Influence of dewatering on movements and distribution of salmon parr (Salmo salar L) in relation to habitat characteristics in an experimental stream

The response of Atlantic salmon parr to major decreases in water levels, typical of summer low flows, is not well documented. Three experiments were conducted in an artificial stream designed with sequences of riffle, flat, and pool habitat, each habitat in a section 10 m long by 3 m wide. In deeper water, parr did not respond to water level or flow decrease. In shallow water, they reduced activity, particularly feeding, and in critical conditions a portion of the population moved into deeper water. The remainder of the parr buried themselves into the gravel. After flow increase, some of the downstream moving parr returned to the riffle habitat.