POPULATION-DYNAMICS AND STOCK SIZE PREDICTION FOR THE SUNRAY SURFCLAM, MACTRA-CHINENSIS, AT TOMAKOMAI, SOUTHWEST HOKKAIDO, JAPAN

Annual fluctuation in the number of newly settled juveniles and in the stock size of the sunray surf clam, Mactra chinensis, were examined f rom 1987 to 1994 off the coast of Tomakomai, southwest Hokkaido. Stock size was estimated with a model based on two known population paramet ers, juvenile density and age composition. Juvenile density and the st ock size (or mass) ranges were 1.3 to 157.0 ind./m(2) and 249.8 to 1,1 27.4 metric tons, respectively; a time lag between the relative fluctu ations of both agreed with age-at-recruitment to the stock. Our result s suggest that population dynamics are directly influenced by the numb er of juveniles. The predicted stock size approximated the measured va lue and, consequently, a long-term prediction of stock size was deemed possible, provided age composition and juvenile density are determine d.