Étude expérimentale de la compétition interspécifique entre juvéniles de saumon coho, Oncorhynchus kisutch, et de saumon atlantique, Salmo salar, en eau douce

Abstract

The risk of accidental introduction of coho salmon in rivers inhabited by Atlantic salmon induced research on competition mechanisms between fry and juveniles of the two species under experimental conditions. Possible consequences of the competition were evaluated in terms of survival, growth, predation, downstream movement and habitat use. Results showed that under good trophic conditions, the presence of coho salmon had no influence on Atlantic salmon fry and juveniles. Microdistribution was different, Atlantic salmon holding position in riffles and coho salmon preferring pools. The pelagic and gregarious behaviour of coho salmon juveniles, that are much larger than Atlantic salmon at the same stage after emergence, contrasted with the benthic substrate-bound behaviour of the latter. These differences increased in sympatry at the expense of Atlantic salmon, which was handicapped by its smaller size. Under limiting trophic conditions, the growth and sedentary behaviour of Atlantic salmon were significantly altered by the presence of coho salmon,:thus justifying explicit doubt on the interest of introducing coho salmon into French rivers.