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Orcas Devouring Harbor Seals

by Associated Press
Seattle Post-Intelligencer - February 25, 2003

Pod in Hood Canal unusually long time; salmon may benefit

BREMERTON -- Scientists estimate that transient orcas in Hood Canal have eaten more than a third of the 1,500 harbor seals believed to have been living in the waterway when the whales arrived seven weeks ago.

That means fewer seals will be feasting on summer chum and chinook salmon, which could turn out to aid the recovery of the threatened fish.

"They've made a significant predation impact on the harbor seal population in Hood Canal, no matter how you look at it," said Steve Jeffries, a marine mammal biologist with the Washington Department of Fish and Wildlife. "The take-home message is that the transient killer whale population is bad for the seal population but good for the salmon population, because seals eat salmon."

For anyone worried about the seals, Jeffries added, "The harbor seal population may have suffered, but we expect they will recover over time."

Resident orcas, like Puget Sound's J, K and L pods, eat fish, and normally enter Hood Canal only briefly, said Candice Emmons, research assistant at the Center for Whale Research in Friday Harbor. Transient orcas eat marine mammals and sometimes birds.

Calculating the number of seals the whales are eating in Hood Canal, a natural channel that forms the eastern boundary of the Olympic Peninsula, is a bit of a guessing game, scientists concede.

Researchers have identified 11 whales in Hood Canal: five females, two males and four calves. Scientists theorize that females eat 100 pounds a day, the males 150 pounds and the calves 50. That adds up to a total consumption of 1,000 pounds a day.

Since the whales have been in Hood Canal more than 50 days, that's more than 50,000 pounds of seals.

Harbor seals weigh between 25 and 200 pounds, said John Calambokidis of Cascadia Research Collective in Olympia. It is hard to say what size animals the orcas are likely to catch, but scientists have used 100 pounds as an average.

That works out to 510 seals, more than a third of the estimated population in Hood Canal.

Using other assumptions, Jeffries has come up with estimates as high as 900 seals -- 60 percent of the population -- eaten by the whales since their arrival Jan. 3.

If calculating the number of seals eaten is tricky, figuring out how many salmon will be saved is even harder. Most salmon won't return until summer or fall, but the reduced number of seals is bound to aid the fish.

A study several years ago by Jeffries and his staff found that seals at the mouth of the Duckabush River, which empties into Hood Canal, ate more than 200 salmon a day during daylight hours.

Another question on scientists' minds: What are the transients still doing there?

For the past 30 years, a group of about a dozen transient killer whales known to travel in southeast Alaska have stayed in one place for no more than a day or two. Researchers can't recall any group staying in one place more than two weeks.

They've been in Hood Canal since early January, and with new sightings as recent as Sunday, observers say there is no indication they're ready to leave.

"This is beyond any precedent," John Ford of the Canadian Department of Fisheries and Oceans told The Sun newspaper in Bremerton.

Some wonder whether the Hood Canal floating bridge is hampering the whales' exit. Ford discounts that theory, noting that transients are known to explore blind channels and probably would have little trouble swimming among the bridge's underwater cables.

Associated Press
Orcas Devouring Harbor Seals
Seattle Post-Intelligencer, February 25, 2003

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