Watershed-scale impacts of human- and beaver-related land use activities on a cold-water fish assemblage

Abstract Understanding long-term effects from land use and land cover (LULC) on watersheds has been essential for the conservation and management of fishes. Watersheds are a mosaic of different LULC types that produce multiple and interactive effects on fishes. Using a combination of field and geoprocessing methods across spatiotemporal gradients, we investigated the effects of LULC on cold-water, stenothermic fishes in a relatively undisturbed yet dynamic watershed (Caldwell Creek, Pennsylvania, USA). Our goals were to (1) describe how watershed-scale LULC from human activities (agriculture and development) and beaver activity ( Castor canadensis ; wetlands) have changed over time and (2) use long-term field surveys of fish assemblages and water quality parameters to determine whether those LULC patterns were associated with subsequent changes in fish and water quality. Results show evidence that human LULC activities from development and deforestation have induced watershed-level shifts from cold-water to warm-water assemblages and that cold-water trout densities are highest in watersheds of higher contemporary agriculture. However, there was also evidence that juvenile and adult stenothermic trout responded differently to long-term LULC activities from beavers and humans. Whereas juvenile cold-water trout densities were negatively associated with developed LULC, adult cold-water trout were negatively associated with wetland activity. Taken together, these results reveal the complex historical and contemporary interactions between beavers, humans, and fishes. Our study emphasizes the need for considering multiple LULC drivers in the context of fish conservation, especially in the realm of watershed restoration.