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

On 22 December 2019, the world of fisheries science and whale conservation lost one of its most ardent champions with the passing of Sidney J. Holt. His career began in 1947 at the age of 21. Ten years later, he and his colleague Ray Beverton published their authoritative monograph on quantitative fish population dynamics. In 1953, he joined the Fisheries Division of the United Nations Food and Agriculture Organization and soon became heavily involved in assessing whale stocks under the auspices of the International Whaling Commission, a role that eventually led to advocating for animal rights and the cessation of commercial whaling. Later in life, he returned to fisheries assessment and management, particularly issues pertaining to the Common Fisheries Policy of the European Union, where he advocated for fishing mortality less than that associated with maximum sustainable yield. This themed set consists of articles written by authors who knew and collaborated with Sidney, who may have met him once or twice at an international meeting, and who only knew of him via his reputation and massive and influential list of publications. Their articles address a wide range of topics relating to his work throughout his career and reflect, in part, the influence that his work has had on thinking about quantitative modelling of animal populations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Highlights • A Jacobian Matrix of all long-term yields on all current fishing mortality rates are shown for each available model. • These enable the principle interactions within and between species in each area to be compared. • These also allow the construction of a simple multispecies index for each species in each model in each area. • These also are used to construct diagnostic tools to detect "weird" aspects of the models. • These also compare the change in each model's fishing mortalities that will move the overall yield towards a maximum. Abstract Like other fisheries models, multispecies models are subject to various sources of error. However, with regard to their use for ecosystem-based fisheries management (EBFM) between model errors are likely to be most important. As multispecies models are by definition many-dimensional, comparing them is potentially a complex task. The paper uses a simple approach. This is to calculate the Jacobian matrix of long term steady state catch by species with respect to the fishing mortality relative to status quo levels on all species. This enables the comparison of the relative strength of species interactions among models both within and between regions. This Jacobian matrix approach to comparing multispecies models is applied to available models for the North Sea, the Baltic Sea and from Icelandic waters. Moreover, this information is used to provide the basis for estimating a multidimensional quadratic yield surface for each model in the near field. Used this way it is possible to compare different model estimations of fishing mortality rate changes needed to approach yield-related management goals. The results suggest considerable variation between models in their detailed results but more coherence in suggesting directions for changing fishing mortality rate. Thus the approach is of considerable importance in specifying the confidence with which it is possible to make multispecies predictions for EBFM. [ABSTRACT FROM AUTHOR]

Larger and older fish contribute disproportionately to spawning and play an important role in the replenishment of exploited stocks. Fishing often removes specific size‐ and age‐classes, with direct impacts on stock productivity and population resilience. Despite this, fisheries advice is commonly based on estimates of spawning stock biomass (SSB) and fishing mortality (F) and makes little reference to the importance of size and/or age structure. Consequently, there is a need for indicators of size and/or age structure to better inform fisheries management and help assess global sustainability goals. Here, we introduce a new age‐based indicator ABIMSY that monitors age structure relative to the equilibrium age structure at FMSY. We apply this new indicator to 72 commercially important stocks in the Northeast Atlantic, covering 26 species, which collectively contributed 86% of all commercial catches in the region in 2019. We estimate that 62% (45 stocks) currently have proportionally fewer older fish relative to FMSY conditions, whereas 38% (27 stocks) have proportionally more older fish; we also note patterns with respect to geographic area and taxonomic family. Simulation testing demonstrated that ABIMSY is responsive to overfishing and generally tracks (with high sensitivity and specificity) a common measure of stock depletion, SSB relative to BMSY. Throughout, we show that ABIMSY provides information on the age structure of exploited stocks that is complementary to conventional reference points for SSB and F. Further, the framework used to estimate ABIMSY make it well placed for integration into current advisory frameworks on fisheries management. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms of spatial population dynamics is crucial for the successful management of exploited species and ecosystems. However, the underlying mechanisms of spatial distribution are generally complex due to the concurrent forcing of both density-dependent species interactions and density-independent environmental factors. Despite the high economic value and central ecological importance of cod in the Baltic Sea, the drivers of its spatio-temporal population dynamics have not been analytically investigated so far. In this paper, we used an extensive trawl survey dataset in combination with environmental data to investigate the spatial dynamics of the distribution of the Eastern Baltic cod during the past three decades using Generalized Additive Models. The results showed that adult cod distribution was mainly affected by cod population size, and to a minor degree by small-scale hydrological factors and the extent of suitable reproductive areas. As population size decreases, the cod population concentrates to the southern part of the Baltic Sea, where the preferred more marine environment conditions are encountered. Using the fitted models, we predicted the Baltic cod distribution back to the 1970s and a temporal index of cod spatial occupation was developed. Our study will contribute to the management and conservation of this important resource and of the ecosystem where it occurs, by showing the forces shaping its spatial distribution and therefore the potential response of the population to future exploitation and environmental changes. [ABSTRACT FROM AUTHOR]

Species diversity is widely recognized as an important trait of ecosystems’ functioning and resilience. Understanding the causes of diversity patterns and their interaction with the environmental conditions is essential in order to effectively assess and preserve existing diversity. While diversity patterns of most recurrent groups such as fish are commonly studied, other important taxa such as cephalopods have received less attention. In this work we present spatio-temporal trends of cephalopod diversity across the entire Mediterranean Sea during the last 19 years, analysing data from the annual bottom trawl survey MEDITS conducted by 5 different Mediterranean countries using standardized gears and sampling protocols. The influence of local and regional environmental variability in different Mediterranean regions is analysed applying generalized additive models, using species richness and the Shannon Wiener index as diversity descriptors. While the western basin showed a high diversity, our analyses do not support a steady eastward decrease of diversity as proposed in some previous studies. Instead, high Shannon diversity was also found in the Adriatic and Aegean Seas, and high species richness in the eastern Ionian Sea. Overall diversity did not show any consistent trend over the last two decades. Except in the Adriatic Sea, diversity showed a hump-shaped trend with depth in all regions, being highest between 200–400 m depth. Our results indicate that high Chlorophyll a concentrations and warmer temperatures seem to enhance species diversity, and the influence of these parameters is stronger for richness than for Shannon diversity. [ABSTRACT FROM AUTHOR]

Eco-labelled seafood is an important tool to promote sustainable development in fisheries. A price premium on eco-labelled seafood signals a return on investment in sustainable fishing methods, providing an incentive for fishers to adopt such methods. This paper investigates whether Swedish fishermen gained a price premium from participating in the Marine Stewardship Council ( MSC)-certified Swedish Eastern Baltic cod fishery in the period 2011-2012. Using a detailed dataset of landing tickets and log books, we apply a panel data methodology to estimate the MSC price premium. We cannot find reliable evidence that the consumer level premium for MCS cod is actually passed back to the producers in this case. [ABSTRACT FROM AUTHOR]

Climate change and anthropogenic disturbances may affect marine populations and ecosystems through multiple pathways. In this study we present a framework in which we integrate existing models and knowledge on basic regulatory processes to investigate the potential impact of future scenarios of fisheries exploitation and climate change on the temporal dynamics of the central Baltic herring stock. Alternative scenarios of increasing sea surface temperature and decreasing salinity of the Baltic Sea from a global climate model were combined with two alternative fishing scenarios, and their direct and ecosystem-mediated effects (i.e., through predation by cod and competition with sprat) on the herring population were evaluated for the period 2010-2050. Gradual increase in temperature has a positive impact on the long-term productivity of the herring stock, but it has the potential to enhance the recovery of the herring stock only in combination with sustainable fisheries management (i.e., Fmsy). Conversely, projections of herring spawning stock biomass ( SSB) were generally low under elevated fishing mortality levels ( Fhigh), comparable with those experienced by the stock during the 1990s. Under the combined effects of long-term warming and high fishing mortality uncertainty in herring SSB projections was higher and increasing for the duration of the forecasts, suggesting a synergistic effect of fishery exploitation and climate forcing on fish populations dynamics. Our study shows that simulations of long-term fish dynamics can be an informative tool to derive expectations of the potential long-term impact of alternative future scenarios of exploitation and climate change. [ABSTRACT FROM AUTHOR]

Catch rates from fisheryindependent surveys often are assumed to vary in proportion to the actual abundance of a population, but this approach assumes that the catchability coefficient (q) is constant. When fish accumulate in a gear, the rate at which the gear catches fish can decline, and, as a result, catch asymptotes and q declines with longer fishing times. We used data from long-term trap surveys (1990-2011) in the southeastern U.S. Atlantic to determine whether traps saturated for 8 reef fish species because of the amount of time traps soaked or the level of fish accumulation (the total number of individuals of all fish species caught in a trap). We used a deltageneralized-additive model to relate the catch of each species to a variety of predictor variables to determine how catch was influenced by soak time and fish accumulation after accounting for variability in catch due to the other predictor variables in the model. We found evidence of trap saturation for all 8 reef fish species examined. Traps became saturated for most species across the range of soak times examined, but trap saturation occurred for 3 fish species because of fish accumulation levels in the trap. Our results indicate that, to infer relative abundance levels from catch data, future studies should standardize catch or catch rates with nonlinear regression models that incorporate soak time, fish accumulation, and any other predictor variable that may ultimately influence catch. Determination of the exact mechanisms that cause trap saturation is a critical need for accurate stock assessment, and our results indicate that these mechanisms may vary considerably among species. [ABSTRACT FROM AUTHOR]

Through the history of ecology, fluctuations of populations have been a dominating topic, and endogenous causes of fluctuations and oscillations have been recognized and studied for more than 80 years. Here we analyzed an historical dataset, covering more than 130 years, of European lobster (Homarus gammarus) catches. The data shows periodic fluctuations, which are first dampened and then disappear over time. The disappearance of the periodicity coincided with a substantial increase in fishing effort and the oscillations have not reappeared in the time series. The shifting baseline syndrome has changed our perception of not only the status of the stock, but also the regulating pressures. We describe the transition of a naturally regulated lobster population into a heavily exploited fisheries controlled stock. This is shown by the incorporation of environmental and endogenous processes in generalized additive models, autocorrelation functions and periodicity analyses of time-series. [ABSTRACT FROM AUTHOR]

Recent analyses of historical data of fish abundance and distribution have shown the importance of a long temporal perspective in the evaluation of the current status of fish populations, but pose numerous difficulties such as fragmentation and inhomogeneities in the amount of available information in space and time. Using mixed-effects models in a multiscale analysis, we identified an appropriate spatiotemporal scale of investigation of a high-quality, spatially explicit historical data set, and we reconstructed the long-term spatial dynamics of Atlantic cod ( Gadus morhua) in the Kattegat-Skagerrak along the 20th century. We identified a northern and southern main aggregation of adult cod in the study area, corresponding to the Skagerrak portion of the North Sea and the Kattegat cod stocks, respectively. The stocks showed specificities in their spatial dynamics, but common extensive loss of coastal aggregations during the last decades when only 13% (Kattegat) and 35% (Skagerrak) of the estimated early century cod biomass was left. Our reconstruction showed that the collapse of the cod stocks in the area followed the peak in landings in the 1960s-1970s, suggesting that the postwar development of the industrial fisheries played a major role in the decrease of local abundances and disappearance of local adult cod aggregations. [ABSTRACT FROM AUTHOR]

Discards represent one of the most important issues within current commercial fishing. It occurs for a range of reasons and is influenced by an even more complex array of factors. We address this issue by examining the data collected within the Danish discard observer program and describe the factors that influence discarding within the Danish Kattegat demersal fleet over the period 1997 to 2008. Generalised additive models were used to assess how discards of the 3 main target species, Norway lobster, cod and plaice, and their subcomponents (under and over minimum landings size) are influenced by important factors and their potential relevance to management. Our results show that discards are influenced by a range of different factors that are different for each species and portion of discards. We argue that knowledge about the factors influential to discarding and their use in relation to potential mitigation measures are essential for future fisheries management strategies. [ABSTRACT FROM AUTHOR]

Increased knowledge on the spatial distribution of marine resources is crucial for the implementation of a true ecosystem approach to management and the conservation of marine organisms. For exploited fish species characterized by aggregation behaviour during spawning time, the identification and tracking of spawning areas is essential for a correct assessment of their productivity and population abundance. To elucidate this concept, we reconstructed the spatio-temporal distribution of adult plaice ( Pleuronectes platessa, Pleuronectidae) during spawning time along the 20th century. Historical data reveal that not only the abundance but also the former population richness was much higher than previously estimated and has declined because of protracted over-exploitation during the last 30 years. We conclude that forecast of stock recovery to former levels of abundance neglecting spatial reorganizations might be over-optimistic and shaded by a lost memory of the past population richness. These results reinforce the importance of managing exploited marine resources at a greater spatial resolution than has been carried out in the history of fishery management. [ABSTRACT FROM AUTHOR]

Abstract: An age-length structured model was built for European hake Merluccius merluccius in the central Mediterranean Sea using Gadget. This analytical framework allowed to integrate multiple sources of information, including fisheries-dependent and fisheries-independent data, collected at different scales and aggregation levels. The model includes the two main fisheries targeting hake in the area, the trawl and the gillnet fisheries, and account for differences in their selectivity and effort. Alternative models were used for testing different assumptions on recruitment and growth. The model is then used to predict the main trajectory of the stock during the next years and to evaluate the potential effects of implementing closed areas management scenarios in the hake nurseries as a specific tool to reduce fishing mortality on recruits. The modelling framework presented performed successfully also in a commercial landing data limited context, common for the Mediterranean. Our results provide statistical support for fast growth and multiple recruitment events assumptions. Including both these key features represent an unprecedented improvement of modelling hake population dynamics in the Mediterranean. We found that the reduction in the fishing effort that characterized the fisheries in the study area during the last few years, coupled with fast recovery abilities of the hake stock, has the potentiality to allow a moderate increase of the stock during the next years. Interestingly, our simulations show that the positive effects which might be expected from protecting hake nursery grounds are only marginally related to a reduction in hake recruits fishing mortality. Although our model relies on assumptions and surely represents an over-simplification of the real world, it still contributed to improve our understanding of the temporal dynamics of one of the most valuable fish stocks in the central Mediterranean. [ABSTRACT FROM AUTHOR]

The spatial dynamics of species are the result of complex interactions between density-independent and density-dependent sources of variability. Disentangling these two sources of variability has challenged ecologists working in both terrestrial and aquatic ecosystems. Using a novel spatially explicit statistical model, we tested for the presence of density-independent and density-dependent habitat selection in yellowfin sole (Limanda aspera) in the eastern Bering Sea. We found specificities in the density-dependent processes operating across ontogeny and particularly with gender. Density-dependent habitat expansion occurred primarily in females, and to a lesser degree in males. These patterns were especially evident in adult stages, while juvenile stages of both sexes exhibited' a mix of different dynamics. Association of yellowfin sole with substrate type also varied by sex and to a lesser degree with size, with large females distributed over a wider range of substrates than males. Moreover, yellowfin sole expanded northward as cold subsurface waters retracted in summer, suggesting high sensitivity to arctic warming. Our findings illustrate how marginal habitats can play an important role in buffering density-dependent habitat expansion, with direct implications for resource management. Our spatially explicit modeling approach is effective in evaluating density-dependent spatial dynamics, and can easily be used to test similar hypotheses from a variety of aquatic and terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Maiorano, L., Bartolino, V., Colloca, F., Abella, A., Belluscio, A., Carpentieri, P., Criscoli, A., Jona Lasinio, G., Mannini, A., Pranovi, F., Reale, B., Relini, G., Viva, C., and Ardizzone, G. D. 2009. Systematic conservation planning in the Mediterranean: a flexible tool for the identification of no-take marine protected areas. – ICES Journal of Marine Science, 66: 137–146.We propose the use of systematic conservation planning in the Mediterranean context for the identification of no-take marine protected areas (NTMPAs). We suggest a logical framework that should be used for the identification of areas to be targeted for multispecies, spatially explicit conservation actions. Specifically, we propose seven steps: (i) definition of the study area; (ii) selection of the species or habitats to be considered; (iii) definition of the planning units; (iv) measurement of the fishing effort; (v) definition of the conservation targets; (vi) review of the existing conservation areas; (vii) selection of additional NTMPAs. Moreover, we consider the potential impact of different conservation plans on existing fishing vessels. A working example is presented, focusing on a limited number of species and on a limited study area. This framework can be easily expanded to include datasets of different origin and to accommodate larger spatial scales. Such a process involves major data-collection and capacity-building elements, and conservation of productive commercial fisheries must be a priority. [ABSTRACT FROM PUBLISHER]

Bartolino, V., Ottavi, A., Colloca, F., Ardizzone, G. D., and Stefánsson, G. 2008. Bathymetric preferences of juvenile European hake (Merluccius merluccius). – ICES Journal of Marine Science, 65: 963–969.The concept of a recruit is a basic notion in fisheries science, but it is still far from being an unequivocal term, and many diverse, even ambiguous, definitions can be found in the literature. We propose a more objective and biologically meaningful way to define the length range of recruits for species that have clear bathymetric segregation during the early stages of their life cycle. The bathymetric distribution of juvenile European hake was studied by fitting a thin plate spline to data from the national autumn trawl survey. Hake showed a stable pattern of depth preference in the 6-year dataset examined. Small hake had the greatest preference for depths of 170–220 m and appeared to move slightly deeper when they reached 10-cm total length. Larger hake persisted on the continental shelf with a preference for water 70–100 m deep, especially when they reached 18–20 cm long. The length at migration was defined as the length at which the minimum depth preference was shown, and it ranged between 13.2 and 15.8 cm depending on the year. There was a relationship between length at and depth of migration, and we provide a full description of the depth preference of juvenile hake, and test the effectiveness of the analytical approach used. [ABSTRACT FROM PUBLISHER]

The vertebral system in Hippocampus hippocampus is highly specialised because of the vertical locomotion and tail prehensility. The vertebral elements represent a special case of morphological changes, being the metameric structures organised along a natural functional series. We investigated the shape changes along the vertebral spine in H. hippocampus through geometric morphometrics, in order to describe functional and structural patterns. Actually, the dorso-ventral tail bending ability in the genus Hippocampus is one of the most impressive morphological modifications in the evolutionary history of fishes. Vertebrae were analysed using a 2D configuration from the left lateral view. The variation along the vertebral series suggests the identification of cervical, abdominal, dorsal, and caudal groups. The first three (cervical) elements and the 10th (supra-dorsal) structure show peculiar morphologies and local adaptations, associated with neck angulation and dorsal fin muscles, respectively. The vertebral size decreases from the anteriormost element backward, with some local variation at the dorsal area. Major changes are related to allometric variation at the neural region. The caudal elements are characterised by a marked size decrease, with consequent allometric shape changes involving the rotation of the posterior vertebral opening. This allometric trajectory leads to a natural ventral bending of the tail, promoting its prehensile function. This morphological survey suggests an interesting structural network between posture, locomotion, and vertebral anatomy, underlying the main functional changes in the Hippocampus biomechanics. Geometric morphometrics is rather suitable to approach metameric studies in terms of serial variation and functional adaptations. [ABSTRACT FROM AUTHOR]

Nine pycnogonid species from four different families were collected. Propallene socotrana n. sp. and Anoplodactylus erythraeus n. sp. are described. Callipallene cf. dubiosa Hedgpeth, 1949 is figured and its systematic position discussed. The Pycnogonida fauna around the Socotra Archipelago (Yemen) supports the hypothesis the Socotra Archipelago represents an important transient zoogeographic region between the Red Sea and the Indian Ocean. [ABSTRACT FROM AUTHOR]

International efforts to assess the status of marine ecosystems have been hampered by insufficient observations of food web interactions across many species, their various life stages, and geographic ranges. Hence, we collated data from multiple databases of fish stomach contents from samples taken across the North Atlantic and Arctic Oceans containing 944,129 stomach samples from larvae to adults, with 14,196 unique interactions between 227 predator species and 2158 prey taxa. We use these data to develop a data-driven, reproducible approach to classifying broad functional feeding guilds and then apply these to fish survey data from the Northeast Atlantic shelf seas to reveal spatial and temporal changes in ecosystem structure and functioning. In doing so, we construct predator-prey body size scaling models to predict the biomass of prey functional groups, e.g., zooplankton, benthos, and fish, for different predator species. These predictions provide empirical estimates of species- and size-specific feeding traits of fish, such as predator-prey mass ratios, individual prey mass, and the biomass contribution of different prey to predator diets. The functional groupings and feeding traits provided here help to further resolve our understanding of interactions within marine food webs and support the use of trait-based indicators in biodiversity assessments. The data used and predictions generated in this study are published on the Cefas Data Hub at: https://doi.org/10.14466/CefasDataHub.149 (Thompson et al., 2024). [ABSTRACT FROM AUTHOR]

Sidney J. Holt (1926–2019) was more than a founding father of quantitative fisheries science, and the man who "helped save the great whales." His accomplishments, over a career spanning seven decades, run deeper: he was a champion of reductionism (i.e. able to identify the factors essential for management) and a systemic thinker who inspired scientists to think critically about marine conservation and management. This article draws on first-hand experiences with Sidney over the last 15 years, when he regularly collaborated with scholars of the ICES Working Group on the History of Fish and Fisheries and the Oceans Past Initiative. Four main themes emerged from our reflections on Sidney's life and legacy, which constitute ongoing scientific challenges: (1) the suitability of maximum sustainable yield as a target reference point for fisheries management; (2) the future of marine mammal conservation; (3) successful implementation of ecosystem-based marine management; and (4) the value of historical perspectives for conservation and management. We consider Sidney's work across these themes, in which he readily collaborated, focused on evidence-based solutions, and, where evidence was lacking, he advocated for the "precautionary principle." We posit there is much that we, and future generations of scientists, can learn from his example. [ABSTRACT FROM AUTHOR]

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

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

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

The original article can be found online at https://doi.org/10.1007/s11160-022-09739-2. B Correction to: Rev Fish Biol Fisheries b https://doi.org/10.1007/s11160-022-09739-2 Following publication of the original article [1], the authors identified an error in Table 1. [Extracted from the article]

Abstract: Dynamics of commercial fish stocks are generally associated with fishing pressure and climate variability. Due to short time series, past studies of the relationships between fish stock dynamics and climate have mainly been restricted to the last few decades. Here we analyzed a century-long time series of plaice, cod and haddock from the Skagerrak–Kattegat, to assess the long-term influence of climate on recruitment. Recruitment success (RS) was compared against sea-surface temperature (SST) and atmospheric circulation indices on large (North Atlantic) and regional (Skagerrak–Kattegat) scales. Our results show that the influence of climate on RS was more pronounced on longer, than on shorter timescales. Over the century-long period, a shift from low to high climate sensitivity was seen from the early to the late part for plaice and cod, while the opposite was found for haddock. This shift suggests that the increasing fishing pressure and the climate change in the Skagerrak–Kattegat have resulted in an increased sensitivity of RS to climate for plaice and cod. The diminishing of climate sensitivity in haddock RS, on the other hand, may be linked to the early twentieth century collapse of the stock in the region. While no long-term relationship between RS and the Atlantic Multidecadal Oscillation (AMO) could be found, large RS fluctuations during the positive phase of the AMO (1935–1960), relative to the cold phases, suggests a changed pattern in recruitment during warm periods. On the other hand, this could be due to the increased fishing pressure in the area. Thus, reported correlations between climate and fish may be caused by strong trends in climate in the late-twentieth century, and coincident reduction in fish stocks caused by intense fishing, rather than a stable relationship between climate and fish recruitment per se. [Copyright &y& Elsevier]

Spatio-temporal density-dependent processes are crucial regulatory factors for natural populations. However, there is a lack of studies addressing spatial density-dependence in fish growth. A previous investigation has suggested spatio-temporal density-dependence in body condition of Baltic sprat. Here, we used different techniques, such as centre of gravity, distance, and homogeneity indices, to better characterize the spatial and temporal variations in sprat density and body condition in the Baltic Proper. Our results evidenced a negative spatio-temporal co-variation between the centres of gravity of density and maximum condition. In the 1980s-early 1990s both centres were located in the middle of the Baltic Proper. From the mid 1990s the centres progressively separated in space, as the sprat population moved towards the north-eastern Baltic Proper, and the centre of maximum condition towards the south-western areas. Moreover, at low abundances, sprat density and condition were homogeneously distributed in space, whereas at high abundances both density and condition showed pronounced geographical gradients. The ecological processes potentially explaining the observed patterns were discussed in the light of the Ideal Free Distribution theory. We provide evidence that the shift in the spatial distribution of cod, the main predator of sprat, has been the main factor triggering the overall spatial changes in sprat density, and thus condition, during the past thirty years. The spatial indices shown here, synthesizing the spatio-temporal patterns of fish distribution, can support the implementation of the EU Marine Strategy Framework Directive. [ABSTRACT FROM AUTHOR]

Fisheries ecologists traditionally aimed at disentangling climate and fishing effects from the population dynamics of exploited marine fish stocks. However, recent studies have shown that internal characteristics and external forcing (climate and exploitation) have interactive rather than additive effects. Thought most of these studies explored how demographic truncation induced by exploitation affected the response of recruitment to climate, identifying a general pattern revealed to be difficult as interactions are often case-specific. Here we compared five exploited stocks of European hake Merluccius merluccius from the Atlantic Ocean and Mediterranean Sea to investigate how the interaction between internal characteristics and external forces affect the variability of the population growth rate and their consequences on recruitment. Our results show that demographic truncation induces a novel population scenario in which the growth rate is maximized when the reproductive stock is younger and less diverse. This scenario is shaped by the climate variability and the fishing pattern. The population growth rate becomes more dependent on the maturation schedule and less on the survival rates. The consequences for the recruitment dynamics are twofold; the effect of density-dependent regulatory processes decreases while the effect of the density-independent drivers increases. Our study shows that the interaction between internal characteristics and external forces changes across geographic locations according to 1) the importance of demographic truncation, 2) the influence of the climate on the regional hydrography and 3) the spatiotemporal heterogeneity of the physical environment to which fish life history is adapted. [ABSTRACT FROM AUTHOR]

Predators often predate on a limited size range of prey, which may or may not overlap with size ranges of same prey targeted by fisheries. When they do overlap, the effect of competition over that prey is immediate, as the predator removes prey, which are at the same time suitable for the fishery. However, if the predator consumes the same prey species as the fishery, but targets smaller prey sizes, this predation on smaller sizes may result in a potential loss of future, rather than current, fishing opportunities. Comparative analyses of predator size preference and fisheries selectivity are scarce, despite their relevance in the context of integrated management of fish populations. We evaluated how size-selective cod predation influences the dynamics of sprat and herring in the Baltic Sea, as well as the competition with pelagic fisheries through immediate and delayed effects. We found a large overlap (30–60%) between prey lengths targeted by cod and fisheries, which was largest in the 1970s–1980s,  when cod had higher abundance and was larger in size. Cod generally consumes herring and sprat, which are smaller than those caught by the fisheries, causing both immediate and delayed effects on prey biomass available for the fisheries. [ABSTRACT FROM AUTHOR]

The advance of ecosystem-based fisheries management worldwide has made scientific advice on fisheries related questions more complex. However, despite the need to take interactions between fish stocks, and between stocks and their environment into account, multispecies and ecosystem models are still hardly used as a basis for fishery advice. Although reasons are numerous, the lack of high-level guidance for target-oriented skill assessments of such models contributes to the mistrust to use such models for advice. In this study, we propose a framework of guiding questions for a pragmatic and target-oriented skill assessment. The framework is relevant for all models irrespective of their complexity and approach. It starts with general questions on the advice purpose itself, the type of model(s) and data available for performance testing. After this, the credibility of the hindcasts are evaluated. A special emphasis is finally put on testing predictive skills. The skill assessment framework proposed provides a tool to evaluate a model's suitability for the purpose of providing specific advice and aims to avoid the bad practice of incomplete skill assessments. In the case of multiple models available, it can facilitate the evaluation or choosing of the best model(s) for a given advice product and intends to ensure a level playing field between models of different complexities. The suite of questions proposed is an important step to improve the quality of advice products for a successful implementation of ecosystem-based fisheries management. • Lack of high-level guidance for skill assessments contributes to the mistrust to use more complex models for fisheries advice. • A framework of guiding questions for a pragmatic and target-oriented skill assessment is proposed. • The framework intends to ensure a level playing field between models of different complexities. • The framework is an important step for a successful implementation of ecosystem approaches to fisheries management. [ABSTRACT FROM AUTHOR]

Abstract Size of predator and prey determines, to a large extent, predator-prey interactions in aquatic systems. Understanding the relationship between predator and prey size in the individual predator's food selection process is a cornerstone of ecological modelling. Stomach content data are used to inform such models, as they provide prey species specific information about the predator diet in the wild. These data are strongly relevant as direct observations of species trophic interactions, but they have limitations, and are costly. Our objective was to develop and test a model which is able to predict changes in the Baltic cod diet by reconstructing the dynamics of cod and its prey, herring and sprat, populations, their length distributions, and parametrizing trophic interactions between them. We analysed time-series of cod stomach data and built an age-length structured multispecies model using Gadget. Both observed and predicted diets of smaller (juvenile) cod consisted mainly of benthos, while larger cod fed mostly on fishes (herring and sprat). Our model could predict the main patterns in species and length composition of cod diet. We also identified important knowledge gaps, especially on benthos dynamics and processes affecting prey availability and predator preference. [ABSTRACT FROM AUTHOR]

Different ecosystem models often provide contrasting predictions (model uncertainty), which is perceived to be a major challenge impeding their use to support ecosystem-based fisheries management (EBFM). The focus of this manuscript is to examine the extent of model disagreements which could impact management advice for EBFM in the central Baltic Sea. We compare how much three models (EwE, Gadget and a multispecies stock production model) differ in 1) their estimates of fishing mortality rates (Fs) satisfying alternative hypothetical management scenario objectives and 2) the outcomes of those scenarios in terms of performance indicators (spawning stock biomasses, catches, profits). Uncertainty in future environmental conditions affecting fish was taken into account by considering two seal population growth scenarios and two nutrient load scenarios. Differences in the development of the stocks, yields and profits exist among the models but the general patterns are also sufficiently similar to appear promising in the context of strategic fishery advice. Thus, we suggest that disagreements among the ecosystem models will not impede their use for providing strategic advice on how to reach management objectives that go beyond the traditional maximum yield targets and for informing on the potential consequences of pursuing such objectives. This is especially true for scenarios aiming at exploiting forage fish sprat and herring, for which the agreement was the largest among our models. However, the quantitative response to altering fishing pressure differed among models. This was due to the diverse environmental covariates and the different number of trophic relationships and their functional forms considered in the models. This suggests that ecosystem models can be used to provide quantitative advice only after more targeted research is conducted to gain a deeper understanding into the relationship between trophic links and fish population dynamics in the Baltic Sea. [ABSTRACT FROM AUTHOR]

A fisheries management model that identifies the economic optimal management of fisheries under the influence of nutrients is presented. The model starts from the idea that growth in fish biomass increases with increasing availability of nutrients owing to higher food availability up to a peak, after which growth falls due to eutrophication. The model is applied to Swedish and Danish cod fisheries in the Western Baltic Sea and identifies the welfare contribution of the fisheries, measured as the sum of resource rent and producer surplus. In 2010, the welfare contribution was −28% of the landing value. Maximizing the model with respect to effort alone and additionally over nitrogen concentration increases the contribution to 11% of the landing value in 2010. The analysis shows that the welfare effect of reducing fishing effort through management reforms is large, but that the effect of incorporating nitrogen in fisheries policy is small. [ABSTRACT FROM AUTHOR]

Increasing the size and number of marine protected areas (MPAs) is widely seen as a way to meet ambitious biodiversity and sustainable development goals. Yet, debate still exists on the effectiveness of MPAs in achieving ecological and societal objectives. Although the literature provides significant evidence of the ecological effects of MPAs within their boundaries, much remains to be learned about the ecological and social effects of MPAs on regional and seascape scales. Key to improving the effectiveness of MPAs, and ensuring that they achieve desired outcomes, will be better monitoring that includes ecological and social data collected inside and outside of MPAs. This can lead to more conclusive evidence about what is working, what is not, and why. Eight authors were asked to write about their experiences with MPA effectiveness. The authors were instructed to clearly define "effectiveness" and discuss the degree to which they felt MPAs had achieved or failed to be effective. Essays were exchanged among authors and each was invited to write a shorter "counterpoint." The exercise shows that, while experiences are diverse, many authors found common ground regarding the role of MPAs in achieving conservation targets. This exchange of perspectives is intended to promote reflection, analysis, and dialogue as a means for improving MPA design, assessment, and integration with other conservation tools. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

How climatic variability and anthropogenic pressures interact to influence recruitment is a key factor in achieving sustainable resource management. However, the combined effects of these pressures can make it difficult to detect non-stationary interactions or shifts in the relationships with recruitment. Here we examine the links between climate and Irish Sea cod recruitment during a period of declining spawning stock biomass ( SSB). Specifically, we test for a shift in the relationship between recruitment, SSB and climate by comparing an additive (generalized additive model, GAM) and non-additive threshold model ( TGAM). The relationship between recruitment success, SSB and the climatic driver, sea surface temperature, was best described by the TGAM, with a threshold identified between recruitment and SSB at approximately 7900 t. The analysis suggests a threshold shift in the relationship between recruitment and SSB in Irish Sea cod, with cod recruitment being more sensitive to climatic variability during the recent low SSB regime. [ABSTRACT FROM AUTHOR]

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

Abstract: Environmental variability is increasingly recognized as a primary determinant of year-class strength of marine fishes by directly or indirectly influencing egg and larval development, growth, and survival. Here we examined the role of annual water temperature variability in determining when and where walleye pollock (Theragra chalcogramma) spawn in the eastern Bering Sea. Walleye pollock spawning was examined using both long-term ichthyoplankton data (N=19 years), as well as with historical spatially explicit, foreign-reported, commercial catch data occurring during the primary walleye pollock spawning season (February–May) each year (N=22 years in total). We constructed variable-coefficient generalized additive models (GAMs) to relate the spatially explicit egg or adult catch-per-unit-effort (CPUE) to predictor variables including spawning stock biomass, season, position, and water temperature. The adjusted R 2 value was 63.1% for the egg CPUE model and 35.5% for the adult CPUE model. Both egg and adult GAMs suggest that spawning progresses seasonally from Bogoslof Island in February and March to Outer Domain waters between the Pribilof and Unimak Islands by May. Most importantly, walleye pollock egg and adult CPUE was predicted to generally increase throughout the study area as mean annual water temperature increased. These results suggest low interannual variability in the spatial and temporal dynamics of walleye pollock spawning regardless of changes in environmental conditions, at least at the spatial scale examined in this study and within the time frame of decades. [Copyright &y& Elsevier]

Fisheries can have a large impact on marine ecosystems, because the effects of removing large predatory fish may cascade down the food web. The implications of these cascading processes on system functioning and resilience remain a source of intense scientific debate. By using field data covering a 30-year period, we show for the Baltic Sea that the underlying mechanisms of trophic cascades produced a shift in ecosystem functioning after the collapse of the top predator cod. We identified an ecological threshold, corresponding to a planktivore abundance of ≈17 x 10[sup10] individuals, that separates 2 ecosystem configurations in which zooplankton dynamics are driven by either hydroclimatic forces or predation pressure. Abundances of the planktivore sprat above the threshold decouple zooplankton dynamics from hydrological circumstances. The current strong regulation by sprat of the feeding resources for larval cod may hinder cod recovery and the return of the ecosystem to a prior state. This calls for the inclusion of a food web perspective in management decisions. [ABSTRACT FROM AUTHOR]