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Killer Whales Have Begun Preying On Sea Otters, Causing Disruption Of Coastal Ecosystems In Western Alaska

SANTA CRUZ, CA--With seals and sea lions in short supply in the North Pacific, killer whales are now feeding on sea otters, causing an abrupt decline in sea otter populations in western Alaska, according to researchers studying the area's marine ecosystems. The decline in sea otters has allowed their primary prey, sea urchins, to increase in number and strip coastal kelp forests over large areas, said James Estes, a marine ecologist with the U.S. Geological Survey and the University of California, Santa Cruz.

The new phenomenon of killer whales preying on sea otters appears to be one link in a chain of interactions extending from the open sea to the coastal zone and involving a wide range of species at different levels of the food chain. Overexploitation of certain North Pacific and Bering Sea fisheries may have initiated this cascade of ecological effects, Estes said.

Estes and his coworkers reported their findings in the October 16 issue of the scientific journal Science.

The researchers have been studying the role of sea otters in the coastal ecosystem of Alaska's Aleutian archipelago since the early 1970s. During their field studies they often saw killer whales swimming near sea otters, but never saw one attack a sea otter until 1991. Since then, about a dozen such attacks have been reported.

Sea otter populations, meanwhile, have declined by about 25 percent each year during the 1990s throughout large areas of western Alaska. In waters inaccessible to killer whales, however, sea otter numbers have remained stable. Otters maintain the coastal kelp forests by controlling populations of sea urchins and other animals that graze on kelp. The kelp forests in turn provide food and habitat for a broad range of species.

Where sea otter populations have dropped, the kelp forest ecosystem is collapsing, said Estes, who has spent years documenting the central role of otters in the ecology of the kelp forests. Exploding sea urchin populations have
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Contact: Tim Stephens
stephens@cats.ucsc.edu
831-459-2495
University of California - Santa Cruz
15-Oct-1998


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