The feeding ecology of Mustelus schmitti in the southwestern Atlantic: geographic variations and dietary shifts

Abstract

The feeding ecology of Mustelus schmitti was studied based on analysis of stomach contents of 525 specimens collected from three research cruises carried out during October 2008 to March 2009 on the Argentinean continental shelf (34º45?S?41ºS). Generalized Linear Models were used to test the effects of Geographic location, Total Length, Sex and Maturity stage on the diet. The most commonly occurring major prey groups differed between Geographic locations. In Río de la Plata (RLP) deep M. schmitti feed on Crustaceans, Fish and Polychaetes, whereas Crustaceans, Polychaetes and Fishes were the main prey in RLP coast, Rincón (RIN) coast and RIN deep, respectively. Moreover, models showed dietary shift related to total length in each Geographic location. In coastal nursery areas Polychaetes decreased and Fishes increased in importance as M. schmitti grew in size; while Crustaceans increased in importance from small to medium size, and then decreased in the large specimens. Deeper areas also show dietary changes related to growth. In coastal Geographic locations trophic level showed lower values (3.48-3.53) than in deeper areas (3.56-3.77) positioning M schmitti in higher trophic roles in deeper communities. It is due to the presence of bigger specimens in deeper communities. Finally, total vacuity index was 2.47 (the lowest in the literature) indicating an intense and continuous feeding activity of the species.