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This study tackles the challenges of providing advice for fishing EU demersal stocks when based solely on single-species data and Total Allowable Catches. Such advice neglects intricate multi-species interactions and could result in the over-exploitation of more vulnerable stocks. In this study, we explore ‘mixed fisheries’, a concept developed within ICES over the past decade. This looks at multi-species fisheries, where different species are caught together, to provide a more holistic approach to assessment, a step beyond single species considerations. To assess mixed-fisheries, scenario-based modelling is carried out considering different fishing regimes. However, the underlying assumptions of each scenario can lead to unrealistic recommendations, risking stock under-utilisation. The primary objective of this study was to analyse these assumptions and their impacts. Case studies in the North Sea, Celtic Sea and Bay of Biscay assess uncertainties and sensitivities of mixed-fisheries assessments used to guide European policy decisions on fishing and stock protection. This study addresses data source and resolution challenges, and shows that accurate fleet activity data are essential for identifying technical interactions. Examining fleet and métier definitions highlights the need to address overall model structural uncertainty, particularly in terms of fleet dynamics models. Characterising uncertainty in mixed-fisheries models sheds light on input parameter significance. Furthermore, this project introduces conceptual frameworks for scenario evaluation, stock rebuilding, adding new stocks and developing models for new areas within mixedfisheries models.

Technical interactions (multiple fleets fishing multiple species with various gears, as either target or bycatch), bycatch regulations through a landing obligation, and biological and economic effects of climate change, affecting fisheries yield and profits, provide a challenge for demersal mixed fisheries of the North Sea. A multi-stock, multi-fleet, bioeconomic model was used to understand management options under these combined influences. Scenarios considered climate change effects on recruitment of three main gadoid stocks (cod – Gadus morhua, saithe – Pollachius virens, whiting – Merlangius merlangus), possible future developments of fuel and fish prices, and strict implementation of a landing obligation. The latter leads to decreased yield and profits in the short term due to increased choke effects, mainly of North Sea cod, being influenced by climate-induced productivity changes. Allowing fishing above FMSY, but within sustainable limits, or limiting year-to-year quota changes, could help buffer initial losses at the expense of decreased profits in the mid- to long-term. Economic performance of individual fleets was linked to their main target's stock status, cost structure, and fuel and fish prices. The results highlight a need to consider both biological and economic consequences of climate change in the management of mixed fisheries.

The ICES Working Group on Mixed Fisheries Methodology (WGMIXFISH-METHODS) met to progress work on the improvement and development of the mixed fisheries considerations. The work addressed in 2023 included improving workflows for the advice process, presenting methodological advances, developing new ecoregions and responding to issues encountered during WGMIXFISH-ADVICE 2022. Additionally, key developments arising from the Second Scoping Workshop (WKMIXFISH2) were discussed. The primary development affecting data workflows related to developing a proactive response to the planned introduction of RDBES for stock assessment purposes. The introduction of RDBES will affect WGMIXFISH by replacing InterCatch and the current data call as a data source. The data access requirements and steps needed to transfer workflows to using RDBES as a data source were outlined and aligned with the timetable for the phased introduction of RDBES. Several methodological advances were presented, many of which derive from either the STAR-MIXFISH project, the outcomes of the Second Scoping Workshop (WKMIXFISH2) or have been identified as a priority by WGMIXFISH. These analyses explored sensitivity to model assumptions, incorporating uncertainty in model parameters and novel methods for using spatial data to define métiers. Additionally, the application of mixed fisheries methods in externally developed models of the Bay of Biscay and Western Mediterranean were presented. Significant improvements were progressed for the Iberian Waters and North Sea models. For the Iberian Waters, the potential for adding pelagic stocks such as mackerel and blue whiting to the model was explored with further work planned in the near future. In the North Sea, developments were made to the fleet data processing workflow to improve consistency with other ecoregions and plans were made to incorporate North Sea brill into the model following its recent move to a category 2 assessm

The ICES Working Group on Mixed Fisheries Advice (WGMIXFISH-ADVICE) held a hybrid meeting to produce mixed fisheries forecasts for the Bay of Biscay, Celtic Sea, Iberian waters, Irish Sea and the 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 considers past fishing patterns and catchability of the different fleets, and the TAC advice produced by the single-stock advice groups, to provide a quantitative forecast of over and underexploitation 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 Irish Sea, and the “FLBEIA” (Bio-Economic Impact Assessment using FLR) methodology for the Bay of Biscay, Iberian waters and the North Sea. The Bay of Biscay mixed fisheries projections consider the single-species advice of 13 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, pol.27.89a, sdv.27.nea, sol.27.8ab, whb.27.1-91214, and whg.27.89a). Given the single-stock catch advice for 2024, the most limiting stock for demersal fisheries in the Bay of Biscay is horse mackerel, due to the zero-catch advice and that almost all fleets within the mixed fishery catch this stock. The least limiting stock is white anglerfish (7 of 21 fleets). However, if horse mackerel were to be excluded as a restrictive stock due to the small contribution made by the demersal fleets to the total stock landings, the most limiting stock would be pollack whose quota is first reached for 7 of 21 defined fleets. The Celtic Sea mixed fisheries projections consider the single-species advice for 15 stocks (cod.27.7e-k, had.27.7b-k, whg.27.7b-ce-k, nep.fu.16, 17, 19, 20–21, 22, and outside FUs, sol.27.7e, sol.27.7fg, mon.27.7

The objective of WKFISHDISH2 was to develop a standardized and open-source way of routinely using trawl survey data to produce distribution maps which can be easily updated. To do so, workshop participants (i) reviewed models that can produce distribution maps from survey data in DATRAS and MEDITS formats, (ii) considered best practice guidance for data, and models, (iii) implemented best practice to produce distribution maps in a transparent manner, and (iv) populated an ICES repository with distribution maps and associated scripts. Nine models were reviewed, seven of which were considered appropriate to produce distribution maps using survey data. The two models excluded failed to estimate gear standardization factors. Best practice for data should consider the following: correct/remove erroneous observations, account for changes in haul duration/timing affecting catchability, use species-specific modelled areas, remove gears/surveys with no observations to reduce model converging time, and include appropriate explanatory variables. A step-by-step list to preprocess survey data was provided. Best practice for models should consider the following: account for skewed distribution of survey data by exploring different statistical error distributions, use open-source models able to reproduce distributions from simulated data, consider the complexity of the model required vs. the run-time (e.g. number of knots), avoid extrapolating the model to areas/depths where the species is not observed, and perform relevant model diagnostics/model selection. To compare distribution estimated by different models, the SPAtial EFficiency metric (SPAEF) was used together with centres of gravity, biomass hot spots (90 th percentile), and effective occupied areas. All seven models were able to produce satisfactory distribution maps for at least one species within the workshop time constraints, both with DATRAS data in the Atlantic and the MEDITS data in the Mediterranean. Comparisons be

An ecosystem approach to fisheries management requires the consideration of commercial species as components of an ecosystem and the acknowledgement of the links between their productivity and the surrounding environment. To provide a knowledge base for such links, SEAwise consulted stakeholders throughout Europe and conducted a systematic review of the scientific literature. The systematic review resulted in 2050 articles from the literature search that were screened for their tile and abstract. 516 of them were retained for data extraction. The majority of studies were conducted in the Baltic Sea and the North Sea, followed by the Western Waters, and with only a few dozen papers in the Mediterranean Sea. Cod and herring were the most studied species, temperature and more generally climate and hydrodynamics indicators were the main drivers investigated, and reproduction was the main productivity-related process. The output of the systematic review is a database of scientific articles organised by regions, species, environmental drivers and productivity-associated processes and where outcomes, but also spatial and time scales, analytical methods etc. are described in a standardised fashion. This database will be analysed in the coming months and used in the downstream tasks of WP3. The most frequently driver identified by stakeholders across regions was climate change followed by species interactions, cod, pollution, commercial fish/shellfish and plankton. Climate change effects on stocks through temperature and salinity are relatively well covered in the literature as are effects of plankton and species interaction. Studies of the effects of pollution do not occur frequently and as a consequence require a dedicated effort is made in SEAwise to remedy this. Species reported frequently by the stakeholders included cod, seabass, sardine, sole, crabs, flatfish, Norway lobster, octopus, shrimps, herring, sprat, anchovy, hake, new species (species increasing in abundance

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, Irish Sea 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 considers 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 Irish Sea, and the “FLBEIA” (Bio-Economic Impact Assessment using FLR) methodology for the Bay of Biscay, Iberian Waters and North Sea. The Bay of Biscay mixed fisheries projections consider the single-species advice of 13 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, pol.27.89a, sdv.27.nea, sol.27.8ab, whb.27.1-91214, and whg.27.89a). Based on current fishing patterns and single-stock catch advice, the most limiting stock for Bay of Biscay demersal fisheries is horse mackerel (hom.27.2a4a5b6a7a-ce-k8), due to the zero-catch advice. The least limiting stock is whiting (whg.27.89a; 8 of 22 fleets). However, if horse mackerel was to be excluded as a restrictive stock due to the small contribution made by the demersal fleets to the total stock landings, the most limiting stock would be pollack (pol.27.89a ) whose quota is first reached for 8 of 22 defined fleets. The Celtic Sea mixed fisheries projections consider the single-species advice for 15 stocks (cod.27.7e-k, had.27.7b-k, whg.27.7b-ce-k, nep.fu.16, 17, 19, 20–21, 22, and outside FUs, sol.27.7e, sol.27.7fg, mon.27.78abd, ank.27.78abd, meg.27.7b-k8

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.

An ecosystem approach to fisheries management requires the consideration of spatially explicit management measures and other impacts on species and the links between the distribution of fished species, their surrounding environment and productivity. Quantification of the spatial aspects of fisheries and ecology of commercially fished stocks may improve the accuracy of the predicted changes in fish productivity, fisheries yield and costs, benefits and selectivity. To provide a knowledge base for spatially explicit considerations, SEAwise consulted stakeholders throughout Europe and conducted a systematic review of the scientific literature. As a first step, engagement with relevant stakeholder groups in each Case Study identified key issues of relevance to spatial management. The input from this stakeholder consultation was supplemented by a systematic literature review with careful consideration of the objectives, search terms, inclusion/exclusion criteria, the method for data/knowledge extraction and ultimately how these data and knowledge will be used. The purpose of the task was to quantify the key drivers and pressures behind the changes occurring in commercial fish stocks and fisheries distribution that have a spatially explicit content, map the relevant existing scientific knowledge and provide input to the subsequent SEAwise tasks. The words identified by the stakeholders consulted focused on factors causing changes to the distribution of commercial fish/shellfish (climate change, MPAs, species interactions, pollution, habitats and invasive species) and fisheries (windfarms, MPAs, Marine spatial planning) as well as the other human impacts. The systematic review extracted data from 331 papers. The most frequently studied topic was the distribution of fish and the region with most papers was the North Sea with about the twice the amount of papers in each of the other regions. The most frequently studied species in the literature were cod, hake and plaice and b

The Workshop on the production of annual estimates of abundance of sensitive species (WKABSENS) met to define sensitive species, collate ICES assessments of abundance where these are available, and estimate indices of their abundance per swept-area where not, for the OSPAR area. The analyses identified 140 potentially sensitive species or species complexes, among which 10 are diadromous and three are coastal, 20 have uncertain species ID and nine were identified as sensitive in only one of the sources examined. Among the sensitive species and species complexes, there was sufficient data to provide abundance indices for 50 species, of which 16 had existing stock assessments whereas the workshop derived abundance estimates for the remaining 34 species from survey data. Three statistical modelling approaches (binomial, General Additive Models (GAMs) and VAST) and were explored and the final abundance indices were calculated using GAMs. The species were divided into stocks before estimating abundance indices where these could be identified from the spatial distribution of the species in the survey. The group considered that a similar analysis using data from additional surveys, commercial indices or data from bycatch observers can potentially provide improved abundance estimates for species with variable or low catchability, such as deep-water and pelagic species.

Rajidae stocks (Raja clavata, Raja brachyura, Raja montagui, Raja microocellata, Leucoraja naevus and Raja undulata) in the English Channel and North Sea (ICES divisions 3a, 4 and 7d) are actually managed as a complex (“skates and rays”) and subject to a single TAC. TAC advices from the ICES are based on scientific survey indices trends from each species. Rajidae catches are mainly bycatch from flatfish fisheries such are sole (Solea solea) and plaice (Pleuronectes platessa) fisheries. Furthermore, because of their top predator position as well as their life history, Rajidae are species sensitive to overfishing. These different factors have led to a revision in stock assessment methods. ICES classified Rajidae as category 3 data limited stocks. The lack of available data does impact stock assessment model choice. As part of SUMARiS Interreg project a set of three data limited models have been tested: CMSY, SPicT and a state space bayesian production model. All of this model results support an increase in Rajidae stock biomass since the implementation of management measures in 2009. However, differences between stocks have been highlighted. The relative biomass of Thornback ray (Raja clavata), the prevailing species in the area, is up to three times more than other species biomass. This report presents the state of art in Rajidae stock data, as well as the different assessment models tested on 30 January 2020., Les stocks de Rajidae (Raja clavata, Raja brachyura, Raja montagui, Raja microocellata, Leucoraja naevus et Raja undulata) en Manche et Mer du Nord (divisions CIEM 3a, 4 et 7d) sont actuellement gérés en tant que complexe multispécifique (« raies ») sujet à un unique TAC. Les recommandations de TAC du CIEM s’appuient sur les tendances des indices d’abondance issus de campagnes scientifiques de chacune des espèces du complexe. Les captures de Rajidae sont principalement constituées de captures accessoires, liées à la pêche de poissons plats tels que la sole (Solea solea) et la plie (Pleuronectes platessa). De plus, du fait de leur position de prédateur supérieur et en raison de leur histoire de vie, les Rajidae constituent des espèces sensibles à la surpêche. Ces différents facteurs ont mené à la révision des méthodes d’évaluation de stock. Les Rajidae font partie des stocks à données limitées du CIEM de catégorie 3. La limitation des données disponibles impacte le choix des modèles d’évaluation de stocks. Dans le cadre du projet Interreg SUMARiS un set de trois modèles à données limitées a été testé : CMSY, SPicT et un modèle de production bayésien hiérarchique. L’ensemble des résultats de ces modèles supporte une augmentation de la biomasse des stocks de Rajidae depuis la mise en place de mesures de gestion en 2009. Cependant des disparités entre stocks ont été mises en évidence. La biomasse relative en 2018 de la raie bouclée (Raja clavata), espèce dominante de la zone, est jusqu’à trois fois plus importante que celle des autres espèces. Ce rapport présente l’état des lieux des données disponibles sur les stocks de Rajidae, ainsi que différent modèles d’évaluation testés au 30 janvier 2020.

The ICES Working Group on Mixed Fisheries Advice (WGMIXFISH-ADVICE) chaired by Claire Moore, Ireland, met at ICES headquarters in Copenhagen, Denmark, 28 October–1 November 2019 to produce mixed fisheries forecasts for the North Sea, Celtic Sea, and Iberian waters 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 for 2019 to provide quantitative forecast of over- and under-exploitation of the different stocks given mixed fishery interactions. Forecasts were based on the “FCube” (Fleet and Fishery Forecasts) methodology for the Celtic Sea and North Sea, and on the “FLBEIA” (Fisheries Library Bio-Economic Impact Assessment) methodology for the Iberian Waters—with a range of potential management scenarios relevant for the specific regional fisheries. The North Sea demersal mixed fisheries projections consider the single-species advice for cod (cod.27.47d20), haddock (had.27.46a20), whiting (whg.27.47d), saithe (pok.27.3a46), plaice (ple.27.420 and ple.27.7d), sole (sol.27.4), turbot (tur 27.4), and Norway lobster Nephrops norvegicus (functional units [FUs] 5–10, 32, 33, 34, and 4 outFU). The most limiting TAC in 2020 will be the TAC for cod for particular fleets (“cod-ns” scenario). The “min” scenario gives a 14% higher catch of cod compared to the “cod-ns” scenario, due to the relaxing of the constraint on a stock where the country is not assumed to be limited for that stock, but the model does not take into account quota reallocation between fleets. Substantial overshoot of TACs can occur under other scenarios (e.g. “max” scenario). This “range” scenario suggests that the potential for mixed fisheries mismatch would be lowered with a 2020 TAC in the lower p

We examine whether the landing rates of Belgian beam trawlers in the Southern Bight of the North Sea were affected through competitive interactions with the Dutch beam trawler fleet and whether the development of a pulse trawler fleet has altered competitive interactions between both fleets. Effects of competition were investigated through a natural experiment based on the different weekly exploitation patterns of both fleets. Logbook data were used to fit a generalized additive mixed model for the daily landing rates of the target species sole (Solea solea) and plaice (Pleuronectes platessa). Results showed that landing rates of sole by the Belgian beam trawlers (>221 kW) from 2006 to 2013 were lower during weekdays than during weekends when the Dutch trawler fleet is in harbour, while no such an effect was found for plaice. After the development of a pulse trawler fleet in 2011, the negative weekday effect in the sole landing rates was much more pronounced in 2012 and 2013. This increased loss of efficiency during weekdays, as a result of increased competition with the Dutch trawler fleet, coincided with a reallocation of fishing effort by the Belgian beam trawler fleet.