Hey Shark Bait! Repellants Might Not Work

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Do a Google search on the technologies for keeping sharks away from humans and you’ll see loads of products. There’s a wetsuit striped to look like a poisonous animal, a device that generates an electric field and chemicals designed to repel sharks.

Unfortunately, not many shark repellants have been rigorously tested. Eric Stroud, senior chemist at Shark Defense, a company that makes and studies repellents, told DNews that before you buy, look up whether independent tests have been done. ” Any product that is not confirmed by at least three independent third parties (on video!) and scientific publications in their name would be suspicious to me,” he said.

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Take the striped wet suit. The suit is black-and-white striped to look conspicuous to a shark — they are colorblind —  and resemble animals sharks don’t eat. It’s a color strategy animals use in nature. Many poisonous or otherwise unpalatable creatures announce themselves with bold colors, and some non-poisonous ones try to imitate that.

The company that makes them, Shark Attack Mitigation Systems, has tested the suits on bait, not on people, and says they will continue testing to see how well the suits work in varied conditions. But the results so far haven’t been published in a peer-reviewed journal.

One researcher, Johann Mourier, who studies the behavioral ecology of sharks, said he was skeptical of the wet suit’s efficacy, due to the lack of replication of the tests. “I wouldn’t wear them,” he said.

Other people in the field think that banded patterns work — Walter Starck, an author of several books on coral reefs, says on his website that the pattern is effective, though it may only be for the kinds of smaller sharks found near reefs.

Scientists have tested some devices that generate a field that the sharks can sense and makes them less willing to approach. For example, a team from the South Australian Research and Development Institute tested the Shark Shield Freedom 7, a gadget that a diver or swimmer wears attached to the ankle. They published the results in the journal PLOS One.

In experiments, the researchers attached the Freedom 7 to both static bait and a towed decoy. In 116 trials, the scientists found that the static bait was still eaten, though it took the sharks — great whites, as it happens — longer to do it. The towed seal decoy, on the other hand, only attracted two sharks to the surface in 91 experimental runs with the device turned on. When it was turned off, out of 98 tows, a shark showed up at the surface 43 times.

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Then there are the chemicals. Stroud’s company makes “necronomes” — chemicals that mimic the signals given off when an animal dies. That will deter some species of shark,  but not all. The tests Shark Defense has conducted show that the chemical repellents work against bull shark species, but it hasn’t been tested against others.

Stroud noted that magnets seem to be effective in keeping sharks away from nets and swimming areas, and further tests are planned, but that doesn’t mean carrying a magnet will keep a shark from biting you.

It would probably do divers and swimmers well to remember the words of the PLOS study about risk reduction, it “is contextually specific and depends on the motivational state of sharks.”