Behavioural response of downstream migrating European eel (Anguilla anguilla) to electric fields under static and flowing water conditions

Like many other species of diadromous fish, the European eel (Anguilla anguilla) is threatened by entrainment at hydropower intakes and resultant injury and mortality during passage through turbines. Historically, physical screens have been installed to prevent European eel access to intakes but these are not wholly effective and can incur high costs of construction and maintenance, especially when regulations require screen retrofits with increasingly fine mesh. There is interest in the use of potentially less expensive behavioural guidance methods to block or guide eel movements. Electric barriers have been developed to guide several species of fish, but information relating to their effectiveness for European eel is limited. In this study, two experiments were conducted to quantify the response of downstream migrating adult (silver-phase) European eel to electric fields and the effectiveness of electricity to block movements. First, a static water tank was used to identify the field strengths (Vcm- 1) required to induce threshold responses for three key behaviours (twitch, loss of orientation and tetany) across three different pulsed direct current (PDC) electric waveforms (single pulse-2 Hz, double pulse-2 Hz and single pulse-10 Hz) (Experiment 1). Second, a recirculatory flume was used to investigate how avoidance responses (acceleration, change in orientation and rejection) differed between two water velocity regimes [0.5 ms-1 and 1.0 ms-1] and two field strengths [approximate to 0.15 Vcm- 1 and approximate to 0.3 Vcm- 1] identified during the first experiment (Experiment 2). In Experiment 1, lower electric field strengths were needed to elicit tetany under the single pulse10 Hz and single pulse-2 Hz compared to the double pulse-2 Hz waveform, but there was no effect of waveform for the other behaviours. In Experiment 2, avoidance was less frequent (31.4%) under the high compared with the low (74.5%) velocity, but electric field strength did not influence the response exhibited. This study provides insights into the potential use of electric fields to deter European eel. The effectiveness of electric barriers to block downstream migrating eel are likely limited at higher water velocities.

Automated summary

This study conducted two experiments to quantify the response of downstream migrating adult European eel to electric fields and the effectiveness of electricity to block movements. The results suggest that the effectiveness of electric barriers to block downstream migrating European eel is likely limited at higher water velocities.