Trophic ecology and ontogenetic shift in the diet of the sicklefin smoothhound (Mustelus lunulatus) in the southeastern Pacific Ocean

The feeding habits of the sicklefin smoothhound (Mustelus lunulatus) were studied on the basis of analysis of stomach contents of 314 specimens, allowing the diet of this species to be determined by sex, size, and stage of sexual maturity and for changes in the dietary ontogeny to be identified. The prey-specific index of relative importance revealed that the sicklefin smoothhound is a crab predator. Female and male sicklefin smoothhounds consumed a swimming crab species, Achelous iridescens, in similar proportions. Adults and juveniles of both sexes complemented their diets with the Panama mantis shrimp (Squilla panamensis), the dart squid, Lolliguncula (Loliolopsis) diomedeae, and the crab species Euphylax robustus, indicating behavioral and habitat segregation. Ontogenetic changes in diet were identified, with juveniles feeding almost exclusively on A. iridescens and adults having a more varied diet. The diet of sicklefin smoothhounds also changed with size: sharks ≤90 cm in total length (TL) consumed more A. iridescens, and sharks >90 cm TL fed on a wider variety of prey. These results indicate that the sicklefin smoothhound is a selective mesopredator in the coastal marine food chain, having a significant influence on populations of benthic crustaceans in the southeastern Pacific Ocean.