For assessment purposes, ICES formerly considered sprat in the North Sea as an independent unit. However, following the results of a recent genetic study, ICES determined it appropriate to merge the North Sea (Subarea 4) and Skagerrak and Kattegat (Division 3a) stocks into a single assessment unit (WKSPRAT 2018 2019). The new area excludes sprat in the Norwegian fjords. 

Uncertainty remains concerning the boundary of this stock with sprat from the Baltic Sea and English Channel (ICES 2018). Local depletion of sprats is an issue of particular ecological concern in areas where there may be geographically or functionally discrete populations (e.g. coastal periphery of Division 3a, and Norwegian fjords) (ICES 2018)(ICES 2019). Further research is recommended. 

In addition to the North Sea and Skagerrak and Kattegat (Subarea 4 and Division 3a) unit; FishSource considers the following assessment units currently defined by ICES: Celtic Sea and West of Scotland (Subarea 6 and Divisions 7a–c and f–k); English Channel (Divisions 7d,e); and Baltic Sea (Subdivisions 22–32).