Shark expert Peter Klimley, a UC Davis researcher, says the recent attack on a swimmer off Avila Pier in Central California supports his belief that adult great white sharks are selective hunters that would rather eat fat seals than bony human beings.

Deborah Franzman was swimming at the surface among a group of pinnipeds -- seals or sea lions -- on Aug. 20 when a great white shark, estimated to be 15 to 18 feet long, grabbed her leg. It stripped the flesh from her left thigh, severing the femoral artery. She was briefly pulled below the surface and then released. When lifeguards reached her a few minutes later, she was facedown in the water. Authorities said she had bled to death.

"Certainly that shark could have consumed her if it had wanted to. But it hit her, then realized she was not a seal and let her go," Klimley said. "Sharks don't eat humans. Humans are not nutritious enough. They are not worth the effort."

Klimley's 30 years of scientific studies of white, hammerhead, nurse and other shark species' behavior are described in lay language in his entertaining new book, "The Secret Life of Sharks" (Simon & Schuster, $25). "I wrote this book as a public service. It provides knowledge, accurate knowledge, about sharks. If people are interested in this attack, or frightened by it, this book will tell them what happened. You can come to Central California and swim. It's safe. You just don't swim with seals or sea lions or near their colonies."

Klimley's studies of the great white (Carcharadon carcharias) include bite-by-bite analyses of 350 written eyewitness accounts of attacks on pinnipeds and 131 videotaped attacks. He has tracked them (including five adults for one month at a seal colony), made numerous discoveries about their hunting and feeding behaviors (they feed rarely, yet can live 45 days on a single bite, and they warn away food competitors by slapping their tails) and measured their stomach temperatures (unusually warm for a fish at 75 degrees F.).

It's the maintenance of that high core temperature that makes him think great whites need the energy contained in seal fat and don't intend to kill humans. "The fat in seals' outer coats makes up half their body weight and has twice the calories of muscle. Seals and sea lions, not people, are Power Bars for the white shark."