Effectiveness of a Strobing Light System for Deflecting Downstream Migrating European Silver Eels (Anguilla anguilla)

Abstract

Anthropogenic structures, such as dams, delay, injure and kill during downstream migrating silver-phase Anguillid eels. To enhance spawner escapement from rivers, efforts are being made to develop devices that guide eels towards safe passage routes. We tested the ability of a strobing light array to deflect downstream migrating European silver eels (Anguilla anguilla) by comparing the distribution of eel catches in a series of nets when lights were on (treatment periods) and off (control periods). Deflection efficiency of the light array was 80.6% (95% CL = 74.3%–85.3%), estimated by comparing the proportion of the total biomass captured in nets located immediately downstream of the light array during control and treatment periods. Eels caught during treatment periods (Mean ± S.E.; 452 ± 11 mm) were significantly smaller than those caught during control periods (538 ± 8 mm), which suggested that smaller eels were less capable of avoiding the light array. Future research should determine specifications for operation of strobe light arrays, including effects of light intensity and strobe rate, angle of array deployment, and effects of environmental factors on deflection efficiency.