Resource Use by Stream-Dwelling Rock Bass and Smallmouth Bass

Abstract

We examined food and habitat use of sympatric smallmouth bass Micropterus dolomieui and rock bass Ambloplites rupestris in the Current and Jacks Fork rivers, Missouri. Use of food resources was similar between species and within a species. On a total caloric basis, the importance of prey ranked crayfish > fish > insects. The similarities of both prey types and the size selection of prey indicated that food resources were not a mechanism of ecological segregation between rock and smallmouth bass. Habitat use was evaluated by underwater observation. Location of both species was highly correlated with some aspect of cover, especially woody structure. Although cover use overlapped among size classes and species, rock bass were more often associated with rootwads and smallmouth bass with log complexes (aggregates of logs and branches). Cover use was independent of rock bass size, but smallmouth bass shorter than 350 mm long more often used vegetation and boulders and were more often found in open water than were smallmouth bass larger than 350 mm. Smallmouth bass used woody structure associated with higher current velocities more often than did rock bass. A positive relation between water depth and fish size was evident for each species, but water depth appeared unimportant in interspecific segregation. Received January 21, 1983 Accepted March 22, 1984