[MARMAM] Masters thesis on Irrawaddy dolphins (Orcaella brevirostris) in Sarawak, Malaysia

Cindy Peter cindycharity.peter at gmail.com
Tue Nov 20 19:00:28 PST 2012

Hi all,

A PDF copy of my Masters thesis on Irrawaddy dolphins (*Orcaella
brevirostris*) in Sarawak, Malaysia is available.

Peter, C. 2012. Distribution patterns, habitat characteristics and
population estimates of Irrawaddy dolphins (Orcaella brevirostris) in
Kuching Bay, Sarawak. Msc Thesis. Insitute of Biodiversity and
Environmental Conservation. Universiti Malaysia Sarawak. 120pp.


Irrawaddy dolphins (*Orcaella brevirostris*) are known to be riverine and
coastal dwelling animals which place them under pressure from human
activities like fishing, coastal developments and environmental pollution.
Previously, there was a lack of baseline information on the population of
Irrawaddy dolphins that are present in Kuching Bay. This lack of data
impeded conservation and management efforts, as no one could determine how
many dolphins there are, how they are distributed on a fine scale, or what
their preferred habitat characteristics are.

In order to overcome this, small boat surveys were conducted in the Kuching
Bay from June 2008-September 2010. The first objective of the study aimed
to map the distribution patterns and determine the relative abundance of
Irrawaddy dolphins in the waters of Kuching Bay. Surveys covered a total of
4,091 km and 317 hours. Irrawaddy dolphins were sighted 41 times on-effort
representing an estimated total of 183 individuals. The mean encounter rate
throughout the 44 days of survey was 0.30 sightings per hour. Analysis of
encounter rates within 2km by 2km grid cells showed high densities of
Irrawaddy dolphins in the Salak estuary, Bako peninsula and offshore of
Telaga Air.

The second objective was to define the habitat preferences of Irrawaddy
dolphins by conducting water parameter samplings and measuring the physical
characteristics of the sighting sites. Kruskal-Wallis U tests showed that
the animals’ distributions are not significantly related to water
temperature, pH, depth or distance to land. However the dolphin
distribution was statistically significant for the different categories of
salinity (p < 0.05) and distance to rivermouth (p < 0.05). Fisher’s exact
test indicated that Irrawaddy dolphins are statistically more likely to be
present in waters within a 6 km radius from rivermouths. Dolphins’
distributions are also affected by tide levels as Mann-Whitney U tests
proved a statistically significant difference (p < 0.05) in dolphin
distribution between tide levels lower than 2.0 m and tide levels higher
than 2.0 m.

The third objective of the study was to obtain absolute abundance estimates
of Irrawaddy dolphins in Kuching Bay. This was achieved by using
mark-recapture techniques on photo-identified individuals to generate
population estimates for the Kuching study area. Based on this, the best
estimate of the Irrawaddy dolphin population in Kuching Bay is 233 dolphins
(CV = 22.5%, 95% CI 151-360).

The fourth objective was to learn about the individual movement patterns of
the Irrawaddy dolphins in Kuching Bay by identifying individual dolphins
through photo-identification and plotting the observed locations of
identified individuals. Seventeen individuals were photographed more than
once and four individuals were photographed in both the Salak–Santubong and
Bako–Buntal bays on a few occasions. The furthest distance an individual
dolphin traveled between sighting locations in the study was approximately
40 km. In addition, resighted individuals were photographed across
different survey months as well as different survey years.

This study showed that the Irrawaddy dolphins of Kuching Bay prefer areas
of lower salinity, closer to land and rivermouths, with tidal state also
playing a significant role in their distribution. The estimate obtained in
this study showed that the population in Kuching Bay is relatively small
and the movement patterns analysis proved that several individual dolphins
utilize both the Salak-Santubong Bay and Bako-Buntal Bay. Therefore, any
management or conservation efforts for the Irrawaddy dolphins will need to
be applied to both bays.

Please let me know if you are interested in reading it and I will send a

Best Regards,

Cindy Peter


Cindy Peter, MSc (Marine Ecology)

Sarawak Dolphin Project

Institute of Biodiversity and Environmental Conservation

University Malaysia Sarawak

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