Sorting grid usage to reduce the catch of undersized narrow-clawed crayfish (Pontastacus leptodactylus Eschscholtz, 1823) in fyke net fisheries

Abstract

Sustainability of natural stocks of crayfish is critical because of their economic and ecological importance. Crayfish (Pontastacus leptodactylus), one of the most important species in Turkish inland fisheries, has been facing serious threats recently. One threat the species faces is high landed bycatch of undersized crayfish because of selective fishing gear, such as fyke nets. We estimated size-selectivity of sorting grids with various bar spacings for crayfish to reduce bycatch. Six bar spacings (15.0, 17.5, 20.0, 22.5, 25.0, and 30.0 mm) were tested alongside commercial crayfish fyke nets. Mean selectivity (L₅₀) (±95% CI) was 6.90 (6.63–6.99) cm for 15.0 mm bar spacing, 7.52 (7.16–8.02) cm for 17.5 mm, 8.52 (8.32–8.71) cm for 20.0 mm, 9.70 (9.28–9.90) cm for 22.5, 10.75 (10.34–11.17) cm for 25.0 mm, 11.80 (11.31–12.24) cm for 30.0 mm, and 8.79 (8.05–9.29) cm for commercial fyke nets. The proportion of undersized specimens caught be reduced from 32.27% for commercial fyke nets to as low as 2.46% by using sorting grids. The codend of 22.5 mm bar spacing was more selective, with significantly lower discard rates, and more effective for individuals above the minimum conservation reference size than commercial fyke nets.