Discard practices in the gulf of Cadiz multispecies trawl fishery. Implications for the EU 'landing obligation'

Discarding has been a common practice in multispecies trawl fisheries since the first trawlers were used. To date there have been no studies reporting an integrated analysis of discarding in the gulf of Cadiz (SW Spain, GoC) to evaluate and support the latest fisheries policies, specifically the Landing Obligation (European Union Regulation 1380/2013). In this study we provide estimates of discard ratios, species composition, reasons for discarding, along with the identification of high-density discard areas (hotspots) over the last decade in the GoC area. The analysis was based on data collected by the Spanish onboard sampling program, involving commercial trawling vessels from 2006 to 2016. In particular, data on catches and discards were analyzed by applying Multivariate Regression Trees (MRTs) to assess the species dominance within the discarded and retained portions of the total catch. Temporal and spatial variability in discard ratios were also explored together with the identification of high-density discard areas (hotspots) modelled using Hierarchical Bayesian Spatial Models (H-BSM). A discard ratio relative to the total catch (i.e. both commercial and by-catch) of 34% in weight was estimated, corresponding to an average at about 3500 t discarded annually by the GoC trawl fleet. Non-commercial by-catch species accounted for more than half of the discarded biomass in weight (59.4%). Finally, our study focuses on research efforts towards relevant and efficient management solutions under the discard ban policy. Recommendations aiming to contribute to the establishment of alternative management strategies for this fishery are further discussed.