Single nucleotide polymorphisms reveal novel insights in biological and management units of common sole (Solea solea) in the Celtic Seas

Common sole (Solea solea) is a key commercial flatfish species in Europe, yet its stock identity in the southern Celtic Sea and southwest of Ireland (ICES area 7h and 7j) is uncertain, resulting in a precautionary approach to fisheries management and declining quota. Here, the structure of sole populations and their connectivity patterns were investigated from the southern North Sea to the Bay of Biscay spanning 10 ICES areas using 55 706 single nucleotide polymorphisms and five biological variables (sex, maturity, age, length, and weight). Our results confirmed the large-scale genetic differentiation between sole in the southern North Sea (ICES area 4c) and Bay of Biscay (8a, 8b). Sole from area 7h was genetically similar to sole from the Celtic Sea (7f and 7g) (both neutral and outlier loci), Western English Channel (7e, only neutral loci), and Irish Sea (7a, only neutral loci). Sole from area 7j showed significant neutral differentiation with sole from areas 7h and 7g, the Western English Channel (7e), and the Irish Sea (7a). These novel insights suggest a current mismatch between the biological populations and stock units of 7h and 7j, currently managed as a single stock, and provide a crucial basis for the re-evaluation of the current stock status, enabling more informed and effective fisheries management.