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Behavioural ecology of Indo-Pacific bottlenose and humpback dolphins
Stockholm University, Faculty of Science, Department of Zoology.
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 [en]
Behaviour, ecology, dolphins, Zanzibar, abundance, distribution, tourism, mixed-species groups, interspecific association, social interaction, swim-with-dolphin
National Category
Ecology
Identifiers
URN: urn:nbn:se:su:diva-96ISBN: 91-7265-837-X OAI: oai:DiVA.org:su-96DiVA: diva2:200729
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
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
Show others...
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. Impact of tourism on nursing female Indo-Pacific bottlenose dolphins off the south coast of Zanzibar.
Open this publication in new window or tab >>Impact of tourism on nursing female Indo-Pacific bottlenose dolphins off the south coast of Zanzibar.
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25878 (URN)
Note
Part of urn:nbn:se:su:diva-96Available from: 2004-04-07 Created: 2004-04-07 Last updated: 2010-01-13Bibliographically approved
3. Mixed species groups in mammals
Open this publication in new window or tab >>Mixed species groups in mammals
2003 (English)In: Mammal Review, ISSN 0305-1838, E-ISSN 1365-2907, Vol. 33, no 3, 205-223 p.Article in journal (Refereed) Published
Abstract [en]

1. Mixed species groups have long been noted in birds, but they also occur among different species of mammals ranging from closely related species to species from different orders. Mixed species groups of mammals occur in many different habitats, e.g. ungulates on the savannah, primates in various types of forests and cetaceans in the oceans. Mixed species groups are very different in their duration, frequency, predominant activity and structure depending on the species interacting and the habitat they occur in. 2. Functional explanations for mixed species groups usually fall within two categories: foraging advantages and predator avoidance. However, there could also be other social and reproductive advantages of mixed species groups that could contribute to their formation and stability. The advantages do not have to be equally distributed between the participating species and can also vary according to season and the presence of predators. 3. It is important that all investigators of mixed species groups take their studies one step further after the naturalistic description and test the function and benefits of mixed species groups in order to give more strength to their conclusions. In this paper we review and discuss the function of mixed species groups in mammals and suggest an approach on how to investigate the function of such groups.

National Category
Zoology
Identifiers
urn:nbn:se:su:diva-25879 (URN)10.1046/j.1365-2907.2003.00022.x (DOI)
Available from: 2004-04-07 Created: 2004-04-07 Last updated: 2014-10-13Bibliographically approved
4. Mixed species groups of Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa chinensis) dolphins off the south coast of Zanzibar, East Africa
Open this publication in new window or tab >>Mixed species groups of Indo-Pacific bottlenose (Tursiops aduncus) and humpback (Sousa chinensis) dolphins off the south coast of Zanzibar, East Africa
(English)Manuscript (preprint) (Other academic)
National Category
Zoology
Identifiers
urn:nbn:se:su:diva-25880 (URN)
Available from: 2004-04-07 Created: 2004-04-07 Last updated: 2013-07-09Bibliographically approved

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