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The ICES herring assessment working group (HAWG) met in Aberdeen, Scotland from 12-21 March 2024 to assess the state of six herring (Clupea harengus) and one sprat (Sprattus sprattus) stock. 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.

Sustainable fisheries management is important for the continued harvest of the world's marine resources, especially as they are increasingly challenged by a range of climatic and anthropogenic factors. One of the pillars of sustainable fisheries management is the accurate identification of the biological units, i.e., populations. Here, we developed and implemented a genetic baseline for Atlantic herring harvested in the Norwegian offshore fisheries to investigate the validity of the current management boundaries. This was achieved by genotyping > 15,000 herring from the northern European seas, including samples of all the known populations in the region, with a panel of population-informative SNPs mined from existing genomic resources. The final genetic baseline consisted of ~1000 herring from 12 genetically distinct populations. We thereafter used the baseline to investigate mixed catches from the North and Norwegian Seas, revealing that each management area consisted of multiple populations, as previously suspected. However, substantial numbers (up to 50% or more within a sample) of herring were found outside of their expected management areas, e.g., North Sea autumn-spawning herring north of 62° N (average = 19.2%), Norwegian spring-spawning herring south of 62° N (average = 13.5%), and western Baltic spring-spawning herring outside their assumed distribution area in the North Sea (average = 20.0%). Based upon these extensive observations, we conclude that the assessment and management areas currently in place for herring in this region need adjustments to reflect the populations present. Furthermore, we suggest that for migratory species, such as herring, a paradigm shift from using static geographic stock boundaries towards spatial dynamic boundaries is needed to meet the requirements of future sustainable management regimes.

The European sprat is a small plankton-feeding clupeid present in the northeastern Atlantic Ocean, the Mediterranean Sea as well as in the brackish Baltic Sea and Black Sea. This species is the target of a major fishery and therefore an accurate characterization of its genetic population structure is crucial to delineate proper stock assessments that aid ensuring the fishery's sustainability. Here we present (i) a draft genome assembly, (ii) pooled whole genome sequencing of 19 population samples covering most of the species' distribution range, and (iii) the design and test of a SNP-chip resource and use this to validate the population structure inferred from pooled sequencing. These approaches revealed, using the populations sampled here, three major groups of European sprat: Oceanic, Coastal, and Brackish with limited differentiation within groups even over wide geographical stretches. Genetic structure is largely driven by six large putative inversions that differentiate Oceanic and Brackish sprats, while Coastal populations display intermediate frequencies of haplotypes at each locus. Interestingly, populations from the Baltic and the Black Seas share similar frequencies of haplotypes at these putative inversions despite their distant geographic location. The closely related clupeids European sprat and Atlantic herring both show genetic adaptation to the brackish Baltic Sea, providing an opportunity to explore the extent of genetic parallelism. This analysis revealed limited parallelism because out of 125 independent loci detected in the Atlantic herring, three showed sharp signals of selection that overlapped between the two species and contained single genes such as PRLRA, which encodes the receptor for prolactin, a freshwater-adapting hormone in euryhaline species, and THRB, a receptor for thyroid hormones, important both for metabolic regulation and the development of red cone photoreceptors.

The European sprat is a small plankton-feeding clupeid present in the northeastern Atlantic Ocean, in the Mediterranean Sea, and in the brackish Baltic Sea and Black Sea. This species is the target of a major fishery and, therefore, an accurate characterization of its genetic population structure is crucial to delineate proper stock assessments that aid ensuring the fishery's sustainability. Here, we present (i) a draft genome assembly, (ii) pooled whole genome sequencing of 19 population samples covering most of the species' distribution range, and (iii) the design and test of a single nucleotide polymorphism (SNP)-chip resource and use this to validate the population structure inferred from pooled sequencing. These approaches revealed, using the populations sampled here, three major groups of European sprat: Oceanic, Coastal, and Brackish with limited differentiation within groups even over wide geographical stretches. Genetic structure is largely driven by six large putative inversions that differentiate Oceanic and Brackish sprats, while Coastal populations display intermediate frequencies of haplotypes at each locus. Interestingly, populations from the Baltic and the Black Seas share similar frequencies of haplotypes at these putative inversions despite their distant geographic location. The closely related clupeids European sprat and Atlantic herring both show genetic adaptation to the brackish Baltic Sea, providing an opportunity to explore the extent of genetic parallelism. This analysis revealed limited parallelism because out of 125 independent loci detected in the Atlantic herring, three showed sharp signals of selection that overlapped between the two species and contained single genes such as PRLRA, which encodes the receptor for prolactin, a freshwater-adapting hormone in euryhaline species, and THRB, a receptor for thyroid hormones, important both for metabolic regulation and the development of red cone photoreceptors.

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

The International Bottom Trawl Survey Working Group (IBTSWG) coordinate fishery-independent bottom trawl surveys in the ICES Area (Northeast Atlantic and North Sea) providing an important platform for the collection of additional data such as sampling larval sprat, stomach contents and fish parasites. These long-term monitoring surveys provide data for stock assessments and facilitate analyses of the distributions and relative abundance of fish. IBTSWG promotes the standardization of fishing gears and methods. This report summarizes national contributions in 2022–2023 and plans for the 2023–2024 surveys. In the North Sea, the surveys are performed in Quarter 1 and Q3. The Northeast Atlantic surveys are conducted mostly in Q1, Q3, and Q4 with a suite of 14 national surveys covering large areas of continental shelf extending from northern Scotland to the Gulf of Cádiz. The 2023-Q1 North Sea IBTS was impacted slightly by mechanical issues on one vessel, resulting in some of the Rectangles in the central North Sea being sampled with a single haul instead of the planned two. The 2022-Q3 North Sea IBTS was broadly complete, with the overall number of hauls comparable to previous years, though some Rectangles close to shore or with obstructions may not have had full coverage. The Northeast Atlantic surveys were mostly completed successfully, with the exception of the Scottish west coast groundfish survey in Q1 (cancelled due to vessel breakdown). There was incomplete survey coverage for some of the surveys, including the EVHOE survey (severe weather) and Portuguese groundfish survey (severe weather and mechanical problems). The Spanish surveys in the Gulf of Cádiz (cancelled in 2021) were undertaken in 2022. Recent updates to DATRAS, where the trawl survey data are stored, were summarised and data quality, including catch weights and species identification, was reviewed. IBTSWG met with members of various data users, including r

WGIPS met in January 2023 to combine and review the results of the annual pelagic ecosystem surveys and provide indices for the stocks of herring, sprat, mackerel, boarfish, and blue whiting in the Northeast Atlantic, Norwegian Sea, North Sea, and Western Baltic. Timing, coverage and methodologies were assessed and coordinated for the upcoming 2023 surveys. Progression on the update of the WGIPS survey manual (SISP 9) in the TIMES format continued, with an expected first draft to be submitted in spring 2023 and the completion planned within the present WGIPS reporting cycle. The group discussed the future and development of databases used by the group (the ICES DB and the PGNAPES database). The use of StoX and progress on TAF were reviewed during a joint session with the ICES Data Centre and the StoX development team. The biological sampling strategies in WGIPS surveys continue to be discussed and progress is being made on documenting the sampling strategies used in all WGIPS surveys in the new format of the sampling manual. The planned workshop on sampling strategies in the HERAS survey has been postponed until further progress is made on data availability for analysis. WGIPS reviewed progress in using genetic stock separation methods for splitting survey results to component herring stocks and assessed ways forward for the development of these methods whilst maintaining the integrity of the survey indices. The group encourages continued close collaboration of the ICES survey and assessment groups and institutes carrying out the genetic analysis work. WGIPS continues to follow progress on mesopelagic fish sampling in the International Blue Whiting Spawning Survey (IBWSS) through updates from the Ecologically and Economically Sustainable Mesopelagic Fisheries EU project (MEESO) and other developments within this area of relevance to the WGIPS surveys.

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

The core objectives of the Working Group on International Pelagic Surveys (WGIPS) are to combine and review the results of annual pelagic ecosystem surveys to provide indices for the stocks of herring, sprat, mackerel, boarfish, and blue whiting in the Northeast Atlantic, Norwegian Sea, North Sea, and Western Baltic; and to coordinate timing, coverage and methodologies for the upcoming 2022 surveys. To support this work, the group is drafting an update to the Series of ICES Survey Protocols 9 - Manual for International Pelagic Surveys (SISP9-IPS). This past year, WGIPS held a number of focal sessions including: (1) a session for presenting auxiliary monitoring of ecosystem components beyond the standard fishery survey results for the target species. This session has been held annually since 2019, with presentations this year on tests with an in-trawl stereo camera system during part of the 2021 International Ecosystem Summer Survey in the Nordic Seas (IESSNS), (2) a session on the future and development of databases used to store data from surveys in WGIPS (ICES Acoustic Database and the “PGNAPES” database), developments and use of the acoustic survey analysis software “StoX” and progress on adopting the ICES Transparent Assessment Framework (TAF) for archiving and documenting acoustic index calculations, and (3) a session on biological sampling strategies in WGIPS surveys. The group is documenting the sampling strategies used in all WGIPS surveys (on request from ICES Working group on Acoustic Trawl Data Portal Governance (WGAcousticGov) and is planning a workshop on sampling strategies in the ICES Coordinated Acoustic Survey in the Skagerrak and Kattegat, the North Sea, West of Scotland and the Malin Shelf area (HERAS). The group also reviewed progress on mesopelagic sampling with an update from the European Union Horizon 2020-programme on Ecologically and Economically Sustainable Mesopelagic Fisheries (MEESO), presentations on new net developmen

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

Habitat changes represent one of the five most pervasive threats to biodiversity. However, anthropogenic activities also have the capacity to create novel niche spaces to which species respond differently. In 1880, one such habitat alterations occurred in Landvikvannet, a freshwater lake on the Norwegian coast of Skagerrak, which became brackish after being artificially connected to the sea. This lake is now home to the European sprat, a pelagic marine fish that managed to develop a self-recruiting population in barely few decades. Landvikvannet sprat proved to be genetically isolated from the three main populations described for this species; that is, Norwegian fjords, Baltic Sea, and the combination of North Sea, Kattegat, and Skagerrak. This distinctness was depicted by an accuracy self-assignment of 89% and a highly significant FST between the lake sprat and each of the remaining samples (average of ≈0.105). The correlation between genetic and environmental variation indicated that salinity could be an important environmental driver of selection (3.3% of the 91 SNPs showed strong associations). Likewise, Isolation by Environment was detected for salinity, although not for temperature, in samples not adhering to an Isolation by Distance pattern. Neighbor-joining tree analysis suggested that the source of the lake sprat is in the Norwegian fjords, rather than in the Baltic Sea despite a similar salinity profile. Strongly drifted allele frequencies and lower genetic diversity in Landvikvannet compared with the Norwegian fjords concur with a founder effect potentially associated with local adaptation to low salinity. Genetic differentiation (FST) between marine and brackish sprat is larger in the comparison Norway-Landvikvannet than in Norway-Baltic, which suggests that the observed divergence was achieved in Landvikvannet in some 65 generations, that is, 132 years, rather than gradually over thousands of years (the age of the Baltic Sea), thus highlighting the pace

The core objectives of The Working Group of International Pelagic Surveys (WGIPS) are to combine and review results of annual pelagic ecosystem surveys to provide indices for the stocks of herring, sprat, mackerel, boarfish, and blue whiting in the Northeast Atlantic, Norwegian Sea, North Sea, and Western Baltic; and to coordinate timing, coverage and methodologies for upcoming surveys. Results from all WGIPS surveys as well as coordination plans for multinational pelagic acoustic surveys and individual surveys were the primary focus at meetings over the past 3 years (2019-2021). WGIPS discussed developments and experiences with the ICES database and the survey analysis software StoX. WGIPS recommends that all surveys use StoX as the primary method for biomass and abundance estimation, and this has been a welcome improvement in the overall working of the group for the surveys that use StoX. Harmonising procedures across surveys increases transparency and promotes understanding and sharing of survey methods within the group. In 2021, a session was held to begin the process of moving surveys onto the Transparent Assessment Framework (TAF). Some surveys had started the TAF process before the meeting and their pro- gress was presented to the group. WGIPS will work with the ICES Data Centre to produce aworkflow and/or documentation to assist with the transition to TAF. Harmonising surveying techniques that measure other aspects of the marine ecosystem has been flagged as requiring attention. As such, the group annually assessed auxiliary pelagic ecosystem surveying techniques currently used on surveys coordinated by WGIPS. The discussions highlighted the range of additional work being undertaken across the group. WGIPS has continued to respond to requests from other ICES expert groups and contribute to workshops. In 2021, WGIPS held a subgroup made up of IBWSS participants (NO, FO, NL, IE, ES) to discuss the formulation of scrutiny procedures t

Sustainable fisheries management requires detailed knowledge of population genetic structure. The European sprat is an important commercial fish distributed from Morocco to the Arctic circle, Baltic, Mediterranean and Black Sea´s. Prior to 2018, annual catch advice on sprat from the International Council for the Exploration of the Sea (ICES) was based on five putative stocks: 1. North Sea, 2. Kattegat‐Skagerrak and Norwegian fjords, 3. Baltic Sea, 4. West of Scotland ‐ southern Celtic Seas and 5. English Channel. However, there were concerns that the sprat advice on stock size estimates management plan inadequately reflected the underlying biological units. Here, we used ddRAD sequencing to develop 91 SNPs that were thereafter used to genotype approximately 2,500 fish from 40 locations. Three highly distinct and relatively homogenous genetic groups were identified: 1. Norwegian fjords, 2. Northeast Atlantic including the North Sea, Kattegat‐Skagerrak, Celtic Sea and Bay of Biscay, and 3. Baltic Sea. Evidence of genetic admixture and possibly physical mixing was detected in samples collected from the transition zone between the North and Baltic seas, but not between any of the other groups. These results have already been implemented by ICES with the decision to merge the North Sea and the Kattegat‐Skagerrak sprat to be assessed as a single unit, thus demonstrating that genetic data can be rapidly absorbed to align harvest regimes and biological units.

The Working Group of International Pelagic Surveys (WGIPS) met in Santa Cruz, Tenerife, Spain on 14–18 January 2019, under the chairmanship of Bram Couperus, Netherlands and Michael O’Malley, Ireland. This was the first meeting in the multi-annual ToR term. The core objectives of the Expert Group are to combine and review results of annual pelagic ecosystem surveys to provide indices for the stocks of herring, sprat, mackerel, boarfish, and blue whiting in the Northeast Atlantic, Norwegian Sea, North Sea, and Western Baltic; and to coordinate timing, coverage and methodologies for the upcoming 2019 surveys. A session was held in 2019 to assess auxiliary pelagic ecosystem surveying techniques currently used on surveys coordinated by WGIPS. It was decided that this approach will be continued in future meetings during this term whereby results from the auxiliary monitoring of ecosystem components will be presented in a separate session from the standard fishery survey results for the target species. In practice this means that the session planned under Term of Reference (ToR) h for 2019 will be repeated in 2020 and 2021. Additionally, progress, developments and experiences with the survey analysis software StoX as well as with the ICES acoustic database repository were analysed and discussed amongst users and developers during the meeting and the intention to further consolidate both the software and the database as common tools to be utilized among all surveys coordinated within WGIPS was stated. Further work progressed on editing the current version of the SISP 9 Manual for International Pelagic Surveys and will continue intersessionally. WGIPS requests a workshop to establish and agree on survey design and protocols for coordinating and conducting acoustic surveys on herring spawning aggregations. The workshop will focus on industry acoustic surveys on herring spawning aggregations in 6.a and in the Irish Sea. WGIPS also requests a workshop o