For the second time in a week, an abalone diver has lost his life in pursuit of the prized mollusk off the North Coast, this time after suffering a heart attack or some other medical emergency, authorities said.

An unidentified man died off the Sea Ranch's Pebble Beach shortly after 7:41 a.m. Thursday after friends saw he was in trouble and ran ashore to call for help, authorities said.

When firefighters arrived, the man was dead, officials said, and they found his body among the rocks in a kelp bed.

The Sonoma County Sheriff's Department helicopter was launched to airlift him to the top of a bluff, where his body was turned over to county coroner's personnel, authorities said.

Three days earlier, waves swept 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 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 people are so bent on snagging the tasty shellfish that they take risks with conditions unsuitable for diving or hunting, or push themselves beyond their physical capability, officials said.

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

The first few days of the 2008 abalone season, two 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 rocks and injured an ankle had to be airlifted from the beach below the same cliff, authorities said.

You can reach Staff Writer Mary Callahan at 521-5249 or mary.callahan@