A Statewide Evaluation of Florida Bass Genetic Introgression in Tennessee

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.

Quantifying contributions to tournament catches among resident, stocked and hybrid black basses (Micropterus spp.)

“…Relating angler catch data to genealogical class (hybrid status) in populations of largemouth bass stocked with Florida bass has lagged behind stocking investments despite millions of Florida bass being stocked in the USA annually (Hargrove, Roger, et al, ). A focus of many Florida bass stocking programmes has been to increase levels of genetic introgression between largemouth bass and Florida bass (e.g.…”

“…Largemouth bass were sampled from Chickamauga Reservoir, a 14,665‐ha impoundment of the upper Tennessee River in southeastern Tennessee, United States. Chickamauga Reservoir was selected as it has been extensively stocked with Florida bass (~2,500,000 over 14 years; Hargrove, Roger, et al, ) and supports a popular recreational fishery for largemouth bass (Maceina & Bettoli, ). Genetic fin clips were collected from largemouth bass via both electrofishing and tournament sampling techniques.…”

“…A genealogical assignment was retained if an individual based on a posterior probability cut‐off of ≥70%, which has been previously identified as a threshold that minimises incorrect assignments (Marie, Bernatchez, & Garant, ). Hargrove, Roger, et al () used hybridlab v 1.0 (Nielsen, Bach, & Kotlicki, ) to generate genotypes for the six genealogical classes described above using the same suite of SNP markers and identified high levels of confidence in the ability for newhybrids to assign an individual to the correct hybrid class (posterior probability of correct assignment ≥0.987).…”

“…Florida bass, Micropterus floridanus Lesueur, has been widely stocked into extant populations of largemouth bass, Micropterus salmoides Lacepède, as a management tool to increase size structure due to the greater trophy fishery potential of Florida bass and resultant hybrids (Forshage & Fries, ; Gilliland & Whitaker, ). Record‐sized catches by anglers following stockings of Florida bass have been documented in six U.S. states and one country outside North America (Arkansas, Lamothe & Johnson, ; California, Chew, ; Louisiana, Hughes & Wood, ; Oklahoma, Horton & Gilliland, ; Texas, Forshage & Fries, ; Tennessee, Hargrove, Roger, Kacmar, & Black, ; South Africa, Weyl, Schirrmann, Hargrove, Bodill, & Swartz, ). Given the potential trophy fisheries resulting from Florida bass introductions, state agencies throughout the Southeast United States (Siepker & Casto‐Yerty, ) have initiated large‐scale stocking programmes placing millions of Florida bass fry into public waters on an annual basis (e.g.…”

“…An assessment of the extent to which F 2 and backcross hybrids contribute to recreational catch is highly relevant given that Florida bass stocking programmes commonly occur over the course of decades (e.g. Forshage & Fries, ; Hargrove, Roger, et al, ), and the abundance of hybrids increases through time in populations of largemouth bass into which Florida bass are stocked (Philipp, ).…”