Beteende inför lek hos odlad respektive vild lax (Salmo salar L.) i Klarälven

Sammanfattning:

In many regulated rivers, authorities have stocked hatchery salmon to compensate for loss of wild populations. However, hatchery fish have not always behaved as wild fish do, and stocking them has not always fully compensated for the loss of wild fish. The purpose of this study was to compare swimming behaviour in the river before spawning, the choice of spawning areas and body size between wild and hatchery-reared salmon in the river Klarälven. Salmon behaviour in the river before spawning was analyzed using radio telemetry. The salmon were caught at Forshaga power plant, radio-tagged and returned to Klarälven at Ekshärad, 107 km from the river’s mouth. Permanent stations with antennas were deployed at seven different locations along the river, to register all radio-tagged salmon. In addition manual tracking from a car was performed every three days, supplementing data from the permanent stations. Without participation in spawning or remaining in the river 71 % hatchery-reared and 6 % wild salmon swam downstream and were registered at the first power plant downstream of their site of release. The average period the returning salmons stayed above the power plants was 22.5 days. Hatchery-reared salmon had significantly more and longer up- and downstream movements than wild salmon in the river. Hatchery-reared salmon were significantly shorter and weighed less than wild salmon. A higher percentage of wild salmon (94 %) than hatchery-reared salmon (24 %) were registered at the spawning grounds. Hatchery-reared salmon spawned at the same spawning grounds and at the same time period as wild salmon