Shark kills woman as she swims with sea lions

California's central coast was on high shark alert yesterday after a woman aged 50 enjoying an early-morning swim with sea lions was mauled to death in full view of a lifeguard training team.

Deborah Franzman, a college sociology lecturer who swam in the Pacific several times a week, died when what is believed to be a great white shark attacked from below, taking a huge bite out of her left leg and severing her femoral artery. Four lifeguards dived in to help her, but by the time she was brought ashore she was dead.

Ms Franzman had been swimming just off the pier at Avila Beach, a picturesque resort town halfway between Los Angeles and San Francisco. Although great white sharks occasionally prowl the coastal waters off California, fatal attacks on humans are relatively rare. There have been 10 since records began in 1952, and none since 1994.

Marine biologists say great whites usually attack humans only when they mistake them for something else. The fact that Ms Franzman was wearing a dark wetsuit and flippers might have been her undoing, said John McCosker, a shark expert with the Californian Academy of Sciences. "If you are wearing a wetsuit and fins and you are swimming with sea lions, you are doing a clumsy job of imitating shark food," Mr McCosker told the San Francisco Chronicle.

Authorities closed beaches for several hours after Tuesday's attack. Even after they reopened, signs were posted warning swimmers not to venture into the water.

Friends and family members said Ms Franzman was an experienced swimmer, and she was well within officially designated safety limits. About 30 lifeguards saw the attack from the beach, where they were doing training exercises.