WYOMING -- New research predicts that both elk numbers and hunting opportunity will decline in northwest Wyoming as a result of Chronic Wasting Disease infection in elk that winter mostly on the National Elk Refuge near Jackson.

The research, published this month, models the spread of the disease, forecasting that CWD infection “may reach a mean prevalence in the population of 12 percent.” There is no vaccine to prevent CWD, which is an incurable cousin of Mad Cow Disease and causes a slow death through wasting of the central nervous system.

The model predicted that CWD prevalence of 7 percent in female elk would result in population declines even if no cow elk were hunted. Wyoming Game and Fish Wildlife Management Coordinator Doug Brimeyer and Elk Refuge biologist Eric Cole were among five co-authors of the paper, which doesn’t predict when effects might occur.

Cole warned of the implication for hunters.

“Currently there is significant cow elk harvest in the Jackson Elk Herd,” he wrote in an update of Refuge conditions Wednesday. “[T]herefore future implications of the recent CWD infection in the Jackson Elk Herd are significant and negative for both future elk population growth rate and hunter opportunity.”

Disease experts discovered CWD in one hunter-killed elk shot in the Grand Teton National Park elk reduction program in 2020, an elk that was part of the Jackson Elk Herd that winters on the elk refuge and nearby state feedgrounds. Experts are fearful that feeding elk in winter concentrates them unnaturally, promoting disease spread.

Authors caution that infection could be higher among fed elk, according to their 14-page paper, “Supporting adaptive management with ecological forecasting: chronic wasting disease in the Jackson Elk Herd,” published in the October 2021 issue of the journal Ecosphere. “[U]ncertainty in this forecast is large and we cannot rule out a mean forecasted prevalence as high as 20 percent,” the paper’s abstract states.

The model and its forecast draw on data from infected elk in Rocky Mountain National Park and detailed demographic information from the Wyoming Game and Fish Department, which closely tracks elk numbers and herd composition. Numerous variables make precise predictions and forecasts difficult, the authors wrote.

“There’s not a really good estimate of what that [CWD] prevalence is at this point,” Brimeyer said in an interview. Consequently, “it is impossible,” authors wrote, “to predict when or if CWD will reach endemic levels” or be found regularly in the Jackson herd.

The paper uses historic elk data to model what could happen to elk numbers had infection been discovered in about 2016. The idea was to show the consequences of infection based on actual population numbers.

That exercise predicted a modest decline in elk — perhaps a loss of 1,000 of the 11,000-strong herd in about five years, and possibly thousands more. But that decline does not account for any hunting of cow elk, Cole said.

“It doesn’t paint a rosy picture for hunter opportunities or the future prospects [for] the Jackson Elk Herd,” he said.

Brimeyer said the paper and model provides another tool for the Game and Fish Department as it recommends hunting seasons and quotas.

“In other herd units in Wyoming we’re certainly providing a lot of opportunity for elk hunting even with the presence of CWD,” he said. The Jackson Elk Herd, however, is the only feedground herd that’s been found to have been infected with CWD.

Wyoming Game and Fish has labeled the park elk-reduction hunt area CWD-positive and put surrounding areas on a list of “CWD monitoring elk focus areas.”

Feedgrounds are expected to increase spread compared to an unconcentrated herd like that in Rocky Mountain National Park. “We hypothesize that this higher density [on the National Elk Refuge and state feedgrounds] would lead to elevated rates of disease transmission on the refuge, increasing impacts on abundance,” the paper states.

Game and Fish deals with numerous influences on the Jackson herd, including declining calf ratios from segments of the herd that live in areas with abundant predators, Brimeyer said.

“We started reducing hunter opportunities in area 79,” north of Jackson in recent years, he said, citing one example of the necessary flexibility with hunting seasons. Today there is no hunting in that area at all.

But it’s likely too soon to change Jackson herd elk hunting regulations based on CWD worries, Brimeyer said. The issue will “probably not” be a factor in the setting of hunting seasons next year, he said.

WyoFile is an independent nonprofit news organization focused on Wyoming people, places and policy.