Testing the effectiveness of an electrosensory deterrent on spiny dogfish (Squalus acanthias) through laboratory experiments

Baited-hook fisheries negatively affect shark and ray populations due to bycatch, the unintentional capture of non-target species. Research focused on repelling technology to mitigate shark bycatch predominantly explores the use of magnetic fields and biomimicry to deter sharks by interfering with their electroreception, olfactory, or visual systems. We examined the effectiveness of three electronic bycatch reduction devices (BRDs) with different signal frequencies and duty cycles (fraction of time an electrical signal is active) through controlled laboratory tank experiments on Atlantic spiny dogfish ( Squalus acanthias ). Randomly selected pairs of spiny dogfish were exposed to either a BRD emitting electrical pulses or an inactive control. Over the course of six minutes, bait consumption, time to eat, and number of bites were recorded. A total of 173 active and 151 inactive trials with 31 wild spiny dogfish were tested. Results suggest that time-varying electrical signals deter spiny dogfish from baited hooks. We observed a reduction in bait consumption, mean bite rate, and probability of bait consumption from all three prototypes (100% duty cycle fixed signal = 32.8%, 50% duty cycle fixed signal = 30.1%, 100% duty cycle quasi-random signal = 50.8%). The lowest bait consumption occurred with the 100% duty cycle, fixed-signal BRD, while the largest treatment differences resulted from the BRD with 100% duty cycle emitting a quasi-random frequency. We surmise that higher duty cycles, where the "on" time is longer within a given period, leads to higher average effectiveness and a more sustained deterrent effect with respect to the study's limitations.