River Otter Research Articles

Effect of Stream Permanence on Predation Risk of Lotic Crayfish by Riparian Predators

Given the importance of crayfish in stream ecosystems, gaining insight into the role of stream permanence in maintaining predator–prey interactions is critical. Our objectives were to determine the influence of stream permanence and season on crayfish predation and assess the role of stream permanence and crayfish density on the presence of predators, while accounting for imperfect detection. We conducted surveys of crayfish density, mammalian scat, and environmental variables within 10 intermittent and 10 permanent streams in the Ozark Highlands. We used occupancy modeling to assess the relationship between predator presence, crayfish density, and environmental variables. Stream permanence did not play a role in determining relative frequency of occurrence or percent volume of crayfish prey in mammalian diets. However, percent volume and relative frequency of crayfish prey found in scats differed by season, with both highest in spring and summer. The relative frequency and percent volume of fish prey showed a significant interaction of season by stream permanence, which may be the first instance of this observation. Procyon lotor (Raccoon) had the highest detection probability (p = 0.39), whereas Neovison vison (American Mink; p = 0.15) and Lontra canadensis (River Otter; p = 0.03) had low detection probabilities. Further study into predator–prey interactions in the context of hydrology, particularly when related to imperiled groups like freshwater crayfishes, is needed since climate change is expected to alter hydrologic patterns.

Sociality and signaling activity modulate information flow in river otter communication networks

Abstract Animal communication networks are built from interactions between senders and receivers of signals. The drivers of signaling decisions, which are the building blocks of such networks, are not well understood. Theory predicts that conditions which ensure information spread to the largest possible number of receivers should be favored. Several carnivores use latrine sites for visual, olfactory, and auditory signaling. We tested the hypotheses that signaling behavior at latrine sites is influenced by social structure and locally acquired information on the presence of conspecifics, using coastal river otters (Lontra canadensis), in Alaska. River otters exhibit a flexible social system of mostly males that communicate through scent marking at latrines. During scent marking, river otters also perform feet stomping, which may add a visual component to their signal. Using trail camera footage, we found that solitary otters were more likely to perform both sniffing and scent marking compared with otters in groups. Feet stomping was more intense for solitary otters but less pronounced during overmarking. Signalers demonstrated a greater tendency to scent mark when in smaller groups at highly active latrines, whereas feet stomping was more intense in recently visited sites. When in groups, scent-marking frequency increased when other individuals were signaling, suggesting a positive feedback, possibly driven by feet stomping. In concert, our results suggest that in river otters, scent-marking decisions minimize signal dilution by being performed in small groups and maximize the receivers through preferential signaling at latrines with higher, more recent activity. Because signaling decisions in social animals are linked to key life-history events such as mating and group membership shifts, understanding their individual and population-level drivers can be crucial.

Co-exposures to trace elements and polycyclic aromatic compounds (PACs) impacts North American river otter (Lontra canadensis) baculum

Environmental loadings of polycyclic aromatic compounds (PACs) and trace elements are increasing in areas with marked oil and gas extraction, such as in the Athabasca oil sands region, Alberta, Canada. Some of these chemicals are recognized as potent endocrine disrupting compounds (EDCs). The impacts of co-exposure to PACs and metals on free-ranging wildlife is of considerable concern. River otters (Lontra canadensis) are sentinel species of aquatic ecosystem health. The baculum (penile bone) is an important part of the reproductive system in otters that ensures successful copulation. Although baculum health is critical to male reproductive success and is sensitive to exposure to EDCs, there is no information available regarding the impact of PAC and metal exposures on measures of baculum health. River otter baculum and livers were dissected from carcasses obtained from the fur trade. Trace element and PAC analyses were carried out in liver with matching baculums subjected to dimensional analysis, bone mineral density (BMD) and mechanical loading testing. Trace elements and select PACs exhibited both protective and deleterious effects on baculum bone health metrics. Alkylated four ring PACs were negatively associated with baculum bone material properties (ex: C4-Chrysene and C4-pyrene). The same compounds have been shown to exhibit strong anti-androgenic activities. Few comparable studies exist related to contamination and adverse effects of PACs in wild terrestrial mammals. Baculum health metrics may be an important tool to include in biomonitoring studies as to date, there are limited means to assess male reproductive performance in wildlife biomonitoring programs.

Improving engagement in managing reintroduction conflicts: learning from beaver reintroduction

Social factors hold implications for the success or failure of wildlife reintroductions. Potential conflict issues may prevent projects from proceeding or succeeding. The manner in which wildlife managers engage with affected people in conflict scenarios may prevent or contribute toward conflict escalation, so an understanding of how to improve engagement is required. We conducted interviews with individuals who reported conflicts with beavers (Castor fiber) within the case study of a reintroduction trial in England, called the ‘River Otter Beaver Trial’. Using a qualitative thematic analysis, we identified five themes to be considered when engaging with affected people in beaver reintroduction conflicts: (1) Proactive Engagement or a Fast Response; (2) Appropriate Communication; (3) Shared Decision-Making; (4) Sense that Humans are Responsible for Conflicts with Reintroduced Species; (5) A Need for Certainty. We conclude that engagement with affected individuals will likely be improved, with reduced conflict potential, where these themes are addressed.

The Gut Microbial Community Structure of the North American River Otter (Lontra canadensis) in the Alberta Oil Sands Region in Canada: Relationship with Local Environmental Variables and Metal Body Burden

The Alberta Oil Sands Region in Canada is home to one of the largest oil bitumen deposits in the world. The North American river otter (Lontra canadensis) is a top predator with a small home range and is sensitive to disturbances; it has been designated as a sentinel species for the potential impacts of the natural resource exploitation on freshwater ecosystems in the Alberta Oil Sands Region. With an increasing interest in noninvasive biomarkers, recent studies suggest that gut microbiota can be used as a potential biomarker of early biological effects on aquatic wildlife. The goal of the present study was to determine the river otter gut microbial structure related to environmental variables characterizing mining activities and metal body burden. We obtained 18 trapped animals from and surrounding the surface mineable area of the Alberta Oil Sands Region. The gut microbial community structure was characterized using high-throughput sequencing of 16S rRNA gene amplicon analyses. Trace metal concentrations in the liver were measured by inductively coupled plasma-mass spectrometry. Our study revealed that the gut bacteria of river otters in the Alberta Oil Sands Region clustered in 4 groups dominated by Peptostreptococcaceae, Carnobacteriaceae, Enterobacteriaceae, Clostridiaceae, and Nostocaceae. We show that arsenic, barium, rubidium, liver-body weight ratio, and δ15 N were associated with each cluster. When comparing affected versus less affected sites, we show that river otter gut bacterial community and structure are significantly related to trophic level of the river otter but not to Alberta Oil Sands Region mining activities. Our study reveals that the gut bacterial dynamics can provide insights into the diet and habitat use of river otters but that more work is needed to use it as a pollution biomarker. Environ Toxicol Chem 2020;39:2516-2526. © 2020 SETAC.

Causes of Mortality in a Population of Marine-Foraging River Otters (Lontra canadensis).

Retrospective analysis of diagnostic findings from 30 marine-foraging river otter (Lontra canadensis) carcasses opportunistically acquired between 2003 and 2013 revealed trauma as the most common cause of mortality (47%). Within this focal population, causes of trauma included vehicular, gunshot, and one case of suspect intraspecific aggression. Other causes of death included idiopathic (20%), infectious (13%), metabolic (10%), nutritional (7%), and neoplasia (3%). One case of neoplasia, a pancreatic islet cell adenoma, was identified in a 12-yr-old female. In six animals, diffuse renal interstitial fibrosis and multifocal glomerulosclerosis of unknown clinical significance were noted.

Urban wildlife in times of COVID-19: What can we infer from novel carnivore records in urban areas?

The onset of the COVID-19 pandemic brought an unusual decrease in human activity associated with partial and total lockdowns. Simultaneously, a series of wildlife sightings—mainly in urban areas—have been brought to public attention and often attributed to lockdown measures. Here we report on a series of wild carnivore records, including threatened species, obtained through camera traps set in urban forests, campuses, suburbs, and peri-urban areas of two cities in Chile, during partial lockdown measures. Our records are novel for Chile, a country where urban carnivore ecology is mostly unknown, and include the detection of four native carnivores, including the vulnerable güiña (Leopardus guigna) and the endangered southern river otter (Lontra provocax). These records also constitute a valuable baseline collected during partial lockdown measures in two cities of the Global South. We emphasize, however, that these findings cannot be used to argue for or against an effect of lockdown measures on wildlife. More generally, we call for caution in the interpretation of seemingly novel carnivore records during periods of lockdown and stress the value of international collaboration in evaluating the effects of the Anthropause on wildlife.

Accessing and Mobilizing “New” Data to Evaluate Emerging Environmental Impacts on Semi-Aquatic Mammals

This paper describes how knowledge mobilization evolved during a study that assessed a proposed increase in industrial water withdrawals from the Athabasca River in northern Alberta, Canada, and potential impacts on a suite of freshwater semi-aquatic mammals in the broader ecosystem. The oil sands region in northeastern Alberta faces various pressures that require rapid knowledge mobilization and decision making, while still acknowledging ecological sensitivities immediately downstream in the Peace-Athabasca Delta (PAD) in the Wood Buffalo National Park. Data were acquired using a multi-faceted approach, including literature reviews, acquisition and synthesis of raw data, and interviews with local knowledge holders. The final outcome of the study was then contextualized relative to elements of knowledge mobilization: (1) research, (2) dissemination, (3) uptake, (4) implementation, and (5) impact. Knowledge mobilization was easiest to quantify for the first two elements, yet was still present in varying forms in the latter stages. The cultural importance of beavers, muskrats, river otters, and mink for communities associated with the Athabasca River and the PAD allowed for increased engagement during all stages of the research process, which then facilitated the co-production of potential solutions among different organization and perspectives.

Beaver genetic surveillance in Britain

Founder genetic composition can affect reintroduction success, especially as the number of animals released tends to be small and therefore less genetically diverse than their source populations. Numerous translocations and reinforcements of beavers, Castor fiber, have occurred with little regard to geographic and/or genetic origin. Beaver reintroduction to Britain has been haphazard and currently disjointed populations of varying status exist – from sanctioned wild releases, unlicensed populations and naturalistic enclosed projects. This study investigated the genetic composition of two originally unofficially released beaver populations in Britain - Tayside, east Scotland, and River Otter, Devon, to provide data to support decision on their future management. From both wild populations (n = 34Tayside, n = 9Devon) all were confirmed as Eurasian beaver. The vast majority, origin was likely assignable to Germany and the mixed founder population of Bavaria. Eighty-two percent of the Tayside individuals examined at 275 loci were at least as closely related as first cousins, with pairwise estimates of relatedness at 26 loci indicated that the Devon beavers were more closely related on average. So far there is no evidence to suggest that beavers are failing to adapt to the British environment despite their reduced genetic founder based, however attention to genetic augmentation and longer-term management of genetic diversity should be factored into comprehensive restoration plans for the species across Britain. Many recent reintroductions are relying on serial founder events from an already limited founder base and that is counter to best practice in reintroduction planning.

COMPARATIVE ANATOMY OF THE LIVER OF WILD FUR ANIMALS: EUROPEAN BADGER (MELES MELES, L), RIVER OTTER (LUTRA LUTRA, L) AND ORDINARY FOX (VULPES VULPES, L)

Fur production is the most valuable field of animal husbandry in the Russian Federation. Domestication, containment, changes in behavior and diet of fur animals have contributed to both exterior and interior changes in their biology. The biggest interior changes have occurred in the volume and functionality of the digestive system, especially liver. European badger’s (Meles meles) liver mass was determined to be 324-389 g making up 3,20-3,44% of the total body mass. River otter (Lutra lutra) has 489,0-500,0 g and 5,1-5,8%, and ordinary fox (Vulpes vulpes) has 183-195g and 3,4-3,9% accordingly. The sharp end of the badger liver peeks out of the lower end of the ribcage, while the otter liver is perpendicular to the ribcage. Badger liver is yellowish-brown, otter liver is cherry-brown, fox liver is brown. All of them are separated by deep grooves to differently sized parts; badger and otter livers have 7 parts, and fox liver lacks the nipple-like protrusion. The gallbladder is located between the square and left medial parts of the liver; the badger’s is pear-shaped and is easily visible from the diaphragmatic and visceral surfaces of the liver; otter’s is elongated and rounded and has a wrinkle, fox’s is pear-shaped. The contents of the gallbladders of badgers and otters is greenish brown, with badger’s contents having pH of 7,2-7,6 pts., otter’s - 6,5-6,8 pts., while fox’s is brown with pH of 6,0-6,2 pts. That way, different diets and habitats form the visual changes in topography and macro morphology of livers not only in members of different biological families, but different species as well.

Spatial patterns of the exposure-response relationship between mercury and cortisol in the fur of river otter (Lontra canadensis)

Fur has been validated as a useful biomarker medium for chemical exposures and biological responses in wildlife. Mercury (Hg) is known to act as an endocrine disruptor by altering brain neurochemistry. In this study, we investigated the spatial patterns of relationships between total Hg (THg) and cortisol in the fur of river otter (Lontra canadensis). Geotagged fur samples were obtained from a wildlife biomonitoring program (n = 72) and the North American Fur Auction (n = 37) between 2014 and 2017. Fur THg was measured using direct thermal decomposition and fur cortisol was measured using an enzyme-linked immunosorbent assay (ELISA). The average fur THg concentration was 11.50 ± 12.40 μg/g fur weight (f.w.), and the fur cortisol concentration was 5.71 ± 8.24 pg/mg. Results from the global ordinary least squares regression show no relationship between THg and fur cortisol concentrations. However, both Hg and cortisol were heterogeneously distributed across the landscape. When a localized geographically weighted regression (GWR) was used, a geographically distinct bi-phasic relationship was observed. We suggest this bi-phasic relationship is associated with a threshold THg concentration, beyond which, there was a negative association with measured fur cortisol. Results of a break-point analysis, with one break, indicate that the threshold is 16 ± 1.27 μg/g f. w of THg in fur. This research highlights the need to use appropriate spatial methods when assessing exposure-response relationships in wildlife across large geographical areas. The identified threshold can be used for regulatory purposes.

AN APPROACH FOR LONG-TERM MONITORING OF RECOVERING POPULATIONS OF NEARCTIC RIVER OTTERS (LONTRA CANADENSIS) IN THE SAN FRANCISCO BAY AREA, CALIFORNIA

We present results from the first 5 y of a long-term monitoring study of recovering populations of the North American River Otter, Lontra canadensis, in Marin County, California. Historically present, but extirpated due to trapping and habitat loss, this apex aquatic predator is recolonizing coastal, lentic, and riverine habitat areas around San Francisco Bay. Using camera traps and a community science effort, we estimated an annual minimum population size at each of 14 focal study sites (FSS). Based on those estimates over 5 y, we developed a new Bayesian-statistics model to estimate population parameters for each FSS, including initial population abundance, annual rate of change in abundance, and probability that abundance is in decline. Our results show significantly different changes in abundance among the various FSS, with annual rates ranging from a high of 0.86 to a low of –0.44. Using a Random Forest framework, we then investigated the relative value of select spatial, environmental, and anthropogenic variables as predictors for each FSS population parameter. In our analysis spatial factors, and specifically latitude, were the best predictor of differences in FSS population parameters. Higher latitudes correlated with higher initial population abundance, greater annual increase in abundance, and lower probability that abundance is in decline. Our results provide new information about the rate and pattern of natural River Otter recolonization of areas from which they have been absent for decades. The results also serve as a demonstration of an approach to long-term monitoring, with the goal of increased understanding of the ecological function of River Otters in the San Francisco Bay Area.

ALARIOSIS OF CARNIVOROUS ANIMALS IN CENTRAL RUSSIA

The spread of alariosis of fishing animals of Central Russia was clarified and a circle of host agents among mammals was identified. The material for the study was the arcasses of trade animals. The period of work was 2018–2020. Animals were studied according to the method of complete helminthological study on K.I. Skryabin (1928). The tissue form of alariosis was examined by trichinelloscopic methods. During the reporting period, 107 heads of carnivorous animals (of which 27 heads (25.2%) are considered stray domestic) extracted in the territory of the Ryazan, Vladimir and Moscow regions. Of the Canidae family, 54 heads have undergone helminthological examination (29 foxes, 17 domestic dogs, 7 raccoon dogs, and 1 wolf). Of the cat (Felidae), 11 heads have been studied (domestic cats – 10, lynx – 1). Martens animals (Mustelinae) have been studied 42 heads (forest мartens – 19, stone мartens – 6, river otter – 4, ermines – 7, badgers – 2, аmerican mink – 4). Adult trematodes have been identified in 37 carnivorous animals (34.6%) in the thin part of the intestine. Canidae animals representing trade species (fox, raccoon dog, wolf) are 100% infected with the agent of alariosis. The intensity invasion of fox was 4–250 copies per head, raccoon dogs – 11–284, wolf – 84. The larval form of the agent was recorded in one fox (3.5%), 2 forest мartens (10.5%) and one аmerican mink (25.0%). Mesocercaries of trematodes were localized in a transparent capsule in lung parenchyma, in diaphragm muscle tissue, in esophageal muscle tissue.

Space Use and Enrichment in a North American River Otter (Lontra canadensis) Exhibit

Exhibit design and environmental enrichment can influence the space use of captive animals. On May 2, 2014, the Tennessee Aquarium opened a new, expanded North American river otter (Lontra canadensis) exhibit, “River Otter Falls.” The exhibit housed 6 otters (5 male and 1 female). A group of three otters was rotated in the exhibit every 2-2 ½ hours. Using a scan sampling procedure with 30 second intervals, the location and number of the otters was marked in one 9 areas of the exhibit. The number of otters not visible was also counted. The study lasted for 4 months, with 43 sessions each lasting ~45 min. The results showed that the otters tended to use all areas of the exhibit rather than confining themselves to one or a few areas. (total SPI = 0.35) and were visible 98% of the time. G-tests showed that the otters were using the areas significantly different from chance with variations in how they are using each individual area of the exhibit. Comparisons of the visibility and location after enrichment showed that the otters tended to use the exhibit less uniformly during enrichment, but increased time spent in areas of the exhibit with greater visibility and proximity to guests. During enrichment sessions, otters were more visible in the areas of the tank that visitors may see most easily, empathizing the role that enrichment can have on space use of an enclosure and visibility of animals in captivity.

LEPTOSPIRA, PARVOVIRUS, AND TOXOPLASMA IN THE NORTH AMERICAN RIVER OTTER (LONTRA CANADENSIS) IN NORTH CAROLINA, USA.

The North American river otter (Lontra canadensis) is the largest mustelid in North Carolina, US, and was once extirpated from the central and western portions of the state. Over time and after a successful reintroduction project, otters are now abundant and occur throughout North Carolina. However, there is a concern that diseases may have an impact on the otter population, as well as on other aquatic mammals, either through exposure to emerging diseases, contact with domestic animals such as domestic cats (Felis catus), or less robust condition of individuals through declines in water quality. We tested brain and kidney tissue from harvested otters for the pathogens that cause leptospirosis, parvovirus, and toxoplasmosis. Leptospirosis and toxoplasmosis are priority zoonoses and are maintained by domestic and wild mammals. Although parvovirus is not zoonotic, it does affect pets, causing mild to fatal symptoms. Across the 2014-15 and 2015-16 trapping seasons, we tested 220 otters (76 females, 144 males) using real-time PCR for Leptospira interrogans, parvovirus, and Toxoplasma gondii. Of the otters tested, 1% (3/220) were positive for L. interrogans, 19% (41/220) were positive for parvovirus, and 24% (53/220) were positive for T. gondii. Although the pathogens for parvovirus and toxoplasmosis are relatively common in North Carolina otters, the otter harvest has remained steady and the population appears to be abundant and self-sustaining. Therefore, parvovirus and toxoplasmosis do not currently appear to be negatively impacting the population. However, subsequent research should examine transmission parameters between domestic and wild species and the sublethal effects of infection.

A New Species of Cryptocotyle (Digenea: Heterophyidae) Infecting Kelp Gull and a Galaxiid Fish in Patagonian Freshwater Environments: Morphological and Molecular Analyses.

Adults of a species of Cryptocotyle were found infecting the intestine of the kelp gull, Larus dominicanus Lichtenstein, 1823, and metacercariae were found in the fins and muscle of the galaxiid fish, Galaxias platei Steindachner, 1898 (local name "puyen grande"), in Nahuel Huapi National Park (Patagonia). Morphometrics and genetic markers of mitochondrial cytochrome oxidase (COI) and ribosomal internal transcribed spacer 1 (ITS1) confirmed that adults and metacercariae were conspecific and represent a new species, Cryptocotyle dominicana n. sp. The only congener known from South America (Cryptocotyle thapari McIntosh, 1953) matures in river otters (Lutra spp. and Pteronura spp.) in Brazil and Bolivia and differs from the new species in the arrangement of the testes, which are located in tandem in the species from otters. Adults of the new species resemble Cryptocotyle lingua (Creplin, 1825) Fischoeder, 1903 from marine environments of the Northern Hemisphere, both species being characterized by having a linguiform body, oblique testes, and vitelline follicles that extend posteriorly to the level of the ventral sucker. Considering the morphological findings that differentiate the new species from other Cryptocotyle, as well as the molecular analysis that shows significant differences from C. lingua, we conclude that these specimens represent a new species, the first of the genus Cryptocotyle to be described from birds in South America.

North American River Otters Followed by Piscivorous Birds, and a River Otter Parental Distraction Display

We observed 2 Lontra canadensis (North American River Otter), likely an adult female and her nearly-grown pup, on a fall 2018 afternoon at a remote lake in Piscataquis County, ME. We witnessed 2 notable animal behaviors, a possible bird-otter foraging association and a River Otter parental display, serendipitously while canoeing. An Ardea herodias (Great Blue Heron) and a Megaceryle alcyon (Belted Kingfisher) watched and followed the River Otters as they fished along the shore of a small cove of the lake. Although neither bird was seen to strike directly at or eat a fish during this episode, the behavior of the piscivorous birds was suggestive of a foraging association with the River Otters, a novel observation in North America. After fishing, the River Otters began traveling along the lake shore and noticed the canoeing human observers. Upon becoming aware of the canoe, the pup apparently hid as the adult female swam toward the canoe while noisily blowing. She then dove and resurfaced farther away from her pup's last-seen position. This routine was repeated several times until the observers paddled away from the female. Despite the large behavioral repertoire known for otters generally, this parental distraction display has not been previously reported.

The genome sequence of the Eurasian river otter, Lutra lutra Linnaeus 1758.

We present a genome assembly from an individual male Lutra lutra (the Eurasian river otter; Vertebrata; Mammalia; Eutheria; Carnivora; Mustelidae). The genome sequence is 2.44 gigabases in span. The majority of the assembly is scaffolded into 20 chromosomal pseudomolecules, with both X and Y sex chromosomes assembled.

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.

Digestible Energy Intake and Digestive Efficiency of Human-Managed North American River Otters (Lontra canadensis).

Diets currently provided to captive North American river otters (Lontra canadensis) are highly variable with different institutions providing various whole foods, commercial complete prepared diets, or combinations of both. This study investigated the digestible energy intake, gastrointestinal transit time, and digestive efficiency of three different diets being fed at three North Carolina institutions. Otters housed at Institution A (n = 3) were fed strictly fish. Otters housed at Institutions B (n = 3) and C (n = 2) were fed a majority fish based diet (58.5 and 74.1%, respectively), supplemented with fruits, vegetables, and supplemental protein sources as enrichment. There was an apparent trend between increased percentage of fish in the diet and faster transit time and higher digestive efficiency. As less fish was included in the diets, the GI transit time was longer (Institution A, 106 minutes; Institution B, 145 minutes; Institution C, 208 minutes). Median digestive efficiency was high for all three groups (A, 91.4%; B, 87.8%; C, 89.8%) but was higher for the institutions feeding fish. Additionally, the overall median gross energy intake for the eight animals in this study was 163.1 kcal/kgBM0.75/day (range: 92.2 to 260.7 kcal/kgBM0.75/day). While all three institutions had healthy otter populations, it appears that a higher fish diet should be further studied as the model North American river otter diet.