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This report investigates how key environmental variables influence the recruitment process of target fish stocks. Understanding how the environment affects recruitment may allow more accurate predictions of fish stock dynamics under scenarios of environmental change and in particular their response to global warming, supporting the development and implementation of robust management policies. Case studies from the four Seawise case study regions have been analysed, and the main results obtained so far are summarized below. In the Baltic Sea, the Gulf of Riga spring spawning herring showed effects of spawning stock biomass on individual weight of age-1 fish, with prey abundance in May and previous year feeding period temperature also playing significant roles. The explanatory power of the final model was moderate. Higher weight of herring is achieved at higher prey densities, lower SSB levels and lower temperatures during the main feeding season of age-0 fish. Recruitment of Western Baltic cod and herring showed decreasing reproductive potential at increasing temperature. In the North Sea, the effects of temperature, salinity, currents, chlorophyll and zooplankton on recruitment of cod, haddock, saithe, whiting, plaice, sole, sprat and herring were investigated using a semi-automated, machine learning framework. The incorporation of environmental signals in recruitment predictions showed improved predictions over a stock recruitment model without environmental effects in six out of the eight stocks. For small pelagic foirage fish, four stock-recruitment models were fitted for three sandeel stocks and the North Sea sprat stock Linear regressions revealed various relationships between recruitment and environmental variables. Short-term time scales based on monthly averages produced a noisier and less consistent pattern for most stock. In the Western Waters, Bayesian online change point detection models were applied to thr

The reform of the European Union (EU)'s Common Fisheries Policy (CFP) in 2013 has led to significant changes in fisheries management, including an obligation to land all catches from regulated stocks, i.e. a ban on throwing unwanted catch back into the sea. The goal of the landing obligation is to promote more selective and targeted fishing that reduces unwanted bycatch. It is possible to put fish back into the sea instead of landing them if it can be scientifically proven that there is a high survival rate in a specific fishery. However, the criterion for what counts as "high" is not set and is evaluated for each individual case by the EU. This report presents the work of DTU Aqua on discard survival of undersized European plaice (Pleuronectes platessa, below 27 cm in the North Sea and Skagerrak, below 25 cm in the Baltic) caught using towed gears in commercial demersal fisheries for human consumption. This work has focused on: • estimate survival rates with the aim of obtaining exemptions from the landing obligation, • improve our understanding of how operational, environmental, and biological stressors affect discard survival rates, • explore the opportunity to create robust discard survival estimates from meta-analysis; iv) investigate the effect of the environment (temperature) on reflex impairment, • develop and test the performance of an optimized reflex and injury index, • use expert knowledge (Bayesian modelling) to predict discard survival. We estimated survival rates as scientific documentation for seeking exemptions from the landing obligation in the EU CFP for three fleets: the Danish seine and bottom otter trawl fleets1 operating in Skagerrak, Kattegat, and the North Sea (ICES subdivision 3a and 4), and bottom otter trawls operating in the Baltic Sea (ICES subdivisions 22-25). Survival estimates considered the characteristics of the gear (gear types and designs), fishing practices (target species, seasonalit

Direct engagement of the fishing industry in the provision and co-creation of knowledge and data for research and management is increasingly prevalent. In both the North Atlantic and North Pacific, enhanced and targeted engagement is evident. More is needed. Science-Industry collaborative approaches to developing questions, collecting data, interpreting data, and sharing knowledge create opportunities for information transfer and improved understanding of ecosystem interactions, stock dynamics, economic incentives, and response to management. These collaborations require clear communication and awareness of objectives and outcomes. These initiatives also require careful attention to conditions and interactions that foster respect, trust, and communication. Respect is critical and entails acknowledging the respective skills and expertise of both scientists and fishers. Trust is needed to build confidence in the information developed and its use. Communication is essential to maintain relationships and leverage shared insights. To assess current trends and future opportunities related to this type of engagement, we convened a networking session of research scientists, industry scientists, industry leaders, and fishers at the Annual Science Meeting of the International Council for the Exploration of the Sea (ICES) to address the following questions: (1) What are scientific needs that could be addressed with industry-collected data or knowledge? And (2) How can science-industry collaboration be made sustainable? Here we identify opportunities and acknowledge challenges, outline necessary conditions for respectful and sustainable collaborative research, and highlight ways to promote stakeholder involvement in developing science. We address industry concerns and solicit industry advice. We also address challenges to scientists in ensuring standards for scientific data, conflict of interest, and applying information to advise management. The discussions in this session and

The present report describes results of the project ”Future perspectives for cod in the Eastern Baltic Sea–stock development, fisheries and management challenges in a changing ecosystem (FREMTOR)”, funded by European Maritime and Fisheries Fund and the Danish Fisheries Agency. The project provides new knowledge on some key aspects of the status of the stock and associated drivers, as well as synthesizes existing information, altogether providing state-of-the art basis for evaluating future perspectives for this stock. Improved understanding of the factors responsible for the low productivity of the stock is crucially important for being able to assess its recovery potential. Furthermore, realistic targets for stock recovery in the current state of the ecosystem need to take account of changes in biological parameters, including growth and recruitment as well as other indicators of stock health, such as body condition and parasite load. In this project, time series of various biological parameters of the Eastern Baltic cod (incl. condition, size at maturity, parasite load, length structure) were extended back to the 1940s, i.e. the beginning of intensive exploitation of this stock. These data show that the cod stock is presently in unprecedented poor state. Cod body condition and infection load of C. osculatum were in similar adverse states in the 1940s–1950s, however, the relatively more favorable states of other biological parameters back then indicate that the stock was overall in a better shape than is presently the case. The long–term data reveal concurrent trends in seal abundance and C. osculatum infection, the latter being inversely related to cod body condition, which provides correlation based evidence regarding potential associations between these variables. Spatial contrasts in the present state of cod are apparent in cod from the Åland Sea being in a substantially better condition and larger in size compared to the average specimen

Changes in physiological processes can reveal how individuals respond to environmental stressors. It can be difficult to link physiological responses to changes in vital rates such as growth, reproduction and survival. Here, bioenergetics modelling can aid in understanding non-intuitive outcomes from stressor combinations. Building on an established bioenergetics model, we examine the potential effects of parasite infection on growth rate and body condition. Parasites represent an overlooked biotic factor, despite their known effects on the physiology of the host organism. As a case study, we use the host–parasite system of Eastern Baltic cod (Gadus morhua) infected with the parasitic nematode Contraceacum osculatum. Eastern Baltic cod have during the past decade experienced increasing infection loads with C. osculatum that have been shown to lead to physiological changes. We hypothesized that infection with parasites affects cod growth negatively as previous studies reveal that the infections lead to reduced energy turnover, severe liver disease and reduced nutritional condition. To test this, we implemented new variables into the bioenergetics model representing the physiological changes in infected fish and parameterized these based on previous experimental data. We found that growth rate and body condition decreased with increased infection load. Highly infected cod reach a point of no return where their energy intake cannot maintain a surplus energy balance, which may eventually lead to induced mortality. In conclusion, parasite infections cannot be ignored when assessing drivers of fish stock dynamics.

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.

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

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 Baltic fisheries are in distress. In the Central Baltic, fisheries management is challenged by reduced cod stock productivity, and altered species interactions. Here, we use an age-structured, ecological–economic multispecies model, which includes latest biological and economic knowledge, to advance our understanding of optimal fisheries management and related trade-offs between user groups under such altered conditions. We contribute to the scientific discussion (i) by showing that the economic importance and optimal stock size of cod largely decreased under prevailing conditions, while clupeids increased in importance. (ii) We challenge the current MSY management objective in a multispecies setting (MMSY) and suggest that an economic multispecies management objective (MMEY) might be more useful for setting future management targets. (iii) We identify new trade-offs and synergies by including a consumer perspective: There is a win–win situation for ecological conservation, and profits in the fishery, while fishery management faces trade-offs between these two on the one hand, and consumer surplus on the other hand. (iv) Finally, we suggest an easy to implement new management approach, called robust management, which is capable of better dealing with variability and time-trends in recruitment, as observed for cod, in order to safeguard the Central Baltic fishery resources.

Improving the health of coastal and open sea marine ecosystems represents a substantial challenge for sustainable marine resource management, since it requires balancing human benefits and impacts on the ocean. This challenge is often exacerbated by incomplete knowledge and lack of tools that measure ocean and coastal ecosystem health in a way that allows consistent monitoring of progress towards predefined management targets. The lack of such tools often limits capabilities to enact and enforce effective governance. We introduce the Baltic Health Index (BHI) as a transparent, collaborative and repeatable assessment tool. The Index complements existing, more ecological-oriented, approaches by including a human dimension on the status of the Baltic Sea, an ecosystem impacted by multiple anthropogenic pressures and governed by a multitude of comprehensive national and international policies. Using a large amount of social-ecological data available, we assessed the health of the Baltic Sea for nine goals that represent the status towards set targets, for example, clean waters, biodiversity, food provision, natural products extraction and tourism. Our results indicate that the overall health of the Baltic Sea is suboptimal (a score of 76 out of 100), and a substantial effort is required to reach the management objectives and associated targets. Subregionally, the lowest BHI scores were measured for carbon storage, contaminants and lasting special places (i.e. marine protected areas), albeit with large spatial variation. Overall, the likely future status of all goals in the BHI averaged for the entire Baltic Sea is better than the present status, indicating a positive trend towards a healthier Baltic Sea. However, in some Baltic Sea basins, the trend for specific goals was decreasing, highlighting locations and issues that should be the focus of management priorities. The BHI outcomes can be used to identify both pan-Baltic and subregional scale management priorities and

The Baltic Sea is a heavily impacted ecosystem with multiple pressures acting simultaneously. In order to quantify ecosystem impacts of integrated climate change and eutrophication pressures under constant high fishing pressure, and to support decision-making and policies in generating environmental and economic sustainable systems, the Baltic Atlantis holistic and mechanistic ecosystem model was applied. The overall aim was to run scenarios of separate and integrated impacts of climate and riverine nutrient load changes, taking into account the interactions of the full food web in the entire Baltic Sea. This was done to identify which of those two pressures will likely dominate the future of the Baltic Sea ecosystem, and to test effects of different riverine nutrient forcing sources as well as the Baltic Atlantis functions in relation to hydrographic spawning thresholds. By integrating the hydrography, the biology covering all trophic levels of the food web, and multiple pressures, i.e. eutrophication, climate change and fishery, we were able to evaluate relative impacts of 3 climate scenarios and 3 nutrient load scenarios, using two sources of nutrient forcing and predict likely trends in ecosystem effects. With focus on major fish stocks, our model, with its assumptions, indicated that nutrient loads are the main driver of the changes in the ecosystem as long as the hydrographic thresholds for spawning are not reached. If the thresholds are reached for the Baltic cod, climate change impact will become most important. Furthermore, higher nutrient loads resulted in cod decrease, and increase in sprat and herring. This effect is amplified by stronger climate change. Overall, it is of crucial importance for the future of the Baltic Sea fisheries and stocks that potential impacts are considered both separate and integrated in a dynamic ecosystem-based management approach.

Forecasting variation in the recruitment to fish stocks is one of the most challenging and long-running problems in fisheries science and essentially remains unsolved today. Traditionally, recruitment forecasts are developed and evaluated based on explanatory and goodness-of-fit approaches that do not reflect their ability to predict beyond the data on which they were developed. Here, we propose a new generic framework that allows the skill and value of recruitment forecasts to be assessed in a manner that is relevant to their potential use in an operational setting. We assess forecast skill based on predictive power using a retrospective forecasting approach inspired by meteorology, and emphasize the importance of assessing these forecasts relative to a baseline. We quantify the value of these forecasts using an economic cost-loss decision model that is directly relevant to many forecast users. We demonstrate this framework using four stocks of lesser sandeel (Ammodytes marinus) in the North Sea, showing for the first time in an operationally realistic setting that skilful and valuable forecasts are feasible in two of these areas. This result shows the ability to produce valuable short-term recruitment forecasts, and highlights the need to revisit our approach to and understanding of recruitment forecasting.

Marine predatory fish face unpredictable prey environments, ranging from abundance to scarcity of food. Dimensioning their assimilative system to accommodate gorging and fasting is therefore a central life history choice. Assimilative capacity experiments typically operate with sustained feeding to satiation, and therefore ignore the fluctuations in natural feeding opportunities. A more relevant description of the adaptive response is the episodic capacity associated with binge feeding (hyperphagia). We develop the theoretical foundation to define episodic and sustained capacity and its allometry. Extensive empirical evidence on marine piscivorous fish at higher latitudes confirms that the episodic capacity scales almost linearly with predator body mass (exponent approximately 0.95), producing an increasing factorial hyperphagic scope (exponent approximately 0.20). Our synthesis overturns the reigning steady state perspective on assimilative capacity. The fish can utilize an episodic capacity, typically twice the size of the sustained capacity, resulting in local dynamics of functional responses with profound implications for scaling-up to ecosystem level.

1. Improving the health of coastal and open sea marine ecosystems represents a substantial challenge for sustainable marine resource management, since it requires balancing human benefits and impacts on the ocean. This challenge is often exacerbated by incomplete knowledge and lack of tools that measure ocean and coastal ecosystem health in a way that allows consistent monitoring of progress towards predefined management targets. The lack of such tools often limits capabilities to enact and enforce effective governance. 2. We introduce the Baltic Health Index (BHI) as a transparent, collaborative, and repeatable assessment tool. The Index complements existing, more ecological-oriented, approaches by including a human dimension on the status of the Baltic Sea, an ecosystem impacted by multiple anthropogenic pressures and governed by a multitude of comprehensive national and international policies. Using a large amount of social-ecological data available, we assessed the health of the Baltic Sea for nine goals that represent the status towards set targets, e.g. clean waters, biodiversity, food provision, natural products extraction, and tourism. 3. Our results indicate that the overall health of the Baltic Sea is suboptimal (a score of 76 out of 100), and a substantial effort is required to reach the management objectives and associated targets. Subregionally, the lowest BHI scores were measured for carbon storage, contaminants and lasting special places (i.e., marine protected areas), albeit with large spatial variation. 4. Overall, the likely future status of all goals in the BHI averaged for the entire Baltic Sea is better than the present status, indicating a positive trend towards a healthier Baltic Sea. However, in some Baltic Sea basins, the trend for specific goals was decreasing, highlighting locations and issues that should be the focus of management priorities. 5. The BHI outcomes can be used to identify both pan-Baltic and subregional scale

Five decades of stomach content data allowed insight into the development of consumption, diet composition, and resulting somatic growth of Gadus morhua (Atlantic cod) in the eastern Baltic Sea. We show a recent reversal in feeding level over body length. Present feeding levels of small cod indicate severe growth limitation and increased starvation-related mortality. For young cod, the low growth rate and the high mortality rate are manifested through a reduction in size-at-age. The low feeding levels are likely the result of a decrease in benthic prey abundance due to increased hypoxic areas, while decreasing abundances of pelagic species in the area of cod distribution have prevented a compensatory shift in diet. Our study emphasizes that environmental forcing and the decline in pelagic prey caused changes in consumption and growth rates of small cod. The food reduction is amplified by stunted growth leading to high densities of cod of smaller size competing for the scarce resources. The average growth rate is negative, and only individuals with feeding levels well above average will survive, though growing slowly. These results suggest that the relation between consumption rate, somatic growth and predatorprey population densities is strongly environmentally mediated.

Direct and indirect biological interactions and trophic cascades suppressing a trophic level in the food web can control entire marine ecosystems. It can, however, be misleading for our understanding and for ecosystem-based management to only investigate the influence of biological interactions and trophic cascades in terms of the biomasses on annual basis, and by comparison of separate species specific data time series in simple food chains. We applied an end-to-end marine ecosystem model including both intra-specific and inter-specific competition and density-dependent regulations to investigate certain trophic interaction dynamics of a disturbed ecosystem. Here all trophic levels of the full Baltic Sea food web were integrated in a holistic mechanistic approach. The model was able to capture the functional responses in interactions of the groups and levels and trophic cascades. Its main results emphasize the importance of integrating the whole food web and the implications of only considering the change in biomass on annual basis, instead of also including the individual condition and the abundance (number of individuals). This should not be neglected as density-dependent interactions will shape the state of the entire ecosystem. We conclude that, in order to better understand ecosystem interactions and trophic cascade state and control mechanisms, a holistic approach is needed integrating multiple processes and seasons and which includes the complexity of all the intra- and inter-specific interactions of the full food web.

In the originally published version of this article there was an error in figure 5. This has now been corrected. (Figure Presented)