An evaluation of methods for monitoring Ensatina eschscholtzii oregonensis in the Reed College Canyon
author: Kyla Zaret
advisor: Robert Kaplan
year: 2002
ABSTRACT: Amphibians are likely indicators of environmental degradation, as evidenced by cases of disappearing and declining amphibian populations worldwide. However, distinguishing between natural fluctuations in amphibian population size and trends due to human impacts is problematic. Consequently, developing standardized methods for efficiently and reliably monitoring amphibian populations over the long-term would greatly enhance conservation efforts.
The use of artificial cover objects (ACOs) in monitoring terrestrial salamander populations is relatively new and has not been extensively tested, though it offers many potential advantages over more traditional methods of monitoring, such as standardization of sampling technique, little between-observer variability, limited habitat disturbance, and relatively less time and money spent collecting data. The Reed Canyon offers a unique opportunity to monitor the sole terrestrial salamander species of a key conservation area. Thus, this study was conducted in order to compare the ACO and quadrat methods for monitoring the population of E. e. oregonensis in the Reed Canyon. The techniques were evaluated based on the number of animals encountered, how salamander encounter was affected by climatic variables, and the power of the techniques to detect trends in population size. In addition, two groups of ACOs were deployed at different times in order to determine the flexibility of a monitoring program that utilizes that sampling method.
It was determined that the ACO and quadrat techniques detected trends in salamander count with similar power. However, sampling ACOs was much less time-consuming than sampling quadrats. Thus, the power of a monitoring program that utilizes ACOs can be adjusted by increasing the number of ACOs sampled without a subsequent increase in the amount of time needed to complete surveying. In addition, salamander encounter under ACOs was less affected by climatic variables than within quadrats. New ACOs did not effectively sample salamanders. The results of this study indicate that ACOs should be used to create an efficient and powerful program to monitor the population of E. e. oregonensis in the Reed Canyon over the long-term.