New research confirms: Shooting too many wolves is bad for them.
Seems obvious, right? But not for states in the Northern Rockies that allow wolf hunting, justified in part by previous ecological studies suggesting that gray wolf populations are not harmed by the hunts.
Those earlier studies argued that because a certain number of wolves will inevitably die each year, it doesn’t matter whether they’re shot or lost to natural causes. Other studies have suggested that birth rates will increase to offset the number of wolves killed. Wildlife managers have touted research supporting the idea that wolves can sustain 28 percent to 50 percent losses due to hunting with little to no impact on the population’s long-term viability.
Not so fast, says a pair of ecologists from Montana State University. Scott Creel and Jay Rotella recently published a paper in the online journal PLoS-ONE that says hunting and other lethal-control methods, such as shooting wolves that attack cattle, have an “additive effect” on some wolf populations, magnifying the mortality rate beyond the actual number of wolves killed by humans. This could be because wolf packs often disband after the loss of breeding or dominant animals, leaving the others more vulnerable, Creel suggests.
“We’ve never seen this level of hunting on a smaller population of wolves,” says Sylvia Fallon, a senior scientist with NRDC. “There are dynamics at play in smaller populations that we don’t fully understand yet, like how it affects their social networks.”
Creel and Rotella analyzed data from 21 separate wolf populations in North America and found that hunting or lethal-control methods skew death rates upward over time, causing populations to get smaller in the long term. Shooting 25 percent of the wolves in a population, for example, could lead to a 50 percent decline over time, the pair says.
Their research shoots a hole in the tortured logic used to support increased wolf-hunting quotas in Montana, which were put into place when the state’s wolves were dropped from the endangered species list in 2009.
This year, Montana wanted to allow even more wolves to be killed than it did last year -- in July, the state increased the hunting quota from 75 to 186 animals. The hunt was stopped though; on August 5, a federal judge returned Montana’s wolves to the endangered species list, which means they can’t be hunted at this time (although they can still be shot for attacking cattle). There are currently at least 524 gray wolves in the state, according to the U.S. Fish and Wildlife Service.
Montana wildlife managers and some scientists who study wolves have criticized Creel and Rotella’s research. Bob Ream, who chairs Montana’s Fish, Wildlife and Parks Commission, said in the comments at PLoS-ONE that their math was “flawed” because births, immigrant wolves, and the formation of new packs were neglected when calculating population changes from year to year. Creel counters that the researchers used population counts provided by the Fish and Wildlife Service, which capture those factors.
“If you look back at the papers stating that wolves can withstand high levels of culling, you’ll find that the papers are not investigating what level of harvesting wolves can withstand sustainably,” Creel says. “Rather, some of these papers are looking at what level of harvesting has to take place before you see a response in the prey populations.” In other words, they weren’t meant to be used as guides for maintaining a sustainable wolf population.
NRDC’s Fallon says a second paper lending credence to Creel and Rotella’s findings was recently published in the journal Biological Conservation. “It also concluded that hunting has an additive effect,” Fallon said.
Idaho, Montana, and Wyoming collectively harbor about 1,700 gray wolves, Fallon says; NRDC would like to see that number at a minimum of about 2,000. “What we’re looking for is a robust population of wolves in the Northern Rockies that is evolutionarily viable and can sustain itself in the long term. We don’t believe the populations are there yet.”