We used genetic markers, namely allozymes, to study the genetic structure (stock unit) and the sardine stocks movement along the Moroccan Atlantic coast and its relationship regarding the environmental features, especially upwelling. In this study, we have combined previous results obtained by analyzing eight samples collected during the spawning season (winter 2004) (chlaida et al.2008) and new data obtained by analyzing eight samples gathered during the feeding season (summer 2006). Therefore, we compiled 765 individuals from an earlier study and the 2006 summer sampling and compared seasons' results. In winter, a substantial heterogeneity (Fst =0.205) is described, with a significant genetic break in the Agadir Bay (latitude 30° 48' N) that cuts the coastal sardine populations in the Moroccan Atlantic into two stocks (north and south). In summer, the genetic structure showing two groups is maintained (Fst= 0.135). Still, the genetic break separating the two stocks arises southward, near Tarfaya (latitude 28°08'10" N), suggesting a spreading out towards the south of the northern stocks. This result seems to be related to the sardine movement along the Moroccan Atlantic coast regarding reproduction needs in winter and for trophic reasons in summer. The species' observed genetic break and seasonal activity along the Moroccan coast are expected to result from the Cape Ghir Hydrological barrier, impermeable in winter and semi-permeable in summer. This barrier comprises currents, gyres, and different mesoscale structures related to upwelling dominating in this zone.