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

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 stations in the Durance catchment area : two of which are located in its main tributaries, the Buech river and the Verdon. An analysis (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 mesological variables associated with the density of invertebrates and the number of degree-days above 12 degrees and 22 degrees 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 flowing 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.