Selectivity Experiments with Square Mesh Cod-Ends on Haddock and Cod

During May 1987, comparative fishing trials were carried out by the Fisheries Development Branch to document the benefits of square mesh cod-ends on immature haddock and cod stocks. Three sizes of mesh were used; 121mm square, 130mm square and 130mm diamond. The trials were intended to be carried out using covered cod-ends but inspection with the underwater video camera, Mermaid Explorer, showed that the covers were collapsing on the cod-ends inhibiting escapement. In consequence, the trials reverted to using a trouser trawl with square mesh cod-ends on one side and diamond mesh on the other. A total of 51 valid sets were made and the results show that an equivalent size square mesh reduces the total catch by about 25% while giving higher 50% retention lengths and selection factors. A comparison was also made of the differences between day and night tows.