Effects of a Short-Term Shooting program on Nonbreeding Cormorants at Inland Fisheries

In Europe, numbers of great cormorants (Phalacrocorax carbo) have increased over the last 25 years, leading to increasing conflict with anglers. We evaluated the effectiveness of shooting in frightening nonbreeding cormorants from inland fisheries in England and Wales. Thirteen amenity fisheries were assigned to one of 3 groups: 1) lethal, 2) nonlethal, and 3) control. Each trial comprised 3 sequential 2-week phases: pretreatment, treatment, and post-treatment. Changes in the mean number of cormorants between phases were compared. Shooting (lethal and nonlethal) reduced cormorants, on average, by over 40% whereas numbers at control sites increased, on average, by over 25% (treatment phase $F_{1,10}=5.04$, P=0.049, post-treatment phase $F_{1,10}=5.52$, P=0.041). We observed no difference between lethal and nonlethal shooting, so we reject the hypothesis that the effect of lethal shooting differed from that of nonlethal shooting (within this specific experimental design). Shooting can be an effective deterrent in reducing cormorant numbers at inland fisheries. As the level of effectiveness varied between individual sites, however, shooting regimens need to be structured to local conditions to maximize cost-effectiveness.