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.”