By: Forrest Cobb, Research Assistant
Texas A&M Natural Resources Institute
Three years ago some of my colleagues and I spent every week checking and rechecking an electric fence we hoped would keep wild pigs out. We were conducting a horticultural study with 1,600 fresh and tender ornamental plants grown over the course of a year. Unfortunately for us, our small plot was not far from a creek that supported a seemingly endless population of wild pigs. Every week we would see damaged brush, dead plants, and clumps of bare loose soil just outside the fence line. Thankfully they never got inside, but while we had the luxury of fencing off and maintaining that relatively small enclosure, that same level of exclusion would not have been feasible for a larger tract of land and certainly is not for stream and rivers courses and their associated wetlands. Impacts on agriculture, plant diversity, and wildlife habitat can be easily observed in areas disturbed by the rooting behavior of wild pigs. One of their less obvious impacts, and the focus of our newest publication, is their impact on water quality in Texas. But before we discuss some of these impacts, let's consider just how serious of an issue wild pigs have become.
Wild pigs now occur in at least 36 states and the economic toll of these animals in the US was estimated to exceed $1.5 billion in 2007, a number likely to be much larger today. Population modeling indicates that as many as 3-5 million wild pigs now inhabit Texas and they are present in almost every county in the state (Figure 1). The number and range of these animals is not surprising considering their incredible adaptability and fecundity. With an average lifespan of 4-5 years, adult sows commonly produce litters of 4-6 offspring and can have 1-3 liters per year. Their population growth is relatively unchecked by predators. Coyotes, bobcats, and feral dogs have been known to prey upon juveniles but humans remain the only significant predators of adult wild pigs. Population modeling has indicated that as much as 66% of the wild pig population would need to be harvested every year for 5 years or more to halt population growth. With humans only harvesting an estimated 29% of the population per year, we will see continued growth and spread of wild pigs. Omnivorous and intelligent, wild pigs are well adapted to conditions across the state and their foraging, opportunistic predation, rooting, and wallowing behaviors are incredibly disruptive, having serious repercussions for the ecological and economic health of our state.
Figure 1. NMFSS data showing 2016 feral swine populations by county. (Image Credit – USDA-APHIS)
A worrisome aspect of wild pigs in Texas is the impact on water quality they have by damaging riparian areas and wetlands. Since wild pigs lack sweat glands, they often stay close to water bodies in order to cool themselves by wallowing in wet, shaded areas. This concentrates wild pig populations in sensitive riparian areas, which are both crucial transitional zones between upland areas and water bodies, and a vital component of maintaining overall water quality. Healthy riparian and wetland communities perform numerous critical functions which maintain water quality including, stabilizing soils, decreasing water velocities during flooding, providing fish and wildlife habitat, mitigating contamination from surrounding storm water runoff, and lowering water temperatures through shading. Because of their disruptive rooting and wallowing behavior, as well as heavy foraging of native mast (fruits and nuts), wild pigs can significantly decrease native vegetation cover in riparian corridors. By reducing native ground cover, native tree abundance, and native seedling establishment, they increase the presence and abundance of invasive plant species, and destabilize stream and river banks leading to increased sedimentation, nutrient loads, turbidity, and altered pH levels.
While they indirectly impact water quality through the destruction of riparian and wetland communities, wild pigs also directly impact water quality through defecation. One study of fecal coliforms in the Buck Creek watershed of Texas found that as much as 50% of E.coli bacteria samples collected were from wildlife sources including wild pigs, while only 20% originated from domestic animals or livestock. With a high defecation rate (1,121 grams per day) when compared to other wildlife species like white-tailed deer (500-772 grams per day), their contribution to bacterial loading and water quality is becoming a growing concern for land managers and regulatory authorities statewide. Especially since, as of 2012, the majority of Texas water bodies were listed as bacterially impaired. Bacterial impairment increases the potential for disease transmission in both wildlife and human populations. Recreational activities such as swimming, wading, and fishing are necessarily restricted as a result of these unsanitary conditions.
Wild pig activity in and near water sources can spread invasive plant species, destabilize soil, reduce native species abundance, alter nutrient and pH levels, increase turbidity, and contribute to increased E. coli bacteria levels in surface water systems.
Agriculture is also impacted when access to high quality water becomes limited. One study found that livestock with a quality water supply can produce as much as 20% more animal gain as compared to livestock with access to impaired water. Furthermore, the low dissolved oxygen and high nutrient levels associated with impairment can reduce aquatic species abundance and diversity, and lead to massive algal blooms and fish kills.
Wild pig populations contribute to impaired water quality in Texas, both directly through fecal deposition, and indirectly by altering wetland and riparian communities. While more research is needed to quantify their impact and contribution to water impairment, wild pig abatement has been shown to benefit riparian ecosystems and overall water quality by reducing bacterial impairment, reducing the spread of invasive species, increasing vegetation cover, facilitating proper nutrient cycling, decreasing erosion, and decreasing surface water turbidity. Given the wide spread and growing challenge posed by wild pigs in Texas, the potential benefits of management and control should be considered in any plan for improving or safeguarding water quality. Application of consistent and widespread abatement efforts remains the only way of stabilizing and thus reducing the impacts of wild pig populations on landscapes and water quality in Texas.
For more information on how wild pigs negatively impact water quality, please click the link below to download a free electronic copy of “Wild pigs negatively impact water quality: Implications for land and watershed management” from the AgriLife Bookstore.
Wild pig resources listed below are available at the AgriLife Bookstore
– L-5523 Recognizing Feral Hog Sign
– L-5524 Corral Traps for Capturing Feral Hogs
– L-5525 Box Traps for Capturing Feral Hogs
– L-5526 Placing and Baiting Feral Hog Traps
– L-5527 Door Modifications for Feral Hog Traps
– L-5528 Snaring Feral Hog
– L-5529 Making a Feral Hog Snare
– SP-419 Feral Hogs Impact Ground-nesting Birds
– SP-420 Feral Hog Laws and Regulations
– SP-421 Feral Hogs and Disease Concerns
– SP-422 Feral Hogs and Water Quality in Plum Creek
– SP-423 Feral Hog Transportation Regulations
– L-5533 Using Fences to Exclude Feral Hogs from Wildlife Feeding Stations
– WF-030 Reducing Non-target Species Interference While Trapping Wild Pigs
– WF-033 Wild Pigs and Ticks: Implications for Livestock Production, Human and Animal Health
– ENRI-005 Wild Pigs Negatively Impact Water Quality: Implications for Land and Watershed Management
Click here for additional resources on wild pigs
For educational programming or technical assistance with wild pigs please contact:
Josh Helcel, 512-554-3785, email@example.com
Baird, J.V. 1990. Soil facts: Nitrogen management and water quality. North Carolina Cooperative Extension AG-439-2.
Campbell, T.A. and D.B. Long. 2009. Feral swine damage and damage management in forested ecosystems. Forest Ecology and Management 257:2319-2326.
Chavarria, P.M., R.R. Lopez, G. Browser, and N.J. Silvy. 2007. A landscape-level survey of feral hog impacts to natural resources of the Big Thicket National Preserve. Human Wildlife Conflicts 1:199-204.
Cushman, J.H., T.A. Tierney, and J.M. Hinds. 2004. Variable effects of feral pig disturbances on native and exotic plants in a California grassland. Ecological Applications 14:1746–1756.
Doupe´ R.G., J. Mitchell, M.J. Knott, A.M. Davis, and A.J. Lymbery. 2009. Efficacy of exclusion fencing to protect ephemeral floodplain lagoon habitats from feral pigs (Sus scrofa). Wetlands Ecology and Management. DOI 10.1007/s11273-009-9149-3
Gingerich, J.L. 1994. Florida’s Fabulous Mammals. World Publications. Tampa Bay.
Giovanni, G. D., L. Gregory, P. Dyer, and K. Wagner. 2007. Bacterial Monitoring for the Buck Creek Watershed – Final Report. Texas AgriLife Research, Texas Water Resources Institute, and Texas AgriLife Extension Service. TSSWCB Project 03-07.
Jay, M.T., Cooley, M., Carychao, D., Wiscomb, G.W., Sweitzer, R.A., Crawford-Miksza, L., Farrar, J.A., Lau, D.K., O’Connell, J., Millington, A., Asmundson, R.V., Atwill, E.R., and Mandrell, R.E. 2007. Escherichia coli O157:H7 in feral swine near spinach fields and cattle, central California coast. Emerging Infectious Diseases 13:1908–1911.
Kotanen, P.M. 1995. Responses of vegetation to a changing regime of disturbance: Effects of feral pigs in a California coastal prairie. Ecography 18:190-199.
Mapston, M. E. 2007. Feral hogs in Texas. AgriLife Extension B-6149 03-07, Texas A&M University, College Station, USA.
Naiman, R.J., H. Decamps, and M.E. McClain. 2005. Riparian: ecology, conservation and management of streamside communities. Elsevier, San Diego, USA.
Ohio State University Extension. 2006. Ohio livestock manure management guide. Bulletin 604. The Ohio State University, Columbus, USA.
Parker, I.D. 2010. The role of free-ranging mammals in the deposition of Escherichia coli into a Texas floodplain. Doctoral Dissertation. Texas A&M University, College Station, TX.
Pimental, D. 2007. Environmental and economic costs of vertebrate species invasions into the United States. Managing Vertebrate Invasive Species. College of Agriculture and Life Sciences, Cornell University, Ithaca, New York, USA.
Siemann, E., J.A. Carrillo, C.A. Gabler, R. Zipp, and W.E. Rogers. 2009. Experimental test of the impacts of feral hogs on forest dynamics and processes in the southeastern US. Forest Ecology and Management 258:546-553.
Singer, F.J., W.T Swank, and E.E.C. Clebsch. 1984. Effects of wild pig rooting in a deciduous forest. Journal of Wildlife Management 48:464-473.
Taylor, R.B., E.C. Hellgren, T.M. Gabor, and L. Ilse. 1998. Reproduction of feral pigs in southern Texas. Journal of Mammalogy 79:1325–1331.
Texas Commission on Environmental Quality (TCEQ). 2013. 2012 Texas Integrated Report of Surface Water Quality for Clean Water Act Sections 305(b) and 303(d).
Timmons, J.B., J. Mellish, B. Higginbotham, J. Griffin, R. Lopez, A. Sumrall, K. Skow, and J.C. Cathey. 2012. Feral hog population growth, density and harvest in Texas. Texas A&M AgriLife Extension Service SP-472.
Williams, W.D., O. Kenzie, D. Quinton, and P. Wallis. 1996. The water source as a factor affecting livestock production. In: Animal Science research Development: Meeting Future challenges. Proceedings, Can. Soc. Anim. Sci., Lethbridge, AB. E
Posted 5th June 2018 by Wildlife and Fisheries Extension
Labels: aerial gunning bacterial source tracking Biology Distribution E. coli Feral Hogs Harvest Hunting Impaired watersPublication Riparian Sus scrofa Trapping water quality concerns Wetlands Wild Pigs