Age and Growth of the Sunray Surf Clam Mactra chinensis in Tomakomai, Southwest Hokkaido.

Abstract

The age and growth of the sunray surf clam Mactra chinensis in Tomakomai were studied by measuring shell rings. Monthly measurement of shell increment from the last ring indicated ring formation to occur annually from November to January when seawater temperature dropped below about 10, and thus to be regardable as an age indicator. Age at the first ring formation was estimated at 0 by observing the shell rings of newly settled clams. Age was determined by counting the number of rings, and the relationship between age and shell length was expressed 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).