Around a quarter of the habitat of oceanic sharks is actively fished, with potentially disastrous consequences, new research shows.

An international team tracked the movements of 1680 sharks of 23 different species using satellite tags and monitored the movements of global fishing fleets to see where their paths crossed.

This revealed that areas frequented by protected species have much higher overlap with longline fisheries, suggesting, they say, that more concerted action may be required to sustain shark populations.

The work brought together scientists from nine universities in Australia and New Zealand, Australia’s CSIRO, and the Marine Biological Association (MBA) Laboratory in the UK.

“Our results show major high seas fishing activities are currently centred on ecologically important shark hotspots worldwide,” says research leader David Sims, from the MBA.

The findings are published in the journal Nature.

Oceanic (pelagic) sharks are highly migratory, but the extent of habitat overlap with industrial fisheries has been difficult to determine because of a lack of data.

However, it is known that large pelagic sharks inhabiting the open ocean account for over half of all identified shark catch globally in target fisheries or as bycatch.

In the latest study, Sims and colleagues combined satellite-tracked movements of pelagic sharks and global fishing fleets. Their results reveal that 24% of the space used by sharks in an average month falls under the footprint of pelagic longline fisheries, which are responsible for catching most sharks from the open ocean.

Areas of ocean that are frequented by protected species, such as great white sharks and porbeagle sharks, had an even higher overlap with longline fleets – around 64%.

“Given the high fishing effort in hotspots of many species for significant portions of the year, and the very few tracked hotspots free from exploitation, our study reveals exposure risk of sharks to fisheries in the high seas is spatially extensive – stretching across entire ocean-scale population ranges for some species,” the researchers write.

“Overall, the patterns suggest a future with limited spatial refuge from industrial longline fishing effort that is currently centred on ecologically important oceanic shark hotspots.

“The distribution maps reported here are, therefore, a first but essential underpinning for a conservation blueprint for pelagic sharks in the high seas.”

One solution, the researchers suggest, would be designation of large−scale marine protected areas (MPAs) around ecologically important areas, “notwithstanding the need for more complete reporting of catch data with enforcement to support stricter conventional management by catch prohibitions, quotas or minimum sizes”.

And while they acknowledge it would be challenging to develop a legally binding treaty for managing high seas fauna, they make the point that “burgeoning technology for global surveillance and enforcement” offers additional options for a step change in ocean management.

“Conservation technology could develop in the future toward incorporation of adaptive management strategies that are actionable in real time to assess risks in the overlap between fishing vessels and sharks across the global ocean,” they write.


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