[MARMAM] New paper - Abundance estimates of an isolated population of bottlenose dolphins in Namibia

Simon Elwen simon.elwen at gmail.com
Tue May 14 12:21:45 PDT 2019

Dear Colleagues -

We are proud to announce the publication of:

*Elwen, S.H*., R.H. Leeney, T. Gridley. (2019). Abundance estimates of an
isolated population of common bottlenose dolphins in Walvis Bay, Namibia
2008-2012. African Journal of Marine Science 41(1).

Take home message:  At under 100 individuals, this is one of the smallest
populations of any mammal in southern Africa but is exposed to an
increasing number of human threats including marine tourism, harbour
expansion and habitat degradation.

Paper available on our website:  http://seasearch.co.za/research/  or
Researchgate profiles.


The coastal population of common bottlenose dolphins (*T. truncatus*) found
in Namibia is regionally isolated and unique. This population faces several
potential anthropogenic threats, especially in Walvis Bay, including
boat-based tourism, a commercial harbour undergoing expansion and
aquaculture for oysters and mussels. Between 2008 and 2012, 238 boat-based
surveys were conducted, resulting in 170 encounters with bottlenose
dolphins. Group size varied from 1 to 45 individuals (mean = 10.7).
Encounter rates, group size and total number of animals identified were
higher in winter than summer seasons. The number, and survival and
immigration parameters of dolphins using Walvis Bay was investigated using
Robust Design and Huggins closed population mark-recapture models. The
highest numbers estimated were in the first and last years of the study,
with estimates of 74 to 82 and 76 to 77 (number identified and upper 95%
confidence interval respectively). The only previously available data from
an incomplete study in the early 1990s suggested that the population was
between 100 and 150 individuals at that time. Although no linear trend in
population size was obvious during this study, the clear evidence of
isolation, small population size, low annual birth rate, and potential
long-term decrease in numbers since the early 1990s is concerning. Further
work to collect data on demographic parameters is urgently recommended with
a view to obtaining increased protection.

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Simon Elwen Ph.D. NRF Research Fellow at the Mammal Research Institute,
University of Pretoria

Based at Sea Search Africa - 4 Bath Rd, Muizenberg, Cape Town.

Phone: +27 21 788 1206 (Office SA),      +27 71 139 5951 (Mob SA)

www.seasearch.co.za &  www.namibiandolphinproject.org

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