Development of habitat use data, detection, and survey methods for the endangered gastropod, Pecos Assiminea (Assiminea Pecos), at Bitter Lake National Wildlife Refuge



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North American freshwater species are facing an extraordinarily high rate of extinction due to numerous anthropogenic influences. Pecos assiminea (Assiminea pecos) is an endangered, semi-aquatic snail endemic to two spring systems located in eastern New Mexico and west Texas. Basic biological information needed for effective monitoring and conservation is currently lacking for this species. My objectives were to determine the habitat use patterns, evaluate the effects of the removal of common reed (Phragmites australis) on habitat use, compare the relative effectiveness of two survey methodologies, and conduct an empirical study to assess the environmental and observer factors influencing the detection probability of Pecos assiminea, at Bitter Lake National Wildlife Refuge in New Mexico. Pecos assiminea sampling occurred during 2013-2015 (nsurveys = 11). Surveys were conducted at two locations, Sinkhole 31 and Bitter Creek using two methods, standard quadrats (n = 528) and weathered wooden tiles left on the substrate (n = 671). Snails were identified and counted, and a suite of habitat variables were collected at each sampling point. In addition, empty phantom springsnail (Pyrgulopsis texana) shells were used as a surrogate for Pecos assiminea to empirically assess detection probability. A total of 0-9 shells were placed in each quadrat (n = 12). Shells were placed in microhabitats where Pecos assiminea is typically found, and 10 observers with varying experience levels searched through the quadrats for 5 minutes each. The results from quadrat survey classification trees suggested that Pecos assiminea presence was associated with general features relating to moisture and temperature, however, the availability and quality of suitable Pecos assiminea habitat differed between Bitter Creek and Sinkhole 31. These differences seemed to be reflected by a larger population of Pecos assiminea at Sinkhole 31. The removal of common reed was expected to allow native vegetation to re-establish itself along the creek, increasing the amount of available habitat. However, survey results from the restored sections did not suggest any effect on Pecos assiminea habitat use compared to that of pre-restoration. Furthermore, the choice of survey methodology did not seem to greatly influence detection, although neither method was sufficient alone for estimating abundance without incorporating detection, since quadrats yielded lower counts and tiles may alter snail behavior. The probability of detection for quadrats was estimated at 72%. The effects of habitat and observer variables on accuracy were the number of snail shells placed in the quadrat (F109,3 = 91.51, P < 0.01) and the order the quadrats were observed (F109,3 = 9.14, P < 0.01) via an ANCOVA. The mean (± SE) observer accuracy produced from the best model was 43.59% ± 17.09 (F109,10 = 60.65, P < 0.01). Improving detection probability and accuracy in Pecos assiminea estimates will aid in the development of survey protocols and thus better guide management decisions impacting conservation efforts. Bitter Creek is susceptible to threats such as aquifer withdrawals and agricultural diversions for irrigation. The increasing use of water withdrawals imperil rare North American spring habitats and the numerous endemic freshwater gastropods dependent upon them. More research is needed to understand the ecology of freshwater gastropods, especially in the face of threats. Incorporating my findings should improve monitoring efforts and aid in the development of restoration and conservation plans for Pecos assiminea.



Gastropods, Methods, Detection, Habitat use, Common reed, Endangered