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

AbstractThe 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.摘要：鳍足类（pinniped）新繁殖集群的建立是复杂动态过程的产物，部分集群可由休憩集群地（haul-out）逐步转变为正式繁殖场所。本文旨在估算乌拉圭两处研究程度较低区域的南美海狮（Otaria flavescens）与南美毛皮海狮（Arctocephalus australis）的种群丰度，这两处区域分别为最东端的“贝尔德岛-科罗尼莱特礁（Isla Verde-Islote Coronilla，简称IV-IC）”与最西端的“帕斯帕斯滩（Las Pipas，简称LP）”。 2008年6月至2009年6月期间，研究团队在LP开展了船舶计数调查，在贝尔德岛开展了航空普查。LP区域同时记录到两种鳍足类动物，种群数量在7月达到峰值，总计202只个体。南美海狮全年均有出现，种群以成年雄性为主；而南美毛皮海狮仅在6月至10月间被观测到。LP被界定为鳍足类的休憩集群地，主要作为南美海狮的休憩场所。 在IV-IC区域，共记录到225至521只南美海狮，种群数量在春季与夏季呈上升趋势，雌性个体为优势类群，且于3月观测到幼崽。结合年龄结构与幼崽的存在特征，我们推断该区域已具备初步的繁殖活动。鉴于该区域属于海洋保护区，建议对该繁殖集群开展长期监测工作。