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Biologists focus on killer whales in study of Steller declines

Posted: Thursday, March 21, 2002

ANCHORAGE (AP) -- Killer whales preying on Steller sea lions might be one reason Alaska's sea lion population remains depressed, scientists say.

Killer whales likely have not been the main reason sea lion numbers have plummeted, but could be helping to hold them down, said biologist Lance Barrett-Lennard during a meeting Wednesday of scientists studying the sea lion problem.

''Sea lions may be caught in a predator pit,'' he said. ''They may be unable to reproduce fast enough to catch up (with predation by killer whales).''

Barrett-Lennard, an adjunct professor at the University of British Columbia, said he first thought of studying whales eating sea lions about eight years ago, after a dead killer whale washed ashore in Prince William Sound.

A necropsy revealed that the whale had in its stomach 14 flipper tags from sea lion pups. That indicated its diet was made up largely of young sea lions. Now that Steller sea lions have been added to the endangered species list, whale biologists are starting to take the question of predation seriously.

Over the past four decades, the Steller sea lion population has plunged more than 80 percent across the Gulf of Alaska and out the Aleutian Chain.

The official endangered listing of the Western stock of sea lions has threatened Alaska's $1 billion ground-fishing industry, which in turn has prompted a flood of money for sea lion studies.

Congress appropriated $40 million for Steller studies in 2002. A small portion of that money -- between $1 million and $2 million -- will investigate questions about killer whales.

Barrett-Lennard, killer whale biologist Craig Matkin from Homer and several other whale biologists will begin collecting data this summer as part of a three-year project.

Scientists are studying a number of theories, including whether a shift in ocean conditions limited the sea lion's food, whether overfishing played a role and whether other changes in the ecosystem affected sea lions.

Several things may be at work. One theory is that whales can't find enough harbor seals to eat, and that may be forcing them to shift to other marine mammals, such as sea lions and sea otters, Barrett-Lennard said.

Biologists have occasionally seen killer whales eating sea lions, he said. But because the whales are such stealthy hunters, it's hard to catch them in the act, particularly from shore.

But Barrett-Lennard and other whale biologists have seen killer whales hanging around sea lion rookeries, making repeated trips to the rookery and then surfacing for air out of sight. He assumes they are killing pups, which are easy prey compared with the adults, which can grow to more than 10 feet long and weigh more than 1,200 pounds.

Killer whales can reach 26 feet and eight tons, but don't like to pick a fight if they can avoid it.

Matkin, a biologist with the North Gulf Oceanic Society, said getting scientific information won't be easy. One of the first steps will be to figure out roughly how many whales roam the Gulf of Alaska and the Aleutian Islands.

Matkin said scientists also must find if the whales are transients or residents. Resident killer whales eat fish, while transients roam large areas and eat marine mammals. Then the biologists must try to find out if they are eating sea lions. They will do that through observation and also recording sounds from beneath the ocean surface.



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