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The ICES Working Group on Mixed Fisheries Methodology (WGMIXFISH-METHODS) met 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 2022.The work addressed included improving workflows for the advice process, presenting methodological advances, developing new ecoregions and responding to issues encountered during WGMIXFISH-ADVICE 2022. Additionally, plans for a second scoping workshop were discussed and the contribution of WGMIXFISH to mixed fisheries information in the Fisheries Overviews was reviewed.A key methodological advance used data on quota exchanges between countries to update the Min mixed fisheries scenario to address concerns over choking behaviour in fleets that generally do not entirely consume their initial quota allocation. This update is predicated on the assumption that when TAC changes become restrictive, the usual quota exchanges will become less likely.An Irish Sea model has been in development for several years and a mature version was presented. A formal review process has been initiated to evaluate this model with a timescale consistent with incorporating this ecoregion into the formal mixed fisheries advice process for 2022.To help improve the understanding of the main outputs from the mixed fisheries model a new design for the headline “advice” plot was approved at this meeting. This new design presents the results from each mixed fisheries scenario for a particular stock. This should enable stakeholders to draw easier comparisons between the different scenarios presented for their stock of interest.Future work ahead of next year’s meeting will focus on finalising the plans initiated at this meeting for a second scoping workshop and refining the contribution of WGMIXFISH to mixed fisheries information presented in the Fisheries Overviews.

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.

https://www.ices.dk/sites/pub/Publication%20Reports/Expert%20Group%20Report/Fisheries%20Resources%20Steering%20Group/2021/WGMIXFISH-ADVICE_2020.pdf, SI

The objective of the inter-benchmark working group was to evaluate whether FLBEIA (Garcia et al., 2017) can be used to generate advice on mixed fisheries considerations in Celtic Sea and Greater North Sea ecoregions. The working group should implement an adequate conditioning of the model and investigate the ability of the model to reproduce single species advice and provide meaningful mixed fisheries advice. The validity of the FLBEIA model implementation in both ecoregions was assessed comparing the parameterisation and forecasted indicators in mixed fisheries scenarios against those obtained by the stock assessment working groups and Fcube model. In both case studies the model was implemented using fleet and métier dependent catch-at-age, and discards and landings weight-at-age. In general, in both case studies, the fishing mortality at age and catch-at-age resulting from aggregating the fleet and métier dependent catch-at-age showed a good match with those calculated and estimated by the assessment working groups in the last assessment year. There were significant differences in some cases attributed to the procedure used to raise the data in the stock assessment working groups and the assumptions of the assessment models used. Regarding FLBEIA model results, in Celtic Sea several problems were encountered in reproducing the advice and forecast of mixed fisheries scenarios. Those were mainly attributed to the use of Cobb-Douglass model at high levels of fishing mortality and the impact of discards weightat-age in the forecast of discards. In the North Sea the reproduction of single stock advice was adequate, and the results of the forecast of mixed fisheries scenarios obtained with FCube and FLBEIA were similar.The group concluded that FLBEIA implementation of mixed fisheries in the Celtic Sea was not ready for provision of advice in 2021. However, for North Sea it was concluded that the FLBEIA implementation with métier dependent catch-at-age structure provides meaningful results to provide advice in mixed fisheries considerations.The working group recommended continuing working in the Celtic Sea model conditioning, the implementation of Baranov catch production function in FLBEIA and identifying the most appropriate way to project over-quota discards and discard weights to be implemented later in FLBEIA. Furthermore, it also recommended to organize a dedicated workshop to address some of these issues and others identified during the meeting.

The ICES Working Group on Mixed Fisheries Methodology (WGMIXFISH-METHODS) met 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 2021.Work continued on the full review and documentation of the mixed fisheries advice production process, including workflows, code repositories, stock annexes, data, and associated documentation for all advice regions.Working group participants responded to the outcomes and issues encountered during WGMIXFISH-Advice 2020 for Bay of Biscay, 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 on the Irish Sea. The working group responded to the outcomes of the Scoping workshop on next generation of mixed fisheries advice (WKMIXFISH 2020), 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.

The ICES Working Group on Mixed Fisheries Advice (WGMIXFISH-ADVICE) met remotely to produce mixed fisheries forecasts for the Bay of Biscay, Celtic Sea, Iberian Waters and 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 takes into account past fishing patterns and catchability of the different fleets, and the TAC advice produced by the single-stock advice groups, to provide quantitative forecast of over- and under-exploitation 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 North Sea, and on the “FLBEIA” (Fisheries Library Bio-Economic ImpaPrct Assessment) methodology for the Bay of Biscay and Iberian Waters.The Bay of Biscay mixed fisheries projections consider the single-species advice of 14 demersal 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, rjc.27.8, rjn.27.678abd, rju.27.8ab, sdv.27.nea, sol.27.8ab and whg.27.89a. Mixed-fisheries projections for 2021 indicate that there is no single stock that restricts all fleets. Smooth-hound (sdv.27.nea), Norway lobster (nep.fu.2324) and both anglerfishes (ank.27.78abd and mon.27.78abd) are the least limiting stocks, resulting in an overshoot of the advised catch for the other considered stocks.The Celtic Sea mixed fisheries projections consider the single-species advice for 12 demersal stocks (cod.27.7e–k, had.27.7b–k, whg.27.7bce–k, nep.fu.16, 17, 19, 20–21, 22, and outside FUs, sol.27.7fg, mon.27.78abd, and meg.27.7b k8abd). The results of the mixed fisheries projections show that cod (cod.27.7e–k ) limits all fleets due to the zero catch advice for cod and that all fleets catch cod to a greater or lesser extent. Sole (sol.27.7fg) and Norway lobster (nep.fu.16, 17, 19, 20–21, 22) are the least limiting stocks corresponding to an overshoot of the advised catch for the other considered stocks.The Iberian waters mixed fisheries projections consider the single-species advice for 5 demersal stocks (ank.27.8c9a, hke.27.8c9a, lbd.27.8c9a, meg.27.8c9a and mon.27.8c9a). The result of the mixed fisheries projections indicate that hake (hke.27.8c9a) will be the most limiting stock, corresponding to an undershoot of the advised catch for the other stocks. Anglerfish stocks (ank.27.8c9a and mon.27.8c9a) are the least limiting stocks, corresponding to an overshoot of the advised catch for the other considered stocks. The North Sea demersal mixed fisheries projections consider the single-species advice for 15 demersal stocks (cod.27.47d20, had.27.46a20, whg.27.47d, pok.27.3a46, ple.27.420, ple.27.7d, sol.27.4, tur 27.4, wit.27.3a47d, nep.fu.5–10, 32, 33, 34, and 4 outFU). The results of the projections indicate that cod (cod.27.47d20) will be the most limiting stock for certain fleets, corresponding to an undershoot for the advised catch for the other stocks considered in the mixed fisheries analysis. The “range” scenario suggests that the potential for mixed-fisheries mismatch would be lowered with a 2021 TAC in the lower part of the FMSY range for North Sea plaice (ple.27.420), saithe (pok.27.3a46), and sole (sol.27.4), and at the highest possible value for cod (cod.27.47d20) in accordance with the MSY approach and the EU multiannual plan.

The Working Group on Multispecies Assessment Methods (WGSAM) aims at enabling research on predator-prey interactions for developing advice on the ecosystem approach to fisheries management.This report details results related to WGSAM term of reference B: “Update of key-runs (standardized model runs updated with recent data) of multispecies and ecosystem models for different ICES regions”. Multispecies model key-runs are used in ICES advice processes, and WGSAM provides critical expert review of these key-runs to recommend appropriate use of results.Although key-run reviews have been conducted in the past, requests for reviews are increasing. Therefore, WGSAM first formalized a consistent set of review criteria to conduct key-run reviews. These are outlined in section 2 of this report and are posted online (https://iceseg.github.io/wg_WGSAM/ReviewCriteria.html). WGSAM then applied these review criteria to one key-run for the North Sea ecosystem. The review is detailed in section 3 of this report. As the review criteria were applied, WGSAM also noted any difficulties with the review process in order to further refine the review criteria and to make future key-run reviews more efficient and effective.WGSAM recommends the use of natural mortality estimates from the North Sea SMS key-run for use in single species stock assessment models of North Sea cod, haddock, herring, Norway pout, southern North Sea sandeel, northern North Sea sandeel, sprat, and whiting.

The Working Group on Multispecies Assessment Methods (WGSAM) aims to advance the operational 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 estimation of biological reference points in the context of multispecies interactions. The updated keyruns for the North Sea and the Baltic Sea provided the best available estimates of predation mortality 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. Results 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. Various 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).

WKRPChange was tasked with examining how ICES handles the estimation of target and limit reference points in the face of changing environmental conditions. In particular, the meeting participants were asked to review the robustness of the current ICES procedures and to suggest specific improvements that could be made, especially relating to changes in stock productivity arising from environmental conditions, species interactions, and density-dependent effects. Part of the work involved reviewing the basis of the ICES reference points and contrasting the ICES procedures with those in the USA and Canada, and part on providing specific guidance for future reference point estimation within ICES. One common approach to changing environmental conditions is to truncate data series. WKRPChange agreed that this may be necessary in some cases, but several studies were presented showing that the estimation of reference points becomes unreliable (both noisy and potentially biased) as the time series is reduced, and therefore recommended that modelling the specific process involved is generally a better approach than truncation. The meeting noted several examples within the current ICES management system for which reference points are allowed to vary (e.g. F in the case of NEA cod, Blim in the case of Iberian Sardine) according the prevailing conditions. WKRPChange noted that this was only required if conditions were expected to change significantly over the lifespan of the reference points, and that where it was implemented the status determination (the “traffic lights”) should be made accordingly.The key recommendation of WKRPChange is consistent with the conclusions of WKGMSE2, namely that a scoping exercise should be undertaken for each stock to identify any key drivers. Where there is good evidence for ecosystem-driven changes in stock productivity that process should be accounted for in setting reference points. The meeting highlighted that reference points have a finite lifespan, generally related to the benchmark cycle, and the estimation of the reference point should predominantly take into account processes likely to be important over that lifespan. WKRChange noted that many ICES stocks are managed by Harvest Controls which are evaluated through a MSE process. In this case there is considerable scope for including such environmentally driven processes in the Operating Model. However, many stocks are managed through the standard ICES HCR with reference points derived through the EqSim program. There is therefore a specific recommendation that the possibility to include density-dependentgrowth be incorporated into EqSim, to allow more realism to be included in the estimation of reference points where the evidence indicates that this is important within the reference point life span. The meeting also highlighted the recent work at WKRISH 6, which gave scope to “fine tune” the Ftarget to account for small changes in environmental drivers without requiring full reestimation of the reference points.

The ICES herring assessment working group (HAWG) met on an interactive virtual platform for eight days in March 2020 to assess the state of five herring stocks and three sprat stocks. HAWG also provided advice for four sandeel stocks but reported on those prior to this meeting in February. The working group conducted update assessments for the five herring stocks. An analytical assessment was performed for the combined North Sea and Division 3.a sprat, and a data limited assessment (ICES category 3) was conducted for English Channel sprat (spr.27.7de). The North Sea autumn spawning herring (her.27.3a47d) SSB in 2019 was estimated at 1.7 mill tonnes while F2–6 in 2019 was estimated at 0.18, which is below FMSY. Recruitment in 2019 is comparable to the 2018 value and remains within the low recruitment regime observed since 2015. Year classes since 2002 are estimated to be consistently weak with year classes 2014 and 2016 some of the weakest on record. ICES considers that the stock is still in a low productivity phase.The Western Baltic spring-spawning herring (her.27.20-24) assessment was updated. The SSB and recruitment in 2019 are record low. SSB is estimated to be around 56 600 tonnes which is below both Bpa and Blim. Recruitment has been low since 2006 and it has been further deteriorating with time. Fishing mortality has decrease in 2019 to 0.382 but is still well above FMSY (0.31). The stock has decreased consistently during the second half of the 2000s and given the continued low recruitments the stock is not able to recover above Blim unless a drastic reduction in fishing effort is applied.The Celtic Sea autumn and winter spawning stock (her.27.irls) is estimated to be at a very low level. SSB is currently estimated to be at the lowest level in the time-series and has been below Blim (34 000 t) since 2016. Mean F(2–5 rings) was estimated at 0.49 in 2019, having decreased from the peak of 1.15 in 2017. Recruitment has been consistently below average from 2013-2018. Recruitment in 2019 is estimated to be above average. The assessment of the combined stocks of herring in 6.aN and 6.aS/7.b, c (her.27.6a7bc) went through an interbenchmark procedure in 2019 and the advice is based on trends from an analytical assessment. SSB and recruitment have been declining since around 2000 and are currently at the lowest level in the time-series. Fishing mortality has reduced since 2016 when catches have been limited to a scientific monitoring TAC but recovery of the stock is hampered by the very low recruitment.Irish Sea autumn spawning herring (her.27.nirs) assessment shows a stable SSB in 2019 compared to previous years at around 24 700 tonnes. The stock has experienced large incoming year classes in recent years. Fishing mortality (F4–6) is estimated at 0.18, one of the lowest in the timeseries and below FMSY (0.266). Catches have been relatively stable since the 1980s, and close to the TAC in recent years. North Sea and 3.a Sprat (spr.27.3a4) were combined into a single assessment unit during the 2018 benchmark. Perception of the status of the stock is dominated by the dynamics in Subarea 4 where most of the catches occur. Despite the fact that fishing mortality in the last years has fluctuated at high levels between 0.6–2.2, recruitments slightly but consistently above the average during recent years have contributed to an increase in SSB well above MSY Bescapement. The estimates for 2020 show an SSB of 266 000 t which is more than double of Bpa (125 000 t).Catch advice for sprat in the English Channel (7.d, e) (spr.27.7de) was based on criteria for an ICES category 3-based method. Data available are landings and a short time-series of acoustic biomass (2013–2019). The acoustic biomass has fluctuated over time and the 2019 biomass has increased from the 2018 estimate. The HAWG reviewed the assessments performed on four sandeel stocks and the related advice of these stocks. Section 9 of this report contains the assessments of sandeel in Division 3.a and Subarea 4. Standard issues such as the quality and availability of data, estimating the amounts of discarded fish, availability of data through industry surveys and scientific advances particularly with respect to stock discrimination relevant to small pelagic fish were discussed. All data and scripts used to perform the assessments and the forecast calculations are available at https://github.com/ICES-dk/wg_HAWG and accessible to anyone.

The Workshop on guidelines and methods for the evaluation of rebuilding plans (WKREBUILD) chaired by Vanessa Trijoulet (Denmark) and Martin Pastoors (Netherlands) met from 24 to 28 February 2020. The workshop attracted 27 participants from the US, Canada, Europe and FAO. When stocks are estimated to be below Blim1 and there is no perceived possibility of rebuilding above Blim within the time-frame of a short-term forecast, ICES has regularly recommended zero catch in combination with the development of a rebuilding plan. A review was carried out on the international experience on the development, evaluation and implementation of rebuilding plans for fisheries management in the Northeast Atlantic and in other fora around the world. In the Northeast Atlantic, rebuilding plans have been implemented in the past (e.g. the cod recovery plans of the early 2000s) but ICES has played a limited role in evaluating the performance of such recovery plans and does not have the tools or criteria to evaluate such plans. Recently, when a rebuilding plan for herring in 6.a 7.bc was submitted to ICES for evaluation, ICES refrained from providing such an evaluation. In the US and Canadian approaches, the legal framework determines the triggering and required elements of rebuilding plans. Such a legal imperative does not exist in the Northeast Atlantic. Nevertheless, the US and Canadian experiences provided useful elements that could be included in establishing ICES approach to rebuilding plans. Several case studies were presented on potential tools for the evaluation of rebuilding plans. Particular attention was given to evaluating options for harvest control rule options of such a plan. The tools focused mostly on short to medium term explorations of the probability of achieving a rebuilding of stocks. Because rebuilding plan evaluations need to be ready and available at short-notice when required, it was concluded that relatively standardized tools (i.e. packages or compiled code) to carry out such evaluations would be preferable over custommade evaluation tools. In addition, certain modelling considerations were highlighted as important such as realistic assumptions of productivity, uncertainty, bias in assessments and implementation error and the possibility of estimating the probability of achieving a rebuilding of stocks.Criteria for the acceptability of rebuilding plans will require an agreed Limit Reference Point (LRP) for initiating a rebuilding plan, definition of targets for fishing mortality or stock biomass, time-frames and the acceptable probabilities whether the rebuilding targets have been achieved. All of these should take into account realistic levels of uncertainty and being consistent with international best (scientific) practices. Although it was recognized that Blim would be the most likely candidate LRP triggering a rebuilding plan, the current approach in ICES for the determination of Blim was questioned during the workshop because it requires a more or less subjective classification of the stock-recruitment pairs into different types. In other regions, the LRP is often set as a certain proportion of the SSB at maximum sustainable yield (BMSY), e.g. 40% BMSY. If changes in productivity have been experienced in recent years at these are taken into account when estimating MSY reference points, the proportion of BMSY approach would likely lead to greater changes in the estimated value of LRP than the current ICES procedures used to estimate Blim, which rely on stock-recruitment pairs or definition of the lowest observed biomass (Bloss). This could have a large impact on the rebuilding target for stocks that experience changes in productivity regimes. Some concerns were raised regarding the often small distance between Blim and MSY Btrigger2 reference points for ICES stocks in comparison to the distance between trigger and limit in other jurisdictions. MSY Btrigger could therefore represent a late trigger to start decreasing fishing mortality when SSB is decreasing. The workshop recommended a future workshop on the revision of the procedure to estimate reference points within the ICES framework.An estimate of the minimum time (TMIN) by which rebuilding may be expected to be achieved, could be calculated by assuming zero catch and should be used as baseline for comparison with other rebuilding scenarios. The maximum time for rebuilding in the US and New Zealand is set to TMAX = 2 * TMIN or to TMIN plus one generation time1 (average length of time between when an individual is born and the birth of its offspring NRC (2014)). While the workshop did not arrive at an overall agreement on a default value for TMAX, it was suggested that TMAX = 2 * TMIN could be explored as a potential bounding on the rebuilding period, even though this should be subject to scientific analysis of potential effects on the stock in question. The workshop generated a guidance table summarizing the best practices for evaluation of rebuilding plans against the potential criteria of acceptability. The guidance table includes elements such as estimation of reference points, time-frames for rebuilding, rebuilding targets, handling uncertainties and bias, probability of achieving rebuilding targets and visualizing results. The workshop recommended that a follow-up workshop (WKREBUILD2) be organized for testing the guidelines with actual test cases, with the aim of defining more specific criteria and guidelines, i.e. learning by doing. Some of the elements that were discussed in the workshop but that have not (yet) entered the guidelines for evaluation of rebuilding plans are socio-economic trade-offs (e.g. between fast and slow rebuilding), mixed fisheries aspects (e.g. unavoidable bycatch due to mixed fisheries) and elements in rebuilding plans other than the HCR part (e.g. monitoring to improve the knowledge base). Most of the discussion at WKREBUILD was centred on stocks with analytical assessments (Category 1+2). Identifying when a data limited stock is in need of rebuilding (or has rebuilt) and how to evaluate rebuilding plan options for such stocks would likely require a separate process.

The Workshop on the Review and Future of State Space Stock Assessment Models in ICES focused on future directions of state-space assessment models for ICES stocks (WKRFSAM), utilising recent advances in fisheries modelling research to help define best practises. State-space models consist of a process model for unobserved quantities (e.g. true stock abundances) and an observation model for observed quantities (e.g. catches or survey data). Standard statistical asassessment models do not include stochastic population processes. Prediction is a natural part of the state-space model formulation which is a more practical advantage of the approach for stock assessment.Lognormal observation error models for survey indices can be parameterized such that the mean or median is proportional to the true stock abundance, but this makes little difference on assessment results. Empirical results for 14 stocks indicated that this is also the case for catch observation models. There is no practical difference whether the mean or median of fishing mortality rates (F’s) are constant for the data period, but there are important differences if F is projected into the future.Including random deviations in the natural mortality rate (M) leads to convergence issues for some stocks, and similar assessment results for other stocks, but this depends on the details of how this is implemented. Including time- and age-varying M increases model flexibility and potential confounding of F, M, and stock size index catchability, Q. When model parameters are confounded then we can anticipate less robustness. Including external variances and correlations that are reliably estimated will be more relevant and useful in situations where these differ substantially over time, such as when a survey in some year has a large set, or poor coverage, etc.Two general criteria to select between alternative models are Goodness-of-it and Out-of-sample prediction. Minimizing out-of-sample prediction error (e.g. Akaike Information Criterion, AIC) is increasingly seen as a better approach for model selection.The main tool for model validation are residuals. However, for state-space models, Pearson are not independent because of the dependence structure of the unobserved states. One-observationahead and one-step-ahead residuals are preferred. These can be formulated to be independent and Gaussian distributed.Key research recommendations involve when and how M can be estimated, how to include information about the precision of model inputs, and improved usage of diagnostics and model selection criteria.