2009 NORTHEASTERN NATURALIST 16(3):317–320 The Status of the Northern Population of the Copper-bellied Watersnake, Nerodia erythrogaster neglecta Omar Attum1,2,*, Yu Man Lee3, and Bruce A. Kingsbury1 Abstract - The Nerodia erythrogaster neglecta (Copper-bellied Watersnake) population north of 40 degrees north latitude is categorized as threatened under the US Endangered Species Act. Previous efforts to use mark-recapture to estimate population size have been unsuccessful because there were so few initial captures. We therefore evaluated the status of the largest presumed subpopulation of this population by using strip transects to provide a conservative (maximum) estimate of density and population size of adults. Our results indicate that the largest presumed adult Copper-bellied Watersnake metapopulation north of 40 degrees north latitude is extremely small, with a total size of 94 ± 22 adults, and is characterized by a population density of 1.17 ± 0.27 adult snakes/ha (95 % CI = 0.73–1.87 snake/ha). This Copper-bellied Watersnake population appears to be in danger of extirpation within the foreseeable future. Recovery will require protecting existing wetland complexes and restoring wetlands and the surrounding upland habitats. Introduction Nerodia erythrogaster neglecta Conant (Copper-bellied Watersnake) is a subspecies of Nerodia erythrogaster (Forster in Bossu) (Plain-bellied Watersnake) (Conant 1949). The Copper-bellied Watersnake has been in decline across its range for some time (USFWS 1997), and populations now persist only in isolated pockets. Populations in Indiana, Michigan, and Ohio north of 40 degrees latitude are listed as threatened under the US Endangered Species Act, and these occur mostly in a small area that borders northwestern Ohio and adjacent southern Michigan. To the best of our knowledge, there are no published size estimates for these metapopulations. Efforts to estimate population size using mark-recapture have failed because of a paucity of captured snakes (B.A. Kingsbury, unpubl. data). We therefore used strip transects to attempt to provide a conservative estimate of the density and population size of the largest Copper-bellied Watersnake (referred to only as watersnake later herein) metapopulation, which is believed to contain most of the individuals of this watersnake north of 40 degrees north latitude. Materials and Methods This study was conducted in northwestern Ohio and adjacent southern Michigan on public and private lands that are believed to contain the largest 1Center for Reptile and Amphibian Conservation and Management, Indiana-Purdue University Fort Wayne, 2101 E. Coliseum Boulevard, Fort Wayne, IN 46805. 2Current address - Department of Biology, Indiana University Southeast, 4201 Grant Line Road, New Albany, IN 47150. 3Michigan Natural Features Inventory, Michigan State University Extension, PO Box 30444, Lansing, MI 48909-7944. *Corresponding author - oattum@ius.edu. 318 Northeastern Naturalist Vol. 16, No. 3 metapopulation of watersnakes (B.A. Kingsbury, unpubl. data). The study area contains a variety of wetland sizes and types, including both ephemeral wetlands and larger, permanent wetlands that had often been artificially created and have water levels controlled for game fishes and birds. These wetlands are fed by spring, river, lake, and local runoff. The St. Joseph River flows through the study site. The upland landscape consists of a matrix of forested, shrub-scrub, old-field, agricultural, and residential habitats and roads. We sampled 34 wetlands, which ranged in size from 0.02–5.26 ha and totaled 34.99 ha surface area. We treated each wetland shoreline as a transect by walking along the shoreline edge or wading through water when necessary for the entire length of each wetland (shoreline length range = 57–2357 m; total shoreline length surveyed = 20,366 m). The transects were 2 m wide, with 0.5 m occurring on the shore and 1.5 m in the water. Each wetland was surveyed four times between 26 April–13 June 2006, when snakes were most likely to be observed because of little vegetation growth and conspicuous basking. We only observed adults during the surveys and therefore our estimates do not include neonates or juveniles. We assumed that animals on the transect were always detected because the observer was presumed to eventually flush snakes near the shoreline while walking the transect. For one wetland, we only surveyed 83 m of 373 m of shoreline because of dense vegetation and deeper water. Wetland size and shoreline length were obtained from past studies (Attum et al. 2008; Roe et al. 2003, 2004). The surveyed wetlands included all the areas known to have the highest watersnake densities, based on previous surveys and telemetry studies (Attum et al. 2008; Roe et al. 2003, 2004). There were an additional 29 ha of low-use or marginal wetland habitat that we did not survey due to time-limit and additional man-power constraints (Attum et al. 2008; Roe et al. 2003, 2004) Several localities, of an unknown total number of wetland ha, where the watersnake is known to have occurred north of 40 degrees latitude were not surveyed as these localities are mostly represented by historic records, with no recent observations (B.A. Kingsbury, unpubl. data). We believe including these areas in our estimates would have increased population size by only a few individuals and would have decreased density estimates. We estimated population size and density from the strip-transect data using DISTANCE 5.0 software (Olson et al. 2005, Thomas et al. 2006). In order to use DISTANCE 5.0 to estimate density with strip-transect data, we set the number of intervals to 1 and then set the interval to half the total width (1 m) of the 2-m wide strip transect. We pooled the data for our analysis, but used the multiplier function in DISTANCE to divide the estimates by four to account for multiple surveys. Results There were 19 watersnake observations on our transects, with density estimated at 1.17 ± 0.27 snakes/ha (95 % CI = 0.73–1.87 snake/ha), with the percent coefficient of variation = 22.94%. The population size for the area 2009 O. Attum, Y.M. Lee, and B.A. Kingsbury 319 surveyed was estimated at 41 ± 9 individuals (95 % CI = 25–66). If we extrapolate densities to the additional 29.31 ha of unsurveyed wetlands for a total of 64.3 ha, then the total adult watersnake population size would be 94 ± 22. Discussion Our density and population estimates can only be considered as the “best case” scenario because of two main sources of bias that inflated our estimates. First, the transects were not randomly placed, but instead occurred on the wetland shoreline. Our transect placement violated an important assumption of density estimation, namely, that transects must be randomly placed. Watersnakes are more likely to be found near the shoreline, especially in palustrine and lacustrine open wetlands (Laurent and Kingsbury 2003). This violation will cause abundance and density to be overestimated because of collecting data in the area of highest watersnake density, and application of that density estimate to the entire wetland. The second main source of bias is that we estimated population size by surveying the wetlands with the presumed highest snake density and applied that density to wetlands that we considered to be low-use watersnake habitat. Despite the inflation biases in our analysis, the density estimates show that this metapopulation is extremely small and characterized by a conspicuously lower density than reported for other populations of Copper-bellied Watersnake. For example, Lacki et al. (1994), in southern Indiana, reported adult densities to be between 10–14 snakes/ha, depending upon locality, in prime habitat, and Laurent (2000), in northwestern Kentucky, reported a density of 11 snakes/ha. According to the Endangered Species Act, a threatened species is one likely to become endangered in the foreseeable future, while an endangered species is "in danger of extinction within the foreseeable future throughout all or a significant portion of its range.” We believe that the northern population of the watersnake is already endangered based on the small size of the largest metapopluation, extremely high extinction probability for small populations, and the definition of endangered as specified by the Endangered Species Act. The small population size and low density of the northern population is most likely the result of insufficient and degraded wetland habitat and negative landscape effects on existing habitat (Attum et al., 2008; Roe et al., 2003, 2004, 2006). The recovery of the watersnake will require protection and restoration of wetland complexes embedded in a forest matrix, and not just of individual wetlands (Roe et al. 2003, 2004). These complexes should contain a mosaic of large, open wetlands surrounded by multiple, ephemeral, and variable types of wetlands (Roe et al. 2003, 2004). To maintain connectivity between wetlands and wetland complexes, forest areas within a 250-m radius of each wetland should be protected (Attum et al. 2008). In addition, the effects of roads as a source of mortality and habitat fragmentation also need to be addressed (Kramer-Schadt et al. 2004, Roe et al. 2006). 320 Northeastern Naturalist Vol. 16, No. 3 Acknowledgments This research was funded by the US Fish and Wildlife Service Section 6 Grant Program, Michigan Department of Natural Resources, and the Center for Reptile and Amphibian Conservation and Management, Indiana-Purdue University Fort Wayne. We are indebted to Nathan Herbert, Kile Kucher, and Sean Zera, who provided field assistance for this project. D. Soards provided logistical support. The following landowners granted permission to survey private property: D. Brown, R. Neely, T. Oberleiter, G. Richards, J. Roden, M. Schauer, D. and J. Wilson, and M. Wilson. We thank the Michigan Nature Association and Toledo Area Council for permitting us to survey their properties. All applicable Animal Care guidelines and required state and federal permits were obtained for this study. Four reviewers made helpful comments during manuscript review. Literature Cited Attum, O., Y. Lee, J.H. Roe, and B.A. Kingsbury. 2008. Wetland complexes and upland-wetland linkages: Landscape effects on the distribution of rare and common wetland species. Journal of Zoology (London) 275:245–251. Conant, R. 1949. Two new races of Natrix erythrogaster. Copeia 1:15. Kramer-Schadt, S., E. Revila, T. Wiegand, and W. Breitenmoser. 2004. Fragmented landscapes, road mortality, and patch connectivity: Modeling influences on the dispersal of Eurasian Lynx. Journal of Applied Ecology 41:711–723. Lacki, M.J., J.W Hummer, and J.L. Fitzgerald. 1994. Application of line transects for estimating population density of the endangered Copperbelly Water Snake in southern Indiana. Journal of Herpetology 28:241–245. Laurent, E.J. 2000. Hierarchical population study of the endangered Copperbelly Water Snake. M.Sc. Thesis. Indiana Purdue University at Fort Wayne, Fort Wayne, IN. Laurent, E.J., and B.A. Kingsbury. 2003. Habitat separation among three species of water snakes in northwestern Kentucky. Journal of Herpetology 37:229–235. Olson, K.A., T.K. Fuller, G.B. Schaller, D. Odonkhuu, and M.G. Murray. 2005. Estimating the population density of Mongolian Gazelles Procapra gutturosa by driving long-distance transects. Oryx 39:164–169. Roe, J.H., B.A. Kingsbury, and N.R. Herbert. 2003. Wetland and upland use patterns in semi-aquatic snakes: Implications for wetland conservation. Wetlands 23:1003–1014. Roe, J.H., B.A. Kingsbury, and N.R. Herbert. 2004. Comparative water snake ecology: Conservation of mobile animals that use temporally dynamic resources. Biological Conservation 118:79–89. Roe, J.H., J. Gibson, and B.A. Kingsbury. 2006. Beyond the wetland border: Estimating the impact of roads for two species of water snakes. Biological Conservation 130:161–168. Thomas, L., J.L. Laake, S.Strindberg, F.F.C. Marques, S.T. Buckland, D.L. Borchers, D.R. Anderson, K.P. Burnham, S.L. HedleyPollard, J.H. Bishop, J.R.B. Marques, and T.A. Marques. 2006. Distance 5.0. Research Unit for Wildlife Population Assessment, University of St. Andrews, UK. Available online at http://www.ruwpa. st-and.ac.uk/distance. Accessed 21 November 2006. US Fish and Wildlife Service (USFWS). 1997. Endangered and threatened wildlife and plants: Determination of threatened status for the northern population of the Copperbelly Watersnake. Federal Register 62:4183–4193.