Using LED lighting on the bottom of surfboards or kayaks can deter great white shark attacks, new research suggests.
In an Australian-led study using seal-shaped lures, bottom lighting disrupted the ability of great whites to see silhouettes against the sunlight above, reducing the rate at which the sharks followed and attacked the artificial prey. The brighter the lights, the more effective the deterrent.
The study’s lead author, Dr Laura Ryan of Macquarie University in Sydney, said white sharks appeared to rely on the visual cues of a dark object silhouetted against a lighter background.
“If you flip it to a light object on a dark background, it doesn’t seem like it’s something they recognize as prey,” she said.
Ryan’s previous research on great whites suggests that attacks on humans a case of mistaken identity. The animal has a much lower visual acuity – the ability to see shapes and details – than humans.
Her work suggested that juvenile great white sharks, from below, are unlikely to clearly distinguish seals from swimmers or people surfing.
Other research has shown that sharks are color blind or at best have only limited color perception abilities.
The new study, which was conducted in Mossel Bay, South Africainvolved in towing lures behind a boat for tens of hours.
The researchers initially found success by completely covering the underside of the lure in lights. “But if you’re actually going to come up with something to protect people, [entirely] covering a surfboard … is just not practical because it’s a huge amount of lighting, which requires a huge amount of battery power,” Ryan said.
The researchers experimented with more sparse lighting options and found that horizontal stripes of LED lights had a similar deterrent effect. “When you do horizontal stripes, the silhouette [appears] wider than it is long, so it’s less like a seal,” Ryan said.
However, longitudinal strips of light were not effective, nor were strobe lights, which gave the sharks fleeting glimpses of the lure silhouette. “Interestingly, just that little glimpse of the whole silhouette was enough for the white sharks to start biting the lures,” Ryan said.
The scientists towed the seal lure to encourage the white sharks to breach – a form of hunting that involves rapid acceleration to the surface to catch prey. They say more research is needed on shark behavior with static lures, which would resemble surfers waiting to catch a wave rather than actively paddling.
The team tests a surfboard prototype with equipped lighting. “Surfers can be a little picky with their surfboards,” Ryan said. “As a surfer, I want it to be usable.”
worldwide, most shark bites is associated with people who surf or participate in other board sports. Fatal shark bites, although rare, are mostly due to great whites.
The study, published in the journal Current Biologynoted that it would be important to test whether lighting was also effective in deterring other species that attack humans, including bull sharks and tiger sharks, as they have different predation behaviors.
