Federal officials have denied a petition by San Joaquin Valley farmers to drop a small West Coast group of killer whales from the endangered species list.
The refusal represents the latest development in a decade-long legal battle over protections for three pods of orca whales that swim off the Pacific Northwest coast, ranging as far south as Central California and as far north as southeastern Alaska.
The southern resident killer whale population, as it is called, was listed as endangered in 2005 after a federal court ordered the National Marine Fisheries Service to reconsider an earlier finding that the pods did not constitute a distinct population segment.
The Pacific Legal Foundation filed a delisting petition last year, arguing that there was no scientific basis to treat the southern orcas as a discrete group.
The foundation was acting on behalf of the Center for Environmental Science Accuracy and Reliability and two San Joaquin Valley growers, Empresas Del Bosque, and Coburn Ranch.
The growers are fighting the listing because orca protections have figured into environmental restrictions on federal water deliveries from the Sacramento-San Joaquin delta.
Federal biologists have found that the delta water operations are a threat to the southern orcas because the whales primarily eat Chinook salmon that are harmed by the pumping.
In a decision that will be published Monday in the Federal Register, the fisheries service said recent genetic and demographic studies reaffirmed the agency's determination that the southern population was biologically unique.
"We find that delisting the southern resident killer whale DPS is not warranted," the agency stated.