In many rivers, downstream‐migrating salmonid smolts must pass multiple dams often with high losses as a result. Fish experience mortality both in dam and reservoir passage, and spilling water might allow fish to avoid turbine passage and hence increase migration survival. In River Klarälven, Sweden landlocked Atlantic salmon smolts migrate along a 180 km long reach passing eight dams. A previous telemetry study estimated an accumulated migration success of 16% under conditions with no or very little spill. Here we repeat this study, under a planned spill regime at a subset of hydropower dams. Overall passage success through the eight dams was 32%, which is greater than the 16% reported from the same river section in a year without spill. Most of this increase, however, was attributable to the situation at one dam, where spill constituted a large proportion of total discharge. In addition, we found that loss rates km−1 were similar over dammed reaches and the lentic habitats, but greater than in the free‐flowing reference reaches. Results for migration speed paralleled this result with the highest speeds observed in the free‐flowing reaches.

中文翻译：

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内陆大西洋鲑鱼在受管制河流中向下游洄游——计划性溢漏大坝多次通过的影响

在许多河流中，向下游洄游的鲑鱼小鲑鱼必须通过多个水坝，这往往会造成很高的损失。鱼类在通过水坝和水库时都会死亡，溢出的水可能会让鱼类避开涡轮机通道，从而增加洄游的存活率。在瑞典克拉拉尔文河，内陆大西洋鲑鱼沿着 180 公里长的河段洄游，途经八座水坝。之前的遥测研究估计，在没有或很少泄漏的情况下，累积迁移成功率为 16%。在这里，我们在部分水电站大坝的计划溢漏制度下重复这项研究。通过八座水坝的整体通行成功率为 32%，高于同一河段在没有溢漏的一年中报告的 16%。然而，这一增长大部分归因于一座水坝的情况，该水坝的泄漏量占总排放量的很大一部分。此外，我们发现损失率 km−1与水坝河段和静水栖息地相似，但大于自由流动的参考河段。迁移速度的结果与在自由流动河段观察到的最高速度相一致。