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Commission Decision of 25 February 2016 setting up a Scientific, Technical and Economic Committee for Fisheries, C(2016) 1084, OJ C 74, 26.2.2016, p. 4–10. The Commission may consult the group on any matter relating to marine and fisheries biology, fishing gear technology, fisheries economics, fisheries governance, ecosystem effects of fisheries, aquaculture or similar disciplines. The Scientific, Technical and Economic Committee for Fisheries held its 73 rd plenary from 10 to 14 July 2023.

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.

The ICES Working Group on Mixed Fisheries Methodology (WGMIXFISH-METHODS) met to progress work on the improvement and development of the mixed fisheries considerations. The work addressed in 2023 included improving workflows for the advice process, presenting methodological advances, developing new ecoregions and responding to issues encountered during WGMIXFISH-ADVICE 2022. Additionally, key developments arising from the Second Scoping Workshop (WKMIXFISH2) were discussed. The primary development affecting data workflows related to developing a proactive response to the planned introduction of RDBES for stock assessment purposes. The introduction of RDBES will affect WGMIXFISH by replacing InterCatch and the current data call as a data source. The data access requirements and steps needed to transfer workflows to using RDBES as a data source were outlined and aligned with the timetable for the phased introduction of RDBES. Several methodological advances were presented, many of which derive from either the STAR-MIXFISH project, the outcomes of the Second Scoping Workshop (WKMIXFISH2) or have been identified as a priority by WGMIXFISH. These analyses explored sensitivity to model assumptions, incorporating uncertainty in model parameters and novel methods for using spatial data to define métiers. Additionally, the application of mixed fisheries methods in externally developed models of the Bay of Biscay and Western Mediterranean were presented. Significant improvements were progressed for the Iberian Waters and North Sea models. For the Iberian Waters, the potential for adding pelagic stocks such as mackerel and blue whiting to the model was explored with further work planned in the near future. In the North Sea, developments were made to the fleet data processing workflow to improve consistency with other ecoregions and plans were made to incorporate North Sea brill into the model following its recent move to a category 2 assessm

The ICES Working Group on Mixed Fisheries Advice (WGMIXFISH-ADVICE) held a hybrid meeting to produce mixed fisheries forecasts for the Bay of Biscay, Celtic Sea, Iberian waters, Irish Sea and the North Sea. Mixed fisheries advice highlights the potential implications of single-stock (total allowable catch and effort) management on the catches of multiple stocks caught together in mixed fisheries. It considers past fishing patterns and catchability of the different fleets, and the TAC advice produced by the single-stock advice groups, to provide a quantitative forecast of over and underexploitation of the different stocks given mixed fishery interactions. The mixed fisheries forecasts were produced using the “FCube" (Fleet and Fishery Forecasts) methodology for the Celtic Sea and Irish Sea, and the “FLBEIA” (Bio-Economic Impact Assessment using FLR) methodology for the Bay of Biscay, Iberian waters and the North Sea. The Bay of Biscay mixed fisheries projections consider the single-species advice of 13 stocks (ank.27.78abd, bss.27.8ab, hke.27.3a46-8abd, hom.27.2a4a5b6a7a-ce-k8, mac.27.nea, meg.27.7b-k8abd, mon.27.78abd, nep.fu.2324, pol.27.89a, sdv.27.nea, sol.27.8ab, whb.27.1-91214, and whg.27.89a). Given the single-stock catch advice for 2024, the most limiting stock for demersal fisheries in the Bay of Biscay is horse mackerel, due to the zero-catch advice and that almost all fleets within the mixed fishery catch this stock. The least limiting stock is white anglerfish (7 of 21 fleets). However, if horse mackerel were to be excluded as a restrictive stock due to the small contribution made by the demersal fleets to the total stock landings, the most limiting stock would be pollack whose quota is first reached for 7 of 21 defined fleets. The Celtic Sea mixed fisheries projections consider the single-species advice for 15 stocks (cod.27.7e-k, had.27.7b-k, whg.27.7b-ce-k, nep.fu.16, 17, 19, 20–21, 22, and outside FUs, sol.27.7e, sol.27.7fg, mon.27.7

The Workshop on Raising Data using the RDBES and TAF (WKRDBES-Raise&TAF) met online (26–30 of September 2022) to evaluate the use of the Regional Database and Estimation System (RDBES) format to reproduce the 2022 InterCatch input and output, identifying a Transparent Assessment Framework (TAF) structure to organize the intermediate steps and to propose standardized output formats. The main outcomes of WKRDBES-Raise&TAF were: · RDBES provides sufficient support for current national estimation protocols. However, some minor issues were reported that hampered an exact reproduction of the estimates. Therefore, adaptations of the data model should not be excluded completely. · All the input to stock assessment that InterCatch currently provides, could be reproduced. The participants started from the current stock extracts that can be downloaded from InterCatch. · A workflow was proposed with a national TAF repository for each country, a stock estimation repository and a stock assessment repository. The intermediate output of those repositories will be stored in an ‘intermediate output database’ and depending on the user role, you will get access to the relevant stages in this workflow. · The following requirements for the standard output formats were defined: they cannot be more restrictive than the InterCatch input and output format; they should present measures of uncertainty and sample sizes (for national estimates) and should have a configurable domain definition (for national estimates). Despite those successful outcomes, the current plan for transition to an operational system was concluded to be too optimistic. WKRDBES-Raise&TAF therefore recommends to the Working Group on Governance of the Regional Database and Estimation System (WGRDBESGOV) to revise the roadmap and allow RDBES to be in a test phase also for 2023. WKRDBES-Raise&TAF felt the need to test the proposed workflow on a small scale and therefore recommends to the WGRDBESGOV to arrange a workshop where

Commission Decision of 25 February 2016 setting up a Scientific, Technical and Economic Committee for Fisheries, C(2016) 1084, OJ C 74, 26.2.2016, p. 4–10. The Commission may consult the group on any matter relating to marine and fisheries biology, fishing gear technology, fisheries economics, fisheries governance, ecosystem effects of fisheries, aquaculture or similar disciplines. The Scientific, Technical and Economic Committee for Fisheries held its 72 nd plenary from 20-24 March 2023.