Reestablishing fish migration at hydropower plants

With two thirds of fish species on the red list, and up to 90% of the potential distribution of fishes being impacted by anthropogenic threats, Switzerland is facing an important challenge in terms of conservation. One of the main factors impacting fish populations is the lack of connectivity. With about 2000 obstacles spread across Swiss rivers, hydropower production plays a big role in this context. Since 2011, a revision of the water protection law requires owners to take measures to mitigate the impacts of hydropower plants on the environment, including the rehabilitation of fish migration. Technical measures for upstream migration, such as fish ladders, lifts or semi-natural bypasses, are well known and can be implemented on most sites. However, implementing measures for downstream migration, where fish should both be protected from entering the turbines and guided towards a safe bypass, remains a challenge. The behaviour and movement needs remain elusive for many species, making it difficult to set species specific quantitative goals for mitigation measures. Moreover, the fine-scale behaviour of fishes approaching hydropower plants is also little known, making the design of technical solutions more challenging. In this presentation, I will give an overview of the Swiss strategy to reestablish fish migration and address the gaps both in terms of knowledge on fish behaviour and technical solutions.