PORTLAND (AP) — The Humane Society of the United States is offering a reward in the recent shootings of sea lions at the mouth of the Columbia River.

About 20 dead sea lions — most with gunshot wounds — have been found in recent months.

The shootings may be related to sea lions eating salmon at Bonneville Dam.

The Humane Society has brought a lawsuit trying to stop state authorities from trapping and killing sea lions that eat salmon waiting to swim the fish ladder at Bonneville Dam.

Sea lions are protected as a marine mammal, and the NOAA Fisheries Service has been investigating.