Abstract
It is well known that shellfish and salmon fry collect around coastal structures.
The topic of this study is fishery of the Japanese surf clam, Pseudocardium sybillae (VALENCIENNES), along the East Water-break of Ishikari New Port located along the central coast of Ishikari Bay in the Hokkaido district. This paper centers its study on the flow along East Water-break in the summer season in which the larvae of Japanese surf clam are found to be floating. The observations of oceanographic conditions during 5 to 7 days were repeated several times using 5 current meters. The flow in upper and lower layers was observed by drifting floats using an aerophotographic and goniometric observations on the shore.
The oceanographic conditions of the inshore currents near the water-break were tested using a hydraulic model and the inshore current and tidal current were simulated by a numerical model composed of partial differential equations.
Following conclusions were obtained through the above-mentioned investigations.
A large-scale and anticyclonic circling current is formed between the water-breaks and inflowing water from the Ishikari River. A small-scale countercurrent near the East Water-break exists. The East and detached water-break influenced the flow in the northeastern part within a radius from the coast to the North Water-break. The above-mentioned current carries larvae of Japanese surf clams and lets some of them settle down in the fishery.
