(Reuters) – The Trump administration on Wednesday unveiled a recovery plan for the endangered Mexican wolf, but environmentalists immediately assailed the program as so deficient it would lead to the demise of one of North America’s most imperiled mammals.

The plan projects returning the Mexican wolf — actually the rarest subspecies of the North American gray wolf — to viable numbers in the U.S. Desert Southwest by 2043, paving the way for removing the animal from the endangered species list.

But environmental groups such as the Center for Biological Diversity said the U.S. Fish and Wildlife Service plan is deeply flawed and would further endanger a creature that has struggled to make a comeback despite decades of conservation efforts.

Specifically, the government’s recovery program would cause further geographic isolation of the wolves, suppressing their numbers and leading to greater inbreeding, said Michael Robinson, a conservation advocate with the center.

“These wolves are being left in the lurch,” he said.

Robinson said the center was among several conservation groups that have notified Fish and Wildlife of their intention to challenge the agency’s recovery plan in court.

Mexican wolves had been shot, trapped and poisoned to the brink of extinction in the American Southwest by 1976, when they gained federal protection under the Endangered Species Act despite opposition from ranchers who regard the animals as a livestock threat.

Eleven wolves were later returned to the wild in New Mexico and Arizona under a captive breeding program. Their numbers have since grown but have plateaued at levels far below what biologists consider self-sustaining.

Current estimates put the wolf’s numbers at 113 animals in Arizona and New Mexico, plus about two dozen believed to roam parts of Mexico.

The Fish and Wildlife Service said the subspecies would be eligible for de-listing once its population reached an average of at least 320 individuals in New Mexico and Arizona, and 200 in Mexico over eight years, assuming a steady growth rate during that period.

Their larger cousins in the Northern Rockies were deemed sufficiently recovered in recent years that they were removed from Endangered Species Act protection, placing the wolves under state wildlife management regimes that include licensed hunting.

The cost of the Mexican wolf recovery plan is estimated at roughly $178 million, to be shared by government and non-governmental agencies in the United States and Mexico.

An agency spokesman did not immediately respond to a request for comment on Wednesday.