New non-breeding colonies of the South American fur seal in central Chile. Is the distribution in the southeastern Pacific waters extending?

Abstract

The South American fur seal (SAFS), Arctocephalus australis, has an estimated abundance of 219,000 individuals. The distribution range of this top marine predator along the Pacifc coast of South America is discontinuous, with a gap between 29°02’S-43°36’S, whereas the Atlantic coast presents a continuous distribution. Little is known aboutthe population dynamics of the species in Chile, as there have been few observations of vagrant individuals within the distribution gap and partial population censuses on dates that do not fit with the reproductive season in northern andsouthern Chile. The aim of this study is to identify the presence of A. australis colonies and summarize the sightings in central Chile. Aerial censuses were performed between 32°12’S-39°24’S during the austral winter and summer (2015) and between 41°44’S-44°55’S during summer (2013, 2016-2018). Official stranding records were also included to complementthe research sightings. We registered a total of 54 SAFS in the Chilean distribution gap, most of them during winter (89%) and with a higher proportion of females (72%). Two non-breeding colonies were found in the Biobío Region during the winter of 2015, Islote del Trabajo (38°25’S) and Islote Quechol (38°26’S), with 27 ± 1 and 16 ± 0 individuals, respectively. The sightings of adult individuals suggest their arrival at these latitudes to carry out foraging and resting activities, probably from Guafo Island (43°36’S). The last Pleistocene glaciation, hunting activities during the eighteenth century and ENSO events could have conditioned the current abundance and range of distribution of A. australis in South America; therefore, the establishment of new non-breeding colonies in the gap of distribution could lead to new breeding grounds in thefuture.