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Big Tracks, Surprising Findings from 2015 Shark Tracking Project
The yellow, green, pink, and white dots and blobs on this Google Earth graphic cover such a large portion of the globe that it is difficult to show the entire picture. And that means a heck of a lot to marine scientists like Drs. Guy Harvey, Mahmood Shivji, and Brad Wetherbee of the Guy Harvey Research Institute at Nova Southeastern University near Fort Lauderdale.
The dots and globs represent the paths of some 40 sharks rigged with satellite tags that the scientists tracked in 2015: three tiger sharks (green); 20 makos (yellow); seven oceanic whitetips (pink); and one dusky, four hammerheads and a sixgill (white and barely visible off Boca Grande, FL and Bermuda).
“Pretty impressive. A huge part of the ocean,” noted Wetherbee of the sharks’ movements.
Satellite tags, which cost upwards of $4,000 apiece, are technology’s most precise method of monitoring the animals’ movements minute to minute. Funded by the non-profit Guy Harvey Ocean Foundation, the transmitters are affixed to the sharks’ dorsal fin, sending their locations to a satellite that beams the information to the researchers’ computers. Wetherbee then plots that information on Google Maps.
What this worldwide splash of color represents is a blueprint for protecting sharks from habitat loss and overfishing. And the tracking data has turned a few shark theories on their heads.
According to Wetherbee, tiger sharks– previously believed to be a coastal species– are nothing of the kind. The data shows they spend half their time in the open ocean thousands of miles from shore, but in winter show a snowbird-like affinity for coral reefs in the Caribbean and Bahamas. One tiger nicknamed Harry Lindo covered 27,000 miles– the longest distance ever tracked for the species.
Mako sharks seem to stick to the open ocean– cruising the edge of the Continental Shelf off the U.S. east coast then making long trips north to New England and Canada.
The oceanic whitetips tend to wander around aimlessly, though whatever they’re doing isn’t aimless to them– sort of like a bee flying over fields and alighting on several flowers in one field but totally ignoring those in another.
The makos and whitetips were named competitors in the Great Shark Race of 2015 created by the Guy Harvey Ocean Foundation and Research Institute to encourage businesses and individuals to sponsor satellite tags. The shark covering the greatest distance in six months– a shortfin mako named Ebenezer that swam 7,387 miles–was declared the winner. Ebenezer– named by Ebenezer Thomas Primary School in Tortola, British Virgin Islands– was sponsored by Sir Richard Branson’s Virgin United. It was tagged off Ocean City, Md. on May 27, made it to Newfoundland in the allotted time, and is still transmitting.
Unlike those free-swimming makos and whitetips, Wetherbee noted that hammerheads tend to stick to coastlines in the U.S. and avoid long-distance travel. Sixgills, he said, stay in deep water and don’t go very far while duskys seem attached to certain sites, but still may travel a few hundred miles.
“There are sharks without a country, moving through 10 to 15 different countries,” Wetherbee said. “They are all over the place.”
The research has important implications for shark management: knowing what countries’ waters the sharks use suggests who is responsible for managing that population and where the animals are most likely to be harvested by fishers.
“Shark populations have been overfished quite a bit. Managing these populations is going to take international cooperation,” Wetherbee said.
Mako sharks, while not classified as overfished, could still be in trouble as they are heavily targeted by commercial longliners and recreational anglers in the U.S. and elsewhere.
“Makos are in a lot of areas with tuna and swordfish,” Wetherbee said. “Everybody is after these makos because they are good to eat.”
Indeed, 13 of the 49 makos tagged by the GHRI scientists over the past four years have been caught and killed by commercial fishers. The tiger sharks, fortunately, escaped those gauntlets.
Wetherbee, Harvey and Shivji plan more shark-tagging expeditions in 2016, hoping to fit another 40 to 50 animals with satellite transmitters.
Sue Cocking chronicles the Guy Harvey Outpost travel and adventure experience in regular blog posts on GuyHarveyOutpostNews.com/. For 21 years, Cocking covered the full spectrum of outdoors adventure opportunities in South Florida and beyond for the Miami Herald, including fishing, diving, hunting, paddling camping, sailing and powerboat racing. She is a certified scuba diver and holder of an IGFA women’s world fly fishing record for a 29-pound permit.
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