PHOENIX - Arizona Game and Fish officials are trying to bolster two herds of pronghorn antelopes whose numbers have seen dramatic declines in an area of Southeastern Arizona along the U.S.-Mexico border.

Game and Fish surveys reported 122 pronghorns in two border-area herds in 2005 but just 26 in a 2012 survey, The Arizona Republic reported.

The department plans to capture pronghorns in the Chino Valley north of Prescott in north-central Arizona to add them to the San Rafael and Sonoita herds to try to make them sustainable.

The herds live in areas around the Huachuca Mountains near Sierra Vista.

Game and Fish has tried twice unsuccessfully to capture pronghorns in the Chino Valley area but will try again, officials said.

Amber Munig, big-game supervisor for Game and Fish, said the goal is to transplant enough animals to boost the San Rafael and Sonoita herds to at least 50 animals each.

A number of factors are cited as reasons for the herds' decline, including the spread of invasive species such as cheat grass and juniper that squeeze out the native plants the pronghorns eat.

However, some environmentalists point to border fences aimed at keeping smugglers and illegal immigrants and say the fences restrict pronghorns that would otherwise roam between Southeastern Arizona and Mexico.

Dan Millis, borderlands program coordinator for the Sierra Club, said there's no question that the border walls harm the environment, "and now Arizonans are stuck with the costs of cleaning up the mess."

However, John Millican, a project manager with the Arizona Antelope Foundation, said the border fence may actually have protected the few pronghorns that are left from being shot by poachers in northern Mexico.

"We have protections in the U.S.; there aren't a lot of protections on the Mexican side," Millican said.

Millican and Millis agree that better studies would make the fences' impact clear.

The U.S. Customs and Border Protection cited mitigation efforts for the Sonoran pronghorns, a subspecies whose population in Southwestern Arizona has rebounded, as "an example of our commitment."

The statement added that the agency "is fully engaged in efforts that consider the environment as we work to secure our nation's border."