The sea lions are protected under the Marine Mammal Protection Act.
Forty California sea lions have been removed since the authority was granted in March 2008, but the practice was stopped by a lawsuit filed by the Humane Society of the United States and the Wild Fish Conservancy.
The Ninth Circuit said the National Marine Fisheries Service did not give sufficient reason to overstep the protections of the Marine Mammal Act.
“Second, the agency has not adequately explained why a California sea lion predation rate of 1 percent would have a significant negative impact on the decline or recovery of these salmonid populations,” the court said.
“Obviously I’m disappointed after receiving what we thought was a strong opinion from the district court,” NMFS’ Garth Griffin said.
NMFS’ had concluded that sea lions must be killed to prevent them from consuming an average of 0.4 to 4.2 percent of salmon returns, even as the agency allows fishermen to take up to 17 percent of the salmon run, according to the plaintiffs.