| Summary: | We have described the physical characteristics of the Garonne-Dordogne river basin. This analysis reveals an high heterogeneity between the different areas, especially concerning distance from the sea, mean flow, slope and number of dams which are very important factors affecting the eel repartition within a watershed. Two main modifications of the eel context appear since 1980. Firstly, like within the majority of European watersheds, the glass eel recruitment has greatly dropped in the beginning of the eighties with a low level observed since this period. Secondly, eel ladders only appear in 1997-1998 on the two first main hydroelectric dams located on the Dordogne river (Tuilières) and the Garonne river (Golfech), the two main axis of the watershed. We have analysed the results of the electrofishing operations performed by the Conseil Supérieur de la Pêche (CSP) within the whole river basin between 1978 and 2003. This analysis shows that available data are too scarce to well study the evolution of the eel colonization level of the river basin during all this period. Only, the recent colonization can be examined. Eel occurrence and density levels seem to remain constant between 1994 and 2003. This analysis also reveals the scarcity of the data concerning the young eels not bigger than 15 centimeters. because they are mostly present in the downstream part of the river basin with water depths often important and electrofishing operations not very efficient. This statement argues for the development of specific operations to survey these young stages, their occurrence along the rivers being able to reveal the difficulty level to swim up within some parts of the watershed and/or the fluvial recruitment intensity (an high eel upstream progression linked with an high estuary escapment). / Le Cemagref de Bordeaux a entamé une démarche sur la colonisation du bassin versant Gironde-Garonne-Dordogne par l'anguille européenne notamment dans le cadre de trois travaux doctoraux. Un premier vise à analyser le comportement de l'anguille dans l'estuaire de la Gironde et un second étudie celui de la civelle face à la salinité. Enfin, le dernier analyse le comportement de l'anguille européenne dans l'ensemble du bassin versant, hors estuaire. L'étude que nous avons menée s'intègre dans ce dernier travail doctoral qui entend apporter de nouvelles connaissances sur les relations pouvant exister entre le phénomène de colonisation observé à l'échelle du bassin versant et les comportements individuels des jeunes anguilles (moins de 30 cm) majoritairement impliquées dans cette migration anadrome. L'analyse des données disponibles sur l'espèce dans le bassin Garonne-Dordogne est apparue indispensable afin de savoir s'il était possible de replacer cette colonisation dans un contexte historique. Afin de mettre en oeuvre cette analyse, différentes approches ont été développées.
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