An abalone diver who died Thursday after suffering a heart attack or some other medical emergency is the second person this week to lose his life in pursuit of the prized mollusk off the North Coast.

The unidentified man died off The Sea Ranch?s Pebble Beach shortly after 7:41 a.m., when friends observed his medical distress and ran ashore to call for help, authorities said.

He was dead by the time firefighters arrived and found him among the rocks, in a kelp bed, officials said.

The Sonoma County Sheriff?s Department helicopter, Henry I, was launched to airlift him to the top of a bluff, where he was recovered by county coroner?s personnel, authorities said.

The man?s death follows three days after waves swept a a San Leandro man away from shore while he was picking abalone from the rocks just north of Mendocino, near Jack Peters Creek, authorities said.

Leo Chen, 39, was later found floating about 200 yards away, officials said.

An autopsy determined he had drowned, Mendocino County Sheriff?s Lt. Rusty Noe said.

Chen was the first to die since the April 1 start of abalone season, which draws large crowds to the North Coast.

Some are so bent on snagging samples of the tasty shellfish that they take risks with rough conditions unsuitable for diving or hunting or push themselves beyond what they can handle physically, officials say.

Six abalone hunters died last season, including three for whom heart conditions were contributing factors.

The first few days of the 2008 abalone season included two occasions on which divers had to be rescued, one after he was found clinging to the side of a 300-foot cliff south of Fort Ross on opening day.

Two days later, a diver who slipped on some rocks and injured an ankle had to be airlifted from the beach below the same cliff, authorities said.