Evaluation of mitigation measures for Atlantic salmon and brown trout at hydropower plants and their prospect as selective agents

Abstract

Renewable energy contributes towards the world`s growing energy demands and urgent need for mitigating climate change. However, these renewable sources of energy may have localized, detrimental environmental effects. For instance, hydropower dams have dramatically affected river ecosystems by changing habitats and hindering fish migration. Especially, in anadromous salmonid fishes, such obstacles are responsible for the decline of many populations. Fish passages, offering a safe migration at hydropower dams, are therefore instrumental to secure populations of anadromous salmonids in regulated rivers. However, the small body size of smolts and their tendency to follow the main current downstream, impose design challenges to measures that prevent migration into turbines. Coherent with this, investigations of fish passages from a range of sites reveal a generally low overall efficiency. Considering that the fish passage and the turbine tunnel offers two migration routes with different survival, surprisingly little attention has been paid to selection regimes acting at hydropower plants. In this doctoral thesis, I evaluated the efficiency of mitigation measures for downstream migrating Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) and their prospect as selective agents. The studies were conducted at Fosstveit hydropower plant in the River Storelva and at Rygene hydropower plant in the River Nidelva located in southern Norway. Results are based on measuring or estimation of behavior and survival from individually PIT-tagged fish and the subsequent detections and recaptures in antennas and traps.