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ESR prepress abstract   -  DOI:

Potential of electric fields to reduce bycatch of highly threatened sawfishes

K√°tya Abrantes*, Adam Barnett, Maarten Soetaert, Peter M. Kyne, Adrianne Laird, Lyle Squire, Jamie Seymour, Barbara E. Wueringer, Jessica Sleeman, Charlie Huveneers

*Corresponding author:

ABSTRACT: Sawfishes are among the most threatened families of marine fishes and are susceptible to incidental capture in net fisheries. Since bycatch reduction devices currently used in trawl fisheries are not effective at reducing sawfish catches, new methods to minimise sawfish bycatch are needed. Ideally, these should affect sawfish behaviour and prevent contact with the fishing gear. We tested the effects of electric fields on sawfish behaviour to assess the potential of electric pulses in mitigating sawfish bycatch. Experiments were conducted in a tank where two electrodes were suspended in the water column, connected to a pulse generator, and placed across the swimming path of sawfish. Two largetooth sawfish Pristis pristis were tested in control conditions, in the presence of a ‘Baseline’ pulse, and of five variations of that pulse where one parameter (polarity, voltage, frequency, pulse shape, pulse duration) was altered at the time. Conditional inference trees were used to identify the effects of various parameters (e.g. treatment, individual) on reaction type, reaction distance, twitching presence and duration, and inter-approach times. Sawfish reacted to electric fields but reaction distances were small (typically <1.2 m) and no field tested consistently led to reactions conducive to escaping from moving nets. The following parameters induced the most response in both individuals: bipolar current, rectangular shaped, 5–10 Hz, ~1500 μs duration, and 100 V. We recommend further research focusing on moving nets, testing a V-shaped electric array preceding the net mouth by at least 5 m, and testing a setup similar to electrotrawling.