Composition and seasonal variation in the diet of the South American sea lion ( Otaria flavescens) from Quequén, Argentina

Abstract

Diet seasonality in South American sea lions, Otaria flavescens, was studied using 252 scats from a male-exclusive haul-out site located in Puerto Quequén (38º37’S, 58º50’W) Argentina during 2001. Prey species were identified from hard remains and their relative importance was assessed considering frequency of occurrence, abundance and biomass. The main prey consumed by sea lions were teleost fish (20 species), followed by cephalopods (four species) and crustaceans. The raneya, Raneya fluminensis, was the most frequent prey year-round, and the most abundant in autumn and winter. The Argentine anchovy, Engraulis anchoita, and the stripped weakfish, Cynoscion guatucupa, were the most abundant prey in spring and summer, respectively. Seasonal differences in the sizes consumed were only found for C. guatucupa. The sea lions from Puerto Quequén showed a diverse diet, mainly feeding on demersal and pelagic prey. Our study fills a geographical gap on the seasonal variation of the diet of South American sea lions. Two main patterns emerged from studies conducted along the geographic range of the species: (1) O. flavescens is a generalist and opportunist feeder, preying on a wide range of species; mainly those of pelagic and demersal habits, (2) South American sea lions change the frequency and/or specific composition of their diet seasonally, possibly as a result of changes in the relative availability of each species in the environment.