AGE AND GROWTH OF THE SUNRAY SURF CLAM MA CTRA-CHINENSIS IN TOMAKOMAI, SOUTHWEST HOKKAIDO

The age and growth of the sunray surf clam Mactra chinensis in Tomakom ai were studied by measuring shell rings. Monthly measurement of shell increment from the last ring indicated ring formation to occur annual ly from November to January when seawater temperature dropped below ab out 10-degrees-C, and thus to be regardable as an age indicator. Age a t the first ring formation was estimated at 0 by observing the shell r ings of newly settled clams. Age was determined by counting the number of rings, and the relationship between age and shell length was expre ssed using von Bertalanffy's growth equation: Lt = 78.31 [1 -exp{-0.67 (t - 0.34)}], Lt being shell length (mm) at age t (years).