Evidence of limited short‐term adverse demographic side effects of chronic wasting disease management

Abstract

AbstractCompeting objectives are common in the management of wildlife diseases. However, the extent to which disease mitigation conflicts with other goals has rarely been quantified. Chronic wasting disease (CWD) is a lethal cervid disease widely distributed in North America and recently detected in Europe. After the detection of CWD among reindeer (Rangifer tarandus) in Norway in 2016, intensified and male‐biased harvesting was used to manage CWD, but this may have adverse side effects. Based on extensive surveillance data (2001‒2022) gathered by the Norwegian Institute for Nature Research (NINA) and local management in addition to harvest statistics, we quantified how CWD management in Hardangervidda, Norway, changed harvest rates and affected population size, operational sex ratio, and age structure, and, in turn, whether recruitment, sex ratio of calves, and calving dates were affected. We used a formal reindeer quality standard to define adverse management. The estimated harvest rate of adult males reached >40% annually; however, the population size was only moderately reduced because the harvest of adult females was similar or decreased. The sex ratio changed from approximately 1:2.2 to 1:6.5 (males ≥3 years: females ≥1 year), which brought the population from good to poor quality according to the reindeer quality standard. The proportion of prime‐aged (≥5 years) males among adult males (≥2 years) in the harvest decreased from >60% to approximately 30%. Demographic changes led to limited side effects in the short‐term, with a delay of 4‒5 days in calving dates and a slightly more female‐biased sex ratio among the harvested calves but without a marked change in early recruitment. Wildlife populations are increasingly threatened by severe disease outbreaks that may require intensive management. Our study highlights the importance of extensive surveillance to document the potential adverse effects on population abundance, demography, and demographic side effects. The fairly limited short‐term adverse impacts can be traded against a higher likelihood of future sustainability without severe diseases; however, this may become an issue of concern if the disease becomes endemic. Balancing these trade‐offs would benefit from good communication between veterinary sciences and wildlife ecology experts.