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The ICES Working Group on Mixed Fisheries Methodology (WGMIXFISH-METHODS) meet to progress work on the improvement and development of the mixed fisheries advice. In this report the group provides a summary of the work completed in 2020. Work continued on the full documentation of the mixed fisheries advice production process, including workflows, code repositories, stock annexes and associated documentation for all advice regions. A review was completed of the new data call and associated quality control procedures to identify possible areas of improvements. Working group participants responded to the outcomes and issues encountered during WGMIXFISH-Advice 2019 for Celtic Sea, Iberian Waters, and North Sea. A full list of issues and solutions were collated and discussed during the meeting. Additionally, work continued on the development of mixed fisheries advice for three new advice regions: Bay of Biscay, Irish Sea, and Kattegat.The working group responded to the outcomes of the Mixed Fisheries Scoping Meeting (WKMIXFISH), identifying timelines and requirements to meet the growing needs for mixed fisheries advice. To support these growing needs the group members presented and discussed new techniques in the field of mixed fisheries.

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 STECF reviewed the report of the EWG on Fisheries-dependent Information during its winter 2019 plenary meeting.

1. Bycatch of Eastern Baltic cod in non-targeted fisheries 1a.Total cod bycatch in 2018 was in the range of 360-1306 *tonnes in subdivisions 25-32 (eastern stock) and 66-417* tonnes in subdivision 24 (eastern and western stock combined). The ranges correspond to different bycatch thresholds from 10 to 50% cod in the landings in a fishing trip. These cod bycatch amounts correspond to fishing patterns in 2018 when cod was a target species, and fishers did not attempt to avoid catching cod. 1b. Bycatch of cod in demersal trawl fisheries for flatfish could be substantially reduced when applying selectivity devices in fishing gear. Three selectivity strategies are possible: i) species specific size selection, ii) selection by behavioural differences of the species and iii) a strategy that combines i and ii. Strategy i can be efficient to reduce bycatch of small but not larger cod, while strategies ii and iii can be applied to minimise bycatches of cod at all sizes in targeted flatfish fisheries. 1c. Cod and flounder overlap in the entire distribution area of the eastern Baltic cod stock; plaice and eastern Baltic cod overlap in subdivisions 24-25. Therefore, there are no areas or months where flatfish fisheries with non-selective gears could be conducted in subdivisions 24-26 without a risk of bycatch of cod. Only a small fraction of EU flatfish landings were taken in subdivision 26 in later years (6% of flounder landings in 2018). Therefore, a potential closure of subdivision 26 for demersal fisheries would have limited implications for EU flatfish fisheries, while protecting a substantial part of the eastern Baltic cod stock. 2. Mixing of eastern and western Baltic cod in subdivision 24 2a Eastern Baltic cod (EBC) occurs throughout subdivision 24 and in all seasons. However, the proportion of EBC is lowest: (i) in the area west of 13°E (on average 47% EBC in last 11 years), compared to the area east of 13°E (on average 78% EBC) and (ii) in waters between 0-10m or 020m deep (on average 27% or 39% EBC, respectively). The latter is assumed not to include the coastal waters around Bornholm Island. The proportion of eastern Baltic cod is lower in fisheries by passive gears due to their use mostly in shallow areas. 2b. Bycatch of eastern Baltic cod in fisheries targeting western Baltic cod can be calculated by multiplying the TAC for the management area with the fraction of it taken in subdivision 24 (0.53 in the last 3 years) and the proportion of cod in subdivision 24 that belongs to the eastern stock (0.74 in the last 3 years). The additional fishing restrictions applied in 2020 in subdivision 24 are expected to reduce the fraction of the cod TAC taken in subdivision 24, and thus reduce the bycatch of eastern Baltic cod. 2c. A closure of subdivision 24 could result in up to 25% loss of western Baltic cod commercial landings, at the fishing patterns observed in latest years. It is difficult to foresee to what extent effort reallocation to subdivisions 22-23 would be possible for different fleets. The cod TAC at 3806 tonnes set for the western Baltic management area for 2020 is close to the amount that has been taken in subdivisions 22-23 in later years. Thus, the TAC at 3806 tonnes would likely be possible to take in subdivisions 22-23. Cod in subdivisions 27-32 3a. Eastern Baltic cod annual catches in subdivisions 27-32 were between 150-400 tonnes in 20102018, with the exception of 2017 (883 tonnes). This corresponds to less than 1% of the total catch from the eastern Baltic cod stock in these years, with the exception of 3% in 2017. Most catches within this area were taken in subdivisions 27-29, both by active (trawls) and passive (gillnets) gears. 3b. Fishing at status quo effort in subdivisions 27-32, corresponding to total cod catch of 168 tonnes in 2020, is estimated to result in 0.08 % lower SSB in 2021 compared to the scenario of zero catch. 3c. Potential effort reallocation to subdivisions 27-32 could result in removing up to 3% of the total biomass of the eastern Baltic cod stock

The ICES Benchmark Workshop on Baltic Cod Stocks (WKBALTCOD2) met at ICES Headquarters in Copenhagen, Denmark on 4–8 February 2019, following a data evaluation workshop (Chair Johan Lövgren) and several preparatory web conference meetings. The meeting, cochaired by Meaghan Bryan, USA (External Chair) and Michele Casini, Sweden (ICES Chair), was attended by two invited external experts, Vladlena Gertseva, USA, and Verena Trenkel, France, and 47 participants from 10 countries. Participants represented a diversity of groups including industry, NGOs, managers, and scientists. The objectives of WKBALTCOD2 were to evaluate the appropriateness of the data and the assessment methods to determine stock status for the Western Baltic cod (SD 22-24) and the Eastern Baltic cod (SD 24-32) stocks, evaluate the short-term forecasting methods, re-examine and update the reference points, and update the stock annex as appropriate to these stocks. The workshop started with a group discussion of data issues and decisions that were integral to both assessments. Subsequent, stock-specific discussions were held in smaller subgroups and the main results and conclusions were presented in plenary. Around 15–20 persons, together with at least one external reviewer/co-chair, participated in each of the subgroups. A single modelling approach, the state-space stock assessment model (SAM), was presented for Western Baltic cod. This model has been used previously to determine stock status of Western Baltic cod and the panel agreed that this model should be used for the current assessment. The main issues that emerged and were addressed during the workshop for this stock were stock mixing in SD 24, the inclusion of new recreational data from Sweden and Denmark, the inclusion of a German pound-net survey index of age-0 fish in the assessment model, the extension of the time-series of the assessment back in time, and the update of reference points. Future efforts should be made to update the mixing proportion of Eastern and Western Baltic cod in SD 24 by length and season, and continue improving the stock splitting methods and the geographical coverage of the samples. An analytical quantitative assessment had been lacking since 2014 for the Eastern Baltic cod stock. The key issues addressed during the benchmark included how to best account for changes in productivity (e.g. growth, mortality, maturity) in the assessment model, stock splitting in SD 24, the use of age–length keys in the assessment, and ageing error and bias. Stock assessment models using Stock Synthesis and the stochastic surplus production model (SPiCT) were put forward for the benchmark as two possible model candidates. The panel agreed that the Stock Synthesis model assuming time-varying growth, natural mortality, and maturity to account for changes in productivity was acceptable to provide scientific advice, while the SPiCT model should be maintained as an alternative approach. The accepted model exhibited some residual patterns that were likely due to assuming that ages were precisely known. Stock Synthesis can accommodate an ageing error matrix to account for precision and bias. Ageing error and bias statistics should be developed and thoroughly reviewed for the next benchmark. Additionally, future work should focus on improving the growth estimates, which will allow a more precise separation between growth and natural mortality. The Stock Synthesis model would also benefit from information on sample size associated with length distributions of commercial catches. Estimates of fishing mortality compatible with a precautionary FMSY was not attainable for this stock, therefore probabilistic forecasts with Markov chain Monte Carlo methods were proposed to be used instead.

The main objective of WGBFAS was to assess the status and produce a draft advice of the following stocks: • Sole in Division 3.a, SDs 20–24 • Cod in Kattegat, Cod in SDs 22–24, Cod in SDs 24–32 • Herring in SDs 25–27, 28.2, 29 and 32 • Herring in SD 28.1 (Gulf of Riga) • Herring in SDs 30-31 (Gulf of Bothnia) • Sprat in SDs 22–32 • Plaice in SDs 21–23, Plaice in SDs 24–32 • Flounder in SDs 22–23 (no catch advice) • Flounder in SDs 24–25 (no catch advice) The WG was not requested to assess the following stocks in 2019, as no advice was needed: • Flounder in SDs 26+28 • Flounder in SDs 27+29–32 • Brill in SDs 22–32 • Dab in SDs 22–32 • Turbot in SDs 22–32 It was, however, decided by the group to compile and update the input data for 2018 and thereby also conduct update assessments for these latest five stocks. In the introductory chapter of this report the WG, in agreement with the ToRs, considers and comments on the ecosystem and fisheries overviews, reviews the progress on benchmark processes, identifies the data needed for next year’s data call with some suggestions for improvements in the data call, and summarizes general and stock-specific research needs. The introduction further summarizes the work of other WGs relevant to the WGBFAS, and the assessment methods used. Finally, the introduction presents a brief overview of each stock and quite extensively discusses the ecosystem considerations of the Baltic Sea and ecosystem changes that have been analytically considered in the stock assessments. The results of the analytical stock assessment or survey trends for the species listed above are presented for all the stocks with the same species in the same sections. The analytical models used for the stock assessments were XSA, SAM and SS3. For most flatfish (data limited stocks), CPUE trends from bottom-trawl surveys were used in the assessment (except plaice in SDs 24–25 for which relative SSB from SAM was used). For cod in SDs 24–32, a full analytical assessment (using SS3) could be performed, after the compilation/benchmark work undertaken in 2018–2019. The report ends with references, annexes with the response to a special request, links to Stock Annexes, and list of Working Documents.

The STECF expert working group (EWG) on Fisheries Dependant Information (FDI) took place in JRC, Ispra from 23 to 27 October 2017 to review the data transmitted by Member States under a new data call (‘New-FDI’). The new data call specification was designed with three broad aims in mind i) Compatibility between the New-FDI data and the data held in the Fleet Economic database. ii) Ability to encompass all EU registered vessels including those from the Mediterranean, Black Sea and external waters fleets. iii) Ability to assess effects of management measures. The main purpose of the EWG was to judge if the call specification was appropriate to accomplish the above aims and to consider any difficulties encountered by member states in fulfilling the data call. Two terms of reference also allowed trial analyses to be conducted of a type relevant to the third broad aim. The EWG addressed all Terms of Reference during the meeting and drew conclusions on the modifications required for the New-FDI data call going forwards. Prior to the EWG it had been agreed by STECF Bureau that the report of the meeting would not be presented to STECF for approval as an STECF report but published separately (as a JRC technical report). This report therefore presents the data, methods observations and findings of an EWG of the STECF but the findings presented in this report do not necessarily constitute the opinion of the STECF or reflect the views of the European Commission and in no way anticipate the Commission’s future policy in this area., JRC.D.2-Water and Marine Resources

The Working Group on Commercial Catches (WGCATCH), chaired by Mike Arm- strong (UK) and Hans Gerritsen (Ireland), met in ICES HQ, Copenhagen, Denmark, 10–14 November 2014. The meeting was attended by 34 experts from 21 laboratories or organizations, covering 16 countries. Currently, an important task for WGCATCH is to improve and review sampling sur- vey designs for commercial fisheries, particularly those for estimating quantities and size or age compositions of landings and discards and providing data quality indica- tors. However, the scope of WGCATCH is broader than this, covering many other aspects of collection and analysis of data on fishing activities and catches. This will be end-user driven, and coordinated with the work of other ICES data EGs such as the Working Group on Biological Parameters (WGBIOP), the Planning Group on Data Needs for Assessments and Advice (PGDATA) and the Working Group on Recrea- tional Fisheries Surveys (WGRFS) to ensure synergy and efficiency. The report of the meeting commences with background information on the formation of WGCATCH and its overall role. The remainder of the report provides the out- comes for each of the Terms of Reference (ToRs) and responses to external requests, the proposed future work plan and the ToRs for the 2015 meeting. The group formed two large subgroups to deal with the two major terms of reference which are the development of guidelines for carrying out sampling of catches on shore and the provision of advice on adapting sampling programmes to deal with the landing obligation. In order to evaluate methods and develop guidelines for best practice in carrying out sampling of commercial sampling of commercial fish catches onshore, a question- naire was circulated before the meeting. This questionnaire was structured around guidelines developed by the ICES Workshop on Practical Implementation of Statisti- cally Sound Catch Sampling Programmes (WKPICS) for best practice at each stage of the sampling process, and asked for a description of current practices at each of these stages. Based on these questionnaires, common and specific problems were cata- logued and potential solutions were identified. At the same time, the discussion of the questionnaires provided a form of peer-review of the sampling designs and iden- tified where improvements could be made. WGCATCH provided guidelines for de- signing a sampling survey and summarized earlier guidelines provided by the 2010 Workshop on methods for merging métiers for fishery based sampling (WKMERGE) The other main subject addressed by WGCATCH concerns the provision of advice on adapting sampling protocols to deal with the impact of the introduction of the land- ing obligation, which will alter discarding practices and result in additional catego- ries of catch being landed. A second questionnaire was circulated before the meeting to allow the group to identify the fleets that will be affected and possible issues that are anticipated, as well as to propose solutions to adapt existing monitoring and sampling schemes and to quantify bias resulting from the introduction of this regula- tion. WGCATCH outlined a range of likely scenarios and the expected effects of these on fishery sampling programmes, and developed guidelines for adapting sam- pling schemes. The group also explored a range of analyses that could be conducted in order to quantify bias resulting from the introduction of the landing obligation. Finally a number of pilot studies/case studies were summarized, highlighting the practical issues involved

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