BILLINGS — Tony Saunders stalked his prey for 35 miles by snowmobile through western Wyoming’s Hoback Basin, finally reaching a clearing where he took out a .270-caliber rifle and shot the wolf twice from 30 yards away.

Gray wolves in the Northern Rockies have been taken off the endangered species list and are being hunted freely for the first time since they were placed on that list three decades ago, and nowhere is that hunting easier than Wyoming.

Most of the state with the exception of the Yellowstone National Park area has been designated a ‘‘predator zone,’’ where wolves can be shot at will.

For Saunders, killing that wolf was a long-awaited chance to even things out because he has lost two horses to wolves and blames the canines for depleting local big game herds.

‘‘It’s hard for people to understand how devastating they can be,’’ said Saunders, 39, who ranches at Bondurant, Wyo., 30 miles southeast of Jackson, Wyo.

Since federal protection was lifted March 28 and states took over wolf management, 37 wolves have been killed, just over 2 percent of their population. Since 66 animals were transplanted to the region 13 years ago, an estimated 1,500 now roam Wyoming, Montana and Idaho.

Environmental and animal rights groups plan to file a lawsuit today seeking an emergency injunction to block the killings and trying to put wolves back on the endangered list.

They predict that if states continue to control the animals’ fate and proceed with public hunts, wolves could be driven back nearly to extermination in the region.

‘‘There will be opportunistic shooting 365 days a year. This will become a continual black hole for wolves,’’ said Franz Camenzind with the Jackson Hole Conservation Alliance, which is joining the lawsuit.

Despite the removal of wolves from the endangered list, killing them in the Northern Rockies is nothing new. Last year, a record 186 were shot, primarily by wildlife agents, for killing and harassing livestock.

But since the beginning of this year, 59 wolves already have been reported killed in the three Northern Rockies states, about three times the 19 killed over the same period last year — most of them just in the month since they lost federal protection.

State officials blamed this year’s increased hunting in part on heavy snow, which kept wolf packs at lower elevations where sheep and cattle range.

‘‘That’s the reality of managing wolves in a modern landscape. Some of them are going to be removed,’’ said Eric Keszler, spokesman for the Wyoming Game and Fish Department. In fact, entire packs have been legally killed off in past years because of livestock conflicts, according to biologist Mike Jimenez with the U.S. Fish and Wildlife Service.

With public hunts planned this year, federal biologists project the three states will maintain a population of 883 to 1,240 wolves at least for the next few years — well above the government’s goal of maintaining a population of at least 300 wolves.

But wolf advocates say the states could systematically cull the population right down to that minimum unless a court intervenes.

Idaho and Wyoming in particular have a ‘‘hostile legal regime’’ that is stacked against wolves, said Doug Honnold, the Earthjustice attorney preparing the lawsuit.

‘‘If anybody can kill wolves, you have no way of ensuring wolf killing isn’t excessive,’’ he said.

Honnold and other advocates say a minimum of 2,000 to 3,000 wolves is needed to protect their genetic diversity. They contend the government was on track to meet that goal when it caved in to political pressure and stripped the species of endangered status.

Some state officials and ranchers, including Saunders, acknowledge a lingering hostility for wolves, which had been exterminated in the region in the 1930s.

‘‘There’s times I’d like to get rid of all of them, but that’s not realistic either,’’ Saunders said. ‘‘And I’d like for my son one day to be able to hunt them, too.’’