Evaluation of a simple means to reduce discard in the Kattegat-Skagerrak Nephrops (Nephrops norvegicus) fishery: Commercial testing of different codends and square-mesh panels

摘要

Discarding of fish species in the Kattegat-Skagerrak Nephrops directed fisheries remains at high levels. In this work we have tested four sets of codends pair-wise with the catch comparison technique under full commercial conditions to assess their potential in reducing the catch of undersized commercial species, in particular cod. We investigate the position of a 90mm square-mesh panel (SMP), the effect of increasing the mesh size from 90 to 120mm in the SMP, the effect of inserting a 90mm SMP in an 80mm codend and the effect of increasing the codend mesh size from 90 to 120mm in a total of 89 hauls. Inserting the SMP 3-6m from the codline compared to 6-9m from the codline, reduced catches of cod above the minimum landing size (MLS) and Nephrops above and below the MLS. Increasing the mesh size in the SMP from 90 to 120mm increased the catch of cod above the MLS in weight with an overall increase of 12% in the revenue. The effect of installing a 90mm SMP 6-9 m from the codline in a nominal 80mm codend had no effect on the catch of cod. Increasing the nominal codend mesh size from 90 to 120mm reduced the catch of all species below the MLS, except monkfish. Catches of Nephrops above the MLS were, however, reduced by approximately one third and the total loss in revenue was 21%.