Electropositive shark repellent

Electropositive metals (EPMs) are a new class of shark repellent materials that produce a measurable voltage when immersed in an electrolyte such as seawater. The voltages produced are as high as 1.75 VDC in seawater. It is hypothesized that this voltage overwhelms the ampullary organ in sharks, producing a repellent action. Since bony fish lack the ampullary organ, the repellent is selective to sharks and rays. The process is electrochemical, so no external power input is required. As chemical work is done, the metal is lost in the form of corrosion. Depending on the alloy or metal utilized and its thickness, the electropositive repellent effect lasts up to 48 hours. The reaction of the electropositive metal in seawater produces hydrogen gas bubbles and an insoluble nontoxic hydroxide as a precipitate which settles downward in the water column.

SharkDefense made the discovery of electrochemical shark repellent effects on May 1, 2006 at South Bimini, Bahamas at the Bimini Biological Field Station. An electropositive metal, which was a component of a permanent magnet, was chosen as an experimental control for a tonic immobility experiment by Eric Stroud using a juvenile lemon shark (Negaprion brevirostris). It was anticipated that this metal would produce no effect, since it was not ferromagnetic. However, a violent rousing response was observed when the metal was brought within 50 cm of the shark’s nose. The experiment was repeated with three other juvenile lemon sharks and two other juvenile nurse sharks (Ginglymostoma cirratum), and care was taken to eliminate all stray metal objects in the testing site. Patrick Rice, Michael Herrmann, and Eric Stroud were present at this first trial. Mike Rowe, from Discovery Channel’s Dirty Jobs series, subsequently witnessed and participated in a test using an electropositive metal within 24 hours after the discovery.

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