Microdistribution of populations of brown trout salmo trutta and juvenile atlantic salmon salmo salar and other species present in the upper scorff river brittany france
Bagliniere, J.L.; Arribe Moutounet, D.
Hydrobiologia 120(3): 229-240
ISSN/ISBN: 0018-8158 Accession: 005898428
The microdistribution of populations of brown trout (S. trutta L.) and of juvenile Atlantic salmon (S. salar L.) in the upstream part of the Scorff river (Brittany) at the end of summer. The salmon population was composed of 1 age class (0+) only; trout age varied from 0+-3+ yr, with a majority in age class 1+. Salmon density increased with current velocity (r = 0.99) and the nature of the substratum. A very favorable habitat for this species was characterized by reduced depth (< 23 cm), a high current velocity (61 cm s-1) and a stony substrate. The largest part of the population (74%) was localized in the center of the running open water. A bank effect was particulary important for brown trout, irrespective of age (80.1%). The trout 0+ is absent from shallow rifles and its presence in the few deep running water areas (41 cm s-1) along the banks involved a spatial segregation with salmon 0+. Trout 1 yr and older were localized in deeper habitats (27 cm) with 0 to medium current velocity (< 28 cm s-1). The bank effect was intensified by the presence of many overhangs along the bank. Among the secondary species, sculpin [Cottus gobio] had the widest distribution, but stone-loached [Nemacheilus barbatulus] and brook lamprey [Lampetra planeri] were the most abundant species and reached high densities in characteristic areas.