Migratory passage structures at hydropower plants as potential physiological and behavioural selective agents

Area of Science:

• Ecology
• Fisheries Science
• Environmental Engineering

Background:

• Anthropogenic activities, particularly river dams, profoundly impact fish populations by altering habitats and impeding migration.
• Hydroelectric power plants implement mitigation measures, but their effectiveness varies, potentially leading to differential survival among fish.
• Fish migration routes are critical, with turbine passage posing a significant mortality risk compared to safe bypass routes.

Purpose of the Study:

• To quantify migration route choices of descending wild Atlantic salmon smolts at a hydroelectric plant.
• To assess the impact of bypass canal placement on fish guidance efficiency (FGE).
• To investigate the relationship between suboptimal mitigation measures and the induction of selection on salmon behavioral traits.

Main Methods:

• Utilizing passive integrated transponder (PIT)-tagged Atlantic salmon smolts released upstream of a hydroelectric plant.
• Quantifying migration route choices by monitoring fish passage through turbine tunnels and bypass routes.
• Manipulating water release from surface gates to alter proximity to turbine intakes and measuring resulting FGE.

Main Results:

• A small displacement of bypass canals (surface gates closer to turbine intake) increased fish usage from 1% to 34%.
• During periods of low FGE, two distinct smolt migratory strategies were observed: rapid turbine passage versus delayed forebay residence.
• Suboptimal mitigation measures at hydropower intakes appear to induce selection on salmon behavioral types.

Conclusions:

• Bypass canal placement is a critical factor in fish guidance efficiency at hydroelectric plants.
• Differential migration strategies suggest potential selection on salmon behavior due to suboptimal mitigation.
• Understanding these selection mechanisms is crucial for balancing turbine mortality risks with sea entrance timing and survival benefits.