Aggressiveness and the Foraging Behaviour of Young-of-the-Year Brook Charr (Salvelinus fontinalis)

Individual young-of-the-year brook charr (Salvelinus fontinalis) were observed in the field to relate their aggressiveness to their body size, the size and quality of their foraging site, and their feeding rate. Aggressive charr were 13% larger than nonaggressive conspecifics observed on the same day in the same area. Aggressive fish had a lateral foraging radius 29% larger than nonaggressive fish and a 45% greater mean distance to neighbours, even when the effect of body size was removed by analysis of covariance. Aggressive fish of two size categories (20–29 and 40–99 mm) made 70 and 55% more feeding attempts per unit time, respectively, than nonaggressive fish of the same size. Number of prey items in stomachs was significantly and positively correlated with feeding attempt rate. In addition, aggressive fish appeared to occupy more preferred sites, since their sites were significantly more likely to be reoccupied after their removal than were sites occupied by nonaggressive fish. These results are consistent with the hypothesis that defence of a foraging site is a better tactic than ignoring conspecifics.