An international team of researchers that tracked sharks by satellite has found that so-called "hotspots" of shark activity are at a far greater risk of being overfished than previously imagined.
According to research just published in the journal Proceedings of the National Academy of Sciences by a team out of the United Kingdom, United States, Spain and Portugal, when more than 100 sharks from six different species were tracked and their paths compared against the GPS movements of nearly 200 fishing vessels, the sharks and the vessels were overwhelmingly in the same places.
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While it's not surprising in and of itself to see fishing vessels and fish in the same spot, it was the sheer scale of the overlap that indeed surprised the researchers and pointed toward an increased chance the fish could be taken out of the sea in overly large numbers.
"Although we suspected overlap might be high, we had no idea it would be this high," said lead author Nuno Queiroz, of the University of Porto, Portugal, in a release. "Space-use overlap on this scale potentially increases shark susceptibility to fishing exploitation, which has unknown consequences for populations."
Two of the most-fished sharks - mako and blue - saw around 80 percent of their range overlapped by the presence of fishing vessels, the team observed.
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The researchers found the greatest risk of overfishing was in waters such as the Gulf Stream, the mid-Atlantic ridge southwest of the Azores, and the North Atlantic current/Labrador current convergence zone near Newfoundland.
There is little in the way of regulation regarding oceanic shark fishing, the scientists said, owing in part to a dearth of information about the places where fishing vessels and sharks overlap.
"Many studies have tracked sharks, and many studies have tracked fishing vessels, but fine-scale tracking of sharks and fishing vessels together is lacking, even though this should better inform how shark fisheries should be regulated," said senior author David Sims, of the University of Southampton.
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With tens of millions of sharks already being hauled from the sea on a yearly basis, the authors suggest that catch quotas or size limits be instated in the hotspots.
"This highlights how broadly the fishing exploitation efficiently ‘tracks' oceanic sharks within their hotspots year-round," Sims said. "In the North Atlantic, it seems threatened sharks have few places left to hide in the face of industrialized, high-seas fishing of the last 50 years."