Samantha E. Allen | Search USGS

USGS2026

Chronic wasting disease reduces mule deer survival and hunter success in the Wind River Basin of Wyoming

Chronic wasting disease (CWD) is a fatal prion disease of cervids that has spread across much of North America and has recently become a global concern. Although CWD typically emerges gradually in new geographic regions, some areas experience rapid increases in prevalence for reasons that remain unclear. Herein, we describe the establishment of CWD in a mule deer (Odocoileus hemionus) population in the eastern portion of the Wind River Basin, WY, USA, where CWD prevalence in adult males (n=249) increased from 0% to 63% within a decade. We provide historical context, including a description of regional anthropogenic changes, and examine the epizootic’s impact on deer survival and hunting. From 2023 to 2025, we captured and monitored 96 adult mule deer. Annual survival was low: 0.38 for adult males (n=21) and 0.53 for adult females (n=75). Before CWD detection in 2012, mean hunter success was 72% (2000 to 2011). After detection, hunter success declined to 30% in 2022. We propose three hypotheses to explain the rapid rise in CWD prevalence, including food hotspots created by agriculture, increased agricultural dependency due to habitat degradation, and declining migratory behavior. Our case study highlights the potential effects of CWD and provides insights into possible drivers of transmission, to support more targeted management.

Wyoming↗

USGS2025

The effectiveness of harvest for limiting wildlife disease: Insights from 20 years of chronic wasting disease in Wyoming

Effective, practical options for managing disease in wildlife populations are limited, especially after diseases become established. Removal strategies (e.g., hunting or culling) are used to control wildlife diseases across a wide range of systems, despite conflicting evidence of their effectiveness. This is especially true for chronic wasting disease (CWD), an untreatable, fatal prion disease threatening cervid populations across multiple countries, for which recreational harvest has been suggested as an important disease control strategy. Using observational data to evaluate whether harvest effectively limits CWD prevalence has been difficult because statistical relationships between harvest and disease prevalence can arise from a causal effect of harvest (i.e., harvest's impacts on prevalence via changes in transmission or demographic structure) or from a number of alternative mechanisms. For instance, correlations between harvest and disease prevalence can also be driven by disease's impacts on population size and harvest (i.e., reverse causality) or from confounding variables (e.g., habitat or geographic location) that impact both harvest rates and disease prevalence. We analyzed two decades of surveillance data (2000–2021) from 10 mule deer herds in Wyoming, using statistical approaches informed by causal inference theory, to test for the effects of harvest on CWD prevalence. Herds with consistently high harvest pressure across 20 years had significantly lower prevalence. Our models predicted that harvesting 40% of adult males per year across 20 years would maintain prevalence below 5% on average, whereas if only 20% of males were harvested in each year, prevalence would increase to >30% by year 20. Moreover, shifting the relative harvest pressure within a herd over a shorter period (3 years) reduced subsequent prevalence, albeit to a smaller degree. Although high harvest is unlikely to completely eradicate CWD, our analysis suggests that maintaining hunting pressure on adult males is an important tactic for slowing CWD epidemics within mule deer herds. Our study also provides guidance for future analyses of longitudinal surveillance data, including the importance of demographic data and appropriate time lags.

Wyoming↗