Why do sharks attack humans? Sharks have such poor eyesight, according to the authors of a scientific study published on Wednesday, that they probably confuse surfers and bathers with their usual prey, such as sea lions for example.
“From a white shark’s point of view, neither movement nor shape allows for an unequivocal visual distinction between pinnipeds and humans”, write the authors ofarticle appeared in Interface, a review of the Royal Society. They conclude that their work “Support the theory of misidentification to explain some bites”.
Shark attacks remain rare
“This is the first study to test this theory from the visual point of view of a white shark”, explains to AFP its main author, Laura Ryan, researcher in the department of biological sciences at Australian University Macquarie.
Shark attacks remain rare (less than sixty worldwide in 2020), according to a specialized department at the University of Florida. But they maintain, according to the study, a climate of fear “Disproportionate”, associated with ignorance about the motives of the animal, especially when the attack is not provoked. Sometimes the consequence is hunting campaigns which also harm other species.
Surfers particularly targeted
Most often incriminated, white sharks, tigers and bulldogs, mostly target surfers. If the white shark is known to detect sounds and smells at great distance, up close it is assumed that it mainly trusts its sight to spot and aim for prey.
However, the shark’s visual system is almost insensitive to color and has a very poor ability to distinguish the details of a shape. Its resolving power, up to six times lower than that of a human, is even lower in young white sharks, which pose the greatest risk of fatal bites to surfers, according to the study.
To test the theory of misidentification, Macquarie’s team performed “Videos taken from a shark’s point of view, and processed them with a program to mimic the shark’s visual system”, and particularly its ability to distinguish a shape and its movement, explains the scientist.
For this, they recorded from the bottom of a basin the images and videos of a sea lion and a fur seal, a delicacy for the shark, which would pass close to the surface, a few meters above sea level. above a shark. They then compared their signals to those of swimmers and surfers paddling with their arms, and with or without kicks, on the three major types of surfboards (longboard, shortboard and hybrid).
A pinniped with folded fins resembles a surfer
From a young white shark’s perspective, the movement signals of a swimmer like those of a surfer paddling his board are nearly indistinguishable from those of a pinniped, according to the study. A fortiori in seawater, where visibility would be less than in the basin used for the experiment.
As for shape, a pinniped with folded fins looks more like a swimmer or surfer on his shortboard than a pinniped with outstretched fins. “Longboards look less like a sea lion”, according to Me Ryan, who remarks that he “There have been incidents of biting on longboards”.
Researchers will now try to determine whether a “Changing the visual signals of potential prey would be an effective protection technique against white sharks”, continues the scientist. With the imperative of solutions that “Not only prevent shark bites, but which do not endanger other marine species”.
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