Feeding and reproductive biology of the Indo-pacific bottlenose dolphin (Tursiops aduncus) caught in the gillnet fishery in Zanzibar

Age and reproductive parameters of 36 and stomach contents of 35 Indo-Pacific bottlenose dolphins (Tursiops aduncus) incidentally caught around Unguja Island (Zanzibar) between January 2000 and August 2002 were investigated. Calves are born at a length of approximately 103 cm and weight 12 kg for females and males at a length around 104.5 cm and weight of 15.5 kg. First ovulation (sexual maturity), as judged by ovarian activity, develops after females are above 6 years old, at a length about 200 cm and weight 92 kg. Males exhibit testicular activity when they are about 13 years old, at a length about 202 cm and weight 112 kg. Both females and males may live more than 36 years, based on counts of GLGs in teeth. The maximum length and weight for females was 221 cm and 148.5 kg respectively, while for males the maximum length and weight was 238 cm and 160 kg respectively. 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 3 species of squid were identified from food remains. There was no significant difference in choice of food or size of prey species between mature male and female dolphins, nor between immature and mature animals. However, there was significant difference between immature and mature dolphins in the number of prey species in the diet where immature animals fed fewer prey species. Ranking the importance of prey species based on an index (including frequency of occurrence, percentage by number and percentage by weight) showed that Uroconger lepturus was the most important prey species for mature animals whereas Apogon apogonides was the most preferred prey by the immature dolphins.