Naturally and hatchery produced European trout Salmo trutta: do their marine survival and dispersal differ?

Abstract

We tested whether marine survival and migration pattern differed between naturally and hatchery produced European trout Salmo trutta of different origins. The hatchery fish were released 150 m above the river estuary of the southwestern, Norwegian River Imsa, the home of the local population. Recaptures were used as proxy for survival. Wild and local hatchery fish survived better than transplanted hatchery stocks. Trout that were 1 year at release survived less well than 2-year olds, and small individuals less well than larger ones. Relative to their body size at release, populations that originated most distant from the River Imsa, the Baltic River Eman and the Norwegian mountain Lake Tunhovd, exhibited the poorest sea survival. At sea, trout chiefly moved less than 240 km from the river of release, but there were significant differences in dispersal among populations. Hatchery-produced River Eman and Lake Tunhovd trout moved farther from the River Imsa than the south Norwegian sea trout populations, and the marine distributions of the former were similar to that of the natural River Imsa trout. Large fish moved farther from the river than smaller ones. Straying to other rivers was low among wild and local hatchery-produced fish, and significantly lower than among most transplanted populations, and River Eman trout in particular. Thus, the River Imsa trout appeared better adapted to survival under the local conditions than non-local trout with consequences for optimal population management.