Re‐evaluating the population size of South American fur seals and conservation implications

Abstract

South American fur seals (Arctocephalus australis) are widely distributed, yet surprisingly little is known about their ecology. In particular, population data are sparse and outdated for many breeding locations, including the Falkland Islands. Data deficiency impedes the development of coherent conservation and management strategies. To address knowledge gaps, for the first time since 1965 an archipelago‐wide census of South American fur seals breeding at the Falkland Islands was undertaken, which provided the first pup abundance estimate since 1926 – data that are critical for assessing population trends. In total, 36,425 South American fur seal pups were counted at the Falkland Islands in 2018, a greater than four‐fold increase since the last census, and far greater than the 7,990 pups counted in Uruguay, which was presumed to be the largest South American fur seal population in the world. Hence, based on pup abundance, the Falkland Islands is presently the largest population of South American fur seals, even when considering a correction factor of 3.9 that was applied to pup counts in Uruguay, which yielded an estimated 31,160 pups. The results redefine South American fur seal abundance, the contribution of breeding locations (Falkland Islands, Uruguay, Argentina, Chile) and the distribution of breeding colonies at the Falkland Islands, which has far reaching implications for conservation and management. In particular, the present study has effectively doubled the Atlantic population size of the species, which is now estimated to comprise about 76,000 pups, of which the Falkland Islands accounts for 48% and Uruguay 41%. Accordingly, changes in the number of South American fur seals breeding at the Falkland Islands will influence the global population trends and conservation status of the species. Monitoring South American fur seals breeding at the Falkland Islands is therefore crucial to understand the impacts of anthropogenic pressures, such as fisheries, and to inform management and conservation policy. The results provide a baseline from which to measure changes in abundance.

Long-Term Stability in the Trophic Ecology of a Pelagic Forager Living in a Changing Marine Ecosystem

“…Among the main changes, Alemany et al (2013) detected a greater abundance of hake and other demersal fish species, increasing hake juvenile size, and a higher proportion of juveniles aged 2+ inside the protected area. In parallel, several high trophic level predator populations began to recover during the 20th century after the implementation of various legal protections (Croxall and Wood, 2002;Schiavini et al, 2005;Crespo et al, 2012Crespo et al, , 2015Ferrari et al, 2013;Raya Rey et al, 2014;Grandi et al, 2015;Baylis et al, 2019).…”

Recovery of South American fur seals from Fuegian Archipelago (Argentina)

“…greater since a recent study of only SAFS pup abundance has almost doubled prior estimates, from 39,000 to 76,000 pups (36,425 Falkland Islands (Malvinas), 31,160 Uruguay,~6,000 Chile, <2,500 Argentina; see Baylis et al, 2019).…”

“…Rookeries have a discontinuous distribution along the Atlantic coast, located only on the northern and southern extremities of their range (Crespo et al, 2015;Túnez, Cappozzo, & Cassini, 2008), with 48% of the pup production located in the Falkland Islands (Malvinas) and 41% in Uruguay (Baylis et al, 2019). The present pattern of distribution has been attributed to natural factors (e.g., distance to the continental shelf break and availability of islands; see Túnez et al, 2008), although it is more likely the result of abundance depletion from intense commercial sealing suffered by the species in the past (Ximénez, 1964), because archaeological evidence shows there were many more colonies with a continuous distribution (Vales, 2015 and references therein).…”

“…However, the estimated population trend for Fuegian archipelago is not available due to the lack of data (Crespo et al, 2015). There are indications of a population increase in Uruguay (Franco-Trecu et al, 2019), central Patagonia (Crespo et al, 2015), and Falkland Islands (Malvinas) (Baylis et al, 2019). In contrast, the population in southern Chile (Magallanes Region) has experienced a decline between 1978 and 2001 (Venegas et al, 2002).…”

“…Females at the end of the breeding season start to alternate feeding trips (which can last for 2-15 days) (Ponce de León & Pin, 2006;Thompson, Moss, & Lovell, 2003), while adult and subadult males start to migrate to other resting areas during the last week of January (Pavés et al, 2016). Finally, pup counts from aerial surveys are underestimated because, despite all pups being on shore at the time of the flights, their small size, the topography of the shore and the tendency of pups to form dense aggregations hinder distinguishing individuals (Baylis et al, 2019;Franco-Trecu et al, 2019). Even though Franco-Trecu et al (2019) developed a correction for SAFS pups from Uruguay, it was not applied to counts at the Fuegian archipelago because pup density is unlikely to be comparable between Uruguay and the study area.…”