A survey of the population characteristics of smallmouth bass (Micropterus dolomieu), rock bass (Ambloplites rupestris), and habitat conditions were conducted in the Powell River, Virginia, to identify potential habitat limitations for these species. The study area consisted of three reaches, which were determined in 1987. The upstream reach was used to monitor effects of coal mining in the upper watershed on the Powell River. The midstream reach, which was below the North Fork Powell River, was used to monitor the possible effects of this tributary and its watershed. The downstream reach appeared to have been impacted by sedimentation less than either of the other reaches.

Habitat Suitability Index (HSI) models were used to identify habitat variables that were below optimum for these species in the Powell River, Virginia. Habitat sampling yielded HSI scores for smallmouth bass at each site ranging from 0.67 to 0.76, with a mean of 0.72; scores for rock bass ranged from 0.65 to 0.70, with a mean of 0.69. No trends in HSIs from upstream to downstream were evident. However, substratum, of which sand was dominant in pools, was the variable most frequently below optimum for smallmouth bass (Sl=0.21) and rock bass (SI=0.20). Values for sediment depth, embeddedness, waterborne sediment, and coal were collected in riffles, runs, and pools at 10 sites. Mean sediment depth in pools, embeddedness in riffles and runs, and waterborne sediment deposited in traps monthly in pools decreased from upstream to downstream; however, waterborne sediment in runs did not decrease. Content (by weight) of coal wastes in the substratum did not decrease from upstream to downstream. The embeddedness index in pools (= 1.0), riffles, and runs was not significantly different among the three river reaches.

No differences in population abundance, biomass estimates, age and growth, or relative weights (Wr) of smallmouth bass and rock bass were found among the three river reaches. Population estimates of smallmouth bass (34.3/ha) and rock bass (116.6/ha) were lower than those in many other streams in the U.S. Catch-per-unit-effort and biomass of smallmouth bass (2.9/h, 2.6 kg/ha) and rock bass (6.6/h, 2.2 kg/ha) also were lower than those in most other streams. A total of 70 stomachs of smallmouth bass and 166 stomachs of rock bass was examined from fish collected between July 1988 and October 1989. Diets for each species, primarily crayfish and insects, showed no apparent differences among the three river reaches. Abundance of crayfish and hellgrammites were compared; greatest hellgrammite abundance was in the downstream reach (P = 0.032), and there were no significant differences in crayfish abundance among the three river reaches.

HSI values showed no significant correlation with catch-per-unit-effort for smallmouth bass or rock bass. No significant correlation was found among sediment depth, catch-per-unit effort, biomass or relative weight of smallmouth bass and rock bass. No correlation was found between the embeddedness index in riffles and biomass of rock bass. There was a significant negative correlation between the embeddedness index in riffles and relative weight of smallmouth bass (P=0.016); however, no correlation existed between the embeddedness index and relative weight of rock bass. There was a significant negative correlation between the embeddedness index in riffles and growth of smallmouth bass (P=0.016); however, there was a significant positive correlation between the embeddedness index and growth of rock bass. There was a significant positive correlation between the embeddedness index in riffles and both hellgrammite abundance (P=0.031) and crayfish abundance (P=0.052) in riffles. No significant correlation was found between the amount of sediment deposited in pools and catch-per-unit-effort of smallmouth bass and rock bass. No significant correlation existed between the amount of sediment deposited in runs and biomass of rock bass. In addition, crayfish density was not correlated with relative weight of smallmouth bass or rock bass. With the available documentation that links population characteristics of smallmouth bass and rock bass to habitat, it is evident that habitat is usually the limiting factor in determining population characteristics; however, there was no significant trend in the correlations presented above.

Habitat for smallmouth bass and rock bass in the Powell River, Virginia was suboptimum and sand was the dominant substratum in pools. Population estimates, catch-per-unit-effort, and biomass of smallmouth bass and rock bass in the Powell River are low compared to other U.S. streams. Although it appears that sedimentation has degraded habitat of smallmouth bass and rock bass and contributed to reduced population levels of these species in the Powell River, Virginia, my results were not statistically different among sites with measurable differences in sedimentation.