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Clupeid fish species are widely distributed and of highly variable stock sizes. In the North Sea, the common clupeid species are herring (Clupea harengus) and sprat (Sprattus sprattus), but during recent decades, the generally more southerly distributed sardine (Sardina pilchardus) have been more frequently observed. Comparative studies of early life stages of small pelagic clupeids are scarce, and their abilities to co-exist and relations to environmental characteristics are vastly understudied. We here investigated and compared distributional patterns of co-occurring larval sprat and sardine in the North Sea, hypothesizing that they are separated into spatial niches linked to specific hydrographical characteristics. Sampling was carried out by a large ring-net during standard fish surveys (IBTS Q3) in August 2018, 2019, and 2020. Sprat larvae were found widespread across the area of investigation, with the highest concentration in the central North Sea off the eastern and northern flanks of Dogger Bank, where abundances could reach 20 larvae/m2. Sardine larvae, on the other hand, showed their highest abundances in the Southern and German Bights. Distributions of the two species appeared complementary, and statistical correlations were indicative of separate hydrographical niches, where sardine larvae resided in relatively warmer and fresher water. The relative abundances of sardine versus sprat varied between years. Sardine larvae were especially abundant in 2020, twice as abundant as sprat, and observations indicate increasing importance of sardines in the North Sea.

I denne rapport beskrives, hvordan de historiske fiskeridata er tilvejebragt og efterfølgende analyseret. Formålet var at tilvejebringe data og undersøge muligheden for at benytte disse data til at forstå omfanget af den tilbagegang i fiskebestandene, som vi formoder har fundet sted i de indre danske farvande og fjorde hen over de forgangne 100 år. Da skrubben (Platichthys flesus) benyttes som indikatorart af bl.a. HELCOM, er der et særligt fokus på netop denne art, men data og analyser for en række andre arter såsom rødspætte (Pleuronectes platessa), torsk (Gadus morhua) og sild (Clupea harengus) (m.fl.) beskrives også. Der er arbejdet med tre typer af data (1) landinger og antal fartøjer per bruttotons-kategori per farvand (2) landinger af skrubbe og antal redskaber for fem fjorde, Sejerøbugten og Øresund, (3) videnskabelige fiskeundersøgelser i Limfjorden. Der benyttes fire forskellige tilgange til at kvantificere ændringer i fiskesamfundet: I) korrigerede landinger af skrubbe per redskab for fem danske fjorde, Sejerøbugten og Øresund, II) biomasseproduktionsmodeller (farvandsdata), III) korrigerede landinger per bruttotons-indsats (farvandsdata) og IV) trawl-undersøgelser i Limfjorden. Trawlundersøgelserne i Limfjorden anses for at inkludere færrest usikkerheder sammenlignet med de andre tre studier, da disse er udformet som en videnskabelig fiskeundersøgelse og giver derved det mest præcise billede af ændringer i fiskesamfundet siden 1926. Antallet af stationer, hvor der kan observeres torsk, skrubbe, rødspætte og ålekvabbe (Zoarces viviparus), er gået tilbage. Antallet af indikatorarten ålekvabbe er reduceret markant. Det er yderligere muligt at analysere de eksisterende data for en række underområder (og alder/størrelse) i Limfjorden, hvilket ikke er gjort i denne rapport. Desværre er der ikke indsamlet data efter 2012. Studiet over skrubbe per indsats, der sammenholder historiske distriktsdata med nøglefiskerdata

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

Er du fritidsfisker, og vil du være med til at dokumentere, hvordan det går med fiskebestandene i de kystnære områder? Så bliv nøglefisker!

Nøglefiskerprojektet (2020-2022), der er finansieret af fiskeplejen, er et samarbejde mellem Dansk Amatørfiskerforening (DAFF), Dansk Fritidsfiskerforbund (DFF) og DTU Aqua. Det en det syvende projekt i træk. Disse treårige projekter har eksisteret siden 2002 og er baseret på en stor og værdifuld frivillig indsats af fritidsfiskere. Formålet med disse projekter er at registrere fiskefangsterne og derigennem få dokumenteret fiskeforekomster langs de danske kyster over en årrække. Sammenlagt repræsenterer disse syv treårige projekter den største, længstvarende og mest sammenhængende indsats der dokumenterer og registrerer fangster i garn og ruser langs de danske kyster. Projekterne bidrager, som de eneste, med en tidsseriedata om de kystnære fiskeforekomster i Danmark, da ingen officiel overvågning finder sted i de danske kystzoner. At denne registrering hviler på frivillig arbejdskraft, er en kæmpe præstation og afspejler fritidsfiskernes interesse i at følge og bevare de naturlige fiskebestande i fjorde, bugter og langs de åbne kyster. Med nøglefiskerprojektet er der blevet skabt tidsseriedata, der dækker 17 år med garn og 20 år med ruser. Redskaberne, der anvendes, er ens for alle deltagerne, positionerne er fastsatte, fiskeriet forgår efter fælles retningslinjer, og der er tilstrækkelige gentagelser over året i de fleste områder. Dette gør datasættet helt unikt, da det tillader en rumlig og tidslig sammenligning samt muligheden for at følge udviklingen af de enkelte fiskearter over tid. I og med at nøglefiskerprojektet er baseret på frivilligt arbejde fra engagerede fritidsfiskere, er det også muligt at indsamle ’prøver’ af det kystnære fiskesamfund, når der nøglefiskes. Det betyder, at der kan indsamles prøver op til tre gange om måneden adskillige steder (50-61 positioner) i indre danske farvande, langs kysterne eller inde i fjordene med garn og/eller ruser. Denne rapport præsenterer resultater for perioden 2020-2022 og sammenligner me

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

En studerende har undersøgt dyrelivet i et nyt ålegræsområde, som 'kysthjælperne' står bag. Resultaterne tyder på, at ålegræsset lokker fisk til, og at især de helt små torsk er glade for 'kysthjælpernes' indsats.

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 correct prediction of the shape and strength of density dependence in productivity is key to predicting future stock development and providing the best possible long-term fisheries management advice. Here, we identify unbiased estimators of the relationship between somatic growth, recruitment and density, and apply these to 80 stocks in the Northeast Atlantic. The analyses revealed density-dependent recruitment in 68% of the stocks. Excluding pelagic stocks exhibiting significant trends in spawning stock biomass, the probability of significant density dependence was even higher at 78%. The relationships demonstrated that at the commonly used biomass limit of 0.2 times maximum spawning stock size, only 32% of the stocks attained three quarters of their maximum recruitment. This leaves 68% of the stocks with less than three quarters of their maximum recruitment at this biomass limit. Significantly lower recruitment at high stock size than at intermediate stock size was seen in 38% of the stocks. Density dependence in late growth occurred in 54% of the stocks, whereas early growth was generally density-independent. Pelagic stocks were less likely to exhibit density dependence in recruitment than demersal and benthic stocks. We recommend that both the degree to which productivity is related to density and the degree to which the relationship changes over time should be investigated. Both of these aspects should be considered in evaluations of whether sustainability and yield can be improved by including density dependence in forecasts of the effects of different management actions.

In ecological sciences, animal diets are often simplified to “resources” or “caloric quantities”. However, in the present study, we investigated the optimal foraging strategy of Atlantic cod (Gadus morhua) when both macro- and micro-nutritional requirements are accounted for. Proteins cannot be synthesized from fatty acids, so the proteins for gonad development must come from other dietary sources. In addition, micronutrients are required in smaller quantities. For example, for cod, arachidonic acid (ARA) acts as a micronutrient precursor for prostaglandins, which is important for reproduction. We formulated a dynamic state-dependent model to make predictions about optimal diet choice and foraging behavior. We applied the model to a case study in the strait between Denmark and Sweden. The model predicted that energy acquired from dietary protein should be twice that acquired from lipids, with a small increase in the lipid requirements when gonads are growing. The model also predicted that the “energy sparing effect of lipids” made it beneficial to engage in risky foraging activity to supplement a lean diet with a little bit of fat. When we constructed the model to also optimize ARA uptake, the cod consumed relatively more ARA-rich crabs in the months prior to spawning, despite the otherwise poor energetic value of this prey. In support of the model predictions, field observations indicated that lipid stores reached a peak shortly after the arrival of the lipid-rich migrating herring and the fatty acid signal of these herring were evident in the liver of nearly all cod. Three month later, only half of the cod contained the herring-derived fatty acid signal, supporting the predicted shift in prey type prior to spawning. From these model predictions and field observations, we conclude that, also in the wild, nutritional requirements can be at least as important as pure energy acquisition.

The ecosystem approach to fisheries management is a key element in the Common Fisheries Policy (CFP). In light of the importance of the North Sea to the Danish fisheries, Denmark needs to take a leading role in the development of best practice and methods for the implementation of the ecosystem approach to fisheries management. The ECOMAN project consisted of five separate work packages. WP1: Sampling designs should ensure the provision of accurate data on biological parameters and stock information to be used as input to single-species assessments and multi-species models. Via this project, we were able to engage in discussions and thereby influence the development of data collection approaches. WP2: The productivity of fish stocks in the North Sea has undergone substantial changes in recent decades, with some species increasing in numbers, while other species have shown prolonged recruitment failure with a resulting decline in stock size. Here we investigated multiple aspects of stock productivity in order to identify important drivers, such as density dependent regulation and spawner quality; all of which are ecological processes not accounted for conventional stock-by-stock fisheries management. Also methods for estimating biomass reference points were scrutinized and changes over time in the environmental conditions were visited. The latter results provided a basis for improving how reference points are defined and which processes needs further attention (i.e. in management strategy evaluations). WP3: Natural mortality is a key component of estimation of historical stock development and the setting of reference points such as Bescapement, MSY Btrigger, FMSY and Fcap. The natural mortality varies considerably over time, and particularly the mortality introduced by grey seal and mackerel has increased for North Sea fish stocks in the most recent decades. The present project was used to built an application that allow scientists and stak

Forbedring af sildebestandsvurdering og -fremskrivning, der udnytter forbedret fiskeridata og biologisk information Projektet havde til formål at udvikle en multiflåde SAM-model, et nyt bestandsspecifikt surveyindeks og en international fangstdatabase med genetisk information til forbedret bestandsvurdering, dataudnyttelse og fremskrivning under komplekse forvaltningsscenarier for sildebestande, der samtidig fanges i flere fiskerier. I forbindelse med benchmark for sild (WKPELA) i 2018 bidrog projektet til udviklingen af en databaseudvikling for internationale fangster med høj geografisk opløsning samt et nyt integreret surveyindeks baseret på de internationale bundtrawlundersøgelser i Kattegat- Skagerrak og den vestlige Østersø (IBTS-BITS). Til bestandsvurdering blev der udviklet en multiflåde version af SAM som blev finjusteret til de fire flåder, der fisker den vestlige Østersø-sild (WBSS). Multiflåde SAM blev implementeret for både efterårsgydende Nordsø-sild (NSAS) og WBSS under benchmark i 2018 (Nielsen et al. 2021). Ny bestandsidentifikationsteknologi blev udviklet ved hjælp af specifikt udvalgte genetiske SNPmarkører koblet til fiske-metrik og otolit-morfologi til effektiv opdeling af prøver i bestande på enkeltfisk-niveau. Metoden blev præsenteret og drøftet på den internationale workshop om bestands klassifikationsmetoder, WKSIDAC (ICES 2018). Bilaterale dansk-svenske kalibreringsøvelser på otolit-mikrostrukturbaseret bestandsidentifikation viste forbedret reproducerbarhed i senere år, men stigende bias i forhold til sand genetisk oprindelse. Genetiske analyser af prøver fra HERAS internationale akustiske sommertogt viste kystnære vandringsmønstre langt nord i Nordsøen, bekræftet af metriske analyser af sild i norsk del af HERAS. Multiflåde-SAM blev senere brugt som operativ model under evalueringen af forvaltningsstrategien for Nordsø-sild (NSAS) i WKNSMSE (ICES 2019). En yderligere udvikling af multiflådeSAM til WBSS blev brugt til at

The aim of the project was to address challenges in relation to sustainable exploitation and the scientific foundation for the catch advice of important industrial species, such as sandeel, sprat and herring (the latter also being an important consumer species). We project contained studies about (1) otolith-based method for separating sandeel species, (2) habitat preference of sandeel, (3) the possibilities for establishing an alternative sprat recruitment index for use in advice, (4) essential spawning and nursery grounds for sandeels in the North Sea, and (5) operational methods for separating herring stocks based on genetics. The project consisted of four scientific work packages (WPs). A summary of the results of each scientific work package (WP 1-4) and links to technical documents are provided below. The studies are directly contributing to ICES working groups and thereby supporting the preservation of sustainable fisheries. Besides the scientific WPs, a fifth WP was about dialogue meetings with the fishing industry to prepare for upcoming benchmarks.

Makrelbestanden i Nordatlanten har gennem de seneste år ændret sig dramatisk, både med hensyn til bestandskomponenterne, bestandsstørrelsen og ikke mindst makrellens udbredelse. Da makrellen desuden er en bestand med et ganske stort udbredelsesområde og med meget stor international interesse, er det vigtigt, at Danmark styrker kapaciteten og vidensgrundlaget indenfor denne bestand for at kunne yde indflydelse på de forvaltningsmæssige beslutninger. I 2020 blev der landet lidt over 1 mio. tons makrel i alt, og af dette var de danske landinger på lidt over 35.500 tons. Projektets formål har været at forbedre bestandsvurderingen og forvaltningen af makrel med fokus på makrellens Nordsøkomponent, hvor der især er en mangelfuld viden omkring udbredelse og biologi. Dette er blevet gjort ved at opbygge viden og gennemføre fire danske trawltogter (2018, 2019, 2020 og 2021) målrettet makrel i Nordsøen, som skal kombineres med de i forvejen gennemførte trawltogter fra det nordlige Atlanterhav. Resultaterne fra de danske trawltogter er blevet præsenteret hvert år til WGIPS og WGWIDE, som er de ICES-arbejdsgrupper, der har ansvar for hhv. makreltogterne og bestandsvurderingen af makrel. Som en del af projektet er der gennemført forsøg med at udvikle en multibeamsonar, der kan registrere de makrel, der søger under det pelagiske trawl under trækket. Projektet har også forsøgt at forbedre de kommercielle biologiske indsamlinger ved at udvælge den del af flåden, der går målrettet efter de pelagiske bestande, for at få en målrettet indsamling på de danske fartøjer, der står for hovedparten af landingerne. Dette er især vigtigt, fordi en meget stor andel af det danske makrelfiskeri landes i udlandet. Som et supplement til de prøver, som fiskerne selv skal indsamle, har vi gennem NordMak-projektet fået et samarbejde op at køre med Skawinspection, som har givet mulighed for at benytte alternative data, som indsamles regelmæssigt af industrien. Her har vi un

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

This study examines the impact of boldness on foraging competition of the highly invasive round goby Neogobius melanostomus Pallas 1815. Individual risk tolerance, or boldness, was measured as the time to resume movement after a simulated predation strike. Fish that resumed movement faster were categorized as "bold," fish that took more time to resume movement were categorized as "shy" and those that fell in between these two categories were determined to have "intermediate" boldness. Competitive impacts of boldness in N. melanostomus were determined in a laboratory foraging experiment in which interspecific (juvenile Atlantic cod Gadus morhua Linnaeus 1758) and intraspecific (intermediate N. melanostomus) individuals were exposed to either bold or shy N. melanostomus competitors. G. morhua consumed fewer prey when competing with bold N. melanostomus than when competing with shy N. melanostomus, whereas intermediately bold N. melanostomus foraging was not affected by competitor boldness. Bold and shy N. melanostomus consumed similar amounts of prey, and the number of interactions between paired fish did not vary depending on the personality of N. melanostomus individuals. Therefore, intraspecific foraging competition was not found to be personality dependent. This study provides evidence that individual differences in boldness can mediate competitive interactions in N. melanostomus; nonetheless, results also show that competition is also governed by other mechanisms that require further study.

Invasive species exert negative impacts on biodiversity and ecosystems on a global scale, which may be enhanced in the future by climate change. Knowledge of how invasive species respond physiologically and behaviorally to novel and changing environments can improve our understanding of which traits enable the ecological success of these species, and potentially facilitate mitigation efforts. We examined the effects of acclimation to temperatures ranging from 5 to 28°C on aerobic metabolic rates, upper temperature tolerance (critical thermal maximum, CTmax), as well as temperature preference (Tpref) and avoidance (Tavoid) of round goby (Neogobius melanostomus), one of the most impactful invasive species in the world. We show that round goby maintained a high aerobic scope from 15 to 28°C; that is, the capacity to increase its aerobic metabolic rate above that of its maintenance metabolism remained high across a broad thermal range. Although CTmax increased relatively little with acclimation temperature compared to other species, Tpref and Tavoid were not affected by acclimation temperature at all, meaning that round goby maintained a large thermal safety margin (CTmax − Tavoid) across acclimation temperatures, indicating a high level of thermal resilience in the species. The unperturbed physiological performance and high thermal resilience was likely facilitated by high levels of phenotypic buffering, which can make species readily adaptable and ecologically competitive in novel and changing environments. We suggest that these physiological and behavioral traits could be common for invasive species, which would only increase their success under continued climate change.

The round goby (Neogobius melanostomus) was first observed in the Baltic Sea in 1990 and has since displayed substantial secondary dispersal, establishing numerous dense populations where they may out compete native fish and negatively impact prey species. There have been multiple round goby diet studies from both the Baltic Sea and the North American Great Lakes where they are similarly invasive. However, studies that quantify their effects on recipient ecosystems and, specifically, their impacts on the benthic invertebrate macrofauna are rare, particularly from European waters. In this study, we conducted the first before-after study of the potential effects of round goby on benthic invertebrate macrofauna taxa in marine-brackish habitats in Europe, focusing of two sites in the Western Baltic Sea, Denmark. Results were in line with those from the Great Lakes, indicating negative impacts on specific molluscan taxa (e.g. Cardiidae bivalves and Neritidae gastropods, which both showed a fall in detected densities of approximately 98% within the Guldborgsund Strait). In contrast, many other groups appeared to be largely unaffected or even show positive trends following invasion. Round goby gut content data were available at one of our study sites from the period immediately after the invasion. These data confirmed that round goby had in fact been preying on the subset of taxa displaying negative trends.

The round goby (Neogobius melanostomus) was first observed in the Baltic Sea in 1990 and has since displayed substantial secondary dispersal, establishing numerous dense populations where they may outcompete native fish and negatively impact prey species. There have been multiple round goby diet studies from both the Baltic Sea and the North American Great Lakes where they are similarly invasive. However, studies that quantify their effects on recipient ecosystems and, specifically, their impacts on the benthic invertebrate macrofauna are rare, particularly from European waters. In this study, we conducted the first before-after study of the potential effects of round goby on benthic invertebrate macrofauna taxa in marine-brackish habitats in Europe, focusing of two sites in the Western Baltic Sea, Denmark. Results were in line with those from the Great Lakes, indicating negative impacts on specific molluscan taxa (e.g. Cardiidae bivalves and Neritidae gastropods, which both showed a fall in detected densities of approximately 98% within the Guldborgsund Strait). In contrast, many other groups appeared to be largely unaffected or even show positive trends following invasion. Round goby gut content data were available at one of our study sites from the period immediately after the invasion. These data confirmed that round goby had in fact been preying on the subset of taxa displaying negative trends.

Projektets formål var at understøtte et bæredygtigt brislingefiskeri i Nordsøen, Skagerrak og Kattegat og sikre at den fælles fiskeripolitik efterleves. Brislingfiskeriet er et fiskeri af stor betydning for danske fiskere og dansk forarbejdningsindustri. Projektet har fokuseret på følgende elementer i den nye Fiskerireform: 1) Bæredygtighed i dybden, 2) Maksimalt Bæredygtigt Udbytte (MSY), 3) Viden om Fiskeri, samt 4) Flerårige Planer. Projektet forløb planmæssigt, hvilket vil sige at samtlige arbejdspakker og i alt fem dialogmøder med repræsentanter for erhvervet er blevet gennemført. Resultaterne har bidraget direkte til en rækker møder og processer i ICES; herunder brisling benchmark WKSPRAT 2018 og evaluering af forvaltningsstrategien WKspratMSE 2019. Projektet har udviklet nye metoder og indhentet ny viden på en række konkrete områder om opnået følgende: (1) en bedre forståelse af bestandstilhørsforholdet for brisling som fanges i Skagerrak/Kattegat, samt et detaljeret arbejde med selve bestandsmodellen, (2) viden om vejrets påvirkning af fangstrater, (3) metode til forudsigelse af vækst og forslag hvordan dette fremadrettet potentielt vil kunne anvendes i udarbejdningen rådgivning, (4) systematiske larveindsamlinger på IBTS Q3 og belysning af muligheden for at udvikle et nyt rekrutteringsindeks (resulterede også i utilsigtet ny viden om udbredelsen af sardin-larver i Nordsøen), og (5) grundig evaluering af den såkaldte Fcap forvaltningsstrategi og det retrospektive mønster i bestandsmodellen. I rapporten her findes en beskrivelse af aktiviteterne og resultaterne i projektets fire arbejdspakker samt en liste over præsentationer og dialogmøder. Der henvises undervejs til vedhæftede tekniske arbejdsdokumenter m.m.

Biomass limit reference points are widely used in fisheries management and defines the biomass threshold below which stock productivity (i.e. recruitment) is likely to be impaired. Scientifically sound and transparent methods for estimating biomass thresholds are therefore needed together with ways of quantifying uncertainties. The main focus of the study was placed on two methods currently applied to several small-bodied pelagic species in the Northeast Atlantic. These methods have not formerly been described in the scientific literature and are in the present study being compared to some already described methods, of which, one is broadly applied outside the Northeast Atlantic. Using a combination of data simulations and data from 51 small-bodied pelagic fish stocks, we analyzed the sensitivity of estimated biomass thresholds to (i) the choice of method, (ii) time-series length, and (iii) stock development (e.g. rebuilding or declining). It was demonstrated that estimated biomass thresholds are associated with considerable uncertainty not previously quantified. Furthermore, the level of the estimated threshold and the amount of uncertainty depended on choice of method, time-series length, and stock development trends. Hence, this study contributes to improving the quality of future biomass limit reference points by providing guidance regarding choice of method and how to demonstrate stock-specific uncertainties.