Several studies indicated absence of population structure for sole populations in the Northeast Atlantic (Rolland et al., 2007). Recently, Cuveliers et al. (2012) revealed a clear genetic structure for sole in this region with at least three different populations: Kattegat/Skagerrak region, the North Sea and the Bay of Biscay, and with indications for a fourth population, namely the Irish/Celtic Sea. This study supports the current approach by ICES for assessing sole as biological stock units in the North Sea (ICES subarea IV), Skagerrak and Kattegat (ICES Division IIIa and Subdivisions 22–24) and Bay of Biscay (ICES Divisions VIIIa,b).

Adjacent sole assessment units defined by ICES- although not clearly identified as biological stocks- are: Eastern Channel (ICES Division VIId), Western Channel (ICES Division VIIe), Celtic Sea (ICES Divisions VIIf,g), Irish Sea (ICES Division VIId, SW of Ireland (ICES Divisions VIIh-k), West of Ireland (ICES Divisions VIIb,c) and Atlantic Iberian waters (ICES Divisions VIIIc and IXa).