Evidence of genetic differentiation in European hake from the Skagerrak

Abstract The stock delineation of European hake, Merluccius merluccius has long been debated due to the persistent discrepancies between biologically defined populations and management units, despite the species’ significant economic importance. This study investigated population genetic structure within the northern European hake stock using 44 SNP markers following linkage disequilibrium-pruning. Whereas two of the loci were identified as consensus candidate outliers for positive selection, no balancing selection was detected. We found further evidence to challenge the current stock delineation by identifying a genetically distinct subunit in the Skagerrak. Likewise, and beyond the management delineation of the northern stock, European hake in a coastal/fjordic area of the Norwegian Sea was found to be significantly different. Our findings suggest that fine-scale genetic population structure should be explored in combination with life history traits to align biologically meaningful units with stock boundaries and facilitate sound resource management. Additionally, this study also contributes to the growing body of literature documenting marine species with populations in the Skagerrak that are genetically or ecologically distinct from those in adjacent seas; a differentiation that is partially driven by the strong salinity gradients resulting from the mixing of saline Atlantic and brackish Baltic waters.