Movements of a juvenile southern sea lion in La Plata River Estuary (Argentina-Uruguay)

Movements of a juvenile southern sea lion in La Plata River Estuary (Argentina-Uruguay)

D. Rodríguez, R. Bastida, D.G. Calkins, and R.W. Davis

Movements of a juvenile southern sea lion in La Plata River Estuary (Argentina-Uruguay)This is part of Sea Lions of the World
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Description

A southern sea lion (Otaria flavescens) juvenile male (50 kg) was instrumented with a location-only satellite telemeter and released in December 2003 in the southern margin of the La Plata River estuary (Argentina-Uruguay). The animal was tracked for 28 days, with an average of 3.7 (SD 1.76; range 1-8) daily locations. The total distance traveled was 1,383 km, at a mean transit speed of 0.9 ± 0.55 m s–1. The sea lion spent 90% of the time at sea in characteristic shallow areas (<50 m), with two short periods at the breeding rookeries of Cabo Polonio and Isla de Lobos (Uruguay). At-sea locations were concentrated in the outer area of the estuary, coinciding with a thermohaline surface front, an area reported to be an important spawning ground for several southern sea lion prey. Travel distances, transit speed, and trip durations were similar to those reported for adults. The La Plata River estuary has a high potential importance as a foraging area, especially for the breeding population in Uruguay. For unknown reasons, southern sea lion stocks that inhabit the central southwestern Atlantic have shown a steady decline during the past 20 years, possibly caused by a decrease in prey availability or increasing competition with fisheries and other top predators. These preliminary results indicate that satellite telemetry can improve our understanding of preferred habitats of southern sea lions and aid in designing conservation strategies for the future.

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