The federal government Tuesday listed Puget Sound's killer whales as an endangered species.

That is a higher level of protection than the government proposed last year, when it said the orcas should be listed as a threatened species.

"Between the time we proposed to list these animals as threatened and now, we've discovered the population is in a more delicate situation than we had assumed," said Brian Gorman, a spokesman for the National Marine Fisheries Service.

Previously, the three pods of orcas that live in Puget Sound for much of the year were protected under the Marine Mammal Protection Act, which kept them from being killed or harassed.

Environmental groups sued to have them listed under the Endangered Species Act, which they said would provide better protection against pollution and other factors blamed for the killer whales' decline.