A statewide evaluation of Florida Bass genetic introgression in Tennessee

Largemouth Bass (Micropterus salmoides) are one of the most popular freshwater sport fish in the United States and managers in southeastern states have stocked the Florida Bass (M. s. floridanus) subspecies outside of its natural range to increase size structure of existing Largemouth Bass populations. In Tennessee, fisheries for Largemouth Bass are concentrated in reservoirs of the Cumberland and Tennessee River systems; however, Florida Bass 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 Florida Bass and Largemouth Bass using 38 species-diagnostic single nucleotide polymorphisms for 979 fish sampled from 14 reservoirs from 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 genetic admixture and associated variation was higher in reservoirs of the Tennessee River (range = 6.3 – 30.4 average percent Florida Bass alleles) relative to the Cumberland River (range = 5.7 – 13.4 %), but admixture was not solely related to stocking rates. The highest levels of Florida Bass 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 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 Florida Bass stocking efforts in Tennessee, and thus, represents a baseline for evaluating future stocking.