Wild and Hatchery Brown Trout Salmo Trutta Interact to Influence Feeding, Growth and Terrestrial Predation of Juveniles

We studied the growth, prey consumption and vulnerability to predation of juvenile hatchery and wild brown trout of similar genetic origin. Two experiments were run: one in in 12 wire mesh cages in a natural stream, and the other one in three semi-natural flumes in North-Eastern Finland. A substitute design with three treatments was used in both experiments: both hatchery trout and wild trout in allopatry, and hatchery and wild trout in sympatry. Wild trout started feeding shortly after the start of the experiment, and clearly earlier than novel hatchery trout, but food consumption was negatively affected by the presence of hatchery trout. When accompanied with wild trout, novel hatchery trout started to feed earlier and consumed more live prey when than when in allopatry. Growth of wild brown trout was negatively affected by the presence of hatchery trout in cage experiment, but not in semi-natural flumes. Two American minks, Neovison vison, entered the area of semi-natural streams and preyed on juvenile brown trout in different treatments. Hatchery trout were consumed significantly more than wild trout. When in sympatry with hatchery trout more wild trout were eaten by minks compared to pure wild trout treatments.