The Influence of Logjams on Largemouth Bass (Micropterus Salmoides) Concentrations on the Lower Roanoke River, a Large Sand-Bed River



This study examines the relation between logjams and largemouth bass (Micropterus salmoides) on the alluvial sand-bed lower Roanoke River. Disparate data sets from previous bank erosion, fisheries, and large wood studies were used to compare the distribution of largemouth bass with logjam frequency. Logjams are related to the frequency of bank mass wasting increasing from near an upstream dam to the middle reach of the study segment and then decreasing as the river approaches sea level. The highest concentration of largemouth bass and logjams was in the middle reach (110 fish per hour and 21 jams per km). Another measure of largemouth bass distribution, fish biomass density (g h−1), had a similar trend with logjams and was a better predictor of fish distribution versus logjams (R2 = 0.6 and 0.8 and p = 0.08 and 0.02 for fish per hour and g h−1 versus logjam, respectively). We theorize that the preference for adult bass to congregate near logjams indicates the use of the jams as feeding areas. The results of a principal component analysis indicate that fish biomass concentration is much more related to logjam frequency than channel geometry (width, depth, and bank height), bed grain size, bank erosion, or turbidity. The results of this research support recent studies on in-channel wood and fisheries: Logjams appear to be important for maintaining, or increasing, both largemouth bass numbers and total biomass of fish in large eastern North American rivers. Persistent logjams, important as habitat, exist where relatively undisturbed river reaches allow for bank erosion inputs of wood and available anchoring locations. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.