Interim Report of the Working Group on Multispecies Assessment Methods (WGSAM)

The pan-regional Working Group on Multispecies Assessment Methods (WGSAM) met in San Sebastian, Spain, 16–20 October 2017. In this eleventh report of the group, work focused on three of the multi-annual ToRs (B, C, D).Based on their knowledge, participants provided an updated inventory of progress of multispecies models in ICES Ecoregions (ToR A), noting those regions where no in-formation was available.A Key Run (ToR B) of the North Sea Stochastic Multispecies Model (SMS) was pre-sented and reviewed in detail by 4 WGSAM experts, and approved by the group following implementation of changes agreed in plenary at the meeting and verified by a subset of experts post-meeting. The Key Run is documented in detail in Annex for ToR B, with key outputs summarised in Section 5 and data files made available on the WGSAM webpage and the ICES expert group Github (https://github.com/ices-eg/wg_WGSAM). Since the M2 values are used for the assessment of important North Sea stocks, it is recommended to publish the annex also on the official stock annex website. In addition, WGSAM does not recommend updating existing data series of natural mortality by simply adding the latest three new years. The time-series as a whole shows patterns which are not retained by this procedure.Multispecies model skill assessment (ToR C) and multi-model ensemble methods (ToR D) were emphasized this year. Considerable progress has been made towards advancing both aspects of multispecies modelling. Investigation of skill assessment and ensemble methods and case studies is critical to ensure that outputs of multi-species assessment models are reliable for use in operational assessment and to in-form management decisions.Progress was also made on investigations of top predator impacts on managed fish across several regions (ToR F), including the North Sea where new information was included in the SMS key run. Further progress was also made on multispecies and ecosystem level reference points and harvest control rules in mixed fisheries (ToR G).