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Feeding ecology of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) incidentally caught in the gillnet fisheriesoff Zanzibar, Tanzania
Stockholm University, Faculty of Science, Department of Zoology. (Marine Mammal)
Stockholm University, Faculty of Science, Department of Zoology. (Marine Mammal)
(Marine Mammal Research and Education)
2005 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 63, no 3, 429-437 p.Article in journal (Refereed) Published
Abstract [en]

The stomach contents of 26 Indo-Pacific bottlenose dolphins (Tursiops aduncus) incidentally caught in gillnet fisheries aroundUnguja Island (Zanzibar) between February 2000 and August 2002 were examined. The relative importance of each prey species wasassessed through indices of relative importance. In total, 1403 prey items comprising 50 species of bony fish and three species ofsquid were identified from food remains. Five species of fish, Uroconger lepturus, Synaphobranchus kaupii, Apogon apogonides,Lethrinus crocineus, Lutjanus fulvus, and three species of squid, Sepioteuthis lessoniana, Sepia latimanus and Loligo duvauceli, werethe most important prey species. Based on an index that included frequency of occurrence, percentage by number and by weight,Uroconger lepturus proved to be the most important prey species of mature dolphins whereas Apogon apogonides was the preferredprey of immature dolphins. These results indicate that Indo-Pacific bottlenose dolphins off the coast of Zanzibar forage ona relatively large number of prey species, but that only a few small- and medium-sized neritic fish and cephalopods contributesubstantially to the diet. Further, the ecology and behavior of the preferred fish prey species indicate that the dolphins forage overreef or soft bottom substrata and near the shore.

Place, publisher, year, edition, pages
2005. Vol. 63, no 3, 429-437 p.
Keyword [en]
Indo-Pacific bottlenose dolphin; Tursiops aduncus; stomach contents; feeding ecology; diet; Zanzibar
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-34448DOI: 10.1016/j.ecss.2004.12.006OAI: oai:DiVA.org:su-34448DiVA: diva2:284811
Projects
Sustainable dolphin tourism in east Africa
Available from: 2010-01-08 Created: 2010-01-08 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Biology, ecology and anthropogenic threats of Indo-Pacific bottlenose dolphins in east Africa
Open this publication in new window or tab >>Biology, ecology and anthropogenic threats of Indo-Pacific bottlenose dolphins in east Africa
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis examines the biology, ecology and anthropogenic threats of Indo-Pacific bottlenose dolphins (Tursiops aduncus) off Zanzibar, Tanzania, based on research conducted and samples collected between 2000 and 2008. Distribution and occurrence are described based on incidental catches (bycatch) in gillnet fisheries. Biology and ecology are examined by ageing and studying the reproductive biology and stomach contents of collected specimens. The composition of organohalogen compounds is determined in blubber samples, and assessment and mitigation of bycatch are conducted using observers onboard fishing vessels. Fisheries bycatch data showed that Indo-Pacific bottlenose dolphins occur year round in all areas around Zanzibar. Sexual maturity was attained between 7 and 8 years and body length 190-200 cm in females and at 16 years and body length 213 cm in males. The gestation period was estimated to be 12.3 months, with calving occurring throughout the year, peaking November-March and with an interval of 2.7 years. The estimated pregnancy rate was between 0.10 and 0.58 depending on methods used. Stomach contents revealed a relatively large number of prey species, but that only a few small- and medium-sized neritic fish and cephalopods contribute substantially to the diet. Estimates of total annual bycatch were >9% which is not considered sustainable. An experiment showed that pingers can be a short term mitigation measure to reduce bycatch of dolphins in both drift- and bottom set gillnets. Methoxylated polybrominated diphenyl ethers (Meo-BDEs) were found at higher concentrations than anthropogenic organic pesticides (OCPs), with only traces of polychlorinated biphenyls (PCBs) detected. This study reveals the magnitude and apparent susceptibility of Indo-Pacific bottlenose dolphins off Zanzibar to anthropogenic threats, especially fisheries bycatch, and it is clear that immediate conservation and management measures are needed to reduce bycatch.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2010. 31 p.
Keyword
Growth, reproduction, feeding ecology, bycatch, organohalogen compounds, dolphins, Tursiops aduncus, Zanzibar, East Africa
National Category
Ecology
Research subject
Animal Ecology
Identifiers
urn:nbn:se:su:diva-34472 (URN)978-91-7447-002-4 (ISBN)
Public defence
2010-02-12, Ahlmansalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Manuscript. Paper 5: Submitted. Available from: 2010-01-21 Created: 2010-01-08 Last updated: 2010-10-14Bibliographically approved

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