Density-dependent habitat selection by juvenile Atlantic salmon (Salmo salar) in experimental riverine habitats

We investigated habitat use of Atlantic salmon (Salmo salar) parr in experi mental riverine enclosures made up of pool, riffle, and run habitats over a range of densities (0.1-1.25 fish m(-2)) to test the implicit assumption i n habitat modelling that habitat selection does not change with population density. Results indicated that habitat use changed with population density , with relatively more parr in pools and fewer in runs at higher population densities. Temperature influenced parr distribution, with relatively more parr in runs and fewer in riffles and pools at higher temperatures. Parr di stribution was primarily affected by hydromorphological differences among p ool, riffle, and run habitats. Effects of population density and temperatur e on use of pool, riffle, and run habitats were often as large as effects o f hydromorphological differences among pool, riffle, and run habitats on fi sh distributions over the range of temperatures and densities observed. Res ults varied considerably, despite controlled experimental conditions. We co ncluded that habitat selection by juvenile Atlantic salmon parr may be dens ity dependent and potentially quite variable.