Shark predation on Indian Ocean bottlenose dolphins <i>Tursiops truncatus</i> off Natal, South Africa

Abstract

The incidence of shark induced scars on Indian Ocean bottlenose dolphins caught in gill nets off Natal, on the south-east coast of southern Africa, was monitored between January 1983 and June 1987. The occurrence of dolphin remains in sharks caught in these nets between January 1980 and December 1985 was also recorded. Of the dolphins caught, 10,3% exhibited scars or wounds consistent with shark bites. Only 1,2% of over 6000 sharks caught contained cetacean remains. Four species of shark, the Zambesi (Carcharhinus leucas), the tiger (Galeocerdo cuvieri),the great white (Carcharodon carcharías) and the dusky shark (Carcharhinus obscurvs) were implicated as dolphin predators. Estimates from the number of these four species caught annually and the frequency of occurrence of dolphin flukes and vertebrae in their stomachs suggest that a mininum of 20 bottlenose dolphins or 2,2% of the estimated population in southern Natal coastal waters are killed each year by sharks.