RECRUITMENT, GROWTH AND PRODUCTION OF GIANT SCALLOPS (PLACOPECTEN-MAGELLANICUS) ALONG AN ENVIRONMENTAL GRADIENT IN BAIE DES CHALEURS, EASTERN CANADA

We measured population structure, growth and production of four beds o f the giant scallop Placopecten magellanicus (Gmelin, 1791) in Bale de s Chaleurs, southwestern Gulf of St. Lawrence, Canada in July 1992. Di fferences in the relative strength of the younger cohorts in each of t he four beds, indicated marked differences in recruitment and/or survi val in individual years over distances of 10 to 40 km. Part of this va riability appeared to be related to environmental conditions prevailin g during and after spawning. The growth rate of small individuals (< 5 0 mm) was correlated with the gradient of increased temperature and fo od availability going up the bay. In all beds, both total production a nd reproductive effort increased with increasing age and then leveled off. Somatic production reached a maximum after 7 to 10 yr and then de creased for older scallops. Reproductive effort (percentage of product ion dedicated to reproduction) increased monotonically with age and, f or any given age, followed the increase in temperature and food availa bility going from the mouth into Bale des Chaleurs. Marked differences in the contribution of different beds to the total reproductive outpu t for Bale des Chaleurs are inferred from inter-bed differences in the lipid content of the oocytes, in the proportion of non-reproductive j uveniles, and in individual reproductive output.