To enhance trophy potential of largemouth bass (Micropterus salmoides) fisheries, state agencies across the southeastern United States commonly stock Florida largemouth bass (FLMB, M. s. floridanus) outside of their native range into native northern largemouth bass (NLMB, M. s. sal- moides) populations. This practice has been ongoing for decades but spatial patterns associated with the spread of FLMB alleles in a reservoir after stocking are not well understood. From 2007–2015 the Arkansas Game and Fish Commission stocked 250 FLMB fingerlings ha–1 into two embayments of Lake Ouachita, a 16,200-ha highland reservoir in western Arkansas. In 2019, we collected 1000 largemouth bass from throughout the reservoir to examine spatial patterns of FLMB introgression using a panel of 35 species-diagnostic single-nucleotide polymorphisms (SNPs). We determined that 30.4% of individuals were NLMB and 69.6% were hybrids of NLMB and FLMB, with no FLMB collected. Average % FLMB alleles across all individuals collected was 11.4%. Spatial analyses found that FLMB alleles were greater in individuals collected in close proximity to stocking areas and then east- ward through the main body of the reservoir. Conversely, FLMB alleles were lower in the western half of the reservoir. Our results provide evidence that localized stocking of FLMB at high densities into a resident NLMB population can lead to widespread genetic shifts even in very large systems, but that most individuals in those systems contain low levels of FLMB alleles.
