Investigation of population abundance, distribution, and population linkage of Indo-Pacific Bottlenose Dolphins (Tursiops aduncus) on the north and south of Zanzibar using mark-recapture and acoustic methods

Master Thesis


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University of Cape Town

Previous studies, using a variety of methods such as photographic identification, fisheries observer programs, or genetic testing, on Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Zanzibar Island, Tanzania, suggest separate populations around the north and south coasts. However, most research around the island has focused on the south coast, and movement of dolphins around the coastline is poorly understood. Photographic identification data, consisting of dorsal fin images, and acoustic data from dolphin whistles, both collected in 2008, were analysed to examine linkages between north and south Zanzibar. Photographic identification data was applied in a Mark-Recapture framework, using open population models, to generate abundance estimates of 149 (95% CI 128-173) and 120 (95% CI 97-149) individuals for the north and south coasts of Zanzibar respectively. As 16 individuals had moved from the south to the north coast of Zanzibar during the two month study, a combined population estimate of 353 (95% CI 290-430) individuals for Zanzibar Island was also generated. Acoustic analysis of standard whistle parameters was used to investigate whether these learned signals shared features between the putative populations, using whistle data collected in Plettenberg Bay, South Africa as an out-group. Discriminant function analysis of whistle parameters indicated high classification success of whistles recorded from animals in the north location (86.2%), moderate classification success for the outgroup (61.8%), and zero classification success for Zanzibar's south coast population. High misclassification rates for south Zanzibar suggest that these whistles cannot be readily discriminated from those of north Zanzibar. Shared whistle features suggest that learning may take place between individuals moving between localities. Coupled with previous genetic studies, this study suggests female philopatry and male mediated gene flow between the two areas; however, more genetic markers are necessary to test this interpretation. Further work is also necessary to quantify the degree of movement of dolphins around Zanzibar Island, and potential migration into the area, which will assist in developing management plans.