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BILLINGS — A scientific study released Wednesday said a proposed hunt for gray wolves in the Northern Rockies would cut the endangered species’ population in Montana by roughly half during a single season.

The study from two Montana State University ecologists raised questions about claims that the wolves could easily withstand hunts proposed this fall in Montana and Idaho. The peer-reviewed report was published online by the Public Library of Science.

Wolves in the Northern Rockies were returned to the endangered species list last month under a federal court order, but state officials still want permission to hold the public hunts.

The MSU study found that Montana stands to lose approximately 50 percent of its wolves under a proposal submitted in mid-September to the U.S. Fish and Wildlife Service.

“The data suggest that a sustainable harvest can be developed. But the thresholds identified (in Montana) appear to be above a sustainable level,” said MSU ecologist Scott Creel, one of the study’s authors.

Wildlife officials in Montana and Idaho said they were not swayed by the MSU study and characterized it as speculative. They added that even if wolf populations get into trouble, they could simply adjust future quota levels to compensate.

State and federal wildlife managers have said repeatedly that about 30 percent of a wolf population can be killed and it still will bounce back the following year.

After analyzing 21 studies of North American wolf populations by government and academic researchers, Creel and colleague Jay Rotella estimated the figure for the Northern Rockies would be much lower, at 22 percent. The study reached the new estimate by using a computer model that compared Montana’s proposed hunting season to how wolf populations have responded to human-caused killings in the past.

The lower estimate means wildlife managers using the old number could inadvertently set wolf quotas too high, threatening the species’ recovery after two decades and more than $30 million spent on restoration efforts.

Montana wants a hunting quota of 186 wolves, on top of 145 wolves that the state expects to be killed this year by wildlife agents responding to attacks on livestock.

Idaho also is seeking a hunt, but its proposed quota has not been released so the potential impact was not measured in the study.

Idaho and Montana had a combined minimum population of 1,367 wolves at the end of 2009. Montana wants to pare back its wolf population by 15 percent this year, while Idaho has a long-term objective of 41 percent fewer wolves.

About 340 wolves live in neighboring states, primarily in Wyoming, but also in Oregon and Washington. No hunts are proposed in those states.

“We understand that if we tried to reduce the population at the same rate for years, it wouldn’t work,” said Jim Unsworth with the Idaho Fish and Game Department. “But that’s not what any of us have proposed.”

“If we’re too heavy with harvest, we can back off,” he added.

Montana Fish, Wildlife and Parks wolf biologist Carolyn Sime said the MSU study was flawed because it failed to account for wolf pups born in the spring. She said that failure overestimated the impacts of hunting.

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Creel responded that his model used an established method to measure population changes between the same day from one year and the next, rendering irrelevant any interim spikes caused by spring births.

A Canadian wolf researcher with a newly published study on the same topic said Wednesday that he reached a conclusion similar to Creel: past research apparently underestimated the impacts human-caused mortality can have on wolves in the Northern Rockies.

Prior assumptions of hunting impacts were based largely on work done in the deep wilderness of Alaska and Canada, said Dennis Murray, a biologist with Trent University in Peterborough and that study’s lead author. Many wolf packs in the Northern Rockies live in proximity to inhabited areas — where they are more likely to be shot for attacking livestock or run over when crossing a highway.

“Based on (the MSU) analysis and our analysis, the high rates of mortality that have occurred so far are probably not sustainable over the long term. That could curtail population growth and, in fact, might cause populations to decline substantially,” Murray said.

The study was based on 22 years of data from more than 700 wolves in the Northern Rockies, appears in the November issue of Biological Conservation. Co-authors included four government wolf biologists from Idaho, Yellowstone National Park and the U.S. Fish and Wildlife Service.

They did not offer a sustainable harvest figure comparable to Creel’s 22 percent.

David Mech, a U.S. Geological Survey wolf biologist based in Minnesota, said both studies underscore that some hunter harvest of wolves is possible without hurting the population.

Those quotas can be set higher, Mech said, if hunters can successfully target wolves that have been attacking livestock. Mech said those animals would be shot anyway by government wildlife agents.

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