Response of fish to electric fields: implications for guidance systems

Abstract

River infrastructure such as dams, weirs and hydropower facilities can reduce habitat connectivity and lead to direct mortality of fish species. Physical devices (e.g. screens or fish passes) designed to mitigate these negative impacts are not wholly effective and can be costly. Behavioural stimuli such as electric fields offer an alternative or enhancement to traditional physical devices. This thesis addresses the response of fish to electric fields through experimental studies conducted under both static and flowing water conditions. Assessing the response of European eel to electric fields has received limited attention. Threshold field strengths (i.e. electrosensitivity) of key physiological responses (twitch, loss of orientation and tetany) were quantified with respect to pulse frequency and width, for the critically endangered European eel (Anguilla anguilla) under static water conditions. Lower field strengths were required to elicit tetany under a higher pulse frequency and longer pulse widths. Research into eel guidance systems has largely focused on downstream migrating adult (silver-phase) using light and acoustics with mixed success. To gain insights into the potential effectiveness of electric fields for guidance, the behavioural responses of three life-stages of European eel (glass, yellow- and silver-phase) were assessed under flowing water conditions. All life-stages showed avoidance to electric fields, with largely more occurring under higher field strengths for juvenile (glass) eel. Avoidance in downstream migrating adults was reduced under a higher water velocity (1.0 ms-1 ) and yellow-phase eel were more likely to respond when travelling upstream. Evidence of any successful guidance by electric fields was only observed for upstream migrating juvenile (glass) eel and efficiency was improved under lower frequencies (2 Hz) and higher field strengths. Ensuring species selective guidance systems is the next challenge for fisheries management in areas where desirable and invasive species co-exist. A direct comparison of electrosensitivity between two known invasive cyprinids, grass carp (Ctenopharyngodon idella) and common carp (Cyprinus carpio), and adult eel was performed. Adult eel had a higher electrosensitivity than both cyprinids indicating the potential for electric fields to provide a species selective fish guidance system. The research presented in this thesis has advanced scientific knowledge of both fundamental physiological and behavioural responses of fish to electric fields with respect to parameters tested. This research will guide future work to optimise parameters of the electric field to translate avoidance behaviours more effectively into reliable guidance for fisheries management.

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Identifiers

ORCID for Paul Kemp: orcid.org/0000-0003-4470-0589

ORCID for Suleiman Sharkh: orcid.org/0000-0001-7335-8503

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