Abiotic and Biotic Factors Associated with Sculpin Presence and Density in Northern Idaho Streams

Abstract Sculpins (family Cottidae) are a group of small nongame fishes, native to Idaho's colder streams, and have value for biodiversity and as indicators of water quality. We analyzed abiotic and biotic data, including habitat characteristics and presence of co-occurring trout and char (family Salmonidae) species, from 115 streams from the northern Idaho Panhandle to identify the physical characteristics and biotic communities of the streams associated with sculpin presence (or absence) and population density. For comparison, and to determine if the results of the northern dataset could be attributed to the rest of the state, a second dataset from state-wide sampling was also analyzed, as was a subset of both datasets that had no observations of non-native brook trout and rainbow trout. Sculpins were more likely to be present and in higher densities in streams with abundant riffle microhabitats that were mostly free of sediment (identified as Rosgen channel types B, C, and F for northern Idaho and types B and C for the entire state). More sculpins were also found in streams lacking brook trout and rainbow trout. Knowledge of sculpin habitats and the impacts of non-native salmonids may be useful in interpreting water quality evaluations, as well as in improving native fisheries restoration projects and fisheries management for Idaho streams.