The National Oceanic and Atmospheric Administration has authorized three northwestern states to continue killing sea lions that prey on endangered fish species as they try to climb the fish ladder at the Bonneville Dam, officials said Wednesday.

California sea lions often congregate at the mouth of the the Columbia River and in the waters just below the dam, the Oregon Department of Fish and Wildlife said in a statement, and the hungry marine mammals have put a big dent in the numbers of salmon and steelhead looking to make their yearly migration upstream.

"Last year sea lions were estimated to have consumed nearly 10,000 adult spring Chinook salmon, amounting to more than 3 percent of returning adult fish," the administration said in a statement. "The impact on individual populations within the run may be much higher. An estimated 25 to 35 percent of the fish consumed are listed under the Endangered Species Act."

The authorization for Oregon, Washington and Idaho to trap and euthanize the sea lions will run for five years, the administration said in a press release, and is just one tactic the government is trying to help bolster the numbers of flagging fish species.

Oregon officials have tried exclusion gates, pyrotechnics and shooting the animals with rubber buckshot to dissuade the animals from congregating to feed at the dam, but all of those efforts only work temporarily, Oregon officials said.

Problematic sea lions that have been observed feeding near the dam's fish ladders are individually identified and trapped. Though officials would prefer to relocate the animals to zoos or aquariums, that isn't always possible and the animals sometimes have to be killed as a last resort.

Since the effort began in 2008, some 166 animals have been removed, 59 of them this year alone. Of 166 sea lions removed, 15 went into captivity, seven died of accidental deaths and 144 were euthanized, a spokesman for NOAA said.

Since the states began the program in 2008, officials estimate 15,000 to 20,000 salmon and steelhead have been saved from predation.

There are about 300,000 California sea lions off the west coast and the authorization only allows for 92 animals to be removed per year. The authorization also precludes removing any Steller sea lions, which are protected by the Marine Mammal Protection Act.

-- Kale Williams

kwilliams@oregonian.com

503-294-4048