AERIAL DISTANCE SAMPLING TO ESTIMATE ABUNDANCE OF TULE ELK POPULATIONS AND A COMPARISON TO A CONCURRENT FECAL DNA SPATIAL CAPTURE-RECAPTURE SURVEY
|Tom Batter; California Department of Fish and Wildlife; Thomas.Batter@wildlife.ca.gov; Russ Landers, Kristin Denryter, Josh Bush|
Tule elk (Cervus canadensis nannodes) populations in California historically have been monitored using aerial surveys to conduct minimum counts that do not address detection biases, thus providing limited inferences. To provide statistically robust abundance estimates, we applied multiple covariate distance sampling (MCDS) during helicopter surveys for tule elk in three Elk Management Units (EMUs) in Colusa and Lake Counties, CA, in 2018 and 2019. We selected covariates to explain detection probability including vegetation cover, group size, and survey year. We also compared estimates and costs with results from a concurrent fecal DNA spatial capture-recapture (SCR) survey. We estimated a two-year average total population size of N = 674 elk (90% CI = 501–907) in our survey area, which was similar to N = 658 elk (90% CI = 577–751) from SCR estimates; overall precision was greater (CV = 0.08; range = 0.11–0.30 by population) for SCR than for MCDS (CV = 0.18; range = 0.22–0.43 by population). Total cost of SCR and MCDS surveys was $98,326 and $147,324, respectively. While SCR efforts were more precise and less expensive overall, our MCDS approach reduced staff time by 64% (587 person-hours) and the number of survey days by 87% (64 days). Our methods using MCDS could be used in other similar study areas to estimate abundance of clustered large mammals at the broad scale, particularly in cases when land access for alternative ground-based surveys is limited.