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Aquatic species
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Semi-pelagic/demersal species
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Pelagic species

Gear types: Midwater pair trawls
Midwater pair trawls
Midwater pair trawls
It has similar characteristics as midwater trawls used with otter boards.
Vessel types: Pair trawlers
In the wet-fish trawler the fish is kept in the hold in the fresh/"wet" condition.

Characteristics
Midwater pair trawling
Midwater pair trawling
Species EnvironmentMidwater pair trawling can be effective in different situations: when fish are aggregated into large dense shoals and when (at another season or time of the day or according to physiological status) fishes are regularly distributed within a given water layer. In addition to the difference it makes whether the fish are aggregated in a small volume or spread within a large one, fish may swim (and avoid the net) at different speeds according to its own physiological status and/or other external conditions. As a result, in addition to the fish which is targeted, other different conditions will affect the design and size of the midwater trawl, as well as the towing speed.Fishing GearA midwater pair trawl has roughly similar design as other midwater trawls. Midwater pair trawls might, however, be designed to have a more rectangular opening than ordinary midwater otter trawls. Midwater pair trawls might be rigged with two towing warps from each vessel or alternatively with one towing warp from each vessel and a bridle arrangement. One of the advantages of pair trawling is the possibility to tow the trawl very close to the surface. Herding effect on fish by the two vessels may increase the capture efficiency in shallow waters and at the surface.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 EnvironmentMarine coastal and high-sea waters; some inland waters e.g. large lakes.Fishing OperationsPair trawling in midwater is by far more common than Bottom pair trawling. Trawling in pair has several advantages over single boat trawling. There is no need for otter boards to open the trawl horizontally and consequently, more power is available for towing the net itself. As a result, a bigger trawl can be used, with bigger mouth opening and, therefore, increased catching power. To a certain extent, two vessels have more chance to find some aggregated fish and location of fish is absolutely essential to fishing in midwater. When towing the trawl, the two boats are sailing over either sides of the fish school and not directly over it as a single trawler is doing; as a result, the fish is less disturbed (and, for instance, will not tend to swim deeper), while when the fish is close to the surface, the drag of the two vessels may have an herding effect grouping fish before the trawl opening. Regarding the rigging, for getting the correct vertical opening, groups of floats or buoys are often attached to each of the upper wings, the headline extremities and weights are hung at the extremities of the two lower wings or a few meters before them. The distance between the two pair trawlers and the towing speed are also very important elements for the trawl opening. In general, a netsounder (vertical echosounder fixed on the trawl itself) is used to control the opening of the trawl and its position versus the surface or the bottom.
1. Searching for fishThe first part of the operation is the search for fish, by means of echosounder and sonar.
2. Setting the netOnce a school of fish is located, and its size and depth (versus the bottom or the surface) determined, the vessels move downwind and the "main boat" on which the trawl was kept starts paying out the net. This is done very quickly. Once the trawl has been completely shot in the water and is clear from any entanglement, the "partner boat" comes alongside and to catch a light heaving line thrown from the main boat for making the transfer of the bridles (one or two according to the type of rigging) or the wing extremities (upper and lower) on one side of the trawl. The ends of the bridles or the wing extremities are tied to the heaving line, pulled quickly aboard partner vessel and connected to its warp. The midwater pair trawl is towed with one or two warps on each vessel; the rigging with two warps from each vessel is more common.
Towing the net
Towing the net
3. Towing the netWhen all the warp is set and the winch brakes applied, the trawlers commence towing on parallel courses. Maintaining the correct spacing between vessels while towing is a crucial factor, in particular for the correct horizontal opening of the mouth. Anyway, it is very important that skippers keep in touch with each other during all the fishing operations.
4. Hauling the netOnce the net has been pulled through the school of fish or after a given duration selected for the haul (according to the density of scattered fish within the water layer), hauling can begin. The hauling operation varies with the type of pair trawl gear in use. Most pair trawlers heave in all the warp which make at the same time that the two boats are gradually coming closer. When both warp ends have been reached, a heaving line is throw across and the bridles or wings ends from one of the vessel are attached to it for being transferred on board the vessel which will haul in the net itself. Then, the "hauling vessel" pulls in together the bridles, the wings and the rest of the net.
Fishery OverviewFleets of pair trawlers operate in midwater from ports in Brittany (France), Denmark, Ireland, Sweden, Germany and Holland. This fishing technique is also used to a lesser degree in Canada and USA.IssuesDiscard In most cases, pair trawling in midwater is almost mono-species fishery or just a few species are caught at the same time (especially when fishing on shoals). Bycatch rates of other species are, in most of the cases, low. Because fishing is in midwater, there is no impact on bottom habitat and bottom structure. In certain fishing area, some incidental catch of dolphins or other marine mammals may be a problem.Source of information
Thomson, D. 1978 “Pair trawling and pair seining; the technology of two-boat fishing.” Fishing New Books. 0-85238-087-9

 
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