Sharks caught in the protective gill nets off Natal, South Africa. 7. The blacktip shark Carcharhinus limbatus (Valenciennes)

Abstract

Between 1978 and 1991, 1 836 blacktip sharks Carcharhinus limbatus were caught in the shark nets which protect the bathing beaches of Natal. The species constituted 9,3% of the total shark catch. Annual catches and catch rates fluctuated about a mean of 131 sharks and 3,3 sharks·km-net⁻¹·year⁻¹ respectively. Mature sharks, which constituted about two-thirds of the catch, were caught in similar numbers throughout the netted region but catches of immature animals increased towards the north. Catches took place throughout the year but were lowest from July to October. Most males reached maturity at 146–150 cm precaudal length (PCL) and females at 151–155 cm. Mean gonad indices in mature males were highest during September and October and in females during November and December. Males and females considered to be in mating condition were found predominantly in November and December. There is some evidence for a three-year reproductive cycle, and gestation lasts about 12 months. The smallest of 151 pregnant females was 146 cm PCL. Median litter size was six embryos (maximum 11) and mean embryo length within a litter ranged from 13 to 49 cm PCL. Larger females had more and larger embryos. Teleosts were found in 83% of non-empty stomachs, but there was regional and seasonal variation in the diet.