Lower CWD Prevalence Seen In Mule Deer Herds With High Hunter Harvest Rates

There’s a little bit of hope on chronic wasting disease in a new paper.

Scientists at the U.S. Geological Survey and University of Wyoming say that a relatively high level of buck harvest in mule deer herds over the long term – and even over shorter periods – can help keep the always-fatal deer family disease in check, a “promising” use of hunting to manage a widening problem.

To be clear, it won’t stop CWD’s inexorable spread but could slow it down, according to research recently published in the journal Ecological Applications, though there may also be negative tradeoffs for hunters, managers and the public.

Data comes from 20 years’ worth of deer harvests and testing from Wyoming, where CWD has existed in free-ranging herds since before 2000.

“We found that harvesting a high proportion of the adult males in the herd – around 40 percent every year for 20 years – is expected to keep chronic wasting disease infections at low numbers,” said lead author Wynne Moss, a USGS scientist.

At that level of harvest, fewer than 5 percent of bucks would be expected to be CWD positive, while a 20 percent harvest rate on bucks would result in a 30 percent infection rate.

A high rate of harvest over a three-year period also “slowed the rate of disease spread within a population but was not as effective as harvesting high numbers over a multiple decades,” according to a press release on the paper.

“Our results suggest that the use of hunting is a promising, scientifically supported way to manage chronic wasting disease; however, it is important to note that this approach is more likely to slow the disease down than eradicate it,” said USGS coauthor Paul Cross in the release. “This study provides important evidence about the effects of hunting on wildlife disease management for deer.”

So far, CWD isn’t known to occur in Washington’s and Oregon’s mule deer herds, but it has been found in Idaho’s near where the three states come together. IDFG has culled mule deer and whitetails there to try and slow the disease’s spread, as well as passed rules that require hunters to get their deer killed in the area tested for the disease.

However, CWD was confirmed last year in six whitetail deer from two Northeast Washington counties, Spokane and Pend Oreille, five of which were bucks harvested by hunters. A dead whitetail doe recovered just north of the city of Spokane in February and tested in July was the state’s first known case. That saw WDFW put similar and other rules in place, which followed increased monitoring efforts in recent years.

The disease also occurs in far North Idaho and extreme southeast British Columbia, as well as across Montana and Colorado and in portions of Utah and California, but so far has not been confirmed in Oregon. ODFW has also stepped up monitoring and testing.

While the paper’s authors state that high harvest pressure on mule deer bucks “can be feasible from a population sustainability perspective,” they add that it has to be balanced with objectives such as management goals and the support of stakeholders, and they note that there could be “undesirable” tradeoffs of trying to achieve consistently kill rates. Also, “few herds will have the ecological or social conditions to support the levels of harvest needed to eradicate the disease.”

Hunters and the public like to see mule deer bucks, or at least know that there are a fair number of them on the landscape so as to provide hope of bumping into some while afield. Some units are also managed for higher numbers of bucks for quality hunting opportunities. Mule deer herds across the West are generally in decline due to a variety of factors, and while does are the reproductive engine of the species and have seen reduced hunting, maintaining a high harvest rate on bucks could be hard to swallow even as it’s shown to slow the spread of CWD, at least in Wyoming animals.

The study’s authors acknowledged they didn’t look at whether high buck harvest rates impacted the risk for does and fawns of becoming infected, “important for understanding transmission and its influence on population dynamics.”

Still, the findings do help corroborate CWD treatments across the continent.

“Overall, our results suggest that maintaining hunting pressure after CWD is detected can have measurable impacts on disease prevalence (and has the additional benefit of providing important surveillance data), but it requires realistic expectations,” researchers state.

Also reporting on the news is Outdoor Life.