Since 1979, the IFREMER Laboratory follows mussel recruitement in the Pertuis Breton. Gametogenesis generally begins in September or October and ends in Décember. Spawning may begin in Februrary and continues up ta the end of April, but it usually occurs in the second fortnigh of March. The most important settlement generaly runs after the middle of May up to the middle of June. Duririg the study period, four years are noticeable by lack of settlement : 1982, 1989, 1990 and 1991. This failure thraughout these three last years resulted in a breakdown of the cultivated biomass. The present paper outlines a preliminary analysis on the influence of temperature and sunshine.