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Selective whiting trawl.

Objective

The aim of the research is to develop a selective whiting trawl which will reduce discards of undersized haddock and cod in mixed fisheries.
The main objective of this project has been to develop a species selective whiting trawl which could separate whiting from cod and haddock and catch commercial amounts of whiting without increasing the bycatch of undersized protected species. The principle used to separate whiting from cod and haddock was based on observations of the behaviour of whiting escaping more readily than cod and haddock through panels of square mesh netting. This resulted in 2 design concepts based upon dividing a trawl with a separator panel into 2 compartments with the whiting gaining access to the upper compartment and codend via square mesh panels DIFTA developed one design was whole trawl separator panel where whiting were separated in the front parts of the trawl belly. The second was a codend separator panel where whiting were separated in an extension piece inserted between the belly and codends. Scale models of the trawls were built and tested flume tanks. These designs were then tested full scale in a twin trawl rig on a Scottish trawler for five cruises. The whole trawl separator only caught half as much whiting as the codend separator and therefore, only the latter design was selected for further testing.

There was an almost complete separation of cod in the bottom codend. For the codend separator an average separation of 53% of whiting in the top codend was accompanied by only 19% of haddock, the optimum percentages obtained being 61% whiting accompanied by 9% haddock in a haul. On the final cruise, the codend separator was tested against a standard trawl. Compared to the standard trawl, the whiting trawl increased the ratio of marketable whiting to total haddock catch from 0.39 to 0.88. The whiting trawl is thus much better at selecting whiting. The whiting trawl increased the catch of marketable whiting by a factor 4.2 but with the penalty of increasing the catch of undersized haddock by a factor of 3.2. Given average North Sea ratios the trawl is likely to be of beneficial use.
The research work comprises the following main phases.

Review of the current work and existing data on gear designs and configurations used to discriminate the 3 species. On the basis of this research, 2 experimental trawl models based on standard trawls, and up to 6 experimental codends will be designed and a test programme devised.

The designs will be tested in flume tanks to optimize net shape and geometry following 2 different trends: one codend solution, focusing on innovations mainly restricted to the codend area; and another trend that includes major alterations in the trawl such as separating panels and square mesh panels in the square or belly. The designs will take into account the different escape patterns and minimum landing sizes of the species. Based on these results 2 trawls will be built.

The nets will be tested in the North Sea and North Atlantic by a commercial trawler, and the species behaviour observed on video film by means of underwater television.

The models and full scale trawls will now be modified by changing one to a standard trawl and the other to the final experimental trawl.

The 2 final trials will last approximately 10 days each, the experimental trawl being tested against the standard trawl on a trawler if possible using the 2 trawl system. The separator trawl will also be towed singly as a reference and to document its performance when operated in the conventional commercial fashion. Underwater observations will be carried out at the same time.

Topic(s)

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Call for proposal

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Funding Scheme

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Coordinator

Danish Institute for Fisheries Technology and Aquaculture (DIFTA)
EU contribution
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Address
Nordsoecentret
9850 Hirtshals
Denmark

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Total cost
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Participants (1)