Feeding ecology of two high-order predators from south-eastern Australia: the coastal broadnose and the deepwater sharpnose sevengill sharks

Abstract

Quantifying the feeding ecology of marine predators is essential for understanding their trophic interactions and their potential regulatory effects in marine ecosystems. I quantified the feed- ing ecology of 2 related predators that overlap only in part in spatial distribution: the coastal broad- nose Notorynchus cepedianus and the deepwater sharpnose Heptranchias perlo sevengill sharks. I found the following: These 2 shark species have different diet specialisation patterns, but show sim- ilarities in their prey handling mode. N. cepedianus has a generalised diet, whereas H. perlo shows high specialisation and lower prey diversity. For both shark species, small, medium and large individ- uals use different strategies for handling different prey groups. H. perlo preys largely on deepwater teleosts, mainly Lepidorhynchus denticulatus, with larger individuals (901 to 1365 mm total length, TL) also consuming high proportions of large predatory teleosts of the families Gempylidae and Trichiuridae. N. cepedianus has a diverse diet. Small individuals (≤900 mm TL) prey largely on teleosts and secondarily on chondrichthyans. Medium individuals (901 to 1520 mm TL) prey primar- ily on chondrichthyans and secondarily on teleosts. Chondrichthyans (mainly Mustelus antarcticus) are also the main prey of large N. cepedianus (>1700 mm TL), but this group also shows a greater preference (than small and medium individuals) for fur seals. Despite the overall differences in dietary composition and the minimal overlap in spatial distribution, the 2 shark species consume prey that migrate from deep to coastal waters (ommastrephid squid and gempylid fish).