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

The 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.     

A Pragmatic Approach for Determining Otter Distribution from Disparate Occurrence Records

Opportunistic records of animal occurrence may be problematic for inferring species distribution and habitat requirements because of unknown and uncontrolled sources of sampling variance. In this study, we used occurrence records for river otters (Lontra canadensis) derived from sign surveys, road kills, trapper bycatch, and opportunistic sightings (n = 185 records collected 2001–2012) to assess the potential distribution and habitat relationships of otters across central and western New York, USA. To mitigate for obvious observation biases, we standardized observation intensity across regions a priori and restricted inference to readily accessible areas (i.e., ≤700 m from the nearest road). Model selection, and the direction of covariate effects, proved robust to these sampling biases although effect sizes varied −7.1% to +48.0% after bias correction, with the coefficient for the proportion of available shoreline being the most unstable. Ultimately, the top bias-corrected model proved a reliable index for otter probability of occurrence given a strong, positive, and linear relationship with a withheld set of standardized survey records for otters collected in winter 2016–2017 (n = 57; R² = 0.90). This model indicated that approximately 20% of the study area represented high probability of otter occurrence. We demonstrated that reliable inference on wildlife habitat requirements can be obtained from disparate records of animal occurrence provided that data biases are known and effectively mitigated. © 2020 The Wildlife Society.     

A Comparison of the diet and distribution of southern river otter (Lutra provocax) and mink (Mustela vison) in Southern Chile

In Chile, between latitudes 39S and 4330'S, southern river otter ( Lutra provocax ) and introduced mink ( Mustela vison ) scats were collected. Mink sign was recorded in 29% of the aquatic habitat where otter sign was found. Sixty-eight per cent of mink scats were collected at otter rest sites. A significant difference between the diets and low percentage of habitat use overlap of the two species (5-22%) suggest that, in Chile, river otter and mink coexist with little competition for space or food. There are no data supporting a relationship between the introduction of mink and the decline of southern river otters.     

Influence of occupation history and habitat on Washington sea otter diet

Habitat characteristics are primary determinants of nearshore marine communities. However, biological drivers like predation can also be important for community composition. Sea otters (Enhydra lutris ssp.) are a salient example of a keystone species exerting top‐down control on ecosystem community structure. The translocation and subsequent population growth and range expansion of the northern sea otter (Enhydra lutris kenyoni) in Washington State over the last five decades has created a spatio‐temporal gradient in sea otter occupation time and density, and acts as a natural experiment to quantify how sea otter population status and habitat type influence sea otter diet. We collected focal observations of sea otters foraging at sites across the gradient in varying habitat types between 2010 and 2017. We quantified sea otter diet composition and diversity, and long‐term rates of energy gain across the gradient. We found that sea otter diet diversity was positively correlated with cumulative sea otter density, while rate of energy gain was negatively correlated with cumulative density. Additionally, we found that habitat type explained 1.77 times more variance in sea otter diet composition than sea otter cumulative density. Long‐term diet studies can provide a broader picture of sea otter population status in Washington State.     

Habitat correlates of the Eurasian otter Lutra lutra recolonizing Central Poland

The increase in Eurasian otter Lutra lutra populations in their natural range and recolonization processes are recently observed in several European countries. We address the process of otter recolonization and habitat utilization in Central Poland over 14 years. Field surveys in 1998 and 2007 documented increase in occurrence of the species. The frequency of positive sites denoted 15 % in 1993, 38 % in 1998, and 89 % in 2007. Otter occurrence at study sites was positively affected by river width while negatively affected by presence of buildings at the site and river regulation. During the most intensive colonization process in the 1990s, the habitat preferences of the otter did not change. However, the sites inhabited by otters after 1998 were characterized by lower river width and tree cover and were more often located on regulated river sections, suggesting change in habitat tolerance during expansion. The otter abundance in transformed habitats is a result of increasing population numbers and the necessity to inhabit suboptimal sections of watercourses. Thus, it seems that presence–absence data for otter populations cannot be considered a reliable indicator of habitat quality, being depended of the population density.     

完达山东部欧亚水獭种群数量及出现频次影响因素

水獭作为淡水生态系统健康的指示种和旗舰物种,在维持水生生态系统平衡与稳定中发挥着重要作用。然而目前对于完达山东部地区水獭种群数量、分布及其生境选择的影响因素的研究较为匮乏,严重影响了对该物种的野外保护与管理工作。于2021年12月至2022年4月冬季河流封冻期,采用沿河随机样线调查和红外相机监测相结合的方法对完达山东部地区8条主河和23条支流内的欧亚水獭(Lutra lutra)种群数量、分布现状进行了调查,并利用广义可加模型探究水獭出现频次与环境因子的关系。研究结果表明:(1)欧亚水獭在完达山东部水獭种群数量为571-661只,水獭种群密度为沿河(0.5559±0.2898)只/km,呈现中间高,四周低的趋势;(2)环境因子对水獭出现频次影响分析表明,河流深度、距农田距离、距居民区距离和距道路距离是影响水獭出现频次的关键因素。水獭出现频次与河流深度(0-40 cm)呈线性正相关,当河流深度达到40-50 cm时,水獭出现频次最高,之后随着河流深度的增加,出现频次降低;水獭出现频次与距农田距离(0-1.5 km)呈非线性正相关,在距农田距离为1.5-2 km范围内,水獭出现频次最高,之后降低;水獭出现频次与距居民区距离呈线性正相关;水獭出现频次与距道路距离呈非线性关系,当距离>7 km时,二者之间呈现为正相关,反之呈现为负相关。因此,水獭选择栖息地偏向于河流深(40-50 cm),远离农田(1.5-2 km)、居民区和道路(>7 km)的水域。研究为完达山东部欧亚水獭物种保护提供了基础数据和理论依据,建议通过河岸土地覆盖类型的管理、在河岸周围建立森林缓冲区及加强水獭保护宣传力度等措施实现对水獭物种及其栖息地的维持和保护。     

River Otter Latrine Site Selection in Arid Habitats of Western Colorado,USA

ABSTRACT River otters (Lontra canadensis) select specific habitat features when establishing latrines, but no studies have described latrine features in arid and semiarid environments. We developed a model describing those habitat features that influence otter latrine site selection on rivers in arid and semiarid watersheds of western Colorado, USA. River otters selected latrine sites with the presence of beaver (Castor canadensis) activity, large prominent rocks, adjacent to deeper water, with shading over the site, and rock or cliff overstory. Our model provides a robust predictive tool for identifying river otter latrine sites in arid environments of southwestern North America.     

Are latrine sites an accurate predictor of seasonal habitat selection by river otters (<Emphasis Type="Italic">Lontra canadensis</Emphasis>) in freshwater systems?

Temporal variation in the availability of food resources is a likely driving factor influencing the distribution and habitat use of river otters (Lontra canadensis). Although latrine sites are commonly used to determine habitat selection, it is unclear if latrine sites are an accurate predictor or even a useful indicator of the seasonal habitat use and distribution of river otters. We apply resource selection functions (RSF) to both latrine and telemetry locations to investigate whether latrine sites identified along lake shorelines during the ice-free season are appropriate predictors of otter habitat selection along shorelines during the ice-free and ice-cover seasons in central British Columbia, Canada. We found that the top models describing otter latrine sites and telemetry locations during the ice-free season were similar. The top RSF models and associated coefficients for the ice-cover season differed, however, with otter presence being positively influenced by shallower water depths. For the spatial extrapolation of averaged RSF coefficients, we found that 21.4 and 69.3 % of predicted latrine habitat along lake shorelines overlapped with ice-cover and ice-free habitat generated from telemetry locations, respectively. The location and activity at latrine sites appear to be a useful method for monitoring otter distribution and habitat use during the ice-free, but not during the ice-cover season. The results of our RSF analyses as well as home range measurements of otters in our study area suggest that cold temperatures and ice cover may be a limiting factor for the distribution of otter populations at northern latitudes.     

Hand‐rearing and rehabilitation of orphaned wild giant otters,Pteronura brasiliensis,on the Rupununi river,Guyana, South America

From 1985–2003, 34 orphaned giant otters, Pteronura brasiliensis, (22 males, 12 females) were hand raised for eventual return to the wild at The Karanambu Cattle Company Limited Ranch (Karanambu), on the Rupununi River, Guyana, South America. The orphans ranged in age from 2 weeks to 9 months old; most were 8–10‐week‐old cubs. Feeding, housing, exercising, veterinary care, and rehabilitation protocols for young giant otters were developed during this period. Six cubs died during hand‐rearing; of these, four died from illness or injury, and two were killed, one by a caiman and one by another orphaned otter. Of 34 giant otters brought to Karanambu, 28 (82%) were reared successfully to an age and condition suitable for rehabilitation, and 18 (53%) returned to the wild. Ten otters survived hand‐rearing but died either before or during the process of rehabilitation. These hand‐reared giant otters were killed by people (3 known, 2 presumed) or other giant otters (5), including one male otter that remained at Karanambu for several years. During rehabilitation, young giant otters chose to spend increasing amounts of time on the Rupununi River away from human care, often interacting with wild giant otters. Although long‐term monitoring was not possible, Karanambu staff observed most (15 of 18) of the rehabilitated otters repeatedly, for as long as 4 years after their return to the river. The giant otter rehabilitation program at Karanambu generated new knowledge about this species, and offered visitors the opportunity to observe them. Zoo Biol 24:153–167, 2005. © 2005 Wiley‐Liss, Inc.     

River otter population size estimation using noninvasive latrine surveys

Across 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.     

Feeding habits of the otter and the American mink in Bialowieza Primeval Forest (Poland) compared to other Eurasian populations

Diets of the otter Lutra lutra and the American mink Mustela vison were studied by scat analysis on five woodland rivers and streams in eastern Poland. Fish constituted 51% of food biomass consumed by otters in spring‐summer and 40% in autumn‐winter, with common fish (perch Perca fluviatilis, pike Esox lucius, and roach Rutilus rutilus) being captured most frequently by the otters. Amphibians (mainly Rana temporaria, which also dominated in the living community) made up 34% of otters’ food biomass in spring‐summer and 58% in autumn‐winter. American mink relied on three prey groups: fish (40% in spring‐summer, and 10% in autumn‐winter), frogs (32% and 51%, respectively), and small mammals (21% and 36%). Out of available Micromammalia, mink strongly selected the root vole Microtus oeconomus. The cold season diet of both otter and mink depended on river size. On small rivers with forested valleys, otters and mink fed nearly exclusively on amphibians (72–90% of food biomass). With size of a river increasing and riverside habitat becoming more open (sedge and reed marshes instead of forests), otters shifted to catching predominantly fish (up to 76% in diet) and mink to preying on small mammals (up to 65% in diet).
Review of literature on otter and mink in Eurasia showed that their diets did not change with latitude (as indicators of climate severity and duration of water freezing) but they depended on habitats. In otter diet, the mean share of fish declined from 94% (SE 1.7) on sea shores, to 71% (SE 2.9) on lakes and fish ponds, to 64% (SE 2.8) on rivers and streams. The roles of amphibians and crustaceans increased in the same gradient (from 0 to 15%, and from 3 to 7%, respectively). On inland waters, the abundance of crayfish was the essential factor differentiating otters’ diet composition. In Eurasia, the staple food types of American mink on rivers and streams were fish (on average, 27% in diet, SE 3.9), mammals (30%, SE 5.0), and amphibians (17%, SE 4.8), whereas on lakes and ponds mink fed predominantly on birds (on average, 33% in diet, SE 10.1) and fish (28%, SE 9.5). In the Palaearctic region, over a wide gradient of habitats, otters appeared strongly specialised on prey taken from water, whereas American mink was a typical generalist capable of utilising several prey groups originating from both water and land.     

Understanding the inter-specific dynamics of two co-existing predators in the Tierra del Fuego Archipelago: the native southern river otter and the exotic American mink

Knowledge about interactions between endangered native southern river otters (Lontra provocax) and introduced American mink (Neovison vison) is essential for effective management of both species. We evaluated competition for spatial and trophic niches between otter and mink in overlapping and non-overlapping areas, comparing distribution, habitat preference, diet and mink marking behavior. We surveyed otter and mink signs along 250 km of Beagle Channel coastline. Habitat suitability models were constructed based on species presence/absence and habitat characteristics, using generalized linear models. Feces were collected for diet analyses. Otters used forested coasts with 12°–32° shoreline slope and without human influence, and our evidence suggests they were not affected by mink presence. Mink preferred forested and shrubland coasts with 10°–28° shoreline slope. Neither human influence nor otter presence affected mink habitat occupation, but in the presence of otters, mink left fewer signs. Otters consumed more aquatic prey than mink, and mink modified their diet in the presence of otters, consuming more exotic small terrestrial mammals and less fish as well as shifting to smaller and shallower fish species that are less consumed by otters. Mink showed more plastic, generalist behavior than otters, being more tolerant of human presence, using more habitat types and having greater diet breadth. At the same time, otters apparently affect mink adversely and could help limit their invasion in sympatric areas. Conservation and recovery of otters, therefore, may produce a secondary benefit of simultaneously reducing the effect of mink, thereby providing an additional way to control this exotic predator’s population.     

Status,trends, and equilibrium abundance estimates of the translocated sea otter population in Washington State

Sea otters (Enhydra lutris kenyoni) historically occurred in Washington State, USA, until their local extinction in the early 1900s as a result of the maritime fur trade. Following their extirpation, 59 sea otters were translocated from Amchitka Island, Alaska, USA, to the coast of Washington, with 29 released at Point Grenville in 1969 and 30 released at La Push in 1970. The Washington Department of Fish and Wildlife has outlined 2 main objectives for sea otter recovery: a target population level and a target geographic distribution. Recovery criteria are based on estimates of population abundance, equilibrium abundance (K), and geographic distribution; therefore, estimates of these parameters have important management implications. We compiled available survey data for sea otters in Washington State since their translocation (1977–2019) and fit a Bayesian state-space model to estimate past and current abundance, and equilibrium abundance at multiple spatial scales. We then used forward projections of population dynamics to explore potential scenarios of range recolonization and as the basis of a sensitivity analysis to evaluate the relative influence of movement behavior, frontal wave speed, intrinsic growth, and equilibrium density on future population recovery potential. Our model improves upon previous analyses of sea otter population dynamics in Washington by partitioning and quantifying sources of estimation error to estimate population dynamics, by providing robust estimates of K, and by simulating long-term population growth and range expansion under a range of realistic parameter values. Our model resulted in predictions of population abundance that closely matched observed counts. At the range-wide scale, the population size in our model increased from an average of 21 independent sea otters (95% CI = 13–29) in 1977 to 2,336 independent sea otters (95% CI = 1,467–3,359) in 2019. The average estimated annual growth rate was 12.42% and varied at a sub-regional scale from 6.42–14.92%. The overall estimated mean K density of sea otters in Washington was 1.71 ± 0.90 (SD) independent sea otters/km² of habitat (1.96 ± 1.04 sea otters/km², including pups), and estimated densities within the current range correspond on average to 87% of mean sub-regional equilibrium values (range = 66–111%). The projected value of K for all of Washington was 5,287 independent sea otters (95% CI = 2,488–8,086) and 6,080 sea otters including pups (95% CI = 2,861–9,300), assuming a similar range of equilibrium densities in currently un-occupied habitats. Sensitivity analysis of simulations of sea otter population growth and range expansion suggested that mean K density estimates in currently occupied sub-regions had the largest impact on predicted future population growth (r² = 0.52), followed by the rate of southward range expansion (r² = 0.26) and the mean K density estimate of currently unoccupied sub-regions to the south of the current range (r² = 0.04). Our estimates of abundance and sensitivity analysis of simulations of future population abundance and geographic range help determine population status in relation to population recovery targets and identify the most influential parameters affecting future population growth and range expansion for sea otters in Washington State.     

Evaluating the current condition of a threatened marine mammal population: Estimating northern sea otter (Enhydra lutris kenyoni) abundance in southwest Alaska

We estimated density and abundance of the threatened southwest Alaska distinct population segment of northern sea otters (Enhydra lutris kenyoni) in two management units. We conducted aerial surveys in Bristol Bay and South Alaska Peninsula management units in 2016, and modeled sea otter density and abundance with Bayesian hierarchical distance sampling models and spatial environmental covariates (depth, distance to shore, depth × distance to shore). Spatial environmental covariates substantially impacted sea otter group density in both management units, but effects sizes differed between the two management units. Abundance (9,733 otters, 95% CrI 6,412–17,819) and density (0.82 otters/km², 95% CrI 0.54–1.49) estimates for Bristol Bay indicated a moderate population size. In contrast, abundance (546 otters, 95% CrI 322–879) and density (0.06 otters/km², 95% CrI 0.03–0.09) estimates indicated a relatively low population size in South Alaska Peninsula. Overall, our results highlight the importance of accounting for the detection process in monitoring at-risk species to reduce the uncertainty associated with making conclusions about population declines.     

水獭的研究与保护现状

目前世界上水獭数量的急剧下降已引起广泛关注.从水獭的分布、生境选择、食性以及种群动态方面综述了近年来世界有关水獭的生态学与保护研究进展,探讨了水獭的保护现状及存在的问题,并结合实际情况提出了对水獭保护的建议.     

AN ESTIMATION OF CARRYING CAPACITY FOR SEA OTTERS ALONG THE CALIFORNIA COAST

Carrying capacity (K) for the California sea otter ( Enhydra lutris nereis ) was estimated as a product of the density of sea otters at equilibrium within a portion of their existing range and the total area of available habitat. Equilibrium densities were determined using the number of sea otters observed during spring surveys in 1994, 1995, and 1996 in each of three habitat types where sea otters currently exist. Potential sea otter habitat was defined as from the California coastline to the 40-m isobath and classified as rocky, sandy, or mixed habitat according to the amount of kelp and rocky substrate in the area. The amount of habitat available to sea otters in California was estimated using a Geographic Information Systems (GIS) program. The estimated mean number of sea otters that could be supported by the marine environment to a depth of 40 m in California was 15,941 (95% CI 13,538–18,577). The GIS-based approach incorporated detailed bathymetric contours, produced repeatable and accurate estimates, and served as an innovative method of measuring sea otter habitat. We believe the approach described in this paper represents the best available information on how a sea otter population at equilibrium would be distributed along the California coast.     

The influence of wave exposure on the foraging activity of marine otter, <Emphasis Type="Italic">Lontra felina</Emphasis> (Molina, 1782) (Carnivora: Mustelidae) in northern Chile

The marine otter Lontra felina has been said to prefer wave-exposed habitats over more protected sites in response to a greater prey abundance in exposed habitat. We examined how the foraging activity of L. felina is affected by the regime of wave exposure and prey availability at Isla Choros, northern Chile. Through focal sampling we recorded time spent by otters in foraging, the duration of dives, and the hunting success on a wave-exposed and a wave-protected site on the island. In addition, we quantified the abundance of prey in both habitats. Marine otters spent more time foraging in the wave-protected site compared with the wave-exposed habitat. Successful dives reached 26.9% in the wave-exposed habitats, and 38.2% in the wave-protected habitat. Foraging dives were 18% shorter in wave-exposed as compared with wave-protected habitat. Numerically, available prey did not differ significantly with habitat. Our results are more consistent with the hypothesis that wave-exposed habitats represent a sub-optimal habitat to foraging marine otters. Marine otters’ use of wave-exposed patches through northern and central Chile coastal areas probably reflects a low availability of suitable protected areas and greater human disturbance of more protected habitat.     

Estimating Carrying Capacity for Sea Otters in British Columbia

ABSTRACT We estimated carrying capacity for sea otters (Enhydra lutris) in the coastal waters of British Columbia, Canada, by characterizing habitat according to the complexity of nearshore intertidal and sub-tidal contours. We modeled the total area of complex habitat on the west coast of Vancouver Island by first calculating the complexity of the Checleset Bay-Kyuquot Sound (CB-KS) region, where sea otters have been at equilibrium since the mid-1990s. We then identified similarly complex areas on the west coast of Vancouver Island (WCVI model), and adapted the model to identify areas of similar complexity along the entire British Columbia coast (BC model). Using survey data from the CB-KS region, we calculated otter densities for the habitat predicted by the 2 models. The density estimates for CB-KS were 3.93 otters/km² and 2.53 otters/km² for the WCVI and BC models, respectively, and the resulting 2 estimates of west coast of Vancouver Island complex habitat carrying capacity were not significantly different (WCVI model: 5,123, 95% CI = 3,337–7,104; BC model: 4,883, 95% CI = 3,223–6,832). The BC model identified the region presently occupied by otters on the central British Columbia coast, but the amount of coast-wide habitat it predicted (5,862 km²) was relatively small, and the associated carrying capacity estimate (14,831, 95% CI = 9,790–20,751) was low compared to historical accounts. We suggest that our model captured a type of high-quality or optimum habitat prevalent on the west coast of Vancouver Island, typified by the CB-KS region, and that suitable sea otter habitat elsewhere on the coast must include other habitat characteristics. We therefore calculated a linear, coast-wide carrying capacity of 52,459 sea otters (95% CI = 34,264–73,489)—a more realistic upper limit to sea otters in British Columbia. Our carrying capacity estimates are helping set population recovery targets for sea otters in Canada, and our habitat predictions represent a first step in Critical Habitat identification. This habitat-based approach to estimating carrying capacity is likely suitable for other nonmigratory, density-dependent species.     

Unveiling the Limitations of Scat Surveys to Monitor Social Species: A Case Study on River Otters

Abstract: We examined the relationship between the production of sites with feces (i.e., latrines) and river otter (Lontra canadensis) abundance to determine whether scat surveys were adequate for monitoring relative population size for species leaving activity signs in a clumped distribution on the landscape. We conducted winter riparian transects to simultaneously monitor otter abundance via snow tracks and latrine sites along the rivers of Kouchibouguac National Park and surrounding area in New Brunswick, Canada. Our data showed that latrine abundance poorly reflected otter abundance for given stretches of rivers because the relationship was nonlinear and reached a plateau. The number of latrine sites was not related to the time period since last snowfall, which indicated that otters repetitively defecated at the same sites. Individual otters and groups did not produce activity signs over larger distances as a function of time, which indicated that they tend to stay in their home ranges in winter. We discuss why scat survey protocols based on determining presence—absence of a species at predetermined search sites may poorly reflect population size, as well as population fluctuations in time. Caution is advised when interpreting data from such surveys for species for which feces or other activity signs surveyed play a role in intraspecific communication and tend to be in a clumped distribution on the landscape.     

Characterizing habitat preference of Eurasian river otter (Lutra lutra) in streams using a self-organizing map

We studied the habitat preferences of Eurasian river otters (Lutra lutra) using the distribution patterns of the numbers of spraints and sprainting spots of otters, as well as related environmental variables (habitat zone, river management, bank type, vegetation coverage, width, depth, etc.) in two streams. The numbers of otter spraints and sprainting spots were sampled monthly in two streams on Geoje Island, Republic of Korea, from January to December 2004. Additional environmental variables were measured at the sampling sites. A self-organizing map (SOM), which is an unsupervised artificial neural network, was used to characterize the habitat preferences of otters. In our results, the SOM classified three different groups of study sites based on their habitat conditions, and the habitat differences were effectively visualized on the trained SOM map. Otters showed spatial and temporal dynamics in the numbers of spraints and sprainting spots, and revealed habitat preferences for shallow, narrow areas of streams and edges of water that were not far from reservoirs but covered with trees and shrubs. Additionally, otters preferred an environment in which weirs reduced the drift of water and gathered fishes and had a natural type of stream bank; these findings are relevant for river management. Otters adapted to places close to roads, residential areas, and agricultural areas with some tolerance of human interference.