Structure and specific features of formation of aggregations of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) in the Norwegian Sea pelagial

Results of studies of the structure and specific features of formation of aggregations of deepwater redfish Sebastes mentella in the Norwegian Sea pelagial are provided. Data on the biological characteristics of S. mentella from different regions of the Norwegian Sea pelagial do not allow us to consider its aggregations as separate populations. On the basis of comparative analysis of the structure of aggregations in the Norwegian Sea and of population parameters and specific features of the life cycle of S. mentella in different parts of the Atlantic Ocean, its complex intraspecies organization at sites of overlapping of two largest populations—North Atlantic and Norwegian-Barents Sea-was established. The formation of pelagic aggregations in the water area of the Norwegian Sea occurs due to migration of maturing and mature individuals from the adjoining water areas. In the southern areas of the Norwegian Sea, dominant recruitment comes from the pelagial of the northeastern part of the Irminger Sea, which is promoted by the direction of streams of the North-Atlantic Current; it is not excluded either that fish can migrate to the southern part of the sea from the slopes of the Faeroes, Faeroes-Icelandic threshold, and the western coast of Norway. Migration to the northern areas of the sea is mainly performed by rapidly maturing fish from the rearing region from the western slopes of the Barents Sea and Spitsbergen Archipelago. The presence of seasonal migrations hinders the formation in the pelagial of perch isolated groups and promotes their migration.     

Structure of aggregations and principal populational characteristics of redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes: Scorpaenidae) in the pelagic zone of the Irminger Sea and adjacent waters

The spatial distribution of redfish Sebastes mentella in the pelagic zone of the northern part of the Atlantic Ocean (the Irminger Sea and the Labrador Sea) is investigated. Analysis of the data on size-age composition, sex ratio, ratio of mature and immature specimens, rate of maturation, composition of the parasite fauna, infestation level, infestation with the copepod Sphyrion lumpi, and occurrence of pigment formations on the body of redfish from the investigated areas indicate the absence of stable isolated aggregations of this species in the oceanic pelagial of the North Atlantic. Pelagic aggregations are formed of rapidly maturating specimens migrated from the slopes of Greenland. The spatial variation of the size-age composition of redfish depends on the life cycle and regional hydrological conditions.     

Recruitment of stock of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes,Scorpaenidae) in the pelagial of the Irminger Sea and adjacent waters

Results of comparative analysis of several ecologo-populational characteristics and fauna of parasites of deepwater redfish Sebastes mentella from the pelagial of the Irminger Sea and slopes of Greenland are provided. It was established that the nursery area of the species in this part of the northern Atlantic is located in the shelf and shallow-water sites of the Greenland slopes. Near the nursery area, at deepwater sites of the Greenland slope, aggregations of mainly immature specimens (68–86%) with an average length of 35–38 cm are located, and, in the oceanic pelagial, there are mainly mature specimens (91–95%) with a length of more than 30 cm. Considerable similarity and specific features of fauna of parasites of S. mentella from the southeastern slope of Greenland and the pelagial of the Irminger Sea indicate the belonging of fish aggregations in these areas to a single intraspecies group and the migration of maturing specimens from the slope to the pelagial. A conclusion is made that the aggregations of S. mentella in the pelagial of the Irminger and Labrador seas represent a pelagic ecological group formed by rapidly maturing specimens; a near-bottom ecological group at deepwater sites of the slope of Greenland is formed by slowly maturing specimens. No mass migration of the redfish from deepwater areas to shallow sites of the slope and to the oceanic pelagial of the northern Atlantic was recorded.     

Ecologal and parasitological chracteristics of redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes: Sebastidae) from the Norwegian Sea and adjacent waters

Special traits of ecology, zoogeography, formation of fauna of parasites, and occurrence of external lesions are investigated in redfish Sebastes mentella from the Norwegian Sea and the adjacent area of the Barents Sea. A considerable weakening of connection with bottom biocenoses in redfish in the pelagial of the Norwegian Sea indicates that it lives here for most of its annual life cycle. In redfish from south of the open part of the Norwegian Sea, there are noticeable differences in the fauna of parasites and in occurrence of external lesions from those in the fish from the north and east of this sea while traits characteristic of redfish from the Irminger Sea are present.     

Productional characteristics of redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaeniformes,Sebastidae) in the Barents Sea and adjacent waters

The annual production of redfish Sebastes mentella of the Norway-Barents Sea population is estimated. The main contribution to the formation of production is made by specimens of the 10–15 year age and in the period of high abundance of recruitment the main contribution is by immature specimens of the 1–8 year age. The generative production of redfish is, on average, by four times lower than the somatic production. The ratio between generative and somatic production is estimated in relation to the population structure. The value of P/B coefficient is in reverse relationship with the individual age and weight. As the part of the junior age groups in the population decreases P/B coefficient increases, and with the increase of the individual average weight in the population it decreases. The relationship between the specific rate of weight growth of redfish and the value of P/B coefficient is shown. The average value of P/B coefficient for the Norway-Barents Sea population of redfish is 0.3.     

The distribution and specific features of the biology of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) during mating in the pelagial of the northern Atlantic

Data on the spatial-bathymetric distribution, size and age composition, sex ratio, and feeding of deepwater redfish Sebastes mentella in the pelagial of the northern Atlantic (Irminger and Labrador seas) during mating are provided. From 1982 to 1999, the mating of S. mentella took place in the central and southern parts of the Irminger Sea (56°–62° N, 30°–43° W); since 2000 it took place in two geographically isolated areas: in the water area of the open part of the Labrador Sea, at sites of the south of the Irminger Sea adjacent to it (54°–58° N, 38°–50° W), and above the western slopes of the Reykjanes Ridge (62°–65° N, 25°–34° W). It is assumed that during mating in the northern area mixed aggregations of two ecological groups of S. mentella—an oceanic group that distributes in the pelagial and a bottom group that inhabits the slopes of Iceland—are formed. The formation of isolated areas of mating of the species is determined by the orientation of feeding migrations that are simultaneously migrations to spawning grounds. Fish of medium sizes migrate to spawning grounds in the southwestern direction, while large fish migrate in the northern direction; the fertilization of females in these areas occurs at the end of summer. In S. mentella, the seasonal and age differences in food composition are clearly pronounced. With the onset of mating, the males’ intensity of feeding in both regions decreases by a factor of 1.5–2.0, while females continue to feed actively.     

Biological and genetic characteristics of deepwater redfish <Emphasis Type="Italic">Sebastes mentella</Emphasis> (Scorpaenidae) from the open part of the Norwegian Sea

The analysis is conducted of the biological and genetic characteristics of deepwater redfish Sebastes mentella from the open part of the Norwegian Sea. A similarity of the studied sample with analogous groups of deepwater redfish from the Northeast Atlantic in biological parameters and their dynamics is revealed. Polymorphism is registered in three of the nine studied enzyme loci: malic enzyme (NADF-dependent malatedehydrogenase), MEP-1*; phosphoglucomutase from the liver, PGM-2*; and glucose-6-phosphateisomerase, PGI*. A pairwise comparison of allele frequencies shows a similarity of the samples of deepwater redfish from the enclave of the Norwegian Sea. In addition, based on a pairwise analysis, significant differences are absent between the samples with similar biological characteristics from the open part of the Norwegian Sea and the Irminger Sea.     

The North Atlantic subpolar gyre and the marine migration of Atlantic salmon Salmo salar: the ‘Merry‐Go‐Round’ hypothesis

One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62° N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62° N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high‐seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium‐137 (¹³⁷Cs) levels in S. salar returning to a Quebec river suggested 62·3% had fed at or east of Iceland, whereas levels in 1 sea‐winter (SW) Atlantic Canada returnees indicated 24·7% had fed east of the Faroes. Lower levels of ¹³⁷ Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open‐ocean migrations of epipelagic fishes.     

Three‐dimensional post‐glacial expansion and diversification of an exploited oceanic fish

Vertical divergence in marine organisms is being increasingly documented, yet much remains to be carried out to understand the role of depth in the context of phylogeographic reconstruction and the identification of management units. An ideal study system to address this issue is the beaked redfish, Sebastes mentella – one of four species of ‘redfish’ occurring in the North Atlantic – which is known for a widely distributed ‘shallow‐pelagic’ oceanic type inhabiting waters between 250 and 550 m, and a more localized ‘deep‐pelagic’ population dwelling between 550 and 800 m, in the oceanic habitat of the Irminger Sea. Here, we investigate the extent of population structure in relation to both depth and geographic spread of oceanic beaked redfish throughout most of its distribution range. By sequencing the mitochondrial control region of 261 redfish collected over a decadal interval, and combining 160 rhodopsin coding nuclear sequences and previously genotyped microsatellite data, we map the existence of two strongly divergent evolutionary lineages with significantly different distribution patterns and historical demography, and whose genetic variance is mostly explained by depth. Combined genetic data, analysed via independent approaches, are consistent with a Late Pleistocene lineage split, where segregation by depth probably resulted from the interplay of climatic and oceanographic processes with life history and behavioural traits. The ongoing process of diversification in North Atlantic S. mentella may serve as an ‘hourglass’ to understand speciation and adaptive radiation in Sebastes and in other marine taxa distributed across a depth gradient.     

On the spatial relationship between the spawning and feeding parts of the range of lumpfish Cyclopterus lumpus (Cyclopteridae) in the Barents Sea and adjacent waters (according to results of analysis of the size composition similarity)

Results of analysis of similarity of size series of mature females of the lumpfish Cyclopterus lumpus collected on the spawning grounds in the Barents and Norwegian seas (Russian and Norwegian coasts), as well as in the areas of its feeding, are provided. The trajectories of feeding migrations of lumpfish in the southern part of the Barents Sea have been revealed. A clinal decrease in the average length of females in the range from west to east is shown. The area of feeding aggregations of lumpfish spawning off the Russian coast is distinguished. The boundaries of the census water area used to assess the commercial stock of lumpfish and to determine the values of its possible catch off the coast of Murmansk are specified.     

Population structure of Atlantic herring, Clupea harengus L.

During the last decade, genetic studies have been carried out on samples of Atlantic herring, CIupea harengus L., from the Baltic, North Sea, British Isles, Norwegian sea-waters and in the western part of the North Atlantic Ocean. Based on direct comparisons of samples drawn from several areas, the available information on allozyme variation was compiled into a comparable data set and analysed for population structure and genetic distance. The results are discussed in relation to the present stock model for herring.     

Population genetic structure of walleye pollock <Emphasis Type="Italic">Theragra chalcogramma</Emphasis> (Gadidae,Pisces) from the Bering Sea and Sea of Okhotsk

Walleye pollock Theragra chalcogramma Pallas occupies a central place in ecosystems of the North Pacific and is an important target species of fisheries. The species is characterized by daily vertical, spawning, feeding, and wintering migrations and spawning occurring under the sea ice. Since population structure estimation by the tagging with recapture is inefficient in walleye pollock, the pollock resources are difficult to estimate by conventional methods, requiring population genetic studies with molecular markers. The population genetic structure of five spawning aggregations from the Bering Sea was for the first time studied with ten microsatellite loci: Tch5, Tch10, Tch11, Tch12, Tch14, Tch16, Tch17, Tch19, Tch20, and Tch22. A spatially distant sample from the Sea of Okhotsk was used as a reference group. Polymorphism for the markers reached 100%, and heterozygosity of individual loci ranged from 41 to 95% in different populations. It was shown the aggregations of interest are in goodness-to-fit the Hardy-Weinberg equilibrium (HWE) at hole, while the Sea of Okhotsk sample demonstrated a sex bias: the heterozygosity at Tch16 in males was significantly lower than in females. The highest discriminative power was observed for Tch10, Tch20, and Tch22. F _ST genetic distances between populations were typical for marine fishes. A mixed composition was supposed for the sample from the region of the underwater Shirshov Ridge, which serves as a natural partial geographic barrier between the Olyutor-Karagin and Koryak walleye pollock stocks. With the Shirshov sample excluded, F _ST scatter plots and the spatial autocorrelation approach supported isolation by distance for the aggregations. An influence of abiotic factors on the population structure was assumed for walleye pollock of the Bering Sea.     

The influence of glacial epochs and habitat dependence on the diversity and phylogeography of a coastal dolphin species: <Emphasis Type="Italic">Lagenorhynchus albirostris</Emphasis>

In this paper we use mitochondrial and microsatellite DNA variation to investigate the mechanisms that underlie the evolution of population structure in a highly mobile marine mammal, the white-beaked dolphin. We found moderate genetic diversity (h) at mtDNA, but low nucleotide diversity (π) (0.7320 ± 0.0031 and 0.0056 ± 0.0004, respectively), consistent with expectations for a recent expansion. Analyses based on mismatch distributions further suggested a demographic expansion in the Norwegian-Barents Sea population and a spatial expansion in the British isles-North Sea population, implying distinct demographic histories. F _ST values showed clear differentiation among these two populations, but no difference was found between putative populations separated by the English Channel. Our data suggest a stepwise pattern of expansion, dependent on available coastal habitat. The conservation implications are a need to protect local populations isolated by an expanse of deep water, and in particular, a population along the British coasts and in the North Sea as separate from the North Norway-Barents Sea population. It is also evident that overall diversity was reduced, probably during the last glacial epoch.     

Two adjacent inversions maintain genomic differentiation between migratory and stationary ecotypes of Atlantic cod

Atlantic cod is composed of multiple migratory and stationary populations widely distributed in the North Atlantic Ocean. The Northeast Arctic cod (NEAC) population in the Barents Sea undertakes annual spawning migrations to the northern Norwegian coast. Although spawning occurs sympatrically with the stationary Norwegian coastal cod (NCC), phenotypic and genetic differences between NEAC and NCC are maintained. In this study, we resolve the enigma by revealing the mechanisms underlying these differences. Extended linkage disequilibrium (LD) and population divergence were demonstrated in a 17.4‐Mb region on linkage group 1 (LG1) based on genotypes of 494 SNPs from 192 parents of farmed families of NEAC, NCC or NEACxNCC crosses. Linkage analyses revealed two adjacent inversions within this region that repress meiotic recombination in NEACxNCC crosses. We identified a NEAC‐specific haplotype consisting of 186 SNPs that was fixed in NEAC sampled from the Barents Sea, but segregating under Hardy–Weinberg equilibrium in eight NCC stocks. Comparative genomic analyses determine the NEAC configuration of the inversions to be the derived state and date it to ~1.6–2.0 Mya. The haplotype block harbours 763 genes, including candidates regulating swim bladder pressure, haem synthesis and skeletal muscle organization conferring adaptation to long‐distance migrations and vertical movements down to large depths. Our results suggest that the migratory ecotype experiences strong directional selection for the two adjacent inversions on LG1. Despite interbreeding between NEAC and NCC, the inversions are maintaining genetic differentiation, and we hypothesize the co‐occurrence of multiple adaptive alleles forming a ‘supergene’ in the NEAC population.     

Climate-Driven Ichthyoplankton Drift Model Predicts Growth of Top Predator Young

Climate variability influences seabird population dynamics in several ways including access to prey near colonies during the critical chick-rearing period. This study addresses breeding success in a Barents Sea colony of common guillemots Uria aalge where trophic conditions vary according to changes in the northward transport of warm Atlantic Water. A drift model was used to simulate interannual variations in transport of cod Gadus morhua larvae along the Norwegian coast towards their nursery grounds in the Barents Sea. The results showed that the arrival of cod larvae from southern spawning grounds had a major effect on the size of common guillemot chicks at fledging. Furthermore, the fraction of larvae from the south was positively correlated to the inflow of Atlantic Water into the Barents Sea thus clearly demonstrating the mechanisms by which climate-driven bottom-up processes influence interannual variations in reproductive success in a marine top predator.     

Genetic population structure of turbot (Scophthalmus maximus L.) supports the presence of multiple hybrid zones for marine fishes in the transition zone between the Baltic Sea and the North Sea

Genetic population structure of turbot (Scophthalmus maximus L.) in the Northeast Atlantic was investigated using eight highly variable microsatellite loci. In total 706 individuals from eight locations with temporal replicates were assayed, covering an area from the French Bay of Biscay to the Aaland archipelago in the Baltic Sea. In contrast to previous genetic studies of turbot, we found significant genetic differentiation among samples with a maximum pairwise FST of 0.032. Limited or no genetic differentiation was found among samples within the Atlantic/North Sea area and within the Baltic Sea, suggesting high gene flow among populations in these areas. In contrast, there was a sharp cline in genetic differentiation going from the low saline Baltic Sea to the high saline North Sea. The data were explained best by two divergent populations connected by a hybrid zone; however, a mechanical mixing model could not be ruled out. A significant part of the genetic variance could be ascribed to variation among years within locality. Nevertheless, the population structure was relatively stable over time, suggesting that the observed pattern of genetic differentiation is biologically significant. This study suggests that hybrid zones are a common phenomenon for marine fishes in the transition area between the North Sea and the Baltic Sea and highlights the importance of using interspecific comparisons for inferring population structure in high gene flow species such as most marine fishes.     

Intraspecific variability in the “vowel”‐like sounds of beluga whales (Delphinapterus leucas): Intra‐ and interpopulation comparisons

The beluga whale (Delphinapterus leucas) has a rich and complicated vocal repertoire. However, different populations use similar and common types of signals. We studied physical features of one of these types, “vowels,” in three Russian populations: the White Sea population (European North), the Chukotka population (the Bering Sea, Chukotka), and the Okhotsk Sea population (Russian Far East) as well as in four summer aggregations of the White Sea belugas over several years in duration. The pulse repetition rate (PRR) at half of the duration of the signal was measured. We found that the PRR of “vowels” collected in the same summer aggregation during different years is stable in time but varies between locations. The degree of variation corresponds with the geographic distance between different locations. Significant differences were discovered between populations separated by thousands of kilometers, and to a lesser extent, between summer aggregations inhabiting different bays of the White Sea. The variation in PRR between the locations can be caused by the divergence of signals owing to the accumulation of random errors during transmission of these signals from generation to generation, which progressed independently in different summer aggregations and populations.     

Female philopatry in coastal basins and male dispersion across the North Atlantic in a highly mobile marine species, the sperm whale (Physeter macrocephalus)

The mechanisms that determine population structure in highly mobile marine species are poorly understood, but useful towards understanding the evolution of diversity, and essential for effective conservation and management. In this study, we compare putative sperm whale populations located in the Gulf of Mexico, western North Atlantic, Mediterranean Sea and North Sea using mtDNA control region sequence data and 16 polymorphic microsatellite loci. The Gulf of Mexico, western North Atlantic and North Sea populations each possessed similar low levels of haplotype and nucleotide diversity at the mtDNA locus, while the Mediterranean Sea population showed no detectable mtDNA diversity. Mitochondrial DNA results showed significant differentiation between all populations, while microsatellites showed significant differentiation only for comparisons with the Mediterranean Sea, and at a much lower level than seen for mtDNA. Samples from either side of the North Atlantic in coastal waters showed no differentiation for mtDNA, while North Atlantic samples from just outside the Gulf of Mexico (the western North Atlantic sample) were highly differentiated from samples within the Gulf at this locus. Our analyses indicate a previously unknown fidelity of females to coastal basins either side of the North Atlantic, and suggest the movement of males among these populations for breeding.     

Population genetic structure and evolutionary history of North Atlantic beluga whales (Delphinapterus leucas) from West Greenland, Svalbard and the White Sea

Population structure in many Arctic marine mammal species reflects a dynamic interplay between physical isolating mechanisms and the extent to which dispersal opportunities are met. We examined variation within mtDNA and eight microsatellite markers to investigate population structure and demographic history in beluga whales in the North Atlantic. Genetic heterogeneity was observed between Svalbard and West Greenland that reveals limited gene flow over ecological time scales. Differentiation was also recorded between Atlantic belugas and two previously studied populations in the North Pacific, the Beaufort Sea and Gulf of Alaska. However, Bayesian cluster analysis of the nDNA data identified two population clusters that did not correspond to the respective ocean basins, as predicted, but to: (1) Arctic (Svalbard–White Sea–Greenland–Beaufort Sea) and (2) Subarctic (Gulf of Alaska) regions. Similarly, the deepest phylogeographic signal was between the Arctic populations and the Gulf of Alaska. Fitting an isolation-with-migration model yielded genetic abundance estimates that match census estimates and revealed that Svalbard and the Beaufort Sea likely diverged 7,600–35,400 years ago but have experienced recurrent periods with gene flow since then, most likely via the Russian Arctic during subsequent warm periods. Considering current projections of continued sea ice losses in the Arctic, this study identified likely routes of future contact among extant beluga populations, and other mobile marine species, which have implications for genetic introgression, health, ecology and behavior.     

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.