Downstream Migration of Atlantic Salmon Smolts Through Fishpass Designed for Upstream Migration of Adult Spawners

Efficient fish migration is vital for anadromous species navigating between freshwater spawning/rearing habitats and oceanic feeding grounds. Mitigation measures past artificial barriers that secure two‐way fish migration at hydropower plants are complex, especially securing safe and efficient downstream migration to the ocean from freshwater. The primary efforts made have been to attract fish towards safe downstream bypasses with a diverse suite of guidance structures. However, comparatively less emphasis has been placed on a conveyance structure that ensures the safe and effective transport of fish further downstream. This study investigates if fishpass designed for upstream migration can function as an effective downstream conveyance structure. Two common fishpass types, vertical slot and pool and weir, were examined using PIT‐tagged wild Atlantic salmon smolts. Downstream progression through the vertical slot fishpass was significantly faster than through the pool and weir fishpass ( p < 0.001). The average progression rate was 3.4 m per hour or 0.0067 body lengths per second. Slower progression rates beyond passages may have ecological consequences. Delayed smolt migration could lead to predation risks, higher energy costs, and changes in migration patterns. To optimize smolt migration, alternative solutions such as pipes or channels should be considered, between the bypass entrance and the downstream facility.