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March 2002 Vol. 17, No. 3   RSS Feed for Undercurrent Issues
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G reat White Sharks Migrate Thousands of Miles

from the March, 2002 issue of Undercurrent   Subscribe Now

Scientists studying great white sharks along the California coast have long believed that they spend most of their lives close to shore, pursuing seals and sea lions. Yet a study in the journal Nature reveals they can range across vast stretches of the open ocean. In fact, one male migrated thousands of miles to the warm waters off Hawaii. I was shocked by the results, noted University of California biologist Burney Le Boeuf.

Researchers attached pop-up satellite archival tags to the backs of six great whites foundnear seal rookeries. The electronic tags recorded depth, temperature and light every two minutes. Each tag was programmed to detach on a specific date, then pop to the surface, where the data were transmitted via satellite to the Hopkins Marine Station.

The four males and two females ranged in size from 11 to 15 feet. Data confirmed that in the fall great whites appear near coastal seal rookeries just as young elephant seals arrive for their annual mating ritual. While near shore, tagged sharks rarely dove more than 90 feet deep, in water that ranged from 50F to 57.2F.

The surprise came in winter when four sharks all headed into the central and eastern Pacific. The male who migrated 2300 miles to the Hawaiian island of Kahoolawe traveled at least 43 miles per day. The animal stayed in Hawaii the entire winter and spring. Two females and a male migrated to the eastern Pacific hundreds of miles west of Baja California. They remained in the open ocean for several months, never venturing near any coastline. What they were doing out there is a mystery, noted Le Boeuf. Such a long migration suggests a possible rendezvous for mating, or a move to feed on different prey.

While they sometimes dove as deep as 2,040 feet, the animals seemed to prefer swimming at two discrete depths one within 15 feet of the surface, the other 900 to 1,500 feet down. All four sharks spent up to 90 percent of the day in these two diving zones and little time at intermediate depths. They experienced a broader range of ambient temperatures from 79 F at the surface to 41 F at their maximum depth. Great Whites are found not only in California, but also in Australia and South Africa.

---- Mark Shwartz, Stanford Report

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