| Summary: | Repeat salmonid spawners potentially make large contributions to total recruitment and long term population stability, and yet, relatively little is known about this phase of salmonid life history. Thus, we studied post-spawning behavior and survival of brown trout and Atlantic salmon in relation to downstream dam passage, in two rivers, the River Emån in southern Sweden and the River Klarälven in south central Sweden. In the River Emån, 48% of radio-tagged brown trout post-spawners reached the Baltic Sea after passing three dams.Post-spawners were delayed at the power plants (median 17 days), with the median time required for downstream migration being 28 days. Many post-spawners were observed swimming back and forth between power station dams. In the River Klarälven, with 8 power station dams, almost none of the radio-tagged Atlantic salmon reached Lake Vänern. Over 40% of the post-spawners died after spawning or during winter, while over 50% died trying to pass the eight dams. Remedial measures such as guidance and bypass systems, organized spill and trap and trucking are potential solutions that need to be tested.
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