Demographic regulation of a southern brook charr population

We assessed the relative importance of density and environmental factors on a variety of demographic characteristics of a southern Appalachian brook charr (Salvelinus fontinalis) population in upper Ball Creek NC. Our study period (1991-2004) encompassed years of high flows and a four year drought (1999-2002) and brook trout densities varied substantially (0.01-0.14 fish/m2) in our permanent study site. PCA demonstrated that habitat availability varied among years (high flows/erosional substrata vs. low flows and depositional substrata).  The only model capable of explaining long-term variation in the per capita rate of change of both the population and young-of-the-year (YOY) was simple density-dependence (population size), and a significant stock-recruitment relationship was present.  Spring YOY density was positively correlated with fall YOY density and with spring mean YOY standard length (SL). There was a negative relationship between fall density and mean SL.  Fall adult densities also were negatively correlated with fall YOY mean SL, providing additional evidence of density dependence. High flows during the year were negatively correlated with both spring and fall YOY density and mean standard length.  This population appears to be strongly regulated by density-dependent processes, but flows also have a significant impact on YOY dynamics.