The stock structure is not totally clear, migrations are detected among the areas according to tagging experiments (Jakobsen and Olsen, 1987; Jákupsstovu, 1999 in ICES, 2014b). Magnitude of migrations seem to differ among the areas studied due to the topography or distance and further studies are recommended (Homrum et al., 2013). Four assessment units are considered within the NE Atlantic region for evaluation of the stock condition as well as for management purposes:
1 – Barents Sea (Subareas I and II, Northeast Arctic) 
2 – Icelandic (Division Va)
3 – North Sea, Skagerrak, west of Scotland and the Rockall (Divisions IIIa, IV and Subarea VI) 
4 – Faroe Islands (Division Vb).