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Social structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off the south coast of Zanzibar
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The social structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) resident in Menai Bay, Zanzibar, east Africa, was investigated using group characteristics and association records collected 1999-2002.  On average, groups were large compared to those reported from other bottlenose dolphin studies. Groups were also significantly larger when the dolphins exhibited socializing behavior or when calves were present, indicating that large groups could be attributed to social benefits related to reproduction and caring for calves. To investigate relationships between identified individuals, an association analysis was performed using half-weight association indices (HWIs), calculated for 67 well-marked individuals sighted 9 or more times. While the overall distribution of HWIs was skewed towards lower values, relationships were stronger and more long-term than would be expected if dolphins were associating at random. A temporal analysis, performed to model the stability of associations, suggested that these relationships may last for as long as 7 years. Multidimensional scaling and cluster analysis revealed two female clusters and a male pair that had high HWIs across all years of sampling. These preferred relationships may be formed to obtain reproductive benefits as well as safety against predators and other threats. For example, the dolphins in Menai Bay are subject to anthropogenic threats from fishing and tourism activities in the area. Unless kept at a sustainable level, such threats could ultimately disrupt the long-term relationships observed in the present study and adversely influence the health of the population.

Keyword [en]
social structure, group characteristics, association indices, bottlenose dolphins, Tursiops aduncus
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-60530OAI: oai:DiVA.org:su-60530DiVA: diva2:435671
Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2011-08-23Bibliographically approved
In thesis
1. Ecology and genetic population structure of Indo-Pacific bottlenose dolphins in East Africa
Open this publication in new window or tab >>Ecology and genetic population structure of Indo-Pacific bottlenose dolphins in East Africa
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2011. 23 p.
Keyword
Tursiops aduncus, population size, distribution, social structure, behaviour, conservation status, mitochondrial DNA, microsatellites, Zanzibar, western Indian Ocean
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-61077 (URN)978-91-7447-293-6 (ISBN)
Public defence
2011-09-23, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript. Available from: 2011-09-01 Created: 2011-08-22 Last updated: 2011-08-24Bibliographically approved

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