The impact of a small hydropower scheme on the migratory behaviour of sea trout (Salmo trutta L.) smolts in the River Frome, southern England

Abstract

The migratory behaviour of emigrating sea trout (Salmo trutta) smolts was monitored in relation to a small low head hydropower scheme on the River Frome, southern England. The majority of the smolts, tagged with miniature acoustic transmitters bypassed the hydropower scheme with only 2.4% of the fish moving downstream through the turbine. No mortalities were recorded in the fish passing through the turbine; but their physical condition is not known. Movement of the smolts was nocturnal within freshwater and occurred during elevated river flows. There was no apparent delay in the movement of the smolts at the turbine intake or at the adjacent weir. Migration of all smolts through the estuary of the River Frome was nocturnal and migration into the sea occurred at all states of the tide. Survival of the sea trout smolts was high during the transition from the fresh to the marine environments.