Assessment of predation at trout hatcheries in central Pennsylvania

The authors identified seven important predators at ten trout hatcheries and quantified their foraging behaviors. Most species devoted <28% of their total time in a hatchery to foraging for fish. As a group, predators fed on fish of variable lengths, but many factors determined specific lengths of fish taken. Most predators foraged equally at earthen and concrete raceways, but great blue herons Ardea herodias foraged only at earthen raceways. Collectively, common grackles Quiscalus quiscula captured and removed the most fish/day, but because mallards Anas platyrhynchos were present for more days/year, they had the greatest total impact. Secondary infection and injuries sustained during attacks by predators also may be important factors in fish loss. -from Authors