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Abstract

Territory shape yields important insights into how animals exploit local resources. Territories of stream-dwelling salmonids are typically (1) mapped around a single central-place, (2) described as circular, elliptical or teardrop-shaped, and (3) believed to reflect their exploitation of drifting invertebrate prey. In this study, we tested the current view of territory shape by mapping multiple central-place territories for 50 young-of-the-year Atlantic salmon. Multiple central-place areas were more elongated (eccentricity: median = 1.301, range = 1.043–2.784) than the foraging patterns around each central place (eccentricity: median = 1.135, range = 1.014–1.385). In addition, multiple central-place areas were elongated along the stream length (33 of 50 fish), whereas the foraging areas around each station tended to be elongated along the stream width (32 of 50 fish). These findings may be explained by the way that stream salmonids interact with drifting prey. At each central place, a wider foraging area should provide an increased access to prey drifting downstream. Similarly, by regularly patrolling a large multiple central-place area along the stream axis, a territorial fish may increase its access to drifting prey by excluding competitors from upstream areas. Further studies are needed on the ecological factors that determine territory shape in stream fish and multiple central-place foragers.