Selectivity experiments with window codends fished in the Baltic Sea cod ( Gadus morhua) fishery

Abstract

The declining cod stock in the Baltic Sea has highlighted a need for the use of more selective fishing gears. From 1995, the use of 105-mm `Danish' and `Swedish' designed escape windows was adopted into legislation in the Baltic Sea, as alternatives to a mesh size increase from 105 to 120 mm. As the legislation was based on very few experiments, one objective of this work was to collect more selectivity data on a `Danish' window codend. The second objective was to test if black netting sections could be used as contrasting colours to manipulate the cod behaviour, and further improve the escape through the window. Experiments were conducted from a commercial vessel. The selectivity of window codends with contrasting colours and conventional green netting, were measured simultaneously using hooped codend covers and a twin trawl rig. Comparative fishing experiments were then conducted using uncovered codends. No significant improvement in the escape of cod was found for the three different types of codends with contrasting colours tested in the experiments. The overall selection factor for cod estimated by combining 25 hauls for a codend with a 115-mm square mesh `Danish' window was 2.84. This is lower than estimates from other experiments with window codends in the Baltic Sea. A significant, but relatively weak, codend catch size effect on the selectivity parameters was found.