Free shrimp cocktail for everyone! Trophic relationships of 13 elasmobranchs in Central Patagonia, Southwestern Atlantic

Abstract

We assessed the trophic roles of 13 medium-sized elasmobranchs in central Patagonia (41°-47°S) by identifying their interspecific relationships and trophic overlap using stomach contents and δ15N and δ13C values. We also conducted a literature review of the available diet information for Argentina. Specimens were collected from the bycatch of the Patagonian red shrimp Pleoticus muelleri trawling fishery and from the sport coastal fishing in areas without trawling. Results showed spatial differences in the diet composition of species between capture sites and from those previous diets reported for Argentina. Trophic levels assessment showed a group of top predators (TP ~ 4) and mesopredators (TP ~ 3.5). Beyond these differences, there was a dietary overlap among almost all elasmobranch species mainly related to the consumption of P. muelleri, an item which had not been reported as a significant prey for several of the studied species. This consumption may be due to the change in prey supply produced by local fisheries' discards and/or to the increased abundance of crustaceans in Central Patagonia during the last decade. These findings underscore the importance of continually updating trophic information in a scenario of global change to contribute with scientific evidence to the development of adaptative management.