Upstream and downstream fish passage experience in France

Plans for the restoration or enhancement of anadromous fish stocks were initiated in France more than 15 years ago. A 1984 law concerning freshwater fisheries requires that any obstruction in streams or parts thereof, in the list specified by decree, must include facilitaties to ensure the passage of migratory fish. As a result, more than 400 fish passes were built or improved, and significant advances in the design of upstream fish passage and facilitaties have occured during the last 15 years. This chapter provides an overview of the functional features and design parameters used in the different types of passage facilitaties : Denil fish passes, pool fish passes, fish elevators and natural bypass channels. The relative advantages and drawbacks of each type of fish pass are discussed, with reference to the requirements of specific migratory species and site specific constraints. Emphasis is placed on the problem of maintenance. The various techniques used in France to evaluate the existing or newly constructed fish passes, as well as the topic of downstream migration at turbine intakes, are reviewed. Recent experiments have tested surface bypasses designed to provide a safe downstream route for smolts at small scale hydroelectric plants. The efficiency of such bypasses is evaluated by radio telemetry and release recapture tests. Results from some field studies are outlined. The effect of mercury lights to increase bypass attraction is discussed. The behaviour of fish in relation to the hydraulic flow patterns at the intake should be considered when designing a downstream bypass system. In conclusion, the author presents his view on the priorities for future research on fish passage facilitaties, insisting on the need for close collaboration between engineers and biologists, in particular fish behaviourists. Some priorities include the use of radio telemetry to track Atlantic salmon Salmo salar on the migratory rivers, and research aimed at gaining a better understanding of downstream migration of salmon, brown trout S. trutta, and European eel Anguilla anguilla.