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Zooplankton in the Barents Sea has been monitored by the Institute of Marine Research in Norway on autumn cruises since 1986, using a standardized procedure with determination of dry weight biomass in three size fractions following splitting of the sample in two halves. Along with summer data for the early 1980s, we can now describe changes of zooplankton biomass over four decades. The biomass of the central Barents Sea has fluctuated inversely with collapses and recoveries of the Barents Sea capelin stock, which is a major planktivore. Zooplankton biomass in the central Barents Sea was low in 1983 and 1984, driven by low abundance of Calanus finmarchicus , followed by a pronounced peak in 1987 associated with a "first" collapse of the capelin stock. Biomass showed another pronounced peak in 1994, driven by the small size fraction and interpreted to reflect an advective signal from the adjacent Norwegian Sea. In the two most recent decades, there have been divergent trends, with a relatively high biomass in the inflowing Atlantic water, reflecting a second summer generation of C. finmarchicus , and decreased biomass in the central area, reflecting a lower abundance of Calanus glacialis driven by a combined effect of capelin predation and climate. [ABSTRACT FROM AUTHOR]

We compared stock origin, size- and age-distributions, and length growth rates derived from Atlantic cod otoliths from archaeological excavations at two sites in northern Norway: Vágar in Lofoten (68°12′N, ad 1156–1285) and the Værbukta site (70°57′N, ad 1450–1680). For comparison, modern otoliths were sampled during 1993–2001 from areas situated close to Vágar and Værbukta. Length-at-age from pre-20th century samples was back-calculated from otolith growth increments. The pre-20th century cod from Vágar was dominated by northeast Arctic cod (NEAC) of age 9–16 years and were much older and larger than the pre-20th century cod from Værbukta, which were dominated by coastal cod of age 2–6 years. Cod from Vágar had smaller increments and a shorter back-calculated length-at-age than modern cod from Lofoten. In contrast, the predominantly coastal cod from Værbukta had similar increments width and length-at-age as in modern samples. Age-distributions and mortality rates of the pre-20th century Vágar cod and NEAC from Lofoten in the 1930s were similar, indicating that both age at maturity and longevity were similar for these time periods. This contrasts with truncated and young age-distributions of spawning NEAC in the 1980s and 1990s following the strong increase in fishing and total mortality rate in the period 1955–2000. [ABSTRACT FROM AUTHOR]

Our research focused on the analysis of interannual variability of zooplankton in the Kola Section (the Barents Sea) in the period of current warming in the Arctic basing on previously unpublished data. The zooplankton community was investigated based on the analysis of 240 plankton samples, collected in late May–early June 2009–2017. A total of 74 zooplankton taxa of nine phyla were identified in the plankton samples, but copepods were the most diverse and numerous taxonomic group. The biodiversity index varied considerably from year to year, but a stable tendency for the index to increase since the beginning of the period studied was observed. Copepods dominated in terms of abundance and biomass, comprising on average 73–96% of the total zooplankton abundance and 81–96% of the total zooplankton biomass. Calanus finmarchicus was the main zooplankton species utterly dominated by abundance and biomass (on average 92 and 97% respectively). Considerable differences in zooplankton abundance and biomass at different stations of the section were observed. Although the investigations were carried out during a warming period, interannual differences in zooplankton abundance and biomass were observed. Zooplankton biomasses were higher in the years with higher temperatures and stronger water inflow. [ABSTRACT FROM AUTHOR]

Marine mammals are important players in the Barents Sea ecosystem but their structural role in the foodweb has been little explored. We compare foodweb-related characteristics within and between phylogenetic groups for 19 marine mammals. As a group, they directly connect to the most central species (i.e cod and haddock) in the Barents Sea (i.e. cod and haddock) and consume over half of the available species. Pinnipeds are the most homogenous phylogenetic group with high omnivory and high prey richness. Mysticetes are split between well-connected species with high omnivory like the humpback whale, and peripheral specialists like the blue whale. Based on foodweb-derived indices some species consistently cluster together forming two groups, suggesting topological redundancy within them. One is dominated by Arctic seals and the other includes most of the baleen whales. Marine mammals generally contribute to network modularity as their trophic links are mainly within their own module. However, Atlantic species such as the grey seal act as a module connector decreasing modularity. This might negatively affect ecosystem robustness with perturbation effects spreading further and quicker in the foodweb. In the Arctic reaches of the Barents Sea, climate warming is likely to bring about extensive changes in the foodweb structure through a redistribution of species. [ABSTRACT FROM AUTHOR]

This paper discusses our research on the interannual variability in the Barents Sea thermal frontal zones. The extent of the frontal zones and their mean temperature gradients at 50 m depth in August–September 1960–2017 were estimated for an area between 73–78°N and 15–43°E, where the frontal zones are more evident. Thermal frontal zones were identified in areas where temperature gradients exceeded 0.04°C km−1. Since the beginning of this century, the extent of the frontal zones has been decreasing and temperature gradients have been weakening. From the 1960s to the 2010s, the decadal mean centroids of thermal frontal zones shifted northeastwards by 150 km. [ABSTRACT FROM AUTHOR]

Combining detailed temporal and spatial catch data, including catch per unit effort, with a high-resolution microsatellite genetic baseline facilitated the development of stock-specific coastal migration models for the four largest Atlantic salmon (Salmo salar) populations, Målselv, Alta, Tana and Kola rivers, contributing to the Barents Sea mixed-stock fishery. Målselv salmon displayed a restricted coastal movement with 85% of the fish captured within 20 km of their natal river. Kola salmon also demonstrated limited coastal movements in Norwegian waters, with most (> 90%) caught in eastern Finnmark. Multi-sea-winter (MSW) Alta salmon were caught west of Alta fjord across a broader stretch of coast while one-sea-winter (1SW) fish migrated more extensively along the coast prior to river entry. Tana salmon, however, were detected over a broad expanse (600 km) of the North-Norwegian coast. For all populations MSW salmon dominating catches earlier in the season (May–June) while 1SW fish were more common from July to August. This study provides an example of how traditional catch and effort information may be combined with genetic methods to obtain insights into spatial and temporal changes in Atlantic salmon catch composition and their associated migration patterns in a mixed-stock coastal fishery. [ABSTRACT FROM AUTHOR]

Atlantic cod (Gadus morhua) is an ecologically and commercially important species in the North-Atlantic region. Cod is a top predator and information on its trophic ecology is integral for understanding predator–prey relationships and food-web dynamics. We present an analysis of the trophic patterns of Barents Sea (BS) cod using a unique 33-year time-series of stomach-content data from 1984 to 2016. We assessed patterns in diet (prey) composition across years, between seasons, as well as ontogenetic trends in diet, including predator–prey size relationships. Ontogenetic shifts in diet were observed, with fish becoming more important prey with increasing cod size. A very early onset of piscivory was found in <20 cm cod. Cannibalism was found in cod > 20 cm and increased with size. Juvenile cod exhibit a tendency towards consuming prey up to 33% of their body length, whereas larger cod feed on all prey sizes, resulting in asymmetric predator–prey size distributions. Diet varied significantly during 1984–2016, consistent with changes in both prey, cod abundance, and distribution. Seasonal differences were observed; capelin dominated the winter diet, whereas cod, polar cod, and other fish species were prevalent in summer/autumn months. This work represents an important step towards understanding trophic linkages that determine BS ecosystem dynamics. [ABSTRACT FROM AUTHOR]

To better understand fin whale vocalization behaviour in the Norwegian and Barents Seas, a large-aperture densely sampled coherent hydrophone array was deployed in late winter 2014 to monitor their vocalizations instantaneously over wide areas via passive ocean acoustic waveguide remote sensing (POAWRS). Here, we (i) provide a time-frequency characterization for different call types observed (20 Hz pulses, 130 Hz upsweeps, 30–100 Hz downsweep chirps, and 18–19 Hz backbeats); (ii) compare their relative abundances in three different coastal regions off Alesund, Lofoten, and Northern Finnmark; (iii) estimate the temporal and spatial distributions; (iv) source level distributions; and (v) probability of detection (PoD) regions for the more abundant 20 Hz pulse and 130 Hz upsweep call types. The fin whale vocalizations received over the diel cycle (24 h) were significantly more abundant by a factor of roughly seven off Northern Finnmark than the other two regions, associated with fish feeding activities. The source levels are estimated to be 190.5 ± 7.4 dB for the fin whale 20 Hz pulses and 170.3 ± 5.2 dB for the 130 Hz upsweeps. We find that fin whales are capable of producing each vocalization type either independently or simultaneously with other types, and the 20 Hz sound production in the fin whales involves a mechanism that generates a significantly less-intense second-order harmonic of the fundamental. [ABSTRACT FROM AUTHOR]

The biogeochemistry from a global climate model (Norwegian Earth System Model) has been compared with results from a regional model (NORWECOM.E2E), where the regional model is forced by downscaled physics from the global model. The study should both be regarded as a direct comparison between a regional and its driving global model to investigate at what extent a global climate model can be used for regional studies, and a study of the future climate change in the Nordic and Barents Seas. The study concludes that the global and regional model compare well on trends, but many details are lost when a coarse resolution global model is used to assess climate impact on regional scale. The main difference between the two models is the timing of the spring bloom, and a non-exhaustive nutrient consumption in the global model in summer. The global model has a cold (in summer) and saline bias compared with climatology. This is both due to poorly resolved physical processes and oversimplified ecosystem parameterization. Through the downscaling the regional model is to some extent able to alleviate the bias in the physical fields, and the timing of the spring bloom is close to observations. The summer nutrient minimum is one month early. There is no trend in future primary production in any of the models, and the trends in modelled pH and Ω Ar are also the same in both models. The largest discrepancy in the future projection is in the development of the CO2 uptake, where the regional suggests a slightly reduced uptake in the future. [ABSTRACT FROM AUTHOR]

Copepods from the genus Calanus are crucial prey for fish, seabirds and mammals in the Nordic and Barents Sea ecosystems. The objective of this study is to determine the contribution of Calanus species to the mesozooplankton biomass in the Barents Sea. We analyse an extensive dataset of Calanus finmarchicus, Calanus glacialis, and Calanus hyperboreus, collected at various research surveys over a 30-year period. Our results show that the Calanus species are a main driver of variation in the mesozooplankton biomass in the Barents Sea, and constitutes around 80% of the total. The proportion of Calanus decreases at low zooplankton biomass, possibly due to a combination of advective processes (low C. finmarchicus in winter) and size selective foraging. Though the Calanus species co-occur in most regions, C. glacialis dominates in the Arctic water masses, while C. finmarchicus dominates in Atlantic waters. The larger C. hyperboreus has considerably lower biomass in the Barents Sea than the other Calanus species. Stages CIV and CV have the largest contribution to Calanus species biomass, whereas stages CI-CIII have an overall low impact on the biomass. In the western area of the Barents Sea, we observe indications of an ongoing borealization of the zooplankton community, with a decreasing proportion of the Arctic C. glacialis over the past 20 years. Atlantic C. finmarchicus have increased during the same period. [ABSTRACT FROM AUTHOR]

The dynamics of marine populations are usually forced by biotic and abiotic factors occurring at different intensity levels and time scales. Deriving the time frame within which each factor has a causal influence is important for predicting population trajectories. This paper presents a statistical methodology for establishing (i) the strength of causal coupling between population dynamics and environmental (biotic and abiotic) factors, and (ii) the time scales over which causal covariates have significant influence on the population dynamics. The methodology is based on combining a multivariate autoregressive model fit to data (to determine causal direction) with a quantification of the RPC of covariates in frequency domain (to quantify the strength of connection). The methodology is applied to test the existence of causal coupling between the capelin biomass and a selected number of covariates identified in the literature. [ABSTRACT FROM AUTHOR]

This study documents how settlement of juvenile Atlantic cod (Gadus morhua) in the Barents Sea affects otolith growth and morphology. A simple method to objectively discriminate between age 0 and age 1 cod sampled in late summer was demonstrated by using only two otolith morphometric descriptors: area and perimeter. In the pre-settled 0-group cod, otolith lobe formation clearly increased with fish size, resulting in high otolith crenulation. This trend was disrupted during settlement, resulting in noticeably less crenulated otoliths of the settled 1-group cod sampled in winter. Combined observations of otolith shape, fish size, and body condition suggest that environmental factors associated with settlement during autumn, particularly reduced food intake, directly affect lobe formation leading to less crenulated otoliths. Comparably reduced body condition and otolith crenulation of 0-group cod in bottom trawls (vs. pelagic trawls) may indicate early settlement or vertical exploratory behaviour in the Barents Sea Ecosystem Survey (in August-September) and, thus, an underrepresentation of 0- group cod from pelagic trawling. [ABSTRACT FROM AUTHOR]

Atlantic water (AW) carries large amounts of salt, oceanic heat, and biological richness into the Arctic Ocean. The inflow of AW has a twobranch structure via the West Spitsbergen Current (WSC) in the Fram Strait and the Barents Sea Opening (BSO), and the impact of AW on the Arctic Ocean ecosystem depends on the entrance route. Using data collected during the summers of 2001-2014, the zooplankton standing stock and community structure were studied in these two branches. Generally, there was a higher abundance and biomass of Calanus finmarchicus in the BSO than in the WSC, where Oithona spp. numerically dominated. The observed AW temperature and volume flux modifications measurably affected zooplankton variability, with additional effects likely related to diverse contributions of advected and local zooplankton production. During the study period, the AW temperature in both branches increased noticeably but in an oscillating manner. This gradual change manifested as C. finmarchicus forming an increasing proportion of the biomass. The high abundances of Oithona spp. (predominantly O. similis) and C. finmarchicus were attributed to warm AW temperature anomalies. During the warm event in 2011, predomination of young copepodids of C. finmarchicus in the WSC was observed, which represented probably the second generation of the species, reported from this region for the first time. The obtained results show the effects of warming on the zooplankton community transported with the Atlantic water, before they enter the Arctic Ocean. In practical terms, the findings can be used to construct and tune the plankton components of ecosystem models. [ABSTRACT FROM AUTHOR]

Balanced fishing proposes a considerable change to current fisheries management to increase overall biomass harvested while reducing the ecosystem impacts of large-scale fisheries. However, to date, the work to a large degree has focused on simplified models, which exclude much of the variability in real ecosystems, as well as basing harvesting rates on a perfect, but unrealistic, knowledge on stock productivity. Furthermore, the published studies have avoided examining the practicalities of implementing balanced fishing in a real world. This has resulted in a gap that remains to be overcome before balanced fishing can be considered a viable management strategy for large marine ecosystems.Wediscuss variability in recruitment, in biology and life history characteristics, in data quality, and in fishing practice and management, and their implications for implementation of balanced fishing, using examples from the Barents Sea. We try to outline the complexities that need to be investigated as a precursor tomoving balanced fishing from an academic exercise to a practical management scheme. Given the difficulties in moving to "full" balanced fishing, we highlight the importance of investigating to what extent benefits can be gained by implementing only the most achievable parts of a balanced fishing regime. [ABSTRACT FROM AUTHOR]

Sampling of euphausiids is difficult because of their intermediate size between macrozooplankton and micronekton. The Barents Sea is one of the few marine areas where there have been long-term studies of euphausiids. We have examined three monitoring datasets on euphausiids and consider likely sources of errors associated with the sampling. Results indicated a high degree of patchiness in the distribution of euphausiids, even at the largest scale of sampling with a pelagic trawl. This indicates that euphausiids may occur in large, but infrequent, swarms that have a low probability of being sampled by small nets. The mean biomass of euphausiids sampled with MOCNESS was 2 g wet weight m-2 integrated over the water column, which is an underestimate due to avoidance of large individuals. The mean biomass obtained with pelagic trawl in the upper 60 m of water at night during an autumn survey was 10 g wet weight m-2. The plankton net on bottom trawl collected mean and median density of euphausiids (0.1-0.2 g wet weight m-3) near bottom during a winter survey similar to the values found with pelagic trawl in the upper layer during autumn. The mean density for the autumn survey showed an increase from 2000 to 2011, while the winter survey showed generally a decrease from 2000-2007 to 2011. The increase in the autumn series coincided with a general warming trend presumably with a larger influx of euphausiids with Atlantic water, notably of Meganyctiphanes norvegica. In contrast, the decline during winter may reflect a decrease, particularly of Thysanoessa raschii in the southeastern Barents Sea in the most recent years. Improvements in sampling gears combined with more and better use of acoustical and optical technologies offer great promise for improved monitoring and quantification of the roles of euphausiids in the Barents Sea ecosystem. [ABSTRACT FROM AUTHOR]

Year-class strength of Barents Sea capelin has been monitored closely since the early 1970s and during this45 years period three short periods of almost total recruitment failure leading to three stock collapses have been observed. These events triggered much attention since there was a large commercial fishery for capelin, but also because of observed ecosystem effects attributed to the first of these collapse events. This attention motivated research to clarify mechanisms behind the recruitment failures, and many papers have been published regarding the causes of these events. Here, we review this literature and try to put the various investigations into context. Most of the research conducted gives evidence in favour of a hypothesis that was formulated after the first recruitment failure event in the mid-1980s that predation on capelin larvae was the main cause of recruitment failure. Most studies also support the hypothesis that young herring (Clupea harengus) was the main predator on capelin larvae, but other predators like young-of-the-year cod (Gadusmorhua) and haddock (Melanogrammus aeglefinus) probably also played a role. Investigations of the effect of predators such as haddock, red king crab (Paralithodes camtschaticus), diving birds, and capelin on the demersal capelin eggs have also been reviewed. Usually, these predators are found to consume capelin eggs, but most likely not to an extent that would affect the recruitment to a noticeable degree. It is concluded that the predation on capelin larvae is the main reason for the observed recruitment failures, although predation from the predators reviewed here can hardly be the only reason for almost total recruitment failures observed in some periods. [ABSTRACT FROM AUTHOR]

Uncovering the relationship between changes in jellyfish abundance and the biological response in the Barents Sea is crucial to understanding the potential effects of jellyfish blooms on ecosystems in general and commercially important fish stocks in particular. The data from autumn surveys (acoustic capelin survey, 0-group survey, and ecosystem survey) were used to explore the effects of jellyfish (i.e. mostly Cyanea capillata) on krill, 0-group fish (capelin, herring, cod, haddock, polar cod, and redfish), and pelagic fish stocks (older capelin, herring, bluewhiting, and lumpfish). The temporal and spatial patterns of the jellyfish, krill, and 0-group fish distributions reflected differences in the drift of these organisms with the inflow of Atlantic waters. During 1993-2013, jellyfish were present in two "waves" in the Barents Sea, namely, in the early 2000s and at the end of the studied period. In the 1990s, jellyfish were found at an average of 40% of stations, whereas in the 2000s, they were found at an average of 80% of stations. The increased occupation area led to increased overlap with other components of the pelagic community. The co-occurrence of the averaged and high concentrations of jellyfish and other studied species/groups indicated a highly productive area most likely defined by ocean currents. The results indicated a lack of robust evidence for the hypothesis that scyphozoan jellyfish limit the habitat of species in the Barents Sea during the late feeding period. However, catches of certain species appear to level off or decrease for notably high catches of jellyfish. [ABSTRACT FROM AUTHOR]

Biodiversity is an increasingly important issue for the management of marine ecosystems. However, the proliferation of biodiversity indices and difficulties associated with their interpretation have resulted in a lack of clearly defined framework for quantifying biodiversity and biodiversity changes in marine ecosystems for assessment purpose. Recent theoretical and numerical developments in biodiversity statistics have established clear algebraic relationships between most of the diversity measures commonly used, and have highlighted those that most directly relates to the concept of biological diversity, terming them "true" diversity measures. In this study, we implement the calculation of these "true" diversity measures at the scale of a large-marine ecosystem, the Barents Sea. We applied hierarchical partitioning of biodiversity to an extensive dataset encompassing 10 years of trawl-surveys for both pelagic and demersal fish community. We quantify biodiversity and biodiversity changes for these two communities across the whole continental shelf of the Barents Sea at various spatial and temporal scales, explicitly identifying areas where fish communities are stable and variable. The method is used to disentangle areas where community composition is subject to random fluctuations from areas where the fish community is drifting over time. We discuss how our results can serve as a spatio-temporal biodiversity baseline against which new biodiversity estimates, derived from sea surveys, can be evaluated. [ABSTRACT FROM AUTHOR]

Assessing the vulnerability of biological communities to anthropic pressures in marine systems may be challenging because of the difficulty to properly model each species' response to the pressure due to lack of information. One solution is to apply factor-mediated vulnerability assessment which combines (i) information on species ecological traits and conservation status organized in a matrix of so-called "vulnerability factors", (ii) a conceptual model of how these factors affect species vulnerability, and (iii) data on the spatial distribution and abundance of each species issued from at-sea surveys. Such factor-mediated vulnerability assessment was originally introduced in the seabird-wind farm context by Garthe and Hüppop (2004. Scaling possible adverse effects of marine wind farms on seabirds: developing and applying a vulnerability index. Journal of Applied Ecology, 41: 724-734) and has since then been expanded to many case studies. However, the mathematical formulations that were proposed at that time are overly simplistic and may overlook critical components of the impact assessment. Our study briefly reviews the original approach and highlights its hidden assumptions and associated interpretation problems, for example, the overestimation of disturbance pressure to the detriment of collision, or the very high contribution of log abundances in vulnerability maps. Then, we propose a revised framework that solves these issues and permits easy transposition to other community-pressure case studies. To illustrate the usefulness and generality of the revised framework, we apply it to two case studies, one concerning the vulnerability assessment of a seabird community to offshore wind farms in the Bay of Biscay, and another focusing on the vulnerability assessment of the benthic megafauna community to trawling pressure in the Barents Sea. [ABSTRACT FROM AUTHOR]

We estimate temporal variation in fecundity, the reproduction rate, for Barents Sea and Greenland Sea harp seals using a state-space approach. A stochastic process model for fecundity is integrated with an age-structured population dynamics model and fit to available data for these two harp seal populations. Owing to scarceness of data, it is necessary to "borrow strength" from the Northwest Atlantic harp seal population in form of prior distributions on autocorrelation and variance in fecundity. Comparison is made to a simpler deterministic population dynamics model. The state-space model is more flexible and is able to account for the variations in the data. For Barents Sea harp seals, the state-space model gives a higher estimate of current population size but also a much higher associated uncertainty. In the Greenland Sea, the differences between the stochastic and deterministic models are much smaller. [ABSTRACT FROM AUTHOR]

Benthos plays a significant role as substrate, refuge from predation and food for a wide variety of fish and invertebrates of all life stages and should therefore be considered in the ecosystem approach (EA) to management. Epibenthos from trawl catches, used in annual assessments of commercial fish stocks, was identified and measured on-board. The 2011 dataset present the baseline mapping for monitoring and included 354 taxa (218 to species level) analysed with multivariate statistical methods. This revealed four main megafaunal regions: southwestern (SW), banks/slopes in southeast and west (SEW), northwestern (NW), and northeastern (NE) which were significantly related to depth, temperature, salinity, and number of ice-days. The SW region was dominated by filter-feeders (sponges) in the inflow area of warm Atlantic water while the deeper trenches had a detritivorous fauna (echinoderms). In the SEW region, predators (sea stars, anemones and snow crabs) prevailed together with filtrating species (sea cucumber and bivalves) within a mosaic of banks and slopes. Plankton-feeding brittlestars were common in the NW and NE region, but with increasing snow crab population in NE. Climate change, potentially expanding trawling activity, and increasing snow and king crab populations might all have impacts on the benthos. Benthos should therefore be a part of an integrated assessment of a changing sea, and national agencies might consider adding benthic taxonomic expertise on-board scientific research vessels to identify the invertebrate “by-catch” as part of routine trawl surveys. [ABSTRACT FROM PUBLISHER]

Little is known about lumpfish (Cyclopterus lumpus) ecology, especially its distribution in the open Barents Sea. This paper describes fluctuations in abundance and biomass indices of lumpfish based on pelagic trawl catches. This long-term monitoring survey has been conducted between August and September since 1980. Investigations show that lumpfish is widely distributed in the pelagic waters of the Barents Sea. Relative biomass and abundance indices were calculated for the period 1980–2012. The mean annual biomass was estimated to be 48 000 t, with a maximum of 143 000 t; the estimated mean annual abundance was 53 million individuals, with a maximum of 132 million individuals. There were more juveniles than adults, with juveniles comprising 40–80% of the total abundance (average 60%). The largest concentrations of both juveniles and adults were in years with warm temperatures. The majority of fish were found in waters of 5–7°C (60% of juveniles) and 4–7°C (70% of adults), indicating a strong association with Atlantic water masses in the Barents Sea. Regulations on the Norwegian and Russian fisheries for prespawning lumpfish are based only on after-the-fact fishery data and, therefore, have been insufficient in preventing negative effects on the lumpfish resource from fishing. Understanding the stock fluctuations and the use of fishery-independent data may improve the precautionary approach to fishery management. The use of lumpfish indices from the scientific surveys in the Barents Sea should be implemented to strengthen the current stock assessment. [ABSTRACT FROM AUTHOR]

The Barents Sea stock of Atlantic cod (Gadus morhua) is currently the world's largest cod stock. It is also a stock for which long time-series are available and much research has been carried out. With this review, we wish to present an overview and evaluation of the knowledge on Barents Sea cod early life dynamics. The focus is on the effects of the biotic and abiotic drivers, which jointly determine the strength of a year class. A stage-by-stage approach is employed. We summarize and assess the significance of the different processes described in the literature to be at play during each specific life stage, from spawning stock, through eggs, larvae, and pelagic juvenile, to demersal juvenile and recruitment at age 3. Also Russian work is included, some of which until now has not been available to non-Russian readers. Physical drivers examined include sea temperature, advection and dispersal, wind-induced turbulence, and light. Biotic mechanisms studied range from maternal effects and skipped spawning in the adult stock through egg quantity and quality, to prey availability for the larvae and effects of cannibalism on the juveniles. Finally, we evaluate the main hypotheses put forth by Johan Hjort a hundred years ago in the light of our synthesis of present knowledge. A main conclusion is that it is unlikely that there is any one single life stage during which recruitment with any generality is determined. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Howell, D., and Filin, A. A. Modelling the likely impacts of climate-driven changes in cod-capelin overlap in the Barents Sea. – ICES Journal of Marine Science, 71: .Recent observations have indicated that the cod distribution within the Barents Sea is expanding towards the northeast. The area into which the cod are expanding has historically been an area with large stocks of polar cod and capelin. It can be expected that the continued expansion of cod into this region would lead to greater availability of these forage fish for cod predation and have a direct impact on the forage fish stock. The distributional shift may also reduce the level of cod cannibalism. Such changes have implications for the management of both cod and capelin fisheries. In this paper, we use two different models (Gadget and STOCOBAR) to examine the effects of the changing overlap on cod and capelin. The results from the two models are compared to reduce uncertainty due to model formulation and exploit the different strengths of the two approaches. Although there are many uncertainties around the ongoing changes, the results indicate that the increased spatial overlap could contribute to modest rises by up to 20% in the average cod stock biomass, but with an increase in the impact of cannibalism, and hence an increased variability in the cod stock size. [ABSTRACT FROM PUBLISHER]

Dvoretsky, A. G., and Dvoretsky, V. G. 2013. Population dynamics of the invasive lithodid crab, Paralithodes camtschaticus, in a typical bay of the Barents Sea. – ICES Journal of Marine Science, 70: 1255–1262.We investigated population dynamics of the introduced red king crab, Paralithodes camtschaticus (Tilesius, 1815), in Dalnezelenetskaya Bay, a typical coastal site of the Eastern Murman (Barents Sea) in summer over an 8-year period. In this bay, as in other coastal sites, juvenile crabs were most abundant. Among large crabs, the sex ratio was highly biased to females suggesting the important role of shallow water areas in reproduction of the red king crab. In 2002–2004, the carapace length (CL) frequency distribution of small crabs tended to be bimodal (30 and 60 mm). In 2005–2007 and 2009, crabs with a modal CL of 20 and 40 mm dominated. For small crabs, weight–length relationships were similar in males and females, while for large crabs the relationships differed significantly between sexes. Large males had a greater carapace width (CW) and merus length (ML), and higher CW/CL and ML/CL ratios, than large females due to sexual dimorphism. In 2002–2007, the total number of red king crabs was estimated to be 4100–7400 individuals; in 2008, we observed a marked decline to 350 individuals; in 2009, the total stock increased again to 3760 individuals. The observed patterns are in accordance with the stock dynamics reported for other coastal areas and could be associated with high levels of illegal fishing including recreational diving. [ABSTRACT FROM PUBLISHER]

Homrum, E. í, Hansen, B., Jónsson, S. Þ., Michalsen, K., Burgos, J., Righton, D., Steingrund, P., Jakobsen, T., Mouritsen, R., Hátún, H., Armannsson, H., and Joensen, J. S. 2013. Migration of saithe (Pollachius virens) in the Northeast Atlantic. – ICES Journal of Marine Science, 70: 782–792.Saithe (Pollachius virens) stocks in the Northeast Atlantic intermingle as a result of migration among stock areas. The extent of migration has been poorly quantified. Here, we estimate measures of the migration based on existing tagging data from Icelandic, Faroese and Continental (Scotland, North Sea and Norway) waters. Saithe tagged in Icelandic waters were seldom caught outside Icelandic waters (<1% of tag returns), whereas 42% of adult saithe tagged in Faroese waters were recaptured outside Faroese waters. Of adult saithe tagged in Norwegian waters 6.6% were recaptured outside Continental waters. In broad terms, there was a net migration of saithe towards Icelandic waters. The distance between tagging and recapture increased with increasing size and age, with saithe tagged in Norwegian waters moving the longest distances. The results demonstrate significant, but variable, migration rates of adult saithe in the Northeast Atlantic. More detailed studies are needed to clarify the mechanisms behind the migration and what causes the differences among the areas. [ABSTRACT FROM PUBLISHER]

Dalpadado, P., Ingvaldsen, R. B., Stige, L. C., Bogstad, B., Knutsen, T., Ottersen, G., and Ellertsen, B. 2012. Climate effects on Barents Sea ecosystem dynamics. – ICES Journal of Marine Science, 69: .Effects of climate variability and change on sea temperature, currents, and water mass distribution are likely to affect the productivity and structure of high-latitude ecosystems. This paper focuses on the Barents Sea (BS), a productive Arcto–boreal shelf ecosystem sustaining several ecologically and economically important fish species. The water masses in the region are classified as Atlantic, Arctic, and mixed, each having a distinct ecological signature. The pronounced increase in temperature and a reduction in the area covered by Arctic water that has taken place during the past decade have affected the ecology of the region. An increase in biomass of lipid-rich euphausiids in recent years, possibly linked to the temperature increase, has apparently provided good feeding and growth conditions for several species, including capelin and young cod. The observed reduction in Arctic zooplankton may on the other hand have negative implications for polar cod and other zooplankton predators linked to the Arctic foodweb. Despite these changes, the BS at present seems to maintain relatively stable levels of boreal zooplankton biomass and production, with no significant changes in the abundances of Calanus finmarchicus or the episodic immigrant C. helgolandicus. [ABSTRACT FROM PUBLISHER]

Johannesen, E., Ingvaldsen, R. B., Bogstad, B., Dalpadado, P., Eriksen, E., Gjøsæter, H., Knutsen, T., Skern-Mauritzen, M., and Stiansen, J. E. 2012. Changes in Barents Sea ecosystem state, 1970–2009: climate fluctuations, human impact, and trophic interactions. – ICES Journal of Marine Science, 69: 880–889.Long time-series of data from the Barents Sea (BS) are analysed to contrast the climate, fishing pressure, plankton, pelagic fish, demersal fish, and interactions between trophic levels in a recent decade (2000–2009) with the period 1970–1999. During the past four decades, fishing pressure and climatic conditions have varied greatly in the BS, and stock levels have fluctuated substantially. Trophic control has changed from mainly bottom–up to top–down, then back to mainly bottom–up. No clear evidence for persistent ecological regimes was found. The past decade has been the warmest on record, with large stocks of demersal and pelagic fish, and increasing abundances of krill and shrimp. Except perhaps for the rather less-studied Arctic species, the short-term effect of the recent warming has been positive for BS stocks. However, as many of the long-established relationships and mechanisms in the BS seem to be changing, the long-term effects of warming are uncertain. [ABSTRACT FROM PUBLISHER]

Eriksen, E., Ingvaldsen, R., Stiansen, J. E., and Johansen, G. O. 2012. Thermal habitat for 0-group fish in the Barents Sea; how climate variability impacts their density, length, and geographic distribution. – ICES Journal of Marine Science, 69: 870–879.Between 1980 and 2008, the climate changed from cold to warm conditions in the Barents Sea. Warmer conditions have been indicated as favourable for cod, haddock, and herring recruitment and unfavourable for capelin, although during recent years these relationships have weakened and need to be revised. Extensive survey observations of temperature and 0-group cod, haddock, herring, and capelin are explored, a bounded temperature range occupied by ∼80–90% of 0-group fish (core thermal habitat, CTH) defined for each species, and an analysis made of how climate variability influenced density, length, and geographic distribution. Maximum fish densities were at 6.2°C for cod, 7.2°C for haddock, 7.0°C for herring, and 5.1°C for capelin. The area of CTH for cod, haddock, and herring increased from cold to warm years, as did the occupation area of each species. Capelin underwent a northeast distributional shift from cold to warm years. The 0-group fish were observed in a broad range of temperatures of −1 to 10.5°C. However, fish densities showed a dome-shaped distribution with temperature. Mean fish length was 7.1 cm for cod, 8.9 cm for haddock, 7.0 cm for herring, and 4.6 cm for capelin, with length distributions exhibiting a non-uniform response to temperature. [ABSTRACT FROM PUBLISHER]

Boitsov, V. D., Karsakov, A. L., and Trofimov, A. G. 2012. Atlantic water temperature and climate in the Barents Sea, 2000–2009. – ICES Journal of Marine Science, 69: 833–840.Year-to-year variability in the temperature of Atlantic water (AW), which has a strong influence on the marine climate and ecosystem of the Barents Sea, was analysed using data from the Kola Section. With a positive trend in mean annual temperature during the late 20th century, only positive anomalies were registered during the past decade. In nine of those years, the temperature was warmer than the 1951–2000 long-term mean by 0.5–1.2°C, and in 2006, the historical maximum for the 110-year period of observations along the section was recorded. High air and water temperature coincided with reduced sea-ice cover, especially between October and April, when there is seasonal enlargement of the ice-covered area. An integral climate index (CI) of the Barents Sea based on the variability in temperature of AW, air temperature, and ice cover is presented. A prediction of future Barents Sea climate to 2020 is given by extrapolating the sixth degree polynomial approximating the CI. [ABSTRACT FROM PUBLISHER]

Planque, B., Johannesen, E., Drevetnyak, K. V., and Nedreaas, K. H. 2012. Historical variations in the year-class strength of beaked redfish (Sebastes mentella) in the Barents Sea. – ICES Journal of Marine Science, 69: 547–552.The present work provides the first quantitative estimate of the historical fluctuations in the year-class strength of beaked redfish in the Barents Sea. The year-class strength index is based on scientific survey data collected by Norway and Russia during the past three decades. It is defined as the effective number of 0-group fish that will eventually enter the fishery. Uncertainties in the year-class strength indices are estimated using a statistical modelling approach, which accounts for observation errors. The reconstructed series indicate clear periods of high recruitment (late 1980s–early 1990s) and 8 years of near complete recruitment failure (1996–2003). The apparent recovery in recent years is highly uncertain and needs to be confirmed by future observations. The modelling approach developed here can be applied to other fish stocks for which catch-at-age data are available from several surveys. [ABSTRACT FROM PUBLISHER]

Rey, F. 2012. Declining silicate concentrations in the Norwegian and Barents Seas. – ICES Journal of Marine Science, 69: 208–212.Since 1990, a decline in silicate concentrations together with increasing salinities has been observed in the Atlantic water of the Norwegian and Barents Seas. This decline in silicate has been found to be related to the relative proportion in which eastern and western source water masses from the northeastern North Atlantic enter the Norwegian Sea. [ABSTRACT FROM PUBLISHER]

Aldrin, M., Mortensen, B., Storvik, G., Nedreaas, K., Aglen, A., and Aanes, S. 2012. Improving management decisions by predicting fish bycatch in the Barents Sea shrimp fishery. – ICES Journal of Marine Science, 69: 64–74.When the bycatch of juvenile fish within the Barents Sea shrimp fishery is too large, the area is closed to fishing for a certain period. Bycatch is estimated from sampled trawl hauls, for which the shrimp yield is recorded, along with the total number of various bycatch fish species. At present, bycatch estimation is based on a simple estimator, the sum of the number of fish caught within the area of interest within a small time window, divided by the corresponding shrimp yield (in weight). No historical data are used. A model-based estimation is proposed in which spatio-temporal models are constructed for the variation in both the yield of shrimp and the amount of bycatch in space and time. The main effects are described through generalized additive models, and local dependence structures are specified through correlated random effects. Model estimation includes historical and recent data. Experiments with both simulated and real data show that the model-based estimator outperforms the present simple estimator when a low or moderate number of samples (e.g. <20) is available, whereas the two estimators are equally good when the number of samples is high. [ABSTRACT FROM PUBLISHER]

Aanes, S., Nedreaas, K., and Ulvatn, S. 2011. Estimation of total retained catch based on frequency of fishing trips, inspections at sea, transhipment, and VMS data. – ICES Journal of Marine Science, 68: 1598–1605.The satellite-based vessel monitoring system in the Norwegian Economic Zone provides detailed information about individual trips by vessels. Vessel sizes are available through official registries, and the storage capacity for fish is estimated using the established conversion factors as a function of the vessel's gross registered tonnage. Scientists have had access to the database of both transport and fishing vessels, with records for individual trips, in addition to information about the total round weight (whole fish) of cod and haddock for trips inspected by the coastguard. The analysis assumes that trips with complete documentation of the fish on board are a random sample, so allowing estimation of the mean amount of both cod and haddock per trip, and annual totals give the number of trips per vessel annually. ICES has accepted this methodology for estimating illegal, unregulated, and unreported (IUU) catches, which has resulted in 15 000–166 000 t (3–35%) being added to the officially reported landings of Northeast Arctic cod during the years 2002–2008. IUU landings have decreased in recent years, but are so important for assessment and management that estimates continue to be made annually. [ABSTRACT FROM PUBLISHER]

Skaar, K. L., Jørgensen, T., Ulvestad, B. K. H., and Engås, A. 2011. Accuracy of VMS data from Norwegian demersal stern trawlers for estimating trawled areas in the Barents Sea. – ICES Journal of Marine Science, 68: 1615–1620.The accuracy of vessel monitoring system (VMS) data, used to determine fishing activity in the trawl fishery for gadoids in the Barents Sea, was studied by observer notes and Global Positioning System (GPS) data from two Norwegian vessels in October 2007. A speed rule of 2–5 knots correctly classified 75–80% of the fishing activity and 85–90% of the non-fishing activity. Linear interpolation between hourly VMS recordings underestimated trawl trajectories by 15%. The median haulwise difference between the VMS and the GPS trajectories was ∼500 m. The interpolated VMS data are appropriate for mapping the large-scale distribution of fishing effort and the area impacted, but to link fishing activities with small-scale mapping of benthos, more-frequent VMS-update times and more-refined interpolation techniques are required. [ABSTRACT FROM PUBLISHER]

Falk-Petersen, J., Renaud, P., and Anisimova, N. 2011. Establishment and ecosystem effects of the alien invasive red king crab (Paralithodes camtschaticus) in the Barents Sea – a review. – ICES Journal of Marine Science, 68: .Since its introduction to the Barents Sea from the North Pacific in the 1960s, the red king crab (Paralithodes camtschaticus) has become invasive. The crab represents an important source of income, but also a potential threat to the highly productive fisheries in the region through its ecosystem impacts. A literature review was conducted, identifying factors contributing to the success of the crab as well as its interactions with native biota. Characteristics of the Barents Sea and the crab itself that may explain its success include suitable habitat for settlement and growth of the larvae; the wide range of habitats occupied throughout its life history, high mobility, generalist prey choice, low fishing pressure during establishment, and the lack of parasites. Being a large, bottom-feeding omnivore of great mobility, the king crab can significantly impact the ecosystem. Reduced benthic diversity and biomass have been registered in invaded areas. Important prey items include large epibenthic organisms whose structures also represent important habitat. Impacts on commercial and non-commercial fish species, through egg predation or indirect interactions, are difficult to detect and predict. [ABSTRACT FROM PUBLISHER]

Yaragina, N. A. 2010. Biological parameters of immature, ripening, and non-reproductive, mature northeast Arctic cod in 1984–2006. – ICES Journal of Marine Science, 67: 2033–2041.Russian samples of cod caught in the Barents Sea during November–February, the period of migration to the overwintering and spawning grounds, were re-analysed by grouping the maturity stages recorded in three classes: immature, ripening, and apparently mature fish, with gonads of uncertain status. When treated by age class and gender, these three classes were characterized by significant differences in size (length and weight) and condition (somatic and a liver index). Within an age group, the group with uncertain status was on average consistently larger than the ripening fish and the latter group was on average larger than the immature component. However, in terms of condition, fish of uncertain status resembled the immature fish. Males and females displayed very similar patterns, although the levels were consistently lower for the former. The patterns are consistent with the interpretation that the gonads of uncertain status represent non-reproductive, mature fish. At the population level, the percentage of mature fish that presumably skip spawning varied annually between 4 and 21%, but this has little effect on the perception of the overall development in spawning-stock biomass. No correlation was found between the non-reproductive fraction and environmental factors examined. [ABSTRACT FROM PUBLISHER]

Howell, D., and Bogstad, B. 2010. A combined Gadget/FLR model for management strategy evaluations of the Barents Sea fisheries. – ICES Journal of Marine Science, 67: 1998–2004.A biologically sensible age–length structured multispecies Gadget model (incorporating minke whales, cod, herring, and capelin) for the Barents Sea—acting as the operating model—has been linked to Fisheries Library in R—acting as the management procedure—to perform management strategy evaluations. Assessments may be run using either XSA, survey-based methods, or by taking modelled stock numbers directly. Total allowable catches are based on the assessment and harvest control rules (HCRs). The tool can be used for assessing a wide variety of sources of uncertainties within the assessment process. Model structure and linkages are described and a fit to the historical data is presented. A base case of future dynamic (non-steady state) stock trends, based on the existing HCRs, is compared with alternative management and environmental scenarios. The relative differences for each scenario in terms of stock size and catches highlight a number of uncertainties within the biological and fisheries system. The results indicate that the current management rules are robust to the range of scenarios examined so far. [ABSTRACT FROM PUBLISHER]

Dolgov, A. V., Johannesen, E., Heino, M., and Olsen, E. 2010. Trophic ecology of blue whiting in the Barents Sea. – ICES Journal of Marine Science, 67: 483–493.Blue whiting (Micromesistius poutassou) are distributed throughout the North Atlantic, including the Norwegian and Barents Seas. In recent years, both abundance and distribution of blue whiting in the Barents Sea have increased dramatically. Therefore, to evaluate the trophic impact of this increase, we analysed the diet of the species. In all, 54 prey species or taxa were identified, the main prey being krill. However, the diet varied geographically and ontogenetically: the proportion of fish in the diet was higher in large blue whiting and in the north of the range. Blue whiting overlap geographically with other pelagic species at the edge of their distribution in the Barents Sea, with juvenile herring in the south, with polar cod in the north, and with capelin in the northeast. The overlap in diet between blue whiting and these other pelagic species ranged from 6 to 86% and was greatest with capelin in areas where both species feed on hyperiids and krill. The importance of blue whiting as prey for predatory fish was highest in the areas of greatest abundance, but overall, blue whiting were seemingly unimportant as prey of piscivorous fish in the Barents Sea. [ABSTRACT FROM PUBLISHER]

Dvoretsky, A. G., and Dvoretsky, V. G. 2010. Epifauna associated with an introduced crab in the Barents Sea: a 5-year study. – ICES Journal of Marine Science, 67: 204–214.Species composition, prevalence, intensity, and spatial distribution of macro-invertebrates colonizing the invasive red king crab (Paralithodes camtschaticus) in a typical bay of the Barents Sea, Dalnezelenetskaya Bay (depths 5–40 m), and adjacent deeper water (120–180 m) were examined in the summers of 2004–2008. In all, 43 associated species were found on the crabs. The most common epibionts were Mytilus edulis (Bivalvia), Obelia spp. (Hydrozoa), and Circeis armoricana (Polychaeta). Symbiotic species included Ischyrocerus commensalis and Ischyrocerus anguipes (Amphipoda), Harmothoe imbricata (Polychaeta), and Johanssonia arctica (Hirudinea). There were no significant differences in the prevalence of infestation between male and female crabs. The prevalence of most of the common species was greater in crabs with old shells than in crabs with new shells. Infestation levels of J. arctica were higher in deeper than in shallow water, and M. edulis was less abundant in deep water. All species found on the crabs appear to be native to the Barents Sea. However, I. commensalis amphipods were not found at the site examined before the introduction of the red king crab, indicating that their distribution may have changed after association with this host species. Introduced hosts may well influence the distribution of rare native species. [ABSTRACT FROM PUBLISHER]

Olsen, E., Aanes, S., Mehl, S., Holst, J. C., Aglen, A., and Gjøsæter, H. 2010. Cod, haddock, saithe, herring, and capelin in the Barents Sea and adjacent waters: a review of the biological value of the area. – ICES Journal of Marine Science, 67: 87–101.Cod, haddock, saithe, herring, and capelin are the most important fish species in the Barents Sea and adjacent waters. Ecosystem-based management requires species-specific knowledge of the biological value and vulnerability throughout their life history and distributional range. For each of the five species and four annual quarters, the spawning (egg) areas, nursery areas for larvae and juveniles, and feeding grounds for adults are described and mapped. Areas of eggs (spawning) and larvae were the most important because these are the life stages when fish are most vulnerable to anthropogenic impact. The greatest overlap of spawning areas was from Røstbanken in the south to the Varanger Peninsula in the northeast, and overlap of larval distribution was more extensive. [ABSTRACT FROM PUBLISHER]

Pedersen, O. P., Pedersen, T., Tande, K. S., and Slagstad, D. 2009. Integrating spatial and temporal mortality from herring on capelin larvae: a study in the Barents Sea. – ICES Journal of Marine Science, 66: 2183–2194.Barents Sea herring and capelin are commercially very important fish stocks. We investigate the spatial and temporal mortality rate of capelin larvae in 2001 as a function of herring predation. Our methods are based on Lagrangian modelling, field surveys, and experimental data. The impact of juvenile herring predation on capelin recruitment is corroborated, in particular the importance of the integrated spatio-temporal overlap between the two stocks. Capelin larvae were reduced to 20–50% in two weeks in accordance with different simulation scenarios. Hamre advanced a hypothesis in 1994 that juvenile herring are important predators of capelin larvae and a main cause of poor capelin recruitment in years when herring are very abundant in the Barents Sea. This hypothesis is supported through the results of this work. [ABSTRACT FROM PUBLISHER]

Johansen, G. O., Godø, O. R., Skogen, M. D., and Torkelsen, T. 2009. Using acoustic technology to improve the modelling of the transportation and distribution of juvenile gadoids in the Barents Sea. – ICES Journal of Marine Science, 66: 1048–1054.Transport of the juvenile stages of gadoids by oceanic currents in the Barents Sea is governed by interactions between the vertical positioning of the fish and the horizontal movement of the water masses. The resulting geographical distribution is important for growth and survival. There is need for observations at proper temporal and spatial scales to improve the representation of vertical distribution in models of the transport process. Stationary acoustic systems are suitable for this purpose. We use such a system to quantify the vertical dynamics of 0-group gadoids with reference to a conceptual model of the temporal variation. The vertical distribution from the conceptual model is applied within a Lagrangian, particle-tracking model. This approach performs better in predicting the geographic distribution of the 0-group during the first 10 months after hatching than a model with random, vertical distribution. The potential of stationary acoustic systems to provide high-quality vertical distributions that improve the predictive power of the transport model is demonstrated. Extensive sampling programmes based on the principles presented here can provide the observations needed to obtain more realistic recruitment–prediction models. [ABSTRACT FROM PUBLISHER]

Ermolchev, V. A., 2009. Methods and results of in situ target-strength measurements of Atlantic cod (Gadus morhua) during combined trawl-acoustic surveys. – ICES Journal of Marine Science, 66: 1225–1232.This paper presents methods for collecting acoustic and biological data, including in situ target-strength (TS) estimates of fish, with results presented for Atlantic cod (Gadus morhua) obtained from combined trawl-acoustic surveys. These include fish in the small, average, and maximum length classes, within the range 5–136 cm (total fish length, LT). The investigations were done using Simrad EK500/EK60 echosounders with split-beam transducers and special post-processing software. Based on an analysis of data collected in the Barents Sea during 1998–2007, a relationship TS = 25.2 log10(LT) − 74.8 was obtained for Atlantic cod at 38 kHz, with TS in dB and LT in centimetres. Seasonally, and for depths between 50 and 500 m, the variability in cod TS was 3.1 dB, decreasing with depth. The largest day–night difference in mean TS was in August–September, with changes as large as 1.0–1.7 dB. In the other seasons, the day–night difference was <1.0 dB. [ABSTRACT FROM PUBLISHER]

Guttormsen, M. A. and Wilson, C. D. 2009. In situ measurements of capelin (Mallotus villosus) target strength in the North Pacific Ocean. – ICES Journal of Marine Science, 66: 258–263.In situ measurements of capelin (Mallotus villosus) target strength (TS) were collected during summer 2001–2003 near Kodiak Island in the Gulf of Alaska, using a calibrated EK500 echosounder with 38 and 120 kHz split-beam transducers. Targets were detected over dispersed, night-time aggregations using standard acoustic methods, then filtered using a quality-control algorithm to reject invalid targets. The 38 kHz-based, fitted model estimate was TS = 20 log10L− 70.3 (r2 = 0.30), where L is total length of fish. Compared with other studies, the TS-fitted model at 38 kHz was similar to that calculated from swimbladder morphology measurements from St Lawrence estuary capelin (TS = 20 log10L− 69.3), but resulted in greater estimates than models based on in situ measurements of capelin TS in the Barents Sea (TS = 19.1 log10L−74.0) and northern Atlantic Ocean (TS = 20 log10L − 73.1). The large intraspecific variability exhibited in the fitted TS – L models for this species suggests the use of TS measurements from the geographic region where the data were collected. [ABSTRACT FROM PUBLISHER]

Ingólfsson, Ó. A., Soldal, A. V., Huse, I., and Breen, M. 2007. Escape mortality of cod, saithe, and haddock in a Barents Sea trawl fishery. – ICES Journal of Marine Science, 64: 000–000.We investigated the survival of gadoid fish in the Barents Sea escaping from a demersal trawl during commercial fishing conditions, with and without a sorting grid, at high and low levels of fishing intensity. The mortality of cod and saithe was negligible and unrelated to experimental conditions. Haddock mortality was generally greater than observed in earlier experiments and inversely related to fish length. Any possible effects of experimental conditions were hidden by large variability in the observed rates of mortality. We conclude that the observed mortality of haddock is confounded by methodological problems, particularly the instability of the observation cages, and does not reflect the true escape mortality. Cod and saithe are capable of surviving the stress of passage through, and escape from, the trawl, whereas haddock are more vulnerable, despite being a closely related species. [ABSTRACT FROM PUBLISHER]

Skaug, H. J., Frimannslund, L., and Øien, N. I. 2007. Historical population assessment of Barents Sea harp seals (Pagophilus groenlandicus). – ICES Journal of Marine Science, 64: 1356–1365: –.Harp seals are an important component of the Barents Sea ecosystem. Population size is estimated to have been around 6 million seals in 1875, when large-scale exploitation by Norwegian and Russian hunters started. The estimate is obtained by fitting a population dynamics model to all available sources of data on Barents Sea harp seals, but because of a lack of information about several key parameters in the model, the uncertainty associated with the estimate is large. A sensitivity study involving three different mechanisms for density-dependence results in a range estimate of 3–7 million seals in 1875. [ABSTRACT FROM PUBLISHER]

Hallfredsson, E. H., and Pope, J. G. 2007. Modelling the growth, mortality, and predation interactions of cod juveniles and capelin larvae in the Barents Sea using a novel proto-moment population dynamics model. – ICES Journal of Marine Science, 64: 1313–1323. Proto-moments of a fish population, the sums of products of powers of length with numbers at length, relate both to the traditional statistical measures, the mean, the variance, the skewness, and the kurtosis of their size distribution, and to the biologically important measures of the abundance and the biomass of the population. Population models based on this approach are constructed as matrix delay-difference equations. They model moments of the length distributions rather than the age distributions, and express population dynamic problems in an analytically tractable form. Here, a modification of this approach is explored for a case involving a predator–prey relationship among young-of-the-year fish. The modelled species are juvenile cod (the predator) and capelin larvae (the prey) in the Barents Sea. Their population dynamics are modelled by the proto-moment method, but using two different approaches for the derivation of the predation mortality term. The first approach, a published matrix-based formulation, is formed purely in terms of the proto-moments. The second approach, developed here, converts the proto-moments back to consistent size distributions to calculate the rates of predation mortality on each proto-moment. The latter model produces a realistic development in time for the predator and prey length distributions, density in numbers, and biomass for their first summer. It also provides estimates of growth for both species along with estimates of the predation mortality that cod generate on capelin in this time period. The estimates permitted the accuracy of the matrix-based approach to be investigated, better understood, and improved. [ABSTRACT FROM PUBLISHER]

A bioeconomic simulation model of the two interacting fish species cod (Gadus morhua) and capelin (Mallotus villosus) and their fisheries is presented and applied to assess the consequences of changes in the population dynamics of these important fish stocks in the Barents Sea. In each scenario, the population dynamics of the fish species are changed by reducing the reproduction-induced productivities and/or the carrying capacities. Stock sizes and landings of fish are calculated for each fishing period, and the net present values of profits from fishing are determined for time periods prior to and after the change in population dynamics. Results show that reduced growth rates or carrying capacities lead to lower stock levels and consequently to smaller catches. There is only a small short-term economic impact on the fisheries, but the long-term consequences are pronounced. In some cases, greater fishing activity in the first few years after the change in population dynamics causes harvests to remain stable despite diminishing stock sizes. This stabilizes the returns from fishing in the short term, but veils the apparent negative long-term impact on the fisheries resulting from adversely affected stock dynamics. [Copyright &y& Elsevier]