Distribution and relative impact of avian predators at aquaculture facilities in the northeastern United States

We conducted on-site interviews at 61 randomly selected aquaculture facilit ies in the northeastern United States and initially censused fish-eating bi rds at 58 of those facilities in June 1995 to determine the distribution of avian predation problems. To examine the relative impact of these birds, w e continued to study bird populations and the fish consumption rates of the se birds at 30 facilities during the summer of 1995 and at 7 facilities dur ing the spring of 1996. Approximately 80% of the fish culturists interviewe d perceived bird predation to be a problem at their facility; this view was even more widely held by trout producers. Consistent with these results, 8 1% of the facilities surveyed during the first phase of study had at least some fish-eating birds present. When asked to list bird predators in order of importance, 76% of 49 managers responding named the great blue heron Ard ea herodias as the most important predator of concern. Consistent with thes e findings was the presence of great blue herons at 90% of the 30 facilitie s repeatedly surveyed during the summer of 1995. Based on damage projection s, common grackles Quiscalus quiscula, mallards Anas platyrhynchos, and gre at blue herons appeared to be the primary species of concern out of 10 bird species observed. However, mallard problems were relatively isolated, and previous damage estimates reported in the literature for mallards, common g rackles, and American crows Corvus brachyrhynchos may have been highly infl ated. Of the 24 trout-rearing facilities surveyed during the summer of 1995 , 21% were estimated to have sustained bird predation losses in excess of U S$10,000. Smaller losses, ranging from several hundred to several thousand dollars, were more typical of the remaining trout and warmwater fish facili ties.