Spawning Migration of Wild and Supplementary Stocked Landlocked Atlantic Salmon (Salmo salar)
Upstream migration by adult salmonids is hindered by dams in many regulated rivers. In the River Klarälven, which possesses a unique population of landlocked Atlantic salmon, Salmo salar,, the loss of fish production is compensated for by stocking hatchery-reared smolts and by collecting upstream migrating spawners in a trap at the lowermost dam and transporting them past 8 dams. To identify the spawning grounds and study their behavior, wild and hatchery-reared, radio-tagged Atlantic salmon were followed during their spawning migration. Approximately 50% of the hatchery-reared salmon “fell” downstream of the uppermost power plant and thus did not reproduce. For wild fish, early migrants fell downstream of the dam to a greater extent than late migrants (50% vs 10% fallbacks). The hatchery-reared salmon’s migration pattern was also more erratic and they held position on the spawning grounds less often and for shorter time than the wild salmon. Our results indicate that the capacity of hatchery-reared salmon as supplementary spawners is limited and hence their reproductive contribution to the wild population is smaller than previously believed.