HADO-RI, South Korea — On a recent morning, as she has for 60 years, Kim Eun-sil carried her diving gear to a rocky beach on the eastern side of this island to spend the day free-diving in water more than 20 feet deep to harvest seafood by hand.

Ms. Kim, 80, figures she can work a few more years at a job women here have done for centuries but which now is fast disappearing.

“I can still manage under the sea,” she said, warming her arthritic body at a fire she built with fruit boxes on a pier while waiting for other women. “My husband had it easy, hardly lifting a finger. Until he died four years ago, he had no complaints against me.”

Ms. Kim, like her mother before her, is a haenyeo, or “sea woman.” For ages, the sea women of Jeju, an island off the southern coast of South Korea, have braved the treacherous waters of the Korea Strait, even during the frigid winters. Using only flippers and goggles — no breathing equipment — they scour the sea bottom for abalone, conch and octopus.