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Young sharks mistake humans for seals, study finds

Great whites are often portrayed as ruthless killers of humans, but a new study suggests that the victims of shark attacks are simply the subject of a mistaken identity.

The ferocious sea beasts can mistake humans for their natural prey, seals, because they look the same when viewed from below, research reveals.

Experts in Australia used ‘shark vision’ to see how seals and humans appear on surfboards when looking at a silhouette on the surface of the water.

They did this by cleverly manipulating images of humans and seals swimming like a shark would see them.

Sharks likely mistake an oval-shaped surfboard for a seal’s body, as well as a human’s arms and legs for a seal’s limbs, the researchers concluded.

They are completely color blind or at best have only limited perception of color, making it difficult for them to make the distinction.

Sharks do not attack humans on purpose, but rather mix them with seals because they are color blind and cannot make the distinction, report researchers in Sydney.

Sharks do not attack humans on purpose, but rather mix them with seals because they are color blind and cannot make the distinction, report researchers in Sydney.

Great white shark (Carcharodon carcharias). White shark attacks on humans are rare, but when they do occur, they can result in the use of lethal shark mitigation measures, damaging population numbers.

WHITE SHARKS

The white shark (Carcharodon carcharias) is the largest of all predatory sharks in the ocean today.

Adult great white sharks grow to a maximum size of about 20 feet in length, weigh up to 6,600 pounds, and are estimated to live 30 years.

Great white sharks have serrated, blade-shaped teeth with the upper jaw containing a row of 23-28 teeth and their lower jaw 20-26 teeth. These triangular teeth can reach up to 6.6 inches in height.

They are very curious and often stick their heads out of the water or follow boats. However, white shark attacks on humans are rare.

The research specifically focused on juvenile white sharks (Carcharodon carcharias), which can be found in the coastal surface waters of the major oceans.

“We specifically look at young sharks and that’s because they are responsible for the majority of fatal bites in humans,” study author Laura Ryan, of Macquarie University, Sydney, told the AAP.

“Until now, the potential similarity between humans and seals has been evaluated based on human vision.

“However, white sharks have a much lower visual acuity than we do, which means they cannot see fine details and lack color vision.”

Juveniles have poorer eyesight than adults, simply because their eyes have not yet grown to full size, just like the rest of their body.

For the study, the researchers used images of two sea lions and a fur seal swimming in a pool at Sydney’s Taronga Zoo from the water, as well as humans ‘paddling puppies’ using a surfboard.

They used mounted cameras and marine scooters to observe how sharks perceive stimuli on the water.

This data was then pumped into a virtual visual system that analyzed the short clips and saw them as the shark’s retina would see it, in black and white and not very clear.

Doorbell dead?  A surfer is photographed from below on Bondi Beach, Sydney, Australia.  The feet look stubby, like the lower limbs of a seal.

Doorbell dead?  A surfer is photographed from below on Bondi Beach, Sydney, Australia.  The feet look stubby, like the lower limbs of a seal.

Doorbell dead? A surfer is photographed from below on Bondi Beach, Sydney, Australia. The feet look stubby, like the lower limbs of a seal.

Videos were recorded of two Australian sea lions (Neophoca cinerea) and a New Zealand sea lion (Arctocephalus forsteri, pictured)

Videos were recorded of two Australian sea lions (Neophoca cinerea) and a New Zealand sea lion (Arctocephalus forsteri, pictured)

Videos were recorded of two Australian sea lions (Neophoca cinerea) and a New Zealand sea lion (Arctocephalus forsteri, pictured)

The team relied on extensive shark neuroscience data to apply filters to the video images, and then created modeling programs to simulate how a juvenile white shark would process the movements and shapes of different objects.

They found that the movement signals of humans swimming, humans paddling surfboards, and seals swimming did not differ significantly.

The low acuity of juvenile white sharks means they cannot discriminate between humans and seals, when viewed from below, according to the researchers.

As a neuroscientist, Dr. Ryan’s interest in this field stems from her own passion for surfing and finding ways to mitigate shark attacks.

“The fear of being bitten by a shark crosses your mind,” he said. “ So for me, having a greater understanding helps me put those thoughts aside when they happen, because I can rationalize that they are quite rare events. ”

The researchers are now exploring other ways to change the way sharks perceive different silhouettes, including the use of LED lights.

Direction and force of motion indications from the researchers' model of (a - c) a seal swimming and (d - f) a human paddling a surfboard

Direction and force of motion indications from the researchers' model of (a - c) a seal swimming and (d - f) a human paddling a surfboard

Direction and force of motion indications from the researchers’ model of (a – c) a seal swimming and (d – f) a human paddling a surfboard

Scientists in the university’s neurobiology laboratory are also working on non-invasive, vision-based devices that can help protect surfers and swimmers from shark bites.

Fatal shark attacks are rare. According to the Australian Institute of Marine Sciences, each year there are around 10 deaths attributable to shark attacks around the world.

This compares with about 150 deaths worldwide per year that are caused by falling coconuts, he says.

But when they do happen, it can result in the use of lethal shark mitigation measures, damaging population numbers, the team warns.

“ Shark bites in humans are rare, but frequent enough to generate substantial public concern, generally leading to measures to reduce their frequency, ” say the authors in their article, published in the Journal of the Royal Society Interface.

“The bites also have negative consequences for sharks as they often result in the implementation or continued use of lethal shark mitigation measures, including the deployment of gillnets and drum lines to reduce shark populations.”

LARGE WHITE SHARKS AMONG 39 THREATENED SPECIES IN AUSTRALIA

More than one in ten of Australia’s shark, ray and ghost species are at risk of extinction, and experts warn that ‘urgent action’ is needed to halt the severe population decline.

The new data comes from the first comprehensive extinction risk assessment, which shows Australia is home to more than a quarter of the world’s shark species, 12 percent of which are at risk.

“While Australia’s risk is considerably lower than the global level of 37 percent, it raises concern for the 39 Australian species assessed as being at high risk of extinction,” said lead study author Peter Kyne of Charles University. Darwin, Australia.

“In Australia, many of our threatened sharks and rays are not commercially important, so they are largely ‘out of sight, out of mind’ but require protection at the national, state and territorial levels.”

For iconic species like the great white shark and the gray nurse shark, Dr. Kyne said there are “positive signs” that protection and management are working, although they remain under threat.

Commercial fishing that affects sharks both as a target species and bycatch for industries like tuna remains a “major threat” facing sharks around the world, Dr. Kyne said.

“Each of our species has a functional role … it is part of that network of the ocean community,” he said, explaining the importance of sharks as predators in a healthy ecosystem.

Released in September 2021, the Australian Sharks and Rays Action Plan is the first attempt at a comprehensive national overview of sharks and their habitats.

“It identifies priority species at risk, those that need the most protection and species that are not of immediate concern,” said the director of the Center for Marine Biodiversity, Alan Jordan.

The data indicates that a “strong focus on sustainable fisheries” is having some benefit, as 80 percent of the country’s 328 species are not threatened.

“In Australia, comprehensive fisheries management together with vast areas of no or low-fishing and the network of marine protected areas have helped to ensure the status of many species,” said co-author Michelle Heupel.

Australian waters also serve as a refuge or ‘lifeboat’ for 45 species that are threatened in other parts of the world, such as the giant guitarfish and the spotted eagle ray.

“These species remain safe in Australian waters,” Dr. Kyne said.

“But while we should celebrate the safety status of many species, we urgently need to increase our research and management efforts for Australia’s threatened sharks and rays.”

The research also found gaps in how much is known about local shark species, and more investment is needed to close the knowledge gap.

“For the 328 species we evaluated in this book, each has knowledge gaps,” said Dr. Kyne.

The Australian Sharks and Rays Action Plan 2021 was published by the Marine Biodiversity Center of the Australian Government’s National Environmental Sciences Program.

Source: AAP

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