Abstract

While predation by pinnipeds is likely to be important in shaping the structure of marine communities, there are few reports from the southeastern Pacific Ocean where pinniped populations are abundant and a massive fishing industry has developed in recent years. The food contents of 29 South American sea lions Otaria flavescens Shaw, 1800 and quantitative information on the occurrence of prey taxa are reported by frequency and mass. Estimates of the relative abundance of prey taxa in the environment, daily and annual food consumption rates, and sea lions'' food selectivity are given. Sea lions tend to consume slow swimming, bentho-demersal fish species, rather than the more abundant pelagic fish species in the study area. The jack mackerel Trachurus murphyi (Nichols) was the most frequent prey item found in the alimentary tracts and in the environment, but it was not preferred nor was it an important contributor of biomass to the diet. The non-commericial hake Macruronus magellanicus (Lonnberg) was the most preferred and the most important by mass in the diet. Estimated annual consumption of cusk eels (Genypterus spp.) revealed that sea lions took .apprx. 7 times more fish in mass than those annually landed in the study area. Unfortunately, estimates of standing stocks of standing stocks for the different prey taxa consumed by the sea lions are not yet available, and so the magnitude of their impact on fisheries is difficult to evaluate.