|Auswirkungen von größeren Steertmaschen bei Grundschleppnetzen auf Plattfischfänge in der Nordsee = Effects of bigger codend mesh sizes in bottom trawls used for the catch of flatfish in the North Sea|
|Wienbeck, H.; Panten, K. (2008). Auswirkungen von größeren Steertmaschen bei Grundschleppnetzen auf Plattfischfänge in der Nordsee = Effects of bigger codend mesh sizes in bottom trawls used for the catch of flatfish in the North Sea. Inf. Fischereiforsch. 55: 15-20|
|In: Informationen aus der Fischereiforschung = Information on Fishery Research. Bundesforschungsanstalt für Fischerei: Hamburg. ISSN 1861-2164, more|
The present fishing effort regulation for bottom trawls in the North Sea (EU 40/2008) reduces the fishing effort with larger codend mesh sizes (> 100 mm mesh opening) to 86 fishing days per year. The aim of this technical measure is the protection of the weak cod stock usually harvested with this mesh opening. By combining the results of our selectivity investigations on plaice during a commercial fishing trip and the samples taken within the frame of the EU data collection regulation (DCR) we could draw conclusions on commercial and non-commercial fish species. When using codend meshes with larger mesh opening the discard was reduced remarkably. In the reference codend with 80 mm mesh opening the undersized bycatch was 47 % of the total catch of plaice, in the experimental codends with 120 mm mesh opening it was only 7 % and with 130 mm mesh opening just 3 %. On the other hand however, the applied mesh openings in the experimental codends let escape marketable plaice to some extent. The loss of catch was assessed on the basis of fish numbers per length class using a length-weight conversion rate from the DCR. The loss by weight of marketable fish with 120 mm codend mesh opening was 18 %, and 28 % with 130 mm codend mesh opening. To assure the protection of young round and flatfish with one general mesh size, a new regulation should prescribe a minimum mesh opening of 120 mm, accompanied by an expansion of the fishing effort.