Evaluating River Otter Demography Using Noninvasive Genetic Methods

The decline in river otter (Lontra canadensis) populations during the late nineteenth and early twentieth centuries throughout North America has led to protective status and strict harvest regulations. Despite sustained interest in protecting river otters, relatively few contemporary studies have evaluated the current status of populations, especially in California. An effective way to estimate river otter population sizes and facilitate monitoring is with noninvasive genetic methods. Our objective was to establish baseline demographic information for an understudied river otter population in northern California by estimating river otter abundance using noninvasive genetic sampling, supplemented with data obtained from an observation-based citizen science project focusing on river otters. We extracted DNA from scat and genotyped samples at 6 microsatellite loci. We used Program MARK to build mark-recapture models to estimate river otter abundance and pooled visual observations from a citizen science project maintained in Humboldt County, California to supplement population estimates with information regarding pups and group size. Between 41 and 44 river otters were in the study area based on noninvasive genetic samples, and group sizes ranged 1–7 or 2–12 based on observational and genetic data, respectively. The Humboldt Bay region had a high density of river otters (0.93 otters/km) as compared to other coastal systems; resource attributes of Humboldt Bay could contribute to this difference. Results reported herein demonstrate methods appropriate for establishing baseline river otter demographics. 2013 The Wildlife Society.