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Cephalopods in the diets of four shark species (galeocerdo Cuvier, sphyrna lewini, S. Zygaena and S. Mokarran) from Kwazulu-Natal, South Africa
Abstract
The cephalopod components of the diets of four species of shark, tiger Galeocerdo cuvier, smooth hammerhead Sphyrna zygaena, scalloped hammerhead S. lewini and great hammerhead S. mokarran, were examined to reveal patterns of prey choice. Although these sharks were caught in the inshore gillnets used in KwaZulu-Natal to protect bathers from shark attack, prey included neritic and oceanic taxa that were pelagic, epibenthic or benthic. In all, 3 387 lower beaks were found in the stomach contents. A total of 15 families was identified from 117 tiger
sharks with cephalopod lower beaks in their stomachs. Sepiidae, Octopodidae and Ancistrocheiridae were most numerous and dominated in terms of mass. Of the 422 scalloped hammerheads with lower beaks in their stomachs, Octopodidae, Octopoteuthidae and Ancistrocheiridae were the most dominant of the 12 families identified. The cephalopod prey items of 258 smooth hammerheads were dominated by Loliginidae. Sepiidae and Ancistrocheiridae were also major components of the 12 families identified. The prey items of seven great hammerheads were dominated by Ancistrocheiridae and Octopoteuthidae, and only six families were recorded. Neritic cephalopods were relatively more important in smaller sharks of each species analysed, whereas pelagic and epibenthic taxa from offshore were more dominant in larger individuals, these findings thus supporting information on shark behaviour derived from previous feeding and telemetry studies. There was overlap in cephalopod taxa taken by these sharks and by marine mammals in the same area, and the high numbers of some of the cephalopods in stomach contents, such as Sepiidae, Octopodidae, Ancistrocheiridae and Octopoteuthidae, suggest that they may be very abundant in the study area.
sharks with cephalopod lower beaks in their stomachs. Sepiidae, Octopodidae and Ancistrocheiridae were most numerous and dominated in terms of mass. Of the 422 scalloped hammerheads with lower beaks in their stomachs, Octopodidae, Octopoteuthidae and Ancistrocheiridae were the most dominant of the 12 families identified. The cephalopod prey items of 258 smooth hammerheads were dominated by Loliginidae. Sepiidae and Ancistrocheiridae were also major components of the 12 families identified. The prey items of seven great hammerheads were dominated by Ancistrocheiridae and Octopoteuthidae, and only six families were recorded. Neritic cephalopods were relatively more important in smaller sharks of each species analysed, whereas pelagic and epibenthic taxa from offshore were more dominant in larger individuals, these findings thus supporting information on shark behaviour derived from previous feeding and telemetry studies. There was overlap in cephalopod taxa taken by these sharks and by marine mammals in the same area, and the high numbers of some of the cephalopods in stomach contents, such as Sepiidae, Octopodidae, Ancistrocheiridae and Octopoteuthidae, suggest that they may be very abundant in the study area.
