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Northwest Diet Switch has Scientists Concerned about Orcas

© Matt Villano

''Some religious moments we've had on the rookeries with these [sea lions],'' said Michael Castellini, a marine biology professor at the University of Alaska at Fairbanks. ''It's dangerous. People get hurt.''

Researchers have checked off various explanations for the population crash: Disease didn't do it. Pups weren't born doomed; their health and blubber levels were good. The animals' blood didn't contain the telltale proteins and carbohydrates that signal they had gone from routine fasting to starving. But the western sea lions do have signs of immune problems that are consistent with animals in trouble; what's causing the inflammation, however, is not clear.

Studies of sea lion diets have been intriguing, suggesting that, as the animals have fed increasingly on the abundant pollock, they don't add an essential blubber layer nearly as well as they did eating the mix of fish they relied on 30 years ago. Sea lions that gain less weight are less likely to survive to adulthood.

Killer whales, or orcas, are waiting for no man. While scientists work to explain the sea lion mystery, the orcas apparently have simply switched to a high-protein diet as the sea lions became less abundant.

In part because of the orcas' more intensive hunting for sea otters, the number of otters in the 78 islands of the Aleutian chain has dropped from 55,000 to 100,000 in the 1980s to only 6,000, according to a recent US Fish and Wildlife Service survey.

''When you see the killer whales up there, they're cruising around the kelp bed. The otters are just on the water surface,'' said Williams, the biology professor at the University of California at Santa Cruz.

But sea otters are far less nutritious than sea lions, since they are both smaller and provide fewer calories per serving. A male killer whale can satisfy his daily nutritional needs with five adult male sea otters or seven adult female otters. A female killer whale would need three male sea otters per day or five female sea otters per day.

Yet, as the sea lion numbers drop and the orcas chase after the cuddly sea otters instead, the main human victims may be the fishermen, from the Seattle-based Pacific trawl fleet to the remote fishing villages that dot the Alaskan coast.

Judge Zilly's closure of the fisheries, announced last month, is supported by conservationists, but fishermen and their allies say they are being unfairly blamed for the sea lions' problems. They argue that the broader ecological changes are far more important in the sea lion slump than the fishermen's nets.