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Bottom trawling is a fishing method consisting in towing trawlnets along the sea floor to scoop up fish. Bottom trawling can be carried out from one vessel (otter trawling) or two vessels (twin-trawling, pair trawling, bull trawling). It is practiced from a very wide range of fishing vessels, starting with small motor boats powered by engines of several tens of HP (horsepower) and ending with large ocean-going trawlers, up to 100 m long, and powered by engines of several thousands HP.
The design, weight, and size of trawlgear, which includes towing cables or "warps", trawl boards (or otterboards, doors), bridles and the trawlnet itself, depend upon the towing power of the trawling vessel, target fish species, and fishing conditions (bottom character and topography).
Trawlnets designed to operate on hard, snaggy bottom are
equipped with large "bobbins" that roll on the sea floor and keep the net's footrope at minimum bottom contact. Where operated over sensitive areas of sea bottom, such as deepwater soft corals reefs, they may cause their partly or full destruction. Excessive fishing on oceanic sea mounts may cause overfishing of long lived but slowly reproducing deepwater fishes.
On the other hand, trawl fishery has been operated for over a century on many trawling grounds of the world and, where overfishing due to excessive fishing pressure has not taken place, it has been producing consistent catches of high value fish for human consumption. About 1/3 of total marine fish delivered to markets worldwide come from the trawl fishery.
On November 18, 2004 the United Nations General Assembly urged nations to consider temporary bans on high seas bottom trawling.
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