Spatial and Temporal Variation in Electrofishing Catch Rates of Three Species of Black Bass (Micropterus spp.) from Normandy Reservoir, Tennessee

Abstract

Largemouth bass Micropterus salmoides, smallmouth bass M. dolomieu, and spotted bass M. punctulatus were sampled by electrofishing in the spring and fall for 6 years in Normandy Reservoir, Tennessee, to assess spatial and seasonal differences in abundance. Bass were collected each season from 40 transects stratified among the following habitats: riprap, rubble, gravel, mixed substrate, and coves. A randomized-block design analysis of variance (ANOVA) was used to partition variation by habitat and year. Abundance was greatest in riprap habitats for largemouth bass and smallmouth bass in spring samples. Abundance was greatest in rubble habitats for spotted bass in spring samples, but in only 2 of 6 years. Abundance of largemouth bass and spotted bass was lowest in gravel habitats and cove habitats, respectively; smallmouth bass abundance was uniform and consistently low in all nonriprap habitats. Abundance trends among habitats in fall samples were similar to spring samples for all three species. Gravel habitats supported the smallest and youngest individuals for all species in both seasons. Catch rates of largemouth bass and spotted bass were lower in fall than spring, whereas catch rates of smallmouth bass were higher in fall than spring. Mean total lengths were smaller in fall samples for all three species. Stratifying samples across habitats identified specific habitats that contributed high variability to overall estimates of density; by allocating more samples to those habitats, variance can be reduced. Managers designing electrofishing surveys to obtain a random sample of black bass should be aware that catch rates from electrofishing surveys vary due to different habitat uses by different sizes and species of black bass.