Trends in annual CPUE and evidence of sex and size segregation of Sphyrna lewini: management implications in coastal waters of northeastern Australia

Abstract

Hammerhead sharks have experienced a drastic global reduction in abundance, yet limited data exist on their general biology and population structure. We use generalised linear models (GLMs) to analyse historical mesh net and drumline catches (1996-2006) of Sphyrna lewini from the Queensland Shark Control Program (QSCP), which covers 10 locations on the north-east coast of Australia. Results show a significant decline in S. lewini female total length over the study period and a significant increase in annual CPUE on the Gold Coast. Sexual segregation was found in Cairns, where S. lewini males were most abundant. A positive linear relationship was found between maternal total length and litter size. Birth-size embryos were found in most months. However, normal birth size (0.50 m) embryos were found in pregnant females most often during spring and summer. Mesh nets were more selective for smaller S. lewini than drumlines. It is recognised that species selectivity of other, more potentially dangerous shark species varies between gear types, but replacement of mesh nets with drumlines would reduce the catch of smaller individuals of S. lewini and assist in their conservation.