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Trawling Modifies the Relief of the Seabed

26 September 2012, at 1:00am

SPAIN - Researchers at the National Research Council (CSIC) and the University of Barcelona have concluded that intensive trawling has changed significantly, in just four decades, the relief of the sea floor.

The study, published in the latest issue of the journal Nature, focuses on the impact of this activity on the seabed of the fishing grounds of the upper continental slope, between 200 and 900 meters deep. The results show that the "plow" has altered the natural sediment dynamics and has softened and simplified the morphology.

The study was conducted in northeastern Catalan coast, in particular in the submarine canyon of La Fonera, also called Palamos. The research team has used various oceanographic instruments to measure the affects of trawlings.

The trawl doors and nets on the seabed remove fine particles that form the surface sediment. "The continental slopes, particularly the flanks or sides of submarine canyons are seafloor regions with a relatively high slope and have traditionally been exploited by the trawling fleets," explains CSIC researcher Pere Puig, who works at the Institute of Marine Sciences in Barcelona.

"Bottom trawling tends to cause the terracing of the slopes of the canyons," says Professor Miquel Canals, Professor of Marine Geology at the University of Barcelona.

The article deals with the morphological transformation of continental slopes by the impact of trawling, compared with the morphological changes caused by agricultural activities on land. "The fishing grounds on the continental slopes would be the equivalent in the sea as a crop field on a mountainside that has been plowed continuously to modify its original relief," explains Mr Puig. "One notable difference is that farmland plowing is usually done once or twice a year, while in the fishing grounds of the continental slope, the drag is done every day," adds Mr Canals.

Scientists have conducted a bibliography of the main areas of intensive trawling on the continental slopes of all the oceans, to highlight the potential global reach of its findings. The work, the result of several research projects, also indicates that the natural conditions of the continental slopes have been affected by the alterations caused by trawling.

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