The great white shark is an ocean icon for many reasons. Its torpedo-shaped body and ability to use intelligent tactics like speed and coloring to hunt sets it apart from other sea creatures. What people most associate with sharks is also their aggression, with reports of “shark attacks” making them out to be killing machines. But new research calls into question this belligerent reputation.
Published this week in Royal Society Interface, the study is a world-first endeavor in answering why sharks bite humans. Turns out, it may be a case of “mistaken identity”; that is, the shark may mistake the human surfer as one of their prey. What do humans look like? Seals, it turns out.
“They’re not these mindless killers, but we just happen to look like their food,” the study’s lead author, Dr. Laura Ryan of Macquarie University, Australia, said. In other words, sharks may not be actively seeking out humans to hunt.
To prove this, the researchers looked at things from the white shark’s view. They placed cameras in a sealed enclosure, collecting footage of people on surfboards, people swimming, and seals from this specific vantage. They stripped the footage of all color because sharks are colorblind; the image quality was also scaled down because sharks have a less accurate vision. While hunting, the sharks rely more on the motion and brightness contrast of their surroundings, the researchers found.
The result: when the shark look up at the water surface, neither the motion cues nor the water silhouettes helped differentiate people from seals or sea lions.
“From the perspective of a white shark…neither visual motion nor shape cues allow an unequivocal visual distinction between pinnipeds and humans, supporting the mistaken identity theory behind some bites,” the study noted.
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The researchers looked at juvenile white sharks in particular for two reasons: they have poorer vision than an adult shark; and since they have just started incorporating seals into their diets, they are more likely to be the perpetrators of shark bites on people.
Even statistically, while shark bites are rare, surfers are at the highest risk of fatal bites, particularly from juvenile white sharks. Instances of shark bites have risen “substantially” over the last two decades, according to research.
If the “mistaken identity” theory fits, research can start finding ways to avoid these attacks. “Once you understand what the drivers are for a shark to bite, then you can develop ways to avoid that mistaken identity,” Nathan Hart, co-author of the paper, said.
The research also strips the bad rep sharks often get. The great whites are vulnerable species — decreasing in numbers due to years of being hunted by man for fins and teeth. Some even use them as a trophies for sport fishing. In January, researchers also found that the sharks and ray populations have declined by 70% globally, with overfishing being the main reason.
This trait of the white shark is then revelatory; it helps change the idea that sharks kill humans mindlessly. “We want to change the idea that sharks are these mindless killers who target humans, and I think the people are gradually understanding that,” Hart said. Most of all, it offers insights into beautiful creatures critical to the marine ecosystem.
“Understanding why shark bites occur can help us find ways to prevent them,” Ryan said, “while keeping both humans and sharks safer.”
