Applying sufficient hunting pressure may be the key to managing chronic wasting disease in mule deer, especially early in outbreaks when the disease is scarce. But reduced harvest prescriptions aimed at growing mature male deer will accelerate the growth of epidemics. These are the main findings reported by Colorado Parks and Wildlife scientists in a new peer-reviewed article published online in the Journal of Wildlife Diseases.
The new paper summarizes an analysis of data from Colorado mule deer across 12 hunting areas, gathered over nearly two decades (2000-2018). 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). Prevalence stayed comparatively flat in most areas where license numbers remained steady or increased. Further analysis showed that 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.
“This is timely information for managers and policy-makers to have as CPW begins to ramp up our statewide efforts to manage CWD," said Matt Eckert, CPW Terrestrial Programs Supervisor and study co-author. “Hunting is a tool we already use to manage our deer and elk herds statewide, and these results show that we can adapt the use of hunting for CWD suppression as well.”
The new study shows that CWD prevalence was cut in half in northern Larimer County through a sustained management effort that began back in 2000. “Our effort to curb CWD in the Poudre-Red Feather deer herd required some short-term sacrifices and was not universally popular when we started out,” said Mark Leslie, CPW Northeast Regional Manager, “but that local community can be proud of the groundbreaking progress made in their area.”
In Middle Park, several factors created the impetus for management changes. CWD was first detected there around the same time CPW Researchers discovered that bucks had CWD prevalence twice that of does. Additionally, the Middle Park deer herd’s ratio of bucks per 100 does was above the Herd Management Plan objective. “The combination of these three things created a sense of urgency for us to increase licenses to get buck to doe ratios down to management objective,” said Andy Holland, former Hot Sulphur Springs Area Wildlife Biologist, now CPW’s statewide Big Game Coordinator and another study co-author.
Local managers began increasing the annual number of licenses for hunting bucks in Middle Park and subsequent managers have stayed the course. Data reported in the new study show how sustained hunting pressure flattened the epidemic curve in Middle Park over the last 15 years even as prevalence in the White River and Bear’s Ears herds increased. “The recent surveys confirmed that our preventive efforts have paid off. Hopefully these findings will pave the way for using hunters to manage the prevalence of CWD in other Colorado herds,” noted Holland.
About chronic wasting disease
Chronic wasting disease (CWD) is a fatal neurological disease found in deer, elk and moose. Colorado Parks and Wildlife researchers and biologists have studied chronic wasting disease on numerous fronts - their work and expertise on this disease is recognized both nationally and internationally. Read CPW’s Colorado Chronic Wasting Disease Response Plan to see how the agency is addressing the problem.
CWD is one area of increasing concern across Colorado. CPW has been actively pursuing management tactics for helping prevent further spread of CWD and managing it in herds that are already affected since the late 1990s.
Controlling chronic wasting disease is critical for the long-term health of deer herds. For Coloradans, quality of life, outdoor heritage, and economic prosperity are dependent on the health and sustainability of these treasures.
CPW staff have worked for well over a century to ensure the health and future of Colorado’s state parks and wildlife for our citizens. Through cutting edge science and innovative conservation practices, we continue to push the boundaries of science to better understand how disease affects the wildlife of Colorado and what practices we can employ to address these challenges.
See answers to frequently asked questions about CWD.
What is chronic wasting disease?
- CWD is an always-fatal disease of deer, elk and moose.
- CWD is not caused by a virus or bacteria, it cannot be treated or prevented through vaccination.
This makes it a real threat to the health and long-term sustainability of herds if not controlled through active management.
How is CWD transmitted?
- CWD spreads through direct or indirect contact between animals. The disease agents, prions (pree-ons ) are present in saliva, feces and carcass parts of infected animals.
- These prions also can stay in the soil for long periods of time which is why it is also very important to monitor and control herds that are infected in order to minimize long-term contamination of their ranges with CWD prions.
Where is this disease found?
Chronic wasting disease occurs in free-ranging and captive cervids (members of the “deer” family) in several parts of North America, including Colorado.
CWD has been detected in 33 of Colorado’s 54 deer herds, 14 of 43 elk herds, and 2 of 9 moose herds. The percentage of sampled animals infected (or “prevalence”) appears to be rising in many affected Colorado herds. Maps and tables on CPW’s website page About CWD and Adaptive Management show current estimates of CWD distribution and prevalence in deer and elk statewide:
- For a summary of chronic wasting disease prevalence estimates in Colorado, by data analysis unit (DAU), for adult elk, mule deer, white-tailed deer and moose, scroll down to click on the CWD prevalence estimate charts.
- For relative rates of infection by game management unit in Colorado, see the elk and mule deer species maps.
Below is a summary of results from the agency’s mandatory chronic wasting disease (CWD) testing in 2019:
- 16 deer herds were included in mandatory testing
- Over 7,700 samples tested statewide for all cervid species
- CWD prevalence now exceeds the 5% management threshold in 18 deer herds statewide.
- Of the 18 herds where CWD prevalence in adult bucks exceeds 5%, 5 herds have prevalence between 5-10%, 7 herds have prevalence between 10-20%, and 6 herds have prevalence that exceeds 20%. When prevalence is 20%, it means 1 out of 5 adult males are infected.
- Data collected from mandatory testing shows CWD prevalence is higher in male deer than female deer.
- Prevalence may be slightly higher in mule deer than in white-tailed deer.
- CWD is a slow-moving disease. Prevalence has gradually increased over time to high levels in some herds. CPW learned of higher prevalence levels once mandatory testing was completed.
For additional information on CWD management and other conservation efforts, visit Colorado Parks and Wildlife at cpw.state.co.us.
Rebecca Ferrell is public information and website manager for CPW.