The carcasses of four California sea lions and two Steller sea lions were found Sunday about noon.
The discovery comes a day after three elephant seals were found shot to death at a breeding ground in central California.
All three species are federally protected. But Oregon and Washington state are trapping some California sea lions to keep them from eating salmon at the Bonneville Dam.
The dead sea lions were found at traps below the dam.
Washington, Oregon and federal investigators are treating the area as a crime scene.
