There has been a rapid increase in development of small-scale hydropower schemes across Europe. Such schemes may impact migratory fish populations through modification of migration pathways. There is a clear need for scientific evidence to inform guidelines for design, placement and management of small-scale hydropower schemes for protection of migratory fish. The proliferation of Archimedean screw turbines (AST) for such low-head applications is concerning because although these turbines are purported to cause negligible damage to fish passing through them, available data is limited.

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 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. The proportion of radio tagged fish passing through the turbine was 27%. 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 schemes with distinctive designs and operational regimes. A mixture of fine-scale radio detection zones and PIT antennas were used to investigate attraction to competing flows at each turbine and fish pass or depleted stretch outflows, and the efficiency and efficacy of the fish pass. Behaviours are related to turbine operation, scheme layout and resulting hydrodynamics at the regions of interest.