Is it possible for magnets to effectively deter sharks?

Humans have devised numerous methods to prevent mosquitoes from biting, protect gardens from deer, and even stop bears from wrecking campsites. However, finding a reliable solution to ward off sharks has remained elusive.

Several companies have experimented with specialized sunscreens, chemical repellents, visual deterrents, and camouflage, but none have shown consistent success. Then, in 2005, researchers stumbled upon a surprisingly simple solution—something that caused sharks to flee as if escaping a fire.

At the Bimini Biological Research Station in the Bahamas, scientists Eric Stroud and Michael Hermann from SharkDefense conducted experiments where they placed a small magnet near a shark. The shark immediately reacted by swimming away. To test the strength of this repellent effect, the researchers induced tonic immobility in the sharks—a natural state of temporary paralysis that occurs when the fish are flipped upside down. Remarkably, the magnets provoked the sharks to break free from this state and swim away [source: Stroud].

What causes such a strong reaction? The combination of salt water and charged metals generates a faint electrical field. When a shark approaches this field, it appears to interfere with their unique sixth sense, known as electroreception. Sharks possess tiny pores around their snouts called ampullae of Lorenzini, which can detect even the slightest electrical changes in seawater—down to one-billionth of a volt. These electrical signals originate from the smallest muscle movements of other sea creatures—or humans—and are transmitted through the ions in salt water. For a deeper dive into electroreception, check out What is electroreception and how do sharks use it?.

Does this imply we should simply pack a few magnets in our beach bags and swim freely in shark-filled waters? Discover the answer on the following page.

Magnetic Response

How is salt water connected to electricity? Salt water is an ionic solution, meaning it contains particles with unpaired electrons. This property allows salt water to conduct electricity. When a charged magnet interacts with salt water, the ions move through the metal to stabilize, creating an electrical field. Sharks can detect changes in underwater electrical fields using their ampullae of Lorenzini. Encountering the stronger fields produced by magnets may overwhelm this sense, causing them to retreat.

However, this presents a significant challenge. Early tests showed that the magnetic field only repels sharks within a distance of about one foot (0.3 meters) [source: World Wildlife Fund]. This means individuals would require several magnets placed strategically across their bodies to ensure sufficient protection [source: Rajewski]. Additionally, the magnets must be positioned with their poles facing outward, as opposite poles attract each other [source: Rajewski]. The added weight and distribution of these metals could hinder swimming efficiency.

Another concern is the phenomenon of shark feeding frenzies. When sharks are extremely hungry, they might ignore the discomfort caused by an electrical field and continue their pursuit [source: Katayama].

Given these limitations, this innovative technology is likely to have a more significant impact on the commercial fishing industry than on individual swimmers or surfers. The World Conservation Union reports that 20 percent of shark species are nearing extinction [source: WWF], largely due to the millions of sharks accidentally caught by commercial fisheries annually.

To address this issue, the patent application suggests incorporating electropositive metals into pelagic fishing hooks and longlines to repel sharks from bait, thereby reducing accidental catches [source: Stroud]. This innovation earned SharkDefense the 2006 grand prize at the World Wildlife Fund's International Smart Gear Competition [source: WWF].

Currently, the National Oceanic and Atmospheric Administration, in collaboration with SharkDefense and other researchers, is conducting an in-depth study on this technology's potential. During the summer of 2008, they will test the effectiveness and reliability of the magnets in open ocean conditions. Ocean Magnetics, a subsidiary of SharkDefense, is also exploring the possibility of creating magnetic barriers to protect swimming areas from sharks.

What other methods have people attempted to deter sharks? Explore the history of shark repellents on the following page.

Other Shark Skullduggery

Interestingly, the development of shark repellents gained momentum in the United States during World War II. Before Julia Child became a famous chef, she assisted the U.S. Navy in developing a coating for underwater torpedoes to prevent sharks from accidentally triggering them [source: NPR]. The Navy also produced a chemical cake called "Shark Chaser" for pilots and sailors stranded in shark-filled waters. This early—and largely ineffective—repellent combined copper acetate with black dye, designed to mimic the scent of dead shark meat and disperse into an inky cloud when released [source: Eilperin].

Jump ahead to the 2000 Summer Olympics in Sydney, Australia. During the triathlon's swimming segment, divers equipped with Protective Oceanic Devices (PODs) patrolled the course to deter sharks. The POD, created by South Africa's Natal Sharks Board, generates a mild electrical field intended to disrupt a shark's electroreception, similar to the effect of magnets.

SeaChange Technology redesigned the POD into a compact device that can be worn around the ankles, known as Shark Shields. However, the Shark Shield website cautions surfers that movement may reduce the device's effectiveness.

Before discovering the magnetic repellent, Eric Stroud of SharkDefense was developing a shark deterrent using chemicals derived from decomposing shark flesh. Sharks avoid the remains of their own kind, inspiring Stroud to explore this as a potential repellent. Tests on the solution, named A2, proved successful [source: Eilperin]. However, it’s unlikely to hit retail stores soon. Instead, the company aims to provide it to lifeguards for emergency use, allowing them to disperse it in the water during a shark attack to create a safe zone for rescues [source: Eilperin].