“…In the Scorff river basin, sympatric populations of these species can occur in the main river (BAGLINIÈRE and ARRIBE-MOUTOUNET, 1985) and in tributaries, where they are the predominant species with eel (BAGLINIÈRE, 1979). Some field and experimental studies have been concentrated on the potential overlap of diets and/or habitat requirements (MAITLAND, 1965;MANN and ORR, 1969;LIEN, 1981 ;NEVEU, 1981 ;BALTZ et al, 1982;WELTON et al, 1983;GLOVA, 1987;BROWN, 1991), but little is known about the temporal aspect of habitat use. On a seasonal scale, habitat shifts are closely related to the life history of species, like ontogenetic changes in habitat requirements (ELLIOTT, 1986 ;BAGLINIÈRE era/., 1989 ;BALTZ et al, 1991 ;SEMPESKI and GAUDIN, 1995 ;KOCIK and TAYLOR, 1996), spawning (BAGLINIÈRE era/., 1987 ;MEYERS et al, 1992) and overwintering migration (CUNJAK and POWER, 1986 ;SWALES ef a/., 1986 ;BROWN and MACKAY, 1995), whereas diel habitat shifts usually correspond to circadian rhythms of resting and feeding activities (CAMPBELL and NEUNER, 1985 ;KWAK et al, 1992 ;HEGGENES era/., 1993 ;ROUSSEL and BARDONNET, 1996).…”