A space-time approach is adopted in an attempt to understand changes in the availability of the central sardine stock along the northwestern Moroccan coast. The warming observed in 1987 and 1989, due to the decline in wind activity, seems to have some repercussions on sardine distribution. The decrease in upwelling activity seems to have favoured concentration in the vicinity of Safi, and thus rendered the sardines more vulnerable to the purse-seiners of this port. We seek to explain the failure of the link established by Belveze and Erzini (1983) between sardine availability and upwelling activity in thc northern area. Two hypotheses, taking into account the local hydrology or the tendency of pelagic species to aggregate in time and space, have been put forward. We believe that the modification of the space-time distribution of the sardine may have two origins: 1) change in stock size and range of distribution; and 2) prevailing environmental conditions which force the sardines to concentrate in favourable areas.