Utilization of half-log structures as spawning sites for smallmouth bass in Norris Reservoir, Tennessee

SCUBA observations were used to evaluate the utilization of half-logs by naturally spawning smallmouth bass (Micropterus dolomieu). Of the 736 half-logs which were installed in Norris Reservoir in 1993, 22% of the total (161) logs were evaluated weekly at three different sites from 2 April 1996 and continuing through 25 June 1996. There were 88 line-transects, each 12.2 m in length, used as controls and positioned in non-structure areas; the transects were located at the same water depths as the half-log structures.

Species found utilizing the half-logs for spawning were smallmouth bass, bluegill (Lepomis macrochirus), black crappie (Pomoxis nigromaculatus), spotted bass (M. punctulatus), and largemouth bass (M. salmoides). Other fish species utilizing the half-logs for cover were flathead catfish (Pylodictis olivaris) and common carp (Cyprinus carpio). Treatment areas produced an average of 1.9 nests per log whereas the controls produced 0.8 nests/transect, indicating a strong preference for overhead cover for spawning. No smallmouth bass were observed nesting around any of the control transects. In the treatment areas all the nests with eggs (61) had a successful hatch. The mean depth at which smallmouth bass nests containing eggs were found was 3.1 m. Half-logs installed on points had a higher percentage utilization (45%) for spawning by smallmouth bass than those located in coves (10%).