MEASUREMENTS OF CODEND SELECTIVITY FOR NORTH-SEA SAITHE BY THE COVERED CODEND AND DIVIDED TRAWL METHODS

Trials for the determination of hitherto non-existing selectivity para meters for North Sea saithe were carried out in 1991 and 1994 with dif ferent mesh sizes and mesh shapes. In contrast to other gadoids marked ly increased selectivity factors were detected for saithe. Square mesh es did not improve the selectivity of bot:tom trawl codends for saithe . This fits with a picture of a vigorous fish which is not influenced by any shape of mesh in its impetuous attempts to escape. Thus, the us e of a strengthening bag leads to no evident deterioration in selectiv ity for a given mesh size. If instead of the conventional covered code nd method, double trawls are used for the determination of selectivity for saithe, an improvement: of selective properties (L-50, selectivit y range) is noted after evaluation by contemporary software. The neces sity of taking the uneven distribution of non-selected fishes into acc ount, however, brings into question the validity of the results obtain ed.