| Summary: | Populations of migratory salmon and trout have worldwide shown a decline due to human activities. Over the years numerous measures have been undertaken to maintain these populations, and conservation of migratory salmonids requires understanding of their ecology atmultiple scales, combined with assessing anthropogenic impacts. The regulated River Klarälven and Lake Vänern host endemic populations of landlocked Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). The historically high abundances of the salmonids in the River Klarälven in the early 1800s have decreased dramatically, reaching all-time lows after the completion of all nine Swedish hydroelectric power stations in the 1960s. After an extensive stocking program and transportation of wild and hatchery-raised spawners past eight hydroelectric plants, catches from commercial, maintenance and sport fishing have again increased. Recently, increases in the proportion of wild salmon returning to the River Klarälven have generated interests in establishment of wild salmon inhabiting the entire River Klarälven, including upstream of the Norwegian border. To obtain information needed to produce a management plan for the salmon, we conducted a number of studies of upstream-migrating spawners and downstream-migrating smolts. For upstream migration, we compared migration behaviour of wild and hatchery reared salmon and found that wild fish swam directly to the spawning grounds and presumably spawned, whereas few salmon of hatchery-origin arrived at the spawning grounds, and if they did so they swam considerably more before settling down at the spawning grounds. Studies of smolt showed that only 16% of the salmon passed all eight dams, and that losses in the dam-free lower 25 km of the river, before the salmon enter the lake, were higher for hatchery-raised smolts than for wild smolt. These differences between wild and hatchery-reared salmon underline the importance of increasing the number of wild salmon in the system and indicate that remedial measures are needed to improve passage success.
|
|---|