Federal authorities are probing the killing of six sea lions who were shot to death over the weekend at a dam on the Columbia river, the dpa reported.
Authorities had been authorized to trap the sea lions in cages at the massive Bonneville dam and transfer them to zoos in bid to help protect the west coast's dwindling salmon population.
The cages are usually left open so the mammals can acclimate to them, but unidentified assailants closed them and shot the six sea lions early Sunday, according to Brian Gorman, a spokesman for the National Marine Fisheries Service.
Until the crime is solved trapping activity at the dam will be suspended.
The discovery came one day after three elephant seals were found shot to death at a breeding ground near San Simeon in central California. Investigators will try to determine whether there is any link between the shootings, Gorman said.
The salmon runs are so low that authorities last week banned commercial salmon fishing for the season. The sea lions have a major impact on salmon population levels since they congregate at the narrow fish ladders that allow the salmon to swim around dams to their spawning grounds.
Fishermen and American Indian tribes have pushed to protect the salmon and remove the sea lions.