Scientists to study walking-dead deer in Wyo’s most CWD-infected herd

Stan Harter works the Wyoming Game and Fish Department’s Lander check station during the 2021 big game hunting season. When hunters stop, agency staff customarily extract a lymph node to test for chronic wasting disease. (Courtesy/Wyoming Game and Fish Department)

By Mike Koshmrl, WyoFile

It’s become a foregone conclusion for Riverton outfitter Ken Metzler that when one of his mule deer hunters shoots a buck, the animal is afflicted with chronic wasting disease, he said.

“We had 98% last year and this year,” Metzler said of the positivity rate. “And we had every one of them tested but a couple.”

Generally, the lethal disease’s sky-high prevalence isn’t a deterrent for the out-of-state hunters eager to target a muley on the Fremont County ranchland where Wyoming Trophy Hunts leads its clients, he said. Applications to hunt with Metzler’s guides are still pouring in, especially since the pandemic began, even though the likelihood of taking home a trophy-class deer has declined. As the population has fallen, hunting licenses have also been cut.

“I’ve dropped from 100 hunters to probably, oh, 20,” said Metzler. Of the clients who do get out to hunt, Metzler said, “we’re not killing big bucks.” Meat from younger, fatter bucks typically goes in the freezer, even though public health experts caution against consuming CWD-positive animals. But when the hunters walk up to a downed animal and find a sickly looking, “flat ass skinny” deer, Metzler calls up the warden and gets the OK to pitch the remains, he said.

Given the condition deer are in, Metzler would support a larger reduction in licenses if it would help the herd bounce back.

Pennsylvania resident Ken Mowen poses with a mule deer buck killed while being guided by Wyoming Trophy Hunts. CWD has had a big effect on deer populations in the area where the Riverton outfitter guides clients. (Courtesy/Wyoming Trophy Hunts via Facebook page)

The Wyoming Game and Fish Department and U.S. Geological Survey researchers share concern and curiosity over what to make of the mule deer herd that Metzler’s business depends on. The Project Herd — as Game and Fish knows it —  is easily Wyoming’s big game herd most ravaged by the degenerative prion disease. In fact,  the data show the herd is also among the most CWD-infected wild cervid populations known to exist in North America.

“We have a proposal for a study for this herd because of the extraordinarily high rates of CWD,” Game and Fish Dubois Wildlife Biologist Zach Gregory said.

Plans are still in the rough, initial phases, Gregory told WyoFile, but researchers intend to find funding for 40 GPS collars that will be fitted to a random sample of deer in the Project Herd as soon as next winter. Some — likely a good portion — will be CWD-positive animals and therefore destined for death, but they’ll be tested while alive using rectal biopsies and then let loose.

-- Advertisement – Story Continues Below --

The hope is to glean some clarity about the factors contributing to the alarming disease prevalence.

“Are these positive deer in different places than these negative deer?” Gregory asked. “That’s going to potentially help us identify the hotspots.”

Just how much CWD?

Only time will tell whether those collared, sickened deer point Gregory and his USGS counterparts toward locations like the ranches where Wyoming Trophy Hunts guides — where, according to Metzler, virtually all buck mule deer are CWD-positive.

What’s already understood is that the Project Herd is an anomaly in the region and is itself a hotspot. The herd roams Wyoming’s deer hunt units 171 and 157, in west-central Wyoming, which are both within the borders of the Wind River Indian Reservation, although non-native hunting is confined to non-tribal lands within.

A buck mule deer was found dead in the part of Fremont County roamed by the Project Herd, Wildlife managers have discovered the herd has the highest prevalence of chronic wasting disease in the state. The deer pictured tested positive for CWD. (Courtesy/Wyoming Game and Fish Department)

The herd is considered a priority for CWD surveillance, and between 2016 and 2020 Game and Fish staff gathered tissue samples from 139 of its bucks. Of those, 85 came up positive, for a prevalence rate of 61%.

Preliminary test results for 2021’s tissue samples showed a higher rate of CWD: 78%, according to Game and Fish Regional Wildlife Coordinator Daryl Lutz.

“It’s the highest that’s been recorded, maybe anywhere in the world in wildlife,” Lutz told attendees at a public meeting last month.

The Wildlife Health Laboratory supervisor for the state of Wyoming, Hank Edwards, wouldn’t go that far, instead emphasizing the multi-year positivity rate. There are agricultural parts in southwest Saskatchewan, he noted, where prevalence has been documented in the 60-70% range. Annual reports from the provincial government confirm it, and say that in over a dozen Saskatchewan wildlife management zones, more than 50% of mule deer bucks are testing positive for the degenerative disease.

-- Advertisement – Story Continues Below --

Edwards did label CWD’s prevalence in the Project Herd “alarmingly high,” and he pointed out it’s Wyoming’s most CWD-infected deer herd by a nearly 20% margin. Statewide, 12.5% of the nearly 6,500 CWD samples processed during 2020 tested positive, statistics that span species, sex and cause of death, according to Game and Fish’s most recent CWD surveillance report.

“Every herd responds differently,” Edwards said, “for a number of reasons.”

In the Sublette Herd, which roams the Green and Snake river basins, CWD is just now arriving, and 0.8% of 375 samples tested to date have hit for the prion disease. There’s also significant variation in herds that for decades have suffered from CWD’s inexorable effects, like listlessness, physical wasting and inevitable death. In southeastern Wyoming’s Laramie Mountains, one of the first places where CWD was found in wild deer, 22% of hunter-killed bucks have been positive in the last five years. But in the Black Hills, the long-term prevalence in mule deer bucks is just 5.9%, though Edwards said that rate may have been dragged down by other diseases, like epizootic hemorrhagic disease (often called blue tongue).

Ahead of the study, wildlife managers hesitate to hazard a guess for why the Project Herd’s disease rates are a whole order of magnitude greater.

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