Trawling the sea bottom causes physical damage to the seabed and its wildlife habitats and captures benthic (bottom living) sea creatures that are not used for food.
Over 2.5 million hours of bottom trawling took place in Europe’s “protected” areas in 2020.
Fishermen are now using military sonar to hunt and trawl in international waters hundreds of metres below the surface. The long, slow life cycles of the species that live in the deep sea means that their populations will collapse if they are exposed to industrial-scale exploitation. For example, on the orange roughy Hoplostethus atlanticus can reach 150 years old and does not even reproduce until it is in its mid-20s to mid-30s. In the 1980s it was reported that, around seamounts in the waters off New Zealand and Australia, catches of 60 tonnes could be made from a 20 minute trawl. In 2000, there is less than 20% of the Roughy there were 10 or 15 years previously.
The impact of fishing in the deep sea goes far beyond just removing the fish. Fisheries are concentrated into places that have the greatest biological significance; places like seamounts and canyon walls where materials that are wafted in on currents support rich communities of species - corals, sponges, seafans and hydroids. Deep-sea fishing is said to be inflicting terrible collateral damage on these species as trawl meshes plough through the water. Off the east coast of North America bizarre and beautiful fields of glass sponges have been trawled to oblivion. In the Southern Ocean lush forests of invertebrates have been literally stripped from the top of seamounts by trawlers targeting Orange Roughy.
The move to deep-water fishing is being encouraged by governments who are offering subsidies to alleviate the hardship that has been brought on by the collapse of shallow-water fish stocks. Forty percent of the world's trawling grounds are now waters that are deeper than the edge of the continental shelves.
If current over-fishing continues, trawlers could soon be left chasing jellyfish and even plankton to make "fake" fish products.