Study to assess the robustness of mixed fisheries scenario assumptions: final report

This study tackles the challenges of providing advice for fishing EU demersal stocks when based solely on single-species data and Total Allowable Catches. Such advice neglects intricate multi-species interactions and could result in the over-exploitation of more vulnerable stocks. In this study, we explore ‘mixed fisheries’, a concept developed within ICES over the past decade. This looks at multi-species fisheries, where different species are caught together, to provide a more holistic approach to assessment, a step beyond single species considerations. To assess mixed-fisheries, scenario-based modelling is carried out considering different fishing regimes. However, the underlying assumptions of each scenario can lead to unrealistic recommendations, risking stock under-utilisation. The primary objective of this study was to analyse these assumptions and their impacts. Case studies in the North Sea, Celtic Sea and Bay of Biscay assess uncertainties and sensitivities of mixed-fisheries assessments used to guide European policy decisions on fishing and stock protection. This study addresses data source and resolution challenges, and shows that accurate fleet activity data are essential for identifying technical interactions. Examining fleet and métier definitions highlights the need to address overall model structural uncertainty, particularly in terms of fleet dynamics models. Characterising uncertainty in mixed-fisheries models sheds light on input parameter significance. Furthermore, this project introduces conceptual frameworks for scenario evaluation, stock rebuilding, adding new stocks and developing models for new areas within mixedfisheries models.