The Effect of Population Density on Competition Between Cutthroat Trout and Brook Trout

Cutthroat Trout (Oncorhynchus clarki) are being displaced rangewide by invasive Brook Trout (Salvelinus fontinalis). There are many potential causes of displacement but the underlying mechanisms of the invasion and displacement are not well understood. Increased population densities in streams in which Cutthroat Trout and Brook Trout occur in sympatry appears to have detrimental effects on Cutthroat Trout. In this study I compared the competitive behaviors and activity allocation patterns of Brook Trout and Cutthroat Trout at varying population densities in a simulated stream aquarium. I concluded that Brook Trout likely have a behavioral advantage over Cutthroat Trout at high population densities and that Cutthroat Trout may not be as energetically efficient as Brook Trout at intermediate densities. Cutthroat Trout are most likely to be at risk in the age 0 and age 1 age classes where the population density can reach high levels.