A PROPOSED FISHWAY TO FACILITATE THE UPSTREAM AND DOWNSTREAM MIGRATION OF FRESHWATER SHRIMPS AND CRABS

摘要

For fishes, freshwater shrimps, and crabs, weirs and drop-structures without fishways are obstacles to both upstream and downstream migrations. In particular, it is important for diadromous shrimps and crabs to migrate upstream over drop-structures from estuaries where their larvae develop and metamorphose to juveniles. A fishway for shrimps and crabs should be required in drop-structures in order to conserve the local populations of such aquatic animals. This paper proposes a type of fishway for shrimps and crabs that has a stepped channel with a trapezoidal cross-section. The effect of this fishway on the upstream migration of freshwater shrimp is discussed on the basis of experimental results concerning flow fields. Also, changes in the number of freshwater shrimps and crabs migrating upstream via the fishway during a 24-hour period are clarified.