Hybridization and Replacement of Roanoke Bass (Ambloplites cavifrons) with Invasive Rock Bass (A. rupestris) in Virginia: How Big is the Problem?

The Roanoke bass (Ambloplites cavifrons) is a sport fish endemic to the Roanoke, Chowan, Tar, and Neuse drainages in Virginia and North Carolina. Virginia populations of this species are threatened by competition and hybridization with rock bass (A. rupestris), an invasive congener introduced from the Gulf slope throughout the early 20th century. Displacement and hybridization were reported as early as the 1950’s, but the current status of this invasion and its impacts on A. cavifrons populations are unknown. Eleven nuclear DNA microsatellite markers were developed to discriminate between A. cavifrons, A. rupestris, and their hybrids, and in doing so to assess the current distribution of A. cavifrons in Virginia. The panel of markers provided a high degree of resolution among these groups, further allowing us to separate F1 hybrids from backcrossed individuals. Our results suggest a complex mosaic of invasion, displacement, and introgression patterns across the range of A. cavifrons in Virginia. A. cavifrons persists in only 4 of the 8 watersheds we examined, but has been mostly to completely replaced by A. rupestris in 3 others. In the Pigg watershed, an ongoing invasion is apparent: A. rupestris and hybrids were distributed throughout this system. Most extant A. cavifrons populations are geographically small, and all are vulnerable to invasion. This highlights the importance of educational campaigns that discourage anglers from transplanting “redeyes” to new waterways and potentially the need to establish new refuge populations of A. cavifrons.