Some pretty out-there ideas have been put forward to protect swimmers from sharks lurking in busy coastal waters. These have included drones to keep watch from above, wetsuits that ruin their appetite and even controversial culling programs. Now a new study is throwing further weight behind the slightly older idea of using electrical pulses to scare off would-be predators by overstimulating their senses, with a comprehensive study finding a device called Shark Shield can deter attacks 90 percent of the time.

The Shark Shield works by emitting low-frequency electrical fields from either an ankle bracelet, leg strap for scuba divers or a device fitted to the tail end of a surfboard. Two electrodes are integrated into the device and create a three-deminsional electronic field when submerged in water, designed to cause the animal's ultra-sensitive electro-receptive system to go into overdrive.

This causes sharks within a few meters to experience muscle spasms, severe discomfort and a sudden urge to get the hell out of there. The technology has actually been in development since the 1990s and the Shark Shield has been available as a commercial product for some time, but a new study carried out by the University of Western Australia has culminated in the most robust analysis of any such device thus far.

"Our study utilized stereo-camera technology to accurately determine the exact proximity that a white shark approached an active Shark Shield device," lead researcher Ryan Kempster explains to Gizmag. "Unlike the previous study of the Shark Shield that only estimated how close sharks approached, our study represents the most accurate assessment of any shark deterrent device to date."

Kempster and his team fixed the Shark Shield to a rig in the waters off South Africa and attracted sharks by attaching a bait-loaded canister. And attract the sharks it did, with the team recording a total of 322 encounters involving 41 individual white sharks varying in length, from two to four meters (6.56 to 13.1 ft).

The setup created a deterrent field with a radius of 1.3 m (4.26 ft) and stopped great white sharks from taking the bait 10 out of 10 times on their first approach. But the animals did become a little accustomed to the electrical pulses. This figure dropped to nine out of 10 on subsequent approaches and the field shrank by an average of 12 cm (4.72 in) each time the same shark approached.

"Although the effectiveness of the Shark Shield likely varies between 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 ocean users," says Kempster.

Questions have emerged over whether the Shark Shield device can actually attract sharks, rather than repel them. In 2008, an inquest into the death of a surfer heard that a female great white actually bit into the device. But across their comprehensive study the researchers say they found no evidence the Shark Shield has this effect, but warn that this does not mean similar devices will be equally successful.

"Thanks to this research, we now know the exact electric field characteristics that will deter a white shark, but the success of the Shark Shield does not imply that other electric devices on the market will also be effective," explains Kemp. "In fact, not only may other devices not be as effective, but there is also the possibility that some devices may in fact attract sharks. As a result, we feel it is important that robust, scientific and independent evaluation of all shark deterrent devices, many of which are entering the market presently, is carried out so that the public can make more informed decisions about how they can reduce their risk of a negative interaction with a shark."

This research was funded by the WA State Government and represents the most robust analysis of the effectiveness of any shark deterrent, including the Shark Shield.

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