Hydropower-related mortality and behaviour of Atlantic salmon smolts in the River Sieg, a German tributary to the Rhine
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We studied downstream migration of 256 radio-tagged Atlantic salmon smolts passing a low-head power station where technical facilities have been improved to allow safe migration via several bypass routes. Extra mortality was 7 and 17% (two years) in the power station reservoir, and a minimum of 10 and 13% at the power station compared to in a control stretch. The majority of the smolts followed the main flow at the power station, towards the turbines. Sloped bar racks with 10 mm bar spacing hindered smolts from entering the turbines, hence there was no turbine mortality. Smolts used surface openings in the racks, which directed them to a bypass route outside the turbines. The extra mortality in the reservoir and at the power station was related to physical injuries in bypass routes and to predation. The mortality risk in the reservoir and at the power station decreased with increasing migration speed. Migration speeds increased with water discharge. Migration was slower when the smolts passed the power station than on other stretches. This study shows that hydropower regulation caused elevated mortality and delays for downstream migrating fish, even with improved technical facilities to reduce mortality.
KeywordsRadio tag Telemetry Salmo salar Downstream migration Migration speed Bypass
This study was commissioned by the Ministry for Climate Protection, Environment, Agriculture, Conservation and Consumer Protection of the State of North Rhine–Westphalia (MKULNV), and funded through the State Agency for Nature, Environment and Consumer Protection of North Rhine–Westphalia (LANUV) to the University of Cologne (JB). We would like to thank Detlev Ingendahl for valuable collaboration, the company Innogy SE for the possibility to perform the study at their power station, Laura Mehner, Florian Kreische, Stefan Scheffels, Marc Steinheuer for help during the fieldwork and Michael Holtegel and colleagues at the LANUV Hatchery Albaum. We would also like to thank two anonymous reviewers for constructive comments to a previous version of the manuscript.
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