Habitat and Diet Partitioning between Shoal Bass and Largemouth Bass in the Chipola River, Florida

Abstract

We investigated the macrohabitat use, microhabitat use, and food habits of shoal bass Micropterus cataractae and largemouth bass M. salmoides in the upper Chipola River, Florida. We electrofished two macrohabitats (pools and shoals) during the summer (May–August) and fall (September–December) of 1999 and 2000. The ratio of shoal bass to largemouth bass differed among macrohabitats, being highest in the shoals and lowest in the pools. Age-0 and adult (age-1 and older) shoal bass were collected in areas of higher-than-average percentages of rocky substrate in both shoals and pools. Age-0 and adult largemouth bass were associated with areas of reduced current velocity and those with higher-than-average amounts of woody debris. Though the diets of age-0 and adult shoal bass and largemouth bass were similar, a few differences were apparent. Age-0 largemouth bass diets contained grass shrimp Palaemonetes spp., whereas age-0 shoal bass diets contained mostly mayflies (order Ephemeroptera: families Baetidae and Isonychidae). Crayfish and fish were the primary food resources of adult shoal bass and adult largemouth bass, and crayfish became more prevalent than fish in larger individuals of both species. Largemouth bass transitioned to a crayfish-dominated diet at a smaller size than did shoal bass. Considering that we found substantial differences in the habitat associations of these species but relatively few diet differences, habitat partitioning may be important for the coexistence of shoal bass and largemouth bass in rivers and streams. Future shoal bass conservation efforts should focus on maintaining a diversity of habitats where these species coexist and on protecting relatively rare shoals.