EVALUATION OF ATLANTIC SALMON PARR RESPONSES TO HABITAT IMPROVEMENT STRUCTURES IN AN EXPERIMENTAL CHANNEL IN NEWFOUNDLAND, CANADA

Distributional patterns and microhabitat selection of Atlantic salmon (Salmo salar) parr were investigated in relation to habitat improvemen t structures in a controlled flow experiment channel at Noel Paul's Br ook, Newfoundland. The channel consisted of six replicates, each conta ining three randomly arranged treatments. Each replicate included a co ntrol treatment with no habitat modification, a mid-channel treatment with a boulder cluster and low-head barrier dam, and a stream bank tre atment with undercut banks and wing deflectors. The influence of size class, density, discharge and diurnal/nocturnal differences on microha bitat selection were evaluated. Results showed that the mid-channel tr eatment did not serve its purpose at lower discharges (0.032-0.063 m(3 ) s(-1)), and as a result was not the treatment of choice. However, as the discharge increased (0.13 m(3) s(-1)), more salmon took up reside nce in this treatment. In all experiments, greater depths were selecte d in the stream bank treatment, and salmon parr in the mid-channel tre atment consistently selected positions closer to cover. Larger parr pr eferred greater depths and were found closer to the improvement struct ures. Benthic and drifting food availability were also estimated, and results showed that 'funnelling effects' of the drift were created nea r the structures. This study indicates that these structures have the potential to create favourable feeding sites, and provide the necessar y physical characteristics required by salmon parr. (C) 1998 John Wile y & Sons, Ltd.