THE DESIGN OF FISHWAYS FOR SHAD

Abstract

Until recent years most fish passage facilities in France had proved to be either totally inefficient or else had only a very low efficiency for Allis shad (Alosa alosa ). The installation of dams on rivers with shad populations had almost always resulted in the species becoming rare in, or even disappearing from, the reaches above the dams. This phenomenon is not restricted to France. In 1923 a commissioner of the Bureau of Fisheries stated in a letter to the Federal Power Commission on the subject of American shad (Alosa sapidissima) “ that it was very doubtful whether any shad would ascend a fishway of any description or any height” . Until 1955, the only facilities that were considered to be effective for this species on the North American continent were the two enormous fishways (around 10 m in width) at the Bonneville dam on the Columbia River. These fishways accounted for around 10% of the total cost of the hydroelectric power station (DALLEY, 1980). It seems appropriate to integrate the experience in fish pass design acquired for both species of shad (Alosa alosa and Alosa sapidissima ) in so far as all the observations made, both in France and North America, indicate that their migratory behaviour is very similar.