A swimmer lagging behind a group training for the triathlon was killed by a great white shark near San Diego yesterday, in a rare fatal attack off southern California.

Dave Martin, 66, a retired veterinarian from Solana Beach, suffered a single huge bite across both legs as he swam in the Pacific Ocean off San Diego County’s Tide Beach, at around 7 am local time. Experts said the shark appeared to be a great white, measuring 12 to 17 feet long, that may have been hunting seals.

Mr Martin was one of a group of about nine triathletes wearing wetsuits as they swam. Two swimmers were about 20 yards ahead of him when they heard him scream.

Rob Hill, a friend and member of the Triathlon Club of San Diego, was running on the beach when the attack took place. “They saw him come up out of the water, scream ‘shark,’ flail his arms and go back under,” Mr Hill said. “The flesh was just hanging.” He said that Mr Martin may have bled to death before he left the water.

Mr Martin was pulled from the water and taken to a lifeguard station for emergency treatment but was pronounced dead at the scene. “It looks like the shark came up, bit him, and swam away,” said Dismas Abelman, the Solana Beach deputy fire chief.

The last death in a shark attack off southern California took place in Malibu when one kayaker was killed and the second disappeared. Before that, there had not been a fatal shark attack in the area since a diver was killed in La Jolla in 1959. There had been several recent reports of shark sightings in the San Diego area, however. A surfer at one local beach said that his board had been bitten by a great white shark.

Experts suggested that the shark may have mistaken the swimmer for one of the seals that congregate in nearly La Jolla Cove, south of Solana Beach. “Great whites normally feed on seals,” said Richard Rosenblatt, a marine biologist at the University of San Diego’s Scripps Institution of Oceanography.

“They attack from below and make a tremendous, powerful rush and a very powerful bite, then pull away and wait for the seal or marine mammal to bleed to death before they come back.”

“A human swimmer is not too unlike a seal,” he said.

There were only 71 confirmed shark attacks worldwide last year, up from 63 in 2006, according to the University of Florida. But only one 2007 attack, in the South Pacific, was fatal.

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