Do erosion control and snakes mesh?
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.
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
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.
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|
|Date:||Mar 1, 2005|
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