Reprint of “A large scale field analysis examining the effect of magnetically-treated baits and barriers on teleost and elasmobranch behavior”

Abstract

Recent studies have demonstrated that elasmobranchs (i.e. sharks, skates and rays) are sensitive and often deterred by electrosensory stimuli (e.g. permanent magnets and electropositive metals). These studies have, however, produced mixed results; but due to the importance of reducing elasmobranch bycatch in fisheries and/or directed shark capture in beach nets, future research on electrosensory repellents is imperative. At the same time, understanding the potential influence of these materials on other marine animals is equally important so that the techniques may be selectively applied to achieve conservation goals while having little impact on non-target species. In the present study, both bait and barrier experiments were conducted in the Bahamas to assess how barium-ferrite (BaFe12O19) permanent magnets might influence teleost and elasmobranch behavior. For both the bait and barrier experiments, teleost species exhibited no significant associations between behavior and treatment type. Furthermore, elasmobranchs exhibited significant behavioral variation towards magnetically-treated baits, in comparison to baited controls and procedural controls. However, during the barrier experiment blacknose sharks (Carcharhinus acronotus) and southern stingrays (Dasyatis americana) exhibited no significant behavioral changes to magnetically-treated barrier regions, whereas Caribbean reef (Carcharhinus perezi) and nurse (Ginglymostoma cirratum) sharks did. This study is the first large-scale analysis of teleost behavior around magnetically-treated baits and barriers, and provides further support to the hypothesis suggesting that electrosensory repellents target and observably alter the behavior of aquatic organisms containing electroreceptors. In addition, the species-specificity of elasmobranch responses which occurred during the barrier experiment provides valuable information for future conservation engineering applications in fishing gears and beach nets.