A plan by federal wildlife officials would increase the critical habitat for a rare spotted frog found in Arizona and New Mexico.

The U.S. Fish and Wildlife Service released a plan this week to add 331 acres in New Mexico’s Catron and Sierra counties, bringing the critical habitat designation for the Chiricahua leopard frog to 11,467 acres in the two states. The areas of west-central and southwestern New Mexico, and central and southeastern Arizona have water sources that the frog needs to rebound.

Kerr Canyon, West Fork Gila River and Palomas Creek were overlooked when the frog was listed as threatened, agency spokesman Jeff Humphrey said. The aquatic-breeding amphibians once found at hundreds of moist sites across the Southwest now exist in less than 20 percent of their historic range.

Environmentalists petitioned the federal government to protect the frog under the Endangered Species Act in 1998. The request was granted four years later, but no critical habitat was proposed. Fish and Wildlife officials said at the time that they were better able to cooperate with private landowners and others on conservation plans without the restrictions of critical habitat.

WildEarth Guardians sued, saying that the designation would help protect the frog’s environment from livestock grazing and predators like bullfrogs and crayfish. Biologists also were concerned about chytrid, a fungus that has been impacting frogs throughout the world.

The environmental group and the federal government reached a settlement in 2009 to consider whether critical habitat would help. The agency issued a proposal earlier this year and amended it this week. The agency also reassessed the status and threats of the frog after discovering that leopard frogs on the eastern slopes of Arizona’s Huachuca Mountains actually are a population of the Chiricahua leopard frog.

The comment period runs for the proposal and a draft economic analysis runs through Oct. 21. Fish and Wildlife is under a court order to issue a final decision by March.

“We know these frogs are disappearing, they’re disappearing fast, and habitat protection is what they need, among other measures,” said Michael Robinson of the Center for Biological Diversity, which petitioned for the listing.

The typically green frog has a stocky body with a leopard-like pattern and can grow more than 4 inches long. The frogs, known for making a noise that sounds like they’re snoring, now exist in headwater streams and springs, and livestock tanks with few or no nonnative predators. Environmentalists have said the amphibian is more vulnerable to local extinction because its remaining populations often are small and isolated from each other.

A recovery plan for the frog includes releases of captive-bred frogs, habitat restoration and monitoring.

Robinson said while the expansion of critical habitat designation is good news, he wants the planned Rosemont copper mine southeast of Tucson, where the frogs are known to live, to be included.

“We see this as an omission that’s not really about whether they’re breeding frogs there or not, but the (U.S.) Forest Service’s apparent intention to authorize a very destructive mine,” he said.

Humphrey said the mine area was not recognized as essential to the population’s recovery.

“If they have information that those frogs in the Rosemont area are indeed a reproductive population or that for some reason not considered by us would be essential to the recovery of the species, we would certainly consider that in our deliberation,” Humphrey said.