A quantitative comparison of the diets of sympatric pelagic sharks in gulf and shelf ecosystems off southern Australia

Abstract

Predator–prey dynamics represent an important determinant in the functioning of marine ecosystems. This study provides the first quantitative investigation of the diets of sympatric pelagic shark species in gulf and shelf waters off southern Australia. Stomachs of 417 sharks collected from fishery catches between 2007 and 2011 were examined, including 250 bronze whalers, 52 shortfin makos, 49 dusky sharks, 39 smooth hammerheads, and 27 common threshers. Dusky sharks had the highest dietary diversity of the five species examined. We found overlap in the consumption of cephalopods, small pelagic teleosts, crustaceans, and benthic teleosts in bronze whalers, dusky sharks, and smooth hammerheads, and preliminary evidence of specialization in the highly migratory species, the common thresher and the shortfin mako. Findings were discussed and compared with previous studies in other temperate marine ecosystems. This study will significantly improve the understanding of the ecological roles of these top predators in the gulf and shelf habitats off southern Australia, and enhance the ecosystem models being developed for this unique bioregion.