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 of the giant scallop Placopecten magellanicus (Gmelin, 1791) in Baie des Chaleurs, southwestern Gulf of St. Lawrence, Canada in July 1992. Differences in the relative strength of the younger cohorts in each of the four beds, indicated marked differences in recruitment and/or survival in individual years over distances of 10 to 40 km. Part of this variability appeared to be related to environmental conditions prevailing during and after spawning. The growth rate of small individuals (< 50 mm) was correlated with the gradient of increased temperature and food availability going up the bay. In all beds, both total production and reproductive effort increased with increasing age and then leveled off. Somatic production reached a maximum after 7 to 10 yr and then decreased for older scallops. Reproductive effort (percentage of production dedicated to reproduction) increased monotonically with age and, for any given age, followed the increase in temperature and food availability going from the mouth into Baie des Chaleurs. Marked differences in the contribution of different beds to the total reproductive output for Baie des Chaleurs are inferred from inter- bed differences in the lipid content of the oocytes, in the proportion of non-reproductive juveniles, and in individual reproductive output.