Feeding ecology of the South American sea lion Otaria flavescens: food contents and food selectivity

Abstract

While predation by pinnipeds is likely to be important in shaping the structure of marine communities, there are few reports from the South Eastern Paciflc Ocean where pinniped populations are abundant and a massive fishing industry has developed in recent years.We report the food contents of 29 South Amer~can sea lions Otaria flavescens Shaw, 1800 and quantitative information on the occurrence of prey taxa by frequency and mass.Estimates of the relative abundance of prey taxa in the environment, daily and annual food consumptlon rates, and sea l~ons' food selectivity are given.Sea lions tend to consume slow swimming, bentho-dernersal fish specles, 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 env~ronment, but ~t was not preferred nor was it an important contributor of biornass to the diet.The non-comrnerc~al hake Macruronus magellanicus (Lonnberg) was the most preferred and the most important by mass in the diet.Estimated annual consumptlon of cusk eels (Genypterus spp.) revealed that sea lions took ca.7 tlmes more fish in mass than those annually landed in the study area.Unfortunately, estimates of standing stocks for the different prey taxa consumed by the sea lions are not yet ava~lable, and so the magnitude of their impact on fisheries 1s difficult to evaluate.