A major study has highlighted how sharks are threatened by commercial fishing around the globe.

A Kiwi co-author of the new research, just published in the journal Nature, says while threats to sharks were closely managed in New Zealand waters, that often wasn't the case in the high seas beyond.

The study, authored by more than 150 scientists from 25 countries, and combining data from nearly 2000 satellite-tagged sharks, revealed a significant overlap between fishery areas and shark hot-spots.

These hot-spots, important for many species, were found in ocean frontal zones, boundaries in the sea between different water masses that are highly productive and food-rich.

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The researchers then calculated how much shark hot-spots overlapped with global longline fishing vessels - which use the type of fishing gear that caught most open-ocean sharks.

The study found that 24 per cent of the space used by sharks in an average month falls under the footprint of longline fishing.

For commercially exploited sharks such as blue and shortfin makos sharks in the North Atlantic, the overlap was much higher, with on average 76 per cent and 62 per cent of their space use, respectively, overlapping with longlines each month.

Even internationally protected species, such as great whites, had over 50 per cent overlap with longline fleets.

In our corner of the planet, hot-spots were identified in New Zealand shelf waters and around the Kermadec Islands northeast of the country, along with the South Australian Basin, northwest Australia and the southern Great Barrier Reef.

Co-author and Niwa fisheries scientists Dr Malcolm Francis said the study included data from locally-tagged great white, mako and porbeagle sharks.

Great whites were known to hang around New Zealand, specifically at seal colonies to the south, but also spent half the year in tropical spots like Tonga, New Caledonia and the Great Barrier Reef.

Makos, juveniles especially, were present in large numbers in our coastal and shelf waters around New Zealand - mainly around the northern North Island.

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"They feed mostly on small schooling fish and can be here all year round – but some of them also migrate to the tropics in winter and spring," Francis said.

Fishing methods in New Zealand's coastal fisheries included set netting, bottom-long lining and trawling, all which could pose a threat to great whites.

Mako shark bycatch had been observed in tuna long-line fishing away from our coasts, and out on shelves in waters more than 1000m deep.

Francis said the threat to these species, and others like blue sharks, had been understood for a long time, "but this study really just quantifies it on a global scale, for the first time".

In New Zealand, porbeagle and mako catches were accounted for under the Quota Management System, and, with shark finning now banned, all were generally thrown back into the water.

Great whites were a protected species so also couldn't be caught.

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"The situation is closely managed here, but on the high seas beyond New Zealand, there is much less in the way of management, and that's what this paper is really trying to highlight."

The team's findings specifically showed how large sharks - some of which were already endangered globally - faced a future with limited spatial refuge from industrial longline fishing effort.

"Currently, little to no protection exists for sharks in the high seas. It's clear from our study that immediate conservation action is needed to prevent further declines of open-ocean sharks," said Neil Hammerschlag, a study co-author and research associate professor at the University of Miami in the United States.

"These finding are concerning because as top predators, sharks help maintain healthy ocean ecosystems."

The researchers propose that designated large-scale marine protected areas around regions of shark activity could be one solution.

The study also suggested that detailed maps of shark hotspots overlapping with longline fishing provided a "blueprint" for deciding where to place large-scale marine protected areas aimed at conserving sharks, along with the need for strict quotas to reduce catches elsewhere.

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