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Investigations of genetic stock structure sometimes reveal a mismatch between management units and biological units. In Scandinavian waters, Norway lobster (Nephrops norvegicus) is divided into two management units (the Skagerrak–Kattegat and the Norwegian Deep). We have tested the population genetic structure of Nephrops within this region using microsatellite DNA markers, and compared the structure with the present management units. Our study suggests no population genetic structure of Nephrops within the Skagerrak, Kattegat, and Norwegian Deep region, whereas a shallow genetic structure was detected on a larger geographical scale when comparing outgroup samples from Scotland and Iceland. We found indications of sex-biased dispersal as the overall genetic differences were larger for females. Ocean current patterns suggest that Nephrops stocks in the region may be connected by larval drift. The two areas differ in fishing pressure, monitoring, assessment, and regulations, which is an argument for maintaining the present two-areas management regime despite the evidence for one biological population.

Environmental DNA (eDNA) has gained popularity as a tool for ecosystem biomonitoring and biodiversity assessment. Although much progress has been made regarding laboratory and fieldwork protocols, the issue of sampling efficiency requires further investigation, particularly in three-dimensional marine systems. This study focuses on fish community composition in marine ecosystems and aims to analyze the efficiency of sampling design given the sampling effort for distinguishing between different communities. We sampled three fjords in Northern Norway, taking samples along fjord transects and at three different depths, and amplified a fragment of the mitochondrial 12S rRNA gene of bony fishes using the MiFish primers. We evaluated the effect of (i) the number of sampling stations, (ii) samples' spatial distribution, and (iii) the data treatment approach (presence/absence versus semiquantitative) for maximizing the efficiency of eDNA metabarcoding sampling when inferring differences of fish community compositions between fjords. We found that the manner of data treatment strongly affected the minimum number of sampling stations required to detect differences among communities; because the semiquantitative approach retained some information about abundance of the underlying reads, it was the most efficient. Furthermore, we found little-to-no difference of fish communities in samples from intermediate depths when comparing vertical fish communities. Lastly, we found that the differences between fish communities at the surface were the highest across the horizontal distance and overall, samples ~30 km apart showed the highest variation in the horizontal distribution. Boosting sampling efficiency (reducing sampling effort without compromising ecological inferences) can significantly contribute to enhanced biodiversity management and efficient biomonitoring plans.

Marine fisheries are often allocated to stocks that reflect pragmatic considerations and may not represent the species’ spatial population structure, increasing the risk of mismanagement and unsustainable harvesting. Here we compile mark–recapture data collected across the North Atlantic to gain insight into the spatial population structure of Greenland halibut (Reinhardtius hippoglossoides), an issue that has been unresolved for decades. The dataset contains 168130 fish tagged from 1952 to 2021, with 5466 (3.3%) recaptured individuals. Our results indicate that fish tagged at

The cold-adapted polar cod Boreogadus saida, a key species in Arctic ecosystems, is vulnerable to global warming and ice retreat. In this study, 1257 individuals sampled in 17 locations within the latitudinal range of 75–81°N from Svalbard to East Siberian Sea were genotyped with a dedicated suite of 116 single-nucleotide polymorphic loci (SNP). The overall pattern of isolation by distance (IBD) found was driven by the two easternmost samples (East Siberian Sea and Laptev Sea), whereas no differentiation was registered in the area between the Kara Sea and Svalbard. Eleven SNP under strong linkage disequilibrium, nine of which could be annotated to chromosome 2 in Atlantic cod, defined two genetic groups of distinct size, with the major cluster containing seven-fold larger number of individuals than the minor. No underlying geographic basis was evident, as both clusters were detected throughout all sampling sites in relatively similar proportions (i.e. individuals in the minor cluster ranging between 4 and 19% on the location basis). Similarly, females and males were also evenly distributed between clusters and age groups. A differentiation was, however, found regarding size at age: individuals belonging to the major cluster were significantly longer in the second year. This study contributes to increasing the population genetic knowledge of this species and suggests that an appropriate management should be ensured to safeguard its diversity.

Blue ling is a deep-water species that has been severely fished upon into coastal and offshore fisheries since the early 1970s, thus causing the collapse of the populations in the last two decades. Genetic information is scarce in this species, and molecular markers are therefore needed to provide advice both for management and for rebuilding the stocks. A suite of 103 SNP markers was identified from ddRAD sequencing data. From those, 81 were organized in three multiplex reactions, and tested on 150 individuals from three different sampling locations. Good-quality amplification products were successfully obtained from 70 of the markers. All SNP loci were biallelic, with averaged He per locus ranging between 0.101 and 0.500.

Coastal Atlantic cod (Gadus morhua) in the Northeast Atlantic has seen a continuous decline since the industrialization of the coastal fishery, and management needs to address the spatial and temporal complexities of coexisting cod stocks. Toward that end, genetic analyses and oceanographic modelling of coastal and oceanic cod larval drift patterns were combined to elucidate the mechanisms responsible for an observed genetic cline over a >1500 km stretch along the coast of Norway. The results indicate that the north–south cline in coastal cod represents an extended contact zone between genetically divergent North Sea and Northeast Arctic cod and is maintained by two-way gene flow: by northward drift of pelagic eggs and larvae and by southward spawning migrations of Northeast Arctic cod. Computer simulations verify that the genetic cline can be established rapidly if gene flow into coastal populations is substantial. The shape of the cline, on the other hand, was found to be largely insensitive to the total amount of gene flow and therefore carries little information on extent of gene flow into and among coastal populations.

Many marine organisms have a permanent presence both inshore and offshore and spawn in multiple areas, yet their status as separate populations or stocks remain unclear. This is the situation for the northern shrimp (Pandalus borealis) around the Arctic Ocean, which in northern Norway represents an important income for a small-scale coastal fishery and a large-vessel offshore fleet. In Norwegian waters, we uncovered two distinct genetic clusters, viz. a Norwegian coastal and a Barents Sea cluster. Shrimps with a mixed heritage from the Norwegian coastal and the Barents Sea clusters, and genetically different from both, inhabit the fjords at the northernmost coast (Finnmark). Genetic structure between fjords did not display any general trend, and only the Varangerfjord in eastern Finnmark displayed significant genetic structure within the fjord. Shrimps in the Finnmark fjords differed in some degree from shrimps both in the adjacent Barents Sea and along the rest of the coast and should probably be considered a separate management unit.

Challenging long‐held perceptions of fish management units can help to protect vulnerable stocks. When a fishery consisting of multiple genetic stocks is managed as a single unit, overexploitation and depletion of minor genetic units can occur. Atlantic cod (Gadus morhua) is an economically and ecologically important marine species across the North Atlantic. The application of new genomic resources, including SNP arrays, allows us to detect and explore novel structure within specific cod management units. In Norwegian waters, coastal cod (i.e. those not undertaking extensive migrations) are divided into two arbitrary management units defined by ICES: one between 62° and 70°N (Norwegian coastal cod; NCC) and one between 58° and 62°N (Norwegian coastal south; NCS). Together, these capture a fishery area of >25,000 km2 containing many spawning grounds. To assess whether these geographic units correctly represent genetic stocks, we analysed spawning cod of NCC and NCS for more than 8,000 SNPs along with samples of Russian White Sea cod, north‐east Arctic cod (NEAC: the largest Atlantic stock), and outgroup samples representing the Irish and Faroe Sea's. Our analyses revealed large differences in spatial patterns of genetic differentiation across the genome and revealed a complex biological structure within NCC and NCS. Haplotype maps from four chromosome sets show regional specific SNP indicating a complex genetic structure. The current management plan dividing the coastal cod into only two management units does not accurately reflect the genetic units and needs to be revised. Coastal cod in Norway, while highly heterogenous, is also genetically distinct from neighbouring stocks in the north (NEAC), west (Faroe Island) and the south. The White Sea cod are highly divergent from other cod, possibly yielding support to the earlier notion of subspecies rank. publishedVersion

The bearded goby Sufflogobius bibarbatus is an abundant endemic small fish species on the continental shelf of the northern Benguela. The goby habitat is characterised by generally low bottom oxygen concentrations that vary spatially and seasonally. In the present study of population structure, 13 samples of S. bibarbatus from inner and outer shelf areas between 19°S and 32°S were screened using ten microsatellite loci. The genetic data were analysed in relation to isolation by distance and depth. Furthermore, for the first time, this study examined genetic data in relation to bottom oxygen concentration at the sampling locations. The data show low but significant genetic heterogeneity (G‐test; FST = 0.007, p < .05). There was weak but significant genetic differentiation along a latitudinal gradient across all sampling sites from 19.50°S to 32.37°S (Mantel test; r = .464, p = .001), but this disappeared when the southernmost sample was removed. On the other hand, a positive correlation of bottom oxygen concentration with pairwise FST (r = .336; p = .017) was observed among the sampling sites from the Northern Benguela shelf area. Overall, the data are complex but suggest that isolation by distance and bottom oxygen concentration may play a role in the genetic structuring of S. bibarbatus. The findings are discussed in relation to the species’ life history features and oceanographic characteristics of the Benguela upwelling ecosystem. Paid Open Access

Background Atlantic cod (Gadus morhua L.) has formed the basis of many economically significant fisheries in the North Atlantic, and is one of the best studied marine fishes, but a legacy of overexploitation has depleted populations and collapsed fisheries in several regions. Previous studies have identified considerable population genetic structure for Atlantic cod. However, within Norway, which is the country with the largest remaining catch in the Atlantic, the population genetic structure of coastal cod (NCC) along the entire coastline has not yet been investigated. We sampled > 4000 cod from 55 spawning sites. All fish were genotyped with 6 microsatellite markers and Pan I (Dataset 1). A sub-set of the samples (1295 fish from 17 locations) were also genotyped with an additional 9 microsatellites (Dataset 2). Otoliths were read in order to exclude North East Arctic Cod (NEAC) from the analyses, as and where appropriate. Results We found no difference in genetic diversity, measured as number of alleles, allelic richness, heterozygosity nor effective population sizes, in the north-south gradient. In both data sets, weak but significant population genetic structure was revealed (Dataset 1: global FST = 0.008, P

Identification of cryptic species can have profound implications in fishery management, conservation and biodiversity contexts. In the North Atlantic, the genus Sebastes is currently represented by four species, although additional cryptic species have been assumed. The connectivity of the gene-pools within the genus in Greenland waters, in particular, remains largely unexplored. Using a panel of 13 microsatellite markers for 720 fish, we explored the species complex of Sebastes norvegicus in Greenland waters. Genetic analyses provided evidence for three cryptic species in samples that were morphologically identified as S. norvegicus. They were termed S. norvegicus-A, S. norvegicus-B, and S. norvegicus-giants. A few phenotypic features exist to identify adult S. norvegicus giants, but no characteristics have been identified for the two other cryptic species. The proposed cryptic species should be recognized in the management regime to ensure sustainable exploitation and conservation of Sebastes species in Greenland waters.

Exploited marine resources can be managed more effectively when accurate information on geographic population structure is available. Genetic markers offer a powerful tool for fisheries management, because they reveal biologically sound management units. Single nucleotide polymorphisms (SNPs) markers derived from restriction-site associated DNA sequencing (RAD-seq) were developed and used to investigate the stock structure of Greenland halibut (Reinhardtius hippoglossoides). A total of 96 SNPs were analyzed from 384 individuals and eight locations across the Atlantic. Our results suggest a subdivision of Greenland halibut into two populations, an eastern Atlantic population and a western Atlantic population, with a proposed border across the Denmark Strait. In general, Greenland halibut display weak but significant population structure (overall FST= 0.003; p < 0.001), which can be explained by connectivity among populations owing to the migratory behavior or egg and larval drift.

Science-based management of marine fisheries and effective ecosystem monitoring both require the analysis of large amounts of often complex and difficult to collect information. Legislation also increasingly requires the attainment of good environmental status, which again demands collection of data to enable efficient monitoring and management of biodiversity. Such data is traditionally obtained as a result of research surveys through the capture and/or visual identification of organisms. Recent years have seen significant advances in the utilisation of environmental DNA (eDNA) in the marine environment in order to develop alternative cost-effective ways to gather relevant data. Such approaches attempt to identify and/or quantify the species present at a location through the detection of extra-organismal DNA in the environment. These new eDNA based approaches have the potential to revolutionise data collection in the marine environment using non-invasive sampling methods and providing snapshots of biodiversity beyond the capacity of traditional sampling. Here we present a non-technical summary of different approaches in the field of eDNA, and emphasise the broad application of this approach, with value for the governance and management of marine aquatic ecosystems. The review focuses on identifying those tools which are now readily applicable and those which show promise but are currently in development and require further validations. The aim is to provide an understanding of techniques and concepts that can be used by managers without genetic or genomic expertise when consulting with specialists to perform joint evaluations of the utility of the approaches. Spanish Ministry of Science, Innovation and Universities through the EDAMAME ("Environmental DNA based approaches for marine and aquatic monitoring and evaluation") project [CTM2017-89500-R]; Scientific Research Network "Eco-evolutionary dynamics in natural and anthropogenic communities" (Research Foundation - Flanders) [W 0.037.10N] info:eu-repo/semantics/publishedVersion

Fish stocks represent fundamental units in fisheries management, and their identification, especially in mixed-fisheries, represents one of the primary challenges to sustainable harvest. Here, we describe the first “real-time” genetic management program used to manage a mixed-stock fishery of a non-salmonid and commercially significant marine fish, the Atlantic cod (Gadus morhua L). Based upon the analysis of >18 000 fish sampled from the commercial catch in Lofoten (Norway), which represents the largest remaining cod fishery in the Atlantic, we estimated the fraction of North East Arctic cod (NEAC), and Norwegian Coastal cod (NCC), just 24 h post-landing. These estimates, based upon the analysis of the Pantophysin gene, were performed weekly in the winter and spring of each year in the period 2007–2017. The program has successfully permitted the Norwegian Directorate of Fisheries to actively manage the commercial exploitation of the highly abundant NEAC stock, while simultaneously limiting exploitation of the fragile NCC stock, both of which overlap at the spawning grounds. Data from this program have also revealed a distinct temporal increase in the fraction of NEAC on the spawning grounds in this region, which is consistent with the overall increased abundance of this stock as estimated by ICES. publishedVersion

The identification of isolated populations in widely distributed marine species is often impeded by low levels of genetic differentiation. However, modern genetic approaches now allow for the efficient detection of potentially large numbers of novel genetic variations, thereby improving the power to identify biologically meaningful management units. To investigate the genetic structuring of saithe (Pollachius virens L.), we applied seascape genetic approaches to 131 single nucleotide polymorphism loci genotyped in 584 fish collected from 11 locations across the North Atlantic. Wombling analysis and the Monmonier algorithm revealed four genetic clusters (Barents Sea, Central Northeast Atlantic, Rockall, and Canada) across the species distribution range. These results imply that genetic structuring in saithe may be influenced by abiotic factors such as geographical distance, and bathymetry as well as biotic factors such as sex-biased migration, and natal homing. The results suggest a potential mismatch between management and biological units across the Northeast Atlantic, which may have implications for sustainable exploitation of the species.

Genetic population structure is often used to identify management units in exploited species, but the extent of genetic differentiation may be inflated by geographic variation in the level of hybridization between species. We identify the genetic population structure of Sebastes mentella and investigate possible introgression within the genus by analyzing 13 microsatellites in 2562 redfish specimens sampled throughout the North Atlantic. The data support an historical divergence between the ‘shallow’ and ‘deep’ groups, beyond the Irminger Sea where they were described previously. A third group, ‘slope’, has an extended distribution on the East Greenland Shelf, in addition to earlier findings on the Icelandic Slope. Furthermore, S. mentella from the Northeast Arctic and Northwest Atlantic waters are genetically different populations. In both areas, interspecific introgression may influence allele frequency differences among populations. Evidence of introgression was found for almost all the identified Sebastes gene pools, but to a much lower extent than suggested earlier. Greenland waters appear to be a sympatric zone for many of the genetically independent Sebastes groups. This study illustrates that the identified groups maintain their genetic integrity in this region despite introgression. This article is protected by copyright. All rights reserved.

With the decline of many of the world’s fisheries, increased regulation, including marine protected areas (MPA), forms an increasingly important role in promoting sustainable resource use. Here, we present a novel “real-time” genetic monitoring programme used to protect the depleted Norwegian coastal cod stock (NCC) in an MPA during the spawning season, while a fishery targeted at the sustainable Northeast Arctic cod stock (NEAC) operates immediately outside. In the period 2009–2016, >6800 cod from the fishery were genotyped with the PanI locus that is discriminatory between these two stocks. The estimated fraction of NEAC increased during the study period until 2014; however, it did not exceed 70% for any sustained period. Therefore, the MPA remained closed for commercial harvest. Genetic analysis of eggs revealed a distinctly lower fraction of NEAC than in the catch from the adult stock, both immediately outside and within the MPA itself. We suggest that this discrepancy is likely to reflect differences in spawning areas used by NCC and NEAC. Estimated fractions of NEAC/NCC using PanI, otolith classification, and 39 single nucleotide polymorphisms were similar, thus validating the use of PanI to estimate NEAC/NCC composition.

The Northeast Arctic cod (Gadus morhua L.: NEAC) remains the most abundant cod stock in the North Atlantic, while the catches of the partially co-occurring Norwegian coastal cod (NCC) stocks have dramatically decreased in recent years. To ensure effective management of the two stocks, it is necessary to know if the population genetic structure is associated with any pattern in the spatial dynamics or whether it is affected by any distinct environmental factors. By combining information from electronic data storage tags (DST) and molecular genetics methods with statistical tools, we have been able to associate spatial dynamics and distinct environmental factors to the two cod stocks. In general, adult NEAC migrate between deep, warm overwintering grounds and shallow summer feeding grounds where water temperatures maybe low. In contrast, NCC do not undertake large-scale seasonal migrations, show little seasonal variation in depth distribution, and experience the opposite seasonal change in temperature compared with NEAC. However, within the NCC group, some individuals did conduct longer horizontal movements than others. Even though the distances calculated in this study represent the shortest distance between release and recapture positions, they are far higher than previously reported by NCC. Distinctive depth profiles indicate that this migrant NCC have moved out of the area, passing the deep trenches outside Lofoten while more stationary NCC occupies shallower depths throughout the year. The temperature profiles also indicate that migrant and stationary NCC has occupied different areas during the year. We demonstrate that the combination of information from DSTs and molecular genetics offers a deeper understanding of individual cod behaviour, provides an insight in the spatial dynamics of the species, and ultimately, improves the scientific basis for management of a complex mixed fishery of Atlantic cod.

Genetic population structure is often used to identify management units in exploited species, but the extent of genetic differentiation may be inflated by geographic variation in the level of hybridization between species. We identify the genetic population structure of Sebastes mentella and investigate possible introgression within the genus by analyzing 13 microsatellites in 2,562 redfish specimens sampled throughout the North Atlantic. The data support an historical divergence between the “shallow” and “deep” groups, beyond the Irminger Sea where they were described previously. A third group, “slope,” has an extended distribution on the East Greenland Shelf, in addition to earlier findings on the Icelandic slope. Furthermore, S. mentella from the Northeast Arctic and Northwest Atlantic waters are genetically different populations. In both areas, interspecific introgression may influence allele frequency differences among populations. Evidence of introgression was found for almost all the identified Sebastes gene pools, but to a much lower extent than suggested earlier. Greenland waters appear to be a sympatric zone for many of the genetically independent Sebastes groups. This study illustrates that the identified groups maintain their genetic integrity in this region despite introgression.

Oceans are experiencing increasing acidification in parallel to a distinct warming trend in consequence of ongoing climate change. Rising seawater temperatures are mediating a northward shift in distribution of Atlantic cod (Gadus morhua), into the habitat of polar cod (Boreogadus saida), that is associated with retreating cold water masses. This study investigates the competitive strength of the co-occurring gadoids under ocean acidification and warming (OAW) scenarios. Therefore, we incubated specimens of both species in individual tanks for 4 months, under different control and projected temperatures (polar cod: 0, 3, 6, 8 °C, Atlantic cod: 3, 8, 12, 16 °C) and PCO2 conditions (390 and 1170 µatm) and monitored growth, feed consumption and standard metabolic rate. Our results revealed distinct temperature effects on both species. While hypercapnia by itself had no effect, combined drivers caused nonsignificant trends. The feed conversion efficiency of normocapnic polar cod was highest at 0 °C, while optimum growth performance was attained at 6 °C; the long-term upper thermal tolerance limit was reached at 8 °C. OAW caused only slight impairments in growth performance. Under normocapnic conditions, Atlantic cod consumed progressively increasing amounts of feed than individuals under hypercapnia despite maintaining similar growth rates during warming. The low feed conversion efficiency at 3 °C may relate to the lower thermal limit of Atlantic cod. In conclusion, Atlantic cod displayed increased performance in the warming Arctic such that the competitive strength of polar cod is expected to decrease under future OAW conditions.

We developed and characterized 20 microsatellite primer loci for the northern shrimp Pandalusborealis. All 20 loci were polymorphic with number of alleles ranging from 3 to 36 and with observed heterozygosity between 0.04 and 0.93. In addition, we tested the utility of these markers in three related shrimp species, P. montagui, Atlantopandaluspropinqvus and Dichelopandalusbonnieri. These new markers will prove useful in the identification of stock structure and hence, assessment of the commercially important species P. borealis.

Summary This study presents a molecular genetic characterization of Atlantic cod reared in commercial marine farms. Samples consisted of approximately 47 fish collected from nine cages located on four farms throughout Norway. In addition, 28 farmed escapees were recaptured in the sea (443 fish in total). Nine microsatellite loci and the Pan I gene were analysed, revealing a total of 181 alleles. Each sample contained 43‐63% of total allelic variation. Comparing variation with published data for wild cod indicates that lower genetic variation exists within single cages than in wild populations. Significant linkage disequilibrium was observed amongst pairs of loci in all samples, suggesting a low number of contributing parental fish. Global FST was 0.049, and the highest pairwise FST value (pooled loci) was 0.085. For single loci, the Pan I gene was the most diagnostic, displaying a global FST of 0.203. Simulations amongst the samples collected on farms revealed an overall correct self-assignment percentage of 75%, demonstrating a high probability of identifying individuals to their farm of origin. Identification of the 28 escapees revealed a single cage as the most likely source of origin for half of the escapees, whilst the remaining fish were assigned to a mixture of samples, suggesting more than one source of escapees.

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.

Effects of global warming on animal distribution and performance become visible in many marine ecosystems. The present study was designed to develop a concept for a cause and effect understanding with respect to temperature changes and to explain ecological findings based on physiological processes. The concept is based on a wide comparison of invertebrate and fish species with a special focus on recent data obtained in two model species of fish. These fish species are both characterized by northern and southern distribution limits in the North Atlantic: eelpout (Zoarces viviparus), as a typical non-migrating inhabitant of the coastal zone and the cod (Gadus morhua), as a typical inhabitant of the continental shelf with a high importance for fisheries. Mathematical modelling demonstrates a clear significant correlation between climate induced temperature fluctuations and the recruitment of cod stocks. Growth performance in cod is optimal at temperatures close to 10°C, regardless of the population investigated in a latitudinal cline. However, temperature specific growth rates decrease at higher latitudes. Also, fecundity is less in White Sea than in North and Baltic Sea cod or eelpout populations. These findings suggest that a cold-induced shift in energy budget occurs which is unfavorable for growth performance and fecundity. Thermal tolerance limits shift depending on latitude and are characterized by oxygen limitation at both low or high temperatures. Oxygen supply to tissues is optimized at low temperature by a shift in hemoglobin isoforms and oxygen binding properties to lower affinities and higher unloading potential. Protective stimulation of heat shock protein synthesis was not observed. According to a recent model of thermal tolerance the downward shift of tolerance limits during cold adaptation is associated with rising mitochondrial densities and, thus, aerobic capacity and performance in the cold, especially in eurythermal species. At the same time the costs of mitochondrial maintenance reflected by mitochondrial proton leakage should rise leaving a lower energy fraction for growth and reproduction. The preliminary conclusion can be drawn that warming will cause a northern shift of distribution limits for both species with a rise in growth performance and fecundity larger than expected from the Q10 effect in the north and lower growth or even extinction of the species in the south. Such a shift may heavily affect fishing activities in the North Sea.

The genomic architecture underlying ecological divergence and ecological speciation with gene flow is still largely unknown for most organisms. One central question is whether divergence is genome-wide or localized in 'genomic mosaics' during early stages when gene flow is still pronounced. Empirical work has so far been limited, and the relative impacts of gene flow and natural selection on genomic patterns have not been fully explored. Here, we use ecotypes of Atlantic cod to investigate genomic patterns of diversity and population differentiation in a natural system characterized by high gene flow and large effective population sizes, properties which theoretically could restrict divergence in local genomic regions. We identify a genomic region of strong population differentiation, extending over approximately 20 cM, between pairs of migratory and stationary ecotypes examined at two different localities. Furthermore, the region is characterized by markedly reduced levels of genetic diversity in migratory ecotype samples. The results highlight the genomic region, or 'genomic island', as potentially associated with ecological divergence and suggest the involvement of a selective sweep. Finally, we also confirm earlier findings of localized genomic differentiation in three other linkage groups associated with divergence among eastern Atlantic populations. Thus, although the underlying mechanisms are still unknown, the results suggest that 'genomic mosaics' of differentiation may even be found under high levels of gene flow and that marine fishes may provide insightful model systems for studying and identifying initial targets of selection during ecological divergence.

In a warmer Arctic, living conditions will change at all trophic levels of the marine ecosystem. Increased air and water temperatures will likely substantially reduce ice coverage. Trophic interactions might change and increased competition between resident Arctic species and invasive species seems likely. A theme session on “Marine harvesting in the Arctic” was held at the international Arctic Frontiers Conference in Tromsø, Norway, in January 2013. The theme session partitioned the topic into two sub-sessions: (i) introduced species, immigration and fate of resident species and (ii) prospective harvesting of marine biological resources in the Arctic. The four articles that follow this introduction are based on presentations made at the Arctic Frontiers theme session. These articles cover topics such as: how ice breeding seals (Pagophilus groenlandicus) can cope with ice retention in the Northwest Atlantic, how planktonic stages of the resident polar cod (Boreogadus saida) and the pole-ward expanding Pacific sand lance (Ammodytes hexapterus) may compete for food in the warming Beaufort Sea, and how the introduced red king crab (Paralithodes camtschaticus) disperse in the Barents Sea. The fourth article shows how differences in the life-history strategies of keystone zooplankton species will likely affect future productivity of commercial fisheries in polar regions.

14 páginas, 4 figuras.--Steve Cadrin ... et al.-- Acceso avanzado online., Throughout their range, Sebastes spp. are adapted to a diversity of ecological niches, with overlapping spatial distributions of different species that have little or no morphological differences. Divergence of behavioural groups into depth-defined adult habitats has led to reproductive isolation, adaptive radiation, and speciation in the genus Sebastes. Recent genetic research, supported by life-history information, indicates four biological stocks of Sebastes mentella in the Irminger Sea and adjacent waters: a western stock, a deep-pelagic stock, a shallow-pelagic stock, and an Iceland slope stock. Congruent differences in fatty acids and parasites suggest that these genetically distinct populations are adapted to disparate trophic habitats in pelagic waters (shallower and deeper than the deep-scattering layer) and in demersal habitats on the continental slope. Morphology of pelagic forms is also more streamlined than demersal forms. Although genetic differences and evidence for reproductive isolation are clear, these populations appear to share common nursery habitats on the Greenland shelf. We propose a redefinition of practical management units near the Irminger Sea based on geographic proxies for biological stocks and minimizing mixed-stock catches according to the spatial patterns of the recent fishery.

Background Marine fishes have been shown to display low levels of genetic structuring and associated high levels of gene flow, suggesting shallow evolutionary trajectories and, possibly, limited or lacking adaptive divergence among local populations. We investigated variation in 98 gene-associated single nucleotide polymorphisms (SNPs) for evidence of selection in local populations of Atlantic cod (Gadus morhua L.) across the species distribution. Results Our global genome scan analysis identified eight outlier gene loci with very high statistical support, likely to be subject to directional selection in local demes, or closely linked to loci under selection. Likewise, on a regional south/north transect of central and eastern Atlantic populations, seven loci displayed strongly elevated levels of genetic differentiation. Selection patterns among populations appeared to be relatively widespread and complex, i.e. outlier loci were generally not only associated with one of a few divergent local populations. Even on a limited geographical scale between the proximate North Sea and Baltic Sea populations four loci displayed evidence of adaptive evolution. Temporal genome scan analysis applied to DNA from archived otoliths from a Faeroese population demonstrated stability of the intra-population variation over 24 years. An exploratory landscape genetic analysis was used to elucidate potential effects of the most likely environmental factors responsible for the signatures of local adaptation. We found that genetic variation at several of the outlier loci was better correlated with temperature and/or salinity conditions at spawning grounds at spawning time than with geographic distance per se. Conclusion These findings illustrate that adaptive population divergence may indeed be prevalent despite seemingly high levels of gene flow, as found in most marine fishes. Thus, results have important implications for our understanding of the interplay of evolutionary forces in general, and for the conservation of marine biodiversity under rapidly increasing evolutionary pressure from climate and fisheries induced changes in local environments.

The genetic population structure of spotted wolffish Anarhichas minor (Olafsen) in the North Atlantic was in- vestigated by allozyme electrophoresis and by PCR based RFLP variation in mtDNA. Samples were collected from five sites distributed across the North Atlantic and from second generation Norwegian broodstock. The present data demon- strates that significant differences exist between almost all sampling sites, indicating biologically different groups of indi- viduals, and thus the existence of different management populations of spotted wolffish in the North Atlantic. Overall, the data indicated that isolation by distance is weak among spotted wolffish at the geographic scale investigated in this study, suggesting that gene flow between neighbouring spotted wolffish populations is low. The present study demonstrates a high level of geographic population structure between the western Atlantic, middle and eastern Atlantic and Baltic Sea, and thus, the findings should be useful in devising overall management and conservation strategies for the species.

SUMMARYThe aim of this study was to determine the effects of seasonal temperature variation on the functional properties of lactate dehydrogenase (LDH) from white muscle and liver of Norwegian coastal cod (Gadus morhua) and the possible relevance of LDH allelic variability for thermal acclimation. Two groups of fishes were acclimated to 4°C or 12°C for one year. Polymorphism was observed in only one (Ldh-B) of the three Ldh loci expressed in cod liver and/or muscle. Isozyme expression remained unchanged regardless of acclimation temperature(TA). The products of locus Ldh-B comprise only 14–19% (depending on the tissue) of total LDH activities and,consequently, differences between phenotypes are negligible in terms of their effect on LDH total performance. No kinetic(\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{m}}^{\mathrm{PYR}}\) \end{document}, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document}, Vmax) or thermodynamic (Ea,Δ G) differences were found among Ldh-B phenotypes. Clear kinetic differences were observed between LDH isoforms in the two tissues. However, the Arrhenius activation energy (Ea) for pyruvate reduction was the same for both tissues (Ea=47 kJ mol–1) at TA=12°C. Factors TA, tissue and phenotype did not reveal a significant effect on the Gibbs free energy change (ΔG) of the reaction(55.5 kJ mol–1). However, at TA=4°C,the Ea was increased (Ea=53–56 kJ mol–1) and the temperature dependence of the constant of substrate inhibition for pyruvate(\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document}) decreased in both muscle and liver.In conclusion, the strategies of LDH adjustment to seasonal temperature variations in cod involve changes in LDH concentration (quantitative),adjustment of thermodynamic (Ea) and kinetic(\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document}) properties of the LDH(modulative) but not the expression of alternative isoforms (qualitative). We assume that the observed increase in Ea and the decrease of temperature dependence of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(K_{\mathrm{si}}^{\mathrm{PYR}}\) \end{document} at low TA is the result of structural changes of the LDH molecule(temperature-driven protein folding). We propose a new mechanism of metabolic compensation of seasonal temperature variations – cold acclimation results in changes in the kinetic and thermodynamic properties of LDH in a way that favours aerobic metabolism through reduction of the competition of LDH for pyruvate in normoxic conditions.

This report summarizes talks, discussions and conclusions from a multi-disciplinary workshop on genetic consequences of fisheries and fisheries management held in Ronne, Bornholm in October 2006. T ...

Activities of citrate synthase (CS), cytochrome c oxidase (CCO) and the electron transport system (ETS) were investigated in white muscle and liver of laboratory-maintained cod, Gadusmorhua, from the North Sea, Norwegian coast and Barents Sea for an analysis of temperature acclimation and adaptation in aerobic metabolism. Cold acclimation within each population led to elevated activities of CS, CCO and ETS in white muscle. In liver, however, only North Sea cod showed cold-compensated CS activities, with CCO and ETS unchanged. In contrast, cold-acclimated Norwegian cod displayed unchanged enzyme activities, and Arctic cod showed elevated activities for CS, but decreased activities for CCO and no change in ETS. Between-population comparisons revealed clear evidence for permanent cold adaptation in white muscle of northern (Norwegian coast and Barents Sea) compared to boreal (North Sea) cod populations, reflected by higher activities of CS, CCO and ETS at the same acclimation temperature. Cold-compensated, mass-specific enzyme activities in liver were found in northern compared to boreal cod for CS and CCO, however, for ETS, after warm acclimation only. When evaluated as capacity in total liver, such activities were only found in northern populations in the case of CS at all temperatures, and for CCO and ETS at 15°C only. Hepatosomatic index (IH) and liver lipid contents were highest in North Sea cod, with similar IH but lower lipid contents in cold- versus warm-acclimated animals. An acclimation effect on IH was found in Norwegian cod only, with higher IH but unchanged lipid contents in the cold. In conclusion, permanent cold adaptation of muscle aerobic metabolism prevails in cod populations at higher latitudes, which is in line with permanently elevated rates of oxygen consumption observed in a parallel study. These differences reflect higher maintenance costs in cold-adapted versus cold-acclimated cod.