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Ecology and genetic population structure of Indo-Pacific bottlenose dolphins in East Africa
Stockholm University, Faculty of Science, Department of Zoology.
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 [en]
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: urn:nbn:se:su:diva-61077ISBN: 978-91-7447-293-6 (print)OAI: oai:DiVA.org:su-61077DiVA: diva2:436098
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
List of papers
1. Population size, distribution, and behavior of indo-pacific bottlenose (Tursiops aduncus) and humpback (Sousa chinensis) dolphins off the south coast of Zanzibar
Open this publication in new window or tab >>Population size, distribution, and behavior of indo-pacific bottlenose (Tursiops aduncus) and humpback (Sousa chinensis) dolphins off the south coast of Zanzibar
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2006 (English)In: Marine mammal science, ISSN 0824-0469, E-ISSN 1748-7692, Vol. 22, no 3, 667-682 p.Article in journal (Refereed) Published
Abstract [en]

Indo-Pacific bottlenose (Tursiops aduncus) and humpback dolphins (Sousa chinensis) off the south coast of Zanzibar, East Africa, have been subject to both direct and indirect takes as well as disturbance from local dolphin tourism during the last decade. Meanwhile, little or no information on population parameters exists for these animals. In order to assess the anthropogenic threats, a study was conducted between 1999 and 2002 to determine population sizes, distribution, and behavior of these animals. Population sizes were calculated for each year using mark-recapture methods applied to photo-identification data. The estimates ranged between 136 and 179 for the bottlenose dolphins and between 58 and 65 for the humpback dolphins in the calculated 26 km2 study area. Patterns in distribution and behavior were investigated using image and spatial statistic software on data from boat surveys. Analyses of spatial densities showed that both species concentrated their activities to smaller areas (2%–11.5%) within the study area. When the study results were considered in light of the anthropogenic threats, it was clear that immediate conservation measures were needed. This is critical if the negative impact on the species is to be minimized and the dolphins are to continue to represent a socioeconomic resource in the region.

Keyword
mark-recapture, photo-identification, population size, distribution, behavioral ecology, hunt, bycatch, dolphin tourism, critical areas, TISS
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-60504 (URN)10.1111/j.1748-7692.2006.00051.x (DOI)
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
2. Social structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off the south coast of Zanzibar
Open this publication in new window or tab >>Social structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off the south coast of Zanzibar
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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
social structure, group characteristics, association indices, bottlenose dolphins, Tursiops aduncus
National Category
Natural Sciences
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-60530 (URN)
Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2011-08-23Bibliographically approved
3. Phylogenetic placement and population structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar, Tanzania, based on mtDNA sequences
Open this publication in new window or tab >>Phylogenetic placement and population structure of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar, Tanzania, based on mtDNA sequences
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2011 (English)In: Marine mammal science, ISSN 0824-0469, E-ISSN 1748-7692, Vol. 27, no 2, 431-448 p.Article in journal (Refereed) Published
Abstract [en]

Phylogenetic placement of bottlenose dolphins from Zanzibar, East Africa and putative population differentiation between animals found off southern and northern Zanzibar were examined using variation in mtDNA control region sequences. Samples (n= 45) from animals bycaught in fishing gear and skin biopsies collected during boat surveys were compared to published sequences (n= 173) of Indo-Pacific bottlenose dolphin, Tursiops aduncus, from southeast Australian waters, Chinese/Indonesian waters, and South African waters (which recently was proposed as a new species) and to published sequences of common bottlenose dolphin, Tursiops truncatus. Bayesian and maximum parsimony analyses indicated a close relationship between Zanzibar and South African haplotypes, which are differentiated from both Chinese/Indonesian and Australian T. aduncus haplotypes. Our results suggest that the dolphins found off Zanzibar should be classified as T. aduncus alongside the South African animals. Further, analyses of genetic differentiation showed significant separation between the T. aduncus found off northern and southern Zanzibar despite the relatively short distance (approximately 80 km) between these areas. Much less differentiation was found between southern Zanzibar and South Africa, suggesting a more recent common evolutionary history for these populations than for the northern and southern Zanzibar populations.

Keyword
bottlenose dolphin, Tursiops aduncus, phylogenetic, mitochondrial DNA control region, population structure, Zanzibar
National Category
Zoology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-60503 (URN)10.1111/j.1748-7692.2010.00416.x (DOI)000289465900019 ()
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
4. Population structure and diversity of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the western Indian Ocean
Open this publication in new window or tab >>Population structure and diversity of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the western Indian Ocean
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Bottlenose dolphin (Tursiops sp.) populations often show small-scale genetic differentiation and have a capacity to adapt both their social strategies and structure to local environmental conditions. Here we investigate population structure and genetic diversity of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the western Indian Ocean, with special reference to Zanzibar, Tanzania. The Indo-Pacific bottlenose dolphins off Zanzibar were previously hunted and are subject to high levels of bycatch and negative impact from tourism. A recent study has indicated a limited exchange of reproducing females between northern and southern Zanzibar. Mitochondrial DNA sequence (mtDNA 429bp) variation and autosomal genotypes (7 microsatellite loci) was used to assess genetic variation and differentiation among tissue samples from Zanzibar (n=91) Mayotte (n=12) and Oman (n=4). The results showed a much higher amount of differentiation for mtDNA than autosomal DNA between northern and southern Zanzibar suggesting female philopatry with greater dispersal by males than females. Genetic diversity levels were relatively high in all areas and there were no indications of any recent reduction in effective population size, except in Mayotte where indications of a recent bottleneck encourage further analyses. Further, the close relationship and lack of clear structuring, with several shared haplotypes among regions, suggest a relatively recent common founder population for the Indo-Pacific bottlenose dolphins in the western Indian Ocean. Based on the high differentiation in mtDNA between northern and southern Zanzibar and that local growth rates in large part will be determined by female breeding success, we suggest that the Indo-Pacific bottlenose dolphins off northern and southern Zanzibar should be treated as separate management units.

Keyword
Zanzibar, Tursiops aduncus, population structure, diversity, female philopatry, mtDNA, microsatellites
Identifiers
urn:nbn:se:su:diva-60529 (URN)
Available from: 2011-08-19 Created: 2011-08-19 Last updated: 2014-10-13Bibliographically approved

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