Size matters for the efficiency of sorting grids in demersal trawls

Size selectivity devices implemented in trawls are often strictly regulated and can remain unchanged over longer periods. This is the case for the Barents Sea gadoid trawl fishery, one of the most important and valuable demersal fisheries in the world, where since 1997 the compulsory gear has been composed of a sorting grid and a subsequent size selective codend. The upscaling and development of the trawl gear typically used in the area in the last three decades has contributed to capacity issues that can lead to inefficiencies in size selectivity and operational problems of grid sections. The present study investigates whether upscaling the mandatory grid by doubling its sorting area can improve the size selectivity in the fishery. A mandatory grid section and an upscaled grid section were directly compared in sea trials in a twin trawl configuration. The data were analyzed considering structural models, which resulted in a more logical representation of the relative performance of the two grid sections compared in the study than traditionally used empirical models. The upscaled grid significantly increased the sorting efficiency for undersized haddock (Melanogrammus aeglefinus), while the catch efficiency of commercial-sized cod (Gadus morhua) and haddock were equal. The additional sorting capacity exhibited by the upscaled grid is expected to play an important role in the future management of the fishery. Further, it demonstrates the importance of revising the efficiency of compulsory selectivity devices periodically and can point to the direction to adopt in other fisheries with similar issues. The upscaled grid did not imply any additional work or challenge for the crew during its operation.