Shifting to sounders: Whole sounder removal eliminates wild pigs

Abstract

Wild pig (Sus scrofa) eradication in demographically open populations has seemed an impossible feat for managers, but more recently, whole sounder removal (WSR) has been proposed as a trapping strategy that has the potential to be successful in eradicating wild pigs from an area. However, little empirical data exist concerning implementation of whole sounder removal strategies. Our objective was to implement and describe wild pig management using WSR. We established a 27‐km2 area (northwest section) where sounders were removed using WSR and a 29‐km2 area (southeast section) where GPS collars were deployed on Lowndes Wildlife Management Area in Alabama. Prior to implementing WSR, we used game cameras over bait at a density of one camera/km2 in November 2014 and counted 65 and 100 individuals in our northwest and southeast sections, respectively. We began WSR July 2015 and by May 2016, we reduced the estimated population by 90%. However, due to births and seasonal movements of pigs in the periphery of the study area, the population fluctuated between 10–20 individuals from May 2016 to December 2017. In December 2017, we removed the last known remaining sounder, and using game cameras, observed no sounders in the northwest section for the following 7 months, the remaining length of the study. We determined that using the WSR approach can lead to a delay before inevitable recolonization. Therefore, WSR can be a successful tool to significantly reduce a wild pig population and potentially provide managers a pig‐free area.

Assessing whole‐sounder removal versus traditional control for reducing invasive wild pig (Sus scrofa) populations

“…Despite its relative success, WSR did not achieve the level of reduction we hoped for or expected. Other recent research evaluating WSR has reported > 85% reduction after 1 year in Oklahoma, USA, 18 and complete eradication of a semi-open population within 2.5 years in Alabama, USA, 19 albeit number of wild pigs removed in these studies were somewhat smaller than in ours, suggesting that initial population sizes may have been smaller or immigration in our areas was greater. However, lacking physical barriers such as fencing to limit immigration and movement, 33 eradication using WSR may not be an achievable goal when populations exist over large, non-insular areas such as SRS, and instead maintaining low densities to minimize damage 34 can be a valid and achievable goal, as our results demonstrate.…”

“…Additional research is needed to determine the duration of the reduced-density condition in locally reduced areas to inform how often such areas must be revisited for maintenance or follow-up control. 19 Although WSR was more effective than TC at reducing wild pig density, it required considerably greater effort, as well as the added investment in more expensive traps. Personnel spent more than twice the number of hours on WSR areas than on TC areas during the first year of trapping, resulting in a number of removals per person-hour much lower on WSR than TC areas and suggesting greater efficiency of TC, although Gaskamp et al 18 reported greater removals per person-hour using WSR than traditional corral traps.…”

“…Choice of M is largely arbitrary, but M must be large enough such that it does not truncate the posterior distribution of N, thus minimizing risk of underestimating the true value of N. However, setting M too large adds unnecessary computational costs. 19,21 Accordingly, we specified M to three times the number of uniquely marked pigs identified from camera survey images from each trap treatment replicate during 2017, 2018, and 2019 to balance risk of underestimating N and computational time. We defined the state-space as the area of remote camera grids plus a 1-km buffer.…”

“…We ran three chains for 500 000 iterations with a burn-in of 100 000 for all units across trap treatments and years in the R statistical environment 23 using the 'scrPID' MCMC algorithm from the contributed package 'scrbook'. 24 US Forest Service staff operated traps on WSR units generally following the procedures described by Lewis et al 19 : bait sites with shelled corn were spread evenly across the area in locations where wild pig activity was present and after a 7-14-day period during which the size and composition of target sounders were identified, those sounders were removed using traps constructed on a single day and equipped with cellular-enabled cameras (JagerPro M.I.N.E. traps, Fortson, GA, USA; BoarBuster traps, W-W Livestock Systems, Thomas, OK, USA).…”

“…In Oklahoma, USA using suspended traps that captured whole sounders reduced the estimated wild pig populations on three tracts ranging in size from 10 to 20 km 2 by 80.7-95.1%, 18 and in Alabama, USA, WSR resulted in complete eradication of the population on a 27 km 2 tract. 19 Our objective was to experimentally assess the relative efficacy of WSR and a traditional control (TC) strategy (primarily involving traditional-style traps but also including hunting with dogs and opportunistic shooting) in reducing wild pig density on each of ten management units ≥ 20 km 2 in size, each randomly assigned to either WSR or TC treatments. We also compare effort between WSR and TC treatments in terms of person-hours per wild pig removed, miles driven per wild pig removed, and trap-nights per wild pig removed to aid in estimation of implementation costs.…”