THE INTERSPECIFIC COMPETITION BETWEEN BRO WN TROUT (SALMO-TRUTTA L) AND RAINBOW-TROUT (ONCORHYNCHUS-MYKISS WALBAUM) - INFLUENCE ON HABITAT MODELS

The influence of interspecific competition on the occupation of physic al habitat of the Estibere stream was studied in two rainbow trout pop ulations (Oncorhynchus mykiss), one in allopatry and the other in symp atry with brown trout (Salmo trutta L.). The occupation of the Weighte d Usable Area (WUA) was calculated by the PHABSIM model of the IFIM me thodology (BOVEE, 1982). The occupation by rainbow trouts was signific antly greater (t test, p < 0.05) for the allopatric population than fo r the sympatric population. Surface of cover, gradient and the occupat ion of the physical habitat by adults of brown trout explained 77% of the variation of the occupation of the physical habitat by rainbow tro ut. For the adults of brown trout, the surface of cover explained 81% of the variation of the occupation of physical habitat. Interspecific competition may influence the occupation of physical habitat by the di fferent species and life-stages.