Small-scale variation in the diet of the South American Sea lion (Otaria flavescens) in northern Patagonia (Argentina)

Abstract

An understanding of the mechanisms that shape animal-population dynamics is a fundamental consideration in conservation biology and ecology. Populations of the species of South-American sea lions (SASLs) Otaria flavescens reveal different growth rates, which variations could be linked to changes in the accessibility of nutritional resources in any given location. The available information on differences in the SASL diet on a local scale, however, is relatively scarce. We therefore searched for evidence of geographical variations in the diet of the SASLs in Northern Patagonia—namely, in the Golfo San Matías (GSM) and the Golfo Nuevo (GN), both of which bays are quite different regarding their physiography, oceanography, and anthropic pressures. From 2005–2013, stomach samples ( nGSM = 39; nGN = 31) were collected from animals found dead on the coast or accidentally caught in fishing nets. The dietary composition differed between the two gulfs with respect to the most common species, the zoological groups, and the sizes of the primary prey. In the GSM, the SASLs fed on demersal–pelagic fish, while in the GN the diet exhibited a high contribution of benthic species. Differences in the items and sizes of prey consumed at each area are discussed in terms of differential prey availability along with the opportunistic feeding behavior of this predator. These differences, in addition to the species’s main prey as targets for major fisheries, must be taken into account in order to understand the different population dynamics of this apex predator and thus ensure its conservation.