The sight of tiger sharks off the coast of South Florida can cause panic, but discoveries in a five-year research study into migration patterns show they travel 5,000 miles in sophisticated, predictable patterns every year and have highly evolved traits which are not designed for attacking humans.
"Sharks are there doing their own business, they're keeping the oceans healthy, they're not there to eat people," says Nova Southeastern University Professor Mahmood Shivji.
The researchers at Nova Southeastern University Guy Harvey Research Institute have been catching and tagging tiger sharks with satellite transmitters since 2010, and now they've just published their discoveries.
"We have tiger sharks that travel over 5,000 miles, making round trip loops, every year, going back to the same place in the winter, spending winters there in the Bahamas or the eastern Caribbean and spending the summers way out there in the middle of the Atlantic Ocean," said Shivji, senior researcher on the project.
The sharks build up an incredible amount of mileage, swimming from north of Bermuda near the Mid-Atlantic Ridge, south to the Bahamas, Hispaniola, the Turks and Caicos, and other nearby islands. No one knows how they navigate back to the same places in such a predictable pattern.
"We think they're using the earth's magnetic field as a means of orientation, there are no road signs out there, they don't have a GPS, how does that work?" said Shivji, laughing in amazement at the tiger shark's abilities.
The NSU scientists are also studying mako sharks, and finding they have similar migration patterns. All sharks, Shivji says, are crucial elements to a healthy ocean.
"They're very important to the marine ecosystem, they play the same role as wolves in Yellowstone or lions on the Serengeti in Africa," Shivji explained.
The satellite transmitters are electrical engineering marvels, but they usually don't last more than a year or two at the most. Also, they have to be above water and the satellite has to be in the correct position at the moment the shark's dorsal fin comes up in order for data to be transmitted. That's why getting three year's worth of data to track sharks is such a treasure trove of information. Turns out tiger sharks have a lot in common with tourists.
"It's a pattern, it's like snowbirds leaving New York and coming down to Florida every year for the winter, then going back to New York the next season, it's just like that," said Dr. Shivji.
There's also an immediate, practical application to the migration information, because now the sharks can be protected from overfishing.
"We know where they are, we know when they go, sharks have been overfished badly all over the place, we can now implement protection and management measures where they spend a lot of time," explains Dr. Shivji.
A handful of shark attacks on humans gets tons of attention every year, but with the world's shark population being decimated by commercial fishing, it's sharks who need protection from humans. The research being done at NSU may help sharks survive.