About 90 percent of northern sea otters live in coastal Alaska, and the Aleutian Islands population was declared threatened three years ago under the Endangered Species Act.
About 40,000 northern sea otters exist today, less than half 1970s estimates. The reasons for the decline aren't known, but increasing predation by killer whales is suspected.
The U.S. Fish and Wildlife Service proposal issued Tuesday would designate nearshore waters in southwest Alaska as critical habitat. Nearshore is defined as within 100 meters, or 328 feet, of the mean tide line.
The agency said nearshore waters provide sea otters with cover and shelter from marine predators, particularly killer whales.
The Center for Biological Diversity petitioned the government eight years ago to protect sea otters. The conservation group maintains that proposals to open Bristol Bay in the Bering Sea to oil development, overfishing and global warming are threatening sea otters.
The agency's designation is a good start, but the protected habitat should extend at least a mile from shore, said Brendan Cummings, the center's oceans program director.
A critical habitat designation requires all federal agencies to ensure that any activities in the area would not harm sea otters.
Fish and Wildlife does not anticipate that the designation would restrict commercial fishing because little is done in the area and because sea otters eat mostly sea urchins, crabs, octopuses and some bottom-dwelling fish that have little or no commercial value.
Public comments can be made until Feb. 17, and the final habitat designation would be made by Oct. 1.