The Effects of Permanent Magnets as an Elasmobranch-selective Repellent

The behavioral responses of southern stingrays (Dasyatis americana) and nurse sharks (Ginglymostoma cirratum) to permanent magnets were evaluated in the Florida Keys, USA. A baited magnetic treatment board consisting of two 15 x 10 x 5 cm grade-C8 barium-ferrite (empirically, BaFe12O19) permanent magnets and a baited procedural control board containing two smooth clay bricks were placed into shallow water to observe behavioral preferences. In the presence of permanent magnets, D. americana and G cirratum demonstrated a significantly greater number of avoidance behaviors towards the magnet side of the apparatus, while both species fed a significantly greater number of times from the procedural control side. That Dasyatis americana and Ginglymostoma cirratum were successfully repelled from baited areas containing magnets supports further investigation of the use of grade C8 barium-ferrite permanent magnets as a repellent to reduce elasmobranch bycatch or mortality during fishing operations