(CNN) -- Beaches along the San Diego, California, coast will be closed Saturday after a 66-year-old man was fatally attacked by what authorities suspect was a great white shark.
Dave Martin, a retired veterinarian, was pronounced dead shortly after the incident, which occurred about 7 a.m. Friday (10 a.m. ET) at Solana Beach, California.
Martin was in a group of nine swimmers "when he was bitten across both thighs by what is believed to be a great white shark," according to a statement issued by the San Diego County Sheriff's Department.
"Some of the other swimmers looked back to see the victim up out of the water flailing, and (he) was pulled back under the water. He came up screaming and was helped to shore by four of the swimmers."
Martin was taken to a nearby lifeguard station, and a medical helicopter was called in, but he apparently bled to death at the scene, the statement said.
Deputy Fire Chief Dismas Abelman said Martin suffered severe injuries to both his legs, although his body was intact. He was pronounced dead at 7:49 a.m. 
Watch officials describe the attack »
The incident occurred in the Fletcher Cove area of Solana Beach near a popular surf spot known as Table Tops, one of the main access areas to Solana Beach, said Sheriff's Lt. Mike McClain.
A sheriff's helicopter was scanning the beaches for the shark, and nearby beaches were contacted, Solana Beach officials said in a statement posted on the city's Web site.
Swimmers were ordered out of the water, and a 72-hour swimming advisory was posted for an 8-mile stretch of beach, said Capt. Craig Miller of the city's marine safety department.
The beaches remain closed and will be patrolled throughout the weekend, city and county officials told The Associated Press.
City officials noted, however, that they were not trying to capture or kill the shark. Great white sharks are protected by law in California.
"I would say from my examination of the wounds on the victim and also the narrative that I got about how the attack happened that this almost certainly was a great white shark," said Richard Rosenblatt, professor emeritus of marine biology at the Scripps Institute of Oceanography.
"I was told that the victim was pushed up out of the water in a violent attack, and that's just typical of white shark feeding behavior. They normally feed on seals," Rosenblatt said. "They attack from below, make a tremendous powerful rush, make a powerful bite and then pull away and wait for the seal or other marine mammal to bleed to death, and then come back."
Although there is not a population of great white sharks in the area, females do come down from colder waters to give birth and then return, he said.
In addition, such sharks are remarkable swimmers. A shark tagged off Monterey, California, turned up in Hawaii, Rosenblatt said, and one tagged in South Africa was found in Australia.
The wounds "were really quite clean and massive," Rosenblatt said, and typical of those a great white might leave. If tooth fragments are found at autopsy, he said, it might be possible to identify the type of shark. However, he said, finding the shark that attacked Martin is unlikely.
Martin leaves behind a family "and a lot of friends that loved him," said Rob Hill, a friend of the family. Watch Hill discuss a "great loss" to community »
Police said three trauma counselors were brought in to assist Martin's swimming partners.
Solana Beach is about 20 miles north of San Diego. Fatal shark attacks in the area are rare. According to the San Diego Union-Tribune, the last time someone was killed by a shark off San Diego was in 1994, when a 25-year-old woman died after being attacked by a great white shark in Ocean Beach. E-mail to a friend 
CNN's Paul Vercammen and Scott Thompson contributed to this report.
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