Several studies have been conducted to understand the European pilchard stock structure widely distributed in the Northeast and Eastern Central Atlantic, and the Mediterranean and Black Sea. There are signs of regional sub-structure and maybe different population dynamics, mostly in the Gulf of Cadiz, but no genetic structure is clear along the distribution range (ICES 2017). It was even postulated that three separate subpopulations, due to different environments affecting mostly the larvae stage, could be managed independently (Leitão et al. 2014). Connectivity and dynamics point to the Gulf of Cadiz being a separate stock (Silva et al. 2019). A recent study on otoliths points to five populations, separating the Cantabrian Sea from the Portuguese coast, and finally, joining the Gulf of Cadiz population with the Mediterranean Sea population (Neves et al. 2021). Different parameters indicate contradicting results surrounding the population structure with uncertainty (ICES 2017)(Caballero-Huertas et al. 2022)​, and therefore here we consider the following assessment units along the European pilchard distribution:

By the International Council for the Exploration of the Sea (ICES):
- Iberian (ICES Divisions VIIIc and IXa) and 2) and Bay of Biscay, Southern Celtic Seas, and English Channel (ICES Divisions VIIIa,b,d and Subarea VII)
By the General Fisheries Commission for the Mediterranean (GFCM; FAO) of the 8 stock assessment units assumed (FAO, 2009; Kasapidis et al., 2012; GFCM, 2014) these 2 are already covered in profiles:
- Adriatic Sea (GSA 17-18) and Northern Alboran Sea (GSA 01)
By the Fishery Committee for the Eastern Central Atlantic (FAO, 2013a,b):
- NW Africa central (zones A+B; 32ºN – 26ºN) and NW Africa southern (zone C; 26ºN – the southern extent of the species distribution).