Study: Sharks have poor eyesight and do not distinguish between humans and fish
Sharks that attack surfers or swimmers are so visually impaired that scientists have concluded that they are more likely to mistake them for their usual prey, such as the sea lion, according to a recent study.
"From the perspective of a great white shark, neither movement nor shape allows for a clear visual distinction between flippers and humans," wrote the authors of the study, the results of which were published in the Interface journal of the Royal Society. They conclude that their work "supports a theory that some shark attacks are due to misidentification".
"This is the first study to test this theory from the optical point of view of a great white shark," study lead author Laura Ryan, a researcher in the Department of Biological Sciences at Macquarie University in Australia, told AFP.
And shark attacks are still rare (less than sixty attacks worldwide in 2020), according to a specialized department at the University of Florida.
But, according to the study, it leads to a permanent climate of "disproportionate" fear associated with ignorance of the animal's motives, especially when the attack is not motivated by any provocation. Sometimes these attacks lead to hunting campaigns that also harm other species.
White sharks are often behind these attacks.
While the great white shark is known to detect sounds and smells from a distance, it is assumed that it mainly trusts its eyesight to spot and target prey.
However, the shark's visual system is almost insensitive to color and has a very poor ability to distinguish details of shape.
The study showed that the analytical power of sharks, which is six times less than that of humans, is lower in young white sharks, which represent the greatest danger to surfers.
To test the misidentification theory, Macquarie's team recorded "video clips taken from a shark's point of view, and processed with software that mimics the visual system" of the fish, specifically its ability to distinguish shape and movement, according to scientist Laura Ryan.
To this end, the researchers recorded from the bottom of the aquarium photos and videos of sea lions and fur seals, a delicacy for sharks, as they passed near the surface a few meters above sea level, above a shark. They then compared these animals' signals to those of swimmers and surfers who paddle their arms, with or without kicks, on the three main types of surfboards (long, short, and hybrid).
From the perspective of a small white shark, it seems almost impossible to distinguish between the movement signals of swimmers or surfers and those of game animals, according to the study.
This is more true in seawater, where visibility is lower than in the aquarium used for the experiment.
The researchers will try to determine whether changing the visual cues of potential prey can be an effective way to protect against white sharks, according to the researcher.
Scientists must find solutions that “not only prevent shark bite incidents, but also endanger other marine species.”
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