Turns out being one of the most admired surfers in the world doesn’t make you immune from promoting bad science.
The interview started off smoothly, with the crew asking Hamilton for his thoughts on the uptick in shark sightings along the California coast in recent weeks and what the odds were of the average beachgoer being attacked.
Hamilton debunked the myth that sharks are bloodthirsty for humans ― which is perpetuated by movies like “The Shallows,” “Jaws” and “Sharknado 4” ― by correctly stating that humans are not typical prey for sharks.
“I mean they say that soda machines kill more people every year than people are bit by sharks,” he said. “Most shark attacks are not fatal. It’s usually a mistaken identity.”
But the interview took a sharp turn when Hamilton said that menstruating women are most likely to be attacked by a shark.
“The biggest, most common reason to be bitten is a woman with her period, which people don’t even think about that,” the surfer said. “Obviously, if a woman has her period, then there’s a certain amount of blood in the water.”
Hamilton may be one of the most experienced athletes in the ocean with slightly more knowledge about sharks than the average person, but it’s not clear where he’s getting his information on women’s menstrual cycles.
Women lose on average 35 milliliters to 50 milliliters (about 1.2 fluid ounces to 1.7 fluid ounces) of blood during a menstruation cycle, research shows.
And although sharks can detect blood in the ocean, menstruation does not produce enough blood to draw in sharks, according to Chris Lowe, a shark researcher at Cal State University of Long Beach.
“This is one of those misconceptions that refuses to die,” Lowe told HuffPost. “In fact, the amount of blood loss during menstruation is probably less than average scrape or cut that a kid or surfer may get while playing in the water.”
Lowe explained that kids with minor injuries aren’t commonly attacked by sharks, so it’s unlikely that the animals would bite menstruating women losing more than 2 fluid ounces of blood over the span of a week.
“The bottom line is it takes a lot more than just a little blood to get a shark’s attention,” Lowe said.
Shark behavior expert Ralph S. Collier once tested to see if wild sharks were attracted to menstrual blood and other bodily fluids, but found that the only liquid that elicited a reaction was liquid from the abdominal cavity ― not menstrual blood, according to Mother Jones. However, blood from sharks’ real prey (sea otters or cetacean) did move the sharks into a feeding frenzy, Collier added.
“Our blood is different from a sea otter’s blood or cetacean blood,” he told Mother Jones.
And as National Geographic points out, sharks don’t really like to eat human beings. They prefer seals and other marine animals.
What’s more, Lowe told Outside Magazine that menstrual blood becomes diffused with other substances in the ocean once it enters the water.
“The amount of blood that is produced during menstruation is so small that it becomes background with all of the other components that are in the water,” Lowe told the magazine. “It would be very difficult for a shark to localize that.”
Hamilton’s chat with TMZ veered back to a slightly more normal course when he began listing other ways people could attract the attention of sharks, including the creatures mistaking a person fishing, surrounded by bloody fish in the water, for a sea lion.
And if you’re really worried about being killed by a shark, keep this in mind: Sand, bicycling and rip currents ― and, as Laird suggested, vending machines and lightning ― are more likely to kill you than a shark.
This story was updated to include more information about how well sharks can detect blood in the ocean.