Inia geoffrensis and Sotalia fluviatilis Monitoring Study: June 2014

Transcription

INIA GEOFFRENSIS AND SOTALIA FLUVIATILIS
MONITORING STUDY
Author: Leah Gainey
June 2014
Contents
Introduction .......................................................................................................................................... 2
1. Inia geoffrensis and Sotalia fluviatilis................................................................................................ 3
1.1 Description .................................................................................................................................. 3
1.2 Distribution in Brazil.................................................................................................................... 4
1.3. Habitat and ecology ................................................................................................................... 5
1.3.1 Inia geoffrensis ..................................................................................................................... 5
1.3.2 Sotalia fluviatilis ................................................................................................................... 6
1.4. Threats ....................................................................................................................................... 7
1.4.1 Inia geoffrensis ..................................................................................................................... 7
1.4.2 Sotalia fluviatilis ................................................................................................................... 7
2. Inia geoffrensis and Sotalia fluviatilis in Borba ................................................................................. 8
3. Why do we want to conserve the river dolphins? .......................................................................... 10
4. Monitoring Inia geoffrensis and Sotalia fluviatilis in Borba............................................................. 11
5. Conclusion....................................................................................................................................... 12
6. References ...................................................................................................................................... 14
Trocano Araretama Conservation Project Inia geoffrensis and Sotalia fluviatilis Monitoring Study 2014
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Introduction
The area comprising the Trocano Araretama project is significant in terms of its biodiversity value, as
it is located in the tropical forest eco-region. For this reason, it can be assumed that there is a high
level of biodiversity present in the project area that is of high ecological significance. However, the
degree of threat that exists there, as well as the ecological importance of land mammals of small,
medium and large size, illustrates the need to search for information on inventories and
environmental diagnostics for this region.
With this in mind, we analysed some of the species documented in the “Research on Madeira River
Biodiversity: Scientific Grounds and Conservation Proposals" (Biodiversidade do Medio Madeira:
Bases Científicas para Propostas de Conservação) written by Rapp Py-Daniel et al (2007), which
detected endemic species found in the region near to the project area and its surroundings. Later,
we checked the threat status of each species on the IUCN Red List, and we discovered that there are
two species of river dolphin in the project area: Inia geoffrensis and Sotalia fluviatilis. The IUCN is
unsure of the status of both species and therefore it is crucial that a monitoring plan be
implemented in Borba to obtain species distribution information and assess their vulnerability.
As one of the main objectives of the Trocano Araretama project is to protect and enhance
biodiversity in the area, it is mandatory to discover which species are threatened or vulnerable
(something that we have already done), identify the threats to those species, study them, and finally
develop conservation actions that improve the conditions of those animals. The Brazilian
Government are also recognising the need to conserve their dolphin populations, which was
indicated by the introduction of legislation on the 3rd of June 2014. The legislation implements a
temporary ban on the fishing of a species of catfish known as the piracatinga, which are illegally
baited with I. geoffrensis flesh, and the new legislation (coming into effect in 2015) is hoped to
improve the status of the species.
In 1994, Drs Vera da Silva and Tony Martin established ‘Project Boto’ in the Mamirauá Sustainable
Development Reserve. The project focused on the conservation of both Inia geoffrensis and Sotalia
fluviatilis through extensive monitoring using a variety of methods that are described further in the
document. The project made some important conclusions surrounding threats to dolphin
populations in the area that are applicable to the proposed study in question. It is our hope to
replicate elements of Project Boto for the Trocano Araretama Project in order to establish
information surrounding existing populations of both I. geoffrensis (boto) and S. fluviatilis (tucuxi) in
Borba.
Thus, with the first step already done, we must focus on the second one, and study the species and
their threats, developing specific biodiversity monitoring plans.
‘Inaction in the past necessitates immediate actions and bold leadership from now on, to save both
river dolphins and ourselves’- WWF Report (2010).
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1. Inia geoffrensis and Sotalia fluviatilis
1.1 Description
I. geoffrensis (Image 1), more commonly known as the boto, is considered the largest freshwater
cetacean. Body length can range from 1.53 m to 2.4 m (5.0 ft. to 7.9 ft.), depending on subspecies.
The largest female Amazon River dolphins can range up to 2.5 m (8.2 ft.) in length and weigh 98.5 kg
(217 lb). The largest male dolphins can range up to 2.0 m (6.6 ft.) in length and weigh 94 kg (207 lb).
Their unfused neck vertebrae give them the ability to rotate their heads 90 degrees. This flexibility
enables their navigation through the flooded forests. Also, they possess long beaks which contain 24
to 34 conical and molar-type teeth on each side of the jaws. In colour, these dolphins can be either
light grey or carnation pink.
Image 1: Inia geoffrensis. Source: animais.cultramix.com
S. fluviatilis (Image 2), more commonly known as the tucuxi is often noted to be similar in
appearance to the bottlenose dolphin, although it is generally smaller at around 1.5 m (4.9 ft.). The
dolphin is coloured light to bluish grey on its back and sides. Their ventral region is much lighter,
often pinkish and they have a slightly hooked dorsal fluke. Their beak is well-defined and of
moderate length containing approximately 26 to 36 pairs of teeth in the upper and lower jaws.
Image 2: Sotalia fluviatilis. Source: The Encyclopedia of Earth
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1.2 Distribution in Brazil
Botos occur throughout the Amazon and Orinoco river basins, from the deltas upstream to where
impassable rapids, waterfalls, lack of water, and possibly low temperatures block their movement
(Best and da Silva 1989a,b). Three geographic populations have been recognised as subspecies: I. g.
geoffrensis in the Amazon basin, except for the Madeira drainage in Bolivia above the Teotonio
rapids, I. g. boliviensis in the upper Madeira drainage, and I. g. humboldltiana in the Orinoco basin
(Rice1998).
Besides the Amazon main stem, I. geoffrensis has been recorded in the Tocantins (and das Mortes
and Verde affluents), Xingu, Tapajós, Madeira (below the Teotonio rapids), Purus, Juruá, Ucayali, and
Marañon (and Samiria affluent) tributaries flowing generally north, and in the Negro, Caqueta
(Japurá), Apaporis, Putumayo, Napo, and Tigre tributaries flowing generally south (partial list from
Best and da Silva 1989a,b; Leatherwood 1996). In the Brazilian portion of the Amazon basin, data are
available on abundance and encounter rates for only a few river segments: 107 individuals counted
(0.19 dolphins/km; ± 0.06) in a 490 km segment of the Solimões River, Brazil in August 1979
(Magnusson et al. 1980); 0.22 dolphins/km (± 0.04) observed in a 1525 km segment of the Solimões
River, Brazil during four surveys in March 1983 - February 1984 (Best and da Silva 1989b).
Figure 1: Boto (Inia geoffrensis) distribution. Source: IUCN
There are no estimates of the total population size for S. fluviatilis, though it appears to be relatively
abundant throughout most of its range (Flores and da Silva 2009). The species have only been
recently differentiated from their marine cousin, S. guianensis (Cunha et al. 2005, Caballero et al.
2007), and this is a major reason as to the lack of information on S. fluviatilis itself. They are found
in the Amazon drainage as far inland as southern Peru, eastern Ecuador, and southeastern Colombia.
They occur in the main tributaries of the Amazon/Solimões River basin and they cross international
boundaries in areas such as Leticia, between Brazil and Colombia. The species does not occur in the
Beni/Mamoré river basin in Bolivia nor in the upper Rio Negro. Its putative presence in the Orinoco is
controversial because of a stretch of rapids and waterfalls that are suspected to block the species
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movements to this area (Flores and da Silva 2009). During the flood season, tucuxi may move into
smaller tributaries, but apparently they do not move into the inundated forest to feed (as botos, Inia
geoffrensis, often do), staying mainly in the main river channels, tributaries and lakes (da Silva and
Best 1996). Tucuxi are largely sympatric with the boto in the Amazon and Orinoco systems but
generally do not interact with that species. Local estimates of relative abundance exist for some
areas. In the Amazon drainage, an average density (encounter rate) of approximately 1.1
dolphins/km of river was estimated between Manaus and Tefé in the Solimões River (Magnusson et
al. 1980). Four boat surveys of about 1,525 km each, from Manaus to Letícia, resulted in a mean
estimate of 768 (± 104.7 SD) dolphins per trip or 1.02 individuals/km² (da Silva and Best 1994). More
recently, mean density along the margins of main rivers in the central Amazon, Brazil (1,320 km of
strip survey) was estimated at 3.2 individuals/km².
Figure 2: Tucuxi (Sotalia fluviatilis) Distribution. Source: IUCN
The population trend for both species is currently unknown.
1.3. Habitat and ecology
1.3.1 Inia geoffrensis
During the high-water season botos are known to swim into the flooded forest and search for prey
among the roots and trunks of partially submerged trees. Martina and da Silva (2004a) carried out a
series of mark/recapture studies which revealed some information regarding their spatial variation
pattern. It was discovered that some individuals are resident to specific areas year-round while
others move several tens to hundreds of kilometres within the rivers. However the study suggested
that there was no evidence of a seasonal migration.
Local people say that botos are highly adaptable to different environments, living in rivers and
streams with white and dark water during the dry season and spreading out to the lakes, varzeas
and igapos during the flood period. Botos are generally concentrated below channel confluences
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(Magnusson et al. 1980; Mead and Koehnken 1991; Leatherwood 1996; Vidal et al. 1997;
Leatherwood et al. 2000), with mixing of white and black waters (Martin et al. 2004). Such areas are
chosen because of the fish, because of their high productivity and because they provide protective
structures. However their affinity for confluences diminishes during the high water season, more
than likely due to the fact that the animals move into appended lakes and flooded forests
(Leatherwood 1996; Leatherwood et al. 2000; Martin and da Silva 2004b). They occur most
frequently within 150 m of the edges of rivers, with lower densities in the centres of large rivers
(Martin et al. 2004).
In regard to their feeding habits, botos feed on a large variety of fishes (over 43 species), generally
near the bottom of the river (Best and da Silva 1993; da Silva 2002).
1.3.2 Sotalia fluviatilis
White water, clear water, and black water make up the three water types of the Amazon Basin, and
tucuxi reside in all three types. This implies that physical factors including visibility and acidity appear
not to affect their distribution directly. They seem to prefer the main channels of rivers and larger
lakes where access is not limited by a narrow or shallow channel, while rapids and fast-moving
turbulent water are avoided. Tucuxi also generally do not enter the flooded forest unlike the botos.
They are mostly found within 50 m of the edges of rivers and channels (Martin et al. 2004). Similarly
to the sympatric boto, the tucuxi shows a distinct preference for junctions of rivers and channels (da
Silva and Best 1996, Leatherwood et al. 2000, Martin et al. 2004). The most preferred habitat is
where a sediment-rich whitewater channel meets the low pH- carrying black water. The resultant
mixing produces productive and obviously attractive conditions for dolphins (Martin et al. 2004). The
large seasonal fluctuation in river levels (10 m) influences the distribution of tucuxi. They enter lake
systems during periods of high water but leave these environments as the waters recede, thus
avoiding entrapment.
Sotalia fluviatilis occurs most often in groups of one to six individuals. Groups of more than nine
animals are rarely observed (da Silva and Best 1994, Faustino and da Silva 2006). The composition of
groups is unknown. Vidal et al. (1997) reported overall mean group size of 3.9 in the upper Amazon.
In a study carried out by Maguire (2002), tucuxi were most frequently seen as singles or pairs in
rivers and lakes of Peru's Pacaya-Samiria Reserve, and any seasonal differences in group size
observed were considered non-significant.
Information regarding their reproduction is lacking. Males reach sexual maturity at approximately
140 cm and females at between 132 and 137 cm (da Silva and Best 1996). In Brazil, gestation lasts
about 11 months and calves are about 80 cm long at birth, which occurs primarily from September
to November during the low-water period (da Silva and Best 1996, Flores and da Silva 2009).
Tucuxi in the Amazon Basin feed on at least 28 species of mostly small schooling fish belonging to 11
families. During the dry season, fish concentrate in the main water bodies and thus are more
vulnerable to predation. During the flood season, many species enter the floodplain and are largely
out of reach of tucuxi.
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1.4. Threats
1.4.1 Inia geoffrensis
Incidental mortality has not been studied systematically in most areas. However, similar to other
small cetaceans, botos are vulnerable to entanglement in a variety of nets (lampara seine nets, fixed
gill nets, drifting gill nets; Best and da Silva 1993; Martin et al. 2004) as well as to drop traps
intended to catch large fish or manatees in the flooded forest in Peru (Leatherwood 1996).
There is an emergent, but already large-scale, problem involving the deliberate killing of botos in
Brazil for fish attractant (IWC 2007). Botos are also killed deliberately in some areas because
fishermen regard them as competitors and because the dolphins damage fishing nets (Caballero et
al., 2006). One positive sign in terms of boto conservation is that on June 3rd 2014 the Fishing and
Aquaculture Ministry announced a temporary ban on the fishing of a species of catfish known as the
piracatinga. Piracatinga is baited, illegally, with the flesh of botos and this moratorium is intended as
an effort to protect existing boto populations from hunting. The temporary ban is intended to come
into effect in 2015, giving fishermen a substantial amount of time to find new bait.
Fishing with explosives, although illegal in most areas, is common in some areas of the Amazon Basin
(Goulding 1983; Smith 1985). This fishing technique threatens botos due to the concussive effects of
explosions. Fishermen also reportedly attempt to kill dolphins that are attracted to prey on the
stunned or dead fish (Best and da Silva 1989a).
The effects of the bioaccumulation of mercury in botos are unknown but the high levels recorded in
the Amazon ecosystem give reason for concern.
1.4.2 Sotalia fluviatilis
Sotalia fluviatilis consumes 14 of the 30 species of commercially exploited fish in the Amazon, and
thus incidental captures during fishing are frequent (da Silva and Best 1994, 1996; Martin et al.
2004). In one study in the central Amazon of Brazil, 74% of 34 tucuxi examined had been killed in gill
nets and 15% in seine nets (da Silva and Best 1985).
Although freshwater dolphins have been protected by superstitions in parts of Amazonia
(Leatherwood and Reeves 1997), in Colombia and Brazil there was and may still be a small market
for the eyes, teeth and reproductive organs of dolphins, used as love charms or aphrodisiacs when
prepared in a special manner (da Silva and Best 1994, 1996; Trujillo and Diazgranados 2002; Alves
and Rosa 2008). While this practice is not believed to be popular nowadays, it has been reported
among some local communities (IWC 2007), and thus an investigation into the presence or absence
of this practice in Borba would be recommended.
Recently, Loch et al. (2009) found two tucuxi and one boto wounded by perforating and cutting
objects, probably harpoons and machetes. Such kills indicate potential conflicts with locals using
tucuxi and boto as bait in a catfish fishery (V. da Silva, pers. comm.).
A number of threats are common to both species:
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1. The need for energy
The construction of dams to generate electricity, along the river, while a clean source of energy,
impacts the dolphin’s movement, prey and habitats. They disrupt the migration patterns of fish thus
reducing the amount of available prey. Additionally they may also alter the water temperature
which effects the spawning of fish, and trap sediment reducing the potential for formation of bars
and islands.
Hydropower dams, while they don’t remove water, change the volume and timing of river flows and
affect the relationship between the river and its floodplains - this can level high and low flows
through the year and cause sharp variations in flow throughout the day or seasons when there is a
high demand for electricity, thus disrupting the natural water cycle for the dolphins.
2. The need for transport
Many areas of the Amazon are almost exclusively accessible by boat alone, and the creation of
subsequent transport corridors results in a change in dolphin behaviour. The acoustic pollution
associated with the boats can disorientate the dolphins and interfere with their echolocation.
Furthermore, direct implications in the form of habitat degradation arise when waterways are
dredged and deepened to allow larger vessels to pass through, which in turn alters the river flow.
Pollution from the ships themselves is also a present threat.
3. The need for flood protection
With a growing human population along river banks, an increase in the need for flood protection
leads to water management strategies that rely heavily on canalisation, embankments and floodcontrol dams and reservoirs, all of which destruct dolphin habitats and behaviour.
2. Inia geoffrensis and Sotalia fluviatilis in Borba
As the Madeira River runs through the project area, it can be said that it is extremely likely that both
species of river dolphin are present in the project area.
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Figure 3: Distribution of I. geoffrensis and S. fluviatilis in the project area of Borba. Source of data for
generation of map: IUCN; map created by CGV
If we want to protect both species, firstly, a study is required to determine their population within
the project area, their ecological requirements and also whether they are at risk of hunting by local
communities. In a previous study of dolphins in Borba, local fishermen complained about the botos
strong interference with the fishing since the dolphins draw the fish from gillnets and sometimes
tear the nets; mostly the boto vermelho (red boto). According to the inquiries, the dolphin
interaction with the fishing increases during the flood period when the fish spread out through
varzea and igapo hindering the hunt even for the botos. For this reason, they resort to gillnets as an
easy way to obtain food. Although many fishermen do not like the botos, there is no apparent attack
against them by the local people, neither hunting for consumption nor other motives. Accidental
cetacean captures in fishing nets previously reported in other Amazonian areas (da Silva & Best
1999) are infrequent in the central Madeira River.
Their protection and conservation would be complemented by educational programmes among the
communities where people can learn how important the preservation of the dolphins is.
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3. Why do we want to conserve the river dolphins?
Conserving the dolphins is not only beneficial to the survival of the species, but also has real benefits
for humans. Figure 4 outlines the mutual benefits of taking action against current threats faced by
the dolphins.
Figure 4: Shared threats and the subsequent benefits of addressing them for both dolphins and people.
Source: WWF Report ‘River Dolphins and People: Shared Rivers, Shared Future’ (2010)
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4. Monitoring Inia geoffrensis and Sotalia fluviatilis in Borba
Correct identification is the first step in determining the population distribution and ultimate status
of both species. This is made possible by the marking of individuals to allow for their individual
identification. A common process of marking is freeze-branding, which involves a chilled metal block
being applied to the dorsal fin of the dolphin for a short amount of time. The chilling damages the
pigment cells and causes them to remain white, while not harming the dolphin in any way. During
this branding process, the measurements and weight as well as a photograph and a sample can be
taken from each dolphin for further analysis and record. This process was demonstrated by da Silva
and Martin who successfully identified over 200 individuals over the 12 year period of Project Boto
(1994-2006).
In each area, visual off-shore line transects and 150 m strip-width transect surveys should then be
conducted, concomitant with recommendations by Trujillo et al (2010).
-
Off-shore transects should be mainly conducted while crossing main rivers from one shore to
the other.
150 m strip-width transects should be orientated parallel to the banks along the river
margins of each river, maintaining an average distance of 100 m from the shore.
For each of the transect types, specific sighting protocols should be implemented:
- Two platforms (one at the bow, one at the stern) should be installed in each ship, and at least
two observers should be present on each platform. Both platforms should be in constant
communication to increase accuracy in dolphin detection and counting.
- The observation height used should be at least 4.5 m above the river surface, allowing a
wider field of vision. This will enhance the ability to detect the dolphins and also reduce the
possibility of interfering with the dolphin’s natural behaviour.
- The time, position, species and number of dolphins should be registered for each sighting by
both the forward and rear platforms.
- The distance from the platform to the dolphin should be estimated by eye with trained
observers.
Additionally there should be environmental data recorded in each transect including date, time,
position, speed (5-19 km/h), direction of travel, and thus the length of transect (the number of
kilometres surveyed).
A classification based on the annual flood cycle should be attributed to each transect; low waters,
high waters, or transitional periods.
During the strip transects, data should be recorded every 10 minutes (including the distance from
the boat to the bank).
The recording of information should be done in a specific way to ensure the most efficient system
was used:
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In the bow:
-
One person should be in charge of recording information in a Progress Log every ten minutes.
Another person should be responsible for permanent observation of the river and measuring
angles at the moment of sighting.
A third person should be responsible for the Bow Record where entries were made at the
moment of each sighting.
In the stern:
-
One person should register all the observations.
Another person should be responsible for observations and measuring angles whenever
dolphins are sighted.
Both linear and strip transects should be distributed as uniformly as possible.
Areas should be chosen where there are both high and low densities of dolphins, in order not to
under/over-estimate the dolphin densities.
A program called Distance can be used to make abundance estimations, all information collected can
be exported to it: http://www.ruwpa.st-and.ac.uk/distance/.
The area of the rivers and other aquatic habitats in the study area can be calculated through satellite
imaging.
Additionally, small radio transmitters can be fitted onto the dolphins which can transmit information
about their spatial location. This can help to identify any potential migration patterns of the dolphins
and help to keep track of existing populations. Project Boto utilised this technique, fitting a total of
56 radio transmitters to dolphins in their reserve. 3 of the transmitters relayed signals via satellite,
and the remaining 53 were tracked locally using receivers mounted above the forest canopy on
towers or trees.
5. Conclusion
As a consequence of lack of good data, both Inia geoffrensis and Sotalia fluviatilis are listed as data
deficient according to the IUCN. Furthermore, the IUCN notes that a significant proportion of the
information utilised in their documents is outdated and may be incorrect at this present moment.
In the project area, both species reside throughout the Madeira River. However, an accurate
estimate of their population and density, as well as their exact spatial requirements, is unknown.
Therefore, it is essential to study this in Borba. It is preferable to carry out new assessments in order
to obtain an up-to-date picture of the dolphin activity in Borba, which is liable to have direct
implications for fish activity in the project area also.
The density and population studies could be carried out thanks to monitoring surveys utilising visual
off-shore line transects and 150 m strip-width transect surveys.
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Taking action to preserve river dolphins is not only the responsibility of the people who live with the
dolphins, but the responsibility of all of us who consume food and other resources produced in or
near their habitats.
Threats to the dolphins are almost exclusively man-made, and saving them will have positive effects
for local freshwater ecosystems, international river basins and ultimately, ourselves.
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6. References
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Inia geoffrensis and Sotalia fluviatilis Monitoring Study: June 2014

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