Under the quiet surface of the oceans, an invisible drama is played at the rhythm of the giant nets dragged on the seabed. The background trawling, formidable industrial fishing method, literally shaves benthic habitats in search of fish and crustaceans, leaving behind devastated expanses. This ballet of chains, cables and heavy nets transforms in a few hours complex ecosystems into lunar landscapes, sustainably upsetting marine life and modifying the fragile balances of the depths.
This process was filmed for the first time from an unprecedented angle in the documentary Ocean directed by David Porteborough. The famous naturalist shows striking scenes there where cephalopods, rays and other species are in vain to escape the inexorable advance of the net, accompanied by a wall of ropes and metals. This brutal vision, relayed by the Iflscience site, illustrates how this technique acts as a bulldozer on the ocean floor. Most of the time, only a small number of commercial species are preserved, while the majority of the bodies captured, more than 75% of the catches, are rejected dead or injured.
In addition to the direct ravages, the background trawling leaves giant scars visible from space. Each passage raises large streaks of sediment which sometimes extend over tens of kilometers. These streaks photographed by satellite mark the destruction of essential habitats whose natural regeneration may require years. With the naked eye, sailors guess nothing of this ecological disaster. David Porterborough underlines it in his film: “From the surface, no one would suspect the extent of the damage”.
Alarming figures: what global studies reveal
Many experts today consider background trawling as one of the main causes of degradation of benthic habitats. A reference study published in Proceedings of the National Academy of Sciences by Jan Geert Hiddink and his team made it possible to estimate with precision the impact of this practice worldwide. According to their analyzes, the nets tear between 6% and 41% of the biomass of the seabed at each pass, depending on the type of equipment used. The panels are the least destructive, with an average penetration of 2.4 centimeters in the sediment. Conversely, hydraulic dredges reach depths of 16 centimeters, causing maximum biodiversity loss.
The study was also interested in the recovery capacity of seabed. Depending on the frequency of trawling and environmental conditions, benthic invertebrates communities need 1.9 to 6.4 years to reconstitute. However, these deadlines do not guarantee a complete return to the initial state, especially when the disturbances are repeated frequently.
The background trawling represents almost a quarter of the world's capture of seafood. However, its real efficiency questions. The energy consumed and the collateral damage inflicted on the marine ecosystem is disproportionate compared to the species actually targeted. This overfishing imbalances food chains, modifies the composition of marine communities and reduces the capacity of these environments to provide essential ecological services such as carbon storage or deep water oxygenation.
The practice is little adapted to the specificities of caught areas, generating a loss of diversity on already fragile seabed. Satellite follow -up has shown that the areas most affected by trawling has become mosaics of partially degraded communities, alternating areas still intact and other permanent depleted.
The awakening of consciences
Faced with this alarming observation, several initiatives have emerged in an attempt to limit the impact of fundamental trawling. A life-size experience took place in Lyme Bay, in the United Kingdom. In this 206 km² area, the authorities have prohibited background trawling while allowing other less destructive forms of artisanal. Fifteen years of scientific monitoring made it possible to measure the ecological benefits of this decision.
The study published in ICE Journal of Marine Science in March 2024 highlights a 95% increase in the diversity of reef species and a spectacular increase of 400% of the number of fish present. These notable gains concerned not only the sedentary species but also the mobile species which benefited from the return of complex habitats. The reconstituted reefs have also proved more resistant to extreme storms.
A particularly interesting phenomenon observed in Lyme Bay is the “spillover”, an ecological overflow effect. Biodiversity restored in the reserve has won neighboring waters, indirectly improving fishing yields in neighboring areas. This result shows that the strict protection of a small portion of ocean can have large -scale beneficial effects.
The scientific community and conservation organizations are placing today for the extension of these protected areas. During the 2022 biodiversity convention, more than 190 countries adopted the international strategy called “30×30”, as relayed by The Nature Conservancy. The objective of this ambitious plan is to protect 30% of the land and oceans of the planet by 2030. To date, only 8% of marine spaces benefit from effective protection.
David Participoorough insistently recalls that “the ocean has a remarkable regeneration power, provided he leaves the possibility”.
