The 9th U.S. Circuit Court of Appeals ruled Tuesday that federal agencies haven't adequately explained how they reached inconsistent conclusions about the issue.
The court questioned how the agencies can say hungry sea lions are a threat to fish survival, but not target human fishing that takes many more salmon and steelhead.
In the past decade, growing numbers of sea lions have found easy pickings among fish waiting to head upriver at Bonneville Dam.
In 2008, the federal government allowed the states of Oregon, Washington and Idaho to kill the hungriest of the sea lions. So far, two dozen have been captured and given lethal injections.