| Summary: | Radiotracking operations conducted in 1995 at the hydroelectric plant of Castetarbe on the Pau River shortly before the dam gave way in November 1995 gave evidence of a large impact of the obstacle on upstream migration of returning adult salmon both in terms of proportions of upstream passages (50%) and migration delays. Such a low upstream passing of the obstacle was partly attributed to (i) the implementation of the fish pass on the left bank in the vicinity of the dam, i.e. on the opposite side from plant turbine discharges and (ii) the fish pass itself, of type Lachadenède, i.e. highly sensitive to variations in upstream water level. At the same time of dam rebuilding, a new upstream fish passage facility of pool-pass type was built on the right bank in the vicinity of the plant and immersed in spring 2000. Radiotracking operations were then proceeding to ascertain the efficiency of this pool fish pass. From July to December 2000, 23 radio-tagged salmon arrived at Castetarbe. All succeeded in passing over the obstacle (23 out of 23, i.e. 100%) with in general short-lived blockade duration (median blockade: 2.1 days; min.: 0.1 day; max.: 77.9 days). Nevertheless, fish pass attractivity was not found optimal as half the fish had to approach to the pool pass entrance up to 15 times (maximum 70 times) before successfully passing over the obstacle. The installation of a simple regulation system main-taining a more or less constant waterfall of about 30 cm at the fish pass entrance would most likely enhance passages over the obstacle so as to make the hydroelectric power plant of Castetarbe nearly transparent to migration and compatible with strategies for restoring Atlantic salmon stocks on the Pau River. Such a decreased impact of Castetarbe plant was all the more important since the obstacle was located on the river well further downstream of major spawning grounds. L'objectif de l'étude était l'évaluation, à l'aide de la technique de radiotélémétrie, de l'efficacité de la nouvelle passe de Castetarbe. De ...
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