Environmental activists are suing the federal government for allegedly failing to prevent longline fishing fleets from repeatedly accidentally snagging a rare whale species off Hawaii.

Earthjustice filed the lawsuit against the National Marine Fisheries Service in U.S. District Court in Honolulu on behalf of three environmental groups yesterday.

The complaint, citing 2007 federal data, alleges longline fishing vessels are accidentally ensnaring false killer whales off Hawaii at twice the rate the species' population can sustain.

"These are intelligent mammals that deserve not to be indiscriminately killed in order to put a tuna fish sandwich together," said David Henkin, the Earthjustice lawyer pursuing the case.

The agency's failure to take steps to protect the whales violates the Marine Mammal Protection Act and the Administrative Procedure Act, the lawsuit said.

Wende Goo, a National Marine Fisheries Service spokeswoman, said the agency's attorneys were reviewing the lawsuit and so she couldn't comment.

Longline fishing vessels string lines in the ocean, ranging from 1 mile to 50 miles long, to catch fish. They run smaller lines with baited hooks off the central line and wait for the bait to attract fish.

Robin Baird, a marine biologist with Cascadia Research Collective in Olympia, Wash., said false killer whales are attracted to fish caught on those lines.

Baird, who has studied the species in Hawaii waters, said false killer whales like to eat yellowfin tuna, mahimahi, and ono — the same fish the lines are catching for people to eat.

False killer whales also habitually share prey with one another and thus may see the fish caught on the line as a gifts to them, he said.

The bycatch danger posed to the species is heightened because there are so few of the whales.

Baird said there are about 120 false killer whales that spend their time in nearshore Hawaii waters. There's another population, genetically distinct from the other, of about 450 whales that lives both near shore and farther out.

Both populations are being snagged in the longline fishery.

The species is particularly vulnerable because the whales don't reproduce quickly or frequently. They're known to start calving at around 15 or 16 years old, and spawn roughly every seven years.

The suit said the National Marine Fisheries Service is required by law to develop a plan to reduce the bycatch of false killer whales.

The lawsuit asks the court to declare the agency has violated the law, and issue an injunction to compel it to comply.

Earthjustice filed the lawsuit on behalf of Hui Malama i Kohola, the Center for Biological Diversity and the Turtle Island Restoration Network.