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A quarter of seafood caught in the ocean is caught by bottom trawling, a method that harms seabed ecosystems.
The technique involves pulling a net along trays and ocean slopes to collect shrimp, cod, redfish, sole and various bottom fish and shellfish.
Other life forms and marine habitats may be inadvertently killed or disturbed as the nets cross the seabed.
Researchers agree that the technique is harmful, but up to now the extent of bottom trawling is still poorly understood.
A new analysis, which brings together the contributions of 57 scientists from 22 countries, suggests that 14% of the ocean floor, from a depth of less than 1,000 m, is trawled.
Most of the trawl fishing is at this depth and the study focused on this seabed range, which covers about 7.8 million km2 of ocean.
Researchers had expertise in mapping fishing activities from satellite monitoring information and fishing logs.
For their report, they used high resolution data for 24 oceanic regions of Africa, Europe, North and South America, and Australasia.
A beam trawl, shown out of the water. (Jan Hiddink/ Bangor University)
An illustration showing the operation of bottom trawling (Jan Hiddink/ Bangor University)
Fourteen percent is significantly lower than previous estimates of what is known as a trawl "footprint," but researchers found that bottom trawling popularity varied considerably across regions.
The authors of the report found that more than 80% of the Adriatic seabeds, a part of the Mediterranean Sea with the most intense footprint, are trawled, whereas this method does is used only on 0.4% of the seabed. in southern Chile.
The researchers also concluded that more than 50% of the seabeds in some European waters are trawled, but that this technique is much less used in the Australian and New Zealand seas, where trawl footprints cover less than 10% of the seabed. .
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In the middle of a flood in Islampur, Jamalpur, Bangladesh, a woman on a raft is looking for a dry place to shelter. Bangladesh is one of the world's most vulnerable countries to sea level rise, which is expected to leave tens of millions homeless by 2050.
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Hanna Petursdottir examines a cave located inside the Svinafellsjökull Glacier in Iceland, whose number has rapidly increased. Since 2000, the size of Icelandic glaciers has been reduced by 12%.
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The floods destroyed eight bridges and destroyed crops such as wheat, maize and peas in the Karimabad Valley in northern Pakistan, a mountainous region with many glaciers. In many parts of the world, glaciers have retreated, creating dangerously large lakes that can cause devastating floods when the riverbanks break. Climate change can also increase rainfall in some areas, while causing drought in others.
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A river once flowed along the dry land depression of this part of Bangladesh, but it disappeared with rising temperatures.
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Pakistan's Sindh province has had a sad mix of two consequences of climate change.
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A shepherd moves his flock while he looks for a green pasture near the village of Sirohi in Rajasthan, in northern India.
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The same goes for the East Bering Sea, the Gulf of Alaska and the waters around the Aleutian Islands of the North Pacific.
"Trawling is a very controversial activity and its footprint has not been quantified at a sufficiently high resolution for so many regions," said lead author, Ricardo Amoroso, of the University of Washington .
"When you do not quantify the impacts of trawling on a fine scale, you end up with an overestimate of the trawl footprint."
A smaller portion of the ocean floor is trawled in areas where rates for commercially caught stocks caught by bottom trawling meet accepted sustainability criteria.
A beam trawler sits on the wharf in Milford Haven, Wales (January Hiddink/ Bangor University)
"In areas where bottom trawls accounted for less than 10% of the seabed, fishing rates on groundfish stocks almost always meet international sustainability criteria," said Simon Jennings, co-trawler -author of the report.
"But when fingerprints exceed 20%, they rarely meet them."
Researchers used information on fishing gear used in commercial operations to help them accurately estimate trawling footprints.
Knowing the length of a trawl has improved the estimate of the area of the affected seabed.
Some areas where bottom trawling is widely used, including Southeast Asia, are not included in the study as detailed data were not available.
Despite this, scientists say their study is the most detailed trawling activity in the world.
The research is published in Proceedings of the National Academy of Sciences.
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