A policy to sustainably manage gray wolves via recreational hunting appears to rely on faulty ecological science, says a new paper published today in PLoS ONE. The paper challenges a long-held assumption that gray wolf populations won't be decimated by hunting and predator-control programs. It has been believed up till now that such efforts can remove as many as 28% to 50% of the animals in a population without causing long-term harm to their numbers.
The paper comes on the heels of last year's first gray wolf hunting seasons in Montana and Idaho. (Wolves are disliked because they eat elk and livestock.) Hunters killed 260 wolves, close to 20% of the two states' wolf populations, including members of one of Yellowstone National Park's research packs. Combined with wolves harvested through predator-control programs, some 37.1% of the wolves in Idaho and Montana were eliminated in 2009. Can the recovering wolf populations, which were removed from the protection of the Endangered Species Act in 2008, be killed at this rate? Although the hunting season for this year has been canceled following a recent court ruling to reinstate the wolves on the federal endangered species list, the question remains important, say Scott Creel and Jay Rotella, ecologists at Montana State University, Bozeman. And the short answer is no, the two say.
"It's long been argued that hunting has little effect on wolves' overall mortality rates, so they can sustain" high harvest rates, Creel says. (One paper arguing that point is here.) But quotas of 28% to 59%—which the two states used for their wolf-hunting policies—are based on a "flawed assumption" in the scientific literature about how hunting affects wolf populations, he says.
That assumption is that hunting and predator control have little effect on the number of wolves that would die in a year, because they simply substitute one type of death for another. According to this assumption, the same number of wolves die each year—but, instead of dying from something like old age, famine, disease, or injury, they are killed by people.
To see if this was actually the case, Creel and Rotella analyzed death data on 21 wolf populations across North America, including those in Idaho and Montana. And they found the opposite result. "Hunting strongly increased the mortality rate for wolves; it was additive," Creel says. That means that if left in place, Idaho's and Montana's hunting and predator-control programs will probably cause gray wolf populations to decline more than state wildlife managers have suggested.
Although wolves will not be hunted in either state this year, both states' wildlife officials expect that they will be in the future. Creel hopes that these wildlife managers will incorporate the new results in their hunting policies. Those policies regard harvests of 35% of their wolf populations as sustainable. "This would be a high level of harvest for any species," Rotella says.
"It's unprecedented for a species to move directly from the endangered species list to a harvest of this magnitude," Creel says. "And, when combined with the predator-control programs, the data suggest the effect will be larger than previously thought." Northern Rocky Mountains wolf packs may be more susceptible to being harmed by hunting because they are generally small, with few adult members. It's thus more likely that any wolf killed in a hunt will be a breeding adult. When a pack loses its breeding adults, it is apt to fall apart.