Wildlife authorities around the world have long turned to culls — a polite word for hunting — to reduce the populations of wild animals living too close to people or livestock.
Advocates have also touted culling as a way to reduce poaching, giving hunters who might otherwise skirt bans a chance to hunt legally under regulated circumstances.
"The harvesting of wildlife on refuges is carefully regulated to ensure an equilibrium between population levels and wildlife habitat," according to the US Fish and Wildlife Service (FWS).
But now researchers claim that killing animals to protect them might not always make sense.
"For about 100 years, the status quo wildlife management assumption is that hunting, trapping, and angling are good conservations strategies," University of Wisconsin-Madison environmental scientist Adrian Treves said. "There is no evidence to suggest that poachers are going to refrain just because there is a legal recourse."
Treves and Guillaume Chapron of the Swedish University of Agricultural Sciences co-authored a report published in the Proceedings of the Royal Society B titled "Blood does not buy goodwill." Their findings suggest that culling can increase poaching — at least when carnivores are prey.
Treves and Capron studied wolves in Michigan and Wisconsin between 1995 and 2012, a period when the animals were taken off the US Endangered Species List in both states and culling was occasionally allowed.
They discovered that wolf populations grew, but around 4 percent less in years when culling occurred. In years when hunting was permitted, the wolf populations grew by 12 percent, compared to 16 percent growth when the wolves were left on their own.
"When the government kills a protected species, the perceived value of each individual of that species may decline; so liberalizing wolf culling may have sent a negative message about the value of wolves or acceptability of poaching," the researchers wrote in the study.
Matt Bishop, an attorney at the Western Environmental Law Center, which litigates endangered species listings and similar cases, said the researchers' thesis made sense.
"Culling sort of makes it somewhat permissible to shoot a wolf. So it's not that much more of a step to shoot one illegally," Bishop said. "It makes it more taboo to shoot it if you can't shoot it at all."
The FWS is now considering whether to take the grizzly bear off the endangered species list within the Greater Yellowstone Ecosystem, an area of more than 34,000 square miles that includes Yellowstone Park. In 2009, a federal judge overturned Fish and Wildlife's delisting of grizzlies two years earlier, but officials now argue that the bears are thriving and don't need extra protections.
The service's proposal doesn't discuss culling exactly, but it mentions the benefits of allowing sportsmen to kill bears. "Authorized hunting through designating the grizzly bear as a game animal may reduce the amount of illegal poaching," the proposal said.
Treves was critical the FWS, saying the agency helped fund his study six years ago after officials asked for data on whether or not culling helped or hurt wolves.
"They didn't respond in 2012," said Treves, who said he shared his preliminary findings with Fish and Wildlife Service officials at the time. "In 2014, they simply said 'We're not concerned.' The Fish and Wildlife Service argument basically says 'There's enough of the large carnivores, trust us.' What we are finding when we look at the evidence is that we shouldn't trust their assertions about carnivores."
A spokeswoman for the service, Vanessa Kauffman, declined to respond to Treves' criticism but provided VICE News a statement.
"We have not had time to evaluate this study but look forward to doing so," Kauffman said. "We base our management and policy decisions on the best available scientific information and to that end, value any and all peer-reviewed science."
Critics have said Treves and Capron's findings were inconclusive because they looked at the wolves' growth rate, not the amount of animals that were poached. "It's an inference," US Geological Survey wolf expert Dave Mech told the Minneapolis Star Tribune. "It's only as strong as that."
It wouldn't be easy to satisfy those critics, Treves countered. A tally of wolf carcasses would be great data, "but poachers don't turn over evidence," he said.
Advocates are already citing the study in the big battle brewing over the FWS move to delist bears in the Yellowstone region.
"We hear over and over that individual wolves have to die in order to placate a wolf-hating public and prevent illegal killing — but this shows that to decrease poaching, the government should send the message that wolves have a high public value," said Michael Robinson of the Center for Biological Diversity in a statement.
It's not clear if agencies would take the study into consideration.
"Predation management is a complex issue, one replete with both biological and social considerations," said Patricia Allen, communications director for the Association of Fish and Wildlife Agencies, a group of American and Canadian wildlife officials. "Regulated hunting and trapping is one tool that may be in the tool box to achieve a particular management outcome."
Wildlife agencies want to keep culling because it lets hunters hunt while retaining protections supported by environmentalists, said Bishop. "They feel like they can do both — they can allow and sell wolf-hunting permits at the right time and manage for viable populations," he said. "They are walking that fine line."
But balancing interest groups is not the same as doing right by nature, he added.
Bishop successfully argued in federal court last month that FWS officials overruled their own scientists when refusing to put the wolverine on the endangered species list. Persuaded by the science — climate change is melting snow that's crucial to wolverine habitat — the judge ordered wildlife officials to protect the ferocious weasel.
Bishop hoped officials would be more careful with grizzlies. "They really should be talking a hard look at the science," he said.
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