Improving selectivity of the Baltic cod pelagic trawl fishery: Experiments to assess the next step

Due to declining cod (Gadus morhua) stocks, the Baltic Sea was one of the first areas regulated by the European Communities where selective escape windows were implemented to improve the exploitation pattern. Increasing discard rates and the potential for a significant increase of the spawning stock and the yield of the fishery are important reasons to further improve the selectivity of the fishery and to asses the potential next step in this process. In this study, we tested three relatively different design concepts, in the Baltic cod pelagic trawl fishery, that are relevant to past or present legislation and that were developed to meet requirements of increased selectivity performance. A standard nominal 135 mm diamond mesh codend, a codend with two nominal 125 mm bottom windows, and a codend with a nominal 125 mm nominal top window were tested using the covered codend method. A Danish and a Swedish commercial vessel were used for the sea trials to account for potential differences between vessels. Potential differences among the three gear variants were assessed by a two-step mixed effects model. The codend catch weight was found to have a significant effect on the selectivity in some cases. We assessed the actual effect of the selectivity performance on the immediate reductions of the proportions of cod being retained below and above the present minimum landing size (MLS) and a potential increased MLS.