The Dublin Bay Prawn

Age and Growth
Nephrops can grow up to ~ 80mm CL but can be legally
caught by the fishery when they are larger than 20mm CL in
the Irish Sea and 25mm in the other Irish fishing grounds.
„
Age and Growth
Due to difficulties
coupled
their
Nephrops
can grow inupageing
to ~ 80mm
CL with
but can
be complex
legally
Nephrops
biology
and
behaviour
stock
assessment
of
caught by the fishery when they are larger than 20mm is
notoriously
difficult.
CL
in the Irish
Sea and 25mm in the other Irish fishing
grounds.
Since 2002 the Marine Institute has been using underwater
television
surveys in
toageing
independently
estimate
Due
to difficulties
coupled with
their abundance,
complex
distribution
and
stock
sizes
on
the
Aran
Grounds,
Western
biology and behaviour stock assessment of Nephrops
is
Irish
Sea
and
the
Celtic
Sea
(Smalls).
This
method
has
great
notoriously difficult.
potential as a basis for assessment and advice for poorly
understood
Nephrops
Since
2002 the
Marinestocks.
Institute has been using
-2°
-6°
-10°
-14°
-18°
underwater television surveys to independently estimate
abundance, distribution and stock sizes on the Aran
Grounds and Western Irish Sea. This method has great
Nephrops
around
potentialfishing
as a grounds
basis for
assessment and advice for poorly
the
Irish
coast
are
shown
in
red
understood Nephrops stocks.
60°
48
The Fisheries Science Services Team
In order to ensure the sustainable harvesting of the fisheries
resources, it is essential that management is underpinned by
sound marine science that is clear, transparent, timely, impartial
and inclusive.
The Marine Institute’s
Fisheries
Science Service
Fisheries
Science
Services
TeamTeam
works
closely with the fishing industry to provide this marine science
Providing
through.the best possible scientific advice for fisheries management requires the collection of a range of datasets from the various
fisheries.
• Research Vessel Surveys (Acoustic, Groundfish, Egg and Larval
Fish, Underwater TV)
•
on Commercial
Vessels
TheSurveys
Marine Institute’s
Fisheries
Science Services Team works
• Market
Landingsto gain this information through:
closely
withSampling
the fishingofindustry
• Discard Sampling at Sea
x
Research vessel surveys (Acoustic, Groundfish, Larval
• Analysis Fish,
of Logbook
DataTV)
Underwater
• Studies on the Biology of Fish
x
Research on commercial vessels
• Working with the Regional Advisory Councils (RAC’s)
x
Market
sampling
of landings
• Articles
in the trade
press
• Working
with our
international
x
Discard
sampling
at sea scientific colleagues
• Regular meetings with Industry Representatives and DCMNR
x
Analysis
Logbook
• Regular
Meetingsofwith
EU data
www.marine.ie
A DEEPER UNDERSTANDING...
THE DUBLIN
B
AY
P
RAWN
The Dublin
A deeper understanding...
Bay Prawn
x
Studies on the biology of fish
This information is essential to our understanding of the current
state
of the fisheries
resources
the ecosystem
which they
This
information
is essential
to our and
understanding
of theincurrent
state
live.of fish stocks.
47
46
More detailed information, as well as similar leaflets on related
issues are available from
45
44
43
58°
VIb
VIa
Marine Institute, Fisheries Science Services (FSS), Rinville,
Oranmore, Co. Galway, Ireland. Phone: + 353(0) 91 387200
42
41
56°
40
39
38
37
36
VIIc
54°
VIIb
35
VIIa
34
Marine Institute,
MARINE
INSTITUTE
Fisheries
Science
ServicesREGIONAL
(FSS),
OFFICES & LABORATORIES
Galway Technology Park,
MARINE INSTITUTE Parkmore,
MARINE Galway,
INSTITUTE
Ireland. MARINE INSTITUTE
Assessing, researching and advising on
the sustainable exploitation of living
marine resources in a healthy
ecosystem
HEADQUARTERS
33
52°
32
31
VIIg
30
29
Or your local Port Based Technician in
Clogherhead
(041) 9889788
Dunmore East
(051) 385011
Castletownbere
(027)
71937 on this topic, as well as
More detailed information
Rossimilar
a Mhíl leaflets (091)
572584
on other
fisheries related issues are
Killybegs
(074)
9741871
available from:
FISHERIES SCIENCE SERVICES
VIIj
VIIf
VIIk
50°
28
VIIe
27
26
the fishing ports of:-
VIIh
25
D2 D3 D4 D5
D6 D7
D8 D9
E0 E1
E2
Rinville,
Furnace
80 Harcourt Street
Phone:+
91 730 400 Newport
Oranmore,
Dublin353(0)
2
Website:
Co. Galway
1 4766500
Co. Mayo
Tel: +353www.marine.ie
Tel: +353 91 387200
Tel: +353 98 42300
Fax: +353 1 4784988
your
local Fisheries Assessment Technician
at
Fax:or
+353
91 387201
Fax: +353 98 42340
E3
E4
E5
E6
E7
48°
Howth
Dunmore East
Castletownbere
(01) 8228200
www.marine.ie
(051) 385011
(027) 71937
Fisheries Science Services
Assessing, researching and advising on the
Recently
hatched egg
Stage I
(~6.5mm total
length)
Stage II
(~9mm total
length)
Nephrops - Dublin Bay Prawn
Nephrops norvegicus, also know as Dublin Bay prawns and
Norwegian lobster, are the second most valuable species fished
by the Irish fleet. In 2002 landings were worth almost €28
million. Nephrops are also a very important species for the
processing industry in Ireland that use prawns to produce the
value added product 'scampi'. Marine Institute scientists have
spent many years researching the biology and stock dynamics
this commercially important species.
Stage III
(~12mm total
length)
Nephrops is a widely distributed species but despite its common
name, the “Dublin Bay Prawn”, this species is not found in
Dublin Bay. It is found, however, in the Irish Sea, the Celtic Sea
and off the West Coast of Ireland. It is also found from Iceland
to Morocco and into the Mediterranean as far as Egypt,
occurring at depths from 15m to 800m.
Biology of Nephrops
Its location is mainly dependent on the availability of soft
substrate in which it can construct its burrows. Nephrops spend
a great deal of time in their burrows and their emergence from
these is related to time of year, light intensity and tidal strength.
These factors are often thought to be responsible for huge
fluctuations in catch size. Burrows are particularly important to
Nephrops as they offer protection from potential predators.
One of their main predators is cod, but other species are also
known to feed on them e.g. rays and dogfish.
Stage IV
(~16mm total
length)
Carapace Length
Adult
They are particularly vulnerable to predation when they have
recently moulted (shed) their old shell and while their new
shell has not yet hardened. During the course of their
lifetime Nephrops will moult at least once a year. This is
because the Nephrops shell cannot grow with the individual
and in order to increase in size they must shed the old one
and a new larger one will replace it. Nephrops tend to remain
in their burrows throughout this period.
Reproduction
Female Nephrops reach maturity at approximately 23 mm
CL (carapace length), while male Nephrops are thought to be
mature at 26 mm CL. Once mature, the female ovary begins
to ripen and slowly changes colour from cream to dark green
through the course of the summer. This colour change can
be seen through the carapace (thorax) wall. The eggs are
spawned and fertilised in autumn. They are carried on the
underside of the female’s tail (abdomen) where they remain
for the eight to nine months incubation period. Females tend
to remain in their burrows during incubation, thus explaining
the disappearance of females from the catch over the winter
months.
Hatching occurs from April until June producing minute
larvae, which bear no resemblance to the adults. These
larvae go through 4 stages (3 of which are free-swimming)
over a 40-day period prior to becoming a juvenile Nephrops.
These juveniles have a carapace length of 2-3 mm. They are
thought to share the burrows of the adults for the first
months of their lives before constructing their own.