The best way to control wolf populations and minimize livestock predation may be to stop shooting, trapping and poisoning them, Washington State University researchers say.

A review of 25 years of data from lethal control programs from the U.S. Fish and Wildlife Services found that shooting and trapping the carnivores leads to more dead sheep and cattle in subsequent years, rather than less.

Writing in the journal PLOS ONE, WSU wildlife biologist Rob Wielgus and data analyst Kaylie Peebles say that, for each wolf killed, the odds of more livestock depredations increase significantly.

Predator control and sport hunting are often used to reduce predator populations and livestock depredations, – but the efficacy of lethal control has rarely been tested.

We assessed the effects of wolf mortality on reducing livestock depredations in Idaho, Montana and Wyoming from 1987–2012 using a 25 year time series. The number of livestock depredated, livestock populations, wolf population estimates, number of breeding pairs, and wolves killed were calculated for the wolf-occupied area of each state for each year.

The trend continues until 25 percent of the wolves in an area are killed, a rate of removal that is unsustainable for maintaining the species. Researchers found that killing one wolf increases the odds of depredations four percent for sheep and five to six per cent for cattle the following year. If 20 wolves are killed, livestock deaths double.

Researchers found that lethal controls of cougars also backfire, disrupting their populations so much that younger, less disciplined cougars attack more livestock.

Wielgus did not expect to see the same result with wolves.

“I had no idea what the results were going to be, positive or negative,” he said. “I said, ‘Let’s take a look at it and see what happened.’ I was surprised that there was a big effect.”

Wielgus said the wolf killings likely disrupt the social cohesion of the pack. While an intact breeding pair will keep young offspring from mating, disruption can set sexually mature wolves free to breed, leading to an increase in breeding pairs. As they have pups, they become bound to one place and can’t hunt deer and elk as freely. Occasionally, they turn to livestock.

Wielgus said wolves generally account for between .1 percent and .6 percent of all livestock deaths — a minor threat compared to other predators, disease, accidents and the dangers of calving. He encourages more non-lethal interventions like guard dogs, “range riders” on horseback, flags, spotlights and “risk maps” that discourage grazing animals in hard-to-protect, wolf-rich areas.

“The only way you’re going to completely eliminate livestock depredations is to get rid of all the wolves,” Wielgus said, “and society has told us that that’s not going to happen.”

Gary Chandler is the CEO of Crossbow Communications — an award-winning public affairs and government affairs firm. We specialize in public health and environmental issues. We serve the world.

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