Untangling unexpected terrestrial conservation challenges arising from the historical human exploitation of marine mammals in the Atlantic sector of the Southern Ocean

Abstract

Intensive human exploitation of the Antarctic fur seal (Arctocephalus gazella) in its primary population centre on sub-Antarctic South Georgia, as well as on other sub-Antarctic islands and parts of the South Shetland Islands, in the eighteenth and nineteenth centuries rapidly brought populations to the brink of extinction. The species has now recovered throughout its original distribution. Non-breeding and yearling seals, almost entirely males, from the South Georgia population now disperse in the summer months far more widely and in higher numbers than there is evidence for taking place in the pre-exploitation era. Large numbers now haul out in coastal terrestrial habitats in the South Orkney Islands and also along the north-east and west coast of the Antarctic Peninsula to at least Marguerite Bay. In these previously less- or non-visited areas, the seals cause levels of damage likely never to have been experienced previously to fragile terrestrial habitats through trampling and over-fertilisation, as well as eutrophication of sensitive freshwater ecosystems. This increased area of summer impact is likely to have further synergies with aspects of regional climate change, including reduction in extent and duration of sea ice permitting seals access farther south, and changes in krill abundance and distribution. The extent and conservation value of terrestrial habitats and biodiversity now threatened by fur seal distribution expansion, and the multiple anthropogenic factors acting in synergy both historically and to the present day, present a new and as yet unaddressed challenge to the agencies charged with ensuring the protection and conservation of Antarctica’s unique ecosystems.

The need for increased protection of Antarctica's inland waters

“…A pertinent example here is the rapid expansion of summer moulting male fur seal numbers in the South Orkney Islands (Waluda et al 2009) and along the west coast of the Antarctic Peninsula in recent decades. This expansion in seal numbers is probably in part a result of protection from human harvest following their extensive overexploitation in the Southern Ocean ecosystem in the late 18th and 19th centuries, and it has caused eutrophication and severe damage to coastal terrestrial habitats and freshwater lakes and streams (Smith 1988, Hawes 1990, Favero-Longo et al 2011, Convey & Hughes 2023.…”

The impact of marine vertebrates on polar terrestrial invertebrate communities

“…Within dry and barren tundra/fellfield habitats invertebrates will aggregate in association with even the smallest vegetation patches (Usher andBooth 1984, 1986;Hertzberg et al 1994;Coulson et al 2003). Although polar primary producers tend to benefit from increased nutrient availability (Smith 1988(Smith , 2008Smith and Froneman 2008;Zwolicki et al 2020) few can cope with the extremely high nutrient loading and physical trampling experienced within the boundaries of dense marine bird or mammal aggregations (Convey and Hughes 2022). The topography surrounding such aggregations also strongly affects nutrient run-off and distribution, thereby affecting how the vegetation develops and, in turn, the associated invertebrate communities.…”

“…1) (e.g. Convey and Hughes 2022). This results in accumulation of faeces, substantial retention of the allochthonous nutrients, and over-fertilization to levels toxic for most organisms within such sites (during the breeding season penguins may deliver up to 10 kg dry mass of excreta per square metre, Tatur and Myrcha 1984).…”

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

“…Without a real and credible baseline, the notion of the Antarctic fur seal as super‐abundant species contributed to (i) unwarrantedly depicting it as an ever‐increasing environmental nuisance (Bonner, 1985; Convey & Hughes, 2022; Foley & Lynch, 2019), despite this being a naturally abundant species (Cook, 1777, v. 2, p. 213; Weddell, 1825, p. 54); and (ii) delisting it as a ‘Specially Protected Species’ in 2006 by the Antarctic Treaty Consultative Parties (SCAR, 2006), without a specific action plan for monitoring and reassessment (Jabour, 2008). Almost coincident with this decision, the population of Bird Island, the likely epicentre of historical recovery at South Georgia, collapsed in 2009 and has continued to decline ever since (Forcada & Hoffman, 2014).…”