Responses of the southern stingray (Dasyatis americana) and the nurse shark (Ginglymostoma cirratum) to permanent magnets

Abstract

The behavioral responses of free-swimming, wild southern stingrays (Dasyatis americana) and nurse sharks (Ginglymostoma cirratum) to permanent magnets were evaluated in the Florida Keys, USA. Animals were attracted to a baited magnetic treatment board consisting of two 15 cm × 10 cm × 5 cm grade C8 Barium-Ferrite (empirically, BaFe₁₂O₁₉) permanent magnets producing a flux of 950 gauss at their surface and a baited procedural control board containing two smooth nonmagnetized clay bricks. In the presence of permanent magnets, D. americana and G. cirratum demonstrated a significantly greater number of avoidance behaviors away from the magnet side of the apparatus, while both species fed a significantly greater number of times from the non-magnetized procedural control side. Thus, D. americana and G. cirratum showed sensitivity to a magnetic field and were successfully repelled from baited areas containing magnets. The results from the current study suggest that the use of grade C8 Barium-Ferrite permanent magnets as an avoidance mechanism (e.g., repellent) to reduce elasmobranch mortalities associated with fishing operations and beach nets merits further investigation.

Keywords:

• elasmobranchs
• behavior
• permanent magnets
• avoidance
• Barium-Ferrite
• repellent
• bycatch
• southern stingrays
• nurse sharks

Acknowledgments

We would like to thank the PADI Foundation, the Slocum-Lunz Foundation, the National Science Foundation GK-12 Program, and Coastal Carolina University for providing funding to allow us to conduct and complete this study. We thank Dr Keith Walters for his assistance in statistical design and implementation and Dr Sharon Gilman for reviewing the manuscript. We would like to thank Dr Samuel Gruber and the staff at the Bimini Biological Field Station for allowing us to use their facilities and conduct countless preliminary experiments using permanent magnets. Also, we would like to thank SeaSquared Charters and Main Attraction Charters from Marathon, Florida, for donations of bait. Lastly, a special thanks to George Mizzell from Engineered Concepts (Birmingham, Alabama), who provided his expertise and the magnets that were used in this experiment.