Feeding ecology of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) incidentally caught in the gillnet fisheries off Zanzibar, Tanzania

The stomach contents of 26 Indo-Pacific bottlenose dolphins (Tursiops aduncus) incidentally caught in gillnet fisheries around Unguja Island (Zanzibar) between February 2000 and August 2002 were examined. The relative importance of each prey species was assessed through indices of relative importance. In total, 1403 prey items comprising 50 species of bony fish and three species of squid 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, were the 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 preferred prey of immature dolphins. These results indicate that Indo-Pacific bottlenose dolphins off the coast of Zanzibar forage on 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. Further, the ecology and behavior of the preferred fish prey species indicate that the dolphins forage over reef or soft bottom substrata and near the shore.