A great white shark nicknamed Nicole logged more than 12,000 miles swimming from Africa to Australia and back in less than nine months. Researchers say it is the first time a shark has been known to cross an entire ocean.
A second report details the movement of dozens of salmon sharks from summer waters near Alaska to warmer winter quarters off Hawaii and Baja California. Both reports appear in today's issue of the journal Science.
In November 2003, Ramón Bonfil of the Wildlife Conservation Society in New York led a team that attached satellite tags to the fins of 32 sharks circling off the coast of South Africa. "It wasn't easy and there were some moments of drama," Mr Bonfil said.
Some tags contained radio transmitters that communicated with a satellite every time the shark surfaced. Others were pre-programmed to detach from the shark after a set period, float to the surface and send their data.
Most of the sharks swam up and down the South African coast, but Nicole - named after the Australian actor and shark lover Nicole Kidman - made a beeline for Australia, where her tag popped up to the surface. In August 2004, her distinctively notched dorsal fin was spotted in South African waters again. The results suggest that one in 32 sharks may have wanderlust.
Peter Klimley, a shark expert at the University of California, Davis, told the Associated Press there had been genetic indications that Australian and African shark groups might be connected, "but that's not the same as showing actual movement".
A group led by Barbara Block of Stanford University tagged 48 salmon sharks in Alaskan coastal waters and tracked them by satellite from 2002 to 2004. They found some sharks remained in the North Pacific all year, eating salmon in summer and herring in winter, while others swam south to Hawaii or Baja California in winter. As they swam south, they dove deeper into cooler waters, the researchers found.
"The shark heart slows down in the cold, just as our own heart would," Professor Block said. "But ... where our heart would simply stop, the salmon shark's keeps on ticking."
The researchers found the hearts had high concentrations of proteins that control the uptake of calcium ions, which help maintain the heart's rhythmic contractions. It was the first time this has been seen in sharks, although Prof Block reported similar proteins in the hearts of giant bluefin tuna last year.