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

• Published in: Global change biology 2023-12, Vol.29 (24), p.6867-6887
• Main Authors: Forcada, Jaume, Hoffman, Joseph I., Gimenez, Olivier, Staniland, Iain J., Bucktrout, Pete, Wood, Andrew G.
• Format: Article
• Language: English
• Subjects: Animal biology; Antarctic fur seal; Antarctic krill; Anthropogenic factors; Aquatic mammals; Arctocephalus gazella; Biodiversity and Ecology; Birds; Commercial fishing; Competitors; decline; depletion; Ecosystem restoration; Endangered & extinct species; environmental change; Environmental changes; Environmental restoration; Environmental Sciences; Euphausiacea; Food chains; Food webs; Global Changes; Indicator organisms; Indicator species; integrated population model; Krill; Life Sciences; Marine crustaceans; Marine ecosystems; Marine mammals; pinniped; Population; Population dynamics; Population growth; Predators; range expansion; Range extension; Recovery; recovery dynamics; Sea surface; Sea surface temperature; Seals; Seals (animals); Sexual maturity; Species extinction; Surface temperature; Surveys; Vertebrate Zoology
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.16947

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. We reconstruct 90 years of recovery trajectory of the Antarctic fur seal at South Georgia (Southwest Atlantic), a key indicator species in the Antarctic krill‐based food webs of the Southern Ocean, harvested to near extinction by the early 1900s. We estimate the population at South Georgia in 2007–2009 as 3,510,283 fur seals [95% CI: 3,140,548–3,919,604], which now constitutes the most abundant otariid in the World. We also report t