Six protected sea lions found dead in government traps this month died of overheating, not gunshots, as had been initially suspected, the National Marine Fisheries Service said on Wednesday.
Investigators had suspected foul play in the deaths after finding sea lions covered in blood and puncture wounds inside a trap at a dam between Washington state and Oregon, but a review found that the deaths were consistent with heat exhaustion.
"There was blood present, puncture wounds and this is a very controversial program. So, the initial hypothesis was that they were shot," said Brian Gorman, spokesman for the National Marine Fisheries Service.
The deaths halted a controversial program that allowed Washington state and Oregon to trap and kill sea lions in an effort to stop the mammals from eating endangered salmon.
Sea lions make the 150-mile trip from the Pacific Ocean up the Columbia River to the Bonneville dam, where the salmon channel through fish ladders to go upriver to spawn. The sea lions are now returning to the California coast to mate as the spring salmon run ends.
The Humane Society sued to stop the trapping and killing program and officials agreed to halt the proposed killing two days after the six sea lions were found dead on May 4.