Morphological and behavioural differences among recently-emerged brook charr,Salvelinus fontinalis, foraging in slow- vs. fast-running water

Abstract

Morphology and resource use were compared among recently-emerged brook charr,Salvelinus fontinalis, sampled from field locations differing in current speed. Individuals from faster running water were slightly longer, and had more fusiform body shapes and larger caudal fin heights, than individuals from slower running water. In addition, individuals from faster running water also directed more foraging attempts toward the middle of the water column and fewer toward the benthos and water surface. They also ate more dipteran larvae, fewer aquatic crustaceans, and fewer insect pupae and adults. Individuals located in the slowest and fastest current speeds made fewer foraging attempts per min, on average, than individuals located in current speeds of intermediate magnitude. Dry weight of stomach contents did not vary significantly with current speed, however. The form of the relationship between body shape and current speed suggests that it is adaptive. Small-scale variation in the location of foraging sites may account for some of the individual variability in resource use often reported for stream salmonids. Variation in the locations of foraging sites may also entail a trade-off between an individual's swimming effort and the quality of prey it consumes.