River Otter Populations Research Articles

Recovering predators link aquatic and terrestrial ecosystems: River otters subsidize coyotes with carrion.

Despite global declines in the abundance and distribution of predators, conservation and reintroduction efforts are increasingly leading to predator recoveries. Unexpected species interactions and ecological consequences often arise when these predator recoveries occur. Here, we describe a novel species interaction in which coyotes (Canis latrans) kleptoparasitize North American river otters (Lontra canadensis) in a region of river otter recovery along the north-central California coast, USA. We describe eight observations of coyotes scavenging otter-killed waterbird carrion, including one observation in which river otters aggressively defended their prey from a coyote kleptoparasite. These observations highlight the importance of carrion provisioning as an overlooked pathway through which river otters facilitate nutrient subsidies to terrestrial scavengers. This behavior may have ecological implications including effects on the abundance, behavior, and health of scavengers as well as their interspecific interactions. We propose hypotheses and questions regarding these ecological consequences to guide further investigations into the cross-ecosystem impacts of recovering river otter populations.

Evidence of River Otter (<i>Lontra canadensis</i>) recolonization of Prince Edward Island, Canada

River Otter (Lontra canadensis) was extirpated from Prince Edward Island (PEI) in the early 1900s as a result of habitat loss and overexploitation. Although there were isolated and sporadic occurrences in PEI coastal and inland waters pre-1975, only anecdotal reports of tracks or sightings of the species had been documented in the 21st century, until an adult male otter was captured in a beaver trap in 2016. Since then, seven additional individuals have been collected opportunistically or as by-catch of beaver trapping, including an adult female and a kit (juvenile). Camera traps have also revealed what appears to be a family group in central PEI. A growing body of evidence strongly suggests a resident River Otter population on PEI. The island is separated from the mainland by the Northumberland Strait, which has a minimum width of 13 km of salt water. River Otters have naturally recolonized PEI by dispersing across the Northumberland Strait.

TOXOPLASMA GONDII PREVALENCE, PARTIAL GENOTYPES, AND SPATIAL VARIATION IN NORTH AMERICAN RIVER OTTERS (LONTRA CANADENSIS) IN THE UPPER PENINSULA OF MICHIGAN, USA.

Toxoplasma gondii is a ubiquitous parasitic protozoan that poses a health threat to wildlife and human health worldwide. Oocysts shed into the environment in felid host feces may persist for several years. Runoff from rainfall and snowmelt may carry the oocysts into waterways. Semiaquatic mammals such as the Northern American river otter (Lontra canadensis) are particularly at risk of exposure, as they may encounter infective stages in both terrestrial and aquatic environments. Despite this risk, only a small number of studies have examined the prevalence of T. gondii in US river otter populations. Tongue tissue was sampled from 124 otters from the Upper Peninsula of Michigan submitted by trappers to the Michigan Department of Natural Resources in the 2018-19 harvest season. Following DNA extraction, a portion of the B1 T. gondii gene was amplified with PCR. A subset of positive samples was genotyped for comparison with known T. gondii sequences. Of the 124 tongue samples, 35 (28%) were positive for T. gondii. Prevalence did not differ significantly between sexes or age classes across the entire study area. Most (53.8%) of the genotyped samples were type 4 (type 12), a genotype commonly found in North American wildlife. Genotypes 127 and 197 were also found. Three clusters of T. gondii prevalence were identified through SaTScan analysis, although they were not significant. When modeling prevalence of T. gondii with covariates at individual otter locations, the top three models included the presence of Sarcocystis, area of exotic plants, area of agriculture, and sex of the otter. Our results suggest that T. gondii is widespread in otter populations in the Upper Peninsula of Michigan.

Evaluating otter reintroduction outcomes using genetic spatial capture-recapture modified for dendritic networks.

Monitoring the demographics and genetics of reintroduced populations is critical to evaluating reintroduction success, but species ecology and the landscapes that they inhabit often present challenges for accurate assessments. If suitable habitats are restricted to hierarchical dendritic networks, such as river systems, animal movements are typically constrained and may violate assumptions of methods commonly used to estimate demographic parameters. Using genetic detection data collected via fecal sampling at latrines, we demonstrate applicability of the spatial capture–recapture (SCR) network distance function for estimating the size and density of a recently reintroduced North American river otter (Lontra canadensis) population in the Upper Rio Grande River dendritic network in the southwestern United States, and we also evaluated the genetic outcomes of using a small founder group (n = 33 otters) for reintroduction. Estimated population density was 0.23–0.28 otter/km, or 1 otter/3.57–4.35 km, with weak evidence of density increasing with northerly latitude (β = 0.33). Estimated population size was 83–104 total otters in 359 km of riverine dendritic network, which corresponded to average annual exponential population growth of 1.12–1.15/year since reintroduction. Growth was ≥40% lower than most reintroduced river otter populations and strong evidence of a founder effect existed 8–10 years post‐reintroduction, including 13–21% genetic diversity loss, 84%–87% genetic effective population size decline, and rapid divergence from the source population (F ST accumulation = 0.06/generation). Consequently, genetic restoration via translocation of additional otters from other populations may be necessary to mitigate deleterious genetic effects in this small, isolated population. Combined with non‐invasive genetic sampling, the SCR network distance approach is likely widely applicable to demogenetic assessments of both reintroduced and established populations of multiple mustelid species that inhabit aquatic dendritic networks, many of which are regionally or globally imperiled and may warrant reintroduction or augmentation efforts.

Metal contamination of river otters in North Carolina.

Aquatic apex predators are vulnerable to environmental contaminants due to biomagnification. North American river otter (Lontra canadensis) populations should be closely monitored across their range due to point and nonpoint pollution sources. Nonetheless, no information exists on environmental contaminants in the North Carolina otter population. Metals and metalloids occur naturally across the landscape, are essential for cellular function, and become toxic when concentrated unnaturally. We conducted our study across the three Furbearer Management Units (FMU) and 14 river basins of North Carolina. We determined the concentrations of arsenic, cadmium, calcium, cobalt, copper, iron, lead, magnesium, manganese, mercury, molybdenum, selenium, thallium, and zinc in liver and kidney samples from 317 otters harvested from 2009 to 2016. Arsenic, lead, and thallium samples were tested at levels below the limit of detection. With the exception of cadmium, we detected all other elements at higher levels in the liver compared with the kidney. Specifically, cadmium, cobalt, copper, iron, magnesium, manganese, mercury, molybdenum, and zinc levels differed by tissue type analyzed. Most element concentrations remained stable or increased with otter age. We detected higher levels of mercury and selenium in the Lower Pee Dee and Cape Fear river basins. River basins within the Mountain FMU were higher in cadmium, copper, iron, lead, and zinc, whereas the Coastal Plain FMU was lower in cobalt and manganese. None of the elements occurred at toxic levels. Our research establishes baseline concentration levels for North Carolina, which will benefit future monitoring efforts and provide insight into future changes in the otter population.

River Otter Status, Management, and Distribution in the United States: Evidence of Large-Scale Population Increase and Range Expansion

Abstract River otter Lontra canadensis populations in the United States have expanded during the past 50 y as a result of improvements in habitat quality and effective management programs implemented by state and federal agencies and native tribes. Periodic assessments of river otter status, population trends, and geographic distribution are needed to detect changes in populations, assess management approaches, and to identify and prioritize conservation efforts. We surveyed state wildlife agency experts to assess the current population and regulatory status of river otters in their jurisdictions. River otters were legally harvested in 40 states as of 2016. Twenty-two states reported increasing populations while 25 reported stable populations. Most states used multiple methods to monitor river otter populations including harvest-based surveys, presence–absence surveys, and empirically derived population model predictions; harvest-based surveys were the most commonly used monitoring approach. As populations have expanded, river otter reintroduction efforts have become less frequent; two additional states had conducted reintroductions since 1998 and only one state had conducted a reintroduction since 2010. We estimated that river otter distribution increased by 10.2% in the continental United States and by 13.7% in the contiguous United States during an 18-y period. Although populations may continue to increase numerically, river otters may be approaching their potential maximum geographic distribution in the United States.

Identity and distribution of the Nearctic otter (Lontra canadensis) at the Rio Conchos Basin, Chihuahua, Mexico

We have identified a scarcely known river otter population from the Upper Rio Conchos basin, northern Mexico, finding a well-established population of the Nearctic otter Lontra canadensis. A pioneer study of these otters at Rio San Pedro, a tributary of the Rio Conchos, described them as Neotropical otters, Lontra longicaudis; at that time, no specimens or photographs of these otters were available from the locality. Therefore, its taxonomic status remained unclear for various decades. Rio Conchos is one of the major tributaries of Rio Grande (Rio Bravo in Mexico) and its headwaters are located high in the Sierra Madre Occidental. A juvenile otter fur obtained from Rio San Pedro was compared to two furs of Neotropical otters from Oaxaca and Sonora, with the aim to compare the structure of primary hairs (PH) and secondary hairs (SH) in order to know their specific status. Camera traps were set-up at Rio San Pedro in Chihuahua and in Arroyo Bamochi (occupied by L. longicaudis) in Sonora in 2015 to compare individuals, population structure and occupation in both places. Two other places were surveyed to confirm the presence of river otters: Rio Conchos and Rio Santa Isabel. Based on hair characteristics (primary and secondary hairs from the juvenile) and photographic evidence from camera-traps, we confirm that otters from Rio San Pedro, belong to the Nearctic otter, Lontra canadensis. And presumably in other localities visited in the Concho’s river basin that also has presence of otters, such as Rio Santa Isabel and Rio Conchos. The population structure from Arroyo Bamochi and Rio San Pedro were similar in both areas, but the density of otters is higher at Arroyo Bamochi than at Rio San Pedro, even though there is no significant difference between the two sites. Specimens of river otters from Rio Grande basin have been identified as L. canadensis lataxina, Cuvier, 1823. The former distribution area of this species ranges from inland US across the Rio Grande basin in the Rocky Mountains, the Rio Pecos, further East, flowing south and southeast into the Gulf of Mexico. The finding reported here represents a major area occupied by this species, and a significant conservation issue for their protection in Mexico, as well as an indicator of the healthy conservation status of the upper Rio Conchos

Survival and Cause-Specific Mortality of River Otters in Southern Illinois

River otter (Lontra canadensis) populations in Illinois have rebounded considerably after >80 y of harvest protection and a successful re-introduction program. However, few studies of river otter survival ecology exist in the Midwestern U.S. We estimated survival rates and mortality causes for river otters in southern Illinois during 2014–2016. Thirty-four (16 F, 18 M) river otters were radio-marked and monitored for 8235 radio-days (x days/river otter = 242.2 ± 20.6 [se throughout]). Two males died (one trapped, one unknown) during the period of radio-telemetry monitoring. Annual survival rates were 1.0 ± 0.00 (lower confidence bound = 0.83) and 0.85 ± 0.09 for females and males, respectively, and similar between sexes (P = 0.19). Pooled-sex breeding season survival was 0.96 ± 0.04. Trapping was the primary cause of mortality during our study, and three river otters were killed after radio-telemetry ended: two were harvested by recreational trappers and one by a vehicle collision. These primary mortality sources (i.e., trapping and vehicle collisions) for river otters in southern Illinois were similar to those reported elsewhere, but the high survival we observed is similar to published estimates for unexploited populations. Our study provides useful demographic information for river otter management in lightly harvested populations in the Midwest.

Wildlife health indicators and mercury exposure: A case study of river otters (Lontra canadensis) in central British Columbia, Canada

Indicators of wildlife health are important elements of a comprehensive approach for assessing and monitoring trends of methyl mercury (MeHg) contamination in the environment. River otters (Lontra canadensis) have been used as a model species for toxicological studies on the effects of MeHg bioaccumulation due to their position as an apex predator in aquatic systems and sensitivity to environmental disturbance. Although laboratory studies suggest that sublethal MeHg exposure may have detrimental effects on wildlife, they are limited in their ability to reflect real world exposure and forecast population level effects. Few studies have identified the threshold at which MeHg exposure results in a population-level effect for wild populations of river otters in marine or fresh-water systems. We used a series of data sets collected over a 7-year period for river otter populations in central British Columbia, Canada, to assess mercury concentrations (river otter fur) and measurements of population status and health relative to a lake with an inactive and reclamated mercury mine along its shoreline (Pinchi Lake). We used a combination of remote cameras, marked individuals, hair snares, and scat counts/inventories to collect measurements of population status and health including: activity levels, population estimates, sex ratios, group sizes, litter sizes, behaviour, stress hormones, diet, and habitat quality. We found that mercury concentrations in river otter inhabiting Pinchi Lake were significantly higher than all other lakes in the study, and were also high relative to other areas in Canada and the United States. We did not, however, detect significant differences between the two lakes in many of the population parameters measured. We discuss the knowledge gaps and challenges of identifying the effects of MeHg for wild populations of mammals, determining sensitive and appropriate methods for measuring these effects, and the implications of our results for monitoring the impacts of natural resources activities. Detailed studies on population effects across a range of exposure and background conditions are required to address these data deficiencies. Typically, river otters are not included as monitoring species in environmental assessments even though their value as an indicator of anthropogenic contaminants has clearly been documented. We encourage inclusion of river otters in environmental assessments pre-, during -, and post-industrial activities as a measure of pollutant exposure and bioavailability as well as a critical first step in addressing knowledge gaps associated with contaminants and its effects on populations.

Assessment of river otter abundance following reintroduction

Context By the early 1900s, river otters (Lontra canadensis) were extirpated across large parts of their range in North America. Over the last several decades they have made a remarkable recovery through widespread reintroduction programs. River otters were reintroduced in Ohio, USA, between 1988 and 1993, and restricted and limited harvesting of this population began in 2005. While circumstantial evidence points to rapid population growth following the reintroduction, changes in population size over time is unknown. Aims We sought to model river otter population growth following reintroduction, and to assess the impact of harvesting. Methods We used empirical and literature-based data on river otter demographics in Ohio to estimate abundance from 1988–2008 using an age- and sex-specific stochastic Leslie matrix model. Additionally, we used statistical population reconstruction (SPR) methods to estimate population abundance of river otters in Ohio from 2006 to 2008. Results Our Leslie matrix model predicted a population size of 4115 (s.d. = 1169) in 2005, with a population growth rate (λ) of 1.28 in 2005. Using SPR methods we found that both trapper effort and initial population abundance influenced our population estimates from 2006 to 2008. If we assumed that river otter pelt price was an accurate index of trapper effort, and if the initial population was between 2000 and 4000, then we estimated the λ to be 1.27–1.31 in 2008 and the exponential rate to be 0.17–0.21 from 2006 to 2008. Conversely, if the river otter population in 2005 was 1000, then we estimated λ to be 1.20 in 2008 and the exponential rate to be 0.08 from 2006 to 2008. Conclusions The river otter population in Ohio appears to have had the potential to grow rapidly following reintroduction. The ultimate effect of the harvesting regime on population abundance, however, remains clouded by limited data availability and high variability. Implications The considerable uncertainty surrounding population estimates of river otters in Ohio under the harvesting regime was largely driven by lack of additional data. This uncertainty clouds our understanding of the status of river otters in Ohio, but a more robust, long-term monitoring effort would provide the data necessary to more precisely monitor the population.

Applying social and ecological approaches to evaluate factors influencing river otter (Lontra canadensis) visitation to fish-rearing facilities in Pennsylvania

In Pennsylvania the production of game and other fish species is a $1.6 billion industry, and loss from depredation can take a serious toll on fish stocks and associated revenues. Following a reintroduction project and natural expansion of native populations, river otters (Lontra canadensis) are now widely distributed throughout Pennsylvania. To determine occurrence and extent of depredation by river otters, we conducted telephone or mail surveys with 156 (80%) of Pennsylvania’s 196 fish-rearing facilities. River otters were reported in the vicinity of 50 (32%) facilities, of which 23 (46%) reported river otter visitation. Of the facilities that reported river otter visitation, most (87%) reported losing 100,000 fish annually, and private facilities were more likely to experience visitation by river otters. Our results demonstrate that the existence of river otter populations in Pennsylvania does not appear to be a significant economic threat to fish-rearing facilities and physical and landscape characteristics of the facilities are important in determining the likelihood of river otter visitation.

Discovery of 20,000 RAD–SNPs and development of a 52-SNP array for monitoring river otters

Many North American river otter (Lontra canadensis) populations are threatened or recovering but are difficult to study because they occur at low densities, it is difficult to visually identify individuals, and they inhabit aquatic environments that accelerate degradation of biological samples. Single nucleotide polymorphisms (SNPs) can improve our ability to monitor demographic and genetic parameters of difficult to study species. We used restriction site associated DNA (RAD) sequencing to discover 20,772 SNPs present in Montana, USA, river otter populations, including 14,512 loci that were also variable in at least one other population range-wide. After applying careful filtering criteria meant to minimize ascertainment bias and identify high quality, highly heterozygous (Ho = 0.2–0.50) SNPs, we developed and tested 52 independent SNP qPCR genotyping assays, including 41 that performed well with diluted DNA. The 41 loci provided high power for population assignment tests with only 1 misassignment (1.6 %) between closely neighboring populations. Our SNPs showed high power to differentiate individuals and assign them to population of origin, as well as strong concordance of genotypes from high and diluted concentrations of DNA, and between original RAD and the SNP qPCR array.

Modeling Population Growth and Response to Harvest for River Otters in Illinois

AbstractPopulation modeling is an invaluable tool for predicting wildlife population dynamics and the effects of management. I created a state‐space population model for unharvested river otters in the Illinois, Kaskaskia, and Wabash river basins in Illinois, and modeled future harvest at 5%, 10%, and 20% levels. River otter populations increased in the absence of harvest during 2000 – 2009 to 8,408 ± 1,934 individuals (λ = 1.11 ± 0.09). Harvest at 0%, 5%, 10%, and 20% levels resulted in continued population growth over time, with annual harvest numbers ranging from 446 – 1,786 in 2010 to 884 – 2,614 in 2014, depending on harvest scenario. I concluded that river otter populations in Illinois were thriving and capable of withstanding a regulated harvest.

Accumulation of PBDEs in an urban river otter population and an unusual finding of BDE-209

River otter scat samples (n=77) and blood samples (n=16) collected through non-invasive field collections and live-capture activities (November 2009 to October 2010) along the coastline of Southern Vancouver Island, near Victoria, British Columbia (BC) were analyzed for polybrominated diphenyl ethers (PBDEs). ∑PBDEs were highest in urbanized regions of Victoria Harbour for blood (1.12μg/g lipid weight) and scat (0.35μg/g lipid weight). A location effect between zones was confirmed statistically for blood but not for scat. Specific congeners with the highest concentrations overall were BDE-47 in blood samples (0.37μg/g lipid weight) and BDE-206 (0.18μg/g lipid weight) and BDE-47 (0.16μg/g lipid weight) in scat samples. There was also an unusual finding of extremely high levels of BDE-209 in 2 scat samples (163 and 956μg/g lipid weight). The patterns of select congeners (BDE 47, 99, 100, 153, 154) measured in blood and scat were found not to be significantly different (Chi-square Test, X2=21.08, DF=4, p=0003). The most prominent congeners within Victoria Harbour were BDE-47 for both blood (0.82mg/kg lipid weight) and scat (0.26mg/kg lipid weight) followed by BDE-206 (0.18μg/g lipid weight) and BDE-207 (0.10μg/g lipid weight) for scat only. Comparable levels of BDE-47 were reported across the study area whereas BDE 206 and 207 were only observed in Victoria Harbour (scat). Toxicological effects of PBDEs in rivers otters from Victoria, BC are still unknown however the predominance of BDE-47 could have negative implication as an endocrine disruptor.

Demographic and Reproductive Characteristics of Reintroduced Northern River Otters in Kentucky: Implications for Population Growth

Reproductive parameters and estimates of population size of northern river otters (Lontra canadensis) are poorly documented in southeastern United States. We examined the current population status of river otters in Kentucky, reintroduced in 1991 to 1994, by deriving demographic and reproductive characteristics from necropsies of river otter carcasses collected during harvests in Nov. through Feb., 2006–2009. We derived age distribution, sex ratio, pregnancy rate, and litter size of river otters and used these data to model future population growth of river otters in Kentucky. Data indicate 35.7% of female river otters in the yearling age class showed evidence of reproductive activity. The pregnancy rate (0.72) and average litter size [3.14 ± 1.46(sd)] of adult females was high compared with values reported for established populations of river otters elsewhere in eastern North America; consistent with an expanding and successfully recolonizing population. The population age distribution was skewed toward young age classes, with sex ratio of juvenile animals (1.58∶1.0) significantly favoring males. Models demonstrated the most plausible population growth estimates when using a 5% additive mortality factor, with extinction a possibility at lower published annual survivorship rates (below 0.73). Our data support a conservative harvest rate for sustained long-term management of river otters in Kentucky, especially for the eastern mountain region.

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.

Early Holocene glacial retreat isolated populations of river otters (Lontra canadensis) along the Alaskan coast

Pleistocene climatic oscillations have resulted in high rates of speciation. Lesser known are speciation events related to recent glacial retreats. During the early Holocene many Alaskan coastal glaciers receded, exposing much of the Kodiak Island Archipelago (KOD), the Kenai Peninsula, and Prince William Sound (PWS). Using fecal DNA analyses on samples collected in KOD, PWS, Kenai Fjords National Park (KEFJ), Katmai National Park and Preserve (KATM), and Vancouver Island, British Columbia (BC), we found isolation by distance to be an important mechanism for the divergence of populations of river otters ( Lontra canadensis (Schreber, 1777)) along the Pacific coast. Nonetheless, our results also demonstrated that KOD river otters appear to be more isolated genetically from their mainland conspecifics (approximately 50 km away), as river otters inhabiting PWS are from those in BC (over 2500 km away). In addition, KATM and KOD otters likely differentiated from one ancestral stock that inhabited the southwestern shores of Alaska during the Pleistocene and was isolated from more easterly populations by distance. The low genetic diversity among KOD river otters, compared with similar subpopulations in PWS, is likely the result of a founder effect and limited gene flow among the different islands within the Archipelago. Our observation that glacial retreat, rising sea levels, and formation of the Gulf of Alaska Coastal Current in the early Holocene likely led to divergence of populations of river otters, a highly mobile semiaquatic mammal, highlights the potential for future speciation events related to current climate change and ocean currents in coastal animal populations.

Fecal genotyping reveals demographic variation in river otters inhabiting a contaminated environment

AbstractThe deposition and accumulation of persistent contaminants into coastal systems can have lingering negative consequences for wildlife populations and their habitats. Using multi‐locus genotyping of non‐invasively collected feces, we assessed the effects of such pollution on reproduction, survival, genetic variability, and abundance of river otters (Lontra canadensis) along a gradient of urban–industrial development on southern Vancouver Island, British Columbia, Canada. Genetic analyses indicated a pattern consistent with small‐scale structuring, with individuals partitioned into 2 local subpopulations—those identified in the contaminated harbors of southern Vancouver Island and points west (Colwood/Harbors), and those inhabiting uncontaminated habitat east of the harbors (Oak Bay). Genetic and demographic analyses for the 2 clusters provide strong support for the conclusion that, despite contamination concerns, Colwood/Harbors river otters exhibited acceptable levels of survival and successfully reproduced (i.e., high levels of relatedness, high self‐recruitment, and high emigration). However, our data indicate that the Colwood/Harbors area constitutes lower quality habitat supporting lower densities of otters, especially during winter, and excess individuals produced in that region emigrate to other areas. Immigration into Colwood/Harbors, however, seems limited, possibly because of behavioral aversion of non‐habituated otters to anthropogenic disturbance associated with the harbors and limited optimal otter habitat. Our findings suggest that the effects of chronic contaminant exposure at the population level may be inadvertently mitigated through the behavioral decisions of individuals to avoid poor quality habitats. We conclude that populations of river otters can persist in and around locally contaminated sites if relatively less disturbed and contaminated habitats remain in the vicinity of the affected areas. © 2012 The Wildlife Society.

The role of demographic and environmental variables on the presence of snow tracks by river otters Lontra canadensis

Unknown causes of heterogeneity in the presence or detection of wildlife tracks and other signs could bias interpretations of population indices derived from surveys. These surveys can be the basis of management decisions for populations of wildlife. However, we know very little about potential biases affecting the presence of tracks in the landscape. We used an Information Theoretic Model Comparison approach to investigate the role of environmental, demographic and behavioural influences on the presence of river otter Lontra canadensis snow tracks in central British Columbia, Canada, from January to March 2008. We repeatedly located five radio‐collared otters and recorded the presence of tracks within an estimated 100‐m radius of the otter's location. We used combinations of five variables to develop logistic regression models that predicted the presence or absence of snow tracks when the location of otters was known. The presence of snow tracks was best described by a model containing covariates for gender and movement distance per day. The probability of detecting snow tracks was higher for male compared to female otters and was positively related to the daily movement distance of the individual animal. Track‐sign heterogeneity among individuals could bias surveys that assess and monitor river otter populations, and should be incorporated into the design and interpretation of track surveys.

Spatio-Temporal Variations in Age Structures of a Partially Re-established Population of Northern River Otters (Lontra canadensis)

Examination of age structures and sex ratios is useful in the management of northern river otters (Lontra canadensis) and other furbearers. Reintroductions and subsequent recolonizations of river otters have been well documented, but changes in demographics between expanding and established populations have not been observed. As a result of reintroduction efforts, immigration from Arkansas and northeastern Texas, and other efforts, river otters have become partially reestablished throughout eastern and central Oklahoma. Our objective was to examine age structures of river otters in Oklahoma and identify trends that relate to space (watersheds, county) and time (USDA Animal and Plant Health Inspection Service county trapping records). We predicted that river otters in western areas of the state were younger than river otters occurring farther east. From 2005–2007, we obtained salvaged river otter carcasses from federal and state agencies, and we live-captured other river otters using leg hold traps. Seventy-two river otters were sampled. Overall, sex ratios were skewed toward females (1F∶0.8M), but they did not differ among spatiotemporal scales examined. Teeth were removed from salvaged and live-captured river otters (n = 63) for aging. One-year old river otters represented the largest age class (30.2%). Proportion of juveniles (<1 y old) in Oklahoma (19.0%) was less than other states. Mean age of river otters decreased from east-to-west in the Arkansas River and its tributaries. Mean age of river otters differed between the Canadian River Watershed (0.8 y) and the Arkansas River Watershed (2.9 y) and the Canadian River Watershed and the Red River Watershed (2.4 y). Proportion of juveniles did not differ among spatiotemporal scales examined. Similar to age structure variations in other mammalian carnivores, colonizing or growing western populations of river otters in Oklahoma contained younger ages than more established eastern populations.