Do elasmobranch reactions to magnetic fields in watershow promise for bycatch mitigation?

摘要

Elasmobranchs are under increasing pressure from targeted fisheries worldwide, but unregulated bycatch isperhaps their greatest threat. This study tested five elasmobranch bycatch species (Sphyrna lewini, Carcharhinus tilstoni,Carcharhinus amblyrhynchos, Rhizoprionodon acutus, Glyphis glyphis) and one targeted teleost species (Lates calcarifer)to determine whether magnetic fields caused a reaction response and/or change in spatial use of an experimental arena. Allelasmobranch species reacted to magnets at distances between 0.26 and 0.58 m at magnetic strengths between 25 and 234gauss and avoided the area around the magnets. Contrastingly, the teleosts showed no reaction response and congregatedaround the magnets. The different reactions of the teleosts and elasmobranchs are presumably driven by the presenceof ampullae of Lorenzini in the elasmobranchs; different reaction distances between elasmobranch species appeared tocorrelate with their feeding ecology. Elasmobranchs with a higher reliance on the electroreceptive sense to locate preyreacted to the magnets at the greatest distance, except G. glyphis. Notably, this is the only elasmobranch species tested witha fresh- and saltwater phase in their ecology, which may account for the decreased magnetic sensitivity. The applicationof magnets worldwide to mitigate the bycatch of elasmobranchs appears promising based on these results.