Shark attack study using light ‘decoys’ to fool great whites could lead to protections for surfers, researchers say
The researchers tested their idea using seal decoys in the South African waters of Mossel Bay based on what they know about how sharks see.
Australian researchers looking for ways to stop shark attacks have found bright lights could be the answer in a study in great white infested waters off the South African coast.
A keen surfer and research fellow in comparative neurobiology, Dr Laura Ryan was studying the visual system of great white sharks when she began thinking about how what she was learning could be used to protect people.
Previous research suggested part of the risk of great white shark attacks is that they confuse a human silhouette with a seal.
"There was a big spate of shark bites and as a really keen surfer I was spending a lot of time thinking about shark's eyesight," she said.
"I started to think what if what I was learning could potentially protect surfers?"
With neurobiologist and head of the Macqaurie University School of Natural Scientists Professor Nathan Hart, Dr Ryan went on to spend six years in Mossel Bay, South Africa to test a theory — could tricking great whites with lights stop them attacking?
"The reason we went to South Africa is there is not many places in the world where you'd have the concentration of sharks you need," she said.
How did it work?
The research involved towing seal-shaped decoys with lighting on the underside behind a boat. The researchers said this reduced the sharks’ ability to see silhouettes against the sunlight above.
This then reduced the rates at which sharks followed and attacked the artificial prey.
They found that sharks were less likely too interact with the objects as they became brighter.
The team also experimented with using LED lights to break up the silhouette of the decoys.
They also tried flashing lights but that proved not to be effective.
After much experimentation they found the ideal pattern to fool the sharks was to place the lights in stripes across the bodies of the seal decoys, perpendicular to the direction they were being towed through the water.
The sharks still saw the decoy, but its shape was broken up and the great whites stopped attacking.
"It's like an invisibility cloak but with the exception that we are splitting the object, the visual silhouette, into smaller bits," says Professor Hart.
"It's a complex interaction with the shark's behaviour. The lights have to be a certain pattern, a certain brightness."
What does the research tell us?
Lights break up the silhouette of seals into smaller shapes which are more difficult for sharks to identify as prey, says Professor Hart.
In every instance the striped design was used on the decoy, there were no attacks.
"So we think this tells us a lot about how sharks see the world and how they detect and target their pray," Professor Nathan Hart said.
"But it also potentially gives us an insight into how we can develop a non-lethal shark deterrent especially for surfers."
So can surfers relax now?
Not quite yet.
The study did not specifically test the effectiveness of the lights mounted under surfboards.
South African authorities wouldn't agree to using surfboard shaped decoys to lure great whites to attack.
There were concerns it might have created greater danger for surfers.
But the system could work on surfboards.
"What we're trying to do now is move from seal decoys into a surfboard prototype by embedding LEDs into the bottom of a surfboard," says Dr Ryan.
She said her team is currently working on a surfboard prototype that could also be applicable to other watercraft and even swimmers.
They are also doing further research to test whether LED lights will still deter great whites when a surfboard is stationary in the water, such as when a surfer is waiting for a wave.
Will it work for other sharks?
Most fatal shark bites and attacks globally are due to great white sharks.
However, bull sharks and tiger sharks also pose a threat.
Dr Ryan says they have started testing the light system with these species.
"We don't know if it will be as effective on them because we're not certain if they rely on visual cues as much as white sharks," she says.
"The idea of mistaking humans as seals is only relevant to great white sharks because seals are a large component of their diet."
By：ABC(责任编辑：admin)
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