A rapid decrease of the stock of Baltic cod (Gadus morhua) has provided the incentive to improve the size selectivity in the trawl fishery. Use of escape windows is permitted in the legislation to give means of improving the size selectivity of cod as an alternative to a traditional standard codend. The history of the use of escape windows in the Baltic Sea cod fishery is reviewed. The present escape windows do not function optimally. The objective of this new experiment was to compare an improved design of escape window, which is placed in the upper panel, with that of standard codend. Three standard codends, with 105, 120 and 140 mm nominal mesh size, and three window codends, with 110, 125 and 135 mm window nominal mesh size, were tested during sea trials conducted in June and July from a commercial trawler using a twin trawl rig and the covered codend technique. A fixed and random effects model of the codend selectivity was formulated to analyse the results and determine the effects of codend type, mesh size and other recorded variables. L50 and SR increased significantly with the mesh size. L50 was significantly increased and SR significantly reduced for a window codend with the same window mesh size (WMS) as that of a standard codend. The L50 of the standard codends decreased with catch weight. An unexplained port- starboard effect was found for the window codends where the L50 depended on which of the two trawls the codend was attached to. The potential of these escape windows as a management tool to improve the size selectivity in the Baltic cod fishery is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
|Publication status||Published - 2002|