Many studies have investigated the stock structure of the European pilchard (or commonly, "sardine") population widely distributed in the Northeast and Eastern Central Atlantic, and the Mediterranean and Black Sea (e.g. (Spanakis et al. 1989)(Tinti et al. 2002)(Atarhouch et al. 2005)(Chlaida et al. 2006)(Silva et al. 2006)(Laurent et al. 2007)(Chlaida et al. 2009)(Antonakakis et al. 2011). However, some uncertainty remains (Kasapidis et al. 2012), and further research into regional stock subunits is needed (ICES 2014)(ICES 2017). The West African European pilchard profiles presented on FishSource reflect two assessment units delineated by the FAO Working Group on Small Pelagic Fish in Northwest Africa, (FAO 2018): one in zones "A + B" (Central) and another in zone "C" (Southern), The recent work of (Shukhgalter 2013) supports the distinction of these two stock units.

The Southern stock unit, considered here, reflects the population occurring between Cap Boujdour at 26ºN through the southern limit of the species extent; while the Central stock unit reflects a population distributed from Cap Boujdour north to Safi, Morocco at 32ºN.

In addition to the West African stocks, FishSource considers the following assessment units throughout the species’ distribution:

International Council for the Exploration of the Sea (ICES) stock assessment units:
- Iberian (ICES Divisions 8.c and 9.a) and Bay of Biscay, Southern Celtic Seas and English Channel (ICES Divisions 8.a,b,d and Subarea 7).

General Fisheries Commission for the Mediterranean (GFCM and FAO 2015) (GFCM/FAO) stock assessment units - of the 8 stock assessment units assumed (Kasapidis et al. 2012)(FAO and GFCM 2017), these 2 are already covered in profiles:
- Northern Adriatic Sea (GSA17) and Northern Alboran Sea (GSA01).

The West African stocks are captured in industrial and artisanal small pelagic fisheries in Morocco, Mauritania, Senegal, and the Gambia that also target European anchovy Engraulis encrasicolus, sardinella Sardinella spp., horse mackerel Trachurus spp. and chub mackerel Scomber japonicus.