In a rare bit of good news about chronic wasting disease, a new paper shows that harvesting more deer — specifically adult bucks — is better for slowing the spread of the contagious neurological disease that’s fatal to deer and elk. The conclusion comes from an analysis of two decades worth of CWD disease trends in 10 Wyoming mule deer herds, where CWD has been linked (among other factors like habitat loss and energy development) to deer declines.
The paper, published Tuesday by the U.S. Geological Survey and the Wyoming Game and Fish Department, concluded that deer herds with consistently high harvest pressure across 20 years had significantly lower prevalence rates of CWD.
After analyzing Wyoming’s CWD track record as it correlates to harvest, the study’s authors predict that harvesting 40 percent of adult bucks (or two out of five) every year for 20 years could keep the prevalence of CWD in that herd at just 5 percent. If wildlife managers were to reduce hunting pressure so that only 20 percent of adult bucks (or one out of five) were killed, CWD rates could surge to more than 30 percent by the end of 20 years.
To date, CWD has been found in 35 of Wyoming’s 37 mule deer herds. Among those 35 herds, some have a prevalence rate higher than 50 percent.
“Although high harvest is unlikely to completely eradicate CWD,” write the paper’s authors, “our analysis suggests that maintaining hunting pressure on adult males is an important tactic for slowing CWD epidemics within mule deer herds.”
There are five key ways that hunting pressure in general helps keep CWD in check, with additional benefits for specifically targeting adult bucks. Here’s why:
- Deer infected with CWD may behave less cautiously (in more established cases), which makes them more likely to be killed by hunters and removed from the landscape.
- Older age-class bucks are often more likely to be infected with CWD.
- Hunters help lower deer densities, which lowers the chance of infection.
- Hunter harvest can lead to increased fawn recruitment, which in turn shifts the age-class structure to a younger, less infected population.
- Harvesting bucks increases adult deer mortality, which shortens the infection period of that animal — and in turn their opportunity to shed infected prions onto the landscape.
The researchers noted that some of the deer in their analysis were managed under a limited quota system, which allows wildlife managers to tightly control the number of available deer licenses — and therefore harvest pressure. Many herds in the study, meanwhile, are managed as general units with unlimited resident licenses. If Wyoming Fish and Game wants to increase deer harvest in those areas, officials might consider increasing nonresident licenses, extending season lengths, and tinkering with antler point restrictions.
While the study analyzed CWD surveillance data from 2000 to 2021, researchers also wondered whether harvest pressure in a much shorter period could also help wildlife managers get a handle on CWD in short order. The study’s authors concluded that ramping up harvest pressure for just three years certainly helped reduce CWD prevalence, but not as much as if it had been in place for all 20 years.
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The study could have wider-ranging implications for deer managers and hunters across the country, though no author was immediately available for comment on that. Just last week, Georgia announced its first positive case of CWD in the state. This month, state officials reported a cow elk at a Wyoming feeding ground had tested positive for CWD.
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