Modelización bioeconómica y análisis de la selectividad de pesquerías del Mediterráneo noroccidental en situación de mejora de la selectividad y reducción de los descartes

With the progressive implementation of the Landings Obligation, selectivity of bottom trawl must be improved to decrease the proportion of unwanted catches. Traditional regulatory meshes are insufficient to guarantee the length of first capture (L50) in line with regulatory minimum landing size (MLS). The fish selection properties of the T90 experimental mesh was studied in the trawl extension piece compared to a standard net fitted with 53 mm diamond mesh (DM53) in NW Mediterranean fisheries. The selectivity parameters were estimated for 3 target species of the fishery (M. merluccius, M. barbatus and M. surmuletus) considering between haul variability. Furthermore, the bioeconomic impact of the adoption of the T90 experimental mesh and a more traditional increase in codend mesh size with a 56 mm diamond net (DM56) were analysed. The results show that L50 of the experimental net is close to minimum conservation reference size (MCRS) for European hake (20 cm TL) and that the amount of retained undersize individuals can be reduced to half in the experimental net. The properties of the experimental net for the two red mullet species are not significantly different than in the standard net because the latter has already good selection properties for red mullets. The results of the bioeconomic simulation show that for the two species under the discards ban in 2017-2018 (hake and red mullet) the T90 modification would allow increasing the relative spawning stock biomass and decrease fishing mortality to a larger extent than the wider-meshed codend (DM56). Both measures ensure an increase in catches and benefits notably in the mid-term, and the reduction of discards, although the T90 is better in all aspects analysed. Adopting relatively inexpensive technological solutions, allow to align trawl exploitation patterns with policy requirements, by increasing selectivity and reducing unwanted catches