Resource Use by Two Sympatric Black Basses in Impounded and Riverine Sections of the New River, Virginia

Abstract

Smallmouth bass Micropterus dolomieu and spotted bass M. punctulatus are sympatric in riverine and impounded sections of the New River, Virginia. Resource use (habitat and food) by the two species was investigated to determine patterns and extent of resource partitioning and how those patterns might differ between lotic and lentic environments. Growth and body condition were also measured to assess performance of populations of the two species in the study areas. Diet analyses showed that similar prey were consumed by the two species. Habitat use differed along a lotic–lentic gradient; spotted bass were predominant in the impoundment, and smallmouth bass were more abundant in the river. Spatial segregation also occurred within river and impoundment habitats. In the impoundment, smallmouth bass were concentrated in areas with steep dropoffs and rocky substrates, and in the river, they used shoreline areas more than midriver areas. Spotted bass were widely distributed in the impoundment but were most common in areas featuring fine substrate that had woody debris and bank vegetation as cover types. In the river, spotted bass were largely restricted to the banks, to areas away from high current velocities, and to areas with fine substrate, woody debris, and overhanging bank vegetation. We observed higher catch rates for spotted bass in the river section downstream from the impoundment than in the section upstream of the lake, whereas the converse was true for smallmouth bass. Measures of physiological well-being for both species were near regional norms in both river and impoundment. Normal condition in populations of the two fishes, combined with the similarity in diets, indicated that food availability was adequate in the study area and that competitive pressures were not intense during the study period. Ecological segregation of the species appeared to be along the spatial rather than the trophic axis.