Six environmental groups have asked a judge to throw out a federal agency rule that concluded oil company exploration off Alaska's northwest coast will have a negligible effect on walrus.

The groups sued the U.S. Fish and Wildlife Service on Monday, claiming the agency understated the effects of petroleum exploration on walrus already harmed by a lack of sea ice in the Chukchi (chuk-CHEE') Sea.

Earthjustice attorney Eric Grafe (GRA'-fee) says the agency acknowledged that noise, vessel traffic or other activity could harm gathered in Hanna Shoal but still issued a rule covering the important feeding grounds.

He says the agency promises to review interactions in Hanna Shoals but only in a forum without public comment.

Fish and Wildlife spokeswoman Andrea Medeiros says the agency doesn't comment on pending litigation.