Northeast Atlantic mackerel defines the mackerel in the region from ICES Division subareas 1–8 and 14, and in Division 9.a. Spawning areas are equally widely distributed but catches are attributed to three spawning components by area – North Sea (4, 3a), Western (6, 7, 8 a,b,d,e) and Southern (8c, 9a). Fish from Southern and Western areas have been shown to migrate to the North Sea, Norwegian Sea and Baltic Sea after spawning where they become indistinct from other components. Given the uncertainties in the determination of a stock structure, an assessment unit is considered in the Northeast Atlantic and adjacent waters (Brunel et al. 2017)(ICES 2019).