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Dieren en planten

Water en land

Beam trawl technique, Ecomare

Beam-trawl fisheries

A beam trawl is a fishing net held open with the help of a steel beam. Two shoes are attached at the ends of the beam. A concave-shaped net hangs behind the beam. A trawler tows two of these nets over the sea floor. The beam trawler is used on the tidal flats and in coastal waters for catching shrimp, using a groundrope with bobbins which roll over the bottom to flush up the shrimp. When fishing flatfish, the nets are provided with heavy chains (tickler chains) which scrape the sea floor. These chains damage vulnerable animals that live on the sea bottom.

  • Most common fishing method
    Beam trawl for catching flatfish, Ecomare

    The flatfish fisheries with beam trawlers occurs primarily in the southern and central part of the North Sea, along the coast and in the sea channels. Enormous amounts of flatfish are caught in these areas. Beam trawl fisheries is the most important form of benthic fishing in the Netherlands. This country possesses the largest and most modern fleet of beam trawlers. Approximately 80% of all the fish landed by Dutchmen are caught with a beam trawl. In Belgium, this percentage is around 65%.
    Those vessels with a large motor capacity have gear extending 12 meters across and a weighing approximately 9000 kilograms. Beam trawlers are equipped on the underside with ten to twenty chains.
    Where the ground is too stony, the tickler chains are sometimes replaced with a mat of chains, greatly reducing the risk of ruining the fishing gear.

  • Fuel guzzler

    When a ship motors at a rapid speed with a relatively light beam trawl, the chances are that the fishing gear will rise up from the floor and not catch any fish. Since more fish are caught with heavier gear, the Dutch captains have been changing over to more powerful vessels and heavier beam trawl gear. While in 1972 the motor capacity never rose above 1100 horsepower, a capacity greater than 2000 HP is no exception nowadays. This form of fisheries is very uneconomic, energy-wise. After fishing for four days, a 2000 HP-beam trawler will have used an average of 4 liters of fuel per kilogram flatfish. Because oil prices are so high, the beam trawl fishermen are closely following the development of the more economic fishing techniques, such as pulse fishing, suspended beam trawl (sumwing) and flyshooting.

  • Effects on sea life
    Influence of heavy tickler chains on the sea bottom, Ecomare

    At the end of the last century, there had been a lot of research on the consequences of beam trawling with tickler chains on the sea floor and the animals that live there. In summary, the studies showed that for every kilogram of by-catch after one sweep with the beam trawl, an additional 2.5 to 3.5 kilograms of shellfish, crabs and lobsters are left damaged on the sea floor. In addition, the trawls leave a visible track behind on the sea floor. The tickler chains plow 4 to 8 centimeters deep so that the tracks sometimes remain visible up to months. Ships with small beams cause just as much damage per square meter as vessels with large beams.

    The community of benthic animals changes in character in many of the areas which are fished by beam trawlers. Sea anemones, shellfish and crustaceans disappear. Worms seem to be the most resistant to the influences of this kind of fishing. And luckily for the fishermen, flatfish are worm-consumers. So in reality, beam trawling changes the sea floor into a pasture for flatfish.

  • Improved techniques

    A lot of experiments are being performed with environmentally friendlier alternatives for beam trawl fisheries.
    One alternative is to replace the tickler chains of the beam-trawler with a device that uses electric shocks to startle the fish: pulse fishing. There are also experiments with beam trawls using jets of water instead of chains: the hydro-rig.
    Otter trawling is less damaging to the sea bottom than beam trawling. The modern variations (twin-trawling, multi-trawling and out-trawling) are attractive alternatives for the fishermen that specialize in plaice.
    Texel fishermen were the first to experiment with the sumwing, a beam-trawler with a horizontal wing which significantly reduces the resistance of the net. This method is being applied more and more, also in combinaton with pulse wires. It seems to be a sustainable way to catch sole.

  • Renovation costs

    The changeover from a beam trawler to a more environmentally friendly method requires a tremendous investment. The table below shows what is necessary to convert a beam trawler into a twin rigger:

    vessel small cutter large cutter
    rebuild ship for twin rigging 90,000* 200,000*
    acquisition twin rigger 20,000* 36,000*
    savings in fuel per week trip 8-12 ton 3-5 ton
    *(in euros) source: RIKZ