Movement and Habitat Differentiation among Adult Shoal Bass, Largemouth Bass, and Spotted Bass in the Upper Flint River, Georgia

The Shoal Bass Micropterus cataractae is a fluvial specialist endemic to the Apalachicola River drainage in Alabama, Florida, and Georgia that has experienced declines throughout much of its range. The Flint River, Georgia, represents the largest remaining intact ecosystem for Shoal Bass in their native range. Spotted Bass M. punctulatus have recently been introduced into this system, causing concern about the potential negative impacts the species may have on the native populations of Shoal Bass and Largemouth Bass M. salmoides. To assess the symmetry and strength of competition and gain the greatest perspective on the interrelationships among these sympatric, congeneric species, we compared the movement patterns and habitat use of all three species of black bass present in this system. Fifteen Shoal Bass, 10 Largemouth Bass, and 6 Spotted Bass were implanted with radio transmitters in the Flint River and tracked for a period of 1 year (2008). Daily and hourly movements did not vary among species or season, though individuals of each species were observed moving >5km to shoal complexes during spring. Habitat overlap varied between species during the study; overlap was highest between Spotted Bass and Largemouth Bass, intermediate between Spotted Bass and Shoal Bass, and lowest between Shoal Bass and Largemouth Bass. Shoal Bass tended to select coarse rocky habitat, while Largemouth Bass tended to select depositional habitat. Spotted Bass exhibited the widest niche breadth and generally used habitat in proportion to its availability. Use of similar habitats by these three species during the spring spawning period highlights the potential risk of genetic introgression of the two native species by introduced Spotted Bass. Physical barriers that restrict access to habitat during long-distance seasonal movements, as observed for several Shoal Bass in this study, may negatively impact populations of this species. Received March 31, 2012; accepted October 12, 2012