An international team of more than 150 scientists from 26 countries, including a King Abdullah University of Science and Technology (KAUST) professor, has collated movement data from nearly 2,000 sharks tracked with satellite transmitter tags.
The groundbreaking study, published in the journal Nature reports, revealed that even the remotest parts of the ocean appear to offer highly migratory sharks little refuge from industrialized fishing fleets.
The researchers, part of the marine megafauna movement, brought together by Carlos Duarte, professor of marine science at KAUST, mapped shark positions and revealed “hotspots” of space use in unprecedented detail.
“This research highlights the need and power of collaboration to better understand global conservation challenges in the open ocean,” said Duarte, co-author of the paper.
Regional declines in abundance of some shark populations such as shortfin mako shark — the fastest shark in the sea — have led to widespread calls for catch limits in the high seas. But precisely where in the vast expanse of the oceans’ sharks aggregate and how much fishing takes place in those chosen habitats remains poorly known globally, even though it will be crucial to selecting sites to conserve sharks.
“By overlaying global maps of shark abundance and movement contributed by over 150 researchers worldwide and fishing vessel movement data retrieved from the automatic identification system vessels to report their position, we have produced a global map of risks to shark conservation from the fishing industry. This work will help to advance conservation of endangered marine life,” Duarte added.
Researchers found multi-species pelagic shark hotspots were mostly located in frontal zones, 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.
Strikingly, they found 24 percent of the mean monthly space used by sharks globally falls under the footprint of pelagic longline fisheries. Commercially exploited sharks such as North Atlantic blue and shortfin mako sharks overlap was much higher, with an average of 76 percent and 62 percent of their space use, respectively, overlapping with longlines each month. Even internationally protected species such as great white and porbeagle sharks had overlap values exceeding 50 percent.
“Our results show major high seas fishing activities are currently centered on ecologically important shark hotspots worldwide,” said Professor David Sims, co-author of the study as part of the Global Shark Movement Project based at the Marine Biological Association Laboratory in Plymouth, UK.
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.