Black Bass Diversity: Multidisciplinary Science for Conservation

Reducing Hybridization and Introgression in Wild Populations of Guadalupe Bass through Supplemental Stocking

B. Paul Fleming, Gary P. Garrett, and Nathan G. Smith

doi: https://doi.org/10.47886/9781934874400.ch40

Abstract.—Interspecific hybridization among micropterids was once thought to be rare but has been documented in several cases of North American endemics. Introduction of the nonnative Smallmouth Bass Micropterus dolomieu across Texas has threatened to eliminate the Guadalupe Bass M. treculii genome throughout its native range via introgression between the species. In 1992, the Texas Parks and Wildlife Department began a stocking program in the Guadalupe River watershed to restore the genetic integrity of the local population. More than 600,000 hatchery-reared Guadalupe Bass fingerlings (~30 mm total length) were stocked in Johnson Creek over a 19-year period, and 360,000 fish were released in the North Fork, South Fork, and main-stem Guadalupe River over a 5-year period. Annual genetic monitoring indicated that hybridization significantly declined in all stream segments (P < 0.001) during the period of time when stocking occurred. Initially high hybridization rates (range, 20–100%; mean = 43.4%) were reduced to 0–24.2% (mean = 11.4%) at the termination of stocking. Linear regression indicated that hybridization in the North Fork and main-stem stream segments declined faster (9.0% per year) than all other test stream segments, whereas the South Fork Guadalupe River and upper Johnson Creek declined at 0.9% per year and lower Johnson Creek declined at 1.9% per year. Our data show that supplemental stocking is an effective approach to genetic restoration of compromised populations and should be considered as a viable management and conservation tool.