An important white shark assaults a dummy seal throughout an experiment the place lights had been used to discourage shark assaults
Nathan Hart, Macquarie College
Putting in lighting on the underside of surfboards, kayaks or wetsuits might stop the vast majority of nice white shark assaults on people.
It has lengthy been identified that sharks typically assault people as a result of they mistake their silhouettes on the floor for prey, corresponding to seals. Now, researchers have carried out an experiment to see what occurs in the event that they break up the silhouette by illuminating the underside of a decoy seal to disguise its form.
Laura Ryan at Macquarie College in Sydney and her colleagues spent almost 500 hours towing seal-shaped decoys round Mossel Bay within the Western Cape area of South Africa, the place nice white sharks (Carcharodon carcharias) collect and hunt in massive numbers.
The crew examined a number of mild remedies: protecting the underside of the decoys with dim, intermediate and brilliant LED lighting and strobe lighting, in addition to horizontal and vertical strip lighting. After every tow with one of many mild remedies, they instantly towed a management decoy seal with none underside lighting. As an additional experiment, they did paired assessments the place the unlit management dummy was towed 3 metres away from the illuminated dummy.
The unlit decoys had been attacked or adopted by sharks greater than any of the illuminated decoys. The brightest mild appeared to be handiest, with zero predator incidents seen when the decoy’s illumination was most radiant.
Vertical strip lighting was much less efficient than the horizontal strips, presumably as a result of it broke the silhouette into longer sections that might nonetheless be recognized as a seal, says Ryan.
The strobe lighting was much less efficient than steady lighting, maybe as a result of the sharks might nonetheless see the silhouette of what they thought was prey between flashes.
Ryan says the crew anticipated it will be necessary for the lighting on the decoys to match the background mild, to make sure it wasn’t brighter than ambient underwater circumstances, however this wasn’t the case.
“The most critical thing was that the brightness on the decoy had to be brighter than or equal to the background light,” she says. “As long as the lighting stopped the silhouette from looking black, it seemed to work.”
The crew has now developed a prototype lighting array for use as an incredible white shark deterrent. “We are now moving from research into providing protection for swimmers and surfers,” says Ryan. “We have taken the approach of understanding these animals’ sensory system and how they see the world, and their behaviour.”
Ryan cautions that the illumination deterrent hasn’t been examined on different species identified to assault folks, corresponding to tiger sharks (Galeocerdo cuvier) and bull sharks (Carcharhinus leucas), which have totally different looking methods.
David Sales space on the College of Know-how Sydney does lots of subject analysis off the Sydney shoreline the place sharks, together with nice whites, are frequent. Primarily based on these findings, he says he will certainly be ordering a counter-illuminated wetsuit when they’re obtainable.
“I’d have thought that background-matching, lower illumination would be most effective, so I was surprised to see that ‘disruptive camouflage’ worked better,” he says.
“These results apply to white sharks only and for this feeding mode only, so it’s unclear how widely applicable they are at present.”
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