Dakin, E.E., B.A. Porter, B.J. Freeman, and J.M. Long. 2015. Hybridization threatens Shoal Bass populations in the upper Chattahoochee River basin. Pages 491-502 in Tringali, M.D., J.M. Long, T.W. Birdsong, and M.S. Allen, editors. Black bass diversity: multidisciplinary science for conservation. American Fisheries Society, Symposium 82, Bethesda, Maryland.
Shoal bass (Micropterus cataractae) are native only to the Apalachicola-Chattahoochee-Flint river system of Georgia, Alabama, and Florida, and are vulnerable to extinction as a result of population fragmentation and introduction of non-native species. We assessed the genetic integrity of isolated populations of shoal bass in the upper Chattahoochee River basin (above Lake Lanier, Big Creek, and below Morgan Falls Dam) and sought to identify rates of hybridization with non-native, illegally stocked smallmouth bass (M. dolomieu) and spotted bass (M. punctulatus). Using ten highly polymorphic microsatellite markers and the population assignment software STRUCTURE, shoal bass below Morgan Falls dam showed evidence for high levels of hybridization with smallmouth bass and possibly spotted bass, while a population of shoal bass in Big Creek showed evidence for the presence of smallmouth bass individuals and lower levels of hybridization between shoal bass and smallmouth bass. The only shoal bass population not impacted by congeneric hybridization was found upstream of Lake Lanier, in the headwaters of the Chattahoochee River. Conservation actions, such as a program to reduce or eliminate non-native black bass species and their hybrids, could help maintain the genetic uniqueness of these shoal bass populations in the upper Chattahoochee River basin and lessen their susceptibility to local extinction.