Spatiotemporal distribution and composition of mixed stock fishery of Atlantic cod (Gadus morhua) in West Greenlandic waters based on retrospective genetic analysis

Historical samples of fish are a unique source of DNA to investigate the temporal dynamics of fish population structure and distribution over time. During the last century Atlantic cod (Gadus morhua) stocks have declined dramatically in Greenlandic Waters. Recent genetic investigations have identified the presence of four genetically distinct spawning groups in the area. We used SNP (Single Nucleotide Polymorphism) analysis of DNA from archived historical cod otoliths (1946-2011) to conduct a retrospective spatiotemporal genetic analysis. The aim was to detect historical changes in the contribution from the different spawning groups in population mixtures of cod in West Greenland Waters in response to climate variability and fisheries. Performing genetic assignment test, we found stable genetic composition of feeding aggregations over decades in some areas, whereas shifts in composition were evident in others. Our findings are consistent with previous results demonstrating that the distribution of different spawning components has changed over time. We discuss how these results will allow a better prediction of future population structure and abundance of cod in a changing environment as in Greenlandic Waters and thus lead to more robust management plans