Years of monitoring wolves in Denali and Yellowstone national parks has led researchers to conclude that hunting the predators just beyond the parks' borders seems to directly impact park visitors' odds of seeing a wolf.

The research, published last week in the PLOS ONE journal, found that Denali visitors "were half as likely to see wolves in their natural habitat when wolf hunting was permitted just outside" the park boundaries.

Other important factors linked to wolf viewing rates, the researchers found, include, the proximity of wolf dens to the Denali Park Road and the regional wolf population.

The study, co-authored by researchers at the University of Washington and the National Park Service, examined wolf harvest and sightings data from Denali and Yellowstone. They found that visitors were almost twice as likely to see a wolf during periods when trapping and hunting wasn't permitted adjacent to the parks.

"This is the first study that demonstrates a potential link between the harvest of wildlife on the borders of a park and the experience that visitors have within the park," said lead author Bridget Borg, a Denali wildlife biologist who completed this research while earning her doctorate from the Institute of Arctic Biology at the University of Alaska Fairbanks.

Researchers looked at the dynamics between harvesting and viewing wolves at these two national parks because they are among the few places in the world where visitors have a good chance of seeing wild wolves. Both parks have long-term monitoring programs that have collected years of data on resident wolf populations, including years when wolf harvest was permitted and years when it was prohibited near the parks’ borders.

Adjacent to Denali National Park, wolves are primarily trapped during legal harvests, while states adjacent to Yellowstone permit shooting wolves during hunting season.

"Denali National Park’s neighbors coexist with wolves, and understand the role wolves have in the state’s ecosystems and economy," a release announcing the study said. "Trappers, hunters, and wildlife viewers share a stake in wolf conservation."

Wildlife viewing is an important economic driver for the states surrounding the two national parks. A 2008 economic assessment determined that wolf-watching activities in Yellowstone after the 1995 recovery program was launched have brought in an estimated $35 million each year to Idaho, Montana, and Wyoming. In Alaska, wildlife viewing activities supported more than $2.7 billion in economic activity in 2011.

According to the study, in 2011 hunting in Alaska supported more than $1.3 billion in economic activity,  while the state of Montana received more than $400,000 from the purchase of wolf tags.

"We have shown there is a tradeoff between harvesting and viewing wolves, but these findings could extend to other large carnivores that also move in and out of parks," said senior author Laura Prugh, an assistant professor of quantitative wildlife sciences in the School of Environmental and Forest Sciences at University of Washington. "In an ideal world, there wouldn't be a tradeoff. You could have wolf harvests outside of the parks, which also bring in a lot of economic activity, and it wouldn't have an effect on the populations or probability that tourists are going to see wildlife in the parks."

Tracking wolf and other wildlife sightings along the Denali Park road is an active area of research with a long history in Denali, according to Denali’s Science and Resources Team Leader Dave Schirokauer.

“This long-term monitoring of wildlife sightings was valuable to draw upon to investigate the role of wolf harvest adjacent to park boundaries,” he said.

The researchers analyzed data on wolf sightings, pack sizes, den locations and harvests adjacent to the parks in Denali National Park from 1997 to 2013, and in Yellowstone from 2008 to 2013. In both parks, visitors were more likely to see wolves when the wolf populations were high and their dens were close to park roads.

The researchers' models also suggest more subtle effects of harvests on the ability of visitors to see wolves.

"Sightings are perhaps driven by specific individuals. As wolves that are less wary may contribute disproportionately to viewing opportunities, sightings could decrease if harvest selects these individuals," the release said.