Implications of territory size for the measurement and prediction of salmonid abundance in streams

Information about territory size is useful for both the measurement and pre diction of salmonid abundance. Percent habitat saturation (PHS), the percen tage of the stream area occupied by the territories of salmonid fishes, is a better measure of abundance than population density because the former in tegrates the effects of (a) several age-classes or species in a stream, and (b) variation in growth rate or sampling date. "Effective density" or "eff ective PHS," calculated by weighting crude density (no.m(-2)) or PHS by the number of organisms in the sampling unit, more accurately reflects density from the organism's point of view than does crude density or PHS. Effectiv e density and PHS of Atlantic salmon (Salmo salar) in Catamaran Brook, New Brunswick, increased by 0.4 fish per m(2) and 4%, respectively, for each or der of magnitude decrease in the area of the sampling unit. Literature data suggested that territory size is inversely related to food abundance and c an be used to predict changes in salmonid abundance that accompany changes in food abundance. The allometry of territory size was a better predictor o f the decline in density of a cohort of Atlantic salmon in Catamaran Brook than the allometry of metabolic requirements.