Evaluation of three levels of selective devices relevant to management of the Danish Kattegat-Skagerrak Nephrops fishery

This study illuminates a range of technological options relevant to present legislation for regulating fish by-catch in a small-meshed Nephrops fishery. The selection of cod, haddock, hake, lemon sole, Nephrops, plaice, saithe, witch, and whiting were evaluated using the twin-trawl technique for: (i) a 90 mm diamond mesh codend (standard codend); (ii) a standard codend with a 120 mm square mesh panel (SMP); and (iii) a standard codend with a 35/80 mm grid mounted in the extension piece to hinder access to the codend for large individuals.

We used selection models to estimate selection parameters by species and confidence bands to compare the selective properties of different gear types. For cod, haddock, hake, Nephrops, plaice, and whiting we obtained estimates for all three gear variants, whereas we obtained estimates for lemon sole and witch only with the standard and the SMP codends and for saithe only for the SMP codend.

The SMP significantly (p <0.05) improved selectivity of haddock in terms of releasing more individuals below minimum landing size (MLS). For a narrow size range of plaice below MLS, the SMP retained more individuals than did the standard codend. No effect of the SMP was detected for any of the other species.

The grid codend significantly reduced catches of all fish species above MLS, but the codend also had an increased retention of cod and haddock below MLS. Furthermore, the grid resulted in a 17% loss of marketable Nephrops.