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The world's first research to test a simulation of shark vision on the swimming patterns of humans and seals has confirmed theories that great white sharks may bite humans.
Lead author Dr. Laura Ryan is a postdoctoral researcher at Macquarie University's Neurobiology Laboratory in animal sensory systems. She says that surfers are at highest risk for shark bites by juvenile white sharks.
They are also known as white sharks and together with bull sharks and tiger sharks, they have the highest number of bites on humans.
She says that surfing, swimmers, and pinnipeds (seals, and sea-lions), on the ocean's surface will all look the same to white sharks looking up from the bottom, as these sharks don't see fine details and colors.
Ryan, who is still a keen surfer despite being immersed in shark-bite researchsays that this study will help scientists better understand why sharks bite humans.
The Neurobiology Lab scientists are developing non-invasive vision-based devices that could protect swimmers and surfers from shark bites.
Ryan states that Ryan's latest study, published in The Journal of The Royal Society Interface was a practical test. It is based on years of research by the team to understand sharks' vision, and the neuroscience of white sharks.
Signing off
The underwater video was a comparison of rectangular floats, seals, and sea lions swimming and humans using different strokes. It was also shown as underwater video of humans paddling on different sizes of surfboards.
Ryan explains that Ryan attached a GoPro camera to an underwater scooter and set it up to travel at the speed of predatory sharks.
The team used extensive shark neuroscience data from Macquarie's Neurobiology Laboratory to apply filters to video footage and create modeling programs that simulate how a juvenile white shark would process different shapes and movements.
Ryan admits that he didn't know being a scientist would require so much coding. Ryan however, was astonished by the results: a juvenile white shark sees humans swimming and paddling surfboards. This is what makes them resemble seals and sea-lions.
The pinnipeds could not distinguish smaller surfboards from their pinnipeds. They might be more attractive than longboards and stand-up paddleboards to white sharks who often target young pinniped pups.
Sharks are most likely colorblind. The main visual cue for white sharks, the silhouette, is their primary visual cue. Wetsuits and boards are unlikely to alter sharks' perceptions of floating people.
Researchers are currently exploring ways to alter the perception of shark silhouettes by using LED lights.
Safety of surfers: A shining light
Although shark bites are very rare, Australia is still the most dangerous shark habitat. In 2020, six shark attacks were recorded in Australia.
Over the past 20 year, shark attacks on humans have increased. Ryan believes that surfers are at greater risk than swimmers because they spend more time in the water and often in deeper waters.
Ryan explains that sharks use a variety of sensory cues in order to differentiate between objects and zero in on food. These differ in sensitivity among species.
White sharks have a high visual ability. Juveniles are more dangerous than older white sharks with better vision.
Professor Nathan Hart is the head of the Neurobiology Laboratory and the senior author on the research. He says white sharks need to learn what they eat and that their diet will change as they get older.
He says that white sharks can reach 2.5m in length and their jaws harden to take on larger prey such as seals.
"They will need to create a search image of these prey items and then combine it with other sensory information. It's a learning process, which could lead to errors."
Sharks are dangerous and endangered. Because of this fear, prevention methods such as drumlines and shark nets have been developed.
Ryan says that understanding shark bites can help us prevent them and keep both sharks and humans safer.
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More information: Laura A. Ryan and colleagues, A shark's eyes view: Testing the'mistaken identification theory' behind shark attacks on humans, Journal of The Royal Society Interface (2021). Journal Information: Journal of the Royal Society Interface Laura A. Ryan and colleagues, A shark's eyes view: Testing the'mistaken identification theory' behind shark attacks on humans, (2021). DOI: 10.1098/rsif.2021.0533
