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Tiger Sharks Behave like Birds?

Jun 12, 2015 07:21 AM EDT
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(Photo : Nick Filmalter/Danah Divers)

Well, not quite. But new remarkable research has shown that in the longest ever tiger tracking study, these predators boast migration patterns more similar to birds, turtles and some marine mammals than other fishes.

Tiger sharks are among the largest and most recognizable sharks on the planet, and yet many of their habits remain a mystery because they are long-distance travelers whose movements are difficult to track.

They were long believed to be a coastal species; however, after following several tiger shark for more than two years with satellite tags, a team from Nova Southeastern University (NSU) have shown otherwise. The studied sharks traveled more than 7,500 kilometers (4,660 miles, round-trip) every year between two vastly different ecosystems - the coral reefs of the Caribbean and the open waters of the mid-North Atlantic. Furthermore, they returned consistently to the same overwintering areas each year, a discovery that could help with conservation efforts.

This study, published in the journal Scientific Reports, has yielded the first ever continuous tracking of these normally elusive creatures.

"As apex predators, the presence of tiger sharks - and other large sharks - is vital to maintain the proper health and balance of our oceans," Dr. Mahmood Shivji of NSU, who helped lead the study, said in a statement. "That's why it's so important to conserve them, and understanding their migratory behavior is essential to achieving this goal."

During the study, the NSU team successfully tagged and tracked tiger sharks near Bermuda, following their every move.

One tiger shark even swam more than 44,000 kilometers (27,000 miles) - that's the longest track distance ever documented for a tiger shark.

More importantly, researchers found that during their annual migrations, male sharks in the Atlantic repeatedly spent their winters in Caribbean island locales, whereas during summers they would travel far north, even reaching Connecticut. These migrations curiously more resemble those of birds, which are known for traveling hundreds of miles annually.

Furthermore, while researchers expected the sharks to hang by the coast, instead they were seen swimming way offshore in nearly the middle of the ocean.

"These repeated journeys were very unexpected," said lead researcher James Lea. "The tiger shark has traditionally been considered a coastal species, and it is rare among sharks to so easily and habitually switch between the two vastly different environments."

What's more curious is that the sharks followed the same pattern each year and returned to nearly the same spot every time.

"Even though they've got a whole range of islands to choose from, it seems like each animal has its favorite winter spot," said Shivji.

The reason why tiger sharks have a favorite spot remains to be seen. But researchers speculate that it's because female tiger sharks frequent the Caribbean come wintertime - easy pickings to find a mate for males.

These migration patterns are unique for tiger sharks, and have only otherwise been seen in the Pacific Ocean's great white and salmon sharks. And given that this species is nearing threatened status - partly due to the shark fin soup trade - NSU researchers hope their findings can lead to better protections for tiger sharks.

"Understanding how these animals use the oceans is the first step toward effective conservation," explained Guy Harvey, one of the researchers. "Protecting migratory species is a great challenge because they can be found in such a wide area. Protecting the areas where animals, such as tiger sharks, spend the most time is a tractable goal once those areas have been identified."

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

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