The most conspicuous population increase among krill predators has been with the Antarctic fur seal (Arctocephalus gazella) which nearly vanished around Antarctica during the 19th century (Fig. 10.1). On the South Georgia islands—where 1 to 2 million fur seals thrived prior to their exploitation—no seals were observed between 1907 and 1919. Following the whale population declines, however, fur seals began rebounding on these islands and across the Scotia Arc where major concentrations of the krill predators had overlapped (Fig. 9.6).
In 1930, 12 fur seal pups were found on South Georgia. By the early 1950s, there was a flourishing fur seal population on South Georgia with more than 5000 pups being produced each year. Between 1958 and 1972, the fur seal population in-
creased nearly 17% per year with a doubling time around 4.5 years. Subsequently, the fur seal population on South Georgia has been expanding geometrically— over six orders of magnitude—to its current population size around 3 million individuals (Fig. 10.8). This recovery of the Antarctic fur seal, with its 20- to 30-year lifespan, is unprecedented among marine mammals.
Fur seals on South Georgia are the nucleus for about 96% of the species' pup production—generating impacts that now radiate from marine into terrestrial ecosystems. With such large populations on South Georgia, excretion by the fur seals is adding large quantities of nutrients to the lakes on South Georgia, which are changing their primary production levels and trophic dynamics. Moreover, the surging abundance of fur seals on South Georgia is now spilling onto millennium-old moss banks, which are being destroyed as the seal colonies expand across these terrestrial ecosystems (Fig. 9.4).
Impacts from whale harvesting (Fig. 10.3) are reverberating among Antarctic marine and terrestrial species at diverse ecological levels (Table 9.1). As experiments in progress, these impacts also illustrate the role of keystone species (Fig. 9.2) in the intertwined dynamics of dependent and associated ecosystems. Consequently, sustainable use of the krill, or any other living resource, requires realistic exploitation limits based on accurate predictions about how harvesting impacts propagate through ecosystems like ripples across a pond (Fig. 2.3).
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