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Do erosion control and snakes mesh?

In the battle to curb soil erosion and sedimentation, numerous techniques and products for controlling erosion and sedimentation have been developed and are being implemented. Rolled erosion control products, such as temporary erosion control blankets and permanent turf reinforcement mats, represent one type of erosion control product that has been used extensively. The rolled products use stitching and net-like mesh fabrics made of various materials (plastic, nylon, twine, etc.) to hold materials (straw, coconut husk, jute, wood, polypropylene, etc.), which serve as an organic matrix to retain soil moisture, promote seed germination, and disperse erosion causing energy from raindrop impact and water runoff. Even though the rolled products have proven their value in erosion prevention and control, potential problems associated with their use were discovered on a project implemented to restore Carolina bay depressional wetlands in South Carolina. We found that the products are a hazard to snakes and possibly other wildlife and suggest the products need a smaller mesh size.

The U.S. Department of Energy's (DOE) Savannah River Site in west-central South Carolina contains approximately 350 Carolina bays. Nearly, two-thirds of the bays were degraded or destroyed prior to federal acquisition of the land. These isolated wetlands range from small ephemeral depressions to large permanent ponds of several hectares in size. They provide habitat to support a wide range of rare plant species and many vertebrates (birds, amphibians, reptiles, bats) (Sharitz, 2003). Historical impacts to the Carolina bays were primarily associated with agricultural activities. Bays were often drained, tilled, and planted to crops. The consequence was a loss in the wetland hydrologic cycle, the native wetland vegetation, and the associated wildlife. In an effort to restore these habitats, sixteen Carolina bays were identified as candidates for restoration.

Due to the small size of the restoration areas (from one and a half acre to six acres) and limited amount of fill material needed for the plug (approxiamately 10 [m.sup.3] per site) the U.S. Army Corps of Engineers issued a Nationwide Permit 27 for the activities. Specified within the permit was that best management practices were to be implemented to minimize erosion and migration of sediments off site. Practices listed in the permit included: hay bales, silt fences, rolled erosion control products, and vegetative cover. The rolled products seemed ideally suited for protecting the sites given that the ditch plugs were generally less than three feet in width and that one blanket could simply be rolled over the exposed soil that formed the plug. As such, two brands of erosion control blankets were used on these sites, one that contained a coconut/straw mix and another containing only coconut fiber. Both blankets were eight feet wide by 90 feet in length and contained an internal and external plastic netting with a mesh size of 10 [mm.sup.2] and 20 [mm.sup.2], respectively. In all, fifteen blankets were utilized for the project, one per wetland site.

Four months after the restoration activities were completed, Bay 5071 was visited and three live snakes--two black racers, Coluber constrictor and one corn snake, Elaphe guttata--were observed entangled in the blanket. The snakes were freed from the blanket by cutting through the plastic mesh using scissors, but all received sever lacerations from the plastic mesh. Later that day, a second site was visited (Bay 5204) and another live black racer was observed entangled in a blanket. Recognizing that a potential problem had arisen, all sites were visited the following day to survey for additional captures. Of the fifteen restoration sites visited, nine (60 percent) contained entangled snakes (Table 1). A total of 19 snakes were found in the 15 sites, which equates to 1.26 captures per blanket roll.

In addition to the species listed earlier, a rat snake (Elaphe obsolete), water snake (Nerodia sp.), and eastern hognose (Heterodon platyrhinos) were identified in the plastic mesh. Snake entanglement has been reported in bird netting and to a lesser extent in erosion control blankets (Stuart et al., 2001), but the magnitude observed in these sites was dramatic considering the small amount of material used and the short timeframe that the mesh was employed on the ground. As a consequence, the blankets were removed from the sites and replaced with wheat straw mulch.

Black racers were the most common of the 19 snakes caught in the blankets used in the Carolina bay restoration project. Black racers are known to exhibit powerful, fast undulatory movement and can twist until the tail breaks away from the body (Greene, 1997). As this twisting behavior is a common escape mechanism for this species, it is likely that once caught by the mesh, the animal began to twist while attempting to escape. Unfortunately the twisting behavior would result in the snake being more firmly entrapped by several squares of the mesh, until the snake is virtually immobile. As the mesh tightens around the snake's body, the plastic cuts into the skin resulting in the severe lacerations we observed. Fourteen of the 19 trapped snakes died as a result of being trapped, either due to the lacerations received, to overheating, or to being unable to escape from predators including fire ants. We have no way of determining the exact cause of death for 14 animals. All deaths were precipitated, however, by the entrapment of the erosion control blanket plastic mesh. The three identified species are similar in body width to the opening of the 20 [mm.sup.2] mesh of the blanket.

While the deaths of common snakes is certainly not an objective of any responsible land manager, the fact that they occur may not be considered a tragic accident. However, the use of these blankets in areas containing federally or state threatened and/or endangered snake species could result in an outcome that results in the land or project manager facing criminal charges. Table 2 outlines areas within the United States where federally threatened and endangered snake species exist and where installation of blankets may not be warranted. In addition, many states have protection for animals on the state threatened and endangered species, which are not threatened nationally. In these zones, the use of blankets may not be totally restricted, but efforts to use products such as permanent turf reinforcement mats that contain a very small mesh size (< 5 [mm.sup.2]) is recommended.

Suggestions

Soil erosion control management is intended to lessen the impacts of physical weathering of the Earth's surface and thereby improve soil health, water quality, water quantity, and the overall health of the ecosystem. Rolled erosion control products are used extensively for this purpose and have proven their usefulness in construction sites across the United States. However, our findings indicate that they pose a potential hazard to snakes and possibly to other wildlife that may get entangled in the plastic mesh that holds the material together.

From an ecosystem health standpoint, we feel that these products are not suitable. It's not our intent to suggest that these products be prohibited for use because of this finding; however, we do suggest that manufacturers of these products consider using a smaller mesh size in their process and that discretion is used when placing these materials in sensitive areas where snakes are common.
Table 1. Snake captures in erosion control blanket at each wetland
restoration site.

Bay #  Captures  Species                           Status

   5   0
 124   1         Black Racer, Coluber constrictor  dead, partially
                                                     decomposed
 126   0
 131   1         Black Racer, Coluber constrictor  dead, recently
       1         Rat Snake, Elaphe obsoleta        dead, recently
       1         Water Snake, Nerodia?             dead, partially
                                                   decomposed
 171   2         Black Racer, Coluber constrictor  dead, recently
5001   3         unknown                           dead, complete
                                                     skeletons
5011   0
5016*  0
5071   2         Black Racer, Coluber constrictor  alive, severe
                                                     lacerations
       1         Corn Snake, Elaphe guttata        alive, severe
                                                     lacerations
5092   0
5128   0
5135   0
5184   2         unknown                           dead, complete
                                                     skeletons
5190   1         Black Racer, Coluber constrictor  dead, partially
                                                     decomposed
       1         Eastern Hognose                   alive, severe
                                                     lacerations (fatal)
5204   1         Black Racer, Coluber constrictor  alive, released
5239   1         Black Racer, Coluber constrictor  dead, partially
                                                     decomposed
       1         unknown                           dead, complete
                                                     skeleton

([section]) Bay 5016 was flooded and could not be plugged until later
that year, so no ECB was installed.

Table 2. Threatened and endangered snakes in the United States.

Common Name             Scientific Name

Atlantic salt marsh     Nerodia clarkii taeniata
snake
Concho water            Nerodia paucimaculata
snake
Copperbelly water       Nerodia erythrogaster neglecta
snake
Eastern indigo          Drymarchon corais couperi
snake
Giant garter snake      Thamnophis gigas
Lake Erie               Nerodia sipedon insularum
water snake
New Mexico              Crotalus willardi obscurus
ridge-nose rattlesnake
San Francisco           Thamnophis sirtalis tetrataenia
garter snake
Whipsnake               Masticophis lateralis euryxanthus
(striped racer),
Alameda

Common Name             Range[dagger]             Status[double dagger]

Atlantic salt marsh     FL (coastal areas of      T
snake                   Volusin, Brevard and
                        Indian River counties)
Concho water            TX (Concho and Colorado   T
snake                   river basins of the
                        Rolling Plains)
Copperbelly water       IL, IN, MI, OH, KY        T
snake                   (IN north of 40[degrees]
                        N. Lat.)
Eastern indigo          AL, FL, GA, MS, SC        T
snake                   (entire range)
Giant garter snake      CA (central Sacramento    T
                        Valley area; San Joaquin
                        Valley)
Lake Erie               OH (shorelines of         T
water snake             islands in western Lake
                        Erie)
New Mexico              AZ, NM (NM)               T
ridge-nose rattlesnake
San Francisco           CA (San Mateo county,     E
garter snake            CA)
Whipsnake               CA (Alameda and Contra    T
(striped racer),        Costa counties, CA)
Alameda

[dagger]Historic range (area of concern)
[double dagger]T = threatened; E = endangered


Acknowledgements

The authors would like to recognize the U.S. Department of Agriculture Forest Service's Savannah River and Center for Forested Wetland Research for support. Special thanks to Todd Kuntz for field assistance.

References Cited

Greene, HW. 1997. Snakes: The evolution of mystery in nature. University of California Press. Berkeley, California.

Sharitz, R. R. 2003. Carolina bay wetlands: Unique habitats of the southeastern United States. Wetlands. 23(3): 550-562.

Stuart, J.N., M. L. Watson, T.L. Brown, and C. Eustice. 2001. Plastic netting: An entanglement hazard to snakes and other wildlife. Herpetological Review. 32(3): 162-164.
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Author:Barton, Christopher; Kinkead, Karen
Publication:Journal of Soil and Water Conservation
Article Type:Cover Story
Geographic Code:1USA
Date:Mar 1, 2005
Words:1661
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