In the meantime, fishery managers are struggling to keep other fish populations from meeting the same fate as the steelhead at Ballard Locks.
"Literally we were watching the steelhead being eaten into extinction," Griffin said.
Sea Lions "Far More Intelligent"
Wildlife officials are trying a number of methods to control the hungry animals, with varying success.
Relocating "nuisance" sea lions has been unsuccessful, says Charlie Corrarino, conservation and recovery program manager at the Oregon Department of Fish and Wildlife.
Some sea lions captured at Ballard Locks were transported hundreds of miles away to their breeding grounds in southern California, he says.
"In one case, they almost literally beat the truck back to Washington State," he said.
"They've demonstrated that they are far more intelligent than we give them credit for."
Corrarino was reminded of this last spring, when about a hundred of the opportunistic mammals made the 146-mile (235-kilometer) trip from the Pacific Ocean up the Columbia to Bonneville Lock and Dam, where fish become easy prey.
One clever sea lion found his way into one of the dam's fish ladders, which allow salmon to bypass the dam's power station on their way to spawning grounds upriver.
The young 400-pound (182-kilogram) male squeezed through an iron gate meant to deter sea lions.
"He almost got too fat this spring feeding in the fish ladder to get back out," Corrarino said.
Successful Methods
Sea lions are not fully to blame for depressed populations of salmon and steelhead trout.
Poor habitat quality, dams without adequate fish passage, ocean conditions, and overharvesting also play a role, biologists note.
And even with the constraints of the 1972 law, a few local governments have found ways to successfully deal with conflict caused by the growing population.
In Gold Beach, Oregon, officials started a new program in July to stop hungry sea lions from snatching fish hooked by amateur anglers on the Rouge River. (See Oregon map.)
The salmon population is thriving there, but the threat to human safety was a concern, says Griffin, the marine biologist.
Under the program, sea lions were chased by boats, access to boat docks was blocked, and fish carcasses were no longer thrown into the estuary.
After three months the effort paid off, Griffin says, with less than one percent of fish netted or hooked lost to sea lions.
Glen Spain, the Northwest regional director for the Pacific Coast Federation of Fishermen's Associations in Eugene, Oregon, says commercial operations aren't experiencing problems with the marine mammals.
"Of course it's annoying to a fisherman to watch his hard-earned catch being hauled off by a sea lion and gobbled up," he said.
"But overall sea lions do not have that much of an impact [on business]."
"If you ignore them, they'll ignore you," he said. "They'll be happy to find food elsewhere."
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