Influence of habitat structure and fish density on Atlantic salmon Salmo salar L. territorial behaviour

A laboratory stream experiment was performed to test the influence of young-of-the-year Atlantic salmon Salmo Salar density on habitat selection (i.e. pools and riffles) and the combined effect of habitat and density on territoriality. Pools were preferred at low and medium fish density. At higher density, the saturation of the riffles led to an equal fish repartition in both habitats. Aggressive interactions increased according to fish density, and the level of aggression was significantly higher in the pools than in the riffles. # 2006 The Fisheries Society of the British Isles Key words: Atlantic salmon; density; habitat; stream aquarium; territoriality. Competition is a common phenomenon that occurs in most animal communities. Both intra- and interspecific competition reduces individual fitness, thereby affecting the dynamics of the population (Connell, 1983; Schoener, 1983). For freshwater fishes, and particularly salmonids, intraspecific competition is usually considered as a density-dependent process leading to modification in such life-history characteristics as growth rate (Deverill et al., 1999; Jenkins et al., 1999; Bohlin et al., 2002; Sundström et al., 2004), mortality and emigration (Elliott