The diet of Mustelus schmitti in areas with and without commercial bottom trawling (Central Patagonia, Southwestern Atlantic): Is it evidence of trophic interaction with the Patagonian shrimp fishery?

Abstract

The study compares the diet composition between juveniles and adults of the narrownose smooth-hound Mustelus schmitti in areas with and without commercial bottom trawling using stomach contents. Individuals (n = 291) were caught as by-catch by the bottom-trawl shrimp fishery and by coastal sport anglers in Central Patagonia (Southwestern Atlantic between 43° and 45° S). Results showed that M. schmitti is a mesocarnivorous with a mean trophic level of 3.58. The diet was based mostly on crustaceans (decapods, stomatopods, isopods and amphipods), polychaetes, fishes and cephalopods, in a decreasing order of importance. The diet varied between juveniles and adults, and between individuals captured by the trawling fishery and sport anglers. Crabs were the main prey item observed in the stomach of individuals caught by anglers while the shrimp Pleoticus muelleri was the most consumed prey by individuals caught as by-catch. Juveniles consumed more polychaetes than adults, while the latter consumed mostly shrimp. The presence of shrimp in stomach contents of M. schmitti caught by the commercial fishery is evidence of a trophic interaction between M. schmitti and the fishery. The interaction may be due to the shark and the fleet targeting the same resource, or due to the shark using the discarded shrimp as a food source.