Some species of elasmobranch (sharks, skates and ray) are deterred by certain permanent magnets and electropositive rare earth metals (EPREM), due to the highly sensitive electroreceptors in their noses, which are able to detect Earth’s magnetic field. Permanent magnets create their own magnetic fields, whilst EPREM create such fields when reacting to seawater, both of which are detectable by most elasmobranchs.
Studies have incorporated magnets and metals into longlines and gill nets, either directly into the hooks or added to lines as metal discs, and onto the ropes of pots and traps. A study in an ocean fish trap fishery targeting snapper in New South Wales, Australia indicated the addition of permanent magnets to traps reduced elasmobranch bycatch by over a third.
Overall, results vary, and studies highlight that elasmobranchs’ responses to magnets and metals depend on the specific species. Further large scale studies are required, and metals and magnets are not currently proven as an effective elasmobranch bycatch mitigation technique. Furthermore, there are concerns over the possibility of sensory habituation to magnetic fields with longlines, as this gear is soaked for long intervals.
This page was last updated on 12.02.21.
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