| Summary: | Territoriality and foraging behaviour can play a major role in determining the abundance and distribution of mobile animals. To date, territorial behaviour of young-of-the-year (YOY) salmonids is typically described for sit-and-wait individuals that defend territories from a single foraging station, but ignored for individuals that are more mobile or use several foraging stations. In this study, I describe the territorial and foraging behaviour of 61 YOY Arctic charr (31) and brown trout (30), in relation to key ecological factors in six rivers (three rivers per species) in NW-Iceland. Individual territory size was estimated, irrespective of mobility, based on locations of all observed foraging and aggressive acts over 40 minutes. Territories were generally larger for Arctic charr than for brown trout, which corresponded with high and low mobility, respectively. Also within each species, more mobile individuals used larger territories. Territories were also influenced by ecological correlates: i.e. territory size generally increased with body size, declined with increased food abundance, but surprisingly, increased as intruder pressure increased. Interestingly, Arctic charr territories overlapped more and appeared to be defended less efficiently than brown trout territories. In general, this study suggests that mapping territories for all individuals, irrespective of whether they remain sedentary at a single foraging station or exhibit more mobility, provides a novel view on territoriality in stream-dwelling salmonids. Multiple central-place territories and territories of widely foraging individuals may not always pertain to the same laws as single central-place territories and highlight the need for further studies on local space use of stream-dwelling salmonids and its population consequences. Háskólinn á Hólum, RANNÍS
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