Correlates of snake entanglement in erosion control blankets

Abstract

In road construction projects across the United States, erosion control methods (e.g., erosion control blankets [ECBs]), are mandated to stimulate seedbed regeneration and prevent soil loss. Previous reports have suggested that snakes are vulnerable to entanglement in ECBs. We conducted a literature review, field surveys, and an entanglement experiment to examine what factors increase a snake's risk of ECB entanglement. Our literature review produced reports of 175 reptiles entangled in mesh products, 89.1% of which were snakes, with 43.6% of snake entanglements occurring in erosion control products. During our field surveys, we found 10 entangled snakes (n = 2 alive; n = 8 dead). From our experiment, we found that ECBs that contain fixed‐intersection, small‐diameter mesh consisting of polypropylene were significantly more likely to entangle snakes compared with ECBs with larger diameter polypropylene mesh or ECBs that have woven mesh made of natural fibers. Snake body size was also associated with entanglement; for every 1‐mm increase in body circumference, the probability of entanglement increased 4%. These results can help construct a predictive framework to determine those species and individuals that are most vulnerable to entanglement. © 2019 The Wildlife Society.

Risk of Snake Entanglement Is Affected by Installation Method of Erosion Control Blankets

“…Previous studies found that ECBs with certain characteristics (e.g., fused apertures, mesh composed of polypropylene) increase the probability of wildlife entanglement (Stuart et al 2001;Ebert et al 2019). For example, ECBs with fixed apertures do not expand to allow snakes (suborder Serpentes) to pass through, whereas woven mesh allows the aperture to expand, permitting snakes to move through the mesh netting and avoid entanglement (Kapfer and Paloski 2011;Ebert et al 2019). Furthermore, some ECBs contain plastic material that is slow to degrade (e.g., 1-3 y) and may pose a long-term threat to wildlife.…”

“…Erosion control blankets (ECBs) pose a threat of entanglement to wildlife that often leads to their mortality because of heat exposure, desiccation, increased vulnerability to predation, or deep lacerations caused by twisting in the mesh (Stuart et al 2001;Walley et al 2005;Ebert et al 2019). Previous studies found that ECBs with certain characteristics (e.g., fused apertures, mesh composed of polypropylene) increase the probability of wildlife entanglement (Stuart et al 2001;Ebert et al 2019).…”

“…Erosion control blankets (ECBs) pose a threat of entanglement to wildlife that often leads to their mortality because of heat exposure, desiccation, increased vulnerability to predation, or deep lacerations caused by twisting in the mesh (Stuart et al 2001;Walley et al 2005;Ebert et al 2019). Previous studies found that ECBs with certain characteristics (e.g., fused apertures, mesh composed of polypropylene) increase the probability of wildlife entanglement (Stuart et al 2001;Ebert et al 2019). For example, ECBs with fixed apertures do not expand to allow snakes (suborder Serpentes) to pass through, whereas woven mesh allows the aperture to expand, permitting snakes to move through the mesh netting and avoid entanglement (Kapfer and Paloski 2011;Ebert et al 2019).…”

“…In their review, Ebert et al (2019) found that reptiles were most frequently entangled in mesh products used for wildlife exclusion, followed by ECBs. Of the reptile taxa entangled, snakes were most vulnerable to entanglement, as they comprised 89.1% of the 175 reports (Ebert et al 2019;9.1% were lizards and 1.7% were turtles). Snakes possess several traits that contribute to their frequent entanglement in ECBs.…”

“…Additionally, roads retain heat and are often used by snakes for thermoregulation (Sullivan 1981), thus increasing the potential encounter rates of snakes with ECBs on the landscape since ECBs are often associated with roads. Ebert et al (2019) found that when a snake does encounter and attempt to pass through an ECB, its risk of entanglement increases with increasing body circumference (e.g., adults, gravid females, larger-bodied species). However, this correlation is dependent upon the characteristics of the ECB (e.g., size of mesh apertures).…”