Kidspace: Shark trackers

There is just a ripple at the surface, nothing more. But Scott Anderson knows what lies below.

"It's a 15-footer," he says.

From a larger boat, I watch the outline of the submerged shark. The great white slides silently alongside the small boat with Mr. Anderson and his colleague, Peter Pyle, aboard. Anderson follows the shark's movements with a small underwater videocamera mounted on a stick.

Later, he and Mr. Pyle will use the video to identify the shark. They'll look for scars and nicks on its fins and body. Is it Tipfin, Cuttail, Bitehead, Whiteslash, Trailtail, or (my personal favorite) Cal Ripfin?

Naming white sharks and watching them year after year would be impossible almost anywhere else. Every fall, however, the Farallon Islands become "shark central."

This pile of barren rocks 30 miles west of San Francisco hosts thousands of elephant seals and sea lions from September through November. The seals and sea lions come here to eat fish and lounge on the rocks. The sharks come, too - for seal meals.

"This is the only place in the world where we can observe white sharks without needing to put chum (cut-up raw fish) in the water," Pyle says. "We have so many sharks and prey at the Farallones, plus we have this lighthouse we can sit in and see shark attacks as soon as they happen."

Besides being a favorite resting place for seals and sea lions, the Farallones host the largest seabird nesting colony in the continental United States. While studying seabirds from an old lighthouse, Pyle, Anderson, and other biologists saw the sharks attacking their prey.

In 1989, they switched from studying birds to studying sharks. At first, when they spotted a shark they would "race out - and race right back in," Anderson says. He glances at Pyle, and they both laugh. Now they're used to being around sharks bigger than their 15-foot research boat.

When the shark research at the Farallones began, scientists knew less about white sharks than about any other large predator on earth. What little they knew came from examining dead sharks. White sharks have patrolled the seas for 11 million years, but they are regularly seen in only a few places: southern Australia, South Africa, Baja California (Mexico), and northern California.

Over the past 13 years, Pyle, Anderson, and other researchers have identified more than 30 sharks in the Farallones. "We know about 15 quite well," Pyle says.

Anderson and Pyle wait for the telltale signs of a shark attack: explosive thrashing in the water, a red stain, and flocks of seabirds looking for leftovers. When feeding is over, Pyle and Anderson move in with their camera. They can tell a shark's sex by videotaping its underside - males have an extra set of fins called "claspers."

"When the sharks see our boat floating above, they come up and swim pretty close," Pyle says. "Sometimes they put their mouth on the motor, but they don't harm themselves. They can feel things with their teeth, and once they know it is not food, they let go."

The white sharks cruise the shallow waters just offshore, waiting for seals and sea lions traveling between resting spots and feeding grounds. The shark's coloring camouflages them. They're called white sharks, but only their bellies are white. A white shark's upper half is dark gray, so a seal looking down won't see the shark against the dark bottom.

Pyle and Anderson are sitting in their research boat when the head of a sea lion pops out of the water about 50 yards away. "We may see an attack right here," Anderson says quietly. "Seals that sit at the surface don't live very long."

White sharks usually ambush their prey by shooting up beneath a seal or sea lion near the surface. White sharks have good vision and a good sense of smell. They don't attack small objects (good news for floating seabirds) or large objects (good news for shark biologists in small boats). They attack only objects about the size and shape of a seal (sometimes bad news for surfers and swimmers).

Biologist Burney LeBoeuf studies elephant seals at Point Año Nuevo, just south of the Farallones. By strapping underwater "critter cams" on seals, he discovered that experienced seals avoid white sharks by swimming fast and deep through the shallow "danger zone" near shore. They spend little or no time at the surface.

The sea lion we're watching disappears - but not into a shark. "Yesterday we had three shark attacks right here," Pyle says.

White sharks don't start out eating seals and sea lions, but they are good-sized predators from the start. No one has ever seen white sharks giving birth, but scientists have been able to examine a few pregnant sharks caught by fishermen. Female white sharks give birth to five to 10 babies, each about four-feet long.

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