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

Summary

This comprehensive study documents 90 years of Antarctic fur seal population changes at South Georgia. The seals recovered from near extinction in 1907 to peak abundance around 2007-2009. The population reached 3.5 million individuals, representing approximately 98% of the global population. Researchers used advanced population models with long-term breeding and survival data. Their analysis revealed that after 75 years of sustained recovery and growth, the Bird Island population collapsed in 2009. The population has since declined by 7.2% annually. This decline correlates directly with climate-driven changes. These changes reduced the availability of krill, the seals' primary food source. The study demonstrates how environmental shifts can rapidly reverse successful wildlife conservation achievements.

The figure shows how environmental changes affected seal populations at South Georgia from 1930-2020. Panel (a) tracks key environmental factors: climate patterns, rising sea surface temperatures, krill availability, and commercial fishing. Panel (b) shows the complete population story - near extinction, recovery to peak abundance, and sharp decline after 2009. Panels (c-h) demonstrate the statistical relationships between environmental changes and population growth.

Key Findings

Antarctic fur seals at South Georgia make up approximately 98% of the world's population, reaching 3.5 million individuals in 2007-2009.

The population recovered over 90 years from commercial hunting extinction in 1907 to become the world's most abundant seal species in this family.

A sharp population crash began at Bird Island in 2009, with numbers declining by 7.2% each year since then.

This decline matches climate-driven changes in ocean surface temperatures and reduced krill availability.

Current population levels at the study site have dropped back to numbers last seen in the 1970s.

Climate change and potential food competition from recovering whale populations may prevent future population recovery.

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.

Published in

Global Change Biology

2023

Authors

Forcada, J., Hoffman, J.I., Gimenez, O., Staniland, I.J., Bucktrout, P., Wood, A.G.

Institutions

British Antarctic SurveyDepartment of Animal BehaviorCEFEInternational Whaling Commission

Methods

Biological sampling DataField

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