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 assump-tions, incorporating uncertainty in model parameters and novel methods for using spatial data to define métiers. Additionally, the application of mixed fisheries methods in externally devel-oped 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, develop-ments were made to the fleet data processing workflow to improve consistency with other ecore-gions and plans were made to incorporate North Sea brill into the model following its recent move to a category 2 assessment. Additionally, work was conducted to explore feasible options for incorporating the new Northern Shelf cod assessment, which consists of 3 sub-stocks, follow-ing the recent benchmark of North Sea cod.

Finally, mixed fisheries analyses for the Baltic Sea were initiated and involved a review of exist-ing data available to WGMIXFISH and the evaluation of alternative data sources. Planned work in this region in 2023 aims to provide an analysis of catch compositions for the ecoregion which will be presented in the Baltic Sea fisheries overview.