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Report: Deep-sea trawling causes widespread ecosystem damage

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Fishing boats at anchor in Appalachicola, Florida.

Study shows losses in seabed biodiversity after regular fishing

By Staff Report

FRISCO — It may be hard to imagine a desert at the bottom of the ocean, but scientists working in the Mediterranean region say that’s exactly what’s happening in areas that are heavily fished by deep-sea fishing trawlers. In some of the studied areas, the number of microorganisms has dropped by 80 percent from pre-trawling days, with an overall drop of 50 percent in biodiversity.

Dragging heavy nets across the ocean flower is inexorably changing the marine ecology by reducing organic carbon content and threatens regional biodiversity, said the scientists from the Polytechnic University of Marche in Ancona, Italy.

Trawling is the most commonly used extraction methods of sea living resources used around the world, but at the same time, it is also one of the main causes of seabed degradation. This fishing practice originated in the second half of the fourteenth century, and in the last thirty years has grown exponentially, progressively expanding into deeper ocean zones.

The study, published in the latest issue of the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), focused on assessing the impact of this activity on the meiofauna (small organisms, between 30 and 500 micrometers) living in marine sediments over the fishing grounds of the continental slope, about 500 meters deep.

 

The study was conducted in northeastern Catalan coast, in La Fonera, also called Palamos, submarine canyon and is the continuation of a previous work where the impact of this method of fishing on the morphology and sedimentary dynamics of this canyon was evaluated1.

“The dragging of the gear on the seabed lifts and removes fine particles of sediment, yet also resuspends small organisms living in the sediment that constitute the base of the food chain at these depths”. Jacobo Martin, also at ICM-CSIC and who currently works at the Centro Austral de Investigaciones Científicas of Ushuaia, Argentina, adds “in the long run, it causes a steady loss of fine sediments, soft and rich in organic matter, leaving a more depleted and compacted seabed sediment surface that it is more difficult to be colonized again”.

The work compares these kinds of impacts of trawling on marine sediments with the loss of fertile soil on land. According to Pere Masqué, researcher at the Department Physics and the Institute of Environmental Science and Technology at UAB, “The fishing grounds are compared to agricultural fields in terms of the morphological change caused to the seabed, and may end up becoming barren if the constant loss of superficial sediment endures over time”.

The paper concludes by warning about the ecological consequences and effects on ecosystem functioning and biodiversity of deep marine sedimentary environments around the world, where it was believed that the impact caused by this type of fishing were lower. The results of this study, therefore, reinforce the need for immediate action for the sustainable management of trawling in deep marine environments.

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