Movement and Habitat Shift Responses of Juvenile Atlantic Salmon (Salmo salar) to Annually Permanent Stream Flooding.

Reservoir formation in a river system changes a lotic environment to more lacustrine conditions with impacts throughout the ecosystem. In this study, a river reach containing typical salmonid riffle/run habitat was flooded to create a large, deep pool from June to September in each of three years. We test the hypothesis that juvenile Atlantic salmon (Salmo salar) with their preference for run/riffle habitats will respond to the transformation to a lentic environment by moving into adjacent lotic environments. Movements of juvenile Atlantic salmon were monitored using a combination of biotelemetry (radio- and Passive Integrated Transponder [PIT]-tagging) and electrofishing. Results showed that no tracked fish moved away from the created pool habitat. Mass-specific growth rates showed the created pool habitat resulted in net growth of juveniles. The results confirm that fish may not immediately (i.e., at least for an approx. two months) respond to rapid, large-scale habitat alterations by moving to find similar habitat conditions outside the altered habitat. This is most probably related to plasticity of behaviour and habitat use, and no change in biological conditions to a point that would negatively impact fish growth and survival, e.g., food availability, competition, or predation. The results also support the hypothesis that the relative importance of physical habitat variables is not universal among streams and populations, and therefore, limiting the value of applying standard habitat suitability criteria and use. This article is protected by copyright. All rights reserved.