Can wearing magnets really repel sharks?

Shark Magnet Stephen Frink/Oxford Scientific/Getty Images

Through various concoctions and customs, humans have found ways to keep mosquitoes from biting, deer from destroying gardens and even bears from tearing campsites into pieces. But we have yet to create a surefire safeguard against sharks.

­Various companies have tried out specialized sunscreens, chemical sprays, visual tricks and disguises, with little documented success. Then, in 2005, scientists accidently discovered something far simpler -- something that sent sharks swimming away from it like people running from a burning building.


During experiments at the Bimini Biological Research Station in the Bahamas, researchers Eric Stroud and Michael Hermann, with the company SharkDefense, dropped a small magnet in the water beside a shark. The presence of the magnet elicited a distinct reaction from the fish -- they darted away from it. To determine the strength of this repugnant force, Stroud and Herrmann held sharks on their backs, inducing a condition called tonic immobility, or a temporary paralysis that naturally occurs when the fish lay in that position. Sure enough, the magnets jolted the sharks into action [source: Stroud].

Why the intense reaction? The interaction of salt water and charged metals produces a weak electrical field. When a shark comes close to that field, the field seems to disrupt the sharks' special sixth sense, electroreception. Many shark species have pores dotted around their snouts called ampullae of Lorenzini that detect minute changes of electricity in the seawater, up to one-billionth of a volt. These electrical impulses come from the tiniest muscle contractions of other aquatic life forms -- or people -- and are carried through the ions in the salt water. For more detailed information on electroreception, read What is electroreception and how do sharks use it?.

Does this mean that we should toss a couple of magnets in our beach bags and splash away with nary a care in shark-infested oceans? Find out the answer on the next page.


Magnetic Response

Hungry sharks may power through an uncomfortable electrical field. See more shark pictures.
Getty Images

What does salt water have to do with electricity? Salt water is an ionic solution, meaning it contains particles with unpaired electrons. Because of this quality, salt water can also act as an electrical conductor. When a charged magnet comes into contact with salt water, the ions flow through the metal to become stabilized, resulting in the electrical field. We know that sharks can sense shifts in the surrounding underwater electrical fields through their ampullae of Lorenzini. Running into these stronger electric fields caused by magnets may overwhelm the sense and send them swimming in the opposite direction.

Yet, therein lies the problem. Initial testing revealed that the magnetic field only deters sharks up to around a foot (0.3 meters) away [source: World Wildlife Fund]. If this is the case, people would need multiple magnets scattered across their bodies for adequate security [source: Rajewski]. Also, you have to arrange the magnets with their poles facing outward because opposite poles attract [source: Rajewski]. The distribution and weight of the additional metals could make it difficult to swim.


Then there's the question of the shark feeding frenzy. When sharks are hungry enough, they may continue to pursue something in spite of an uncomfortable electrical field [source: Katayama].

Because of these potential pitfalls, this new technology will probably make a greater impact on the commercial fishing industry rather than on swimmers and surfers. According to the World Conservation Union, 20 percent of sharks are on the brink of extinction [source: WWF]. Much of this problem stems from the millions of sharks commercial fisheries accidentally hook and net each year.

To alleviate this problem, the patent application also proposes using the electropositive metals on pelagic fishing hooks and long lines to divert sharks from the bait, reducing the number unintentionally caught [source: Stroud]. This idea earned SharkDefense the 2006 grand prize from the World Wildlife Fund's International Smart Gear Competition [source: WWF].

Now, the National Oceanic and Atmospheric Administration is conducting a more detailed study on the potential of this technology, together with SharkDefense and other researchers. During the summer of 2008, it will test the magnets' deterrent strength and consistency in open ocean waters. Ocean Magnetics, an offshoot company of SharkDefense, also is looking into the feasibility of magnetic fences that could be installed around swimming areas to keep sharks out.

What else have people tried to use to keep sharks away? Read about the history of shark repellents on the next page.


Other Shark Skullduggery

A diver tries on an electronic shark repellent unit, which sends out an electrical field in the water to repel sharks.
SeaChange Technology/Getty Images

Interestingly, shark repellent development began in earnest in the United States during World War II. Before Julia Child attained celebrity chef status, she helped the U.S. Navy come up with a recipe for a substance to coat its underwater torpedoes that would halt sharks from bumping into them and setting them off prematurely [source: NPR]. The military branch also created a chemical cake, "Shark Chaser," for pilots and sailors in case they ended up in shark-infested seas. The rudimentary -- and ineffective -- repellent consisted of copper acetate and black dye scented like dead shark meat that spread into an inky cloud when released in the water [source: Eilperin].

­Fast forward to the 2000 Summer Olympics in Sydney, Australia. During the swimming portion of the triathlon, divers wearing gadgets called Protective Oceanic Devices (PODs) bordered the route to ward off any sharks. South Africa's Natal Sharks Board invented the POD that generates a weak electrical field aimed at overwhelming a shark's electroreception sense, much like the magnet effect.


A company called SeaChange Technology repackaged the POD into a smaller compartment that people can strap around their ankles, called Shark Shields. The Shark Shield Web site does warn surfers that motion can upset the effectiveness of the technology.

Before stumbling on the magnet discovery, Eric Stroud of SharkDefense was working on a shark repellent made from chemicals extracted from the flesh of rotting sharks. Sharks are known to stay away from the rotting corpses of their brethren, so Stroud took that as a cue to research it as a possible repellent. Testing the solution referred to as A2, it had the desired effect [source: Eilperin]. But you probably won't see it on drugstore shelves anytime soon. Instead, the company wants to make it for lifeguards to toss in the water in the case of a shark attack to clear the area for a rescue [source: Eilperin].

To learn more about sharks and related information, dive into the links on the next page.


Lots More Information

Related HowStuffWorks Articles:

More Great Links:


  • Clausen, Lisa. "How to Switch Off Sharks." Time South Pacific. April 8, 2002.
  • Eilperin, Juliet. "Repellent Could Save Humans and Sharks, Too." The Washington Post. Aug. 8, 2005. (June 9, 2008) /AR2005080700593.html
  • Graber, Cynthia. "Fishing Lines That Repel Sharks." Scientific American Podcast. May 2, 2008. (June 9, 2008)
  • Katayama, Lisa. "Mixed Signals." Popular Science. July 2008.
  • Moskowitz, Clara. "Electric Signals Could Ward Off Sharks." LiveScience. May 6, 2008. (June 9, 2008)
  • Page, Michael Le. "Shark shifter." New Scientist. Feb. 26, 2005.
  • Rajewski, Genevieve. "Geeky Rare-Earth Magnets Repel Sharks." Wired Magazine. May 15, 2007. (June 9, 2008)
  • SharkDefense. "Magnetics." (June 9, 2008)
  • Stroud, Eric. "Elasmobranch-Repelling Electropositive Metals and Methods of Use." United States 11/800,545. Nov. 8, 2007. (June 9, 2008) 4&dq=shark+repellent#PPA1,M1