FAO/FIIT Fishing Gear Type Fact-Sheet Beam trawls [TBB] updated : 10-mai-2001 ISSCFG Classification : > Category : Trawl nets > Type : Bottom trawls > Subtype : Beam trawls Profile General Description: A beam trawl consists of a cone-shaped body ending in a bag or codend, which retains the catch. In these trawls the horizontal opening of the net is provided by a beam, made of wood or metal, which is up to 12 m long. The vertically opening is provided by two hoop-liketrawl heads/shoes mostly made from steel. No hydrodynamic forces are needed to keep a beam trawl open. Technical Plan: Specific Equipment: While fishing for flatfish the beam trawl is often equipped withtickler chains to disturb the fish from the seabed. For operations on very rough fishing grounds they can be equipped withchain matrices. Chain matrices are rigged between thebeam and thegroundrope and prevent boulders/stones from being caught by the trawl.Shrimp beam trawls are not so heavy and have smaller mesh sizes. Abobbin of groundrope withrubber bobbins keeps the shrimp beam trawl in contact with the bottom and gives flatfish the opportunity to escape. Specific Handling Equipment: Beam trawl is normally towed onoutriggers, one trawl on each side. Fishing Vessels using this gear: Beam trawlers are in most cases specialized medium size vessels, equipped with powerful engines arranged with large outriggers tow two parallel beam trawls. Fishing Operations: Close bottom contact is necessary for successful operation. To avoid bycatch of most juvenile fishesselectivity devices are assembled (sieve nets, sorting grids, escape holes). While targeting flatfish the beam trawls are towed with up to seven knots, therefore the gear is very heavy; the largest gears weight up to 10 tons. The towing speed for shrimp is between 2,5 and 3 knots. Features Target Species: Beam trawls are used mainly forflatfish andshrimp fishing. Areas: This technique is very successful used in many parts of the word for catching shrimp andflatfish normally in shallower depth than 100 meters. The Gear and its Environment: Deployment Area: Beam trawls are towed with very close bottom contact. Impact on the Environment: Conclusions from some recent research on the physical impact of beam trawls on the sea bed are: 1) the penetration depth of a beam trawl depends on sediment characteristics and varies between 1 cm and 8 cm; 2) the pressure force exerted on the sea floor is strongly related to towing speed and the warp length to depth ratio; 3) beam trawls leave detectable marks on the seabed. The duration that the beam trawl marks remain visible depends on the upper sediment layer and on the hydrographic conditions. On the seabed consisting of medium to coarse sand, tracks have been observed to remain visible for up to 6 days. On sediments with mainly finer particles a corresponding figure of 37 hours was observed. Impact on Aquatic Species: The major impact of beam trawl on species is capture and removal from the ecosystem of small sized organisms (juveniles) and non-target species, which frequently are discarded at sea. Sieve netting and selection grids together with larger codend mesh sizes are used to mitigate this problem, particularly in shrimp trawl fisheries. Square mesh panels are used with some success to reduce capture of non targets species in flatfish fisheries.