The paper, Sequential megafaunal collapse in the North Pacific Ocean: An ongoing legacy of industrial whaling?, offers a unified explanation for why populations of harbor seals, fur seals, sea lions and sea otters in Western Alaska have crashed during the last several decades.
Lead author Alan Springer (University of Alaska, Fairbanks) and his co-authors propose that the decimation of great whale (baleen and sperm) populations by overfishing removed a major source of food for killer whales. This may have forced some killer whales to "fish down the food web," preying on other marine mammals which in turn has had devastating impacts on marine ecosystems.
"The lightening rod issue in Alaska is the decline of Steller sea lions," says Springer. "100 million dollars have been spent in the last three years to study Stellers because they are so intimately connected with species of commercial interest. But Stellers aren't the only species of marine mammals in collapse up here." Harbor seals declined first, followed by fur seals, then sea lions and most recently sea otters.
Springer, an oceanographer who was investigating causes of marine mammal collapse due to food limitation and ocean changes, approached coauthor Jim Estes (University of California, Santa Cruz) to explore the possibility that the declines might also be linked to the historical removal of great whales. Estes had demonstrated (Science 282,1998) that killer whale predation was driving down sea otter populations and affecting kelp forest ecosystems. Springer had researched the whaling records and wondered whether the massive extraction
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