The deal - involving five state and federal agencies and several American Indian tribes - still limits where bison can go during their winter migrations. Officials say those that move beyond the newly opened habitat and head north into the Paradise Valley will continue to be shot to protect livestock against a disease carried by the wild animals.
But supporters say the agreement will bring some relief to the state's bison management dilemma, which has dragged on for two decades and resulted in the slaughter of 3,800 bison.
A copy of the agreement obtained by The Associated Press shows bison will be free to roam within an area known as the Gardiner Basin when they migrate from the mountainous park during winter to graze. A map attached to the document depicts a "Bison Conservation Area" estimated by a U.S. Forest Service official at 75,000 acres, although some of that land is too steep to support bison.
State veterinarian Marty Zaluski said Tuesday that increased bison hunting would be allowed in the basin as a way to control their population without resorting so often to slaughter.
Letting the population grow unchecked is not considered a viable option by government officials. About 40 percent of more than 600 bison captured this year have tested positive for exposure to brucellosis. The disease causes pregnant animals to abort their young.
"We need to get rid of 400 bison on an annual basis. Hunting is the most palatable option," Zaluski said. The population is now estimated at 3,500 animals. However, park officials have yet to say if they will spare about 250 bison slated to be killed before Gov. Schweitzer intervened in February and imposed a 90-day prohibition on shipments to slaughter.
That ban is due to expire May 15. Captured bison still are being held in corrals near the Montana-park border.
Some Republican state lawmakers have argued against opening new territory to bison, saying it sets a dangerous precedent that could increase the livestock industry's exposure to disease.
Meanwhile, wildlife advocates have sought even more habitat for bison, such as the Dome Mountain area in the Paradise Valley.
Until last year, the federal government imposed stiff restrictions on states with brucellosis and forced ranchers with infected cattle to kill off their entire herds.
Schweitzer has said easing those rules allowed the state to pursue the Gardiner Basin agreement, which had long been sought by conservation groups and the U.S. Park and Forest Services.
"This adaptive management change is a very significant change to (bison) tolerance outside the park's northern boundary," park spokesman Al Nash said Tuesday.
The Gardiner Basin includes about 55,000 acres of Forest Service land, 20,000 acres of private land and a small amount of state land, said Gallatin National Forest spokeswoman Marna Daley.