A Statewide Evaluation of Florida Bass Genetic Introgression in Tennessee

Abstract

Abstract The Largemouth Bass (LMB) Micropterus salmoides is one of the most popular freshwater sport fish in the United States, and managers in southeastern states have stocked its subspecies, the Florida Bass (FLB) M. salmoides floridanus, outside of the subspecies’ natural range to increase the size structure of existing LMB populations. In Tennessee, fisheries for LMB are concentrated in reservoirs of the Cumberland and Tennessee River systems; however, FLB stockings have to date been restricted to two reservoirs of the Tennessee River and have varied significantly in extent and duration. We quantified levels of genetic admixture between FLB and LMB by using 38 species-diagnostic single-nucleotide polymorphisms for 979 fish sampled from 14 reservoirs within the Cumberland and Tennessee River systems. We tested for differences in genetic admixture across river systems and evaluated the relative importance of fish stockings in explaining observed levels of genetic admixture. Levels of admixture and associated variation were higher in Tennessee River reservoirs (average percentage of FLB alleles: range = 6.3–30.4%) than in Cumberland River reservoirs (range = 5.7–13.4%), but admixture was not solely related to stocking rates. The highest levels of FLB introgression were detected in Chickamauga Reservoir, the most extensively stocked reservoir in the state. Linear models identified fish stocked as a significant overall predictor of admixture, but we also observed stocked and unstocked reservoirs with similar levels of admixture, suggesting that factors other than stocking influence population genetics. Our statewide assessment of reservoir-level patterns of hybridization among black bass was performed prior to the recent expansion of FLB stocking efforts in Tennessee and thus represents a baseline for evaluation of future stocking.