These Korean women spend more time underwater than any other humans

On Jeju Island in South Korea live women who dive deep into the East China Sea. There, they harvest sea urchins and shellfish. Known as Haenyeo, or sea women, they spend more time underwater than any other humans studied. That’s one to five hours a day.

Researchers shared their findings August 18 in Current Biology.

“It’s as close as you get to studying a mermaid,” says Chris McKnight. He’s a marine-mammal biologist at the University of St. Andrews in Scotland.

McKnight is part of a team that worked with seven Haenyeo divers. Over 1,786 dives, these women wore devices that monitored how long they stayed underwater. The devices also measured how deep the women dove. They even tracked oxygen levels in the women’s brains and muscles.

The women dove repeatedly for two to 10 hours each day. And they spent an average of 56 percent of that time beneath the surface. This is more time than many aquatic mammals spend underwater, the researchers say. That includes beavers, polar bears and sea otters.

Chronicles of female divers in this part of Asia date back 3,000 years. Researchers have studied some of these divers in the lab. McKnight’s team wanted to monitor them in a real-life setting. This new study put the women’s abilities into context with other water-dwelling mammals. Such research could shed light on how the ancestors of whales and other marine mammals transitioned from land to water, McKnight says.

Surprising findings

The team expected to see low oxygen levels and slow heart rates in the Haenyeo. That’s how other mammals have adapted to diving. Instead, it was the opposite. These women had elevated heart rates. And oxygen levels in their brain and muscles barely decreased while diving.

This surprise might be explained by the style of the women’s dives. They don’t make long, deep dives, like a whale might. Instead, dives by these women range from one to three meters (three to 15 feet) deep. They average just 11 seconds in length. These women make lots of dives, surfacing for an average of only nine seconds before diving again.

What makes their feats even more impressive is the divers’ average age: 70. “This speaks to an incredible health span,” says study coauthor Melissa Ilardo. She’s an evolutionary geneticist at the University of Utah in Salt Lake City. That “is really exciting, because we could really dig into what’s allowing that to be possible in this population,” she says.

Ilardo led a lab-based study that compared the Haenyeo women with non-diving Koreans. The study uncovered genetic variations in the Haenyeo. Those variations were associated with their blood pressure as well as their ability to withstand cold water. That may contribute to skillful diving. Ilardo and her colleagues reported this on May 27 in Cell Reports.

McKnight says that the Haenyeo also may have adapted to tolerate high levels of carbon dioxide (CO2). This gas builds up in the body after repeated breath holds. Elevated CO2 levels are “incredibly uncomfortable” for most people, McKnight notes. They can cause anxiety and panic. He hopes to monitor the women’s CO2 levels in the future.

The Haenyeo’s foraging practices are similar to “a surface-oriented, shallow-diving marine mammal like a sea otter,” says Ted Cheeseman. A marine biologist, he heads Happywhale. It’s an online photo database of marine mammals. He did not take part in the new study. Adaptations that allow these women to spend more than half their time underwater “really speaks to culture driving evolution,” Cheeseman says.