Durant, J. M. | Search bioRxiv

bioRxiv2025

On the status of Atlantic cod in the Oslofjord

There are serious concerns about the status of the Atlantic cod (Gadus morhua) in the Oslofjord region. However, quantitative estimates of the cod biomass are scarce. Typically, analysis of juvenile fish has been used to assess the state of the cod, and datasets that contain recruited individuals tend to be limited. We here quantify the biomass, with an estimate of uncertainty, over the last 25 years based on a large dataset of commercial landings. By accounting for the number of boat-landing events, we can account for the variation in effort over this period. Our analysis indicates that cod biomass has been reduced by more than 80% from a peak in 2004-2005 to 2018. After 2018, the biomass was further reduced below 10% of the previous levels, but these estimates are more uncertain. Given large public interest and a recent decision to close large areas in the Oslofjord for fishing, our results are highly topical and can serve as a baseline for further investigations into why the cod has collapsed in this area, as well as a contrast to potential future recovery.

ecology↗

bioRxiv2024

Population divergence manifested by genomic rearrangements in a keystone Arctic species with high gene flow

Genomic rearrangements have in recent years gained attention due to their evolutionary role in processes related to adaptation to local environmental conditions as well as diversification and speciation. In this study, we report on genomic rearrangements in the cold-water adapted polar cod (Boreogadus saida), a keystone Arctic fish species. By taking advantage of a new chromosome-level genome assembly in combination with whole-genome population sequencing data from specimens across the northern Barents Sea and adjacent regions, we identified a substantial number of larger chromosomal inversions (n=20) and characterized the previously identified chromosomal fusions (n=5). These genomic features -- encompassing over 20% of the genome -- exhibited genetic divergence, strong internal linkage disequilibrium, and signals of selection. Two of the identified inversions were associated with the two previously described hemoglobin clusters, while a third chromosomal region was found to differentiate between males and females. Moreover, clustering analyses on genotype frequencies of inversions revealed sub- structuring according to five geographic sub-groups suggesting sub-populations and/or the existence of cryptic ecotypes. These results provide novel insights into the impact of genomic rearrangements in population divergence and thus, potentially local adaptation, especially in species with high gene flow.

genomics↗