River‐Scale Evaluation of a Floating LED Light Array for Behavioral Guidance of American Eel

Exploiting the sensory physiology of migratory fishes to guide them away from hazards like hydroelectric turbines is of interest to regulatory agencies and hydropower operators to achieve conservation and management goals. Here we describe a river‐scale experiment where out‐migrating adult American eel ( Anguilla rostrata ) were tracked downstream via acoustic telemetry as they encountered a 216 m long floating LED light array on the St. Lawrence River. Eel ( N = 51) spatial responses to light were compared to eels detected on control (no light) nights with the expectation that light would cause eels to deflect laterally along the light array toward the river‐right shore. Eels generally swam near the surface at night, and 39.5% of eels that encountered the light altered their downstream trajectories consistent with lateral deflection, although those responses were relatively modest. However, 76.7% of eels demonstrated diving responses of ≥ 4 m, consistent with seeking darker passage under the light field. Although we observed some degree of light avoidance, additional research is needed to optimize use of light for effective behavioral guidance in large rivers.