Fig. 2.

Schematic diagram of ecosystem perturbations in the Scotia Sea. From 1820–1860 Antarctic fur seal populations were extirpated rapidly after the discovery of South Shetland Islands (28–30). From 1900–1970 commercial whaling resulted in the near extirpation of all large baleen whales (31, 32). From 1960–1980 fishing for ice fishes and Notothenioids resulted in severe population declines in the Scotia Sea; populations remain well below historical levels (44). The serial depletion of krill predators was mirrored by large increases in Adélie and chinstrap penguin populations throughout the Scotia Sea region (6–9, 19–22, 42, 45, 46). From 1970–1990 climate-change effects were becoming evident in this highly altered ecosystem, with marked declines in sea ice, episodic recruitment in krill populations, and declining krill density. A pelagic trawl fishery for krill developed at this time. In the 2000s once-depleted marine mammal populations have recovered or are recovering; the krill fishery is expanding; rapid, well-documented climate change is progressing; and Adélie and chinstrap penguin populations are declining.