"But why do they move all the way to Brazil?" he asked. "There is plenty of food for them in northern Florida."
One theory is that they're heading to undiscovered nursery grounds.
Scientists have never seen a young basking shark. "We still have no idea where they give birth," Skomal said.
Mauvis Gore, a biologist from Marine Conservation International, was involved in a 2007 study that tracked a basking shark crossing the Atlantic, east to west.
"Tracing basking sharks on these journeys begins to tell us much more about the population structure," Gore said.
For example, study co-author Skomal said, based on tracking data, "What were thought to be regional stocks may in fact belong to a single, oceanwide population."
(See shark pictures.)
Key to Saving Sharks?
The International Union for Conservation of Nature lists basking sharks as being vulnerable to extinction. And "any kind of impacts on basking sharks in one region may affect the entire population," Skomal said.
The new discovery could help address threats facing the sharks, Skomal said—perhaps sooner rather than later.
In August the Save Our Seas Foundation is holding a workshop to bring together basking shark researchers from around the world.
"We hope to develop a program of how best to move forward in working out just what is happening with populations of basking sharks worldwide," Marine Conservation International's Gore said.
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