California ? A shark believed to be a great white killed a 66-year-old swimmer with a single, giant bite across both legs Friday as the man trained with a group of triathletes, authorities and witnesses said.

Dave Martin, a retired veterinarian from Solana Beach, was attacked at San Diego County’s Tide Beach around 7 a.m., authorities and family friend Rob Hill said.

Martin was taken to a lifeguard station for emergency treatment but was pronounced dead at the scene, according to a statement on the Solana Beach city Web site. His injuries crossed both thighs, San Diego County sheriff’s Sgt. Randy Webb said in a news release.

Scripps Institution of Oceanography shark expert Richard Rosenblatt says the shark was probably a great white between 12 and 17 feet long.

“It looks like the shark came up, bit him, and swam away,” said Dismas Abelman, the Solana Beach deputy fire chief.

There was a single bite across both of Martin’s legs, Abelman said.