Halvor Knutsen

• Saha, Atal; Quintela, Maria; Nedreaas, Kjell Harald; Rodríguez-Ezpeleta, Naiara; Besnier, Francois & Gerritsen, Hans [Show all 11 contributors for this article] (2026). Genomic Insights Into Population Structure and Demographic History of White Anglerfish (Lophius piscatorius) Throughout Its Range. Evolutionary Applications. 19(7), p. 1–14. doi: 10.1111/eva.70288. Full text in Research Archive Show summary

  Understanding population structure and clarifying species boundaries are essential for the sustainable management of exploited marine species. Although genomic resources for shallow-water taxa have expanded rapidly, open-water species remain comparatively understudied. Here, we present a comprehensive genomic analysis of the white anglerfish (Lophius piscatorius), a commercially important species that occupies a wide depth range. We examined genetic structuring and verified species identity across its distribution range in the North Atlantic and Mediterranean. We combined whole-genome sequencing of selected individuals with targeted SNP genotyping of 897 specimens from 35 locations. Our results support a panmictic or nearly panmictic population of white anglerfish throughout the Northeast Atlantic, consistent with earlier studies, here extended northward to about 68° N. We found no evidence of local adaptation or selection. Like earlier studies, we detected apparently misclassified specimens of the closely related black anglerfish (L. budegassa) and extensive hybridization with up to 20% hybrids in local samples from around the Celtic Sea and nearby waters. Most or all hybrids appear to be first generation (F1), with a few potential backcrossed individuals of less certain identification. Demographic analyses indicate a recent colonization of the North Atlantic, with black anglerfish diverging more recently and maintaining a smaller effective population size. These results underscore the value of integrating genomic tools into monitoring frameworks to improve species identification, delineate population units, and inform sustainable fisheries management.

• Ciannelli, Lorenzo; Espeland, Sigurd Heiberg; Albretsen, Jon & Knutsen, Halvor (2026). The pervasiveness of fish spawning along a complex coastline. Reviews in Fish Biology and Fisheries. ISSN 0960-3166. 36(1). doi: 10.1007/s11160-026-10046-3. Full text in Research Archive Show summary

  Spawning locations of marine fish set the initial conditions for processes that influence survival, abundance, distribution, and the structure of the adult populations. The prevailing paradigm suggests that fish spawning is aggregated in few and spatially well-defined geographic areas. While corroborated, this view is biased by the sampling strategy. Here, we challenge the main paradigm and analyze an extensive and unique 16-year dataset of egg catches along the entire Norwegian coast to examine spawning patterns of Atlantic cod (Gadus morhua). Our results reveal that cod populations exhibit persistent spawning aggregations throughout the entire coastline, spanning a large range of oceanographic conditions. Distinct regional patterns were identified, linking egg abundance to habitat characteristics, including temperature, salinity, distance from coastline, and advective potential of the spawning site, pointing to a high degree for local adaptations. We found that regional differences are driven by the cod spawning strategies that are directed more toward fresher, warmer, and less advective body of waters, going from North-Norway to the Skagerrak area. Collectively our results demonstrate that spawning in marine fish can comprise a series of events at multiple locations and times, each uniquely associated with oceanographic variables. This research provides a foundation for developing a new framework to characterize marine fish life cycle closure and population structure, offering a critical baseline for conserving coastal marine habitats.

• Henriksson, Simon; Jorde, Per Erik; Berkström, Charlotte; Søvik, Guldborg; Wit, Pierre De & Knutsen, Halvor [Show all 9 contributors for this article] (2025). Connectivity and Population Structure in a Marginal Sea—A Review. Diversity and Distributions: A Journal of Conservation Biogeography. ISSN 1366-9516. 31(7). doi: 10.1111/ddi.70056. Full text in Research Archive Show summary

  ABSTRACT Aim The current biodiversity crisis calls for conservation measures that limit or reduce the negative human impact on key habitats and vulnerable wild populations. To effectively protect biodiversity at all levels, including intra‐specific diversity, conservation measures should, ideally, be aligned with the connectivity and genetic structure of wild populations. In this review, we synthesise the scientific literature on connectivity and population structure of marine species in a marginal sea. Location The study focuses on the Skagerrak—a marginal sea in the northeast Atlantic Ocean. Methods We reviewed a total of 172 scientific publications assessing connectivity or population structure in 48 species. From this material, we summarised the main patterns of connectivity and population structure across species, as well as the taxonomic and geographic representation of the scientific literature within this field. Results Our review shows that contemporary connectivity with adjacent seas is high, but asymmetric, for most species. Simultaneously, most species have multiple distinct populations in the Skagerrak, separate from those in adjacent seas. Within the Skagerrak, population structure is common both among coastal populations and between coastal and offshore populations, but less frequent among offshore populations. In many mobile species, multiple populations temporarily overlap in certain areas, but retain their genetic divergence through homing or other barriers to gene flow. Main Conclusions Even in one of the most intensively studied marine regions within the field of connectivity and population structure, there are still large knowledge gaps limiting both our understanding of connectivity and its application in management decisions. Nevertheless, it is evident that the presence of population structure despite high connectivity, and temporal variability in population assemblages, poses a challenge for area‐based protection measures. This underscores the need for adaptive management that monitors and manages intra‐specific diversity on multiple temporal and spatial scales.

• Saha, Atal; Jorde, Per Erik; Sodeland, Marte; Albretsen, Jon; Korslund, Lars & Knutsen, Halvor (2025). Genomic population structure and local adaptation in the emerging commercially exploited Littorina littorea. ICES Journal of Marine Science. ISSN 1054-3139. 82(7). doi: 10.1093/icesjms/fsaf119. Full text in Research Archive Show summary

  To address food deficit, stakeholders continuously diversify food systems by exploiting new commercially viable species. However, the absence of sustainable management measures often conflicts with global biodiversity policies. In light of this challenge, understanding genetic diversity and the geographic scale of population connectivity is essential. We employ ddRAD sequencing in Littorina littorea, a low-trophic, emerging commercial species, to investigate its genetic population structure in Norwegian coastal waters. From an initial detection of over two million SNPs (single nucleotide polymorphisms), 60 831 loci were retained for downstream genomic analyses in 189 individuals sampled across 17 coastal sites. Our results revealed significant isolation-by-distance across the study area, likely reflecting genetic divergence between populations along the west and southern coasts of Norway. While the overall genetic structure appears to be primarily shaped by genetic drift, our genome scan analyses provided evidence for selection acting on specific loci. We identified 39 SNPs potentially under selection, of which 16 overlapped with genes encoding proteins involved in transmembrane transport, metabolic processes, and pathogenesis-related functions. We found no evidence supporting the presence of chromosomal inversions. Oceanographic modelling suggests a likely link between observed genetic divergence and the prevailing ocean current in the region. Our findings demonstrate the adaptive potential of distinct populations to varying environmental conditions and highlight the importance of preserving their full genetic diversity to ensure long-term resilience and sustainability.

• Martinossi-Allibert, Ivain; Ratikainen, Irja Ida; Albretsen, Jon; Eknes, Eirin Jetmundsen; Ellingsen, Ingrid Helene & Estalella, Claudia Aparicio [Show all 13 contributors for this article] (2025). Meeting the challenge of latitude: a climatic gradient shapes the reproductive strategy of a nest-brooding marine fish. Marine Ecology Progress Series. ISSN 0171-8630. 767, p. 101–120. doi: 10.3354/meps14895. Full text in Research Archive Show summary

  High-latitude environments represent climate-related challenges, imposing a limit on species distributions. By elucidating how marine species adjust their reproductive strategy to cope with climatic variation, we can better predict the resilience of populations to environmental change. We addressed this question with a large-scale field study of a marine fish with a central role in the northeast Atlantic coastal ecosystem: the two-spotted goby Pomatoschistus flavescens . We developed a multi-faceted approach to examine how the species’ reproductive strategy and life history change along a climatic gradient. Six populations were surveyed along a gradient of 10° latitude, nearly reaching the northern limit of the species’ range, combining environmental, physiological, phenotypic and demographic data with a genomics investigation of population connectivity. Northern fish experienced colder environments for growth and reproduction than their southern counterparts, occurred at lower adult density and had lower body condition. At high latitudes, a different life history strategy emerged, whereby adults reproduced as 2 yr olds rather than 1 yr olds. Genomics analyses unveiled a clear genetic structure, with a break in connectivity between Skagerrak and the Norwegian coast further north, consistent with findings in other marine species. However, our genomic analyses did not provide clear evidence of adaptation to ecological variables, leaving open questions about the roles of adaptation and plasticity in latitudinal shifts in reproductive strategy. The study highlights the complex life history adaptations to high latitudes in a marine species with high gene flow and underscores the importance of sea temperature on fish reproductive strategy.

• Saha, Atal; Jorde, Per Erik; Sodeland, Marte; Korslund, Lars & Knutsen, Halvor (2025). Pelagic Larval Duration and Isolation by Distance in Coastal Species. Evolutionary Applications. 18(12). doi: 10.1111/eva.70187. Full text in Research Archive Show summary

  Dispersal among populations is crucial both for demographic stability and for the evolutionary potential of species. In marine organisms, dispersal has been shown to be prevalent during pelagic early life stages. Consequently, pelagic larval duration (PLD) has been proposed as an important driver of gene flow in marine species and is influencing genetic differentiation among populations. Despite this prediction, empirical studies have often failed to find the expected correlation between PLD and genetic metrics of gene flow. This could mean either that PLD is a poor predictor of gene flow or that differences in methodology, oceanography or sampling design across studies obscure the underlying mechanisms of gene flow. In the present study, we address these issues by using a consistent sampling design for 10 coastal species with previously published genetic data (ddRAD and microsatellites), and that differ in PLD. We investigate gene flow using an isolation-by-distance (IBD) model with pairwise FST-estimates regressed against distances measured along the prevailing coastal ocean current in the study region. We find a significant (p < 0.05) correlation between species' PLD and IBD slopes, with a moderately strong correlation (r2 > 0.5), These findings support the notion of PLD as a key factor determining dispersal and gene flow among populations of coastal species. Our findings reiterate genetics as a useful tool for inferring population dispersal in marine organisms when potentially confounding factors are eliminated by adopting a consistent sampling design.

• Dornelas, Maria; Antão, Laura H.; Bates, Amanda E.; Brambilla, Viviana; Chase, Jonathan M. & Chow, Cher F. Y. [Show all 485 contributors for this article] (2025). BioTIME 2.0: Expanding and Improving a Database of Biodiversity Time Series. Global Ecology and Biogeography. ISSN 1466-822X. 34(5), p. 1–18. doi: 10.1111/geb.70003. Full text in Research Archive Show summary

  Motivation Here, we make available a second version of the BioTIME database, which compiles records of abundance estimates for species in sample events of ecological assemblages through time. The updated version expands version 1.0 of the database by doubling the number of studies and includes substantial additional curation to the taxonomic accuracy of the records, as well as the metadata. Moreover, we now provide an R package (BioTIMEr) to facilitate use of the database. Main Types of Variables Included The database is composed of one main data table containing the abundance records and 11 metadata tables. The data are organised in a hierarchy of scales where 11,989,233 records are nested in 1,603,067 sample events, from 553,253 sampling locations, which are nested in 708 studies. A study is defined as a sampling methodology applied to an assemblage for a minimum of 2 years. Spatial Location and Grain Sampling locations in BioTIME are distributed across the planet, including marine, terrestrial and freshwater realms. Spatial grain size and extent vary across studies depending on sampling methodology. We recommend gridding of sampling locations into areas of consistent size. Time Period and Grain The earliest time series in BioTIME start in 1874, and the most recent records are from 2023. Temporal grain and duration vary across studies. We recommend doing sample‐level rarefaction to ensure consistent sampling effort through time before calculating any diversity metric. Major Taxa and Level of Measurement The database includes any eukaryotic taxa, with a combined total of 56,400 taxa. Software Format csv and. SQL.

• Hagen, Ingerid Julie; Skaala, Øystein; Quintela, Maria; Dahle, Geir; Fiske, Peder & Foldvik, Anders [Show all 13 contributors for this article] (2025). The genetic structure of sea trout (<i>Salmo trutta</i> L.) in Norway. ICES Journal of Marine Science. ISSN 1054-3139. 82(9). doi: 10.1093/icesjms/fsaf151. Full text in Research Archive Show summary

  Sea trout is the anadromous form of brown trout (Salmo trutta) and is culturally, economically, and ecologically important across its native distribution. Here, we describe the genetic structure of sea trout caught in 105 rivers from the 2600 km long Norwegian coast using &gt;3000 individuals genotyped for 93 SNPs. Our results indicated that most of the study populations are genetically different from each other with a mean pairwise FST of 0.067. While most genetic variation was found within the different populations (93.2%), around 4.5% variation was found between rivers within the different fjord systems and neighbor joining analysis generally grouped together populations from the same fjord or geographic region. Isolation by distance (IBD) for the 105 populations was significant (r2 = 0.21), but the same analysis on three smaller spatial scales revealed different patterns: significant IBD in the Hardangerfjord, moderate IBD in the Sognefjord, and no IBD for the 28 most northern populations, altogether suggesting that there is not a simple relationship between geographic distance and genetic isolation. This documentation of sea trout intra-specific biodiversity must be considered in conservation of the intra-specific diversity of sea trout, including prioritizing habitat restoration, stocks included in genebank, and protection from negative impacts from aquaculture.

• Pereyra, Ricardo T.; Kinnby, Alexandra; Le Moan, Alan; Ortega-Martinez, Olga; Jonsson, Per R. & Piarulli, Stefania [Show all 12 contributors for this article] (2025). An Evolutionary Mosaic Challenges Traditional Monitoring of a Foundation Species in a Coastal Environment—The Baltic Fucus vesiculosus. Molecular Ecology. ISSN 0962-1083. 34(23). doi: 10.1111/mec.17699. Full text in Research Archive Show summary

  During periods of environmental change, genetic diversity in foundation species is critical for ecosystem function and resilience, but it remains overlooked in environmental monitoring. In the Baltic Sea, a key species for monitoring is the brown seaweed Fucus vesiculosus, which forms sublittoral 3D habitats providing shelter and food for fish and invertebrates. Ecological distribution models predict a significant loss of Baltic F. vesiculosus due to ocean warming, unless populations can adapt. Genetic variation and recombination during sexual reproduction are essential for adaptation, but studies have revealed large-scale clonal reproduction within the Baltic Sea. We analysed genome-wide single nucleotide polymorphism (SNP) data from the east Atlantic, the “Transition zone,” and the Baltic Sea, and found a mosaic of divergent lineages in the Baltic Sea, contrasting an outside dominance of a few genetic groups. We determined that the previously described endemic species Fucus radicans is predominantly a large female clone of F. vesiculosus in its northern Baltic distribution. In the two Estonian sites, however, individuals earlier referred to as F. radicans are sexually and reproductively isolated from Baltic F. vesiculosus, revealing a separate lineage that may have diverged long before the formation of the Baltic Sea. Monitoring Baltic Fucus without considering this genetic complexity will fail to prioritise populations with adaptive potential to new climate conditions. From our genomic data, we can extract informative and diagnostic genetic markers that differentiate major genetic entities. Such a SNP panel will provide a straightforward tool for spatial and temporal monitoring and informing management decisions and actions.

• Digre, Sander Vollmerhaus; Jorde, Per Erik; Folkvord, Arild; Hemmer-Hansen, Jakob & Knutsen, Halvor (2025). Prematuration differences in male and female Atlantic cod: Investigating sex ratio, length and ecotype disparities in juveniles. Journal of Fish Biology. ISSN 0022-1112. 107(2), p. 1–11. doi: 10.1111/jfb.70070. Full text in Research Archive Show summary

  Sexual size dimorphism (SSD) and skewed sex ratios are common in the animal kingdom, and marine fishes, such as the Atlantic cod (Gadus morhua), are no exception. This study utilized newly discovered sex-linked genetic markers to investigate young-of-the-year cod in the Skagerrak system, comprising approximately 2700 individuals from North Sea and fjord ecotypes. Overall, no significant difference in sex ratio was observed overall (51% females, 49% males), with consistent findings across 14 locations and three sheltering degrees. Although slightly more females were found in exposed areas, and slightly more males in sheltered regions, these differences were not significant. Size variation between female and male cod was generally negligible. These results indicate a likely purely genetic sex determination system in Atlantic cod and a lack of prematuration growth differences between sexes. This research enhances our understanding of the Atlantic cod, providing more insight into the Atlantic cod population in the Skagerrak and emphasizing the importance of genetic factors in sex determination.

• Norderhaug, Kjell Magnus; Knutsen, Halvor; Filbee-Dexter, Karen; Sodeland, Marte; Jorde, Per Erik & Wernberg, Thomas [Show all 8 contributors for this article] (2024). The International Union for Conservation of Nature Red List does not account for intraspecific diversity. ICES Journal of Marine Science. ISSN 1054-3139. 81(5), p. 815–822. doi: 10.1093/icesjms/fsae039. Full text in Research Archive Show summary

  The International Union for Conservation of Nature (IUCN) Red List identifies threatened and endangered species and is a key instrument in global biodiversity conservation efforts. Our understanding of the structure and value of genetic biodiversity below the species level is rapidly increasing. Nonetheless, the IUCN assessment criteria overlook genetic variation within species. Here, we address this blind spot and discuss the principles of species conservation status classification relative to intraspecific biodiversity. We focus on coastal species, which thrive in heterogeneous environments known to drive genetic differentiation. The focal example species, Atlantic cod and sugar kelp, have contrasting life histories, are ecologically and economically important constituents of the coastal ecosystem, and are currently not classified as threatened in Norway and Canada. We expose important variation in population structure, the presence of ecotypes and genetic-environment covariation, as well as loss of ecotypes that threatens the conservation of these species. Because the genetic makeup of species directly influences their resilience, omitting this information from conservation status assessments can result in loss of adaptive capacity to future stressors, such as climate change. Consequently, recognizing and preserving intraspecific variation emerges as vital for species’ abilities to adapt to and survive in future ocean conditions.

• Gustafsson, Malin; Strand, Åsa; Laugen, Ane Timenes; Albretsen, Jon; André, Carl & Broström, Göran [Show all 13 contributors for this article] (2024). Unlocking the secret life of blue mussels: Exploring connectivity in the Skagerrak through biophysical modeling and population genomics. Evolutionary Applications. 17(5), p. 1–18. doi: 10.1111/eva.13704. Full text in Research Archive Show summary

  Knowledge of functional dispersal barriers in the marine environment can be used to inform a wide variety of management actions, such as marine spatial planning, restoration efforts, fisheries regulations, and invasive species management. Locations and causes of dispersal barriers can be studied through various methods, including movement tracking, biophysical modeling, demographic models, and genetics. Combining methods illustrating potential dispersal, such as biophysical modeling, with realized dispersal through, e.g., genetic connectivity estimates, provides particularly useful information for teasing apart potential causes of observed barriers. In this study, we focus on blue mussels (Mytilus edulis) in the Skagerrak—a marginal sea connected to the North Sea in Northern Europe—and combine biophysical models of larval dispersal with genomic data to infer locations and causes of dispersal barriers in the area. Results from both methods agree; patterns of ocean currents are a major structuring factor in the area. We find a complex pattern of source-sink dynamics with several dispersal barriers and show that some areas can be isolated despite an overall high dispersal capability. Finally, we translate our finding into management advice that can be used to sustainably manage this ecologically and economically important species in the future.

• Bekkevold, Dorte; Knutsen, Halvor; Hemmer-Hansen, Jakob; Sodeland, Marte; Höjesjö, Johan & Bleeker, Katinka [Show all 9 contributors for this article] (2024). Genetic monitoring uncovers long-distance marine feeding coupled with strong spatial segregation in sea trout (Salmo trutta L.) consistent at annual and decadal time scales. ICES Journal of Marine Science. ISSN 1054-3139. 81(8), p. 1655–1668. doi: 10.1093/icesjms/fsae114. Full text in Research Archive Show summary

  Genetic data have greatly increased means to understand fish marine migration behaviours at large spatial scale within a quantitative framework. The anadromous sea trout is a prized target of recreational fishery and an important ecosystem component in freshwater and marine coastal habitats in large parts of temperate northern Europe. Nonetheless, little is known about population distributions while feeding at sea. To reconcile notions about feeding migrations being predominantly locally restricted or not, we used SNP data for 3465 trout representing >100 rivers to identify population origins of 903 coastally feeding fish captured throughout the North Sea-Baltic Sea transition area. Across areas, coastal collections generally showed marked stock-mixing and overall 70:30% native:non-native fish with seasonal variation corresponding with spawning run timing. Data revealed strong spatial feeding segregation between trout from the Scandinavian Peninsula and the European continent. This is surprising given the short distances between areas, but is in alignment with strong genetic differentiation between populations in these areas. Estimation of stock complexity of coastal feeding aggregations showed no spatial trend through the North Sea-Baltic Sea transition area otherwise characterized by strong environmental clines. Analyses of scale samples collected in the 1950s indicate that stock-mixing was consistent over almost 70 years.

• Kvalheim, Lone; Stensrud, Eivind; Knutsen, Halvor; Hyvärinen, Olli Petteri & Eiler, Alexander (2024). Integration of citizen science and eDNA reveals novel ecological insights for marine fish conservation. Environmental DNA. 6(4). doi: 10.1002/edn3.584. Full text in Research Archive Show summary

  In the face of climate change, the accelerating nature crisis, and other anthropogenic impacts, conserving biodiversity demands effective monitoring. While innovative approaches have emerged to enhance biodiversity assessment, significant data gaps persist, particularly within marine ecosystems. In this study, we assess the utility of combining citizen (community) science with environmental DNA (eDNA) metabarcoding for characterizing and quantifying marine fish biodiversity. Over the summer of 2022, 32 volunteers conducted extensive water sampling in a large Norwegian fjord, yielding 96 samples. Contrasting eDNA findings with conventional observational surveys (such as a national species registration database and beach seine surveys) unveiled a substantial overlap in recorded species inventories. The eDNA citizen science initiative identified previously undocumented species and rediscovered others emphasizing an increase in warm-water species within the study area. Additionally, eDNA data unveiled reduced diversity within the inner fjord relative to the outer fjord. To conclude, our study demonstrates the successful integration of eDNA within a citizen science framework, facilitating comprehensive biodiversity tracking across coastal marine regions. These findings hold promise for advancing marine conservation efforts by providing valuable data to inform critical decision-making processes.

• Helmerson, Cecilia; Weist, Peggy; Brieuc, Marine Servane Ono; Maurstad, Marius Filomeno; Schade, Franziska Maria & Dierking, Jan [Show all 14 contributors for this article] (2023). Evidence of hybridization between genetically distinct Baltic cod stocks during peak population abundance(s). Evolutionary Applications. 16(7), p. 1359–1376. doi: 10.1111/eva.13575. Full text in Research Archive Show summary

  Range expansions can lead to increased contact of divergent populations, thus increasing the potential of hybridization events. Whether viable hybrids are produced will most likely depend on the level of genomic divergence and associated genomic incompatibilities between the different entities as well as environmental conditions. By taking advantage of historical Baltic cod (Gadus morhua) otolith samples combined with genotyping and whole genome sequencing, we here investigate the genetic impact of the increased spawning stock biomass of the eastern Baltic cod stock in the mid 1980s. The eastern Baltic cod is genetically highly differentiated from the adjacent western Baltic cod and locally adapted to the brackish environmental conditions in the deeper Eastern basins of the Baltic Sea unsuitable for its marine counterparts. Our genotyping results show an increased proportion of eastern Baltic cod in western Baltic areas (Mecklenburg Bay and Arkona Basin)—indicative of a range expansion westwards—during the peak population abundance in the 1980s. Additionally, we detect high frequencies of potential hybrids (including F1, F2 and backcrosses), verified by whole genome sequencing data for a subset of individuals. Analysis of mitochondrial genomes further indicates directional gene flow from eastern Baltic cod males to western Baltic cod females. Our findings unravel that increased overlap in distribution can promote hybridization between highly divergent populations and that the hybrids can be viable and survive under specific and favourable environmental conditions. However, the observed hybridization had seemingly no long-lasting impact on the continuous separation and genetic differentiation between the unique Baltic cod stocks.

• Jansson, Eeva; André, Carl; Quintela, Maria; Halvorsen, Kim Aleksander Tallaksen; Besnier, Francois & Ayllon, Fernando [Show all 10 contributors for this article] (2023). Genetic study reveals local differentiation persisting in the face of high connectivity and a genomic inversion likely linked with sexual antagonism in a common marine fish. ICES Journal of Marine Science. ISSN 1054-3139. 80(4), p. 1103–1112. doi: 10.1093/icesjms/fsad042. Full text in Research Archive Show summary

  Sustainable harvest of wild populations requires knowledge of the underlying population structure. The focus of this study is on goldsinny wrasse (Ctenolabrus rupestris), a small marine fish inhabiting coastal waters of the north-eastern Atlantic. This species is caught in large numbers to serve as cleaner fish in salmonid aquaculture. We genotyped 2073 goldsinny wrasse from 43 sites along the Scandinavian coastline with 143 SNPs. Seven of the SNPs were linked and likely reside within a large genomic inversion dominated by one haplotype. The heterokaryotype of the putative inversion displayed sex-specific growth patterns, potentially resolving sexual antagonism for this trait. The unlinked 134 SNPs showed modest isolation-by-distance with samples from the northernmost locations showing highest divergence, whereas sites farther south were much more interconnected. Genetic divergence (FST) was highly variable among sites within regions, suggesting a varying degree of connectivity and local divergence. We conclude that despite a high degree of gene-flow mediated through pelagic dispersal in early life stages, regional and some local population structure remains due to limited adult movement in addition to other unidentified factors. Consequently, the species might be more vulnerable to local disturbances than previously anticipated.

• McGill, L.; McDevitt, A.D.; Hellemans, B.; Neat, F.; Knutsen, Halvor & Mariani, S. [Show all 10 contributors for this article] (2023). Population structure and connectivity in the genus Molva in the Northeast Atlantic. ICES Journal of Marine Science. ISSN 1054-3139. 80(4), p. 1079–1086. doi: 10.1093/icesjms/fsad040. Full text in Research Archive Show summary

  In fisheries, operational management units and biological data often do not coincide. In many cases, this is not even known due to the lack of information about a species’ population structure or behaviour. This study focuses on two such species, the common ling Molva molva and the blue ling M. dypterygia, two Northeast Atlantic gadoids with overlapping geographical distribution, but different depth habitats. Heavily exploited throughout their ranges, with declining catches, little is known about their population structure. Genotyping-by-sequencing at thousands of genetic markers indicated that both species are separated into two major groups, one represented by samples from the coasts of western Scotland, Greenland, and the Bay of Biscay and the other off the coast of Norway. This signal is stronger for the deeper dwelling blue ling, even though adult dispersal was also identified for this species. Despite small sample sizes, fine-scale patterns of genetic structure were identified along Norway for common ling. Signatures of adaptation in blue ling consisted in signs of selections in genes involved in vision, growth, and adaptation to cold temperatures.

• Synnes, Ann-Elin; Olsen, Esben Moland; Jorde, Per Erik; Knutsen, Halvor & Moland, Even (2023). Contrasting management regimes indicative of mesopredator release in temperate coastal fish assemblages. Ecology and Evolution. 13(12). doi: 10.1002/ece3.10745. Full text in Research Archive Show summary

  The absence of functional top predators has been proposed as a mechanism acting to shape fish assemblages in temperate marine ecosystems, with cascading effects on lower trophic levels. We explore this scenario by comparing the trophic and functional status of fish assemblages in Norwegian marine national parks, open to fishing, to a nearby coastal seascape that harbors a system of marine protected areas (MPAs) including a no-take zone. Demersal fish assemblages were sampled using fyke nets over three consecutive seasons. Atlantic cod (Gadus morhua) is potentially a dominant top predator in this ecosystem, and historically, this and other gadids have been targeted by the full range of former and present fisheries. In the present study, we find that average body size of the Atlantic cod was significantly larger in the zoned seascape compared to the unprotected areas (mean ± SD: 36.6 cm ± 14.38 vs. 23.4 ± 7.50; p < .001) and that the unprotected seascape was characterized by a higher abundance of mesopredator fish species. These observations are consistent with the hypothesis that the protection of top predators within MPAs aids to control the mesopredator populations and provides empirical support to the notion that the present state of many coastal fish assemblages is driven by mesopredator release linked to functional depletion of large top predators.

• Knutsen, Jan Atle; Kleiven, Alf Ring; Olsen, Esben Moland; Knutsen, Halvor; Espeland, Sigurd Heiberg & Sørdalen, Tonje Knutsen [Show all 15 contributors for this article] (2022). Lobster reserves as a management tool in coastal waters: Two decades of experience in Norway. Marine Policy. ISSN 0308-597X. 136. doi: 10.1016/j.marpol.2021.104908. Full text in Research Archive Show summary

  The positive effects of reduced fishing pressure in marine protected areas (MPAs) are now well documented globally. Yet, evidence of MPA benefits from long-term replicated before-after control-impact (BACI) studies and their usefulness in protecting target species are still rare, especially in northern temperate areas. Scientific rigor in the monitoring of MPAs is considered important for obtaining trust and compliance and can increase interest and enthusiasm for the benefits of marine conservation. Off the coast of southern Norway, a MPA imple- mentation process started up in 2002. Based on comprehensive consultations with local fishers and managers, four experimental lobster reserves were appointed in 2004. Two years later (2006), the reserves came into effect as the Norwegian Directorate of Fisheries implemented regulations as a by-law of the Saltwater Fisheries Act that effectively banned all fixed gear. Long-term monitoring of the MPAs and adjacent control areas has enabled a rigorous scientific evaluation of the effects of these MPAs on lobster populations, including effects on density, growth, demography, behavior, and phenotypic diversity. As protection effects started to manifest, the lobster reserves attracted high public attention and were soon considered a credible supplement to traditional fisheries management. In the period from 2002 to 2021, more than 50 lobster reserves have been implemented in Norway. Here, we review the experiences since the lobster reserves were designated, implemented, and embraced by local communities in Norway, and over two decades have become an important tool for fishery management. Thoughts on the future of MPAs along the coast of Norway are discussed.

• Sodeland, Marte; Jentoft, Sissel; Jorde, Per Erik; Mattingsdal, Morten; Albretsen, Jon & Kleiven, Alf Ring [Show all 12 contributors for this article] (2022). Stabilizing selection on Atlantic cod supergenes through a millennium of extensive exploitation. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 119(8). doi: 10.1073/pnas.2114904119. Full text in Research Archive Show summary

  Life on Earth has been characterized by recurring cycles of ecological stasis and disruption, relating biological eras to geological and climatic transitions through the history of our planet. Due to the increasing degree of ecological abruption caused by human influences many advocate that we now have entered the geological era of the Anthropocene, or “the age of man.” Considering the ongoing mass extinction and ecosystem reshuffling observed worldwide, a better understanding of the drivers of ecological stasis will be a requisite for identifying routes of intervention and mitigation. Ecosystem stability may rely on one or a few keystone species, and the loss of such species could potentially have detrimental effects. The Atlantic cod (Gadus morhua) has historically been highly abundant and is considered a keystone species in ecosystems of the northern Atlantic Ocean. Collapses of cod stocks have been observed on both sides of the Atlantic and reported to have detrimental effects that include vast ecosystem reshuffling. By whole-genome resequencing we demonstrate that stabilizing selection maintains three extensive “supergenes” in Atlantic cod, linking these genes to species persistence and ecological stasis. Genomic inference of historic effective population sizes shows continued declines for cod in the North Sea–Skagerrak–Kattegat system through the past millennia, consistent with an early onset of the marine Anthropocene through industrialization and commercialization of fisheries throughout the medieval period.

• Seliussen, Bjørghild Breistein; Dahle, Geir; Johansen, Torild; Besnier, Francois; Quintela, Maria & Jorde, Per Erik [Show all 11 contributors for this article] (2022). Geographic variation in gene flow from a genetically distinct migratory ecotype drives population genetic structure of coastal Atlantic cod (Gadus morhua L.). Evolutionary Applications. 15(7), p. 1162–1176. doi: 10.1111/eva.13422. Full text in Research Archive Show summary

  Identifying how physical and biotic factors shape genetic connectivity among populations in time and space is essential to our understanding of the evolutionary trajectory as well as the management of marine species. Atlantic cod is a widespread and commercially important marine species displaying several ecotypes with different life history strategies. Using three sets of SNPs: neutral, informative, and genome-inversion linked, we studied population genetic structure of ~2500 coastal Atlantic cod (CC) from 40 locations along Norway's 2500 km coastline, including nine fjords. We observed: (1) a genetic cline, suggesting a mechanism of isolation by distance, characterized by a declining FST between CC and North East Arctic Cod (NEAC—genetically distinct migratory ecotype) with increasing latitude, (2) that in the north, samples of CC from outer-fjord areas were genetically more similar to NEAC than were samples of CC from their corresponding inner-fjord areas, (3) greater population genetic differentiation among CC sampled from outer-fjord areas along the coast, than among CC sampled from their corresponding inner-fjord areas, (4) genetic differentiation among samples of CC from both within and among fjords. Collectively, these results permit us to draw two main conclusions. First, that differences in the relative presence of the genetically highly distinct, migratory ecotype NEAC, declining from north to south and from outer to inner fjord, plays the major role in driving population genetic structure of the Norwegian CC. Second, that there is limited connectivity between CC from different fjords. These results suggest that the current management units implemented for this species in Norway should be divided into smaller entities. Furthermore, the situation where introgression from one ecotype drives population genetic structure of another, as is the case here, may exist in other species and geographical regions, thus creating additional challenges for sustainable fisheries management.

• Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland; Jentoft, Sissel; Stenseth, Nils Christian & Hutchings, Jeffrey (2022). Warming Accelerates the Onset of the Molecular Stress Response and Increases Mortality of Larval Atlantic Cod. Integrative and Comparative Biology. ISSN 1540-7063. 62(6), p. 1784–1801. doi: 10.1093/icb/icac145. Full text in Research Archive Show summary

  Temperature profoundly affects ectotherm physiology. Although differential thermal responses influence fitness, thus driving population dynamics and species distributions, our understanding of the molecular architecture underlying these responses is limited, especially during the critical larval stage. Here, using RNA-sequencing of laboratory-reared Atlantic cod (Gadus morhua) larvae of wild origin, we find changes in gene expression in thousands of transcripts consistent with a severe cellular stress response at both ambient and projected (+2°C and +4°C) temperatures. In addition, specific responses to stress, heat, and hypoxia were commonly identified in gene ontology enrichment analyses and 33 of the 44 genes comprising the minimum stress proteome of all organisms were upregulated. Earlier onset of the stress response was evident at higher temperatures; concomitant increased growth and mortality suggests a reduction in fitness. Temporal differences in gene expression levels do not correspond to differences in growing degree days, suggesting negative physiological consequences of warming beyond accelerated development. Because gene expression is costly, we infer that the upregulation of thousands of transcripts in response to warming in larval cod might act as an energetic drain. We hypothesize that the energetically costly stress response, coupled with increased growth rate at warmer temperatures, leads to faster depletion of energy reserves and increased risk of mortality in larval cod. As sea surface temperatures continue to rise over the next century, reduced fitness of Atlantic cod larvae might lead to population declines in this ecologically and socioeconomically important species. Further, our findings expand our understanding of transcriptomic responses to temperature by ectothermic vertebrate larvae beyond the critical first-feeding stage, a time when organisms begin balancing the energetic demands of growth, foraging, development, and maintenance. Linking the molecular basis of a thermal response to key fitness-related traits is fundamentally important to predicting how global warming will affect ectotherms.

• Henriksson, Simon; Pereyra, Ricardo; Sodeland, Marte; Ortega-Martinez, Olga; Knutsen, Halvor & Wennhage, Håkan [Show all 7 contributors for this article] (2022). Mixed origin of juvenile Atlantic cod (Gadus morhua) along the Swedish west coast. ICES Journal of Marine Science. ISSN 1054-3139. 80(1), p. 145–157. doi: 10.1093/icesjms/fsac220. Full text in Research Archive Show summary

  Cryptic population structure in exploited fishes poses a major challenge for fisheries management. In Atlantic cod, sympatric ecotypes are well-known, for instance off the coast of northern Norway. Recently, two sympatric cod ecotypes have also been documented in the Skagerrak and Kattegat, where adult cod has declined dramatically. One ecotype has an apparent offshore origin and displays a more migratory lifestyle than the other, which is generally resident at the coast throughout its life. To investigate their relative abundances along the Swedish west coast, juvenile cod were collected at high spatial resolution along the coast and genetically assigned to ecotypes. The results reveal large proportions of the coastal ecotype in the southern Kattegat, Öresund, and inshore Swedish Skagerrak, whereas the offshore ecotype dominates in offshore areas. A regression model comparison suggests that differences in bottom depth, rather than distance from the open sea, explain the heterogeneous spatial distribution of the two ecotypes. In addition, the two ecotypes display genetic differences suggesting adaptation to different environments. The results underline that successful fisheries management requires identification and consideration of locally adapted sympatric ecotypes.

• Knutsen, Halvor; Catarino, Diana Sofia de Oliveira; Rogers, Lauren; Sodeland, Marte; Mattingsdal, Morten & Jahnke, Marlene [Show all 15 contributors for this article] (2022). Combining population genomics with demographic analyses highlights habitat patchiness and larval dispersal as determinants of connectivity in coastal fish species. Molecular Ecology. ISSN 0962-1083. 31(9), p. 2562–2577. doi: 10.1111/mec.16415. Full text in Research Archive Show summary

  Gene flow shapes spatial genetic structure and the potential for local adaptation. Among marine animals with nonmigratory adults, the presence or absence of a pelagic larval stage is thought to be a key determinant in shaping gene flow and the genetic structure of populations. In addition, the spatial distribution of suitable habitats is expected to influence the distribution of biological populations and their connectivity patterns. We used whole genome sequencing to study demographic history and reduced representation (double-digest restriction associated DNA) sequencing data to analyse spatial genetic structure in broadnosed pipefish (Syngnathus typhle). Its main habitat is eelgrass beds, which are patchily distributed along the study area in southern Norway. Demographic connectivity among populations was inferred from long-term (~30-year) population counts that uncovered a rapid decline in spatial correlations in abundance with distance as short as ~2 km. These findings were contrasted with data for two other fish species that have a pelagic larval stage (corkwing wrasse, Symphodus melops; black goby, Gobius niger). For these latter species, we found wider spatial scales of connectivity and weaker genetic isolation-by-distance patterns, except where both species experienced a strong barrier to gene flow, seemingly due to lack of suitable habitat. Our findings verify expectations that a fragmented habitat and absence of a pelagic larval stage promote genetic structure, while presence of a pelagic larvae stage increases demographic connectivity and gene flow, except perhaps over extensive habitat gaps.

• Berg, Paul R.; Jorde, Per E.; Glover, Kevin A.; Dahle, Geir; Taggart, John B. & Korsbrekke, Knut [Show all 12 contributors for this article] (2021). Genetic structuring in Atlantic haddock contrasts with current management regimes. ICES Journal of Marine Science. ISSN 1054-3139. 78(1), p. 1–13. doi: 10.1093/icesjms/fsaa204. Full text in Research Archive Show summary

  The advent of novel genetic methods has made it possible to investigate population structure and connectivity in mobile marine fish species: knowledge of which is essential to ensure a sustainable fishery. Haddock (Melanogrammus aeglefinus) is a highly exploited marine teleost distributed along the coast and continental shelf on both sides of the North Atlantic Ocean. However, little is known about its population structure. Here, we present the first study using single-nucleotide polymorphism (SNP) markers to assess the genetic population structure of haddock at multiple geographic scales, from the trans-Atlantic to the local (fjord) level. Genotyping 138 SNP loci in 1329 individuals from 19 locations across the North Atlantic revealed three main genetic clusters, consisting of a Northwest Atlantic cluster, a Northeast Arctic cluster, and a Northeast Atlantic cluster. We also observed a genetically distinct fjord population and a pattern of isolation by distance in the Northeast Atlantic. Our results contrast with the current management regime for this species in the Northeast Atlantic, as we found structure within some management areas. The study adds to the growing recognition of population structuring in marine organisms in general, and fishes in particular, and is of clear relevance for the management of haddock in the Northeast Atlantic.

• Fernández-Chacón, Albert; Buttay, Lucie; Moland, Even; Knutsen, Halvor & Olsen, Esben Moland (2021). Demographic responses to protection from harvesting in a long-lived marine species. Biological Conservation. ISSN 0006-3207. 257, p. 1–10. doi: 10.1016/j.biocon.2021.109094. Full text in Research Archive Show summary

  Marine protected areas (MPAs) are usually considered to have positive effects on the recovery of over-exploited populations. However, resolving the extent to which MPAs function according to their conservation goals requires that essential demographic information such as individual survival and population size are quantified. To this end, we analyzed a 16-year replicated mark-recapture study on European lobster (Homarus gammarus, n = 8793) conducted at several protected and unprotected sites in southern Norway, quantifying the impact of MPAs on local population dynamics by means of a “before-after control-impact” study approach (BACI). Lobster survival and abundance were estimated by applying multi-state and robust design models to the mark-recapture data. These models revealed underlying positive responses to protection. Annual survival rates and population abundances reached higher values in the MPAs, compared to the unprotected sites (abundance range: MPAs = 96–1172, control areas = 92–747). In general, female survival was higher than male survival (range of survival: male = 0.13–0.75, female = 0.37–0.85), while larger males benefited more from protection compared to smaller males (range of increase in survival after protection: big = 100–125%, small = 55–101%). We also detected regional differences in demographic responses to protection, as not all MPAs showed the same changes in abundance over time. Our results show that MPAs can reach conservation goals by increasing the local survival and abundance of lobster, but they also highlight demographic differences between sexes and geographic areas that are worth considering for the management and design of both current and future MPAs.

• Kristensen, Martin Lykke; Olsen, Esben Moland; Moland, Even; Knutsen, Halvor; Grønkjær, Peter & Koed, Anders [Show all 8 contributors for this article] (2021). Disparate movement behavior and feeding ecology in sympatric ecotypes of Atlantic cod. Ecology and Evolution. 11(16), p. 11477–11490. doi: 10.1002/ece3.7939. Full text in Research Archive Show summary

  Coexistence of ecotypes, genetically divergent population units, is a widespread phenomenon, potentially affecting ecosystem functioning and local food web stability. In coastal Skagerrak, Atlantic cod (Gadus morhua) occur as two such coexisting ecotypes. We applied a combination of acoustic telemetry, genotyping, and stable isotope analysis to 72 individuals to investigate movement ecology and food niche of putative local “Fjord” and putative oceanic “North Sea” ecotypes—thus named based on previous molecular studies. Genotyping and individual origin assignment suggested 41 individuals were Fjord and 31 were North Sea ecotypes. Both ecotypes were found throughout the fjord. Seven percent of Fjord ecotype individuals left the study system during the study while 42% of North Sea individuals left, potentially homing to natal spawning grounds. Home range sizes were similar for the two ecotypes but highly variable among individuals. Fjord ecotype cod had significantly higher δ13C and δ15N stable isotope values than North Sea ecotype cod, suggesting they exploited different food niches. The results suggest coexisting ecotypes may possess innate differences in feeding and movement ecologies and may thus fill different functional roles in marine ecosystems. This highlights the importance of conserving interconnected populations to ensure stable ecosystem functioning and food web structures.

• Synnes, Ann-Elin; Huserbråten, Mats Brockstedt Olsen; Knutsen, Halvor; Jorde, Per Erik; Sodeland, Marte & Moland, Even (2021). Local recruitment of Atlantic cod and putative source spawning areas in a coastal seascape. ICES Journal of Marine Science. ISSN 1054-3139. 78(10), p. 3767–3779. doi: 10.1093/icesjms/fsab226. Full text in Research Archive Show summary

  Increased knowledge on connectivity is crucial to our understanding of the population dynamics, genetic structure, and biogeography of many coastal species. In coastal marine populations, the main factor for structuring is thought to be the degree of isolation and confinement, limiting genetic exchange between populations. However, many offshore populations use the coastal areas as nursery grounds, but venture back to natal spawning grounds as adults. Therefore, increased knowledge on the connectivity between coastal and offshore populations is crucial to ensure correct assessment of coastal living resources. Here, we combine genetic assignment data of Atlantic cod recruits sampled in 2017 and 2018 (as 0- and 1-group cod, respectively) in outer Oslofjord (eastern Skagerrak) with a biophysical model for the Skagerrak region over the time period from spawning to settlement in 2017. We located the most probable spawning locations of Atlantic cod recruits by “back-tracking” larval drift trajectories and found putative source areas on both sides of the outer Oslofjord, as well as potential upstream sources in the North Sea and Kattegat. Findings are discussed with regards to suitable management strategies and potential for restoration of coastal cod populations.

• Kjesbu, Olav Sigurd; Sundby, Svein; Sandø, Anne Britt; Alix, Maud; Hjøllo, Solfrid Sætre & Tiedemann, Maik [Show all 43 contributors for this article] (2021). Highly mixed impacts of near-future climate change on stock productivity proxies in the North East Atlantic. Fish and Fisheries. ISSN 1467-2960. 23(3), p. 601–615. doi: 10.1111/faf.12635. Full text in Research Archive Show summary

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

• Faust, Ellika; Jansson, Eeva; André, Carl; Halvorsen, Kim Aleksander Tallaksen; Dahle, Geir & Knutsen, Halvor [Show all 8 contributors for this article] (2021). Not that clean: Aquaculture-mediated translocation of cleaner fish has led to hybridization on the northern edge of the species' range. Evolutionary Applications. 14(6), p. 1572–1587. doi: 10.1111/eva.13220. Full text in Research Archive Show summary

  Translocation and introduction of non-native organisms can have major impacts on local populations and ecosystems. Nevertheless, translocations are common practices in agri- and aquaculture. Each year, millions of wild-caught wrasses are transported large distances to be used as cleaner fish for parasite control in marine salmon farms. Recently, it was documented that translocated cleaner fish are able to escape and reproduce with local wild populations. This is especially a challenge in Norway, which is the world's largest salmon producer. Here, a panel of 84 informative SNPs was developed to identify the presence of nonlocal corkwing wrasse (Symphodus melops) escapees and admixed individuals in wild populations in western Norway. Applying this panel to ~2000 individuals, escapees and hybrids were found to constitute up to 20% of the local population at the northern edge of the species’ distribution. The introduction of southern genetic material at the northern edge of the species distribution range has altered the local genetic composition and could obstruct local adaptation and further range expansion. Surprisingly, in other parts of the species distribution where salmon farming is also common, few escapees and hybrids were found. Why hybridization seems to be common only in the far north is discussed in the context of demographic and transport history. However, the current lack of reporting of escapes makes it difficult to evaluate possible causes for why some aquaculture-dense areas have more escapees and hybrids than others. The results obtained in this study, and the observed high genomic divergence between the main export and import regions, puts the sustainability of mass translocation of nonlocal wild wrasse into question and suggests that the current management regime needs re-evaluation.

• Thorbjørnsen, Susanna Huneide; Moland, Even; Villegas-Ríos, David; Bleeker, Katinka; Knutsen, Halvor & Olsen, Esben Moland (2021). Selection on fish personality differs between a no-take marine reserve and fished areas. Evolutionary Applications. 14(7), p. 1807–1815. doi: 10.1111/eva.13242. Full text in Research Archive Show summary

  Marine reserves can protect fish populations by increasing abundance and body size, but less is known about the effect of protection on fish behaviour. We looked for individual consistency in movement behaviours of sea trout in the marine habitat using acoustic telemetry to investigate whether they represent personality traits and if so, do they affect survival in relation to protection offered by a marine reserve. Home range size had a repeatability of 0.21, suggesting that it represents a personality trait, while mean swimming depth, activity and diurnal vertical migration were not repeatable movement behaviours. The effect of home range size on survival differed depending on the proportion of time fish spent in the reserve, where individuals spending more time in the reserve experienced a decrease in survival with larger home ranges while individuals spending little time in the reserve experienced an increase in survival with larger home ranges. We suggest that the diversity of fish home range sizes could be preserved by establishing networks of marine reserves encompassing different habitat types, ensuring both a heterogeneity in environmental conditions and fishing pressure.

• Moland, Even; Fernández-Chacón, Albert; Sørdalen, Tonje Knutsen; Villegas-Rios, David; Thorbjørnsen, Susanna Huneide & Halvorsen, Kim Aleksander Tallaksen [Show all 14 contributors for this article] (2021). Restoration of Abundance and Dynamics of Coastal Fish and Lobster Within Northern Marine Protected Areas Across Two Decades. Frontiers in Marine Science. 8(674756). doi: 10.3389/fmars.2021.674756. Full text in Research Archive Show summary

  This article reviews a suite of studies conducted in a network of coastal Marine Protected Areas (MPAs) in Skagerrak, Southeast Norway. In 2006, Norway’s first lobster reserves were implemented, with the aim of protecting European lobster (Homarus gammarus) through a ban on fixed gear. A before–after control-impact paired series (BACIPS) monitoring program was initiated to evaluate effects of protection on depleted lobster populations. Experimental trapping and capture-recapture techniques were combined to track demography of populations, also including movement of individuals within and beyond MPAs and adjacent control areas. Further, population genetics and parentage studies were applied, allowing for estimation of gene flow, and novel work on sexual selection in lobsters. Additional studies have evaluated MPA effects on coastal cod (Gadus morhua), and on commercially harvested labrids (Ctenolabrus rupestris and Symphodus melops) and anadromous brown trout (Salmo trutta). Together, these studies reported effects of protection pertaining to increased population density, survival, body size and phenotypic diversity, changes in emigration and interaction with surrounding fisheries, and alteration of selection pressure on morphological- and behavioral traits. Designation of MPAs in close collaboration with fishers and managers, long-term monitoring, inclusion of citizen science and evolving research protocols—also including fisheries data—have revealed novel effects of protection and harvesting on marine populations, thus providing substantial contributions to conservation science. Moreover, knowledge of MPA effects on coastal species has impacted harvest regulations showing the utility of MPAs as empirically documented management tools in Norway.

• Jørgensen, Kris-Emil M.; Neuheimer, Anna B.; Jorde, Per Erik; Knutsen, Halvor & Grønkjær, Peter (2020). Settlement processes induce differences in daily growth rates between two co-existing ecotypes of juvenile cod Gadus morhua. Marine Ecology Progress Series. ISSN 0171-8630. 650, p. 175–189. doi: 10.3354/meps13433. Full text in Research Archive
• Chung, Ming-Tsung; Jørgensen, Kris-Emil Mose; Trueman, Clive N.; Knutsen, Halvor; Jorde, Per Erik & Grønkjær, Peter (2020). First measurements of field metabolic rate in wild juvenile fishes show strong thermal sensitivity but variations between sympatric ecotypes. Oikos. ISSN 0030-1299. 130(2), p. 287–299. doi: 10.1111/oik.07647. Full text in Research Archive
• Seljestad, Gaute; Sanchez, Maria Quintela; Faust, Ellika; Halvorsen, Kim Aleksander Tallaksen; Besnier, Francois & Jansson, Eeva [Show all 11 contributors for this article] (2020). “A cleaner break”: Genetic divergence between geographic groups and sympatric phenotypes revealed in ballan wrasse (Labrus bergylta). Ecology and Evolution. 10(12), p. 6120–6135. doi: 10.1002/ece3.6404. Full text in Research Archive Show summary

  Capture and long‐distance translocation of cleaner fish to control lice infestations on marine salmonid farms has the potential to influence wild populations via overexploitation in source regions, and introgression in recipient regions. Knowledge of population genetic structure is therefore required. We studied the genetic structure of ballan wrasse, a phenotypically diverse and extensively used cleaner fish, from 18 locations in Norway and Sweden, and from Galicia, Spain, using 82 SNP markers. We detected two very distinct genetic groups in Scandinavia, northwestern and southeastern. These groups were split by a stretch of sandy beaches in southwest Norway, representing a habitat discontinuity for this rocky shore associated benthic egg‐laying species. Wrasse from Galicia were highly differentiated from all Scandinavian locations, but more similar to northwestern than southeastern locations. Distinct genetic differences were observed between sympatric spotty and plain phenotypes in Galicia, but not in Scandinavia. The mechanisms underlying the geographic patterns between phenotypes are discussed, but not identified. We conclude that extensive aquaculture‐mediated translocation of ballan wrasse from Sweden and southern Norway to western and middle Norway has the potential to mix genetically distinct populations. These results question the sustainability of the current cleaner fish practice.

• Ono, Kotaro; Knutsen, Halvor; Olsen, Esben M; Ruus, Anders; Hjermann, Dag Ø & Stenseth, Nils Chr (2019). Possible adverse impact of contaminants on Atlantic cod population dynamics in coastal ecosystems. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 286(1908), p. 1–9. doi: 10.1098/rspb.2019.1167. Full text in Research Archive Show summary

  While many in-laboratory ecotoxicological studies have shown the adverse impact of pollutants to the fitness of an individual, direct evidence from the field on the population dynamics of wildlife animals has been lacking. Here, we provide empirical support for a negative effect of pollution on Atlantic cod (Gadus morhua) population dynamics in coastal waters of Norway by combining unique time series of juvenile cod abundance, body size, environmental concentration of toxic contaminants and a spatially structured population dynamics model. The study shows that mercury concentration might have decreased the reproductive potential of cod in the region despite the general decline in the environmental concentration of mercury, cadmium and hexachlorobenzene since the implementation of national environmental laws. However, some cod populations appeared to be more resistant to mercury pollution than others, and the strength and shape of mercury effect on cod reproductive potential was fjord-specific. Additionally, cod growth rate changed at scales smaller than fjords with a gradient related to the exposure to the open ocean and offshore cod. These spatial differences in life-history traits emphasize the importance of local adaptation in shaping the dynamics of local wildlife populations. Finally, this study highlights the possibility to mitigate pollution effects on natural populations by reducing the overall pollution level, but also reveals that pollution reduction alone is not enough to rebuild local cod populations. Cod population recovery probably requires complementary efforts on fishing regulation and habitat restoration.

• Barth, Julia Maria Isis; Villegas-Ríos, David; Freitas, Carla; Moland, Even; Star, Bastiaan & André, Carl [Show all 15 contributors for this article] (2019). Disentangling structural genomic and behavioral barriers in a sea of connectivity. Molecular Ecology. ISSN 0962-1083. 28(6), p. 1394–1411. doi: 10.1111/mec.15010. Full text in Research Archive Show summary

  Genetic divergence among populations arises through natural selection or drift and is counteracted by connectivity and gene flow. In sympatric populations, isolating mechanisms are thus needed to limit the homogenizing effects of gene flow to allow for adaptation and speciation. Chromosomal inversions act as an important mechanism maintaining isolating barriers, yet their role in sympatric populations and divergence with gene flow is not entirely understood. Here, we revisit the question of whether inversions play a role in the divergence of connected populations of the marine fish Atlantic cod (Gadus morhua), by exploring a unique data set combining whole‐genome sequencing data and behavioural data obtained with acoustic telemetry. Within a confined fjord environment, we find three genetically differentiated Atlantic cod types belonging to the oceanic North Sea population, the western Baltic population and a local fjord‐type cod. Continuous behavioural tracking over 4 year revealed temporally stable sympatry of these types within the fjord. Despite overall weak genetic differentiation consistent with high levels of gene flow, we detected significant frequency shifts of three previously identified inversions, indicating an adaptive barrier to gene flow. In addition, behavioural data indicated that North Sea cod and individuals homozygous for the LG12 inversion had lower fitness in the fjord environment. However, North Sea and fjord‐type cod also occupy different depths, possibly contributing to prezygotic reproductive isolation and representing a behavioural barrier to gene flow. Our results provide the first insights into a complex interplay of genomic and behavioural isolating barriers in Atlantic cod and establish a new model system towards an understanding of the role of genomic structural variants in adaptation and diversification.

• Svedang, Hendrik; Barth, Julia Maria Isis; Svenson, Anders; Jonsson, Patrik; Jentoft, Sissel & Knutsen, Halvor [Show all 7 contributors for this article] (2019). Local cod (Gadus morhua) revealed by egg surveys and population genetic analysis after longstanding depletion on the Swedish Skagerrak coast. ICES Journal of Marine Science. ISSN 1054-3139. 76(2), p. 418–429. doi: 10.1093/icesjms/fsy166. Full text in Research Archive Show summary

  Dramatic and persistent reductions in Atlantic cod (Gadus morhua) are common in many coastal areas. While offshore cod stocks still were abundant and productive, the Swedish west coast showed signs of diminishing adult cod abundance at the beginning of the 1980s, where the local cod component was considered to be extirpated. To survey the present cod spawning activity and stock composition, we initiated egg trawling over two consecutive years (203 hauls in total) in combination with population genetic analyses (425 individually genotyped eggs). Here, we provide evidence of cod spawning at the Swedish Skagerrak coast, suggesting recolonization or that local cod has recovered from a nearly depleted state. Early stage eggs were found inside fjords too far to have been transported by oceanic drift from offshore spawning areas. The cod eggs were genetically similar in early to late life-stages and cluster mainly with the local adult cod, indicating that eggs and adults belong to the same genetic unit. The cod eggs were genetically differentiated from adult North Sea cod, and, to a lesser degree, also from the Kattegat and Öresund cod, i.e. indicating a possible recovery of local coastal stock. The patterns of the genetic structure in the inshore areas are, however, difficult to fully disentangle, as Atlantic cod in the North Sea-Skagerrak area seem to be a mixture of co-existing forms: local cod completing their entire life cycle in fjords and sheltered areas, and oceanic populations showing homing behaviours. The egg abundances are considerably lower compared with what is found in similar studies along the Norwegian Skagerrak coast. Nevertheless, the discovery of locally spawning cod along the Swedish west coast—although at low biomasses—is an encouraging finding that highlights the needs for endurance in protective measures and of detailed surveys to secure intraspecific biodiversity and ecosystem services.

• Mattingsdal, Morten; Jorde, Per Erik; Knutsen, Halvor; Jentoft, Sissel; Stenseth, Nils Christian & Sodeland, Marte [Show all 10 contributors for this article] (2019). Demographic history has shaped the strongly differentiated corkwing wrasse populations in Northern Europe. Molecular Ecology. ISSN 0962-1083. 29(1), p. 1–12. doi: 10.1111/mec.15310. Full text in Research Archive Show summary

  Understanding the biological processes involved in genetic differentiation and divergence between populations within species is a pivotal aim in evolutionary biology. One particular phenomenon that requires clarification is the maintenance of genetic barriers despite the high potential for gene flow in the marine environment. Such patterns have been attributed to limited dispersal or local adaptation, and to a lesser extent to the demographic history of the species. The corkwing wrasse (<i>Symphodus melops</i>) is an example of a marine fish species where regions of particular strong divergence are observed. One such genetic break occurred at a surprisingly small spatial scale (<i>F</i>_ST ~0.1), over a short coastline (<60 km) in the North Sea‐Skagerrak transition area in southwestern Norway. Here, we investigate the observed divergence and purported reproductive isolation using genome resequencing. Our results suggest that historical events during the post‐glacial recolonization route can explain the present population structure of the corkwing wrasse in the northeast Atlantic. While the divergence across the break is strong, we detected ongoing gene flow between populations over the break suggesting recent contact or negative selection against hybrids. Moreover, we found few outlier loci and no clear genomic regions potentially being under selection. We concluded that neutral processes and random genetic drift e.g., due to founder events during colonization have shaped the population structure in this species in Northern Europe. Our findings underline the need to take into account the demographic process in studies of divergence processes.

• André, Carl; Barth, Julia Maria Isis; Jonsson, Patrik; Jentoft, Sissel; Knutsen, Halvor & Svedäng, Henrik (2019). Response to comments by Cardinale et al. on “Local cod (Gadus morhua) revealed by egg surveys and population genetic analysis after longstanding depletion on the Swedish Skagerrak coast” by Svedäng et al. (2019). ICES Journal of Marine Science. ISSN 1054-3139. 76(4), p. 1212–1213. doi: 10.1093/icesjms/fsz125. Full text in Research Archive
• Thorbjørnsen, Susanna Huneide; Moland, Even; Simpfendorfer, Colin A.; Heupel, Michelle R.; Knutsen, Halvor & Olsen, Esben Moland (2019). Potential of a no‐take marine reserve to protect home ranges of anadromous brown trout (Salmo trutta). Ecology and Evolution. 9(1), p. 417–426. doi: 10.1002/ece3.4760. Full text in Research Archive Show summary

  The extent to which no‐take marine reserves can benefit anadromous species requires examination. Here, we used acoustic telemetry to investigate the spatial behavior of anadromous brown trout (sea trout, Salmo trutta) in relation to a small marine reserve (~1.5 km2) located inside a fjord on the Norwegian Skagerrak coast. On average, sea trout spent 42.3 % (±5.0% SE) of their time in the fjord within the reserve, a proportion similar to the area of the reserve relative to that of the fjord. On average, sea trout tagged inside the reserve received the most protection, although the level of protection decreased marginally with increasing home range size. Furthermore, individuals tagged outside the reserve received more protection with increasing home range size, potentially opposing selection toward smaller home range sizes inflicted on fish residing within reserves, or through selective fishing methods like angling. Monthly sea trout home ranges in the marine environment were on average smaller than the reserve, with a mean of 0.430 (±0.0265 SE) km2. Hence, the reserve is large enough to protect the full home range of some individuals residing in the reserve. Synthesis and applications: In general, the reserve protects sea trout to a varying degree depending on their individual behavior. These findings highlight evolutionary implications of spatial protection and can guide managers in the design of marine reserves and networks that preserve variation in target species' home range size and movement behavior.

• Roney, Nancy; Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland & Hutchings, Jeffrey (2018). Temporal variability in offspring quality and individual reproductive output in a broadcast-spawning marine fish. ICES Journal of Marine Science. ISSN 1054-3139. 75(4), p. 1353–1361. doi: 10.1093/icesjms/fsx232. Full text in Research Archive
• Delaval, Aurelien Nicolas; Dahle, Geir; Knutsen, Halvor; Devine, Jennifer Ann & Salvanes, Anne Gro Vea (2018). Norwegian fjords contain sub-populations of roundnose grenadier Coryphaenoides rupestris, a deep-water fish. Marine Ecology Progress Series. ISSN 0171-8630. 586, p. 181–192. doi: 10.3354/meps12400. Full text in Research Archive
• Sørdalen, Tonje Knutsen; Halvorsen, Kim Aleksander Tallaksen; Harrison, Hugo B.; Ellis, Charlie D.; Vøllestad, Leif Asbjørn & Knutsen, Halvor [Show all 8 contributors for this article] (2018). Harvesting changes mating behaviour in European lobster. Evolutionary Applications. 11(6), p. 963–977. doi: 10.1111/eva.12611. Full text in Research Archive Show summary

  Removing individuals from a wild population can affect the availability of prospective mates and the outcome of competitive interactions, with subsequent effects on mating patterns and sexual selection. Consequently, the rate of harvest‐induced evolution is predicted to be strongly dependent on the strength and dynamics of sexual selection, yet there is limited empirical knowledge on the interplay between selective harvesting and the mating systems of exploited species. In this study, we used genetic parentage assignment to compare mating patterns of the highly valued and overexploited European lobster (Homarus gammarus) in a designated lobster reserve and nearby fished area in southern Norway. In the area open to fishing, the fishery is regulated by a closed season, a minimum legal size and a ban on the harvest of egg‐bearing females. Due to the differences in size and sex‐specific fishing mortality between the two areas, males and females are of approximately equal average size in the fished area, whereas males tend to be larger in the reserve. Our results show that females would mate with males larger than their own body size, but the relative size difference was significantly larger in the reserve. Sexual selection acted positively on both body size and claw size in males in the reserve, while it was nonsignificant in fished areas. This strongly suggests that size truncation of males by fishing reduces the variability of traits that sexual selection acts upon. If fisheries continue to target large individuals (particularly males) with higher relative reproductive success, the weakening of sexual selection will likely accelerate fisheries‐induced evolution towards smaller body size.

• Jorde, Per Erik; Synnes, Ann-Elin; Espeland, Sigurd Heiberg; Sodeland, Marte & Knutsen, Halvor (2018). Can we rely on selected genetic markers for population identification? Evidence from coastal Atlantic cod. Ecology and Evolution. 8(24), p. 12547–12558. doi: 10.1002/ece3.4648. Full text in Research Archive Show summary

  The use of genetic markers under putative selection in population studies carries the potential for erroneous identification of populations and misassignment of individuals to population of origin. Selected markers are nevertheless attractive, especially in marine organisms that are characterized by weak population structure at neutral loci. Highly fecund species may tolerate the cost of strong selective mortality during early life stages, potentially leading to a shift in offspring genotypes away from the parental proportions. In Atlantic cod, recent genetic studies have uncovered different genotype clusters apparently representing phenotypically cryptic populations that coexist in coastal waters. Here, we tested if a high‐graded SNP panel specifically designed to classify individual cod to population of origin may be unreliable because of natural selection acting on the SNPs or their linked background. Temporal samples of cod were collected from two fjords, starting at the earliest life stage (pelagic eggs) and carried on until late autumn (bottom‐settled juveniles), covering the period during summer of high natural mortality. Despite the potential for selective mortality during the study period, we found no evidence for selection, as both cod types occurred throughout the season, already in the earliest egg samples, and there was no evidence for a shift during the season in the proportions of one or the other type. We conclude that high‐graded marker panels under putative natural selection represent a valid and useful tool for identifying biological population structure in this highly fecund species and presumably in others.

• Jorde, Per Erik; Kleiven, Alf Ring; Sodeland, Marte; Olsen, Esben Moland; Ferter, Keno & Jentoft, Sissel [Show all 7 contributors for this article] (2018). Who is fishing on what stock: Population-of-origin of individual cod (Gadus morhua) in commercial and recreational fisheries. ICES Journal of Marine Science. ISSN 1054-3139. 75(6), p. 2153–2162. doi: 10.1093/icesjms/fsy080. Full text in Research Archive
• Knutsen, Halvor; Jorde, Per Erik; Hutchings, Jeffrey; Hemmer-Hansen, Jakob; Grønkjær, Peter & Jørgensen, Kris-Emil Mose [Show all 10 contributors for this article] (2018). Stable coexistence of genetically divergent Atlantic cod ecotypes at multiple spatial scales. Evolutionary Applications. 11(9), p. 1527–1539. doi: 10.1111/eva.12640. Full text in Research Archive Show summary

  Coexistence in the same habitat of closely related yet genetically different populations is a phenomenon that challenges our understanding of local population structure and adaptation. Identifying the underlying mechanisms for such coexistence can yield new insight into adaptive evolution, diversification and the potential for organisms to adapt and persist in response to a changing environment. Recent studies have documented cryptic, sympatric populations of Atlantic cod (Gadus morhua) in coastal areas. We analysed genetic origin of 6,483 individual cod sampled annually over 14 years from 125 locations along the Norwegian Skagerrak coast and document stable coexistence of two genetically divergent Atlantic cod ecotypes throughout the study area and study period. A “fjord” ecotype dominated in numbers deep inside fjords while a “North Sea” ecotype was the only type found in offshore North Sea. Both ecotypes coexisted in similar proportions throughout coastal habitats at all spatial scales. The size‐at‐age of the North Sea ecotype on average exceeded that of the fjord ecotype by 20% in length and 80% in weight across all habitats. Different growth and size among individuals of the two types might be one of several ecologically significant variables that allow for stable coexistence of closely related populations within the same habitat. Management plans, biodiversity initiatives and other mitigation strategies that do not account for the mixture of species ecotypes are unlikely to meet objectives related to the sustainability of fish and fisheries.

• Roney, Nancy; Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland & Hutchings, Jeffrey (2018). Fine-Scale Population Differences in Atlantic Cod Reproductive Success: A Potential Mechanism for Ecological Speciation in a Marine Fish. Ecology and Evolution. p. 1–11. doi: 10.1002/ece3.4615. Full text in Research Archive Show summary

  Successful resource‐management and conservation outcomes ideally depend on matching the spatial scales of population demography, local adaptation, and threat mitigation. For marine fish with high dispersal capabilities, this remains a fundamental challenge. Based on daily parentage assignments of more than 4,000 offspring, we document fine‐scaled temporal differences in individual reproductive success for two spatially adjacent (<10 km) populations of a broadcast‐spawning marine fish. Distinguished by differences in genetics and life history, Atlantic cod (Gadus morhua) from inner‐ and outer‐fjord populations were allowed to compete for mating and reproductive opportunities. After accounting for phenotypic variability in several traits, reproductive success of outer‐fjord cod was significantly lower than that of inner‐fjord cod. This finding, given that genomically different cod ecotypes inhabit inner‐ and outer‐fjord waters, raises the intriguing hypothesis that the populations might be diverging because of ecological speciation. Individual reproductive success, skewed within both sexes (more so among males), was positively affected by body size, which also influenced the timing of reproduction, larger individuals spawning later among females but earlier among males. Our work suggests that spatial mismatches between management and biological units exist in marine fishes and that studies of reproductive interactions between putative populations or ecotypes can provide an informative basis on which determination of the scale of local adaptation can be ascertained.

• Mattingsdal, Morten; Jentoft, Sissel; Tørresen, Ole K.; Knutsen, Halvor; Hansen, Michael Möller & Robalo, Joana I. [Show all 9 contributors for this article] (2018). A continuous genome assembly of the corkwing wrasse (Symphodus melops). Genomics. ISSN 0888-7543. 110(6), p. 399–403. doi: 10.1016/j.ygeno.2018.04.009. Full text in Research Archive
• Faust, Ellika; Halvorsen, Kim Aleksander Tallaksen; Andersen, Per; Knutsen, Halvor & André, Carl (2018). Cleaner fish escape salmon farms and hybridize with local wrasse populations. Royal Society Open Science. 5(3), p. 1–12. doi: 10.1098/rsos.171752. Full text in Research Archive Show summary

  The genetic impact of farmed fish escaping aquaculture is a highly debated issue. However, non-target species, such as cleaner fish used to remove sea lice from farmed fish, are rarely considered. Here, we report that wild corkwing wrasse (Symphodus melops), which are transported long distances to be used as cleaner fish in salmon farms, escape and hybridize with local populations. Recently, increasing numbers of corkwing wrasse have been reported in Flatanger in Norway, north of its described distribution range, an area heavily relying on the import of cleaner fish from Skagerrak. Using genetic markers identified with 2bRAD sequencing, we show that, although the Flatanger population largely is a result of a northward range expansion, there is also evidence of considerable gene flow from southern populations in Skagerrak and Kattegat. Of the 40 corkwing wrasses sampled in Flatanger, we discovered two individuals with clear southern genotypes, one first-generation hybrid, and 12 potential second-generation hybrids. In summary, we provide evidence that corkwing wrasse escape from fish farms and hybridize with local populations at the leading edge of an ongoing range expansion. Although the magnitude and significance of escapees warrant further investigation, these results should be taken into consideration in the use of translocated cleaner fish.

• Dornelas, Maria; Antão, Laura H.; Moyes, Faye; Bates, Amanda E.; Magurran, Anne E. & Adam, Dusan [Show all 270 contributors for this article] (2018). BioTIME: A database of biodiversity time series for the Anthropocene. Global Ecology and Biogeography. ISSN 1466-822X. 27(7), p. 760–786. doi: 10.1111/geb.12729. Full text in Research Archive Show summary

  <p><i>Motivation</i>: The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community‐led open‐source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.</p> <p><i>Main types of variables included</i>: The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.</p> <p><i>Spatial location and grain</i>: BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km² (158 cm²) to 100 km² (1,000,000,000,000 cm²).</p> <p><i>Time period and grain</i>: BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.</p> <p><i>Major taxa and level of measurement</i>: BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.</p> <p><i>Software format</i>: .csv and .SQL.

• Coscia, Ilaria; Castilho, Rita; Massa-Gallucci, Alexia; Sacchi, Carlotta; Cunha, Regina L. & Stefanni, Sergio [Show all 9 contributors for this article] (2018). Genetic homogeneity in the deep-sea grenadier Macrourus berglax across the North Atlantic Ocean. Deep Sea Research Part I: Oceanographic Research Papers. ISSN 0967-0637. 132, p. 60–67. doi: 10.1016/j.dsr.2017.12.001. Full text in Research Archive
• Spies, Ingrid; Hauser, Lorenz; Jorde, Per Erik; Knutsen, Halvor; Punt, André E. & Rogers, Lauren [Show all 7 contributors for this article] (2018). Inferring genetic connectivity in real populations, exemplified by coastal and oceanic Atlantic cod. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 115(19), p. 4945–4950. doi: 10.1073/pnas.1800096115. Full text in Research Archive Show summary

  Genetic data are commonly used to estimate connectivity between putative populations, but translating them to demographic dispersal rates is complicated. Theoretical equations that infer a migration rate based on the genetic estimator FST, such as Wright’s equation, FST ≈ 1/(4Nem + 1), make assumptions that do not apply to most real populations. How complexities inherent to real populations affect migration was exemplified by Atlantic cod in the North Sea and Skagerrak and was examined within an age-structured model that incorporated genetic markers. Migration was determined under various scenarios by varying the number of simulated migrants until the mean simulated level of genetic differentiation matched a fixed level of genetic differentiation equal to empirical estimates. Parameters that decreased the Ne/Nt ratio (where Ne is the effective and Nt is the total population size), such as high fishing mortality and high fishing gear selectivity, increased the number of migrants required to achieve empirical levels of genetic differentiation. Higher maturity-at-age and lower selectivity increased Ne/Nt and decreased migration when genetic differentiation was fixed. Changes in natural mortality, fishing gear selectivity, and maturity-at-age within expected limits had a moderate effect on migration when genetic differentiation was held constant. Changes in population size had the greatest effect on the number of migrants to achieve fixed levels of FST, particularly when genetic differentiation was low, FST ≈ 10−3. Highly variable migration patterns, compared with constant migration, resulted in higher variance in genetic differentiation and higher extreme values. Results are compared with and provide insight into the use of theoretical equations to estimate migration among real populations.

• Thorbjørnsen, Susanna Huneide; Moland, Even; Huserbråten, Mats Brockstedt Olsen; Knutsen, Jan Atle; Knutsen, Halvor & Olsen, Esben Moland (2018). Replicated marine protected areas (MPAs) support movement of larger, but not more, European lobsters to neighbouring fished areas. Marine Ecology Progress Series. ISSN 0171-8630. 595, p. 123–133. doi: 10.3354/meps12546. Full text in Research Archive Show summary

  The European lobster Homarus gammarus is heavily exploited in the Norwegian fishery, and several management actions have been implemented to protect the species. Three marine protected areas (MPAs) excluding all but hook and line type fishing gear were established along the Skagerrak coast in 2006, effectively banning the trap-based fishery for European lobster. Lobster populations within MPAs and adjacent control areas were studied by capture-mark-recapture and recovery methods every year from prior to MPA establishment to the present. During 2006-2014, a total of 4682 and 3317 lobsters were captured (including recaptures) in the MPAs and control areas, respectively. In all MPAs, protection led to a shift in demography, with an increase in mean total length of 15% during 2006-2014, thereby opposing the effects of a size-selective fishery. No difference was found in rates of movement out from MPAs and control areas, but lobsters moving from MPAs and caught in fished areas were significantly larger than lobsters moving out of control areas. In instances where lobsters tagged in a control area moved into an MPA, the immigrating lobsters had a larger body size than the mean in their area of origin. The range of movement undertaken by recovered lobsters extended beyond the home range sizes suggested by previous shorter-term studies, and well beyond the sizes of the small coastal MPAs studied herein. In summary, demographic changes should be accounted for when interpreting the value of spillover from MPAs, and also potential ‘spill in’ from fished areas to MPAs.

• Laurel, Benjamin J.; Cote, David; Gregory, Robert S.; Rogers, Lauren; Knutsen, Halvor & Olsen, Esben Moland (2017). Recruitment signals in juvenile cod surveys depend on thermal growth conditions. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 74(4), p. 511–523. doi: 10.1139/cjfas-2016-0035. Full text in Research Archive
• Halvorsen, Kim Aleksander Tallaksen; Larsen, Torkel; Sørdalen, Tonje Knutsen; Vøllestad, Leif Asbjørn; Knutsen, Halvor & Olsen, Esben Moland (2017). Impact of harvesting cleaner fish for salmonid aquaculture assessed from replicated coastal marine protected areas. Marine Biology Research. ISSN 1745-1000. 13(4), p. 359–369. doi: 10.1080/17451000.2016.1262042. Full text in Research Archive Show summary

  Wrasse (Labridae) fisheries have increased markedly in Norway since 2010. Wrasse are being used as cleaner fish in salmonid aquaculture to control sea-lice infestations. However, fundamental knowledge on the demography and abundance of the targeted wrasse populations in Norwegian waters is lacking, and the consequences of harvesting at the current intensity have not been assessed. Here, we compared catch per unit effort (CPUE), size, age and sex ratio of goldsinny wrasse (Ctenolabrus rupestris) and corkwing wrasse (Symphodus melops) between marine protected areas (MPAs) and control areas open for fishing at four localities on the Skagerrak coast in Southern Norway. The CPUE of goldsinny larger than the minimum size limit was 33–65% higher within MPAs, while for corkwing three of four MPAs had higher CPUE with the relative difference between MPAs and control areas ranging from −16% to 92%. Moreover, corkwing, but not goldsinny, was significantly older and larger within MPAs than in control areas. Sex ratios did not differ between MPAs and control areas for either species. Our study suggests that despite its short history, the wrasse fisheries have considerable impacts on the target populations and, further, that small MPAs hold promise as a management tool for maintaining natural population sizes and size structure. Goldsinny, being a smaller-sized species, also seems to benefit from the traditional minimum size limit management tool, which applies outside MPAs. The final version of this research has been published in Marine Biology Research. © 2017 Taylor & Francis

• Catarino, Diana; Stefanni, Sergio; Jorde, Per Erik; Menezes, Gui; Company, Joan B. & Neat, Francis [Show all 7 contributors for this article] (2017). The role of the Strait of Gibraltar in shaping the genetic structure of the Mediterranean Grenadier, Coryphaenoides mediterraneus, between the Atlantic and Mediterranean Sea. PLOS ONE. 12(5), p. 1–24. doi: 10.1371/journal.pone.0174988. Full text in Research Archive Show summary

  Population genetic studies of species inhabiting the deepest parts of the oceans are still scarce and only until recently we started to understand how oceanographic processes and topography affect dispersal and gene flow patterns. The aim of this study was to investigate the spatial population genetic structure of the bathyal bony fish Coryphaenoides mediterraneus, with a focus on the Atlantic–Mediterranean transition. We used nine nuclear microsatellites and the mitochondrial cytochrome c oxidase I gene from 6 different sampling areas. No population genetic structure was found within Mediterranean with both marker types (mean ΦST = 0.0960, FST = -0.0003, for both P > 0.05). However, within the Atlantic a contrasting pattern of genetic structure was found for the mtDNA and nuclear markers (mean ΦST = 0.2479, P < 0.001; FST = -0.0001, P > 0.05). When comparing samples from Atlantic and Mediterranean they exhibited high and significant levels of genetic divergence (mean ΦST = 0.7171, FST = 0.0245, for both P < 0.001) regardless the genetic marker used. Furthermore, no shared haplotypes were found between Atlantic and Mediterranean populations. These results suggest very limited genetic exchange between Atlantic and Mediterranean populations of C. mediterraneus, likely due to the shallow bathymetry of the Strait of Gibraltar acting as a barrier to gene flow. This physical barrier not only prevents the direct interactions between the deep-living adults, but also must prevent interchange of pelagic early life stages between the two basins. According to Bayesian simulations it is likely that Atlantic and Mediterranean populations of C. mediterraneus were separated during the late Pleistocene, which is congruent with results for other deep-sea fish from the same region.

• Rogers, Lauren; Storvik, Geir Olve; Knutsen, Halvor; Olsen, Esben Moland & Stenseth, Nils Christian (2017). Fine-scale population dynamics in a marine fish species inferred from dynamic state-space models. Journal of Animal Ecology. ISSN 0021-8790. 86(4), p. 888–898. doi: 10.1111/1365-2656.12678. Full text in Research Archive Show summary

  Identifying the spatial scale of population structuring is critical for the conservation of natural populations and for drawing accurate ecological inferences. However, population studies often use spatially aggregated data to draw inferences about population trends and drivers, potentially masking ecologically relevant population sub-structure and dynamics. The goals of this study were to investigate how population dynamics models with and without spatial structure affect inferences on population trends and the identification of intrinsic drivers of population dynamics (e.g. density dependence). Specifically, we developed dynamic, age-structured, state-space models to test different hypotheses regarding the spatial structure of a population complex of coastal Atlantic cod (Gadus morhua). Data were from a 93-year survey of juvenile (age 0 and 1) cod sampled along >200 km of the Norwegian Skagerrak coast. We compared two models: one which assumes all sampled cod belong to one larger population, and a second which assumes that each fjord contains a unique population with locally determined dynamics. Using the best supported model, we then reconstructed the historical spatial and temporal dynamics of Skagerrak coastal cod. Cross-validation showed that the spatially structured model with local dynamics had better predictive ability. Furthermore, posterior predictive checks showed that a model which assumes one homogeneous population failed to capture the spatial correlation pattern present in the survey data. The spatially structured model indicated that population trends differed markedly among fjords, as did estimates of population parameters including density-dependent survival. Recent biomass was estimated to be at a near-record low all along the coast, but the finer scale model indicated that the decline occurred at different times in different regions. Warm temperatures were associated with poor recruitment, but local changes in habitat and fishing pressure may have played a role in driving local dynamics. More generally, we demonstrated how state-space models can be used to test evidence for population spatial structure based on survey time-series data. Our study shows the importance of considering spatially structured dynamics, as the inferences from such an approach can lead to a different ecological understanding of the drivers of population declines, and fundamentally different management actions to restore populations.

• Barth, Julia Maria Isis; Berg, Paul Ragnar; Jonsson, Per R; Bonanomi, Sara; Corell, Hanna & Hemmer-Hansen, Jakob [Show all 16 contributors for this article] (2017). Genome architecture enables local adaptation of Atlantic cod despite high connectivity. Molecular Ecology. ISSN 0962-1083. 26(17), p. 4452–4466. doi: 10.1111/mec.14207. Full text in Research Archive Show summary

  Adaptation to local conditions is a fundamental process in evolution; however, mechanisms maintaining local adaptation despite high gene flow are still poorly understood. Marine ecosystems provide a wide array of diverse habitats that frequently promote ecological adaptation even in species characterized by strong levels of gene flow. As one example, populations of the marine fish Atlantic cod (Gadus morhua) are highly connected due to immense dispersal capabilities but nevertheless show local adaptation in several key traits. By combining population genomic analyses based on 12K single nucleotide polymorphisms with larval dispersal patterns inferred using a biophysical ocean model, we show that Atlantic cod individuals residing in sheltered estuarine habitats of Scandinavian fjords mainly belong to offshore oceanic populations with considerable connectivity between these diverse ecosystems. Nevertheless, we also find evidence for discrete fjord populations that are genetically differentiated from offshore populations, indicative of local adaptation, the degree of which appears to be influenced by connectivity. Analyses of the genomic architecture reveal a significant overrepresentation of a large ~5 Mb chromosomal rearrangement in fjord cod, previously proposed to comprise genes critical for the survival at low salinities. This suggests that despite considerable connectivity with offshore populations, local adaptation to fjord environments may be enabled by suppression of recombination in the rearranged region. Our study provides new insights into the potential of local adaptation in high gene flow species within fine geographical scales and highlights the importance of genome architecture in analyses of ecological adaptation.

• Jansson, Eeva; Sanchez, Maria Quintela; Dahle, Geir; Albretsen, Jon; Knutsen, Halvor & André, Carl [Show all 12 contributors for this article] (2017). Genetic analysis of goldsinny wrasse reveals evolutionary insights into population connectivity and potentialevidence of inadverent translocationvia aquaculture. ICES Journal of Marine Science. ISSN 1054-3139. 74(8), p. 2135–2147. doi: 10.1093/icesjms/fsx046. Full text in Research Archive Show summary

  The salmon industry is heavily dependent on wrasse for delousing infected fish. The goldsinny wrasse is numerically the most important, and each year, millions are harvested from the wild and transported large distances into fish farms. Population genetic knowledge is required to sustainably exploit this species. Here, 1051 goldsinny wrasses from 16 locations across Scandinavia, the British Isles, and Spain were genotyped with 14 microsatellite and 36 SNP markers. Within-population genetic diversity decreased towards north, and a genetic break was observed across the North Sea. Samples from Northern Norway differed from rest of the Scandinavian samples, and samples from the British Isles differed from the Spanish ones. Within Scandinavia, isolation-by-distance was detected. Observed genetic patterns fitted well with expectations derived from oceanographic drift simulations. A sample from mid-Norway deviated from these patterns however, and was genetically very similar to southern Scandinavian samples. We conclude that the population structure of this species is primarily determined by the opposing evolutionary forces of passive drift, limited adult migration and spawning-site fidelity, whereas the deviation in isolation-by-distance observed in mid-Norway is potentially caused by inadvertent translocations of wrasse from southern Scandinavia via current aquaculture practise. Inclusion of outlier loci gave greater resolution, suggesting that diversifying selection may also affect population structuring among goldsinny wrasses.

• Westgaard, Jon-Ivar; Saha, Atal; Kent, Matthew Peter; Hansen, Hanne Hellerud; Knutsen, Halvor & Hauser, Lorenz [Show all 9 contributors for this article] (2017). Genetic population structure in Greenland halibut (Reinhardtius hippoglossoides) and its relevance to fishery management. Canadian Journal of Fisheries and Aquatic Sciences. ISSN 0706-652X. 74(4), p. 475–485. doi: 10.1139/cjfas-2015-0430. Full text in Research Archive
• Star, Bastiaan; Boessenkool, Sanne; Gondek, Agata Teresa; Nikulina, Elena A.; Hufthammer, Anne Karin & Pampoulie, Christophe [Show all 16 contributors for this article] (2017). Ancient DNA reveals the Arctic origin of Viking Age cod from Haithabu, Germany. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 114(34), p. 9152–9157. doi: 10.1073/pnas.1710186114. Full text in Research Archive Show summary

  Knowledge of the range and chronology of historic trade and long-distance transport of natural resources is essential for determining the impacts of past human activities on marine environments. However, the specific biological sources of imported fauna are often difficult to identify, in particular if species have a wide spatial distribution and lack clear osteological or isotopic differentiation between populations. Here, we report that ancient fish-bone remains, despite being porous, brittle, and light, provide an excellent source of endogenous DNA (15–46%) of sufficient quality for whole-genome reconstruction. By comparing ancient sequence data to that of modern specimens, we determine the biological origin of 15 Viking Age (800–1066 CE) and subsequent medieval (1066–1280 CE) Atlantic cod (Gadus morhua) specimens from excavation sites in Germany, Norway, and the United Kingdom. Archaeological context indicates that one of these sites was a fishing settlement for the procurement of local catches, whereas the other localities were centers of trade. Fish from the trade sites show a mixed ancestry and are statistically differentiated from local fish populations. Moreover, Viking Age samples from Haithabu, Germany, are traced back to the North East Arctic Atlantic cod population that has supported the Lofoten fisheries of Norway for centuries. Our results resolve a long-standing controversial hypothesis and indicate that the marine resources of the North Atlantic Ocean were used to sustain an international demand for protein as far back as the Viking Age.

• Sodeland, Marte; Jorde, Per Erik; Lien, Sigbjørn; Jentoft, Sissel; Berg, Paul Ragnar & Grove, Harald [Show all 10 contributors for this article] (2016). "Islands of divergence" in the Atlantic cod genome represent polymorphic chromosomal rearrangements. Genome Biology and Evolution (GBE). 8(4), p. 1012–1022. doi: 10.1093/gbe/evw057. Full text in Research Archive Show summary

  In several species genetic differentiation across environmental gradients or between geographically separate populations has been reported to center at “genomic islands of divergence,” resulting in heterogeneous differentiation patterns across genomes. Here, genomic regions of elevated divergence were observed on three chromosomes of the highly mobile fish Atlantic cod (Gadus morhua) within geographically fine-scaled coastal areas. The “genomic islands” extended at least 5, 9.5, and 13 megabases on linkage groups 2, 7, and 12, respectively, and coincided with large blocks of linkage disequilibrium. For each of these three chromosomes, pairs of segregating, highly divergent alleles were identified, with little or no gene exchange between them. These patterns of recombination and divergence mirror genomic signatures previously described for large polymorphic inversions, which have been shown to repress recombination across extensive chromosomal segments. The lack of genetic exchange permits divergence between noninverted and inverted chromosomes in spite of gene flow. For the rearrangements on linkage groups 2 and 12, allelic frequency shifts between coastal and oceanic environments suggest a role in ecological adaptation, in agreement with recently reported associations between molecular variation within these genomic regions and temperature, oxygen, and salinity levels. Elevated genetic differentiation in these genomic regions has previously been described on both sides of the Atlantic Ocean, and we therefore suggest that these polymorphisms are involved in adaptive divergence across the species distributional range.

• André, Carl; Svedang, Hendrik; Knutsen, Halvor; Dahle, Geir; Jonsson, Patrik & Ring, Anna-Karin [Show all 8 contributors for this article] (2016). Population structure in Atlantic cod in the eastern North Sea-Skagerrak-Kattegat: early life stage dispersal and adult migration. BMC Research Notes. 9(63). doi: 10.1186/s13104-016-1878-9. Full text in Research Archive Show summary

  Background In marine fish species, where pelagic egg and larvae drift with ocean currents, population structure has been suggested to be maintained by larval retention due to hydrographic structuring and by homing of adult fish to natal areas. Whilst natal homing of adults has been demonstrated for anadromous and coral reef fishes, there are few documented examples of philopatric migration in temperate marine fish species. Results Here, we demonstrate temporally stable genetic differentiation among spawning populations of Atlantic cod (Gadus morhua L.), and present genetic and behavioural evidence for larval drift and philopatric migration in the eastern North Sea-Skagerrak-Kattegat area. We show that juvenile cod collected in the eastern Skagerrak and central Kattegat are genetically similar to cod from offshore spawning areas in the eastern North Sea. Genetic assignment of individual 2–5 year old fish indicates that cod residing at, or migrating towards, spawning areas in Kattegat and the North Sea display philopatric behaviours. Conclusions Together these findings suggest a loop between spawning, larval drift and adult return-migrations to spawning areas and underlines that both oceanographic processes and migratory behaviour in the adult phase may be important for stock separation and integrity in marine temperate fishes such as Atlantic cod.

• Sanchez, Maria Quintela; Danielsen, Elin A.; Lòpez, Lùa; Barreiro, Rodolfo; Svåsand, Terje & Knutsen, Halvor [Show all 8 contributors for this article] (2016). Is the ballan wrasse (Labrus bergylta) two species? Genetic analysis reveals within-species divergence associated with plain and spotted morphotype frequencies. Integrative Zoology. ISSN 1749-4869. 11(2), p. 162–172. doi: 10.1111/1749-4877.12186. Full text in Research Archive
• Halvorsen, Kim Aleksander Tallaksen; Sørdalen, Tonje Knutsen; Durif, Caroline; Knutsen, Halvor; Olsen, Esben Moland & Skiftesvik, Anne Berit [Show all 9 contributors for this article] (2016). Male biased sexual size dimorphism in the nest building corkwing wrasse (Symphodus melops): implications for a size regulated fishery. ICES Journal of Marine Science. ISSN 1054-3139. 73(10), p. 2586–2594. doi: 10.1093/icesjms/fsw135. Full text in Research Archive
• Kleiven, Alf Ring; Chacon, Albert Fernandez; Nordahl, Jan-Harald; Moland, Even; Espeland, Sigurd Heiberg & Knutsen, Halvor [Show all 7 contributors for this article] (2016). Harvest pressure on coastal atlantic cod (Gadus morhua) from recreational fishing relative to commercial fishing assessed from tag-recovery data. PLOS ONE. 11(3). doi: 10.1371/journal.pone.0149595. Full text in Research Archive Show summary

  Marine recreational fishing is a popular outdoor activity. However, knowledge about the magnitude of recreational catches relative to commercial catches in coastal fisheries is generally sparse. Coastal Atlantic cod (Gadus morhua) is a target species for recreational fishers in the North Atlantic. In Norway, recreational fishers are allowed to use a variety of traps and nets as well as long-line and rod and line when fishing for cod. From 2005 to 2013, 9729 cod (mean size: 40 cm, range: 15–93 cm) were tagged and released in coastal Skagerrak, southeast Norway. Both high-reward (NOK 500) and low-reward tags (NOK 50) were used in this study. Because some harvested fish (even those posting high-reward tags) may go unreported by fishers, reporting rates were estimated from mark-recovery models that incorporate detection parameters in their structure, in addition to survival and mortality estimates. During 2005 to 2013, a total of 1707 tagged cod were recovered and reported by fishers. We estimate the overall annual survival to be 33% (SE 1.5). Recreational rod and line fishing were responsible for 33.7% (SE 2.4) of total mortality, followed by commercial fisheries (15.1% SE 0.8) and recreational fixed gear (6.8% SE 0.4). Natural mortality was 44.4% (SE 2.5) of total mortality. Our findings suggest that recreational fishing—rod and line fishing in particular—is responsible for a substantial part of fishing mortality exerted on coastal cod in southern Norway.

• Freitas, Carla; Olsen, Esben Moland; Knutsen, Halvor; Albretsen, Jon & Moland, Even (2016). Temperature-associated habitat selection in a cold-water marine fish. Journal of Animal Ecology. ISSN 0021-8790. 85(3), p. 628–637. doi: 10.1111/1365-2656.12458. Full text in Research Archive Show summary

  1. Habitat selection is a complex process, which involves behavioural decisions guided by the multiple needs and constraints faced by individuals. Climate-induced changes in environmental conditions may alter those trade-offs and resulting habitat use patterns. 2. In this study, we investigated the effect of sea temperature on habitat selection and habitat use of acoustically tagged Atlantic cod (Gadus morhua) at the Norwegian Skagerrak coast. 3. Significant relationships between ocean temperature and habitat selection and use were found. Under favourable sea temperature thresholds (<16 °C), cod selected vegetated habitats, such as eelgrass and macroalgae beds, available in shallow areas. Selection for those habitats was especially high at night, when cod tended to ascend to shallower areas, presumably to feed. Selection and use of those habitats decreased significantly as temperature rose. Under increased sea surface temperature conditions, cod were absent from vegetated shallow habitats, both during the day and night, and selected instead non-vegetated rocky bottoms and sand habitats, available in deeper, colder areas. 4. This study shows the dynamic nature of habitat selection and strongly suggests that cod in this region have to trade off food availability against favourable temperature conditions. Future increases in ocean temperature are expected to further influence the spatial behaviour of marine fish, potentially affecting individual fitness and population dynamics.

• Roney, Nancy E.; Hutchings, Jeffrey; Olsen, Esben Moland; Knutsen, Halvor; Albretsen, Jon & Kuparinen, Anna (2016). Fine-scale life-history structure in a highly mobile marine fish. Evolutionary Ecology Research. ISSN 1522-0613. 17, p. 95–109. Full text in Research Archive
• Gonzalez, Enrique Blanco; Knutsen, Halvor & Jorde, Per Erik (2016). Habitat discontinuities separate genetically divergent populations of a rocky shore marine fish. PLOS ONE. 11(10). doi: 10.1371/journal.pone.0163052. Full text in Research Archive Show summary

  Habitat fragmentation has been suggested to be responsible for major genetic differentiations in a range of marine organisms. In this study, we combined genetic data and environmental information to unravel the relative role of geography and habitat heterogeneity on patterns of genetic population structure of corkwing wrasse (Symphodus melops), a rocky shore species at the northern limit of its distribution range in Scandinavia. Our results revealed a major genetic break separating populations inhabiting the western and southern coasts of Norway. This genetic break coincides with the longest stretch of sand in the whole study area, suggesting habitat fragmentation as a major driver of genetic differentiation of this obligate rocky shore benthic fish in Scandinavia. The complex fjords systems extending along the western coast of Norway appeared responsible for further regional genetic structuring. Our findings indicate that habitat discontinuities may lead to significant genetic fragmentation over short geographical distances, even for marine species with a pelagic larval phase, as for this rocky shore fish.

• Barceló, Caren; Ciannelli, Lorenzo; Olsen, Esben Moland; Johannessen, Tore & Knutsen, Halvor (2016). Eight decades of sampling reveal a contemporary novel fish assemblage in coastal nursery habitats. Global Change Biology. ISSN 1354-1013. 22(3), p. 1155–1167. doi: 10.1111/gcb.13047. Full text in Research Archive
• Berg, Paul Ragnar; Star, Bastiaan; Pampoulie, Christophe; Sodeland, Marte; Barth, Julia Maria Isis & Knutsen, Halvor [Show all 8 contributors for this article] (2016). Three chromosomal rearrangements promote genomic divergence between migratory and stationary ecotypes of Atlantic cod. Scientific Reports. 6, p. 1–12. doi: 10.1038/srep23246. Full text in Research Archive Show summary

  Identification of genome-wide patterns of divergence provides insight on how genomes are influenced by selection and can reveal the potential for local adaptation in spatially structured populations. In Atlantic cod – historically a major marine resource – Northeast-Arctic- and Norwegian coastal cod are recognized by fundamental differences in migratory and non-migratory behavior, respectively. However, the genomic architecture underlying such behavioral ecotypes is unclear. Here, we have analyzed more than 8.000 polymorphic SNPs distributed throughout all 23 linkage groups and show that loci putatively under selection are localized within three distinct genomic regions, each of several megabases long, covering approximately 4% of the Atlantic cod genome. These regions likely represent genomic inversions. The frequency of these distinct regions differ markedly between the ecotypes, spawning in the vicinity of each other, which contrasts with the low level of divergence in the rest of the genome. The observed patterns strongly suggest that these chromosomal rearrangements are instrumental in local adaptation and separation of Atlantic cod populations, leaving footprints of large genomic regions under selection. Our findings demonstrate the power of using genomic information in further understanding the population dynamics and defining management units in one of the world’s most economically important marine resources.

• Catarino, Diana; Knutsen, Halvor; Verissimo, Ana; Olsen, Esben Moland; Jorde, Per Erik & Menezes, Gui [Show all 14 contributors for this article] (2015). The Pillars of Hercules as a bathymetric barrier to gene flow promoting isolation in a global deep-sea shark (Centroscymnus coelolepis). Molecular Ecology. ISSN 0962-1083. 24(24), p. 6061–6079. doi: 10.1111/mec.13453. Full text in Research Archive
• Knutsen, Halvor; Jorde, Per Erik; Gonzalez, Enrique Blanco; Eigaard, Ole Ritzau; Pereyra, Ricardo T. & Sannæs, Hanne [Show all 9 contributors for this article] (2015). Does population genetic structure support present management regulations of the northern shrimp (Pandalus borealis)in Skagerrak and the North Sea? ICES Journal of Marine Science. ISSN 1054-3139. 72, p. 863–871. doi: 10.1093/icesjms/fsu204. Full text in Research Archive

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• Stensrud, Eivind; Hyvärinen, Olli Petteri; Rostum, Tarjei; Angell, Thorvald; Knutsen, Halvor & Lundström, Karl [Show all 8 contributors for this article] (2026). PREDATORS AS SENTINELS: UNRAVELING TROPHIC SHIFTS IN A DARKENING FJORD USING dDNA AND STABLE ISOTOPES OVER THE LAST 20 YEARS. Full text in Research Archive Show summary

  The Greater Oslofjord, like many other coastal systems, is undergoing rapid ecological shifts driven by climate change, coastal freshening and darkening. To understand how these bottom-up stressors restructure food webs, we utilized a multi-trophic approach analyzing three sympatric predators (approx. 500 individuals): Harbour seals (Phoca vitulina), Great Cormorants (Phalacrocorax carbo), and Atlantic Cod (Gadus morhua). We combined dietary DNA (dDNA) metabarcoding with stable isotope analysis (δ13C, δ15N) to trace temporal and spatial dietary changes over 20 years. Traditional morphological methods often fail to capture soft-bodied prey and secondary consumption; thus, we used dDNA combined with novel reference databases to maximize taxonomic resolution. Our dDNA results revealed high-resolution predation data, including the detection of secondary consumption (zoo- and phytoplankton) alongside primary prey, effectively mapping the food web from top predators down to primary producers. Isotope data complemented this by delineating trophic niche widths and source of primary production (land vs. sea). We observed distinct dietary variations linking predator foraging behavior to environmental gradients. This included observable changes over the last 20 years, such as an increase in invasive species in their diet and a shift in zoo- and phytoplankton composition. These findings demonstrate that combining molecular and isotopic analysis of top predators provides a powerful tool for monitoring the cascading effects of anthropogenic changes on marine food webs.

• Stenseth, Nils Christian; Jentoft, Sissel; Haugen, Thrond Oddvar; Bekkby, Trine; Walday, Mats Gunnar & Berg, Paul Ragnar [Show all 11 contributors for this article] (2024). Økosystemet i Oslofjorden kollapser – vi trenger tiltak. Khrono.no. ISSN 1894-8995. Full text in Research Archive
• Stenseth, Nils Christian; Jentoft, Sissel; Moland, Even; Knutsen, Halvor; Haugen, Thrond Oddvar & Colman, JE [Show all 9 contributors for this article] (2023). Langsiktig forskning og modige tiltak må til om vi skal redde Oslo­fjorden. Debattinnlegg i Khrono, 14.08.2023. khrono.no/langsiktig-forskning-og-modige-tiltak-ma-til-om-vi-skal-redde-oslofjorden/800689. Khrono.no. ISSN 1894-8995. Full text in Research Archive
• Oomen, Rebekah Alice; Knutsen, Halvor; Moland, Even; Olsen, Esben Moland; Knutsen, Jan Atle & Bernatchez, Louis [Show all 8 contributors for this article] (2022). Nothing so boundless, nothing so patient: Obituary for Professor Jeffrey Alexander Hutchings (1958–2022). Fish and Fisheries. ISSN 1467-2960. 23(3), p. 519–521. doi: 10.1111/faf.12661. Full text in Research Archive
• Karlsson, Sten; Skaala, Øystein; Knutsen, Halvor; Lo, Håvard & Sægrov, Harald (2020). Nasjonal kartlegging av genetisk struktur hos sjøørret. Full text in Research Archive
• Stige, Leif Christian; Langangen, Øystein; Durant, Joel Marcel; Knutsen, Halvor; Olsen, Esben Moland & Ottersen, Geir (2019). Forskning på torsk. Biolog. ISSN 0801-0722. 37(2), p. 46–49. Full text in Research Archive
• Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland; Jentoft, Sissel; Stenseth, Nils Chr. & Hutchings, Jeffrey (2018). Transcriptomic variability in population responses of Atlantic cod to temperature. Full text in Research Archive
• Gonzalez, Enrique Blanco; Jentoft, Sissel; Hansen, Michael Møller; Knutsen, Halvor; Sodeland, Marte & Mattingsdal, Morten [Show all 9 contributors for this article] (2018). Understanding adaptation in translocating wrasses. Full text in Research Archive
• Thorbjørnsen, Susanna Huneide; Moland, Even; Villegas-Rios, David; Knutsen, Halvor & Olsen, Esben Moland (2018). Personality of sea trout and consequences for survival quantified using detailed movement data from a telemetry study in a southern Norwegian fjord. Full text in Research Archive
• Barth, Julia Maria Isis; Star, Bastiaan; Matschiner, Michael; André, Carl; Knutsen, Halvor & Bradbury, Ian [Show all 13 contributors for this article] (2017). Chromosomal rearrangements as barriers to homogenization in highly mobile fish. Full text in Research Archive
• Thorbjørnsen, Susanna Huneide; Moland, Even; Simpfendorfer, Colin A.; Heupel, Michelle R.; Knutsen, Halvor & Olsen, Esben Moland (2017). A no-take marine reserve provide benefits to anadromous sea trout (Salmo trutta). Full text in Research Archive
• Barth, Julia Maria Isis; Star, Bastiaan; Matschiner, Michael; André, Carl; Knutsen, Halvor & Bradbury, Ian [Show all 13 contributors for this article] (2017). Chromosomal rearrangements as barriers to homogenization in highly mobile fish. Full text in Research Archive
• Thorbjørnsen, Susanna Huneide; Moland, Even; Villegas-Rios, David; Knutsen, Halvor & Olsen, Esben Moland (2017). Repeatability of sea trout behavioural traits and potential for detecting behavioural syndromes. Full text in Research Archive
• Oomen, Rebekah Alice; Knutsen, Halvor; Olsen, Esben Moland; Jentoft, Sissel; Stenseth, Nils Christian & Hutchings, Jeffrey (2016). Genetic variability in population responses of Atlantic cod to temperature. Full text in Research Archive
• Gonzalez, Enrique Blanco; Knutsen, Halvor & Jorde, Per Erik (2016). Seascape genomics in a growing fishery: the case of a translocated cleaner fish, the corkwing wrasse (Symphodus melops). Full text in Research Archive
• Gonzalez, Enrique Blanco; Jorde, Per Erik & Knutsen, Halvor (2015). Climate change and the development of the corkwing wrasse (Symphodus melops) fishery in Scandinavia: genetic population structure and potential implication of translocated cleaner fish. Full text in Research Archive
• Huse, Geir; Agnalt, Ann-Lisbeth; Axelsen, Bjørn Erik Eversvik; Eriksen, Elena; Fossheim, Maria & Frøyland, Livar [Show all 13 contributors for this article] (2025). Havforskningsinstituttets langsiktige overvåkingsplan 2025. Havforskningsinstituttet. doi: https:/www.hi.no/hi/nettrapporter/rapport-fra-havforskningen-2025-54. Full text in Research Archive Show summary

  En av Havforskningsinstituttet sine store styrker er de lange tidsseriene som er avgjørende for vår rådgivning og forskning. Overvåkingsstrategien ble ferdig i 2014,og basert på strategien utviklet vi i 2016 den første versjonen av overvåkingsplanen etter bestilling fra Nærings og fiskeridepartementet. Overvåkingsplanen beskriver alle våre repeterende overvåkingsserier fordelt på 6 tematiske pilarer. Siden 2016 har vi utviklet overvåkingsplanen i forskjellige versjoner og etterhvert har mer informasjon kommet til inkludert kostnad, finansieringskilde og beskrivelse av datainnsamlingsplattform. For å øke kvaliteten og tilgjengeligheten på overvåkingsplanen publiserer vi den nå i Rapport fra havforskningen. Planen er å oppdatere overvåkingsplanen årlig fremover.

• Stock, Brian; Knutsen, Halvor; Nedreaas, Kjell Harald; Otterå, Håkon Magne; Fall, Johanna Jennifer Elisabeth & Denechaud, Côme [Show all 9 contributors for this article] (2025). Oppdatert status om torsk langs Vestlandet- og Skagerrakkysten: potensial for bestandsvurdering. Havforskningsinstituttet. Full text in Research Archive Show summary

  Det har lenge vært enighet om at tilstanden til torsk langs kysten av Vest- og Sørlandet er dårlig og i tilbakegang, selv om det ikke finnes noen formell bestandsvurdering sør for 62°N (Stad). Mange kilder indikerer dårlig status, som synkende fiskeri- og toktfangster. Imidlertid bør disse dataene integreres i en populasjonsvurderingsmodell for å estimere bestandsstatus og -trend med usikkerhet. En slik vurdering vil gi et bedre grunnlag for å iverksette, eller ikke iverksette, tiltak for å gjenopprette kysttorsken, samt for å måle effekten av eventuelle tiltak. Denne rapporten arbeider mot målet om å utvikle en eller flere vurderinger av kysttorsk sør for 62°N ved å gjennomgå og oppdatere potensielt nyttige datakilder, samt spesifisere kunnskap og data som mangler.

• Marquez, Jonatan Fredricson; Meeren, Gro Ingleid van der; Meeren, Terje van der; Albretsen, Jon; Ross, Rebecca & Steen, Henning [Show all 43 contributors for this article] (2024). Liste over forvaltningsrelevante naturenheter - Oppfølgende informasjon til rapporten "Forvaltningsrelevante naturenheter i sjø". Havforskningsinstituttet. Full text in Research Archive Show summary

  I forbindelse med forvaltningens oppgave om å lage en framtidig samlet offentlig instruks for kartlegging av marin natur, bestilte fiskeridirektoratet i en oversikt over der havforskningsinstituttet ville foreslå som "Forvaltningsrelevante naturenheter i sjø". Denne rapporten ble levert og publisert 29.04.2024. I den rapporten foreslo Havforskningsinstituttet å utvide begrepet naturenheter til også å omfatte funksjonsområder for arter, og områder viktig for struktur og sentrale økosystemprosesser. Totalt ble det foreslått 20 abiotiske fysiske enheter, 3 biotiske fysiske enheter, 6 hovedgrupper av funksjonsområder (for totalt 46 arter) og 9 struktur og prosessområder som kunne danne grunnlag for kartlegging av marin natur. Denne rapporten er en utdyping av rapporten "Forvaltningsrelevante naturenheter i sjø", der alle naturenhetene som er foreslått blir nærmere forklart samt at det presenteres et perspektiv på ulike aspekter som kan være viktig for prioritering av hva som skal kartlegges. Enkelte naturenheter har fått mindre endringer i navn og innhold til det opprinnelige forslaget, men den første rapporten har vært førende for innhold. Det kan være aktuelt å revidere hvilke naturenheter som vil være viktige og om noen naturenheter ikke nødvendigvis har samme betydning for forvaltningen på et senere tidspunkt.

• Espeland, Sigurd Heiberg & Knutsen, Halvor (2023). Rapport fra høstundersøkelsene med strandnot i indre og ytre Oslofjord 2022. Havforskningsinstituttet. Full text in Research Archive Show summary

  Rapporten oppsummerer resultater fra funn som ble gjort ved gjennomføring av forsøksfiske med strandnot i indre og ytre Oslofjord frem til 2022. Registreringene er gjort som del av Havforskningsinstituttets høstundersøkelse som har pågått siden 1919 (med de tilleggsstasjoner som er dekket for formål av denne rapporten). Rekruttering av torsk i Indre Oslofjord har vært svært lav de siste årene, også sett i forhold til de siste årene hvor trenden har vært på et historisk lavt nivå. Andre arter som sjøørret, er et eksempel på en art som gjør det bedre, og har hatt en liten økning de senere årene. Mer generelt har de varmekjære artene hatt et oppsving de siste 20 årene, der de pelagiske arter overtar for bentiske. Varmere klima med mer avrenning som både bidrar og til overgjødsling og formørkning gjør at naturen blir enda mer sårbar for fiske.

• Knutsen, Halvor; Espeland, Sigurd Heiberg & Moland, Even (2022). Evaluering av tiltak for vern av kysttorsk i sør innført juni 2019. Havforskningsinstituttet. Full text in Research Archive Show summary

  Vi ser i våre data ingen tegn til at bestandssituasjonen for torsk er endret i indre Skagerrak, ytre- og indre Oslofjord siden tiltak ble innført i 2019. Havforskningsinstituttets data viser stabilt lave fangster av torsk i hele tiltaksområdet, selv om årene 2017 og 2019 viste forholdsvis sterke årsklasser. Landingene i yrkesfisket viser en vedvarende nedgang siden 2019. Fravær av torsk på strandnotsstasjoner i Oslofjorden innenfor Drøbak knyttes til flere forhold. Særlig er vegetasjonen på tidligere gode habitater klart dårligere sammenholdt med andre deler av Skagerrakkysten. Økt temperatur i overflaten og tilgroing av habitater med hurtigvoksende trådformede alger («lurv») bidrar trolig til dette. Avrenning, næringsbelastning og formørkning av kystvannet er også påvirkninger som bidrar i negativ retning for torsk og andre bunnfiskbestander.

• Asplin, Lars; Bienfait, André Marcel; Espeland, Sigurd Heiberg; Fall, Johanna Jennifer Elisabeth; Gagnon, Karine & Grøsvik, Bjørn Einar [Show all 17 contributors for this article] (2022). Svar på høring om tillatelse til utslipp fra foreløpig anleggsvirksomhet samt mudring, dumping og utfylling i forbindelse med bygging av Stad skipstunnel. Havforskningsinstituttet. Full text in Research Archive
• Moland, Even; Synnes, Ann-Elin; Naustvoll, Lars Johan; Freitas, Carla; Norderhaug, Kjell Magnus & Thormar, Jonas [Show all 15 contributors for this article] (2021). Krafttak for kysttorsken - Kunnskap for stedstilpasset gjenoppbygging av bestander, naturtyper og økosystem i Færder- og Ytre Hvaler nasjonalparker. Havforskningsinstituttet. Full text in Research Archive Show summary

  Ytre Oslofjord har en unik kystnatur av svært stor verdi for både fastboende og tilreisende. Færder- og Ytre Hvaler nasjonalparker ligger side om side ytterst i fjorden, og skal sikre naturverdiene for kommende generasjoner. Nasjonalparkene har utformet egne forvaltningsplaner og -mål, som gjenspeiler et ønske om å legge best mulig til rette for at fiskearter, fugler, planter og insekter skal fortsette å trives innenfor parkenes grenser. Generelle mål for naturverdiene er at de skal opprettholdes med god økologisk funksjon, og et høyt biologisk mangfold.

• Boitsov, Stepan; Knutsen, Halvor; Simonsen, Jan Henrik & Frantzen, Sylvia (2020). Undersøkelse av mageinnhold i fiskeyngel og kystnære fiskearter etter utslippet av plastpellets fra M/V Trans Carrier. Havforskningsinstituttet. Full text in Research Archive Show summary

  Havforskningsinstituttet har på oppdrag fra Kystverket gjennomført en undersøkelse av mageinnhold i fiskeyngel og kystnære fiskearter fra området utpekt som mest påvirket av plastpellets-utslippet fra M/V Trans Carrier tidligere i år. Det ble i september-oktober 2020 samlet inn 633 individer av ni fiskearter langs kysten i Østfold. Prøvetakingen ble utført som en del av Havforskningsinstituttets strandnotserie. Samtlige individer av fisk ble undersøkt visuelt på Havforskningsinstituttets laboratorium for mageinnhold. Det ble ikke funnet plastrester i noen av individene. Det vurderes derfor at utslippet ikke har påvirket de undersøkte fiskeartene i det berørte området.

• Espeland, Sigurd Heiberg & Knutsen, Halvor (2019). Rapport fra høstundersøkelsene med strandnot i indre og ytre Oslofjord 2018. Havforskningsinstituttet. Full text in Research Archive Show summary

  Rapporten oppsummerer resultater fra funn som ble gjort ved gjennomføring av forsøksfiske med strandnot i indre og ytre Oslofjord i 2018. Registreringene er gjort som del av Havforskningsinstituttets høstundersøkelse som har pågått siden 1919 (med de tilleggsstasjoner som er dekket for formål av denne rapporten). Rekruttering av torsk i Indre Oslofjord var i 2018 svært lav, også sett i forhold til de siste årene hvor trenden har vært på et historisk lavt nivå. Det ble fanget kun 3 yngel av torsk på 56 trekk fra Sandefjord og østover. Det ble på de samme stasjonene også bare fanget 1 eldre torsk ved årets nottrekk. De varmekjære artene har hatt et oppsving de siste 20 årene, og spesielt ser vi at pelagiske arter overtar for bentiske.

• Aglen, Asgeir; Nedreaas, Kjell Harald; Moland, Even; Knutsen, Halvor; Kleiven, Alf Ring & Johannessen, Tore [Show all 11 contributors for this article] (2016). Oppdatert kunnskapsstatus om kystnær torsk i Sør Norge. Havforskningsinstituttet. Full text in Research Archive Show summary

  English: In a report from 2008 an assessment of coastal cod in southern Norway, from the Swedish border to Stad, was presented, together with suggestions to management initiatives. This report shortly summarize the 2008-report, but new knowledge attained the last 10 years is the main part. The cod along the coast in southern Norway are made up of possibly there different components: 1) stationary, local stocks in the fjords, 2) cod from the North Sea along the outer coast, and 3) possibly a more “ migrating cod” along the outer coast. The latter type of coastal cod, if existing, has genetic similarities with the North Sea cod. Much new knowledge indicate that the cod along the coast in southern Norway are exposed to increasing pressure from multiple factors, not at least from recreational fisheries. Local stocks of cod in fjords are the smallest and accordingly most vulnerable stocks of cod. Future regulations should aim at a best possible conservation of the local stocks of cod in the fjords, but also reduce mortality of cod living along the outer parts of the coast. This report also suggest some, possible management initiatives. Norsk:2008 kom en rapport som vurderte status for kysttorsk på strekningen Svenskegrensa-Stad, og som også inkluderte forslag til forvaltningstiltak. Denne rapporten starter med en kort oppsummering av oversikten fra 2008, men bringer i hovedsak ny kunnskap som er kommet til de siste 10 årene. Historisk er det en klar nedgang i fangstene av årets yngel (0-gruppe torsk) i strandnotserien fra Havforskningsinstituttet. De siste ca. 20 årene har nedgangen vært størst. Torskeforekomstene langs kysten ser ut til å være sammensatt av tre komponenter: 1) lokale, stasjonære stammer av fjordtorsk, som særlig forekommer i de indre kystområdene/fjordene, 2) nordsjøtorsk og 3) muligens også en mer vandrende komponent av kysttorsk med genetisk likhetstrekk med nordsjøtorsken, som særlig forekommer i de ytre kystområdene. Det er nå dokumentert at torsken langs kysten både på Vestlandet og Sørlandet er utsatt for økende press fra flere påvirkningsfaktorer, ikke minst et betydelig fritidsfiske. Lokale stammer av fjordtorsk er de klart minste og mest sårbare bestandene langs kysten. Fremtidige reguleringer bør gi best mulig vern for lokale stammer av fjordtorsk, men også redusere fiskedødeligheten for «nordsjøtype» torsk langs den ytre delen av kysten. En rekke forslag til tiltak er oppsummert i rapporten.

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