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(Reuters) – Bottom trawling by fishermen, long believed to harm marine life, may be even more damaging than previously thought, affecting the seabed as seriously as intensive ploughing of farmland erodes the soil, according to a new Spanish study.

Bottom trawling – dragging nets across the sea floor to scoop up fish – stirs up the sediment lying on the seabed, displaces or harms some marine species, causes pollutants to mix into plankton and move into the food chain and creates harmful algae blooms or oxygen-deficient dead zones.

Scientists from the Marine Sciences Institute in Barcelona and the University of Barcelona found that trawling displaced sea floor sediment and made the seabed smoother over time.

“Bottom trawling has been compared to forest clear-cutting, although our results suggest that a better comparison might be intensive agricultural activities,” they said in a study published on the journal Nature’s website on Wednesday.

During the 20th century, more intensive farming techniques and changes in land use reduced the diversity of landscapes almost everywhere, the study said.

Ploughing up land exposes the top soil to erosion by wind and water, destroying or weakening nutrients in the soil which are essential for many plant species to survive.

Fishing has also become increasingly industrial. As technology has improved and traditional fish stocks have been depleted, trawling fleets have gone into ever deeper waters in search of fish.

As with soil, the seabed is composed of layers of sediment, holding nutrients that are vital for marine life. Read the full article