A year-long trial of a square mesh panel in a commercial demersal trawl

Trials were carried out to evaluate the effects of a square mesh panel on the catches of a demersal trawl during normal commercial fishing operations over a period of 1 year. A 100 mm cod-end fitted with a 90 mm mesh square mesh panel between 6.3 and 9.3 m from the cod-line was compared with an identical cod-end with no panel, attached to the same net, using the alternate haul method. The square mesh panel significantly reduced the catch of undersized whiting (by an estimated 34%; p < 0.001) and of whiting greater than the minimum landing size up to lengths of about 32 cm (p < 0.05). However, the square mesh panel had no significant effect on the catches of haddock, cod or monkfish. Hauls with a small-mesh cod-end showed that large numbers of small haddock were present in the areas where the trials were carried out. Few of these fish were retained by the normal cod-end, either with or without the square-mesh panel, suggesting that fitting the square mesh panel did not appreciably improve the selectivity of the cod-end design used in these trials.