(Adnkronos) – The use of LED lights on surfboards or kayaks helps to counteract white shark attacks: according to a study, the lighting disrupts the ability of the largest predatory fish in existence to identify the silhouettes of prey on the surface against the light. This was the conclusion reached by Dr. Laura Ryan of Macquarie University in Sydney, who used seal-shaped decoys for her study, and found that more lights applied to the underside of the dummy decoy acted as a deterrent, and the stronger they were, the better they worked.
The white shark – she concluded – seems to rely on the visual perception of a dark object that stands out against a lighter background. “If it becomes a light object on a dark background, it doesn’t seem recognizable as prey.” Ryan’s previous research on white sharks suggests that attacks on humans could be the result of a mistake. The animal has a much lower ability to identify shapes and details visually than humans do. Her work shows that young white sharks are unlikely to be able to distinguish prey from swimmers or people paddling on surfboards. Other research – writes the Guardian – has also shown that sharks have an inability to perceive colors, entirely or in part.
The new study, conducted in Mossel Bay, South Africa, used decoys that were towed behind boats for tens of hours. The first phase of the experiment involved completely covering the underside of the decoy with lights. “But it’s not practical, because it’s a huge amount of lights, which have to be powered,” Ryan explains.”The researchers then experimented with simpler lighting options, discovering that horizontal strips of LED lights had a similar deterrent effect, partly because the silhouette appears wider than it is long, and therefore less like that of a seal. (continued)
Longitudinal light strips, on the other hand, were not effective, nor were strobe lights, which allowed sharks to glimpse the silhouette of the decoy at times. “Interestingly, just that brief glimpse of the entire silhouette was enough for white sharks to begin biting the decoys,” Ryan explained.
Scientists towed the seal decoy by encouraging sharks to accelerate rapidly toward the surface to catch their prey. More research is needed on shark behavior with static decoys, more similar to surfers waiting to catch a wave, the scientists said. The team is testing a prototype surfboard equipped with lighting. “Surfers can be a bit picky with their surfboards,” Ryan said. “As a surfer, I want it to be usable.”
Globally, most shark bites are associated with people surfing or participating in other board sports. Fatal shark bites, while rare, are mostly due to white sharks. The study, published in the journal Current Biology, points out that it would be important to verify whether this ploy is also effective in deterring other species that attack humans, including bull sharks and tiger sharks.
