Effect of codend mesh size on size selectivity and catch efficiency of common sole (Solea solea)

Abstract

Fisheries targeting sole (Solea solea) are primarily conducted using demersal beam and otter trawls. Despite the economic importance of sole across its wide distribution range, there is limited knowledge regarding its size selectivity in trawl codends. Understanding how codend mesh size and shape influence the size selection of sole is critical for defining technical measures and assessing the implications of regulatory changes for both the stock and the fisheries targeting this species. We developed a morphology-based model to predict size selectivity for sole across a range of sizes and mesh openings in both diamond and square mesh configurations, following the FISHSELECT methodology. This methodology has been successfully applied to several fish and crustacean species. The predicted size selectivity for sole codends aligns well with the relatively limited number of experimental estimates available, providing a morphologically based explanation for sole size selectivity. We predict size selectivity for diamond mesh codends ranging from 50 mm to 120 mm and estimate the number and weight of sole retained above and below the minimum conservation reference size (MCRS), using an experimentally derived population. Our results demonstrate that the various technical regulations implemented across the broad distribution area result in markedly different catch efficiencies and potential discard ratios for sole.