ABSTRACT:

Hokkaido.s Okhotsk Sea coast is covered with drift ice in winter. This drift ice originates to the northeast of Sakhalin and arrives on Hokkaido coast in the beginning of January. Saroma Lagoon is located at the coast of Hokkaido facing the Sea of Okhotsk. It has two lagoon-mouths and leads to the Sea of Okhotsk. On the other hand, aquaculture is performed in the Saroma Lagoon. Therefore, the influence on the aquaculture by inflow of drift ice had been serious. Then, authors considered the influence on aquaculture by experimental research on the movement of drift ice.

INTRODUCTION

The placement of Saroma Lagoon is shown in Fig.1. Its area is 151.2km2, distance around is 91.1km and maximum water depth is 19m. The lagoon is a brackish water lagoon and it has two mouths which are opened to Sea of Okhotsk. On the other hand, Sea of Okhotsk is covered by drift ice from the beginning of January to the beginning of April. If the inside of Saroma Lagoon is frozen over before drift ice comes, drift ice will not flow into Saroma Lagoon. However, if the inside of Saroma Lagoon has not frozen over, drift ice used to flow into Saroma Lagoon and causes serious damages to the fisheries of scallops and oysters, and their facilities. The damage cost for the year 1973 reached approximately twenty-two billions yen, as an outstanding example. In order to prevent the drift ice flowing into the lagoon from the Sea of Okhotsk, the ice boom. was constructed in 2001 at the lagoon-mouth. However, it is concerned that ice jamming caused by ice boom might decrease the amount of seawater exchange. Decreasing the amount of seawater exchange could bring serious effect to the fisheries of scallops and oysters in the lagoon.

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