FACTORS EFFECTING ON MORTALITY RATE OF Corbicula japonica IN LAKE JUSAN, JAPAN

Some areas in Lake Jusan disparate extremely in population of Corbicula japonica (Yamato shijimi), and this disparity remain constant every year, indicating variation of mortality rate. Most of the low population areas are located in the deeper area where silt-clay concentration is high. Population growth simulation by using dynamic energy budget (DEB) model is used to identify the difference of mortality rate. The results show that the rate varies from 0.001 to 0.01 and this variation tends proportional to the population density. Effect of silt-clay content was not identified for the concentration lower than 26%. Although water depth is shallower than a maximum suitable depth, but in bottom layer in the deeper area, DO always lower than 3 mg.l-1 in summer. This low DO represents low pH, indicating that dissolution mortality occurs every year in Lake Jusan