Fabien Cousteau is smiling. The sky is perfectly clear, the wind is still, and the ocean is almost flat. The ten-foot swells that kept Cousteau's dive team grounded all week have melted away completely. We drop anchor just off the Farallones, a barren chain of craggy lumps that jut above the Pacific, 26 miles west of San Francisco. Each fall, when the harbor seals come to molt, these waters grow thick with great white sharks.

Cousteau is here to shoot a program for PBS about the National Marine Sanctuary System (the Gulf of the Farallones is one of fourteen federal underwater preserves), and while he's spent the last half hour assuring me that the giant predators are shyer than you'd think, the nervous banter on deck tells another story. Cousteau zips his dry suit over jeans and a fleece pullover, checks and rechecks his air tanks and regulator, slips on a pair of long, dartlike fins, and, ready to dive, turns to his crewmates and asks, "Okay, who's got the tuna heads?" A goateed crewman laughs, "They're in your pants!" Two more chum jokes and five splashes later, Cousteau and crew are in the water.

Don Santee, who has worked with the Cousteau family since Fabien's grandfather Jacques was just beginning to reveal the wonders of the undersea world to television viewers around the globe in the 1960s, squints intently after the divers and orders those of us left on deck to keep an eye out for fins. "All you need," says Santee, the expedition leader for this dive, "is one retarded shark that doesn't know it's not the right season."

There are no sharks today, but he is right to be wary: Troubles have been circling the Cousteau clan for years. It's been almost a decade since Captain Cousteau died at 87, and the family has been torn by all-too-public rifts, court battles, and revelations that the patriarch was not the salty saint we all wanted to think he was. "When my grandfather died, he pretty much left the ship without a helmsman," Fabien says discreetly. Until recently, it was easy to believe that the Cousteau legacy would go the way of the Calypso, which has been left to quietly rot in the French port of La Rochelle while the family fights over its title.