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In the second part of the experiment, Lowe puts a sensor-equipped shark into the open bay and follows it as it darts back and forth. After two days of nonstop tracking, he and his exhausted crew have a precise record of where the baby has gone and, by counting its tail beats, how much energy it has used. "We still have a lot of data to gather," he says, "but once we really understand what role the hammerhead pups play here, we can use that to begin understanding how adults fit into the ecosystem of the open ocean."
Back in Honolulu, on the other side of Oahu, the tiger-shark tagging is another high-tech effort to understand a different aspect of shark behavior. In 1992 two people were killed by tiger sharks in Hawaiian waters, the first such deaths there in three decades. An earlier spate of killings had provoked an all-out program to eradicate tiger sharks, but it was never clear whether that slaughter had been really effective.
This time Kim Holland, director of the shark lab, suggested a more judicious approach: first figure out how the sharks actually behave. If they keep to a small territory, a locally targeted eradication program could reduce the danger. But if they have no territorial allegiance, an aggressive animal might kill and disappear, never to return, and slaughtering the sharks that remained might not help at all.
With funding from the federal Sea Grant Program and help from students, including Lowe and Meyer, Holland began hooking tiger sharks off Waikiki Beach. Smaller specimens get old-fashioned tags; if a tagged shark is recaptured, the scientists know that it has returned to the same spot at least once.
Sharks that are at least 10 ft. long get a 6-in.-long cylindrical beeper deposited inside an incision in the belly. Every time the shark nears an acoustic receiver anchored on the ocean floor, it leaves a record of its visit. Based both on these records and on open-ocean shark chases, Holland has come to several conclusions. "First," he says, "we've established that tiger sharks do have home ranges." Those ranges, however, are huge: Holland's crew has tracked sharks all the way to Molokai, 25 miles away.
Moreover, the sharks patrol these ranges randomly. They may return to a given spot twice in one week, then not again for months. "It's clear," says Holland, "that you can't significantly reduce the local shark population by fishing for a limited time in a single area. You'd have to reduce the general population to have any effect--and that's not acceptable anymore."
Signals from beeper-equipped tigers have revealed that they dive much deeper than anyone had suspected--as far down as 1,000 ft. and back within 15 min.--and that they can swim in an absolutely straight line for miles at a time. "Every time you get a chance to follow a shark around in its natural environment," marvels Holland, "you get a new, incredible insight."
Halfway across the Pacific, marine biologist A. Peter Klimley of the University of California at Davis has for decades been getting his own incredible insights into shark behavior, frequently by taking risks others would call insane. While a graduate student in the 1970s, Klimley became the first scientist ever to swim directly into schools of adult hammerhead sharks. He dived as deep as 70 ft. without scuba gear so his air bubbles wouldn't disturb the skittish fish.