| Summary: | [Departement_IRSTEA]GMA [TR1_IRSTEA]GMA2-Déterminants physiques du fonctionnement des hydrosystèmes d'eau courante National audience A study of the Lower Rhône ichthyocenosis (hydropower schemes of Montélimar and Donzère-Mondragon) allowed us to identify the interannual variability of fish assemblages from 1983 to 1994. Observations concerned three stations representative of the artificially modified main channel : dyked lotic channel, storage reservoir and diversion canal. Twenty-nine species among the thirty-three known from this part of the river have been captured in the three stations during Spring. Five euryoecious species (Rutilus rutilus, Alburnus alburnus, Leuciscus cephalus, Anguilla anguilla and Lepomis gibbosus) with strong occurences in samples (more than sixty percent) represent ninety-two percent of catches. During the last decade, three new species appeared in the Lower Rhône fish community : Silurus glanis (1987), Pseudorasbora parva (1989) and Carassius auratus (1990). Apart from anthropogenic disturbances, interannual variability in species richness and fish abundances are principally determined by: successive and significant hydroclimatic events (hydrological deficit from 1989 to 1993) and high floods (october 1993 and january 1994), ecological strategies of species facing abiotic and biotic constraints. The results prove the interest of long-term studies to appreciate actual variability in large river fish assemblages. Le suivi du peuplement piscicole du Bas-Rhône (aménagements de Montélimar et de Donzère-Mondragon), réalisé entre 1983 et 1994, permet d'aborder la variabilité interannuelle au sein de l'ichtyocénose. L'étude porte sur 3 stations représentatives des configurations artificielles du cours principal : le chenal lotique, la retenue et le canal. Parmi 33 espèces connues à l'échelle de ce secteur, 29 ont été capturées au printemps dans ces 3 stations. Cinq espèces euryoeciques (Rutilus rutilus, Alburnus alburnus, Leuciscus cephalus, Anguilla anguilla et Lepomis gibbosus) dont ...
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