Many species of elasmobranchs (sharks and rays) are incidentally caught in pelagic longline fisheries. Sometimes shark bycatch exceeds the amount of target fish that is caught (e.g. tuna).
An array of recent studies have shown that some species of sharks have an aversion resonse to certain electromagnetic metals, alloys, and strong magnets. This is a presumed result of an overstimulation of the sensitive electroreceptors present in elasmobranchs. Past and present studies sponsored by the Consortium have investigated several different metallic elements to evaluate their potential as reliable (i.e. consistent, practical) shark repellent devices for fishing gear.
Previous studies have examined the reactions of captive spiny piked dogfish (Squalus acanthias) and dusky smoothhound (a.k.a. smooth dogfish) (Mustelus canis) sharks to two metals - a lanthanide/cerium alloy (mischmetal) and a rare-earth magnet (neodymium-iron-boride).
The data collected from these studies suggest that the repellent effects of each metal vary from one shark species to another. The spiny dogfish were more averse to the mischmetal, while the smooth dogfish were more deterred by the magnet. However, both species were more likey to ignore the repellents if they were hungry. Overall, electronic mischmetal would not be an effective and/or practical deterrent to interactions between fishing gears and these species.
Researchers at Florida Atlantic University (FAU) tested the efficacy of various lanthanide elements and their alloys as potential shark repellents. First, the metals were examined for output voltage (uVolts/gram), dissolution rate, machinability, and cost to determine which to use for furher testing. Based on these criteria, the lanthanide element, neodymium (Nd) was selected for use in behavioral trials with sharks.
The behavioral trials were conducted by FAU and NEAq on lemon sharks (Negaprion brevirostris) and bonnethead sharks (Sphyrna tiburo). These species represent two families (Carcharhinidae and Sphyrnidae, respectively). At the same time, additional trials were conduced on the spiny dogfish and the smooth dogfish. Preliminary results suggest that Nd is effective for deterring individual bonnethead and smooth dogfish sharks and groups of spiny dogfish. However, it was an ineffective deterrent when presented to groups of lemon sharks, bonnethead sharks, and smooth dogfish.
