Allelic variation at nine microsatellite loci and the Pan I locus provides evidence that Atlantic cod (Gadus morhua) around Iceland is genetically structured (F ST = 0.003 and F ST = 0.261, respectively). A total of 2534 cod were sampled at 22 spawning locations. For both types of markers, most of the significant pairwise F ST resulted from northeastern-southwestern comparisons. A multidimensional scaling analysis based on F ST , a spatial hierarchical analysis of molecular variance (SAMOVA) and a hierarchical analysis of molecular variance (AMOVA), conducted on both types of markers confirmed a genetic differentiation between cod from the northeastern and southwestern regions. Genetic discontinuities were revealed across two main current fronts in the southeast and northwest, where the cold and warm water masses meet. The AMOVA also detected genetic differences with depth. Expected and observed heterozygosity of microsatellite loci significantly decreased with depth, whereas the B allele frequency at the Pan I locus increased. A tagging experiment of spawning fish conducted during the same years as the genetic work revealed that tagged individuals released in the southwestern region seldom migrated to the northeastern region and vice versa, suggesting that the southwestern and northeastern populations of Atlantic cod around Iceland represent two distinct spawning components.Résumé : La variation allélique de neuf microsatellites et du locus Pan I met en évidence une structure génétique chez la morue Atlantique (Gadus morhua) dans les eaux islandaises (F ST respectifs, F ST = 0,003 et F ST = 0,261). Un total de 2534 morues a été échantillonné sur 22 sites de ponte. Pour les deux marqueurs génétiques utilisés, la majorité des valeurs significatives de F ST par paires de populations est due à des comparaisons nord-est et sud-ouest. Une analyse multidimensionnelle basée sur les F ST par paires de populations, une analyse spatiale hiérarchique de variance molécu-laire (SAMOVA) et une analyse hiérarchique de variance moléculaire (AMOVA), réalisées sur les deux types de marqueurs génétiques, révèlent une différenciation significative entre les échantillons du nord-est et du sud-ouest. La recherche de discontinuités génétiques indique la présence de deux barrières au flux génique correspondant aux principaux fronts de courants océaniques localisés dans le nord-ouest et le sud-est du pays aux points où les masses d'eaux chaudes et froides entrent en contact. L'analyse AMOVA détecte aussi des différences génétiques en fonction de la profondeur. Une analyse approfondie montre que les hétérozygoties observées et attendues des microsatellites diminuent significativement avec la profondeur, alors que la fréquence de l'allèle B du locus Pan I augmente. Une expérience de « capture-recapture » réalisée sur les sites de pontes en même temps que les études génétiques révèle que des individus marqués et relâchés dans la région du sud-ouest migrent rarement vers la région du nord-est et vice versa, ce qui confirme que les population...

Cadrin, S. X., Bernreuther, M., Daníelsdóttir, A. K., Hjörleifsson, E., Johansen, T., Kerr, L., Kristinsson, K., Mariani, S., Nedreaas, K., Pampoulie, C., Planque, B., Reinert, J., Saborido-Rey, F., Sigurðsson, T., and Stransky, C. 2010. Population structure of beaked redfish, Sebastes mentella: evidence of divergence associated with different habitats. – ICES Journal of Marine Science, 67: 1617–1630. Throughout their range, Sebastes spp. are adapted to a diversity of ecological niches, with overlapping spatial distributions of different species that have little or no morphological differences. Divergence of behavioural groups into depth-defined adult habitats has led to reproductive isolation, adaptive radiation, and speciation in the genus Sebastes. Recent genetic research, supported by life-history information, indicates four biological stocks of Sebastes mentella in the Irminger Sea and adjacent waters: a western stock, a deep-pelagic stock, a shallow-pelagic stock, and an Iceland slope stock. Congruent differences in fatty acids and parasites suggest that these genetically distinct populations are adapted to disparate trophic habitats in pelagic waters (shallower and deeper than the deep-scattering layer) and in demersal habitats on the continental slope. Morphology of pelagic forms is also more streamlined than demersal forms. Although genetic differences and evidence for reproductive isolation are clear, these populations appear to share common nursery habitats on the Greenland shelf. We propose a redefinition of practical management units near the Irminger Sea based on geographic proxies for biological stocks and minimizing mixed-stock catches according to the spatial patterns of the recent fishery.

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

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Lumpfish, or lumpsucker, Cyclopterus lumpus (Linnaeus, 1758) is widely distributed in the North Atlantic Ocean. It has a considerable economic value and substantial fisheries occur in several North Atlantic regions owing to the use of its fully ripe internal egg masses in the ovaries as an alternative to sturgeon caviar. Despite being intensively fished in several locations, biological knowledge is limited and no genetic structure information is available. In this study, the stock structure of C. lumpus was investigated across the North Atlantic using ten microsatellite loci. Out of ten loci, two exhibited higher level of differentiation but their inclusion/exclusion from the analyses did not drastically change the observed genetic pattern. A total of three distinct genetic groups were detected: Maine–Canada–Greenland, Iceland–Norway and Baltic Sea. These results, discussed in terms of origin of differentiation, gene flow, and selection, showed that gene flow was rather limited among the detected groups, and also between Greenland and Maine–Canada.