SAN DIEGO — Jim Stewart, an innovative Scripps Institution of Oceanography diver-educator who helped open the world’s oceans to scientists in the 1950s and ’60s by training them to use some of the first scuba equipment, has died. He was 89.

Stewart died from natural causes Wednesday in Irvine, California, according to Scripps.

During a five-decade career, Stewart helped design and carry out some of the most rigorous training ever done for scuba gear, which revolutionized science and military diving after it was introduced in the United States in the late 1940s.

Jacques Cousteau and Emile Gagnan created the so-called aqualung underwater breathing device to enable divers to roam the depths without being tethered to air hoses attached to boats. The device was a godsend to Stewart, who had spent much of his childhood free-diving and spear fishing in the marine wonderland that is La Jolla Cove.

He would later spend 30 years as the dive officer at Scripps, where he trained thousands of divers and explored the Channel Islands and the submarine canyon off the Scripps Pier. He also descended 600 feet in a saturation bell.

In 1962, Stewart helped rescue famed Swiss deep diver Hannes Keller, who got into trouble after descending 1,000 feet in a diving bell off Santa Catalina Island.

Historians also note that Stewart explored an underwater crater in the Pacific only days after it was hit by a hydrogen bomb, and he helped standardize the protocol for safe dives in the Antarctic.

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“Among scientific and technical divers, Jim Stewart enjoys the status that Chuck Yeager has among professional pilots,” San Diego dive historian Eric Hanauer wrote in a 1999 book about diving pioneers. “He organized it, standardized it and spread that knowledge around the country and around the world.”

He was with diver Connie Limbaugh and researcher Wheeler North in 1959 when they discovered underwater sandfalls off Cabo San Lucas. A year later, Limbaugh died diving in a cave. Stewart succeeded him as Scripps’ dive officer.

In 1969, he made his first dives beneath the ice in Antarctica, an experience he compared to floating above the Grand Canyon in a 1991 interview with The San Diego Tribune.

James Ronald Stewart was born Sept. 5, 1927, in National City, California, and fell in love with the ocean early. In a 2000 interview, he keenly remembered fishing with his father from the Scripps Pier.

“When he’d catch a fish, I would take a look at it and run up to the old Scripps aquarium and see what that fish was,” Stewart recalled. “Little did I think I would spend 50 years of my life here.”