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The Northeast Arctic stock of haddock (Melanogrammus aeglefinus) is the most northerly stock of the species. It is one of the largest haddock stocks but not the most studied. Similar to the more extensively studied sympatric cod (Gadus morhua) and herring (Clupea harengus) stocks, it relies on Atlantic currents for egg and larvae transportation from spawning grounds to nursery areas in the Barents Sea. The exact locations of the spawning grounds have not been known and the maps that have been published differ substantially. Here, we present results from the first survey dedicated to exploring the spawning habitat of Northeast Arctic (NEA) haddock, and a particle drift and larvae growth model with physical forcing from a high‐resolution ocean model. Gadoid eggs, later identified as haddock by DNA analyses, as well as spawning individuals were sampled at the survey. Spawning haddock was found in Atlantic water in temperatures 3.6–6.2°C and depths of 240–560 m. Sampled eggs were mostly in early development stages, suggesting that they were largely spawned in the surveyed area. Using the drift model, we found that most of the modelled particles released as eggs at our surveyed area ended up in the nursery area in the Barents Sea. A crude estimate of the spawning stock biomass based on the survey suggests that the most updated spawning ground map of NEA haddock might be too restricted in its extent. Particle drift and growth with physical forcing for the years 2012–2022 indicated small interannual variation in aberrant drift, and that growth driven by ambient temperature could be important in explaining interannual variation in haddock recruitment. [ABSTRACT FROM AUTHOR]

The survival of animals is impacted by landscapes of spatially varying mortality factors including habitat type, predation risk or harvest risk, among others. Characterization of these spatial mortality processes is important for managing animal populations and their habitats, yet this information has proved challenging to capture. Advances in telemetry now make it possible to monitor tagged individuals' locations through time for a wide range of taxa, providing opportunity to assess movement and mortality simultaneously through spatial time‐to‐event data. Existing time‐to‐event modelling frameworks have largely ignored spatially varying mortality processes or have treated an animal's location as fixed at a regional level.Here we present a general spatial survival model for analysing time‐to‐event data arising from animal telemetry. Our model has a flexible Cox regression form and can estimate the effects of conventional non‐spatial risk factors (size, seasonality, etc.), spatial covariates (e.g. habitat type) and spatial variation in risk not explained by covariates on mortality. We show how to fit our model using Bayesian methods and demonstrate applications of our model with several simulated examples and two animal telemetry case studies.Our model produced consistent and unbiased parameter estimates throughout simulations with a variety of spatial and non‐spatial hazards. In the first case study, data from 147 tagged caribou in British Columbia, Canada, revealed a spatially heterogeneous mortality landscape with caribou survival varying by elevation, likely in response to space use by predators. Our second case study involved a dataset of 390 acoustically tagged Atlantic cod in a southern Norwegian fjord where a marine protected area (MPA) was established during the study. We found that the MPA led to a shift from mostly fishing mortality to mostly natural mortality within the fjord and that these risks had markedly different spatial hazard patterns.Our spatial time‐to‐event model can make use of data from a variety of widely used telemetry technologies to characterize landscapes of mortality risks for different taxa. Our work provides new opportunities to inform the spatial ecology and management of fish and wildlife populations. [ABSTRACT FROM AUTHOR]

The status of Eastern Baltic cod (EBC) Gadus morhua has remained poor despite low fishing mortality for over a decade, including a fishing ban since 2019. Although the decline in productivity can be explained by lower individual growth and survival rates, other aspects of life‐history changes such as maturation patterns for EBC has so far not been sufficiently explored. According to current stock assessments, the median size at maturity (L50) has halved from 40 to around 20 cm in total length since the 1990s, while the overall size distribution has become increasingly truncated. It has previously been suggested that changes in L50 can be attributed to both fishing‐induced evolution and phenotypic plasticity induced by growth rates. However, since L50 is currently occurring around 20 cm, the maturation process must have been initiated at much smaller sizes, that is, long before the fish could be caught in the dominant trawl fishery at around 35 cm. In this study, we aimed to further investigate what drivers may have led to reduced productivity in EBC by determining variations in size at sexual maturity in longer time series than has been done before (1930s to 1980s) and include prey productivity and quality. We found that L50 declined already in the 1930s and thereafter remained stable at around 40 cm up to the 1990s. On a centurial perspective, L50 has been positively correlated to growth potential (L95), length diversity, total stock biomass, total catch and yield per recruit, while Fulton's condition factor was not related to L50. Our results suggest that the links between life‐history parameters and external drivers are complex, but the present unprecedented early onset of maturity and hence decline in L50 since the 1990s signals a decline in growth potential, which also has hampered the productivity of EBC. [ABSTRACT FROM AUTHOR]

The gross pathology and the histopathological alterations identified in juvenile specimens of the European hake (Merluccius merluccius), one of the most important target species of commercial fisheries in the northwest Mediterranean, are described. A qualitative and semi‐quantitative histological approach was performed in specimens from 2007 and 2019. Prevalence and mean intensity of parasites and histopathological changes were calculated in both years. No macroscopic alterations were found in any organ but several parasites (e.g., copepods, nematodes, digeneans) were detected. Microscopically, alterations identified in gills included foci of inflammation and hyperplasia (present in 77.38% of hakes from both years), extensive hyperplasia (33.33%), and inflammation (16.65%) that were potentially related to the mechanical effects of monogeneans and copepods, cysts of unknown etiology (62.69%), and lamellar inflammation associated to Aporocotyle spinosicanalis eggs (8.33%). Granulomas and inflammatory focus were detected in the liver, spleen, and stomach, apparently associated with the presence of nematodes. Coelozoic myxosporean parasites were detected within the renal tubules (66.66%). Most of the pathologies detected were similar to those described in other gadoid species (i.e., Gadus morhua) and were usually related to the presence of ecto and endoparasites. The potential impact of parasites on the health of this fish species is discussed for improving the knowledge and management of these valuable fishing stocks. [ABSTRACT FROM AUTHOR]

Summary: The composite film with collagen as the main component has been widely used due to its characteristics of non‐toxicity, environmental protection and health. Fish skin, a by‐product of fish, is an excellent source of collagen. Thus, collagen was extracted from an under‐utilised species, Atlantic cod (Gadus morhua) skin, and the composite film of fish skin collagen–chitosan–cinnamon essential oil was prepared by casting. The effects of the ratio of collagen to chitosan (2:8, 4:6, 5:5, 6:4, 8:2) and the concentration of essential oil (0%, 0.1%, 0.2%, 0.3%, and 0.4% (v/v)) on the composite film were studied. The structures of the composite films were analysed using scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and X‐ray diffractometry (XRD). The collagen content of Atlantic cod skin is approximately 50.12%, which is significantly higher than that found in basa fish and Nile tilapia (P < 0.05). The content of hydroxyproline was 4.51%. Analyses of tensile strength, elongation at break, water vapor permeability, and water solubility showed Co4Ch6 (Co:Ch = 4:6) had the optimal comprehensive performance, and Co4Ch6–0.2 (Co4Ch6 with 0.2% CEO) had high water resistance in the high‐humidity environment. As the CEO concentration rose, the composite films' infrared absorption bands were enhanced in amplitude, and the XRD peaks were gradually intensified, indicating the internal crystallinity and, thereby, the opacity of the composite films were improved. The bacteriostasis zones Co4Ch6–0.4 against Escherichia coli and Staphylococcus aureus were 2.02 cm and 1.73 cm, respectively. The DPPH radical scavenging rate of Co4Ch6 rose with the increase in CEO concentration, and the DPPH radical scavenging rate of C04Ch6–0.4 was up to 48.56%. Thus, the composite films prepared from fish skin collagen, chitosan, and cinnamon essential oils have outstanding mechanical properties, barrier ability, and antimicrobial activity and are promising for application in food packaging and storage. In addition, the composite films showed a potential antioxidation ability, which might be used as green bioactive films to preserve nutraceutical products. [ABSTRACT FROM AUTHOR]

Understanding and predicting interactions between predators and prey and their environment are fundamental for understanding food web structure, dynamics, and ecosystem function in both terrestrial and marine ecosystems. Thus, estimating the conditional associations between species and their environments is important for exploring connections or cooperative links in the ecosystem, which in turn can help to clarify such directional relationships. For this purpose, a relevant and practical statistical method is required to link presence/absence observations with biomass, abundance, and physical quantities obtained as continuous real values. These data are sometimes sparse in oceanic space and too short as time series data. To meet this challenge, we provide an approach based on applying categorical data analysis to present/absent observations and real‐number data. The real‐number data used as explanatory variables for the present/absent response variable are discretized based on the optimal detection of thresholds without any prior biological/ecological information. These discretized data express two different levels, such as large/small or high/low, which give experts a simple interpretation for investigating complicated associations in marine ecosystems. This approach is implemented in the previous statistical method called CATDAP developed by Sakamoto and Akaike in 1979. Our proposed approach consists of a two‐step procedure for categorical data analysis: (1) finding the appropriate threshold to discretize the real‐number data for applying an independent test; and (2) identifying the best conditional probability model to investigate the possible associations among the data based on a statistical information criterion. We perform a simulation study to validate our proposed approach and investigate whether the method's observation includes many zeros (zero‐inflated data), which can often occur in practical situations. Furthermore, the approach is applied to two datasets: (1) one collected during an international synoptic krill survey in the Scotia Sea west of the Antarctic Peninsula to investigate associations among krill, fin whale (Balaenoptera physalus), surface temperature, depth, slope in depth (flatter or steeper terrain), and temperature gradient (slope in temperature); (2) the other collected by ecosystem surveys conducted during August–September in 2014–2017 to investigate associations among common minke whales, the predatory fish Atlantic cod, and their main prey groups (zooplankton, 0‐group fish) in Arctic Ocean waters to the west and north of Svalbard, Norway. The R code summarizing our proposed numerical procedure is presented in S4S1. [ABSTRACT FROM AUTHOR]

Despite decades of active fisheries management, many stocks of Atlantic cod in its southern range are in a depleted state and mortality estimates remain high. Recovery of these stocks, as defined by management areas, could be confounded by cod distributions shifting outside of these areas. Here, we assess data from internationally coordinated trawl surveys to investigate the distribution of three cod stocks in the Celtic Seas ecoregion, Irish Sea, Celtic Sea, and West of Scotland, from 1985 to 2021. We mapped cod densities, analyzed trends in mean weighted depth and bottom temperature, and calculated the center of gravity and equivalent area of the stocks. The distribution of the West of Scotland stock shifted north and east, spilling into the North Sea, while the Irish Sea and Celtic Sea stocks shifted west. Each stock showed decreasing trends in equivalent area, but there were no clear trends in the average depth occupied by the fish. There was no apparent relationship between temperature and the distribution of cod, as bottom temperature varied little from 1993 to 2021. Although Irish Sea cod showed a shift into warmer water, this was due to changes in survey distribution. The shift in distribution of the West of Scotland cod stock towards the North Sea whilst impairing local recovery provides further justification for the recent definition of its incorporation into a larger stock unit that includes the northwest of the North Sea. The Irish Sea and Celtic Sea cod stocks are neither shifting northwards, nor into deeper waters, but remained within current boundaries. This suggests that recent temperature conditions did not affect their distribution, but this may change as temperatures increase towards the limit for reproduction. [ABSTRACT FROM AUTHOR]

Globally, aging offshore oil and gas (O&G) platforms face resource depletion, and regulations often demand platform removal through decommissioning. In the North Sea, >€90 billion will be needed for decommissioning by 2060. However, the influence of O&G platforms on fish communities is poorly understood. This challenges predictions of possible fisheries scenarios associated with different decommissioning options. Here, we examined the role that North Sea platforms played on fish communities. We explored patterns of fish abundance and body size variation along transects from O&G platforms comparing catch per unit effort data. Fish abundance was positively associated with O&G platforms. Atlantic cod, plaice, saithe, and mackerel were most abundant near platforms. Similarly, larger Atlantic cod were near the O&G platforms. Our study provided information for decision‐making regarding platform decommissioning scenarios by evidencing O&G platform habitat provisioning for various commercial fish species. [ABSTRACT FROM AUTHOR]

During recent years, there has been a renewed interest in establishing farming of Atlantic cod (Gadus morhua) in Norway. However, a fatal abdominal disorder compromises animal welfare and causes economic losses. A similar problem was present during a previous attempt to establish Atlantic cod farming more than a decade ago. In this paper, we provide the first in‐depth description of this intestinal disorder, which is correctly denoted 'strangulating obstruction'. In affected fish, part of the intestine is permanently entrapped (incarcerated) under fibrous strands in the mesentery. The entrapment interferes with blood flow and physically blocks the intestine, causing a strangulating obstruction with severe venous congestion and ischemia of the intestinal wall. Furthermore, comparison of macroscopical and histological anatomy of farmed and wild Atlantic cod is presented and risk factors associated with the anatomical differences are discussed. [ABSTRACT FROM AUTHOR]

Many coastal ecosystems are impacted by human pressures. Rocky reefs are structurally complex habitats that often support elevated fish abundance and marine biodiversity. In the Baltic Sea, rocky reefs have suffered from extraction for decades, leading to a decrease in hard substrata and complex habitat availability.This study is the first to restore cobble reefs and examine the biological effects.Baited and unbaited underwater video systems (BRUVS and UBRUVS, respectively) were employed across five years to monitor fish communities before reef deployment in 2017 and after reef deployment in 2018 and 2021.Using a before–after control‐impact (BACI) study design with replicates, relative abundances of Atlantic cod (Gadus morhua), herring (Clupeidae sp.), goldsinny wrasse (Ctenolabrus rupestris), two‐spotted goby (Pomatoschistus flavescens), shore crab (Carcinus maenas), and flatfish (Pleuronectiformes spp.) were compared across time and test sites. Comparisons were conducted across 1) restored cobble reefs, 2) natural cobble reefs, and 3) sand‐bottom test sites.This study found positive reef restoration effects revealed consistently by BRUVS and UBRUVS in three species: Atlantic cod, goldsinny wrasse and two‐spotted goby. These findings indicate that A) it is possible to restore cobble reefs and the associated mobile fauna, but also that B) continued marine extraction of cobble degrades complex habitats to the detriment of various marine species.To preserve Atlantic cod, and other sensitive species, we emphasize ecosystem restoration and warn against marine cobble reef extraction in vulnerable areas. Restoration of marine habitats may contribute to achieving the UN sustainable development goal covering life below water. [ABSTRACT FROM AUTHOR]

Nitrogen isotope analyses of amino acids (δ15N‐AA) are being increasingly used to decipher trophic dynamics. Interpretation of δ15N‐AA in consumers relies on the assumption that consumer physiological status and nutritional status of prey have negligible influences on the trophic discrimination factor (TDF), hence a constant TDF value is used in trophic position (TP) equations. Recent experiments have shown that this is not always the case and there is also a need to validate derived TP estimates in the field. We take advantage of the uniquely long time series of environmental monitoring data and archived (frozen) samples from the species‐poor Baltic Sea. We analyzed δ15N‐AA in similar sized individuals of cod and in its prey herring from four decades, 1980–2018; including time periods where dramatic reduction in condition status of cod has occurred. We expected that TDF in trophic AAs would increase during periods of poor cod condition, resulting in inflated TP estimates. We found that calculated TP and empirical estimates of TDF (difference in δ15N in trophic AAs between cod and herring) for cod increased in recent decades and that this was linked to condition status, herring (prey) lipid content and the hypoxic state of the ecosystem. Statistically adjusting TP for condition and prey lipid content as well as environmental stress (hypoxia) resulted in lower cod TP which better resembled the observed decrease in herring TP in recent decades. TP calculated from stomach analysis data in cod individuals over the same period showed no trend over time and confirmed that adjusted TP estimates mirror the real dietary TP better than unadjusted. By simultaneously measuring condition/nutritional status in both predator and prey it is possible to adjust for them as confounding variables and decipher actual consumer TP, partly overcoming the issues of unknown and variable TDF‐values. Our study also highlights the importance of including environmental stressors (here hypoxia) when interpreting TP and reconstructing food webs. [ABSTRACT FROM AUTHOR]

Rationale Methods Results Conclusion Increasing demand for fish and seafood means that the traceability of marine products is becoming ever more important for consumers, producers and regulators. Highly complex and globalised supply networks create challenges for verifying a stated catch region. Atlantic cod is one of the most commercially important species in the northeast Atlantic. Several regional fisheries supply cod into the trade network, of which some are at greater risk of overexploitation than others. Tools allowing retrospective testing of spatial origin would significantly assist sustainable harvesting of fish, reducing incentives for illegal fishing and fraud.Here, we investigate whether stable isotope ratios of carbon, nitrogen and sulphur can be used to retrospectively identify the catch region of Atlantic cod (Gadus morhua). We measured the isotopic composition of muscle tissue from 377 cod from 10 catch regions across the northeast Atlantic and then applied three different assignment methods to classify cod by region of most likely origin. The assignment method developed was subsequently tested using independently sourced, known‐origin samples.Individual cod could be traced back to their true origin with an average assignment accuracy of 70–79% and over 90% accuracy for certain regions. Assignment success rates comparable to those using genetic techniques were achieved when assigning among restricted and pre‐selected regions. However, assignment accuracy to the fishery region estimated from independent samples across the whole geographic range of cod averaged ~25% overall, highlighting the need for careful application of isotope‐based approaches.Stable isotope techniques can provide effective tools to test for origin in Atlantic cod, but not all catch regions are isotopically distinct. Stable isotopes could be combined with genetic techniques to result in higher assignment accuracy than could be achieved using either method independently. Assignment potential can be estimated from reference datasets, but estimates of realistic assignment accuracy require independently collected data. [ABSTRACT FROM AUTHOR]

Many management and conservation contexts can benefit from understanding relationships between species abundances, which can be used to improve predictions of species occurrence and abundance.We present conditional prediction as a tool to capture information about species abundances via residual covariance between species. From a fitted joint species distribution model, this framework produces a species coefficient matrix that contains relationships between species abundances. The species coefficients allow co‐observed species to be treated as a second set of predictors supplementing covariates in the model to improve prediction. We use simulations to demonstrate the potential benefits and limitations of conditional prediction across data types and species covariance before applying conditional prediction to two management contexts with real data.Simulations demonstrate that conditional prediction provides the largest benefits to continuous data and when there is residual covariance between many species.In our first application, we show that conditioning on other species improves in‐sample and out‐of‐sample predictions of fish and invertebrate species, including Atlantic cod. In our second application, we show that the species coefficient matrix can be used to identify bird species at risk of nest parasitism by Brown‐headed Cowbirds.Synthesis and applications. We present guidelines for using conditional prediction, which can help understand relationships between species abundances, improve predictions and inform conservation in a variety of contexts. [ABSTRACT FROM AUTHOR]

Seagrass meadows provide an important nursery and feeding habitat for fish, globally. However, limited data exist on how these vegetated coastal ecosystems affect local fish stocks over longer time periods. By means of beach seine hauling with a bio‐monitoring seine net, we collected fish data in Kronborg Bay (Denmark) over 4 years. The bay contains both vegetated and bare sediment areas in close proximity to Kronborg Castle in Elsinore and is part of the Øresund strait; a dynamic marine environment linking the Baltic Sea with the inner Danish waters (Kattegat). We investigated the biodiversity and fish abundance in a healthy seagrass meadow and compared it with a bare adjacent sediment area. We show that seagrass is important for fish species like the Atlantic cod, the two‐spotted goby, and the broadnosed pipefish. The seagrass meadow harboured more fish species and higher biodiversity, while the number of individuals was higher in the adjacent bare sediment area as a result of high abundances of lesser sand eel. Pilou's evenness and the Shannon‐Wiener index showed 2–4‐fold higher biodiversity in the seagrass meadow. The seagrass meadow harboured about 35% more fish species than the bare adjacent sediment. The Atlantic cod was almost entirely found in the seagrass meadow, while lesser sand eel that showed an overall increase in abundance in both habitats, represented the largest proportion of the total number of fish individuals (up to about 60%) and was mostly found on the bare adjacent sediment. Species abundance was analysed for changes over time, where, for example the European plaice showed an increase in abundance over the 4‐year period of investigation. Seagrass meadows can thus be very important for the Atlantic cod population in the Øresund strait and generally for local fish productivity, abundance and diversity. [ABSTRACT FROM AUTHOR]

Seasonal migrations of marine fish between shallow summer feeding habitats and deep overwintering grounds are driven by fluctuations in the biotic and abiotic environment as well as by changes in the internal state. Ontogenetic shifts in physiology and metabolism affect the response to environmental drivers and may lead to changes in migration timing and propensity. In this study, we investigated the effect of temperature and body size on migration timing and depth distribution in acoustically tagged Atlantic cod, Gadus morhua, and saithe, Pollachius virens, during the period of seasonal migration from shallow summer habitats. The results from our study revealed a wide range of horizontal and vertical distribution of age 1 and 2 G. morhua within the fjord. Larger G. morhua inhabited deeper, cooler waters than smaller juveniles, likely reflecting size‐dependent thermal preferences and predation pressure. Conversely, juvenile P. virens occupied primarily shallow waters close to land. The variation in depth distribution of G. morhua was mainly explained by body size and not, against our predictions, by water temperature. Conversely, the dispersal from the in‐fjord habitats occurred when water temperatures were high, suggesting that seasonal temperature fluctuations can trigger the migration timing of P. virens and larger G. morhua from summer habitats. Partial migration of small juvenile G. morhua from in‐fjord foraging grounds, likely influenced by individual body condition, suggested seasonal migration as a flexible strategy that individuals may use to reduce predation and energetic expenditure. Predation mortality rates of tagged juveniles were higher than previously suggested and are the first robust predation mortality rates for juvenile G. morhua and P. virens estimated based on acoustic transmitters with acidity sensors. The results have relevance for climate‐informed marine spatial planning as under the scenario of increasing ocean temperatures, increasing summer temperatures may reduce the juveniles' resource utilization in the shallow summer nurseries, resulting in lower growth rates, increased predation pressure, and lower chances of juvenile winter survival. [ABSTRACT FROM AUTHOR]

Benchtop diffusion nuclear magnetic resonance (NMR) spectroscopy was used to perform quantitative monitoring of enzymatic hydrolysis. The study aimed to test the feasibility of the technology to characterize enzymatic hydrolysis processes in real time. Diffusion ordered spectroscopy (DOSY) was used to measure the signal intensity and apparent self‐diffusion constant of solubilized protein in hydrolysate. The NMR technique was tested on an enzymatic hydrolysis reaction of red cod, a lean white fish, by the endopeptidase alcalase at 50°C. Hydrolysate samples were manually transferred from the reaction vessel to the NMR equipment. Measurement time was approximately 3 min per time point. The signal intensity from the DOSY experiment was used to measure protein concentration and the apparent self‐diffusion constant was converted into an average molecular weight and an estimated degree of hydrolysis. These values were plotted as a function of time and both the rate of solubilization and the rate of protein breakdown could be calculated. In addition to being rapid and noninvasive, DOSY using benchtop NMR spectroscopy has an advantage compared with other enzymatic hydrolysis characterization methods as it gives a direct measure of average protein size; many functional properties of proteins are strongly influenced by protein size. Therefore, a method to give protein concentration and average size in real time will allow operators to more tightly control production from enzymatic hydrolysis. Although only one type of material was tested, it is anticipated that the method should be applicable to a broad variety of enzymatic hydrolysis feedstocks. [ABSTRACT FROM AUTHOR]

Lumpfish (Cyclopterus lumpus) mortalities have been reported during the summer at some North Atlantic salmon cage‐sites where they serve as "cleaner fish." To better understand this species' physiology and whether limitations in their metabolic capacity and thermal tolerance can explain this phenomenon, we compared the aerobic scope (AS) of 6°C‐acclimated lumpfish (~50 g and 8.8 cm in length at the beginning of experiments) when all individuals (N = 12) were given a chase to exhaustion, a critical swim speed (Ucrit) test, and a critical thermal maximum (CTMax) test (rate of warming 2°C h−1). The Ucrit and CTMax of the lumpfish were 2.36 ± 0.08 body lengths per second and 20.6 ± 0.3°C. The AS of lumpfish was higher during the Ucrit test (206.4 ± 8.5 mg O2 kg−1 h−1) versus that measured in either the CTMax test or after the chase to exhaustion (141.0 ± 15.0 and 124.7 ± 15.5 mg O2 kg−1 h−1, respectively). Maximum metabolic rate (MMR), AS, and "realistic" AS (ASR) measured using the three different protocols were not significantly correlated, indicating that measurements of metabolic capacity using one of these methods cannot be used to estimate values that would be obtained using another method. Additional findings include that (1) the lumpfish's metabolic capacity is comparable to that of Atlantic cod, suggesting that they are not as "sluggish" as previously suggested in the literature, and (2) their CTMax (20.6°C when acclimated to 6°C), in combination with their recently determined ITMax (20.6°C when acclimated to 10°C), indicates that high sea‐cage temperatures are unlikely to be the primary cause of lumpfish mortalities at salmon sea‐cages during the summer. [ABSTRACT FROM AUTHOR]

Increasing ocean temperature will speed up physiological rates of ectotherms. In fish, this is suggested to cause earlier spawning due to faster oocyte growth rates. Over time, this could cause spawning time to become decoupled from the timing of offspring food resources, a phenomenon referred to as trophic asynchrony. We used biological data, including body length, age, and gonad developmental stages collected from >125,000 individual Northeast Arctic cod (Gadus morhua) sampled between 59 and 73° N in 1980–2019. Combined with experimental data on oocyte growth rates, our analyses show that cod spawned progressively earlier by about a week per decade, partly due to ocean warming. It also appears that spawning time varied by more than 40 days, depending on year and spawning location. The significant plasticity in spawning time seems to be fine‐tuned to the local phytoplankton spring bloom phenology. This ability to partly overcome thermal drivers and thus modulate spawning time could allow individuals to maximize fitness by closely tracking local environmental conditions important for offspring survival. Our finding highlights a new dimension for trophic match–mismatch and should be an important consideration in models used to predict phenology dynamics in a warmer climate. [ABSTRACT FROM AUTHOR]

Aquaculture provides an important and expanding source of protein rich and healthy food to the world. However, to minimize environmental harm from aquaculture, interactions with wild fish communities need to be thoroughly assessed. Here, we characterize the existing knowledge pertaining to such interactions, exemplified with Atlantic salmon (Salmo salar) farming in open net pens along the Norwegian coast and potential consequences for wild Atlantic cod (Gadus morhua) populations. Importantly, the wild cod fishery also provides a protein rich, high quality food source with high economic value. We identify seven risk sources that may affect behaviour, physiology, and survival in wild cod. Of particular importance is the large amount of waste feed that causes wild fish to aggregate around farms, thereby altering a multitude of ecological interactions including predation and disease transmission. Moreover, altered food quality in pellets may alter physiological processes and cause mortality to vulnerable life‐stages in wild cod. More research is needed on mechanisms and thresholds for harm. As the most important cod fisheries are found in northern Norway, where climate change also is rapid, we expect stronger and potentially more harmful interactions between fish farming and wild cod fisheries as aquaculture continues to expand. We hope that our analysis will inspire further research, on farmed salmon and wild cod interactions, but also on aquaculture and wild fish interactions in general. Such research is fundamental for the development of management systems that can reduce the impact of aquaculture on fisheries and the environment. [ABSTRACT FROM AUTHOR]

Adaptation enables natural populations to survive in a changing environment. Understanding the mechanics of adaptation is therefore crucial for learning about the evolution and ecology of natural populations. We focus on the impact of random sweepstakes on selection in highly fecund haploid and diploid populations partitioned into two genetic types, with one type conferring selective advantage. For the diploid populations, we incorporate various dominance mechanisms. We assume that the populations may experience recurrent bottlenecks. In random sweepstakes, the distribution of individual recruitment success is highly skewed, resulting in a huge variance in the number of offspring contributed by the individuals present in any given generation. Using computer simulations, we investigate the joint effects of random sweepstakes, recurrent bottlenecks and dominance mechanisms on selection. In our framework, bottlenecks allow random sweepstakes to have an effect on the time to fixation, and in diploid populations, the effect of random sweepstakes depends on the dominance mechanism. We describe selective sweepstakes that are approximated by recurrent sweeps of strongly beneficial allelic types arising by mutation. We demonstrate that both types of sweepstakes reproduction may facilitate rapid adaptation (as defined based on the average time to fixation of a type conferring selective advantage conditioned on fixation of the type). However, whether random sweepstakes cause rapid adaptation depends also on their interactions with bottlenecks and dominance mechanisms. Finally, we review a case study in which a model of recurrent sweeps is shown to essentially explain population genomic data from Atlantic cod. [ABSTRACT FROM AUTHOR]

Elucidating the effects of domesticated organisms escaping into the natural environment represents a topic of importance in both evolutionary and conservation biology. However, when excluding the abundant data on salmonids, there is a lack of knowledge on this topic for marine fish aquaculture, which continues to expand globally. In order to bridge this empirical gap, we investigated a suspected escape of sexually mature domesticated Atlantic cod from a commercial marine fish farm in northern Norway. This involved genotyping samples of fish from cages on the farm, putatively identified escapees and wild cod captured in the region and samples of recently spawned eggs collected in the sea. Genetic analyses confirmed a farmed ancestry of the suspected escapees, and significantly, 27% of the sampled cod eggs. Furthermore, statistical analyses revealed a strong reduction in genetic variation in all samples of the farmed cod, including low effective population size and high degree of siblingship. These results thus document the escape of sexually mature adult cod and the release of fertilized domesticated cod eggs into the natural environment. Although it is possible that some of the mature escapees spawned post‐escape, the fact that only a single egg of potential hybrid farmed × wild origin was identified, together with the high number of mature cod in the farm, points to within cage spawning as the primary source of these eggs. This suggestion is supported by oceanic particle‐drift modelling, verifying that transport of eggs between the farm and the egg sampling locations was plausible. This study represents a rare documentation of interaction between domesticated and wild populations for a marine fish, pointing towards potential impacts on the local wild population. [ABSTRACT FROM AUTHOR]

Predator–prey interactions in time and space determine stock productivity, making them an important consideration when managing marine resources, rebuilding stocks or considering reopening a fishery.We analysed fine‐scale diet data from surveys conducted in 2009–2010 and 2018–2019 in three fjords in northern Norway with geostatistical models investigating how predation varied in space, time and between predator species. Our focus prey species was northern shrimp (Pandalus borealis), valuable both as a commercial resource and a major food source for other important species like Atlantic cod (Gadus morhua).Diet composition of fish predators differed clearly between fjords. While predator species and size were good predictors of shrimp predation, the relationships with bathymetry, prey density and geospatial variables were complex.Our study indicates that predation of forage species, such as shrimp, varies spatially in heterogenous fjord ecosystems. Shrimp consumption was not highest in the fjord with highest predator density, indicating a higher dependency of cod on shrimp in specific areas.Realized predation is a complex combination of predator and prey densities and predator ecology that differed in each of the three fjords.Synthesis and applications. Ignoring spatial variations in predator–prey interactions may lead to an inaccurate perception of stock productivity, suboptimal management and possibly unsustainable management targets. We recommend spatially explicit assessment and management for fish stocks where predator–prey interactions vary substantially in space, such as fjords and reefs. [ABSTRACT FROM AUTHOR]

Ample evidence has indicated shifts in distribution of fish populations in response to environmental stress. However, most studies focused at the whole population scale. This neglects the spatial dynamics between groups of different body size (body size groups), that fundamentally shapes the spatial structure of a population. Here, we explored the mechanisms that modulate spatial dynamics of body size groups, and applied our analyses to three North Sea fish populations which experienced severe declines in biomass from 1977 to 2019: Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus and whiting Merlangius merlangius. All three populations exhibited strong declines in the overlapped area between body size groups in winter over 43 years, yet their mechanisms differed. These declines were either due to 1) different magnitudes of contraction of the distribution area of body size groups; and/or 2) different speeds and directions of spatial shift among various body size groups, both increasing spatial segregation within populations. These patterns were either associated with ocean warming, and/or declining population biomass, and such associations often varied according to distinct body size groups. Increasing spatial segregation between size groups of a population likely hampers life‐cycle connectivity and stability to local perturbations. Our analytical approach provides a powerful tool for identifying vulnerable populations under environmental stress and can be generalized to study a variety of size/age structured populations at various ecosystem types. [ABSTRACT FROM AUTHOR]

Early life stages of fish are widely used for regulatory toxicity testing, and marine fish display high sensitivity to pollutant exposure. Exposure to pollutants during embryogenesis causes acute effects on embryonic development and survival, but also sub‐lethal impacts manifested as maldeveloped larvae. Acquiring time‐ and exposure‐dependent responses to pollutant exposure and other stressors in small organisms is labor intensive and often subjective. This leads to studies obtaining small sample sizes, with measurements often made infrequently during development. Automated monitoring methods can maintain consistency between measurements and allow many more measurements to be made, improving the quantity and quality of such data. We exposed Atlantic cod embryos to 3,4‐dichloroaniline, a reference chemical widely used as a positive control agent in regulatory fish embryo toxicity testing. We monitored their growth through daily imaging with an automated flow‐through imaging system. Biologically relevant sublethal endpoints were estimated from these images with a neural network and traditional machine vision methods. We demonstrate the automated capture and analysis of tens of thousands of images, producing detailed morphometric data from hundreds of fish over a 10‐d study period, and assess the effectiveness of the automated system. The automated method presented allows measurements to be made frequently without sacrificing the sampled organisms, making detailed time series of development obtainable. We show dose‐dependent effects of the toxicant on development and capture nonlinear responses that would not be attainable under a conventional manual sampling regime. [ABSTRACT FROM AUTHOR]

The absence of functional top predators has been proposed as a mechanism acting to shape fish assemblages in temperate marine ecosystems, with cascading effects on lower trophic levels. We explore this scenario by comparing the trophic and functional status of fish assemblages in Norwegian marine national parks, open to fishing, to a nearby coastal seascape that harbors a system of marine protected areas (MPAs) including a no‐take zone. Demersal fish assemblages were sampled using fyke nets over three consecutive seasons. Atlantic cod (Gadus morhua) is potentially a dominant top predator in this ecosystem, and historically, this and other gadids have been targeted by the full range of former and present fisheries. In the present study, we find that average body size of the Atlantic cod was significantly larger in the zoned seascape compared to the unprotected areas (mean ± SD: 36.6 cm ± 14.38 vs. 23.4 ± 7.50; p <.001) and that the unprotected seascape was characterized by a higher abundance of mesopredator fish species. These observations are consistent with the hypothesis that the protection of top predators within MPAs aids to control the mesopredator populations and provides empirical support to the notion that the present state of many coastal fish assemblages is driven by mesopredator release linked to functional depletion of large top predators. [ABSTRACT FROM AUTHOR]

Foraging is a behavioural process and, therefore, individual behaviour and diet are theorized to covary. However, few comparisons of individual behaviour type and diet exist in the wild.We tested whether behaviour type and diet covary in a protected population of Atlantic cod, Gadus morhua.Working in a no‐take marine reserve, we could collect data on natural behavioural variation and diet choice with minimal anthropogenic disturbance. We inferred behaviour using acoustic telemetry and diet from stable isotope compositions (expressed as δ13C and δ15N values). We further investigated whether behaviour and diet could have survival costs.We found cod with shorter diel vertical migration distances fed at higher trophic levels. Cod δ13C and δ15N values scaled positively with body size. Neither behaviour nor diet predicted survival, indicating phenotypic diversity is maintained without survival costs for cod in a protected ecosystem.The links between diet and diel vertical migration highlight that future work is needed to understand whether the shifts in this behaviour during environmental change (e.g. fishing or climate), could lead to trophic cascades. [ABSTRACT FROM AUTHOR]

In the North Sea and North Atlantic coastal areas, fish experience relatively high background levels of persistent organic pollutants. This study aimed to compare the mode of action of environmentally relevant concentrations of mixtures of halogenated compounds in Atlantic cod. Juvenile male cod with mean weight of 840 g were exposed by gavage to dietary mixtures of chlorinated (PCBs, DDT analogs, chlordane, lindane, and toxaphene), brominated (PBDEs), and fluorinated (PFOS) compounds for 4 weeks. One group received a combined mixture of all three compound groups. The results showed that the accumulated levels of chemicals in cod liver after 4 weeks of exposure reflected concentrations found in wild fish in this region. Pathway analysis revealed that the treatment effects by each of the three groups of chemicals (chlorinated, brominated, and fluorinated) converged on activation of the unfolded protein response (UPR). Upstream regulator analysis predicted that almost all the key transcription factors (XBP1, ERN1, ATF4, EIF2AK3, and NFE2L2) regulating the UPR were significantly activated. No additive effect was observed in cod co‐treated with all three compound groups. In conclusion, the genome‐wide transcriptomic study suggests that the UPR pathway is a sensitive common target of halogenated organic environmental pollutants in fish. Juvenile Atlantic cod (mean weight of 840 g) were exposed by gavage to environmentally realistic dietary concentrations of chlorinated, brominated, and fluorinated chemical mixtures. After 1 month of dietary exposure, the accumulated levels of the studied chemicals in cod liver reflected concentrations reported in wild fish from the North Atlantic. Transcriptomic analysis showed that all three types of chemicals most strongly affected the unfolded protein response (UPR). The study suggests that the UPR pathway is a sensitive target of halogenated compounds in fish liver. [ABSTRACT FROM AUTHOR]

Understanding individual growth in commercially exploited fish populations is key to successful stock assessment and informed ecosystem‐based fisheries management. Traditionally, growth rates in marine fish are estimated using otolith age‐readings in combination with age‐length relationships from field samples, or tag‐recapture field experiments. However, for some species, otolith‐based approaches have been proven unreliable and tag‐recapture experiments suffer from high working effort and costs as well as low recapture rates. An important alternative approach for estimating fish growth is represented by bioenergetic modelling which in addition to pure growth estimation can provide valuable insights into the processes leading to temporal growth changes resulting from environmental and related behavioural changes. We here developed an individual‐based bioenergetic model for Western Baltic cod (Gadus morhua), traditionally a commercially important fish species that however collapsed recently and likely suffers from climate change effects. Western Baltic cod is an ideal case study for bioenergetic modelling because of recently gained in‐situ process knowledge on spatial distribution and feeding behaviour based on highly resolved data on stomachs and fish distribution. Additionally, physiological processes such as gastric evacuation, consumption, net‐conversion efficiency and metabolic rates have been well studied for cod in laboratory experiments. Our model reliably reproduced seasonal growth patterns observed in the field. Importantly, our bioenergetic modelling approach implementing depth‐use patterns and food intake allowed us to explain the potentially detrimental effect summer heat periods have on the growth of Western Baltic cod that likely will increasingly occur in the future. Hence, our model simulations highlighted a potential mechanism on how warming due to climate change affects the growth of a key species that may apply for similar environments elsewhere. [ABSTRACT FROM AUTHOR]

Mass mortality (MM) events affecting early life stages of fish can have strong and long‐term consequences for population abundance and demography as well as the economic activity supported by exploited stocks. Adaptive fishery management may help mitigate economic impacts and ensure sustainable resource use following a MM event.Using a state‐space life cycle model, we simulated 'what‐if' scenarios of MM on Northeast Arctic cod (Gadus morhua) eggs and larvae. We compared the expected catches, total stock biomass (TSB), and interannual variability in catches over a period of 10 years after the simulated disturbance. We further evaluated a range of management mitigation strategies, namely reductions in fishing mortality of varying duration (1–10 years) and intensity (no fishing reduction to full ban).A large range of reductions in fishing led to an increase in expected catches over 10 years compared to no reductions, especially when applied immediately after the perturbation and when the cod population was characterized by a high mean age and high TSB. Severe fishing reductions can increase catches substantially but are associated with high interannual variability. Fishing reductions of moderate intensity applied between 1 and 4 years would allow to increase catches with only a slight increase in interannual variability.Our findings demonstrate the potential benefits of an adaptive approach to fisheries management and highlight that mitigation actions may ensure the sustainable exploitation of fish stocks in the wake of unexpected disturbances.Synthesis and application. Mass mortality events during early life stages of fish can potentially have substantial and long‐term effects on the population. Mitigation is more efficient when the affected population has a diverse age structure and when the mitigation strategy is applied immediately after the perturbation. Severe reduction in fishing mortality is an efficient measure to increase the expected average catch but is associated with high interannual variability. Fishing reduction of moderate intensity applied during 1–4 years after the event also increases the expected average catch with only slightly higher interannual variability in catches. [ABSTRACT FROM AUTHOR]

Movement diversity within species represent an important but often neglected, component of biodiversity that affects ecological and genetic interactions, as well as the productivity of exploited systems.By combining individual tracking data from acoustic telemetry with novel genetic analyses, we describe the movement diversity of two Atlantic cod Gadus morhua ecotypes in two high‐latitude fjord systems: the highly migratory Northeast Arctic cod (NEA cod) that supports the largest cod fishery in the world, and the more sedentary Norwegian coastal cod, which is currently in a depleted state.As predicted, coastal cod displayed a higher level of fjord residency than NEA cod. Of the cod tagged during the spawning season, NEA cod left the fjords permanently to a greater extent and earlier compared to coastal cod, which to a greater extent remained resident and left the fjords temporarily. Despite this overall pattern, horizontal movements atypical for the ecotypes were common with some NEA cod remaining within the fjords year‐round and some coastal cod displaying a low fjord fidelity. Fjord residency and exit timing also differed with spawning status and body size, with spawning cod and large individuals tagged during the feeding season more prone to leave the fjords and earlier than non‐spawning and smaller individuals.While our results confirm a lower fjord dependency for NEA cod, they highlight a movement diversity within each ecotype and sympatric residency between ecotypes, previously undetected by population‐level monitoring. This new knowledge is relevant for the management, which should base their fisheries advice for these interacting ecotypes on their habitat use and seasonal movements. [ABSTRACT FROM AUTHOR]

Investigating the effects of underwater noise on aquatic animals is a research field that is receiving rapidly increasing attention. Despite this, surprisingly few studies have addressed the potential impacts of noise in a marine animal husbandry setting. In this regard, the behaviour of fish in public aquariums can be used as an indicator of well‐being, and noise is known to cause behavioural changes. This case study investigates the behaviour of cod (Gadus morhua) and saithe (Pollachius virens) in a large public aquarium when exposed to increased noise levels originating from an aquarium renovation carried out by construction divers. Swimming behaviour, group formation and vertical distribution, along with yawning and scratching frequencies of the fish, were analysed from video recordings made before, during and after the exposure to increased noise levels. The same parameters were also analysed to evaluate potential effects of the presence of divers when not making renovation noise, compared to fish behaviour prior to the renovation. There was a slight change in the depth distribution of both species and a decrease in the number of scratches in cod due to the presence of divers that were not making renovation noise. In the presence of construction noises in the tank, however, both cod and saithe showed a wider array of behavioural changes, including increased swimming speed, changes in depth distribution and increased yawning frequencies. The results from this case study demonstrate that an underwater renovation with increased noise levels impacts fish behaviour and suggests that underwater noise should be considered during the management of aquatic environments, including public aquaria. [ABSTRACT FROM AUTHOR]

Climate change has a profound impact on species distribution and abundance globally, as well as local diversity, which affects ecosystem functioning. In particular, changes in population distribution and abundance may lead to changes in trophic interactions. Although species can often shift their spatial distribution when suitable habitats are available, it has been suggested that predator presence can be a constraint on climate‐related distribution shifts. We test this using two well‐studied and data‐rich marine environments. Focusing on a pair of sympatric fishes, Atlantic haddock Melanogrammus aeglefinus and cod Gadus morhua, we study the effect of the presence and abundance of the latter on the former distribution. We found that the distribution of cod and increased abundance may limit the expansion of haddock to new areas and could consequently buffer ecosystem changes due to climate change. Though marine species may track the rate and direction of climate shifts, our results demonstrate that the presence of predators may limit their expansion to thermally suitable habitats. By integrating climatic and ecological data at scales that can resolve predator–prey relationships, this analysis demonstrates the usefulness of considering trophic interactions to gain a more comprehensive understanding and to mitigate the effects of climate change on species distributions. [ABSTRACT FROM AUTHOR]

BACKGROUND: Species adulteration has been widely revealed around the world, and the possible reasons include declining stocks in most source areas of the world, poor transparency in the global supply chain, and difficulty in distinguishing the features of processed products. The present work selected Atlantic cod (Gadus morhua) as a case study, and developed a novel loop‐mediated isothermal amplification (LAMP) assay for Atlantic cod authentication, where a self‐quenched primer and a newly designed reaction vessel were used to realize the endpoint visual detection of the target‐specific products. RESULTS: A novel LAMP primer set was designed for Atlantic cod, and the inner primer BIP was selected to label the self‐quenched fluorogenic element. The fluorophore's dequenching only occurred along with LAMP elongation for the target species. No fluorescence could be observed with both single‐stranded DNA and partially complementary dsDNA of the non‐target species. With the novel reaction vessel, both amplification as well as detection were operated in an enclosed device, and visual differentiation of Atlantic cod, negative control, and false positive generated from primer dimers was achieved. The novel assay has proved its specificity and applicability, and could detect as little as 1 pg of Atlantic cod DNA. Moreover, Atlantic cod adulteration as low as 10% could be detected in haddock (Melanogrammus aeglefinus), and no cross‐reactivity was observed. CONCLUSION: The established assay could be a useful tool to detect mislabeling incidents involving Atlantic cod considering the advantages of speed, simplicity and accuracy. © 2023 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Downscaling physical forcing from global climate models is both time consuming and labor demanding and can delay or limit the physical forcing available for regional marine ecosystem modelers. Earlier studies have shown that downscaled physics is necessary for capturing the dynamics of primary production and lower trophic levels; however, it is not clear how higher trophic levels respond to the coarse resolution physics of global models. Here, we apply the Nordic and Barents Seas Atlantis ecosystem model (NoBa) to study the consequences of using physical forcing from global climate models versus using that from regional models. The study is therefore (i) a comparison between a regional model and its driving global model to investigate the extent to which a global climate model can be used for regional ecosystem predictions and (ii) a study of the impact of future climate change in the Nordic and Barents Seas. We found that few higher trophic level species were affected by using forcing from a global versus a regional model, and there was a general agreement in future biomass trends and distribution patterns. However, the slight difference in temperature between the models dramatically impacted Northeast Arctic cod (Gadus morhua), which highlights how species projection uncertainty could arise from poor physical representation of the physical forcing, in addition to uncertainty in the ecosystem model parameterization. [ABSTRACT FROM AUTHOR]

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

Range expansions can lead to increased contact of divergent populations, thus increasing the potential of hybridization events. Whether viable hybrids are produced will most likely depend on the level of genomic divergence and associated genomic incompatibilities between the different entities as well as environmental conditions. By taking advantage of historical Baltic cod (Gadus morhua) otolith samples combined with genotyping and whole genome sequencing, we here investigate the genetic impact of the increased spawning stock biomass of the eastern Baltic cod stock in the mid 1980s. The eastern Baltic cod is genetically highly differentiated from the adjacent western Baltic cod and locally adapted to the brackish environmental conditions in the deeper Eastern basins of the Baltic Sea unsuitable for its marine counterparts. Our genotyping results show an increased proportion of eastern Baltic cod in western Baltic areas (Mecklenburg Bay and Arkona Basin)—indicative of a range expansion westwards—during the peak population abundance in the 1980s. Additionally, we detect high frequencies of potential hybrids (including F1, F2 and backcrosses), verified by whole genome sequencing data for a subset of individuals. Analysis of mitochondrial genomes further indicates directional gene flow from eastern Baltic cod males to western Baltic cod females. Our findings unravel that increased overlap in distribution can promote hybridization between highly divergent populations and that the hybrids can be viable and survive under specific and favourable environmental conditions. However, the observed hybridization had seemingly no long‐lasting impact on the continuous separation and genetic differentiation between the unique Baltic cod stocks. [ABSTRACT FROM AUTHOR]

The authors assessed the importance of the round goby Neogobius melanostomus as prey for three native predatory fish species, Atlantic cod Gadus morhua, European perch Perca fluviatilis and northern pike Esox lucius, in a northern and southern area of the Baltic Proper, using a combination of visual analysis and DNA metabarcoding of predator stomach contents. To explore the influence of environmental abundances of N. melanostomus on predation, they related the occurrence of N. melanostomus in predator diets to its abundance in survey fishing. Gadus morhua and E. lucius in the southern area showed the highest tendency to feed on N. melanostomus when it was abundant, as N. melanostomus occurred in up to 100% of stomachs and constituted up to 88% of the total diet volume proportion. The diet contribution of N. melanostomus was associated with N. melanostomus abundances for G. morhua and E. lucius, and when N. melanostomus was abundant, these predators exhibited lower prey richness and a higher degree of piscivory. G. morhua and P. fluviatilis also fed less on crustacean prey when N. melanostomus was abundant. The high importance of N. melanostomus in diets of native fish predators may modify indirect interactions between N. melanostomus and native prey species in invaded coastal communities. [ABSTRACT FROM AUTHOR]

Animals show among‐individual variation in behaviors, including migration behaviors, which are often repeatable across time periods and contexts, commonly termed "personality." These behaviors can be correlated, forming a behavioral syndrome. In this study, we assessed the repeatability and correlation of different behavioral traits, i.e., boldness, exploration, and sociality, and the link to feeding migration patterns in Atlantic cod juveniles. To do so, we collected repeated measurements within two short‐term (3 days) and two long‐term (2 months) intervals of these personality traits and genotypes of the Pan I locus, which is correlated with feeding migration patterns in this species. We found high repeatabilities for exploration behavior in the short‐ and long‐term intervals, and a trend for the relationship between exploration and the Pan I locus. Boldness and sociality were only repeatable in the second short‐term interval indicating a possible development of stability over time and did not show a relation with the Pan I locus. We found no indication of behavioral syndromes among the studied traits. We were unable to identify the existence of a migration syndrome for the frontal genotype, which is the reason that the link between personality and migration remains inconclusive, but we demonstrated a possible link between exploration and the Pan I genotype. This supports the need for further research that should focus on the effect of exploration tendency and other personality traits on cod movement, including the migratory (frontal) ecotype to develop management strategies based on behavioral units, rather than treating the population as a single homogeneous stock. [ABSTRACT FROM AUTHOR]

Atlantic Cod Gadus morhua, which are overfished in the United States, are potentially vulnerable to disturbance from offshore wind energy (OWE) construction and operation during their spawning period. While many aspects of Atlantic Cod biology are well studied, little is known of their habitat use and spawning behavior at the extreme southern extent of the species' range. As Atlantic Cod form dense spawning aggregations and produce sounds associated with courtship behaviors, we used a combination of fixed-station and glider-based passive acoustic monitoring methods to evaluate the spatiotemporal spawning dynamics of Atlantic Cod in the Georges Bank stock. Additionally, we assessed potential interactions with OWE in designated offshore wind lease areas within southern New England waters of the western North Atlantic Ocean. Generalized linear modeling was used to evaluate correlations between cod grunt activity and multiple environmental cycles. Results from the southern New England spawning grounds were compared to similar data describing the geographically separated Massachusetts Bay winter-spawning subpopulation within the western Gulf of Maine stock. Temporal patterns in Atlantic Cod grunts suggest that spawning in southern New England waters is concentrated in November and December and is greatest near the new and full moons. Although there were fine-scale differences in the temporal dynamics of grunt presence between the two regions, the overall seasonality of inferred spawning was similar. Results suggest that Atlantic Cod spawning in southern New England overlaps with planned OWE construction in time and space. An understanding of cod spawning phenology in the western North Atlantic can be used to minimize disturbance to spawning through limiting construction timelines and consideration of turbine or cable placement. [ABSTRACT FROM AUTHOR]

Perceptions of past ecological change affect views of current ecosystem state, but how do baselines help to shape stakeholders' visions of an idealized future?Here, we investigate links between perceptions of natural baselines and visions for the nearshore Gulf of Maine among a key stakeholder group, active lobster fishers. We ask three related questions: (1) What do fishers perceive as a 'natural' Gulf of Maine? (2) How do perceptions of the past predict individual and collective visions of an ideal future? and (3) How is existing management perceived as supporting these visions?We found that fishers perceived the ecosystem to be 'natural' an average of one decade before they started fishing. Three species dominated views of natural systems: cod Gadus morhua, lobster Homarus americanus, and herring Clupea harengus, but while long‐time fishers associated abundant cod with a natural nearshore Gulf of Maine, memories of a historically cod‐rich Gulf of Maine were fading among some younger fishers who began their careers after the cod crash in the 1990s. Perceptions of 'natural' ecosystems dictated future visions for the majority of taxa; on average, fishers remembered and desired abundant cod and herring, but perceived halibut Hippoglossus hippoglossus and endangered right whales Eubalaena glacialis to have always been rare.Fishers described a vision for the future based on views of past ecological and social baselines, including fisheries deconsolidation and diversification, but expressed a lack of shared vision with and trust in federal management institutions to achieve these goals. In particular, memories of cod abundance in the 1970s and 1980s were coupled with memories of a diversified and accessible fishery, but fishers doubted that the recovery of cod would result in their restored access to cod fisheries.Together our results demonstrate that past personal experiences limit perceptions of what is possible, highlighting both the value and limitations of local ecological knowledge in places that have experienced ecological change over centuries. They also demonstrate how stakeholder perceptions of both social and ecological baselines shape visions for future ecosystems but are mediated by contemporary issues like trust in institutions and fisheries access. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

The reproductive success of marine ectotherms is especially vulnerable in warming oceans due to alterations in adult physiology, as well as embryonic and larval survival prospects. These vital responses may, however, differ considerably across the species' geographical distribution. Here we investigated the life history, focusing on reproductive ecology, of three spatially distant populations (stocks) of Atlantic cod (Gadus morhua, Gadidae) (50–80° N), in the Irish/Celtic Seas‐English Channel Complex, North and Barents Seas, under past and projected climate. First, experimental tracking of spawning behaviour evidenced that the ovulation cycle is highly distressed at ≥9.6 (±0.25)°C (Tup). This knife‐edge threshold resulted in erratic spawning frequencies, whereas vitellogenin sequestration remained unaffected, indicating endocrine rather than aerobic scope constraints. Cod in the Celtic Sea‐English Channel are, therefore, expected to show critical stock depensation over the next decades as spawning grounds warm above Tup, with Irish Sea cod subsequently at risk. Second, in the relatively cooler North Sea, the northward retraction of Calanus finmarchicus (Calanidae) and Para‐Pseudocalanus spp. (Clausocalanidae) (1958–2017) limit cod larvae feeding opportunities, particularly in the southernmost subarea. However, the contrasting increase in Calanus helgolandicus (Calanidae) does not counteract this negative effect, likely because cod larvae hatch ahead of its abundance peaks. Overfishing again comes as a twin effect. Third, in the still relatively cold Barents Sea, the sustainably harvested cod benefit from improved food conditions in the recent ice‐free polar region but at the energetic cost of lengthier and faster spawning migrations. Consequently, under climate change local stocks are stressed by different mechanistic factors of varying management severity. [ABSTRACT FROM AUTHOR]

Fisheries management needs to ensure that resources are exploited sustainably, and the risk of depletion is at an acceptable level. However, often uncertainty about resource dynamics exists, and data availability may differ substantially between fish stocks. This situation can be addressed through tiered systems, where tiers represent different data limitations, and tier‐specific stock assessment methods are defined, aiming for risk equivalence across tiers. As case studies, we selected stocks of European plaice, Atlantic cod and Atlantic herring, where advice is provided by the International Council for the Exploration of the Sea (ICES). We conducted a closed‐loop simulation to compare risk equivalence between the data‐rich ICES MSY rule, based on a quantitative stock assessment, and the revised data‐limited empirical management procedures of the ICES advice framework. The simulations indicated that the data‐limited approaches were precautionary and did not lead to a higher risk of depletion than the data‐rich approach. Although the catch based on generic data‐limited approaches was lower, stock‐specific optimisation improved management performance with catch levels comparable with the data‐rich approach. Furthermore, the simulation indicated the ICES MSY rule can fail to meet management objectives due to increased depletion risk when management reference points are set suboptimally. We conclude that the recent revisions of the ICES system explicitly account for risk equivalence for data‐limited fisheries management and are a major step forward. Finally, we advocate further consideration of simple empirical management procedures irrespective of data limitations due to their ability to meet fisheries management objectives with greater simplicity. [ABSTRACT FROM AUTHOR]

Large‐scale, climate‐induced synchrony in the productivity of fish populations is becoming more pronounced in the world's oceans. As synchrony increases, a population's "portfolio" of responses can be diminished, in turn reducing its resilience to strong perturbation. Here we argue that the costs and benefits of trait synchronization, such as the expression of growth rate, are context dependent. Contrary to prevailing views, synchrony among individuals could actually be beneficial for populations if growth synchrony increases during favorable conditions, and then declines under poor conditions when a broader portfolio of responses could be useful. Importantly, growth synchrony among individuals within populations has seldom been measured, despite well‐documented evidence of synchrony across populations. Here, we used century‐scale time series of annual otolith growth to test for changes in growth synchronization among individuals within multiple populations of a marine keystone species (Atlantic cod, Gadus morhua). On the basis of 74,662 annual growth increments recorded in 13,749 otoliths, we detected a rising conformity in long‐term growth rates within five northeast Atlantic cod populations in response to both favorable growth conditions and a large‐scale, multidecadal mode of climate variability similar to the East Atlantic Pattern. The within‐population synchrony was distinct from the across‐population synchrony commonly reported for large‐scale environmental drivers. Climate‐linked, among‐individual growth synchrony was also identified in other Northeast Atlantic pelagic, deep‐sea and bivalve species. We hypothesize that growth synchrony in good years and growth asynchrony in poorer years reflects adaptive trait optimization and bet hedging, respectively, that could confer an unexpected, but pervasive and stabilizing, impact on marine population productivity in response to large‐scale environmental change. [ABSTRACT FROM AUTHOR]

Stock structure is of paramount importance for sustainable management of exploited resources. In that context, genetic markers have been used for more than two decades to resolve spatial structure of marine exploited resources and to fully fathom stock dynamics and interactions. While genetic markers such as allozymes and RFLP dominated the debate in the early era of genetics, technology advances have provided scientists with new tools every decade to better assess stock discrimination and interactions (i.e. gene flow). Here, we provide a review of genetic studies performed to understand stock structure of Atlantic cod in Icelandic waters, from the early allozyme approaches to the genomic work currently carried out. We further highlight the importance of the generation of a chromosome‐anchored genome assembly together with whole‐genome population data, which drastically changed our perception of the possible management units to consider. After nearly 60 years of genetic investigation of Atlantic cod structure in Icelandic waters, genetic (and later genomic) data combined with behavioural monitoring using Data Storage Tags shifted the attention from geographical population structures to behavioural ecotypes. This review also demonstrates the need for future research to further disentangle the impact of these ecotypes (and gene flow among them) on the population structure of Atlantic cod in Icelandic waters. It also highlights the importance of whole‐genome data to unravel unexpected within‐species diversity related to chromosomal inversions and associated supergenes, which are important to consider for future development of sustainable management programmes of the species within the North Atlantic. [ABSTRACT FROM AUTHOR]

We propose a new method for estimating fish density using catches obtained by gillnets of given mesh size. This method builds on work for estimating the number of fish approaching a gillnet by modelling the fish movement that leads to a gillnet encounter. The theoretical framework is developed, and the method is tested on catch data for cod Gadus morhua and Dolly Varden Salvelinus malma to demonstrate how the method can be applied. The method relies on knowledge of geometric properties of the net, and morphological and behavioural properties of the fish, so we explore the sensitivity of the estimates to some of these parameters. Estimates are most sensitive to the morphological parameter of the angle the mouth is open while swimming and largely invariant to estimates of uncertain parameters like maximum number of fish that can be caught by the particular net. [ABSTRACT FROM AUTHOR]

Apple growers have pursued the use of exclusion netting to reduce pesticide inputs and maintain control of codling moth.It is uncertain if these nets provide a physical or behavioural behaviour, and if they prevent codling moth establishment.To address this, we conducted field trials testing the ability of commercial netting to exclude codling moth using small (3 trees) and large (48 trees) cages. Experiments were conducted to evaluate both the permeability by releasing marked sterile moths either inside or outside the small cages, and the establishment of wild codling moth in the large cages.Results from the small cage study showed that netting reduced codling moth movement out of the netted plots, but virtually prevented codling moth dispersal into the plots. Codling moth capture inside the large cage plots was significantly less than in uncaged plots, but no differences were found in codling moth damage at harvest.These results indicate that the netting is physically permeable to codling moth adults; however, it acts as a behavioural barrier to moth immigration. These outcomes agree with existing literature that net enclosures can provide a non‐insecticidal tool to improve codling moth management, although it may not be a stand‐alone technique. [ABSTRACT FROM AUTHOR]

Fish populations may spawn a vast number of offspring, while only a small and highly variable fraction of a new cohort survives long enough to enter into the fisheries as recruits. It is intuitive that the size and state of the spawning stock, the adult part of the fish population, is important for recruitment. Additionally, environmental conditions can greatly influence survival through vulnerable early life stages until recruitment. To understand what regulates recruitment, an essential part of fish population dynamics, it is thus necessary to explain the impact of fluctuations in both spawning stock and environment, including interactions. Here, we examine if the connection between the environment and recruitment is affected by the state of the spawning stock, including biomass, mean age and age diversity. Specifically, we re‐evaluate the hypothesis stating that recruitment from a spawning stock dominated by young fish and few age classes is more vulnerable to environmental fluctuations. We expand upon earlier work on the Barents Sea stock of Atlantic cod, now with data series extended in time both backwards and forwards to cover the period 1922–2019. While our findings are correlative and cannot prove a specific cause and effect mechanism, they support earlier work and strengthen the evidence for the hypothesis above. Furthermore, this study supports that advice to fisheries management should include considerations of environmental status. [ABSTRACT FROM AUTHOR]

Marine fish populations of the global oceans and particularly large‐bodied, continental shelf‐dwelling groundfish species of the North Atlantic, such as cod (Gadus morhua), have been strongly perturbed by over‐fishing, frequently beyond levels that may have altered their capacity to recover. Age and size structure, spatial structure, reproductive potential, and other traits that convey fitness advantages are commonly lost when prolonged and excessive fishing pressure is exerted. Fisheries management protocols implemented to recover collapsed populations have been numerous and varied with all attempting to reduce or eliminate fishing pressure. Such measures, employed singly or in multiple combinations, typically involve quota reductions or fishing moratoria, area closures and other technical measures, as well as enhanced enforcement of fishing practices. A striking geographic pattern exists in the efficacy of such measures to regain lost population attributes and hence recovery. Some regional populations have recovered while others, despite management interventions lasting decades, notably, but not exclusively, those aimed at cod populations of the Northwest Atlantic, have yet to fully recover, an endpoint analogous to the conclusion of the famous nursery rhyme of Humpty Dumpty. Here we examine the dynamics of multiple collapsed populations exhibiting varying responses to recovery initiatives from the perspective of the Humpty Dumpty metaphor. [ABSTRACT FROM AUTHOR]

Patterns of genetic differentiation across the genome can provide insight into selective forces driving adaptation. We used pooled whole genome sequencing, gene annotation, and environmental covariates to evaluate patterns of genomic differentiation and to investigate mechanisms responsible for divergence among proximate Pacific cod (Gadus macrocephalus) populations from the Bering Sea and Aleutian Islands and more distant Washington Coast cod. Samples were taken from eight spawning locations, three of which were replicated to estimate consistency in allele frequency estimation. A kernel smoothing moving weighted average of relative divergence (FST) identified 11 genomic islands of differentiation between the Aleutian Islands and Bering Sea samples. In some islands of differentiation, there was also elevated absolute divergence (dXY) and evidence for selection, despite proximity and potential for gene flow. Similar levels of absolute divergence (dXY) but roughly double the relative divergence (FST) were observed between the distant Bering Sea and Washington Coast samples. Islands of differentiation were much smaller than the four large inversions among Atlantic cod ecotypes. Islands of differentiation between the Bering Sea and Aleutian Island were associated with SNPs from five vision system genes, which can be associated with feeding, predator avoidance, orientation, and socialization. We hypothesize that islands of differentiation between Pacific cod from the Bering Sea and Aleutian Islands provide evidence for adaptive differentiation despite gene flow in this commercially important marine species. [ABSTRACT FROM AUTHOR]

The effects of marine reserves on the life history and demography of the protected populations are well‐established, typically increasing population density and body size. However, little is known about how marine reserves may alter the behavior of the populations that are the target of protection. In theory, marine reserves can relax selection on spatial behavioral phenotypes that were previously targeted by the fishery and also drive selection in favor of less mobile individuals. In this study, we used acoustic telemetry to monitor the individual spatial behavior of 566 Atlantic cod (Gadus morhua Linnaeus, 1758) moving within a marine reserve and a control site in southern Norway, starting 1 year before the implementation of the marine reserve and lasting up to 9 years after. Following a before‐after‐control‐impact approach, we investigated changes in (1) survival, (2) selection acting on behavioral traits, and (3) mean behavioral phenotypes, after the implementation of the marine reserve. We focused on three behavioral traits commonly used to describe the mobility of aquatic animals: home range size, depth position, and diel vertical migration range. Survival increased after reserve implementation, but contrary to our expectations, it subsequently decreased to preprotection levels after just 3 years. Further, we found no significance in selection patterns acting on any of the three behavioral traits after reserve implementation. Although some changes related to water column use (the tendency to occupy deeper waters) were observed in the marine reserve after 9 years, they cannot unequivocally be attributed to protection. Our results show that survival and behavioral responses to marine reserves in some cases may be more complex than previously anticipated and highlight the need for appropriately scaled management experiments and more integrated approaches to understand the effects of marine protected areas on harvested aquatic species. [ABSTRACT FROM AUTHOR]