Natural Barrier Assessment and Modeling for Fish Communities in Delaware Water Gap National Recreation Area

Natural barriers may play an important role in structure and composition of stream fish habitat. Determining the effects of natural barriers on fish communities is important for understanding ecological processes that may occur throughout barrier-affected habitats. Additionally, modeling the likelihood of natural barrier occurrence using spatial data can reduce survey effort in the field and make management of fisheries in barrier-affected systems more efficient. I surveyed 446 natural barriers within the Delaware Water Gap National Recreation Area using a standardized field protocol to assess passability for fishes. I measured natural barriers individually based upon individual morphology and developed a scoring system to determine difficulty for fish passage. Fish communities were then sampled at 65 paired sites for richness and density upstream and downstream of natural barriers. The results were analyzed using pair-wise comparisons for upstream and downstream sites and showed significant species richness differences between sites separated by barriers while both brook and brown trout densities showed little to no differences among sites with and without barriers present. I modeled barrier occurrence across the study area using spatial data variables and developed rules criteria for prediction of natural barrier occurrence hot spots. Slope, flow accumulation number (watershed area) and soil type were found to be important for predicting natural barrier occurrence within our study area. Higher slopes increased the likelihood of natural barrier occurrence while lower drainage area had a similar effect. Soil types with highly erodible, rocky compositions associated with steep slopes also increased the odds of natural barrier incidence.