Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Development of a species selective industrial fishing trawl

Pout fishing was identified as the industrial fishing with the greatest bycatch problems with whiting and herring each providing 5% to 10% of total catch weights in recent years and haddock 1%. 3 different devices were tested for reducing these bycatches. A horizontal separator panel divided the trawl into 2 chambers and attempted to separate species as they entered the trawl mouth above the footrope. A 90 mm square mesh escape panel attempted to allow the bycatch species, which it was assumed would have stronger escape reactions, to exit from the upper part of the trawl immediately in front of the codend. Finally an inclined metal grid was inserted in the upper half of the trawl immediately in front of the codend. The intention was for pout to pass through the grid into an upper codend and the bycatch species to be diverted by the grid through an opening in the grid base into a lower codend.

The horizontal separator panel trawl proved difficult to design. Substantial reshaping of the basic trawl was necessary in order to obtain an acceptable opening between the separator panel and trawl lower panel. Trawl drag increased by approximately 10%. The proportion of pout entering below the separator panel was highly variable and could not be controlled. The horizontal panel could not achieve any suitable consistent species separation.

The square mesh escape panel was straightforward to design and gave a minimum of alterations to trawl construction and operation. 27% of the pout, 16% of the small whiting, 22% of the large whiting, 5% of the haddock and 12% of the herring escaped through the square mesh panel. The relative ability of the different species to escape had not been as anticipated and no satisfactory species separation was achieved.

The grid caused severe handling problems on a typical commercial fishing vessel as it could not be wound round the net drum and the large codend catches could not be hauled aboard in the normal safe manner. In trials large quantities of fish were trapped round the trawl immediately in front of the grid. There was no evidence of species separation just size separation.

It can be concluded that it is not possible to reduce bycatch levels of protected human consumption species in pout trawls by separating species within the trawl. This is an important result as use of a species selective trawl if possible would have been an attractive management strategy.

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David WILEMAN
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