Analysis of permanent magnets as elasmobranch bycatch reduction devices in hook-and-line longline trials

The presence of permanent magnets on hook and line and inshore longline gear was tested for its ability to reduce the bycatch of sharks and rays.  Neodymium-iron-boron magnets were affixed to hook and line gear and barium-ferrite magnets were attached to longline gear.  Both types of fishing gear showed species specific responses but overall elasmobranch capture was significantly reduced when magnets were used. In the hook and line fishery catches of the Atlantic sharpnose shark (Rhizoprionodon terraenovae) and smooth dogfish (Mustelus canis) were both significantly reduced when magnets were used but catches of spiny dogfish (Squalus acanthias) and clearnose skate (Rostroraja eglanteria) were not.  Similarly, in the longline fishery, blacktip sharks (Carcharhinus limbatus) and southern stingray (Hypanus americanus) catch rates were reduced but sandbar shark (Carcharhinus plumbeus) catch rates were not when magnets were used. There were no differences in the catch rates of several fish species, including Atlantic croaker (Micropogonias undulatus), oyster toadfish (Opsanus tau), black sea bass (Centropristis striata) and bluefish (Pomatomus saltatrix) when magnets were used.