FAO Fisheries & Aquaculture - Fishing technique fact sheets placeholder

Source | Citation

Search fishing techniques

Fishing Techniques

Bottom Pair Trawling

Main Components

Aquatic species

Target Species
Bottom species

Target Species
FlatfishTarget Species
Shrimps

Gear types: Bottom pair trawls

Bottom pair trawls

A bottom pair trawls is a cone-shaped net consisting of a body, normally made of two or four panels, ending in a codend and the net has lateral wings extending forward from the opening.

Vessel types: Pair trawlers

In the wet-fish trawler the fish is kept in the hold in the fresh/"wet" condition.

Characteristics

Bottom pair trawling

Species EnvironmentTarget species can be isolated or aggregated close to the bottom.Fishing GearAs no otter boards are necessary, the trawl gear arrangements are simplified, the warps beings connected directly to the bridles from each wing. Normally, a greater warp length/water depth ratio than for otter trawling is used; a ratio of 5:1 being common. The vessels maintain a distance apart that will provide the mouth opening and headline height found most effective for the gear and species being fished; an average lateral spacing is in the order of half the length of the warp run out.Vessel OverviewA pair trawler may be an open boat with an outboard engine, or any vessel up to 60 meters decked Trawlers. The pair trawlers are commonly of similar sizes and power. It is however possible to fish successfully with boats of different size and power as long as the difference is not too important.Handling ModeThe modern distant waters pair trawlers are equipped to freeze or salt their catch. They may also have liver oil extractors and drinking water evaporators.Fishery Production SystemsPossible exploitation forms using bottom pair trawling are: small scale and semi industrial.Fishing EnvironmentBottom pair trawls are operated in very shallow waters (2-5 meters) till depths down to 5-800 meters, in both marine and inland waters.Fishing OperationsWhile pair trawling is perhaps more common for midwater trawling, it is also used for bottom trawling. Regarding pair trawling, in general, by utilizing the combined towing pull of the two vessels, and as no otter boards are needed, a larger net can be worked than would be possible by a single vessel; alternatively, two vessels of low horse-power, which could not undertake single boat otter trawling, can operate this method together efficiently. The two main advantages of pair trawling are: Pair trawlers operate trawling without otter boards and they consequently may pull a net which is at least twice, or slightly more, the size of trawls that can be towed by a single vessel. The setting and hauling operations are carried out by one vessel, while the other is used only during the towing sequence; often each will take turns at these operations.

Shooting the net

1. Shooting the netThe pair trawl is set out from the side or the stern of the so called "main boat". Once the net is in the water and safely clear of the setting vessel, the "partner boat" come close enough to the main boat and throws a light heaving line to it. The end of the bridles are tied to the heaving line and are pulled quickly aboard the partner vessel and connected to its warp. In general, each of the boat trawling in pair keep a single warp each. At a given signal the winch brakes are released and the two boats shoot their warps taking care of shooting at the same speed.

Towing the net

2. Towing the netWhen the required length of warp has been set, the trawlers start towing on parallel courses. It is important that the skippers keep permanent contact with each other during all the operations.

Hauling the net

3. Hauling the netWhen the time comes to haul back, both vessels haul on their warps until the bridles reach the gallows. The vessels then draw nearer, up to a safe distance apart, and a heaving line is used again to transfer a messenger line fastened to the bridle end on one vessel to the other; the partner boat then disconnects the bridle from its warp so that the other, the main boat, may heave in the messenger on the winch through its second gallow block. When the bridles have been hove up all to the gallows, the net is brought aboard and the codend emptied in the usual manner. Either quarter ropes, a drum or ramp arrangement may be used.

Fishery AreaPair trawling fleets fishing on the bottom currently operate in Europe, Scandinavia, North America, Japan, Taiwan, Korea and Thailand.IssuesDiscard The potential negative impact may consist in too large bycatch and/or discards (undersize specimens, no marketable specimens, non target species, etc.) resulting mainly from the use of too small meshes. Adjustment of the mesh size in the codend and, sometimes, certain selective devices are ways to reduce capture of non-target species and/or too small sizes of fish.Source of information

Thomson, D. 1978 “Pair trawling and pair seining; the technology of two-boat fishing.” Fishing New Books 0-85238-087-9.

Logon name:
Password:
×