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Growth and reproduction of Indo-Pacific bottlenose dolphins (Tursiops aduncus) incidentally caught in gillnets off 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)
(English)Article in journal (Refereed) Submitted
Abstract [en]

Life history parameters of Indo-Pacific bottlenose dolphin (Tursiops aduncus) were examined in 69 specimens incidentally caught in gillnet fisheries off Zanzibar, Tanzania between 2000 and 2008. Calves were born at a body length of 103 cm and a weight of 12-15 kg. Sexual maturity in females was reached at 7-8 years and body length 190-200 cm. Sexual maturity in males was attained at 16 years and a body length of 213 cm. Calving occurred throughout the year with a peak November-March, after a gestation period of 12.3 months. The estimated pregnancy rate was 0.10 based on the proportion pregnant mature females in the sample and 0.58 based on the occurrence of Corpora Lutea in the ovaries. The average calving interval was calculated to 2.7 years. The results are important for assessment of fisheries bycatch mortality and conservation and management of Indo-Pacific bottlenose dolphins in western Indian Ocean

Keyword [en]
Indo-Pacific bottlenose dolphin, Tursiops aduncus, life history parameters, growth, reproduction, sexual maturity, ovary, Corpora Lutea, pregnancy rate, gestation period, calving interval, gillnet fisheries, byctach, Zanzibar, Tanzania, Indian Ocean.
National Category
Ecology
Research subject
Animal Ecology
Identifiers
URN: urn:nbn:se:su:diva-34454OAI: oai:DiVA.org:su-34454DiVA: diva2:284839
Available from: 2010-01-08 Created: 2010-01-08 Last updated: 2010-10-14Bibliographically 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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