Influence of environmental variables on the growth ofLeuciscus cephalus(Linnaeus 1766), in the River Durance, South-east France

Abstract

mesologic parameters. The chub, Leuciscus cephalus, colonizes the Durance river from its confluence with the Rhone river (alt. 13 m) up to the Serre Poncon dam (alt. 780 m.). The Durance has been exposed to strong human pressure, notably dam construction, reduction of flow rate and perturbation of the natural zonation patterns. The linear growth of chub was studied by scale measurement at six sta­ tions in the Durance catchment area : two of which are located in its main tributaries, the Buech river and the Verdon. An ana­ lysis (ANOVA) of the mean size of fish from one to five years of age shows significant differences between the stations. Principal Component Analysis, in which the stations are characterized by eight nosological variables associated with the density of inver­ tebrates and the number of degree-days above 12° and 22°C established a correlation between chub growth and species habitat, defined in terms of current flow rate, depth and substrate type and temperature. This correlation could be explained in two ways : 1- in slow-flowing homogenous riffle zone, the low water depth and absence of shelters limit the diversity of habitats and the biological richness; nevertheless the abundance of invertebrates does not seem to play an important role ; 2 - in zone of slow flo­ wing riffles subjected to large daily and seasonal variations in water temperature, as in this mediterranean river, temperature might be quite high. Fish older than two years, therefore prefer zones of deep water, where the thermic inertia is stronger.