SAN FRANCISCO -- California sea otters, hunted to near extinction and more recently denied the chance to roam freely in the southern part of their coastal range, may now swim wherever they choose under a new policy announced by the federal Fish and Wildlife Service.
The otters, whose numbers dropped below 15 at their low point two decades ago, have rebounded to a population of about 2,800. When that number reaches 3,090, the federal government could begin the process of taking the southern sea otter off the endangered species list, which categorizes the animal as threatened.
The formal end of the otter-free zone off the coast of California, announced this week, is a victory for environmental groups that objected to any efforts to control the natural migration of the species, which ranged from the western coast of Mexico to San Francisco before the animals' glossy pelts made them a target of 19th-century fur traders.
"It's a watershed moment," said Lilian Carswell, who coordinates the service's otter recovery program from an office in Santa Cruz. "We're embracing the return of this keystone predator to the near-shore ecosystem."
In 1987 the Fish and Wildlife Service moved 140 otters to San Nicolas Island off Southern California from the central California coast, where they thrive in waterways like Elkhorn Slough, north of Monterey. The idea was to establish a separate population in case an oil spill wiped out the original colonies.
At the same time, the agency established an otter-free zone to address the concerns of fishermen and Navy officials, who feared that the otters would deplete sea urchin and shellfish stocks and that they would necessitate burdensome paperwork requirements before military training exercises.
Yet most of the relocated otters quickly swam away from San Nicolas and roamed where they chose, including the otter-free zone south of Point Conception. Fishermen's groups sued the Fish and Wildlife Service over the issue in the 1990s after dozens of otters from the original Central Coast population moved into the otter-free zone.
That suit was withdrawn when the agency said it would review the entire management plan.
Like the endangered wolves of the Rocky Mountains, the otters are still viewed as predators competing with humans for a food source. About 300 divers, who are part of a multimillion-dollar industry, collect sea urchins for sale to sushi restaurants, said David Goldenberg, executive director of the California Sea Urchin Commission.
He said the group was "hugely disappointed" by the government's decision. Mr. Goldenberg asserted that the service took "the easiest and path of least resistance," letting the otter population expand southward "and take the commercial fishery away from 300 fishermen."
The recovery of the otters proved not to be a substantial problem for the Navy. Officials had feared that having an endangered species in the vicinity, however small, might require the military to conduct extensive environmental impact reviews before each training exercise and to face penalties if otters were killed.
Navy officials worried that they could face legal challenges to these operations, just as the presence of endangered whales off both the Atlantic and Pacific coasts more recently led environmentalists to file a lawsuit to curb Navy experiments with low-frequency sonar.
As part of the agreement on the otter-free zone, the Navy was exempted from any penalties associated with harm done to the otters during operations.
In the end, it was the agency's failure to establish a robust auxiliary population and the tendency of the central California otters to migrate southward regardless of the zone's limits that prompted the agency to begin rethinking its policy. It took a decade to reach a formal decision eliminating the no-otter zone, however.
For now, the ultimate status of the otter population remains unclear, Ms. Carswell of the Fish and Wildlife Service said. The animal has rebounded in fits and starts over the last decade but has not increased recently, she explained.
"Right now we're in a period of stagnation," she said. "There are things going on that we don't understand," including an increased incidence of otters being killed by sharks.
Nonetheless, the elimination of restrictions on the otters' expansion is a victory for the natural environment, she said. "There really are real ecosystem benefits when we allow these predators to return," Ms. Carswell said. "It gives a richness and integrity to our natural system."
Jim Curland, who directs advocacy programs for Friends of the Sea Otter, said in a statement, "It's long overdue, but a great day for sea otters to have this impediment to natural range expansion lifted."
This article originally appeared in The New York Times.