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This article is more than 1 year old

The world’s shark populations are at increasing risk of becoming bycatch of international fishing fleets, which harvest them in open oceans where no legal protections exist, Australian researchers have said.

Prof Rob Harcourt, from Macquarie University, said large sharks were more vulnerable to longline fishing and called for urgent action to protect them by implementing management strategies on the high seas.

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Harcourt joined colleagues from Australia and 25 other countries to collect and collate data from nearly 2,000 sharks tracked using satellite transmitter tags.

According to a paper published on Wednesday in the journal Nature, more than 150 scientists found the larger shark species accounted for more than half of all identified sharks caught globally as fisheries targets or bycatch.

“This paper shows that pelagic sharks converge on what we call ‘hotspots’ in the oceans, where there are high concentrations of prey,” Harcourt said. “Unfortunately, for the very same reason, fishing fleets head there, too. This makes the sharks more vulnerable and the need to protect them much more urgent.”

The findings indicate large sharks face a future with limited refuge from industrial longline fishing.

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Harcourt said the shortfin mako had “quite good status” in Australian waters, because fish stocks are managed reasonably well.

But he said “sharks don’t see the boundaries of our exclusive economic zone” and head off into deeper waters, where there is much less protection from international fishing fleets.

“So even though we protect them well, unless we can create the same levels of protection right across Oceania they will remain in danger of severe depletion,” he said.

Researchers from the Australian Institute of Marine Science, Deakin University and University of Western Australia were also involved in the study.