Sharks at risk in key Atlantic fishing zones

A whitetip reef shark. Photo courtesy NOAA.
A whitetip reef shark. Photo courtesy NOAA.

New research can guide conservation efforts

Staff Report

A four-year study that followed about 100 tagged sharks shows that commercial fishing operations overlap with shark hotspots in the ocean. The findings suggest that sharks are at risk of being overfished in some areas.

“Our research clearly demonstrates the importance of satellite tagging data for conservation,” said Neil Hammerschlag, director of the shark research program University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science. “The findings both identify the problem as well as provide a path for protecting oceanic sharks,” Hammerschlag said.

The study tracked six different species of sharks, as well as  186 Spanish and Portuguese GPS-equipped longline fishing vessels. They found that the fishing vessels and sharks occurred in ocean fronts characterized by warm water temperature and high productivity, including the Gulf Stream and the North Atlantic Current/Labrador Current Convergence Zone near Newfoundland.

“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 Professor David Sims of the Marine Biological Association, and the senior author of the study that was published in the journal Proceedings of the National Academy of Sciences.

The authors reported that catch quotas for sharks by commercial fishers might be necessary to protect oceanic sharks. About 80 percent of the range for two of the most heavily fished species tracked–the blue and mako sharks–overlapped with the fishing vessels’ range, with some individual sharks remaining near longlines for over 60 percent of the time they were tracked. Blue sharks were estimated to be vulnerable to potential capture 20 days per month, while the mako sharks’ potential risk was 12 days per month.

“Although we suspected overlap might be high, we had no idea it would be this high. Space-use overlap on this scale potentially increases shark susceptibility to fishing exploitation, which has unknown consequences for populations,” said Nuno Queiroz of the University of Porto, Portugal, the lead author of the study.

Tens of millions of ocean-dwelling sharks are caught by commercial fishing operations each year. The researchers suggest that a lack of data on where sharks are likely to encounter fishing vessels has hampered current shark conservation effort.

The researchers propose that because current hotspots of shark activity are at particularly high risk of overfishing, the introduction of conservation measures such as catch quotas or size limits will be necessary to protect oceanic sharks that are commercially important to fleets worldwide at the present time.

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