When the harassment wouldn't scare them away, fishery managers turned to deadly force. They used traps and euthanasia, giving lethal injections to 30 sea lions from 2008 to 2010.
This spring, the sea lions have found safe harbor at the dam, about 50 miles east of Portland, Ore., after an appellate court in San Francisco ruled that states and the National Marine Fisheries Service had to stop the killings.
But the reprieve could be short-lived: The issue has found its way to Capitol Hill, where Congress is being urged to intervene.
Seeking to put an end to the invaders' free lunch once and for all, four members of the House of Representatives -- Democrat Norm Dicks and Republicans Doc Hastings and Jaime Herrera Beutler, all of Washington state, and Oregon Republican Rep. Greg Walden -- have teamed up on a bill that would give both states and Indian tribes a quicker way to get federal permission to kill the sea lions.
"With all other methods exhausted, lethal removal of the most aggressive sea lions is often the only option left," Hastings said.
The issue is an example of the delicate work involved in trying to manage animal populations. In this case, both the salmon and sea lions are protected by the federal government -- the salmon by the Endangered Species Act, and the sea lions by the Marine Mammal Protection Act.
As a result, the federal government goes to great lengths to try to protect both. Under normal conditions, killing a sea lion is a serious crime, punishable by up to a year in prison and a fine of up to $100,000.
Guy Norman, regional administrator for the Washington Department of Fish and Wildlife in Vancouver, said the number of California sea lions has surged from about 30,000 to more than 300,000 in the past 35 years. He said the sea lions have learned that they have "a tremendous opportunity" to prey on the salmon while they're delayed before passing over the dam.
Last spring alone, the sea lions killed an estimated 5,000 salmon at Bonneville Dam, situated where the Columbia River passes through the Cascade Mountains and separates Washington and Oregon.
If the bill is passed, roughly 85 sea lions could get killed this year, under a complicated formula that would change the number each year based on population estimates.
The issue is pitting Pacific Northwest fishermen against animal rights advocates.
"Commercial fishermen are not excited about having to kill sea lions," said Bruce Buckmaster of Astoria, Ore., a board member of the group Salmon For All, comprised of commercial fishing interests. "There's no blood thirst here, but we just have way too many. ... Like everything to do with salmon in the Pacific Northwest, it's complicated. And it's hard to grasp how one thing makes a difference in the system."
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