Danish experiments with a grid system tested in the North Sea Shrimp fishery

Grids have been proven successful worldwide as bycatch reducers in shrimp fisheries but have never been tested in the North Sea shrimp fishery. The objectives of this experiment were to develop and test a flexible grid system for the Danish Fladen Ground shrimp (Pandalus borealis) fishery, which can retain marketable catches of roundfish and Norway lobster (Nephrops norvegicus). The grid system was made of polyamide with a fish escape hole at the top and a Norway lobster escape hole at the bottom. Hinges made the grid flexible. The grid system was developed and tested in a flume tank and during sea trials. Two experiments were conducted with a commercial trawler at the Fladen Ground. A standard shrimp codend was compared to a codend with the grid system simultaneously in a twin trawl rig. There was a relatively large and significant reduction in the grid codend of cod (Gadus morhua), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), saithe (Pollachius virens), Norway pout (Trisopterus esmarki), Norway lobster, herring (Clupea harengus) and witch (Glyptocephalus cynoglossus) but no significant difference in weight of shrimp and monkfish (Lophius piscatorius) in the first experiment. The grid system was altered in experiment 2 resulting in no significant difference in the catch of cod and saithe above the minimum landing size while the catch of Norway lobster and shrimp improved significantly. Experiments with collecting bags indicated that most fish went through the top fish escape hole, shrimp and Norway pout through the grid or the bottom Norway lobster hole and Norway lobster mainly through the Norway lobster hole.