Joseph C. Mitchell

Department of Biology

University of Richmond

Richmond, VA 23173

Introduction

On 28 March 1993, a rupture in an underground pipeline caused a large spill (407,736 gallons) of number 2 oil that flowed into Sugarland Run, a second order stream that originates south of Herndon in Fairfax County and passes through northeastern Loudoun County where it enters the Potomac River at Lowes Island. The list of animals affected includes birds, mammals, fishes, amphibians, and reptiles (Research Planning, Inc., 1993; B. Stinson, VA Dept. Game & Inland Fisheries, pers. comm.). Amphibians and reptiles found dead included toads (Bufo spp.), gray treefrogs (Hyla chrysoscelis or versicolor), bullfrogs (Rana catesbeiana), green frogs (Rana clamitans), and box turtles (Terrapene carolina). Reptiles that were caught, treated, and released included northern water snakes (Nerodia sipedon), snapping turtles (Chelydra serpentina), painted turtles (Chrysemys picta), wood turtles (Clemmys insculpta), and box turtles.

In seeking financial retribution from the pipeline company, the state sought information on the populations of species that may have been affected by the oil spill. The immediate problem was that there was no information on which species occurred in Sugarland Run and its floodplain. No biodiversity surveys had been conducted for any taxonomic group prior to the oil spill. No surveys for vertebrates were conducted in the months immediately following the spill. Thus, when Virginia's Department of Environmental Quality began building its information base, there were no data for many basic survey questions. In March 1994, I was asked by the Department of Game & Inland Fisheries to generate a best estimate of the herpetofaunal species richness, their numbers, and their value for Sugarland Run and its floodplain. Although an accurate species list could be generated, estimates of the numbers of individuals was impossible because no previous baseline knowledge of the area was available. However, given these constraints, the following report, reproduced here in its entirety, was my attempt to assign a monetary value to the potential loss of amphibians and reptiles that occurred as a result of the oil spill.

Two obvious points can be made. First, estimates derived without previous field inventories on a site are educated guesses at best. There are simply too many assumptions about population sizes that could be easily violated during the reconstruction process. Thus, the second point, that we should obtain baseline biodiversity survey data (including estimates of relative abundance) for all Virginia's watersheds is blatantly obvious. State-funded programs, as well as private initiatives, that inventory natural areas are invaluable in this regard.

Such a dearth of information leads to opportunities. Amateur and professional herpetologists should conduct such surveys wherever possible and the data and field notes made available to future researchers in permanent form, such as the Virginia Herpetological Society Archives. Watershed surveys would be excellent class projects for all grade levels. The results of such surveys could be published and made available to everyone. We should always, of course, seek ways to prevent oil spills and other environmental catastrophes from occurring in the first place. Realistically, however, such problems will continue. As concerned citizens and people interested in herpetology and the quality of our environment, we can contribute to the cleanup and mitigation process simply by doing what many of us like to do best, observe and collect herps. Maintaining consistent, accurate field notes on all observations could yield valuable information for future researchers and regulatory personnel.

Statement of the Problem

Amphibians and reptiles inhabit riparian zones in and along creek and river courses in the eastern United States. In northern Virginia, the creeks that feed into the Potomac River and their associated watersheds harbor a rich herpetofauna. At least 20 species of amphibians and 30 species of reptiles are known from the northern Virginia area (Fairfax and Loudoun counties). All are known to inhabit riparian zones in this area.

The impact of the large oil spill that occurred in Sugarland Run in March 1993 is unknown because this tributary of the Potomac River was not previously inventoried for amphibians and reptiles, nor were density estimates made after the spill. Unfortunately, a parallel study of a nearby watershed was also not conducted after the spill to obtain comparable area-specific data. Thus, the only way to estimate the numbers of amphibians and reptiles in the Sugarland Run and its riparian zone is to use existing data from other studies. I have conducted several studies in northern Virginia and can estimate the numbers of most amphibians and several of the reptiles. The population size of the remainder of the reptiles cannot be estimated with regional data. Thus, density estimates for these species must be derived from literature sources.

The estimates provided in this report are admittedly crude. However, there are no other numbers available. These estimates should be viewed as ballpark figures that would be possible for any watershed in the northern Virginia area.

Methods

Species list -- The species listed in Table 1 were derived from two sources. The list of reptiles was based on distribution maps in Mitchell (1994). The amphibian list was derived from distribution maps in Tobey (1985) and unpublished updated maps for this fauna (J.C. Mitchell, unpublished). All of the species listed have been documented from the Piedmont physiographic region of Fairfax and Loudoun counties, Virginia.

Amphibians -- Estimation of numbers of each amphibian species was based on the results of a study conducted in Prince William Forest Park (PWFP), Prince William County, VA (J.C. Mitchell, unpublished). In this study, a drift fence array with pitfall traps (3 arms in a Y configuration with a 5 gallon bucket sunk in the ground at each end, n = 6 buckets) sampled each of four riparian zones over a 12 month period. The estimated sampling area was 100 x 20 meters of riparian habitat on one side of the adjacent stream (2,000 m2; 5 of these areas = 1 ha). This was a removal study, so the numbers represent minimum estimates. The number of individuals per species was averaged over the four sampling sites in the PWFP study, providing the number per hectare for each species in Table 1 (2000 m2 x 5 = 1 ha). I assumed that the width of the riparian corridor was 20 meters wide on each side (equal to the estimated sampling area above), so the total estimated area for a 500 meter (0.5 km) length of Sugarland Run floodplain riparian zone was 10,000 m2 (1 hectare). With each ha being 500 m long and 20 m wide, the number of hectares for the each km of Sugarland Run affected by the oil spill is 2. Thus, the total number of ha for Sugerland Run is 2 x 15 km x 2 sides = 60 ha.

Turtles -- Population estimates of freshwater turtles were derived from several sources, as follows: most species (Mitchell, 1994), Chelydra serpentina (Bury, 1979), and Chrysemys picta (Mitchell, 1994 and MacCulloch and Secoy, 1983). The numbers of per stream kilometer Clemmys insculpta, a species listed as endangered or threatened in most of its range, was derived from Kaufmann (1992). His results were for a pristine stream, so I have taken half of the numerical value he reported as the estimate for Sugarland Run. The number for Pseudemys rubriventris was an educated guess based on my experience with this animal in stream and riverine systems in Virginia. The number of some species were estimated in N/ha and for others the estimate was in N/km of stream. These estimates depended on the kind of data reported in the literature.

Lizards -- Population estimates of lizards were derived from the following sources: Mitchell (1994) for Scincella, Fitch (1954) for Eumeces fasciatus, and Carpenter (1959) for Sceloporus. For Eumeces inexpectatus and Eumeces laticeps, I estimated the densities to be half of that for E. fasciatus, based on my experience with these species in Virginia. The densities of lizards were estimated in N/ha.

Snakes -- Population estimates of this group are the most difficult to obtain because of the secretive nature of these animals. Because no population studies have been conducted on these animals in Virginia, density estimates were obtained from the technical literature. These sources have been summarized by Ernst and Barbour (1989). There was no information available for Thamnophis sauritus, Lampropeltis getula, and Lampropeltis triangulum, so based on my experience with these species, I estimated their densities to be half that of their closest relatives in the same genus (Thamnophis, Lampropeltis). The number of some species were estimated in N/ha and for others the estimate was in N/km of stream, depending on the way the data were reported in the literature.

Estimation of Value -- Costs for amphibians were derived from the information provided by the SSAR Monetary Value of Amphibians Subcommittee (1989). Their price estimates were based on wholesale prices (retail less 40%) based on pet trade price lists available at the time. The costs of amphibians (and reptiles) have, however, increased substantially since 1989, largely because of the tremendous increase in demand for these animals in the pet trade. The rate of inflation for 3 species I found in a 1994 price list (see below) indicated increases of 2.5 to 7 times the 1989 price. Therefore, to be conservative I have simply doubled the 1989 price for each species of amphibian in Table 1.

There is no comparable list of prices for reptiles. However, I consulted a recent commercial price list (Dec. 1993; Hogtown Herpetological Supply, Gainesville, FL) for retail prices for many species. For each species in Table 1 I used the estimated wholesale price (retail less 40%) which was determined to be in line with the methods used in SSAR Monetary Value of Amphibians Subcommittee (1989). For reptilian species for which there were no listings, I used the lowest commercial price available ($10.00 less 40%). The prices listed in Table 1 reflect the demand the public has placed on these animals.

NOTE: the prices listed in Table 1 do not include estimates for amphibian larvae (e.g., overwintering ranid tadpoles and marbled salamander larvae) nor for reptile eggs (e.g., overwintering turtle eggs). Thus, because the estimated costs would have been substantially more if these life history stages were included, the total estimated monetary value of the amphibian and reptilian faunas is conservative.

Conclusions

Sugarland Run has most certainly harbored a rich herpetofauna in the past. Although it has never been adequately inventoried, it is possible to provide a reasonably accurate list of species that occur there. This is based on the type of habitats, species known for the area, and estimated densities at which these species are reported to occur at other sites. This list (Table 1), along with the estimates of population sizes and numbers found in Sugarland Run, indicate that these species constituted a valuable natural resource based on commercial values alone. These values do not take into account their ecosystem functions and values as aesthetic resources. Thus, the estimated monetary value of these animals ($870,131) is probably underestimated by several orders of magnitude.

Literature Cited

Bury, R.B. 1979. Population ecology of freshwater turtles. Pp. 571-602 In

M. Harless and H. Morlock (eds.) Turtles, Perspectives and Research. John Wiley & Sons, New York, NY.

 

Carpenter, C.C. 1959. A population of Sceloporus undulatus consobrinus

in Oklahoma. Southwestern Naturalist 4:110-111.

 

Ernst, C.H. and R.W. Barbour. 1989. Snakes of Eastern North America.

George Mason University Press, Fairfax, VA.

 

Fitch, H.S. 1954. Life history an ecology of the five-lined skink, Eumeces

fasciatus. Univ. Kansas Publications, Museum of Natural History 8:1-156.

 

Kaufmann, J.H. 1992. The social behavior of wood turtles, Clemmys

insculpta, in central Pennsylvania. Herpetological Monographs 6:1-25.

 

Mitchell, J.C. 1994. The Reptiles of Virginia. Smithsonian Institution

Press, Washington, D.C.

 

MacCulloch, R.D. and D.M. Secoy. 1983. Demography, growth, and food

of western painted turtles, Chrysemys picta bellii (Gray), from southern Saskatchewan. Canadian Journal of Zoology 61:1499-1509.

 

Research Planning, Inc. 1993. Colonial pipeland company's Sugarland

Run pipeline spill 28 March 1993. Draft report prepared for NOAA/Damage Assessment Center, Silver Spring, MD. 48 pp + appencides.

 

SSAR Monetary Value of Amphibians Subcommittee. 1989. Monetary

Value of U.S. Amphibians. Herpetological Review 20(2S):1-4.

 

Table 1. Amphibians and reptiles known to occur in the vicinity of Sugarland Run, Fairfax and Loudoun counties, Virginia. Numb. = estimated number of each species per hectare or kilometer of stream, N-SR = total number of each species for Sugarland Run, Price = dollar (U.S. $) value per individual (see text for derivation of these values), and TOTAL = total $$ value for the estimated numbers for each species in Sugarland Run. N-SR numbers and monetary figures are rounded to the nearest dollar.

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Species Numb. N-SR Price TOTAL

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