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Population size, distribution, and behavior of indo-pacific bottlenose (Tursiops aduncus) and humpback (Sousa chinensis) dolphins off the south coast of Zanzibar
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
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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.

Place, publisher, year, edition, pages
2006. Vol. 22, no 3, 667-682 p.
Keyword [en]
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: urn:nbn:se:su:diva-60504DOI: 10.1111/j.1748-7692.2006.00051.xOAI: oai:DiVA.org:su-60504DiVA: diva2:435295
Available from: 2011-08-17 Created: 2011-08-17 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Behavioural ecology of Indo-Pacific bottlenose and humpback dolphins
Open this publication in new window or tab >>Behavioural ecology of Indo-Pacific bottlenose and humpback dolphins
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dolphins in East Africa face various threats, such as direct hunt, bycatch and habitat degradation. It is therefore important to undertake research that can facilitate necessary conservation and management actions to minimize these threats. This thesis investigates the behavioural ecology of the populations of Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa chinensis) dolphins inhabiting the waters off the south coast of Zanzibar. Dolphins were identified using photo-identification techniques and information on behaviour, location and depths were collected during boat surveys conducted between 1999 and 2002. Mark-recapture methods were used to estimate population sizes of 161 (95% CI 144-177) Indo-Pacific bottlenose dolphins and 71 (95% CI 48-94) humpback dolphins in the 26 km2 study area in 2001. High frequency of re-sightings indicated that both species were resident in the area. Analyses of spatial distribution, corrected for survey effort, showed that both bottlenose and humpback dolphins primarily utilized only a small part of the study area. These areas may be regarded as critical areas for respective species, given the relatively high density of groups encountered. The impact of dolphin tourism on female bottlenose dolphins was investigated both on individual and group level using follows of focal females and scan-sampling of focal groups. Increased level of tourism activities increased the proportion of travel, non-directional movement patterns and active dives. These changes can have adverse effects on both individual and population level by giving dolphins less time for nursing and causing shifts in habitat use. Further, this could also lead to reduced dolphin tourism potential. The explanations for mixed species groups in mammals are reviewed and an approach for investigating such groups is proposed. Mixed species groups of Indo-Pacific bottlenose and humpback dolphins frequently occur off the south coast of Zanzibar. Anti-predator coupled with social advantages, may offer a likely explanation for the formation of these groups. Mixed-species groups may have different functions depending on the individuals that participate. The findings in this thesis will be essential when planning future conservation and management actions to protect the dolphins as a socio-economic important resource.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen, 2004. 33 p.
Keyword
Behaviour, ecology, dolphins, Zanzibar, abundance, distribution, tourism, mixed-species groups, interspecific association, social interaction, swim-with-dolphin
National Category
Ecology
Identifiers
urn:nbn:se:su:diva-96 (URN)91-7265-837-X (ISBN)
Public defence
2004-04-30, sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-04-07 Created: 2004-04-07 Last updated: 2011-08-22Bibliographically approved
2. 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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