms of barotraumas.
Medium-term repair of the swimbladder
During initial dissection to determine internal symptoms of barotrauma it was noted that
hottentot generally displayed smaller ruptures of the swimbladder, in the order of two to five
millimetres in width, as opposed to carpenter with five to 25 mm tears in the swimbladder. The
repair to the swimbladder started out as a thin, transparent layer of tissue over the rupture,
progressing to an opaque scar that in some cases was still discernible in hottentot after 180 days.
A high percentage of hottentot had repaired swimbladders after nine days and the swimbladders
of all fish was complete by day 24 (Fig. 7). In contrast, the swimbladders of only 43% of the
carpenter were repaired after 21 days. Ninety percent of the swimbladders of the carpenter
were repaired after 41 days (Fig. 8). Unfortunately, the experiment did not continue further due
to the limited number of carpenter available. However, the data suggested that swim bladder
repair in carpenter took significantly longer than in hottentot. Although swimbladder repair
was relatively quick, a number of the fish of both species showed signs of infection around the
damaged area often with a pussy substance present. In both, carpenter and hottentot, evidence
was found of organs adhering together probably due to the stimulus of repairing cells in the
adjacent swimbladder (Fig. 9). The stomachs of several carpenter were also found to still be
partially inverted with the tissue adhering together thus diminishing the full volume of the
stomach. One of the fish detected in this condition had recently fed prior to being culled with
food remains still in the stomach thus suggesting that the partial damage to the stomach did not
prohibit feeding.
Figure 7: Rate of swimbladder repair by hottentot (Pachymetopon blochii) after barotrauma
induced rupture.
Figure 8: Rate of swimbladder repair by carpenter (Argyrozona argyrozona) after barotrauma
induced rupture
Figure 9: Example of two repaired hottentot (Pachymetopon blochii) swimbladders and
complete organ adhesion after repair in a carpenter (Argyrozona argyrozona).
Discussion
Our results indicate that most of the fishes experience barotrauma even when caught at
relatively shallow depths. External signs include protrusion of the inflated, inverted stomach
through the mouth, distended eyes, protrusion of the hind-gut and other organs through the
cloaca and gas bubbles in the dermal tissue between the fin rays. The absence of any obvious
external signs of barotrauma can be misleading as dissections of non-symptomatic fish revealed
ruptures of the swim bladder and other internal injuries consistent with barotrauma. The results
of this study indicate that there might be significant post-release mortality, which should be
considered during stock assessment predictions and the implementation of catch restrictions.
References
Arlinghaus R, Cooke SJ, Lyman J, Policansky D, Schwab A, Suski C, Sutton SG, Thorstad EB. 2007.
Understanding the complexity of catch-and-release in recreational fishing: An integrative
synthesis of global knowledge from historical, ethical, social, and biological perspectives.
Reviews in Fisheries Science 15: 75-167.
Brown I, Sumpton W, McLennan M, Mayer D, Campbell M, Kirkwood- J, Butcher A, Halliday I,
Mapleston A, Welch D, Begg GA, Sawynok B. 2010. An improved technique for estimating
short-term survival of released line-caught fish, and an application comparing barotrauma-relief
methods in red emperor (Lutjanus sebae Cuvier 1816). Journal of Experimental Marine Biology
and Ecology 385: 1-7.
Shasteen S P, Sheehan RJ. 1997. Laboratory evaluation of artificial swim bladder deflation in
largemouth bass: potential benefits for catch-and-release fisheries. North American Journal of
Fisheries Management 17: 32-37.
Woodward R T, Griffin WL 2003. Size and bag limits in recreational fisheries: theoretical and
empirical analysis. Marine Resource Economics 18: 239-262.
Preliminary results of the life history of red stumpnose
(Chrysoblephus gibbiceps) an endemic seabream
Megan van Zyl
Marine Research Institute, Department of Zoology, University of Cape Town, Private Bag X3,
Rondebosch 7701, South Africa.
Introduction
Seabreams are important to a number of recreational, commercial and artisanal fisheries
around the world. Seabreams are long-lived, slow growing and sex-changing: characteristics
that make them vulnerable to the effects of overfishing. In southern Africa, our most prized and
sought after recreational and commercial species are seabreams; 41 seabream species occur in
our waters, 25 of which are endemic to the region. Red stumpnose is an important linefish but
catches of this species have been declining. The red stumpnose is a prized angling fish and has
been described as being “extremely charismatic” with “prominent eyes and high forehead give
the stumpnose a ‘scholastic’ appearance” (Biden 1930). Little is known about this species and
baseline data is required to understand changes in their stock dynamics.
Methods
From September 2010, specimens were collected on a monthly basis from Struisbaai. To date,
221 red stumpnose have been captured. Morphological measurements were taken from all
specimens and otoliths, stomach and gonads were preserved. The dataset was supplemented by
the 448 red stumpnose records from the NMLS database, of which 306 records contained viable
otolith samples which were added included in the age study.
Otolith samples were embedded in polyester resin and sectioned through the nucleus at
a thickness of between 0.25-0.35 mm using twin diamond wafering blades. Sections were
mounted on glass slides using DPX mountant. Samples were photographed under a dissecting
microscope using transmitted light.
It was not possible to age and validate all 526 samples, therefore a subset of 37 otoliths were
aged and validated to provide a preliminary insight into the growth of this species.
Macroscopic gonad stages were evaluated to produce maturity ogives for both males and females.
Results and Discussion
Age
This study provides a snapshot of the age of red stumpnose, finding that these fish attain a very
old age; the oldest fish aged to date was estimated to be 31 years old with a fork length of 590
mm. This age is comparable to a number of other long-lived seabreams, such as the red and
white steenbras and the white and black musselcracker (Buxton and Clarke 1989, Buxton and
Clarke 1991, Smale and Punt 1991, Bennett 1993). The youngest fish was aged at 3 years with a
fork length of 215 mm.
Reproduction
A sex ratio of 1:1.6 between male and female red stumpnose was recorded. Both sexes were
present throughout all size classes, this would indicate that this species is gonochoristic.
Yet there was evidence of hermaphroditism in the smaller size classes, indicating that this
species may exhibit some rudimentary degree hermaphroditism, which is quite common in
the seabreams (Buxton and Garratt 1990). Histological studies are necessary to confirm the
reproductive strategy of red stumpnose.
Batch fecundity analysis is planned to provide an indication of the number of eggs spawned per
batch. The female ogive estimated that the length-at-50%-maturity was 261 mm (Fig. 2). Red
stumpnose females were found to mature at a small size. This could explain why this species has
been able to withstand fishing pressure for so long. This also indicates that the minimum size
limit is appropriate for this species.
Figure 1: Age and length data modeled using the Von Bertalanffy growth model.
Figure 2: Female maturity ogive indicating Lm50 = 261 mm.
The male ogive was inconclusive and no length-at-50%-maturity could be estimated (Fig. 3).
This is a result of the limiting number of immature fish and the high number of large fish not
fully mature.
Figure 3: Male maturity ogive, there is no clear indication of Lm50.
This study, when completed, should provide valuable insight into the biology of red stumpnose
to better manage and conserve this fish.
References
Biden CL. 1930. Sea-angling fishes of the Cape. Oxford University Press. London: Humphrey
Milford.
Bennett BA. 1993. Aspects of the biology and life history of white steenbras Lithognathus
lithognathus in southern Africa. South African Journal of Marine Science 13:83-96.
Buxton CD, Clarke JR. 1989. The growth of Cymatoceps nasutus (Teleostei: Sparidae), with
comments on diet and reproduction. South African Journal of Marine Science 8:57-65
Buxton CD, Clarke JR. 1991. Biology of the white musselcracker Sparodon durbanensis (Pisces:
Sparidae) on the Eastern Cape coast, South Africa. South African Journal of Marine Science
10:285-296.
Buxton CD, Garratt PA. 1990. Alternative reproductive styles in seabreams.(Pisces: Sparidae).
Environmental Biology of Fishes 28: 113-124.
Smale MJ, Punt AE. 1991. Age and growth of the red steenbras Petrus rupestris (Pisces: Sparidae)
on the south-east coast of South Africa. South African Journal of Marine Science 10:131-139.
Preliminary findings on the reproductive
characteristics of yellowtail (Seriola lalandi) in South
African waters
K.J. Dunn
Marine Research Institute, Department of Zoology, University of Cape Town, Private Bag X3,
Introduction
Seriola lalandi, a circum-global species occurring in temperate and subtropical waters, is
an important species in the recreational, commercial and aquaculture sectors throughout its
distribution range. S. lalandi occurs along the majority of the South African coastline, west of
Aliwal Shoal. Its movements are thought to be related to hydrographical conditions and prey
availability with the South African population considered to be one stock (Wilke & Griffiths 1999).
Commercial fisheries for S. lalandi are focused in the South western and Western Cape. Landings
have fluctuated between 166 and 890 tons over the last 25 years, with an average annual reported
harvest of 500 tones. The recreational catch is not monitored, but is likely to be substantial.
Despite its importance, very little is known about the biology of S. lalandi in South African
waters. Penny (1982) conducted a study on the movement of S. lalandi and its diet has been
documented (Nepgen 1982), however studies on reproduction, age and growth are lacking. The
reproduction (Baxter 1960, Gillanders et al. 1999b, Poortenaar et al. 2001, Moran et al. 2007,
Shiraishi et al. 2010), diet (Baxter 1960, Schmitt and Strand 1982, Crooke 2001, Vergani 2005)
and age and growth (Baxter 1960, Gillanders et al. 1999a, Shiraishi et al. 2010) of S. lalandi have
been well described outside of South African waters.
This study aims to fill the knowledge gap and update our knowledge on the diet, reproduction,
age and growth of S. lalandi in South African waters.
Methods
Data were obtained from two sources, a database compromising of 6198 samples collected from
1971 to 2010 and from fresh samples caught during 2011-2012. Specimens were measured,
weighed and dissected. Gonads, stomachs and otoliths were removed. Gonads and stomachs
were weighed and stored in 10% formalin. Gonads were staged macroscopically before
preservation. Otoliths were sectioned in two media formats. The first were whole otoliths set
in clear resin and the second otoliths previously set whole in plastic trays covered in resin
and a glass cover slip. Sections were cut at 0.25 mm using a slow rotation saw and mounted
on glass slides with DPX mounting medium. Images of sectioned otoliths were taken at 100x
magnification with a Nikon Eclipse 50i compound microscope.
Results
A total of 6253 specimens were sampled ranging in size from 340 mm FL to 1290 mm FL (Fig 1).
Of these 1914 were male and 2199 female. A sex ratio of 1:15 males to females was found not to
be significantly different from 1:1 (p<0.05). Males ranged in size from 340 mm FL to 1110 mm
FL and females from 380 mm FL to 1290 mm FL. Males and females had similar length-mass
relationships (Fig 2).
The gonado somatic index (GSI) was elevated between November and February for both males
and females (Fig 3). Average female GSI peaked at 1.25 in October, while males peaked at the
same value in December (Fig 3). Mean GSI values decreased rapidly from March reaching a
low of 0.11 in August and 0.49 in May for males and females respectively (Fig 3). A brief winter
peak in GSI was observed in both males and females (Fig 3). The broader spawning season was
observed between November and February with a peak in December. Ripe gonads were present
in males between November and February and between December and March for females with
both sexes peaking in December.
Figure 1: Size frequency histogram for males and females in 50 mm size classes.
Figure 2: Grouped male and female length-Weight relationship for S. lalandi in South
African waters.
Figure 3: Mean annual GSI values for male and female S. lalandi.
The estimated size at which 50% of individuals were mature was 730 mm FL and 647 mm FL for
males and females respectively (Fig 4). The smallest mature male observed in this study was 470
mm FL and 100% of males were mature at 1060 mm FL. The smallest mature female observed
in this study was 480 mm FL and 100% of females were mature at 1190 mm FL.
Preliminary ages ranged from 1 (510 mm FL) to 13 (950 mm FL) years of age. Of the initial
sectioned otoliths 30% were considered unreadable and discarded.
Discussion
Aging fast growing pelagic species has always been a difficult task and S. lalandi is no exception.
The initial aging of S. lalandi in this study has shown a high level of variability with regard to
the ledgeability of sectioned otoliths resulting in inconsistent age readings and 30% of sectioned
otoliths being discarded. The range of ages observed (1-13 years) is on par with other studies,
however very few fish under 3 years of age were found in this study. Further investigation into
the position of the first growth ring may resolve this issue and provide more accurate aging of
younger fish.
As observed in other studies (Baxter 1960, Gillanders et al. 1999a, Poortenaar et al. 2001, Moran
et al. 2007, Shiraishi et al. 2010) S. lalandi appears to be a summer spawner. Male gonadal
activity was elevated between November and February with a single peak in December (Fig 3).
Female gonadal activity begins to rise earlier in September and reaches two summer peaks in
October and December, with the October peak slightly exceeding the December peak (Fig 3).
This early peak in female GSI was also observed by Poortenaar et al. (2001), but no explanation
was given. Only a small percent of fish was found with ripe gonads in this study. This has been
the case in most studies covering the reproduction of S. lalandi. Based on the presence of ripe
gonads and elevated GSI values, the peak spawning season of S. lalandi in South African waters
appears to be between November and February. A winter peak in GSI was also observed for both
sexes in the month of July. There is a definite rise in GSI for July, however the sample size for
that month was low in comparison to summer months and further sampling in July is required
to substantiate this peak.
Figure 4: Length at maturity for male and female S. lalandi.
Size and first maturity, size at 50% maturity and size at 100% mature varied greatly between
various populations of S. lalandi throughout its distribution. In studies documenting these
populations females always matured at lager sizes than males. Gillanders et al (1999b) obtained
an L50 of 470 mm FL for males and 834 mm FL for females in NSW Australia, Poortenaar et
al (2001) obtained and L50 of 812 mm FL for males and 944 mm FL for females in Northern
New Zealand. However in this study males matured at lager sizes than females at 730 mm FL
and 646 mm FL respectively (Fig 4). A sex-ratio significantly different from 1 may explain this
through competition between males, but this was not the case. Females did however reach first
maturity and 100% maturity at larger sizes than males in this study.
S. lalandi has been commercially harvested in South African waters for decades through
various techniques from hand lines to purse seining and accounts for the fourth highest line
fish landings annually. Although S. lalandi stocks are thriving in our waters currently, the
population crash in the early 1980’s serves as a reminder that knowledgeable management is
needed for all exploited species. Looking at the size structure of S. lalandi in this study, 59%
of landed fish fell below the female L50 of 646 mm FL, indicating that most of the fish taken in
our fishery are harvested before contributing to recruitment. This is also typical of S. lalandi
fisheries in New Zealand and NSW Australia where up to 90% of harvested fish fall below the
female L50 (Gillanders et al 1999b). Implementing a size limit to the fishery would greatly aid
stock recovery when needed and could be considered as a management option.
The findings of this study are expecting to increase our knowledge of this species and aid
provide guidelines for its future management. At the completion of this project, an appropriate
aging protocol for the species should have been developed and histological techniques employed
to improve current understanding of this species’ reproductive biology.
References
Baxter JL. 1960. A study of the yellowtail Seriola dorsalis (Gill). State of California Department of
Fish and Game.
Crooke SJ. 2001. Yellowtail. California’s Living Marine Resources: A Status Report. California:
California Department of Fish and Game.
Gillanders BM, Ferrell DJ, Andrew NL. 1999a. Aging methods for yellowtail kingfish, Seriola lalandi,
and results from age- and size-based growth models. Fisheries Bulletin 97:812-827.
Gillanders BM, Ferrell DJ, Andrew NL. 1999b. Size at maturity and seasonal changes in gonad
activity of yellowtail kingfish (Seriola lalandi; carangidea) in New South Wales, Australia. New
Zealand Journal of Marine and Freshwater Research 33 457-468.
Moran D, Smith CK, Gara B, Poortenaar CW. 2007. Reproductive behavior and early development in
yellowtail kingfish (Seriola lalandi Valenciennes 1833). Aquaculture 262 95-104.
Nepgen CS. Dev. 1982. Diet of predatory and reef fish in the False Bay and possible effects of pelagic
purse-seining on their food supply. Fisheries Bulletin South Africa 16: 75-93.
Penny AJ. 1982. The southern Cape yellowtail fishery – a research prospective and preliminary
results. Internal Report No. 108. Sea Fisheries Institute. Cape Town,
Poortenaar CW, Hooker SH, Sharp N. 2001. Assessment of yellowtail kingfish (Seriola lalandi lalandi)
reproductive physiology, as a basis for aquaculture development. Aquaculture 201:271-286.
Schmitt RJ, Strand SW. 1982. Cooperative foraging by yellowtail, Seriola lalandi (Carangidae), on
two species of fish prey. Copeia 3:714-717.
Shiraishi T, Ohshimo S, Yukami R. 2010. Age, growth and reproductive characteristics of gold
striped amberjack 1 Seriola lalandi in the waters off western Kyushu, Japan. New Zealand
Journal of Marine and Freshwater Research 44:117-127.
Vergani, M. 2005. Feeding of the yellowtail kingfish, Seriola lalandi (Valenciennes, 1833 in Cuvier
y Valenciennes, 1833) in waters from Buenos Aires province. Thesis for degree in biological
sciences. University of Mar del Plata. Mar del Plata.
Wilke CG Griffiths MH. 1999. Movement patterns of offshore linefish based on tagging results In:
Mann BQ (ed.), Proceedings of the third South African marine linefish symposium. 28 April – 1
May 1999. Arniston. South Africa: MLRG. pp 95-105.
Session 3 – Fish Movement Studies: Chair Paul Cowley
Movement patterns and genetic stock structure of
an estuarine-dependent, overexploited fish species,
white steenbras Lithognathus lithognathus (Teleostei: Sparidae)
RH Bennett1,2, PD Cowley2*, A-R Childs1,2, G Gouws2, K Reid3, P Bloomer3 and TF Næsje4
1
Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94,
Grahamstown, 6140, South Africa.
2
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown, 6140, South
Africa.
3
Department of Genetics, University of Pretoria, Pretoria, 0002, South Africa
4
Norwegian Institute for Nature Research, P.O. Box 5685, Sluppen, NO-7485 Trondheim,
Norway.
Introduction
White steenbras Lithognathus lithognathus (Pisces: Sparidae) has been a major target species
of numerous fisheries in South Africa since the late 19th century. Historically, the species
contributed substantially to annual catches in commercial net fisheries and became dominant in
recreational shore catches in the latter half of the 20th century (Bennett 1993a, Lamberth et al.
1994). However, overexploitation in both sectors resulted in severe declines in abundance. The
linefish emergency declared in 2000 (Government Gazette No. 21949, December 2000) resulted
in a ban on the commercial harvest of white steenbras. The collapse of the stock by the end
of the 20th century and the failure of traditional management measures to protect the species
highlight the need for an improved management approach. However, certain aspects of the
species’ ecology required for effective management of the fishery stock are poorly understood.
Estuarine and coastal movement behaviour and genetic stock delineation were identified as
research priorities for the species (van der Elst and Adkin 1991, Lamberth and Joubert 1999).
Estuarine movement patterns
Acoustic telemetry was used to assess the movement patterns of juveniles in two Eastern
Cape estuaries. Fifteen white steenbras (235 – 302 mm FL) were tagged in the small (3.5 km),
temporarily open/closed East Kleinemonde Estuary, and ten individuals (215 – 379 mm FL)
were tagged in the large (17.5 km), permanently open Kariega Estuary. Acoustic transmitters
were surgically implanted into fish and movements passively tracked using arrays of stationary
automated acoustic receivers, or manually tracked using a portable receiver and hydrophone.
The tagged fish exhibited site fidelity, restricted area use, small home ranges relative to the size
of the estuary, and high levels of residency within both estuaries. Behaviour was dominated by
station-keeping, with fish spending the majority of their time in the lower reaches and mouth
region (Fig. 1). These results agree with those from a preliminary assessment of the movements
of this species in the permanently open Great Fish Estuary (Bennett et al. 2011).
In the East Kleinemonde Estuary, station-keeping was superimposed onto a strong diel
behaviour. This behaviour was presumably in response to feeding and/or predator avoidance,
with individuals entering the shallow littoral zone at night to feed, seeking refuge in the deeper
channel areas during the daytime. In the permanently open Kariega Estuary, movements were
influenced by a more complex interaction between diel and tidal cycles. Tagged fish moved onto
the shallow banks as they became inundated during the incoming tide, retreating to the deeper
channel areas as the water receded.
Coastal movement patterns
Conventional dart tagging and recapture data were extracted from four ongoing, long-term
coastal fish tagging projects covering the species’ distribution to assess the level of alongshore
coastal movements and the existence of an annual spawning migration. These data were
obtained from tagging programmes conducted in the De Hoop (DEH), Tsitsikamma (TNP) and
proposed Greater Addo Elephant National Park (GAENP) marine protected areas (MPAs), and
the Oceanographic Research Institute’s (ORI) national tagging project. By the end of 2011, 5 775
white steenbras had been tagged, with 292 reported recaptures (5.1%). The four programmes
produced similar results, with late juvenile and sub-adult fish exhibiting high levels of residency
in the surf zone (Fig. 2). The results agree with those of a preliminary conventional dart tagging
study conducted for white steenbras in the Tsitsikamma MPA (Cowley 1999).
Figure 1: Mean proportions (%) of time spent in different regions of a) the temporarily
open/closed East Kleinemonde Estuary (n = 15) and b) permanently open Kariega Estuary
(n = 10), based on distances (km) from the mouth, for juvenile white steenbras tracked
using acoustic telemetry
Figure 2: Frequency distributions of distances moved by recaptured white steenbras (n = 292),
for a) all studies combined and b) the DEH, TNP, GAENP and ORI tagging projects separately.
It has been hypothesized that adult white steenbras undertake large-scale coastal spawning
migrations (Bennett 1993b). The scale of coastal movements in the current study was
significantly positively correlated with fish size (Fig. 3, R2 = 0.148, p < 0.001) and age (R2 =
0.170, p < 0.001), with adult fish (>600 mm FL) undertaking considerably longer-distance
coastal movements (up to 620 km) than smaller individuals, supporting this hypothesis.
Genetic stock structure
Effective management of exploited fish stocks requires an understanding of the genetic
structure of the stock. The genetic structuring of white steenbras had not previously been
assessed. Further, despite the robust results obtained through conventional dart tagging, a lack
of empirical evidence of fish migrating between False Bay, in the south-western Cape, and the
former Transkei coastline, areas identified as summer aggregation and winter spawning areas
(Penney 1991, Bennett 1993b), remained. Therefore, the genetic structure of the stock and the
uncertainty in the level of connectivity among coastal regions were assessed using mitochondrial
DNA (mtDNA) sequencing and genotyping of microsatellite repeat loci in the nuclear genome.
The results of both techniques showed no evidence of major geographic barriers to gene flow,
no isolation by distance, and no localised spawning within this species (Bennett 2012). Samples
collected throughout the white steenbras core distribution showed high genetic diversity, and
low genetic differentiation based on pairwise genetic comparisons between sampling localities
(Tables 1 and 2).
Figure 3: Linear regression of distance moved (km) against fork length (mm) for 207 white
steenbras accurately measured at the time of recapture.
Table 1: Pairwise genetic diversity (FST) values (above diagonal) and associated p-values (below
diagonal) between sampling localities (n = 8 localities, no significant differences), based on 720base pair mtDNA sequences of 307 individual white steenbras.
Transkei
Transkei
East
London
-0.007
Kleinemonde
Algoa
Bay
Knysna/
Swartvlei
Breede/
De Hoop
Langebaan
-0.012
-0.008
0.006
-0.002
0.015
-0.013
-0.015
-0.012
-0.002
-0.001
0.000
-0.007
-0.010
0.002
0.000
0.009
-0.015
0.003
0.002
0.015
-0.015
-0.001
-0.007
0.000
0.007
0.002
East London
0.651
Kleinemonde
0.749
0.946
Algoa Bay
0.667
0.977
0.807
0.227
0.540
0.337
0.274
0.443
0.455
0.400
0.286
0.428
False Bay
0.088
0.393
0.144
0.051
0.872
0.145
Langebaan
0.703
0.614
0.792
0.899
0.381
0.336
Knysna/
Swartvlei
Breede/De
Hoop
False
Bay
0.021
0.052
Table 2: Pairwise genetic differentiation (RST) values (above diagonal) and associated p-values
(below diagonal) between sampling localities (n = 8 localities, no significant differences), based
on 11 polymorphic microsatellite loci from 330 individual white steenbras.
Transkei
East
London
Kleinemonde
Algoa
Bay
Knysna/
Swartvlei
Breede/
De Hoop
False
Bay
Langebaan
Transkei
-0.002
0.007
-0.006
-0.015
-0.013
-0.007
0.007
-0.004
-0.007
-0.001
-0.001
-0.004
-0.008
0.005
0.003
-0.001
-0.005
0.010
-0.005
-0.003
0.002
-0.008
-0.007
-0.005
-0.002
-0.005
-0.005
East London
0.407
Kleinemonde
0.231
0.596
Algoa Bay
0.566
0.774
0.207
0.965
0.419
0.243
0.643
0.928
0.397
0.428
0.495
0.861
False Bay
0.660
0.567
0.661
0.215
0.652
0.652
Langebaan
0.191
0.660
0.192
0.675
0.423
0.581
Knysna/
Swartvlei
Breede/De
Hoop
0.005
0.210
Discussion
Trends in white steenbras catch-per-unit-effort (CPUE) have shown consistent declines over
the past 40 years (Bennett 1993a, Bennett 2012). Furthermore, management interventions,
including maximum daily bag, minimum size limits for recreational anglers, and increasingly
stringent catch and gear restrictions on commercial fishers (Penney 1991, Bennett 1993) have
failed to prevent overexploitation or restore spawner biomass levels. The collapsed status of the
stock suggests that the species requires more intensive management. The linefishery in South
Africa is plagued by problems such as low compliance (Cowley et al. 2004) and low enforcement
capacity, and alternative management measures need to be evaluated for this species.
The use of shallow littoral areas as critical habitats within estuaries highlights the vulnerability
of the species to habitat degradation, while the high level of residency within and dependence
on estuaries at the juvenile life stage makes white steenbras vulnerable to overexploitation in
estuaries. However, residency within estuaries suggests that juvenile white steenbras could
be effectively protected through strategically positioned estuarine protected areas (EPAs).
Similarly, high levels of residency within the coastal zone render late juvenile and sub-adult
white steenbras vulnerable to localised overexploitation, but simultaneously provide the
opportunity for effective protection through MPAs. At the migratory adult life stage, the
management value of MPAs is questionable, without the protection of adults at spawning and
aggregation sites.
However, existing MPAs cumulatively encompass a low proportion of sandy shoreline, for
which white steenbras exhibits an affinity (Bennett 2012). Furthermore, recreational shore
angling, which currently accounts for the greatest proportion of the total annual catch of white
steenbras, is currently permitted within many of the MPAs within the species’ core distribution.
In addition, EPAs within the juvenile distribution protect a negligible proportion of the total
available surface area of estuaries – habitat on which this species is wholly dependent. The
current network of estuarine and marine protected areas is therefore insufficient for the effective
protection of white steenbras.
Despite some evidence of recent increases in abundance in estuaries and the surf zone in certain
areas, white steenbras meets the criteria for “Endangered” on the IUCN Red List of Threatened
Species, and for “Protected species” status under the National Environmental Management:
Biodiversity Act (Act No. 10 of 2004) of South Africa (Bennett 2012). The species therefore
requires improved management strategies that include considerations of its life-history
style, estuarine dependency, surf zone residency, predictable spawning migrations and poor
conservation status. This will require increased protection levels within certain existing MPAs,
expansion of the current EPA network, and further investigation of the suitability of closed
seasons for the protection of spawning adults.
References
Bennett BA. 1993a. The fishery for white steenbras Lithognathus lithognathus off the Cape coast,
South Africa, with some considerations for its management. South African Journal of Marine
Science 13: 1-14.
Bennett BA. 1993b. Aspects of the biology and life history of white steenbras Lithognathus
lithognathus in southern Africa. South African Journal of Marine Science 13: 83-96.
Bennett RH. 2012. Movement patterns, stock delineation and conservation of an overexploited
fishery species, Lithognathus lithognathus (Pisces: Sparidae). PhD thesis, Rhodes University:
387 pp.
Bennett RH, Childs A-R, Cowley PD, Næsje TF, Thorstad EB, Økland F. 2011. First assessment of
estuarine space use and home range of juvenile white steenbras, Lithognathus lithognathus.
African Zoology 46: 32-38.
Cowley PD. 1999. Preliminary observations on the movement patterns of white steenbras
Lithognathus lithognathus and bronze bream Pachymetopon grande (Teleostei: Sparidae) in
the Tsitsikamma National Park Marine Reserve. Proceedings of the third Southern African
Marine Linefish Symposium, Arniston, 28 April – 1 May 1999: 106-108.
Cowley PD, Wood AD, Corroyer B, Nsubuga Y, Chalmers R. 2004. A survey of fishery resource
utilization on four Eastern Cape estuaries (Great Fish, West Kleinemonde, East Kleinemonde
and Kowie). Protocols Contributing to the Management of Estuaries in South Africa, with a
Particular Emphasis on the Eastern Cape Province Volume III Project C, Supplementary Report
C5: 129-165
Lamberth SJ, Bennett BA, Clark BM. 1994. Catch composition of the commercial beach-seine fishery
in False Bay, South Africa. South African Journal of Marine Science 14: 69-78.
Lamberth SJ, Joubert A. 1999. Prioritizing linefish species for research and management: A first
attempt. Proceedings of the third Southern African Marine Linefish Symposium, Arniston, 28
April – 1 May 1999: 130-133.
Penney AJ. 1991. The interaction and impact of net and linefisheries in False Bay, South Africa.
Transactions of the Royal Society of South Africa 47(4/5): 661-681.
van der Elst RP, Adkin F. 1991. Marine linefish – Priority species and research objectives in southern
Africa. Oceanographic Research Institute Special Publication 1: 125pp.
Fish movements in the Pondoland Marine Protected
Area: balancing conservation and fisheries
enhancement
JQ Maggsa, BQ Manna and PD Cowleyb
Oceanographic Research Institute, PO Box 10712, Marine Parade, Durban, 4056, South Africa
b
Africa.
a
Introduction
In 2000, a state of emergency was declared in the South African marine linefishery. For nearly
20 years, these fisheries had been managed in the conventional way using daily bag limits,
minimum size limits and closed seasons. Unfortunately, this approach had failed to arrest a
decline in the fishery. Since the emergency was declared, marine protected areas (MPAs) have
been increasingly promoted as an additional tool to manage and rebuild depleted linefish stocks.
In June 2004, the Pondoland MPA was proclaimed on the Eastern Cape coast of South Africa.
A 400 km2 no-take zone, closed to vessel-based exploitation, is situated between two controlled
exploitation zones, altogether giving an area of 800 km2 (Figure 1).
Recovery of fish stocks within the boundaries of a no-take area provides insurance against
management failure in fished areas (Bohnsack 1998), and can lead to spillover onto nearby
fished reefs (Russ 2002). Recovery of over-exploited fish stocks is dependent on the residency
of fishes within a no-take area, whereas the benefit to adjacent fisheries relies on the dispersal of
fishes from the no-take area. The two main objectives of area closure may therefore be in conflict
(Tolimieri et al. 2009).
Could the no-take zone of the Pondoland MPA retain sufficient fish biomass to ensure stock
recovery while still contributing post-larval fishes to adjacent fished reefs? Movement patterns
of four important linefish species (Scotsman Polysteganus praeorbitalis, slinger Chrysoblephus
puniceus, yellowbelly rockcod Epinephelus marginatus and catface rockcod E. andersoni),
occurring in the Pondoland MPA, were investigated.
Material and methods
Between April 2006 – July 2010, fish movement data were collected quarterly in and around
the Pondoland MPA. Four 2 km2 offshore areas, in water depth of 10-30 m were chosen as study
sites with two sites in the no-take zone (Mtentu and Mkambati) and two in the adjacent fished
area Mzamba and Mnyameni(Fig. 1). The Mnyameni site lies within the MPA’s exploited zone
and the Mzamba site lies entirely outside the MPA, but both sites are similarly open to vesselbased linefishing and spearfishing.
Fishes were captured by linefishing from a ski-boat at randomly chosen GPS coordinates within
each of the four study sites. Fishes, >300 mm, were tagged with plastic dart tags (Hallprint Pty
Ltd, Australia), each marked with a postal address and a unique alphanumeric code. Besides
fishes recaptured by the research team within the four study sites, members of the public also
reported recaptures from areas outside the no-take zone.
Data analysis
Dingle (1996) provided a simple classification of animal movement, which is suitable for
assessing the movement patterns of fishes in the current study (Table 1). Station-keeping is a
good indicator of the potential for biomass retention within a protected area, while ranging (or
possibly migratory) behaviour indicates the potential for export to adjacent fisheries. In the
current study, station-keeping movements were also used to estimate home range size to further
quantify the degree of residency.
Home range
Home range length was estimated for each species by taking the 95th percentile of intra-study
site movements only, excluding all long distance movements (Maggs 2011). The resulting
estimate of home range length is referred to as single linear distance (SLD) in the current
study (Fig 2a). Assuming that a fish is randomly drawn from within the boundaries of its home
range at first capture (tag-release) and then re-drawn from that same home range at a later
stage (recapture), the Euclidean distance between the two points (SLD) can be considered to
represent a proportion of the length of the actual home range. Repeating this several times, with
different individuals of the same species increases the probability of obtaining the mean length
of the home range for that species. To prevent pseudo-replication the calculation of SLD used
only the distance between the tag-release and first recapture.
Figure 1: The Pondoland MPA on the Eastern Cape coast of South Africa. All vessel-based
exploitation is prohibited in the 400 km2 no-take zone, but vessel-based linefishing and
spearfishing are permitted in the two exploited zones.
Table 1: Classification of animal movement behaviour proposed by Dingle (1996).
Movement type
Characteristics
Station-keeping:
Kinesis
Movements that serve to keep an animal stationary
Foraging
Movements within a home range
Commuting
Diel movements between day & night locations
Territoriality
Territorial defence & aggression, non-overlapping home ranges
Ranging
Exploratory movements over wide areas in search of
resources
Migration
Persistent, directed, non-exploratory, predictable, physiological
adaptation
Multiple recaptures, having three or more capture points were less frequent. These records
provided a two-dimensional representation (polygon) of area utilisation by an individual fish.
An alternative estimate of home range length was calculated by taking the 95th percentile of the
greatest linear distance (GLD) across the interior of the polygon (Fig 2b). The resulting estimate
was used to validate the SLD calculated above.
Ranging (dispersal to fished reefs)
The potential of the no-take zone to export fish biomass was evaluated using records of longdistance movement for each species (i.e. tagged fish leaving the study site). The recovery of
ranging fishes was reported exclusively by recreational and commercial fishers through the ORI
Tagging Project. While relatively few long-distance movements were reported, the potential for
non-reporting exists (Dunlop 2010).
Figure 2: Calculation of home range length used in this study. a) single linear distance (SLD):
distance between release and first recapture and b) greatest linear distance (GLD): greatest
distance between all capture points of an individual fish.
Results
Overall, 1022 fishes of the four study species were tagged in the four study sites (April 2006 July 2010) and 220 of these were recaptured at least once (Table 2). The overall recapture rate,
including individuals recaptured more than once, ranged between 8% for slinger and 61% for
yellowbelly rockcod. Of the 1022 fishes tagged, 780 were tagged at the two no-take sites (Mtentu
and Mkambati) and 242 at the two exploited sites (Mnyameni and Mzamba).
Movement patterns
Ninety-four per cent of recaptured individuals of the four study species were within the same
study site where they were originally tagged. Nineteen fishes left the study sites, 13 of which
moved between 150-1059 km towards the north-east, suggesting a distinct separation between
station-keeping and ranging movements (Fig 3). The majority of recaptures (Scotsman 72%,
slinger 76%, catface rockcod 90%, yellowbelly rockcod 97%) were within 250 m of the release
site (Fig 4). Little association existed between distance moved and fish length (Fig 4), although
the longest distances moved by yellowbelly and catface rockcod were by larger individuals.
There was also no correlation between distance moved and time at liberty (Fig 5). Some
individuals remained resident for extended periods, while others moved long distances shortly
after being released.
Station-keeping
In all species and in all four study sites, it was found that the mean distance between fishing
stations was significantly (P<0.05) greater than the mean distance moved by each fish species.
That is, fishing stations within each 2 km2 study site were scattered over an area which was
greater than the mean recorded movement distance of the tagged fish, providing confidence in
home range estimates. Recorded movements, representative of station-keeping behaviour, were
small resulting in estimates of home range (SLD/GLD) in the order of a few hundred meters
(Table 3). Estimates varied among the species but home range estimates were considerably
smaller than the size of the no-take zone.
Ranging
Six per cent of recaptures were reported from outside the 2 km2 study site in which the fish had
originally been tagged and released. Besides six intermediate movements by Scotsman (3-14
km), ranging movements for the four study species varied between 153-1059 km with time at
liberty between 264-1316 days. Scotsman had the greatest proportion of ranging individuals of
all four species. With only two exceptions (Scotsman), recaptured fishes reported beyond the
boundaries of the 2 km2 study sites had moved in a north–easterly direction, up the east coast
of KZN. Most recorded ranging movements saw fish moving out of the no-take zone of the
Pondoland MPA and into deeper water, as indicated by members of the public who had reported
these recaptures.
Table 2: Tag-recapture summary for the four study species in the Pondoland MPA between
April 2006 and July 2010.
Overall
Exploited
area
No-take
zone
No. of individuals tagged
385
80
305
No. of individuals recaptured
98 (25%)
24 (30%)
74 (24%)
more than once
23
2
21
4
5
Scotsman
Most times an individual was
recaptured
Overall recapture rate
36%
39%
35%
Slinger
308
12
296
26 (8%)
0
26 (9%)
more than once
None
n/a
n/a
recaptured
8%
0%
9%
161
33
128
51 (32%)
8 (24%)
43 (34%)
more than once
22
4
18
5
9
recaptured
61%
61%
61%
168
117
51
45 (27%)
32 (27%)
13 (25%)
more than once
18
12
6
5
5
Catface rockcod
recaptured
1
Yellowbelly rockcod
n/a
45%
43%
49%
Figure 3: Two movement behaviours exhibited by Scotsman Polysteganus praeorbitalis in
and around the Pondoland Marine Protected Area. As an example, station-keeping movements
within the Mtentu 2 km2 study site were between 4-987 m, while ranging movements,
originating in both the exploited area and no-take zone, were between 153-357 km toward the
north-east (six intermediate movements excluded).
Discussion
Two types of movement behaviour were apparent in all four species. Station-keeping behaviour
was commonly observed during research fishing. Ranging behaviour was also apparent as
members of the public occasionally reported tagged fish that had been recaptured hundreds of
kilometres north-east of the Pondoland MPA. Several tag-recapture studies undertaken along
the southern Cape coast of South Africa (Attwood 2002, Brouwer 2002, Cowley et al. 2002,
Griffiths and Wilke 2002, Brouwer et al. 2003) and in Australia (Gillanders et al. 2001, Russell
and McDougall 2005) have noted similar variation in fish movement behaviour. On a smaller
scale, acoustic telemetry studies have also reported similar variation in movement behaviour
amongst individuals within a local population, with a high degree of station-keeping and a
smaller element of nomadic behaviour (Egli and Babcock 2004, Kerwath et al. 2007, Childs et
al. 2008, Hedger et al. 2010).
Home range size
Home ranges calculated in this study varied between 125 m for yellowbelly rockcod and 748 m
for Scotsman. Such small home ranges inevitably lead to localised depletion of the species in
exploited areas, but can also be of benefit to such species in protected areas. Compared to the
size of the Pondoland no-take zone, which is ~40 km long and ~10-15 km wide, these home
ranges are very small. In other words, the day-to-day movements of the four species in the notake zone will not expose them to fishing in the adjacent fished areas, and will allow fish stocks
to recover. This is supported by the findings of Maggs (2011), who found greater abundance
and mean length of slinger, Scotsman and yellowbelly rockcod in the Pondoland no-take zone.
In this way, the MPA provides insurance against management failure in fished areas; but the
immediate benefit of the no-take zone to the adjacent fishing community is less certain.
Figure 4: Frequency histograms of all movements (station-keeping and ranging) made by the
four species tagged between 2006 and 2010 in the Pondoland MPA. ▲ indicates mean fork/total
length of recaptured fishes. Non-compatible measurements reported by the public were omitted
(e.g. fork length measured at release and total length measured at recapture).
Table 3: Estimates of home range for the four study species using the 95th percentile of intrastudy site movements. Expressed as single linear distance (SLD) and greatest linear distance
(GLD). Values in meters.
SLD (m)
GLD (m)
Scotsman
748
642
Slinger*
696
Yellowbelly rockcod
125
154
Catface rockcod
270
164
*Limited to SLD observations obtained in no-take zone
Dispersal to fished reefs
In this study, 68% of the movements recorded beyond the borders of the home range were
greater than 150 km and took the fish outside the entire MPA. Without exception, members of the
public, who had been fishing on exploited reefs north-east of the Pondoland MPA, reported these
recaptures. No recaptures were reported from the Wild Coast, south-west of the Pondoland MPA,
but ski-boat fishing effort in these areas are relatively low. Nevertheless, exploitable reefs in KZN
were supplied with fishes, which had been under temporary protection in the Pondoland MPA.
This supply was limited to a low percentage of the protected populations.
Many studies have failed to discriminate between spillover and variability in individual
movement patterns (Zeller et al. 2003). Density dependent spillover implies the net export of
adult fishes from a no-take area, where there is a high concentration of large individuals, to
nearby areas where fishing has reduced the numbers and size of fishes. The greater abundance
and mean size of fishes in the no-take zone reported by Maggs (2011), and the fact that the
current study shows fishes moving out of the no-take zone and being caught in the adjacent
exploited area, is suggestive of density dependent spillover. However, long distance, ranging
movements were undertaken by fishes tagged in both the exploited area and no-take zone,
implying that export was not necessarily density dependent and was probably associated with
individual behaviour.
Figure 5: Relationship between all distances moved and times at liberty for the four study
species tagged between 2006 and 2010 in the Pondoland MPA.
Reasons for dispersal
If movement of these four species out of the no-take zone is not density dependent, then what other
factors could drive their dispersal? Some fish moved long distances shortly after being released,
while others stayed resident for years. Mounting evidence from other studies in South Africa
suggests that many typically resident species occasionally move long distances up the East Coast to
warmer water, possibly for reproductive purposes. Such behaviour has been recorded in a number
of sparids, including poenskop Cymatoceps nasutus (Buxton and Clarke 1989), red steenbras Petrus
rupestris (Brouwer 2002), white steenbras Lithognathus lithognathus (Bennett 1993) and white
musselcracker Sparodon durbanensis (Buxton and Clarke 1991, Watt-Pringle 2009).
Reproductive studies of slinger (Garratt et al 1993) and catface rockcod (Fennessy and Sadovy
2002) have shown that there is little or no spawning activity in the Pondoland region. Fennessy
(2006) also cited an anecdotal source that suggested very limited spawning of yellowbelly
rockcod south of KZN. A north-eastward spawning migration is thus likely if individuals located
in the southern regions of their distribution range were to spawn (Garratt et al. 1993). The
locality of spawning grounds of Scotsman is not known. Garratt et al. (1994) and Mann et al.
(2005) found very few reproductively active Scotsman along the entire KZN coast. However,
they did find a greater percentage of large, reproductively active fish in northern KZN, again
suggesting that spawning takes place predominantly in the north-eastern parts of their
distribution range.
Along southern Africa’s east coast, the south flowing Agulhas Current facilitates the southward
dispersal of juvenile fishes towards nursery areas (Beckley 1993). In typically resident species,
where there are individuals that occasionally move long distances towards the north-east,
juveniles are generally more abundant in the southern reaches of their distribution. Considering
the general southward movement of fish larvae, migrating north to spawn may prevent fish eggs
and larvae from moving beyond southern distribution limits where environmental conditions
are intolerable. Along the east coast of Australia, the eastern Australian yellowfin bream
Acanthopagrus australis (Sparidae) is believed to follow a similar dispersal pattern (Roberts
and Ayre 2010). In that region, the East Australian Current (a western boundary current similar
to southern Africa’s Agulhas Current) is thought to facilitate southward larval dispersal, while
adults actively swim north to spawning sites.
Conclusion
Small home ranges indicate that the four species are afforded sufficient protection within the
Pondoland MPA to allow stock rebuilding. In reality, this may not hold true for catface rockcod,
which were reported to be more abundant in the exploited area (Maggs 2011). Nevertheless,
tag-recapture data provided conclusive proof that some fishes, including one catface rockcod,
crossed the no-take boundaries into exploitable areas, having taken temporary refuge in the
no-take zone. It therefore appears that the no-take zone has the potential to contribute fish
biomass sustainably to adjacent fisheries. A considerable body of evidence has been collected
in South African fisheries research to suggest that long distance migration is associated with
the requirement to spawn in warmer water. For these species, additional no-take areas along
the KZN coast are essential to protect the reproductive capacity of depleted stocks. At the same
time, further scientific fish tagging projects are required in the offshore environment north-east
of Pondoland (KZN), to investigate the return migrations of these species to colder waters.
Acknowledgements
We thank DEA, Eastern Cape Parks and Tourism Agency, the Wild Coast Project and SAAMBR,
for providing funding. We are grateful to the KZN Sharks Board for allowing use of their vessels
and skippers, and to EKZNW for providing accommodation during field trips. Guest anglers are
thanked for their participation in field trips.
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Bohnsack JA. 1998. Application of marine reserves to reef fisheries management. Australian
Journal of Ecology 23: 298-304.
Brouwer SL. 2002. Movement patterns of red steenbras Petrus rupestris tagged and released in the
Tsitsikamma National Park, South Africa. South African Journal of Marine Science 24: 375-378.
Brouwer SL, Griffiths MH, Roberts MJ. 2003. Adult movement and larval dispersal of Argyrozona
argyrozona (Pisces: Sparidae) from a temperate marine protected area. African Journal of
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comments on diet and reproduction. South African Journal of Marine Science 8: 57-65.
Buxton CD, Clarke JR. 1991. The biology of the white musselcracker Sparodon durbanensis (Pisces:
Sparidae) on the eastern Cape coast, South Africa. South African Journal of Marine Science 10:
285-296.
Childs AR, Booth AJ, Cowley PD, Potts WM, Næsje TF, Thorstad EB, Økland F. 2008. Home range
of an estuarine-dependent fish species Pomadasys commersonnii in a South African estuary.
Fisheries Management and Ecology 15: 441-448.
Cowley PD, Brouwer SL, Tilney RL. 2002. The role of the Tsitsikamma National Park in the
management of four shore-angling fish along the south-eastern Cape coast of South Africa.
South African Journal of Marine Science 24: 27-35.
Dingle H. 1996. Migration: the biology of life on the move. New York: Oxford University Press.
Dunlop S. 2010. Low reporting rate for the recapture of tagged fish. In: Bullen E, Mann BQ, Everett
BI (eds), Tagging News. Durban: Oceanographic Research Institute. p 11.
Egli DP, Babcock RC. 2004. Ultrasonic tracking reveals multiple behavioural modes of snapper
(Pagrus auratus) in a temperate no-take marine reserve. ICES Journal of Marine Science 61:
1137-1143.
Fennessy ST. 2006. Reproductive biology and growth of the yellowbelly rockcod Epinephelus
marginatus (Serranidae) from South-East Africa. African Journal of Marine Science 28: 1-11.
Fennessy ST, Sadovy Y. 2002. Reproductive biology of a diandric protogynous hermaphrodite, the
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Garratt PA. 1993. Slinger - The final analysis? In: Beckley LE, van der Elst RP (eds.), Fish, fishers
and fisheries - Proceedings of the second South African marine linefish symposium, 23-24
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A review of the Oceanographic Research Institute’s
(ORI) Voluntary Tagging Project: 27 years down the line
SW Dunlop and BQ Mann
Oceanographic Research Institute, PO Box 10712, Marine Parade 4056, South Africa.
Introduction
The ORI Tagging Project was initiated in 1984 and is currently considered to be one of the most
successful collaborative environmental projects of its kind in South Africa. Although instances of
fish tagging in South Africa had been conducted as early as the 1930s on Cape snoek (De Jager
1955) and later on other species (Davies and Joubert 1966, Newman 1970, Bass et al. 1973, Bass
1977, van der Elst 1990), these were limited species-specific projects, not all of which yielded
relevant results (van der Elst 1990). Furthermore, much of the data remained unpublished and/
or unavailable for dissemination (van der Elst 1990). These two factors were the driving force
behind the initial development of the ORI Tagging Project.
The majority of the tagging projects that existed prior to 1984 involved experienced/trained
personnel, such as scientists and conservation officers. In contrast, the ORI Tagging Project
involves the cooperation of voluntary, conservation-conscious anglers (i.e. anglers who
voluntarily release their fish) and the marine angling public at large who report the majority
of the recaptures (i.e. a fish that is recaught with a tag in it). There is also a large proportion of
institutional scientific tagging that takes place along our coast, particularly in Marine Protected
Areas (MPAs), that is incorporated into the ORI Tagging Project. The information obtained
from this project has proved extremely valuable and has been utilised throughout southern
Africa by students and scientists to study linefish species and make recommendations regarding
improving management of their stocks. Furthermore, the ORI Tagging Project allows fishers to
actively participate in the accumulation of data that could ultimately improve conservation and
management of important linefish species.
Development of the Tagging Project
Participation in the Tagging Project is restricted and anglers are not simply accepted as
members in the program. Only anglers displaying an above average desire to contribute to the
Tagging Project may formally request participation. Tagging kits are issued to individuals in
custom designed pouches containing promotional matter, an instruction manual, tape measure,
one, or more, types of tags attached to postage paid tag return cards, and associated tag
applicators. From 2010, an instructional DVD was provided to members in order to improve fish
handling and tagging techniques.
Prior to the implementation of the ORI Tagging Project, a number of studies were conducted for
various tag types to determine the associated rates of tag loss/shedding and tag-induced mortality
on captive fish. From these results, a suite of suitable tag types were selected for the ORI Tagging
Project. These tag types were issued to member anglers depending on their target species and
capabilities. However, over the years, improving technology has resulted in some of these types
of tags being discontinued, while new types of tags have been incorporated into the project. The
following types of tags have been, or are still, being used in the ORI Tagging Project:
Type A: Spaghetti type, plastic-barb dart tags used on most teleost fish, stingrays and sharks
greater than 60 cm in length.
Type B: Spaghetti type, dart tags with an inner length of stainless steel wire attached to a stainless
steel anchor. These are used on billfish or large tuna and sharks in excess of 25 kg. The use of this
tag has now been limited to scientists and specialised shark anglers (e.g. KwaZulu-Natal Sharks
Board). This tag has been replaced by Type M tags for the tagging of billfish (see below).
Type C: These were locally manufactured plastic disk tags and were originally used for insertion
into small sharks and guitarfishes under 25 kg. Although not intended for skates and rays, many
have been tagged off South Africa using this tag (inserted into the ‘wing’ of the ray ) with very
few recaptures (van der Elst 1990). Use of these tags was discontinued in 1998 due to poor tag
retention (splitting of the dorsal fin) and extreme biofouling.
Type D: This tag type is similar in design to Type A tags, but restricted for the tagging of
smaller teleosts between 30-60 cm in length, although they may also be used for some small
elasmobranchs. This is the most commonly used tag type in the project.
Type M: Spaghetti type, dart tags with a wire enforcement and an inert bullet shaped head with
two spliced wing barbs with a whole through the centre introduced in late 2011. The tag head
is attached to the marker by a length of high tensile strength monofilament leader (or stainless
steel wire). This tag was only used on billfish and tuna in excess of 25 kg and has replaced the
Type B tags.
Other Types: Other types of tags that have been used in the ORI Tagging Project include BT
and DT tag types. These tag types are identical to the Type B and D tags respectively, but are
orange in colour, as opposed to the standard yellow tags. These tags indicated that the fish had
been injected with oxytetracycline during tagging for validation of ageing and, if recaptured, the
fish itself should be kept and returned to ORI.
Conservation Impacts Achieved
By the end of 2011, a total of 5 130 anglers were participating the ORI Tagging Project. Of these
members, only 34% (1 753) had tagged 10 or more fish. Between 1997 and 2005 there was a
steady decline in annual membership with the lowest number of new members joining the
project in 2002 (only 54) (Fig 1). The reasons for this decline are unclear but may be related
to marketing and management of the project itself. Although a similar decline in the number
of fish tagged per year for the same period was observed (Figs 2 and 3), this was not related
to a decline in overall fish abundance. Although there has been an overall decrease in the
number of members joining the project since its inception, this decline was related to a policy
implemented in the project to improve the quality of tagging data received from anglers as
opposed to increasing the quantity of fish tagged. Furthermore, in the last 10 years the ORI has
struggled to secure sufficient funding for the Tagging Project which has subsequently resulted in
stricter protocols in purchasing equipment and issuing out tagging kits and tags. The increased
number of members joining the project from 2005 onwards can be related to technological
advancements (e.g. e-mail/internet/cellular phones) and the active promoting of tag and release
in the media.
Figure 1: Annual number of new and active members in the ORI Tagging Project over a
27-year period.
Interestingly, despite the number of anglers that join the Tagging Project each year, the
cumulative number of active members (i.e. tag one or more fish) remains fairly low (484
members/year). Furthermore, the number of active members also steadily decreased between
1997 and 2005, mimicking the trends in annual membership. These results indicate the
importance of new members joining the project each year as the novelty of being a regular
tagger soon dissipates. This is partly explained by the fact that ‘tag and release’ goes beyond
simply catching and releasing a fish but requires extra effort by the angler to tag the fish and
record and submit the data. Committed taggers that have remained active for long periods are
therefore relatively scarce.
Figure 2: Annual number of tags bought, issued and used in the ORI Tagging Project over a 27year period. Note that data for the number of tags issued during 1984 was missing.
Figure 3: Total number of fish tagged per year (primary axis) and the average number tagged
per angler per year (secondary axis) in the ORI Tagging Project over a 27-year period.
In the Tagging Project’s 27-year history, a staggering 251 969 fish (Fig 3) from 368 different
species (ca. 166 species/year) have been tagged and released, of which 5.2% (ca. 489 fish/year;
Fig 4) have been recaptured. The average number of fish tagged per year (ca. 9332 fish/year) has
remained relatively constant since the projects inception. The declines between 1998 and 2002
can be explained by the change in management of the program over that period rather than a
decrease in fish abundances. Although the number of members tagging fish decreased between
1997 and 2005, the number of fish tagged per angler per year remained higher. The drop
recorded between 1998 and 2002 can be explained by the lower number of tags issued during
this period (Fig 2).
Figure 4: Percentage of fish recaptured per year in the ORI Tagging Project over a
27-year period.
Despite the observed trends in tagging effort, the number of recaptures reported has shown a
consistent increase since the start of the project in 1984 (Fig. 5). This reflects an ever-increasing
pool of tagged fish available for recapture. On-going attempts to educate the angling public
through various media (television programs and magazine articles) may have assisted with
improving reporting rates. Another factor contributing to the increase in reported recaptures
has been the establishment of on-going fish tagging projects in a number of South African
MPAs. In these projects, tagging and reporting of recaptures is performed by trained anglers and
scientists. The recapture rates of certain reef fish species tagged in these projects is particularly
high and thus has increased the overall recapture rate.
Most of the tagging has taken place in the Western Cape (41%) (Fig 5). Despite the relative
length of the Eastern Cape and KwaZulu-Natal coastlines, both provinces contributed only 27%
and 24% to the total tagging effort respectively. Although the tagging of fish in Namibia with
ORI tags was discontinued in 1999, Namibia still accounts for 6% of the total number of fish
tagged and Mozambique 2%.
The five most commonly tagged fish species in the ORI Tagging Project include galjoen (21.3%),
dusky kob (5.5%), dusky shark (4.5%), garrick/leervis (3.9%) and spotted grunter (3.5%) (Table
1). Although there have been a large number of lesser sandsharks/guitarfish (6357) tagged in
the ORI Tagging Project’s 27-year history (Table 1), the tagging of this species was discouraged
from 1998 onwards due to the low recapture rate and the low research priority attributed to this
species. The large number of galjoen tagged to date is partly due to the institutional scientific
tagging that takes place in the De Hoop MPA and along the Cape Peninsula (Attwood 2002).
Figure 5: Percentage of fish tagged along the southern African coastline in the ORI Tagging
Project over a 27-year period.
Table 1: Tag and recapture data for the top ten species tagged in ORI Tagging Project over a
27-year period.
Species
Total tagged
Total Recap.
% Recap.
Galjoen
53565
3674
6.9
Dusky kob
13750
825
6
Dusky shark
11345
732
6.5
Garrick/leervis
9826
680
6.9
Spotted grunter
8832
253
2.9
Copper shark
8585
266
3.1
Blacktail
8324
207
2.5
Spotted gully shark
7743
413
5.3
Shad/elf
7180
270
3.8
Lesser sandshark/guitarfish
6357
70
1.1
Other
116462
5725
4.9
Discussion
The results presented here represent an enormous conservation achievement. Information
from the Tagging Project has been extensively used in numerous research projects, scientific
publications and post-graduate degrees (from Honours to PhD level). In addition, numerous
popular articles, newspaper reports, radio broadcasts and television documentaries have
highlighted various aspects of the Tagging Project. This project has also provided information
influencing policy and decision making for linefish management in South Africa. However, despite
these contributions, the ORI Tagging Project database remains under-utilized. The valuable data
stored in the tagging database is readily available to scientists and managers and should be utilised
more widely as a key component towards better management of our linefish stocks.
In general, the ORI Tagging Project should be stricter in prioritising which species are targeted
for tagging. Several species have been extensively researched through tagging programmes
and it could be argued that the continued tagging of these species may not be providing
further useful information as our knowledge of their biology and movement behaviours is
comprehensive based on existing tag and recapture data. For example, in the last 27 years
there have been more than 50 000 galjoen tagged and numerous publications produced based
on this tagging data. Other common species, such as blacktail, lesser sandsharks/guitarfishes
and slinger, have been found to be less suitable for tagging studies due to their low recapture
rates which are likely as a result of high tag loss/shedding and/or high induced tagging
mortality. Although a priority species list has been established for the project, it needs to be
clearly communicated and more stringently implemented by members of the Tagging Project.
Furthermore, emphasis needs to be placed on important migratory linefish species, such as king
mackerel, geelbek and englishman, whose distribution patterns are not clearly understood.
One of the major constriants of the ORI Tagging Project is the rate of reporting recaptured fish
by the angling public. As a result, ORI has implemented a number of initiatives to increase
the reporting rate. These include a dedicated e-mail address ([email protected]@ori.org.
za) and cellular phone number (+2779 529 0711); the printing of the cellular phone number
and e-mail address directly onto the streamers of all new ORI tags (previously only the postal
address printed was included); the production of an instructional DVD for both current and new
tagging members; and the improvement of tag types. Tagging projects that rely solely on mail
services are known to record the poorest tag return rates (Moringa 1980). The postal address
currently printed on the tags will be replaced by the cellular phone number and e-mail address.
Biofouling of tags also needs urgent attention and studies reviewing anti-biofouling techniques
are required. Regular evaluation of the long-term tagging project and the tag types used is
required and we recommend that the recent initiatives implemented in the ORI tagging project
be reviewed in 2013, a full year following introduction.
The tagging of fish in competitions has recently been raised as a controversy. Although
promoting ‘tag and release’ in a competition environment seems ideal as fish are released
as opposed to being killed, numerous problems associated have arisen. Firstly, anglers are
competing for points or prizes and need to comply with the competition rules such as for lineclass strength. As a consequence, the fight is often extended, especially for lighter tackle and
thus many fish captured on light tackle have a decreased chance of survival once landed and
tagged. Secondly, when a fish is tagged in a competition, the tagging data (i.e. tag number,
locality, fish species etc.) is often misplaced, there is little incentive in returning the data as after
the tagging event as the points/prizes for the tagged fish have already been awarded (i.e. anglers
are tagging for points or prizes rather than for science). In competitive situations we believe
that it is better to adopt a “catch and release” policy as this will maximise the fish’s chance of
survival and minimize the tagging of weakened fish. For ‘tag and release’ programme to be
effective in competitions, trained staff should be present to tag fish and record the relevant data
independently of the competition.
A further weakness of the ORI Tagging Project is the lack of accurate geographical referencing
regarding where a fish is tagged and recaptured. Currently tag localities are based on a system
of locality codes reflecting the distance in kilometres the locality lies from the northern
Mozambique border. These localities are not GIS referenced and are thus less accurate.
Furthermore, if a fish is caught upstream in an estuary or offshore, this information is lost as
only one locality code is allocated to that point along the coastline. Introducing a GIS-based
system would considerably improve the accuracy of the project and are being investigated for
implementation in the near future.
Although there are several limitations and biases associated with the ORI Tagging Project, there
are also numerous strengths. For example, the use of conventional external tags by volunteers
allows large numbers of fish to be tagged for a relatively low cost. This is in contrast to the use
of internal acoustic or archival tags, which are expensive and, in most cases, difficult and time
consuming to insert (i.e. tags need to be inserted internally under anaesthetic by trained staff).
Furthermore, internal tags are not visible to fisherman and have a high setup cost for both tags
and the associated detection equipment.
The ORI Tagging Project has undoubtedly improved angler awareness and scientific knowledge
of our linefish resources and has made a significant contribution towards changing anglers
perceptions towards the ethics of ‘catch and release’. This contribution goes far beyond the
scientific value of the data collected. Not only can anglers justify the capture and release of a
fish, they are also contributing to scientific understanding of the biology and helping improve
the conservation and management of their targeted fish species. This goes a long way towards
improving angler awareness about our marine linefish species and contributing towards more
sustainable fishing.
In conclusion, we believe that the information generated by the ORI Tagging Project adequately
justifies its continuation. Furthermore, the relative value of such long-term projects is often only
realised after many years. To terminate such a successful project will not only be detrimental
to the linefishery, but also to the angling community. The future success of this project will
undoubtedly be determined by its flexibility in adapting to new tagging and reporting methods
and technologies. The incorporation of electronic, archival, and satellite tags will strengthen
the tagging project considerably and provide opportunities to answer many movement and
migration questions that traditional tagging projects have not answered to date. However,
the use of these new tag types should complement the current tagging methodologies and not
supress the cooperative, voluntary nature of the ORI Tagging Project. The lack of dedicated,
secure funding continues to threaten the future of the ORI Tagging Project and we extend a
plea for support, from both the scientific community and the angling public, to ensure the
continuation of this important project.
Acknowledgements
We would like to express our sincere gratitude for all the financial support received over the
years for the continuation of this valuable project. In particular we would like to thank Distell
(Sedgwick’s Old Brown Sherry), The Tony and Lisette Lewis Foundation, WWF South Africa and
SAAMBR (with support from the KZN Department of Agriculture, Environmental Affairs and
Rural Development). Most of all, we would like to thank all our active tagging members for their
on-going contributions towards linefish research and conservation. A special word of thanks
must also go to the previous Tagging Officer Elinor Bullen. Elinor put a great deal of her working
life into the Tagging Project and made a huge contribution to its long-term success. David Hall
(Hallprint© Australia) is thanked for his excellent service and on-going supply of high quality
tags and applicators. Lastly, we thank all of the other smaller sponsors who have contributed in
some way over the past 27 years, there are simply too many to mention.
References
Attwood CG. 2002. Spatial and temporal dynamics of an exploited reef-fish population.
Unpublished Ph.D Thesis. University of Cape Town Cape Town, South Africa.
Bass AJ. 1977. Long-term recoveries of tagged sharks. Copeia 1977: 574-575.
Bass AJ, D’ Aubrey JD, Kristnasamy N. 1973. Sharks of the east coast of southern Africa. I. The
genus Carcharhinus (Carcharhinidae). Investigational Report, Oceanographic Research
Institute, Durban. Report No. 33
Davies DH, Joubert LS. 1966. Tag evaluation and shark tagging in South African waters.
Investigational Report, Oceanographic Research Institute, Durban. Report No. 12.
De Jager BVD. 1955. The South African pilchard (Sardinops ocellata). The development of the snoek
(Thyrsites atun) a fish predator of the pilchard. Investigational Report, South African Division
of Sea Fisheries, Cape Town. Report No. 19.
Moringa JR. 1980. Nonreporting of recaptures of tagged rainbow trout from an Oregon Stream. The
Progressive Fish-Culturist 42: 113-115.
Newman GG. 1970. Migration of the pilchard Sardinops ocellata in southern Africa. Investigational
Report, South Africa Division of Sea Fisheries, Cape Town. Report No. 86.
van der Elst RP. 1990. Marine fish tagging in South Africa. American Fisheries Society Symposium
7: 854-862.
Session 4 – Fish Stock Assessment: Chair Henning
Winker
Assessment of five South African linefish species with
biomass production models
SE Kerwath1,2, H Winker1, and CG Attwood1
1
Zoology Department, University of Cape Town, Private Bag Rondebosch 7700, South Africa.
2
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, South Africa.
Introduction
The South African boat-based, commercial linefish sector comprises a multi-species, multi-area
cluster of low to medium technology inshore fisheries in which fish are caught manually with
hand-lines or rods and reel (Winker et al. 2012). The target species landed by this mixed fishery
can be grouped into to three major ‘guilds’ including pelagic shoaling species such as yellowtail
(Seriola lalandi) and snoek (Thyrsites atun), migratory, demersal species such as silver kob
(Argyrosomus inodorous) and geelbek (Atractoscion aequidens) and resident, demersal species
such as carpenter (Argyrozona argyrozona), slinger (Chrysoblephus puniceus) and hottentot
(Pachymetopon blochii). Monitoring of the linefishery started at the turn of the 20th century with
JDF Gilchrist, the Government Marine biologist of the Cape of Good Hope, the first concerns
about overfishing of some linefish species were voiced as early as the 1940’s (Griffiths 2000).
Despite this, the sector was only formally recognized in 1985, when national legislation was
introduced to limit effort and fishing mortality. Despite these efforts, spawner-biomass per-recruit
assessments and comparisons with historical catch data in the 1990’s indicated that many linefish
stocks were in an alarming state of decline and a state of emergency was declared for this fishery
in 2000. The numbers of medium- and long-term commercial fishing rights were reduced and
the linefish management protocol developed (Griffiths 1997a), to guide the management of stocks
according to biological reference points based on spawner biomass per-recruit models. In cases
were assessments were not available, indicators such as Catch per Unit Effort (CPUE), proportion
in catches, and even public concern could be used to invoke management action. Owing to the
large numbers of species and stocks, reassessments were scheduled at intervals equivalent to half
of the maximum life-span of the species, whereas indicators would be reviewed annually.
The recovery of the linefish stocks has not been observed, however, there are some evidence
suggesting that some of the dominant species have responded to the reduction in effort and
stricter management regulations. However, the assessment of recovery as outlined in the
linefish management protocol might be inappropriate as it assumes constant fishing mortality
and constant recruitment, which has not been the case following the declaration of the state
of emergency. To circumvent this problem, we developed Graham-Schaefer biomass dynamic
assessment models (Schaefer 1954) based on the time series of standardized CPUE and total
landings data for five important linefish species, silver kob (Argyrosomus inodorus), yellowtail
(Seriola lalandi), carpenter (Argyrozona argyrozona), slinger (Chrysoblephus puniceus)
and hottentot (Pachymetyopon blochi) Biomass dynamic models were selected over agestructured production models because the later require updated age length keys and consistent
size frequency data, which were not available for all stocks considered. Moreover, 26-years of
standardized CPUE data (Winker et al 2012) and sufficient contrast between effort and CPUE
should allow for a reasonable estimate of the parameters required for a biomass production
model (Hilborn and Walters 1992). The main output of the assessment model, a biplot graph
that depicts the ratio of annual fishing effort and fishing effort at Maximum Sustainable
Yield (MSY) against the ratio of annual biomass against the biomass at MSY, allows one to
simultaneously track the trajectory of the stock biomass against the target biomass at MSY, as
a measure of the resource status, and the levels of fishing effort against the target fishing effort
at MSY, as an indicator for fisheries management. The results of the assessments are presented
and their potential application for an update of the linefish management protocol is discussed.
Materials and methods
In the Schaefer surplus-production model, the biomass dynamics of a fish stock are governed by:
(1)
(2)
where By is the unobserved biomass at the start of year y, r is the intrinsic rate of population
increase, K is pristine biomass at carrying capacity, Cy is the catch in year y in tons, q is
catchability coefficient and εy is the observation error during year y, εy ~ N(0,σ2).
As the exploitation of the linefish resource commenced in the mid-1800s, it would be unrealistic
to assume that the biomass in 1985 approximated the pristine biomass prior to exploitation.
The initial biomass, B1985, was therefore specified by fixing the ratio B1985/K for each stock.
The B1985/K ratios used in this report were derived from a review of available literature and in
correspondence with the Linefish Scientific Working Group. The B1985/K ratios for the basecase scenarios were fixed at 0.15 for carpenter, 0.10 for silver kob, 0.40 for yellowtail, 0.40 for
hottentot and 0.25 for slinger.
Fisheries management measures
Five fisheries management scenarios were derived from the Schaefer model (equations 1, 2).
These were the Maximum Sustainable Yield (MSY), the fishing effort at MSY (EMSY), the biomass
at MSY (BMSY), the percentage recovery in biomass between 2000 and 2010 (Rec(%)) and
the ratio B2010/K, where MSY (t) = rK/4, EMSY (boat trips) = r/(2q) and Rec(%) = 100 – B1985/
B2010*100. The main output of the assessment model was presented in form of a biplot graph
that plots the ratio By/BMSY on the y-axis against the ratio Ey/EMSY on the x-axis, where Ey is the
expected effort in year y that is given by Ey = Cy / qBt (Fig. 1). Note that, as effort levels were
derived based on standardized CPUE data (Winker et al. 2012), one standard unit effort refers
to an average boat trip with eight crew members who spent eight hours on sea, fished in the 5
× 5 km2 grid and exclusively targeted the species under assessment during the months with the
highest effort frequency.
Figure 1:Bi-plot with an example of a trajectory and recovery of a typical fishery stock. As the
effort exceeds MSY, exploitation levels become unsustainable resulting in the stock biomass
dropping below the MSY. Reducing the effort to levels below the MSY is required to induce the
recovery of the stock biomass.
Parameter estimation and measures of uncertainty
The model parameters K, r and q and the model standard deviation σ were estimated by
minimizing the negated normal log-likelihood function of the form:
(12)
,
where n is the number of years with available CPUE data. The joint posterior distributions for
all model parameters and fisheries management measures of interest were estimated with the
Markov Chain Monte-Carlo (MCMC) algorithm (Hastings 1970, Punt and Hilborn 1997). The
results are based on parameter vectors of 4000 draws from the posterior distribution. The total
number of cycles was one million, of which the first 200 000 were ignored as a ‘burn-in’ period.
The 2.5th and 97.5th percentile of the MCMC vectors were calculated to obtain an estimate for the
95% confidence intervals. All analyses were carried out using AD Model Builder (ADMB; http://
admb-project.org/).
Spatial resolution
The South African coast was divided into five fishing regions: (i) west coast, (ii) south-west
coast, (iii) south-central coast, (iv) south-east coast and (v) east-coast (Fig.2). These regions
were selected on the basis of the geography of the fishery and with the objective of incorporating
the spatially-dependent variability in species composition and fishing techniques. Datasets for
silver kob and carpenter were subset into the three regions south-west coast, south coast and
south-east coast. These three regions cover the major fishing grounds of these two species along
the South African coastline. Subsequently, south-west coast and south coast data was combined
for carpenter as these regions are unlikely to constitute separate stocks. For yellowtail and
hottentot, we focused our analyses on the south-west coast region. Slinger is only caught along
the east coast, but extends into Mozambique, for which data were not available.
Figure 2: Map of the South African EEZ showing the five geographical regions selected to
reflect difference in targeting and fishing characteristics in the linefishery and to allow for
separate modeling of discrete stocks which might exist for some species.
Results
Silver kob
The production model fits suggest carrying capacity values of the exploitable fish for the
south-western, southern and eastern stocks of 44 000, 29 000 and 18 000 t, respectively, and
population growth rates of 0.05, 0.15 and 0.12 y-1 (Table 1). All stocks were below BMSY, but effort
has reduced below EMSY, which is estimated at 1149, 2166 and 1098 hours per annum for the
three stocks, respectively. Although the south-western stock is predicted to be in a recovery and
the reduction in effort in 2000 effectively halved the EMSY, the expected biomass recovery has
not materialized (Fig. 3). This stock is predominantly targeted in False Bay, where recreational
catches may account for some additional effort which is not recorded on the NMLS. The low r
value of the model fit for the south-western stock suggests some underreporting of catches.
The southern stock remained overexploited despite the effort reduction to approximately EMSY.
Most recent data suggested that effort is slightly above EMSY. The only strong recovery of this
species was observed in the eastern stock, where slight but consistent increases in biomass
where observed during the last 8 years.
These assessments were in agreement with the per-recruit analyses for this species
(Griffiths1997b). SB/R values for the three stocks were between 4.4 and 10.4% for the southwestern stock, between 6.5 and 12.5% for the southern stock and between 2.9 and 9.8% for the
eastern stock, based on data collected between 1986 and 1994. Biomass is currently estimated
at 11, 14 and 19% of pristine biomass for the south-western, southern and eastern stocks,
respectively. However, these increases cannot be taken as evidence of marginal improvement
because biomass estimates and per-recruit estimates are not directly comparable.
Figure 3. Annual CPUE and landings for three srocks of silver kob (Argyrosomus inodorus)
compared to the CPUE predicted by the Schaefer surplus production model.
Figure 4. Bi-plot indicating the modelled trajectory of biomass and effort for three stocks of
silver kob (Argyrosomus inodorus), relative to the respective estimates at MSY.
Table 1. Production model estimates and 95% confidence limits (in brackets) for the silver kob
(Argyrosomus inodorus) fisheries in the south-western, southern Cape and south-eastern stocks.
Region
SW
S
SE
K
43872.5 [40721.0, 48197.2]
29218.3 [22774.0, 43067.8]
18292.8 [15411.8, 22826.4]
q
0.022 [0.018, 0.026]
0.034 [0.022, 0.045]
0.053 [0.042, 0.066]
r
0.050 [0.049, 0.052]
0.146 [0.096, 0.199]
0.118 [0.095, 0.139]
σ
0.0109 [0.083, 0.151]
0.113 [0.086, 0.158]
0.078 [0.059, 0.108]
MSY
553.4 [515.2, 606.4]
1068.2 [1043.3, 1086.7]
537.3 [528.2, 551.6]
EMSY
1148.6 [979.9, 1377.2]
2166.3 [1992.7, 2391.41]
1097.9 [1021.4, 1196.17]
BMSY
21936.3 [20360.5, 24097.6]
14609.2 [11387.0, 21533.9]
9146.4 [7705.9, 11413.2]
B2010/K
0.11 [0.10, 0.13]
0.14 [0.11, 0.20]
0.19 [0.16, 0.22]
rec(%)
27.4 [25.8, 28.9]
37.0 [26.8, 45.4]
52.8 [46.1, 58.3]
Estimates
Carpenter (Argyrozona argyrozona)
The production model fits for carpenter suggested carrying capacities of 28 000 and 15 000
t, and population growth rates of 0.13 and 0.19 y-1,for the Central and Eastern Agulhas Bank
stocks, respectively (Table 2). Effort reduction reduced the effort below EMSY, estimated at 4406
and 2242 targeted boat days per annum, respectively, for the two stocks. Both stocks were
steadily recovering, but biomass levels at 32% and 42% of pristine biomass (K), respectively, the
stock biomass remained below BMSY (Fig. 6), even though the effort was estimated to be at less
than half of the EMSY. The analysis did not consider the recreational boat fishing effort.
Brouwer and Griffiths (2006) conducted Egg per Recruit (Egg/R) analyses on both stocks
and found Egg/R had declined to between 6 and 14% of the pristine value, based on sizestructure data collected between 1986 and 2001. Our analyses are in agreement with Brouwer
and Griffiths’ model findings suggesting improvements in the status of the resource prior to
the emergency declaration. These changes are thought to be due to the termination of fishing
activities by the Japanese and inshore trawl fleets in 1991. No attempt was made, however, to
account for the trawl caught catch of carpenter in this analysis.
Table 2. Production model estimates and 95% confidence limits (in brackets) for the carpenter
(Argyrosona argyrosona) fisheries in the south-western, southern and south-eastern stocks.
The first zones two have been combined in the model to correspond with the central Agulhas
Bank stock.
Region
Estimates
SW
S
SE
K
43872.5 [40721.0, 48197.2]
29218.3 [22774.0, 43067.8]
18292.8 [15411.8, 22826.4]
q
0.022 [0.018, 0.026]
0.034 [0.022, 0.045]
0.053 [0.042, 0.066]
r
0.050 [0.049, 0.052]
0.146 [0.096, 0.199]
0.118 [0.095, 0.139]
σ
0.0109 [0.083, 0.151]
0.113 [0.086, 0.158]
0.078 [0.059, 0.108]
MSY
553.4 [515.2, 606.4]
1068.2 [1043.3, 1086.7]
537.3 [528.2, 551.6]
EMSY
1148.6 [979.9, 1377.2]
2166.3 [1992.7, 2391.41]
1097.9 [1021.4, 1196.17]
BMSY
21936.3 [20360.5, 24097.6]
14609.2 [11387.0, 21533.9]
9146.4 [7705.9, 11413.2]
B2010/K
0.11 [0.10, 0.13]
0.14 [0.11, 0.20]
0.19 [0.16, 0.22]
rec(%)
27.4 [25.8, 28.9]
37.0 [26.8, 45.4]
52.8 [46.1, 58.3]
Figure 5. Annual CPUE and landings for two stocks of carpenter (Argyrosona argyrosona)
Yellowtail (Seriola lalandi)
Yellowtail is a nomadic, pelagic species of the continental shelf, and is not confined to
South Africa or the African continent. There is no evidence of stock separation within South
African waters. In this analysis, we only consider the south-western stocks of yellowtaail. The
production model fitted the data, but errors on estimates were considerably wider than for silver
kob or carpenter. The 95% confidence intervals for the carrying capacity, for example, were
estimated between 5 738 and 52 720 t (Table 3). The stock was over-exploited from the late
1980’s, but has now recovered to above MSY. The position in 1985 (over-exploited but below
EMSY) can probably be explained by large catches of this species that were taken by pure-seiners
up to the early 1980’s, which are believed to have severely impacted on the stock.
CPUE increased abruptly after the emergency, but the increase was not sustained. The CPUE
has been more variable during the last 10 years than during the period prior to the emergency.
The last five years of the study period show a decline in CPUE and landings. Catches have been
erratic throughout the period and suggest either a volatile stock dynamic, or unusually high
variability in the availability of the stock to fishers (Figs. 7, 8).
Even the most pessimistic scenario suggests that the stock is not less than 44% of carrying
capacity. EMSY is estimated at 3316 boat days, and commercial effort is currently well below
this target. However, the absence of recreational data. Yellowtail is a very popular target of this
sector, and recreational effort and catch need to be included for a refined assessment.
Figure 6. Bi-plot indicating the modeled trajectory of biomass and effort for two stocks of
carpenter (Argyrosona argyrosona), relative to the respective estimates at MSY.
Table 3. Production model estimates and 95% confidence limits (in brackets) for the yellowtail
(Seriola lalandi) fishery in the south-western stock.
Region
Estimates
SW
K
10057.5 [5737.8, 52720.7]
q
0.042 [0.07, 0.255]
r
0.277 [0.080, 0.487]
σ
0.181 [0.137, 0.255]
MSY
698.3 [666.0, 1035.5]
EMSY
3316.0 [2730.8, 5578.5]
BMSY
5028.6 [2868.9, 26360.4]
B2010/K
0.66 [0.44, 2.01]
rec(%)
35.9 [18.1, 48.2]
Figure 7. Annual CPUE and landings for three stocks of yellowtail (Seriola lalandi) compared
to the CPUE predicted by the Schaefer surplus production model.
Figure 8. Bi-plot indicating the modelled trajectory of biomass and effort for the yellowtail
(Seriola lalandi) fishery in the south-western Cape, relative to the respective estimates at MSY.
No previous assessments of yellowtail are available for comparison. This species has not been
targetted for as long as other linefish species, and its nomadic nature and fast population growth
(r = 0.28 y-1) suggest that yellowtail may be less susceptability to the fishery exploitation than
other species. The estimates of fishing mortality F quoted reported by Thompson and Penney
(in prep.) cited by (Mann 2000) could not be verified. The reference material is unfortunately
unavailable.
Hottentot (Pachymetopon blochii)
Hottentot was the most common reef fish landed by the linefish in the south-werstern and
western stocks, however, catches showed a long-term downward trend from the late 1980’s until
at least 2006 (Fig. 9).
The production model provided a reasonable fit to the observed data and the carrying capacity
was estimated at between 10 000 and 23 000 t (Table 4). The model output shows that the stock
has been over-exploited for almost the entire assessment period, but is now approaching the
target of BMSY and could be considered underexploited (Fig. 10).
Table 4. Production model estimates and 95% confidence limits (in brackets) for the hottentot
(Pachymetopon blochii) fishery in the south-western stock.
Region
Estimates
SW
K
13140.8 [9879.8, 22722.2]
Q
0.018 [0.009, 0.027]
R
0.053 [0.050, 0.059]
σ
0.181 [0.137, 0.255]
MSY
174.6 [135.9, 293.6]
EMSY
1443.5 [984.3, 2793.1]
B2010/K
0.55 [0.33, 0.87]
BMSY
6969.0 [4939.9, 11361.1]
rec(%)
19.13 [18.0, 20.9]
Figure 9. Annual CPUE and landings for three stocks of hottentot (Pachymetopon blochii)
Figure 10. Bi-plot indicating the modeled trajectory of biomass and effort for the hottetot
(Pachymetopon blochii) fishery for the south-western stock, relative to the respective estimates
at MSY.
Slinger (Chrysoblephus puniceus)
The single stock of slinger is shared with Mozambique, is a reef-associated species, which is
expected to be resident.
Carrying capacity was estimated at between 6 000 and 12 000 t (Table 5). Currently the stock
remains below BMSY, but has recovered substantially from a more severe depletion in the early
1990’s when catches reached record levels (Fig. 11). Effort is currenty below EMSY, and the stock
is recovering slowly (Fig. 12).
Table 5. Production model estimates and 95% confidence limits (in brackets) for the slinger
(Chrysoblephus puniceus) fishery for the east stock.
Region
Estimates
SW
K
7789.1 [5969.3, 11692.5]
q
0.034 [0.021, 0.046]
r
0.149 [0.103, 0.192]
σ
0.080 [0.062, 0.114]
MSY
289.5 [283.6, 305.6]
EMSY
2200.4 [2029.8, 2466.8]
B2010/K
0.37 [0.27, 0.48]
BMSY
rec(%)
3894.5 [2984.6, 5846.3]
30.0 [23.0, 36.2]
Figure 11. Annual CPUE and landings for three stocks of slinger (Chrysoblephus puniceus)
Figure 12. The modelled trajectory of biomass and effort for the slinger (Chrysoblephus
puniceus) fishery along the east coast, relative to the respective estimates at MSY.
Discussion
The assessments presented here, especially in combination with the standardization of the
CPUE (Winker et al. 2012), mark a significant improvement of our understanding of the
response to the management interventions after the declaration of the linefish emergency. The
bi-plots illustrated not only the current state of the fish stock, but also the trajectory followed
towards the current state. For each of the fisheries and stocks modeled, the emergency declared
in 2000 appeared to be the single most important factor influencing the stock dynamics.
Overall, the nominal effort cut was in the region of 70%, but the real effort reduction, in terms
of boat days, was lower, but still substantial. The response of the stocks to a reduction in effort
was as expected with an increase in the CPUE and an overall decline in the total catch in all
stocks. Although most stocks are being harvested at EMSY or below, most remain over-exploited
as they have not attained BMSY. Although these assessments are useful to gauge the current
state of the linefishery, a number of improvements are still required to improve our confidence
in the predictions. The most important improvement would be a test of the robustness of the
models by incorporating different base case scenarios for the B1985/K ratios. Although there are
sufficient data to run age-structured models for some of the stocks, the results of a preliminary
analysis on one of the carpenter stocks showed the same general patterns predicted by the
surplus production model. A further improvement would be the inclusion of the catch by other
fishing sectors into the models. Once this has been done, the framework outlined in this paper
will be incorporated into the updated Linefish Management Protocol. The output of the surplus
production model could be used to simulate the impact of management scenarios, changes in
effort, and to provide resource managers with a measure that determines sustainable effort for
the new long-term rights allocation.
References
Brouwer SL, Griffiths MH. 2006. Management of Argyrozona argyrozona (Pisces: Sparidae) in
South Africa based on per-recruit models. African Journal of Marine Science 28: 89-98.
Griffiths MH. 1997a. Towards a management plan for the South African linefishery: objectives and
strategies. In: Penney AJ, Griffiths MH, Attwood CG (eds.), Management and Monitoring of the
South African Marine Linefishery. South African Network for Coastal and Oceanic Research,
Occasional Report No. 3, Cape Town, pp. 3-11.
Griffiths MH. 1997b. The application of per-recruit models to Argyrosomus inodorus, an important
South African sciaenid fish. Fisheries Research 30: 103-115.
Griffiths MH. 2000. Long-term trends in catch and effort for the Cape commercial linefishery:
snapshots of the 20th Century. South African Journal of Marine Science 22: 81-110.
Hastings WK. 1970. Monte Carlo sampling methods using Markov chains and their applications.
Biometrika 57: 97–109.
Hilborn R, Walters CJ. 1992. Quantitative fisheries stock assessment: choice, dynamics and
uncertainty. Chapman and Hall, New York.
Mann BQ. 2000. South African marine linefish status reports. Oceanographic Research Institute,
Special Publication no. 7. Durban, South African Association for Marine Biological Research.
Punt AE, Hilborn R. 1997. Fisheries stock assessment and decision analysis: the Bayesian approach.
Reviews in Fish Biology and Fisheries 7: 35-63.
Schaefer MB. 1954. Some aspects of the dynamics of populations important to the management of
the commercial marine fisheries. Inter-American Tropical Tuna Commission Bulletin 1: 26-55.
Winker H, Kerwath SE, Attwood CG 2012. Report on stock assessments of important South African
linefish resources. Report of the Linefish Scientific Working Group, no. 3. Department of
Agriculture, Forestry and Fisheries, Cape Town.
Long-term changes in a surf zone fish community
associated with the linefish collapse in the Eastern
Cape, South Africa
GM Rishworth1 and NA Strydom1
1
Nelson Mandela Metropolitan University, South Africa.
Introduction
Surf-zones are an important habitat for many fish species across a range of their developmental
stages, however, our understanding of how fish utilise this environment is generally poor
(Strydom 2008; Able et al. 2010), partially due to the difficulty of sampling fish communities
comprehensively in these habitats (Beyst et al. 2001; Strydom 2007). Further, in South Africa,
surf-zones have been neglected in favour of studies of fish utilisation of other coastal nursery
habitats, such as estuaries (Able 2005; Strydom 2008). Nonetheless, there is growing evidence
suggesting that surf-zones are important nurseries and feeding areas for many fish species (e.g.
Beyst et al. 2001; Strydom & d’Hotman 2005; Félix et al. 2007; Able et al. 2010). Surf-zones also
act as transient habitats for young fishes recruiting into estuaries from the ocean (Strydom 2003).
Many of the fish species that utilise surf-zones are commercially and economically important.
Some of these species have faced major stock declines largely due to overfishing (Attwood
& Farquhar 1999; Griffiths 2000). At the turn of the millennium, a state of emergency was
declared on the linefish stocks in South Africa (linefish generally refers to all fish species caught
using a hook and line but excluding commercial long-lines), calling for action to restore these
stocks to a viable state (Palmer et al. 2008). Prior to the major effects of the linefish stock
collapse (primarily noticed in the 1980’s and 1990’s), a comprehensive assessment by Lasiak
(1982) was made of the surf-zone fish community at King’s Beach in Algoa Bay on the warm
temperate, south-east coast of South Africa. This study identified a distinct adult fish assemblage
and recorded high densities of juvenile fishes; classified this surf-zone as a nursery habitat
(Lasiak 1981; Lasiak 1983).
In review of this, two hypotheses have been formulated for follow-up studies in the surf-zone
at King’s Beach:. the current fish community at King’s Beach will be significantly different
from that of three decades ago (reduced abundances and size-class shifts of higher trophiclevel fishes as a result of the linefish collapse) and King’s Beach serves as a nursery for earlier
developmental stages of several fishes, i.e. an increase over time in mean length within a species
or high densities of young fish.
The study site, King’s Beach, is located south of the Port Elizabeth Harbour (33°58’S, 25°19’E)
and stretches for approximately 1.3 km. It can be classified as an intermediate energy surf-zone
and the surf generally extends from 50 to 100 m (McLachlan 1980). Since the late 1980’s and
early 1990’s, the sand accumulation against the harbour breakwater wall has remained relatively
constant in that the physical position of King’s Beach has not changed significantly since the
Lasiak (1982) study (Goschen & Schumann 2011).
In the Lasiak (1982) study, a 60 m and 30 m seine net were used to sample the adult and
juvenile fish community, respectively. In the current study a 100 m and 30 m seine net were
used to sample these communities and mean size selectivity between the respective nets used
in each study was not significantly different for the most common species caught (p > 0.05;
df = 5 and 9, respectively). Sampling protocol was standardized so as to best replicate that
of the Lasiak (1982) study to allow for direct comparisons to be made between the two fish
communities. In this respect, sampling occurred when high tide coincided within two hours of
sunset and was done bimonthly from the end of February 2011 to the beginning of August 2011.
On each occasion, the 100 m, 30 m and a further 4.5 m seine (which targeted the larval fish
community) were pulled through the surf before, at and after sunset.
All fish caught were identified in the field whenever possible and then safely released. The
samples from the 4.5 m larval seine net were preserved in 10 % formaldehyde and seawater; for
identification in the laboratory. In the last three months of the study, coinciding with the period
of peak late-summer and autumn juvenile recruitment into South African coastal nurseries,
all fish greater than 150 mm (total length; TL) were tagged using spaghetti tags (Hallprint,
Australia). Care was taken to sterilise all equipment (using 99.9 % ethanol) and to minimise
handling of fish. Fish caught in subsequent samples were inspected for tag loss.
At each bimonthly sampling trip, abiotic variables of the seawater were recorded, such as
temperature, salinity, pH and turbidity. A measure of suspended seaweed in the surf-zone was
also recorded.
Data were analysed descriptively or with the software package PRIMER for community analysis
using the BIO-ENV routine (Clarke & Warwick 1994). Non-parametric tests were performed to
compare between the current study to that of Lasiak (1982). To standardise comparisons, data from
the current study were only compared for the months corresponding to those of Lasiak’s study.
In the juvenile fish community, at least three species (piggy Pomadasys olivaceus; blacktail
Diplodus capensis and southern mullet Liza richardsonii) demonstrated growth in the surf-zone
as reflected by a mean increase in total length over several weeks, recruiting into the surf as latestage larvae. It is likely that several other fishes are utilising this surf-zone as a nursery (e.g. white
stumpnose, Rhabdosargus globiceps) but the numbers caught were not suitable for generating
meaningful results. Although these results were generated over a preliminary sampling period,
it is evident that some species show distinct periods of recruitment into the surf-zone nursery
environment (e.g. P. olivaceus appeared to recruit into this habitat during April).
The larval fish community was dominated by late-stage postflexion larvae (59 %), primarily from
reef-associated species (such as the Gobiidae and Gobisocidae). Sand-associated species (such
as the Haemulidae and Soleidae) were less prominent in catches (comprising 14.2 % and 12.5 %,
respectively). This trend is similar to other surf-zone studies in temperate South Africa (Strydom
& d’Hotman 2005). Species from some of the prominent linefish families (Sparidae, Haemulidae
and Sciaenidae) were caught sporadically, but often in low densities.
This research shows that King’s Beach is operating as a nursery for young fishes, supporting
several other studies which have highlighted the nursery value of surf-zones (e.g. Beyst et al. 2001;
Strydom & d’Hotman 2005; Félix et al. 2007; Able et al. 2010). The suitability of this surf-zone as
a nursery could best be explained by the intermediate energy of the surf zone. Some authors have
suggested that surf-zones of intermediate energy are suitable nursery habitats for fishes as they are
less abrasive than high-energy surf-zones, offer greater protection from predators and increased
foraging opportunities than low-energy surf-zones (Lasiak 1983; Clark 1997; Vasconcellos et al.
2007). Although present in considerably lower densities, some of the most targeted and exploited
linefish species (e.g. the dusky kob (Argyrosomus japonicus)) continue to make use of King’s
Beach as a nursery, for both larval and juvenile developmental stages.
Growth within the surf-zone amongst some species was the only evidence of residency. Of the 47
fish tagged (12.5 % were juveniles) in this preliminary study, no recaptures were recorded. These
results concur with similar international studies which have assessed residency of juvenile fish
in the surf-zone (Miller et al. 2002; Ross & Lancaster 2002), supporting the hypothesis that fish
are highly mobile amongst surf-zones.
When the catch compositions of Lasiak (1982) were compared to those of the current study, an
obvious shift in the larger fish community, more so than in the smaller juvenile community, was
evident (Table 1). Amongst the smaller juveniles, the Haemulidae was the dominant family in both
studies and the Sparidae also contributed a significant and similar proportion (~ 20 %). However,
the Mugilidae in the small juvenile community made a larger contribution (16.4 %) in the current
study to that found by Lasiak (1982). Amongst the larger juvenile and adult community, the
dominant Sparidae family in the Lasiak (1982) study is far out-weighed by the Mugilidae in the
current study (Table 1). This remains evident after a large catch of L. richardsonii is omitted from
analysis whereby the Mugilidae still dominate over 50 % of the catch when they only contributed
6.5 % of the catch in the study by Lasiak (1982). For both net comparisons, family composition
was significantly different between the two studies (p < 0.05; χ2 analysis).
On a finer scale, two of the most exploited linefish families, the Sparidae and Sciaenidae
(Heemstra & Heemstra 2004), have exhibited declines in terms of total numbers displaying a
shift towards smaller individuals recorded in the Lasiak (1982) study. Lasiak (1982) caught 1132
sparids and 190 sciaenids, while, in the current study, a ~10-fold decrease for these groups was
noted (only 89 Sparids and 5 Sciaenids caught). Amongst the Sparidae, 61.9 % were smaller
than 8 cm (TL) in the Lasiak (1982) study and this fraction increases to 83.1 % in the current
study. Also evident in the current study was the total absence of two Sparidae species (strepie,
Sarpa salpa and sand steenbras, Lithognathus mormyrus) both dominant contributors to the
juvenile and adult communities three decades ago.
Table 1: Proportional composition of the dominant fish families to the catches for this study
(2011) and that of Lasiak (1982). For the larger net, two values are indicated for each family
in the 2011 study: the value on the left is the proportion when the entire catch is included and
the value on the right is the proportion after an obviously large catch of 1,552 Liza richardsonii
(Mugilidae) is omitted.
Small juveniles
Adults and large juveniles
(30 m net)
(60 m and 100 m nets)
Lasiak
(1982)
This study
(2011)
Lasiak
(1982)
This study (2011)
Atherinidae
3.5%
0.5%
0.5%
-
/
-
Carangidae
0.9%
-
-
-
/
-
Clupeidae
0.4%
1.7%
-
-
/
-
Dasyatidae
-
-
1.4%
-
/
-
Dichistiidae
-
-
-
0.1%
/
1.0%
Haemulidae
70.1%
61.4%
8.3%
0.2%
/
4.1%
Kyphosidae
-
0.2%
-
-
/
-
Monodactylidae
-
-
8.5%
0.1%
/
1.0%
Mugilidae
1.6%
16.4%
6.5%
97.3%
/
54.6%
Pomatomidae
-
-
1.1%
0.4%
/
6.2%
Rhinobatidae
0.3%
1.0%
4.6%
0.4%
/
7.2%
Sciaenidae
0.6%
-
6.0%
0.3%
/
5.2%
Sparidae
21.9%
18.6%
59.4%
0.7%
/
11.3%
Tetraodontidae
-
0.2%
1.5%
0.5%
/
9.3%
Others
0.6%
-
2.3%
-
/
-
χ2 analysis of
similarity
Similar composition
between studies but still
significantly different (p <
0.05)
Markedly different composition
between studies and significantly
different (p < 0.05)
In this preliminary assessment of the fish community at King’s Beach it is evident that there
have indeed been major shifts in the trophic structure of the fish community since the Lasiak
(1982) study. Higher-level trophic feeding piscivores and other predators (such as the Sparidae
and Sciaenidae) have been replaced by lower-level feeders such as the planktivorous Mugilidae.
The primary reason for this community shift appears most likely attributable to the collapse in
linefish stocks in South Africa due to overfishing.
Conclusion
This study provides robust evidence for the effects of wide-scale depletion of linefish stocks on
the fish community in a surf-zone nursery area. The three classic signs of overfishing are evident
in the community at present and further support the reasoning that it was indeed overfishing
of local linefish that contributed to this community shift. These are a reduction in the overall
abundance of higher-level predators, a shift in the size-class frequencies of fish towards a greater
proportion of smaller individuals and, a simplification of the food-chain whereby lower-level
planktivores become more prominent (Jackson et al. 2001; Yemane et al. 2004). This study
also highlights the nursery role played by coastal surf-zones in South Africa and makes a useful
contribution towards advocating the formal protection of a network of these surf-zones in a
holistic approach towards conservation of all life-stages of exploited fishes.
Acknowledgements
Dr. Warren Potts is thanked for his guidance in project inception, tagging and sampling
protocol. The National Research Foundation is also thanked for partially funding this project.
Many thanks are also given to the numerous willing field-assistants who invaluably helped out
with this research.
References
Able K. 2005. A re-examination of fish estuarine dependence: Evidence for connectivity between
estuarine and ocean habitats. Estuarine, Coastal and Shelf Science 64: 5-17.
Able KW, Wilber DH, Muzeni-Corino A, Clarke DG. 2010. Spring and summer larval fish
assemblages in the surf zone and nearshore off northern New Jersey, USA. Estuaries and Coasts
33: 211-222.
Attwood CG, Farquhar M. 1999. Collapse of linefish stocks between Cape Hangklip and Walker Bay,
South Africa. South African Journal of Marine Science 21: 415-432.
Beyst B, Hostens K, Mees J. 2001. Factors influencing fish and macrocrustacean communities in the
surf zone of sandy beaches in Belgium: temporal variation. Journal of Sea Research 46: 281294.
Clark BM. 1997. Variation in surf-zone fish community structure across a wave-exposure gradient.
Estuarine, Coastal and Shelf Science 44: 659-674.
Clarke KR, Warwick RM. 1994. Change in marine communities: an approach to statistical analysis
and interpretation. Plymouth Marine Laboratory, Plymouth.
Félix FC, Spach HL, Moro PS, Schwarz RJ, Santos C, Hackradt CW, Hostim-Silva M. 2007.
Utilization patterns of surf zone inhabiting fish from beaches in Southern Brazil. Pan-American
Journal of Aquatic Sciences 2: 27-39.
Goschen WS, Schumann EH. 2011. The physical oceanographic processes of Algoa Bay,
with emphasis on the western coastal region. A synopsis of the main results of physical
oceanographic research undertaken in and around Algoa Bay up until 2010. South African
Environmental Observation Network (SAEON) Institute for Maritime Technology (IMT), on
behalf of the South African Navy.
Griffiths MH. 2000. Long-term trends in catch and effort of commercial linefish off South Africa’s
81-110.
Heemstra PC, Heemstra E. 2004. Coastal Fishes of Southern Africa. National Inquiry Service
Centre, South Africa, and the South African Institute for Aquatic Biodiversity, Grahamstown.
488 p.
Jackson JBC, Kirby MX, Berger WH, Bjorndal KA, Botsford LW, Bourque BJ, Bradbury RH, Cooke
R, Erlandson J, Estes JA, Hughes TP, Kidwell S, Lange CB, Lenihan HS, Pandolfi JM, Peterson
CH, Steneck RS, Tegner MJ, Warner RR. 2001. Historical overfishing and the recent collapse of
coastal ecosystems. Science 293: 629-637.
Lasiak TA. 1981. Nursery grounds of juvenile teleosts: evidence from the surf zone of King’s Beach,
Port Elizabeth. South African Journal of Science 77: 388-390.
Lasiak TA. 1982. Structural and functional aspects of the surf-zone fish community in the Eastern
Cape. Ph.D. Thesis. University of Port Elizabeth, South Africa.
Lasiak TA. 1983. Recruitment and growth patterns of juvenile marine teleosts caught at King’s
Beach, Algoa Bay. South African Journal of Zoology 18: 25-30.
McLachlan A. 1980. The definition of sandy beaches in relation to exposure: A simple rating system.
South African Journal of Science 76: 137-138.
Miller MJ, Rowe PM, Able KW, Schaefer SA. 2002. Occurrence and growth rates of young-of-year
northern kingfish, Menticirrhus saxatilis, on ocean and estuarine beaches in southern New
Jersey. Copeia 2002: 815-823.
Palmer RM, Cowley PD, Mann BQ. 2008. A Century of Linefish Research in South Africa:
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Strydom NA. 2003. Occurrence of larval and early juvenile fishes in the surf zone adjacent to two
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The Kosi Bay fishtrap catches, impacts and
management
Scotty Kyle
Ezemvelo KwaZulu-Natal Wildlife, Private Bag x3, Congella, Durban, 4013.
Introduction
The Kosi Bay estuarine lakes system is situated on the Indian Ocean shore in the extreme north
eastern corner of South Africa. It is the second largest estuarine area in South Africa, after St.
Lucia, and has been said to perform critical functions in terms of recruitment of several marine
fish and invertebrate species. It also still has viable populations of animals such as hippo and
some crocodiles. Until recently, access to the region was restricted result in limited development
in the area. Although some resources are heavily used, the system has remained unchanged in
many respects.
The very high biodiversity and natural beauty of the area has resulted in the region being
proclaimed a Nature Reserve, Ramsar Wetland of International Importance, and was listed as
part of the iSimangaliso World Heritage Site in 1999. These actions have also recognized the
rights of the local traditional community to continue using the vast array of natural resources for
food, fuel, building materials and medicines.
Recognising and consolidating traditional rights has, however, often resulted in serious challenges
where progressively increasing human populations, combined with improving materials and
techniques, transform traditional sustainable activities into unlimited commercial operations.
At Kosi Bay, the first written accounts, dating back almost 400 years, record fishtraps in the
lakes and usage of these traps has continued to date. The local residents also speared fish and
collected crabs and prawns and harvested wild fruits. All these traditional, and apparently
mostly sustainable, activities continued, but access to markets has improved and the local
population has grown and replaced the predominantly barter with a cash based economy.
By 1980 there was a perceived conflict between the traditional fish trappers and new
recreational fishers who fished for enjoyment, not out of need, but seemed to target the same
fish stocks as the traps. Due to the rural, undeveloped nature of the area and its sandy nutrient
deficient soils the best development option identified and adopted by the authorities was that of
conservation and tourism.
The recreational anglers were all from outside the region and relatively affluent while the
trappers were exclusively local residents and mostly poor, at least at the beginning of the study.
The Kosi Bay traps are similar in design and construction to those used in other parts of the
world including the Philippines, Cuba, India, and several areas in Africa. The use of fishtraps has
declined in many areas, or has been replaced by gillnets and other fishing methods, but in Kosi
Bay, the use of traps has not declined and has been actively supported by the authorities despite
their “informal” legal status.
A typical trap consists of a double row of sticks thrust into the sand from a bank and curving
upstream. The rows are about half a metre apart and are filled with smaller branches forming
a thick barrier to large fish movement. At the inside, upstream, end of the fence a heart shaped
palisade is built and, at the apex of this, is a circular terminal basket with a valve by which the
fish may enter the basket but not return. Once a fish is in the terminal basket it usually stays
there swimming around until the trapper comes and spears it and takes it out. No bait is used
and the traps catch mostly fish moving through the channels at night on their way to the ocean.
There was initially a clear apparent conflict between the recreational and traditional fishers in
the lakes where the target species overlapped and, at that stage, the trap numbers seemed to be
declining and ever larger numbers of recreational anglers entered the region. The authorities
instituted a programme to monitor fish catches as well as fishtrap and recreational angler
numbers. At the same time a comprehensive fish mark and recovery initiative was undertaken
to try and establish recovery rates of the various fishing methods as well as estimates of the
population and information on fish movement and growth.
The traps were numbered and monitors, selected from the fishing community, were appointed
trained and equipped to check the traps catches daily. The monitoring, as well as the need for
it, was carefully explained to the local people through their traditional structures and their full
support was obtained. From 1980 to 1985 the catches of all the traps were monitored and from
then, on an ongoing basis, a known proportion of the fishtraps was monitored and estimates
of total catch were generated. At the same time 500 riverbream, Acanthopagrus vagus, were
caught, tagged using spaghetti tags, and released back into the lakes of the system. As all the
trap catches were examined the monitors were made aware of the fish tagging and a small cash
reward was given for the return of a tagged fish.
Initial results from the monitoring and tagging showed an apparently stable, sustainable and
harmonious situation. The total number of traps at that time was fairly stable (Fig 1) while
they caught about 40 000 fish weighing about 40 metric tons each year (Fig 2). The recovery of
tagged fish (Fig 3) also initially suggested a stable and sustainable fishery with about five percent
of the fish recovered annually in the traps. In addition, the recreational fishers recovered about
one percent of tagged fish each year and their annual catch was estimated at about ten tons.
Figure 1. Total number of fishtraps counted annually from 1981 to 2010 in the Kosi Bay lakes,
no data being available for 2002.
There appeared to be no crisis in the Kosi Bay fishery. Nearly all the species caught were of
marine origin and required stable ocean conditions to spawn. Spawning took place outside,
or very near, the mouth of the Kosi system and the fish would recruit, mostly at a very small
size, through the trap surrounded channels into the lakes. Due to their small size and the trap
construction, the recruits would seldom be caught in the traps on their way to the lakes and the
recreational fishers could only retain limited numbers of mostly mature fish due to the enforced
size and bag limits.
The recreational anglers could thus not complain too loudly about traps stopping immigration
or seriously reducing recruitment while, as the recreational anglers only caught about
one percent of available fish, trap catches were not markedly reduced by current levels of
recreational fishing.
In the early 1980s, it appeared that adequate numbers of adult fish successfully migrated
through the traps to the spawning grounds. Traps were made almost exclusively of indigenous
branches bound together by dried wild banana (Strelitzia nicolae) leaves and this resulted in
substantial gaps between the sticks resulting in very few fish smaller than about 20 cm. being
caught. Almost all the traps also curved upstream and thus targeted fish exiting the lake system.
Figure 2. Total catch estimates, in numbers, of the Kosi Bay fishtraps from 1981 to 2010.
Figure 3. Percentages of marked fish recovered in the Kosi bay lakes from 1983 to 2010.
At this time, most traps were managed by older men, often on pensions, and most of the fish
were consumed by his family, given away, or bartered locally. Few fish, except during times of
excellent catches, were sold.
Tourists were also strictly controlled in that, although no marine fishing licenses were issued at
that time, size and bag limits were enforced as all recreational anglers lodged at the then Natal
Parks Board Camp.
Catch monitoring, trap counting and fish marking data indicate that trap numbers and total
catches have increased (Figs 1 & 2) and that the proportion of marked fish recovered in the traps
has progressively increased (Fig 3).
Monitoring results clearly show predictable annual cycles in fish abundance for each species,
with some species showing particularly strong seasonal patterns (Fig 4). It is probable that not
all fish migrations are directly related to spawning, although some species, such as riverbream,
appear to conform closely to the spawning cycle. Within this cycle, very pronounced daily catch
fluctuations are also evident and most show very strong links to water height measured in a
channel situated in the middle of the Kosi Bay system. This water height closely follows the
lunar cycle and while some species show no preference for full or new moon phases, others, such
as Liza allata (Fig 5), display a strong preference for the darker moon phases. The best catches
of many species of fish are associated with strong winds, heavy rain and take place over full
moons in the summer months. Traps are often renovated just before summer for this reason.
The catch species composition (Table 1) also changed markedly during the data capture period
even though the top few species mostly remained similar. In the beginning the most important
species was spotted grunter (32.4%) followed by flathead mullet (25.1%) and then largescale
mullet (10.6%). While the two most important species declined in importance during the study,
both the largescale mullet and the Natal stumpnose became much more important in catches
towards the end of the monitoring period.
Figure 4. Total monthly Kosi Bay fishtrap catches of Riverbream, Acanthopagrus vagus, from
January 1981 to March 1985.
Table 1. Species composition, by number, of the most important species in the catches of the
Kosi Bay fishtraps in 1985 and 2010.
Common name
Scientific name
1985
2010
%
%
Spotted grunter
Pomadasys commersonni
32.4
13.9
Flathead mullet
Mugil cephalus
25.1
18.7
Largescale mullet
Liza macrolepis
10.6
27.2
Largescale pursemouth
Gerres methueni
9.1
6.4
Riverbream
Acanthopagrus vagus
6.5
3.7
Natal stumpnose
Rhabdosargus sarba
4.7
20.0
Bluetail mullet
Valamugil buchanani
2.2
4.1
Kingfishes
Carangidae
1.9
1.9
Diamond mullet
Liza alata
1.6
0.2
River snapper
Lutjanus argentimaculatus 0.9
2.0
Other species
5.0
1.9
Total
100.0
100.0
Figure 5. Total daily catches of diamond mullet, Liza allata, from 25 May 1985 to 20 June
1985. New moon periods being 3 May and 4 June and full moon periods 17 May and 18 June.
Various factors have contributed to the increases in effort and catch during the study, the most
important being the political transformation in South Africa in 1994 and the establishment of a
new, democratic government. One of the foundations of the old regime was the migrant labour
system that resulted in many young people from rural areas working in urban areas and sending
money home. Many of these people returned to the Kosi Bay area and needed to find means
of supporting themselves and their families. One of the few options was building fishtraps and
many of the Indunas (sub chiefs) offered unused fishtrap areas to these young men. As a result,
the number of traps increased (Fig 1) causing a “spike” in trap catches (Fig 2). Not only were
there more traps being built, but those in operation were often taken over by younger men and
a new management approach arose. Rather than being a supplement to a pension, catches were
now used to sustain the urban lifestyle to which the younger men had become accustomed.
Apart from an increase in the number of traps, road access to the region had improved, allowing
more efficient export of materials, including fish. Local people and outside buyers soon realized
that large numbers of fish were available from the traps at Kosi Bay and lucrative markets were
available within reasonable driving distance. Some trappers organized fish buyers who could be
contacted to export and sell the fish when good catches were made. While it seems reasonable
that people should be allowed to sell to best advantage, one of the main arguments to allow
trapping to continue was that the traps provided relatively cheap and abundant high-quality
protein for the poorer local residents. A large number of local women made extra money by
selling fish at the local market. Under the management of the younger men, the majority of the
fish were exported from the area and the income opportunities for the local women reduced. A
small number of men now made a large amount of money from the fish traps.
With the focus moving from a subsistence fishery to a lucrative business, some trappers began
exploring ways to increase the efficiency of the traps. Rather than using the clumsy and thick
traditional binding material, they began using nylon rope and string, often taken from old
fishing nets washed up on the shore. Not only were these stronger, and longer lasting, they
allowed the sticks of the terminal basket to be brought closer together, thus retaining smaller
fish. Further, traditional sticks used in trap constructions were often gnarled often resulting in
large gaps between the sticks. By replacing the traditional sticks with gumpoles or bamboo, the
gaps between the sticks could be reduced, thus retaining even smaller fish. All fish caught could
be sold; therefore, all size classes were targeted. Information from the monitoring (Fig 6) shows
that most spotted grunter (Pomadasys commersonni) caught at the beginning of the study were
mature and larger than the legal size limit, by the end of the study this proportion had dwindled
markedly. Gillnet was being used by several trappers to cover their baskets to prevent species
like bluefin mullet, Valamugil buchanani, from leaping out or fish eagles from “stealing” the
fish. Nets were also set along fence lines and round baskets to prevent fish passing through.
Figure 6. Lengths of spotted grunter Pomadasys commersonni collected during Kosi Bay
fishtrap monitoring programme from 1981 and 2010.
By using modern materials the new trappers were not only able to retain more fish in the traps,
they could catch ever smaller fish and build traps into the deeper or faster moving water of the
channels. Further, traditionally almost all traps faced upstream and caught fish exiting the lake
system, new baskets facing downstream were being added. The traditional constraint of only
using indigenous materials ensured a limited number of larger fish were caught while upstream
facing baskets allowed recruiting or returning fish free access to the lakes. The downstream
facing baskets now targeted larger numbers of recruits and returning fish. Recent monitoring
suggests that some species, such as spotted grunter, undergo massive recruitment of 20 cm fish
and that the traps are now harvesting large catches of these fish.
The net result of the influx of younger trappers and the modifications to the traps has been the
progressive increase in the proportion of tagged fish recovered (Fig 3). While many would argue
that a recovery rate of about five percent of marked fish might be sustainable, few would do so
when this rate rose to more than one third of the fish marked. It is not known what proportions
of tags remained on the fish, marked fish died as a result of capture and marking, left the system
or were caught and not reported. It is likely that a recorded recovery rate of about 35% actually
indicates a much larger proportion of the fish are caught annually.
While the earlier scenario was reassuring from a management perspective in that there
appeared to be little competition between trappers and recreational anglers, and an overall
sustainable level of harvesting, the more recent situation is concerning. Not only has a higher
proportion of tagged fish been caught, but, while the recreational fishers still only harvest about
one percent of marked fish, the traps accounted for almost the entire remainder. The traps were
thus reducing the numbers of fish heading for the spawning grounds as well as directly reducing
subsequent recruitment.
In the past it was assumed that many species of fish undertook single, annual migrations
to the ocean usually associated with spawning. Recent fish telemetry work suggests that
Acanthopagrus vagus often undergoes multiple migrations through the trap areas. This would
explain the marked decline in abundance of this species in recent years.
The situation has been exacerbated because the trappers have never applied for fishing
licenses, in terms of the Marine Living Resources Act, despite numerous and lengthy attempts
to get them to do so. This means that, not only are the traps illegal, but no conditions, such as
restrictions on the use of nylon rope, are currently possible.
I see two management alternatives available to the authorities: issue licenses to the trappers, in
terms of the current Operational Management Plan that prohibits the use of modern materials
and reduces the efficiency of the traps back and promotes sustainable utilization of the fishery
resource; or recognize the traps as a full scale commercial fishery and manage it as such,
optimizing catches and prices and improving freezing and transport facilities. The former is
easily compatible with the values and mission of a World Heritage Site while the latter is not.
The former will be an asset to tourism in the area whereas the latter will have a very negative
effect on it.
The former option is relatively easy to implement, in theory, as the constraints are mostly
the same as the traditional ones and many local people want them reinstated. All that needs
to happen is for licenses to be issued in terms of the conditions of the fishtrap Operational
Management Plan. The alternative management approach will all but destroy the local
recreational fishing and tourism industry but also seriously impact the capacity of the Kosi Bay
system to act as a nursery and source of recruits for many marine fish and invertebrate species
and a refuge for others. Several of the Kosi Bay estuarine species, such as Acanthopagrus vagus,
may have already been severely reduced in abundance while other species that enter Kosi Bay
from an external “metapopulation” often do not return to the ocean. Rather than Kosi Bay acting
as a source of recruits for many fish species, it has possibly become a sink.
The main management recommendations are as follows:
• Issue fishtrap licenses in terms of the Marine Living Resources Act, with OMP conditions
• Ensure only indigenous materials may be used in trap building
• Ensure that the traditional 30 metre trap free channel is maintained to the ocean
• Prohibit the construction of downstream facing traps
• Prevent the construction of traps near channel mouths
The situation in the Kosi Bay fishery has become clear after over thirty years of monitoring,
and the necessary management steps are obvious. What is required is that the few people who
have blocked the process to date step aside and allow the sustainable management of the fish
resources of Kosi Bay.
Session 5 – Monitoring: Chair Colin Attwood
Monitoring the recovery of a previously exploited
surf-zone habitat in the St Lucia Marine Reserve using
a no-take sanctuary area as a benchmark
BQ Mann1 and M Tyldesley2
Oceanographic Research Institute, P.O. Box 10712, Marine Parade, Durban, 4056.
2
Ezemvelo KwaZulu-Natal Wildlife, Private Bag X3, Congella, Durban, 4013.
1
Introduction
In January 2002, a ban on beach driving in South Africa was implemented (Government Gazette
No. 22960) in terms of the National Environmental Management Act (Act No. 107 of 1998). While
unpopular with more affluent recreational shore anglers (Dunlop 2011), this legislation effectively
reduced angler access to large areas of the coastline, particularly in less developed areas (Mann
et al. 2008). In November 2001, a project was established in the St Lucia Marine Reserve in the
iSimangaliso Wetland Park to compare shore fish populations inside the St Lucia Marine Reserve
Sanctuary (Red Cliffs to Leven Point) with those in the adjacent exploited area (Leven Point to
Cape Vidal). This project provided the opportunity to monitor the potential recovery of shore fish
populations in the area north of Cape Vidal as anglers could no longer access this area because of
the prohibition of beach driving.
The aim of this aspect of the study was to compare the species composition, catch per unit
effort (CPUE) and population size structure of shore angling species within the St Lucia Marine
Reserve Sanctuary (i.e. benchmark area) with that of the adjacent, previously exploited area
south of Leven Point and to monitor whether there was evidence of a recovery over a 10-year
time period (2002 to 2011).
Methods
A trained team of volunteer anglers undertook four 4-day field trips to Cape Vidal each year. Prior
to 2007 (i.e. from November 2001 to November 2006), six field trips were carried out per year (i.e.
once every two months), whereas quarterly field trips (Feb, May, Aug, Nov) were conducted per
year between February 2007 and November 2011. During each field trip, fishing was conducted
by eight trained anglers in four selected 2km areas marked off at 100m intervals using numbered
poles and a GPS. Two of the 2km areas were inside the no-take sanctuary area (between Leven
Point and Red Cliffs) and two were in the previously exploited area (between Leven Point and
Cape Vidal) (Fig 1). All four areas were selected to be as similar as possible in terms of habitat (i.e.
all contained both sandy and rocky shores with some patchy reef habitat sub-tidally).
Standardised rock and surf fishing gear and barbless hooks were used and all fish caught were
carefully handled and quickly measured on plastic stretchers before being returned unharmed
to the water. Targeted species greater than 30cm fork length (FL) were tagged using plastic dart
tags (Hallprint) supplied by the ORI Tagging Project. All catch and effort data, as well as tagging
information, was recorded by each angler on a daily basis and subsequently captured onto a MSAccess database for later analysis.
Two 4x4 vehicles were used to transport the anglers along the beach to the selected fishing areas and
all beach driving was restricted to three hours either side of low tide. All field trips were conducted
over spring tides, or as close to spring tides as logistically possible.
Results
Species composition
A total of 50 field trips were undertaken between November 2001 and July 2011 during which 12 367
fish were caught comprising 88 species from 38 families. Of the fish caught, 5 299 were tagged and
701 (13.4%) were recaptured. The species composition was similar in each of the four sampling areas
being dominated by three species: speckled snapper (Lutjanus rivulatus), largespotted pompano
(Trachinotus botla) and grey grunter (Pomadasys furcatum), hereafter referred to as the ‘dominant
trio’. For purposes of comparison, the species composition from the two previously exploited areas
(EA & EB) and the two sanctuary areas (SA & SB) were pooled (Fig 2).
Figure 1: Map of the St Lucia Marine Reserve and Sanctuary showing the four 2km sampling
sites used in this study (EA & EB are in the previously exploited area, while SA & SB are within
the sanctuary area).
Analysis of species composition over the 10-year study period revealed subtle differences in each
of the four sampling areas (Fig 3a-d). In addition to the afore mentioned dominant trio, blacktail
(Diplodus capensis) and catface rockcod (Epinephelus andersoni) comprised the top five
species in EA (Fig 3a). An increase in the percentage composition of grey grunter from 2008-11
and a decrease in the percentage composition of catface rockcod during 2010-11 were the only
discernible changes in species composition in the EA area over the 10-year study period (Figure
3a). In the EB area, cave bass (Dinoperca petersi) replaced catface rockcod as one of the top five
species (Figure 3b). An increasing trend in percentage composition of both speckled snapper
and grey grunter was apparent in the EB area (Fig 3b).
Figure 2: Species composition recorded in a) the previously exploited areas (EA & EB) and b) the
sanctuary areas (SA & SB) in the St Lucia Marine Reserve between November 2001 and July 2011.
Figure 3a-d: Trends in fish species composition in the four sampling areas in the St
Lucia Marine Reserve between 2002 and 2011 (SSNP=speckled snapper; GGRN=grey
grunter; LPMP=largespotted pompano; CRCD=catface rockcod; NSTM=Natal sumpnose;
BLTL=blacktail; LPFS=cave bass; BSTM=bigeye stumpnose).
Catface rockcod and Natal stumpnose (Rhabdosargus sarba) combined with the dominant trio
to dominated catches in the SA area (Fig 3c). Species composition fluctuated widely in the SA
area over the 10-year period with sand inundation of the subtidal reef habitat in 2005 resulting
in an increase in catches of largespotted pompano and a subsequent decrease in percentage
composition of reef fish such as grey grunter and speckled snapper. This pattern was reversed
in 2009 when scouring of the reef habitat resulted in an influx of reef-associated species
(Fig 3c). Percentage composition of Natal stumpnose in the SA area became progressively
smaller throughout the sampling period, probably linked to the lack of recruitment into the
adult population following the closure of the St Lucia Estuary in 2002 (Mann and Pradervand
2007). Bigeye stumpnose (Rhabdosargus thorpei) and blacktail combined with the dominant
trio, dominated catches in the SB area (Fig 3d). An increase in the percentage composition
of speckled snapper from 2008-11 was the most evident trend in this area over the 10-year
sampling period. It is believed that this may have been due to improved angler skills in targeting
this species and increased targeting of this species after dark during February field trips.
Catch per unit effort (CPUE)
Fishing effort (angler hours) in all four sampling areas was similar throughout the 10-year study
period. The decrease in effort from 2007 onwards was as a result of reducing the annual number
of field trips from six to four (Fig 4). CPUE was calculated as the number of fish caught per
angler per hour in each of the four sampling areas and averaged per field trip. In order to avoid
bias from large catches of small fish that were not being targeted, CPUE was standardized to
only include fish that were tagged or recaptured (i.e. targeted fish over 30cm FL).
Figure 4: Annual fishing effort in terms of angler hours expended in the two previously
exploited areas (EA & EB) and the two sanctuary areas (SA & SB) from 2002-11.
The average CPUE was lowest in the previously exploited areas, gradually (but significantly)
increased as one moved from the EA area closest to Cape Vidal (0.30 fish.angler-1.hour-1 + 0.24
sd) to the SB area in the middle of the Sanctuary (0.58 fish.angler-1.hour-1 + 0.37 sd) (Fig 5).
There was a rapid increase in standardized CPUE during the first three years (2002-2004) in
the EA area after which the catches stabilized at ~0.3 fish.angler-1.hour-1 (Fig 6a). Overall there
was a slight, non significant increasing trend in this area (P=0.32). Clear seasonal peaks in catch
rates were evident during the summer months. The rapid increase in CPUE during the first three
years was also observed in the EB area. However, this trend was significant (P=0.003) for the
duration of the study and the CPUE had doubled by the end of the study period (Fig 6b). The
CPUE in the SA area remained remarkably stable throughout the study with a mean of 0.4 fish.
angler-1.hour-1 (Fig 6c). There was a gradual increase in CPUE in the SB area although this trend
was not significant (P=0.08). It is believed that the increase in catches during latter part of the
study (2008-11) may have been partly as a result of improved angler skill and knowledge of the
area (Fig 6d).
Figure 5: Average standardized CPUE calculated for the four study areas using the entire 10year data set.
In order to examine the temporal trends for individual species, un-standardised CPUE data was
calculated as the number of fish caught per species over the total number of angling hours per
field trip. Data from the two previously exploited areas (EA & EB) and the two sanctuary areas
(SA & SA) was pooled for comparative purposes.
Figure 6a: Trends in standardized CPUE (+ sd) for the four study areas in the St Lucia Marine
Reserve from November 2001 to July 2011.
Figure 6 b-d: Trends in standardized CPUE (+ sd) for the four study areas in the St Lucia
Marine Reserve from November 2001 to July 2011.
There was a significant increase in the CPUE for speckled snapper in both the previously
exploited (P=0.023) and sanctuary areas (P=0.015) (Fig 7a) during the study period. Both these
trends may have been influenced by recruitment variability, possibly increased angler skill in
targeting this species, and changes in the sampling protocol, especially after 2008 when more
night fishing was undertaken. Catches of large spotted pompano were highly seasonal in both
areas with higher catches being made during the summer months (Fig 7b). A slight increasing
trend was observed in the previously exploited areas although this was not significant (P=0.42).
Although there was a significant decline recorded in the sanctuary areas (P=0.03), this was
possibly as a result of a switch in targeting towards reef-associated species rather than a decline
in abundance of large spotted pompano per se. There was an increase in the relative abundance
of grey grunter in both areas (Fig 7c). The increase in the previously exploited areas was highly
significant (P<0.001), while that recorded in the sanctuary areas was not significant (P=0.08).
This result does suggest a recovery of this species in the previously exploited areas. There was
a decline in the relative abundance of Natal stumpose in both the previously exploited and
sanctuary areas (Fig 7d). It is believed that this decline was the result of the closure of the St
Lucia Estuary in 2002 and the consequent reduction of adult recruitment into the area (Mann
and Pradervand 2007).
Figure 7a-b: Trends in CPUE of four important shore angling species caught in the previously
exploited and sanctuary areas of the St Lucia Marine Reserve from Nov 2001 to Jul 2011.
Figure 7c-d: Trends in CPUE of four important shore angling species caught in the previously
exploited and sanctuary areas of the St Lucia Marine Reserve from Nov 2001 to Jul 2011.
Size frequency
Mean size + standard deviation (mm fork length) was calculated for all fish caught in each area
per year. For comparison, the lengths of fish were pooled for the two exploited (EA & EB) and
sanctuary areas (SA & SB). The mean size of speckled snapper was significantly smaller in the
previously exploited areas from 2002-2005 where after sizes in the two areas were very similar
(Fig 8a). This provided evidence that the size structure of the population was recovering from
the affects of exploitation in the previously exploited areas. The mean size of large spotted
pompano was consistently smaller in the previously exploited areas throughout the study
period except in 2009 (Fig 8b). While these differences were seldom significant, there was little
evidence to suggest a recovery in the populations size structure of this species. However, since
recent research has shown that large spotted pompano are underexploited (Parker 2012), these
results are therefore more likely to be indicative of subtle differences in surf-zone habitat in the
four sample areas. Grey grunter captured during the first two years of the study (2002-2003)
were significantly smaller (Fig 8c), and suggests that the size structure of the population was
recovering from the affects exploitation in the previously exploited areas. The mean size of
Natal stumpnose did not reveal any clear trends (Fig 8d). However, it was interesting to note
that although they were less abundant, the mean size of stumpnose in the previously exploited
areas were significantly bigger during the period 2006-2009. The reason for this difference
is hard to explain but may be as a result of a few large adults being left in the population with
limited recruitment (Mann and Pradervand 2007). An interesting anomaly to the general trend
observed was the case of catface rockcod which showed the occurrence significantly larger fish
in the previously exploited areas almost throughout the study period (Fig 8e). It is believed
that this may be due to habitat preference or the possibility that catface rockcod are a “pioneer”
species that have occupied niche space of more resident reef fish species such as speckled
snapper and yellowbelly rockcod (Epinephelus marginatus) that had been “fished out” in the
previously exploited areas. A similar trend was observed in the Pondoland MPA (Maggs 2011)
giving greater credibility to this speculation.
Figure 8a-b: Annual mean length (+ sd) of five important shore angling species caught in the
St Lucia Marine Reserve Sanctuary areas and the previously exploited areas south of Leven
Point between 2002 and 2011.
Figure 8c-d: Annual mean length (+ sd) of five important shore angling species caught in the
St Lucia Marine Reserve Sanctuary areas and the previously exploited areas south of Leven
Point between 2002 and 2011.
Figure 8e: Annual mean length (+ sd) of five important shore angling species caught in the St
Lucia Marine Reserve Sanctuary areas and the previously exploited areas south of Leven Point
between 2002 and 2011.
Discussion
The data collected during this study provided evidence for the recovery of some surf-zone fish
populations in the previously exploited areas south of Leven Point following the implementation
of the beach driving ban in January 2002. This evidence was strengthened by using the
sanctuary area as a benchmark and ensured that false assumptions were not made. However,
despite a concerted effort to ensure that the selected 2km sampling sites were as similar as
possible, subtle differences in the habitat structure in each of the four areas resulted in slight
differences in species composition and these differences complicated analysis. For example, the
trends in catch composition revealed annual changes in fish abundance that were most likely
linked to a variety of factors. Uncoupling the affects of these factors is critical before the CPUE
data can be used as evidence for of stock recovery.
These primary factors influencing CPUE includes recruitment variability, habitat changes (e.g.
periodic sanding up or scouring of subtidal reefs) and improved fishing skill. The influence of
improved fishing skill is seldom taken into account when evaluating long-term catch and effort
data sets but there is no doubt that it affected the results of this study. After 10 years of fishing
the same 2km areas we learnt where the most productive areas were to fish and fishing effort
became more concentrated in these areas. We also learnt how best to target certain desired
species such as speckled snapper (e.g. best terminal tackle, bait type, bait presentation, etc.) and
we learnt that this species feeds more prolifically in the first few hours of darkness resulting in
extended fishing times. These changes improved catch rates but were not necessarily related to
increased fish abundance.
Overall trends in CPUE revealed high variability but a gradual increase in fish abundance from
the “most exploited” (EA) to “least exploited” (SB) (i.e. although the EA area is 8km north of
Cape Vidal, avid anglers did occasionally walk up the beach and fish in this area). This result
is not unexpected and serves to highlight the value of no-take MPAs in protecting a greater
biomass of fishery species (Attwood et al. 1997). Trends in CPUE suggested a rapid initial
recovery (3-4 years) in both previously exploited sample areas (EA & EB), similar to the findings
after the De Hoop Marine Reserve (Bennett and Attwood 1991). However, the recovery in the
EB area was more significant and sustained. The proximity of the EB area to the sanctuary
(4km) suggests that this area has received greater benefit from spillover than the EA area
which is further away (12km). Such fishery benefits close to the boundaries of no-take MPAs
are well documented in the literature (Gell and Roberts 2003). While the un-standardized
species-specific CPUE trends presented in this paper provide useful indicators of trends in fish
abundance, these are preliminary data which require standardization to reduce the effects of
recruitment variability (e.g. large catches of small fish). Furthermore, use of General Linear
Models (GLMs) is strongly recommended to enable better interpretation of trends in CPUE.
Variation in the mean size of the target species such as speckled snapper and grey grunter
provided evidence of increases in the previously exploited areas within the first 3-4 years. These
increases were expected as generally resident fish are able to increase in size (and number as
shown above) with a cessation in fishing. However, unexpected results were obtained for some
species, such as the catface rockcod. Complex inter-specific interactions such competition
between species may thus affect the time that it takes for fish communities to return to a
“climax” state. This emphasizes the need to conduct studies of this nature over a long period
of time, especially in monitoring slow growing, long-lived fish species. One observation made
during the study was the small mean size of many of the fish species caught, especially the
serranids, suggesting that the surf-zone provides an important nursery habitat for these species,
with adults moving out into deeper water with size/age. A final point to emphasize with regard
to monitoring of fish size structure in no-take MPAs is that this information is extremely
useful for the calculation of reliable estimates of natural mortality rates (M) for comparison to
exploited populations (Gotz et al. 2008).
Recommendations
•
•
•
•
Use of no-take MPAs as a benchmark in long-term monitoring programmes is highly
desirable to enable distinction between natural variability and human-induced changes.
Monitoring programmes of this nature must be carefully designed, rigidly implemented and
run for a long time period (> 5-10 years) with adequate, secure funding.
Consequences of any changes to the sampling design in such programmes must be carefully
evaluated before being implemented.
As areas immediately adjacent to no-take MPAs will receive greater benefit from spillover,
MPA planners should consider different levels of zonation to provide adjacent “buffer zones”
(e.g. B2 zonation).
Acknowledgements
We are grateful to the following organisations for the funding received for this long-term
monitoring project: South African Association for Marine Biological Research; Department
of Agriculture, Forestry and Fisheries /National Research Foundation (2002-2005), DAFF
(2006-2009), iSimangaliso Wetland Park Authority (2011). Ezemvelo KwaZulu-Natal Wildlife
is thanked for providing logistical support. Finally, this project would not have been possible
without the ongoing support and commitment of all the anglers that have participated. A big
thank you to all of you!
References
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South Africa. South African Journal of Marine Science, 18: 341-367.
Bennett BA, Attwood CG. 1991. Evidence for recovery of a surf-zone fish assemblage following
the establishment of a marine reserve on the southern coast of South Africa. Marine Ecology
Progress Series 75: 173-181.
Dunlop SW. 2011. An assessment of the shore-based and offshore boat-based linefisheries of
KwaZulu-Natal, South Africa. Unpublished MSc thesis, University of KwaZulu-Natal, Durban,
South Africa.
Gell FR, Roberts CM. 2003. Benefits beyond boundaries: the fishery effects of marine reserves.
Trends in Ecology and Evolution 18: 448-455.
Gotz A, Cowley PD, Winker H. 2008. Selected fishery and population parameters of eight shoreangling species in the Tsitsikamma National Park no-take marine reserve. African Journal of
Maggs JQ. 2011. Fish surveys in exploited and protected areas of the Pondoland Marine Protected
Area with consideration of the impact of the MPA on coastal fisheries. Unpublished MSc thesis,
University of KwaZulu-Natal, Durban South Africa.
Mann BQ, Nanni G, Pradervand P. 2008. A monthly aerial survey of the KwaZulu-Natal marine
shore fishery. Oceanographic Research Institute, Durban, Unpublished Report 264, 12pp.
Mann BQ, Pradervand P. 2007. Declining catch per unit effort of an estuarine-dependent fish,
Rhabdosargus sarba (Teleostei: Sparidae), in the marine environment following closure of the
St Lucia estuarine system, South Africa. African Journal of Aquatic Science 32: 133-138.
Parker D. 2012. The life history and fishery assessment of largespot pompano, Trachinotus
botla, in northern KwaZulu-Natal, South Africa. Unpublished MSc thesis, Rhodes University,
Status of chondrichthyans in False Bay
N Best1 and C Attwood2
1
Percy FitzPatrick Institute of African Ornithology, Zoology Department, University of Cape
Town, South Africa.
2
Abstract
Commercial fishing in False Bay, South Africa, began in the 1600s. Today chondrichthyans are
regularly taken in multiple fisheries throughout the bay. Using a combination of time series
data and life history information the vulnerability of chondrichthyans to exploitation in False
Bay was assessed. Catch trend analyses for chondrichthyan species was conducted using time
series data from five fishing methods (1897 to 20110. Of the 38 species found to occur in False
Bay, 28 showed no significant trends for any fishing methods, possibly as a result of poor species
identification. Of the 10 species and one genus displaying catch trends, two were increasing
(Mustelus mustelus and Carcharhinus brachyurus) and three were decreasing (Galeorhinus
galeus, Triakis megalopterus and Raja spp.) across capture methods. An index of productivity
was used, in conjunction with information on life history, and level of population decline, to
assess the state of chondrichthyans in False Bay. The assessment identified populations as
stable (M. mustelus and C. brachyurus), vulnerable (Callorhinchus capensis and Raja spp.), or
threatened (G. galeus and T. megalopterus) by exploitation. A further 13 species were identified
as species of conservation concern. The status of the remaining 20 species and one genus were
recorded as unknown due to inconclusive results or insufficient data.
Introduction
The harvest of chondrichthyan (shark, skates, rays and chimaeras) species has been identified
as the greatest current threat to their diversity and abundance, with risk from commercial
and industrial fisheries far out-weighing that of artisanal and subsistence harvests (Stevens
et al. 2005; Worm et al. 2005). Chondrichthyans are broadly of conservation concern, firstly,
because their life history traits result in low intrinsic rates of populations increase, rendering
them more susceptible to fishing mortality than the earlier-maturing, shorter-lived and more
fecund bony (teleost) fishes with which they are frequently caught (Musick et al. 2000).
Secondly, chondrichthyans are positioned high in the food chain as predators, many as top order
predators, and thus have comparatively low abundances (Bonfil 1994). In addition, predators,
influence prey communities through direct predation and by inducing costly anti- predator
behaviour (Creel & Christianson 2008). Therefore, chondrichthyans have a fundamental impact
on the structure and function of marine ecosystems (Heithaus et al. 2008; Myers et al. 2007)
and are considered indicators of ecosystem health (Jackson 2008).
False Bay is the largest true bay in South Africa (Spargo 1991), and has a long history of
commercial exploitation, dating back to the 17th century (Penny 1991), utilising all major fishing
methods. False Bay has also had the longest protection from trawling (Scott 1949). Additionally,
the threat of shark attack is a concern. A spate of attacks could quickly incite public demand for
shark-nets such as those used in KwaZulu-Natal (Dudley & Simpfendorf 2006), increasing the
risk to vulnerable chondrichthyan populations. Due to the importance of chondrichthyans in the
ecosystem, any population losses caused by the implementation of shark-nets could result in a
cascade of impacts throughout the bay (Stevens et al. 2005).
Although concern has been expressed regarding chondrichthyan exploitation based on their
biological and ecological traits, and historical exploitation patterns, protection of these species
from the impacts of fisheries is not impossible. To objectively assess the current state of sharks
and their relatives, increased knowledge of the diversity in the respective fisheries, the species
exploited, the size of the catches, and harvesting practices is required (Bonfil 1994). Only
through improved knowledge can effective management and protection of chondrichthyans be
established. A consolidation of all available fishing and survey data was therefore conducted to
describe the chondrichthyan community of False Bay, characterize changes in exploitation, and
assess their vulnerability to present and future threats.
Methods
Data collection
Historical and contemporary fisheries records were compiled to reconstruct the history
of chondrichthyan exploitation and to evaluate trends in population abundance in False
Bay during the 20th century. Different sources of information, including commercial and
recreational fisheries landings, scientific surveys and underwater records were used to compile
time series data of abundance from 1897 to 2011. The subsequent fishing or sampling methods
were trawl surveys, demersal longline catch returns, commercial linefish catch returns, beach
seine scientific surveys and commercial catch returns, recreational angling, SCUBA diving
underwater census, spearfishing and rotenone (poison) surveys.
Data analysis
Data were analysed for trends within and between fishing methods. Various metrics were used
to assess the extent of exploitation of various chondrichthyan species in each of the major
fishing methods. These metrics were catch, relative species catch and catch per unit effort
(CPUE). The annual proportion of all chondrichthyans combined relative to the total catch, as
well as, annual species-specific proportions was calculated for the majority of fishing methods.
All multivariate analyses were performed in PRIMER analytical package (Clarke 1993). Cluster
analyses were preformed using the Bray-Curtis index of similarity. These relationships were
further investigated using multi-dimensional scaling (MDS) to produce a two-dimensional
representation of the relationships between samples. Further, clustering and ordination
techniques were used to illustrate the degree of similarity in the species composition of catches
from different methods across time.
Trend analysis
Trends in the absolute CPUE of all chondrichthyans combined were tested using simple
linear regression procedure (Zar 1984) for commercial beach seine, commercial linefishing,
and demersal longline. CPUE data were not available for recreational angling, therefore, the
proportion of chondrichthyans in the total catch was analysed.
Species-specific trends in abundance for each of the primary fishing methods (commercial
linefish, commercial beach seine, recreational angling, demersal longline and trawl) were
analysed using a rank correlation for annual CPUE or catch proportion (recreational angling)
data. Rank correlation was used in preference to simple linear regression because the dependent
variable was seldom normally distributed and usually included a high frequency of zeros.
It was expected that the information contained in the abundance indices would be low for some,
or all, fishing methods related to difficulties in species identification and the quality of reporting.
For this reason, it was deemed necessary to determine congruence in trends across the four
fishing methods for each particular species. Agreement across the fishing methods was accepted
if either of the following criteria was met:
•
•
a trend was detected with p < 0.01 for at least one method in which the species was a
substantial part of the catch, and no opposing trend being detected by any other method.
a trend was detected with p < 0.1 in at least two methods with no opposing trend from any
other method.
Vulnerability assessment
Life history characteristics for the majority of the species were used to determine an index
of productivity or resilience using the parameters defined by Musick (1999): intrinsic rate
of population increase (r), von Bertalanffy k, fecundity, age at maturity, and maximum age.
Each species was allocated to one of four productivity categories (very-low, low, medium, and
high) using the corresponding value ranges suggested for each parameter (Musick 1999). In
addition to population productivity, the following criterion were also taken under consideration
when evaluating risk of chondrichthyan fishes to exploitation: small population, habitat, small
distribution range or endemicity, mortality threat associated with habitat, and population decline.
Evaluating the aforementioned risk criteria identified species populations that were stable,
vulnerable, threatened, of conservation concern or had unknown exploitation status in False Bay,
thus identifying those species in need of monitoring, conservation management or protection.
Results
Sample size
The three longest time series data sets were commercial beach seine returns, commercial
linefish returns, and recreational angling records, listing 27 150 338, 13 297 523, and 23 752
fish records, respectively. Two equally productive sampling techniques, beach seine surveys and
trawl surveys, were comparatively brief time series data and provided only 85 500 and 109 077
fish records, respectively. Demersal longlining for chondrichthyans is a relatively recent and
heavily restricted fishery in False Bay and yielded only 12 612 fish records. Longlining is the only
fishing method aimed exclusively at chondrichthyans – although teleosts may have been caught
and not recorded. Among the other time series data sets, the percentage of chondrichthyans by
number in the samples range from 0.02% in commercial beach seine to 30.7% in recreational
angling. The three shortest time series data sets were the underwater methods SCUBA,
spearfishing and poisoning which listed 4 842, 1 174 and 1 199 fish records, respectively.
Species diversity and composition
A diversity analysis of chondrichthyan species found recreational angling, survey beach seine and
commercial linefishing to be the highest in terms of species number with 24, 19 and 17 respective
species. These three methods had the highest alpha diversity and evenness (Shannon Index) and
provided the broadest spectrum of information on chondrichthyan communities.
Combined records revealed 38 chondrichthyan species caught and/or sighted at least once in
False Bay (Table 1). The five most commonly caught species were Galeorhinus galeus (soupfin
shark) with 25 085 recorded individuals, Mustelus mustelus (smooth-hound shark) with 18 087,
Rhinobatos annulatus (lesser guitarfish) 6 386 individuals, Callorhinchus capensis (St. Joseph
shark) 4 545, and Notorynchus cepedianus (broadnose sevengill) with 3 705 individuals reported.
Of the chondrichthyans recorded, 14 species (37%) were considered to be of primarily Atlantic
origin and seven species (18%) were predominately from the Indo-pacific region (Smith &
Heemstra 1986; Compagno et al. 2005b). Of the chondrichthyans with restricted distributions
eight (21%) were endemic to Southern Africa and four (11%) to South Africa. The remaining five
species (13%) were cosmopolitan pelagic sharks found across the world.
The prevalence of each species in the various types of data differs markedly. However, the
shape of the species dominance curves for methods with the highest diversity were similar.
Commercial linefish returns, recreational angling and beach seine, for example, each had
five shark species that constituted between 73 and 98% of the total chondrichthyan catch. In
contrast an average of 15 species in each case made up less than 1% of the total chondrichthyan
catch. The most common species for each method, however, had only moderate overlap. These
were, in order of prevalence, Triakis megalopterus (spotted gully shark), Squalus megalops
(bluntnose spiny dogfish), N. cepedianus, M. mustelus, and G. galeus from commercial linefish;
R. annulatus, C. capensis, Myliobatis aquila (eagle ray), M. mustelus, and Dasyatis chrysonota
(blue stingray) from beach seine surveys; and G. galeus, D. chrysonota, R. annulatus,
Carcharhinus brachyurus (copper shark), and T. megalopterus from recreational angling
Analysis of commercial linefish catch returns
Data from the National Marine Linefish System (NMLS) recorded 179 197 commercial linefish
boat-trips in total from False Bay, however, effort showed a fairly steady decline from the
inception of the NMLS. Though the linefishery showed a slight recovery in the last two years
of the time series. The proportion of chondrichthyans in the total commercial linefish catch
increased considerably after 2005, and reached a peak proportion of 0.09 cartilaginous fish in
2008, but declined again to the long-term average of around 0.01 in 2010.
Table 1. Chondrichthyan species recorded in the nine sampling methods in False Bay in the 20th
century and their current conservation status and population trend globally.
Family
Species
Common
Name
IUCN
Statusa
Population Trendb
Hexanchidae
Notorynchus cepedianus
Broadnose sevengill
DD
Unknown
Dalatiidae
Etmopterus granulosus
Southern lantern
shark
LC
Unknown
Squalidae
Squalus acanthias
Spotted spiny
dogfish
LC
Decreasing
Squalidae
Squalus megalops
Bluntnose spiny
dogfish
DD
Unknown
Carcharhinidae
Carcharhinus
brachyurus
Copper shark
NTc
Unknown
Carcharhinidae
Carcharhinus
brevipinna
Spinner shark
NT
Unknown
Carcharhinidae
Carcharhinus limbatus
Blacktip shark
NT
Unknown
Carcharhinidae
Prionace glauca
Blue shark
NT
Unknown
Traikidae
Galeorhinus galeus
Soupfin shark
V
Decreasing
Traikidae
Mustelus mustelus
Smooth-hound
shark
V
Decreasing
Traikidae
Triakis megalopterus
Spotted gullyshark
NT
Unknown
Scyliorhinidae
Halaelurus natalensis
Tiger catshark
DD
Unknown
Scyliorhinidae
Haploblepharus
edwardsii
Puffadder shyshark
NT
Unknown
Scyliorhinidae
Haploblepharus pictus
Dark shyshark
LC
Unknown
Scyliorhinidae
Poroderma africanum
Striped catshark
NT
Unknown
Scyliorhinidae
Poroderma pantherinum Leopard catshark
DD
Unknown
NT
Unknown
Scyliorhinidae
Scyliorhinus capensis
Yellowspotted
catshark
Sphyrnidae
Sphyrna zygaena
Smooth
hammerhead
V
Decreasing
Lamnidae
Carcharodon carcharias
Great white shark
V
Unknown
Lamnidae
Isurus oxyrinchus
Shortfin mako
V
Decreasing
Alopiidae
Alopias vulpinus
Thintail thresher
shark
V
Decreasing
Odontaspididae
Carcharias taurus
Spotted raggedtooth
V
Unknown
Pristiophoridae
Pliotrema warreni
Sixgill sawshark
NT
Unknown
Torpedo fuscomaculata
Blackspotted
electric ray
DD
Unknown
Torpedinidae
Torpedinidae
Torpedo marmorata
Marbled electric ray
DD
Unknown
Narkidae
Narke capensis
Onefin electric ray
DD
Unknown
Rajidae
Rostroraja alba
Spearnose skate
E
Decreasing
Rajidae
Raja clavata
Thornback skate
NT
Decreasing
Rajidae
Raja miraletus
Twineye skate
LC
Stable
Rajidae
Raja straeleni
Biscuit skate
DDc
Unknown
Rhinobatidae
Rhinobatos annulatus
Lesser guitarfish
LC
Unknown
Myliobatidae
Myliobatis aquila
Eagleray
Myliobatidae
Pteromylaeus bovinus
Dasyatidae
Dasyatis brevicaudata
Dasyatidae
DD
c
Unknown
Bullray
DD
c
Unknown
Short-tail stingray
LC
Unknown
Dasyatis chrysonota
Blue stingray
LC
Unknown
Dasyatidae
Dasyatis thetidis
Thorntail stingray
DD
Dasyatidae
Gymnura natalensis
Diamond ray
DD
Callorhinchidae
Callorhinchus capensis
St. Joseph shark
LC
Unknown
c
Unknown
Stable
Current species status worldwide, taken from the IUCN Red List. Categories: DD (data
deficient); LC (least concern); NT (near threatened); V (vulnerable); E (endangered); and CR
(critically endangered).
b
Population trends taken from the IUCN Red List species assessment
a
Least Concern in South Africa
The years 2006-2009 represent an anomalous period during which the principle target of the
linefishery, Thyrsites atun (snoek) yielded the lowest catches on record. The relative increase
in chondrichthyans is not only an artefact of the disappearance of the principle target, but
primarily reflects a shift in targeting towards chondrichthyans in that period. The increase in
total catch of chondrichthyans exceeded the increase in the CPUE of all chondrichthyans, which
indicates that more boats were shifting towards a chondrichthyan target. In contrast, at the
peak of the linefish catch in 1988, the proportion of chondrichthyans in the catch was negligible.
Long-term trends in commercial linefish CPUE of all chondrichthyans indicate an increase from
a mean of 0.03 chondrichthyans per boat trip per annum in 1988 to 6.2 individuals per boat trip
per annum in 2008.
c
The chondrichthyan species composition taken in the linefishery has changed over time and
a shift in primary target species is clear. In 1985, G. galeus made up 95% of the reported
chondrichthyan catch but, over the last 15 years, the proportion has declined, contributing just
over 7% of the chondrichthyan catch in 2010. At the same time steadily the proportion of M.
mustelus increased, averaging over 40% of the chondrichthyan catch. The combined proportions
of the remaining chondrichthyan species in the linefishery catch have also fluctuated over
time, ranging from 0.01% to 40.9% of the total chondrichthyan catch. However, overall, the
proportion of all other species remained low, averaging 13% annually.
Mean CPUE for specific species showed a significant catch declines in G. galeus and Raja spp.
(p<0.01 and p<0.1, respectively), and significant increases in abundance of M. mustelus, C.
brachyurus and N. cepedianus (p<0.001, p<0.1 and p<0.1, respectively).
Analysis of beach seine catch returns
A total of 11 953 commercial beach seine hauls were reported in False Bay between 1974 and
2003. Beach seine effort peaked between 1983 and 1987, thereafter effort declined steadily. This
decline largely reflects the removal of seine net permit holders from False Bay in an effort to
reduce impact on surf zone teleosts. In contrast, beach seine surveys were limited to 586 hauls
between 1991-1993 and were not carried out at any other time.
Similarity analysis of catch composition between commercial- and survey-seining catches
indicated a significant difference (R = 0.444; p<0.01). This difference is likely due to the poor
resolution of chondrichthyan identification and selectivity of reporting in the commercial catch
data. Therefore, commercial and survey data sets could not be combined in a trend analysis, and
because the survey data time series was so brief, long-term catch trends could not be inferred.
The proportion of chondrichthyans in the commercial catch peaked prior to 1984 at 1.4% but
remained between 0.01 and 0.4% for the remainder of the time series. In addition, long-term
trends in commercial CPUE of all chondrichthyans indicate a decline from a mean of one
individual per haul per annum in 1979 to 0.032 individual in 2003. Correspondingly, individual
species trends in CPUE indicate significant (p<0.1) declines for two chondrichthyans, G. galeus
and C. capensis, however these species were the only chondrichthyans well represented in the
commercial catch returns. In the case of G. galeus no catches were reported after 1984.
Analysis of recreational angling catch records
The annual catch of all fish and the proportion of chondrichthyans in the total catch of False Bay
recreational anglers has changed dramatically since records began in 1969. The proportion of
chondrichthyans in the total catch increased from its lowest point of only 3% chondrichthyans
in 1969, to the peak proportion of 98% chondrichthyans in 2011. This trend appears to represent
an increased relative appearance of cartilaginous species in anglers’ catch.
Rank correlation analysis revealed that the angling catch proportions for some of the species
with larger abundances in the angling time series data, G. galeus, N. cepedianus, Raja spp.,
Rostroraja alba (spearnose skate) and T. megalopterus, all showed a significant (p<0.1)
declines. In contrast, M. mustelus, R. annulatus, and Dasyatis spp. (including D. chrysonota),
all of which showed a significant (p<0.1) increases in catch.
Analysis of demersal longline catch return
Between 1992 and 2011 (excluding 1993-1995 and 2004-2006) 225 commercial longline boat
trips set 228 951 hooks in False Bay specifically targeting sharks. Effort (number of hooks)
remained relatively low in the outset of the fishery, averaging under 3 500 hooks across 3.8
boat trips per annum. However, after 2007 effort increased considerably, averaging 48 350
hooks across 47.3 boat trips per annum. The peak year in shark catch was 2008, with 3 180
individuals, there after the number of sharks caught per annum declined to just under 900
individuals in 2011, suggesting an overall decrease in abundance. Correspondingly, longline
mean CPUE for chondrichthyans combined decreased over time, from 0.21 sharks per hook in
1992 to 0.02 sharks in 2011.
Individual mean CPUE trends for four target species in the False Bay demersal longline fishery
(G. galeus, M. mustelus, C. brachyurus and P. glauca) showed opposing trends. G. galeus was
declining significantly (p<0.01), while mean CPUE for M. mustelus, C. brachyurus and Prionace
glauca (blue shark) showed a significant (p<0.1) increase in catch. However the latter two
species were not recorded prior to 2007, possibly indicating that these species had been dumped
in those years.
Analysis of historical trawl surveys
Between 144 trawl surveys, spread over 35 years in the early part of the 20th century, 10
chondrichthyan species, five genera and one general ‘shark’ category were recorded in False
Bay. Catch trend analysis of CPUE for each revealed three highly significant (p<0.01) declines in
catch of Dasyatis spp., Raja spp. and Torpedo spp.
Chondrichthyan vulnerability assessment
A majority of the 38 chondrichthyan species found in False Bay, excluding Raja straeleni,
and Torpedo fuscomaculata, had life history parameters available to estimate population
productivity. Twenty-eight species were considered to have very-low productivity, seven were
low productivity species, and only one species had medium productivity (Table 2). Productivity
for two genera, Dasyatis spp. and Raja spp., were also estimated because of the frequency
of taxonomic lumping in these groups, and they were considered to have very-low and low
productivity, respectively.
Individual catch trend analysis across all major fishing methods in False Bay provided several
trend estimates per species. These were insignificant, increasing or decreasing (Table 2). Five
species and one genus showed significant (p<0.1) declining trends (CPUE or proportion of
catch) in at least one fishing method in False Bay. However, only one of these species and
one genus, G. galeus and Raja spp., had a decline recorded by more than one method. N.
cepedianus, showed a decline in one fishing method, but increased in another. From the
remaining 33 species and one genus, three species and one genus showed significant population
increase in only one fishing method, and C. brachyurus and M. mustelus increased in more
than one method. The remaining 28 species showed no significant catch trends for any fishing
method utilised in False Bay.
Abundance indices and productivity categories for each chondrichthyan species were compared
to other risk criteria, including small population or endemicity, primary habitat and mortality
threats in False Bay (Table 2). Sixteen species had either a small population or were endemic
to South or Southern Africa and thus were range restricted. Those species experiencing catch
declines, and/or low or very-low productivity, were classified at least as conservation concern.
The remaining 22 species were either cosmopolitan species or had large connected ranges
extending further than Southern Africa (nominally from Namibia to Mozambique) and therefore
were not threatened by range restriction.
After considering the risk criteria outlined above, the susceptibility to exploitation of the 38
chondrichthyan species and two genera in False Bay was evaluated (Table 2). Populations of
two species, representing 5% of chondrichthyans, were considered stable in False Bay. One
shark species and one genus, 5% of chondrichthyans, were vulnerable to exploitation. A further
5%, representing two species, were threatened by exploitation, and 34%, 13 species, were of
conservation concern. Finally the majority, 20 species and one genus, were classified as having
unknown status and may require further investigation. At least ten species were rarely caught by
any fishing method, and therefore the lack of catch trend was likely an indication of low power.
Conclusion
Amidst the continued and increasing exploitation threat in False Bay, shown by an increased
proportion of chondrichthyans in fisheries catch over the 20th century, some species were shown
to have increased in abundance while others decreased. The vulnerability assessment conducted
identified species threatened or vulnerable to exploitation, stable populations, in addition to
populations of conservation concern or having unknown status. The assessment cannot be
considered as proof of the impact of fishing on chondrichthyans, or the lack thereof, but rather
a means to prioritise research, conservation action, and fishing management to minimize the
impacts of further exploitation.
The total chondrichthyan diversity found within False Bay (23 sharks, 14 skates/rays and one
chimaera) is relatively high and comparable to other areas around the world, many of which
encompass significantly larger areas and deeper depths. To maintain such diversity, monitoring
of these populations is critical. However, the assessment and monitoring of chondrichthyan
fishes is primarily dependant on reliable fisheries data.
An important aim of this work was to identify the most effective data sources to monitor the
status of the full spectrum of chondrichthyan species. The fishing methods targeting the highest
chondrichthyan diversity contain information on fish abundance in the majority of the habitats
in False Bay. Recreational angling and commercial linefish, combined provide data for 76%
of chondrichthyan species in False Bay, while beach seine surveys provided a further 16%.
Although the combination of these three methods is strong sources of data for the monitoring
of chondrichthyans, they may underrepresent the deep (> 40 m), soft sediment habitat that
dominates False Bay.
Finally, only a small proportion of the chondrichthyan species in False Bay are directly
targeted for commercial exploitation, the majority are caught as bycatch in the commercial
and recreational fisheries. The bycatch are often discarded, unrecorded in commercial catch
and represent a substantial threat to the survival of chondrichthyan species. As a result,
improvements in taxonomic resolution of catch and reporting of bycatch are imperative for
chondrichthyan conservation and fishery management.
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Attempts to contribute to a better understanding of
the mortality of linefish due to recreational angling
Malcolm Grant
Western Province Deep Sea Angling Association, South Africa.
[email protected]
Introduction
I have become aware of the plight of our marine linefish resources through my involvement
as the RMO for the Western Province Deep Sea Angling Association (WPDSAA) and the
inshore officer for the Cape Boat and Ski-boat Club (CBSBC) and from my involvement with
SAMLMA and the recently established Recreational Fishing Forum chaired by the DAFF. I now
understand that there are large gaps in the quantity and quality of data surrounding mortalities
caused by recreational angling. I also realized that WPDSAA had data relating to the inshore
and offshore league competitions that could be made available to scientists concerned with fish
management and research.
Greg Pengelly and I approached ORI, DAFF, Anchor Environmental, the WWF-SA, and others
to establish guidelines for a web based catch report site that would be sustainable and stand
as a reputable repository for recreational catch data. In developing the website, we realized
that this tool could be employed to collect data from all recreational fraternities. We have been
overwhelmed by the support we received from all parties. However, we seem to have found a gap
in the market, but no market in the gap.
The material contained in this contribution was presented at a WWF-SA sponsored workshop
held in August 2001 and summarises the outcomes of this workshop. We are extremely grateful
to the WWF-SA for their interest and support, particularly Samantha Petersen and John Duncan
and, indeed, all those who took part in the workshop. I also want to thank Bruce Mann and the
SA Marine Linefish Management Association and Dennis Fredricks of the Recreational Fishing
Forum at DAFF for affording us the opportunities to presenting our work to them. I also want to
thank Greg Pengelly without whom none of this would have been possible.
Background
To quote from the UNs’ Food and Agriculture Organisation: “more than 75% of global fish
stocks are fully exploited, overexploited or depleted”. In 2000, a state of emergency was
declared for the Linefish fishery in South Africa. Currently, 6 of the 10 most significant
commercial stocks (silver and dusky kabeljou, geelbek, red stumpnose, roman and carpenter
and red steenbras) are still at critically low levels. These species are also targeted by recreational
anglers. The de-commercialised fish species (baardman, galjoen, blacktail, bronze bream,
garrick, kingfish, knifejaws, white musselcracker, pompanos, river bream, river snapper,
rockcods, spotted grunter, springer, west coast and white steenbras, and cape stumpnose) are
also of concern to recreational anglers. It is on these species that recreational anglers have the
greatest impact and, possibly, where they have the potential to add constructively to the body of
knowledge. Currently, there are no requirements for recreational anglers to record catches for
these species.
The enormous socio-economic benefits of recreational fishing and its supportive industries
are beginning to be recognized. However, there seems to be a growing realization globally
that, due to changes in fishing effort across the fisheries, the impact of recreational fishing on
the fish resources needs to be more closely monitored. The work being of the International
Programme on the State of the Ocean may not be fully appreciated, or even acknowledged,
by the average recreational angler. The general angling population does not appear to
adequately realize the enormous and unparalleled threats to marine resources caused by
global warming, ocean acidification, industrial fishing, IUU Fishing, discard practices, habitat
destruction, environmental degradation, ocean pollution of all kinds, fish farming, alien species
introductions and recreational angling.
In our attempt to understand and contribute more fully to what extent recreational angling
impacts on the total fishing mortality of the de-commercialised species, we established a
Web Based Recreational Catch Report Site (WBRCRS) to which records for recreational angling
catches can be submitted online. At present, we acknowledge that this represents a small portion
of the recreational angling sector, but it is our vision that these data may be assimilated into
databases from other data capturing programmes.
Origins and History
In the early 2000s, Kenny Owen of the WPDSAA initiated a basic paper based catch return
form which met with resistance and non-compliance and was eventually abandoned. The backup copies of the collected data was subsequently lost when computer on which it was stored
crashed. In August 2008, we conducted a simple CPUE analysis of 3 years data obtained from
the Cape Boat and Ski Boat Club’s ‘Club of the Bay’ competitions. We concluded that the fish
in False Bay were in decline and contacted Colin Attwood of UCT for advice on how we could
contribute towards mitigating this apparent trend. This analysis provided a wake-up call and
resulted in the first sense of wanting to contribute positively towards the sustainability of our
sport and the resource that it relied upon.
In 2009, WPDSAA mandated the re-initiation of the catch return form. We consulting with
Bruce Mann of ORI and Barry Clark of Anchor Environmental, who were both commissioned by
DAFF to conduct the Land Based Line Fish Monitoring Programme. The project was designed to
assist in updating the National Marine Linefish System which DAFF introduced in 1982. We met
with Sven Kerwath of DAFF to identify the fields of data that would make our data compatible
with the NMLS requirements. The information requested in both the paper and web based
approaches tried to balance the requirements of the NMLS and what the anglers are prepared
to divulge. Resistance to subscribing to each of these approaches still exist as many of our
members fear that the information submitted may be used against them. A common retort was
“What’s in it for us?” for which we had no positive answer at the time. It did however force us to
re-evaluate our approach and build in aspects which would be of benefit to our members.
Following consultation with ORI, Anchor Environmental and DAFF, the WPDSAA introduced
an expanded paper based catch return form in April 2010. This re-introduction was again
met with resistance and non-compliance. We realized that social outing data contains many
biases and may be of little use to fisheries researches. Therefore, we did not actively pursue the
collection of data for social fishing outings, although this is still being practiced in some clubs.
We were advised to concentrate on compiling a database of league and competition results
which could be verified by cross-checking with official weigh-sheets. Of course, these data
require an understanding of the rules under which these competitions are held (e.g. gear types,
minimum weight requirements for point scoring, etc.) for properly analysis of these data. With
the assistance of Greg Pengelly, a database was established to store this data. We initially aimed
to record data from our own association’s but soon realized that this database could be used by
all provincial associations affiliated to SADSAA. We approached them with a proposal which was
accepted and work on compiling a national database has commenced. A website was set up to
act as the repository for all historical data and a portal for competition data to be submitted in
the future.
We then expanded our vision to include all fishing disciplines. We envision an interface where
all facets of angling could be accommodated within the same website. This could provide a more
detailed picture of recreational angling impacts and avert duplication of effort.
Progress to date
The first challenge was to expand the WPDSAA’s scoring system such that data could be reassimilated into the database. A consulting firm was then commissioned to design the database
design and set up the reporting back end such the data could be accessed. Currently, a pilot
site is live on the internet. The site is fully functional and one could, for example, query all the
yellowfin tuna catches made in a given year, or all years, in a specific league. This data could also
be downloaded and saved as an Excel spreadsheet where further analysis can be conducted.
The data presently entered into the database includes the Western Province Deep Angling
Association league data, inshore and offshore (2000 to date); some Tuna Nationals; the
CBSBC October Competition data; and league data from Simon’s Town Defence Ski Boat Club
(1994 to date).
Additional data is being compiled into the required format for uploading into the database. We
have not acquired all the competition data from the individual club’s (Western Province) but
have acquired a limited amount of social data from the paper based questionnaires that needs to
be compiled and entered.
We believe the pilot website is suitably developed to demonstrate the functionality of the
database design and to evaluate its potential as a tool to aid researchers, resource managers or
even as an aid to help recreational anglers administer future league activities or competitions.
WWF Workshop
A workshop, funded by WWF-SA was held to present WPDSAA’s proposed web-based catch
return system to recreational linefishery stakeholders. The aims of the workshop were to:
•
•
•
establish which data fields should be included in the WBCRS;
determine the extent other formal recreational facets were willing to support the initiative; and
determine the way forward in monitoring of the catches of recreational fisheries.
Although the Web Based Catch Report System was discussed at length, the online
demonstration was aborted due to a technical failure of the ADSL connection at the workshop
venue. Valuable advice and suggestions were received from the participants including:
•
•
•
•
•
•
•
•
•
making provision for all species caught during an event to be recorded (non edibles, non
target species and undersized targeted species) and recording releases to better estimate
CPUE;
recording which species were going intentionally targeted;
initially concentrating on league and competitions;
rolling out to encompass all affiliated SADSAA associations first;
providing access to the rules and rules changes for competitions for appropriate analysis of
the results;
all recreational fishing facets should be encouraged to record the same type of data;
protocols be established to verify the data;
investigate the possibility of incorporating photographs; and
revamping of the existing league and competition weigh sheets to include the above
suggestions.
The major achievement of the workshop was the establishment of a high powered volunteer
task team derived from most stakeholder groups including Colin Attwood (UCT); Chris Wilke
(DAFF); Barry Clark (Anchor Environmental); Bruce Jones (SA Deep Sea Angling Association);
Joseph van Huyssteen (SA Shore Angling Association); Hymie Steyn (SA Sport Angling and
Casting Confederation); Greg Pengelly and Malcolm Grant (WPDSAA); Bruce Mann (ORI
available for comments and input); and Sven Kerwath (DAFF provided terms of reference are
agreed upon). This demonstrated conclusively that there is a groundswell of support for the
WBCRS, albeit with improvements and modifications. The function of the task team is to plan
the way forward, address funding, and strategize how the initiative can be rolled out to all facets
of recreational angling.
The following are observations, concerns and outcomes resulting from the workshop.
To improve the understanding of the mortality caused by the recreational fishery
The workshop I think failed to adequately improve a common understanding of the mortalities
caused by recreational angling. We were told that 90% of the ‘value’ of the linfishery accrues to
the recreational sector; however, 75% of the catch comes from the commercial sector.
To establish a common understanding of the current status of data capturing for
the linefishery.
We heard that commercial catches are estimates and not 100% accurate. That the locality is
only reported for the main fishing site in a day, multiple sites are not taken into account. That
species are sometimes misidentified or lumped together into categories. It was maintained that
the trends are reliable and the resolution is higher than most other fisheries and the data can be
verified against observer programmes, harbour data and VMS.
To determine what gaps exits in current data capture processes for the
recreational fishery.
As far as recreational data is concerned, data after 1995 is lacking due to budgets being
constantly withdrawn. The requirements for statistically comparable data meant that sampling
intensity has become unmanageable and prohibitively expensive. In order to mitigate these
factors an ongoing permanent observer programme (creel surveys) has been instituted within
which direct biological sampling and socioeconomic surveys are inserted as required or needed.
To gain accreditation that the site’s database is peer reviewed so it may play a
part in promoting more participation from the recreational fishing fraternity.
So far we have received the support, endorsement and encouragement to continue from
SADSAA who wishes to expand the project to include all the other provinces. The WWF-SA and
the SAIAB have also encouraged us to continue with this work. Some of the different fishing
facets, notably the SA Shore angling Association, have indicated that they have a large quantity
of data that they could make available.
To discuss how to improve the WBCRS so to build a universal recreational catch
report system that is useful to all recreational anglers, researchers, provincial
associations and the national recreational bodies as well as government.
The WBRCRS task team will be responsible for achieving these objectives. Unfortunately,
due to work pressure and conflicting calendars, this task team has not had the opportunity of
assembling to develop these goals.
To establish roles and responsibilities to achieve sustainability.
The WBRCRS task team will be responsible for ensuring sustainability.
To obtain an assurance from government that the data made available through the WBCRS will
not be used against the angler concerned so as to encourage participation.
Although indicated in conversations no formal declaration has yet been forthcoming.
Funding
To date, the project has been funded by a donation from Kevin Hodgson which was used for the
database design and writing the report software. All other associated activities have been out of
pocket. To roll the project out will require additional funding. The CBSBC and WPDSAA have
donated a small amount and the WPDSAA have established a fund to administer donations.
Other clubs in our association have been requested to make similar donations. Advertising on
the site could possibility provide a small income. We have also submitted an application for a
Rolex Award for Enterprise for this project.
Recent Developments
Since the August 2011 workshop, various people have approached us offering to collaborate
on the project including Joey de Silva of FishingManiacs.com and Terry Collinson of
WildLifeHeros.com.
Conclusions
Movies like ‘The End of the Line’, ‘A Sea Change’ and ‘Oceans’ all predict the collapse of our fish
resources if action is taken soon. The work of the International Programme on the State of the
Ocean predicts imminent mass extinctions of valuable fish stocks. Jared Diamond, in his book
“Collapse – How Societies Choose to Fail or Survive”, highlights environmental degradation as a
major cause of societal havoc.
If this project gains a wide acceptance, I hope that it will help educate recreational anglers and
the generally public to be more aware of the imminent dangers inherent in carrying on ‘business
as usual’ in blissful unawareness of the perilous situation we find ourselves in. We hope to add
our contribution to the effort of NGO’s in spreading the message that how we harvest fish in
South Africa is unsustainable, and that time is running out for us to make changes to allow our
children to inherit an environment where our marine resources are better managed, where our
catches are better recorded, and the threat of extinction for many species is reduced.
I want to bring about changes in the attitude and behaviour of many anglers who may still have
little realisation of the cumulative impact of our activities. Although some may say we have a
democratic right to go out and catch fish, I believe the time has come for recreational anglers to
realize that we have a responsibility that goes along with that right. The WBCRS is a way we can
exercise that responsibility
Session 6 – Socio-Economic Research: Chair John Duncan
The recreational and subsistence linefisheries in the
Knysna and Swartvlei Estuaries – some concerns and
management challenges
MKS Smith1 and N Kruger1
South African National Parks, Conservation Services, Garden Route, South Africa.
1
Abstract
In compliance with the National Environmental Management: Protected Areas Act, South
African National Parks has been conducting roving creel surveys of the Knysna and Swartvlei
estuarine recreational and subsistence fisheries since July 2008. During the first year of
monitoring these surveys were designed to gather information on catch and effort, specific
socio-economic parameters of participants, and angler awareness and knowledge of fishery
regulations. Subsequent years focused on catch and effort with limited socio-economic
information. Results showed that in both fisheries, despite the majority of anglers being local
and falling predominantly within the recreational category, there was poor knowledge amongst
anglers regarding species specific regulations combined with low levels of accountability and
ultimately high retention rates comprising a large proportion of undersized fish. In this paper
we explore some of the possible drivers for non-compliance including economic background
of interviewed anglers, their knowledge of species specific regulations and their personal
sense of accountability. We also evaluate the efficiency of SANParks law enforcement on these
two estuaries, through interrogation of electronically captured patrol data and fine records.
Continued non-compliance amongst recreational anglers remains a persistent threat to the
sustainability of our recreational fisheries. The challenge is to gain a better understanding of the
non-compliance drivers, whilst seeking solutions to limit their occurrence.
Introduction
The South African linefishery can be broken into various sectors, namely subsistence
(incorporated into the new draft small-scale fisheries policy), recreational fishers and
commercial fishers with both offshore and inshore components. Collectively over 200
demersal and pelagic fish species are exploited, of which 95 are regarded as economically
important (Griffiths 2000). Due to the large number of users, launch sites and species targeted,
management of the fishery has been based on the control of effort through input, (number of
commercial participants) and output (bag and size limit) measures (Sauer et al. 1997).
Catch regulations for the South Africa linefisheries were first promulgated in 1973 under the
Sea Fisheries Act No. 58 of 1973, these were modified and revised in 1984 (Government gazette
No. 9543 of 1984) and 1988 (Sea Fisheries Act No. 12 of 1988). Various studies conducted in the
late 1980s and 1990s showed decreased catch rates in both the shore (Bennett 1991, Attwood
& Farquhar 1999, Cowley et al. 2002) and ski-boat fisheries (Hecht & Tilney 1989, Penney
et al. 1999, Griffiths 2000, Brouwer & Buxton 2002) had and changes in species composition
of catches (Crawford & Crous 1982, Hecht & Tilney 1989, Bennet et al. 1994, Brouwer et al.
1997, Penney et al. 1999, Griffiths 2000, Brouwer & Buxton 2002). By the late 1990s, trends in
catch-per-unit-effort and spawner biomass per recruit models were showing that many of South
Africa’s linefish species stocks were over-exploited or collapsed (Griffiths 2000) and in 2000
the Minister of Environmental Affairs and Tourism declared the linefishery to be in a state of
emergency. This precipitated a number of changes in the management of line fisheries including a
substantial reduction in commercial effort. Further revisions to the recreational regulations were
implemented in April 2005 (Gazette Vol: 478 No. 27453). Different explanations were put forward
why management of the fishery had failed including the complexity of managing a multi-species
multi-user fishery with a poor historical collection of catch statistics (Attwood & Farquhar 1999,
Griffiths & Lamberth 2002), a lack of institutional capacity and inadequate levels of funding
for linefish research and management (Bennett 1991, Griffiths & Lamberth 2002) and noncompliance by anglers.
Non-compliance by anglers, and the increase in illegal harvesting of undersized fish negatively
impacts on a regulations effectiveness (Gigliotti and Taylor 1990). Greater non-compliance
could be expected in situations where anglers do not agree with, or are unaware of, the species
specific regulations. In South Africa Bennett (1991) suggested that species specific daily take
(bag) and size limits were largely unsuccessful due to a lack of support from the majority of
anglers. However, results from the South African National Marine Linefish Survey conducted
between 1994 and 1996 (Brouwer et al. 1997) showed that although anglers generally supported
linefish management regulations, their knowledge of and compliance with these regulations was
very poor. The level of non-compliance varied along the coastline with increased compliance
coinciding with increased law enforcement patrol frequency. The poor regulatory knowledge
base combined with poor compliance has since been shown for a number of recreationally
dominated estuarine fisheries in South Africa (Cowley et al. 2009, Potts et al. 2005).
Recreational and subsistence fishing currently occurs within a number of areas under the
management jurisdiction of South African National Parks (SANParks) and in order for
SANParks to comply i) with the National Environmental Management: Protected Areas Act
(Act 57 of 2003) legislation and ii) as part of the organisations adaptive management strategy
philosophy (Biggs & Rogers 2003) long term monitoring programs on catch and effort within
the areas of the Garden Route National Park were initiated in 2008 to assess recreational and
subsistence angling and provide information on which to develop management policies.
Although the main purpose of the monitoring programme is to assess trends in catch and effort,
this paper concentrates on the observed level of non-compliance and attempts to elucidate
some of the possible drivers for this. We also attempt to evaluate aspects of SANParks law
enforcement efficiency.
Material and methods
Study sites
The Knysna and Swartvlei estuaries on the south coast of South Africa, fall within the Garden
Route National Park and are under the management jurisdiction of South African National
Parks (Fig 1).
Figure 1: Map showing the Garden Route National Park boundaries and the position of the
Swartvlei and Knysna estuaries.
The Knysna estuarine system (33o04’ South; 23o04’ East) is a warm-temperate, estuarine bay
(Whitfield 2000), located adjacent to the town of Knysna roughly 60km east of George. The
Knysna estuary has been calculated (based on size, habitat importance, zonal type rarity and
biodiversity importance), as the most important estuarine system in South Africa (Turpie &
Clark 2007). Over the years a large amount of research work has been conducted on a wide
selection of aspects of the Knysna estuarine system and it has a rating of excellent (Whitfield
2000) in terms of available information. On a scale of Poor to Excellent overall condition
is ranked as Good. Access to the mudbanks and water channels is generally good with the
exception of the water ways within the Thesen housing development. An invertebrate reserve in
the south east of the lagoon restricts invertebrate harvesting, but not fishing. A large number of
slipways are available for public use. The survey area covered during this programme extended
from the mouth through to the N2 Bridge (Fig 2).
A
B
Figure 2: Map of the Knysna (A) and Swarvlei (B) estuaries showing access roads and public slipways.
The Swartvlei estuarine system (34o00’ South; 22o48’ East) is a warm-temperate, estuarine
lake system comprising two main sections, the lower estuary and upper lake section (Whitfield
1983). The system is located near Sedgefield on the south coast of South Africa and has been
extensively studied including details on hydrography, geology, physico-chemical limnology
and the biology of organisms resulting in a rating of excellent in terms of available information
(Whitfield 2000). The overall conservation importance, based on criteria including size, habitat
importance, zonal rarity and biodiversity ranks the Swartvlei system 6th in South Africa (Turpie
et al. 2002) and the overall condition is ranked as good (Whitfield 2000). The east bank is easily
accessible along the entire length but access is limited along the west bank becoming more
restricted towards the mouth. Two slipways are available for public use. The survey area covered
during this programme extended from the mouth through to and including the train bridge
separating the lake and estuary (Fig 2).
Survey Method
This study represents a combination of monthly on-site direct-contact roving creel surveys
(RCS’s) and a series of instantaneous resource user counts. Within each study area a total of
three survey days were completed per month. Survey days were randomly chosen prior to each
month and stratified according to week versus weekend with two week days and one weekend
day being completed per month. On each sampling day, two “instantaneous” effort counts
were completed, one in the morning (between 06:00 – 12:00) and one in the afternoon (12:00
- 18:00) with the starting times and place being randomly chosen but with a minimum of four
hours between counts. On each of these circuits, the number of anglers and bait collectors
were counted, their demographics, the number of lines or rods being used and their spatial
distribution noted. Only new entrants were counted during the second circuit on each sampling
day. Surveys were conducted on foot around Swartvlei estuary and by boat on Knysna. Initially
boat anglers on Swartvlei were intercepted with the use of a kayak but this was stopped due to
the length of time taken in approaching the anglers and the low contact rate with boat anglers.
Interviews
During the RCS’s, only those people actively involved in fishing or packing up after a fishing
outing were interviewed. Three questionnaires were utilized. A comprehensive questionnaire
used to gather socio-economic data, catch and effort (both fish and bait), management
attitudes and to gain an idea of angler knowledge and awareness regarding the relevant fishery
regulations. Due to the length of this interview and the time taken the questionnaire was only
asked to a sub set of the anglers. A shorter questionnaire relating to limited socio-economic
information and catch and effort relating to both the fish and bait resources was used for the
majority of first contact interviews whilst only catch and effort was recorded when anglers were
re-observed on subsequent survey days. No anglers under the age of 16 were interviewed and
when groups of anglers were encountered an attempt was made to interview a sub-sample of
the anglers with catches being recorded on an angler-specific basis. An attempt was made to
interview anglers within each of the survey sections. During periods of high activity this required
a sub-sample of anglers being interviewed in each area. These anglers were randomly chosen.
Effort counts were uninterrupted on both systems but no interviews were conducted between
September 2010 and February 2011 on Swartvlei or between September 2010 and October 2011
on Knysna due to personnel limitations.
Angler knowledge awareness and attitudes towards fishery regulations was only gathered during
the first years of sampling while limited socio-economic data was collected during the first two
years of sampling.
Data Analysis
Effort
Fishing effort was represented as angler outings. Daily fishing effort was taken as the sum
of both instantaneous effort counts completed on that day. Total monthly fishing effort was
obtained by multiplying the total estimated daily fishing effort for the weekend day by the
number of weekend days in that month and adding this to the average estimated week day (of
the two week day surveys) effort multiplied by the number of week days in that month. Total
estimated annual effort was taken as the sum of the monthly estimates.
Catch
During all interviews anglers were asked as to what species they were targeting and the species
and number of any fish caught (including those released). All retained catch was identified,
counted and measured.
Retention Rates
Retention rates were worked out as a) the proportion of total fish retained by each angler b) the
proportion of undersized fish retained and c) the proportion of cape stumpnose, white steenbras
and spotted grunter retained (all and undersized). In order to increase sample sizes respondents
from Knysna and Swartvlei fisheries were combined. Retention rates were then evaluated
against fishing sector (recreational vs subsistence), and within the recreational category against
angler knowledge and angler self-accountability. Angler knowledge was evaluated by scoring
individuals on their knowledge of fishery regulations (bag & size limit) for three targeted or
caught fish species (total of 6 marks). Self-accountability was crudely estimated on a score of 0
to 2 and was dependent on angler response to questions on what they perceived as threats to fish
stocks within the Swartvlei / Knysna estuary. If anglers mentioned over-exploitation in general
they received a score of one, it they mentioned their type of angling (e.g. recreational fishing)
they were awarded a two. Any other threat (e.g. pollution) mentioned by the angler was scored
as a zero.
Law enforcement
Ranger patrol records were examined to obtain information on number of patrols, number
of transgressions and ranger response. Ranger patrols were logged on a pocket PC running a
data capture sequence developed in the freeware Cybertracker. By capturing daily patrol data
the sequence was designed to be a useful management reporting tool. Three years of data were
examined (June 2009 to June 2011).
Results
Participation and demographics
During the first 24 months of the fishery surveys a total of 2 498 anglers were interviewed
during the roving creel surveys whilst 6 922 anglers were counted during the instantaneous
effort counts.
Overall the Knysna fishery was dominated by shore anglers (72%) and by coloured males
comprising 50% of all anglers counted during the survey period. This was followed by white
males (33%) and coloured females (14%). Most anglers (79%) were local either from Knysna
or the surrounding communities whilst 6% came from within the Garden Route and a further
14% were national visitors. Education levels amongst anglers was generally low with 16%
having some form of primary school education and 63% some level of high school or secondary
education. Only 29% had completed their matric (grade 12) whilst 19% had some form of
tertiary education (diploma or degree). Of the anglers interviewed 28% indicated that they were
currently unemployed. Corresponding to the low education and high unemployment rate was
a generally low income level with the majority of anglers 32% having no set monthly income
or earned less than R1000 per month. Due to the above results and in using the criteria as
proposed by Branch et al. (2002) 21% were considered to be subsistence in the first 12 months
but this increased to 29% in the following 12 months.
The Swartvlei fishery was dominated by shore anglers (92%) with white males comprising 49%
of all anglers counted during the first 24 months of the survey period. This was followed by
coloured males (34%) and coloured females (10%). Most anglers (51%) were local either from
Swartvlei or the surrounding communities whilst 23% came from within the Garden Route and
a further 25% were national visitors with the majority of these coming from the Western Cape
(19%). Education levels amongst anglers varied with 15% having only some form of primary
school education and 58% some level of high school. Only 35% had completed their matric
(grade 12) whilst a surprisingly high 27% indicated they had some form of tertiary education.
Although 17% of anglers indicated they had a monthly income of less than R1000 a further
16% had low incomes between of one and five thousand rand, 23% of anglers had an income of
between 10 and 20 thousand rand and a further 16% indicated they were retired and on pension.
An estimated 10% of anglers interviewed fitted the description of subsistence fishers in the first
12 months but this increased to 16% in the second 12 month period.
Effort
Total annual estimated fishing effort fluctuated annually for each estuary ranging between 5
763 and 8 984 outings on Swartvlei and between 21 497 and 25 189 on Knysna (Fig 3). The
annual fishing effort was lowest in 2010 and highest in 2009 for both estuaries. Fishing effort
showed seasonal trends with the highest effort being recorded over the holiday periods. In
particular peaks were seen during January/December and again in April (Figure 3). The mean
turnover time (time spent fishing per day by an individual angler) for all fishery sectors was
approximately 4.5 hrs on Swartvlei and 6hrs on Knysna.
Figure 3: Estimated angler effort (angler outings) for A) Knysna and B) Swartvlei estuaries.
Catch Composition
During the first year of surveys most anglers on both Knysna (45%) and Swartvlei (45%)
indicated that they were not targeting specific species and would be happy catching anything.
Spotted grunter was the most commonly targeted species (17% on Knysna and 28% on
Swartvlei) followed by white steenbras (10%), cape stumpnose (6%) and strepie (5.5%) on
Knysna whilst leervis (9%), white steenbras (7%) and cape stumpnose (4%) were targeted on
Swartvlei. However, analysis of anglers catches (Table 1) shows that despite not being actively
targeted Cape stumpnose was the most frequently caught species (44%) on Knysna followed
by strepie (19%) and white steenbras (12%). On Swartvlei catches were dominated by Cape
stumpnose (43%) followed by white steenbras (30%), spotted grunter (10%) and leervis 4%.
Differences in catch composition on each estuary were noted between the first and second year
of sampling (Table 1) particularly with a decrease in catches of white steenbras on Swartvlei.
Table 1: Target rates and species catch composition (in brackets) for the Knysna and Swarvlei
estuaries over a two year period.
Knysna
Swartvlei
Target Species
2008 - 2009
2009 - 2010
2008 - 2009
2009 - 2010
Any fish species
46
46
45
28
Cape stumpnose
6 (43)
7 (33)
4 (43)
10 (64)
Spotted grunter
17 (4)
16 (8)
27 (11)
29 (9)
White steenbras
10 (12)
12 (12)
7 (30)
12 (8)
Leervis (Garrick)
5 (2)
6 (3)
9 (4)
9 (4)
Mullet species
-
-
2 (4)
<1 (1)
Strepie
5 (18)
4 (16)
-
-
Other
11 (21)
9 (28)
6 (8)
11 (14)
Retention Rates and non-compliance
The overall retention rates of caught fish was high and very similar on both estuaries across
the first two years of sampling with a slight increase in the second 12 month period (Table 2).
However, the proportion of undersized fish retained differed between the estuaries with far
more undersized fish being kept within the Swartvlei fishery for both years. When looking at
three of the commonly caught species (Cape stumpnose, spotted grunter and white steenbras)
retention rates were generally higher on Swartvlei and in particular the proportion of undersized
fish (non-compliance) was higher with an increase during the second sampling period. For both
years all the white steenbras retained and measured by the survey clerks on Swartvlei were
below the legal size limit of 60cm whilst 89% of retained white steenbras within the Knysna
fishery were undersized during the first years sampling. Both the retention rates and proportion
of undersized spotted grunter was fairly stable across both estuaries and for each year (Table 2).
Table 2: Retention rates (%) for two years of sampling on both Swartvlei and Knysna estuaries.
The proportion (%) of undersized fish is given in brackets.
Species
Knysna
Swartvlei
2008 - 2009 2009 - 2010
2008 - 2009 2009 - 2010
Overall
74 (31)
76 (18)
71 (72)
78 (83)
Cape stumpnose
75 (44)
69 (25)
75 (74)
85 (93)
Spotted grunter
81 (4)
88 (6)
82 (14)
77 (18)
White steenbras
67 (89)
63 (65)
82 (100)
81 (100)
Retention rates for all species was high for both Recreational anglers and Subsistence fishers
(Fig 4) with recreational anglers keeping 74% of all fish they caught and subsistence anglers
91%. There was a greater difference in the retention rate of white steenbras between the groups
with more steenbras being kept by subsistence fishers (97%) than recreational anglers (63%).
Fifty three percent of all fish retained by subsistence fishers were undersized whilst 29%
retained by recreational anglers were undersized.
Figure 4: Retention rates of caught fish between recreational anglers (R) and subsistence
fishers (S). Data from both Knysna and Swartvlei surveys for the first two years of sampling have
been combined.
Increasing knowledge of the fishery regulations did not seem to have much impact on the
overall retention rate (Fig 5) although those scoring less than 50% may keep slightly more fish.
However, the retained catch of those scoring less than 50% on the knowledge test comprised
more undersized fish than those anglers who had greater knowledge.
A
B
Figure 5: Overall retention rates (A) and retention rates of undersized fish (B) amongst anglers
with increasing knowledge of fishery regulations. Scores were from 0 – no correct answers
through to 6 – all correct answers. Data from both Knysna and Swartvlei surveys for the first two
years of sampling have been combined.
Although six percent of interviewed anglers believed there were no threats to fish stocks within the
Knysna and Swartvlei estuaries, 26 percent believed that general over-exploitation was a potential
threat (Fig 6). Pollution was seen as threat by 22 percent whilst less than 10% thought subsistence
or recreational fishing was a threat. Overall retention rates were slightly higher for anglers
who scored a zero on self accountability (Fig 7) and in particular there seems to be difference
in retention rates of white steenbras with 68% of fish being retained by anglers with zero self
accountability versus 10% by those who had some level of self accountability. Anglers who scored
zero retained more undersized fish (23%) as opposed to those who scored one (5%). Unfortunately
none of the anglers who scored a two on self accountability had actually caught a fish.
Figure 6: Perceived threats to fish stocks within the Knysna and Swartvlei estuaries. Results
from the two estuaries have been combined.
Law enforcement
Of those anglers interviewed during the RCS’s on Knysna estuary 71% had at some point had
their fishing permit inspected by SANParks law enforcement officials whilst 53% of anglers
interviewed on Swartvlei had been inspected (Table 3). The inspection rate for bait collected and
catch caught was much lower for both estuaries with 48 and 31% respectively for Knysna and
only 28 and 13% for Swartvlei anglers. Despite a lower permit inspection rate on Swartvlei 84%
of anglers could produce a valid fishing permit when asked, however, the number of anglers who
had collected bait with a valid bait collection permit was lower at 66% (Table 3).
Figure 7: Retention rates of caught fish between anglers with varing levels of self
accountability. Self accountability was scored on a rating of 0 – none, 1 – some and 2 – high. No
anglers who scored a 2 during the interviews had caught a fish.
Table 3: The proportion of interviewed anglers on Knysna and Swartvlei estuaries who had
been inspected by SANParks law enforcement (during their entire fishing experience on that
water body) and the proportion of interviewed anglers who could produce a valid fishing and
bait permit when requested.
Estuary
Permits
Inspected
Catch
Inspected
Bait Inspected
Produced
Fishing Permit
Produced Bait
Permit
Knysna
71 %
31 %
48 %
82 %
82 %
Swartvlei
53 %
13 %
28 %
84 %
66 %
Recorded law enforcement patrols in the Wilderness section of the Garden Route National Park
over the same period numbered 1207 with 511 patrols occurring within the first 12 month period.
However, Wilderness section patrols were not specific to the Swartvlei estuary and also covered
coastal areas and the Wilderness Lakes. Number of patrols to specific areas could not be deduced
from the current patrol record format. Over the two year period 612 people were intercepted with
525 permit inspections occurring, 54 bait inspections, 20 catch inspections and 13 bait and catch
inspections (Table 4). During these inspections only 12 people were found to be in transgression
of one or more of the Marine Living Resource Act (MLRA) laws resulting in 14 actions being taken
of which seven were admission of guilt fines (J534 fines) (Table 5). Transgressions included no
permit (4), exceeding bag limit (3 people), illegal fishing method e.g. spearfishing in an estuary /
use of throw net after sunset (4), and keeping a fish out of season (1).
The total number of recorded law enforcement patrols within the Knysna estuary over a three
year period was 1240 with 687 patrols occurring within the first 12 month period (Fig 8). During
these patrols 1557 people were intercepted with 1302 permit inspections occurring, 163 bait
inspections, 32 catch inspections and 58 bait and catch inspections (Table 4). A total of 192
anglers were transgressing one or more of the MLRA laws resulting in 225 actions of which 37
were admission of guilt fines (J534 fines) and 141 verbal warnings and request to leave (Table
5). Prominent transgressions included no permit (152), exceeding bag limit (19 people), illegal
fishing method e.g. spearfishing in an estuary / use of throw net after sunset (11 people), and
undersized fish (5 people).
Figure 8: Recorded law enforcement patrols carried out by SANParks marine rangers within
two sections of the Garden Route National Park.
Table 4: The number of patrols and number of inspections logged on the cybertracker
sequencet by law enforcement officials in the Wilderness and Knysna sections of the Garden
Route National Park.
No.
Patrols
No. of
People
Checked
Check
Angling
Catch
Check
Bait
Collected
Check
Permit
Only
Check
Angling &
Bait Catch
Check Net
Collection
Wilderness
1207
612
20
54
525
13
0
Knysna
1240
1557
32
163
1302
58
2
Total
2447
2169
52
217
1827
71
2
Table 5: Number of transgressions logged and law enforcement responses between June 2008
and June 2011 in the Wilderness and Knysna sections of the Garden Route National Park.
No of
Transgressors
No of
Reactions
Verbal
Warning /
Request to
leave
Written Fine
(J534)
Confiscation
of Goods
Report
to Police
Arrest
No
Reaction
Other
Wilderness
12
14
2
7
2
1
1
1
0
Knysna
192
225
141
37
35
2
0
1
9
Discussion
Recreational fishing is a popular activity in many countries undertaken by large numbers of
participants (Brouwer et al. 1997, Beckley et al. 2008, McPhee et al. 2002, Cooke & Cowx
2004, Veiga et al. 2010) and participation is likely to be increasing. Within South Africa, fishing
pressure on estuaries is high due to the close proximity to urban developments, general ease
of access, all year round fishability and as an indirect impact of the beach driving ban shifting
pressure from the coastline to the estuaries (Mackenzie 2005).
The Knysna and Swartvlei linefisheries conform too many other estuarine fisheries (Mann et al.
2002, Pradervand & Baird 2002, Cowley et al. 2009 and Beckley et al. 2008) in that participants
are generally male, live locally and fish primarily for recreational purposes. According to the
Knysna 2012 -2017 Integrated Development Plan (IDP) the greater municipal population (which
includes communities around Knysna and Swartvlei) was 63 306 in 2010 with 14.2% of the
labour force (those eligible to work) being unemployed in 2009 and half the population living
in relative poverty (referring to people where basic needs are met proportionately but who in
terms of their social environment still experience some disadvantages). In both the Knysna and
Swartvlei linefisheries the number of subsistence fishermen increased over the two year period
and is more than likely due to the high unemployment within the area and the general economic
slowdown experienced. The greater number of subsistence type fishermen on Knysna would
be expected due to the proximity of poverty stricken communities such as Hornlee, Sizamile,
White Location, Rheenendaal and Khayalethu (Knysna IDP 2006). The unemployment rate and
poverty level will continue to be a major driver in motivating people to fish for either household
consumption or to sell their catch to supplement any income placing increasing pressure on
these systems.
It would be expected that the necessity for food would dictate that a subsistence type fisher
would be more likely to keep undersized fish and have a general overall higher retention rate
than recreational anglers. However, of particular concern is the high retention rates and
seemingly poor lack of self-regulation, accountability and fishery regulation knowledge amongst
recreational anglers. This is despite the majority of anglers interviewed in this study stating that
they agree with and support the current regulations.
Recreational anglers frequently dispute their impact on fish stocks (Sauer et al. 1997, Cooke
& Cowx 2006) and tend to blame commercial or subsistence fishing, impacts of pollution or
habitat degradation from coastal development and the same trend was seen in this study with
the majority of anglers tending to blame factors other than their own angling fraternity for
declines in catch rates. In reality recreational fishing pressure is often higher than perceived with
total catches exceeding the commercial sector for certain species (McPhee et al. 2002, .Cooke
& Cowx 2004, Veiga et al. 2010). The dispute could be due to an individual anglers generally
low catch rate without the angler taking into account the cumulative impacts of a large number
of anglers. Unfortunately the sample size of interviewed recreational anglers with higher levels
of accountability and who had caught fish was low within this study, but, there may be trend
of increasing accountability with a decrease in the retention rate of undersized fish. Similarly,
samples size of anglers with high regulatory knowledge scores were low (n = 6 for angler scoring
6 and catching fish) but there does seem to be some trend pointing towards an increase in
knowledge with a decrease in retention rates, particular for undersized fish. The general low
level of regulatory knowledge is not new but is a continuing concern within the South African
recreational estuarine and rock and surf linefisheries. Poor knowledge of species-specific linefish
regulations has been shown within the Sundays estuary (Cowley et al. 2009) and angler education
programmes and improved law enforcement for recreational fisheries were advocated by Brouwer
et al. (1997) and Mann et al. (2003). It seems that 12 years later little has changed with the current
fisheries regulations largely being ignored by many recreational anglers.
The importance of recreational fishery law enforcement and its impact in improving angler
compliance has been shown for the St. Lucia system (Mann et al. 2002) and the KwaZuluNatal coastline when compared to other sections of the South African coast (Brouwer et al.
1997). However, a general lack of and necessity for improved law enforcement has been shown
along most of the South African coastline (Brouwer 1997, Mann et al. 2003) and in particular
on a number of estuaries including the Great Fish estuary (Potts et al. 2005) and the Sundays
estuary (Cowley et al. 2009). Although the patrol rate (number of patrols per year) within
the two sections of the Garden Route National Park seem to be quite high (over 500 patrols
per year) the contact rate is low averaging just over 1.2 anglers per patrol on Knysna and 0.5
anglers in the Wilderness section (which includes the Swartvlei estuary). Furthermore, law
enforcement concentrated on permit requirements rather than enforcing species-specific
linefish and associated bait regulations. The low catch inspection rate is not restricted to these
two case studies and has been shown within the Great Fish Estuary (Potts et al. 2005) and in a
more recent assessment of the Kwazulu-Natal shore based linefisheries (Dunlop 2011). Possibly
the most concerning aspect of the current law enforcement is the high level of verbal warnings
being issued as opposed to admission of guilt fines. If compliance is linked to law enforcement it
would likely be due to a) the possibility of being caught (inspected) and b) the level of fine being
issued. A simple model being an increase in compliance with an increase in expected monetary
costs for being non-compliant.
The present study has begun to highlight some of the possible drivers for non-compliance
including necessity, lack of knowledge and a lack of self-accountability or the belief that
recreational angling cannot be impacting fish stocks. However, it is unrealistic to assume that
such factors would be driving non-compliance in isolation and a combination of factors is
more likely. A more complete model would need to look at a number of factors including law
enforcement, the perceived legitimacy of the regulations and regulatory body by anglers, moral
values and social or peer influence. In this regard more research should be directed at gaining
a better understanding of angler behaviour whilst seeking solutions to limit non-compliance.
Efficient law enforcement has a role to play and the current law enforcement effort (number and
types of patrols) and the efficiency (number and type of inspections and resultant actions) needs
to be revisited with patrols and data logging techniques structured to enable robust analysis of
trends in fishing effort and non-compliance. The present situation of increasing fishing pressure,
greater dependence on fish resources for food or income supplement, high retention rates, lack
of self-regulation, high non-compliance and limited law enforcement continues to place the long
term sustainability of South Africa’s estuarine linefisheries under threat.
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Enactments, Disconcertments and Dialogues:
Regarding marine social-ecological systems through
the lens of relational ontologies
G Duggan1 ,2,, J Rogerson1,2, L Green1, A Jarre2
Department of Social Anthropology, University of Cape Town, Private Bag X3, Rondebosch,
7701.
2
Marine Research Institute (Ma-Re), University of Cape Town, Private Bag X3, Rondebosch,
7701.
1
Abstract
This paper emerges out of observations of ethnographic fieldwork amongst commercial handline
fishers in two sites, one on the Southern Cape coast (Stilbaai) and the other on the West coast
(Lamberts Bay). The approach presented herein, termed a relational ontology, posits a possible
collaborative avenue in social-ecological research in which natural science, social science and
local knowledge might be brought into conversation in more equal terms.
Introduction
In 2000, with a looming stock crisis in the country’s commercial line fisheries, government
took steps to mitigate against widespread collapse by adopting a policy of reduced effort on
the part of fishers. What transpired was a dramatic reduction in the number of licences and
permits in traditional handline fisheries, concomitant with the introduction of the Marine Living
Resources Act (MLRA) of 1998, which left many fishers without legal rights to catch fish. This
disenfranchisement lead to widespread dissatisfaction resulting in instances of political action
and an increase in poaching in a number of instances (Schultz 2010).
It is our belief that in order to conduct more effective management and research (both natural
and social science) of marine ecosystems and fisheries, the suite of knowledge offered by local
fishers is an essential key in figuring out a way forward. Working with these multiple ways of
knowing (what we refer to here as ‘knowledges’) is certainly a difficult prospect but a necessary
one. The reasons for this are as complex and messy as knowledge itself however, for the sake of
the current work, we suggest that conservation science generally does not lend itself as an arena
of ready agreement with fishers, many of whom reject conservation arguments and policy on
grounds of knowing the sea and fish very differently from what is presented to them in official
science and management. This paper is a mediation of knowledge: it asks how fishers know
and how making space available to understand this knowledge opens possibility for dialogue
and possible collaboration. We by no means make any claim to offer a panacea for collaborative
work between management, fishers and researchers with this work, but rather set out to explore
a different way of knowing. Furthermore, our intention is not to romanticise, nor vilify, the
knowledge of social or natural science nor that of fishers. Rather we hope to tease out some of
the messiness and complexity which goes into the production of particular meanings that alter
with context with the intention of opening dialogue which might lead to new understanding and
possible collaborative work.
Over the past two decades, growing evidence of stock collapses and associated failures of
centralized, quantitatively managed fisheries in many parts of the world have led to a number
of calls for alternative approaches to fisheries management which address the concerns of
biophysical ecosystems as well as human wellbeing (FAO 1998; Maurstad 2000; Neis & Felt,
2000; Zwaneburg et al 2000; Ommer and Team 2007). Recent research (Neis et al 1999; Neis &
Felt 2000; Stanley & Rice 2003; Stead et al 2006; Murray et al 2006; Ommer and Team 2007;
Murray et al 2008) suggests that working with the knowledges of fishers within the fisheries
management context offers the possibility of augmenting scientific knowledges by contributing
locally-grounded experiential understandings and strategies for dealing with the variability of
fish and climate.
In 1992, the Convention on Biological Diversity (CBD) was formulated to address the growing
concerns of the time surrounding the preservation and safeguarding of the earth’s natural
resources. Enshrined in the Convention was a commitment that contracting states “respect,
preserve and maintain the knowledge, innovations and practices of indigenous and local
communities” (Haggan et al 2007: 21). In terms of fisheries management the guidelines
outlined in the CBD laid the foundations for a significant shift away from established ‘topdown’ management paradigms, which ignored local people and their concerns, towards more
inclusive approaches which worked with local people and ecologies (Haggan et al 2007; Erdelen,
2007; Sowman, 2011). One of the more prominent approaches to fisheries management
which emerged (and continues to do so) from the guidelines of the Convention is known as an
Ecosystems Approach to Fisheries Management, or EAF (Shannon et al 2010; Sowman, 2011). A
somewhat radical departure from established norms of fisheries management, an EAF adheres
to a number of core premises which challenge conventional management structures. One of
the guiding principles of an EAF is summed up by Fikret Berkes, who has argued (2011: 9) that
“the delineation between social and ecological systems is artificial and arbitrary”. As such, an
EAF seeks to work with complex social-ecological systems and perceives these as engaged in
feedback relationships of mutual influence (Berkes. 2011). In 2002, at the Johannesburg World
Summit for Sustainable Development, South Africa committed to the implementation of an EAF
by 2010. This however, has been slow coming and is now being slated for 2012. As an EAF takes
fishers’ knowledge into account and is in the process of being implemented, beginning to look at
ways of knowing is important.
This paper reports on initial findings from an on-going extensive interdisciplinary research
project which has been running for the past four years. A collaborative undertaking between
the UCT Ma-Re BASICS and Fishers Knowledge Projects, the research has involved Honours,
Masters and Doctoral students from UCT’s Department of Social Anthropology working with
students, researchers and supervision from the Marine Research Institute (Ma-Re) to rethink
the complexity and interface of multiple knowledges in fisheries on the West and Southern Cape
coasts as well as in Namibia.
In response to the growing concerns surrounding climate change and variability and the
perceived shortcomings of the MLRA and the failure of conventional top-down, stock
assessment-based management paradigms, Ma-Re initiated the Marine Research in the
Benguela and Agulhas Systems for supporting Interdisciplinary Climate-Change Science
(BASICS) project in 2010. The approach is interdisciplinary in nature and directly challenges
established management protocols by explicitly seeking to investigate an EAF through socialecological research and collaboration with fishers with considerable support through the South
African Research Chair in Marine Ecology and Fisheries. Incorporating “physical and ecological
modelling studies at a range of scales” as well as complementing these with a broader regional
approach (Ma-Re 2010: 1), the BASICS project incorporates perspectives from industry,
government, fisheries management and academia as well as case studies working with fishers’
knowledges from within the Benguela ecosystem. The objective of this multi-sited, multi-scalar
project is to provide understanding of the impacts of climate variability as well as predict future
outcomes at various levels including marine ecosystems, individual species and human coastal
communities (Ma-Re, 2010).
The Fishers Knowledge Project is a collaborative interdisciplinary and multi-sited research
project funded by PERC as part of the University of Cape Town’s project for rethinking the place
of African knowledges in research projects. Bringing the objectives of Ma-Re BASICS and the
Fishers Knowledge Project together, Prof. Jarre (Ma-Re) and Dr. Green (Social Anthropology)
have co-supervised a number of social anthropology theses focusing on fisheries and fishers
knowledges in a range of fisheries along the Benguela current ecosystem coastline. Starting
in 2007, Marieke van Zyl (2008) began research amongst small-scale handline fishers in the
Southern Cape town of Kassiesbaai where the impacts of the MLRA were felt particularly
keenly. Van Zyl took as her focus the ways in which the implementation of the MLRA affected
the wellbeing and economic stability of the Kassiesbaai fishers and their families. The site was
highly contested and van Zyl’s focus on discursive differences revealed the divergent and often
disconcerting ways in which the MLRA was enacted1 by local fishers, government officials, DAFF
fishery managers and marine fisheries experts. Van Zyl’s work concluded that the relative failure
of the MLRA in this fishery was due to an inherent lack of trust between these groups, fostered
in large by the divergent ways in which people perceive, talk about and enact their versions of
fish, fishing, fishers and the sea.
Following on from van Zyl’s work, 2009 saw Jennifer Rogerson and Tarryn-Anne Anderson
conducting field research in Simonstown and Kalk Bay respectively, both working with smallscale fishers. In 2010 the group expanded further when Rogerson and Anderson, returning
to conduct masters fieldwork (Anderson returning to Kalkbay and Rogerson now electing to
work with small-scale handline fishers in Lambert’s Bay on the West Coast), were joined by
Sven Ragaller and Greg Duggan at two new sites in the Southern Cape: Gansbaai and Stilbaai
respectively (Ragaller, 2012; Duggan, 2012).
Rogerson’s (2011) work in Lambert’s Bay took as its focus the ways in which different groups
perceive and interact with the sea, how different people assemble and enact different versions of
the marine environment and in so doing, a strong sense emerged of the embodied ways in which
fishers come to know the sea. In her work, Rogerson suggested that, somewhat paradoxically,
the science which informs state-regulated fisheries policies such as the MLRA often leads to
‘epistemological policing2’ of local fishers, disenfranchising them from the very seas they have
fished for generations. Rogerson’s study found that the fishers with whom she worked related to
fish as more than objects for capture, suggesting a relational ontology in which fishers and fish
acted as engaged subjects rather than the subject (human) - object (fish) distinction which forms
the conceptual basis of a modernist3 nature-culture dualism.
Taking as her entry point, the logbooks which skippers use to keep track of catches and items of
interest in the fishery, Anderson’s (2011) focussed on logbooks as devices for transforming and
transferring knowledge between fishers and fisheries researchers. The process of what she refers
to as ‘tracking the movements of fish’ were instrumental in her research into understanding how
fishers go about making and sharing knowledge.
Sven Ragaller’s (2012) research was conducted amongst commercial fishers in Gansbaai who
engage in both handlining and purse seining. Dyer Island in the bay is a highly contested
space and home to a threatened penguin colony. Recent evaluation by fisheries managers and
scientists to potentially close the waters adjacent to the island in order to protect food supplies
for the embattled penguins have lead to a series of disconcertments and moments of knowledge
tension between them and the local fishers who feel their fishing grounds are being threatened
and removed to their detriment.
Greg Duggan’s (2012) field research was conducted in the small commercial handline fishery in
the Southern Cape town of Stilbaai. Over a seven month period, Duggan conducted participant
observation-type research amongst fishers, spending time with them at work both at sea and
on land. The work revealed a complex set of relational interactions between fishers and fish in
which fishers knew fish as intelligent, reactive beings and sought to balance a range of objectives
including ecological, economic and ethical concerns via a range of complex adaptive strategies
which aimed to effectively cope with variability in the fishery at all levels.
With the proliferation of research sites along the West and Southern Cape coasts of South
1. To enact something is to perform or bring about a particular representation of that thing based on a particular understanding of reality
– when one has a version of reality, it is through one’s practices that this version is ‘enacted’ into reality.
2. Epistemological policing refers to a way of working whereby only one particular way of knowing is understood to be legitimate and
authorative. When another kind of knowledge is presented, it is not considered but is ‘policed’ by being portrayed as incorrect and
therefore unable to be used.
3. Modernism is the movement of separating nature and culture, i.e. people from environment.
Africa, Kelsey Draper’s (2011) work in the Namibian commercial trawling industry expanded
the research further in terms of spatial and economic scales. Taking as her focus the networks of
technology, knowledge and capital at play in a fishery, Draper’s work explored the possibilities of
formulating a political ecology centred on the Walvis Bay hake fishery. Through this approach,
the research found that tracing networks of knowledge is a vital process in understanding
context and formulating meaningful policy accordingly4.
The common thread running through these theses has been a specific focus on trying to
understand how fishers see the sea and fish. The intention of this focus has been to look for
possibilities for facilitating productive dialogues between marine conservationist, researchers,
managers and fishers. This paper reports on findings in two of the studies where small-scale
fisheries are particularly important. We focus on specific ethnographic case studies of the ways
in which in Lambert’s Bay and Stilbaai fishers think about marine ecology. The work moves
towards an exploration of an approach in contemporary philosophy of science called relational
ontologies. In the conclusion we make a case that such an approach is helpful in mediating
knowledge disputes in fisheries management.
Our research forms part of a broader ongoing dialogue in the global South (Australia, Latin
America and Southern Africa) that seeks to rethink the interface between the sciences and local
knowledge in different contexts. Those dialogues encompass a rethinking of the distinctions
between notions and distinctions between nature and culture, knowledge and belief as well as
theoretical and practical knowledge, challenging established stereotypes and binary hierarchies5
of knowledge with the intention of creating more equal representation of knowledge.
Research Findings
The fishers with whom we worked and who are referred to in this paper were of varying ages and
levels of experience. Oom Louis and Oom Koos between them have nearly 65 years of experience
on the sea in commercial fishing for example while many of their peers had spent over forty
years as a commercial fisherman working in a range of fisheries at locations in the Benguela
and Agulhas ecosystems. The commonality shared by all the people in the conversations which
follow is a self-identification as fishers. The group includes Oom Koos and Oom Louis from
Stilbaai and from Lamberts Bay: Dikkie; Hennie O; Hennie W; Willem; Jacques; George;
Ernest; Rosie; Kelvin and Joanne.
It is our experience, having worked with scientists and fishers during our research, that there
are many times when the most useful ideas and insight come from scientists who are fishers
and fishers who approach their task using the tools of science. For example, we have noted
instances of fishers who consistently and accurately monitor water temperature (Duggan, 2012),
and scientists who have a deep ecological understanding of the sea based on decades of fishing
experience (ibid.). In order to open up the conversation we begin with a consideration of two
different ways of knowing and relating to the fish Kob. In a weighty tome released in 2001 by
the Department of Environmental Affairs and Tourism (DEAT) entitled the Coastcare Factsheet
Series, government scientists and “specialists” set out to document, for public dissemination,
elements of South Africa’s marine ecosystems and coastline considered important. Included
in the Fact Sheet is an introduction to various species including a number of fish. In section
3, entitled “Coastal and Marine Life – Animals: Vertebrates – Fishes”, is a subsection, 3C,
dedicated over two pages to ‘Kob’. A single colour picture of what we are told is a ‘Snapper
Kob’ is shown at the bottom of the page. The description starts with an account of how many
species of Kob are found on the South African coastline (“about nine”). It then proceeds with
a description of what Kob is: under different headings such as ‘Breeding Habits’, ‘Feeding
Habits’, ‘Life Cycle’ and highlighted section covering ‘Commercial Importance’ the reader is
presented with a very neat, uniform version of Kob – what can be expected of it, where to find it,
4. Draper’s research was co-supervised by Barbara Paterson, a post-doctoral researcher at Ma-Re, based in Namibia and associated with
the Fishers Knowledge Project. With a background in philosophy and computer science, Paterson’s development of decision support tools
seek to incorporate human dimension indicators into the fisheries management process.
5. A binary hierarchy in regard to knowledge, entails the ways in which knowledge is understood as either right or wrong. An example of
this is scientific knowledge vs. indigenous knowledge.
how it operates and so forth. The account describes all Kob as having “a coppery sheen…fairly
robust with an elongated body and a rounded tail fin” and it continues, stating that “various
Kob species are superficially very similar, making it difficult for non-scientists to distinguish
between them”.
We now consider the way in which two fishers from Stilbaai know the same fish in a somewhat
different way.
I6 arrived at Oom Koos’ house just before 10am. Various boats, motors, trailers, tow-vehicles
and a small freezer truck stood parked around the front and back of the house in various states
of repair. The large white double storey home was bustling with movement when I arrived,
two domestic workers going about their work so busily that they seemed to not even notice me
as I stepped over the threshold and into the lounge. The lounge served as an entrance to the
home and I knocked on the door announcing my arrival. Oom Koos turned round in his seated
position at his desk, and, beaming at me over his glasses, extended a massive calloused hand
to envelope mine in a firm, friendly handshake. As he gestured to a couch and told me to sit,
Oom Koos informed me that he had invited his friend and fellow skipper Oom Louis to join our
conversation. I was here to talk about the Kob and both Oom Koos and Oom Louis were happy
to do so. The discussion below picks up approximately twenty minutes into our conversation:
Greg: how many types of Kob are there?
Oom Koos: there’s about three, four…five
G: that you catch here?
OK: ja, that you catch here, that is different from each other.
Oom Louis: there’s seven different species of Kob. The only one that you don’t get here definitely
is the Snapper Salmon that you get in Durban.
OK: but we catch the square-tail also here!
G: so the main ones I know of are the Dusky, the mini-Kob, the Square Tail and the Silver…
OK: ja, but the Silver Kob, neh, the Silver Kob – there’s more subspecies of Silver Kob –
there’s not only one. There’s one with the long tail, the one with the funny fins – I showed the
researchers the other day – what the difference is – there’s a seven kilo fish, his tail is like that
(broad), there’s the other seven kilo fish and his tail is like that (thin, flat) – there’s a hell of a
difference between the fins – it’s a different species, neh. And then there’s one of the fish where
his head is small, and his body is fat –
OL: - and then the other one with that rounded nose –
OK: - ja, his top of his mouth is shorter than the bottom of his mouth.
OL: now they, if you look when the one’s got a thick tail and the other a thinner tail, for the same
size fish, they will, for the fun of it – not the fun, to get the knowledge – they will open both, see
whether its male, whether its female – and you do get females with different bodies, males with
different bodies. So it’s definitely different species.
G: But are you catching them all together?
OK & OL: together ja, together!
OK: but some times of the year, that short fish –
OL: - the thick one –
6. The following ethnography is taken from Duggan’s 2012 MSocSci thesis.
OK: - the thick one, yes, is at a certain time of the year, I think its September, October, we catch
plenty, plenty, plenty of it.
OL: you know where you get that is in Namibia as well.
OK: really?
OL: it’s different!
OK: scientists don’t class it differently but it’s different.
OL: ja but to me it’s still a Kob and a Kob is a Kob oubroer.
OK: (laughing) But we as fishermen see that as another species – we know it’s another species
and its fighting more than the other species of Kob when it’s on the line. That shorter fish is
much stronger, much, much stronger than the other Kobs. Much, much, much, much stronger!
And I show that to Lloyd the other day, I said “look here, can you see the difference?” and he
said yes, he can see the difference…but when you get to the harbour, neh, the inspector doesn’t
want to know it and the factory guy, he doesn’t care either. You have a Kob and for them it is a
Silver Kob and that is so.
OL: ja, he doesn’t care because he gets his same price. Look if he turned around and said it was
something else –
OK: - or if we said it was something else –
OL: ja, if we said it was something else, we and him would get a different price. And probably
not a better one, you understand? So we must look and speak about it to each other and leave it
at that.
OK: but that factory guy, he knows it’s different, he sees it every day – a different shaped fish
that’s not a Dusky but that he sells as a Silver but clearly isn’t a Silver.
What emerges from the two accounts presented above are two very ways of knowing Kob which
manifest as knowledge claims which at times contradict one another. Two networks of actors
narrate their knowledge and research in the same environment featuring the same actor –
Kob. Yet their descriptions clearly reference two different interactions with the fish. Through
the actor7 Kob, it is possible to witness the narratives of two perceptions emerging and being
played out in the same environment. In the knowledge claims of official state science, Kob is a
clearly defined, universalized fact whilst knowable for scientists is “difficult for non-scientists
to distinguish” (Coast Care Fact Sheet, 2001). The narrative suggests that the version of Kob
presented in the Fact Sheet is true for all Kob. In effect it is a representation of Kob.
In Oom Koos and Oom Louis’ version of Kob, the definition is not as clear. They identify both
officially-recognised and classified species such as ‘Silver Kob’, and ‘Snapper Salmon’ but also
talk about subspecies, a point developed later in this paper. Their descriptions, rather than being
about a singular Kob, speak of heterogeneity, complexity, multiplicity and many subspecies.
Rather than being universalized and removed from context, their narrative speaks of identifying
the fish through interaction when they are fighting the line. In other words, the fishers’ way of
knowing Kob is mediated through a relational framework in which they know through their
interactions which change with context and time.
7. An actor is a term borrowed from Latour (2000), to describe all things that produce an effect on the world; these could be humans
through to boats and fish.
Returning to the harbour with Oom Koos, we have made a good haul of Kob, slightly over 800
kilograms by his estimate. Arriving at the quayside, we winch the boat up onto the trailer and
tow her over to the Viking Fishing factory where the buyer, Willie, is waiting next to the scales.
As the crew begin offloading the bakke (large plastic containers) of fish, the process begins:
at sea, Oom Koos had shown me some of the characteristics of different subspecies of Silver
Kob – the different fin, tail, head and body types. Opening some of them up, he showed me that
these were both males and females and that there were indeed distinct differences between the
subspecies, even though these swam together. Now, however, as Willie draws closer and the fish
come to the scale, the different species of Kob we had identified at sea quickly and seamlessly
became one – Silver Kob. It is a game, a performance for one another by fisher and buyer. As
every fish is taken from the boat a length and weight measure are taken. Nothing else seems to
matter. Individual characteristics are unimportant - in fact I get the sense that Oom Koos would
rather not discuss these while Willie is around. The different individuals are thus transformed in
a moment, becoming numbers. Then, once all of their number had been tallied, they became a
single whole – the catch for the day, represented in kilograms and currency and later to be filled
in on the log sheet which Oom Koos will submit to DAFF at year end.
8
Upon arriving at the quayside and pulling the boat out of the water, Oom Koos now related
to Kob differently, seeing them no longer as interesting individuals but as a number. It was a
relationality into which Oom Koos entered tacitly with Willie in which both agreed to a description
of Silver Kob in line with a Linnean classification of what Kob is. On the boat, Oom Koos had been
quick to point out differences in subspecies of Kob but outside the factory an altogether different
account of nature again took place in Oom Koos’s interaction with Willie. Now, Oom Koos’
enactment and knowledge claim about the fish shifted – in order to sell the fish to the factory
the multiple subspecies of Kob were referred to by one name - Silver Kob – thus becoming and
becoming recognized as a unified entity. This shift was characterized by a seeming detachment
from the fish, which were being thrown from the boat into waiting plastic bakke. The individual
characteristics that had mattered at sea were no longer important in the relationship. Willie’s
compliance with this enactment of Silver Kob was also important in securing a price for the catch
and together the fisher and the buyer engaged in a process of transforming fish into figures. In so
doing the complexities observed at sea – the individual subjective characteristics such as nose,
tail and body shape – were now of no importance, smoothed over and translated into object via
number, an artful deletion of characteristics which transformed the fish. Later that evening while
writing up the day’s experience Duggan (2012) noted:
“Perhaps it was just my perception of them or the sun and water reflecting off of their skin, but
when we were at sea the Kob, although dead, had still seemed lively. Now they appeared grey
and waxen, bereft of their individual characteristics, flung unceremoniously as objects through
the air. Suddenly they were lifeless numbers…one…two…thirty…forty five…I could almost see
the fish being transformed from subjects as they were tossed off the boat and landed with a
dull wet thud as an object in the bakke.”
In effect, the process of creating a number from fish represented a change in the relationship
between fisher and fish and the fish’s entry into another part of the network, entering into new
relationships with other sets of actors. The numbers generated in the fishery enter into networks
of resale, consumption, research and management, moving through processes which work
with and shape them into accounts of reality. In this way the end of the fish’s interactions with
fishers and their translation into numbers marks an entry into new networks in which they are
further enacted. Lien and Law (2010: 7) argue that “the inscription of a number in a notebook
serves as a first point of making them real”. In other words where management, research and
the sale of fish are concerned, the creation of a number is a means of quantifying the existence
of a thing. The day’s total catch weight would be added to the month total for Kob which in
turn would be written down by Oom Koos on his catch log sheet and submitted to DAFF at
the end of the year. At this point it would serve a range of purposes within DAFF research
and management as well as informing future stock models in government’s regulation of the
country’s commercial fisheries. The individuality and conditions of each fish and its capture are
8. Ethnography taken from Duggan’s 2012 thesis.
omitted at this stage. There is no space available to talk about different species or subspecies,
water conditions, location, wind, currents, bait or fish behaviour. The log sheet simplifies and
expedites data capture, severing ties between fishers and fish and the time-space in which they
interacted. Only the month’s total catch of the fish type is entered in each corresponding column
and row. In this way, the messiness of the story of the catch is transformed, retold as simple
representative numbers in a log. The number comes to represent all of the fish – they have
become universalized in a series of digits which now represent them. The complex, multiple,
dynamic, unpredictable, sought after are, through this simple process of enumeration, rendered
knowable, quantified, simple, predictable, singular, ready for entry into a stock assessment
model or levy accounting sheet for next season’s licensing purposes. In other words, in the
moment of translation the object of attention (in this case Kob), although ostensibly the same
being (a physical biological organism) can be very different – multiple versions of itself are
simultaneously brought about dependent upon who is interacting with it and the context in
which this interaction takes place.
In this section, we look at how people interact with sea and come to know the sea. For many of
the people working in Lamberts Bay, while they did not see the sea or the fish there as persons,
they seemed to share a relationship with them that was more than one of fisher and catch.
Willem spoke of how they needed to go out to sea with positive attitudes and with a smile on
their faces or else fishing would not be successful. This is because, according to Willem, the sea,
fish and lobster could sense moods and act accordingly. In particular, the sea was given a type of
agency, whereby the sea has an emotional relationship with people. It could become confusing
at times during fieldwork because one person could be talking about how the sea gave him so
much trouble and a minute later, Rosie, the only woman fisher, would be talking of how much
she loved the sea and how she felt free there. After a while, no longer a complete outsider, these
apparent contradictions began to appear complementary to me. As Willem put it:
Sometimes the sea will give you so you can save, on other days nothing, so you can come back on
those days that you have saved for.
The sea9, in this example was a provider to Willem, generous on some days, as on other days,
said Willem, would be unsuccessful. The sea was bountiful but it did not allow fishers to have
excess fish, meaning planning ahead and saving was always necessary. Often, while we spoke,
Willem’s face became animated and excited when he spoke of the sea and how it works with
him. In this way, Willem and Hennie spoke of their relationship with the sea:
W: Its like the sea is in love with us because before he will take you he will warn you and then if
you are reckless, careless then something will happen to you, but at least he has warned you.
J: The sea almost gives you a chance.
W: Yeah.
H: I’ll share a personal experience of where the sea, he warned me. One day we were working
close to Muisbosskerm, south of Lamberts Bay. There are lots of reefs and we work, putting a
set of nets there. There is a wave coming but its not breaking, its coming and we could see. I told
my bakkie mate that we have to leave and we leave. At that time another bakkie came and that
morning they smoked something, you could see. I went to them and I warned them, I said guys
we’ve just been out there and we see the sea is standing up so I warned them and they ignored
me, went in there and I warned my bakkie mate, I said you don’t go after them we wait outside.
They went a little bit deeper but we could still see them, they put their nets in the water. Then
suddenly, the waves start to break and it turned them upside down. Capsized the whole boat, but
from the head down, right over and we had to rush back to save them. The point is the sea warns
you and you have to listen to that.
W: I wouldn’t say the sea is like a person but the sea it will tell you its my area, I’m in control of
it and we have to listen to that. There are so many chances that the sea will show you.
9. Note that this analysis is not concerned with contesting facts: it is rather about the differences in relationship and ways of relating to
the sea amongst positivist science and fishers.
J: It communicates with you in a way.
W: Yes.
In the conversation below, one sees how Jacques and Ernest accord seals living in the bay with
more than a need to collect food. The seals in this example actually learn how to get fish from
fishermen and the best ways to do it. The seals directly affect fishers fishing attempts and the
safety of their hands; Jacques and Ernest acknowledge this fact.
J: The seals are really clever, the one seal, we don’t know where he got his education but you can
put your net in the water and the you put down your bait and without destroying your net he will
take out the bait.
E: The seals aren’t stupid, in the past I’ve caught mullets and you catch mullets with a net so
when they come into the net there heads get stuck and they can’t go back so you can’t pull them,
you have to push them through the nets. So the seals catch mullets from the nets, they pull them
out and they are well educated. If you fight with seal, hit him with rocks, disturb him, then he
will cause trouble for you and destroy your net. But if you leave him he will just take your bait.
J: If the boats come in with catches of snoek then you can come and see what the seals are doing
in the harbour. We have a way that we wash the fish, we take it and hit the water with it. Now the
seals are clever, they won’t come for the head or the middle part of the snoek, they will come for
your hand so that you have to let go. And twice now, recently, there were seals who bit fishers.
A significant point, from the preceding account, was how Jacques acknowledged the effect seals
had in their fishing attempts. Seals needed to be factored into one’s fishing ventures as they
interacted with both human and nonhuman sea-users, as if they had “an education”. Ernest
described how seals were clever in stealing fish. From what they said, it would seem, Ernest and
Jacques did not separate themselves from the ‘nature’ around them. In the way the modernist
project10 seeks to separate subjects and objects, Jacques, Ernest and Willem acknowledged their
daily interactions with those traditionally deemed objects. This is one way that people in their
practices produced versions of nature. In these versions, seals learned from people watching them
carefully, finally stealing their fish, according to Ernest. For Willem, the sea worked with him. For
those practicing scientific methods, they produce versions of nature as object. This means that
the version of nature that Jacques, Willem and Ernest assembled through their practices, for the
sciences, is not possible because nature as an object is not multiple or human-like.
In these conversations, Jacques and his peers accorded the sea and marine creatures a kind
of agency and understood themselves to be involved in a relationship that extended beyond
that of subject/object, culture/nature, hunter/prey. Rather, these fishers knew the sea and its
inhabitants as entities with whom they could engage. As Willem noted, the relationship was
not always a positive one as the sea could take as much as it could give. While this provides an
example of how these fishers engage with the sea relationally, and the Kob examples provide
a means of considering Kob in the multiple, how might these ways of knowing be useful to
management? In management, one may or may not see these knowledges as legitimate or
useable – perhaps seeing multiple Kob or the sea as possessing agency may prove to be difficult
to work with within established management paradigms. It is our belief that in order to establish
whether or not a particular way of knowing is helpful in addressing a particular issue it is
imperative that knowledge be worked with through collaborative research. Through working
collaboratively, taking as many knowledges into account allows for more to be worked with. In
what follows we consider how and when fishers’ knowledge may be useful to management.
10. The modernist project attempted to separate nature and culture – in other words it separates people from the environment in which
they live.
Discussion
How are our findings relevant and useful to this symposium and fisheries management in South
Africa moving forward? As much research has suggested an approach that criminalises and
disenfranchises those who fish for a living (particularly small-scale commercial handliners)
is ineffective in the management of fisheries because communication is foreclosed and often
poaching and other criminal misdemeanours result (Isaacs and Hara 2008, van Zyl 2008).
Thus far, we have shown that all knowledge positions undertake deletions and translations
in order to tell their way of knowing the world. It is precisely because of the deletions and
translations that they have to make in order to be heard by researchers and managers that
certain conversations are rendered very difficult and daunting for fishers. Likewise, for the
purposes of eliminating complexity from research and management objectives, it is often
necessary that scientists undertake ‘artful deletions’ as evidenced in the Fact Sheet.
What is necessary moving forward is a conversational space which allows for views that
are different from science. The question thus becomes: how do we go about opening up
conversations given that people feel that they need to undertake artful deletions in order
to speak to us as researchers? One possible avenue, we suggest, is evidenced in the earlier
discussion on subspecies of Kob. It is important to note here that we are not making a claim
either way about the existence of a genetic subspecies population in Stilbaai. Rather, the
question of Kob genetics points to a possible research project in which fishers and scientists
might discuss their ways of knowing Kob and come to new understanding of the ways in which
each knows fish. An example of such discussion is found in the work of Helen Verran (2013).
Describing an interaction between an Australian Yolgnu Aboriginal elder and environmental
scientists, Verran describes what she calls a moment of ‘epistemic disconcertment’, an
interaction which results in discord and unease where the knowledge claims of experts come
into contact in what both feel is their ‘home turf’, revealing divergent ways of perceiving,
receiving and being in the world.
In the context of a bush burning operation in the Australia North, it was found by the scientists
that the Aboriginal burning practice consistently maintained a higher biodiversity than the
scientific one. Collecting two sticks from what are classified in the Linnean system as two different
tree species, a senior Yolgnu man suggested to the assembled scientists that these were in fact the
same thing, being in a relationship of grandparent and grandchild. A moment of disconcertment
arose as a scientist, drawing on his knowledge of Linnean taxonomy and plant botany, tried to
demonstrate that the two were in fact not related. Eventually, the awkwardness of the situation
eased when the scientist provided an allegory to explain away the disconcertment. However,
Verran warns that the use of allegory as a ‘soothing balm’ risks cutting off the possibility of
what she refers to as “generative tensions” (2011: 75 forthcoming), the ability of a situation of
disconcertment to force invested parties to invent new ways of working with each other and
their knowledges. In the context of an EAF, in which a multitude of disciplines, objectives and
knowledges are brought together in close working contact, Verran’s suggestions are of great
significance. If participants are to work meaningfully and respectfully with knowledges and the
often divergent perspectives that attend these, it is important to work with difference generatively
or else risk marginalizing certain positions through the use of allegory.
In the first ethnographic piece presented in this paper is to be found a moment of epistemic
disconcertment in which Oom Louis and Oom Koos spoke of subspecies of Silver Kob not
recognized by DAFF scientists or the Linnean system of biological classification. In the
conversation, the Ooms initially spoke in terms of common names recognized in the Linnean
system, used by DAFF and the Fact Sheet. However once they had discussed these species
briefly, the picture began to change. Where they were speaking in terms which resonated with
an official scientific version of Kob, the fishers began to speak from their own experience in
which they had come to recognize a range of what they referred to as “subspecies” of Kob not
recognized by marine biologists. The means by which they recognised and categorised these
subspecies are markedly different from the means scholarly taxonomists would employ within
a Linnean system. The fishers identified the subspecies by a range of characteristics including
long tail and ‘funny’ fins; broad tail; thin, flat tail; small head and fat body; rounded nose with
protruding lower jaw with the fishers agreeing on naturalness of these subspecies classifications
to the extent that they are able to finish each other’s descriptions. They catch these species
together with what they identify as Silver Kob (in Linnean terms) but at certain times of the year
the “thick one” comes in droves and is identified by its strength on the line when hooked.
Writing on the migration and stock structure of cod in the Northern Gulf of St. Lawrence,
Murray et al (2008) found that in working with local fishers’ in conjunction with scientists,
while a more nuanced map of cod population structure and their movements was produced,
neither group had been in procession of a complete understanding of these prior to the exercise.
Conducting research with local fishers, argue the authors (ibid.), presents the potential to
augment scientific data with higher local resolution, suggesting the prospect of identifying
local cod populations. Working with fishers and scientists in Gilbert Bay in Southern Labrador,
Wroblewski (2000) explains how scientists, working with data supplied by local fishers, were
able to conduct a taxonomic study which revealed a genetically distinct population of Cod which
warranted separate management. Oom Louis’ and Oom Koos’ identification of subspecies of Kob
points to a possible collaborative project in Stilbaai in which fishers and scientists might explore
the fishers’ relational engagements and identification with a view to identifying a possible
genetically distinct local Kob population. Even if subspecies in the Linnean sense may not be
identified (i.e. in contrast to the Gilbert Bay example), a further worthwhile collaboration might
explore the circumstances in which it may be of advantage to use the fisher’s relationality and
classificatory system rather than the Linnean one without carrying out translations (i.e. using
allegory) between these two relational ‘taxonomies’.
In this paper we have shown that knowledge is always in a constant state of mediation and
translation. People engage in ‘artful deletions’ for a number of reasons. On the one hand, the
complexity and messiness of knowledge is often smoothed in the final description of a thing in
order to render the subject knowable and more accessible to research and management. On the
other, fishers, for example, feel compelled to undertake a series of artful deletions when dealing
with researchers, managers and factory buyers in order to be heard.
In the case of Stilbaai fishers identification of Kob subspecies a significant point emerges:
that fishers identify multiple subspecies of Silver Kob is certainly debatable. However, their
observations suggest, in line with Verran’s (2011, forthcoming) work that there may be
instances in which the knowledge of local people may be more effective and appropriate
than scientific knowledge and may not be translatable into the Linnean system or existing
management paradigms. The task in these instances becomes one of working respectfully with
knowledge which is not necessarily translatable into the Linnean system but which may be more
appropriate to the given context.
As it is not possible to include all knowledge about, for example the sea or Kob, in a factsheet or
a knowledge base, a series of ‘artful deletions’ will always be necessary, if only for the purpose of
pragmatics. While this process is neither a cure-all nor a fast process, we argue it is nonetheless
a necessary one and work around collaborating around different ways of knowing is integral to
effective management. The latter point is vital; work has to happen collaboratively as having
scientists talk for fishers may not be helpful as fishers continue to feel sidelined. Rather working
and speaking together is something to consider.
The interactions and relationships as seen with Kob multiple and the sea as actor in Lamberts
Bay, are filtered out of what is officially acknowledged. The shift we have proposed in our work
is one which seeks to move beyond an identity politics to a relational way of knowing in which
knowledge is an open and continual process of evaluating what is known. The strength of
working with relationality is its positing of knowledges on an equal footing. Certainly there are
many possible pitfalls associated with a new way of going about research and the imperative
here is to move slowly through the terrain. However, as challenging as this step is it is a
necessary one if South Africa’s conservation science is to work effectively with social-ecological
systems in times of increasing variability.
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Trade dynamics of South African Linefish
John Duncan1 and M Burgener2
1
WWF-SA, Bridge House, Boundary Terraces, Mariendahl Lane, Newlands, Cape Town,
P.O.Box 23273, Claremont 7735.
2
TRAFFIC East/Southern Africa, South African National Biodiversity Institute.
Abstract
Despite the collapse of a number of linefish species in South Africa, many of them remain a
popular item on restaurant menus and regularly found on the shelves in retailers and fish
delis around the country. While there is a growing body of science around the life histories
and impacts of fishing on these linefish species, there is very little known about what happens
to these species in the market. Considering the growing interest in creating market-based
incentives for sustainable fisheries, understanding the factors driving demand for these species
is increasingly recognised as a key aspect in developing sustainable long-term solutions for
these fisheries. Better understanding of the supply chain in terms of where they are sold in
South Africa, in what quantities and through which outlets, can help to shed light on where the
critical points for intervention in the supply chain are and which companies/institutions are
key stakeholders in this process. WWF-SA, through its Southern African Sustainable Seafood
Initiative (SASSI), has recently commissioned a study through TRAFFIC (The Wildlife Trade
Monitoring Network) to look at the trade dynamics of seafood on the South African market. This
paper provides a brief overview of the critical findings of this study, highlighting the important
supply chain links in the local linefish market.
Introduction
WWF’s Southern African Sustainable Seafood Initiative (WWF-SASSI) was established in 2004
and engages with multiple stakeholders in the seafood supply chain ranging from consumers,
through restaurants, retailers and suppliers right back to the fisheries from which the seafood
is sourced. One of WWF-SASSI’s key objectives is focused on shifting consumer demand away
from over-exploited species towards more sustainable options. In order to achieve this objective,
the programme has adopted a market-based approach which is focused on developing market
incentives for seafood-related companies (retailers, restaurants, fishing companies etc.) to
pursue sustainable seafood strategies and in so doing drive positive change on the water. These
incentives may range from preferential procurement retail agreements for sustainable seafood
products to publicity campaigns in support of responsible fisheries/seafood traders.
In order to maximise the power of these types of market-based conservation approaches, it is
critical to understand which seafood products are available on the market, where they originate
from, and through which outlets they reach the end consumer. Better understanding these
variables enables conservation organisations such as WWF to identify where the important
leverage points are in the seafood supply chain for each species. For example, if the majority of
a specific fishery’s products were being sold to a market which was sensitised to environmental
issues, it would be relatively easy to incentivise sustainability improvements in that fishery
through engaging with the market through the retailers/suppliers who deal in these products.
Conversely, if a fishery’s products were predominantly sold to consumers whose seafood choices
were made purely on the basis of price, a market-based approach would have little impact.
To date, apart from some cursory industry reports, there has been no comprehensive analysis
of the trade dynamics of the South African seafood sector. In 2011, WWF-SASSI identified this
research as a critical component of its on-going work and commissioned a report to achieve this
goal. The objective of this report was to assess the dynamics of the South African seafood market
by identifying the different species that occur on the South African market, their importance in
the market, and the main stakeholders engaged in the trade of these species. As some of South
Africa’s most threatened marine resources, linefish111 constitute one of the priority groups of
species in need of conservation interventions with the most recent available data suggesting
that 68% of commercial linefish species stocks have collapsed (WWF-SA 2011). As linefish are
targeted by a diverse range of fisheries, they have a number of different routes to market and
thus pose a particularly difficult challenge to a market-based conservation approach.
This paper presents the findings of WWF-SASSI’s seafood trade dynamics report with a
particular focus on linefish, looking at which species are commonly found on the market in
South Africa, where they are traded and through which outlet types. It concludes with some
discussion of the trade patterns observed and makes suggestions for WWF-SASSI’s future
engagement with the linefish sector and the institutions responsible for managing this complex
and diverse seafood sector.
The information presented in this paper originates from an unpublished 2012 report
commissioned by WWF-SA on the trade dynamics of the South African seafood market which
was compiled by TRAFFIC (The Wildlife Trade Monitoring Network). TRAFFIC’s report was
compiled using data gathered from a number of different sources, namely the following:
Surveys: Surveys were conducted in four provinces; the Western Cape, Gauteng, KwaZulu-Natal
and the Eastern Cape, based on a standard survey template, with the primary focus on outlets
operating in the major urban centres of each province. Outlets were identified using online and
printed directories, and personal knowledge. A total of 147 outlets (retailers, restaurants, seafood
shops/delis, markets) were surveyed through walk-in surveys which noted all of the different
seafood products on sale on the shelves/delis/fridges/menus of each of the outlets.
Questionnaires: Of the 147 outlets that were surveyed, a total of 95 outlets also completed
questionnaire interviews which were used to assess a number of areas of the outlet owner/
manager’s knowledge around the seafood trade including most popular seafood species,
compliance with the law, awareness of SASSI and their perceptions of the state of the South
African seafood industry.
Catch Data: Catch data was sourced from the South African Department of Agriculture,
Forestry and Fisheries (DAFF), the agency responsible for the management of all South African
fisheries. For the majority of fisheries, catch data was only available for the period 2003 – 2010.
Trade data: South African export and import data was sourced from South African Revenue
Service (SARS) for the period 2000 - 2010. In certain cases, SARS trade data does not provide
the level of detail required for effective trade analysis. In such cases data was sourced from the
customs or statistics agencies of the relevant country or from UN COMTRADE and/or Eurostat.
Results
An analysis of the questionnaire responses indicated that of the top ten most commonlyavailable species across the four provinces, hake was by far the most commonly available
seafood choice with prawns, calamari and kingklip also featuring regularly in the top 5 most
common species available (Table 1).
Traditional linefish species212 (highlighted in grey in Table 1) did not feature very regularly in
any of the provinces, with kob being the most commonly found linefish species across all four
1. The term ‘linefish’ is a uniquely South African term which is used to describe a group of unrelated fish species which were traditionally
caught using hooks and lines. Although many of these species are now also caught using more industrial fishing methods such as
longlines or trawl nets (some are even farmed), the term ‘linefish’ is still used to describe species which were originally targeted by
traditional linefishers. As local linefish populations have declined, a number of alternative imported species are now also marketed locally
as ‘linefish’, further complicating this already misused terminology.
2. Due to the nature of product information available, it was not possible to identify whether or not these species were in fact caught in
the traditional linefishery, however, for the purposes of this paper all species which may have originated from this fishery are included
under the term ‘linefish’, regardless of their country of origin or catch method.
provinces. Dorado and geelbek were the only other linefish species found across more than one
province. However, a number of questionnaire responses in the Western Cape recorded species
in the open-ended ‘linefish’ category, making it difficult to know which species exactly were
being sold.
An analysis of the survey data indicates that of the 15 most commonly-found species on the
South African market by outlet (Hake made up the majority of seafood sales volumes across
the different outlet types surveyed, with prawns, squid and kingklip also featuring regularly.
Restaurant trade volumes (Figure 2) indicated that, despite most restaurant menus listing
a ‘linefish’ option, prawns, calamari, hake and Norwegian salmon make up almost 75% of
the volumes sold with the only linefish species in the top ten being dorado and kob which
contributed approximately 6% and 4% respectively.
The estimated relative volumes of the seafood sold through retailers (Figure 3) is based on
data provided by one of South Africa’s major retail chains for a year’s worth of seafood sales in
their fresh seafood department (i.e. excluding canned and frozen products). While there is no
data on seafood sales in the other major retailers, it is assumed that these data are relatively
representative of all South African retailers. While the majority of the seafood volumes sold in
retailers is made up of hake, snoek makes up approximately 10% of the volumes sold, yellowtail
makes up a further 4%. Unfortunately, it is not clear from the sales data whether the snoek and
yellowtail, which are both linefish species, are in fact locally caught or are imported as there are
known imports of both these products from foreign countries.
The estimated relative volumes of the seafood sold through seafood suppliers (Figure 4) is based
on a year’s worth of seafood sales data provided by a large seafood supplier in the Western
Cape. Seafood suppliers are largely responsible for supplying the hospitality trade (hotels and
restaurants) in South Africa. Although it is unlikely that this data is representative of all South
African seafood suppliers because of the differing clientele of different suppliers, this data helps
to paint a broad picture of overall trends. Hake once again makes up by far the most seafood
sold by volume, however a number of linefish species, namely kob, yellowtail, Cape salmon and
barracouta (another name for snoek caught in New Zealand) also make up a significant part of
the suppliers sales volumes.
The estimated relative volumes of the seafood sold through fish shops (Figure 5) is based on
a year’s worth of seafood sales data provided by a popular fish shop in a Garden Route town.
Fish shops generally sell directly to the public with a variable percentage of their sales being
generated by supplying specialist products to restaurants and hotels. Again it is unlikely that
this data is representative of all South African fish shops because of the differing clientele of
different fish shops around the country, however this data helps to paint a broad picture of
overall consumer trends at a coastal fish shop. As with the other outlets, hake makes up by
far the most seafood sold by volume, however a number of potential linefish species, namely
kob, Cape salmon and snoek also make up a significant part of the suppliers sales volumes.
However, once again it is unclear what portion, if any, of the snoek sold is imported rather than
originating from the local linefishery.
Figure 1), there is a lot of overlap of the most popular species between fish shops and
restaurants (hake, kingklip, mussels, calamari and prawns). While retailers tend to stock similar
species, they do not appear to be as commonly found in these outlets. Predictably, fish shops
appear to have the widest range of seafood products. In terms of linefish species, snoek, kob, red
roman, yellowtail, carpenter (silvers), white stumpnose, dorado and cape salmon (geelbek) were
commonly found, although only red roman and yellowtail were found at all three outlet types.
Table 1: Ranking of key seafood species traded by occurrence as indicated by survey
respondents across targeted provinces.
Western Cape
Gauteng
KwaZulu-Natal
Eastern Cape
26 respondents
22 respondents
25 respondents
19 respondents
Species
Count
Species
Count
Species
Count
Species
Count
Hake
20
Hake
6
Prawns
24
Hake
17
Kingklip
13
Prawns
4
Calamari
24
Prawns
15
Kob
12
Sole
3
Dorado
20
Calamari
15
Prawns
11
Kingklip
2
Mussels
20
Mussels
12
Tuna
9
Norwegian
salmon
2
Kingklip
18
Kingklip
11
Calamari
8
Snoek
2
Hake
16
Norwegian
salmon
7
Yellowtail
8
Yellowtail
1
Norwegian
salmon
10
Gurnards
6
Geelbek
7
Calamari
1
Oysters
8
Kob
5
Linefish
6
Dorado
1
Sole (prefer
EC )
8
Sole (prefer EC ) 5
Norwegian
salmon
5
Mussels
1
Sole , WC
7
Butter bream
(St Joseph)
3
Gurnard
5
Panga
1
Tuna
8
Sole , WC
3
Crayfish
5
Kob
4
Oysters
3
Angelfish
3
Swordfish
3
Mackerel
(peppered)
2
Mussels
2
Geelbek
3
Carpenter
(Silver)
2
Hake made up the majority of seafood sales volumes across the different outlet types surveyed,
with prawns, squid and kingklip also featuring regularly. Restaurant trade volumes (Figure 2)
indicated that, despite most restaurant menus listing a ‘linefish’ option, prawns, calamari, hake
and Norwegian salmon make up almost 75% of the volumes sold with the only linefish species in
the top ten being dorado and kob which contributed approximately 6% and 4% respectively.
The estimated relative volumes of the seafood sold through retailers (Figure 3) is based on
data provided by one of South Africa’s major retail chains for a year’s worth of seafood sales in
their fresh seafood department (i.e. excluding canned and frozen products). While there is no
data on seafood sales in the other major retailers, it is assumed that these data are relatively
representative of all South African retailers. While the majority of the seafood volumes sold in
retailers is made up of hake, snoek makes up approximately 10% of the volumes sold, yellowtail
makes up a further 4%. Unfortunately, it is not clear from the sales data whether the snoek and
yellowtail, which are both linefish species, are in fact locally caught or are imported as there are
known imports of both these products from foreign countries.
The estimated relative volumes of the seafood sold through seafood suppliers (Figure 4) is based
on a year’s worth of seafood sales data provided by a large seafood supplier in the Western
Cape. Seafood suppliers are largely responsible for supplying the hospitality trade (hotels and
restaurants) in South Africa. Although it is unlikely that this data is representative of all South
African seafood suppliers because of the differing clientele of different suppliers, this data helps
to paint a broad picture of overall trends. Hake once again makes up by far the most seafood
sold by volume, however a number of linefish species, namely kob, yellowtail, Cape salmon and
barracouta (another name for snoek caught in New Zealand) also make up a significant part of
the suppliers sales volumes.
The estimated relative volumes of the seafood sold through fish shops (Figure 5) is based on
a year’s worth of seafood sales data provided by a popular fish shop in a Garden Route town.
Fish shops generally sell directly to the public with a variable percentage of their sales being
generated by supplying specialist products to restaurants and hotels. Again it is unlikely that
this data is representative of all South African fish shops because of the differing clientele of
different fish shops around the country, however this data helps to paint a broad picture of
overall consumer trends at a coastal fish shop. As with the other outlets, hake makes up by
far the most seafood sold by volume, however a number of potential linefish species, namely
kob, Cape salmon and snoek also make up a significant part of the suppliers sales volumes.
However, once again it is unclear what portion, if any, of the snoek sold is imported rather than
originating from the local linefishery.
Figure 1: Comparison of the percentage of outlets stocking the top 15 ranked species groups per
outlet type
Figure 2: Estimated relative seafood volumes of the top ten species of seafood sold in
restaurants in South Africa based on a sample of 62 restaurants.
Figure 3: Relative seafood volumes of the top ten species of seafood sold in 2011 through a
major South Africa retail chain excluding canned and frozen seafood products.
Estimated consumption figures (Table 2) provide a useful breakdown of the relative importance
of imported seafood on the South African market. It is clear that locally caught hake and
sardines make up the large majority (almost 80%) of all seafood consumed locally. It is also
interesting to note that there are significant imports of species such as squid, tuna, Norwegian
salmon, prawns and mackerel, most of which is probably directed at the formal seafood market
(retailers, restaurants, suppliers, fish shops). In terms of linefish, it appears that all of the locally
caught linefish are sold on the local market rather than being exported, similarly for kingklip.
Although there were no recorded imports of linefish, as snoek imports were recorded separately,
it is well known that a number of imported species are being sold on the local market as linefish,
in particular large volumes of fresh linefish are known to be imported from Mozambique. It is
also interesting to note that over 33% of the snoek available on the local market is likely to have
been imported, most likely from New Zealand.
large Western Cape seafood supplier.
Garden Route fish shop.
The breakdown of the top five linefish species caught per region (Table 3) indicates that the
linefishery in the Western Cape makes up the large majority of all linefish catches and is
particularly focused on snoek, followed by the Southern Cape and the South Western Cape with
many of the same species being targeted in these areas. Although the catches are significantly
lower in KwaZulu-Natal and the Transkei, it is clear that the species targeted in these regions are
very different to those in the more Western regions. Interestingly, Cape salmon (geelbek) is the
one species that is consistently found in the top five species in all of the regions except for the
Western Cape.
Table 2: An estimate of seafood consumption for top ten seafood products in South Africa, 2010
Catch
Export
Import
Estimated
consumption
Sardines
112,386,000
18,041,163
36,681,223
131,026,060
Hake
108,695,000
31,322,900
11,285,733
88,657,833
Snoek
10,221,000
5,690,139
15,911,139
Tuna (canned)
12,355,641
12,355,641
Squid
3
7,794,790
7,794,790
Prawns
66,190
145,833
6,050,348
5,970,705
Linefish (excluding snoek)
4,410,545
4,410,545
Salmon (fresh, frozen and
canned)
3,591,344
3,591,344
Kingklip
2,685,297
2,685,297
Mackerel (canned)
1,963,014
1,963,014
Source:Catch – Department of Agriculture, Forestry and Fisheries
Imports and exports – South African Revenue Services, UN COMTRADE and Namibian Bureau
of Statistics
Discussion
The trade in seafood on the South African market, and linefish in particular, is very difficult to
monitor based on the informal nature of the market for many of the linefish species. As noted by
previous authors (von der Heyden et al. 2009), the use of group names and generic terms such as
‘linefish’ to market a broad range of species also makes it very difficult to accurately assess exactly
which species are being offered for sale on the South African seafood market under this seafood
category. The high levels of mislabelling of seafood on the South African market add further
complexity to this challenge, with estimates of up to 31% of retail seafood products being mislabelled
(Cawthorn et al. 2012) and rising to up to 84% for some popular species such as kob (von der
Heyden et al. 2009). Notwithstanding these challenges, this study identified a number of linefish
species on the South African market across the different outlets, enabling further discussion of some
of the major issues surrounding the trade in linefish on the South African market.
Traditional linefish species appear to be more commonly found in the restaurant and fish shop
trade with relatively few linefish species turning up in retailers other than snoek, which was
not commonly found in the other outlet types. It is interesting to note that despite the collapse
of kob species (Griffiths 2000), this group of species was still one of the most commonly found
linefish species throughout all of the different market outlets. This raises a number of questions
as to whether these species are in fact kob, as previous studies have shown this species to be
particularly prone to mislabelling (von der Heyden et al. 2009). Analysis of reported linefish
catches indicates that although kob are caught in significant numbers in the South-Western
Cape, where they make up the majority of the catch, in most other regions species such as snoek,
yellowtail, geelbek, slinger and carpenter are more commonly caught and yet they do not seem
to appear on the formal market as regularly as kob.
The analysis of seafood imports also provides some interesting insights into South Africa’s
seafood market. As suspected, locally caught linefish are almost exclusively sold on the local
market, with very little evidence of any of the traditional linefish species being sold to export
3. This figure is an estimate based on the following: Reported catch of barracouta in 2010 was 28,450,694 kg (New Zealand Ministry of
Fisheries, 2012). Statistics New Zealand notes that 25% of barracouta go to South Africa. There is limited domestic consumption. Until
further information on exports is obtained, South African imports of New Zealand snoek have been estimated at 20% of catch in 2010:
5,690,139 kg.
markets. However, it is clear from the import analysis that there are an increasing number
of imported species which are being sold under the category of ‘linefish’, although it is highly
unlikely that these imported species were caught using traditional linefishing methods. Known
imported linefish species such as snoek and yellowtail are also not adequately distinguished on
the market, and although it was not possible to distinguish the amounts of imported yellowtail
on the market, the large volumes of imported snoek (5690 tonnes in 2010) suggest that the
import market is having an increasing impact on the economics of the local linefishery. This
issue has been raised by linefishers during the Ecological Risk Assessment process (see Petersen
et. al. 2010) as a major economic risk as these species are in direct competition with the
traditional linefishery.
Table 3: Top five linefish by volume (kg) caught per region over the period 2000 – 2010,
(excluding hake, squid and tuna)
Region
KwaZulu Natal
Slinger
Geelbek
Santer
Rockcods and seabass
Kob
South Eastern Cape
Geelbek
Carpenter
Kob
Panga
Santer
South Western Cape
Snoek
Geelbek
Yellowtail
Carpenter
Soupfin shark
Southern Cape
Kob
Sharks
Carpenter
Geelbek
Kingklip
Western Cape
Snoek
Mackerels and tunas
Yellowtail
Hottentot
White Stumpnose
Transkei
Slinger
Poenskop
Englishman
Geelbek
Rockcods and seabass
Total catch (2000 - 2010) kg
% of total catch (2000
-2010)
1 765 737
722 521
608 157
360 643
317 570
36%
15%
12%
7%
6%
1 657 104
1 155 963
565 290
233 344
123 510
37%
26%
13%
5%
3%
5 366 577
2 514 523
2 249 977
1 180 000
672 417
37%
17%
15%
8%
5%
2 920 025
704 366
435 558
393 103
140 275
56%
13%
8%
7%
3%
52 993 038
3 530 317
2 016 667
1 280 619
387 291
87%
6%
3%
2%
1%
8 342
2 425
2 199
1 975
1 819
33%
10%
9%
8%
7%
Source: Department of Agriculture, Forestry and Fisheries (National Marine Linefish System)
The fact that so few consumers are aware of the large amount of imported seafood on the South
African market, including popular species such as dorado, yellowtail and snoek, remains a major
concern. The lack of differentiation between local and imported species creates a number of
loopholes which marketers are increasingly known to exploit. For example, while the sale of ‘nosale’ species caught in South African waters is illegal, there are currently no regulations preventing
the import and sale of the same species if they are caught in foreign waters. This creates a ‘grey
area’ for Fisheries Compliance Officers (FCOs) charged with enforcement of the law as they are
unable to distinguish between legally imported products and illegal locally-caught products. The
absence of accurate labelling also makes it difficult for conscientious consumers to make informed
decisions about the sustainability of their seafood choices, as they are unable to relate the species
on offer to the sustainability advice offered by sustainability guides such as WWF’s Southern
African Sustainable Seafood Initiative (WWF-SASSI). Because of the completely different
environmental impacts and management regimes of the different fisheries, it is critical that
imported products should be differentiated from locally-caught products with country of origin
labelling and ideally some indication of the catch method as well.
The study was also interesting in what it didn’t find, in that a number of species which
are known to be caught in the traditional linefishery such as slinger, hottentot and sharks
(smoothhound and soupfin) did not feature at all in the surveys despite being some of the more
commonly caught linefish species in KZN and the Western Cape respectively. This would suggest
that these species are likely to be sold through different market channels such as the informal
market (hottentot & slinger) and the export market (sharks). This is an important finding in
that it indicates that, barring some high-value species such as kob and Cape salmon (geelbek),
local linefish species are not generally very commercially important species in the formal
market outlets (retailers, restaurants, suppliers and fish shops) and market-based sustainability
initiatives such as WWF’s SASSI Retailer Participation scheme, which works closely with key
retailers, suppliers and restaurant chains, may not be able to shift current practices in the
linefishery through working with these partners.
Key findings of the study include the fact that many of the traditional linefish species, once the
mainstay of South African seafood dishes, are no longer very commonly sold through formal
market outlets. This is likely to be a result of both the massive declines in linefish stocks that
have taken place over the last 50 years as well as the fact that some of these species may also
be marketed through more informal market outlets. The study also highlighted the growing
prevalence of imported seafood on the South African market, much of which may be competing
with species from the local linefishery. This is strongly related to the challenges associated
with current seafood naming and labelling practices in South Africa which allow for fraudulent
labelling or the misrepresentation of seafood products. Besides short-changing consumers
and local fishers, the misrepresentation of seafood poses significant health risks by relabeling
potentially toxic species as common species and undermines the work done by the WWFSASSI awareness campaign as the consumers ability to choose sustainably sourced seafood
is compromised. This highlights the need for the broader seafood industry and associated
stakeholders to develop better regulations in this regard.
References
Cawthorn D, Steinman HA, Witthuhn RC. 2012. DNA barcoding reveals a high incidence of fish
species misrepresentation and substitution on the South African market. Food Research
International, 46, 30-40.
Cape Province: Snapshots of the 20(th) century. South African Journal of Marine Science 22,
81-110.
Petersen SL, Kerwath S, Paterson B and N Okes. 2010. Ecological Risk Assessment for the South
African Linefishery. In Petersen S., Paterson B., Basson J., Moroff, N., Roux J-P., Augustyn, J.
and D’Almeida, G. (eds) Tracking the Implementation of an Ecosystem Approach to Fisheries in
Southern Africa. WWF South Africa Report Series – 2010/Marine/001.
Von der Heyden, S, Barendse, J, Seebreghts, AJ and Matthee, CA. 2009. Misleading the masses:
detection of mislabelled and substituted frozen fish products in South Africa. ICES Journal of
World Wide Fund for Nature- South Africa (WWF-SA) 2011. Fisheries: Fact & Trends http://assets.
wwfza.panda.org.wwf-web-1.bluegecko.net/downloads/wwf_a4_fish_facts_report_lr.pdf
(accessed on 27 December 2011).
Session 7 – Fish Distribution and Stock Delineation:
Chair Meaghan McCord
Movement behaviour and genetic stock delineation
of a coastal reef fish species, poenskop, Cymatoceps
nasutus (Teleostei: Sparidae)
TS Murray1, G Gouws2, PD Cowley2, JQ Maggs3 and BQ Mann3
1
Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94,
Grahamstown, 6140, South Africa.
2
Africa.
3
Oceanographic Research Institute, P.O. Box 10712, Marine Parade, Durban, 4056, South
Africa.
Introduction
The poenskop, or black musselcracker, is an endemic South African sparid distributed from
the south of Saldahna Bay in the Western Cape to Cape Vidal in northern KwaZulu-Natal. This
distribution is shared by the juveniles and adults. Spawning locations are unknown, and even
after extensive larvae surveys along the coastline of South Africa, poenskop larvae have never been
documented (see Beckley and van Ballegooyen 1992, Tilney et al. 1996, Wood et al. 2000, Roberts
and van der Berg 2005, Connell 2010). Poenskop are slow-growing, long-lived, sex-changing,
late-maturing and show a high degree of residency at certain life-history stages. Collectively, these
attributes make the species acutely sensitive to over-exploitation. The poenskop is one of South
Africa’s most sought-after recreational angling species (Biden 1930, Smith and Heemstra 1986).
It is predominantly caught by members of the recreational shore and skiboat sectors and is also
targeted by spearfishers, but is of low commercial value due to low abundance (Coetzee and Baird
1981, Hecht and Tilney 1989, Brouwer et al. 1997, Mann et al. 1997). Despite interventions such
as the imposition of size and bag limits, catch-per-unit-effort (CPUE) trends reflect a severe and
consistent stock decline over the last two decades. Management is compromised by the deficiency
of information and the efficacy of the current management strategies is questionable. As a result of
its importance as a recreational angling species, Wallace and van der Elst (1983) identified it as a
priority species urgently in need of investigation.
Although aspects of the biology of this species were documented by Buxton and Clarke (1989),
little is known about the movement behaviour of poenskop. Furthermore, there is a complete
lack of information on its genetic stock structure. Therefore, the primary aim of this project was
to investigate the movement behaviour and genetic stock structure of poenskop. The specific
objectives included:
•
•
•
Evaluating current and historic trends in catch and CPUE of poenskop,
Determining patterns of residency and movement of juvenile, sub-adult and adult poenskop
by analysing existing tag-recapture data from several dedicated tagging studies,
Determining genetic diversity of poenskop across its distribution, identifying possible
stock substructure.
Catch trends
Current and historic trends in catch and CPUE of poenskop were reviewed and evaluated.
This was achieved by making use of published and unpublished survey and research data.
Information regarding poenskop catches was sourced from the National Marine Linefish
System, personal angling records, and a popular fishing magazine, Stywe Lyne/Tight Lines.
In addition, information from the primary literature was used. Numerous studies have been
conducted to assess the catch, effort, species composition and value of the shore and skiboat
fisheries along different parts of the coastline (see Coetzee and Baird 1981, Coetzee et al. 1989,
Bennett 1990, Hecht and Buxton 1993, Hanekom et al. 1997, Penney et al. 1999, Griffiths 2000,
Brouwer and Buxton 2002). Due to differences in survey techniques, analyses, time periods and
angler behaviour (e.g. competitive vs. recreational), the studies could not be directly compared
(Bennett and Attwood 1993). However, the results allow one to assess catch and effort trends
over time.
A number of different coastal regions were described in these studies. This, combined with
the changing of provincial boundaries in recent years, makes the interpretation of these
studies rather complex. For the purpose of change in catch trends and movement behaviour
components of the study, five coastal sections were defined: (a) south-west coast (Strand to
Cape Infanta), (b) southern coast (Cape Infanta to St Francis Bay), (c) south-east coast (St
Francis Bay to Kei River), (d) Transkei (Kei River to Umtamvuna River), and (e) KwaZulu-Natal
(Umtamvuna River to Kosi Bay) (Fig 1).
Figure 1: Map of South Africa showing the different coastal regions used in the changes in
catch trends and movement behaviour components of this study.
Movement behaviour
Conventional dart tagging and recapture data for assessment of movement patterns of poenskop
were obtained from three ongoing, long-term coastal fish-monitoring projects, conducted at
different spatial scales; the first covered the entire South African coastline (Oceanographic
Research Institute (ORI) Tagging Project), and two were research-based projects conducted in
marine protected areas (Tsitsikamma National Park (TNP) and Pondoland MPA (PLD) linefish
tagging projects) (Fig 2).
A number of differences exist between the available data (Table 1). The data obtained from the
MPA projects were fine-scale, high resolution data with a precision of 15 to 100 m, while the
information from the ORI Tagging Project was large-scale low resolution data where localities
reported were on a scale of > 1 km. Information for poenskop was obtained from both inshore
(shore-angling) and offshore (boat-based angling) records in the ORI Tagging Project. The TNP
provided inshore tagging effort, while the PLD fish were only tagged offshore. Collectively, these
data provided a good platform on which to base the analyses of poenskop movement patterns.
a
b
c
Figure 2: Study areas of (a) the ORI Tagging Project, that spanned the entire South African
coastline, and two research-based tagging projects: (b) Tsitsikamma National Park (TNP) and
(c) Pondoland (PLD) MPAs.
Despite considerable tagging effort along the South African coastline, there remains limited
information on the connectivity of different populations along the South African coastline.
This was addressed using mitochondrial DNA sequencing. The mitochondrial DNA control
region was used due to its high substitution rate, haploid nature, maternal inheritance and
absence of recombination. In order to determine the genetic diversity of the poenskop, fin
clips were collected during tagging work, fishing competitions and recreational shore and boat
fishing, from a total of 370 specimens from 35 locations (from Stilbaai in the Western Cape to
Umtentwini in KwaZulu-Natal). DNA was extracted from samples using commercially available
kits. A fragment of the highly variable mitochondrial control region was amplified by PCR using
newly designed, species-specific primers, CNCR1-F and –R. Samples were then sequenced by
Rhodes University’s Sequencing Unit and a commercial sequencing facility (Macrogen). Data
were analysed using standard population genetic and phylogeographic approaches.
Table 1: Summary information on the data sets derived from the Oceanographic Research Institute
(ORI), Tsitsikamma National Park (TNP) MPA and Pondoland (PLD) MPA tagging projects.
Dataset Study site
Distance
resolution
Distance
error
Information
recorded
Inshore/
offshore
ORI
Entire South
African coast (3
000 km)
km
1 – 5 km
Tag number
Date
Location
Inshore
Offshore
TNP
Tsitsikamma
National Park
MPA (5 km
research site)
m
10 – 50 m
Inshore
Tag number
Date
Location
Angler effort
Water temperature
PLD
Pondoland MPA
(four 1 x 2 km
sites)
m
15 – 100 m
Tag number
Date
Location
Angler effort
Offshore
Results
Catch trends
Analysis of this available catch data (published and unpublished) revealed a decline in the
number of poenskop caught over the last two decades, ultimately reflecting the collapse of the
stock. Various technological developments have also increased the probability of landing a
poenskop (besides other species). The size of fish caught has steadily declined with almost 100%
of fish caught, at present, weighing less than 5 kg. However, the declaration of a crisis in the
linefishery (in 2000) and subsequent reduction in commercial effort has yielded some positive
trends. Furthermore, improved CPUE from the Tsitsikamma National Park Marine Protected
Area (MPA) (Fig 3), and larger poenskop being caught in the no-take areas than adjacent
exploited areas of the Pondoland MPA (Maggs 2011) confirmed that MPAs can be effective for
the protection and management of poenskop.
Movement behaviour
Conventional dart tagging and recapture information indicated high levels of residency at all
life-history stages. Of 2 704 poenskop tagged, 189 (6.99%) were recaptured, with approximately
90% of all recaptures (from combined data) being made within 5 km of the tagging site (Table
2). All recaptures within the PLD were made within 650 m of the tagging site, while all poenskop
in the TNP were recaptured within 250 m of the tagging site. This information confirms the
extreme residency displayed by poenskop.
Within the ORI Tagging Project, recaptures were made from Cape Point to KwaZulu-Natal,
spanning the core distribution of the species. Coastal region, seasonality and time at recapture
did not appear to have a significant effect on the level of movement or distance moved. However,
on correlating coastal movements with fish size (and ages), larger and older fish (adults) moved
greater distances, with juveniles and sub-adults showing high degrees of residency (Figure 4,
Table 3).
Figure 3: Trend in mean annual CPUE (fish.angler-hour-1) for poenskop recorded during
research angling in the Tsitsikamma National Park MPA over the period 1995 to 2009 (PD
Cowley, unpublished data).
Table 2: Summary of recapture data obtained for poenskop tagged along the South African
coast between 1984 and 2010.
Recaptures
Distance travelled (km)
Days at liberty
Tagging No.
No.
project tagged
%
Mean
Min
Max
Mean
Min
Max
ORI
1 935
74
3.82
24
0
483
430
0
3 295
TNP
556
73
13.13
0.04
0
0.25
393
0
2 407
PLD
213
42
19.72
0.12
0
0.64
468
59
1 390
Total
2 704
189
6.99
9
0
483
424
0
3 295
Sequences were approximately 334 base pairs in length and 29 different haplotypes were seen
across all the samples, with one haplotype being shared amongst 52 individuals, representative
of all the different study regions. Haplotype diversity was high for all regions, ranging from
0.795 ±0.109 (Western Cape) to 0.903 ±0.031 (KwaZulu-Natal). Nucleotide diversity was fairly
constant among each region, ranging from 0.0048 ±0.0034 (Western Cape) to 0.0075 ±0.0048
(KwaZulu-Natal). Overall, the mtDNA sequencing showed no evidence of major geographic
barriers to gene flow in this species. Samples collected throughout the core distribution of
poenskop showed high genetic diversity, no spatial genetic structure and no evidence of
isolation by distance.
Figure 4: Mean (± SD) distance moved (km) by size class (mm FL) for all recaptures in all
projects (n = 189). Sample sizes are presented above each bar.
Table 3: Mean (± SD) lengths (mm FL), length ranges, mean (± SD) ages (years) and age
ranges of poenskop recaptured within various distance bins (n = 189).
Distance
moved
(km)
Number
measured
Mean (± SD)
size (mm FL)
Size range Mean (± SD)
(mm FL)
ages (years)
Age range
(years)
0–1
165
377 (± 117)
220 – 920
5.9 (± 4.0)
1.2 – 34.2
> 1 – 10
9
414 (± 74)
307 – 526
6.7 (± 2.2)
3.7 – 10.2
> 10 – 100
8
388 (± 117)
250 – 579
6.1 (± 3.5)
2.3 – 12.2
> 100
7
650 (± 58)
562 - 740
14.85 (± 2.7)
11.6 – 19.8
Large-scale movements (> 100 km), in the Eastern Cape (n = 6) and KwaZulu-Natal (n = 1)
provinces, of up to 483 and 148 km, respectively, were only recorded in the ORI Tagging Project
(Fig 5). An estimation of home-range size indicated smaller poenskop to hold smaller homeranges at shallower depths, while larger poenskop hold larger home-ranges. Large easterly
displacements undertaken by a number of adult poenskop indicate the probability of this species
undertaking a unidirectional migration up the coastline of South Africa, settling in Transkei and
KZN waters for the remainder of their lives.
Figure 5: Long-distance movements (> 15 km) of recaptured poenskop along the South African
coastline recorded in the ORI Tagging Project. Arrows connect tagging and recapture locations.
Discussion
This study successfully addressed two research priorities for poenskop, namely an investigation
of its movement behaviour and genetic stock structure (Booth 2000). Analyses of the
mitochondrial DNA control region revealed that this species has a high level of haplotype- and
nucleotide diversity, and exists as a single, well-mixed population. The movement component
of the study revealed that poenskop exhibits a high degree of residency in both juvenile and
adult life-history stages. Results also suggested that large adult poenskop progressively migrate
up the coastline of South Africa to KwaZulu-Natal and Transkei waters (being found in the
highest numbers, and of a larger size, in these regions). Therefore, extensive mixing of the
population may result from the southward transport of eggs and larvae from KwaZulu-Natal and
Transkei waters to other reaches of the coastline. The presence of large adult poenskop in the
Western Cape (along the south-western coast of South Africa) could also suggest the possibility
of different spawning areas along the coast (even though the majority of poenskop move up
the coastline to Transkei and KwaZulu-Natal). The location of these areas will most likely take
advantage of the prevailing oceanographic currents, maximising transport of eggs and larvae to
areas of the coast with suitable rocky intertidal nursery habitat.
The effectiveness of particular management measures is dependent on patterns of exploitation
of individuals or populations. Poenskop is appreciably exploited in recreational fisheries with
no effort restrictions. Therefore, management measures need to be developed in order to afford
this species maximum protection. Conventional management tools include minimum size and
bag limits, gear restrictions, and closed seasons. However, these conventional management
measures will be biased, favouring the protection of the smaller poenskop, where the protection
of large adults (breeding-stock) is, arguably, more important. As poenskop have life-history
characteristics which make them vulnerable to overexploitation, no-take MPAs could be a useful
management tool for this species. MPAs will especially provide protection for resident juveniles
and sub-adults, allowing these fish to reach sexual maturity. The MPA network in South Africa is
already well-established and because MPAs are not single species management tools, other resident
reef species would also be afforded protection. Finally, due to its low importance in the commercial
sector, consideration should be given to de-commercialise this iconic recreational species.
References
Beckley LE, van Ballegooyen RC. 1992. Oceanographic conditions during three ichthyoplankton
surveys of the Agulhas Current in 1990/91. South African Journal of Marine Science 12: 83-93.
Bennett BA. 1990. Long-term trends in the catches by shore anglers in False Bay. Transactions of the
Royal Society of South Africa 47: 683-690.
Bennett BA, Attwood CG. 1993. Shore-angling catches in the De Hoop Nature Reserve, South Africa,
and further evidence for the protective value of marine reserves. South African Journal of
Biden CL. 1930. Sea-angling fishes of the Cape: A natural history of some of the principal fishes
caught by sea anglers and professional fishermen in Cape water. London: Oxford University
Press.
Booth AJ. 2000. Poenskop (Cymatoceps nasutus). In: Mann BQ (ed.) Southern African marine
linefish status reports. Oceanographic Research Institute Special Publication 7: 145-146.
Brouwer SL, Mann BQ, Lamberth SJ, Sauer WHH, Erasmus C. 1997. A survey of the South African
shore-angling fishery. South African Journal of Marine Science 18: 165-177.
Brouwer SL, Buxton CD. 2002. Catch and effort of the shore and skiboat linefisheries along the
South African Eastern Cape coast. South African Journal of Marine Science 24: 341-354.
comments on diet and reproduction. South African Journal of Marine Science 8: 57-65.
Coetzee PS, Baird D. 1981. Catch composition and catch per unit effort of anglers’ catches off St
Croix Island, Algoa Bay. South African Journal of Wildlife Research 11: 14-20.
Coetzee PS, Baird D, Tregoning C. 1989. Catch statistics and trends in the shore angling fishery of
the East coast, South Africa, for the period 1959-1982. South African Journal of Marine Science
8: 155-171.
Connell AD. 2010. A 21-year ichthyoplankton collection confirms sardine spawning in KwaZuluNatal waters. African Journal of Marine Science 32: 331-336.
Government Gazette No. 9543, 31 December 1984.
Cape Province: Snapshots of the 20th century. South African Journal of Marine Science 22:
81-110.
Griffiths MH, Lamberth SJ. 2002. Evaluating the marine recreational fishery in South Africa.
In: Pitcher TJ, Hollingworth C (eds), Recreational fisheries: ecological, economic and social
evaluation. Oxford: Blackwell Science. pp 227-251.
Hanekom N, Mann-Lang JB, Mann BQ, Carinus TVZ. 1997. Shore-angling catches in the
Tsitsikamma National Park, 1989-1995. Koedoe 40: 37-56.
Hecht T, Tilney RL. 1989. The Port Alfred fishery: A description and preliminary evaluation of a
commercial linefishery on the South African east coast. South African Journal of Marine Science
8: 103-117.
Hecht T, Buxton CD. 1993. Catch trends in the Transkei commercial linefishery. In: Beckley LE, van
der Elst RP (eds), Fish, Fishers and Fisheries. Proceedings of the second South Africa marine
linefish symposium, Durban, 23-24 October 1992. Oceanographic Research Institute, Durban.
ORI Special Publication 2: 127-133.
Hutton T, Pitcher TJ. 1998. Current directions in fisheries management policy: a perspective on
co-management and its application to South African fisheries. South African Journal of Marine
Science 19: 471-486.
Mann BQ, Scott GM, Mann-Lang JB, Brouwer SL, Lamberth SJ, Sauer WHH, Erasmus C. 1997. An
evaluation of participation in and management of the South African spearfishery. South African
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Penney AJ, Mann-Lang JB, van der Elst RP, Wilke CG. 1999. Long-term trends in catch and effort in
the KwaZulu-Natal nearshore linefisheries. South African Journal of Marine Science 21: 51-76.
Roberts MJ, van den Berg M. 2005. Currents along the Tsitsikamma coast, South Africa, and
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Are changing water temperatures in the Benguela
about to alter the evolutionary history of our
Argyrosomus fishes?
WM Potts1, R Heriques2, WHH Sauer1, CV Santos3 and P Shaw4
Department of Ichthyology and Fisheries Science, P.O. Box 94, Rhodes University,
2
Royal Holloway University of London, United Kingdom.
3
Department of Zoology, University of Agostinho Neto, Angola.
4
Institute of Biological, Environmental and Rural Sciences, University of Aberystwyth, Wales.
1
Introduction
Global hotspots of ocean warming are defined as areas where ocean temperatures are warming
at a rate faster than the global average (0.07˚C/decade, Burrows et al. 2011). These hotspots
are critical research areas because they are the first to show warming impacts and can be used
to test predictive models and provide testing grounds for adaptation strategies. The southern
Angolan coastal region has been recognised as a global hotspot with ocean temperatures
(between 1982 and 2009) warming at a rate of approximately 0.80˚C/decade (Munnick et al.
this volume, Potts et al. in prep). The primary consequence of ocean warming around the world
has been a poleward distributional shift of temperature sensitive fish species (Stebbing et al.
2002, Perry et al. 2005, Masuda 2008, Last et al. 2009).
Distributional shifts can be dramatic for a species; besides local extinctions these shifts can
result in alterations to growth, feeding, reproduction and migration patterns. Since not all
species respond to ocean warming in the same manner, ecosystem imbalances are extremely
likely. The loss of a key predator (such as A. coronus) in a core area of its current distribution
will have major implications down the food chain. In terms of fisheries, distributional shifts can
have major impacts on the catch rates of important fishery species, with obvious socio-economic
consequences. Furthermore, the stock assessment of species with shifting distributions provides
a significant challenge (Link et al. 2011). Managers who rely on assessments conducted on
shifting stocks, or species, are faced with considerable uncertainty, further complicating
the already difficult job of managing coastal resources. This is further exacerbated when the
distributional shifts of fishes are transboundary (Potts et al. in prep).
To date the evolutionary consequences of distributional shifts in fishes have been largely
ignored during the broader discussions of climate change and the emergence of predictive
models. Theoretically, distributional shifts may reunite previously isolated species and stocks.
If the isolation of these species is prezygotic, with species occupying different areas, then there
is potential for hybridisation, which in turn, may have significant evolutionary consequences,
positive or negative. For example, a positive response may accrue through the introduction of
novel genotypes promoting adaptability (Hoffman and Sgro 2011).
The genus Argyrosomus belongs to the family Sciaenidae. Fish in this genus are commonly
known as drums, croakers, meagre or kob, primarily inhabit coastal waters and are important
in coastal fisheries. There are four species of Argyrosomus fishes in the eastern Atlantic. Three
of these occur in southern Africa. A. coronus is distributed from northern Namibia to northern
Angola (Griffiths and Heemstra 1995), A. inodorus is distributed from northern Namibia to the
south coast of South Africa and A. japonicus from north east coast to the south western Cape
coast of South Africa.
Of the species in the southern Angolan coastal region, Argyrosomus coronus (Griffiths and
Heemstra 1995) appears to have undertaken the most dramatic southward distributional shift.
This was evidenced in a 58% reduction in the relative abundance and a 27% reduction in the
average length of the species in the recreational fishery, despite increased catches in the other
dominant species (Potts et al. in prep). This southward distributional shift has changed the
composition of the kob catch in Namibia. In 1995 the ratio of A. inodorus to A. coronus was
1.0:0.1 (Kirchner 1999) compared with 1.0:1.5 in 2009 (Potts et al. in prep.).
Due to the morphological similarity of A. coronus and A. inodorus, Potts et al. (2010) used a
molecular technique to validate their identification during a study of their life history in Angola
and Namibia. During this study allele’s characteristic of A. coronus were identified in a number
of individuals with the A. inodorus genotype. This suggested that the distributional shift may
have prompted recent hybridisation between the two species.
The aims of this study were to investigate potential hybridization between A. coronus and A.
inodorus and to consider the potential consequences of shifting distributions for the evolution of
this genus by comparing the phylogenetic patterns of the east Atlantic Argyrosomus species.
Materials and Methods
A total of 220 Argyrosomus genetic samples were collected from central and northern Namibia
and from southern, central and northern Angola for the hybridization investigation. A fin clip
was removed from each individual and fixed in 95% ethanol. DNA extraction was performed as
outlined by Sambrook et al. (1989). Polymerase Chain Reaction (PCR) was conducted for amplification
and two mitochondrial DNA regions, the Control Region (CR) and the cytochorme c oxidase I (COI) gene
region were sequenced using universal CR and COI primer pairs. Hybrid identification was based on
multilocus (6 microsatellite loci) assignment tests which were performed in STRUCTURE. The
Bayesian approach implemented in NewHybrids (Anderson & Thompson 2002) was used to
corroborate the results obtained in STRUCTURE.
A total of 25 genetic samples from the four east Atlantic Argyrosomus species from four
countries were used in the phylogenetic analysis (Table 1).
Table 1: Capture locations of the four east Atlantic Argyrosomus specimens used in the
phylogenetic study.
Species
Country
Region
n value
Coordinates
Argyrosomus regius
Portugal
Quarteria
3
37°3.346’N 8°6.43’W
Argyrosomus coronus
Argyrosomus coronus
Argyrosomus coronus
Angola
Angola
Namibia
Luanda
Flamingo
Hentiesbaai
2
4
4
8°47.263’S 13°14.32’E
15°10.374’S 12°04.863’E
22°7.404’S 14°16.139’E
Namibia
South Africa
Hentiesbaai
Port Alfred
4
4
22°7.404’S 14°16.139’E
33°36.500’S 26°54.00’E
Algoa Bay
4
33°49.53’S 25°52.31’E
Argyrosomus japonicus South Africa
Phylogenetic relationships within the Argyrosomus fishes were reconstructed by combining
information from the mtDNA CR and COI sequences with two further regions, mtDNA
cytochrome b (cytb) and the 1st intron of the nuclear ribosomal gene S7. Amplification and
sequencing of Cytb used the universal primer pair H16460 / GLUDLC following the original
protocols (Palumbi et al. 2002). Amplification of the S7 1st intron was obtained with newly
developed primers (Henriques 2011). Assessment of gene trees was conducted using the
Maximum Likelihood (ML) and Bayesian analysis (BA) inference methods. Time since
most common recent ancestor (tmrca) was estimated based on a species-level phylogeny, as
implemented in BEAST 1.3.1 (Drummond & Rambaut 2007) under a strict molecular clock. The
calibration of the molecular clock was performed by fixing the mean sequence divergence rate
per lineage at 1.5% per MY for the mtDNA dataset (considered the universal rate in marine fish
COI and cytb regions - Bermingham et al. 1997), and at 0.23% per MY for the nDNA dataset
(a value obtained from the divergence of Anisotremus spp. after the closure of the Isthmus of
Panama - Bernardi & Lape, 2005).
Results
Hybridisation
Five of the 180 A. coronus and three of the 40 A. inodorus individuals were identified as having
admixed origins using the STRUCTURE analysis (Fig 1). No F1or F2 hybrids were identified but
six of the eight hybrids were identified to be backcrosses with parental A. coronus. All of the hybrid
specimens were captured in central (Henties baai) and northern Namibia (Cunene mouth).
Phylogenetic patterns
Reconstruction of Argyrosomus spp. phylogenetic relationships retrieved identical topologies
for the Argyrosomus species independent of the inference method (ML or BA) and the
datasets (mtDNA or nDNA) used. All trees exhibited four clear, reciprocally monophyletic and
statistically well-supported clades, corresponding to the four identified kob species (Fig 2). Two
major clades could be identified corresponding to the northeastern Atlantic (A. regius) and the
southeastern Atlantic (Benguela Current species), suggesting that these taxa shared a common
ancestor in the past. Within the Benguela clade, A. inodorus appears to have diverged earlier
from a possible common ancestor, that later speciated into A. coronus and A. japonicus, which
appeared to be sister species (Fig 2).
Figure 1: Multilocus assignment tests performed in STRUCTURE for hybrid identification
based on 6 microsatellite loci: dark background indicates Argurosomus coronus genotypes, light
background indicates Argyrosomus inodorus genotypes. Dashed lines indicate probability of
assignment: q < 0.1 - pure A. coronus, q > 0.9 – pure A. inodorus, 0.1 < q > 0.9 – putative hybrid.
Figure 2: Reconstruction of phylogenetic relationships within Argyrosomus spp. using a
concantenated mtDNA-nDNA dataset. Statistical support for nodes is given for both Bayesian
and Maximum likelihood analysis. Outgroup = Cynoscion nebulosus.
The estimated time since the most recent ancestor (tmrca) showed similar patterns regardless
of the calibration method and dataset used. However, there was considerable variation in the
estimates of tmrca using the different methods. Divergence of northeastern / southeastern
Argyrosomus (A. regius) appears to have occurred between the late-Pliocene and early
Pleistocene (4 – 1.12 MYA). This was followed by two speciation events within the Benguela
Current region with divergence of A. inodorus in the early- to mid-Pleistocene (2.5 – 0.9 MYA),
and divergence of A. coronus and A. japonicus in the mid- to late- Pleistocene (0.9 - 0.1 MYA)
(Table 2).
Discussion
The timing of the evolution of the genus can provide some indication of the historical climate
patterns that have driven speciation events. In the east Atlantic Argyrosomus the separation
of the historical northeastern and southeastern populations (Figure 2, Table 2) is most
likely associated with historical glacial and interglacial periods. It is thought that the basal
Argyrosomus species may have originated either in the northern or southern hemisphere.
However additional Indian Ocean Argyrosomus species should be included in the analysis to
confirm the origin of Argyrosomus in the eastern Atlantic. This basal population is thought to
have been driven to the east Atlantic equatorial region by a glaciation event during the great
glaciations, just after the Pliocene epoch. It is thought that this population was subsequently
split into the northeastern and southeastern populations through rapid warming at the equator
during an interglacial period approximately 3.78 -1.68 mya.
Table 2: Estimates of the tempo of evolution of the eastern Atlantic Argyrosomus species. tmrca
– estimated time since most common ancestor (95% HPD in brackets).
mtDNA
nDNA
mtDNA-nDNA
Calibration
method
Northeastern
vs
Southeastern
A. inodorus
vs
A. coronus /
A. japonicus
A. coronus
vs
A. japonicus
1.5%
2.165
(1.85-2.47)
2.038
(1.74-2.33)
1.277
(1.04-1.53)
2 MY
1.617
(0.31-3.37)
1.542
(0.28-3.17)
0.965
(0.16-2.03)
0.26%
4.365
(2.65-6.34)
3.326
(1.98-4.78)
2.298
(1.25-3.41)
2 MY
1.127
(0.12-3.26)
0.869
(0.1-2.48)
0.586
(0.07-1.75)
1.5%
1.849
(1.59-2.13)
1.743
(1.49-2.01)
1.097
(0.90-1.32)
2 MY
1.045
(0.15-2.77)
0.989
(0.14-2.62)
0.617
(0.9-1.65)
Two more speciation events occurred within the southeastern African Argyrosomus population.
Argyrosomus inodorus speciated from the coastal Argyrosomus species. This is thought to have
been a sympatric speciation event with the cooler water tolerant individuals in the population
began spawning in separate grounds from the warmer water individuals. This isolation event is
thought to have occurred in the early – mid Pleistocene (2.41 -1.33 mya).
The final speciation event in the eastern Atlantic is thought to have been an allopatric isolation
of the warm water tolerant coastal Argyrosomus species into what are now A. japonicus and A.
coronus. This separation is thought to have been driven by the formation of the cold Benguela
Current in the mid – late Pleistocene (2.19 -0.93 mya).
The distribution of Argyrosomus coronus in Namibia was described by Griffiths and Heemstra
(1995) as confined to a narrow zone along the central and northern coasts. Until recently
(early 1990’s) the A. coronus population in this area has been comprised of juveniles and subadult specimens (Griffiths and Heemstra 1995). Adult A. coronus were distributed between
the Cunene River mouth and northern Angola and undertake an annual temperature driven
migration to the northern part of their distribution in the austral winter. However, relative
abundance, size frequency and genetic information has indicated a recent southward shift
of the migrating adult A. coronus (Potts et al. in prep). This situation has led to two possible
hybridisation scenarios. Firstly, the spawning grounds of the adult A. coronus may have shifted
southward into the distribution of A. inodorus. Secondly, the migration of at least a proportion
of the adult A. coronus may now have moved southward to Meob Bay, the spawning grounds of
A. inodorus.
The results of the phylogenetic study suggest that the evolution of this genus in the eastern
Atlantic was a slow process and although closely related, Argyrosomus coronus and A. inodorus
have been evolving separately for the last ~2 MY. However, climate induced distributional
shifts can bring species previously isolated species into contact (Hill et al. 2011; Lo Brutto et al.
2011). If the species have not yet evolved postzygotic isolation mechanisms, and lost the ability
to produce fertile offspring, there is potential for hybridisation. The presence of hybrid fishes
suggests that the isolation of A. inodorus and A. coronus is prezygotic, which implies that adults
of the two species need only to be together during spawning periods for hybridisation to occur.
In addition, the presence of backcrossed individuals suggests that these hybrids are viable and
thus these two species may now be subject to rapid evolutionary change. As far as we are aware
this study provides the first evidence for climate driven hybridisation in coastal marine fishes.
Besides altering the evolution of the genus, hybridisation can have a major impact on the life
history of a species. Life history and physiological traits of the hybrids may either be similar
to one of the parental species, within the range of the parent species or out of the range of the
parent species (Chevassus 1983). Thus continued monitoring of the proportion of hybrids in
Namibia and Angola and both biological and physiological studies on these animals are required
to determine the consequences for fisheries and to propose mitigative management strategies.
One potential benefit of hybridisation may be the introduction of novel genotypes into
populations. This may provide organisms with additional opportunities to adapt to the
additional selection pressures. Ultimately, this may contribute to species adapting to rapid
climate change (Hoffman and Sgró 2011).
In terms of South African Argyrosomus, this study has shown that the isolation of the
Argyrosomus fishes remains prezygotic. Therefore, if climate change drives adults from one
species into the spawning grounds of another, hybridisation can occur. Presently, the most
likely of these scenarios may be the hybridisation of A. japonicus with A. coronus. Specimens
of A. coronus have been reported on the west coast of South Africa, including St Helena
Bay (Lamberth et al 2008) and adult specimens are captured fairly regularly by anglers at
Dwarskersbos. A further southward movement of these specimens will reunite the sister species
and may also result in hybridisation.
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Identification of a warming hotspot in the northern
Benguela, and the possible effects of this on
Argyrosomus coronus
Munnik K1, 2, Potts WM3, Ansorge I1, Sauer WHH3
Department of Oceanography, University of Cape Town, Private Bag, Ronderbosch, 7700, South Africa.
2
Marine Research Institute, University of Cape Town, Private Bag, Ronderbosch, 7700, South Africa.
3
Department of Ichthyology and Fisheries Science, Rhodes University
1
Abstract
Seasonal migrations are undertaken by Argyrosomus coronus (west coast dusky kob) in
avoidance of pulses of tropical Angolan Current water into the northern Benguela. This, together
with evidence of temperature related evolution, suggests that this species exhibits a relatively
narrow thermal tolerance. However, a lack of comprehensive oceanographic datasets in the
region makes monitoring of this species in relation to environmental parameters difficult. A
spatial and temporal solution to temperature monitoring was found in satellite derived sea
surface temperature estimates. Moderate-Resolution Imaging Spectroradiometer (MODIS)
data was compared to in situ temperature data collected at Flamingo Lodge, southern Angola
with the Aqua and Terra products showing a 0.8°C and 0.7°C over estimate respectively.
Using MODIS Terra SST data an inshore linear warming trend of up to 1.5°C/decade (20002010) above the global average (0.07°C/decade) has been found in the northern reaches of A.
coronus’ distribution, identifying this area as a warming hotspot. This warming trend, coupled
with amplifications of the seasonal warm water intrusion into the region (Benguela Niños),
may explain the discovery of A. coronus individuals in the southern Benguela. If such trends
continue, it is expected that this species may undergo a southerly distribution shift and become
targeted by the already well established recreational kob fishery in northern Namibia.
Introduction
The oceans are warming globally, at a rate of 0.07°C per decade (Burrows et al. 2011). This
threatens many fish species which, as poikilotherms have evolved to tolerate a limited
temperature range. The physiological processes of poikilotherms have evolved to function
optimally within a specific environmental temperature regime and as a result these organisms
are unable to function efficiently outside of their tolerable temperature range (Helfman et al.
2009). When a fish is exposed to temperatures above its thermal tolerance limit, it experiences
among other physiological changes, an elevated metabolism increases oxygen demand. In a
warming ocean this problem is confounded, as the solubility of oxygen decreases with increasing
temperature, limiting the amount of oxygen available for metabolism (Pörtner and Knust 2007).
Fish must, therefore, move away from unfavourable conditions such as increased temperatures,
or face eventual mortality.
This study aimed to determine the extent of environmental change in the inshore region of the
Angola-Benguela frontal zone (ABFZ) and predict the impact of this change on the distribution
of the west coast dusky kob A. coronus.
Any responses to temperature changes by A. coronus in the region could only be assessed once
the optimum temperature range of this species had been identified. Catch per unit effort (CPUE)
data from Flamingo Lodge, southern Angola (2005 – 2009), in conjunction with daily MODIS
Aqua and Terra satellite imagery was analysed to identify inshore temperatures on occasions
when CPUE was greater than 0.01 fish.anglerhour-1 . For the west coast dusky kob, the optimum
temperature range was considered to be 16-22°C. The optimum ranges of salinity and dissolved
oxygen were to be identified. However, due to the lack of in situ data available for these
parameters, modelled monthly data was used as rough estimates.
A warming hotspot in the northern Benguela
Temperature changes in the northern Benguela over the past 25 years were investigated using
corrected satellite sea surface temperature (SST) retrieval data. A linear trend of ~0.6°C.decade-1
was found to have occurred between 1985 and 2009 in the Angola-Benguela frontal zone in
particular and this trend was found to have increased to >0.8°C for the last decade. The majority
of the northern Benguela region has experienced warming at a much faster rate than the global
mean (0.07°C.decade1) over the last decade (Fig 1). Furthermore, two inshore (<200m depth)
hotspots of localised warming were identified at 15.5-17°S and 18.5-20°S where the linear trend
of warming over the last decade (2000-2010) was found to be significant at the 90-95% level.
Figure 1: Linear warming trend in the northern Benguela using (a) Pathfinder (1985-2009) 4x4
km resolution, (b) MODIS Terra (200-2010) 4x4 km resolution and MODIS Terra (2000-2010)
2x2 km resolution data.
Warming hotspots are areas where warming rates are greater than the global mean. Organisms
become stressed in these regions and their responses could be used to predict biological
responses in regions where warming is currently slower. The described warming trends were
investigated further through analysis of the surface expression of the 20 and 22 °C isotherms
(Fig 2). The 22°C isotherm is considered to be the upper limit of the optimum thermal tolerance
range for A. coronus and thus could indicate the northern limit of its distribution in the region.
Although the seasonal temperature cycle of the ABFZ is clear, both the 20 and 22°C isotherms
appear to have shifted slightly southwards between 1985 and 2009 (Fig 2). An increase in the
southerly influence of warm events and their residence time is evident.
Figure 2: The annually averaged location of the 20 and 22°C isotherms between 15 and 20 °S
along 11.58°E measured using Pathfinder (1985-2009) 4x4 km resolution data. The extreme
nature of the 1995 Benguela Nino is also evident in this image.
The warming trends observed over the last decade (2000-2010) are likely to be the caused by
decadal variability in the region. However the existence of a significant linear warming trend
over a 25 year period indicated that the recent warming in the northern Benguela may be related
to more than just decadal variability and may persist into the future. The localised warming in
the ABFZ region is thought to be caused by an increase in the residence time of the seasonal
intrusions by Angola Current water into the region. This is brought about by a decadal scale trend
in weakened upwelling in the central Benguela (Hutchings et al. 2009). These warming trends
(and their persistence) pose a threat to the temperate biota of the region and may result in a shift
of organisms to cooler waters at higher latitudes, which has been observed in other temperate
regions of the world (Parmesan and Yohe 2003, Parmesan 2006, Burrows et al. 2011).
The response of west coast dusky kob
Due to the thermal stability of water, warming generally occurs relatively slowly and organisms
have time to adapt. Shifts in the distributional ranges of marine organisms have been observed
in response to extreme warming events as well as general warming trends in temperate regions
(Parmesan and Yohe 2003, Parmesan 2006, Pörtner and Knust 2007, Hutchings et al. 2009,
Burrows et al. 2011). This has been especially apparent in pelagic species, or species with pelagic
larval stages, and these species are expected to undergo further distributional variations in the
future (Harley et al. 2006).
A. coronus has shown signs of a potential distribution shift in recent years. Between 2005 and
2010 the CPUE for A. coronus at the Flamingo Lodge study site, southern Angola, decreased
while that of other important fishery species in the region (shad Pomatomus saltatrix and
leervis Lichia amia) has increased (Fig 3). Furthermore, wet coast dusky kob experienced a 27%
reduction in average length between 2005 and 2009, and it seems that the adult portion of the
population has largely disappeared compared to the local populations of shad and leervis. The
potential distributional shift is also evident in genetic results. In 1995 a study was carried out in
northern Namibia and southern Angola where 100% of the kob caught in southern Angola were
identified as A. coronus while this species only represented 10% of the kob caught in northern
Namibia. The other 90% of the catch was made up of A. inodorus (silver kob) individuals.
However, when the study was repeated in 2009, although A. coronus still comprised 100% of
the southern Angola kob catch, they now represented 60% of the northern Namibian kob catch.
This evidence confirms that we expect this species to follow its optimum temperature range and
move south.
Figure 3: Catch per unit effort (CPUE) data for west coast dusky kob (A.coronus), leervis
(Lichia amia) and shad (Pomatomus saltatrix) between 2005 and 2010 at Flamingo Lodge,
southern Angola. A dramatic decrease in the CPUE of .A.coronus is evident.
If warming trends in the region continue at the present rates, and this species continues to
shift southwards, current management strategies for Argyrosomus coronus would need to
be adapted to encompass the expected changes in the species distribution. The vulnerability
of a species generally increases if it undergoes a range contraction (Parmesan 2006), as its
catchability may increase. This is particularly relevant in the case of the west coast dusky kob as
a southerly range shift and possible range contraction (associated with strengthened upwelling
at Luderitz) would concentrate this species in central and northern Namibia. This is a region
known for its well established recreational fisheries (Kirchner 1998) and A. coronus will likely
be caught in these fisheries. The Skeleton Coast National Park (17.5-21.1°S) in Namibia however,
could provide some protection from fishing pressure unless the population shift extends further
south of 22°S. On a positive note, the large size attained by the west coast dusky kob (max
77kg, common to 50kg) (Griffiths and Heemstra 1995), when compared with the Namibian
kob species, the silver kob (Argyrosomus inodorus) (max 36.5kg, common to 15kg) (Griffiths
and Heemstra 1995) will provide the recreational fishery of northern and central Namibia with
a major boost. The Namibian recreational fishery is extremely important for the economy of
coastal communities (Stage and Kirchner 2005) thus it is critical that a new resource such
as this is well managed to maximise its long-term benefit. The required management plan
is complicated by the extremely similar morphological characteristics of the two kob species
and the vastly different life histories. For example, A. coronus matures at approximately 90
cm (Potts et al. 2010) compared with 40 cm (Griffiths and Heemstra 1995) for A. inodorus.
Therefore, future management plans must recognise the potential of the A. coronus resource
and will need to incorporate the seasonal trends in relative dominance of the two species. For
example, the west coast dusky kob may be the dominant species during the summer and autumn
months and fishery regulations should be designed towards this species during that time. This
will ensure that A. coronus is protected when it is dominant in the Namibian fishery.
Unfortunately, Namibia’s gain is southern Angola’s loss and a southerly shift in the distribution
of A. coronus will negatively impact the artisanal fishery for this species in southern Angola
(Potts et al. 2010). In addition, continued warming in the region could lead to similar spatial
distribution shifts of other important fishery species in the future. Coastal communities and
local economies would then suffer from a decrease in abundance of economically important
fisheries resources. It is recommended that experimental fishing for tropical species be initiated
in this area, to ensure that communities can quickly respond to the arrival of new fisheries
resources from the north.
Conclusions
The results of this study suggest that if current warming trends in the ABFZ region continue,
the spatial distribution of A. coronus will shift southwards into northern and central Namibia.
This would result in this species becoming targeted in the recreational fisheries of Namibia,
and would require major changes to existing management plans if new kob resource was to
be protected. It was demonstrated that the approximate changes in spatial distribution of this
species can be assessed using satellite derived SST information. These movements can then be
incorporated into management plans for the west coast dusky kob to ensure its protection in the
heavily fished Namibian waters.
However this approach relies on the accurate determination of the optimum temperature
range of the species, which is only possible if accurate CPUE and in situ water temperature
data are available. This study, therefore, recommends the installation of temperature loggers at
strategic positions along the Angolan and Namibian coasts, followed by the addition of dissolved
oxygen and salinity sensors onto the same mooring. The installation of temperature loggers
at strategic locations along the coast, corresponding with sites of ongoing CPUE monitoring
would benefit studies such as this one where in situ oceanographic data is limited. Temperature
loggers can be placed in the water column on a permanent basis and remotely relay data to a
laboratory computer. The loggers can be set to specific satellite overpass times to encourage a
direct comparison between locally observed sea surface temperatures and those derived from
satellite sensors. This would improve the correction factors applied to satellite data used here
and thus enable a more accurate understanding of surface temperature variability in the region.
Temperature loggers also allow for the monitoring of temperature change with depth, and
could shed light on the characteristics of warming events which are too thought to increase if
the identified warming of the northern Benguela continues. Information collected using this
equipment would significantly contribute to our understanding of the ecology of the northern
Benguela. Without this, resource managers in the northern Benguela would not be able to plan
for future scenarios of marine resource abundance and spatial distribution changes. This could
lead to unsustainable exploitation of these resources and significant socioeconomic problems in
the region.
Studies such as this one demonstrate the applicability of satellite data to marine resource
management. As the global oceans continue to undergo major temperature changes
in response to our changing climate, many marine species are expected to shift their
distributional ranges. Methodologies similar to the one used in this study could describe these
changes in spatial distribution and could be applied to a range of different species to ensure
their successful management.
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thermal tolerance. Science 315:95–97.
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Session 8 – Fish Movement Studies: Chair Tor Næsje
The genetic stock structure of slinger (Chrysoblephus
puniceus) in the South West Indian Ocean
Murray Duncan1, Monica Mwale2, Sean Fennessey3
Rhodes University, PO Box 94, Grahamstown 6140, South Africa.
2
South African Institute of Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South
Africa.
3
Oceanographic Research Institute, PO Box 10712, Marine Parade 4056, Durban, South Africa.
1
Introduction
The slinger, Chrysoblephus puniceus, a seabream of the family Sparidae, is one of the most
important linefish species in South Africa and Mozambique (Garratt 1985, Lichucha 1999). It
contributes between 31 – 34% to the commercial line fishery catch in KwaZulu-Natal (Lamberth
et al. 2009), and about 40% to the semi-industrial linefish catch in southern Mozambique
(Instituto de Investigacao Pesqueira, unpubl. data). C. puniceus is endemic to South Africa and
Mozambique with its core distribution stretching from Vilankulos in southern Mozambique
to the Transkei in South Africa (Garratt 1985). Like most sparids, C. puniceus is a relatively
slow-growing protogynous hermaphrodite, which makes it more susceptible to fishing pressure
(Garratt et al. 1993, Garratt 1986). Despite its fisheries importance, very little is known about C.
puniceus’ genetic stock structure, larval dispersal and migration.
Concern over decreasing C. puniceus catch trends in the 1990s led to stock assessments based
on per-recruit analysis in South Africa (Punt et al. 1993) and Mozambique (Lichucha 2001),
both of which indicated that stocks were overexploited; the former authors also noted the
possible dependence of South African stocks on recruitment from Mozambique. These stock
assessments helped contribute to the minister’s declaration of a crisis in the South African
linefishery in 2000. In South Africa, management tools such as the declaration of additional
Marine Protected Areas and a reduction in commercial fishing effort were enforced to rebuild
linefish stocks. Although these assessments are currently being updated, the degree to which
South Africa and Mozambique share this stock needs to be investigated. An understanding of
the genetic diversity and isolation among C. puniceus populations is imperative for the better
management of the species since the resource may be a trans-boundary stock shared between
South Africa and Mozambique. Garratt (1985) and Punt et al. (1993), suggest that larvae drift
from north to south, with a return migration of fish from the south to the north.
A first step would therefore be to establish the degree to which populations of C. puniceus
in South Africa and Mozambique are genetically isolated. Population genetic methods
offer different tools for identifying, classifying and investigating stock structure at both the
population and stock level (Shaklee et al. 1999; Oosthuizen et al. 2004; Teske et al. 2010).
Genetic studies can advise management decisions through the estimation of the genetic
variation of a species over time, the historical changes in stock structure, annual recruitment
success as well as the patterns of dispersal and connectivity of larvae and adults among areas
(Shaklee et al. 1999; Chow et al. 2000; von der Heyden et al. 2007). Such studies can form the
basis, or reference point, for future stock assessment studies on C. puniceus when combined
with traditional approaches such as CPUE and per recruit data.
The aim of this study was therefore to provide an assessment of the genetic structure,
connectivity and levels of variability throughout C. puniceus’ range. The provision of this
information can complement ongoing stock assessments and be integrated into marine
biodiversity conservation planning and the management of exploited resources.
Genetic tissue samples were collected at sampling locations throughout the distributional range
of C. puniceus, stored in 90% alcohol and grouped based on geographic proximity for analysis
(Table 1). Genetic material was extracted using the commercially available Wizard® Genomic
DNA purification kit as per the manufacturer’s instructions (Promega, USA). One mitochondrial
gene region (Control region) and 10 microsatellite loci were selected for amplification through
polymerase chain reaction (PCR). Processing of control region primers and PCR conditions
followed Teske et al. (2010), while Processing of microsatellite primers and PCR conditions
followed Chopelet et al. (2009). PCR product purification and sequencing was done through a
commercial sequencing facility (Macrogen inc., Korea).
Table 1: Sampling location, number of samples per location and geographic grouping.
Location
Number
Group
Ponta de Barra
36
1
Ponta Zavora
30
2
Quissico
16
2
Xai Xai
30
3
Bilene
6
3
Inhaca
30
4
Ponta do Ouro
30
5
Richards Bay
40
6
Shelly Beach
30
7
Rocky Bay
15
7
Pondoland MPA
31
8
Southern Transkei
8
9
Control region sequence chromatograms were cleaned in Chromas lite v2.01 (Technelysium
Pty Ltd) and aligned in Seqman proTM (DnaStar). Summary statistics of aligned sequences were
calculated in DnaSPv5 (Librado and Rozas 2009). Analysis of molecular variance (AMOVA) and
pairwise (FST) population comparisons were done in Arlequin 3.5 (Excoffier and Lischer 2009). A
median joining haplotype network was calculated in network 4.6 (Fluxus Technology Ltd). Spatial
analysis of molecular variance (SAMOVA) was calculated in SAMOVA 1.0 (Dupanloup et al. 2002).
A mantel test for isolation by distance was done in IBDWS 3.23 (Jensen et al. 2005).
Microsatellite scoring was done using Genemarker ver 2.2.0 (Softgenetcis® LLC). AMOVA and
pairwise (RST) population comparisons were estimated in Arlequin 3.5 (Excoffier and Lischer
2009). SAMOVA and Mantel tests followed the procedure used for the Control region data set. A
structure analysis was done using Structure 2.3.3 (Pritchard et al. 2000) and negative ln likelihood
means for each possible number of populations were analysed in Statistica ver 10 (Statsoft).
Results
A 944 base pair (bp) sequence was obtained for the Control region from 282 viable samples.
The 944 bp sequence set had a large haplotype diversity (0.99) which made statistical analysis
difficult. A shorter, more conserved region consisting of the first 270 bp was subsequently
selected for analysis as the haplotype diversity was reduced to 0.86, enabling greater statistical
rigour. From the microsatellite data 300 viable samples were obtained with 10 polymorphic loci.
Pairwise FST population comparison P-values for both the 944bp and 270bp samples showed
no significant difference (P > 0.05) between sampling localities except for some fine scale
structuring between Xai Xai versus Ponta do Ouro and Richards Bay, and between Inhaca
and three localities (Ponta de Barra, Quissico and Richards Bay). Pairwise RST population
comparison P-values showed no significant difference (P > 0.05) between localities except
between Shelly Beach and Ponta de Barra.
AMOVA for both Control region sequence sets and microsatellite data showed no significant
differences at any hierarchical level, with close to 100% of the variance being explained within
populations and within individuals respectively. SAMOVA analysis found no groupings that
had significant differences or which had a possible biological basis. A median joining haplotype
network for the 270bp Control region sequence indicated a single panmictic stock.
Isolation by distance mantel tests showed no significance (P > 0.05) for either the 270 bp
Control region sequence set or the microsatellite data, with weak R2 values of 0.017 and 0.004
respectively. The structure analysis based on mean negative ln likelihoods showed a significantly
higher probability (Kruskal-Wallace ANOVA, P < 0.05) of their being one population
throughout the distribution of C. puniceus, rather than multiple populations.
Conclusions and Discussion
The extreme variability of the mitochondrial control region makes it an unsuitable marker for
population genetic studies on C. puniceus and other sparids in this genus (Teske et al. 2010).
This variability was also observed in swordfish, Xiphius gladius, population genetic studies
(Rosel and Block 1996, Alvarado Bremer et al. 1996), resulting in a shorter more conserved
region of the gene being considered. Bradman et al. (2011) compared the Control region to ND2
for X. gladius population studies and found that the slower-evolving ND2 defined more genetic
structure. These results and the findings of this study suggest that the control region should not
be used when doing population genetic studies.
Microsatellite data provided strong evidence that C. puniceus exists as a single, well-mixed
stock through its distribution and can thus be considered a single trans-boundary stock. The
lack of genetic differentiation throughout C. puniceus’ distribution is in accordance with other
population genetic studies on endemic sparids of southern Africa. Roman, Chrysoblephus
laticeps (Teske et al. 2010), and Cape stumpnose, Rhabdosargus holubi (Oosthuizen 2006),
both were found to show genetic homogeneity throughout their distribution. It is believed that
the broadcast spawning and long larval phase of some marine species contributes to low levels
of genetic differentiation (Grant and Bowen 1998).
The prevailing North to South flow of the Mozambique and Agulhas Currents, in combination
with southward-migrating Mozambique Channel eddies and shelf currents passing through C.
puniceus habitat are likely to facilitate southward larval dispersal. One would therefore expect
a genetic isolation by distance with higher genetic variability in the southern region compared
to the northern region, which is not the case. It is therefore likely that there is a return northern
migration of at least part of the population at some point in their life history, as hypothesized by
Garratt (1985). Limited tagging studies have indicated that adult C. puniceus are fairly resident
(Garratt 1993, Maggs 2011) suggesting that it is most likely juvenile fish that move northwards.
The indication that C. puniceus exists as a single trans-boundary stock in Mozambique and
South Africa is a cause for concern if the management strategies in the two countries are not
aligned. Punt et al. (1993) suggested that the relative lack of fishing effort in Mozambique at
that time may be masking the effects of overexploitation in South Africa. Fishing effort in the
southern Mozambique linefishery has increased markedly since the mid 1990’s (Lichucha
1999) which is likely to have affected catches in the South African linefishery for C. puniceus by
reducing recruitment. Increased recruitment into the fishery through MPA networks such as the
St Lucia Marine Reserve and the Ponta do Ouro Partial Marine Reserve, protecting spawning
adults, thus becomes increasingly important. Catch data and trends from Mozambique should
be investigated as they would likely add value to South African assessments, providing a more
holistic view of the fishery and could assist in interpreting catch trends in the South African
linefishery for C. puniceus.
Acknowledgements
SWIOFP, DAAD and WIOMSA for funding. Bruce Mann and Rui Jorge Mutombene for samples.
Rhett Bennett for help with microsatellite analyses.
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sparids Chrysoblephus puniceus and Cheimerius nufar. Investigational Report 62. Durban:
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fishes: insights from Sardines and Anchovies and lessons for conservation. The Journal of
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Arniston, Western Cape: SANCOR Occasional Report Series 5.
Lichucha I. 2001. Management of the linefish resource in Southern Mozambique: A case study for
Marreco (Chrysoblephus puniceus). MSc Thesis, University of Kwa-Zulu Natal, South Africa.
Maggs JQ. 2011. Fish surveys in exploited and protected areas of the Pondoland marine protected
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Does the restricted movement paradigm apply to the
estuarine-dependent spotted grunter Pomadasys
commersonnii?
PD Cowley1, TF Næsje2, A-R Childs1, RH Bennett1, EB Thorstad2, CM Chittenden3 and R Hedger2
1
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown, South Africa.
2
Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen, NO-7485 Trondheim, Norway.
3
Department of Arctic and Marine Biology, University of Tromsø, NO-9037 Tromsø, Norway.
Introduction
Movement studies are necessary to gain information on the spatial and temporal distribution of
fishes, which, in turn, is important for the identification of appropriate management measures
for fishery species. In South Africa, studies conducted on the movement patterns of inshore
coastal fishery species have revealed the dominance of restricted movement (resident/station
keeping) behaviour and highlighted the importance of no-take marine protected areas (MPAs)
(e.g. Cowley 1999; Cowley et al. 2002; Attwood and Cowley 2005; Kerwath et al. 2009; WattPringle 2009; Bennett et al. 2012). The benefits of station keeping behaviour are apparent,
particularly for reef-associated species, as knowledge of a small home range area with fixed
structures and resources allows for efficient refuge from predators and foraging (Eristhee and
Oxenford 2001). However, not all coastal environments offer the same degree of uniformity
in terms of habitats and physico-chemical conditions. For example, estuaries are subject to
tidally-driven changes in salinity, temperature and turbidity. These rhythmic and sometimes
abrupt changes in environmental conditions can place considerable physiological demands on
station keeping fishes that reside in estuaries, forcing them to undertake movements to decrease
stresses associated with unfavourable environmental conditions. Indeed this “riding the tide”
behaviour has been observed in several estuarine-associated species (e.g. Almeida 1996; Hartill
et al. 2003), including the local dusky kob Argyrosomus japonicus (Næsje et al. 2012).
In recent years, acoustic telemetry has been used to study the behaviour of several important
coastal fishery species. In particular, the spotted grunter Pomadasys commersonnii has
received considerable attention. Research conducted on the Great Fish Estuary investigated the
movements, space use patterns, home range parameters, influence of environmental parameters
and vulnerability to exploitation (Næsje et al. 2007, Childs et al. 2008a,b,c). Similarly, studies
conducted in the intermittently open East Kleinemonde Estuary examined movement patterns,
home range dynamics and space use patterns in relation to prey abundance (Kerwath et al.
2005, O’Connell 2008, O’Connell et al. in prep.). The motivation for this research attention was
based on the findings of roving creel surveys conducted on numerous estuarine systems, which
revealed that the spotted grunter is one of the most targeted estuarine fish species. These fishery
surveys also revealed that the majority of fish captured were retained and many were below
the legal size limit (e.g. Cowley et al. 2004, Potts et al. 2004). This lack of compliance indicates
that there is a need for assessment of alternative management measures, such as no-take area
closures. To date, acoustic telemetry studies on the juvenile spotted grunter (e.g. Childs et al.
2008b) have provided empirical evidence that they display restricted movements during their
estuarine-dependent phase. However, little is known about the movement patterns of adults.
This study aimed to investigate estuarine residency, dispersal and movements of sub-adult and
adult spotted grunter between estuaries and coastal areas using a regional network of acoustic
receivers. Of particular interest was to identify a synchronized, collective movement away from
the array of estuarine receivers, indicative of a spawning migration. A minimum of two acoustic
receivers was deployed in eight neighbouring estuaries, spanning 271 km of coastline (Figure
1). The two ports within Algoa Bay (Port Elizabeth Harbour and Port of Ngqura) were also
equipped with acoustic receivers. A total of 26 fish were tagged with one-year lifespan acoustic
transmitters (Vemco V13) in the Kariega (n = 17) and Bushmans (n = 9) estuaries.
Estuarine residency and habitat connectivity
The mean observation period (confirmed by receiver detections) for fish tagged in the Kariega
and Bushmans estuaries was 417 and 328 days, respectively. On average, the fish tagged in the
Kariega estuary spent 57% of their time in their home estuary, 29% of their time at sea and 14%
of their time in other monitored estuaries (Fig 2). In contrast, the fish tagged in the Bushmans
Estuary (n = 9) spent 88%, 11% and 1% of their time in their home estuary, at sea and in other
estuaries, respectively (Fig 3).
Figure 1: Map of the study area showing the eight estuaries and two ports that were equipped
with acoustic receivers (numbers represent the number of acoustic receivers in each system).
Fish were tagged in the Kariega (n = 17) and Bushmans (n = 9) estuaries
Figure 2: Proportion of time spent in different environments by 17 spotted grunter tagged in
the Kariega Estuary. Stippled bars = time spent in home estuary, black bars = time spent in
other estuaries and grey bars = time spent at sea. Arrow indicates 24 December 2008
Figure 3: Proportion of time spent in different environments by nine spotted grunter tagged in
the Bushmans Estuary. Stippled bars = time spent in home estuary, black bars = time spent in
other estuaries and grey bars = time spent at sea. Arrow indicates 24 June 2009
Most of the fish (n = 12) tagged in the Kariega Estuary went to sea and re-entered estuarine
habitats, of which nine returned to their home estuary (Kariega), seven went into the
neighbouring Bushmans Estuary (2 km away), six entered the Kowie Estuary (22 km away),
two went into the Great Fish Estuary (49 km away), three went into the Sundays Estuary (82
km away) and seven entered Swartkops Estuary (109 km away). No tagged fish were recorded
in the ports in Algoa Bay or the two estuaries furthest away (Gamtoos - 196 km and Kromme
- 225 km). Of the fish tagged in the Bushmans estuary, all went to sea but only two were
recorded elsewhere, both in the nearby Kowie Estuary (24 km away). Observations on the wide
ranging behaviour and visits to other estuaries once leaving their home estuary were made
possible by the expanded telemetry network that covered sheltered habitats along 271 km of
coastline. However, it was possible that the tagged individuals moved further afield or entered
other unmonitored estuaries, but considering that none of the tagged fish entered the furthest
estuaries monitored, it is proposed that the findings are representative of the level of habitat
connectivity displayed by the tagged fish.
Estuarine movements
The Kariega Estuary was equipped with 16 acoustic receivers to monitor the movements of
tagged fish (n = 17) within the system. All tagged fish remained resident in one portion of
the estuary that corresponded with their capture and release site, for the duration of their
monitored estuarine residency periods (mean = 92% of their time; range 8-100%). This pattern
is in agreement with earlier studies conducted in the Great Fish Estuary (Næsje et al. 2007,
Childs et al. 2008a,b) and the East Kleinemonde Estuary (Kerwath et al. 2005; O’Connell
2008; O’Connell et al. in prep.). In all cases tagged spotted grunter exhibited station keeping
behaviour, with few up- and down-estuary movements, and maintained small home ranges
relative to the size of the estuary.
Spawning migration
The extended estuarine residency period displayed by four individuals that remained in the
Kariega Estuary (mean = 419 days; range = 331 - 547) suggests that some individuals do not
undertake annual spawning migrations to sea. Despite the ability to migrate to known spawning
areas in KwaZulu-Natal (Wallace 1975a,b; Connell 1996) without being detected by the receiver
array, there was no evidence of a synchronous collective departure with an absence period long
enough to confirm such a migration. However, two collective seaward emigrations were observed.
In December 2008, eight of the 15 tagged fish still present in the Kariega Estuary went to sea, of
which four never returned (Fig 2). Similarly, all eight tagged fish still present in the Bushmans
Estuary made a short sea trip in June 2009 (Fig 3). Initially, it was thought that these seawards
migrations (particularly the former) could be attributed to spawning activity. However, upon
further investigation these events were ascribed to some instinctive behaviour in response
to extreme weather conditions. On 24 December 2008 and 24 June 2009, the south eastern
seaboard of South Africa experienced some of the roughest seas and sharpest drops barometric
pressure ever recorded (South African Weather Services; Cowley et al. unpublished data).
Considering that reproductively active (ripe or ripe running) spotted grunter have not been
reported from the south east coast of South Africa, Webb (2002) proposed that they migrate
to KwaZulu-Natal to spawn. However, this suggestion is not supported by unpublished tagging
data collected by the Oceanographic Research Institute’s national tagging project, which
revealed that only 2% of recaptured fish moved more than 100km, while 95% of the recaptures
were made within 3.5 km of where they were tagged. The conventional tagging data provide
supportive evidence of the findings of this study.
Conclusion
The results indicate that while sub-adult and adult spotted grunter display high levels of
connectivity between estuarine and marine environments, they do conform to the restricted
movement paradigm and display a high degree of site fidelity within estuarine environments,
thereby highlighting the dependence of this species on estuarine habitats throughout ontogeny.
Fisheries and environmental management authorities need to be aware of the implication
of these findings to ensure corrective management of this important fisheries species.
Furthermore, aspects of the reproductive biology and spawning of spotted grunter populations
in waters of the Eastern Cape and Western Cape Provinces require additional research attention.
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Spatio-temporal dynamics of fish and fisheries in the
Breede River estuary, South Africa
ME McCord1, SJ Lamberth2, SE Kerwath2, C Erasmus2, T Zweig1, C da Silva2 and CG Wilke2
1
South African Shark Conservancy, Old Harbour Museum, Market Square, Marine Drive,
Hermanus 7200, South Africa.
2
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, Cape
Town, South Africa.
Abstract
The Breede River estuary is a permanently open warm-temperate system located on the
southwest coast of South Africa. It provides essential habitat for a number of recreational fishery
species – dusky kob (Argyrosomus japonicus), spotted grunter (Pomadasys commersonnii)
and Zambezi sharks (Carcharhinus leucas). Since 2009, five sharks and 11 spotted grunter were
tagged with acoustic transmitters and movement patterns examined during two study periods.
Preliminary results indicated Zambezi sharks are tolerant of large variations in environmental
conditions, but alter their position in response to changes in turbidity and dissolved oxygen. The
Breede Estuary is subject to significant anthropogenic changes which may drive changes in fish
species behaviour. Improved understanding of the spatio-temporal dynamics between fishes,
fisheries and environment will assist in developing system- and species-specific management
strategies in the Breede Estuary.
Introduction
Estuaries are important transition zones between freshwater and marine environments,
providing critical nursery and refuge habitats for many fish species and important recreational
and cultural services for humans (Nicolas et al. 2010, Costanza et al. 1997). Although it is widely
accepted that species found in estuaries are subject to considerable environmental variability
(e.g., salinity, turbidity, temperature) and anthropogenic impacts (e.g., fishing, agriculture,
habitat alteration) (Heupel and Simpfendorfer 2008, Nicolas et al. 2010), the degree to which
spatio-temporal behaviour and ecological function is influenced by these factors remains
largely unknown (Edgar et al. 2000). It is increasingly recognised, however, that an integrated
approach to understanding linkages between ecological and biotic processes, as well as human
dynamics, is required to improve management and conservation approaches at both the microand macro-ecosystem scale.
This study used an integrated approach to improve understanding of relationships between
three recreational fishery species - dusky kob (Argyrosomus japonicus), spotted grunter
(Pomadasys commersonnii) and Zambezi sharks (Carcharhinus leucas) - their fisheries
and environment in a permanently open warm-temperate estuary in South Africa. Multiple
techniques, including conventional tagging, acoustic telemetry, environmental monitoring, and
fisheries surveys, were employed to evaluate the efficacy of existing species-specific conservation
and management strategies. This paper introduces the project and provides preliminary results
from the first study period of the project.
Study site
The Breede River is 322km long with a catchment area of about 12 600km2. Situated on the
southwest coast of South Africa it enters the Indian Ocean in San Sebastian Bay, and falls within
the warm-temperate Agulhas biogeographical region (Emmanuel et al. 1992). The Breede Estuary
covers 455ha and tidal influence stretches to 55km upriver (Taljaard et al. 2001). It is permanently
open with mean depth of 4.6m, and is characterized by strong seasonal flows which peak in winter
months (May-September). Strong currents and high flows completely flush and reset the system
within one tidal cycle (Taljaard et al. 2001). It is an important nursery and refuge area for several
fish species and is heavily utilised by recreational fishers throughout the year.
Movement and environmental variables
Acoustic telemetry methods were used to track fish movement during two separate periods.
In the first study period (January 2009 to April 2011), one female and three male sharks (301400cm TL) were externally tagged with continuous acoustic transmitters (VEMCO Ltd., Halifax,
69KHz R69K) and manually tracked using a VEMCO VR100 acoustic receiver for 470 total
hours. All fishes were also tagged with conventional plastic dart tags (Hallprint Ltd.). During
tracking, the position of each shark was recorded every 15 minutes and environmental data
(temperature, salinity, dissolved oxygen, and turbidity) were recorded every 30 minutes using
a YSI 6600 Multi-parameter Environmental Monitoring System. One individual was fitted with
a pop-up archival tag (PAT tag) (Wildlife Computers Ltd.) to examine broad-scale movement
outside the estuary.
In the second study period, which began in January 2012 and is ongoing until January 2015,
one shark (256cm TL) and 11 spotted grunter (52.6-73cm TL) were tagged with coded acoustic
transmitters (VEMCO Ltd., model V9-2L-R256, 69 KHz, random pulse rate 20-60 s). All fishes
were also tagged with conventional plastic dart tags. Eighteen VR2W acoustic receivers and
nine temperature-pressure minilogs were deployed at strategic locations from 0-21km upriver
(Fig. 1). An additional five, nine and 20 coded acoustic transmitters will be deployed in sharks,
grunter and dusky kob, respectively, during the remaining study period. Two smart positioning
tags (SPOTs) and two PAT tags will also be deployed on each shark.
Habitat types and estuarine characteristics
To quantify estuarine habitat types and characteristics, high resolution bathymetric mapping
was conducted in first study period. To quantify temporal shifts in these characteristics and to
determine how potential shifts influence fish movement, mapping and telemetry data from the
first study period will be compared to the second study period.
Surveys
To assist in mitigating human-shark conflict, preliminary surveys to explore perceptions and
knowledge about sharks in estuaries were conducted during the first study period. These surveys,
and additional surveys to quantify depredation events (sharks foraging on fish captured by
recreational fishers) and monitor fish catches, will be conducted during the second study period.
Data analyses
Movement data from the first study period were mapped using GIS (ArcView GIS3.2;
MapWindow GIS). The proportion of positional fixes describing shark location and
environmental variables was calculated and averaged to determine frequency of occurrence in
specific ecological zones. For the second study period, the influence of habitat, diel cycle, tide,
season, and year on shark and fish movement will be analysed using a General Linearized Model
(GLM) and compared with the results obtained during the first study period.
Results
Due to the preliminary and ongoing nature of study period two, data for period one were
analyzed separately. Data analyses for period two are not within the current scope of this paper.
Movement
A total of 470 hours of manual tracking indicated sex- and individual-specific differences
in spatio-temporal behaviour of the sharks. Female shark (S1) exhibited tidally-dependent
movement, swimming upriver on the incoming tide and downriver on the outgoing tide. The
maximum distance travelled by S1 during a 24hr tracking period was 93km. Male 1 (S2) spent
75% of the time between 11km-17km upriver and male 2 (S3) spent 100% of the time between
3km and 11km. The remaining 25% of the time, S2 was located between 2km and 11km upriver.
Maximum distances travelled by S2 and S3 during a 24hr tracking period were 37km and 24km,
respectively. The female shark left the estuary for two hours post-release and then re-entered
the system. The two male sharks did not exit the estuary throughout the study. The second
male shark (S3) was recaptured in the estuary one year after initial tagging in January 2011. It
was fitted with a second acoustic tag and a PAT tag. However, the acoustic tag failed to operate
after deployment and no further estuarine movement data was collected for S3. The PAT tag
was programmed to pop-up 100 days after deployment however it released prematurely 53
days after tagging. The data indicated that S3 moved over 2000km from the Breede Estuary to
Bazaruto, Mozambique during this time (Fig. 2).
Environmental variables
Salinity
Sharks were located in salinities ranging from 15-36ppt, with a mean salinity of 27ppt. The
medians for S1, S2 and S3 were 25, 28 and 31ppt, respectively.
Temperature
Mean water temperature where tagged sharks were located was 23°C (range 20-25°C). The
medians water temperature were uniform at 23°C or 24°C for all sharks.
Oxygen
Sharks were located in water with dissolved oxygen levels ranging from 75-100%. The medians
of the positional fixes were between 75% and 87%.
Turbidity
Sharks were located in waters ranging from 0-25NTU, with a median of 5NTU.
Figure 1. Placement of the 18 VR2W acoustic receivers (R) deployed in the Breede Estuary,
from 0-21km.
Discussion
Estuaries are essential habitats, providing nursery and refuge areas for many commercially
and recreationally important fish species (Nicolas et al. 2010). Increasingly, however, these fish
populations are being adversely affected by the loss of estuarine habitats due to anthropogenic
impacts, climate change and inadequate management (Whitfield 1998, Beck et al. 2001, Courrat
et al. 2009). This is often compounded by a lack of baseline information on basic biotic and
ecological processes and an understanding of how shifts within these processes could impact
fish behaviour, ecology and conservation in and around estuaries.
The current study employs a multi-species approach to understanding linkages between fish,
fisheries and environment in a South African estuary. Although preliminary, the results of
the study show that Zambezi sharks, though physiologically capable of adapting to changes in
environment, selectively utilise areas of the estuary to remain in optimal conditions. Sharks
appeared to be tolerant to wide ranges in salinity, temperature, turbidity, and dissolved oxygen,
but preferred areas of the estuary with the lowest turbidity and highest dissolved oxygen.
Further investigation into the spatio-temporal behaviour of their preferred prey in the Breede
Estuary – dusky kob and spotted grunter – will assist in determining the degree to which shark
behaviour and movement is affected by prey behaviour.
As estuaries are particularly susceptible to external perturbation (Whitfield 1998, Cattrijse et
al 2002, Childs et al 2008), and long-term monitoring is required to improve system-specific
management and meet conservation goals. Through continued examination of the spatiotemporal dynamics of fishes and fisheries in the Breede Estuary, it will be possible to elucidate
how anthropogenic change affects these variably impacted fishery species in South Africa.
Figure 2. Track illustrating the 2000km migration of a male Zambezi shark (Carcharhinus
leucas) (S3) tagged with a pop-up archival tag in January 2011 in the Breede Estuary.
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Patterns and volumes of commercial and recreational
harvest of white stumpnose in Saldanha Bay: an
assessment of the fishery
Tor F. Næsje1, Colin G. Attwood2, Felicia Keulder3, Clement Arendse2
1
Norwegian Institute of Nature Research, P. O. Box 5685 Sluppen, NO-7485 Trondheim, Norway.
2
Marine Research Institute, Zoology Department, University of Cape Town, Private Bag X3,
3
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, South
Africa.
Introduction
Together with Table Bay and False Bay, Saldanha Bay has the longest history of linefishing
in South Africa dating back to the 1700s (Thompson 1913, Lees 1969). Today Saldanha Bay’s
linefishing is composed of three sectors, boat-based commercial, boat-based recreational and
recreational shore angling, yet the magnitude of the fishery and the impact of each sector have
never been studied. Such information is now required for environmental impact assessments
and for the regulation of activities in the area. Specifically, the importance of linefishing needs
to be assessed in relation to competing fisheries and potential negative impacts of port activities
(shipping and aquaculture), housing and tourism developments.
Of equal concern is the state of the fish stocks themselves. Earlier assessments have shown that
South Africa’s linefish resources, which include approximately 200 species, are poorly managed,
with many species having collapsed to a small fraction of their pre-exploitation biomass
(Brouwer 1997, Sauer 1997, Griffiths 2000, Lamberth 2003). The over-exploited species are
mostly endemic, long-lived species that inhabit coastal waters.
The purposes of the study were to quantify the effort and catches of commercial and recreational
linefishers in Saldanha Bay, and to describe the size- and age-structure of catches of white
stumpnose Rhabdosargus globiceps. The fisheries of Saldanha Bay were monitored by counting
boats and shore-fishers in the bay, and inspecting catches at slipways (access point surveys) and
along the shore (roving creel surveys) between April 2006 and March 2008.
Methods
Fishing effort and fish catches were sampled monthly by a single observer from April 2006 to
March 2008. Boat-based catches were monitored by an access point survey, whereas shore
anglers’ catches were monitored by the roving creel method (Pollock et al. 1984).
Instantaneous boat counts of the number of boats fishing were made from four viewpoints around
the Saldanha Bay. These viewpoints were chosen to ensure that every part of the bay could be
seen from at least one of the points. Saldanha Bay was divided into eight zones and the counts
were recorded against each zone (Fig. 1). The commercial boat fishers consisted of two licensed
groups; set-net mullet (Liza richardsonii) fishers fishing inside and outside the marine protected
area, and commercial linefishers targeting various species outside the marine protected area
only. However, commercial and recreational boats outside the marine protected area could not be
reliably distinguished from the view points. Day-time counts covering the entire lagoon were made
12 times per month. A random-stratified schedule was adopted, according to which count dates
and times were randomly assigned within the months, on condition that eight week-day and four
weekend-days (and public holidays) were covered each month.
Figure 1. A map of Saldanha Bay showing the eight zones used for counting boats, the four
access points (Langebaan Yacht Club, Alabama, Club Mykonos and Pepper Bay), and the four
beaches that were patrolled (Langebaan rocks, Mykonos beach, Dam, and Saldanha) in the
survey from April 2006 to March 2008.
Four stretches of shore around the bay were selected for roving creel surveys, namely:
Langebaan rocks, Mykonos beach, Dam, and Saldanha (Fig. 1). These were the only parts of
the shore where public angling was practiced, the remaining areas being private land and
inaccessible, having restricted access, or being in the no-take part of the marine protected
area. The observer walked along the shore of these areas, and counted anglers along the route.
Anglers were interviewed to obtain data on effort, fishing time and catches. Catches were
identified, counted and measured. A random-stratified survey schedule was used. Roving creel
surveys were performed four times per month in daylight hours in each of the four routes. The
dates and times of each survey were randomly selected, provided that one weekend-day and
three week-days were covered for each route per month.
The recreational and commercial boat fisheries were surveyed at the four slipways (boat launch
sites) in Saldanha Bay, namely Langebaan Yacht Club slipway, Alabama slipway, Club Mykonos
slipway and Pepper Bay slipway (Fig. 1). The number of fishing boats launching and returning
was recorded. One angler, usually the skipper, on each returning fishing boat was interviewed
to obtain data on effort and catches. Fish were identified, counted and measured. A randomstratified survey schedule was used. Access surveys were performed four times per month at
each of the four slipways. The dates and times of each survey were randomly selected, provided
that one weekend-day and three weekdays were covered for each slipway per month.
Data analysis
The analytical methods followed Pollock et al. (1994) closely. Counts (of boats, anglers or
catches) were averaged per zone and per day-type over each month. These averages were then
scaled up to yield totals for each area and each month. Area-month estimates were added to
yield annual estimates per sector.
The size data from each sector were combined to estimate the total rate of mortality, by
converting to age with an age-length key (Attwood et al. 2009). The age distribution was used in
a regression to estimate the exponential rate of decline of catch-by-age. This rate was equated to
the total mortality rate.
Results
Boat counts peaked in March, with an average of 27.5 boats per day (Fig. 2). The minimum was
in mid-winter when scarcely any boats were out fishing. The seasonal cycle shows that this is
clearly a spring and summer fishery. The same holds for the shore-based fishery, in which the
period September to April had consistently high angler densities, between 30 and 50 anglers
in instantaneous counts at all four beaches combined (Fig. 3). From May to August the average
counts were below ten.
Figure 2: Average daily boat counts per month across all zones in Saldanha Bay from April 2006
to March 2008.
Fishing boats included commercial and recreational linefish and set-net boats. These were
easily distinguished by the observer in the slipway survey. In total we counted 10 commercial
linefish boats and 550 recreational boats. Set-net boats did not form part of the survey, and their
methods and targets were not comparable.
Access point interviews revealed that the average recreational fishing trip lasted 4.9 hours,
whereas the average commercial trip was 7.8 hours. Another difference was the crew size:
commercial boats took an average of 7.9 fishers (range 4-11), whereas recreational boats had an
average of 2.7 fishers and was more variable (range 1-13).
Catch composition was remarkable similar between all three sectors. White stumpnose
dominated with over 79% in all sectors (commercial = 78%, recreational boat = 78 %, shore
= 82%), with steentjie (Spondyliosoma emarginatum) being the next important species for
recreational fishers (boat = 13% , shore = 12%) and hottentot (Pachymetopon blochii) in
commercial boat catches (21%).
Figure 3. The average ashore angler counts per month (±1 SE), across all beaches in Saldanha
Bay from April 2006 to March 2008.
Catch rates of white stumpnose were greatest for commercial fishers, 39.2 fish per person per
day, to whom bag limits do not apply. Recreational boat and shore anglers averaged 2.9 and 1.1
fish per person per day. Recreational anglers were limited to ten fish per day.
The total annual catch of white stumpnose in Saldanha Bay, estimated over the period, was
147 000 fish, equivalent to approximately 92 tons. Of this total, 44 % was taken by commercial
fishers, and 39 % by recreational boat anglers and 16 % by shore anglers.The total mortality rate
for age classes 3-10 years (cohorts 1997-2007) was estimated to be 0.53 y1 (Fig. 4)
Figure 4. Catch-at-age distribution of white stumpnose in Saldanha Bay for age classes 3-10
years. The fitted regression provides an estimate of the total mortality rate.
Compliance with regulations was remarkably good. Only 1.5 % of fishing trips exceeded the bag
limit, and only 0.8 % of fish were under-sized. Transgressions of the MPA boundary were not
uncommon, although linefish boat that crossed the borders were seldom observed to penetrate
far into the MPA. Most merely crossed the line by a few hundred meters.
Discussion
Roving creel surveys and access point surveys are widely used survey methods employed
in coastal fisheries (Pollock et al. 1994), particularly where estimating the total catch is an
objective. Both methods have been used in South African bays and estuaries at St. Lucia (Mann
et al. 2002), Richards Bay (Beckley et al. 2008), Mgeni, Durban (Pradervand et al. 2003),
Knysna (Smith, 2013) and the Berg River (Hutchings et al. 2008). In addition, open coast
applications have been conducted along the entire South African coast (Brouwer et al. 1998,
Pradervand 2004), and specifically at Betty’s Bay (Attwood and Farquhar 1999), Goukamma
(Pradervand and Hiseman 2000) and Port Alfred (Donovan and Hecht 2013). In virtually all
surveys including the present, night activity was unmonitored, which is the greatest weakness
of the implementation of the method in South Africa. Reasons for daylight limitation are most
often security concerns and cost implications.
Saldanha Bay is conveniently monitored because it is a relatively closed system with good access
due to a good road network. In addition the species which are caught here are not caught outside
the area in appreciable quantities, which means that population changes should be well reflected
in the local catch rates. There is a high degree of isolation of the main target species (Attwood et
al. 2007, Kerwath et al. 2009, and Hedger et al. 2010, da Silva et al. in press). Catch estimates
should therefore be very useful in local stock assessments, provided that these are unbiased.
An advantage of the relief around Saldanha Bay was the possibility to count boats remotely,
which allowed a cheap method to verify the spatial and temporal distribution of effort. Although
this information could be accessed from access point surveys, skippers often
do not report accurately or do not report all positions that were visited. Knowledge of the
distribution of boats is very useful for zoning plans.
There are several reasons to suspect that night fishing patterns differ from day fishing, due
to changes in fish behaviour and due to differing motivations of anglers who operate at
night. However, we suspect that night fishing is not a major contributor to the catch of white
stumpnose as boats that fished at night and surveyed in the early morning, had a preference for
targeting of silver kob Argyrosomus inodorus. This is a far larger and more valuable species,
which would provide suitable reward for the inconvenience of night fishing. Nevertheless, the
estimates of total catch of white stumpnose are conservative by not including the night catch.
The boats in Saldanha Bay are predominantly recreational, but the few commercial vessels make
this fishery different from the two large estuarine ports of the KwaZulu-Natal coast (Beckley
et al. 2008, Pradervand et al. 2003). Saldanha Bay is also considerably more productive,
producing at least 92 t of white stumpnose alone per annum. An adjustment to include other
species would push the total production up to minimum of 108 t. By comparison, the total
harvest in Durban Bay is approximately 17 t per annum, and 8.5 t per annum in Richards
Bay. In neither of these latter cases is commercial fishery permitted. Catch per unit effort is
approximately an order of magnitude higher for boat and shore fishing in Saldanha Bay, than
either of these comparably sized systems of the east coast.
The difference in fisheries yield might be related to the varying productivity of the east and
west coast. Although the Benguela Upwelling Ecosystem rates as among the most productive
marine ecosystem in the world (Shannon 1989), the estuaries of the east coast are also highly
productive, benefiting from a mixture of marine and terrestrial nutrients, and considerable
allochthonous inputs of organic material (Branch and Branch 1980).
Another explanation is that heavy pressure of the more populous east coast has led to overexploitation. By comparison Durban Bay had 22 232 shore-angler outings and 6661 boat trips
based on instantaneous counts (Pradervand et al. 2003), as opposed to the 11 242 and 4197
respectively in Saldanha Bay. Richards Bay was similar to Durban Bay, with 23 021 angler
outings per annum (Beckley et al. 2008). Mann (1995) reported that, apart from high levels
of effort, the rate of transgressions of fishery regulations in St Lucia was very high, a situation
that is likely reflected in the other two large east coast systems. By comparison, transgressions
of fishery regulations were far lower in Saldanha Bay. This situation may be the result of better
enforcement, less impoverished fishers or the greater availability of fish.
A third probable explanation is the level of industrialisation and habitat modification. All
three systems are disturbed, but the proportion of shoreline modified is greater in the two east
coast systems. It is the shallow waters that are important nursery grounds of fish, yet these
are extensively modified by breakwaters and canals in Richards Bay and Durban, whereas the
shoreline of Saldanha Bay is affected to a far lesser degree.
A fourth likely reason for the difference is the presence of a marine protected area in Langebaan
Lagoon within the Saldanha Bay. Although occupying only 4% of the fish habitat of Saldanha
Bay, it is shallow, productive and has a disproportionately large positive impact on the
conservation of the white stumpnose (Kerwath et al. 2009).
The scale of the linefish harvest in Saldanha Bay is also impressive when compared to trawl
fisheries. By comparison, the total annual harvest of white stumpnose from the two east coast
stocks by trawlers amounts to approximately 230 t per annum (Attwood et al. 2011). These
trawlers operate over an area two orders of magnitude larger than Saldanha Bay. The difference
in yield is likely a result of the varying productivity of the west coast and the central Agulhas
Bank. The white stumpnose in Saldanha Bay grow faster, which attests to the more productive
feeding ground and warmer water in this area (Attwood et al. 2010).
The mortality rate of white stumpnose in Saldanha Bay, as estimated from size structure data,
is high. Even allowing for a natural mortality rate of 0.2 y-1, which is higher than that predicted
from the Pauly’s (1984) regression for white stumpnose, fishing mortality accounts for more
than half of the total mortality, which is not likely to be sustainable. By comparison, the heavily
exploited roman population near Goukamma has a fishing mortality rate of approximately 0.21
y-1, which is similar to the natural mortality rate of that species (Götz et al. 2008)
The split between the various sectors of linefishing reveals an interesting pattern that should
have a bearing on management options. Recreational fishing effort (boat and shore) far
outweighs the commercial effort, but the total catch from each sector is roughly equivalent. The
skill of the commercial fishers, their incentive to turn a profit and the absence of a commercial
bag limit means that they harvest more efficiently. The commercial catch per unit effort is
approximately 17 times greater than that of recreational fishers. Assuming that the white
stumpnose stock is maximally exploited and that the towns of Saldanha and Langebaan are
increasing, placing more demands on the fishery, a pertinent question is which of these two
sectors should be the target of further restriction.
Something which is rarely considered in linefish management in South Africa is the broader
social and economic implications of catch restrictions. Commercial fishers have been granted
a right to make a business of catch and selling fish. They do so more efficiently than the
recreational sector, and in theory are more easily monitored and controlled. Commercial boats
are fewer in number and land their catches at predictable sites. The sale of fish also leaves a
paper trail, which is another source of data. In an area where environmental impacts of boats
are of particular concern, the lighter boat traffic associated with commercial effort should be a
positive attribute.
In the favour of the recreational sector is that these fishers are prepared to pay to catch fish,
whereas the commercial fishers expect to be paid. Managing the stock for recreational use
should attract more money to the area by way of tourism, and ultimately might provide more
employment on the impoverished west coast. Reducing the bag limit on commercial fishers
would not be a viable option, as the economic feasibility of this sector depends on attaining
large catches for a given outlay in hardware, fuel and wages. The only possibility of reducing
the commercial fisher’s impact is by zoning the area further to exclude commercial boast
from certain areas, which might also reduce their economic viability, or to remove some or all
commercial right holders from the area. It would be legally and politically difficult to implement
either of these options. Nevertheless, a detailed study of the recreational angler’s spending
patterns and the importance of this source of revenue for the district and the National Park
should be done before further restrictions are applied to this sector.
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white stumpnose Rhabdosargus globiceps (Sparidae) in a South African marine protected area.
African Journal of Marine Science. 29(1): 147-151
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stumpnose Rhabdosargus globiceps in Saldanha Bay, with evidence of stock separation. African
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Notes on the spatio-temporal behavior of the
smoothhound sharks of Langebaan Lagoon
C da Silva1, S E Kerwath1,2, C G Attwood2, E B Thorstad3, P D Cowley4, F Økland3,
C G Wilke1, T F Næsje3,4
1
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, South Africa.
2
3
Norwegian Institute for Nature Research, P.O. Box 5685 Sluppen, NO-7485 Trondheim, Norway.
4
South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown, South Africa.
Abstract
It has been shown that sharks may benefit from the protection of marine protected areas
(MPAs), however, the degree of protection has not been quantified for a commercially valuable
elasmobranch species. The movements of 24 smoothhound sharks (Mustelus mustelus) in
and adjacent to a small (34 km2) no-take MPA situated on the West Coast of South Africa were
investigated over two years using acoustic telemetry. The sharks spent the majority of their time
(average 79%) inside the reserve and some sharks (n = 5 of 15) did not leave the MPA during
the observation period. Time spent inside the MPA and the number of crossings of the MPA
boundary was strongly influenced by season. The sharks concentrated inside the MPA during
summer and were widely distributed throughout the study area during winter months. Six
sharks left the Saldanha Bay embayment during spring and winter periods for durations ranging
from two to 156 days (median = 111 days). All sharks returned to the bay within the study
period. During 2007 and 2008, the sharks spent an average of 74% and 80% inside the MPA,
respectively. The extended residency of smoothhound sharks within the MPA suggests that notake area protection is a viable management option for this species.
Introduction
The evolutionary success of elasmobranchs is based on morphological design and life-history
traits alternative to those of modern teleosts (Ferretti et al. 2010). General characteristics
include relatively large body size, longevity, low natural mortality, low productive rates and
in many cases, viviparity (Compagno 1990). These traits make this group susceptible to overfishing (Holden 1973). Although increased exploitation of sharks is a global phenomenon, efforts
to manage their exploitation sustainably have been limited (Walker 1998). Few shark species are
comprehensively assessed due to the fact that the majority are caught as by-catch (Myers et al.
2007). In the absence of effective regulations, closed areas have been advocated as an effective
conservation method to sustain some teleost and elasmobranch fisheries (Denny and Babcock
2004; Garla et al. 2006; Worm et al. 2009).
In this study, we investigated the spatio-temporal behaviour of the smoothhound shark,
(Mustelus mustelus) in and around a small MPA and quantified the proportion of time spent
in the different areas over a period of two years. The smoothhound shark is a small, benthic
species, which is commercially fished around the world (eg. Costantini et al. 2000; da Silva
2007; Saidi et al. 2008). Globally it provides an alternative target in the absence of high
value teleosts. Although considerable movement of more than 200 km has been reported,
conventional tagging studies in South Africa have shown that most smoothhound sharks were
recaptured close to their release site, regardless of time at liberty (Mann and Bullen 2009).
Based on their morphological traits and the tag and recapture information, we hypothesized that
these sharks might exhibit site-fidelity within a small area and therefore benefit from spatial
fishery closures in the absence of species-specific management for this species.
There are currently eight no-take MPAs in South Africa where smoothhound sharks are known
to occur (Fernández 2011). The Langebaan Lagoon MPA (LMPA) is a small no-take MPA
situated inside Saldana Bay, a coastal embayment on South Africa’s West Coast. An array of
underwater receivers enabled us to track the movements of 24 acoustically tagged smoothhound
sharks inside, outside and across the MPA boundary and to evaluate the role of fishery closures
in the conservation and management of this species.
General Methods
The Langebaan Lagoon Marine Protected Area (LMPA) (34km2) is a no-take MPA situated on
the west coast of South Africa (Fig.1). Twenty-four smoothhound sharks, 12 females and 12
males (81-147 cm total length) were tagged with coded acoustic transmitters (VEMCO Ltd.,
Halifax, model V9-2L-R256, 69 KHz, random pulse rate 20-60 s). Due to the physiological
consequences of capture stress data from the first seven days after tagging were removed from
analysis. Twenty-eight acoustic receivers (VR2, VEMCO Ltd., Halifax) were moored at strategic
positions throughout the bay (Fig. 1). When sharks passed through the detection range of a
receiver, time and tag identification number were recorded. Only sharks present at least one
annual cycle were included in the quantitative analyses.
Figure 1. Saldanha Bay on the west coast of South Africa and its southern extension, the
Langebaan Lagoon, which includes the no-take MPA. Small squares denote individual receiver
positions within the four receiver locations (1-4, indicated by circles). The grey shaded area
within the LMPA boundary represents shallow sandbanks
The position of an individual within a particular hour was determined and these hour bins were
used for the majority of analyses. The time spent inside and outside the LMPA was summed
over the total period of detections. It was assumed that the sharks could not cross the LMPA
boundary without detection. The data were split into two different datasets: dataset 1, from the
1st November 2006 to the 1st November 2007, when 15 sharks were still present in the system,
and dataset 2, from the 1st November 2006 to the 1st November 2008, which included only the 9
sharks that were still transmitting at the end of the study.
Between 2007 and 2010 229 sharks were captured inside the LMPA and dissected to determine
aspects of reproductive biology and feeding. Data from previous telemetry studies on the same
system (Attwood et al. 2007; Hedger et al. 2010) were used to determine whether seasonal
movements were related to food. The number of individual sharks detected per day per receiver
was calculated and plotted separately for dataset one and two to visualize the area utilization
across the study area over the study period. Similarly the number of individual white stumpnose
(Rhabdosargus globiceps), elf (Pomatomus saltatrix) and smoothhound sharks detected per
day per receiver was calculated and plotted for representative months within each season.
Temporal patterns on MPA utilization
The influence of diel cycles, season and year on the presence of sharks inside the MPA was
examined with the use of a Generalised Linear Model with a logit-link function. As the sharks
cannot be pooled into a sample for these analyses due to autocorrelation, the models were
applied to individual sharks for both datasets (R development Core Team 2008; http:///
CRAN.R-project.org).
Therefore the presence of a shark in the MPA was expressed as:
p=exp ()1+exp()
p=exp ()1+exp()
for datasets 1 and 2, respectively. The GLMs could not be applied to analyse movements out of
Saldanha Bay due to the small number of detections at receiver location one. Instead, detections
at this receiver location were individually examined
Results
General movement patterns
Receivers within the LMPA (location 4) detected the presence of individual sharks more
frequently than receivers at locations 1 and 2 for both datasets. The detection frequency
increased from receiver location 1 to 4 (Fig 2 and 3). Sharks were more frequently recorded
at receiver locations 3 and 4 i.e. inside and at the boundary of the MPA. Only eight sharks
were recorded at receiver location 1 at the Saldanha Bay mouth (~15 km from the release site),
whereas 14 sharks were detected at the southern-most site inside the MPA (location 4, ~3 km
from the release site). Seven individuals were recorded on both the southern-most (4) and the
northernmost receiver location (1), a distance of 17 km apart.
Within the first study year, tagged sharks (n=15) spent more time (mean=79%,range = 44-100%,
SD = 21%) inside the MPA than outside. Two sharks never left the MPA, whilst the remaining
sharks (n=13) frequently crossed into the fishing area (mean number of crossings per individual
= 40, range 1-163, SD = 51).
Movements out of Saldanha Bay
Eight individual sharks were recorded at the Saldanha bay mouth, of which only six left the
Bay during both study periods and ventured into the Atlantic Ocean for durations ranging from
two to 157 days (median = 111 days). Four sharks left the embayment only once during 2007
(4 July (112 days), 20 September (10 days), 14 September (two days) 12 May (157 days)) and
one shark left twice (19 May (139 days). All sharks returned and remained in the bay until their
transmitters expired. Only one shark left the bay in 2008 but did so on three separate occasions,
once during winter (6 May (10 days)) and twice during spring (19 September (13 days) and 2
October (two days)). Movements out of Saldanha bay occurred during the African winter (May
and July) and spring (September and October). Movements out of the bay in winter were
generally longer than those in spring.
Temporal patterns on MPA utilization
Although sharks were detected at all receiver locations in all four seasons, strong seasonal
variation was observed in the frequency of detections (Figs 2 and 3). Few detections occurred
at receiver location 1 in summer, when most sharks were concentrated inside the MPA. In
autumn, the frequency of sharks detected at receiver location 1 in the mouth of the embayment
increased and remained higher during winter and early spring, in contrast to the MPA receivers
that recorded the lowest numbers of detections in winter. In spring, the frequency of detections
increases again at receiver locations 3 and 4 (Fig 2).
Figure 2. The cumulative number of acoustically tagged sharks recorded per day at the 28
receivers over the period between November 2006 and November 2007 (n=15). Receiver
locations are denoted on the left side of the graph.
Figure 3. The cumulative number of acoustically tagged sharks recorded per day at the 28
receivers over the period November 2006 to November 2008. (n=9). Receiver locations are
denoted on the left side of the graph.
For the 15 sharks considered in dataset one, season had the biggest effect on the proportion of
time sharks spent inside the MPA (period 1: mean = 0.30, range 0.04-0.53, SD 0.17) but the
proportion of deviance explained by season varied considerably among individual sharks.
For the nine sharks considered in dataset two, the predictor season was still significant, but had
less explanatory power (mean proportion of time spent inside the MPA= 0.17, range =0.06-0.39,
SD= 0.12, Table 2). Although significant responses were observed for some individuals, less than
1% of mean deviance was explained by the addition of diel period to the model. All sharks with
significant responses to diel period had a marginally higher fraction (<0.01) of time spent inside
the MPA during assigned daytime hours. The predictor variable year, which was included in the
model applied for dataset 2, was significant for all sharks and on average explained a higher the
proportion of deviance than diel period and season (mean proportion of time spent inside the
MPA = 0.18, range = 0.01-0.55, SD = 0.17).
A preliminary analysis of the reproductive biology of smoothhound sharks caught within the
LMPA was completed. Animals were caught within all size classes (40-180 cm TL).
A peak in uterine mass in mature females and the observation of free swimming newborn
individuals (~40cm) with open umbilical scars between September and October points at a
spring pupping season. As males and females reached 50% maturity at 100 and 110 cm TL,
respectively and animals within this study ranged between 81 and 147 cm TL it is possible that
several individuals engaged in reproductive activity within the study period. Movements outside
the Saldanha Bay area coincide with the spring pupping period.
A preliminary analysis of feeding was also completed on smoothhound sharks caught within
the LMPA. Frequencies of occurrence of prey species within the stomachs of smoothhound
sharks were calculated. The most prevalent prey was the crown crab (Hymenosoma orbiculare),
followed by mud prawns (Upogebia africana) and sand prawns (Callianassa kraussi) at 68%,
60% and 19% respectively. Other prey items occurred within frequencies below 10% such as
three spot crab (Ovalipes trimaculatus), smoothhound shark, sandsharks (Rhinobatos spp),
west coast rock lobster (Jasus lalandii), and unidentified teleosts, cephalopods and nematodes.
No change in diet with size was observed. Fig 4 shows the cumulative number of stumpnose,
elf and smoothhound sharks present per day per receiver within selected months within each
season. Trends in time spent inside the MPA were similar for elf and smoothhounds during
spring and summer, however the decreasing trend in proportion of time spent inside the MPA in
winter were similar for white stumpnose and smoothhound sharks.
Discussion
Receiver coverage and general movement patterns inside and out of Saldanha bay
The results of this study showed that smoothhound sharks were resident within Saldanha bay
over prolonged periods. Site fidelity has been commonly documented in sharks such as cownose
rays (Rhinoptera bonasus), blacktip reefsharks (Carcharhinus limbatus), and bull sharks
(Carcharhinus leucas) (Collins et al. 2007; Heupel et al. 2004; Simpfendorfer et al. 2005). The
repeated movements of sharks across wide areas suggest that these animals are familiar with the
area and are able to navigate between preferred sites (Papastamatiou et al. 2011).
Although sharks were present in the southern lagoon during the entire study, seasonal variation
in area utilization was evident. During autumn, winter and early spring, some sharks dispersed
more widely across the bay and beyond, whereas only a few outings beyond receiver location
2 occurred during summer. White stumpnose and smoothhound sharks showed a similar
decrease in time spent inside the LMPA during winter. The similar diet of white stumpnose and
smoothhound sharks as opposed to elf suggests that this movement may be related to feeding or
ability to catch prey.
The seasonal movement between Langebaan Lagoon and Saldanha bay, and even out of the
Saldanha bay, had a strong seasonal component and can be considered an annual migration as
defined by Dingle (1996) as it occurred during a specific, predictable time period and included a
return movement and was repeated in the second year of the study. However, most individuals
did not move over a larger distance than 16 km (i.e., distance between the two most distant
recordings). Although most of the sharks remained within the Saldanha bay, some individuals
left the bay in spring and winter for the open Atlantic Ocean, before returning again to the
protected area within the Langebaan Lagoon. Due to the size range of the acoustically tagged
animals and the spring pupping season, it is possible that the seasonal movements recorded
were related to reproduction. However, neonates were commonly found within the MPA it is
therefore likely that individuals left the MPA after pupping. Such a migration of mature sharks
after or during pupping may be a mechanism to avoid competition for the same food resource or
cannabilism. The reasons that few individuals left the Bay during winter are unknown but may
be related to behavioural thermoregulation, food or predator avoidance.
a)
a)
.
b)
b)
c)
c)
Spring
Summer
Autumn
Winter
Figure 4. The cumulative number of acoustically tagged stumpnose (a) (n=13), elf (b) (n=14)
and smoothhound (c) (n=15) sharks recorded per day at the 28 receivers between 2006 and
2008. (n=9). Receiver locations are denoted on the left side of the graph.
Movement around the MPA from a management perspective
MPAs have been acknowledged as a possible conservation method for sharks in the absence
of fishing regulations (Bonfil, 1999; Barker and Schleussel, 2005). However, few studies have
examined the movement patterns of sharks in relation to existing MPAs. The results in this
study in the Langebaan Lagoon and surrounding Saldanha bay show that the MPAs may provide
significant protection to the smoothhound shark, since they spent a large proportion of their
time (average 79%) within the boundaries of the MPA, although the MPA represents only 35%
of the entire bay area (Kerwath et al. 2009). Most telemetry studies of fish behaviour are shortterm studies covering from a few weeks maybe up to one year. The strength of the present study
is the long-term recording of the same individuals, and a confirmation that the behavioural
patterns and protection by the MPA were consistent among years. The least protection was
offered during winter, which was the period with the highest frequency of recordings outside the
fished area.
Moreover smoothhound sharks were protected during their pupping period in spring, neonates
are not commonly caught outside the MPA indicating that the area represents a nursery ground
where neonates are protected. Summer is the busiest time for recreational fishing inside
Saldanha Bay. Although recreational fishing in Saldanha Bay is primarily targeting edible
teleosts, smoothhound sharks are commonly caught due to their abundance within the area.
The fact that smoothhound sharks spend the majority of their time inside the MPA during
summer during peak fishing effort increases the protection of smoothhound sharks in the area.
Smoothhound sharks in the MPA are therefore protected whilst spawning, whilst neonate and
during peak fishing periods. To date, this is the first study that has quantified the protected area
usage of individuals by being able to account for each hour of an acoustically tagged animals life
for a meaningful time period.
Acknowledgements
The study was financed by the NORSA fund, the Marine Living Resources Fund South Africa
and the Norwegian Institute for Nature Research (NINA). We would like to thank Vincent
Taylor, Tony Booth and Steve Lamberth for advice and support. Furthermore we would like
to thank technical and support staff at the Department of Agriculture Forestry and Fisheries:
Linefish research for technical and logistical support.
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mustelus (L.) in the Gulf of Gabès (south-central Medeterranean Sea). Journal of Fish Biology.
72: 1343-1354.
Simpfendorfer CA, Freitas GG, Wiley TR, Heupel MR. 2005. Distribution and habitat partitioning
of immature bull sharks (Carcharhinus leucas) in a Southwest Florida estuary. Estuaries 28:
78-85.
Smale MJ, Compagno LJV. 1997. Life history and diet of two southern African smoothhound sharks,
Mustelus mustelus (Linnaeus,1759) and Mustelus palumbes (Smit,1957) (Pisces: Triakidae).
Walker TI. 1998. Can shark resources be harvested sustainably? A question revisited with a review of
shark fisheries. Marine and Freshwater Research 49: 553-572.
Worm B, Hilborn R, Baum JK, Branch TA, Collie JS, Costello C, Fogarty MJ, Fulton EA, Hutchings
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A, Ricard D, Rosenberg AA, Watson R, Zeller D. 2009. Rebuilding Global Fisheries. Science 325:
578-584.
Session 9 – Fish Stock Assessment: Chair Sven
Kerwath
A comparison of the commercial and recreational
sectors in the Port Alfred linefishery and their
response to management changes between 1985 and 2008
B Donovan1, T Hecht2, O Weyl3
South African Environmental Observation Network, Grahamstown, South Africa.
2
Department of Ichthyology and Fisheries Science, Rhodes University, South Africa.
3
South African Institute of Aquatic Biodiversity, Grahamstown, South Africa.
1
Abstract
Numerous changes in South African linefish management have changed the structure and
functioning of fisheries. The aims of this study were to take a descriptive snapshot of commercial
and recreational sectors of the Port Alfred linefishery between 2006 and 2008, identify the
difference between the two, and compare these metrics with those estimated from suitable
historical data (various periods from 1985 to 2005). In 2008 the commercial fishing effort
decreased to less than 20% of the peak effort in 1991 due to legislated reduction in commercial
fishing effort. The recreational sector, however, increased steadily (1.5% per annum) as previous
commercial licence holders started fishing recreationally. Commercial fishing patterns in 200608 were largely governed by increasing overhead costs, which resulted in operators fishing
closer to access points and targeting higher valued species, such as silver kob (Argyrosomus
inodorus) and Geelbek (Atractoscion aequidens). Despite evidence of a declining linefishery
countrywide, the overall CPUE in 2006-08 remained roughly as high as it was in 1996-98. This
was mainly due to the fishers tending to only go to sea on days when good catches were likely
and is not representative of comparative stock status. Recreational fishers were also fishing
closer to access points and, due to bag limit restrictions, had shorter trip durations in 2006-08
than previously. One point of concern was that, in 2006-08, the recreational fishers tended to
target an increased proportion of the more vulnerable shallow-water reef associated species.
This study provides evidence that the recreational sector is not as benign as once thought, and
has had an increasing impact on the fishery as a whole, emphasising the need for monitoring
and control of both sectors of the linefishery.
An assessment of the shorefishery for largespot
pompano, Trachinotus botla, in KwaZulu-Natal, South Africa
D Parker1, A J Booth1 & B Q Mann2
1 Department of Ichthyology and Fisheries Science, PO Box 94, Rhodes University,
Grahamstown 6140, South Africa.
2 Oceanographic Research Institute, PO Box 10712, Marine Parade, Durban 4056, South Africa.
Abstract
The Trachinotus botla shorefishery in KwaZulu-Natal appears to be in a stable state and
underexploited (SBR = 75% of pristine levels). The fishery displays considerable spatial and
temporal variability with resource abundance increasing north-easterly towards Mozambique
and CPUE peaking during summer. Movement was random and can be described as “ranging”.
An increasing trend in mean annual CPUE since 2002 suggests that either the resource is
increasing since the promulgation of the beach driving ban or possibly as a result of increased
targeting of this species using “dropshot” fishing. It is likely that the beach driving ban has
shifted fishing effort to accessible nodes along the coast where there is some evidence of
localised overexploitation.
Introduction
Rock-and-surf angling in South Africa is a popular recreationally attracting thousands of
participants because of its affordability and open-access nature (Brouwer et al. 1997). Although
recreational fisheries do not produce the direct financial benefits commonly seen in commercial
fisheries, the knock-on economical and social implications of an accessible recreational fishery
are considerable (McGrath et al. 1997). Recreational fishing in southern Africa therefore has
huge economical potential.
As recreational fishing continues to increase in popularity so will the increased fishing effort
place additional pressure on the targeted species. Declines in population sizes of recreationally
important species, as inferred through decreases in angler catch rates, have sometimes been
disregarded by both anglers and fisheries managers because of a widespread perception that
recreational fishing is a benign activity (Cooke and Cowx 2006). However, dramatic declines in
catches and catch rates in the South African, Namibian and Angolan inshore fisheries as a direct
result of recreational fishing pressure have been observed (Brouwer et al. 1997, Holtzhausen and
Kirchner 2001, Potts et al. 2009) and have necessitated direct management intervention.
Largespot pompano, Trachinotus botla, is a medium-sized (60 cm FL and 2kg) surf zone
carangid that is widely distributed in subtropical and tropical waters of the Indian and Pacific
oceans. Within South African waters, the species occurs from Port St Johns northeastwards
to the Mozambique border (Heemstra and Heemstra 2004). It is an important recreational
shore angling species where it accounts for up to 30% of the shore angling catch composition in
northern KwaZulu-Natal (KZN) (Maggs 2011). Despite the potential economic importance of T.
botla, there is little available information on its abundance and resource status.
This study provides a spatial and temporal assessment of the T. botla shorefishery using
historical catch and effort in conjunction with catch-and-release tagging data. It is hypothesised
that a “recovery” period would be detectable in the fishery after the implementation of the ban
on beach driving in 2002. The driving ban is known to have affected the behaviour of resource
users, particularly with regards to the spatial distribution of fishing effort (Mann et al. 2008).
Effort has shifted and concentrated in areas in close proximity to public beach access, particularly
in Maputaland (i.e. within the iSimangaliso Wetland Park) where access areas are dispersed.
Evidence of localised overexploitation is expected in these areas of concentrated fishing effort.
Seasonal fishing patterns are also expected within the Maputaland fishery, and recreational
angling effort is likely to increase over the holiday periods in these more remote areas.
Methods and Materials
Fishery trends
Catch and effort data were obtained from shore patrols conducted by Ezemvelo KwaZulu-Natal
Wildlife (EKZNW) and stored on the National Marine Linefish System (NMLS) (Maggs 2011).
While the database includes data from 1985 to 2010, only data from 1987 onwards were used
as reporting rates and accuracy of the first two years of data collection was considered to be
unreliable. EKZNW conducts routine daily shore patrols in 15 designated zones along the KZN
coast. Catch-per-unit-effort (CPUE) was calculated as the number of fish caught per angler
outing inspected (fish.outing-1), and was assumed to provide a relative index of fish abundance.
Catch data were pooled into three specific areas (Fig 1).
Figure 1: Zones used by Ezemvelo KwaZulu-Natal Wildlife to conduct shore patrols to assess
angler catch and effort along the Kwazulu-Natal coastline in South Africa.
Movement
Movement was assessed based on data obtained from the Oceanographic Research Institute
(ORI) Tagging Project (Dunlop and Mann 2011).
Mortality rates
Instantaneous total mortality (Z) and natural mortality (M) rates were both calculated from
the inverse-variance weighted average of estimates obtained from linearized catch-curves
(Ricker 1975) and the Chapman Robson (1960) estimator applied to age-frequency data. Fishing
mortality, F, was determined by subtraction as Z=M+F.
Total mortality data were from Sodwana Bay (Parker 2012) and from a long-term monitoring
project in the St Lucia Marine Reserve north of Cape Vidal. Natural mortality data were from
the “no take” marine sanctuary zone within the St Lucia Marine Reserve. Length frequencies
were converted to age-frequencies using a normalised age-length key. For the catch-curve
analysis, Zcc and its asymptotic standard error, SEZcc, were estimated from the negated slope
of a linear regression fitted through the natural logarithm-transformed descending limb of
the age-frequency data (Ricker 1975). The Chapman and Robson (1960) estimate for survival
was
where ā is the mean age at and older than the peak of the agefrequency distribution (where the peak age is recoded as age-0), and n is the number of fish in
the sample. The estimates of total mortality and its asymptotic standard error was calculated
from survival as
and
, respectively, where
.
Per-recruit analysis
Data available for the assessment of the T. botla resource are restricted to non-standardised
CPUE estimates and relevant biological information (Parker 2012). A per-recruit assessment
was therefore considered to be the most suitable approach as has been applied to many other
South African linefish species (Chale-Matsau et al. 2001, Mann et al. 2002, Richardson 2010).
Sex-independent age, growth, maturity and the length-weight relationship parameters were
obtained from Parker (2012) and are summarized in Table 1.
Table 1: Parameter estimates which were used in the per-recruit analyses of Trachinotus botla
from KwaZulu-Natal.
Parameter
Estimate
Description
L1
132.66 mm FL
Average length of youngest age
448.79 mm FL
Average length of oldest age
a
1.37 year-1
Growth curvature parameter
b
-5.84 year-1
Growth curvature parameter
t1
0.17 years
Known minimum age
6.75 years
Known maximum age
M
1.04 year
Asymptotic natural mortality rate
F
0.27 year
tmax
6 years
L2
t2
-1
Asymptotic fishing mortality rate
-1
Observed maximum age
α
0.00002 g mm
Length-weight regression parameter
β
2.96
Length-weight regression parameter
2.31 years
Age-at-50%-maturity
0.33 year-1
Inverse rate of maturity
2.03 years
Age-at-50%-selectivity
-1
0.14 year-1
Inverse rate of selectivity
Growth was modelled using the Schnute (1981) model of the form:
where
and
are the length of fish at the youngest (
) and oldest (
) aged fish, and
and
are the growth curvature parameters. Age-at-50% maturity was modelled as a logistic
function as:
where ψt is the proportion of mature fish at age t, ψ50 is the age at 50% maturity and δψ is the
inverse rate of maturity.
Hook selectivity was assumed to be sigmoidal with 100% selection achieved at the peak of the
age-frequency distribution. Selectivity was, therefore, modelled by fitting a logistic ogive to the
normalised ascending limb of the age-frequency distribution as:
where Sa is the hook selectivity on a fish of age a, a50 is the age-at-50%-selectivity and δs is
inverse rate of selectivity. Model parameters were estimated using a non-linear, least-squares
regression.
Spawner biomass-per-recruit (SBR) and yield-per-recruit (YPR) were calculated as a function of
both fishing mortality (F) and age-at-selectivity (St) as:
and respectively, where F is the instantaneous rate of fishing mortality on fully selected fish, tmax is
the maximum observed age, M is the instantaneous rate of natural mortality, St the selectivity
at age t, Wt the mass of fish at age t and calculated as
(with α and β the
length-weight regression coefficients),
the proportion of mature fish at age t, and Ñt is the
relative number of fish at age t calculated recursively as:
Results
Description of the fishery
Annual catches reported in EKZNW shore patrols ranged from 860 individual fish in 1994 to
2354 individuals in 1995, while effort ranged from 186 731 outings in 1987 to 96 462 outings
in 1996. Both T. botla catch and total angling effort were unevenly distributed across the KZN
coastline (Fig 2). Cape Vidal zone produced the highest catches (10 734 fish recorded) and was
almost double that of the second highest location, namely Durban (5 481 fish). Fishing effort
was particularly high in the Durban zone, an urban centre, and both St Lucia and Cape Vidal
which are both popular holiday destinations.
Mean CPUE was variable and consistent between years indicating a stable fishery. CPUE records
displayed a latitudinal trend, and areas north of St Lucia having a higher mean annual CPUE
than those areas south of St Lucia (Fig 3). CPUE appears to have increased in the Maputaland
and North Coast areas since the ban on beach driving in 2002. The trend was not significantly
different to period prior to the ban due to data variability (ANCOVA; t = 0.97, df = 23, p = 0.34).
Figure 2: Total catch (number of largespot pompano) and total effort (fishers inspected) per
EKZNW patrol zone.
Figure 3: Annual trends in mean CPUE for the Trachinotus botla shore fishery in three areas of
the KwaZulu-Natal coast from 1987–2010. The dashed line indicates the implementation of the
beach driving ban.
Long-term CPUE trends for Sodwana Bay exhibited a steady decline from 1985 to 2010 (Fig 4).
Prior to the implementation of the beach driving ban annual CPUE records for this area were
highly variable that is consistent with the overall CPUE trend for T. botla within KZN. Since
2002 CPUE has remained consistently low. CPUE trends illustrate the seasonal nature of the T.
botla fishery with catches peaking in the summer months (Fig 5).
Figure 4: Mean annual CPUE for Trachinotus botla in Sodwana Bay, KwaZulu-Natal.
Unshaded circles indicate post-beach driving ban data.
Figure 5: Variations in mean monthly CPUE for each zone patrolled by Ezemvelo KwaZuluNatal Wildlife. The data is standardised, and is described as a proportion of the maximum
monthly CPUE observed per zone, so as to facilitate comparisons between zones.
Movement
A total of 2391 T. botla were tagged between 1984 and 2010, of which only 46 (1.88%) have been
recaptured (Dunlop and Mann 2011). The average time at liberty was 210 days (± 243 days), with a
maximum of 1236 days. Distance moved averaged 6.8 km (± 22.8 km), and 78% of all recaptured
fish were within 1 km of their release site (Fig 6). Two fish were observed to have made significant
northeast movements of 114 km and 107 km (St Lucia Marine Reserve Sanctuary to Kosi Bay).
Both fish were mature (335 and 401 mm FL) when released and were at liberty for 301 and 299
days, respectively. Overall, the average distance moved by tagged fish along the coastline in a
northeasterly and southwesterly direction was 44.3 km and 4.7 km, respectively.
Figure 6: Movement patterns of Trachinotus botla tagged in South Africa. Movement is
described as the distance from the tagging site to recapture site, as either a function of time or
length. Positive values depict movements in a northeast direction, while negative values depict
movements in a southwest direction.
Mortality
The total mortality estimate for Sodwana Bay was 1.32 y-1 (ZCR = 1.26 y-1, ZCC = 1.37 y-1), and the
total mortality estimate for the St Lucia Marine Reserve was 1.30 y-1 (ZCR = 1.27 y-1, ZCC = 1.55
y-1) resulting in an inverse-variance weighted mean of Z = 1.31 y-1. Natural mortality for T. botla
was estimated as M = 1.04 y-1 and was calculated as the inverse-variance weighted mean of the
two independent methods applied to data from the Sanctuary zone (ZCR = 1.03 y-1, ZCC = 1.13 y-1).
Fishing mortality was estimated as F = 0.27 y-1 (Fig 7).
Per-recruit analyses
The per-recruit analyses estimated that SBR was currently at 75% of pristine levels with the
response of SBR to different values of fishing mortality (F) and age-at-50%-selectivity (S)
are presented in Fig 8. At low values of S, maximum SBR was attained at correspondingly
low levels of fishing mortality. At high values of F (>1.5 y-1), SBR was largely dependent on S
and the effects of increased fishing effort became negligible. SBR decreased relatively rapidly
when fish under the age of sexual maturity (< 2.3 years) are harvested after which increasing
S makes no functional difference as there is always a reservoir of unexploited mature fish. The
sensitivity of alternative natural mortality scenarios on both YPR and SBR were examined and
are summarised in Table 2.
Discussion
Trachinotus botla abundance increases northwards, with Maputaland having a higher mean
annual CPUE than any zones highlighting the tropical nature of the species and its affinity to
warmer waters (McPhee 1995, Heemstra and Heemstra 2004). Overall, the shore fishery has
shown relative long-term stability with regards to catch rates with peak catches occurring over
the summer months, despite shore angling effort for the region peaking during winter with
anglers targeting Pomatomus saltatrix and Sarpa salpa (Brouwer et al. 1997). On the South
Coast T. botla is a by-catch. On the North Coast, particularly north of St Lucia, it is actively
targeted by both light-tackle anglers and subsistence fishers (Dunlop 2011). Trachinotus botla
are susceptible to small lures and flies and the fairly recent development (since the early 2000s)
of an angling technique known as “dropshot” fishing.
Table 2: The response of Trachinotus botla spawner biomass-per-recruit reference points to
three natural mortality (M) scenarios.
M( yr-1)
Fmax
Fcurrent
F0.1
FSB50
FSB40
0.94
∞
0.24
1.05
0.72
1.11
1.04
∞
0.27
1.29
0.84
1.32
1.14
∞
0.31
1.59
0.99
1.6
Figure 7: Length- and age-frequency distributions of Trachinotus botla from three different
data sources. Estimates of Z (± standard error) are provided from both linearized catch-curve
analysis (ZCC) and the Chapman and Robson estimator (ZCR).
Figure 8: Isopleth plot describing the response of the percentage of spawner biomass-perrecruit to unexploited levels to different combinations of fishing mortality (F) and age-at-50%selectivity (S) for Trachinotus botla in KwaZulu-Natal. Natural mortality was M = 1.04 yr-1 and
the current status of the resource is denoted as “X”.
The promulgation of the beach vehicle ban in January 2002 has led to substantial decreases
of shore angling effort in areas that are not directly adjacent to beach access areas (Mann
and Pradervand 2007, Mann et al. 2008). This regulation has effectively created numerous
inaccessible areas where fishing exploitation has been drastically reduced, in some cases to
being negligible. The effects of this regulation on the T. botla fishery are likely to have been
positive. An increasing trend in mean annual CPUE since 2002 suggests that the resource is
increasing under lowered fishing effort conditions. The ban on beach driving appears to have
had least effect on the South coast region, as access areas are more common in this region.
It can also be argued that these regulations have merely shifted the fishing effort to more
accessible areas, concentrating effort into a fraction of the original fishing area. In doing so,
accessible areas have endured increased fishing effort which is potentially unsustainable and
may have led to localised overexploitation. As T. botla appear to remain in relatively small
areas (<7 km) for extended periods of time, localised depletion in accessible areas is possible.
Mann and Pradervand (2007) noted that T. botla CPUE increased within the St Lucia Marine
Reserve north of Cape Vidal between 2002 and 2005. In contrast, long-term CPUE trends at
Sodwana Bay (± 70 km north of Cape Vidal) have shown a steady decline from 1987 to 2010.
Sodwana Bay remains the only beach in South Africa where driving is still permitted within a 2
km stretch for purposes of beach parking. As such, the vast majority of the shore angling effort
(and patrolling effort by EKZNW shore patrols) is localised within this 2 km stretch of beach.
While this indicates the potential susceptibility of this species to localised overexploitation,
the overall benefits of area protection remain and furthermore highlight the importance of
Marine Protected Areas (MPA) in marine conservation. MPAs are regarded as a fundamental
component of the precautionary approach to fisheries management (Clark 1996). One of the
primary benefits of MPAs is the exportation of larvae, recruits and adult fish into adjacent
fishing grounds; described as the “spillover” effect (Clark 1996, Attwood et al. 1997, McClanahan
and Mangi 2000).
The low tag recapture rate of T. botla is indicative of a large population, high tagging mortality,
and/or tag shedding. While the data are limited to only 46 recaptures, evidence suggests that
majority of the population resides within a relatively small area with a small proportion of
the population exhibiting the tendency for large scale movements. Trachinotus botla is a surf
zone species inhabiting an environment that is dynamic and is altered over extremely short
time periods if there is inclement weather and rough sea conditions. The paucity of constant
visual cues for defining a home range suggests that it may rely on other factors, such as prey
availability (McPhee 1995). Prey items within a surf zone are generally motile and unevenly
distributed (temporally and spatially) (Lasiak and McLachlan 1987). Individuals may move
when prey encounter rates in their home range falls below a critical level, and continue to
move until suitable concentrations of prey items are relocated. This hypothesis may explain the
apparently random observed movement patterns.
The selection of any stock assessment methodology is largely based on data availability. In the
case of T. botla, a per-recruit assessment approach was adopted because the only reliable data
available were life-history data together with length frequency distributions from three different
sources. Measurements of T. botla from Sodwana Bay (Parker 2012) and from the St Lucia
Marine Reserve north of Cape Vidal were considered to accurately reflect the size structure
of the T. botla population, while length data used from the ORI Tagging Project would have
been biased by fish > 300 mm FL, which is the minimum required tagging length. Current SBR
was estimated as 75% of pristine levels. It is generally accepted that the risk of recruitment
overfishing is greatly increased if SBR levels drop below 40% of pristine. Based on the current
mortality and selectivity estimates the target reference point would be reached if fishing
mortality increased to 1.32 year-1, which is almost five times greater than the current fishing
mortality estimate. This assessment suggests that the current levels of stock exploitation of T.
botla in KZN are relatively low and that the species is underexploited.
To conclude, the assessment outcomes are not surprising given the life history traits of the
species. T. botla exhibits fast growth, early maturation and has a short life span. These are all
characteristics that facilitate a resource that is more suitable, and perhaps better able, to cope
with high levels of exploitation. The T. botla fishery in KZN is exclusively shore-based and
almost entirely recreational, with a limited subsistence sector. The commercial sale of T. botla
is prohibited in South Africa and the fishery is strictly limited to rod and line angling. Therefore
the nature of the fishery itself inherently limits its exploitation.
Acknowledgements
This study was funded by the National Research Foundation (NRF) of South Africa’s African
Coelacanth Ecosystem Programme and Rhodes University. The iSimangaliso Wetland Park
Authority is thanked for allowing access for this study at Sodwana Bay and the Oceanographic
Research Institute (ORI) for making catch and effort and tagging data available for analyses.
Matt Parkinson and Reece Wartenberg are thanked for assisting with the research.
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Standardization of the Catch per Unit Effort for albacore
(Thunnus alalunga) for the South African tuna-pole
(baitboat) fleet for the time series 1999-2010
W West1, SE Kerwath1,2 and H Winker2
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Roggebaai 8012, Cape
Town, South Africa.
2
Zoology Department, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
1
Abstract
The tuna pole/baitboat fishery was initiated in the late 1970s and originally targeted yellowfin
tuna, Thunnus albacares. To date, however, albacore Thunnus alalunga is the main
target caught in waters up to 1000 km off the South and West coast of South Africa and off
Namibia. The pole fishery sector exploits the majority of the albacore within South Africa and
Namibian waters. The tuna pole fishery was initially managed as part of the linefishery but
became a separate sector in 2000 at the onset of the declaration of the linefish emergency.
The International Commission for the Conservation of Atlantic Tuna (ICCAT) is one of the
tuna Regional Fisheries Management Organisations (RFMOs) tasked with conducting stock
assessments of albacore. In this study, a generalized linear model was developed to standardize
the CPUE of albacore within the tuna pole sector. Covariates examined included area, distance
from shore, vessel-type, season and species targeting. Standardized CPUE was found to be
similar to the nominal CPUE with no overall significant temporal trend, an indication that South
Africa’s baitboat fishery for albacore has been stable over the last decade. The inclusion of the
effect of targeting other species of tuna, yellowfin in particular, caused the greatest improvement
in explanatory power.
Introduction
Periodically, the tuna regional fisheries management organisations (RFMOs) conduct
stock assessments on tuna and billfish. In this case the International Commission for the
Conservation of Atlantic Tuna (ICCAT) set out to update the stock assessment of albacore as
the previous stock assessment was completed in 2007. ICCAT separates the albacore stocks in
the Atlantic into the south Atlantic stock, north Atlantic stock and the Mediterranean stock.
When stock assessments are conducted, each country fishing for albacore in these areas are
tasked with formulating a standardized catch-per-unit-effort (CPUE) for their fishery. In South
Africa, the majority of the harvest is made by the tuna pole sector in the Atlantic Ocean and
a standardized CPUE index for albacore caught in the tuna pole fishery was formulated. The
ICCAT stock assessment in 2007 concluded that there were concerns over the state of the south
Atlantic albacore stock (Anon., 2008) and a similar concern was expressed in 2010 (Anon.,
2011). The CPUE standardization for albacore has been conducted previously by South Africa in
1996 (Butterworth, 1996), 2000 (Leslie, 2000), 2004 (Leslie et al., 2004) and 2007 (Smith and
Glazer, 2007). Each time, this analysis being no exception, an improvement on the methods and
the model is sought after.
The fishery initiated in the late 1970s and originally targeted yellowfin tuna, T. albacares,
but switched to albacore when yellowfin moved off the Cape waters in 1980 (Penney et al.,
1992). This pattern repeated itself in the middle of the first decade of the 21st century when
the yellowfin became abundant again around the Cape. The tuna pole fishery was originally
managed as part of the linefishery (Penney, 1993), but it became a separate sector after an
emergency was declared in the linefishery in 2000 due to the collapse of most of the targeted
sparid and sciaenid stocks. Since the medium term rights allocation in 2002 the tuna pole
fishery sector consists of 191 vessels of more than 10 m length (to avoid conflict with the linefish
fishery), of which 136 are active.
South Africa’s tuna pole fishery catches mainly juvenile to sub-adult albacore in surface waters.
Albacore is of a much lower value than species such as yellowfin and bigeye tuna and the
albacore are destined for canning overseas. Because yellowfin tuna is of a higher value, vessels
will target this species when it is available. Skipjack and bigeye tuna are caught in smaller
quantities as the albacore fishing grounds are at the edge of their distributions. The albacore
fishing grounds are along the South West coast and Namibia and the fishery is very seasonal
from around November to May. The average annual tuna pole albacore catch for South Africa is
apprximately 5000t. The other major albacore fishing nations in the Atlantic Ocean are ChineseTaipei, Brazil and Namibia using longline and tuna pole methods.
Time-series of standardized CPUE can be an indicator of abundance trends and are commonly
used in stock assessments. Various methods are used to standardize CPUE the most common
being generalized linear models (GLMs). The function of GLMs when standardizing CPUE is to
reduce the influence of factors/variables other than fish abundance on the catchability. Once
the series is standardized, trends between countries and fisheries and data over time can be
compared and combined into a full assessment model.
Methods
Deciding on the most appropriate variables to include in a GLM can be challenging; too few
variables and the model will not be able to account sufficiently for effects influencing CPUE,
whereas too many variables and the model could remove trends that should be attributed to
the year effect. Data were extracted from the National Marine Linefish System (NMLS) and
two datasets were prepared for the analyses. The first dataset, Dataset 1, included all tuna pole
vessels with tuna catch and effort records from 1999 to 2010. The second dataset, Dataset 2,
contained of catch and effort records for 40 indicator vessels, which were selected based on the
number of years they operated in the fishery, i.e. 11 or more years fishing in the sector. By using
indicator vessels that fished over the entire time series, we aimed to minimize variation in the
data caused by vessels that have fished intermittently over short periods, which might be less
consistent in targeting and catch reporting.
The data was cleaned up with regards to targeting, unspecified tuna, constant multi-day catches
and erroneous catches. To analyse albacore-directed trips, all trips with catches of albacore,
yellowfin, big-eye, skipjack and unspecified tuna were extracted. Catches of unspecified tuna
that could not be identified as albacore using a set of rules were removed from the datasets. In
instances where the skipper totalled the catch for the entire trip instead of recording the weight
caught per day, those data were removed. Catches may have been recorded as numbers instead
of weight. Catches below small thresholds were removed from the datasets.
The covariates that were considered were year (1999 -2010), month, area (South: south of
33°, south west: 30° – 33° and north: north of 30°), distance from shore (Inshore: <100 nm,
Offshore: <200 nm and High seas: >200 nm), vessel type (ski boat, ice and freezer) for Dataset
2 only, and target (the fraction of albacore in the total catch). The model was executed in R (R
Development Core Team (2010).
The full GLM was formulated as:
Ln(CPUE + ∆) = β0 + βy + βm + βa + βd + βv + βln(t+1) +є
(1),
where Δ is the offset and є the error. Based on preliminary model runs, the offset was set at Δ
= 0.1 as this value resulted in the most “normal-like” distribution of the residuals (Butterworth
1996). The intercept is denoted by β0 and the β’s with corresponding subscripts denote the
coefficients for each effect: y = year, m = month, a = area, d = offshore distance, v = vessel
type and t = target. The factor target , the ratio of albacore to yellowfin catches (Battaile and
Quinn 2004), was included to account for the large bycatch of yellowfin tuna, which periodically
becomes available in the Cape waters and significantly affect the albacore catch. 95% confidence
limits for standardized CPUE indices were determined by non-parametric bootstrapping.
Results and discussion
Analyses of deviance, based on a step-wise regression procedure, showed that all of the covariates
considered were significant. Total variance explained by the full model was 49.4% for Dataset 1
and 41.3% for Dataset 2, which indicates a considerable improvement to earlier analysis, although
not directly comparable (Table 1). The effect target explained by far the largest proportion of the
deviance in both datasets, whereas distance offshore had the least effect. As in Smith and Glazier
(2007), residuals were approximately normal (Figure 1) for both datasets.
The standardized CPUE trends derived from the analysis were fairly stable for both datasets,
which is in agreement with the results by Smith and Glazer (2007). The standardized CPUE
tracked the nominal CPUE closely with no significant upward or downward trends (Figure
2). The trend over the overlapping years was similar to those presented by Smith and Glazer
(2007) with slight increases in 2001 and 2003. The analyses indicate that the CPUE for the
South African baitboat fishery for albacore has been stable over the last decade. The model
based on the full dataset (Dataset 1) should be adopted for standardization (Table 2). Further
improvements are possible on all levels, i.e. improved reporting of species targeting and fishing
position, more detailed classification of fishing time and vessel power and possibly the inclusion
of environmental parameters such as sea surface temperature derived from satellite imagery.
The standardized CPUE based on the full dataset was submitted to ICCAT and used in the 2011
albacore stock assessment. The outcome of the stock assessment revealed that the standardized
CPUE trends for other countries fishing in the south Atlantic using pelagic longline gear were
generally declining (Figure 3). The albacore assessment calculated the Maximum Sustainable
Yield (MSY), however, with wide confidence limits. In response to the B/BMSY = 0.88 and the F/
FMSY = 1.07, the albacore quota in the south Atlantic was reduced from 29 900t to 24 000t. South
Africa was allocated 10 000 t to share with Namibia. The data requirements from ICCAT for
albacore have increased in an attempt to keep a tighter control over the fishery and the catches
made in the year. South Africa manages the tuna pole fishery as a total applied effort (TAE) of
200 vessels and 3600 crew and in order to receive better quotas from RFMOs, South Africa
aims to improve its catch performance with this management method. ICCAT does acknowledge
that there are uncertainties in the stock assessment and that there is still missing data that was
not included in the assessment. An example of this uncertainty is expressed in the albacore
assessment that ‘[c]onsidering all scenarios, there is 54% probability for the stock to be both
overfished and experiencing overfishing, 10% probability for the stock to be either overfished
or experiencing overfishing, and 36% probability that biomass is above and fishing mortality is
below the Convention objectives. (Anon., 2011)’
This is the fourth time that a standardization of catch and effort for albacore has been conducted
by South Africa. Further scope for improvement has been identified and it will be implemented
into the routine catch statistic data collection. With the strong RFMO involvement in stock
assessments, steps have been put in place almost immediately at the end of 2011, in the form
of quota adjustments and data collection requirements, to improve the albacore stock status
in the south Atlantic. A dedicated tuna pole fishery at the onset of the emergency in 2000 was
necessary for studies such as these to be conducted. There is, however, an overlap between the
tuna pole fishery and sectors such as linefish (in reference to the yellowtail quota allocation) and
small pelagics (in reference to the bait fish used by the tuna pole vessels). Overall, fishing sectors
cannot be managed in isolation and it is important that management plans take conflicts of
interest into account.
References
Anon. 2008. Report of the 2007 albacore assessment meeting (Madrid, Spain, 5 – 12 July 2007).
Collective Volume of Scientific Papers, SCRS/2007/015 Madrid, Spain.
Anon. 2011. Report of the 2011 ICCAT South Atlantic and Mediterranean albacore stock
assessment sessions (Madrid, Spain, 25 – 29 July 2011). Collective Volume of Scientific Papers,
SCRS/2011/019. Madrid, Spain.
Battaile B C, Quinn TJ 2004. Catch per unit effort standardization of the eastern Bering Sea walleye
pollock (Theragra chalcogramma) fleet. Fisheries Research 70: 161-177.
Butterworth, D.S. 1996. A possible alternative approach for generalized linear model analysis of tuna
CPUE data. ICCAT Col. Vol. Sci. Pap. 45: 123–124.
Leslie, R.W. 2000. Updated standardized south Atlantic albacore Thunnus alalunga CPUE for the
South African baitboat fishery, 1985 – 1999. Col. Vol. Sci. Pap. ICCAT. Madrid, Spain.
Leslie, R.W., Restrepo, V. and Antony, L. L. 2004. Standardized south Atlantic albacore CPUE for
the South African baitboat fishery, 1985-2002. Col. Vol. Sci. Pap. ICCAT. Madrid, Spain. 56(4):
1504-1524.
Penney, A.J., Krohn, R. G. and Wilke, C. G. 1992. A description of the South African tuna fishery in
the southern Atlantic Ocean. Col. Vol. Sci. Pap. ICCAT. Madrid, Spain. 37: 218-229.
Penney, A.J. 1993. The National Marine Linefish System. In Beckley, L.E. and R.P. van der Elst
(eds). Fish, Fishers and Fisheries. ORI Spec. Publ. 2: 68-72.
R: A language and environment for statistical computing. R Foundation for Statistical Computing,
Vienna, Austria. ISBN 3-900051-07-0. URL http://www.R-project.org.
Smith, C. D. and Glazer, J. 2007. New standardized south Atlantic albacore CPUE for the South
African baitboat fishery, 1999-2005. Col. Vol. Sci. Pap. ICCAT. 60 (2): 481-491.
Wood, S.N. 2000. Modelling and smoothing parameter estimation with multiple quadratic penalties.
Journal of the Royal Statistical Society (B). 62 (2):413-428.
Venables, W. N. and Ripley, B. D. 2002. Modern Applied Statistics with S. Fourth Edition. Springer,
New York. ISBN 0-387-95457-0.
Table 1. Summary statistics of the model fits for (a) Full Dataset 1 (all vessels) and (b) Indicator
Dataset 2 (indicator vessels). The terms were added sequentially, first to last. Interactions were
not considered. Res. df: Residual degrees of freedom.
a)
Parameter
Res. df
Df
AIC
D AIC
Res.Dev. D Dev
%
p
explained
r2adj
b0
30656
135686
150025
by
30645
11
134798
888
145638
4387
2.9
***
0.03
bm
30637
8
134353
445
143463
2175
1.4
***
0.04
ba
30635
2
133755
599
140670
2792
1.9
***
0.06
bd
30633
2
133598
156
139936
734
0.5
***
0.07
bln(t+1)
30632
1
114867
18732
75954
63983
42.6
***
0.49
49.4
% deviance
explained
b)
Parameter
Res.
d.f.
d.f.
AIC
D AIC
Res.Dev. D Dev
%
explained
p
r2adj
b0
17882
74589
67807
by
17871
11
74390
198
66977
830
1.2
***
0.01
bm
17863
8
74288
102
66536
441
0.7
***
0.02
ba
17861
2
74005
283
65476
1060
1.6
***
0.03
bd
17859
2
73980
25
65370
107
0.2
***
0.03
bv
17857
2
73844
136
64861
508
0.8
***
0.04
bln(t+1)
17856
1
65126
8853
39831
25030 36.9
***
0.41
% deviance
explained
41.3
a)
b)
Figure 1. Diagnostic plots of quantile and residual distributions for (a) Dataset 1, and (b
Dataset 2.
a)
b)
Figure 2. Normalised CPUE for the base-case scenario for (a) Dataset 1 and (b) Dataset 2.
Confidence intervals (2.5% and 97.5%) are shown by the stippled lines, nominal CPUE is
depicted by open circles.
Figure 3. CPUE trends of albacore for the top five fishing nations contributing to catches in the
south Atlantic from 1999 to 2010. LL = pelagic longline, BB = baitboat/pole fishing (Anon., 2011)
Session 10 – Miscellaneous: Chair Chris Wilke
Variation in shore-angler effort on the South African
coast 1994 -2011
JA Sterley1, BM Clark1, K Hutchings1, C Attwood2, W West3
Anchor Environmental Consultants, Tokai, Cape Town, South Africa.
2
3
Department of Agriculture, Forestry and Fisheries, Cape Town, South Africa.
1
Abstract
Evidence of stock declines in all fishing sectors, seen by the decline in CPUE and shift in catch
composition, have been reported since the 1980s; with over fishing considered to be the driving
force. Knowledge on the shore angling fishery is sparse, particularly with regard to total national
effort and CPUE, with the most comprehensive data collected being the National Line Fish
Survey in 1995. Data was collected on the shore-angling effort by the Lotto Coastal Monitoring
Programme from January 2010 to August 2011 using the Roving Creel survey technique in
six areas, Kogelberg, Agulhas, Stilbaai, Mossel Bay, Plettenberg Bay and East London. A total
of 1298 surveys from 1995 were compared to 2343 surveys conducted in 2011. The results
indicated an overall decrease in shore-angling effort by 51%. In the five areas surveyed,
significant declines in effort were recorded at both the Kogelberg sites (65% and 91%), two of the
three Agulhas sites (46% and 88%), the Mossel Bay site (45%), and one of the two East London
sites (27%). These declines are considered to be the result of a combination of factors; the major
drivers being: the ban of vehicles on the beach restricting access to remote areas; the increased
cost of living expenses such as fuel prices; and security concerns (a number of these sites are
well-known for criminal activity). The mass decline in effort may have improved the shoreangling fishing stocks, a hypothesis that will be assessed during the analyses of the survey’s
CPUE data.
Baited Remote Underwater Video (BRUV) in the
Stilbaai Marine Protected Area: a survey of reef fish
with an assessment of monitoring requirements
L De Vos1, A Götz1, H Winker1 and C G Attwood1
1
Background
There is a need to objectively assess the progress of existing MPAs towards achieving biodiversity
conservation and fisheries management goals (Hockey and Branch 1997, Tunley 2009). In
order for these assessments to be effective for MPA management, monitoring efforts should be
sustainable in the long-term (Gislason et al. 2000, Jones 2002, Colton and Swearer 2010). Baited
remote underwater video (BRUV) surveys present a clear advantage for South African MPA
management in that they are relatively cost-effective with a low environmental impact and modest
requirements for skilled labour. BRUV monitoring was developed in Australia and has been tested
internationally (Cappo et al. 2003, Harvey et al. 2007, Watson et al. 2010). Several studies have
suggested that BRUV presents key advantages over traditional monitoring techniques, driving
BRUV’s evolution from a purely research-orientated technique to a sustainable monitoring
solution (Willis et al. 2000, Stobart et al. 2007, Langlois et al. 2010).
Controlled angling surveys (CAS) and underwater visual census (UVC) form part of the current
preferred monitoring toolbox for South African MPAs. Whilst CAS are widely-accepted as a
sound monitoring technique, the high post-release mortality rates associated with CAS (Götz
et al. 2007) raise questions regarding their applicability within MPAs (Willis et al. 2000).
This may conflict with MPA objectives and would be unsuitable for species-specific sampling
where population numbers are either unknown, or low enough to be of conservation concern
(Ackerman & Bellwood 2000, Willis et al. 2000). UVC surveys may be biased by the differential
attraction to, and avoidance of, SCUBA divers (Watson et al. 2010). Furthermore, data collection
is restricted because UVC is limited by depth, time spent underwater, and availability of
experienced, scientifically-qualified divers (Stobart et al. 2007).
By contrast, BRUV requires lower manpower, time and boat requirements to collect sound
scientific data with higher statistical power and lower variability (Langlois et al. 2010).
The system is operational where SCUBA techniques are considered unsafe, increasing the
underwater data-collection time and extending monitoring scope to deeper waters (Cappo
et al. 2004, Stobart et al. 2007, Watson et al. 2010). As a non-extractive method, it falls in
line with MPA objectives, and the retention of footage for independent re-analysis also opens
opportunities for use in long-term ecosystem comparisons and public awareness (Parker et al.
1991, Willis et al. 2000, Langlois et al. 2010).
As South African MPAs are poorly resourced (Tunley 2009), there is a clear need to develop
cost-effective, yet scientifically credible, monitoring techniques that can be applied across
a number of MPAs. This study employed BRUV across the Stilbaai MPA to estimate the
minimum length of camera deployment and number of deployments to achieve effective,
long-term reef fish monitoring. The study provides a first assessment of species diversity
and relative abundance since the closure of the Stilbaai MPA in 2008, and assesses whether
measured environmental variables can explain patterns of reef fish distribution, abundance,
and community composition within the MPA. This information can be reviewed to guide future
management decisions and inform area-selection for possible expansion of the MPA.
Methods
Situated west of Mossel Bay in the Western Cape, the Stilbaai MPA is one of South Africa’s
newest proclaimed MPAs (Tunley 2009). The MPA protects a coastline of 13.5 km from
Noordkapperspunt to the historical fish traps, and 15.7 km of the Goukou estuary. Skulpiesbaai,
the Geelkrans reef, and the Goukou estuary are no-take zones where all commercial, recreational
and subsistence fishing is prohibited.
GPS-linked echosounder data from transects across the Stilbaai MPA provided spatially
referenced depth measurements. Based on this information, a study area was selected within the
no-take zone that protects the Geelkrans reef where depth ranged from 5 m – 41 m. A random
selection of 29 paired latitude and longitude values were plotted within the delineated study
area and sampled sequentially from a randomly-ordered list. This approach was adopted so
that no assumptions were made ahead of sampling about reef fish habitat association, and the
monitoring protocol could be conducted in any of South Africa’s existing, or future, MPAs where
little may be known of reef profile and where no bathymetry data are available.
Figure 1. The Stilbaai Marine Protected Area (MPA) in the context of the Western Cape (a)
and South Africa (b). Shaded regions indicate the restricted (no-take) zones of the MPA.
Interpolated depth is graded and ranges from 5 m to 37 m. The study area is indicated by a grey
rectangular outline and sampling sites are indicated in white.
The BRUV set-up comprised a standard definition camera mounted facing horizontally from the
apex of a weighted, stainless steel tripod (20 kg) and was deployed for one hour per sampling
site. A stainless steel rod extended 1 m from the tripod and held a perforated PVC bait canister
containing one kilogram of pilchard (Sardinops sagax) homogenate (Cappo et al. 2004) in the
camera’s field of view. The camera was operated remotely using a surface control box. Recording
started when the tripod had settled on the seafloor.
A temperature logger attached to the BRUV tripod logged sea temperature every five minutes for
the study’s duration. Visibility was measured in metres with a secchi disc deployed from the boat
before each BRUV deployment and depth was read from the boat’s echo sounder to verify with
map bathymetry data. Reef profile and bottom sediment-type were described at each sampling
site. One researcher identified all species in a video and a Max N measure was obtained for each
species at every site. Max N is the maximum abundance of a species in any one frame for the
duration of a video, to avoid pseudo-replication by recounting individuals that swim in and out
of the camera’s field of view (FOV) (Willis and Babcock 2003).
Patterns of habitat association were investigated by analysing differences in species composition
between sites in PRIMER-E version 6 (Clarke and Gorley 2006). A cluster analysis and MDS plot
assessed the similarity of species composition among the 29 sites, and ANOSIM tests on depth and
profile assessed the significance of these two variables’ influence on species composition.
A total of 29 BRUV sites were completed during seven fieldtrips to Stilbaai spanning 11 October
to 30 November 2011. Site depths averaged 22 (+ 9.6 SD) m. Only one site was classified as
sand, whilst 17 sites represented low profile reef and 10 sites were classed high profile reef.
Visibility ranged from 2.5 to 10 m and averaged 6.2 (+ 1.6 SD) m. Water temperature varied
from 15 to 20°C, with an average of 17 (+ 1.2 SD) °C.
BRUV sampling in Stilbaai obtained a higher estimate of species diversity than UVC and CAS in
the Castle Rocks, Goukamma and Tsitsikamma MPAs (Lechanteur 2000, Götz 2006, Bennett
et al. 2009, Götz 2009), with 38 species from 14 families being recorded. Twenty-eight species
representing 11 families were recorded by UVC surveys in the Castle Rocks MPA (Lechanteur
2000). It is expected, given biogeography, that more species would be recorded in the Stilbaai
MPA (Turpie et al. 2000). It is worth noting, however, that these findings may also point to the
ability of BRUV monitoring to overcome differential attraction to, and avoidance of, SCUBA
divers (Watson et al. 2010).
An angling survey in Tsitsikamma recorded 14 species and UVC recorded 17 species (Bennett et
al. 2009). It is unlikely that the Stilbaai MPA is more diverse than Tsitsikamma, given patterns
of biogeography along the South African coastline (Turpie et al. 2000) and that the latter has
a longer history of protection (Buxton 1992) and encompasses more high profile reef (Bernard
2012). These results appear to corroborate international findings that BRUV surveys record
higher species richness, a wider range of families, and a higher abundance of predators than
traditional monitoring methods such as UVC (Cappo et al. 2004, Watson et al. 2010) and
suggest that BRUV is a more broadly representative monitoring tool.
In order to be useful for management, BRUV deployments must not only be representative,
but efficient. In total, 88 point counts, 44 UVC transects and 10 angling hours at 16 stations
were conducted to achieve the Tsitsikamma estimates (Bennett et al. 2009). When this effort
is compared to the six sampling days in Stilbaai to achieve 29 samples and an overall higher
species diversity estimate, it is clear that BRUV monitoring is more time-efficient.
A criticism that may be levelled against BRUV is that it tends to exclude species not attracted
to bait. However, species composition obtained using UVC, CAS and BRUV are similar across
Goukamma, Tsitsikamma and Stilbaai (Bennett et al. 2009, Götz et al. 2009b, Bernard 2012).
This finding strengthens recommendations to apply BRUV as a monitoring technique. This
study corroborates findings that BRUV samples many different species, including herbivorous
fish, but may underrepresent their diversity (Watson et al. 2010).
Soupfin, smooth-hound and spotted-gully sharks feature more frequently in this study than in
other studies employing UVC (Bennett et al. 2009, Götz et al. 2009b). This confirms the finding
that BRUV records a higher presence of elasmobranch species due to bait attraction (Stobart et al.
2007, Colton and Swearer 2010). Controlled angling surveys in Goukamma also sampled smoothhound sharks, most likely as a similar result of bait attraction. However, the opportunity to obtain
measures of a commercially exploited species without using an extractive method is more suited to
research and monitoring of exploited species in MPAs (Willis et al. 2000).
Environmental variables explaining differences in species composition across sites
The understanding that some species are confined to favoured habitats is essential to ensure
that monitoring is representative across habitats (Colton and Swearer 2010). Several reef fish
species may be of special interest for monitoring in the Stilbaai MPA because they face fishing
pressure outside MPAs (Buxton and Clarke 1989, Buxton 1993). To detect significant change in
these species’ abundance over time, an understanding of how environmental variables influence
their distribution can direct monitoring efforts towards their preferred habitats. This is an
important consideration for monitoring to be effective within a reasonable annual timeframe
and with limited resources.
Understanding that species composition differs with substrate, depth, profile and sea
temperature is important to direct future monitoring efforts, and will assist in a meaningful
interpretation of the data (Colton and Swearer 2010). Whilst depth appeared to be the singlemost important predictor of species distribution and abundance, it was the interaction between
depth, sea temperature and reef profile that emerged as the best explanatory combination of
variables in this and previous studies (Buxton and Smale 1989). The reason for this finding may
be explained by what this combination of variables offers fish in feeding opportunities, shelter
and mobility (Buxton and Smale 1989, McCormick 1994, Friedlander and Parrish 1998). This
study suggests that BRUV can detect broad patterns of species composition and abundance
across different habitats, just as traditional monitoring techniques do, which is important if
BRUV is to be added to South African monitoring toolbox.
Required number of samples and deployment time for BRUV in Stilbaai
For an unstratified sampling design, it was found that a deployment of 49 minutes should record
95% of the species present across all depths and profiles in the MPA.
Monitoring of changes in abundance is desirable for management to assess the efficacy of a MPA
in achieving conservation goals (Kelleher 1996, Hockey and Branch 1997, Turpie et al. 2000).
The potential for population increase from low levels of abundance is limited by the intrinsic
rate of increase for a species (r), the rate of decrease in fishing mortality, and the abundance of
the remnant population in a MPA (Jennings 2001). For many species, this r value typically falls
in the region of 0.05 to 0.15 per year (Buxton and Clarke 1989). These low rates of increase are
typical of long-lived reef fish (Buxton 1993, Pinnegar et al. 2000).)
To detect changes in abundance for long-lived species, it is expected that annual sampling over
a period of at least five to ten years would be required. This study employed a power analysis to
assess the number of samples required annually to detect a significant (α = 0.05) five percent
increase in population abundance over ten years for roman (Chrysoblephus laticeps), santer
(Cheimerius nufar), red steenbras (Petrus rupestris) and red stumpnose (Chrysoblephus
gibbiceps) with a power of 80 % (Fig 2).
Figure 2. Results from a power analysis detailing the required sample size to detect a significant
(α = 0.05) five-percent increase in population abundance over ten years, with a power of 80 %.
The required sample size increases with increasing rarity of the species in question. Thus, the
annual sample size required for roman and santer is achievable on a management timescale.
However, sample size requirements for red steenbras and red stumpnose of 50 samples and
above are more impractical to attain within a reasonable annual timeframe. It is, in this
instance, most important to consider the sampling effort required for UVC and CAS to achieve
the same outcome and assess whether BRUV monitoring is significantly more time and labour
efficient. Certainly, if one looks to the future evolution of the BRUV system, it appears that this
is the case.
Conclusion
This study shows that BRUV monitoring is a practical and time efficient solution to the question
of sustainable monitoring in the Stilbaai MPA. The increasing availability of affordable, high
quality cameras makes the evolution of the BRUVs from a single-camera system to one which
deploys multiple camera rigs to collect data simultaneously a plausible solution to annual
monitoring. Certainly, a multiple-BRUV deployment approach will make the sample sizes
required to detect long-term changes in the abundance of rare species a practical reality.
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Competition between line and trawl fisheries on the
Cape south coast
C G Attwood1, S L Petersen2, S E Kerwath3, R Mussgnug1 and L Palframan4
2
WWF South Africa, PO Box 23273, Claremont 7735, South Africa.
3
Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012.
4
Zoology Department, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa.
1
Abstract
The inshore trawlers of the Cape south coast have been accused of impacting on non-target
stocks and reducing fish available to the linefishery. The on-board observer programme which
ran between 2002 and 2006, revealed that inshore trawlers take 130 species, but 20 of these
constitute 98% of the pre-discard catch. Discarding is not estimated to be substantial. Only
two bycatch species, silver kob and carpenter, are caught in similar quantities by trawlers and
linefishers. Spatial overlap between the fisheries is between 10 and 35%, although, in most cases,
the linefishery encroached more heavily on the trawl grounds than vice-versa. Precautionary
catch limits administered by way of an industry-managed multispecies individual transferable
quota system is recommended for the trawl fishery. Other restrictions could include additional
closed areas and a night trawling ban on the hake grounds.
Introduction
The south coast inshore trawl fishery is South Africa’s oldest trawl fishery. The fishery is
concentrated on unconsolidated sediment shallower than 110 m between Cape Infanta and
Algoa Bay. The trawlers target east coast sole Austroglossus pectoralis, and shallow-water hake
Merluccius capensis.
Given the recent attention on the worldwide failure of fisheries, it is remarkable that catches of
east coast sole have remained stable over the course of a century (Fairweather and Glazer 2010).
A possible reason for this persistence is the large area of untrawlable rough ground on the wide
Agulhas Bank (Japp 1994). However, the fishery does incur a substantial bycatch, amounting
to approximately 38% of the total catch by mass, constituting at least 130 species (Attwood et
al 2011). Only two species, shallow water hake and the east coast sole, are controlled by quota
in the inshore fishery, precautionary upper catch limits (PUCL) have been set for monkfish,
kingklip, horse mackerel and silver kob.
Concerns over the consequences of bycatch and dumping by sole trawlers along South Africa’s
south coast were discussed as early as 1931 (Marchand 1933). It was noted then that the sole
grounds off Cape Infanta were inhabited by silver kob and young of other species in great
quantity. The capture of young sole was also considered as a possible cause of the perceived
decline in productivity on the sole grounds. Investigations of that period resulted in a
recommendation to limit the mesh size to 3 inches (75 mm), which remains the regulation for
sole-directed trawlers today. The current mesh-size for hake-directed trawlers is 90 mm.
An important consideration for the management of the inshore trawl fishery is the extent to
which the industry depends on by-catch species. The top twenty species in the pre-discard
catches by mass are all marketable (Table 1), with the possible exception of Squalus spp, which,
although marketed elsewhere, has no demand in South Africa (Attwood et al. 2010). That
much of the by-catch is utilised is a positive feature of the fishery, in contrast to many other
trawl fisheries which have high discard rates. Many of the non-target species make a useful
contribution to the profitability of the fishery (Walmsley et al. 2007, SADSTIA 2010). For
fishermen with small hake quotas, the bycatch species play a relatively more important role in
their business.
Concerns regarding to the bycatch species is primarily directed towards the lack of monitoring
and the Table 1. Average estimated annual catch taken by inshore trawlers in the years 2003
to 2006 (Attwood et al. 2011). The top 20 species are listed. Plurals indicate an assemblage of
species, usually at the generic level. It is likely that much of the deep-water hake total was misclassified and should be lumped with shallow-water hake.
Species
Average annual catch (kg)
%
Cumulative %
Shallow water hake
9653757
55.37
55.4
Horse mackerel
1345028
7.71
63.1
Panga
1050173
6.02
69.1
Skates
833321
4.78
73.9
Gurnards
824164
4.73
78.6
East coast sole
504049
2.89
81.5
St Joseph
503551
2.89
84.4
Deep-water hake
427844
2.45
86.9
Dogsharks
409203
2.35
89.2
Silver kob
294264
1.69
90.9
Chokka squid
283206
1.62
92.5
White stumpnose
230517
1.32
93.8
Kingklip
216156
1.24
95.1
Carpenter
107176
0.61
95.7
Monkfish
86891
0.50
96.2
Geelbek
83984
0.48
96.7
Houndsharks
82249
0.47
97.1
Snoek
56909
0.33
97.5
Ribbonfish
44138
0.25
97.7
Cape dory
41609
0.23
98.0
lack of an effective mechanism to retrain catches of species that are not quota-restricted. There
is specific concern over the effect of catches of silver kob, and the small size at which it is caught,
on the linefishery, particularly in the Still Bay area. Competition between the line and trawl
fisheries on the Agulhas Bank is limited to only five species, of which silver kob and carpenter
are the most equitably shared (Table 2).
The purpose of this paper is to outline a number of possible mechanisms to reduce the extent
of bycatch. Broadly speaking, this can be achieved in two ways. In the first, it should be possible
to extend the management of this fishery to explicitly include species other than shallow-water
hake and east coast sole. The view expressed by Davies et al. (2009) is that any catch which is
unused or unmanaged qualifies as bycatch. By specifically managing more species, the pool of
bycatch species is reduced. The second approach is to reduce the catches of unmanaged species
relative to the nominal target species. We discuss MPAs and time-area closures. Walsmley et al.
(2006) also listed a number of possible mechanisms to reduce bycatch, including alterations to
mesh size, closure of certain areas, enforced observer coverage, individual transferable quotas,
and fixed bycatch-proportion limits.
Table 2. Comparison of the total declared catch of selected species taken by the South African
linefishery and inshore trawl fishery over the period 2003–2006.
Species
Linefishery
(t)
Trawl pre-discard
(t)
Trawl landed weight
(t)
187
107
41
Atractoscion aequidens
546
84
11
339
294
197
Pterogymnus laniarius
27
1 050
910
Cheimerius nufar
75
1
30
231
Galeorhinus galeus
44
38
83
Blank cells indicate unavailable estimates.
Managing a broader spectrum of species
Background
Only two species are effectively managed in the inshore trawl fishery, namely hake and east
coast sole, notwithstanding The PUCLs that apply to four other species. These limits have yet to
be tested. Chokka squid are also managed, but the controls on squid are applied in the squiddirected fishery only.
At the very least, the management of a fishery should entail (1) a set of objectives, (2) a set of
indicators which can be used to measure the degree to which objectives are satisfied and (3)
a mechanism to adjust the fishery to improve the likelihood of satisfying objectives. Although
objectives may change of over time, it is the set of indicators and the adjustment mechanism
which require regular, usually annual, revision. Recently abundance trends in most non-target
species have been inferred from regressions of survey CPUE over the period 1985 to 2008.
Although a crude assessment, this work could form the basis of more rigorous analyses on
species where negative trends are apparent.
The general concern in multi-species fisheries is the inequality of the productive capacity of the
constituent species in the catch. As is the case in the inshore trawl, the target species is often
the dominant catch. Other species with lower surplus production are not likely to withstand
the same effort that is applied to optimally harvest the target (Sparre and Venema 1998). It is
not possible to manage every species at maximum sustainable yield (MSY). Some will be overexploited, and may be reduced to unsafe levels, as a consequence of managing for the optimal
benefit from the resources as a whole. An attempt to prevent over-exploitation of every species
will result in a total harvest that is only about 10 % of the multi-species optimum (Branch and
Hilborn 2008).
The various species that frequent the same grounds as hake (skates, panga, gurnard, white
stumpnose etc) are very poorly managed. This situation is somewhat surprising, given the
statement by the industry that many of these species represent an important economic resource,
which it could not easily forgo. Would it be possible to attempt management of the 20 species?
Following discussions at the recently constituted bycatch task team, lead by DAFF, a model
of multi-species catch control that involves government and industry in a co-management
arrangement was suggested. The proposal is that a set of PUCLs be introduced for each of the
main species. Suggested candidates are horse-mackerel, panga, silver kob, St Joseph, white
stumpnose, carpenter and kingklip. A maximum annual tonnage is determined for each species
for the entire inshore fleet. DAFF will review PCLs annually, based on assessments.
Whereas DAFF will manage the individual quota system with respect to hake and sole, it is
proposed that the allocation of the PUCLs among the various rights holders be managed by
South East Coast Inshore Fishing Association (SECIFA). As a starting point each vessel could
get a pro-rata share of the PUCLs, in proportion to their effort allocation (based on the effort
formula). Individual PUCL-quotas could be traded among companies, either in advance of the
season or at an advanced stage during the season once it is known how the catches proportions
have developed. It is suggested that DAFF does not manage the PUCL-quotas. This should be
left to SECIFA in the spirit of co-management.
The intention is to offer the opportunity to SECIFA to ensure that PUCLs are not exceeded.
By allowing trading of PUCL-quotas among right-holders, the incentive to dump fish will be
reduced. The situation may arise when the combined catches approach the PUCLs of one or
more species, after the PUCL-quotas have been allocated. SECIFA should be able to pre-empt
such an event and issue instructions to relevant members to reduce or avoid catches of the
affected specie(s) for the remainder of the year.
In the event that catches do exceed the PUCL of one or more species, DAFF will need to react,
either to prevent further catches of that specie(s) for the remainder of the year, or to prevent a
recurrence of over-catching in the following year. DAFF could achieve this in at least three ways:
•
•
•
Close certain grounds for the remainder of the year, or part of the following year;
Reduce the effort allocation for the following year across the entire fleet, by adjusting the
formula;
Reduce the hake or sole quota for the following year, which would have the effect of
reducing the effort (sea-days) allocation.
These steps will act on the fleet as a whole, not as a punitive measure, but as a last resort to reduce
mortality on affected species. Although the intention is that DAFF does not manage individual
PUCL-quotas, the final allocation of PUCL quotas among right-holders will need to be recorded.
Reduction of the volume of bycatch by input controls and gear restrictions
The most direct method of reducing total bycatch is simply an overall reduction in effort
(Alverson et al. 1996). As this will impact of total landings and revenue, other mechanisms need
to be explored first. These include gear modifications and area and time closures.
Area and time closures
Marine protected areas (MPAs) have been declared in the coastal zone largely for the protection
of coastal biodiversity and the management of non-quota regulated fisheries (Attwood et al. 1997).
The application of MPAs offshore in South Africa is still untested, but it is the recommendation
of the South Africa’s National Biodiversity Institute to establish MPAs for the conservation of
offshore biodiversity, consistent with national policy guidelines (Sink and Attwood 2008). The
closure of fishing grounds has long been regarded as a possible mechanism to regulate the impact
of fisheries. Hilborn et al. (2002) list the potential applications in fisheries and the situations in
which such regulations are more likely to be effective. They cite reduction of collateral damage as
one such application, with reference to habitat damage and bycatch. However, they also caution
that effort displacement may cause undesirable consequences elsewhere.
Attwood et al. (2010) identified several areas of similarity with respect to species assemblages
in catches. Lombard et al. (2010) searched for potential areas for closure, using catch per unit
effort data averaged over 20’ x 20’ grid-blocks across as a surrogate for species abundance.
These data were used in a decision support software tool, Marxan (Possingham et al. 2000) to
identify areas that achieved quantitative targets for bycatch reduction, while minimizing the cost
to the industry. Marxan uses an objective function to identify the best set of areas for closure, or
a number of possible sets that will meet the objectives. The objective function does not explicitly
consider effort displacement, so this component is handled separately, once the best set(s)
has(ve) been identified.
The objective function that was used to define the search required selection of areas that
represented 20% for all 27 species (as measured by CPUE) while selecting grid-blocks for
closure with the lowest recorded trawl effort. The rationale was that the industry would be less
willing to forgo heavily-trawled than lightly-trawled areas. No attempt was made to clump
the solutions, i.e. to choose grid-blocks that are adjacent. Although this may have presented a
solution that is easier to manage, it generally comes at the cost of having to select more gridblocks to achieve the objective.
Seven grid-blocks were selected for the most efficient solution. These included 553 (Blues), 513
(Mossel Bay), 515 (Knysna), 517 (Tsitsikamma), 629 (South of Algoa Bay), 632 (Bird Island)
and 640 (Port Alfred). The cost amounted to a 10% loss of trawl tracks, i.e., the areas selected
contained 10% of the trawling effort.
The fact that areas selected are widely separated reflects the need to protect the full diversity. Fig
1 shows the trawl tracks super-imposed on the ‘best solution’, from which it is clear why certain
grid-blocks were selected. Marxan searched using average CPUE and not total catch, while
selecting for grid-blocks with the lowest effort. Grid-block 553, for example, is representative of
the ‘Blues’, but is only partially trawled, presumably as the north-western part of the grid-block is
rough ground. Likewise the remaining inshore blocks contain relatively low effort, yet represented
sole grounds (Algoa Bay region and Mossel Bay), and the cold water intrusion off Tsitsikamma.
The lack of a grid-block selected off the Infanta to Still Bay coast reflects the intensity of trawling
there, and the fact that similar species assemblage is found in the Algoa Bay region. Another
explanation for the selection of lightly-trawled areas is that they represent marginal habitat for
target species, and as a result contain a higher biomass of non-target species.
Figure 1. The best solution that achieves the target of representing 20% of the abundance of 27
bycatch species, while minimizing the loss of fishing ground. Red blocks represented grid-blocks
selected for closure. Green represents the trawl tracks.
The danger of effort displacement is not a concern if the Marxan solution attempts to reduce
effort as little as possible. A number of modeling studies have recommended effort reduction
as a means to overcome the displacement problem (Guénette et al. 2000, Hilborn et al. 2006),
but none of these have reckoned with the plasticity provided by spatial variation in species
composition across the ground.
Are the selected grid-blocks a practical set for closure? It might not be practical to close the
entire grid-blocks, where selections entirely block trawl tracks. The Marxan solution needs
to be treated with some flexibility. Closure would not have to follow grid-block shapes, or
even be limited to the grid-block selected, but would need to be located in that region to be
representative. Shapes should be selected to interfere with trawling as little as possible, and may
need to be aligned with the tracks.
An advantage of opting for closed areas is that it may coincide with the recommendations
emerging from the broader Protected Area Expansion Strategy. As there will be pressure to
declare marine protected areas in the offshore environment, it would preferable to ensure that
these will not disadvantage the industry, and that it will promote the protection of unregulated
species after effort displacement.
The existing closed areas include all shallow bays, as defined by a series of straight lines joining
prominent Capes. The rationale for these closures was to protect nurseries of fish such as
shallow-water hake (Badenhorst and Smale 1991) and silver kob (Smale and Badenhorst 1991).
The time-area closures have been suggested for the Infanta region as a possible means to protect
silver kob (SADSTIA 2010). To assess this idea, we need to examine the seasonal trends in silver
kob and other species.
Seasonal closures
Placing a moratorium on trawling in some months and in some areas may reduce the catch
of species that are known to aggregate in those areas. The kingklip box south-west of Port
Elizabeth is an example of such a restriction applied to the offshore fishery. In that case the
restriction is applied to protect spawning aggregations of kingklip.
Are there aggregations of species on the inshore trawl ground at certain times of the year? CPUE
records from the observer data were averaged by month for each area. The areas used for this
analysis were the seven broad areas defined in Attwood et al. (2010) (Fig 2).
Figure 2. A map showing demersal trawl grid and the seven areas defined on the basis of
species composition.
Hake showed no clear seasonal trends in CPUE (Fig 3). No trend is evident on individual
grounds either. The same is true of dogfishes which are 9th on the catch list. There is no
obvious explanation for the consistently low catch in June of dogfishes, and this merits further
investigation. Gurnards catch rates across all areas were highest from August to November, but
the variability was too high to confirm any trend. May to July showed unusually low catches
rates of gurnard. In the case of east coast sole, 6th on the catch list, it would appear that January
and February trawling yields the worst results, but again, no clear agreement with respect the
remainder of the year on each of the grounds. It is quite conceivable that that sample sizes were
too small to detect clear trends on individual grounds.
Figure 3. Seasonal trends in the catch per unit effort of species caught by inshore trawlers from
2003 to 2006. Where clear trends are evident, the data are split into the various zones. Data are
only shown for zones where the species are commonly caught. The absence of a bar indicates
insufficient data (n < 10 trawls). Error bars indicate standard error.
Clear seasonal trends were evident in a number of other species despite small sample sizes. The
first of these is silver kob, which is tenth on the list. This species is clearly more available to
trawlers in winter on the three major grounds where it is caught. The inshore-offshore migration
of this species was first mentioned by Griffiths (1996), who noted higher linefish catches in
shallow water in summer. There is some indication of an east-west migration in panga, the third
most abundant catch. These fish are abundant off Algoa Bay in winter and abundant off Still Bay
in summer. This trend confirms previous findings (Uozumi et al. 1984, Badenhorst and Smale
1991). Panga seem to spawn predominantly in the east in late winter and recruit in the west.
Average panga sizes increase from west to east.
White stumpnose is fairly low on the catch list (12th) and variances are high, but again there is
an indication of higher CPUE in winter and spring. Similar to silver kob, this species spawns
offshore in spring, and migrates to shallow water in summer (Griffiths et al. 2002).
The lumping of skate species is likely to obscure species-specific trends. Nevertheless, a seasonal
trend is evident, again peaking in late winter. The trend for zone 3 (Blues) may in fact be
spurious, because of one very large catch taken in July which pushed up the variance. The other
two zones (4 and 6) show elevated catch rates in winter (July to September).
The onshore-offshore migration seems to be a pattern followed by several unrelated species.
The shallow waters are more productive and warmer in summer. In winter these species seek
refuge in the cooler and deeper water, less affected by the seasons, where they build gonads for
spawning. For the reduction of bycatch, time-area closures could include zones 2, 4 and 6 during
late winter.
Restrictions on night trawls
The fishery shows a strong diurnal pattern with typically four trawls in daylight hours, and, in
approximately one third of voyages, two additional trawls at night. Night trawls are directed at
sole. The net-on-bottom time was 2.6 h for day-time trawls and 4.7 h for night-time trawls. This
difference is significant. Night trawls accounted for more than 15% of all trawls in grid-blocks
521, 523, 524, 536, 537 and 539 (i.e. zones 2 and 4). Night trawls in zone 6 made up about 8%
of all trawls. Elsewhere night trawling was infrequent. Duration of net tow differed significantly
between day and night.
Diversity per haul is partly a function of trawl duration. The longer the trawl, the greater
diversity of habitat covered (Alverson et al. 1996). Survivorship of incidental bycatch is also
reduced by longer tows. For bycatch species such as large sharks and turtles, it would be
advisable to keep the tows short, to increase their chances of survival. However, the bycatch in
the inshore trawl does not include incidental catches of large mammals, birds or reptiles. The
majority of the bycatch are marketable fish and sharks, and there will not be much incentive to
return fish. Survivorship of incidental bycatch is not a major concern in this fishery.
Figure 4. Comparison of catch per unit effort between day and night trawls by zone. The error
bar refers to one standard error.
There may, however, be a difference in the availability of certain bycatch species to trawls
between day and night. If so, restrictions could limit trawls to a particular time of day when a
cleaner catch can be expected. Given that night trawls were only a feature on sole grounds, the
catches of east coast sole and silver kob were examined in these zone (Fig 4). For neither of these
species was there a significant difference between day and night catch per unit effort, except for
east coast sole in zone 2, where daytime catches were greater.
Other species were examined comprehensively during the Japan/South Africa joint trawling
survey (Hatanaka et al. 1980). In these surveys, it was found that panga catches did not differ
between day and night on the central Agulhas bank, but catches were greater in the daytime on
the eastern Agulhas bank. Hake and horse mackerel catches were greater in the day everywhere.
These two species migrate off the bottom at night. Investigations into other species were not
attempted, as it does not seem there is much merit in a night trawling ban, given the good
availability of east coast sole at night and the lack of diurnal differences in catch rates with
respect to silver kob and panga.
Recommendations
The bycatch of the inshore trawl can be addressed simply by re-classifying many of commonly
caught species from bycatch to targets. This shift will properly reflect the status of the fishery
as a mixed trawl fishery, which depends on a variety of species. These multiple targets need to
managed, which will entail setting objectives (targets and limit reference points), implementing
an effective monitoring and assessment framework, and regulating the fishery to achieve these
objectives. The recommendation to involve SECIFA in a co-management arrangement partly
reflects the lack of capacity in DAFF, and partly the desire to prevent the implementation of
strict quotas from providing an incentive to dump.
This document follows from a number of other documents (Japp 1994, Smale and Badenhorst
1996, Walmsley et al. 2006 and SADSTIA 2010), each recommending and evaluating options.
There seems to be some commonality in respect of the desire to expand the quota system to
other species and try closed areas. Above all, the value of the observer program is highlighted as
the best method to gain insights into the bycatch problem.
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Poster Contribution
Shore-based recreational angling catches and catch
per unit effort adjacent to Agulhas and West Coast
National Parks
M T Dopolo
South African National Parks, Conservation Services Division
Cape Research Centre, P. O. Box 216, Steenberg, 7947
South Africa.
Abstract
Marine resources are difficult to manage due to uncertainty regarding population sizes and
recruitment variability as a result of shortfalls in data (i.e. monitoring). To address this, South
African National Parks has established a marine resource monitoring program to assess shorebased recreational angling patterns adjacent to the Agulhas National Park (ANP) and West
Coast National Park (WCNP, Langebaan Lagoon marine protected area). Data were collected
using a roving creel survey where recreational, shore-based anglers were counted and a
proportion interviewed. A total of 301 and 274 shore patrols were completed adjacent to ANP
and Langebaan Lagoon marine protected area (MPA) respectively. A total of 11 families (6
teleosts and 5 elasmobranchs) representing 19 species of fish were recorded in the area adjacent
to ANP, while only one family representing four teleosts species were recorded in Langebaan
Lagoon MPA. Catches adjacent to ANP were dominated by silver kob Argyrosomus inodorus
(26%), sand shark Rhinobatos annulatus (22%) and elf Pomatomus saltatrix (11%). At the
WCNP, catches were dominated by white stumpnose Rhabdosargus globiceps (64%) and
steentjie Spondyliosoma emarginatum (30%). Overall shore angling catch per unit effort (cpue)
adjacent to ANP was stable at about 2 fish per 10 angler days during the four month period,
while Langebaan Lagoon MPA cpue was highly variable (1-6 fish per 10 angler days) over the
three year period (2009-2011). Anglers adjacent to ANP appeared to be more knowledgeable
about fishing regulations as they often released undersized fish, and most of the elasmobranchs.
Even though temporal and spatial coverage of the study area was limited due to financial and
logistical constraints, results provide useful insights into the catches and cpue for shore-based
recreational fishing.
Introduction
The demand for access to marine natural resources for subsistence, recreational and
commercial use is increasing, despite the decline in many of the actively managed resources
(Love 2006). Marine resources are difficult to manage because of high levels of uncertainty
regarding population sizes and recruitment variability, principally because of a lack of data
(i.e. monitoring). In addition, poorly controlled fishing effort has resulted in the collapse of
many of South Africa’s linefish stocks (Sauer et al. 2003). To address this challenge of a lack of
data to support management decisions, South African National Parks (SANParks) developed
a Biodiversity Monitoring System (BMS) (McGeoch et al. 2011) that guides the development
of a prioritized system of Monitoring Programs. For example, the Resource Use Monitoring
Program, aims to quantify the amount (e.g. catches or catch per unit effort) of various resources
are being harvested for different purposes within National Parks (including marine protected
areas) and areas adjacent to the Parks. Monitoring of recreational shore-based catches has
previously been neglected for logistical reasons despite scientists highlighting the need for a
standard monitoring approach to allow collation of the quantitative data on recreational fishing
effort, catches, and cpue (Attwood 2003). Thus monitoring of catch and effort is essential for
management interventions because changes in measured variables would highlight collapse
of stocks or ecosystems, and can bring about a quicker response from management (Griffiths
2000). This study provides a snapshot assessment of shore-based recreational fishing catches
and catch per unit effort (cpue) from a roving creel survey. These data will also contribute to the
national recreational linefish research program.
Methods
Study Area
The Agulhas National Park is located approximately 260 km south east of Cape Town and 37 km
south-west of Bredasdorp. It covers and area of approximately 72 km from Gansbaai (34º 35’
S, 19º 21’ E) in the west to Struisbaai (34º 49’ S, 20º 03’ E) in the east (Fig. 1a). The shoreline
adjacent to the Park is however not a marine protected area. The West Coast National Park is
located approximately 100 km northwest of Cape Town on the Atlantic seaboard in the Western
Cape Province. The Park includes the Langebaan lagoon and the offshore islands of Marcus,
Malgas, Schappen and Jutten (Fig. 1b).
The monitoring program in ANP was designed to cover the area between Buffelsjags on the
east and De Mond Estuary on the far west adjacent to ANP, and the total length of the coastline
covered by the program is approximately 70 km (Figure 1). The WCNP the monitoring program
was designed to cover the area between Klein Oostewal within the Langebaan Lagoon MPA
and Sea Harvest Fish Factory in Saldanha Bay. The total length of the coastline covered by the
program is approximately 40 km (Figure 1). For the purpose of the shore patrols, the coastline
was broken into short sections that could be covered on foot in a period of no more than 2-3
hours each, i.e. each patrol beat is in the range of 5-8 km. The end of each beat corresponded
with a convenient access point at which monitors could be collected and/or dropped off.
Survey technique
A roving creel survey (RCS) was used to collect data from shore-based anglers. RCS is an on-site,
intercept design method that is widely used to gather recreational fisheries catch and effort data.
Monitoring patrols are set out according to a predetermined and randomised schedule, with
randomised areas and start times. Because anglers are intercepted during the act of fishing, and
not when trips are completed, this type of RCS is an incomplete survey and thus total catch is
not estimated directly but calculated as the product of effort and catch rates. The randomised
selection of areas and start times was constrained by budgetary and logistical constraints, as
well as security of monitors.
The number of sampling days and patrol areas was allocated such that all the abovementioned
constraints were minimised. Patrol days were randomly selected such that monitors worked five
to seven days a week, including a weekend or public holiday. Start times were randomly selected
such the start time ranged between 07h00 and 16h00.
On any sampling day, the monitor(s) moved unidirectionally through the coastal strip, stopping
only for angler interviews. When more than two anglers fish as a group, only a representative
number of a group of anglers is interviewed. The daily survey was terminated when all anglers
were interviewed within that particular coastal strip. During the interview, the fishing start
time and interview time were recorded. All captured fish were identified, and then measured
individually (nearest millimetres total length, TL).
ANP PATROL AREAS
(1) Buffelsjags – Quin Point
(2) Quin Point – Caravan Park
(3) Caravan Park – Ratelriviermond
(4) Ratelriviermond – Rietfontein se Baai
(5) Rietfontein se Baai – Brandfontein
(6) Brandfontein – Doug Jeffery’s
(7) Doug Jeffery’s – Suidestrand
(8) Suidestrand – Agulhas Campsite
(9) Agulhas Campsite – Struisbaai Harbour
(10) Struisbaai Harbour – Andrews Field
(11) Andrews Field – De Mond Estuary
WCNP PATROL AREAS
(1) Klein Oostewal – Alabama Slipway
(2) Alabama Slipway – Club Mykonos
(3) Spruwall – Die Dam
(4) Blue Water Bay – Sea Harvet
(Saldanha Bay)
Figure 1: Site map showing the spatial location of the roving creel survey shore patrol areas
adjacent to Agulhas and West Coast National Parks during the period of the study.
Catch per unit effort (cpue)
The daily catch per unit effort (CPUE) for recreational shore anglers was estimated based on the
formula described by Lo et al. (1992):
where TCmonth,i is the total number of fish caught each month, of an interviewed angler in the
sample having caught per i month. Ei is the total effort per i month estimated as the total
number of anglers interviewed during the total surveys conducted during each i month.
Results
Sampling effort
A total number of 301 (75 ± 12.5 per month) shore patrols for the period December 2011 until
end of March 2012 were completed in the coastal areas adjacent to ANP, whereas only 274 (11
± 1.8 per month) shore patrols were completed off the Langebaan Lagoon MPA for the period
September 2009 until end of December 2011. The average number of patrols per month off the
Langebaan Lagoon MPA was substantially lower than that completed off ANP or any other area
monitored by SANParks. The monitor’s effort in this area was split between Boat Point Count
Survey and Roving Creel Survey thus the average and total effort was substantially lower. This
will in the near future change as Boat Point Count Surveys will no longer be conducted due
to unreliability of the data and a Shore-Based Boat Count Program will be initiated, which is
envisaged to minimise the amount of error in the data.
Species catch composition
In total, 11 families (six teleosts and five elasmobranchs) representing 19 species were recorded
during the roving creel survey shore patrols adjacent to Agulhas National Park during the four
month study period (Table 1). Teleosts dominated the species composition by constituting 14
species, and elasmobranchs constituting the remaining 6 species. Silver kob Argyrosomus
inodorus, sand shark Rhinobatos annulatus and elf Pomatomus saltatrix were the dominant
species caught by shore-based anglers, accounting for over 70% of the catch composition
adjacent to ANP.
Only one teleost family that represented four species recorded during the roving creel survey
shore patrols adjacent to West Coast National Park (Langebaan lagoon MPA) during the over
two year study period (Table 2). White stumpnose Rhabdosargus globiceps and steentjie
Spondyliosoma emarginatum were the dominant species caught by shore-based anglers,
accounting for over 90% of the catch composition.
Size frequency distribution
Size frequency distributions for the most commonly caught fish by shore-based anglers adjacent
to ANP and WCNP are illustrated in Figure 2. The size frequency distribution of silver kob
was bimodal with a primary peak at 60-75 cm TL, and a secondary peak at 15-20 cm. The
distribution was right skewed, with the largest fish caught recorded at 1.7 m and the smallest at
15 cm (Fig. 2a). The size distribution for white stumpnose was unimodal with a peak between
26 and 32 cm (Fig. 2b). The size distribution for steentjie was bimodal with a primary peak
between 22 and 30 cm, and a secondary peak at 64 cm. The curve was right skewed with the
largest fish caught recorded at 66 cm and the smallest at 18 cm (Fig. 2c). These results show that
a substantial proportion of silver kob were below the minimum size limit of 50 cm despite the
numbers caught being very low. For white stumpnose, only a small proportion of fish recorded
were below the minimum size limits of 25 cm. There is no minimum size limit for steentjie.
Catch per unit effort (cpue)
Figure 3 illustrates a pooled monthly cpue during the four months period in the area adjacent to
the ANP and the two year period in the area adjacent to the WCNP (Langebaan Lagoon MPA).
Pooled cpue was stable at approximately two fish per 10 angler days adjacent to ANP (Fig. 3a).
The highest pooled cpue was recorded in September in Langebaan Lagoon MPA, and
subsequent to that it ranged just below 1 and 2 fish per 10 angler days. The highest cpue was
only observed at the start of the program in 2009. This is possibly an artefact of the change in
sampling effort. During the first year (2009), monitoring was conducted throughout the week
to include weekends and public holidays. This changed in the subsequent years due to labour
practice regulations.
Table 1: Recorded species composition for shore-anglers adjacent to ANP for the period
December 2011 until end of March 2011. Note this list is subject to misreporting by anglers and /
or monitors.
Species
Number
Percentage
3
1
4
2
8
3
27
11
63
27
Umbrina species
7
3
1
0
Diplodus sargus
5
2
Teleosts
Carangindae
Lichia amia
Clinidae
Several species
Dichistiidae
Dichistius capensis
Pomatomidae
Pomatomus saltatrix
Sciaenidae
Sparidae
Diplodus hottentotus
4
2
8
3
Lithognathus lithognathus
6
2
Sarpa salpa
25
10
Sparodon durbanensis
8
3
3
1
1
0
4
2
Haploblepharus pictus
4
2
Poroderma africanum
2
1
52
21
Elasmobranchs
Carcharhinidae
Carcharhinus brachyurus
Dasyatidae
Dasyatis pastinaca
Ondontaspidae
Carcharias taurus
Scyliorhinidae
Rhinobatidae
Rhinobatos annulatus
Table 2: Recorded species composition for shore-anglers adjacent to Langebaan Lagoon MPA
(WCNP) for the period September 2009 until end of December 2011. Note this list is subject to
misreporting by anglers and /or monitors.
Species
Number
Percentage
Diplodus sargus
11
2
296
64
Sarpa salpa
18
4
Spondyliosoma emarginatum
140
30
Sparidae
Discussion
Understanding the level of catch and effort associated with shore-based recreational fishing
is essential for the sustainable management of several fish stocks along the South African
coastline. However, surveying recreational shore-based fishing can be complex because it occurs
over wide spread areas and temporal scales and it is challenging to design a robust survey
(Smallwood et al. 2011). The monthly average shore-based fishing effort was estimated to be
362 (SE± 25.8) at ANP and 195 (SE± 7.7) at WCNP. The differences in angler effort may be
an artifact of sampling effort as the number of shore patrols was substantially low in WCNP
(11 ± 1.8) than in ANP (75 ± 12.5). The catch data showed that the shore-based recreational
angling adjacent to ANP was targeting a diverse range of species, which is attributed the highly
dynamic hydrographic nature of the Agulhas Bank region (Shannon 1966). Silver kob is the
most sought after species in the area. Most (~95%) of the elasmobranchs species caught were
released back into the water. The Langebaan Lagoon MPA catch composition was characterized
by less diverse species family (Spariade only) and species level (only four species recorded) than
ANP. The roving creel surveys is the only method from which data on trip length and the catch
of shore-based fishers could be obtained, which will subsequently enable calculation of catch
rate. This information cannot be collected cost-effectively using other methods, such as phone/
diary surveys, without a known sampling frame. These preliminary findings will contribute
to the establishment of a benchmark from which changes in catches and cpue of shore-based
recreational fishing activity can be monitored by the South African National Parks.
Acknowledgements
Thanks are due to Alban Blake (Research assistant for the Cape Research Centre based in
Langebaan) for capturing the data sheets. Zishan Ebrahim (Biodiversity Data Scientist/
GIS Technician, Cape Research Centre) is thanked for producing the maps. Jolene Waller
(Administrative Assistant, Cape Research Centre) is thanked for proof reading the first draft
manuscript. A special thanks to my boss, Professor Extraordinary Melodie McGeoch, Head of the
Cape Research Centre for invaluable comments to improve the quality of this extended abstract.
References
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Figure 2: Size frequency distributions of the most common species (a) silver kob Argyrosomus
inodorus, (b) white stumpnose Rhabdosargus globiceps and (c) steentjie Spondyliosoma
emarginatum caught by shore-based anglers recorded off the ANP and WCN coastlines during
the study period. Note: The dotted vertical line marks the minimum size limit for each species.
In Fig. 2c, the dotted vertical line marks what might be a minimum size limit for steentjie
based on the life history parameters reported by Fairhurst et al. (2007), which currently has no
minimum size limit. Note: The scales on the y-axes are not equal between figures.
Figure 3: Pooled monthly catch per unit effort (CPUE) per 10 angler days adjacent to (a)
Agulhas National Park and (b) West Coast National Park for the duration of the study.
Report at a
Glance: 2013
21
250
Species caught in local
linefishery
450
Number of commercial
linefish boats
1658
The year that Jan Van
Riebeeck passed the first
linefishing regulation in
South Africa
The Proceedings of the 4th Linefish Symposium
Number of marine protected areas along
South Africa’s coastline

A DecADe After the emergency

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