Otaria flavescens and Arctocephalus australis abundance in poorly known sites: a spatial expansion of colonies?

The establishment of new pinniped colonies is a consequence of complex dynamics in which some colonies may transform from haul-outs into breeding sites. The aim of this article was to estimate the abundance of Otaria flavescens and Arctocephalus australis at two poorly known sites of Uruguay, the easternmost Isla Verde-Islote Coronilla (IV-IC) and the westernmost Las Pipas (LP). From June 2008 to June 2009 count from boats were conducted at LP, and aerial censuses at Isla Verde. At LP both pinniped species were recorded, and the abundance was maximum in July with a total of 202 animals. O. flavescens was present throughout the year, mainly adult males, while A. australis was only observed from June to October. LP is defined as a haul-out structure used as resting area, especially for O. flavescens. At IV-IC between 225 and 521 O. flavescens were recorded. The number of animals increased in Spring and Summer. Females were the most abundant category and pups were recorded in March. According to the age structure and the presence of pups, we propose it would have and incipient reproductive activity. This colony should be monitored in relation with its category as a marine protected area.