The Southern Resident killer whale population suffered a 20 percent decline in the 1990s, with many of the creatures scooped up for use in commercial aquariums, according to the National Oceanic and Atmospheric Administration.

There are 89 of the whales left, one of them a male loner that has taken refuge in a small inlet in British Columbia, federal officials reported.

"Recent information and further analysis leads our agency to conclude that the Southern Resident killer whale population is at risk of extinction and should be listed as endangered," said administration regional director Bob Lohn.

Among the threats to the whales are shipping traffic, toxic chemicals, and scarcity of food such as salmon, according to federal officials.

The whales, along with all other marine mammals, were already protected by the US Marine Mammal Protection Act, which listed the whales as "depleted stock" more than two years ago.

The new listing will require federal agencies to make certain their actions are not likely to harm the whales.

The federal fisheries service is trying to restore salmon stock in the Puget Sound, where Seattle is located in the state of Washington, Lohn said.

Researchers have yet to figure out where the whales go when they leave the Puget Sound. Scientists have studied the mammals for about 30 years, but the creatures' estimated life span is 90 years.

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