A new international study published in the journal Nature shows just how vulnerable migratory species of sharks are to commercial fishing when they swim into open water.
According to the study by Flinders University, large sharks inhabiting the open ocean account for more than half of all identified shark catch globally in target fisheries or as bycatch. Currently, there is little or no management for sharks caught in areas beyond national jurisdictions.
In the study, Flinders University associate professor Charlie Huveneers mapped shark positions used satellite tracking data and revealed “hotspots” were mostly located in boundaries in the sea between different water masses that are highly productive and food-rich.
They then calculated how much the hotspots were overlapped by global fleets of large, longline fishing vessels—the type of fishing gear that catches most pelagic sharks—with each vessel capable of deploying 100 km long lines bearing 1200 baited hooks on a daily basis.
“We found 24 percent of the mean monthly space used by sharks globally falls under the footprint of pelagic longline fisheries,” Huveneers said. “It means about one-quarter of shark habitats fall within active fishing zones, presenting a threat to these iconic ocean predators and demonstrating an urgent need for conservation efforts to protect declining pelagic shark populations.”
The study was led by Professor David Sims, as part of the Global Shark Movement Project based at the Marine Biological Association Laboratory in Plymouth, England. The team’s findings indicate large sharks—some of which are already endangered globally—face a future with limited spatial refuge from industrial longline fishing effort.
The researchers propose that the detailed maps they have produced of shark hotspots and exposure to longline fishing effort can provide a blueprint for use in deciding where to place large-scale marine protected areas (MPAs) aimed at conserving sharks, in addition to the need for strict quotas to reduce catches elsewhere.
“Some of the shark hotspots we studied may not be there in as little as a few years’ time if management measures are not put in place now to conserve the sharks and the habitats on which they depend,” Sims said.
Additional findings include:
- Major high seas fishing activites are centred on ecologically important shark hotspots worldwide
- North Atlantic blue sharks and shortfin mako have an average 76 percent and 62 percent of their space use, respectively, overlapped by longlines each month
- Even internationally protected species, such as white shark and porbeagle sharks, are at risk
- Results could provide a blueprint for use in deciding where to place large-scale marine protected areas (MPAs)
- There is a danger of accelerating decline in populations and disappearance of hotspots without immediate action