A Predictive Model for Brook Trout Restoration in the Cherokee National Forest

Over the course of the last century, Brook Trout (Salvelinus fontinalis) have been reduced in abundance and extirpated from many high elevation streams throughout the southern Appalachian Mountains. These fish have been threatened by anthropogenic factors that restrict their distribution across the longitudinal gradient of the streams they occupy. A large portion of Tennessee's Brook Trout streams are located within the Cherokee National Forest (CNF). Many agencies in the southern Appalachian Mountains are working to restore Brook Trout populations throughout this species’ historic native range. The purpose of this research is to develop a model of important habitat variables used to characterize the suitability of a stream for Brook Trout restoration based on its predicted biomass in the CNF. Thirty streams across the CNF known to support Brook Trout were evaluated by completing a three-pass depletion fish survey, quantifying instream habitat characteristics, and examining riparian forest structure. Habitat characteristics were modeled against Brook Trout biomass (kg/ha) to determine significant variables that characterize Brook Trout abundance. Ten additional streams on the CNF were sampled to validate the accuracy and precision of the models. A Random Forest model determined the significant habitat variables (n=11), then a multi-nomial logistic regression model predicted Brook Trout biomass based on these variables. For optimal biomass, values of the important variables should be: percent riffle area <25%, >350 m to the nearest road, >13% slope, elevation ≥1,000 m, >55% boulder substrate, Rhododendron cover <10% or 25-40%, canopy cover 92-97% or ≥98%, dominant geologic rock type of gneiss, granite, or sandstone, <25% cobble substrate, total volume of 1 to 7.5 m³, and total dissolved solids >12 ppm. This model provides a technique for rapid habitat assessment to aid in the decision-making process of Brook Trout restoration site selection. Based on these selected variables, efforts to improve Brook Trout habitat should focus on four primary areas: reduction of riffle habitat (i.e., creating more pools), maintaining canopy closure, reducing Rhododendron cover, and preventing sediment run-off from nearby roads.