Scared of sharks? Fitting an electric device to your surfboard could halve your risk of getting munched.
Shark attacks are rare but increasingly common, climbing from about 20 to 80 global cases per year over the last three decades. This has prompted the development of many shark repellent products for surfers, but few have been rigorously and independently evaluated.
Charlie Huveneers at Flinders University in Australia and his colleagues decided to put five of the most popular shark deterring products to the test. These included two devices that create electric fields, two that create magnetic fields, and a smelly surfboard wax.
Each was attached to a surfboard sitting 30 kilometres off the coast of South Australia. A piece of tuna bait was dangled below the board to mimic a surfer’s foot, and an underwater camera recorded any shark interactions. A total of 50 trials were conducted per product.
Four of the products had no significant effect. But an electric device made by Australian company Ocean Guardian halved the number of shark attacks on the bait.
The device attaches to the tail of the board and is designed to create a strong electric field. The aim is to overwhelm the sensory receptors that sharks use to detect weak electric signals of their prey, says Huveneers.
Although it didn’t eliminate shark attacks entirely, it may work better in real-life contexts, says Huveneers. The testing was done in relatively shark-infested waters, and the tuna was probably more enticing to sharks than human flesh because it is part of their natural diet, he says.
The other electric field device in the tests didn’t seem to have much effect. This could be because it emits a different type of electric pulse, says Huveneers.
Two of the products tested – a bracelet and a leg rope – were magnet-based. Sharks can also detect fields produced by magnets, so these are also meant to overwhelm their senses, says Huveneers. It’s possible that the magnets are not strong enough to repel sharks, he says.
The last product was a surfboard wax containing smelly substances like citronella, tea tree oil, cayenne pepper and cloves designed to mask the odour of surfers’ flesh. But it may not be quite pungent enough, says Huveneers.
“I think that overall, there’s probably never going to be one silver bullet that stops all shark attacks,” he says. “That’s why we need to keep doing research on all possible mitigation strategies.”
First published in New Scientist on 31 May 2018.