MORPHOLOGICAL AND BEHAVIORAL-DIFFERENCES AMONG RECENTLY-EMERGED BROOKCHARR, SALVELINUS-FONTINALIS, FORAGING IN SLOW-RUNNING VS FAST-RUNNING WATER

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 height s, than individuals from slower running water. In addition, individual s from faster running water also directed more foraging attempts towar d the middle of the water column and fewer toward the benthos and wate r surface. They also ate more dipteran larvae, fewer aquatic crustacea ns, and fewer insect pupae and adults. Individuals located in the slow est and fastest current speeds made fewer foraging attempts per min, o n average, than individuals located in current speeds of intermediate magnitude. Dry weight of stomach contents did not vary significantly w ith current speed, however. The form of the relationship between body shape and current speed suggests that it is adaptive. Small-scale vari ation in the location of foraging sites may account for some of the in dividual variability in resource use often reported for stream salmoni ds. Variation in the locations of foraging sites may also entail a tra de-off between an individual's swimming effort and the quality of prey it consumes.