Wildlife advocates scored a major victory Tuesday when Mendocino County agreed to terminate its contract with the federal agency that helps ranchers kill predators such as mountain lions and coyotes that feast on livestock.

Environmental groups have long crusaded against what they characterize as indiscriminate killing of wildlife by an agency whose philosophy amounts to “the only good predator is a dead predator.” The decision by Mendocino County supervisors to sever ties with the division of the U.S. Department of Agriculture marks a rare instance of a California county opting to consider nonlethal methods of carnivore control.

Environmentalists had accused the county of violating the California Environmental Quality Act by hiring the Agriculture Department division known as Wildlife Services. Six environmental and animal protection groups claimed in a lawsuit that the county failed to consider nonlethal methods of animal control and should have done an environmental study on the effect that killing predators would have on the ecosystem before signing a contract with Wildlife Services.

“We’re thrilled,” said Jessica Blome, senior staff attorney for the Animal Legal Defense Fund, one of the plaintiffs in the case. “This is the first lawsuit in the country that attacks Wildlife Services based on its relationships with local governments.”

Todd Smith of Oakland’s Thomas Law Group, which represented Mendocino County, said the Board of Supervisors had agreed to set aside the contract while conducting an environmental study.

“The county is happy to undertake this analysis so the members of this community can understand the benefits and the impacts associated with the wildlife management program,” Smith said. “The program has been effective for almost 30 years, so the county was a little surprised (by the lawsuit). That said, the county wants to comply with the law. In the end, the analysis will drive what the program looks like in the future.”

The issue has exacerbated tensions between ranchers and conservationists. Livestock owners in the far northern part of the state have threatened to use the “three S’s” — shoot, shovel and shut up — when confronted with environmentalists’ efforts to protect wolves, coyotes and other “vermin.”

Ranchers’ concerns

There are as many as 700,000 coyotes in the state, according to the California Department of Fish and Wildlife. Mountain lions are also abundant, and both predators kill a lot of livestock, which are commodities that contribute to the state and local economy, said the California Cattlemen’s Association.

The recent discovery of a wolf pack in Siskiyou County has turned the issue of predator control into a major area of concern among ranchers.

The USDA Animal and Plant Health Inspection Service, which oversees the wildlife management program, told The Chronicle last year that agency trappers use nonlethal techniques when appropriate.

Some 47,000 animals were nevertheless killed by Wildlife Services trappers in California in 2014, while 2.7 million animals were done away with nationwide, including wolves, coyotes, bears, mountain lions, beavers, foxes and other animals deemed pests, federal records show.

In Mendocino County, federal wildlife specialists working under a $144,000 contract used traps, snares, poison and other devices to kill hundreds of coyotes, mountain lions, bears, bobcats and other wildlife last year, according to the plaintiffs in the case.

Paul Trouette, president of the nonprofit Mendocino County Blacktail Deer Association and a former county Fish and Game commissioner, said guardian dogs, fencing and other nonlethal methods aren’t always appropriate in the county because of the rugged terrain. Many predators climb fences, he said, and coyotes and cougars have been known to run sheep and other prey into them for easy kills.

“I think we have a perfect program right now. These guys who make a living can’t be out there shaking noisemakers all night” to scare away predators, Trouette said.

He argued that Wildlife Services trappers are the best available experts on predation, the spread of wildlife diseases and protection of livestock.

“Who is going to handle all the sick animals and the rabies or other diseases and provide technical assistance to ranchers if they get rid of the professionals?” he asked. “The county doesn’t have any programs set up for that. It’s going to be a nightmare.”

Environmentalists skeptical

Wildlife advocates say the current system is both immoral and unnecessary.

“What we’re really talking about is the legitimacy of our federal government using American tax dollars to kill wildlife and ecologically valuable predators in huge numbers every year to benefit a tiny minority of ranchers and the agricultural industry,” said Camilla Fox, executive director of Project Coyote, a wildlife advocacy organization that was also a plaintiff in the lawsuit. “That’s the crux of this case.”

The county must now complete an environmental report that evaluates nonlethal predator control methods before it can enter into a contract with Wildlife Services in the future. Blome said the settlement could serve as a precedent for wildlife management programs in California and around the country.

“It’s a monumental achievement that we plan to use as a model,” she said. “We’ll go county by county if we have to, to force these counties to evaluate whether lethal control is necessary.”

Wildlife advocates are pushing for government support for a variety of nonlethal management techniques, including the use of guardian dogs, fencing, hazing of carnivores using lighting and flag techniques, night corrals and the placing of sheep in lambing sheds at night.

Fox cited research suggesting ways in which the killing of native predators harms the ecosystem. Coyotes, for instance, provide poison-free rodent control, while mountain lions can keep populations of other carnivores down.

In addition, wildlife advocates said, killing predators can make things worse — such as when trappers kill an alpha pair of coyotes. That ruins the pack structure, leaving coyote pups and young adults on their own. The result is a lot of coyotes that don’t have hunting skills going after the easiest prey they can find, which is livestock.

There is an example in the Bay Area of how a kill-as-a-last-resort predator control program can work. In Marin County, a nonlethal control program was adopted in 2000. It essentially used the money once paid to federal trappers to help ranchers build fences, night corrals and lambing sheds and purchase guardian dogs.

Financial assistance key

At the time, coyotes were killing hundreds of lambs and ewes every year in Marin County. Most sheep ranchers in Marin purchased guardian dogs, which naturally bond with sheep and goats and aggressively protect them. Ranchers credit the dogs with reducing predation.

County financial assistance was crucial, according to many ranchers, given that a guard dog can cost $1,000 or more. The program also helped pay for fences, electrification, noisemakers, lights and motion sensors — all at one-third the cost of predator control under the Wildlife Services program, according to county agricultural officials.

“It’s very easy to convince people that nonlethal predator control works when you look at the research that has been done,” Blome said. “Without exception, every rancher that has converted to nonlethal predator control is an advocate of it.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com Twitter: @pfimrite