Increasing catch efficiency for Nephrops in deep-water shrimp (Pandalus borealis) trawl fisheries

In Skagerrak and the North Sea, coastal vessels harvest deep-water shrimp (Pandalus borealis) in a mixed fishery, in which catches of Nephrops (Nephrops norvegicus) are of economic importance for the fleet. Fishermen targeting shrimp in this area must use a sorting grid with a maximum bar spacing of 19 mm, which means that only the smallest Nephrops can pass through the grid to be retained in the main codend. Although fish collection bags may be mounted to the grid’s fish outlet, most Nephrops escape through the large meshes in these bags. Using data from 70 hauls collected during three different commercial cruises, we investigated whether inserting a 15 cm gap in the lower part of the compulsory sorting grid could help retain a higher fraction of the commercial sizes of Nephrops. We also evaluated whether this lower gap in the grid would change the catch pattern for the most relevant fish bycatch species in the fishery. The results showed that the gap in the grid significantly increased the catches of Nephrops above the minimum legal size and increased the catches of commercial-size shrimp. However, absolute catch rates of Nephrops were still low and, from a management point of view, the modest catch increase does not justify the significant increase in the catch of juveniles of a range of fish species as well as undersized Nephrops.