Beam-trawl fisheries

STUDENT : EYHAB GAMAL BADRAMARINE FISHING ENGINEERING DEPARTMENT FISH RESOURCES COLLEGE – SUEZ UNIVERSITY

Characteristics♦Overview

♦EVOLUTION♦Plan

♦Accessory Equipment♦Handling Equipment♦Vessel Overview♦Fish Operation♦Target Species♦Water Area Overview♦Gear Environment

overviewA 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-like trawl mostly made from steel. No hydrodynamic forces are needed to keep a beam trawl open.heads/shoes

beam trawl

EVOLUTION

The beam trawl is one of the earliest forms of towed fishing gear, being used in the Southern North Sea by the sailing smacks from Grimsby and Lowestoft in the latter part of the 19th century. The net is held open by a rigid framework ensuring it maintains its shape and effectiveness despite changes in towing speed. This made it ideal for towing behind early sailing boats with their unpredictable course and speed. As diesel engines were developed along with mechanised hauling methods the gear was made larger and towed at faster speeds in an effort to improve catches. In the early days of beam trawling only one net was towed from the stern of the boat. Nowadays most commercial beam trawlers tow two beam trawls from long derricks projecting over each side of the vessel.

Plan

Principal features of a beam trawl

Plan ( continued )

Accessory Equipment

While fishing for flatfish the beam trawl is often equipped with tickler chains to disturb the fish from the seabed. For operations on very rough fishing grounds they can be equipped with chain matrices. Chain matrices are rigged between the beam and the groundrope and prevent boulders/stones from being caught by the trawl. Shrimp beam trawls are not so heavy and have smaller mesh sizes. A bobbin of groundrope with rubber bobbins keeps the shrimp beam trawl in contact with the bottom and gives flatfish the opportunity to escape.

Handling Equipment

Beam trawl is normally towed on outriggers, one trawl on each side.

Vessel Overview

 Beam trawlers are in most cases specialized medium size vessels, equipped with powerful engines arranged with large outriggers tow two parallel beam trawls

Fish Operation

Close bottom contact is necessary for successful operation. To avoid bycatch of most juvenile fishes selectivity 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 tonnes. The towing speed for shrimp is between 2.5 and 3 knots

Target Species

Beam trawls are used mainly for flatfish and shrimp fishing.

Water Area Overview

This technique is very successful used in many parts of the world for catching shrimp and flatfish normally in shallower depth than

100 meters.

Gear Environment

Beam trawls are towed with very close bottom contact.ImpactsSpecies 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. 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.

References

://http . . / / /www ecomare nl en encyclopedia://http . . / /www fao org fishery en://http . . / / _en wikipedia org wiki bottom vesselBASIC FISHING METHODS pdf