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ABSTRACT The Greenland–Scotland Ridge is a submarine mountain that rises up to 500 m below the sea surface and extends from the east coast of Greenland to the continental shelf of Iceland and across the Faroe Islands to Scotland. The ridge not only separates deeper ocean basins on either side, that is, the North Atlantic and Arctic oceans, but also forms a geomorphological barrier between the cold arctic water masses of the Nordic Seas and the comparably contrastingly warmer water of the North Atlantic Ocean. It is therefore situated at a strategic geographical position in relation to the effect of climate change in the Arctic region. Both the Arctic and the Atlantic subpolar ecosystems are facing each other at the ridge, creating oceanic fronts in the Denmark Strait and in the Iceland–Faroe ridge alike. This ridge in the subarctic area forms the southern boundary of the North Atlantic Gateway to the Arctic Ocean, affecting exchanges of oceanic currents and of marine organisms between the two main ecosystems in the Nordic polar region. For example, the appearance of natural invasive species such as the Atlantic mackerel in this region mainly occurred along the ridge, with arrival through the Scotland–Faroe Islands mount with subsequent waves of colonization which eventually reached the southern tip of Greenland. With the increasing impacts of climate change, such natural colonization through the ridge is likely to happen more frequently and affect regional ecosystems. Yet, the human resources and the economy of the local nations on the ridge are rather limited compared to neighboring countries. With a total of less than half a million people inhabiting the area and a total ocean surface of circa 3 million km2 of continental shelf, Greenland, Iceland, the Faroe Islands, and Scotland will face critical challenges in the coming years with respect to biodiversity conservation and sustainable management of marine resources. Here is a summary of what we know, what we might expect, and an opening to potential discussions for the future of research in this region. The main objective of this paper is calling attention to much needed additional research effort on the marine environment around the Greenland–Scotland Ridge, instead of presenting a comprehensive overview of research in this area. [ABSTRACT FROM AUTHOR]

Black ruff (Centrolophus niger) is a rare and poorly studied species found in both the Atlantic and Pacific Oceans and also in the Mediterranean Sea. It is sporadically caught south of Iceland during the annual International Ecosystem Summer Survey of the Nordic Seas. In total, 43 specimens were caught from 2009 to 2021, of which 41 specimens were caught during 2017–2021. All specimens, except one, were caught using a pelagic trawl (cod‐end mesh‐size: 50 mm) close to the surface (trawl depth: 0–35 m) with in situ temperature ranging from 9 to 13°C. The area south of Iceland is characterized by having warmer temperatures than other areas around the island, which might be indicative of a northern limit for the distribution of black ruff. The fish were primarily in the range of 29–46 cm with a few larger individuals up to 71 cm. Fourteen fish, caught in 2017 and 2021, were dissected to gather biological information on this species. These fish were all juveniles with no obvious sign of gonad development. Correlations between total length, fork length, and standard length are presented. Otoliths were thin and delicate with a length of ~13–16 mm, and otolith size (length, width, and area) was correlated with fish size. Much of the stomach content was at an advanced stage of digestion, but some contents could be identified and consisted of invertebrates, primarily of the orders Amphipoda and Calanoida with some unidentified fish also present. [ABSTRACT FROM AUTHOR]

Stock structure is of paramount importance for sustainable management of exploited resources. In that context, genetic markers have been used for more than two decades to resolve spatial structure of marine exploited resources and to fully fathom stock dynamics and interactions. While genetic markers such as allozymes and RFLP dominated the debate in the early era of genetics, technology advances have provided scientists with new tools every decade to better assess stock discrimination and interactions (i.e. gene flow). Here, we provide a review of genetic studies performed to understand stock structure of Atlantic cod in Icelandic waters, from the early allozyme approaches to the genomic work currently carried out. We further highlight the importance of the generation of a chromosome‐anchored genome assembly together with whole‐genome population data, which drastically changed our perception of the possible management units to consider. After nearly 60 years of genetic investigation of Atlantic cod structure in Icelandic waters, genetic (and later genomic) data combined with behavioural monitoring using Data Storage Tags shifted the attention from geographical population structures to behavioural ecotypes. This review also demonstrates the need for future research to further disentangle the impact of these ecotypes (and gene flow among them) on the population structure of Atlantic cod in Icelandic waters. It also highlights the importance of whole‐genome data to unravel unexpected within‐species diversity related to chromosomal inversions and associated supergenes, which are important to consider for future development of sustainable management programmes of the species within the North Atlantic. [ABSTRACT FROM AUTHOR]

The collapse of marine fisheries worldwide has forced recognition of the fact that sustainable fisheries management cannot be achieved without a reasonable understanding of stock structure. Fisheries focusing on species that exhibit seasonal migrations between spawning and feeding grounds should consider the composition of feeding aggregations of presumed mixed origin. Using nine microsatellites and the Pan I locus, we assess the contribution of two previously described major spawning components of Icelandic cod Gadus morhua (southwest and northeast) to two large feeding and two large juvenile aggregations of presumed mixed origin and situated in the northwest and northeast of Iceland. The Bayesian approaches (STRUCTURE and BAYES) revealed that, with the exception of the juvenile samples collected in 2002 and 2003 in the northeast, most of the individuals originated from the southwest. These results confirmed that the Icelandic cod exhibit a complex biological pattern involving spawning site fidelity and migration to and from feeding aggregations. The sustainable management of the Icelandic cod is likely to be compromised if its complex dynamics is not properly integrated into fisheries management plans. L'effondrement des peches marines a travers le monde oblige a reconnaitre que la gestion durable de la peche ne peut etre atteinte sans une comprehension raisonnable de la structure des stocks exploites. Les peches exploitant les especes qui font des migrations saisonnieres entre les aires de ponte et les aires de nourrissage communes doivent egalement tenir compte de la composition de ces rassemblements de nourrissage presumes d'origine mixte. Utilisant neuf microsatellites et le locus Pan I, nous avons evalue la contribution des deux principales sous-populations de la morue islandaise Gadus morhua precedemment decrites (sud-ouest et nord-est de l'Islande) aux deux grands rassemblements alimentaires et aux deux rassemblements de juveniles, d'origine mixte presumee, et situes dans le nord-ouest et nord-est du pays. Les deux approches bayesiennes utilisees (STRUCTURE et BAYES) revelent que, a l'exception des echantillons de juveniles collectes en 2002 et en 2003 dans le nord-est, la plupart des individus semblent provenir de la population du sud-ouest. Ces resultats confirment que la morue islandaise presente un modele biologique complexe impliquant la fidelite au site de ponte et une migration aller-retour vers les rassemblements de nourrissage. Par consequent, la gestion durable de la morue d'Islande est susceptible d'etre compromise si cette dynamique complexe n'est pas correctement integree dans les plans de gestion des peches., Introduction The depletion and collapse of marine fish stocks worldwide has now been widely interpreted as a failure of sustainable fisheries management (Myers et al. 1996; Cook et al. 1997). [...]

Abstract: Allelic variation at nine microsatellite loci and the Pan I locus provides evidence that Atlantic cod (Gadus morhua) around Iceland is genetically structured ([F.sub.ST] = 0.003 and [F.sub.ST] = [...]