Sharks caught in the protective gill nets off Natal, South Africa. 1. The sandbar shark<i>Carcharhinus plumbeus</i>(Nardo)

Abstract

Abstract Between 1978 and 1987, 291 sandbar sharks Carcharhinus plumbeus were caught in the gill-nets which protect the tourist beaches of Natal. They represented 2,1 per cent of the total catch of sharks for this period, and the catch per unit effort ranged from 0,2 to 1,4 sharks·km-net−1·year−1. The mean sex ratio for embryos was unity, compared with the 0,5 males: 1 female for free-swimming sharks. The length frequency distributions for both sexes were bimodal, the modes representing immature and mature sharks respectively. Males matured at about 1 290 mm precaudal length and females at 1 300 mm. Mating seemed to be taking place north of the netted region between late October and January, and the gestation period was about 12 months. There was a positive correlation between length of female and litter size, which averaged 7,2 embryos. The hepatosomic index of mature females was highest at the onset of pregnancy. Teleosts and cephalopods dominated the food in terms of frequency of occurrence.