Mitochondrial DNA polymorphism of atlantic cod of the Barents and White seas

High level of intraspecific polymorphism of the mtDNA cytochrome b gene in the Atlantic cod Gadus morhua L. from the northeastern part of the species range (Barents and White seas) is detected. The absence of genetic differentiation between the samples from different areas of the Norwegian and Barents seas is shown, and the fact that these samples belong to the same population of Northeast Arctic cod is confirmed. Significant differences in the frequences of mitochondrial DNA haplotypes between the cod from the Barents and White seas, as well as from the northwestern part of the range, are found. The cod Gadus morhua kildinensis Derjugin, 1920 from Mogilnoye Lake and Gadus morhua marisalbi Derjugin, 1920 from the White Sea were revealed to have common haplotypes with the cod from the Barents Sea, confirming the recent origin of these forms from the Atlantic cod G. morhua.     

Resource‐driven colonization by cod in a high Arctic food web

1. Climate change is commonly associated with many species redistributions and the influence of other factors may be marginalized, especially in the rapidly warming Arctic.
2. The Barents Sea, a high latitude large marine ecosystem in the Northeast Atlantic has experienced above‐average temperatures since the mid‐2000s with divergent bottom temperature trends at subregional scales.
3. Concurrently, the Barents Sea stock of Atlantic cod Gadus morhua, one of the most important commercial fish stocks in the world, increased following a large reduction in fishing pressure and expanded north of 80°N.
4. We examined the influence of food availability and temperature on cod expansion using a comprehensive data set on cod stomach fullness stratified by subregions characterized by divergent temperature trends. We then tested whether food availability, as indexed by cod stomach fullness, played a role in cod expansion in subregions that were warming, cooling, or showed no trend.
5. The greatest increase in cod occupancy occurred in three northern subregions with contrasting temperature trends. Cod apparently benefited from initial high food availability in these regions that previously had few large‐bodied fish predators.
6. The stomach fullness in the northern subregions declined rapidly after a few years of high cod abundance, suggesting that the arrival of cod caused a top‐down effect on the prey base. Prolonged cod residency in the northern Barents Sea is, therefore, not a certainty.

     

The stress hormone corticosterone in a marine top predator reflects short‐term changes in food availability

In many seabird studies, single annual proxies of prey abundance have been used to explain variability in breeding performance, but much more important is probably the timing of prey availability relative to the breeding season when energy demand is at a maximum. Until now, intraseasonal variation in prey availability has been difficult to quantify in seabirds. Using a state‐of‐the‐art ocean drift model of larval cod Gadus morhua, an important constituent of the diet of common guillemots Uria aalge in the southwestern Barents Sea, we were able to show clear, short‐term correlations between food availability and measurements of the stress hormone corticosterone (CORT) in parental guillemots over a 3‐year period (2009–2011). The model allowed the extraction of abundance and size of cod larvae with very high spatial (4 km) and temporal resolutions (1 day) and showed that cod larvae from adjacent northern spawning grounds in Norway were always available near the guillemot breeding colony while those from more distant southerly spawning grounds were less frequent, but larger. The latter arrived in waves whose magnitude and timing, and thus overlap with the guillemot breeding season, varied between years. CORT levels in adult guillemots were lower in birds caught after a week with high frequencies of southern cod larvae. This pattern was restricted to the two years (2009 and 2010) in which southern larvae arrived before the end of the guillemot breeding season. Any such pattern was masked in 2011 by already exceptionally high numbers of cod larvae in the region throughout chick‐rearing period. The findings suggest that CORT levels in breeding birds increase when the arrival of southern sizable larvae does not match the period of peak energy requirements during breeding.     

Ticket to spawn: Combining economic and genetic data to evaluate the effect of climate and demographic structure on spawning distribution in Atlantic cod

Climate warming and harvesting affect the dynamics of species across the globe through a multitude of mechanisms, including distribution changes. In fish, migrations to and distribution on spawning grounds are likely influenced by both climate warming and harvesting. The Northeast Arctic (NEA) cod (Gadus morhua) performs seasonal migrations from its feeding grounds in the Barents Sea to spawning grounds along the Norwegian coast. The distribution of cod between the spawning grounds has historically changed at decadal scales, mainly due to variable use of the northern and southern margins of the spawning area. Based on historical landing records, two major hypotheses have been put forward to explain these changes: climate and harvesting. Climate could affect the distribution through, for example, spatial habitat shifts. Harvesting could affect the distribution through impacting the demographic structure. If demographic structure is important, theory predicts increasing spawner size with migration distance. Here, we evaluate these hypotheses with modern data from a period (2000–2016) of increasing temperature and recovering stock structure. We first analyze economic data from the Norwegian fisheries to investigate geographical differences in size of spawning fish among spawning grounds, as well as interannual differences in mean latitude of spawning in relation to changes in temperature and demographic parameters. Second, we analyze genetically determined fish sampled at the spawning grounds to unambiguously separate between migratory NEA cod and potentially smaller sized coastal cod of local origin. Our results indicate smaller spawners farther away from the feeding grounds, hence not supporting the hypothesis that harvesting is a main driver for the contemporary spawning ground distribution. We find a positive correlation between annual mean spawning latitude and temperature. In conclusion, based on contemporary data, there is more support for climate compared to harvesting in shaping spawning ground distribution in this major fish stock in the North Atlantic Ocean.     

Parasites as Biological Tags for Stock Discrimination of Beaked Redfish (Sebastes mentella): Parasite Infra-Communities vs. Limited Resolution of Cytochrome Markers

The use of parasites as biological tags for discrimination of fish stocks has become a commonly used approach in fisheries management. Metazoan parasite community analysis and anisakid nematode population genetics based on a mitochondrial cytochrome marker were applied in order to assess the usefulness of the two parasitological methods for stock discrimination of beaked redfish Sebastes mentella of three fishing grounds in the North East Atlantic. Multivariate, model-based approaches demonstrated that the metazoan parasite fauna of beaked redfish from East Greenland differed from Tampen, northern North Sea, and Bear Island, Barents Sea. A joint model (latent variable model) was used to estimate the effects of covariates on parasite species and identified four parasite species as main source of differences among fishing grounds; namely Chondracanthus nodosus, Anisakis simplex s.s., Hysterothylacium aduncum, and Bothriocephalus scorpii. Due to its high abundance and differences between fishing grounds, Anisakis simplex s.s. was considered as a major biological tag for host stock differentiation. Whilst the sole examination of Anisakis simplex s.s. on a population genetic level is only of limited use, anisakid nematodes (in particular, A. simplex s.s.) can serve as biological tags on a parasite community level. This study confirmed the use of multivariate analyses as a tool to evaluate parasite infra-communities and to identify parasite species that might serve as biological tags. The present study suggests that S. mentella in the northern North Sea and Barents Sea is not sub-structured.     

Distribution and diet of 0-group cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and haddock (<Emphasis Type="Italic">Melanogrammus aeglefinus</Emphasis>) in the Barents Sea in relation to food availability and temperature

Distribution of 0-group cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in August–September 2005 and 2006 was mainly restricted to the Atlantic waters of the western and central areas of the Barents Sea. The main distribution of 0-group fish overlapped largely with areas of high biomass (>7 gm⁻² dry weight) of zooplankton. The copepod Calanus finmarchicus and krill Thysanoessa inermis, which are dominant zooplankton species in both Atlantic and boreal waters of the Barents Sea, were the main prey of 0-group cod and haddock. The main distribution, feeding areas and prey of 0-group cod and haddock overlapped, implying that competition for food may occur between the two species. However, though their diet coincided to a certain degree, haddock seems to prefer smaller and less mobile prey, such as Limacina and appendicularians. As 0-group fish increased in size, there seems to be a shift in diet, from small copepods and towards larger prey such as krill and fish. Overall, a largely pelagic feeding behaviour of 0-group cod and haddock was evident from this study.     

Comparative analysis of genetic variability of white sea cod (Gadus morhua marisalbi) at allozyme and microsatellite markers

Variability of cod spawning and feeding schools from Kandalaksha Bay of the White Sea, was examined at six allozyme and eight microsatellite loci. The degree of genetic differentiation at allozyme loci constituted θ = 0.36% [95% bootstrap interval 0.0458; 0.6743]. The differentiation estimates obtained using microsatellite markers were higher, θ = 1.33% [0.057; 3.11]. It was demonstrated that the level of genetic diversity in the White Sea cod was lower than that established for the Atlantic cod from Barents Sea using the same set of allozyme and microsatellite markers. The genetic data obtained support the opinion that the White Sea cod is a reproductively independent group formed as a result of the Holocene dispersal of Atlantic cod.     

Atlantic cod <Emphasis Type="Italic">Gadus morhua</Emphasis> (Gadiformes: Gadidae) from the Gulf of Ura: Morphobiological characteristic

Analysis of variation of biological and morphometric characteristics of cod Gadus morhua from the Gulf of Ura-a water area in the composition of Motovskii Bay of the Barents Sea was performed. The material was collected from 1999 to 2006 during spawning of the Atlantic cod. Parameters such as length, weight, sex composition, maturity stage, age, otolith structure, and variation of plastic characters were analyzed. It was shown that the Gulf of Ura, parallel to individuals of junior age groups, is inhabited by cod in the spawning state aged 5–6 months and older with coastal and Atlantic types of otolith.     

Zooplankton biomass variation in relation to climatic conditions in the Barents Sea

Over the last two decades, there have been large changes in the zooplankton biomass in the Barents Sea. These biomass variations are mainly attributed to predation pressure and environmental factors (e.g. advective transport). When stock size of capelin (Mallotus villosus), a major planktivorous fish in the Barents Sea ecosystem, was quite low as in 1986 and 1994, the zooplankton biomass showed marked increase. However, the increase in the zooplankton biomass occurred in different water masses during 1986 and 1994. In 1986, a climatically cold year, the plankton biomass was highest in the Arctic waters of the northeastern Barents Sea. This is probably due to the increase in larger Arctic amphipod species, such as Themisto libellula. In 1994, a climatically warm year, the zooplankton biomass was high in the Atlantic waters of the southwestern Barents Sea. The large increase in zooplankton biomass in the Atlantic waters in 1994 was presumably due to the higher inflow of advected organisms, e.g. Calanus spp., as well as high temperatures, which may lead to high growth rates of zooplankton. Throughout the studied region, the plankton biomass in the "cold year" of 1986 was generally much lower than in the "warm year" of 1994.     

The abundance and patterns of the egg and larval spatial distribution of Eastern Baltic cod Gadus morhua callarias (Gadidae) in 1931–1996

According to ichthyoplankton surveys of AtlantNIRO and published sources, the data on abundance of eggs and larvae of eastern Baltic cod Gadus morhua callarias at different spawning grounds of the Baltic Sea in 1931–1938, 1949–1956, and 1991–1996 are considered. We show that a similar type of spatial distribution of eggs and larvae of cod with localization of the greatest amount of its early ontogenetic stages in the Bornholm Basin in the southwest of the sea was observed in the 1930s and 1990s. The extension of the area of distribution was accompanied by an increase in the numbers of eggs and larvae of cod in all areas of the sea, and its decline was followed by a decrease in numbers, in the first turn, at northeastern spawning grounds in the Gotland Basin. The period of high numbers of eggs in 1949–1956 coincided with the century maximum of salinity of the near-bottom water layer.     

Early Environmental Influences on Growth of Arcto-Norwegian Cod, Gadus Morhua, From The 0-group To Adults

A high growth rate for Arcto-Norwegian cod, Gadus morhua, in the Barents Sea and adjacent areas from the larva period to the 0-group enhances survival and ultimately recruitment to the fishery. However, it appeared that high growth rates for a cohort through the 0-group were not continued as the cohort ages. Based on survey data, there was a significant negative correlation between the average length at the 0-group and its average length at ages 2 through 8. We provided evidence suggesting that this phenomenon was caused by the inter-annual variability in inflow of warm, prey-rich Atlantic water into the Barents Sea from the Norwegian Sea. Enhanced inflow provided favorable conditions for cod growth during the larva and juvenile pelagic intervals. However, this same strong inflow carried a proportion of the cohort farther to the east in the Barents Sea, where the bottom water is colder than in the west. The colder conditions experienced by such cohorts, as compared to cohorts that have a more westerly settlement, led to slower growth prior to age 2. Slow growth during this interval appeared to be the reason for these cohorts' relatively smaller mean length at older ages.     

Concerning range expansion of the crabGeryon tridens in the Barents Sea

This paper presents data on 48 individuals of the rare high-boreal crab speciesGeryon tridens Krøyer, 1837, retrieved from the stomachs of cod caught in the southwestern part of the Barents Sea and adjacent waters in 1987–1997. There was only one large male with a carapace width of 58 mm; the other individuals were juveniles with carapace widths of 21–48 mm and masses of 3.2–27.5 g. The length: width ratio of the crab carapaceL=(0.85±0.06)H and the dependence of mass on carapace width (cm)W=0.4637H ^2.73 atr=0.99 were calculated. Analysis of the data provides evidence that this crab species is expanding its range to the northeast and is sustaining its invasion of the Barents Sea, where it was first recorded no less than 10–15 years. It is concluded that this species now permanently inhabits the region of the Finmarken and Rybach'ya banks, forming rather dense aggregations there, and, on sites of cod catches, it predominantly inhabits depths of 180–320 m, where the warm Atlantic waters dominate and sand-silt bottoms prevail. These bottoms are favorable for the sheltering of crabs, which have a burrowing mode of life.     

Recolonization history and large-scale dispersal in the open sea: the case study of the North Atlantic cod, Gadus morhua L.

Most studies of the genetic structure of Atlantic cod have focused on small geographical scales. In the present study, the genetic structure of cod sampled on spawning grounds in the North Atlantic was examined using eight microsatellite loci and the Pan I locus. A total of 954 cod was collected from nine different regions: the Baltic Sea, the North Sea, the Celtic Sea, the Irish Sea and Icelandic waters during spring 2002 and spring 2003, from Norwegian waters and the Faroe Islands (North and West spawning grounds) in spring 2003, and from Canadian waters in 1998. Temporal stability among spawning grounds was observed in Icelandic waters and the Celtic Sea, and no significant difference was observed between the samples from the Baltic Sea and between the samples from Faroese waters. F -statistics showed significant differences between most populations and a pattern of isolation-by-distance was described with microsatellite loci. The Pan I locus revealed the presence of two genetically distinguishable basins, the North-west Atlantic composed of the Icelandic and Canadian samples and the North-east Atlantic composed of all other samples. Permutation of allele sizes at each microsatellite locus among allelic states supported a mutational component to the genetic differentiation, indicating a historical origin of the observed variation. Estimation of the time of divergence was approximately 3000 generations, which places the origin of current genetic pattern of cod in the North Atlantic in the late Weichselian (Wisconsinian period), at last glacial maximum.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 315–329.     

Productivity in the Barents Sea - Response to Recent Climate Variability

The temporal and spatial dynamics of primary and secondary biomass/production in the Barents Sea since the late 1990s are examined using remote sensing data, observations and a coupled physical-biological model. Field observations of mesozooplankton biomass, and chlorophyll a data from transects (different seasons) and large-scale surveys (autumn) were used for validation of the remote sensing products and modeling results. The validation showed that satellite data are well suited to study temporal and spatial dynamics of chlorophyll a in the Barents Sea and that the model is an essential tool for secondary production estimates. Temperature, open water area, chlorophyll a, and zooplankton biomass show large interannual variations in the Barents Sea. The climatic variability is strongest in the northern and eastern parts. The moderate increase in net primary production evident in this study is likely an ecosystem response to changes in climate during the same period. Increased open water area and duration of open water season, which are related to elevated temperatures, appear to be the key drivers of the changes in annual net primary production that has occurred in the northern and eastern areas of this ecosystem. The temporal and spatial variability in zooplankton biomass appears to be controlled largely by predation pressure. In the southeastern Barents Sea, statistically significant linkages were observed between chlorophyll a and zooplankton biomass, as well as between net primary production and fish biomass, indicating bottom-up trophic interactions in this region.     

Temporal Dynamics of Top Predators Interactions in the Barents Sea

The Barents Sea system is often depicted as a simple food web in terms of number of dominant feeding links. The most conspicuous feeding link is between the Northeast Arctic cod Gadus morhua, the world''s largest cod stock which is presently at a historical high level, and capelin Mallotus villosus. The system also holds diverse seabird and marine mammal communities. Previous diet studies may suggest that these top predators (cod, bird and sea mammals) compete for food particularly with respect to pelagic fish such as capelin and juvenile herring (Clupea harengus), and krill. In this paper we explored the diet of some Barents Sea top predators (cod, Black-legged kittiwake Rissa tridactyla, Common guillemot Uria aalge, and Minke whale Balaenoptera acutorostrata). We developed a GAM modelling approach to analyse the temporal variation diet composition within and between predators, to explore intra- and inter-specific interactions. The GAM models demonstrated that the seabird diet is temperature dependent while the diet of Minke whale and cod is prey dependent; Minke whale and cod diets depend on the abundance of herring and capelin, respectively. There was significant diet overlap between cod and Minke whale, and between kittiwake and guillemot. In general, the diet overlap between predators increased with changes in herring and krill abundances. The diet overlap models developed in this study may help to identify inter-specific interactions and their dynamics that potentially affect the stocks targeted by fisheries.     

Long-term variations of biotic and abiotic conditions in the ecosystem of the Barents Sea

Synchronism of year-class strength was noted for the majority of commercial fish in the Barents Sea. The reason for this is probably connected with a common factor, namely the intensity of water inflow which influences spawning efficiency, zooplankton food production, fish larval drift to the feeding grounds, and consequent survival of juvenile fish. Consequently, the established regular relationships of hydrological and weather processes in the ecosystem can serve as basis for long-term fishing forecasts. The overall pattern of the Barents Sea water circulation, long-term climatic changes in this region, and their effect on the fish stock reproduction are considered, using Arctic cod as an example.     

Interannual fluctuations of zooplankton in the Kola Section (Barents Sea) in relation to environmental factors

An analysis of interannual variations of zooplankton composition and biomass in the Kola Section (Barents Sea) in summer was conducted based on the data of 2003–2010. Maximum values of the mean water temperature and temperature anomaly were found in 2006 and in 2007. Variations in the zooplankton composition and relative biomass of common species were studied in relation to climatic factors. It is discussed which parameters may be used as indicators of climatic changes in the southern Barents Sea.     

New data on distribution of Norwegian (Atlantic) pollock Theragra finnmarchica (Gadidae) in the Barents Sea

New data have been acquired on the biology, morphological features and distribution of Norwegian (Atlantic) pollock Theragra finnmarchica in the Barents Sea. Two individuals of this rare species gadoid (Gadidae) were caught in June and July 2012 in the south-eastern part of the Barents Sea, indicating a wider distribution area of this species than previously thought. It has been confirmed that a number of morphological features of Norwegian pollock is different from T. chalcogramma, and that it feeds on macroplankton (Euphausiidae, Hyperiidae).     

The barnacles (Cirripedia: Thoracica) collected by the Viking expedition in chemobiotic benthic communities of the Norwegian and Barents Seas

The barnacles (Cirripedia Thoracica) collected by the Viking expedition in chemobiotic benthic communities of Arctic Ocean-Nyegga area in Norwegian Sea and Håkon Mosby Mud Volcano area in the Barents Sea are investigated. The species (Weltnerium nymphocola in Håkon Mosby Mud Volcano area and Hamatoscalpellum hamatum in Nyegga area) that were found are common inhabitants of the Barents and Norwegian sea benthic communities. The absence of obligatory barnacle fauna that was revealed in investigated chemobiotic benthic communities of the Arctic Ocean shows they are similar to corresponding communities of the Atlantic Ocean, while the specific obligatory barnacle fauna is noted for chemobiotic benthic communities of the Pacific and Indian oceans.