The last ‘women of the sea’ to dive like aquatic mammals

New research from the University of St Andrews has found that a remarkable group of women who free dive for seafood without oxygen, spend more time under water than some diving mammals like sea beavers, and rival others like sea otters and sea lions. 

Published in Current Biology , the study assessed the women on the island of Jeju, off the coast of South Korea. These women are known as the Heanyeo, or jawmnye in Jeju language, which literally means women of the sea. The Haenyeo’s breath-hold diving are so integral to Jeju’s culture that the often-shortening characteristic of Jeju language is colloquially attributed to divers’ need to communicate quickly at the water’s surface. 

Researchers tracked the natural diving behaviour and physiology of seven Haenyeo, aged 62 to 80, as they harvested sea urchins. Researchers used an instrument designed for measuring the behaviour and physiology of wild marine mammals that can track the women’s diving and swimming behaviour, as well as heart rate and blood oxygen with an optic sensor.  

Despite their age, these women spent an astonishing 56% of their time underwater across the 2 to 10 hours of diving per day, the greatest proportion than any humans previously studied.  

Whilst their diving performance overall rivalled marine mammals; their total time at sea diving per day was lower than their animal counterparts.  

Surprisingly, the Haenyeo didn’t display the classic mammalian “dive response”, a slowing of the heart and reduced blood flow to muscles during dives. Instead, they showed elevated heart rates and only mild oxygen reductions in the brain and muscles, suggesting their unique style of short, shallow, and frequent dives may trigger different adaptations. 

Lead Author of the study, Dr Chris McKnight, Senior Research Fellow at the Scottish Oceans Institute (add – in St Andrews) said: “The Haenyeo are just incredible humans. Their diving abilities are known to be exceptional, but being able to measure both their behaviour and physiology while they go about their routine daily diving is really unique. I think using animals we consider as aquatic animals to contextualise and give perspective on the Heanyeo divers really helps to demonstrate just how incredible they are.” 

The Haenyeo are a culturally significant group and recognised by UNESCO as an Intangible Cultural Heritage. However, this is endangered as 90% of the women divers are now over 60.   

Dr Melissa Ilardo, Assistant Professor in evolutionary genetics at the University of Utah who co authored the study, said: “We are so grateful that these incredible women were willing to participate in this project. They welcomed us into their gathering spaces, called bulteok, in the mornings before their dives, shared their pre-dive snacks and tea, and told us stories from a lifetime of diving. They gave us lots of feedback that helped us think about how to interpret the results and design future studies. Their humor and spirit is so fun to be around, we feel incredibly lucky to be able to partner with them.”

As Potentially  the last generation of Haenyeo, this study offers a rare glimpse into a vanishing tradition and is a powerful example of human physiological resilience and cultural heritage beneath the waves.