Stream-dwelling salmonid populations may be affected by both density-dependent and density-independent processes, but the relative im- portance of each may vary both spatially and temporally. We quantified population fluctuations of two unexploited rainbow trout (Oncorhynchus my- kiss) populations in western North Carolina over a 10-year period and examined the effects of spring discharge and adult abundance on recruitment. Both rainbow trout populations exhibited high degrees of temporal variability in density during the study. High spring flows that occurred during the incubation and emergence periods of rainbow trout were associated with densities of age-0 and age-1 trout in both streams. Age-0 densities were also associated with adult densities in one stream but with no evidence of a density dependent relationship. These results suggested that fluctuations in rain- bow trout density in these two streams were determined primarily by a density-independent factor. Knowledge regarding the magnitude and causes of salmonid population fluctuations can allow managers to account for the high variability and statistically control for it so responses to conservation actions or perturbations are easier to detect and better inform the public about population fluctuations of a popular game fish.
