Satellite Tags Keep Track of Great White Sharks

Seals have so much fat, Klimley explained, that a shark that eats just half of one can keep going for a month and a half.

Satellite and Acoustic Tags

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Scientists know little about where great white sharks migrate when they stray from coastal feeding areas.

Satellite tracking has surprised researchers by showing that some sharks even make round trips from California to Hawaii between winter and spring—up to 40 miles a day, said Andre Boustany, a graduate student at Stanford University in Palo Alto, California.

After six months the satellite tags pop off the shark and float to the surface, where they transmit data.

"Knowing that sharks travel so far brings up new conservation issues," Boustany said. "We may need to look at protecting the animal on an international level."

According to estimates, 100 to 300 great white sharks frequent areas near the California coast.

"We don't really think they're terribly endangered, but it's worth looking at," Klimley said. "There's not been a good population estimate because it involves significant tagging of individuals and tracking over long periods of time."

The science of tagging sharks is still relatively new. Researchers use acoustic tags, which transmit radio signals over a short range, in addition to the newer satellite tags.

Acoustic tags send continuous radio signals, even while underwater, providing a real-time window into the shark's world: how far and how fast the shark is moving, its body temperature and water depth and even how many tail flicks it takes to propel the shark along.

For Van Sommeran, the close encounters are brief but intimidating. "Afterwards you do notice that your hands are trembling," he said. "This is 'Jaws' after all."

Van Sommeran doesn't believe that the great whites, for all their ferociousness, want to prey on him. "They're essentially indifferent to humans," he said. "We're just not fat enough."

Sharks have an image as terrifying, mindless feeding machines. In fact, the great white, Klimley said, is "a beautiful, awe-inspiring, gigantic animal, but it also has interesting, complex behavior that we're only starting to understand."

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Smithsonian References on Sharks

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