The U.S. Fish and Wildlife Service designated nearly 5,900 square miles as critical habitat for sea otters in the Aleutian Islands, Bering Sea and Alaska Peninsula. The designated area includes all nearshore waters.
"Critical habitat has a proven record of aiding the recovery of endangered species," said Rebecca Noblin, a lawyer for the Center for Biological Diversity, which filed two lawsuits and engaged in years of litigation to get the animals protected under the federal Endangered Species Act. The otters in southwest Alaska were listed as threatened in 2005.
"This has been a long time coming," she said.
Critical habitat gives the sea otters - the smallest of marine mammals - a "fighting chance of recovery," she said.
Nearshore areas were chosen because most of the creatures that sea otters eat - sea urchins, crabs, octopuses and some bottom fish - are found in shallow waters. Areas close to shore also provide the best protection from marine predators, especially killer whales, according to the Fish and Wildlife Service.
Federal law requires that critical habitat be designated at the time of listing. But when that didn't happen under the Bush administration, the Center for Biological Diversity filed a federal lawsuit in 2006. The following year an agreement was reached that critical habitat would be designated by this October.
Fish and Wildlife said it needed time to conduct an economic impact analysis on what the designation could mean to southwest Alaska. The agency found that designation would not have a large impact and should not result in any commercial fishing closures.
About 90 percent of the world's sea otters are in Alaska waters. There were more than 100,000 sea otters in southwest Alaska waters in the 1970s but there are fewer than 40,000 now. Some areas have seen numbers plummet 90 percent.
The reason for the decline is not known but one credible theory is that killer whales are preying on more sea otters, perhaps because other larger marine mammals such as sea lions are also in decline.
Noblin said there isn't much that can be done about killer whales but there are other stressors than can be addressed such as overfishing, the potential for oil development in Bristol Bay and climate change in the Bering Sea.
Critical habitat gives the animals an extra layer of scrutiny when entities are applying for federal permits in the designated area. However, it does not mean that development will stop, Noblin said.
"It just means the developer has to go through an additional process to determine how what they are doing will impact sea otters," she said.