(Paris) Sharks that feed on surfers or swimmers have such poor eyesight that scientists have concluded they may be mistaking them for their usual prey, such as the sea lion, a study showed on Wednesday.
The authors of the article wrote in user interface, Review of the Royal Society. They concluded that their work “supports the theory of misidentification to explain particular bites.”
“This is the first study to test this theory from the point of view of a visual white shark,” lead author Laura Ryan, a researcher in the Department of Biological Sciences at Australia’s Macquarie University, told AFP.
Shark attacks are still rare (fewer than sixty attacks globally in 2020), according to a specialist department at the University of Florida. But they maintain, according to the study, a climate of “disproportionate” fear, which is associated with ignorance of the animal’s motives, especially when the attack is not provoked. Sometimes the result is hunting expeditions that also harm other species.
White sharks, tigers, and bulldogs often attack surfers.
If the white shark is known to detect sounds and smells at a great distance, it is assumed that it mainly trusts its eyesight to spot and target prey.
Not sensitive to color
However, the shark’s visual system is almost insensitive to color and has a very poor ability to distinguish details of shape. According to the study, its ability to analyze, which is up to six times less than that of a human, is lower in small white sharks, which pose the greatest risk of fatal bites for surfers.
To test the misidentification theory, Macquarie’s team made “videos taken from a shark’s point of view, and processed with software to mimic the shark’s visual system,” specifically its ability to distinguish shape and movement, the scientist explains.
For this, they recorded from the bottom of the aquarium photos and videos of a sea lion and a fur seal, a delicacy of a shark, which will pass near the surface, a few meters above sea level, above a shark. They then compared their signals to those of swimmers and surfers paddling their arms, with or without kicks, on the three main types of surfboards (longboards, shortboards, and hybrids).
From the perspective of a small white shark, the movement cues of a swimmer like those of a surfer paddling its board are nearly indistinguishable from those of ungulates, according to the study.
Especially in sea water, where visibility is lower than in the aquarium used for the experiment.
As for shape, a batter with folded fins looks more like a swimmer or surfer on its short board than with elongated fins. says mNS Ryan, who notes that “there have been accidents biting longboards.”
The researchers will now try to determine if a change in the visual cues of potential prey would be an effective way to protect against white sharks, the scientist continues.
With the imperative of solutions that “not only prevent shark bites, but do not endanger other marine species.”
