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, josh.helcel@tamu.edu
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