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

Information on connectivity and genetic structure of marine organisms remains sparse in frontier ecosystems such as the Arctic Ocean. Filling these knowledge gaps becomes increasingly urgent, as the Arctic is undergoing rapid physical, ecological and socio‐economic changes. The abundant and widely distributed polar cod (Boreogadus saida) is highly adapted to Arctic waters, and its larvae and juveniles live in close association with sea ice. Through a reduced‐representation sequencing approach, this study explored the spatial genetic structure of polar cod at a circum‐Arctic scale. Genomic variation was partitioned into neutral and adaptive components to respectively investigate genetic connectivity and local adaptation. Based on 922 high‐quality single nucleotide polymorphism (SNP) markers genotyped in 611 polar cod, broad‐scale differentiation was detected among three groups: (i) Beaufort –Chukchi seas, (ii) all regions connected by the Transpolar Drift, ranging from the Laptev Sea to Iceland, including the European Arctic and (iii) West Greenland. Patterns of neutral genetic structure suggested broadscale oceanographic and sea ice drift features (i.e., Beaufort Gyre and Transpolar Drift) as important drivers of connectivity. Genomic variation at 35 outlier loci indicated adaptive divergence of the West Greenland and the Beaufort–Chukchi Seas populations, possibly driven by environmental conditions. Sea ice decline and changing ocean currents can alter or disrupt connectivity between polar cod from the three genetic groups, potentially undermining their resilience to climate change, even in putative refugia, such as the Central Arctic Ocean and the Arctic Archipelago.

In this work, we studied the intraspecific polymorphism of pink salmon, Oncorhynchus gorbuscha (Walbaum, 1792), the least genetically explored species among Pacific salmon and one of the central fisheries objects in the Russian Far East. The most urgent task facing Russian fishery science is to determine the proportion of fish from the main reproduction areas in mixed stocks and, based on these data, predict the number of pink salmon returning to these regions for spawning. Due to the unique feature of the species, which evolved into two allochronous lineages, these lineages have been explored independently in parallel. We designed and used here two sets of outlier SNP markers, and this allowed us to reliably distinguish the most northern (Western Kamchatka and the Magadan coast) and the most southern (Iturup Island) regional stocks as well as intermediate stocks from Sakhalin Island and the Mainland coast in both even and odd lineages of pink salmon. In addition, in odd-year lineage, we discovered pronounced genetic differences between early-run and late-run spawners in Sakhalin Island and the proximity of this early spawning form to the mainland stocks. The created baseline covers the main areas of pink salmon reproduction in the Sea of Okhotsk basin and underlies the regional identification of pink salmon in mixed marine stocks.

We investigated polymorphisms in the pantophysin gene (Pan I locus) in a population of Northeast Arctic cod, Gadus morhua L., throughout its foraging area in the Barents Sea and adjacent waters. Correlations between the frequencies of Pan I alleles and habitat conditions, such as depth and temperature, were explored. This study was based on a large number of specimens (2210 individuals) of different age and wide geographic sampling coverage. The frequency of the Pan I^A allele, a known genetic marker of coastal cod, varied from zero to 0.47. Allele frequencies correlated with depth at the sampling location but not with bottom water temperatures. We observed variations in Pan I^A frequencies among different age cohorts from the same area. The most prominent shift in Pan I polymorphism was detected at the early stages of the fish life cycle, between pelagic juveniles and benthic cod. We found that the Pan I^A allele frequency in pelagic yearling cod was essentially same throughout the studied areas in the Barents Sea. In turn, juveniles settling at the northern and deep water locations showed a significant decrease in the allele frequency. In contrast, the frequency of the Pan I^A allele remained constant in juveniles settling in shallow waters when compared to the pelagic stage. These results confirm the selective nature of the cod Pan I locus and indicate that selection process acting on individuals with different genotypes at the Pan I locus leads to the formation of a stable spatial distribution of allele frequencies observed in adult cod.