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.

Evaluating river otter demography using noninvasive genetic methods

The Asian small-clawed otter is the smallest among the 13 extant species of otters. It has a large distribution range extending from India in South Asia through Southeast Asia up to Taiwan and Philippines in the east and Southern China in the north. It is considered ‘Vulnerable’ due to habitat loss and degradation, depletion of prey species and exploitation. Being adapted to live in shallow streams and water bodies, they are more vulnerable to modification of these habitats by anthropogenic as well as climate change impacts. This paper summarizes the state of knowledge on the biology and ecology of this little known species. Over the years, the IUCN SSC Otter Specialist Group has developed a cadre of biologist across Asia to conduct field surveys and has popularized otter conservation by promoting otter as the ambassador of wetlands. However, concerted effort is needed for its long-term survival. Policy based action, research on factors affecting survival, habitat-based actions on creation and where required expansion of protected areas and communication and awareness building among local communities are suggested.

Biology and Ecology of Asian Small-Clawed Otter Aonyx cinereus (Illiger, 1815): A Review

Environmental DNA (eDNA) is an effective tool for the detection of elusive or low-density aquatic organisms. However, it has infrequently been applied to mammalian species. North American river otters (Lontra canadensis) are both broad ranging and semi-aquatic, making them an ideal candidate for examining the uses of eDNA for detection of mammals. We developed a species-specific assay for detection of North American river otters using eDNA. The assay was tested for specificity against closely-related mustelids native to western North America, and was validated through testing environmental samples.

https://www.fs.fed.us/rm/pubs_journals/2016/rmrs_2016_padgett_stewart_t001.pdf

An eDNA assay for river otter detection: a tool for surveying a semi-aquatic mammal

Populations of North American river otters (Lontra canadensis) declined throughout large portions of the continent during the early 1900s due to habitat degradation and unregulated trapping. River otters had been extirpated in North Dakota (ND), but the Red River Valley has since been recolonized, with potential source populations including the neighboring states of Minnesota or South Dakota, or the Canadian province of Manitoba (MB). We genotyped 9 microsatellite loci in 121 samples to determine the source population of river otters in the Red River Valley of ND, as well as to assess population structure and diversity of river otters in central North America. Overall, genetic diversity was high, with an average observed heterozygosity of 0.58. Genetic differentiation was low (F ST < 0.05) between river otters in ND and those of Minnesota, suggesting that eastern ND was recolonized by river otters from Minnesota. River otters from MB were genetically distinct from all other sampled populations. Low genetic differentiation (F ST = 0.044) between South Dakota and Louisiana (LA) suggested that reintroductions using LA stock were successful. The genetic distinctiveness of river otters from different geographic regions should be considered when deciding on source populations for future translocations.

/pdf/impact-of-population-expansion-on-genetic-diversity-and-1g5arlzv38.pdf

Impact of Population Expansion on Genetic Diversity and Structure of River Otters (Lontra canadensis) in Central North America

During 2006, we conducted riparian surveys to detect river otter Lontra canadensis latrines at 15 bridge-suites along riverine habitats in southwestern Pennsylvania and western Maryland, USA. We defined a bridge-suite as consisting of survey locations at the bridge, a random site and a site chosen by application of a Pattern Recognition Model developed for predicting the location of latrines, with each survey location consisting of both shorelines along a 200-m section of the river. We used occupancy modeling to assess the influence of the continuous covariate SiteScore (a probability derived from Pattern Recognition modeling, with higher scores predicting habitat conditions where river otters are most likely to establish latrines). We also included two categorical covariates with the modeling, each with three factor levels: SiteType (consisting of the three survey locations within a bridge-suite: Bridge, Random and Select, chosen based on having the highest SiteScore among non-Bridge sites within a bridg...

https://bioone.org/journals/Wildlife-Biology/volume-18/issue-3/11-042/Detecting-river-otter-Lontra-canadensis-latrines-near-bridges--does/10.2981/11-042.pdf

Detecting river otter Lontra canadensis latrines near bridges: does habitat and season influence survey success?

Riparian sign surveys near bridge crossings are commonly used to detect the presence of river otters. However, the efficacy of using such surveys for determining river otter presence has not been evaluated relative to habitat conditions. We conducted surveys to detect latrines (locations where scats are deposited in riparian areas) from reintroduced populations of river otters at 26 bridge-suites in northern Pennsylvania. A bridge-suite consisted of a bridge site, a random site and a selected site (i.e., high quality site based on several habitat variables), <2.5 km upstream or downstream from the bridge. Sites consisted of both shorelines along a 200-m section of stream or river. Site quality was determined by applying a modified Pattern Recognition model (PATREC) previously developed to provide a probabilistic assessment for predicting the occurrence of river otter latrines based on the presence or absence of certain riparian and riverine habitat features. Sites were surveyed in fall 2003 and s...

Emily H. Just

Papers

The Influence of Habitat Quality on the Detection of River Otter (Lontra canadensis) Latrines Near Bridges