The efficacy of wildlife fences for keeping reindeer outside a chronic wasting disease risk area.
1. Emerging wildlife diseases often comeswith negative cultural and economic impact. Limiting disease spread is a recurrent goal and challenge, but the efficacy of various mitigation measures is rarely assessed. 2. Chronic wasting disease (CWD) is a lethal disease among cervids that was discovered among alpine reindeer (Rangifer tarandus) in the Nordfjella mountain range of Norway in 2016. After de-population, the entire range was fallowed to avoid re-emergence from environmental pathogen reservoirs. This involved installing perimeter fences in the alpine areas in order to keep reindeer from adjacent populations outside of the CWD risk area, while other cervids (red deer Cervus elaphus, roe deer Capreolus capreolus and moose Alces alces) were likely to enter through the forested areas. 3. We used camera trapping and surveillance reports to assess the efficacy of the perimeter fences. All four species of cervids were documented inside the CWD risk area. For reindeer, only 12.0% of observations were inside the CWD risk area, while this was 28.7% for the other cervids. The higher proportion of observations outside of the fenced area indicate that fences provided a barrier and lowered the number of crossings also of red deer, roe deer and moose. 4. Fences do not provide complete barriers, and we discuss practical solutions for how to avoid 'intruders' entering a given area, such as maintenance at critical points (e.g. river and road crossings) and height of fences (e.g. species variation in jumping; deep snow) to uphold their desired effect. 5. We argue that two fence lines with a buffer zone would be required when reintroduction of reindeer are planned in the CWD risk area after fallowing, similar to what has been suggested for other wildlife diseases.