Effects of local-scale removals on feral swine populations in southern Texas

Feral swine (Sus scrofa) are one of the most threatening mammalian pest species in North America owing to the damage they cause to natural habitats and agroecosystems, and the risk of disease transmission they pose to wildlife, livestock, and humans. The long-term (> 1 year) effects of lethal control efforts on feral swine populations at local scales are largely unknown. Using a panel of molecular markers, we assessed the effects of lethal control efforts on selected populations of feral swine in southern Texas. We collected tissue samples from two sites during removal campaigns, extracted and amplified DNA, and assessed population structure, genetic clustering, and immigration. We removed 145 individuals (9.7 swine per km²) at one site and 204 individuals (6.6 swine per km²) at another site. Fixation indices, Bayesian clustering, and assignment tests based on allele frequencies all produced similar results, indicating little or no differentiation among removals at either site. Localized feral swine removals aimed at reducing damage had no long-term impact on population parameters. Removals occurred at sites in which the swine groups were contiguous with neighboring feral swine family units and groups. This may have resulted in immigration of adjacent, but not genetically distinct, feral swine onto sites following the initial removals. To achieve long-term reduction of damage by feral swine populations, additional information is needed to enable genetic populations and corresponding management units to be defined.