PARENT SESSION
Oral Session 14: Reptiles and Amphibians I: Salamanders and Newts.
Presiding: K McCoy
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room D 136.
Proportion Area Occupied: Using historical data for an endangered tiger salamander to design an effective monitoring strategy.
Allison, Linda*,1, Collins, James2, Averill-Murray, Roy1, 1 Arizona Game and Fish Department, Phoenix, Arizona2 Arizona State University, Tempe, Arizona
ABSTRACT- Large fluctuations in numbers and the need to measure non-catastrophic declines have contributed to a recent focus on proportion area occupied (PAO) as a measure for detecting population trends in amphibians. Delisting criteria for the Sonoran tiger salamander, Ambystoma tigrinum stebbinsi, require monitoring to estimate PAO with no demonstrable decline over a 5-year period. We used survey data collected from 1994 through 2000 to estimate baseline PAO parameters, as well as the detection probability for tank occupancy. Using Program MARK, we estimated annual occupancy of 60%. Detection rate was best modeled as a function of season and was highest from November through July (60-80%), with lower rates (30-50%) otherwise. We used these parameter estimates in simulations to compare potential monitoring designs. All designs required either 80 or 100 site-visits per year, but we allocated visits differently for each design. In a given year, some tanks were surveyed once, but to estimate detection rate another subset of tanks was visited 2 or 3 times. The most powerful designs sampled the same tanks each year, with multiple surveys of the same subset of tanks each year. The best of these designs required 100 visits each year surveying 30 tanks twice and 40 tanks once. Power to detect a true trend of 5% annual decline was only 0.44 after 5 years, 0.95 after 10 years, and 0.87 if sampling were conducted every other year for 5 years. For declines of 10% per year, this design had 0.85 probability of detecting a trend after 5 years.
Key words: monitoring design, detection probability, Ambystoma tigrinum stebbinsi, metapopulation