The man who died while abalone diving off The Sea Ranch on Thursday has been identified as Yasufumi Hamamoto of Fresno, the Sonoma County Coroner's Office said.
Friends who were with him said Hamamoto was in some kind of medical distress, and he died before emergency response personnel could get to the scene.
Hamamoto had a history of diabetes, and his physician determined that he died of cardiac arrest, coroner's Sgt. Mitch Mana said Friday.
He was the second man to die in the quest of abalone this week. Three days earlier, Leo Chen, 39, of San Leandro drowned after being swept off the rocks north of Mendocino in rough surf, Mendocino County authorities said.
Chen was the first to die while abalone diving off the North Coast since the season opened April 1.
Six people died while hunting abalone off the Sonoma and Mendocino coasts last year; in three of those deaths, a heart condition was a contributing factor, authorities said.
-- Mary Callahan