Some effects of shark nets in the Natal nearshore environment

Synopsis Protective gillnets (shark nets) have been successful in reducing the frequency of shark attacks on the coast of Natal, South Africa. This is achieved primarily through a reduction in numbers of large sharks. The nets also take a by catch of dolphins, sea turtles, batoids and teleosts. Concern has been expressed over the direct effect of mortalities on the various stocks and also the broader, indirect effects on the inshore system. Catch rates of most shark species declined initially but have shown no trend since the mid-1970s. A first estimate of the reduction in total shark numbers is provided, and factors such as stock identity and net avoidance are discussed. Turtle and teleost stocks do not appear to be threatened by net mortalities but marine mammalogists are investigating the sustainability of catches of two dolphin species. Certain batoids may have declined despite a high release rate, but more data are needed. A published contention that shark netting has resulted in a proliferation of small sharks through reduced predation is re-examined and considered to be exaggerated. Reduced predation on dolphins, as a result of shark netting, is estimated.