GROWTH AND AGE STRUCTURE OF 2 POPULATIONS OF THE PELECYPOD ELLIPTIO-COMPLANATA (LIGHTFOOT) IN THE FRESH-WATER ESTUARY OF THE ST-LAWRENCE-RIVER

A comparison study of the growth rate and the age-structure was conduc ted on the freshwater pelecypod Elliptio complanata (Lightfood) at two stations, one in the upper section of the upper St. Lawrence river es tuary (Gentilly) and the other in the lower section (Deschambault), wh ere the amplitude of the tide is respectively 1,0 m and 3,8 m. Growth of the clams was assessed by using the Walford Plot model and the von Bertalanffy growth curve model. Results have demonstrated that the rel ative and absolute growth rates are statistically similar at the two s ites. Mean age of clams does not differ between the upper and lower se ctions of the upper estuary. Age-frequency distributions indicated tha t clam populations at the two sites are dominated by individuals of 6- 10 years old. The difference in the tide oscillation between the two l ocalities does not seem to influence the growth of these molluscs.