Diet of demersal sharks and chimaeras inferred by fatty acid profiles and stomach content analysis

Obtaining adequate dietary information for many shark and chimaera species has long been a challenge for ecosystem managers, largely due to logistical difficulties in the collection of large sample sizes required for stomach content analyses. Here, we use multivariate analysis of signature fatty acid (FA) profiles as a complementary method to examine the diet composition of 16 demersal shark and chimaera species, collected off south eastern Australia. Comparative results of FA profiles of potential prey and chondrichthyan species mostly agree with the stomach content data. Multivariate analysis correctly classified chimaeras as prominent low-order and benthic consumers, medium-sized dogfish as predators of mid-trophic fish and squid, catsharks as dominant cephalopod consumers, and larger and deeper dwelling dogfish as feeders of bathypelagic fish, squid and feeding on higher order species (cetaceans and seals). Our results demonstrate that signature FA analysis can be applied in dietary studies of sharks and chimaeras to (1) distinguish interspecific differences in general resource (diet and habitat) use patterns; (2) identify degrees of dietary specialisation; and (3) detect niche partitioning of resources by co-occurring species. The FA profiling approach is particularly valuable where sample numbers are likely to be low, such as for these deep-sea and threatened organisms.

► Diet & niche partitioning of 16 co-occurring sharks & chimaeras was examined.
► Stomach content analysis & fatty acid (FA) profiling were used in combination.
► The FA approach is novel to chondrichthyan ecology & proved valuable.
► New dietary information was obtained for the 16 species analysed.
► FA profiling is a promising tool for assessing deep-sea trophic relationships.