Impact of weirs and dams on the anadromous migration of the Atlantic salmon (Salmo salar L.): characterization and modelling of the processes for clearing obstacles

• Main Author: Croze, O.
• Other Authors: Groupe d'hydraulique appliquée aux aménagements piscicoles et à la protection de l'environnement (UR GHAAPPE), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF), Doctorat Fonctionnement des Ecosystèmes et Agrosystèmes, Université de Toulouse
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2008
• Subjects: thesis; MONTAISON; thèse; [SDE]Environmental Sciences; Atlantic salmon; Salmo salar
• Online Access: https://hal.inrae.fr/tel-02591601; https://hal.inrae.fr/tel-02591601/document; https://hal.inrae.fr/tel-02591601/file/pub00025830.pdf

As is the case in many other countries, France's rivers are obstructed by tens of thousands of artificial weirs and dams. These structures disturb the fish population in many ways, particularly by modifying water quality and habitat. But above all they hinder their up and downstream circulation, with migratory species suffering the most. Over the last few decades, different types of fishway have been developed to reduce the impact of these obstacles. Their efficiency has only been evaluated more recently, however: the earliest results have proved rather disappointing, and have highlighted the need for progress in the field. To improve fish passage at these obstacles, including those which are already equipped with fishways, will require more knowledge of the factors that facilitate the passing of fish, and also the processes involved during passing. The Atlantic salmon, Salmo salar L., was selected as the biological model, because of its long migrations through inland waterways and the many obstacles it has to overcome. The approach followed by this thesis consisted in acquiring a large set of pass attempts occurring at a series of obstacles. Two rivers were used for this study, the Aulne, a small coastal river, and the Garonne, the third largest river in France by flow. These two rivers share the characteristic of being obstructed by a large number of weirs and dams of different kinds. Fish movements on the Aulne and the Garonne were tracked by telemetry (radio-tracking), the only technique able to identify upstream passes while monitoring fish behaviour during pass attempts. The first part of the study consisted in characterising the impact of the dams being studied. An analysis of each found that there was considerable variation between the sites in passage rates and delays to migration, and also between years for a given site. In both cases, the cumulative effect of the obstacles seems to be highly significant because they provide the principal factor for loss' during anadromous migration on both rivers. An ...