Federal officials yesterday designated the southwest Alaska sea otter -- a species that teetered on the edge of extinction in the late 1800s -- as threatened under the Endangered Species Act, alarmed that its numbers have dipped sharply over the past 15 years.

Fur hunters nearly wiped out the otters, whose range stretches from Cook Inlet to the Alaska Peninsula and Kodiak Island, by 1911, at which point the otters received international protection. By the mid- to late 1980s, as many as 74,000 otters thrived in Alaska's Aleutian Islands alone, but this number has now dropped to below 9,000.

Bruce Woods, a spokesman for the U.S. Fish and Wildlife Service's Alaska region, said government scientists are still searching for the reason the population has declined so quickly. Predatory orca whales may account for the drop, he said, but officials are still not sure. Sea otters on the Russian side of the Aleutian Islands are doing better than their American counterparts.

Environmentalists hailed the move, saying it is the otters' best chance of survival. Brent Plater, a lawyer at the Center for Biological Diversity who sued the Interior Department in 2003 to list the species, called the agency's decision "a positive step toward sea otter conservation and recovery."

"We owe it to future generations to protect the sea otters and the special places they call home, and the Endangered Species Act provides resource managers with the best tools available to ensure that sea otters are brought back from the brink of extinction," Plater said.

The new federal protection is not likely to incite controversy, Woods said, because commercial fishermen in the area do not target the sea otters' main source of food, sea urchins.

Subsistence hunters in the area take about 100 otters a year, and some subsistence hunting will continue even though the species is now listed as threatened.

While officials are still searching for the best way to proceed, he added, they expressed confidence that the sea otter population could rebound.

"This species does have the capacity to recover," Woods said. "It's proven it in the past."

A sea otter floats in Kachemak Bay, Alaska.