Sharks Could Be Overfished Because Fishing Vessels Share Their Hotspots

In the North Atlantic, commercial fishing vessels are spending a great deal of time in shark hotspots, says a new study. The researchers feel that sharks may be in danger of being overharvested in these areas.

A team from the University of Miami (UM), the Marine Biological Association (MBA), University of Porto (Portugal) and other institutions recently published their findings in the journal Proceedings of the National Academy of Sciences. It might be necessary to institute quotas on the catch levels for sharks for commercial fishing, the authors noted in the study.

"Our research clearly demonstrates the importance of satellite tagging data for conservation," Neil Hammerschlag at UM said in a release. "The findings both identify the problem as well as provide a path for protecting oceanic sharks."

The study took place from 2005 to 2009, when researchers followed the movements of 100 sharks wearing satellite tags, from six species in the North Atlantic. At the same time, the scientists kept track of 186 Spanish and Portuguese longline fishing vessels equipped with GPS.

Findings included that the sharks and fishing vessels both were present in ocean fronts defined by warm waters and high productivity. These included the North Atlantic Current/Labrador Current Convergence Zone, near Newfoundland; and the Gulf Stream.

"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," Professor David Sims of the MBA said in the release.

In the study, about 80 percent of the range for blue and mako sharks, two of the most strongly fished species in the tracking - were in the same range as the fishing vessels. Some sharks remained near longlines for more than 60 percent of when they were being tracked. Blue sharks seem to be vulnerable to possible capture 20 days each month; mako sharks may be at risk 12 days a month.

Each year, scores of millions of sharks in oceans are caught by commercial fishing each year. The researchers propose that quotas or size limits may be necessary going forward.

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