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The occurrence and distribution of dolphins in Zanzibar, Tanzania, with comments on the differences between two species of Tursiops
Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. (Marine Mammal)
(Marine Mammal Research and Education)
Stockholms universitet, Naturvetenskapliga fakulteten, Zoologiska institutionen. (Marine Mammal)
2005 (Engelska)Ingår i: Western Indian Ocean journal of marine science, ISSN 0856-860X, Vol. 4, nr 1, s. 85-93Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Incidental catches (bycatch) in gillnet fisheries off Zanzibar (Unguja Island), as asource of mortality among several species of dolphins, were reported in a questionnaire surveyconducted in 1999. As a follow-up to that survey, from January 2000 to August 2003, wemonitored the incidental catches of dolphins collected from 12 fish landing sites. Six species ofdolphins were recorded from 143 specimens retrieved from bycatches in drift- and bottom setgillnets. Of these, 68 (48%) were Indo-Pacific bottlenose dolphins (Tursiops aduncus), 44 (31%) spinner dolphins (Stenella longirostris), 12 (8%) Risso’s dolphins (Grampus griseus), 11 (8%) Indo-Pacific humpback dolphins (Sousa chinensis), 6 (4%) Pan-tropical spotted dolphins(Stenella attenuata) and 2 (1%) common bottlenose dolphins (Tursiops truncatus). Most of thebycatches (71%) were in nets set off the north coast of Unguja Island. In this paper, bycatchrecords are examined to describe the occurrence and distribution of dolphin species in UngujaIsland coastal waters. The relatively large numbers of bycatch dolphins recorded indicate thatbycatch may be a potential threat to local populations that need to be addressed in futureconservation and management efforts in the region.

Ort, förlag, år, upplaga, sidor
2005. Vol. 4, nr 1, s. 85-93
Nyckelord [en]
incidental catch, occurrence, distribution, dolphins, Unguja Island, Zanzibar
Nationell ämneskategori
Ekologi
Forskningsämne
zoologisk ekologi
Identifikatorer
URN: urn:nbn:se:su:diva-34438OAI: oai:DiVA.org:su-34438DiVA, id: diva2:284796
Projekt
Sustainable dolphin tourism in east AfricaTillgänglig från: 2010-01-08 Skapad: 2010-01-08 Senast uppdaterad: 2017-12-12Bibliografiskt granskad
Ingår i avhandling
1. Biology, ecology and anthropogenic threats of Indo-Pacific bottlenose dolphins in east Africa
Öppna denna publikation i ny flik eller fönster >>Biology, ecology and anthropogenic threats of Indo-Pacific bottlenose dolphins in east Africa
2010 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: Department of Zoology, Stockholm University, 2010. s. 31
Nyckelord
Growth, reproduction, feeding ecology, bycatch, organohalogen compounds, dolphins, Tursiops aduncus, Zanzibar, East Africa
Nationell ämneskategori
Ekologi
Forskningsämne
zoologisk ekologi
Identifikatorer
urn:nbn:se:su:diva-34472 (URN)978-91-7447-002-4 (ISBN)
Disputation
2010-02-12, Ahlmansalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning
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. Tillgänglig från: 2010-01-21 Skapad: 2010-01-08 Senast uppdaterad: 2010-10-14Bibliografiskt granskad

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Amir, Omar A.Berggren, Per
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Western Indian Ocean journal of marine science
Ekologi

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