Ferrite magnets do not deter blue sharks (Prionace glauca) from bait strikes in behavioural trials

Blue sharks ( Prionace glauca ) are the most-commonly caught species of shark globally with evidence of decreasing populations. Sensory deterrents, inducing weak electromagnetic fields, have been used to deter sharks from fishing gear, while maintaining target catch quality and quantity. Here, we conducted trials on the efficacy of ferrite magnets as a deterrent on blue sharks off the southwest coast of the UK. We tested behavioural responses of blue sharks to ferrite magnets in a field experiment comparing simulated fishing lines (hooks removed) with and without magnets. There was no statistically significant difference in bait choices between the control (n = 14) and magnet (n = 12) lines. Time to strike, number of prior interactions, number of sharks present or number of people in the water did not influence bait choice in the trials. Our study adds to conflicting findings on electrosensory deterrents' effectiveness on shark species. Ferrite magnets, with fixed magnetic fields, are currently not suitable for widespread implementation in fisheries and alternative strategies should be explored to reduce shark mortality. • Blue sharks showed no deterrent response to ferrite magnets in field trials. • Bait choice was unaffected by shark number, time to strike, or prior interactions. • Findings add to inconsistent results on electrosensory deterrents in sharks.