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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. Key runs of multispecies and ecosystem models provided by WGSAM are integral to this mission. They serve as a robust component of ecosystem science that seamlessly integrates into the ICES advice. This report presents an update of the multispecies SMS key-run model for the North Sea and its review by the working group based on established review criteria. The updated model extends to input time-series to 2022 and includes a more extensive revision of the time-series of marine birds and grey seal population numbers. Additional improvements of this key-run include (i) one extra year of grey seal diet data (i.e., 1985, 2002, 2010); (ii) plaice is now a prey species, although predation is at the moment limited to grey seal; (iii) improved compilation of fish diet data including estimation of variance of the estimated prey proportions. 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 haddock, herring, Norway pout, sandeel (estimates are disaggregated for the southern and northern North Sea), sprat, and whiting. The SMS key-run continues to assume a single North Sea cod stock in contrast to the recent split into three components which makes assimilation of the natural mortality estimates into the new cod assessments problematic. More work is needed to harmonise the new fish stomachs with the old ones before they could be integrated in the North Sea key-run.

Population identification plays an important role in the assessment of Atlantic herring (Clupea harengus). Several morphological/traditional methods have been applied in the past to split catches (both within survey and commercial samples) and to identify herring populations. However, in recent years advances in genomics have provided a robust and precise method to genetically identify herring populations. WKSIDAC2 reviewed the current status of genetic population identification for herring and outstanding issues affecting identification accuracy/success. The genetic methods using single nucleotide polymorphism (SNP) as genetic markers to identify herring population are considered appropriate. Depending on the region of interest, different sets of markers are used to identify herring populations. The differences in the set of markers have only minor influence on the population identification and can be negligible. However, it is recommended to choose sets of markers which will allow a direct comparison between institutes undertaking the classification. Furthermore, the review concluded that 26 different herring spawning populations can be currently identified using genetic methods in the northeastern Atlantic. However, future genetic studies may increase the number of identified populations and also provide a greater resolution for the spatial distributions. For example, from the genetic markers presented during WKSIDAC2, we are not able to genetically differentiate between Icelandic summer spawners, Faroese autumn spawners, and Norwegian autumn spawners. These three populations are currently combined as a single genetic unit. Future work incorporating whole genome sequencing data, is recommended to investigate this issue in more detail. In addition, of the 26 identified genetic populations only some can directly and uniquely be assinged to a particular stock (management unit) and for this reason WKSIDAC2 refrained from establishing such correspondence which

The Benchmark Workshop on Sandeel (Ammodytes spp.) (WKSandeel) was conducted over an extended period, spanning 2021-2023, to agree the assessment methodology to be used in future update assessments of sandeel in areas 1–4 (Figure 1). The benchmark had a strong focus on investigating spatial stock boundaries within the North Sea, bringing catch and survey data compilation and standardization up to standard with the latest insights in ICES and updating the assessments accordingly. The data compilation workshop was preceded by several informal sessions to present the latest findings from an extensive study on stock structure identification, including tagging, otolith micro-chemistry, drift modelling and genetics research. The workshop proposed two alternative stock structure delineation scenarios as presented in Figure 2. The different research projects provided contrasting views on appropriate stock structure delineation, with evidence for residence within the delineated sandeel areas but also migration across the a and b borders as denoted in Figure 2. The group reached consensus that, as a pragmatic way forward, only scenario WKSAND2022a would be put forward for evaluation in the assessments, together with the existing WKSAND2016 delineation as a baseline. Catch numbers at age, fishing effort, maturity at age, weight at age, natural mortality at age and survey indices were recalculated based on the latest insights and tools provided through the ICES RDBES and statistical standardization. Key to this process was also the re-definition of sandeel banks, which are used directly to derive standardized survey indices for the different assessments (Figure 3). For all four sandeel areas, updated assessments were prepared for the WKSAND2022a and WKSAND2016 (baseline) area delineation scenarios. There is no change in area delineation for area 4 under both scenarios. Diagnostics on catch and survey residuals, parameter uncertainty

We developed and validated a mixed-stock analysis (MSA) method with 59 single-nucleotide polymorphisms selected from genome-wide data to assign individuals to populations in mixed-stock samples of Atlantic herring from the North and Baltic seas. We analysed 3734 herring from spawning locations and scientific catches of mixed feeding stocks to demonstrate a "one-fits-all" tool with unprecedented accuracy for monitoring spatio-temporal dynamics throughout a large geographical range with complex stock mixing. We re-analysed time-series data (2002-2021) and compared inferences about stock composition with estimates from morphological data. We show that contributions from the western Baltic spring-spawning stock complex, which is under management concern, have likely been overestimated. We also show that a genetically distinctive population of western Baltic autumn spawners, ascribed low fisheries importance, contributes non-negligible and potentially temporally increasing proportions to mixed-stock aggregations, calling for a re-evaluation of stock definitions. MSA data can be implemented in stock assessment and in a variety of applications, including marine ecosystem description, impact assessment of specific fleets, and stock-rebuilding plans.

A first workshop on guidelines and methods for the design and evaluation of rebuilding plans for category 1-2 stocks, WKREBUILD, took place in 2020. WKREBUILD generated a guidance on best practices for evaluation of rebuilding plans against potential criteria of acceptability. However, it did not propose specific rebuilding plans or harvest control rules (HCRs). Instead, the workshop recommended that a follow-up workshop be organized for testing the guidelines with actual test cases, with the aim of defining more specific criteria and guidelines. Thus, the main objective of WKREBUILD2 was to propose performance indicators and thresholds for the implementation and acceptability of rebuilding plans and a framework for the integration of rebuilding advice rules within the ICES advice framework. To facilitate the evaluation of rebuilding plans a simulation tool was developed. The tool is based on FLR libraries and the application to specific cases is facilitated through a template consistent with TAF (Transparent Assessment Framework) and ensures an easy integration of the analysis into the ICES TAF system. The tool was tested in three specific case studies, Celtic Sea Whiting, Western Horse Mackerel and Western Baltic Herring. The application to the case studies served to validate the tool and to provide the science base to propose operational performance thresholds and criteria for the evaluation and implementation of rebuilding strategies in ICES. WKREBUILD2 proposes to use BPA as the entry point to the rebuilding phase and MSY Btrigger as the exit point. Once a stock is estimated to be below BPA in the last assessment year, stock specific rebuilding strategies should be tested by means of simulations, preferably using the WKREBUILD2 simulation tool as the performance of HCRs are dependent on depletion rate and life history. The harvest control rule that fulfils the rebuilding criteria could then be selected to provide headline catch advi

The ICES herring assessment working group (HAWG) met online for nine days in March 2023 to assess the state of six herring (Clupea harengus) and three sprat (Sprattus sprattus) stocks. Additionally, HAWG provided advice for eight Sandeel (Ammodytes spp.) in January 2023. The working group conducted update category 1 assessments for four of the herring stocks and category 3 assessments for 2 herring stocks. An analytical assessment was performed for the combined North Sea and Division 3.a sprat, and data limited assessment (ICES category 3) was conducted for English Channel sprat (spr.27.7de). Biennial advice is given for sprat in the Celtic Seas and West of Scotland with advice provided in 2023. North Sea autumn spawning herring (her.27.3a47d). SSB in 2022 was estimated at 1.65 million tonnes while F 2–6 in 2021 was estimated at 0.23, which is below FMSY. Recruitment in 2022 is at its highest since 2014, which is expected to contribute positively to SSB levels from 2024 onwards. ICES considers that the stock is still in a low productivity phase. Western Baltic spring-spawning herring (her.27.20-24). SSB in 2022 was estimated at 75,548 tonnes and is below MSY Btrigger, Bpa, and Blim. Recruitment has been low since 2007 and has been deteriorating further with time. F3-6 has been decreasing since 2018 and is now week below FMSY (0.31) at 0.05. 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 for several years. Celtic Sea autumn and winter spawning stock (her.27.irls). SSB in 2022 was estimated at 16,539 tonnes, though is increasing from its lowest level seen in 2018 (6,474 tonnes), but remains below Blim (34,000 tonnes). F(2-5 rings) in 2022 was estima

Incorrect Affiliation In the published article, there was an error regarding the affiliation for Jasper Van Vlasselaer. Instead of: 13 Spanish Institute of Oceanography (IEO-CSIC) (Palma), Ecosystem Oceanography Group (GRECO), Palma de Mallorca, Spain, he should have: 11 Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Fisheries and Aquatic Production, Oostende, Belgium. In the published article, there was an error regarding the affiliation for Luc Van Hoof. Instead of: 14 Department of Marine Sciences, University of the Aegean, Mytilene, Greece he should have 3 Wageningen Marine Research, Wageningen University and Research, Ijmuiden, Netherlands The authors apologize for this error and state that this does not change the scientific conclusions of the article in any way. The original article has been updated.

Fisheries management has historically focused on the population elasticity of target fish based primarily on demographic modeling, with the key assumptions of stability in environmental conditions and static trophic relationships. The predictive capacity of this fisheries framework is poor, especially in closed systems where the benthic diversity and boundary effects are important and the stock levels are low. Here, we present a probabilistic model that couples key fish populations with a complex suite of trophic, environmental, and geomorphological factors. Using 41 years of observations we model the changes in eastern Baltic cod (Gadus morhua), herring (Clupea harengus), and Baltic sprat (Sprattus sprattus balticus) for the Baltic Sea within a Bayesian network. The model predictions are spatially explicit and show the changes of the central Baltic Sea from cod- to sprat-dominated ecology over the 41 years. This also highlights how the years 2004 to 2014 deviate in terms of the typical cod–environment relationship, with environmental factors such as salinity being less influential on cod population abundance than in previous periods. The role of macrozoobenthos abundance, biotopic rugosity, and flatfish biomass showed an increased influence in predicting cod biomass in the last decade of the study. Fisheries management that is able to accommodate shifting ecological and environmental conditions relevant to biotopic information will be more effective and realistic. Non-stationary modelling for all of the homogeneous biotope regions, while acknowledging that each has a specific ecology relevant to understanding the fish population dynamics, is essential for fisheries science and sustainable management of fish stocks.

Understanding the drivers behind fluctuations in fish populations remains a key objective in fishery science. Our predictive capacity to explain these fluctuations is still relatively low, due to the amalgam of interacting bottom-up and top-down factors, which vary across time and space among and within populations. Gaining a mechanistic understanding of these recruitment drivers requires a holistic approach, combining field, experimental and modelling efforts. Here, we use the Western Baltic Spring-Spawning (WBSS) herring (Clupea harengus) to exemplify the power of this holistic approach and the high complexity of the recruitment drivers (and their interactions). Since the early 2000s, low recruitment levels have promoted intense research on this stock. Our literature synthesis suggests that the major drivers are habitat compression of the spawning beds (due to eutrophication and coastal modification mainly) and warming, which indirectly leads to changes in spawning phenology, prey abundance and predation pressure. Other factors include increased intensity of extreme climate events and new predators in the system. Four main knowledge gaps were identified related to life-cycle migration and habitat use, population structure and demographics, life-stage specific impact of multi-stressors, and predator–prey interactions. Specific research topics within these areas are proposed, as well as the priority to support a sustainable management of the stock. Given that the Baltic Sea is severely impacted by warming, eutrophication and altered precipitation, WBSS herring could be a harbinger of potential effects of changing environmental drivers to the recruitment of small pelagic fishes in other coastal areas in the world.

The global response to the challenge of increasingly rapid and severe climate change is shifting from a focus on mitigation and remediation of impacts to a pragmatic adaptation framework. Innovative adaptive solutions that transform the way in which we manage the world's oceans and, particularly, the harvesting of marine resources in a sustainable manner, are urgently needed. In that context, ICES Journal of Marine Science solicited contributions to the themed article set (TS), “Exploring adaptation capacity of the world's oceans and marine resources to climate change”. We summarize the contributions included in this TS that provide examples of emerging climate change impacts, assess system risks at subnational and international scales, prove and evaluate different adaptation options and approaches, and explore societal and stakeholder perceptions. We also provide some “food for thought" on possible future developments in a transdisciplinary “adaptation science” working at the interface between ecology, socio-economics, and policy-governance, and that will have to provide concrete solutions to the challenges represented by climate-change and anthropogenic activity. Success will depend on the extent to which new knowledge and approaches can be integrated into the decision-making process to support evidence-based climate policy and ecosystem-based management. This includes testing their effectiveness in real systems, but also consider how social acceptance of adaptive measures will/will not support their full implementation.

To effectively future-proof the management of the European Union fishing fleets we have explored a suite of case studies encompassing the northeast and tropical Atlantic, the Mediterranean, Baltic and Black Seas. This study shows that European Union (EU) fisheries are likely resilient to climate-driven short-term stresses, but may be negatively impacted by long-term trends in climate change. However, fisheries’ long-term stock resilience can be improved (and therefore be more resilient to increasing changes in climate) by adopting robust and adaptive fisheries management, provided such measures are based on sound scientific advice which includes uncertainty. Such management requires regular updates of biological reference points. Such updates will delineate safe biological limits for exploitation, providing both high long-term yields with reduced risk of stock collapse when affected by short-term stresses, and enhanced compliance with advice to avoid higher than intended fishing mortality. However, high resilience of the exploited ecosystem does not necessarily lead to the resilience of the economy of EU fisheries from suffering shocks associated with reduced yields, neither to a reduced carbon footprint if fuel use increases from lower stock abundances. Fuel consumption is impacted by stock development, but also by changes in vessel and gear technologies, as well as fishing techniques. In this respect, energy-efficient fishing technologies already exist within the EU, though implementing them would require improving the uptake of innovations and demonstrating to stakeholders the potential for both reduced fuel costs and increased catch rates. A transition towards reducing fuel consumption and costs would need to be supported by the setup of EU regulatory instruments. Overall, to effectively manage EU fisheries within a changing climate, flexible, adaptive, well-informed and well-enforced management is needed, with incentives provided for innovations and ocean liter

To effectively future-proof the management of the European Union fishing fleets we have explored a suite of case studies encompassing the northeast and tropical Atlantic, the Mediterranean, Baltic and Black Seas. This study shows that European Union (EU) fisheries are likely resilient to climate-driven short-term stresses, but may be negatively impacted by long-term trends in climate change. However, fisheries’ long-term stock resilience can be improved (and therefore be more resilient to increasing changes in climate) by adopting robust and adaptive fisheries management, provided such measures are based on sound scientific advice which includes uncertainty. Such management requires regular updates of biological reference points. Such updates will delineate safe biological limits for exploitation, providing both high long-term yields with reduced risk of stock collapse when affected by short-term stresses, and enhanced compliance with advice to avoid higher than intended fishing mortality. However, high resilience of the exploited ecosystem does not necessarily lead to the resilience of the economy of EU fisheries from suffering shocks associated with reduced yields, neither to a reduced carbon footprint if fuel use increases from lower stock abundances. Fuel consumption is impacted by stock development, but also by changes in vessel and gear technologies, as well as fishing techniques. In this respect, energy-efficient fishing technologies already exist within the EU, though implementing them would require improving the uptake of innovations and demonstrating to stakeholders the potential for both reduced fuel costs and increased catch rates. A transition towards reducing fuel consumption and costs would need to be supported by the setup of EU regulatory instruments. Overall, to effectively manage EU fisheries within a changing climate, flexible, adaptive, well-informed and well-enforced management is needed, with incentives provided for innovations and ocean liter

The ICES Workshop on ICES reference points (WKREF2) was tasked review the WKREF1 report and based on the outcome develop updated guidelines for the ICES reference points system and recommendations for ACOM consideration. The WKREF1 report has suggested 5 key recommendations to simplify and harmonise the ICES reference points framework representing a major change to the current guidelines. At WKREF2, we detailed discussions and four key concerns were raised about the proposed approach. The first related to the simplification of rules to define Blim. Around two thirds of category 1 stocks would end up as WKREF1 “Blim Type 2” where Blim would be set as a fraction of B0. The Allee effect or “depensation” maybe more important than previously thought and should be furthered explored for ICES stocks since it has important consequences for Blim. A number of challenges and issues around defining Blim using the current guidelines were documented. Some suggestions on improvement criteria were discussed including using classifiers to define spasmodic stocks and using change point algorithms to address non-stationary productivity regimes. However, further work is need to make these approaches operational and there was no consensus that the WKREF1 Blim types should replace the current guidelines. WKREF1 recommended that the FMSY proxy should be based on a biological proxies and should be less than the deterministic FMSY. It was pointed out that the stochastic FMSY estimated in EqSim for example, is lower than the deterministic FMSY and that the current guidelines ensure that the FMSY should not pose a more than 5% risk to Blim. A large amount of work described in WD 1 was carried out to develop an MSE framework to consistency and robustness test a candidate reference point system for North East Atlantic stocks. However, WKREF2 recommended tha

Regionalisation was established to enable a bottom-up approach to fisheries governance by allowing lower-level authorities and stakeholders to step into the fisheries management process and design tailor-made management on a regional scale. A review has been undertaken to provide improved understanding on how regionalisation has worked until now and contribute information towards the European Commission (EC) report on the functioning of the Common Fisheries Policy (CFP). Findings show that there are large differences in how regional groups operate and whether they have formal working procedures. The Advisory Councils (ACs) have clear working procedures and are transparent in the work that they do. However, this is not the case for the Member State Groups (MSGs), for which a lot of information regarding structure, working procedures and meeting outcomes are not publicly available. The onset of the Landing Obligation resulted in a large increase in the number of measures (i.e. discard plans) for several geographical areas. Stakeholders feel that there are gains and losses in participating in the regionalisation process, stating that regionalisation has provided a useful channel for individuals to put their points across and discuss them with a broader spectrum of stakeholders as opposed to writing individual position papers. The distribution of the ACs (different seas basins) is also seen as a gain as it provides EU-wide fora for discussions in fisheries management issues. The direct and closely working among different institutions (EC, ACs, scientists, MSGs) is also seen as an advantage of regionalisation. However, many of the perceived benefits have not yet been realised. Overall, regionalisation is necessary and has fulfilled its expectations although not in all fields. Regionalisation has given powers to Member States to perform functions that used to be the preserve of the EU. Without regionalisation, it would be difficult to get the same level of detail towards

The global response to the challenge of increasingly rapid and severe climate change is shifting from a focus on mitigation and remediation of impacts to a pragmatic adaptation framework. Innovative adaptive solutions that transform the way in which we manage the world's oceans and, particularly, the harvesting of marine resources in a sustainable manner, are urgently needed. In that context, ICES Journal of Marine Science solicited contributions to the themed article set (TS), “Exploring adaptation capacity of the world's oceans and marine resources to climate change”. We summarize the contributions included in this TS that provide examples of emerging climate change impacts, assess system risks at subnational and international scales, prove and evaluate different adaptation options and approaches, and explore societal and stakeholder perceptions. We also provide some “food for thought" on possible future developments in a transdisciplinary “adaptation science” working at the interface between ecology, socio-economics, and policy-governance, and that will have to provide concrete solutions to the challenges represented by climate-change and anthropogenic activity. Success will depend on the extent to which new knowledge and approaches can be integrated into the decision-making process to support evidence-based climate policy and ecosystem-based management. This includes testing their effectiveness in real systems, but also consider how social acceptance of adaptive measures will/will not support their full implementation

A successful discrimination of fish populations is essential for sustainable management and assessment. Otolith shape analysis has been used on several species to reveal their population structure. Our aim was to use the otolith shape of European sprat (Sprattus sprattus) to investigate large- and small-scale geographical variability across the Greater North Sea ecoregion. The otolith shape was extracted from digitalised images and transformed into Wavelet coefficients to be analysed with multivariate statistics. Otolith shape was observed to follow the genetic population structure recently defined for the region, supporting the latest revision of the stock boundaries. Four main groups were identified based on phenotypic variability: (i) Norwegian fjords; (ii) North Sea and offshore Skagerrak–Kattegat; (iii) coastal Skagerrak–Kattegat; and (iv) Uddevalla fjord. However, 4-fold cross-validations based on Linear Discriminant Analysis resulted in low accuracy limiting at the moment the ability to use otolith shape analysis for population identification at an operational basis. Our results show the importance of coastal areas, which might be inhabited by distinct populations of sprat that are currently not acknowledged in the management and assessment.

The ICES Workshop on ICES reference points (WKREF1) was tasked to provide a thorough review of the ICES reference points system as a basis to re-evaluate the process for estimating, updating and communicating reference points in the context of the ICES advice. As part of the preparation leading to WKREF1 a large database of the most recent assessment outputs for 78 Category 1 stocks were collated in the form `FLStock` objects, which formed the basis for several components of the presented analyses. The first part of the meeting involved a detailed overview of the history and basis of the ICES references points system, which was aligned with the results of an empirical review of the procedures and choices made to derive ICES reference points for category 1 stocks. The ICES procedures were then contrasted with those used in the USA, Canada, New Zealand and across tuna Regional Fishery Management Organizations. A limitation in terms of transparency of the ICES procedures is a lack of complete documentation of the settings used for deriving reference points using, e.g., the EQSIM software. In comparison to other international standards, the main differences identified include the absence of a target biomass reference point and inconsistent estimates of the limit biomass reference point Blim, which is estimated to be below 10% of the unfished biomass (B0) for a high proportion of analysed stocks (around 50%). In addition, an important difference is that direct estimates of FMSY are used in ICES (which can be unreliable), whereas elsewhere FMSY is often replaced by more conservative biological proxies, such as Fspr% and FB%. The second part focused on the robustness evaluation of the current ICES reference point system. Work presented included examples that demonstrate differences in reference point estimates between standard ICES procedures (EQSIM) and full Management Strategy Evaluation (MSE) simulations, and a study th