A computer model that is the basis of the Colorado Division of Wildlife’s controversial strategy to kill larger numbers of deer and elk to curb the spread of chronic wasting disease has a fundamental flaw, according to researchers in Illinois.
That flaw, according to a paper published last fall in the Wildlife Society Bulletin, could be leading Colorado to incorrectly assume the worst about the disease – mainly that it could wipe out mule deer populations if left alone. Division of Wildlife officials have used the model to justify their thin-the-herd strategy to fight the disease, which includes loosening hunting limits in many areas, issuing more licenses and employing government sharpshooters to cull certain herds.
Experts agree that it’s far too early to know whether those tactics have worked, although the overall infection rate in northeastern Colorado’s “established area” for CWD dropped from 2002 to 2003. Even so, several more years of data are needed to get a true picture, state wildlife managers say.
But Colorado’s technique, which at one point in 2002 saw the division shoot more than 600 deer and elk near Craig in a two-week span, has drawn criticism from some scientists and community activists unhappy with an approach that often results in killing dozens of healthy animals to find a single infected one.
Now, a pair of academics at Southern Illinois University has given critics more ammunition. They say the DOW model has a significant problem because it assumes the number of potentially disease-spreading contacts between deer remain constant, even as the population declines. That notion is probably wrong, said one of the researchers, Eric Schauber, because it doesn’t make sense that a deer would make as many contacts with other deer when many of its neighbors are dying off.
“Normally, if its neighbors are dying off . . . the frequency of contact is not enough to keep the epidemic going,” Schauber said.
The upshot: Colorado’s computer model could be flawed in projecting the speed and rate the disease spreads and, therefore, could be overly dire, particularly in predictions that the disease could wipe out deer populations.
A 2001 paper written by John Gross, of Colorado State University, and DOW veterinarian Michael Miller put it this way: The model’s “projected trends are, to say the least, unsettling. Left unmanaged, our model forecasts two- to fourfold increases in CWD prevalence over the next several decades with disease abating only with the extinction of infected deer populations.”
Asked to comment on the Southern Illinois paper, Miller said in an e-mail that he was preparing a scientific paper in response. He cautioned that it’s wrong to place too much emphasis on the importance the agency gives to its model.
Even so, division officials have often cited the model’s findings as a key factor in CWD management efforts.
Miller already has heard plenty of criticism from pockets of residents in Boulder and Larimer counties, as well as animal rights groups such as the Fund for Animals.
Another frequent critic, University of Colorado professor emeritus of biology Charles Southwick, believes the agency is overreacting to a disease that he believes will likely settle into the deer and elk herds at a low rate, flaring up from time to time, like many wildlife diseases.
At least one former Division of Wildlife biologist is expressing his distaste for the agency’s CWD management efforts as well. Gene Schoonveld said the approach is too aggressive.
“They call it culling; I call it slaughter,” Schoonveld said. “They go in with a scorched-earth policy and shoot deer to pieces.”
Division officials dispute that representation, having long said they take no joy in having to shoot the very animals they built careers trying to protect.
Miller frames the issue in a rhetorical question: “If someone comes out with an alternative model that says there’s nothing to worry about, would you recommend to DOW that we stop trying to manage CWD?”
SIU researchers say they understand the predicament Colorado officials are in, trying to manage a new wildlife disease they know little about.
“While we acknowledge that rapid management action to control CWD may be warranted and that wildlife managers invariably must act without the luxury of complete knowledge,” the authors write, “we propose that science-based wildlife management will advance if competing models and management alternatives are carefully explored.”
Developing a strategy
State Division of Wildlife officials are using a computer model, in part, to devise a strategy to fight chronic wasting disease. The model has been questioned by some researchers who say it is flawed. The strategy has led to the following tactics:
- Loosening of hunting limits in many areas.
- Issuing of more hunting licenses.
- Hiring sharpshooters to cull certain herds.
Gary Gerhardt contributed to this report.