Session E9: Migration of Atlantic Salmon (Salmo Salar) at Low-Head Archimedean Screw Hydropower Schemes

Abstract: There has been a rapid increase in development of small-scale hydropower schemes across Europe. Such schemes may impact upon migratory fish populations through modification of migration pathways. There is a clear need for scientific evidence to inform guidelines for the design, placement and management of small-scale hydropower schemes for the protection of migratory fish. The proliferation of the Archimedean screw turbine (AST) for lowhead applications is concerning because although these turbines are purported to cause negligible damage to fish passing through them, the available data is limited. The studies presented assess the impacts of low-head AST hydropower schemes on migrating populations of anadromous Atlantic salmon (Salmo salar) in Scotland. Smolts were tracked through an AST hydropower scheme on the river Don using radio tags and passive integrated transponder (PIT) tags. Smolt movements through alternative passage routes were observed using an array of fixed loggers at the hydro scheme. The proportion of radio tagged fish which passed through the turbine was 27% (7/26). The majority of PIT tagged smolts passed through the turbine channel within 27 minutes. Passage behaviour is considered in the context of the scheme’s operation and environmental conditions. Adult fish were tracked using radio and PIT tags at three AST hydropower schemes with distinctive designs and operational regimes: on the middle reaches of the river Don, the upper reaches of the Don, and on the Ettrick water. A mixture of fine-scale radio detection zones and PIT antennas was used to investigate attraction to the competing flows at each of the turbine and fish pass or depleted stretch outflows, and the efficiency and efficacy of the fish pass. Behaviours at these regions are related to the turbine operation, scheme layout and the resulting hydrodynamics at the regions of interest