Targets
A wide variety of benthic species (those that spend most of their lives on the seabed), especially flatfish.
How they work
A type of bottom trawl in which the horizontal opening of the net is provided by a heavy beam mounted at each end on guides or skids that travel along the seabed. On sandy or muddy bottoms, a series of 'tickler' chains are strung between the skids ahead of the net to stir up the fish from the seabed and chase them into the net. On rocky grounds, these tickers are replaced with chain matting. Several trawls are towed, one on each side of the vessel, and the largest trawls have beams up to 12 m long.
Problems
Bottom trawling and dredging are destructive and wasteful, especially beam trawling - seabed ecosystems are ploughed up and a wide range of organisms are crushed in the path of the trawl or scooped up in the nets. While the magnitude of these impacts are not the same for all bottom trawl fisheries, and depend on certain factors (e.g. the type of trawl gear used, habitat composition, life history of component species, the natural disturbance regime), even for those bottom trawls operating in the least sensitive benthic environments, these areas are often regularly trawled so have little chance to recover, and there are significant levels of bycatch. Fish that are too small or of the wrong species are thrown overboard, dead or dying. Demersal otter trawls commonly throw away over 30% of their catches (by weight) while beam trawls throw away up to 70% of their catches (by weight).
Considering, firstly, that management bodies have tended to put very few limits on where bottom trawls can operate, and secondly, that there is a serious lack of marine reserves to allow for both recovery and for scientific comparison of unfished and fished areas, Greenpeace does not currently support the use of bottom trawling.