A long-running study near Glenrock foretells a dire future for whitetail deer populations that have been carrying chronic wasting disease for decades.
Research headed by Dave Edmunds during his University of Wyoming doctoral studies found that whitetail afflicted with the degenerative and always fatal condition are nearly five times more likely to die in a given year than disease-free deer. The study suggests that the diseased whitetail east of Casper are declining 10 percent a year, and face extinction within half a century.
“About 40 percent of the CWD-positive deer that enter a year are going to survive to the end,” Edmunds said in an interview. “It doesn’t bode well, especially in our population, where we have these high prevalence and incidence rates in female deer.
“In ungulate populations,” he said, “females are what drive population dynamics and so when you’re having only 40 percent of a large percentage of your female population survive through the year, that’s where we’re getting these population declines.”
Whitetail deer free of the neurological disease, by contrast, survived through the year 80 percent of the time.
Edmunds’ study found that hunting was the main cause of mortality for diseased buck whitetail. Before the disease manifested itself in significant physical changes, he found, it apparently triggered subtle behavioral changes that made whitetail bucks more susceptible to hunters’ bullets.
Chronic wasting disease itself, which causes deer to waste away in body and mind, was the leading cause of death for does.
The population he homed in on over a seven-year period, whitetail that live in southern Converse County, live within Wyoming deer hunt area 65. It’s an area where Wyoming Game and Fish Department hunter harvest samples showed that 32 to 43 percent of all deer, including mule deer, carried the condition between 2003 and 2010.
Modeling that Edmunds conducted suggests that without chronic wasting disease the whitetail deer population in the Glenrock area would be healthy and slightly growing. Remove doe harvest from the equation and the diseased population would also be stable, he said.
“It’s that combined effect of shooting female deer and the high mortality rate of CWD that is causing this population to decline,” Edmunds said. “The good news is ... there’s a management scenario where you could at least maintain the deer numbers if you halted harvest of does.
“However,” he said, “we don’t know what the end game would be, because then you’re leaving more CWD-positive deer on the landscape, which could then facilitate increasing prevalence faster.”
A cousin of mad cow disease in bovines and Creutzfeldt-Jakob disease in humans, CWD can persist in the landscape without an animal host, has no known cure and is moving toward Jackson Hole and other parts of western Wyoming where elk in wintertime are concentrated on feedgrounds and more prone to transmitting diseases.
Edmunds, who today works as a research scientist at Colorado State University, said he never anticipated disease-driven population declines of 10 percent annually. CWD, he said, is a disease that needs be taken seriously.
“We’ve documented that it has the potential to cause population declines,” Edmunds said. “The cautionary tale is don’t allow CWD to get into populations at this point, because we have no treatment and/or management options to deal with CWD once it’s established.”