SEASONAL CYCLES, REPRODUCTION AND OOCYTE QUALITY IN PECTEN-MAXIMUS FROM THE BAY OF BREST

This work is part of the program <<recruitment determinism in scallops >> initiated in 1992 by the ''Contrat de Baie''. The aim of this resea rch was to explain interannual abundance fluctuations observed for Pec ten maximus, in the Bay of Brest. To this end an analytical approach t o the life cycle of the species was undertaken to determine its critic al phases. A phase may be considered as ''critical'' if the mortality rate at its level varies from one year to the other. Using data from 1 989 to 1994, a precise time-table of the <<physiological year>> of the scallop in the Bay of Brest was determined. Fecundity and gamete prod uction kinetics were estimated from the annual variation in the weight indices of the gonad. In the laboratory, egg quality was estimated Fo llowing stimulated spawning of newly caught individuals. The digestive activity was estimated by amylase activity measurements during a thre e year period. Spawning lasts 6 months in the Bay of Brest from March to October. Spawning, muscle and digestive gland growths, are intimate ly linked to phytoplancton blooms. Gonad production shows a maximum in April-May, and two relative minima in March and November. These resul ts, which provide detailed understanding of the adult's annual cycle i n the Bay of Brest, will be used to interpret the relationship between the annual cycle and larval and post larval abundance and survival. A lready, these results are being used to improve spat production in hat cheries.