Six federally protected sea lions were apparently shot to death on the Columbia River as they lay in open traps put out to ensnare the animals, which eat endangered salmon. State and federal authorities are investigating.
The discovery came one day after three elephant seals were found shot to death at a breeding ground in central California.
Trapping will be suspended during the investigation, said Rick Hargrave, a spokesman for the Oregon Department of Fish and Wildlife who was at the scene Sunday.
The carcasses of the four California sea lions and two Steller sea lions were found Sunday around noon below the Bonneville Dam on the Columbia River on the border of Oregon and Washington.
The six animals appear to have been shot by somebody on the Washington side during the night, said Brian Gorman, a spokesman for the National Marine Fisheries Service.
Two open cages each contained the carcasses of two California sea lions and one Steller sea lion, he said.
Necropsies were planned for all the animals, and the area was being treated as a crime scene by state and federal agencies, Gorman said.
Investigators will try to determine whether there is any link between the animals killed Sunday on the Columbia and the elephant seals killed Saturday near San Simeon in California, Gorman said.
Seven California sea lions were trapped on the Columbia starting April 24 after the 9th U.S. Circuit Court of Appeals approved their capture. One died during a medical inspection before transfer to a Sea World park.
Washington and Oregon have been granted federal authorization to capture or kill as many as 85 sea lions a year for five years at the base of the dam, where they feed on endangered salmon headed upriver to spawn.
Fishermen and American Indian tribes have pushed to protect the salmon and remove the sea lions, by lethal force if necessary, forcing a delicate balancing act by the federal government.
The Humane Society of the United States has gone to court to challenge the authorization, with another hearing set for May 8. Until a judge rules, no animals may be legally killed.
"We're really shocked," said Sharon Young, a Humane Society spokeswoman, who learned about the sea lion deaths from a reporter.
"We're a nation of laws, and we should expect people to abide by them," Young said.