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Since the first observation of snow crab (Chionoecetes opilio) in the Barents Sea in 1996, the population has increased significantly, supporting a commercial fishery on the Norwegian shelf since 2012. To investigate whether the availability of benthic prey organisms may support a continued geographical snow crab expansion, benthic invertebrate production was studied across the central parts of the Barents Sea and around Svalbard, where snow crabs are currently absent or at low densities. Annual productivity (P/B ratio) from 66 stations collected by grab and beam trawl was estimated using a multiparameter artificial neural network model. Mean infaunal productivity and production were 0.43 yr−1 and 38.4 g ww m−2 yr−1, respectively, while the epifaunal production was considerably lower with 2.5 g ww m−2 yr−1. The proportions of epi- and infaunal production suitable as prey for snow crab were 98 and 96%, respectively. Areas close to the Polar Front represent the most attractive snow crab foraging region, having the highest benthic secondary production, high estimated primary production, and bottom water temperatures within the snow crab’s preferences. At snow crab densities of 12800 ind. km−2, high enough to support commercial fishing, their mean consumption rate was estimated to be around 1.5 g ww m−2 yr−1, which amounts to 4% of mean infaunal prey production. Food availability is, therefore, not expected to be a hindrance to further population expansion of the snow crab in the Barents Sea.

The snow crab (Chionoecetes opilio) is a newly established species in the Barents Sea, increasing in both distribution and abundance in recent years. We explore the potential importance of North-east Arctic cod (Gadus morhua) predation in structuring the snow crab population expansion in the Barents Sea, through an analysis of cod stomach content data from 2003 to 2018. Spatio-temporal patterns of snow crab within cod diet are assessed across years, between seasons, as well as ontogenetic trends, including predator–prey size relationships. Snow crab represents a new prey item for cod and in recent years the most dominant demersal crustacean species in cod diet. The proportion of snow crab within cod diet increases over time. Primarily 60–110 cm cod prey upon snow crab, mainly during the summer/autumn season. Our results support the idea that the snow crab is still expanding, shifting distribution north and westwards. Cod has the potential to regulate the snow crab population but is unlikely to be in direct competition with the fishery in the Barents Sea. This work suggests that cod can be used as biological sampling tools together with other monitoring programmes to elucidate how new species may affect predator–prey and food-web dynamics within an ecosystem context.

The symposium, Shellfish—Resources and Invaders of the North, took place 5–7 November 2019 in Tromsø, Norway. Approximately 110 participants presented and discussed 60 talks and 25 posters. Of these, ten articles are published in this symposium issue. The goal of this symposium was to discuss the role of shellfish, both as harvestable resources and as important ecosystem players in northern hemisphere cold marine environments. To provide perspective for the symposium, the development of four major crustacean fisheries (northern shrimp, snow crab, Homarus, Norway lobster) are reviewed. Our review showed that landings of all these fisheries are still in a state of flux due to inherent population dynamics, fishing, and climate change. The talks and posters covered a broad range of state-of-the-art bioecological knowledge and present challenges in the assessment and management of the most ecologically and/or commercially important cold-water shellfish species belonging to the phyla Arthropoda, Mollusca, and Echinodermata. Various alternative harvesting and management techniques were presented along with perspectives for shellfish aquaculture. Methods and models for stock assessment were thoroughly covered as well as the ecological role of shellfish, their population dynamics, new insights into their biology and genetics, and their changing distribution and significance as invasive species.

Impacts of climate change on ocean productivity sustaining world fisheries are predominantly negative but vary greatly among regions. We assessed how 39 fisheries resources—ranging from data-poor to data-rich stocks—in the North East Atlantic are most likely affected under the intermediate climate emission scenario RCP4.5 towards 2050. This region is one of the most productive waters in the world but subjected to pronounced climate change, especially in the northernmost part. In this climate impact assessment, we applied a hybrid solution combining expert opinions (scorings)—supported by an extensive literature review—with mechanistic approaches, considering stocks in three different large marine ecosystems, the North, Norwegian and Barents Seas. This approach enabled calculation of the directional effect as a function of climate exposure and sensitivity attributes (life-history schedules), focusing on local stocks (conspecifics) across latitudes rather than the species in general. The resulting synopsis (50–82°N) contributes substantially to global assessments of major fisheries (FAO, The State of World Fisheries and Aquaculture, 2020), complementing related studies off northeast United States (35–45°N) (Hare et al., PLoS One, 2016, 11, e0146756) and Portugal (37–42°N) (Bueno-Pardo et al., Scientific Reports, 2021, 11, 2958). Contrary to prevailing fisheries forecasts elsewhere, we found that most assessed stocks respond positively. However, the underlying, extensive environmental clines implied that North East Atlantic stocks will develop entirely different depending upon the encountered stressors: cold-temperate stocks at the southern and Arctic stocks at the northern fringes appeared severely negatively impacted, whereas warm-temperate stocks expanding from south were found to do well along with cold-temperate stocks currently inhabiting below-optimal temperatures in the northern subregion.

Source at https://doi.org/10.1093/jcbiol/ruz039. The snow crab Chionoecetes opilio Fabricius, 1788 is a newly established species in the Barents Sea. Since the first individuals were recorded in 1996, the population has increased and a fishery was initiated in 2012. Mature female snow crab caught in the central Barents Sea were investigated with regards to fecundity. Ovigerous females (N = 185) ranged from 48 to 100 mm carapace width (CW). Fecundity was 15,000–184,000 eggs per female with 100% clutch fullness, and was positively related to body size (fecundity = 0.233 * CW2.944) consistent with relationships described for other snow crab populations. Eight females had less than 100% clutch fullness, two of which had only 10% clutch fullness along with an old shell, indicating senescence. Dry egg weight was on average 0.065 mg and was hardly affected by CW. Females across all sizes invest similarly in individual eggs, and potential size-dependent differences in fitness are more related to the number of eggs produced than to the investment into individual eggs. We conclude that the fecundity-at-size of females is overall comparable to that of other populations, although the presence of large females results in high maximum individual fecundity estimates.

Understanding the impacts of fishing on the seabed is a basic requirement for ecosystem-based marine management. It is only recently that we have begun understanding how fisheries-driven perturbations affect ecosystem function, biodiversity, productivity, and resilience. Technical solutions aimed at minimizing seabed impacts are starting to appear, but their efficacy remains to be demonstrated. In 2014, ICES held a symposium on the effects of fishing on benthic fauna, habitat, and ecosystem function, in Tromsø, Norway. The main goals of the symposium were to summarize current understanding of the physical and biological effects of fishing activities on benthic ecosystems, and to review the diversity of technical measures currently available to mitigate these effects. Here, we briefly describe the background to the scientific symposium and highlight the main contributions.

Source at https://doi.org/10.1016/j.fishres.2018.03.024. Edible crab, Cancer pagurus, is a valuable North Atlantic fishery resource distributed from Morocco to northern Norway, covering a wide range of temperatures and other oceanographic variables. Knowledge on how local environmental conditions affect life history traits like maturity and growth in this species is however lacking, despite its importance in science-based management. Through analyses of field data and fishers’ reports from different areas along the west coast of Norway (between 59°N and 69°N), latitudinal differences in size at onset of sexual maturity and molting probabilities of female C. pagurus were investigated. The size at which 50% of crabs were found to be mature (CW50) did not differ between areas and was consistent with historical investigations, i.e. overall CW50: 112.3 mm, and CW50 for each area/year between 108 and 117 mm. Generalized additive modelling was used to predict probability of molting (occurrence of soft crabs) during late summer/autumn, with ‘area’ as a categorical variable, and ‘day of year’ and crab size as continuous non-linear predictors. The predictor variables had low explanatory power (16.4% deviance explained by full model), demonstrating the complexity of the process regulating molting. However, frequency of molting decreases and peak periods of molting occur later at higher latitudes, suggesting that lower temperatures have an impeding effect on growth in northern populations. Overall, our findings suggest that current minimum legal catch sizes for crabs in Norwegian waters are sufficient to restrict the catch of immature females, but that crabs in different geographical regions appear to be variably tolerant to fishing pressure following differences in growth.

The aim of this study was to explore the effect of sex, size, region, and density on dispersal rate of the introduced red king crab (Paralithodes camtschaticus) in Norwegian waters. We examined the effect of these factors using logistic regression analysis. Tag-recapture data corrected for fishing effort enabled us to estimate dispersal rates from four main regions along the Norwegian coast: Varangerfjorden, Tanafjorden, Laksefjorden, and Porsangerfjorden. The probability of dispersal was independent of sex and size, but both the logistic regression and the evaluation of corrected tag-recapture data revealed differences in dispersal between region and with increasing duration. The recapture data indicated a relationship between population density and dispersal within research regions but not between population density and dispersal between research regions. Our main conclusion is that there are large individual differences in dispersal ability and the range expansion of red king crab is a result of (i) the presence of long-distance dispersers and (ii) time-dependent slow migration by short distance dispersers. We also conclude that there appears less dispersal in Norwegian waters than in native waters, which might be caused by differences in geographical complexity.

The introduced red king crab ( Paralithodes camtschaticus ) is abundant in the coastal waters off northern Norway. We developed Bayesian hierarchical models to estimate growth parameters of a von Bertalanffy growth function using tag–recapture data. Individual variability in L ∞ (asymptotic length) was incorporated in the analysis. The models successfully estimate female red king crab lengths at intervals where data were sufficient. The length of small males was overestimated. The results indicate a difference in growth rate of male and female juvenile red king crab. The importance of including individual variability was confirmed: Variability in L ∞ for individuals was high compared to population variability in L ∞ . The model that incorporated individual variation resulted in more plausible values for the growth parameters and increased the precision of length estimates compared to the model that estimate a common L ∞ .

Hvingel, C., Kingsley, M.C.S., and Sundet, J.H. 2012. Survey estimates of king crab (Paralithodes camtschaticus) abundance off Northern Norway using GLMs within a mixed generalized gamma-binomial model and Bayesian inference. – ICES Journal of Marine Science, 69: . A trawl survey provides information on number and biomass of introduced king crab (Paralithodes camtschaticus) to the management of a fishery off the coast of Northern Norway; the annual catch quotas are largely set as a percentage of the survey estimate. A specially built sledge trawl was designed for the survey. It needs only small areas of trawlable bottom, performs well on a wide range of bottoms, and appears to have good catchability for benthic organisms. Many survey hauls catch no crabs and the non-zero catches have a highly skewed distribution. Data were therefore analysed with a compound model, in which separate predictors were fitted for the proportion of zero catches and for the catch size of the non-zero catches. The compound model was fitted by Bayesian methods using WinBUGS. The distribution of non-zero catches fitted well to a generalized gamma distribution, but with parameter values that made it approximate a lognormal distribution. Numbers of fishable crabs peaked in 2003, and total numbers in 2010 were about two-fifths of the 2003 maximum.

The large-scale population genetic structure of northern shrimp, Pandalus borealis, was investigated over the species’ range in the North Atlantic, identifying multiple genetically distinct groups. Genetic divergence among sample localities varied among 10 microsatellite loci (range: FST = −0.0002 to 0.0475) with a highly significant average (FST = 0.0149; P

During 2006 and 2008 two bottom trawl surveys were conducted at East Greenland to 72°N covering depths down to 1500 m. In the 149 trawl hauls in total 113 fish species were recorded of which 37 were considered pelagic and excluded from the analyses. As a first step the abundance data for the 76 benthic species were used for analyses of the fish fauna diversity and fish assemblages. Nine assemblages were found by a standard type of cluster analysis. A Bayesian multinomial logit model was then applied to calculate vectors of probabilities defining the likelihood of each haul belonging to each of the nine clusters. By means of a geostatistical tool the spatial distribution of the conditional probabilities for each cluster (assemblage) was mapped. Each of the nine assemblages was further defined by indicator species, depth and temperature. The assemblages were well defined regarding geographical distribution, species composition, temperature and depth. Three of the assemblages were located in the cold Iceland Sea while six were found in the somewhat warmer Irminger Sea

A new integrated Bayesian framework for making quantitative assessments, predictions, and risk analyses of shrimp (Pandalus borealis) stock development is constructed. A biomass dynamic model, based on the logistic function but including an explicit term for cod predation, suggests that the quantity of shrimp consumed by cod could equal that taken by the fishery. The model proved superior to an alternative model in its ability to estimate parameters central to the assessment; the alternative model subsumed cod predation as part of an overall population growth effect without a time trend. Two series of shrimp biomass indices, catch, cod biomass estimates, cod consumption estimates, and prior distributions of model parameters provided information to the models. Process and observation errors were incorporated simultaneously using a state-space modelling framework. A Bayesian approach was used to construct posterior probability distributions of model parameters and derived variables relevant for management advice, including quantification of future risk of transgressing reference points in relation to alternative management options.