CONICET | Buscador de Institutos y Recursos Humanos

The southern sea lion (Otaria flavescens) population in Uruguay has declined severely during the past few decades. Hypotheses on the cause(s) include a decrease in prey availability which could be caused or exacerbated by environmental changes, increasing competition with other top predators and overlap with commercial fisheries. Breeding colonies in this area are within the La Plata River Estuary (LPRE), a hydrographically complex environment that supports an important fishery jointly administrated by Argentina and Uruguay. Although southern sea lions have been identified as a species for conservation, there is little information about its role in this ecosystem. As a result, the two countries developed a co-managed research project focused on the identification of foraging areas, at-sea movements and foraging behavior of adult females, the most vulnerable component in a decreasing population. A total of 22 females were instrumented at Isla de Lobos (N2007=12; N2010=10) with location only telemeters (n = 10) and with satellite-linked dive recorders (STDR-S16=6). The foraging area (ca. 30.000 km2) was similar between 2007 and 2010 and was mostly located in the Uruguayan-Argentinean common fishery zone. Foraging occurred primarily in south-southeast quadrant on the continental shelf. Mean duration of foraging trips was ca. 5 days, reaching a maximum of 14 days. Most animals returned to the same area on successive foraging trips, and there was little overlap among individuals. Site fidelity to the rookery was high regardless of reproductive condition. Our results show that the main foraging areas of this species lie within the LPRE but are not coincident with the high priority protected areas This research will contribute to our understanding, management and conservation of the LPRE by including top predators.

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