Sequential megafaunal collapse in the North Pacific Ocean: An

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ongoing legacy of industrial whaling?

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stron

2518

ID

Institute of Marine Science

2003

rok

Populations of seals, sea lions, and sea otters have sequentially collapsed over large areas of the

northern North Pacific Ocean and southern Bering Sea during the last several decades. A bottom-up

nutritional limitation mechanism induced by physical oceanographic change or competition with

fisheries was long thought to be largely responsible for these declines. The current weight of

evidence is more consistent with top-down forcing. Increased predation by killer whales probably

drove the sea otter collapse and may have been responsible for the earlier pinniped declines as

well. We propose that decimation of the great whales by post-World War II industrial whaling caused

the great whales’ foremost natural predators, killer whales, to begin feeding more intensively on the

smaller marine mammals, thus ‘‘fishing-down’’ this element of the marine food web. The timing of

these events, information on the abundance, diet, and foraging behavior of both predators and

prey, and feasibility analyses based on demographic and energetic modeling are all consistent with

this hypothesis.