Dragnet fishing. Fishing boat operating two trawl nets mounted on beams on either side of the boat. As the boat moves forwards through the water it drags the nets behind it. The nets trap fish in the water or on the seabed, and are then hauled onboard the boat to sort the catch. The nets can either be used to trawl the seabed (in which case it is called dredging), or to trawl the open water (in which case it is called pelagic trawling). The nets can be many hundreds of metres long. There is concern about the environmental damage some forms of industrial fishing can cause. Photographed in the North Sea.