MONITORING MARTES POPULATIONS IN CALIFORNIA - SURVEY DESIGN AND POWERANALYSIS

Fishers (Martes pennanti) and American martens (M. anericana) have bee n protected from trapping in California since the mid-1900s, yet in po rtions of each of their historic ranges their numbers are extremely lo w, perhaps due to the effects of timber harvest. We propose a method c apable of detecting declines in the occurrence and distribution of fis hers or martens using baited track-plate stations. The proposed sampli ng unit is a small grid of stations that has a high probability of det ecting animals when they are present. These multistation units are suf ficiently spaced to meet the assumption of independence for a binomial model. We propose a stratified random sampling design with strata sam pled for proportions of occurrence at discrete points in time. Stratif ication is based on variation in occurrence by region and is estimated from preliminary survey data. A previously published bias adjustment is applied to the proportion of units with detections to adjust for po ssible failure to detect resident individuals at a sampling unit. A Mo nte Carlo simulation model was developed to determine the sample size necessary to detect 20 and 50% declines, with 80% power, in the propor tion of sampling units with occurrence. We assume a 10-yr sampling int erval. Sensitivity analysis, using a range of values for means and sta ndard deviations of strata proportions, determined that power was much more sensitive to changes in mean than the standard deviation. When t he best current estimates of the fisher strata proportions were input for 10 strata (five regional and two habitat) in California, 115 and 1 7 sampling units per stratum were necessary to detect 20 and 50% decli nes, respectively. For some circumstances this sampling effort was als o sufficient to achieve strata estimates with 5% error and to detect s tatistical differences between individual stratum proportions. The ste ps in the process of implementing a monitoring program for Pacific fis hers in California are outlined as an example of the planning and prep aration necessary to monitor changes in the distribution of a rare for est carnivore.