Estimating Abundance and Survival in the Endangered Point Arena Mountain Beaver Using Noninvasive Genetic Methods

Abstract

The Point Arena mountain beaver (Aplodontia rufa nigra) is federally listed as an endangered subspecies that is restricted to a small geographic range in coastal Mendocino County, California. Management of this imperiled taxon requires accurate information on its demography and vital rates. We developed noninvasive survey methods, using hair snares to sample DNA and to estimate abundance and survival at two sites, Kinney Beach and Alder Creek, within Manchester State Park. We extracted DNA and genotyped 371 hair samples resulting in the identification of a total of 54 individuals during annual sampling from 2006–2009. Estimated population numbers were small, ranging from 9–18 individuals at Kinney Beach and 14–18 individuals at Alder Creek. Neither location demonstrated a trend in abundance over the 4-year sample period. There was weak support (evidence ratio 2.15) for higher apparent survival probabilities at Alder Creek (0.75) than Kinney Beach (0.59) and no support for time or site effects on recruitment. Recruitment ranged from 0.25 to 0.46 and was highest during the same interval (2007–2008) at both locations. The time series of estimates from 2006–2009 does not suggest that abundance at either study site is declining; while reassuring, concern still remains due to low total numbers at this, one of the few protected sites for this endangered subspecies.