What does new CWD study mean for the average hunter?

New Colorado Parks and Wildlife study indicates hunting pressure can help control the spread of chronic wasting disease.
Mule deer
Photo by © Wayne Lewis/CPW.

Applying sufficient hunting pressure can help control the spread of chronic wasting disease (CWD) in mule deer, especially early in outbreaks when the disease is scarce, according to a study published this month by Colorado Parks and Wildlife in the Journal of Wildlife Diseases.

The 18-year retrospective study revealed that areas with the largest declines in annual hunting license numbers (pressure) showed the largest increases in the percent of infected adult male deer killed by hunters (prevalence). Increasing the number of licenses lowered the risk of hunters harvesting an infected deer 1-2 years later, and decreasing license numbers increased that risk.

The results of the study suggest that reducing harvest pressure in order to grow mature male deer may accelerate the growth of CWD. And other studies in Colorado and Wyoming have shown that at high prevalence CWD can eventually harm a deer herd.

So what does this mean for the average deer hunter in Colorado?

Two things:

  1. If you’re hunting in a mandatory CWD testing unit, be sure to submit your harvest at one of CPW’s many collection sites, including mobile options in more rural areas of Colorado. The data are critical for CPW’s wildlife biologists to understand how their management actions are affecting infection rates. Herds are only surveyed every 3⎼5 years, so please do your part to participate whenever asked to do so. Plus testing is free in mandatory units. 
  2. If the test comes up positive, you have removed an infected animal from the population and have lowered the chance of hunters harvesting an infected animal in this area in subsequent years. (Thank you!)

CPW surveys of hunters who participated in mandatory testing in recent years have indicated they may be less likely to hunt in a particular area if they harvest a CWD-positive animal. CPW understands your concern and disappointment. You harvested an animal you hoped would fill your freezer with meat this winter only to discover you will need to dispose of it. This is an important reason to keep the number of infected animals as low as possible.

But remember, despite that empty freezer you did have the experience of hunting and harvesting a big game animal in Colorado. And you contributed to our efforts to control this disease. And if you choose to hunt in that area again, you should be much less likely to harvest another CWD-infected animal.

Hunting is the best and most practical tool we have to control CWD in Colorado and ensure healthy herds for future generations. Ultimately, healthy and productive deer herds provide more hunting and wildlife viewing opportunities. For more information about what CPW is doing to combat CWD, visit cpw.state.co.us/cwd.

Frequently Asked Questions

Does this mean that CPW will now stop managing for quality deer hunting (mature bucks)? 

CPW will continue to use the Herd Management Planning process to establish management objectives for each herd. Herd Management Plans (HMPs) are a public process and plans are approved by the Colorado Parks and Wildlife Commission. Herd Management Planning is always about balancing biological and social aspects of wildlife management. In the short term this does mean we may need to deemphasize quality management in places where we’re trying to get the disease under control. 

What does this mean for elk populations? Colorado Parks and Wildlife does not have mandatory testing for elk on a statewide level. We know that mule deer bucks are the most susceptible, but we also know that elk contract CWD as well. Is that not a concern?

It’s not a question of concern, but one of CPW working to make the biggest impact it can with the resources available. Elk and moose can also be infected with CWD. At least 16 of Colorado’s 42 elk herds and 2 of 9 moose herds are known to have some level of infection. But in general, deer herds tend to be more heavily infected than elk herds living in the same geographic area. And by comparison, CWD is relatively rare in moose in Colorado. 

There may come a day when CPW enacts mandatory testing for elk and moose units in Colorado. But right now, the agency is focusing its efforts on mule deer because we know that is where the highest levels of infection exist. There’s even a chance that by getting the disease under control in deer that we can keep it under control in elk and moose as well. 

By increasing the hunting pressure and by harvesting more deer, won’t the deer population ultimately reach a critical tipping point?

Doe deer are the most important factor to ensure a stable population. In herds that exceed the 5% CWD infection level, CPW’s wildlife biologists will be working to set hunting license numbers that bring buck-to-doe ratios down to the bottom of the buck-to-doe ratio objective range. The Middle Park and Red Feather/Poudre Canyon deer herds offer good examples of how biologists have been able to suppress CWD and yet still maintain robust, thriving deer herds with excellent hunting opportunities. 

The press release states: “Further analysis showed that increasing the number of licenses lowered risk of hunters harvesting an infected deer 1-2 years later, and decreasing license numbers increased that risk.” 

Does this mean hunters have to thin the herd and not eat the meat (if their test comes back CWD positive) in order for that to happen? Is CPW taking steps to manage the herd without hunters having to harvest CWD-infected animals? 

Hunting is the best tool CPW has to reduce CWD in herds, but it is not the only tool. 

Reducing repeated deer visitation to artificial concentration points should reduce localized environmental contamination and transmission. This is yet another reason why it is important to not feed wildlife. 

Page 23 of the Colorado Chronic Wasting Disease Response Plan outlines the suite of options available to herd managers once the 5% prevalence threshold for bucks is reached. Increased harvest through targeted population reductions not related to hunter harvest is one option. In areas where hunters are not able to access herds, CPW will consider the use of focused herd reduction measures as a last resort. But surveyed deer hunters overwhelmingly support CPW using hunting as the main tool for controlling CWD, so that’s what we are striving to do wherever feasible. 

Is CPW making progress in reducing CWD in deer and elk herds?  

In short, yes. Implementing mandatory testing is giving our herd managers a better picture of the infection rate in our herds. And this retrospective analysis lends scientific support for using hunting and a management tool, and also identifies management practices we should avoid. With that knowledge, herd managers can begin taking steps to lower prevalence in herds where the infection levels meet or exceed 5%. There are already several examples of herds in Colorado where the epidemic curve for CWD has been flattened, including Middle Park, Red Feather/Poudre Canyon, Big Thompson, and Grand Mesa North. Managers will be able to assess the efforts undertaken in the Uncompahgre and Cimarron herds along with the others after the next round of mandatory testing. The idea is to learn as we go, identifying pitfalls to avoid and doing more of the things that appear to be helping us make progress toward local disease management goals.  

Visit the Colorado Parks and Wildlife website for additional CPW information and FAQs.


Travis Duncan is a public information officer for Colorado Parks and Wildlife in Denver. Travis has lived in Colorado nearly 20 years and loves the outdoors. If you have a question, please email him at travis.duncan@state.co.us

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