Size selecting for flatfish while avoiding cod

Optimizing exploitation patterns for multiple species in trawl fisheries simultaneously presents both technological and managemental challenges. In the Baltic Sea demersal trawl fisheries targeting flatfish, fishers must avoid catching cod ( Gadus morhua ) due to its critical stock status. This study investigates the selectivity performance of a codend with large and rigid square-meshes (LRSM) optimized for size selection of plaice ( Pleuronectes platessa ). The expectation was that the LRSM would effectively release cod and other non-target species while providing an optimal exploitation pattern for the targeted flatfish species. For plaice 85% of the target sizes were retained and 92% of the unwanted sizes were released with the LRSM. The LRSM significantly reduced the capture of undersized plaice and flounder ( Platichthys flesus ) by 49% and 30%, respectively compared to a square-mesh codend (SMC125) implemented in the Baltic Sea to protect cod stocks. For target-sized flatfish species, there was no significant difference in retention probability. The LRSM retained only 3% of the cod that entered the codend, representing a significant reduction of 31% compared to the SMC125. However, the results also demonstrated that cod and flounder did not fully utilize the release potential of the LRSM, which needs to be addressed to achieve the full benefit of the LRSM.