Working Group on Multispecies Assessment Methods (WGSAM)

The Working Group on Multispecies Assessment Methods (WGSAM) aims to advance the oper-ational use of knowledge on predator-prey interactions for advice on fisheries and ecosystem management. This report summarises the achievements of a 3-year cycle during which the group consolidated criteria to evaluate key-runs and more in general the skills assessment of multispecies models, released key-runs for the Baltic Sea, North Sea and Irish Sea all evaluated with those criteria, progressed in the areas of multiple models comparison, ensemble modelling and on the estima-tion of biological reference points in the context of multispecies interactions. The updated key-runs for the North Sea and the Baltic Sea provided the best available estimates of predation mor-tality for a number of key commercial stocks in these two ecoregions which have been already integrated into the stock assessments throughout benchmarks and inter-benchmarks. Analyses accumulate showing that ignoring strong trophic interactions may lead to bias in the perception of stocks status and in the calculation of reference points. Evaluations show advantages of using multi-model ensembles to capture the dynamics of the main stocks and the system overall. Re-sults accumulated so far suggest that the benefits of ensemble modelling exist for both simple models, i.e. multispecies production models, as well as more complex ecosystem models. Vari-ous approaches are available to the practice of ensemble modelling, including a fully Bayesian ensemble framework suitable also for multi-model forecasts. The report includes also progresses with software developments to enhance accessibility of some complex routines, including ensemble modelling beyond “just a simple average approach” and computation of multispecies reference points, to a broader group of modellers and users. The group sees these developments as a great opportunity to work more towards cross-platform comparisons and further on multispecies skill assessment which will remain important themes for continuation of the work. To further progress the use of multispecies and ecosystem models, collection of ecosystem data remains highly relevant, with priority on stomach data and other information on processes affecting trophic interactions and trophodynamics of ecosystems (i.e., predator-prey overlap, temperature-dependent consumption, availability of other food)