Ninety years of change, from commercial extinction to recovery, range expansion and decline for Antarctic fur seals at South Georgia

Abstract

With environmental change, understanding how species recover from overharvesting and maintain viable populations is central to ecosystem restoration. Here, we reconstruct 90 years of recovery trajectory of the Antarctic fur seal at South Georgia (S.W. Atlantic), a key indicator species in the krill‐based food webs of the Southern Ocean. After being harvested to commercial extinction by 1907, this population rebounded and now constitutes the most abundant otariid in the World. However, its status remains uncertain due to insufficient and conflicting data, and anthropogenic pressures affecting Antarctic krill, an essential staple for millions of fur seals and other predators. Using integrated population models, we estimated simultaneously the long‐term abundance for Bird Island, northwest South Georgia, epicentre of recovery of the species after sealing, and population adjustments for survey counts with spatiotemporal applicability. Applied to the latest comprehensive survey data, we estimated the population at South Georgia in 2007–2009 as 3,510,283 fur seals [95% CI: 3,140,548–3,919,604] (ca. 98% of global population), after 40 years of maximum growth and range expansion owing to an abundant krill supply. At Bird Island, after 50 years of exponential growth followed by 25 years of slow stable growth, the population collapsed in 2009 and has thereafter declined by −7.2% [−5.2, −9.1] per annum, to levels of the 1970s. For the instrumental record, this trajectory correlates with a time‐varying relationship between coupled climate and sea surface temperature cycles associated with low regional krill availability, although the effects of increasing krill extraction by commercial fishing and natural competitors remain uncertain. Since 2015, fur seal longevity and recruitment have dropped, sexual maturation has retarded, and population growth is expected to remain mostly negative and highly variable. Our analysis documents the rise and fall of a key Southern Ocean predator over a century of profound environmental and ecosystem change.

Avian influenza overview December 2023–March 2024

“…Respiratory signs in elephant seals have been observed (The Guardian, online-b). South Georgia is reported to be the habitat of 98% of the world's population of Antarctic fur seals, which are at constant threat (Forcada et al, 2023; The Guardian, online-b).…”

Little evidence for inbreeding depression for birth mass, survival and growth in Antarctic fur seal pups

“…1). The 2019 season was among the worst on record 42 , as indicated by substantially lower numbers of breeding females (Fig. 1b), reduced pup birth mass (Fig.…”

“…Alternatively, viability selection may operate during the time-window after weaning and prior to recruitment at around 4–6 years of age 42 . Indeed, one might expect selection against inbred animals to be stronger during this period as the sub-adults are nutritionally independent from their mothers and have to fend for themselves.…”

Future climate‐induced distribution shifts in a sexually dimorphic key predator of the Southern Ocean

“…The Antarctic fur seal, Arctocephalus gazella, is a highly dimorphic, non-pagophilic species with a breeding distribution restricted to the Southern Ocean, in its Atlantic and Indian sectors (Kaschner et al, 2019). It is the second most abundant pinniped in the world and the most abundant species in the Southern Hemisphere (Forcada et al, 2023). Male and female Antarctic fur seals differ not only in body size (120-140 kg males vs. 25-50 kg females; Blanchet et al, 2013) but also in their winter habitats (Arthur et al, 2015(Arthur et al, , 2017Lowther et al, 2020;March et al, 2021).…”

“…Global warming was initially predicted to have a neutral effect on Antarctic fur seal populations (Siniff et al, 2008), but there is increasing evidence of population declines both in colonies breeding close to the Antarctic Convergence (Forcada et al, 2023;Forcada & Hoffman, 2014) and in the South Shetland Islands (Krause et al, 2022(Krause et al, , 2023Schwarz et al, 2013). It is worth noting that the three subpopulations in the Atlantic Sector of the Southern Ocean (South Georgia Islands, South Shetland Islands and Bouvet Island) are demographically independent (Krause et al, 2023) and that the reasons for their decline are also different, although at least partially related to global warming (Forcada et al, 2023;Krause et al, 2022Krause et al, , 2023. For all these reasons, the species constitutes an excellent model to test whether males and females will respond differently to global warming.…”