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Across the Mediterranean and the Black Sea, an improvement in technological adoption which optimizes the environmental benefits of fisheries is needed. The testing of quality standards in trawl fishing is one of the essential components. In an experiment, we tested four bottom trawl cod-ends in the western Black Sea to determine the characteristics of the catch composition. Fishing trials were conducted by 40 mm diamond (40D), 44 mm diamond (44D), 40 mm square (the 40S), and 40 mm 90-degree turned (40T) mesh cod-ends for 31 bottom trawling hauls. The multivariate analysis of catch composition indicated a significantly higher differentiation between 40D and 40T cod-ends, mainly characterized by five species: Merlangius merlangus, Mytilus galloprovincialis, Trachinus draco, Mullus barbatus, and Uranuscopus scaber. The difference in the shape of cod-end meshes reflected the variation in the catchability and catch composition. However, the 40S and 40T showed 80% similarity in catch composition. Among cod-ends, 40T yielded in lowest catch per unit effort for both commercial and other species. Adoption of gear specially made to catch more target species can help bottom trawl fisheries further improve their ecological and economic sustainability. [ABSTRACT FROM AUTHOR]

The stock structure and productivity components (growth, maturity and mortality) of the Black Sea whiting Merlangius merlangus were studied in the western Black Sea for a year. The results aim to improve fisheries management of whiting in the Black Sea. Fresh samples were collected from commercial bottom trawlers between October 2017 and September 2018. Using monthly length-frequency data set for the growth trajectories, a bootstrapped procedure was employed to improve parameter optimization. Duration and timing of the spawning season and size at sexual maturity were modelled using generalized additive models (GAMs). The presence of clear differences in oocyte size groups indicates that oocyte development of Black Sea whiting is a 'group synchronous' ovarian developmental process characterized by continuous reproduction. From the gonadosomatic index values, their spawning activity intensifies especially between October and April, captured also in the time component in the GAM modelling. The length at first maturity was 13.9 cm for females and 12.5 cm for males. The mortality rates, yield per recruit analyses, and length-based indicators suggest that whiting is heavily exploited with alarming signs of overexploitation. Undoubtedly, setting catch limits and re-establishing management plans will be the first two steps to ensure reproductive success and prevent overfishing (F > Fmsy). [ABSTRACT FROM AUTHOR]