Satellites Spy on Lives of Great White Sharks

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Great whites are pursued by trophy-hunting fishermen for sport and for their jaws, which can fetch tens of thousands of dollars. Many also die as bycatch, drowned on commercial longlines or in gill nets that catch everything that swims by.

A recent study by scientists at Dalhousie University in Nova Scotia, Canada, revealed that North Atlantic great white shark populations fell by 79 percent from 1986 to 2000.

Depleted populations are slow to recover. Great whites grow slowly, not reaching maturity until around the age of 12, and then produce few offspring. Globally, they are classified as a vulnerable species.

Great white sharks are protected off coastal waters in just five nations, including South Africa, the United States, Malta, Namibia, and Australia. But these countries' 200-mile-wide (322 kilometers) coastal areas may prove insufficient to protect great whites from fishing fleets. "The problem is that there aren't any global conservation laws," said Andre Boustany, a marine biologist at Stanford University in Palo Alto, California.

Tracking Great Whites

Tagging sharks is a difficult process and transmitters are expensive, but this technology is helping to identify great whites' home ranges—and how much time they spend outside protected areas.

Researchers at Stanford began tagging sharks off California's Farallon Islands in 1999. Studies had revealed that whites congregated there from late summer to early winter—then disappeared. "We wanted to figure out where they were the other half of the year," said Boustany.

"The most startling discovery was how much time these sharks were spending thousands of miles from land." One shark traveled 2,360 miles (3,798 kilometers) to Hawaii. Another three were tracked to the subtropical eastern Pacific between Baja California and Hawaii, about 1,500 miles (2,414 kilometers) from land.

They spent up to six months there—and did lots of deep diving, down to nearly 2,000 feet (610 meters). Subsequent tagging corroborated these routes.

Wide-Ranging Sharks

"We assumed that these were coastal fish, hanging out in temperate waters, but found out that they spend about half their life in deep, subtropical waters," said Boustany.

To adjust from temperate 50- to 60-degree waters (10-16 degrees Celsius) to 80-degree (27 degrees Celsius) subtropical waters, the sharks may have some thermo-regulatory ability, says Michael Domeier, president of the Pfleger Institute of Environmental Research in Oceanside, California, whose team tracked whites who spend half the year near Guadalupe Island off Baja.

Both Domeier's Mexican whites and Bonfil's South African whites also showed wide-ranging, deep-diving behavior. Bonfil followed one shark over three months that traveled 1,000 miles (1,609 kilometers) into unprotected waters in Mozambique.

Other researchers documented the same behavior across the globe. In 2000, scientists with the Commonwealth Scientific and Industrial Research Organization in Victoria, Australia, traced a young male shark's route from the Victorian Coast to Tasmania and back—1,830 miles (2,945 kilometers) in 129 days—until communication was lost.

Spying on Great Whites to Protect Them

Ultimately, researchers hope these studies will provide the scientific evidence needed to better protect great whites. Defining migratory routes and birthing grounds could help conserve sharks—and be used in public safety, said Domeier.

"We're finding that [California whites] spend half or more of their time in international waters—so we need international management to protect them effectively," said Boustany.

Bonfil would like to see the sharks listed as part of the Convention on International Trade in Endangered Species, which could limit or prohibit trade in jaws and other great white parts. "They're not the killing machines we see in the movies," said Bonfil. "They are a potentially dangerous top predator, like a lion or a tiger, that has an important role in the ecosystem," said Bonfil.



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