River Otter Populations Research Articles

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

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 spring 2004. Latrines were detected at 19 (73.1%) of the 26 bridge-suites. Of these 19 bridge-suites, 17 (65.3%) were positive for latrines in spring, 15 (57.7%) in the fall and 13 (50.0%) in both seasons. Among the 78 survey sites (i.e., 3 sites per bridge-suite), 32 (41.0%) were positive for latrines [21 sites (26.9%) in spring and 22 sites (28.2%) sites in fall]. Repeated measures logistic regression was used to assess the influence of the covariates season (spring or fall), type of site (i.e., site type: bridge, random or selected) and quality of site (site score) on the probability of detecting latrines. Two models were useful in describing the occurrence of a positive site (i.e., a site with ≥1 latrine), and both included site type as a variable. The odds of a selected site being positive ranged from 7.8 to 9.3 times the odds of random or bridge sites being positive. We concluded that monitoring the presence of river otters based on searching for latrines at bridge or random sites was considerably less effective than by using the a priori selection of surveys areas based on riparian habitat features.

Age-Specific Reproductive Rates of River Otters in Southern Missouri

Abstract Sustained reproduction is critical for successful restoration of extirpated populations. Evaluating success of restoration efforts requires an understanding of reproductive capacity in such populations. We examined age-specific reproductive capacity of a Lontra canadensis (River Otter) population in southern Missouri that was the focus of intense restoration efforts in the 1980s and early 1990s. We collected carcasses of 387 legally harvested female Otters from 1996–1999. Otters ranged in age from 1–11 years, with juveniles ( 1 yr) Otters. Our results indicate that the southern Missouri River Otter population has one of the greatest recorded potential reproductive capacities for that species.

River otter population size estimation using noninvasive latrine surveys

AbstractAcross much of North America, river otter (Lontra canadensis) populations were extirpated or greatly reduced by the early 20th century. More recently, reintroductions have resulted in restored populations and the recommencement of managed trapping. Perhaps the best example of these river otter reintroductions occurred in Missouri, regarded as one of the most successful carnivore recovery programs in history. However, abundance estimates for river otter populations are difficult to obtain and often contentious when used to underpin management activities. We assessed the value of latrine site monitoring as a mechanism for quantifying river otter abundance. Analyses of fecal DNA to identify individual animals may result in an improved population estimate and have been used for a variety of mammal species. We optimized laboratory protocols, redesigned existing microsatellite primers, and calculated genotyping error rates to enhance genotyping success for a large quantity of river otter scat samples. We also developed a method for molecular sexing. We then extracted DNA from 1,421 scat samples and anal sac secretions (anal jelly) collected during latrine site counts along 22–34‐km stretches representing 8–77% of 8 rivers in southern Missouri in 2009. Error rates were low for the redesigned microsatellites. We obtained genotypes at 7–10 microsatellite loci for 24% of samples, observing highest success for anal jelly samples (71%) and lowest for fresh samples (collected within 1 day of defecation). We identified 63 otters (41 M, 22 F) in the 8 rivers, ranging from 2 to 14 otters per river. Analyses using program CAPWIRE resulted in population estimates similar to the minimum genotyping estimate. Density estimates averaged 0.24 otters/km. We used linear regression to develop and contrast models predicting population size based on latrine site and scat count indices, which are easily collected in the field. Population size was best predicted by a combination of scats per latrine and latrines per kilometer. Our results provide methodological approaches to guide wildlife managers seeking to initiate similar river otter fecal genotyping studies, as well as to estimate and monitor river otter population sizes. © 2011 The Wildlife Society.

Deciphering Ecological Barriers to North American River Otter (Lontra canadensis) Gene Flow in the Louisiana Landscape

For North American river otters (Lontra canadensis) in Louisiana, statewide distribution, availability of aquatic habitats, and the absence of physical barriers to dispersal might suggest that they exist as a large, panmictic population. However, the wide variety of habitat types in this region, and the dynamic nature of these habitats over time, could potentially structure river otter populations in accordance with cryptic landscape features. Recently developed landscape genetic models offer a spatially explicit approach that could be useful in identifying potential barriers to the movement of river otters through the dynamic aquatic landscape of Louisiana. We used georeferenced multilocus microsatellite genotypes in spatially implicit (STRUCTURE) and spatially explicit (GENELAND) models to characterize patterns of landscape genetic structure. All models identified 3 subpopulations of river otters in Louisiana, corresponding to Inland, Atchafalaya River, and Mississippi River regions. Variation in breeding seasonality, brought about by variation in prey abundance between inland and coastal populations, may have contributed to genetic differentiation among populations. It is also possible that the genetic discontinuities we observed indicate a correlation between otter distribution and access to freshwater. Regardless of the mechanism, it is likely that any genetic differentiation among subpopulations is exacerbated by relatively poor dispersal.

Habitat use and spatial behaviour of the endangered Southern river otter ( Lontra provocax) in riparian habitats of Chile: Conservation implications

The spatial behaviour of 10 Southern river otters Lontra provocax was analysed using radio-tracking data collected in the Queule River, Southern Chile. The estimated otter density was 0.25 individuals km −1. Females with cubs and adult otters displaying mating behaviours were the only social group recorded. Studied otters were solitary and observed behaviour patterns suggest an intrasexual territoriality. No home range overlap among males existed while an average of 33% and 87% home range overlapped among females and between sexes, respectively. In the situation of core areas, only one case of overlapping between an adult male and an adult female was observed. Average home range and core area lengths were 11.3 km and 0.9 km, respectively. Otters used rivers more frequently than expected, whereas they avoided small streams. Low intensity livestock farming, without canalization of watercourses and riparian vegetation extraction practices, seems compatible with the presence of Southern river otter populations since the spatial behaviour of the studied otters was not affected under these circumstances. Based on the present official reserve sizes and distribution within the country, and also the increase of variant anthropogenic land uses outside these areas that result with consequent habitat loss and deterioration, we strongly recommend considering the importance of spatial dimension in quantity and quality habitats in further conservation planning for the Southern river otter using an integrated catchment management.

Hair Sampling Techniques for River Otters

ABSTRACT River otter (Lontra canadensis) populations have been difficult to monitor and information on densities is lacking throughout their range. To obtain DNA‐based population estimates of river otters we developed 2 traps to capture hair; a modified body‐snare and a modified foot‐hold trap. Of 82 traps activated 77 captured hairs (94%). Traps snagged 3–20 guard hairs per capture. Our capture rates of otter hair ranged from one capture per 3.6 trap nights to one capture per 156.6 trap‐nights. Our traps provide an effective, noninvasive technique for obtaining hair DNA from individual river otters.

Use of Shelters by the Neotropical River Otter (Lontra longicaudis) in an Atlantic Forest Stream, Southeastern Brazil

Use of shelters by the Neotropical river otter (Lontra longicaudis) was studied in a head-water stream of the Atlantic Forest, southeastern Brazil, during 1994. L. longicaudis used almost all types of natural cavities available along river banks, and they excavated burrows or found shelter in dense grass. Two large caves were used as shelters and also to raise young. The degree of conservation of the forest and human disturbance around the shelters did not influence use by otters. However, otters used shelters located higher on the river banks more frequently, probably because they were less vulnerable to flooding. Considering all shelters found during 1 year, shelters of L. longicaudis were distributed at random along the stream, and scent marks were not concentrated around them. Number of shelters in use per month was constant throughout the year, indicating that this can be used to monitor populations of river otters.

Genetic Variation among Populations of River Otters in North America: Considerations for Reintroduction Projects

Horizontal starch gel electrophoresis was used to assess variability at 23 presumptive gene loci of 732 river otters obtained from fur-trappers in 18 states and three Canadian provinces. States and provinces providing otters were sorted into eight geographic regions for genetic comparisons. Multilocus heterozygosity and polymorphism ranged from 0.018 to 0.032 and 0.044 to 0.087, respectively. One locus, esterase-2, (EST-2) demonstrated a high level of polymorphism throughout all regions. Malate dehydrogenase-1 (MDH-1) was polymorphic throughout the Mississippi drainage but not elsewhere. Heterozygosity, occurrence of rare alleles, and mean number of alleles per locus were associated positively with estimated population sizes. Average heterozygosity and polymorphism values for otters within regions were lower than overall averages reported for mammals but similar to the range of those observed in other mammalian carnivores. Patterns of gene flow suggested by the distribution of polymorphism at the MDH-1 locus do not concur with the current taxonomic classification of river otters. Levels of genetic variation detected in this investigation present a positive outlook for the maintenance of genetic diversity in river otter populations, if sound management principles are applied for reintroductions.

Wetland Use by River Otters in Massachusetts

Wetland loss and vegetational change in the northeastern United States could affect river otter (Lutra canadensis) populations, but few studies have addressed river otter use of wetlands in this region. We documented wetland types used by river otters during 1988-89 in central Massachusetts by using latrine revisitation rates as an index to habitat use. We determined whether use varied by season or wetland type by comparing revisitation rates of river otters at 86-134 otter latrines located in different wetland types. We also characterized shoreline habitats at latrines by comparing habitat features at 132 river otter latrines with nearby, unused shoreline sites, using uni- and multivariate techniques