Funding by the Pennsylvania Game Commission

River otters (Lontra canadensis) are of interest to wildlife managers because of their role as tertiary consumers in riparian ecosystems, and economic significance as furbearers. River otters are difficult to monitor because of their cryptic behavior, however the use of non-invasive genetic methods targeting scat has been shown to be an effective monitoring method for populations of river otter. River otters are of particular interest in Pennsylvania because of their history of near-extirpation, and their subsequent reintroduction and spread across the state over the past 30 years. We used non-invasive genetic sampling with a capture-recapture framework to estimate population size and density in northeastern Pennsylvania. From January to April 2013 and 2014, we collected scat samples from latrines on lakes and rivers across seven counties, with sites revisited at least three times. We used primers designed for eleven polymorphic microsatellites in two multiplex PCR reactions to obtain genotypes for DNA extracted from scat samples. A consensus genotype at a microsatellite loci was conditional upon two identical heterozygous genotypes for two or greater runs, and at least three identical runs for a homozygote genotype. Of the 629 samples collected, our sample success rate for each month, with success demonstrated by ability to reach a consensus genotype at seven or greater loci for a sample, was 51.2% in January (80/156), 59.9% in February (109/182), and 60.7% in March (153/252). We were able to identify 144 unique individuals, with the number of observations per individual ranging from one to seven.