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

Abstract

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.

The northernmost haulout site of South American sea lions and fur seals in the western South Atlantic

“…This was also reported by two other previous studies 16,40 that counted a high numbers of South American sea lions (n = 102) at Ilha dos Lobos in September of 1994. Both previous studies conducted a systematic census during a complete year, reporting the greatest concentrations of individuals between July and September, a pattern also observed in the nonbreeding site Las Pipas, in Uruguay (which is ~ 1000 km far away from the WRIL) 65 as well as in the present study. The arrival and presence of South American fur seals and sea lions in the WRIL correspond to the dispersal period after the breeding season, which is the least known period of the life cycle of these species 15,16 .…”

“…Therefore, the decreased numbers of sea lions observed in the WRIL in November, relative to September (excepting 2018) is likely associated with the southwards return of sea lions from the WRIL to the WRML, where the number of pinnipeds remains high until the end of December 10,40 . After this period, these pinnipeds returned to their breeding colonies in Uruguay, and perhaps Argentina, to start the next breeding season 2,17,65 .…”