An assessment of potential stressors to the Dunes Sagebrush Lizard (Sceloporus arenicolus) habitat in western Texas and an analysis of the Endangered Species Act (ESA) classification

The U.S. Fish & Wildlife Service (FWS) recently considered whether to list the Sceloporus arenicolus or Dunes Sagebrush Lizard (DSL) as “endangered” under the Endangered Species Act (ESA). During the listing period, it analyzed particular stressors, which included habitat modification and the presence of chemicals associated with oil and gas development and range management. In 2012, the FWS withdrew the proposed rule to list the DSL under the ESA largely based on voluntary conservation plans adopted by Texas and New Mexico.
Like many threatened species, the DSL is considered a “habitat specialist,” remaining closely linked to and dependent upon its current habitat of a shinnery oak dunes complex located in a specific region of southeastern New Mexico and western Texas (Sabath,1960). The FWS proposed the listing in 2010 largely based on evidence that oil and gas production in the area resulted in a reduction of the DSL population. The reduction has been attributed to multiple theories regarding potential DSL habitat stressors including direct habitat loss due to road/well pad construction and increased traffic, as well as potential exposure to pollutants resulting from oil and gas development. These concerns have been supported by previous studies that included evidence of direct effects of habitat modification in the area due to construction and development of well pads and roads, and the possible historical use of tebuthiuron (an herbicide historically sprayed to reduce shinnery oak). In addition to habitat modification, the FWS also identified potential indirect effects including possible exposure to chemical releases from oil and gas activity including hydrogen sulfide gas (H2S) and total petroleum hydrocarbons (TPH). However, from the time that the FWS proposed to list the DSL as an “endangered species” in December 2010, substantial disagreement occurred regarding the amount of credible scientific data and interpretation of these data (76 Fed. Reg. 233, 75858). Because of limited information on the DSL’s presence, particularly in Texas, concerns about the science underlying the FWS’s analysis of the status of the lizard were raised. Since studies evaluating these effects were relatively few in number, lawmakers called for additional collection and analysis of scientific data. Following these concerns, on December 5, 2011, the FWS announced a six-month extension of its final determination of whether to list the DSL as endangered and reopened the comment period on the proposed rule to list the species.
It was during that time period that much of the data in this study was collected and analyzed. The goal of this study was to address the potential stressors in a defined DSL habitat area within Andrews County in order to provide additional data and some clarity with regard to the presence of chemical stressors, the amount of habitat modification and what type of impact they had on the DSL habitat and population. In particular, we evaluated the presence of H2S, TPH and tebuthiuron. Overall, we found very low concentrations, if any, of these chemical stressors within dunes areas that would be an ideal habitat for the DSL. Additionally, we analyzed sand samples from in and around the DSL habitat for sulfate (SO4-2) concentrations, pH and sand particle size. Although sulfate concentrations and pH from the study sites varied slightly from western Texas sand samples collected outside of Andrews County, the variance was minimal. Sand particle size was also fairly consistent among samples at all study sites, regardless of the amount of oil and gas development. Finally, we created a method, using Arc-GIS and aerial imagery from 1996-2012, to quantify oil and gas development (well pads and roads) within delineated dunes on University of Texas (UT) Lands in Andrews County. Our data revealed a two-fold increase in development from 2004-2012 throughout most of these areas. We concluded that habitat modification, as opposed to chemical stressors, remains the primary threat to the DSL. Our hope is that this preliminary data will provide information for ongoing risk assessment and evaluation of the current DSL population in western Texas and assist all parties involved in implementing an effective voluntary conservation plan.