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Marine life, such as these invertebrates and small fish, can be inadvertently disrupted when trawling on the seabed. Credit: Jan Hiddink / Bangor University
About a quarter of seafood caught in the ocean comes from bottom trawling, a method of pulling a net along trays and ocean slopes to pick up shrimp, cod, redfish, sole and other species of fish. bottom fish and shellfish. The technique has an impact on these seabed ecosystems, as other habitats and marine life can be inadvertently killed or disturbed when nets sweep the seabed.
Scientists agree that intensive bottom trawling can have negative effects on marine ecosystems, but it remains difficult to pin down the question of how much seabed is trawled or what is called the trawl footprint.
A new analysis that uses high resolution data for 24 oceanic regions of Africa, Europe, North and South America, and Australasia shows that 14% of the time is spent in the US. seabed, which is less than 1,000 meters (3,280 feet) deep, are trawled. Most trawl fishing takes place at this depth along the continental shelves and the slopes of the world's oceans. The study is focused on this range of depths, covering an area of about 7.8 million square kilometers of ocean.
The newspaper, published on October 8 in the newspaper Proceedings of the National Academy of Sciences, brought together 57 scientists based in 22 countries and has expertise in mapping fishing activities from satellite monitoring data and fishing logs. It shows that the footprint of bottom trawling on the continental shelves and the slopes of the world's oceans has often been considerably overestimated.
"Trawling is a very controversial activity and its footprint has not been quantified at a sufficiently high resolution for as many regions," said lead author Ricardo Amoroso, who carried out the research as as a postdoctoral researcher at the School of Aquatic. Fisheries science. "When you do not quantify the impacts of trawling on a fine scale, you end up with an overestimate of the trawl footprint."
A beam trawler sits on the wharf in Milford Haven, Wales, UK. Credit: Jan Hiddink / Bangor University
Previous analyzes, for example, mapped trawling on grids of 1000 km 2 or more, compared to the 1 to 3 km 2 grids used in this analysis.
The footprint estimates presented in this new article are also more accurate than those described in previous studies, as they use information on gear used by fishing fleets, the authors explained. For example, knowing whether a trawl net covers 10 meters or 100 meters improves the estimate of the area of the affected seabed.
Although the authors found that 14% of the regions included in the study were trawled, there were major regional differences. For example, only 0.4% of the seabed in southern Chile is trawled, while more than 80% of the bottom of the Adriatic Sea, part of the Mediterranean Sea with the most intense footprint, is trawled.
In addition, trawl footprints covered less than 10% of the sea floor in Australian and New Zealand waters, as well as in the Aleutian Islands, the Bering Sea and the Gulf of Alaska in the North Pacific, but exceeded 50% in some European seas.
The study also provided evidence of the associated environmental benefits. In areas where fishing rates for commercially caught trawl fish met sustainability criteria, trawl marks were generally smaller, explained co-author Simon Jennings of the International Council for the Conservation of Trawlers. exploration of the sea
Examples of high resolution mapping of trawl intensity (or "trawl footprint") at 1,000 meters depth or less. The dotted line represents the study area and the blue line continues the 1,000-meter depth zone. The scale bar is 100 kilometers away. Credit: University of Washington
"In areas where bottom trawling accounted for less than 10% of the seabed, groundfish fishing rates almost always met international sustainability criteria, but when they were above 20 %, they rarely reached them, "said Jennings.
The authors acknowledge that some areas known to have significant trawl activity were not included in this study as data providing a detailed picture of fishing activity was not available. Southeast Asia is one of these regions.
Still, this new article offers the most comprehensive look at trawling activity in the world, said co-author Ray Hilborn, professor at UW in Aquatic Sciences and Fisheries. It also describes a way to estimate the trawl footprint in areas where gear size, vessel speed and total number of trawling hours are known, but without the data. location specific to ships currently collected by certain fleets.
"We can use this method to reasonably estimate the impact of trawling in places where we do not have fine-scale spatial data," Hilborn said.
Other researchers involved in the design of the study are Michel Kaiser of Bangor University in the UK and the Marine Stewardship Council; Roland Pitcher of CSIRO Oceans and Atmosphere in Australia; Adriaan Rijnsdorp of Wageningen Marine Research in the Netherlands; Robert McConnaughey of NOAA Fisheries, Alaska Fisheries Science Center; Ana Parma of the Centro Nacional Patagónico in Argentina; Petri Suuronen of the United Nations Food and Agriculture Organization and the Finnish Natural Resources Institute; Jeremy Collie from the University of Rhode Island; and Jan Hiddink from Bangor University. A complete list of co-authors is available in the document.
This group is also evaluating the impact of trawling on plants and animals that live on the sea floor and how changes in these plants and animals affect the main fish species.
Explore further:
Bottom trawling techniques leave different traces on the seabed
More information:
Ricardo O. Amoroso et al., "Bottom Trawling Footprints on the Continental Shelves of the World" PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1802379115
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