Downstream Migration of Atlantic Salmon – Possibilities for Wild Smolts and Quality of Reared Smolts

Populations of migratory salmon and trout have shown a decline worldwide due to human activities, and over the years, numerous measures have been undertaken to maintain these populations. The regulated River Klarälven-Lake Vänern ecosystem hosts endemic populations of landlocked Atlantic salmon (Salmo salar), but at much lower abundances than in the early 1800s. After the completion of the last of nine Swedish hydroelectric power stations in the 1960s, the Klarälven salmon population reached an all-time low, and an extensive stocking and transportation of spawners past the dams has resulted in a population increase. To obtain information needed to produce a management plan we conducted a series of studies of downstream-migrating smolts to estimate hydropower station passage success and to compare migratory success of wild and hatchery reared smolts. Only 16-30% of the wild smolts passed all eight power plants, and losses were generally lower for wild than hatchery smolts in the dam-free lower 25 km of the river. Moreover, the large differences in migration success of the hatchery smolts could be related to feeding routines in the hatchery. We conclude that production of high quality hatchery-raised smolts, together with remedial measures to increase the number of wild salmon, are needed.