Behavioral Responses of Two Species of Sharks to Pulsed, Direct Current Electrical Fields: Testing a Potential Shark Deterrent
To describe and contrast the behavioral responses of two species of sharks to an electrical deterrent, sharks were baited to a food odor source within a strong pulsed, direct current electrical field. A head twitch behavior was elicited in scalloped hammerhead (Sphyrna lewini) and leopard sharks (Triakis semifasciata) at mean voltage gradient thresholds of 4.16 ± 0.59 V/m (X ± SD) and 4.30 ± 0.78 V/m, respectively, and did not differ significantly. A shimmy behavioral response was elicited in some hammerhead sharks at a mean threshold of 5.54 ± 1.55 V/m. A retreat behavioral response occurred in hammerhead and leopard sharks at a mean, maximum threshold of 18.50 ± 13.27 V/m and 9.64 ± 10.28 V/m, respectively. The hammerhead sharks retreated at significantly stronger field strengths than the leopard sharks, suggesting that some species may require stronger electrical fields for effective deterrence. Both species of shark remained significantly further away and spent less time near the food odor source when the electrical field was on versus off. The maximum voltage gradient threshold required to cause the sharks to retreat was much higher than previously reported, and the electrical field was not 100% effective at excluding sharks. The sharks only retreated after involuntary muscle contractions were induced by the electrical field.