Download As river dolphins are indicator species it is

The conservation and population structure of Amazon River Dolphins, Boto Inia
Geoffrensis and Tucuxi Sotalia Fluviatillis within the Pacaya Samiria National
Reserve, Peru.
By Emma Ford.
2011
Practical Research Project: DI522
BSc Wildlife Conservation.
Supervisor: Dr Peter Bennett.
Durrell Institute of Conservation and Ecology.
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
(Cover photograph source: kevinschafer.com)
Acknowledgements.
I would like to thank my supervisor Dr Peter Bennett for his guidance and encouragement
throughout my project.
Also thanks goes to Dr Mike Walkey for providing support whilst in the field and everyone
who was part of the ‘dolphin boat’ for making our dolphin transects so entertaining.
Thank you to my family for their continual interest in my project, especially my Mum and a
special thanks to my Nan June who helped fund the field work. And finally thank you to Dan
for always being there.
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Contents
Abstract. ................................................................................................................................................... i
List of Figures .......................................................................................................................................... ii
List of Tables .......................................................................................................................................... iii
Chapter 1 Introduction. .......................................................................................................................... 1
1.1
River cetaceans ....................................................................................................................... 1
1.1.1
Pontoporia genera (Pontoporia blainvillei) ..................................................................... 1
1.1.2
Lipotes genera (Lipotes vexillifer).................................................................................... 2
1.1.3
Platanista genera (Platanista gangetica) ........................................................................ 2
1.1.4
Inia genera (Inia geoffrensis) .......................................................................................... 2
1.1.5
Tucuxi (Sotalia fluviatilis) ................................................................................................ 3
1.2
Conservation of river dolphins. ............................................................................................... 4
1.2.1
1.3
Threats ............................................................................................................................ 5
Local Taboos surrounding river dolphins. ............................................................................... 6
1.4 Aims and objectives of study ....................................................................................................... 7
Chapter 2 Methods. ................................................................................................................................ 8
2.1 Study site....................................................................................................................................... 8
2.1.1 Transects .............................................................................................................................. 10
2.2 Data collection ............................................................................................................................ 11
2.2.1 Identification of boto and tucuxi. ........................................................................................ 11
2.2.2 Observational effort. ............................................................................................................ 13
2.2.3 Measuring water depth. ...................................................................................................... 13
2.2.4 Identifying groups. ............................................................................................................... 13
2.2.5 Measures for double counting. ............................................................................................ 13
2.3 Statistical analysis ....................................................................................................................... 14
Chapter 3 Results. ................................................................................................................................. 15
3.1 Abundance. ................................................................................................................................. 16
3.1.1 Trends in abundance ............................................................................................................ 18
3.2 Water depth. ............................................................................................................................... 19
3.3 Group structure........................................................................................................................... 20
3.3.1 Trends in Group structure. ................................................................................................... 25
3.4 Age composition. ........................................................................................................................ 27
3.4.1 Trends in age composition. .................................................................................................. 32
Chapter 4 Discussion. ............................................................................................................................ 34
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
4.1 Abundance and conservation implications. ................................................................................ 34
4.2 Water depth and ecology of the Amazon river basin. ................................................................ 36
4.3 Group structure and conservation implications. ........................................................................ 37
4.4 Age composition and conservation implications. ....................................................................... 38
4.5 Limitations................................................................................................................................... 40
Chapter 5 Conclusion. ........................................................................................................................... 41
5.1 Further study of river dolphins. .................................................................................................. 41
5.1.1 Photo identify....................................................................................................................... 42
5.1.2 Mark-recapture .................................................................................................................... 42
5.2 Future conservation of river dolphins......................................................................................... 43
5.2.1 River dolphin reserves ......................................................................................................... 43
5.2.2 Development of fishing techniques. .................................................................................... 44
5.3 Conservation implications........................................................................................................... 45
References. ........................................................................................................................................... 46
Appendix 1. ........................................................................................................................................... 50
Appendix 2 ............................................................................................................................................ 51
Appendix 3. ........................................................................................................................................... 52
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Abstract.
This report studies the population structure of South American river dolphins the Boto Inia
geoffrensis and the Tucuxi Sotalia fluviatilis who share a habitat in the Amazonian river system. River
dolphins are a specialist mammal adapted to live in freshwater river systems, they are also an
indicator species and so studying them is important for the whole ecosystem in which they inhabit.
The study took place within the Pacaya Samiria National Reserve, Peru. This is pristine habitat of
tropical Amazonian rainforest. Data was collected on group structure, age composition and
abundance for both species. A total of 5 transects were surveyed for this report, there was a
statistical difference in population structure for both species across the 5 transects. The data was
also analysed across the study period which was between the 16th June 2010 – 10th July 2010 and
found significant differences in the population structure for both species across this study period.
The data of this survey were compared with previous studies to allow the trends in the species
population structure to be studied. The findings of this report suggest a healthy and abundant
population for both species. Conservation of the river dolphins and the importance of studying them
is investigated, to ensure the future protection of these species from threats including entanglement
in fishing nets and habitat degradation.
Despite the apparent abundance of the boto and tucuxi complacency is not an option, conservation
programmes are required to preserve the pristine habitats within the boto and tucuxi range and to
prevent the increasing conflict with the growing human population.
Key words. boto, tucuxi, population structure, conservation
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
List of Figures
Figure 1. The Boto.
Figure2. The Tucuxi.
Figure 3. Map of the Pacaya-Samiria National Reserve.
Figure 4. The Study Site.
Figure 5. Boto and Tucuxi abundance over the transects.
Figure 6. Boto and Tucuxi abundance over the study period.
Figure 7. Trends in Boto and Tucuxi abundance.
Figure 8. Water depth over the study period.
Figure 9. Water depth of the transects over the study period.
Figure 10. Boto and Tucuxi group structure.
Figure 11. Boto group structure over the transects.
Figure 12. Tucuxi group structure over the transects.
Figure 13. Boto group structure over the study period.
Figure 14. Tucuxi group structure over the study period.
Figure 15. Trends in Boto group structure.
Figure 16. Trends in Tucuxi group structure.
Figure 17. Boto and Tucuxi age composition.
Figure 18. Boto age composition over the transects.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Figure 19. Tucuxi age composition over the transects.
Figure 20. Boto age composition over the study period.
Figure 21. Tucuxi age composition over the study period.
Figure 22. Trends in Boto and Tucuxi age composition.
List of Tables
Table 1. The Transects
Table 2. Identification guide for the Boto and Tucuxi.
Table 3. Boto and Tucuxi abundance over the transects.
Table 4. Boto and Tucuxi abundance over the study period.
Table 5. Trends in Boto and Tucuxi abundance.
Table 6. Boto and Tucuxi group structure over the transects.
Table 7. Boto and Tucuxi group structure over the study period.
Table 8. Trends in Boto and Tucuxi group structure.
Table 9. Boto and Tucuxi age composition.
Table 10. Boto and Tucuxi age composition over the transects.
Table 11. Boto and Tucuxi age composition over the study period.
Table 12. Trends in Boto and Tucuxi age composition.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Chapter 1 Introduction.
Most cetaceans are found in the world’s seas and oceans, but there are a select group of species
which reside within large freshwater river systems across South America and Asia. The world’s river
dolphins are grouped into four genera, Inia, Pontoporia, Lipotes and Platanista, these four genera
are poorly studied compared to oceanic cetaceans and also include highly endangered species
(Hamilton, H. et al 2001). River dolphins are specialist cetaceans and an important indicator species
of large river systems as they are a top predator within the ecosystem.
The Amazon basin is home to two species of river dolphin, the Boto (Inia geoffrensis) and the Tucuxi
(Sotalia fluviatillis), which are the two species studied within this report.
1.1 River cetaceans
A fragmented fossil record makes it difficult to conclude the phylogeny of river dolphins (Nikaido et
al, 2001). It is thought flooding which occurred in the Miocene period may have caused the
branching of cetaceans into freshwater habitats (Nikaido et al, 2001).
River dolphins from the 4 genera all commonly have long slender beaks with differentiated teeth
which are thought to help them eat their varied fish diet (Macdonald, 2001).
1.1.1 Pontoporia genera (Pontoporia blainvillei)
This genera has only one species which is native to South America this species does not strictly live in
freshwater, it is found in estuaries and along the coast of Brazil, Argentina and Uruguay, however it
has the characteristic long beak and un-fused neck vertebrae of river dolphins. This species is
commonly known as the La Plata river dolphin and is listed as Vulnerable under the IUCN Red List
(Reeves, R.R et al. 2008).
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
1.1.2 Lipotes genera (Lipotes vexillifer)
Listed as Critically Endangered under the IUCN Red List (Smith, B.D. 2008). The singular species of
this family is widely thought to be extinct as it has not been officially sighted since the year 2000.
This makes in an interesting case study for river dolphin conservation. Its historical range is the
Yangtze River in China (Turvey et al 2007) however an extensive study in 2006 resulted in no signs of
the baiji’s existence.
1.1.3 Platanista genera (Platanista gangetica)
There are two subspecies within this genera, the Platanista gangetic is the Ganges river dolphin,
whilst the Platanista minor is the Indus river dolphin. Both are found in South Asia and are IUCN
listed as Endangered (Smith & Braulik, 2008). This is one of the better studied genera of river dolphin
with a full census being completed for the Platanista minor estimating that there were 965
individuals (Smith & Braulik, 2008).
1.1.4 Inia genera (Inia geoffrensis)
Inia geoffrensis is better known as the Amazon pink river dolphin or the boto. It appears to be
abundant throughout the Amazonian and Orinoco river systems, with its range extending across
South America including Brazil, Peru, Ecuador and Colombia. The boto also enters flooded forests
during high water season to feed, their flexible bodies and un-fused neck vertebrae makes this
easier for them to travel between the trees. The boto is one of the most sexual dimorphic cetaceans
with males being larger in size and pinker in colouration (Martin & Da Silva, 2006). There are three
subspecies of Inia geoffrensis, with the development in molecular genetics leading to the discovery
of these subspecies. I.g.geofrensis (Figure 1) is the Amazon subspecies and the one which is studied
in this report, it is found in the Amazon River system of Brazil, Peru, and Ecuador. While
I.g.boliviensis is found in Bolivia and I.g.humboldtiana in the Orinoco basin of Venezuela and
Colombia (Secchi et al, 2008).
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Figure 1 (Source: arkive.com)
The boto is one of only three obligate freshwater river dolphins, with Lipotes vexillifer and
Platanista gangetica being the other two obligate freshwater species.
1.1.5 Tucuxi (Sotalia fluviatilis)
The tucuxi which is also referred to as the grey river dolphin, resembles a Bottlenose dolphin in
some respects and has a marine subspecies the Sotalia fluviatilis guianensi, this species lives in
coastal bays and estuaries off the coast of Brazil. The freshwater species Sotalia fluviatilis fluviatili
(Figure 2) is the species which is studied in this report. It lives within the Amazon River basin and its
range spreads across Brazil, Peru, eastern Ecuador, and southeastern Colombia (Secchi, 2010).
3
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Figure 2 (Source: wdcs.org)
Unlike the boto the tucuxi does not enter flooded forests to feed, this is thought to be due to them
being less flexible and they have a preference for deeper water (Secchi, 2010). The tucuxi is one of
the least studied cetaceans but is present in a range of habitats including freshwater rivers,
mangroves, estuaries and bay (Alves & Rosa, 2008).
1.2 Conservation of river dolphins.
Legal protection is given to the Baiji and the Ganges river dolphin across their range, this prevents
the deliberate killing of river dolphins. The legal protection seems to have had a more beneficial
effect on the Ganges dolphin as enforcement prevented dolphin hunting to an extent that the Indus
population decline halted in the 1970s (Smith & Braulik, 2008). The Baiji did not have the same
success as indirect threats such as habitat degradation was doing the greatest harm to Baiji
populations. This implies that conservation should focus on both direct and indirect threats to
ensure the river dolphin populations are able to recover.
Both the boto and tucuxi are protected under Brazilian federal law, however this only gives them
protection from direct killings and will only be effective if it is enforced. Both species are classified
as Data Deficient by the IUCN, however the boto is on the CITES Appendix II and the tucuxi is on
Appendix I. Appendix I prohibits the international commercial trade of the species, while appendix II
allows trade only with the provision of an export permit.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Conservation of river dolphins includes designating protected areas such as reserves which prohibit
fishing. Fishing techniques need to be developed to reduce by-catch and further research is required
to develop a better understanding of the river dolphin’s ecology and threats. Only a greater
understanding of these species will enable the implementation of effective conservation
programmes.
1.2.1 Threats
The main threat to all river cetaceans is anthropogenic pressure. Pollution, deforestation and dam
construction are causing habitat degradation (McGuire & Winemiller, 1998) and threatening the
river dolphins existence. However a threat becoming increasingly more common is entanglement in
fishing nets with gill nets and dynamite fishing being a common problem (McGuire & Winemiller,
1998). Direct killing of river dolphins is also becoming more common.
The construction of dams and water development projects greatly modifies the dolphins habitat.
Heavy boat traffic causes noise pollution which affects the river dolphins sonar. This can lead to
cetaceans starving to death and stranding as they cannot effectively navigate through their
environment.
There are no natural predators of the boto or tucuxi making humans their only threat. The river
dolphins are at a greater risk than their marine cousins due to living in close proximity to humans. It
has already caused the downfall of the baiji which is one of the closest relatives to the boto. The
botos habitat is not highly modified such as the baijis, however pollution into the Amazon is
increasing with organochlorines and heavy metals such as mercury being found within the Amazon
river (Reeves et al, 2008). Pollutants such as these can accumulate in the river dolphins bodies, with
older individuals being at a greater risk (Bennett, et al. 2000) . Heavy metals are immunosuppressive
and so can lead to the dolphins being at greater risk of infectious disease (Bennett, et al. 2000).
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Furthermore the human population in continuing to increase which may cause more pressure on the
Amazon ecosystem leading to greater habitat degradation in the future.
Botos are also deliberately killed in some regions of the Amazon as they are seen as a competitor for
fish, dead botos are also used to process bait for catfish used by fishermen. Historically in Brazil and
Columbia river dolphins have been killed for body parts which are sold on the market, including
teeth and reproductive organs which are thought to have magical powers (Alves & Rosa, 2008). This
is not currently deemed a major threat as these markets are small scale.
For the boto and tucuxi the main threat is the fishermen, entanglement in fishing nets plus direct
killing of river dolphins makes fishermen an increasing threat.
1.3 Local Taboos surrounding river dolphins.
There are local taboos surrounding the boto which helps to prevent the direct killing of individuals,
the myth states that anyone who kills a boto will not be successful in killing anything else and will be
punished (Alves & Rosa, 2008). It is also an Amazonian tale that botos leave the river in human form
and impregnate local women. The tucuxi is often regarded as a sacred and is believed to bring the
bodies for drowned people back to the shore (Nowak, 1999).
Despite these myths surrounding the river dolphins killing of the river dolphins is becoming more
common especially in Brazil, as taboos are losing their effectiveness as new generations start to see
the boto as a threat to their fish supplies. Taboos also surround the Baiji in China, it was traditionally
known as the ‘goddess of the river’ (Smith, 2008) and the killing of the Baiji was forbidden. However
a loss of tradition and new generations lead to the stigma of killing a Baiji to be less of a problem,
this coupled with increased habitat degradation lead to its apparent demise.
Myths and taboos can help to minimize the direct killing of river dolphins in some cultures, however
they cannot be relied upon as an effective form of protection. In some instances local myths are
causing a market for dolphin products, this is occurring in northern Brazil where dolphin products
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
are being sold for medicinal and mythological purposes. Dolphin oil and fat is used for the treatment
of 12 diseases, whilst reproductive organs of the dolphins are used to attract members of the
opposite sex ( Alves & Rosa, 2008).
1.4 Aims and objectives of study
The aim of this report is to contribute to the long term monitoring of the boto and tucuxi population
structure and for this to lead to a greater understanding of the two species of river dolphin. The aim
of this study is to collect data to establish the abundance and population structure for the boto and
tucuxi within the Pacaya Samiria National Reserve. With the main aim being to monitor these
aspects for change since 2001.
The objectives of this report are:

Establish the abundance for the boto and tucuxi and to compare this with previous
studies dated back to 2001.

Obtain data on group structure and age composition and compare with previous studies
dated back to 2001.

Monitor dolphin abundance and population structure over the study period for change.
The hypothesis (H1) for this report is that there will be a significant difference between the dolphin
abundance and population structure over the period between 2001-2010. The null hypothesis (H0) is
that there is no significance between the abundance and population structure over the period
between 2001-2010.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Chapter 2 Methods.
2.1 Study site
This study was conducted within the Pacaya Samiria National Reserve, which is the largest national
reserve in Peru (figure 3) and the second largest within the Amazon basin as it expands to 2,080,000
ha (Bodmer et al, 2010). It is an area rich in biodiversity and as such is an area extremely important
for conservation. For this reason studies should be conducted to monitor the demography of species
within the reserve, this ensures any potential issues are highlighted quickly and also expands
knowledge on the species found within this complex ecosystem.
Figure 3 (source: expphoto.com).
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
The area has a complex ecology, with seasonal changes in water depth. The reserve contains mainly
Varzea, which is white water flooded forests (Bodmer et al, 2010) these waters are high in sediment
and nutrients. The study site was located on the Samiria river at PV3 Ungurahui (figure 4) this is
located in the near up river section of the Samiria basin.
Figure 4 (Source: Bodmer. R, Fang. T, Puertas. P. 2007)
The surveys focused on both the boto and tucuxi, data were collected on population dynamics
between the 16th June 2010 until the 10th July 2010. This is at the beginning of the low water season
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
and is when the water level falls. This is the season in which boto are thought to be most abundant
(McGuire & Winemiller, 1998).
2.1.1 Transects
There were 5 different line transects surveyed to ensure a range of habitats were covered and this
also helps to prevent bias. The transects surveyed are shown in table 1. It shows the proposed
number of surveys done for each transects and the actual number of times that each transect was
surveyed, the differences between the numbers are due to logistics and other intervening factors.
The transects.
AM transects
(between 9am-12pm)
Actual
Proposed
PM transects
(between 3pm to
6pm)
Actual
Proposed
Total
5km upriver transect. ( 5km
upriver from Pv3)
7
5
4
5
11
10
5km downriver transect. (5km
downriver from Pv3)
6
5
2
5
8
10
5km Lower channel transect. (The
6
first 5km up the channel which was
to the right of Pv3)
5
3
5
9
10
5km upper channel transect. (This
transect began 5km up the channel
and continued for a further 5km)
4
5
0
5
4
10
500m mouth transect (This was a
500m transect located between
the beginning of the upriver
transect up until the beginning of
the downriver transect, it was
located at Pv3).
6
5
2
5
8
10
Actual
Proposed
Table 1
It can be seen from table 1 that all transects were planned to be surveyed equally, however in reality
this did not occur.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
All transects were marked out with the use of a GPS (Global Positioning System). The morning
transect was started at approximately 9am and as from the 28th June 2010 afternoon transects were
conducted, this was due to logistics such as boat availability. Afternoon transects took place
between 3pm-6pm. Another alternation to the scheduled transects is that the upper channel had to
be discontinued after the 5th July as it became too shallow for the study boat. A 5km transect would
take approximately 3hours to complete although this varies slightly. The transects were completed
using a motor boat, the motor was only used for transportation to the transect and was turned off to
allow the boat to drift through the transect, as such this helped prevent noise disturbance to the
river dolphins. Although at times when the current was very weak the motor was used lightly.
2.2 Data collection
At the beginning for each transect the date, start time, weather conditions and transect type were
all recorded for future reference. At the end of each transect the end time was also recorded. The
dolphins were only visible when they surfaced and broke the water’s surface, this meant swift
identification and close observation was essential for accurate identification.
2.2.1 Identification of boto and tucuxi.
The main differences between the two species are the size, colouration and vocal sounds. The
variations between the two species are listed in the table 2.
Individuals were classified as unidentified when a dolphins species or age class was unclear.
The sex of individuals was too difficult to attain with this survey method.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Boto.
Physical
characteristics.
Age class.
Tucuxi.

Majority of adults are pink and blotchy,
however some younger individuals are grey.

Light grey, with light
pink under belly.

Larger in body size.

Smaller in body size.

Large protruding melon and bulging cheeks.

Rounded melon with
no budging cheeks.

Makes loud ‘rasping coughs’ when inhaling
and exhaling.

Makes short ‘puff’
noise when inhaling
and exhaling (Kendall,
1995).

Long rounded beak,
less slender.

Triangle shaped dorsal
fin.

Can jump clear of the
water (Kendall,1995)

Long slender beak

Humped dorsal ridge, as oppose to a fin.

Rarely jumps clear of the water

(Kendall,1995), more commonly shows
melon and dorsal ridge when swimming.
Adult
Sub adult
Juvenile
Adult
Juvenile
Large, 1.5m-2.5m
Medium,1m-
Small, <1m
Large, >1m
Small <1m.
in length
1.5m
in length
Should be
(WDCS,2010)
In length
and grey
seen
They weigh
Slightly more
colouration
swimming
between 85kg to
grey than
Should be
alongside
160kg (Carwadine,
pink in
seen
an adult.
1995)
colouration.
swimming
More likely to have
alongside
greater amount of
an adult.
pink colouration.
Table 2 (Adapted using Yamamoto, 2008 and Harrington, 2004.)
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
2.2.2 Observational effort.
On board the boat there were approximately 5 people all of whom helped to spot and identify the
dolphins. Only one person on the boat had experience in spotting and identifying the dolphins,
however language barriers meant they had limited input into the recording of dolphins. The
observers identification skills progressed with time as experience was gained.
2.2.3 Measuring water depth.
Water depth was measured and recorded as part of this study to gain a greater understanding of the
dolphins ecology. Water depth was measured using a depth finder, the model used in this study was
manufactured by Zhejiang Lucky Sporting Products Co., Ltd. and the model number was FF1108-1
(Liebthal, A. 2011), at the beginning of the study river depth measurements were taken at both sides
of the river and the middle for each of the 5 transects ( Liebthal, A. 2011). Further measurements
were taken each time a dolphin of either species was seen, these measurements were taken from
where the dolphin was first observed. At the end of the study both sides of the river and the middle
were measured again for each transect. The average water depth for each transect was then
calculated for across the study period.
2.2.4 Identifying groups.
Dolphins were counted as being within the same group if they were within a 2 metre radius of each
other (Blackburn, 2002) and especially if they were displaying the same behaviour and travelling in
the same direction.
2.2.5 Measures for double counting.
Careful observation of dolphins helped to reduce double counting, when in doubt the dolphin was
only recorded once. The direction of which the dolphin was travelling was noted to help to prevent
double counting.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
2.3 Statistical analysis
The abundance (A) was calculated with the following equation:
A=N/L
N= total number of observed dolphins, L= total length in km of all transects surveyed (Yamamoto
2008).
Trends in abundance were compared with past studies ( Blackburn 2002, Harrington 2004, Whittaker
2006, Yamamoto 2008, Williams 2010). Data was displayed as a percentage (%) for trends in group
structure and age composition, this allowed an easier comparison of current results with past results.
The Chi squared test (X2) was done to highlight any significance comparisons in the categorical data.
The following equation was used:
X2= ∑ (O-E)2/E
O = Observed frequency, E= Expected frequency (Fowler et al. 1998)
The mean water depth for each transect was found for across the study period. This was done by
using all of the depth measurements gathered, for each transect the measurements taken were
summed together and then divided by the total number of measurements taken. The following
equation was used:
X
= ∑x/N
N = Total number of measurements taken. ∑ x = summed total of measurements.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Chapter 3 Results.
The results were collected from the study site between the 16th of June 2010 and the 10th July 2010.
40 transects were surveyed within this time period which summed to 164km in length. A total of
131 botos were recorded, tucuxi were slightly more common with 152 individuals recorded. The
results are shown for each of the 5 transects to show how the dolphins abundance and population
structure may alter across the transects. The results are also displayed in 5 day intervals across the
study period. The intervals are the 16th-20th June 2010, 21st-25th June 2010, 26th-30th June 2010, 1st
July-5th July 2010 and the 6th July-10th July 2010. By breaking the results down into these intervals it
shows how the dolphin abundance and population structure may change over this time period. It is
of special interest as this time period is at the beginning of the low water season and so the change
of water depth over this time period may be a factor which alters the dolphins population structure
and abundance.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
3.1 Abundance.
The total mean abundance (N/KM) for the boto is 0.8 while the total mean abundance for the tucuxi
is 0.93. This shows the tucuxi was slightly more abundant in this study. Abundance of river dolphins
across the transects is significant (X24= 23.01 p < 0.001) with the mouth transect having a greater
abundance of both species as shown in figure 5.
12
10
N/KM
8
6
Boto mean abundance
4
Tucuxis mean abundance
2
0
Figure 5.
Upriver
Downriver Channel
Upper
Mouth
channel
Boto
0.62
0.8
0.6
0.6
6.5
0.73
1.12
0.38
0.45
10.25
abundance
(N/km)
Tucuxi
abundance
(N/km)
Table 3
16
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
The dolphin abundance over the study period was not significant (X24= 3.95 NS) which indicates that
there was no significant changes in dolphins abundance across the study (16th June-10th July 2010).
Figure 6 does show that there was a decline in the abundance of both species within the first week
of the survey and a slight increase in abundance during the last 10 days of the study.
2
1.8
1.6
N/KM
1.4
1.2
Boto mean abundance
1
0.8
Tucuxis mean
abundance
0.6
0.4
0.2
0
Figure 6
16th-20st June
2010
21st-25th June
2010
26th-30th June
2010
1st-5TH July
2010
6th-10th July
2010
Boto
abundance
(N/km)
1.33
0.59
0.56
0.72
0.85
Tucuxi
abundance
(N/km)
1.76
0.82
0.48
0.99
0.79
Table 4
17
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
3.1.1 Trends in abundance
Data was used from previous studies to allow a comparison of the dolphins abundance over a long
time period (2001-2010). The trend in abundance is significant (X25= 30.53 p < 0.001) as the
abundance of both species fluctuates over the years, with neither the boto or tucuxi consistently
dominating. This is shown well in figure 7, it also shows that in some years such as 2009 and 2003
there is a large difference between the abundance of the two species. Whilst in other years including
2008 and 2010 there is little difference between the abundance of the two species.
2.5
N/KM
2
1.5
Boto mean abundance
1
Tucuxis mean
abundance
0.5
0
RY
PS
RY
RY
PS
PS
2001 2003 2005 2008 2009 2010
Figure 7
(Data referenced from: Blackburn 2002, Harrington 2004, Whittaker 2006, Yamamoto 2008, Williams
2009).
Year and
study area.
2001.
Rio
Yavari
(RY)
2003.
Pacaya
Samiria
(PS)
2005.
RY.
2008.
RY
2009.
PS.
2010.
PS.
Boto
abundance
(N/km)
0.52
0.93
0.44
0.44
2.16
0.8
Tucuxis
abundance
(N/km)
0.5
1.8
0.65
0.55
0.58
0.93
Table 5
18
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
3.2 Water depth.
Figure 8 shows the average water depth across the study period, it slowly declines with time which is
correct for the time of year as it is the beginning of the low water season.
6
5
Metres
4
3
average water depth
2
1
0
16th-20th 21st-25th 26th-30th 1st-5th
6th-10th
Axis Title
Metres
Figure 8
10
9
8
7
6
5
4
3
2
1
0
Upriver
Downriver
Channel
mouth
upper channel
Figure 9
There is no statistical significance (X24=7.61 NS) between water depth of the transects and the study
period. However figure 9 shows that the upriver transect declined the most in depth, the downriver
19
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
transect also declined in depth at the beginning of the study but was the only transect to increase in
depth near the end of the study period. Both the channel and upper channel were the most shallow
of the transects, with the upper channel having to be discontinued half way through the study
period.
3.3 Group structure.
Group structure was surveyed to help identify the social structure of the two species. Figure 10
shows that the boto is commonly seen solitary (N=47) whilst the tucuxi is more likely to be seen in
pairs (N=27).
There is no significant difference (X23 6.66 NS) between group size and the two species of dolphins,
this indicates that the two species of dolphins have similar group structures. Both species were
commonly seen as singles however the tucuxi was observed in larger group sizes than the boto, with
the largest observed group of tucuxi being 7. This is shown in figure 10.
50
Number of individuals
45
40
35
30
25
Boto (N)
20
Tucuxis (N)
15
10
5
0
Singles Pairs
Goups Groups Groups Groups Groups
of 3
of 4
of 5
of 6
of 7
Figure 10
20
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Boto
Number of Individuals
25
20
15
Groups of 4 +
Groups of 3
10
Pairs
Singles
5
0
Upriver Downriver Channel
Upper
Channel
mouth
Figure 11
Group size across the transects for the boto is significant (X24=20.45 p < 0.001) as singles were
commonly observed in the downriver transect, whilst in the upper channel they are most commonly
seen in pairs. This indicates that location has an effect on boto group size.
Tucuxi
Number of Individuals
25
20
15
Groups of 4 +
Groups of 3
10
Pairs
Singles
5
0
Upriver Downriver Channel
Upper
Channel
Mouth
Figure 12
21
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Group size across the transects for the tucuxi is also significant (X24= 20.58 p < 0.001) with the
channel transect having the majority of solitary tucuxi whilst pairs where commonly seen in the
upriver transect. The downriver transect had the largest frequency of groups of 4+.
Upriver
Downriver
Channel
Extended
Mouth
channel
Boto (N)
Singles
13
15
10
1
8
Pairs
6
5
4
4
4
Groups of
3
1
3
1
2
0
1
0
0
1
Singles
5
6
11
2
5
Pairs
10
8
1
2
6
Groups of
5
2
0
1
5
0
3
1
0
2
3
Groups of
4+
Tucuxi (N)
3
Groups of
4+
Table 6
22
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Boto
Number of individuals
30
25
20
Groups of 4
15
Groups of 3
Pairs
10
Singles
5
0
Figure 13
The majority of solitary botos were observed between the 1st-5th July, this was also when the total
highest frequency of botos were observed. Group size across the study period for the boto is
significant (X24= 13.17 p < 0.05) this is mainly due to the fluctuations in the frequencies of solitary
botos. Groups of 3 boto were observed at higher frequencies at the beginning and at the end of the
study period. However solitary botos were the dominant category throughout the study as shown in
figure 13.
23
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Tucuxi
Number of individuals
25
20
15
Groups of 4 +
Groups of 3
10
Pairs
Singles
5
0
Figure 14
The highest frequency of tucuxi observations came between the 16th-20th June, the tucuxi were also
seen in larger groups more often between these dates, there is a significant difference between
tucuxi group size across the study period (X24=26.86 p < 0.001). No solitary tucuxi were observed
between the 21st- 25th June.
16th-20th
Boto
Tucuxis
21st-25th
26th-30th
1st-5th
6th-10th
Singles
8
3
7
19
10
Pairs
5
3
5
4
6
Groups of 3
Groups of 4
+
Singles
4
1
1
0
1
0
1
0
3
1
10
0
2
8
9
Pairs
5
5
3
8
6
Groups of 3
Groups of 4
+
4
3
3
1
3
0
2
1
1
1
Table 7
24
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
3.3.1 Trends in Group structure.
The boto group size appears fairly consistent over a long time period, with singles consistently being
the most frequently observed group size
Boto
80
70
60
%
50
Singles
40
Pairs
30
Groups of 3+
20
10
0
2001
2003
2005
2008
2010
Figure 15
Tucuxi
60
%
50
40
Singles
30
Pairs
20
Groups fo 3+
10
0
2001 2003 2005 2008 2010
Figure 16
Data referenced from Blackburn (2002), Harrington (2004), Whittaker (2006), and Yamamoto (2008).
The tucuxi group size appears to be less consistent and there appears to be a decline in solitary
individuals and an increase in pairs in 2008 and 2010. There also appears to be a slight increase in
larger groups of 3+ for both species.
25
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
This is encouraging for conservation as a decline in group size often implies that the population is
declining, however future studies will be vital in following this trend to ensure this is the case.
Boto (%)
2001
2003
2005
2008
2010
Singles
53
55
43
67
57
Pairs
32
31
29
20
28
Groups of
15
14
28
12
15
3+
Tucuxis
Singles
51
57
41
49
39
(%)
Pairs
30
33
26
29
36
Groups of
19
10
33
22
25
3+
Table 8
Data referenced from Blackburn (2002), Harrington (2004), Whittaker (2006), and Yamamoto (2008).
26
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
3.4 Age composition.
To compare the age composition between the two species the sub-adult category for the boto was
added into the adult category. This resulted in the adult/sub-adult category being the most
abundant for both species. This is shown in figure 17.
0.9
0.8
0.7
N/KM
0.6
0.5
Boto
0.4
Tucuxis
0.3
0.2
0.1
0
adult/subadult
juvenile
Figure 17
Adult/Sub-adult
Juvenile
Boto (N/km)
0.68
0.12
Tucuxis
0.81
0.12
(N/km)
Table 9
27
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
N/KM
Boto
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
adult
subadult
juvenile
Figure 18
The boto had three categories of age class with the most common one being adults, the sub-adult
and juvenile categories were similar in abundance. All three categories were used for the boto when
comparing age class with the transects. Age composition across the transects for the boto is
significant ( X24 =31.97 p < 0.001) as adult botos dominated especially in the mouth transect which
had a high frequency of adults, as shown in figure 18.
28
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Tucuxi
12
10
N/KM
8
6
Adult
4
Juveneile
2
0
Upriver Downriver Channel
Upper
Channel
Mouth
Figure 19
The adult category for the tucuxi was also the most abundant and it dominated within the mouth
transect, this resulted in a significant difference (X24 =12.44 p <0.05) between in the tucuxi age
composition across the transects.
Upriver
Downriver Channel Upper
Mouth
channel
Boto
Adult
0.45
0.65
0.44
0.5
4.75
(N/km)
Sub-
0.05
0.05
0.06
0.05
0.75
Juvenile
0.11
0.1
0.09
0.05
1
Tucuxis
Adult
0.62
0.9
0.38
0.35
9.75
(N/km)
Juvenile
0.1
0.22
0
0.1
0.5
adult
Table 10
29
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
During the study period the adult category dominated for both species, the sub-adult and juvenile
categories for the boto were similar although there did appear to be slightly more juveniles for the
majority of the study period. There was a significant difference ( X24 = 24.39 p < 0.001) in the botos
age composition across the study period. This is likely to be due to the sharp decline in abundance of
adult botos within the first week of the study. There were no drastic changes in the sub-adult or
juvenile abundance over the study period.
N/KM
Boto
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Adult
Sub-adult
Juvenile
Figure 20
30
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
N/KM
Tucuxi
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Adult
Juvenile
Figure 21
There was a significant difference (X24 = 18.38 p < 0.01) in the tucuxi age composition across the
study period as there was a large drop in adult abundance within the first 2 weeks of the study,
although the adult abundance did start to increase slightly after the initial decline. The juvenile
abundance was fairly consistent throughout the study period.
16th-20th
21st-25th
26th-30th
1st-5th
6th-10th
Boto
Adult
0.94
0.49
0.49
0.65
0.59
(N/km)
Sub-adult
0.24
0
0.07
0.02
0.07
Juvenile
0.16
0.1
0.09
0.05
0.2
Tucuxis
Adult
1.57
0.73
0.46
0.82
0.73
(N/km)
Juvenile
0.19
0.1
0.1
0.17
0.05
Table 11
31
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
3.4.1 Trends in age composition.
2001
2003
2005
2008
2010
87
98
86
96
85
Juvenile
13
2
14
4
15
Tucuxis
Adult/sub-
86
79
96
90
87
(%)
adult
14
21
4
10
13
Boto
Adult/sub-
(%)
adult
Juvenile
Table 12
Data referenced from Blackburn (2002), Harrington (2004), Whittaker (2006), and Yamamoto (2008).
120
100
%
80
Boto adult/subadult
Boto juvenile
60
Tucuxis adult/subadult
40
Tucuxis juvenile
20
0
2001
2003
2005
2008
2010
Figure 22
Figure 22 shows that the age composition for both species of dolphin has been fairly consistent
throughout the years, with the adult/sub-adults always dominating. Although the survey in 2010
32
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
found that there was an increase in juvenile botos and a decrease in adults/sub adult botos.
However the tucuxi age composition is very consistent.
Consistent results such as these are reassuring that there is no conservation issue relating to age
composition.
33
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Chapter 4 Discussion.
4.1 Abundance and conservation implications.
Both species of river dolphin were most abundant in the mouth transect, however this may have
been due to the fact that the mouth transect is shorter in length than the other transects and so the
abundance calculation may have been bias towards the mouth transect. Factors which may have
caused the dolphins to congregate in the mouth include anthropogenic influences as the main
research boat was located within this transect with food waste regularly being thrown into the river
this attracted a large amount of fish, which in turn would attract the dolphins. There is uncertainty
as to which habitats the boto favours with several different studies finding different results (McGurie
& Winemiller, 1998). The data gathered within this report seems to agree with Martin & Da Silva
(2004b) that the boto has a preference for confluences with slow currents as there was a high
abundance of boto in the mouth transect. Another theory is that as the water level falls the fish
leave side channels and pass through confluences (McGurie & Winemiller, 1998). As the survey was
conducted at the beginning of the low water season this theory is feasible. The tucuxi however is
thought to prefer deeper waters within main channels (Secchi, 2010).
The channel and upper channel transects were slightly less favoured by both species of dolphin, this
could have been due to having to motor the boat the majority of time whilst surveying these
transects, the motor had to be used as the current was extremely slow in both of these transect.
Boats are known to disturb river dolphins especially in side channels (McGurie & Winemiller, 1998).
Also the upper channel had to be discontinued from the 5th of July onwards due to the decline in
water depth and so this is a bias as the other transects were surveyed for the entire study period.
There was a drop in dolphin abundance during the first week of the survey, this could have been due
to double counting as during the first week of this survey the observers were still learning how to
identify the dolphins correctly and had little experience in surveying techniques. It could be that
34
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
after the weeks experience in dolphin surveying, the observers were more efficient and skilled in
recording dolphins correctly and so frequency of double counting was reduced. However the dolphin
abundance continued to decline very slightly for the first 15 days of the study. After this time period
the abundance of both species no longer declined and actually increased very slightly. This slight
increase could be due to river dolphins being observed which are moving through the area in
response to water levels declining in shallow areas.
The abundance of both species of river dolphin appears to fluctuate slightly since the year 2001, this
indicates that across the years the abundance of the river dolphins changes with neither of the two
species consistently dominating. The reliability of the data used in this report has to be questioned
due to the variation across the years in observers experience and observational effort. However the
continuation of the river dolphin surveys is vital to highlight long term trends in abundance. It is
encouraging that there is not a downward trend in abundance for either species as this would
indicate a threat which is having a detrimental impact on the river dolphins abundance and would
require conservation effects to reverse the declining trend.
As river dolphins are indicator species it is beneficial for the ecosystem to survey the abundance of
these two dolphin species. A decline in the dolphin species could be an indication of a wider problem
which will affect other species which share the dolphins ecosystem. Pollution is a current threat to
the dolphins ecosystem with mercury continually building up in the river dolphins bodies, the botos
milk has been found to contain levels of methylmercury which is close to the minimum level of
toxicity (Lehti & Rosas, 1996). Gold mining is thought to be the main source of the methylmercury
within the Amazon river system (Lehti & Rosas, 1996).
35
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
4.2 Water depth and ecology of the Amazon river basin.
There was not a significant drop in water depth during the study period, however it was at the
beginning of the low water season and there was a slight decline in water depth for most of the
transects across the study period. The mouth transect kept its depth consistently and did not drop in
depth a great amount, this may have contributed to the fact that it was favoured by both species of
dolphin. The upper channel was the most shallow transect which resulted in discontinuation of
surveys for this transect.
The seasonal fluctuations of water depth across the Amazonian basin results in drastic habitat
alterations for the species which live within these habitats, which result in a concentration of
terrestrial species for 6 months and then a concentration of aquatic species for the other 6 months
(Goulding, M. 1993). Water levels can change from between 7metres to 13 metres (Goulding, M.
1993). This affects the habitats and species ecology, with flooded forests being a seasonal habitat.
Flooded forests make up approximately 3 percent of the Amazon rainforest (Goulding, M. 1993) and
it is a habitat used by the boto, this habitat is thought to have existed since at least 65million years
ago (Goulding, M. 1993). Botos swim in water as shallow as 1.5m in depth while tucuxi tend to avoid
shallow waters (Martin & Da Silva,2004b). The botos flexible body and sonar location makes it easier
for them to move through flooded forests while the tucuxi prefers deeper waters and stays within
the river channels. This gives the boto an advantage over the tucuxi as it has access to fish
populations which are within the flooded forest. Many fish species enter the flooded forest to feed
on fruits and seeds of the trees (Goulding, M. 1993), the botos diet consists for a large and varied
amount of fish species with over 50 fish species known to be eaten by the boto (Kastelein et al.
1999). These fish species include sciacienids, cichlids and characins which are all important prey for
the boto (Kastelein et al. 1999).
36
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
4.3 Group structure and conservation implications.
The Botos were commonly seen as singles, whilst the tucuxi were seen in larger groups and are
thought to be more social. There is a significant difference for both species group structure across
the transects, this is due to the fluctuations in group structures across the different transects. There
was a high frequency of single botos in the downriver transects and pairs of botos were commonly
seen in the upriver transect. The upriver, downriver and mouth transects had a large proportion of
tucuxi in pairs or in groups of 3 +, in contrast the channel transect had the majority of single tucuxi.
There was also significant difference in both species group structure over the study period, with
solitary botos becoming more common in the last 10 days for the study.
The differences in groups structure across the study period and transects is thought to be due to the
fluctuations in group sizes in general, as this was a short study it would not be accurate to draw
conclusions on what makes the group structure change over these variables. However it is clear to
see that the groups structure for both species ranges, but with the general trend of botos being
commonly seen as singles and tucuxi being commonly observed in pairs. Possible reason for this is
that the tucuxis surfacing behaviour can make identifying groups of them easier as they tend to
surface in synchrony and in close proximity to each other (Macdonald, 2001) whilst botos surface
independent of each other. Also a high majority of tucuxi pairs were mother and calf, this may
indicate that tucuxi are solitary as adults but there was a high frequency of mothers and calves
during this study which may have skewed the results.
The largest group recorded in this study was compromising of 7 individual tucuxi, it is thought that
river dolphins do not live in groups any larger than 10 and they are also commonly seen as solitary
individuals (Macdonald, 2001). Tucuxi are thought to live in larger groups as a form of protection as
they are much smaller in body size compared to the boto. The group structure of river dolphins are
poorly studied and so the river dolphins social composition is not fully understood. As is common in
37
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
mammals the river dolphin nurtures its young, with river dolphin calves thought to stay with their
mother for up to 17 months before becoming fully independent, during this period the juvenile
learns from it mother (McGuire & Winemiller, 1998). Many of the pairs recorded in this study were
thought to be mother and calf, the large proportion of tucuxi pairs could indicate that the tucuxi are
reproducing readily in this area and season, this is encouraging from a conservation prospective as
this is a sign of a healthy population.
Other group compositions are thought to include multi-male groups which were sighted commonly
during low water season (McGuire & Winemiller, 1998), this could be explained due to habitat
preferences which may lead dolphins to congregate together, for example areas with a large fish
population could result in larger groups of river dolphins. In contrast to this, it has been recognised
that adult males are aggressive towards each other in conflict over mating (Martin & Da Silva, 2006).
This could indicate that the multi-male groups are adolescent males which have not yet reached
sexual maturity. There is also a theory that botos are monogamous which would explain pairs of the
opposite sex (McGuire & Winemiller, 1998). This study did not identify the sex of individuals and so it
cannot support any of these theories.
When river dolphins are in decline the group size also naturally decreases, this makes monitoring of
group size important as a decline in group size could mean there is a threat to the river dolphin
which is causing its demise. A better understanding of group composition will also aid the
development of conservation programmes.
4.4 Age composition and conservation implications.
In both the boto and the tucuxi adults dominated throughout the study and across the transects.
The mouth transect had a very high frequency of adults, this is thought to be due to the high
abundance of fish in this transect which attract the river dolphins. There was a decline in the
abundance of adults for both species during the first few weeks of the study period, this could have
38
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
been due to dolphins moving out of the area in response to the water levels declining. There was a
slight increase in adult tucuxi abundance after the decline but this may have been due to surveying
individuals which were moving out of the channel and upper channel transects as these transect was
becoming increasingly shallow during this time period and so the river dolphins would have been
moving into deeper areas.
Juveniles are thought to prefer areas where small fish are abundant, with lagoons thought to be
juvenile’s favoured habitat (McGuire & Winemiller, 1998). Unlike the tucuxi the boto has a sub-adult
category which is for individuals between the adult and juvenile stage. There was not a high
proportion of botos in groups of 3+ this indicates that the sub-adult usually leaves its mother before
she has another calf, although there were a few groups which compromised of a juvenile, sub-adult
and adult.
The boto gives birth after a 10-12 month gestation period (Macdonald, 2001), they are thought to
give birth when fish density is high such as the falling water period (McGuire & Winemiller, 1998) as
high food availability will sustain the mother throughout pregnancy and lactation.
After comparing results with past studies it is reassuring that the age composition for both species is
consistent. Although my survey in 2010 found that there was a slight increase in juvenile botos and a
decrease in adults/sub adult individuals compared to previous studies, this could indicate that 2010
was a reproductively successful year for the boto. The tucuxi age composition is very consistent, if
there was a decline in a certain age class it could have meant there was a threat with an age bias. For
example inexperienced juveniles may be at a greater risk of getting entangled in fishing nets.
However this does not appear to be a problem within this study. The age trends found in this report
indicate a stable population with good fecundity.
Continuation of studies on age composition will monitor for any drastic changes which may occur in
the future and will also help to clarify any impact age class has on habitat preferences.
39
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
4.5 Limitations
The limitations of this study may cause the results to be less reliable, the main limitation of this
study is the length of the study. This was preset and was restricted to approximately 5 weeks. This is
a relatively short study and a longer study period would have allowed more data to be gathered
giving more accurate results.
The method of this study was also limited as the observers had very limited experience in surveying
river dolphin and so it took time and practice to enable the observers to identify the species, their
age and group structure.
The environment caused some difficultly in identifying dolphins, as the sediment rich waters meant
dolphins were only seen when they broke the water’s surface, in some instances this meant
observers only got a glimpse of the river dolphins making it difficult to record the group size and age
of the dolphins spotted.
It is also important to remember that the data from previous years which are used as a comparison
was collected from different study sites. This means this report is not a reliable study for the long
term trends in river dolphin abundance and population dynamics within Pacaya Samiria, however it
is still within Peru and so the trends found within this report are still of importance to understanding
river dolphin ecology. The time length of previous studies also varied, with some years having a
larger data set than others due to having more time to collect data.
40
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Chapter 5 Conclusion.
The aims and objectives have been achieved within this report. The abundance for both species has
been established and then compared with previous studies dating back to 2001. This study has
found that there is a significant difference between the boto and tucuxi abundance between 20012010. This proves the hypothesis (H1) correct within this report.
Abundance, group structure and age composition were all monitored across the study period and
transects for change. This contributes to the understanding of the river dolphins complex ecology.
Data on group structure and age composition was successfully compared with previous studies to
contribute to the long term monitoring of the species and to gain a greater understanding of the
river dolphins social composition.
A study such as this one can be beneficial to conservation programmes as it highlights areas
which the dolphins congregate and long term studies can show trends in the river dolphins
population structure, it can also show if there is a decline in the species abundance which in
turn can highlight threats. Ultimately a greater understanding of the boto and tucuxi can allow for
conservation programmes to be more effective and so further studies are important for the future
conservation of the river dolphins.
5.1 Further study of river dolphins.
It is vital to continue to collect and process data on the Amazon river dolphins, this report used
visual observations to record individuals, however there are other methods which can be used and
are often more effective in monitoring individual river dolphins. This provides a greater insight into
the river dolphins population structure and movements. Methods for surveying river dolphins have
improved over the years, however it is important to continue the development of new survey
methods.
41
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
5.1.1 Photo identify
This method involves taking and storing high quality photos of the river dolphins, this allows the
dolphins to be identified in the future with the use of the photo. Photos of the dolphins fins and
flukes as well as natural markings including distinctive scars and colouration makes identifying
individuals easier and having a photographic record allows information on individual dolphins
movements and group structure (Wursig & Jefferson, 1990). The photographs have to be taken at a
consistent angle to make future identifying is easier (Kreb, 2004).
However this method has its disadvantages, one being that the dolphins appearance changes over
time, especially in the boto as their colouration changes with age. The dolphins surfacing behaviour
also makes it difficult to identify an individual from a photo (Martin & Da Silva, 2004a). This method
is thought to be easier for larger cetaceans, although more effort is required it is still an effective
method for surveying river dolphins and with the use of video recording equipment it can be made
easier (Kreb, 2004).
5.1.2 Mark-recapture
Mark recapture methods involve capturing the cetacean marking it and then releasing it, then in the
future the cetacean can be identified and recorded. Freeze bands, identity tags, radio tagging and
satellite are all forms of tagging used within this method. This method has the disadvantage of
causing stress to the cetacean due to handling, the effect of tagging boto has been studied and it
was concluded that tagging did not have a significant impact on the botos survival (Martin et al,
2006). Satellite tracking is the most recent method developed and is used for a range of marine
mammals, it has the potential to track the precise movements of an individual as a satellite linked
radio transmitter is attached to the dorsal fin. Attachment can be done by drilling holes with a
modified electric drill (Elwen et al. 2006) and then corrodible nuts are used to attach the tag which
allow the tag to fall off after a certain time period (Elwen et al. 2006). For large cetaceans sub-
42
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
dermal attachments are inserted into the dorsal fin and transmitters are attached to these with a
modified air gun (Andrews et al. 2008). Satellite tracking is the most effective form of mark
recapture as it gives detailed locations of individuals and so allows a comprehensive study of the
cetaceans movement patterns and habitat use to be done.
5.2 Future conservation of river dolphins.
For the boto and tucuxi a greater understanding is required on their ecology and threats, this will
allow for the best conservation actions to be implemented. However based on current knowledge
and examples from other species of river dolphin there are conservation programmes being put in
place for the boto and tucuxi.
Examination of river dolphin carcasses and establishing the cause of death can be useful in
establishing some common threats to the river dolphins, however this method is often not feasible
in the tropics due to rapid decomposition of the dolphins carcass. But it can be used for individuals
kept in captivity to help understand the effects of disease and it is often done on species of dolphins
found out of the tropics where decomposition is not as rapid.
The conservation actions reviewed in this report should ideally work together to give the boto and
tucuxi maximum protection against extinction.
5.2.1 River dolphin reserves
The most effective form of conservation for the boto and tucuxi is thought to be designation of
protected areas (McGuire & Winemiller, 1998), reserves which preserve the dolphins habitat will
control threats such as fishing and pollution to give the river dolphins the best chance of survival as
habitat degradation is a major threat to river dolphins. The designation of these protected areas will
require a baseline population data to ensure the protected areas are effective. Studies such as this
one will help to acquire the data and will also ensure that the method of data collection is effective.
43
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Once baseline population data is acquired it will also help to establish an IUCN status for the boto
which is currently classed as Data Deficient. Currently the botos abundance and range is not known
to be reducing (Reeves et al, 2003) however this is mainly due to the lack of studies done on the
boto, the tucuxi is in a similar situation.
Further studies on the distribution of the boto and tucuxi will allow areas with high river dolphin
densities to be identified and so the reserves can be designated in the most effective area. River
dolphin reserves will have to be managed well for them to be effective and monitoring of river
dolphin populations should be on going to monitor the effectiveness of the reserve.
5.2.2 Development of fishing techniques.
Both the boto and tucuxi are known to follow the fish populations and congregate in areas which
have a high fish abundance. This leads to the obvious problem of entanglement in local fishermen’s
nets (Martin & Da Silva,2004a). Gill nets are the main cause of by-catch but other issues including
conflict between the fisherman and cetaceans continues to increase with the demand of fish. Deep
lacerations are an indication of machete wounds were river dolphins have been cut out of fishing
nets (Loch et al. 2009).
This sort of conflict can be reduced by a community approach to conservation as it changes the
activities of local people through education and incentives. Local fisherman can be trained in
conservation to give them a new livelihood or on new fishing techniques which reduce the rate of
by-catch. However it is thought to be the commercial fishermen which are the main threat to river
dolphins, as oppose to the local fishermen. Educating commercial fishermen on the role that the
river dolphin play within the ecosystem and the importance of them as an indicator species will raise
awareness of the consequences of losing river dolphins.
44
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
It is important to remember that even ‘dolphin friendly’ fishing techniques can still have a
detrimental effect on the cetaceans environment and so the promotion and implementation of
sustainable fishing is important as it will help to prevent heavy fishing.
5.3 Conservation implications
All of the mentioned conservation actions should work together to form a conservation network
which covers the Amazon river dolphins range across South America , this will require international
cooperation and scientific knowledge, this study aims to contribute to the latter. Continuation of
studies are of high importance to monitor the river dolphins and to develop a deeper understanding
of these specialist species. Ultimately the conservation of the river dolphins will conserve the distinct
and biodiverse ecosystem in which they inhabit, benefiting a multitude of species.
45
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Appendix 1.
Example of data Collection Sheet.
Transect= Mouth.
End time= 10.00
Date = 8/7/10 Weather= sunny, 30% cloud
Start time= 09.30
Species
GPS Location
Age Composition
Time of sighting
Group size
Pink
0.03
1 Adult, 1 Juvenile
09.43
2
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Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Appendix 2
Raw data across the transects.
Boto
Tucuxi
Upriver
Downriver
Channel
Upper
Channel
Mouth
Length of
transect
surveyed
(km)
55
40
45
20
4
Total
individuals
Adults
34
32
27
12
26
25
26
20
10
19
Sub-adults
3
2
3
1
3
Juveniles
6
4
4
1
4
Singles
13
15
10
1
8
Pairs
6
5
4
4
4
Groups of 3
3
1
3
1
2
Groups of 4
0
1
0
0
1
Groups of 5
0
0
0
0
0
Total
individuals
Adults
40
45
17
9
41
34
36
17
7
39
Juveniles
6
9
0
2
2
Singles
5
6
11
2
5
Pairs
10
8
1
2
6
Groups of 3
5
2
0
1
5
Groups of 4
0
0
1
0
1
Groups of 5
0
2
0
0
1
Groups of 6
0
0
0
0
0
Groups of 7
0
1
0
0
0
51
Conservation and population structure of Amazon River Dolphins. E. Ford, 2011.
Appendix 3.
Raw data across the study period.
16th
June20th
June.
25.5
21st
June25th
June.
20.5
26th
June30th
June.
35.5
1st July5th July.
6th July10th
July.
41.5
41
34
12
20
30
35
Adults
24
10
15
27
24
Sub-adults
6
0
2
1
3
Juveniles
4
2
3
2
8
Singles
8
3
7
19
10
Pairs
5
3
5
4
6
Groups of 3
4
1
1
1
3
Groups of 4
1
0
0
0
1
Groups of 5
0
0
0
0
0
Total individuals
45
17
17
41
32
Adults
40
15
14
34
30
Juveniles
5
2
3
7
2
Singles
10
0
2
8
9
Pairs
5
5
3
8
6
Groups of 3
4
3
3
2
1
Groups of 4
1
1
0
0
0
Groups of 5
1
0
0
1
1
Groups of 6
0
0
0
0
0
Groups of 7
1
0
0
0
0
Total length surveyed
(km)
Total individuals
Boto
Tucuxi
52