Multi-scales approach of the relationships between brown trout (Salmo trutta L) populations and habitat features in the central Pyrenees

The influence of spatial scales, of reach, of sequence and morphodynamic units on occupation by trout populations of the physical habitat calculated by IFIM methodology was studied on 264 morphodynamic units of 15 streams of the Central Pyrenees (France). A variance analysis model explained respectively 51.1% and 69.8% of the variability of the occupation of physical habitat by total density and by total biomass of trout. The results are discussed in relation to the interest of multi-scales approach for the carrying capacity concept of salmonid streams and the relation between biological processes and spatial scales.