Ecology and genetic population structure of Indo-Pacific bottlenose dolphins in East Africa

Abstract: Many marine mammal populations are threatened by anthropogenic activities. The Indo-Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar are subject to high levels of bycatch, negative impact from tourism and were previously hunted. To assess conservation status and to formulate necessary management actions for viable dolphin populations, knowledge of their population ecology is vital. This thesis provides information on population size, distribution, social structure, genetic diversity and population differentiation for Indo-Pacific bottlenose dolphins off southern Zanzibar. To investigate these parameters, individual identification and group structure data collected during boat based surveys were used in combination with genetic analyses of tissue samples from bycaught animals and skin biopsies from free ranging animals. The results show that the area off southern Zanzibar potentially constitute an important nursing ground (Paper I, II) for the relatively small population of Indo-Pacific bottlenose dolphins present year round (Paper I). The dolphins in this area live in a fission-fusion society where some animals also form long-term relationships (Paper II). Genetic analyses indicate limited exchange of reproducing females between northern and southern Zanzibar suggesting female philopatry with a greater dispersal by males (Paper III, IV). The relatively high genetic diversity of the Indo-Pacific bottlenose dolphins off Zanzibar indicates no current threat to their genetic health, despite recent anthropogenic impacts. (Paper IV). On a greater geographical scale the results show that the Indo-Pacific bottlenose dolphins in the western Indian Ocean, ranging from Oman to South Africa, share a relatively recent common founder population and belong to a proposed third species within the genus Tursiops (Paper III, IV). Finally, the results presented demonstrate the value of a multi-disciplinary approach to determine the conservation status of animal populations.