Do Shark Repellents Work?
Electric fields can be masked or cranked up. Science answers which works best.
Scientists have been trying to figure out how to keep sharks at a distance from swimmers, divers and surfers since World War II, when Navy pilots were issued a chemical dye laced with copper called "shark chaser" in their survival kits. It worked, for a while, but the dye soon dissipated, and sharks aren't known to give up easily when faced with a decent meal.
In the 1970s, marine biologists thought that striped wetsuits might confuse sharks, making a person wearing one appear to be a giant sea snake. It seemed like a good idea, according to Stephen Kajiura, a shark biologist at Florida Atlantic University, until someone found that tiger sharks often ate sea snakes.
"That idea was fundamentally flawed," Kajiura said.
Next came a wetsuit that looked like a giant orca, which is a predator of some shark species. That didn't work so well either.
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Now, with the ability to embed microelectronics into various fabrics, some companies are promoting shark-repellent suits or other devices. While the odds of getting attacked by a shark are slim-to-none for most of us, people who spend more time in the water, such as commercial divers, might be at slightly greater risk.
One New Zealand company, HECS Aquatics, says it has designed a wetsuit that acts as an underwater Faraday Cage, a device that blocks electric fields from the person inside.
The concept is that sharks won't be able to detect the small electric field generated by human muscles and therefore won't think someone in the water is either predator or prey.
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But Kajiura notes a couple of problems with this concept. One is that our weak electric field comes out through the openings in our bodies, such as eyes, nose and mouth. Covering up the rest of the body might not really work – unless you are completely covered up, say in a tiny sub. But then you wouldn't need the wetsuit.
The second problem, said Kajiura, who is an expert in shark sensory apparatus, is that a human's electric field is too low for sharks to detect.
"The shark has to be very close to you to be able to even detect it," Kajiura said. "Less than a meter. There's no need to reduce the electric component of your presence. At that point, you're going to already be chomped on."
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Kajiura is skeptical of the Faraday-inspired wetsuit. He says a better idea is to understand the shark's behavior -- whether there is a lot of bait fish or other food in the water that sharks might like -- and then avoid the area.
"If you are in with lots of bait activity, then you are putting yourself in trouble," said Kajiura, who swims with sharks every year for various research projects. "If you are in a calm situation, you will do fine. We don't use any protective gear. There are a lot of people out there who are real daredevils. That is on them."
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If trying to block your electric signal doesn't work, perhaps doing the opposite thing might do the trick. That's the theory behind the Shark Shield, a device that tries to repel sharks with an electric field. Australian researchers gave it a try in a study and found that some sharks don't like it.
"We concluded that the device produced an effective deterrent field on average of 1.3 meters [4.3 feet] from the device's electrodes, which was sufficient to prevent all white sharks (Carcharodon carcharias) from interacting with static bait on their first approach," said Ryan Kempster, a shark biologist at the University of Western Australia and founder of the group "Support Our Sharks."
Kempster's study was published this month in the journal PLOS One "Although the effectiveness of the Shark Shield likely varies between [shark] species, the fact that white sharks are implicated in the majority of fatal incidents globally suggests that a deterrent that effectively deters this species should be an important safety consideration for a range of ocean users," Kempster said in an email to Discovery News.
Both Kajiura and Kempster say that shark attacks on humans are extremely rare, and that sharks are in greater danger from human attacks on them.