A great white shark named Nicole logged more than 12,000 miles swimming from Africa to Australia and back, the first proof of a link between the two continents’ shark populations, researchers say.
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.
“Sharks have home ranges that are at the scale of ocean basins,” said researcher Barbara Block of Stanford University. She added that conservation management of sharks such as the white shark and salmon shark will require international cooperation.
Tracking a shark from Africa to Australia “is one of the most significant discoveries about white shark ecology and suggests we might have to rewrite the life history of this powerful fish,” said Ramon Bonfil, lead author of that study.
Both reports appear in Friday’s issue of the journal Science.
George Burgess, a shark expert at the Florida Museum of Natural History, said while sharks are known to travel long distances, this was the first evidence of movement between Australia and Africa.
“These are large animals that have the capability of making large movements,” he said.
Enric Cortes of the National Oceanic and Atmospheric Administration’s Shark Population Assessment Group in Panama City, Fla., agreed this is the first direct evidence of a connection between African and Australian white sharks.
Using satellites to track sharks is new technology that may provide new perspective on their movements, he said.
Peter Klimley, a shark expert at the University of California, Davis, called a trip of that length “amazing.” He said there have been genetic indications that these two shark groups might be connected, “but that’s not the same as showing actual movement.”
Bonfil, of the Bronx, N.Y.-based Wildlife Conservation Society, said he “suspected that these sharks could be doing these kinds of travels ... but there was previously no proof of this. Everybody thought they were mostly coastal in behavior.”
A satellite tracking device temporarily attached to Nicole documented her 99-day swim from South Africa to Australia. About six months later, she was identified from photos back off the coast of South Africa.
Some 24 other white sharks tagged off South Africa engaged in wide-ranging coastal migration, but only Nicole headed out to sea. Nonetheless, Bonfil said, “I don’t think we got one in a million.”
Nicole was tagged in November 2003 with a device that reports her position. The researchers said the shark was renamed Nicole in honor of Australian actress Nicole Kidman.
Alaskan salmon shark study
Block’s group 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,” Block said. “But ... where our heart would simply stop, the salmon shark keeps on ticking.”
The researchers found the hearts had high concentrations of proteins that control uptake of calcium ions, which help maintain the heart’s rhythmic contractions.
It was the first time that has been seen in sharks, but Block reported similar proteins in the hearts of giant bluefin tuna last year.
“The sharks are expressing mammalian levels of these cardiac proteins, which is highly unusual for a gill-breathing shark,” she said.
Could there be human applications?
“We could potentially recommend that, when subject to cold stress, stimulation of these pathways with drugs may have potential benefit for getting the heart going and delivering its oxygen,” she said.
Funding for the Nicole study came from conservation groups and the South African government, while the salmon shark research was funded by the U.S. Office of Naval Research, National Science Foundation and private foundations.