Characterization of discards along a wide bathymetric range from a trawl fishery in the NW Mediterranean

Abstract

Discards represent a loss of natural resources and negatively affect the sustainability of fisheries. Information on discards, such as diversity and size of the species discarded is essential to better manage trawl fisheries. Thus, this study aims to gain knowledge on discards from the Catalan bottom trawl fisheries in the NW Mediterranean Sea to offer information needed for fisheries management. Discard ratios, species composition of discards and lengths of the discards were analyzed from data collected on board commercial trawlers, from November 2018 to December 2020 and analyzed by depth, zone, and season. Discard ratio varied among depths from 30.5% in the shallowest depth (20 – 70 m) to 14.3% in the deepest (400–700 m), with depth being the main factor determining the species composition of discards. This study also focused on the discards of six main commercial species, i.e. European hake (Merluccius merluccius), red mullet (Mullus barbatus), black-bellied angler (Lophius budegassa), poor cod (Trisopterus capelanus), deep-water pink shrimp (Parapenaeus longirostris) and Norway lobster (Nephrops norvegicus). The length at which 50% of individuals were discarded (L50d) was lower than the Length at First Maturity (LFM) and the Minimum Conservation Reference Size (MCRS) for the six species. These findings provide relevant information to comply with the Marine Strategy Framework Directive’s (EU Directive 2008/56/EC) ecosystem approach to fisheries and to evaluate the implementation of measures for fisheries’ best management practices, such as gear selectivity and spatial planning.