Microprocessor-based prototype bycatch reduction device reduces bait consumption by spiny dogfish and sandbar shark

Elasmobranchs contribute heavily to bycatch in longline fisheries globally, and an effective method of deterring them from baited fishing gear is needed. Electrosensory stimulus holds promise as a method of disrupting elasmobranch close-range feeding responses as their electric sense guides their final strike during prey capture. We used laboratory experiments to test the hypothesis that weak electric stimuli generated by a prototype electronic bycatch reduction device (BRD) could deter sandbar shark (Carcharhinus plumbeus) and spiny dogfish (Squalus acanthias) from eating bait. Voltage gradients <1mVcm(-1) at the location of bait were produced by an Arduino microcontroller powered by a 9 V battery and attached to carbon electrodes. Median bait consumption by groups of juvenile sandbar shark declined by 74% when bait was located 10 cm vs. 2m from active electrodes. Spiny dogfish median bait consumption halved when bait was located 10 cm from active vs. inactive electrodes. Although laboratory studies often produce a larger effect for electrosensory shark deterrents than can be demonstrated during field trials, if the effects seen in our laboratory studies produced similar effects in the field, it could meet fishermen's requirements for a BRD.