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

BELLEGGIA MAURO; FIGUEROA DANIEL E.; SÁNCHEZ FELISA; BREMEC CLAUDIA

Rhode Island

Congreso; Joint Meeting of Ichthyologists & Herpetologists; 2010

AES American Elasmobranch Society

Mustelus schmitti is distributed from Brazil (22°S) to Argentina (47º45´S) and occurs from shallow waters to 120m. Food habits of M. schmitti  were studied based on analysis of stomach contents. Specimens were collected from three research cruises carried out by (INIDEP) during 2008-2009 at four different regions on the Argentinean continental shelf (34ºS - 43ºS). Prey items were identified to the lowest possible taxon, counted and weighted. The hypothesis that the consumption of each prey group is determined by total length was assessed by fitting generalized linear models (GLM), and using the Maximum Likelihood Estimation to fit a model to data by maximizing an explicit likelihood function. 97.5% of 525 stomachs analyzed contained food. The %IRI revealed that the species fed mostly on Decapods (54.7%), followed by Polychaets (24%) and Fishes (15.9%). Regional differences were observed among the prey species. M. schmitti  showed plasticity in its feeding behavior, factor that contributes to the extensive latitudinal and bathymetrical range exhibited by this species. Models show that Polychaets decreased and Fish increased in importance as the narrownose smoothhound grew in size; while Crustaceans increased in importance from small to medium size, and then decreased in the large specimens. The feeding on different preys at different stages of the species life cycle suggests an efficient resource partitioning in the study area. Dietary shifts, in general, minimize intraspecific competition and could also favor the wide distribution of this species.