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.     

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.     

Comparing direct and indirect methods to estimate detection rates and site use of a cryptic semi-aquatic carnivore

Monitoring animal populations can be challenging, particularly when working with species that are cryptic, rare, or occur at low densities. The northern river otter (Lontra canadensis) is a cryptic, semi-aquatic carnivore that has been intensively studied in recent decades, yet much of what is known about its ecology is a result of studies that have employed indirect methods of detection and monitoring. These indirect methods, such as latrine or other sign surveys, have been the primary approach used for studying distribution, abundance, and habitat use of otters, with minimal representation of direct methods. In this study, we compared direct (camera traps) and indirect (scat count surveys) methods of evaluating detection probabilities and site use patterns of otters at latrines. We found that the direct method produced a significantly greater monthly detection probability than the indirect method and that camera surveys resulted in fewer occurrences of false negatives than scat surveys. However, the number of scats deposited at a site was positively correlated with number of visits by otters at a site (Tau-b = 0.675). Thus, while cameras outperformed scat counts in terms of detection, the two methods were comparable in determining intensity of site use. We conclude that, depending on the parameter of interest, scat counts may be an acceptable surrogate for more direct methods of monitoring otters and other cryptic species. We caution, however, that in the absence of comparative methodological data, direct methods such as camera trapping should be preferred when making inferences about animal distribution, abundance, or habitat use.     

Do alien North American mink compete for resources with native South American river otter in Argentinean Patagonia?

American mink Mustela vison , originally bred in fur farms, have become established in areas occupied by native endangered Southern river otter Lontra provocax , in Patagonia. In accordance with European experience, this biological invasion in South America raises questions about the interaction between invasive mink and native otter, from the viewpoints of both community assembly and conservation. We set out (1) to find which aspects of habitat structure were related to the distribution of signs of both this invasive species and Southern river otter Lontra provocax , in Argentinean Patagonia and their most common prey and (2) to test general predictions of niche partitioning between these two species. Based on surveys of 447 of 600 m transects for otter and mink scats/footprints along the waterside of lakes and rivers in the Andean Patagonian region, we compared diet composition (from scat analysis) and micro-habitat preferences (from field signs) of the two species. Otters were more specialist than mink in habitat use and diet. Mink used different habitats in other river basins where otters were absent. Where they occurred together in the basin of the Limay River, the distributions of their signs were similar, and mink diet was more similar to that of otters. There was no detectable difference in otter diet before and after mink arrival in the Limay basin. Contrary to the prediction of niche partitioning, and to the findings of European studies, resource use by mink was more similar to that of otters where the species occurred sympatrically than where they were allopatric.     

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.     

Modeling Behavior by Coastal River Otter (Lontra Canadensis) in Response to Prey Availability in Prince William Sound,Alaska: A Spatially-Explicit Individual-Based Approach

Effects of climate change on animal behavior and cascading ecosystem responses are rarely evaluated. In coastal Alaska, social river otters (Lontra Canadensis), largely males, cooperatively forage on schooling fish and use latrine sites to communicate group associations and dominance. Conversely, solitary otters, mainly females, feed on intertidal-demersal fish and display mutual avoidance via scent marking. This behavioral variability creates “hotspots” of nutrient deposition and affects plant productivity and diversity on the terrestrial landscape. Because the abundance of schooling pelagic fish is predicted to decline with climate change, we developed a spatially-explicit individual-based model (IBM) of otter behavior and tested six scenarios based on potential shifts to distribution patterns of schooling fish. Emergent patterns from the IBM closely mimicked observed otter behavior and landscape use in the absence of explicit rules of intraspecific attraction or repulsion. Model results were most sensitive to rules regarding spatial memory and activity state following an encounter with a fish school. With declining availability of schooling fish, the number of social groups and the time simulated otters spent in the company of conspecifics declined. Concurrently, model results suggested an elevation of defecation rate, a 25% increase in nitrogen transport to the terrestrial landscape, and significant changes to the spatial distribution of “hotspots” with declines in schooling fish availability. However, reductions in availability of schooling fish could lead to declines in otter density over time.     

Use of non-invasive techniques to determine population size of the marine otter in two regions of Peru

The marine otter (Lontra felina) can be found on rocky shores from the northern coast of Peru (9°S) to the extreme south of Argentina (56°S). This species is currently classified as endangered but there is little information on population size because marine otters are very difficult to observe and count. Between June and August 2012 we collected 240 samples of marine otter feces from seven localities in Peru. All locations were visited four times. One-hundred and thirty-three samples (55%) were successfully amplified at five to seven microsatellite loci and a sex-linked marker. We identified a minimum of 80 individuals (41 males and 39 females) across all locations for a density estimate of 4.4 otters per km, a value about 2X higher than estimates based on previous visual counts. Estimates using the program CAPWIRE averaged 12.6 otters/km, a value six times higher than estimates based on previous visual counts, although confidence limits were large due to the low number of recaptures. There was a strong positive relationship between the number of fresh scats and the number of unique genotypes, suggesting scat counts might be used to estimate the minimum number of otters at a site. Non-invasive genotyping of marine otter feces and scat counts will be valuable tools for estimating population sizes and monitoring movements of this secretive species.     

Possible influence of increased riparian activity (stream modification and agricultural intensification) on abundance of South African otters

Otters are threatened by habitat loss and the pollution of their riverine habitat. Environmental impacts on top predators are often the first indication of habitat deterioration. It is rare for predator‐prey‐habitats to be monitored over long time intervals (decades), however necessary that may be. Here, we report on the decline in otter relative abundance in a previously pristine habitat and speculate on its causes. We surveyed sign of coexisting otters (Aonyx capensis and Lutra maculicollis) along a river in Kamberg Nature Reserve in uKhahlamba Drakensberg Park, KwaZulu‐Natal, South Africa. The area, Stillerust, lies downstream of a commercial dairy farm and a rural village–subsistence farming area. Data collected recently were compared with two previous surveys, carried out in 1972–1974 and 1993–1994, and were also compared with a pristine section of river in the nature reserve, upstream of the farming areas. At Stillerust, the number of spraint (scat) sites found, for each otter species, approximated only 25% of those recorded in the earlier studies. In the pristine section of the river, the amount of sign and abundance of otters were similar to those recorded in 1993. Assessments of stream biota and water quality analyses revealed negative changes in the river below the pristine area, down to, and including, Stillerust. Visible signs of pollution were evident. Since the 1970s, the rural village population has increased ca eightfold, and the commercial farm has changed from an extensive livestock enterprize to an intensive dairy farm.     

Why do river otters scent-mark? An experimental test of several hypotheses

We tested several alternative hypotheses about the function of scent marking by the North American river otter, Lontra canadensis. Otters may mark at latrine sites with spraints (faeces) to (1) signal species identity, (2) advertise their reproductive status, (3) establish and maintain territories, and (4) communicate social status and identity to group members. Olfactory preference tests were conducted at the Alaska Sealife Center in Seward, Alaska, on a group of 15 wild-caught male otters in February 1999. We found that male otters investigated otter scent more than sealion faeces. The male otters also showed a preference for male scent over the scent of anoestrous females. No preference for the scent of unfamiliar males, compared with the scent of familiar males, was observed, and no preference for the scent of close kin was detected. However, an investigation of dominant relationships of the captive otters showed that dominant males spent more time investigating male scent than did subordinate males. Thus, spraints deposited at latrine sites may function to communicate social status of males.     

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。     

Some factors influencing the distribution of otters (Lutra lutra)

The number of sites at which evidence of otters was found and the total number of signs were recorded on fifty 5-km stretches of rivers in Wales and the West Midlands of England. Data were collected on fifteen parameters of habitat considered to be of importance to otters and subjected to a multivariate analysis.
Evidence of otters was found at thirty-four stretches. The distribution of sites and signs was correlated with the presence of potential holts (of which 107 were found) and with mature sycamore and ash trees. The measured variables accounted for 52 5% of the overall variation in otter sites and 60 2% of the variation in otter signs. The conservation of otters is discussed in light of the results of the analysis.     

Effects of freshwater availability on the summer distribution of otters Lutra lutra in the southwest coast of Portugal

The availability of freshwater has been suggested to strongly influence the distribution of coastal otters Lutra lutra The test this hypothesis, a study was undertaken on the relationships between otter distribution and freshwater availability in a coast where freshwater is a very scarce resource during the summer In this area otters occur mostly in a few small coastal streams but feed largely in the sea Twentynine streams were surveyed in the summer of 1990, and the presence/absence of otter signs was related to nine habitat variables Freshwater availability was found to be the most important factor influencing the occurrence of otters in summer It is suggested that otters favour large streams with good vegetation cover, for these are the most likely to maintain frestwater during the dry periods The distribution of otter signs m streams was also analysed, and it was found that signs tend to concentrate particularly near the mouth of the streams This habitat analysis has some conservation implications, indicating that the decrease of freshwater availability or quality of streams can make these unsuitable for otters, severely decreasing the areas suitable for the species in the southwest coast of Portugal     

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.     

A systematic re-sampling approach to assess the probability of detecting otters Lutra lutra using spraint surveys on small lowland rivers

Assessing and monitoring populations of elusive species frequently rely on the identification of indirect signs such as faeces. The absence of signs does not necessarily denote the absence of a species, thus, the ability to determine the presence/absence is susceptible to false negative results. The probability of detection is central to the interpretation and utility of data from field sign surveys. A low probability of detection may introduce considerable error into distribution patterns, resulting in inaccurate ecological conclusions.We used a systematic resampling approach, based on sequential spatial replication of spraint surveys, to investigate the probability of detecting Eurasian otters (Lutra lutra L.) with different survey designs. This included the standard otter transect survey methodology, which is widely used in conservation and scientific studies. In particular, we focus on the impact of applying broad scale population assessment techniques at smaller spatial scales. Fortnightly catchment-level otter surveys were undertaken on four lowland rivers in South Wales, over a period of two years. GIS was used to construct binary vectors for each survey, denoting the presence (1) or absence (0) of otters at each 50 m section of river. Vectors from all study rivers were pooled and resampled to test the different survey designs. The mean probability of detecting otters based on the standard protocol of a single 600 m transect survey was very low (0.26 ± 0.01 SE). The best way of obtaining a detection probability of 0.8 was to undertake three repeat surveys at two separate sites, using a transect of 800–1000 m.We demonstrate how sequentially collected spatial data can be analysed to determine the reliability of field sign surveys. Increasing the number of visits and study sites was a more efficient means of improving detection power than increasing transect length alone. The study emphasises the importance of determining detection probabilities and designing field sign surveys according to study scale and objectives. Our findings question the value of survey designs that aim to provide an instantaneous assessment of species presence/absence.     

Spatial distribution and diet of the Neotropical otter<Emphasis Type="Italic">Lontra longicaudis</Emphasis> in the Ibera Lake (northern Argentina)

The seasonal spatial distribution and diet of the Neotropical otterLontra longicaudis (Olfers, 1818) were studied on Ibera Lake within the Esteros del Ibera, an important wetland of NE Argentina (Ramsar site no. 1162). Twelve lake perimeter sites were regularly checked for otter tracks and signs. The amount of signs was compared to environmental parameters to test their influence on otter presence and movements. A positive correlation was found between the amount of signs and the physical structure of the littoral areas, as well as vegetation structure. Lakeside otter presence decreased during the summer sampling throughout all sites. In order to determine otter diet, 205 spraints were examined. Otters fed mainly on fish (mostly Cichlidae), but also on crustaceans and molluscs. Other fish consumed were Characidae, Synbranchidae, Loricariidae and Erythrinidae. Seasonal variation was observed in diet composition: in summer, diet crustaceans and vertebrates other than fish increased. A higher percentage of benthic fish species was also observed in summer, while pelagic and benthopelagic species increased in winter. Such dietary changes may be explained by the different habitat use of otters in different seasons, from the lake coast (winter) towards more internal marshy areas of the wetland (summer).     

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.     

Eurasian otter (<Emphasis Type="Italic">Lutra lutra</Emphasis>) diet and prey selection in Mediterranean streams invaded by centrarchid fishes

The diet of the Iberian otter (Lutra lutra) was determined by analysing 547 spraints collected at 28 sites within a wide area invaded by centrarchid fishes (pumpkinseed sunfish, Lepomis gibbosus and largemouth bass, Micropterus salmoides): the middle Guadiana basin (South-west Iberian Peninsula). Fish was the otters’ main prey, representing more than 60% of total individuals and more than 80% of total biomass. Otters preyed on most of the fish species captured in the field; however, the consumption of centrarchids was low compared to their abundance in the streams, and Jacobs’ index of preference showed a clear rejection of both species by the otter. Consumption of native fish genera (Squalius, Barbus and Chondrostoma) by otters increased in relation to their increase in the environment. In contrast, increasing numbers of L. gibbosus in the field was not reflected in otter consumption. The general decline of native freshwater fishes in Iberian rivers, the preferred prey of otters, together with the spread of exotic fish species (centrarchids and others) could put otter populations at risk.     

Establishing the foundation for an applied molecular taxonomy of otters in Southeast Asia

Four species of otters (Mustelidae, Lutrinae) occur in Southeast Asia and are considered to be of conservation concern: Aonyx cinerea (Asian small-clawed otter), Lutra lutra (Eurasian otter), Lutra sumatrana (Hairy-nosed otter), and Lutrogale perspicillata (Smooth-coated otter). Among these, L. sumatrana is endemic to the region, yet little is known about its biology, and the precise distribution of all four species in Southeast Asia is not well known. Furthermore, the taxonomy and systematics of L. sumatrana and L. perspicillata have been the subject of controversy, which has implications for the legal protection and for conservation programs of these taxa. To resolve these controversies, we used a multigene data set comprised of segments from 13 nuclear and 5 mitochondrial loci (11,180 nucleotides) to evaluate the phylogenetic relationships of Asian Old World otters. Phylogenies were also estimated using two mitochondrial loci (1,832 nucleotides) obtained from two or more individuals of the four Southeast Asian species. The results from maximum parsimony, maximum likelihood and Bayesian inference showed that L. sumatrana and L. lutra are sister taxa, whereas L. perspicillata is sister to A. cinerea. Furthermore, the results from the two-mitochondrial gene analyses indicate that L. sumatrana is reciprocally monophyletic with respect to L. lutra, supporting the specific validity of the former taxon. Signs such as tracks and feces are often used in field surveys to provide information on the distribution and abundance of otters, but the accuracy of these methods may be compromised when several closely related species occur sympatrically. Therefore, the two-gene data set was used to develop a provisional set of diagnostic nucleotides that can be potentially used to identify the four species of Southeast Asian otters from noninvasively collected biological samples, such as feces. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Competition between Eurasian otter Lutra lutra and American mink Mustela vison probed by niche shift

Interspecific competition is one of several constraints that might prevent an individual from maximising its energy intake. When an interspecific competitor is introduced, an individual is often forced to shift its diet according to the intensity of the competitive pressure. In this paper, we explore whether the introduced American mink ( Mustela vison Schreber) shifts its diet when the density of its potential competitor, the Eurasian otter ( Lutra lutra L.), is increased. We compared the diets of otter and mink at the same location but at two moments in time when the relative densities of these two species were different while controlling for the abundance of aquatic prey. Mink and otters are semi-aquatic mammals belonging to the same guild of mustelids and otters are expected to be the dominant competitor because they are larger and better at hunting underwater. The diets of otters and mink overlap to a great extent but while otters specialise mainly on aquatic prey, mink are able to exploit both aquatic and terrestrial prey. These observations prompted the hypothesis investigated in this work that at higher otter densities the diet of mink should change to include a higher proportion of terrestrial items. This hypothesis was supported by the data and at higher otter densities mink diet was observed to consist of a higher proportion of mammals and birds while fewer fish were present, although this pattern was present only in winter while no changes were observed in spring. Meanwhile the diet of otters remained basically unchanged. In the second part of the study, we investigated whether niche breadth and niche overlap between otter and mink changed at different otter densities. We found that niche overlap declined as the density of otters increased, in agreement with the prediction of habitat selection theory.     

Applying social and ecological approaches to evaluate factors influencing river otter (<Emphasis Type="Italic">Lontra canadensis</Emphasis>) 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 <5% of fish stock to otters and 91% reported an annual economic loss of <$500 from river otter depredation. Binary logistic regression determined that greater amounts of tree cover (%), facilities that reared >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.