Competition between Bonneville cutthroat trout and brook trout in laboratory and field experiments (Salvelinus fontinalis, Oncorhynchus clarki)

We conducted short-term laboratory and field experiments to document competition between Bonneville cutthroat trout Oncorhynchus clarki utah and introduced brook trout Salvelinus fontinalis. Results from our laboratory experiments indicate that brook trout outcompete cutthroat trout for limited food and habitat resources. Brook trout captured more food, displayed more aggression, and were located more frequently in preferred stream positions than cutthroat trout. Brook trout also gained more weight, defended territories more, and were engaged in more feeding activity. Results from our field studies also appear to indicate that brook trout is dominant over cutthroat trout. In all four density treatments, brook trout gained more weight than cutthroat trout, with cutthroat trout losing weight at the two highest densities. At higher densities, cutthroat attempted to emigrate more than brook trout. These findings support the hypothesis that interference competition with introduced brook trout contributes to the decline in native cutthroat trout populations.