Beam Trawl - Chain Mat Gear

Summary

This beam trawl is similar to other beam trawls in that its held open by a steel bar with shoes on each end. However the chain mat gear is rigged with a matrix of chains across its mouth to prevent stones entering the trawl and enable the gear to be towed over fairly rough ground.

A diagram of chain mat gear

Environmental impact

Beam trawling  catches a large range of bottom living species and is not a well targeted fishery with often poor selectivity and the potential to catch a wide variety of non target by-catch. This can include crabs, starfish, other shellfish and many other seabed dwelling organisms.

A substantial amount of research in recent years has focused on increasing species selectivity in beam trawls to reduce unwanted by-catch. Recently there has been a big push to improve the selectivity and reduce by catch in the beam trawl fishery. Project 50% introduced benthic panels, coverless trawls, large mesh top panels and larger mesh nets and cod ends into the UK beam trawl fishery. This reduced the discard rate by about 50% and many skippers continue to use this modified gear.

There is much criticism of beam trawling due to the belief that it is doing a lot of damage to the seabed. Measures are being put in place and tested to improve on this image. modifications such as fitting the beam with large rubber wheels, fitting rolling rubber bobbins to the footrope, both to help the gear over the seabed with minimum seabed damage. The main driver to introducing  the pulse trawl was to improve the environmental credentials of a beam trawl.

Other information

The beam trawl is one of the earliest forms of towed fishing gear. Its origins are claimed to date as far back as the late 18th century, in Brixham SW England where they developed a sailing boat specifically for towing a trawl. The net is held open by a rigid framework to maintain the opening of the trawl irrespective of changes in towing speed. This made it ideal for towing behind early sailing boats with their unpredictable course and speed. As the vessels evolved with modern engines and mechanised gear handling, the size of the gear and towing speeds increased in an effort cover a larger area of seabed to increase catches. In the early days of beam trawling, only one net was towed from the stern of the boat. Nowadays, most commercial beam trawlers use two beam trawls towed from long derricks projecting over each side of the vessel. The beam trawl consists of a heavy tubular steel beam supported by steel beam heads at each end. These beam heads have wide shoes at the bottom which slide over the seabed. The beam and beam heads form a rigid framework that keeps the mouth of the trawl open and supports the net. On the early beam trawls, and some modern day small scale trawls, timber was used for the beam. The cone-shaped net is towed from this framework with the head rope attached to the beam, and each end of the footrope connected to the bases of the shoes. As the gear is towed over the seabed, the footrope forms a ‘U’ shape curve behind the beam and shoes, with the net and cod-end behind this. The headline height of the trawl is limited to the height of the beam off the seabed. The beam is usually towed using a chain bridle arrangement from both shoes and the centre of the beam attached to the end of the trawl warp leading to the vessel. There are two common types of beam trawl, referred to as ‘open gear’ and ‘chain mat gear’. Open gear is a lighter rig with several chains, called ticklers, towed on the seabed across the mouth of the net. These ticklers help to disturb the fish from the muddy seabed, causing them to rise and be caught by the net. This rig is used on clean, soft ground (seabeds).

The chain mat gear is used for towing over harder, stony areas of seabed, and it is more commonly used by the bigger class of vessels. In this rig, there is a lattice work of chains towed from the back of the beam, sloping down to the footrope of the net. The purpose of this is to guide the trawl over any rough ground and boulders on the seabed, thereby minimising damage to the netting. Some beam trawls are also fitted with ‘flip up ropes’ to prevent stones from entering the net and damaging it. This is a fence-like structure made of rope covered with plastic tube, towed around the mouth of the trawl to lift the footrope over any obstacles on the seabed.

Lighter styles of beam trawl, with fewer tickler chains and without a chain mat, are used in several locations in the UK to target shrimp.

The largest class of beam trawlers are around 25 - 40 metres long, generally having in the region of 1,000 horse power, towing two beam trawls 12 metres wide. This size of beam trawl can weigh up to nine tonnes each, enabling the trawler to tow at speeds up to seven knots. The medium class of beamers, from 12 — 18 metres, usually have between 300 - 500 horsepower to tow 4 - 7 metre beams. Many of the vessels under this size would tow just one trawl from the stern of the vessel. The size of beams towed, and the horsepower of many vessels, is restricted by fishery regulations in the area that they fish. The beam trawls need to be heavy to ensure that the trawl maintains good seabed contact while the vessels are towing at relatively high speeds, to cover enough ground to remain viable.

The majority of the UK beam trawl activity is in ports on the South coast of England, with one or two vessels scattered throughout the other fishing ports in the UK. The UK fishing effort is concentrated mainly in the South West Approaches and English Channel with some in the Southern North Sea and up into the Irish Sea. Beam trawling is very popular with the Belgian and Dutch fishing fleets, many of these vessels work similar areas to the UK vessels. The target species are Dover sole, plaice, shrimp, lemon sole, skate, cuttlefish, with megrims and monkfish being caught in deeper water.

Gear classification

Main target species (UK)

  • Cuttlefish
  • Dover Sole
  • Lemon Sole
  • Monkfish

Possible bycatch

  • Any demersal species
  • Brill
  • Dab
  • Dover Sole
  • Flounder
  • Flats
  • Lemon sole
  • Megrims
  • Monkfish
  • Plaice
  • Rays
  • Scallops
  • Skates
  • Witch