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].
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