Abstract
Sarobetsu river and Panke swamp which connect to Teshio River are the northern limit of Corbicula Japonica fisheries in japan. However, Fish catches continued to decrease and it is necessary that the effecttive measures are taken for resource conservation.
In this study, we cleared the hydraulic structure of Sarobetsu River, and analized the relationship between fresh water clam habitat and hydraulic stracture. First, we performed continuous flow observation at plural points of Sarobetsu River, and examined water balance of Sarobetsu River. As a result, it was found that the outflow is dominant in Sarobetsu River, and then salt water intrusion is suppressed Also it was found that the dilution of salt water proceed after summer season because of preferentially freshwater supply into Panke swamp.In view of the salt supply to Panke swamp, flow rate of Sarobetsu River is important. Flow rate of Sarobetsu River is in increasing trend since 1980, as response to fish catches showed a decreasing trend. Flow rate increase is dependent on rainfall intensity, a change in rainfall condition of near 30 years is presumed to be a main cause of Corbicula Japonica decrease.
