Marine-foraging river otters in the Salish Sea
While not true marine mammals, river otters do use and rely on marine resources. The expansion of their populations since the early 1900s is a true conservation success story. Ecosystem recovery efforts and river otter reintroductions restored otter populations to much of their historic range. River otters often live in small social groups that include mother and offspring or other unrelated adults.
Overview
North American river otters (Lontra canadensis) are semi-aquatic mammals that range over most major river drainages, large lakes, and coastal marshes of North America. On the west coast, from Northern California (Bouley et al., 2015) to Alaska (Bowyer et al., 2003), river otters forage in and rely on healthy subtidal and intertidal zones where they feed on a variety of marine fish and invertebrates. The subspecies L. c. pacifica is found throughout the Salish Sea’s rivers, estuaries, coastlines, and coastal islands and plays an important role in the nearshore marine ecosystem. They are often confused with sea otters (Enhydra lutra) by the public because they are otters swimming in the sea. River otters do use and rely on marine resources, but taxonomically, they are not considered marine mammals like sea otters.
Status & trends
Unregulated trapping and water pollution reduced river otter populations over 75% of their historical range by the early 1900s, but ecosystem recovery efforts and river otter reintroductions restored otter populations to much of this range (Erb et al., 2018; Roberts, et al., 2020). Now river otters can be found in most historical locations in the United States, where they may be approaching their maximum potential distribution (Erb et al., 2018). This recovery is a true conservation success story (Roberts et al., 2020). It is important to recognize that in addition to translocating over 4,100 river otters from stable populations to recovery areas, improvements in water quality related to the US Federal Clean Water Act and better protection of riparian areas, some attributable to the US Federal Farm Bill, were also essential components of river otter population recovery (Bricker et al., 2022). In contrast to the United States, there has not been a detailed evaluation of the distribution, conservation status, and management of river otters in Canada, although they are reported to occupy all provinces and territories except Prince Edward Island (Bricker et al., 2022).
Using harvest data from 2006-2009, river otter population trends in Washington State were reported as stable, but not expanding, with an estimated harvest of approximately 250 animals a year (Bricker et al., 2022). In Washington State, the river otter is classified as a furbearer and a trapping license and open season are required to trap river otters.
In Washington State, river otters are included in the Woodland Park Zoo’s Carnivore Spotter community-based science program through which the public can report river otter sightings. Biased by variability in community participation, lack of data does not mean river otters do not occur in an area, only that they have not been spotted and reported.
In Canada, the river otter is federally considered secure and does not warrant candidate status under the Commission on Status of Endangered Wildlife in Canada (COSEWIC). The province of British Columbia lists it as yellow, which means it is not designated endangered or threatened (B.C. Conservation Data Centre, 1997).
As reviewed by the International Union for the Conservation of Nature (IUCN), North American river otters have a Red List Status of Least Concern (IUCN, 2020). They are included in Appendix II of the Convention on International Trade of Endangered Species (CITES Identification Manual Reference Number A-112.004.023.001), not because of concern for species status, but to assure that legal trade does not contribute to illegal trade of similar “look-alike” species of otters with a higher level of conservation concern (IUCN, 2020).
Biology
General Characteristics
Members of the Mustelidae family, river otters have an elongate body with a long tail that can be one-third the length of the animal. Sexual dimorphism exists with males being larger than females.
Diving
The diving ability of river otters has been studied, specificially in relationship to how exposure to hydrocarbons affects river otter exercise physiology and diving behavior (Ben-David et al., 2000). In that work, Ben-David et al. (2000) calculated the aerobic dive limit (the maximum breath hold possible without an increase in blood lactate concentration during or after a dive) as 51.4 seconds and found that captive river otters usually dove within their aerobic limits, but were capable of performing longer anaerobic dives. In the wild, their maximum recorded diving depth is approximately 10 fathoms (60 ft or 18.3 m) from two river otters that drowned in a crab pot set at that depth in Fish Bay near Sitka, Alaska in 1949 (Scheffer, 1952).
Reproduction
Males may produce sperm as early as eight months of age and females can breed as early as one year of age (Melquist et al., 2003). River otters are induced ovulators, triggered by copulation. The copulation to parturition period is approximately 336.5 days with a delayed implantation period of 273.5 days and a true gestation of approximately 63 days (Melquist et al., 2003). Photoperiod is thought to be the trigger for hormonal control of implantation and pups are born in the spring (Melquist et al., 2003). In Alaska, neonates remain in the den for approximately 8 weeks before emerging (Noll, 1988).
Longevity
River otters can be classified into four age groups (1 yr old, 1–4 yr old, 4–8 yr old, and >8 yr old) by subjective examination of dental wear (Baitchman and Kollias, 2000). They also can be reliably aged to year by microscopic calculation of cementum annuli from an upper canine tooth (Tabor et al., 1977). Within the Salish Sea, the oldest documented river otter is a 13-year-old male that was found dead in the San Juan Islands (Gaydos et al., 2020).
Sociality
Marine-foraging river otters can be solitary but often live in small social groups that include mother and offspring or unrelated adults, with males being more social than females. A study in Alaska showed that female group size did not vary by month, but male group size did and was related to forage fish abundance. Males were found in groups of up to nine individuals with group size being largest between May and October. Social groups were not kin-based, instead social groups facilitated cooperative foraging, which increased hunting efficiency and reduced home range (Blundell et al., 2002; 2004).
Male and female river otters scent mark for communication. Signaling and scent marking include multiple behaviors for receiving data (sniffing) as well as for sending data (scent marking, defecating and urinating; feet stomping; digging; and allo-grooming and rubbing). These behaviors are influenced by social factors with differences displayed between otters that were solitary or in a group (Barocas et al., 2021). Sex differences in latrine site use have been identified in marine-foraging otters from Alaska where females irregularly visit numerous latrines, likely to establish the boundaries of their territories, while males use fewer sites with higher intensity (Ben-David et al., 2005). In a small sample of river otters on the Duwamish River(Washington), there were no clear spatial differences in latrine use between the sexes, with females and males ranging between latrines as far as 25 and 32 km apart, respectively (Wainstein et al., 2022). The function of latrine use can also vary by solitary versus social males; solitary male otters likely use latrines to facilitate mutual avoidance while social male otters may use latrines for intra-group communication (Ben-David et al., 2005).
Although otters may not be aware of it, or even care, the deposition of feces and urine also moves marine-derived nitrogen into terrestrial plants at latrine sites, which Ben-David et al. (1998) showed had significantly higher values of marine nitrogen than did plants collected from non-latrine sites. The exception to this was alder (Alnus crispa ssp. sinuata), which derives nitrogen from the atmosphere.
Natural history
Diet
Marine-foraging river otters are generalists, consuming a wide variety of intertidal and subtidal fish and invertebrates as reported by numerous scatological studies from California (Penland and Black, 2009; Cosby and Gunther, 2021), Oregon (Toweill, 1974), Washington (Jones, 2000; Buzzell et al., 2014; Russell, 2015), British Columbia (Stenson et al., 1984; Guertin et al., 2010a), and Alaska (Larsen, 1984; Bowyer et al., 2003). While occasional species of concern like rockfish (Sebastes spp.) and salmon (Onchorrhyncus spp.) have been noted in these diet studies, the majority of fish eaten by marine-foraging river otters in the Salish Sea tend to be common, slow-moving intertidal and subtidal fishes like those in the Pholidae, Cottidae, and Stichaeidae families (Buzzell et al., 2014; Guertin et al., 2010a). Otter prey composition varies by season (Jones, 2000), year (Bowyer et al., 2003) and by otter social organization (Blundell et al., 2002). Work conducted in Alaska showed that solitary animals consumed slower-moving intertidal and subtidal fishes, while cooperatively foraging males consumed a higher proportion of fat-rich schooling fish species such as Pacific herring (Clupea pallasi) and Pacific sandlance (Ammodytes personatus) (Blundell et al., 2002; Ben-David et al., 2005).
Marine-foraging otters also will prey on numerous species of birds including ducks and gulls (Toweill, 1974; Hayward et al., 1975; Verbeek and Morgan, 1978; Larsen, 1984; Speich and Pitman, 1984; Jones, 2000; Penland and Black, 2009; Cosby and Gunther, 2021). In one report, otters were noted killing more gulls than they could consume (Verbeek and Morgan, 1978). Although data are sparse, it is not unreasonable to believe that river otters also will prey on non-native rodents. After a survey of 14 islands in the San Juan Islands, Washington failed to find evidence of invasive mice (Mus musculus) and rats (Rattus spp.), the investigators hypothesized that the almost ubiquitous presence of river otters could have been at least partially responsible (Kurle et al., 2013).
River otters near Makah Bay, Washington have been shown to eat invasive European green crab (Carcinus maenas), but with a low occurrence in their scat (0.7-5.2%) suggesting that they are not an important prey item (Buzzell, 2021).This does not necessarily mean that river otters are not capable of consuming more green crabs and could just be a reflection on the density of green crabs at the time of the study relative to other prey items. It does suggest that river otters could play a role in controlling green crab invasion, which warrents further study.
Habitat and Density
Marine-foraging river otters preferentially use rugged coastal areas with irregular shorelines associated with short intertidal lengths over coastal areas with long intertidal lengths and limited shoreline vegetation (Melquist et al., 2003). In a study conducted in Prince William Sound, Alaska, Ben-David et al. (1996) showed that river otters preferred habitats with overstory cover and high wave action when compared to sympatric mink (Neovison vison), which . The two species also varied in the timing and location of foraging; mink primarily foraged at low tide in the intertidal area, while river otters showed no preference for tidal status (Ben-David et al., 1996).
A study in the Salish Sea estimated marine-foraging river otter density on southern Vancouver Island, British Columbia at 1 otter per 2.3 km to 0.8 km of shoreline (Guertin et al., 2012).This density likely depends on habiat quality, which may be mitigated by some combination of prey availability, anthropogenic disturbance, and prey contaminant levels (Guertin et al., 2012).
Threats
Diseases
Because diseases like morbillivirus have the potential to regulate river otter density, investigation into the diseases of free-ranging and captive river otters is part of the International Union for the Conservation of Nature (IUCN) Species Survival Commission's (SSC) primary conservation priority for this species. Diseases detected in river otters inhabiting fresh water have been reviewed (Kimber and Kollias, 2000; Kimber et al., 2000). Less is known about diseases in marine-foraging river otters. In the Salish Sea, Gaydos et al. (2007a) identified antibodies to Toxoplasma gondii and Leptospira interrogans in trapped otters that appeared healthy and suggested higher exposure to these pathogens could be related to marine-foraging river otters living in closer proximity to humans and domestic pets (Gaydos et al., 2007a). Cryptosporidium and Giardia spp. also have been isolated from feces of otters of unknown health status (Gaydos et al., 2007b). A small pathology study of river otters found in the San Juan Islands, Washington showed a wide range of causes of mortality, including trauma, infections, and neoplasia, as well as infection by parasites like Sarcocystis spp., Coccidia sp., and an intrabronchial metazoan parasites suspected to be Paragonimous kellicotti (Gaydos et al., 2020). The acanthocephalan, Corynosoma strumosum, a widely distributed parasite of pinnipeds, was found in the intestine of a marine-foraging river otter from Vancouver Island, British Columbia with no associated pathology (Shanebeck et al., 2022). Although pathology was not documented, a study that included marine-foraging otters near California’s San Francisco Bay isolated four species of marine bacteria (Vibrio algynoliticus, V. cholera, V. metschnikovii, and V. parahemolyticus) from dead otters (Bouley et al., 2015).
Toxicants
Mercury (Ben-David et al., 2001), organochlorine pesticides (Elliott et al., 2008; Guertin et al., 2010b; Wainstein et al., 2022), polychlorinated biphenyls (PCBs - Elliott et al., 2008; Guertin et al., 2010b; Wainstein et al., 2022), polychlorinated dioxins (Elliott et al., 2008), polybrominated diphenyl ethers (PBDEs - Elliott et al., 2008; Guertin et al., 2010b; Nelson et al., 2015; Wainstein et al., 2022), polychlorinated furans (Elliott et al., 2008), and polycyclic aromatic hydrocarbons (PAHs - Wainstein et al., 2022) have been detected in marine-foraging river otters, with PCBs identified in some geographic locations at levels potentially harmful to the reproductive capacity or health of individual animals (Elliott et al., 2008; Guertin et al., 2010b; Wainstein et al., 2022). Despite river otters in some areas being exposed to toxicologically significant levels of PCBs (>9.0 mg/kg lipid weight; Guertin et al., 2010a), movement data suggested that otters with access to uncontaminated adjacent sites may inadvertently mitigate exposure levels (Guertin et al., 2012). In the Duwamish River estuary in Puget Sound, Wainstein et al. (2022) showed that concentrations of PCBs, PBDEs, dichlorodiphenyl-trichloroethane (DDT), and PAHs in otter feces increased directly with urbanization and were best predicted by models that included development zone.
Oil Spills
The threat of oil spills to river otters has been well studied and documented in Alaska. River otter mortality related to the massive Exxon Valdez oil spill in Prince William Sound, Alaska may have occurred directly from toxicity of petroleum hydrocarbons and indirectly from hydrocarbon damage to the ecosystem. The 1989 spill appears to have reduced suitable habitat for river otters and changed prey availability, resulting in, among other things, river otters requiring larger home ranges in oiled compared to non-oiled areas (Bowyer et al., 2003). Otters living on oiled shores also had lower body mass, larger home ranges, and less diverse diets relative to those in non-oiled areas (e.g., Bowyer et al. 2003). After the Exxon Valdez oil spill, river otters had an increased probability of mortality likely due to the combined effect of direct physiological damage from chronic exposure to oil, decreased ability to dive and forage, and increased energy demands to avoid oiled beaches (Bowyer et al., 2003). Oil spills are bad for river otters, immediately and during the ecosystem’s long recovery.
Water quality
Water pollution and other degradation of aquatic and riparian habitats was thought to play a role in river otter declines across much of North America prior to 1900, and restoration of water and habitat quality played a role in population recovery (Bricker et al., 2022). Looking forward, water quality and habitat destruction has the potential to limit distribution of otters and could pose long-term threats if enforcement of water quality standards is not maintained and enforced (IUCN, 2020).
Predators
While numerous river otter predators have been reported (Melquist et al., 2003), little of this work originates from the Salish Sea. Based on data from other regions, potential river otter predators in the Salish Sea include the bald eagle (Haliaeetus leucoephalus), killer whale (Orcinus orca), gray wolf (Canis lupus), coyote (Canis latrans), domestic dog (Canis familiaris), red fox (Vulpes vulpes), bobcat (Lynx rufus), mountain lion (Puma concolor), black bear (Ursus americanus) and brown bear (Ursus arctos), with most predation directed toward juveniles.
Human conflict
Despite data showing that most of their diet consists of non-game fish, in some states the media has reported on animosity about river otters due to their consumption of fish deemed valuable to recreational anglers (Melquist et al., 2003). At times state wildlife agencies responsible for managing trapping of river otters appear to have been complicit in fostering negative portrayals about river otter predation to gain public support for trapping seasons (IUCN, 2020; Bricker et al., 2022). This has not been noted in Washington State or British Columbia, though gunshot animals have been reported in the San Juan Islands, Washington (Gaydos et al., 2020) and a recent study reported that public perception of river otters in Washington State was divided between positive and negative (Bricker et al., 2022).
Although extremely rare, river otters have been documented to attack humans in freshwater settings (Potter et al., 2007; Seattle PI, 2014). Such attacks also have occurred in marine settings, including the Salish Sea (Seattle Times, 2024). River otters have been documented to attack (and drown) dogs as well, although this too is very rare (St. Petersburg Times, 2001).
Ecosystem indicators
Marine-foraging river otters have been shown to be good biomarkers for environmental contamination and could be used as tools for evaluating contaminant remediation success (Guertin et al., 2012; Wainstein et al., 2022). The Eurasian otter (Lutra lutra) has been used extensively and successfully as a flagship to promote clean-water initiatives in Europe (IUCN, 2020) and there is no reason why marine-foraging river otters should not be used for similar clean water efforts in the Salish Sea.
Population monitoring
While many states are actively monitoring river otter populations (Erb et al., 2018; Roberts et al., 2020), Washington State and British Columbia are not (Bricker et al., 2022) and neither has river otter population estimates. If closer monitoring of marine-foraging river otter populations were to become a priority, available tools could be improved to non-invasively collect DNA from scat to monitor populations (Guertin et al., 2012; Wainstein et al., 2022).
References
Barocas, A., H.N. Golden, M. Dudenhoeffer, M. Ben-David. 2021. Sociality and signaling activity modulate information flow in river otter communication networks. Behavioral Ecology 32(1):60-68. doi:10.1093/beheco/araa102
Ben-David, M., R.T. Bowyer, J.B. Baro. 1996. Niche separation by mink and river otters: Coexistence in a marine environment. Oikos 75(1):41-48.
Ben-David, M., R.T. Bowyer, L.K. Duffy, D.D. Roby, D.M. Schell. 1998. Social behavior and ecosystem processes: river otter latrines and nutrient dynamics of terrestrial vegetation. Ecology 79(7):2567-2571.
Ben-David, M., T.M. Williams, O.A. Ormseth. 2000. Effects of oiling on exercise physiology and diving behavior of river otters: a captive study. Canadian Journal of Zoology 78:1380-1390.
Ben-David M., G.M. Blundell, J.W. Kern, J.A.K. Maier, E.D. Brown, S.C. Jewett. 2005. Communication on river otters: creation of variable resource sheds for terrestrial communities. Ecology. 86:1331–1345.
B.C. Conservation Data Centre. 1997. Species Summary: Lontra canadensis. B.C. Ministry of Environment. Available: https://a100.gov.bc.ca/pub/eswp/ (accessed Nov 25, 2024)
Blundell, G., M. Ben-David, R.T. Bowyer. (2002). Sociality in river otters: cooperative foraging or reproductive strategies? Behavioral Ecology, 13(1): 134-141.
Blundell, G., M. Ben-David, P. Groves, R.T. Bowyer, E. Geffen. 2004. Kinship and sociality in coastal river otters: are they related? Behavioral Ecology 15(5):705-714. doi:10.1093/beheco/arh110
Bouley, P., M. Isadore, T. Carroll. 2015. Return of North American river otters (Lontra canadensis) to coastal habitats of the San Francisco Bay Area, California. Northwestern Naturalist, 96(1): 1-12.
Bowyer, R.T., Blundell, G.M., Ben-David, M., Jewett, S.C., Dean, T.A., and Duffy, L.K. 2003. Effects of the Exxon Valdez oil spill on river otters: injury and recovery of a sentinel species. Wildlife Monographs No. 153.
Bricker, E.A., T.L. Serfass, Z.L. Hanley, S.S. Stevens, K.J. Pearce. 2022. Conservation Status of the North American River Otter in the United States and Canada: Assessing management practices and public perceptions of the species. In Small Carnivores: Evolution, Ecology, Behaviour, and Conservation, 1st Edition. Eds. E.D. Linh San, J.J. Sato, J.L. Belant, M.J. Somers. John Wiley & Sons Ltd.
Buzzell, B., M.M. Lance, A. Acevedo-Gutierrez. 2014. Spatial and temporal variation in river otter (Lontra canadensis) diet and predation on rockfish (Genus Sebastes) in the San Juan Islands, Washington. Aquatic Mammals 40(2):150-161. doi: 10.1578/AM.40.2.2014.150.
Buzzell, B. 2021. Holistic approaches for invasive species management: Exploring biotic resistance of green crab (Carcinus maenas) via river otter (Lontra canadensis) diet. MS Thesis. WWU Graduate School Collection. 1035. https://cedar.wwu.edu/wwuet/1035
Cosby, H., M.S. Gunther. 2021. Variation in diet and activity of river otters (Lontra canadensis) by season and aquatic community. Journal of Mammalogy 102(2):520-529. doi:10.1093/jmammal/gyaa165
Erb, J., N.M. Roberts, C. Dwyer. 2018. An otterly successful restoration. The Wildlife Professional May/June 2018:45-49.
Gaydos, J.K., P. A. Conrad, K.V. Gilardi, G.M. Blundell, M. Ben-David. 2007a. Does human proximity affect antibody prevalence in marine-foraging river otters? Journal of Wildlife Diseases 43: 116-123.
Gaydos, J., W. Miller, K. Gilardi, A. Melli, H. Schwantje, C. Engelstoft, H. Fritz, and P. Conrad.2007b. Cryptosporodium and Giardia in marine foraging river otters (Lontra canadensis) from the Puget Sound Georgia Basin ecosystem. Journal of Parasitology, 93(1): 198-202.
Gaydos, J.K., S. Raverty, M. Delaney. 2020. Causes of mortality in marine-foraging North American river otters (Lontra canadensis). Journal of Wildlife Diseases 56(4). doi: 10.7589/JWD-D-20-00031
Guertin, D.A., A.S. Harestad, J.E. Elliott. 2010a. Summer feeding habits of river otters inhabiting a contaminated coastal marine environment. Northwest Science, 84(1): 1-8.
Guertin, D.A., A.S. Harestad, M. Ben-David, K.G. Drouillard, J.E. Elliott. 2010b. Fecal genotyping and contaminant analyses reveal variation in individual river otter exposure to localized persistent contaminants. Environmental Toxicology and Chemistry, 29(2): 275-284.
Guertin, D.A., M. Ben-David, A.S. Harestad, J.E. Elliott. 2012. Fecal genotyping reveals demographic variation in river otters inhabiting a contaminated environment. Journal of Wildlife Management, 76(8): 1540-1550.
Hayward, J.L. Jr., C.J. Amlaner Jr., W.H. Gillett, J.F. Stout. 1975. Predation on nesting gulls by a river otter in Washington State. The Murrelet, 56(2): 9-10.
IUCN. 2020. IUCN Red List Status for Lontra canadensis by T. Serfass.
Jones, C. 2000. Investigations of prey and habitat use by the river otter (Lutra canadensis) near San Juan Island, Washington. MS Thesis, Western Washington University. Bellingham, Washington.
Kimber, K.R., G.V. Kollias. 2000. Infectious and parasitic diseases and contaminant-related problems of North American river otters (Lontra canadensis): A review. Journal of Zoo and Wildlife Medicine 31: 452-472.
Kimber, K.R., G.V. Kollias, E. J. Dubovi. 2000. Serologic survey of selected viral agents in recently captured wild North American river otters (Lontra canadensis). Journal of Zoo and Wildlife Medicine 31: 168-175.
Kurle, C.M., C.V. Kappel, D.D. Hope, A. Lam. 2013. Invasion status of terrestrial mammals on uninhabited islands within the San Juan Archipelago, Washington. Northwest Science 87(2):178-184.
Larsen, D.N. 1984. Feeding habits of river otters in coastal southeastern Alaska. Journal of Wildlife Management 48: 1446-1452.
Melquist, W.E., P.J. Polechla, D. Toweill. 2003. River otter (Lontra canadensis). pp. 708–734. In: Feldhamer, G.A., B.C. Thompson, and J.A. Chapman (eds.). Wild Mammals of North America: Biology, Management, and Conservation. 2nd ed. The Johns Hopkins University Press, Baltimore, Maryland.
Noll, J.M. 1988. Home range, movement, and natal denning of river otters (Lutra canadensis) at Kelp Bay, Baranof Island, Alaska. MS Thesis, Fairbanks: University of Alaska Fairbanks.
Penland, T.F., J.M. Black. 2009. Variation in river otter diet in coastal Northern California. Northwestern Naturalist 90(3):233-237.
Potter, T.M., J.A. Hanna, L. Freer. 2007. Human North American river otter (Lontra canadensis) attack. Wilderness and Environmental Medicine 18:41-44.
Raesly, E.J. 2001. Progress and status of river otter reintroduction projects in the United States. Wildlife Society Bulletin 29(3):856-862.
Roberts N.M., M.J. Lovallo, S.M. Crimmins. 2020. River otter status, management, and distribution in the United States: Evidence of large-scale population increase and range expansion. Journal of Fish and Wildlife Management 11(1):279–286; e1944-687X. https://doi.org/10.3996/102018-JFWM-093
Russell, A. 2015. Dietary patterns of Lontra canadensis in the Lower Snohomish River Estuary, Washington. Northwest Science, 89(2):182-187.
Scheffer, V.B. 1952. Otters diving to a depth of sixty feet. Journal of Mammalogy 34(2):255.
Seattle PI. 2014. It felt like knives: Victims of otter attack home, recovering. August 5, 2014.
Seattle Times. 2024. River otter pulled child into water at Bremerton Marina, officials say. September 13, 2024.
Shanebeck, K.M., C. Thacker, C. Lagrue. 2022. Corynosoma strumosum (Acanthocephala) infection in marine foraging mink (Neogale vison) and river otter (Longra canadensis) and associated peritonitis in a juvenile mink. Parasitology International 89: doi: https://doi.org/10.1016/j.parint.2022.102579
Speich, S.M., R.L. Pitman. 1984. River otter occurrence and predation on nesting marine birds in the Washington Islands Wilderness. The Murrelet 65:25-27.
St. Petersburg Times. 2001. Unusual otter attack kills dog. May 4, 2001.
Stenson, G.B., G.A. Badgero, H.D. Fisher. 1984. Food habits of the river otter (Lutra canadensis) in the marine environment of British Columbia. Canadian Journal of Zoology 62(1): 88-91.
Tabor, J.E., J.M. Wright. 1977. Status of river otter in Western Oregon. Journal of Wildlife Management 41(4):692-699.
Toweill, D.E. 1974. Winter food habits of river otters in western Oregon. The Journal of Wildlife Management 38(1):107-111.
Verbeek, N.A.M., J.L. Morgan. 1978. River otter predation on Glaucous-winged gulls on Mandarte Island, British Columbia. The Murrelet 59(3):92-95.
Wainstein, M., L.B. Harding, S.M. O-Neill, D.T. Boyd, F. Koontz, B. Miller, C.F.C. Klutsch, P.J. Thomas, G.M. Ylitalo. 2022. Highly contaminated river otters (Lontra canadensis) are effective biomonitors of environmental pollutant exposure. Environmental Monitoring and Assessment 194:670. https://doi.org/10.1007/s10661-022-10272-9
Links
WDFW: https://wdfw.wa.gov/species-habitats/species/lontra-canadensis#conflict
Woodland Park Zoo Carnivore Spotter: https://carnivorespotter.org
Acknowledgments
I really appreciate the help of Ysmine Hentati and Michelle Wainstein who provided important comments and edits that really improved the quality of this species profile.
Licensing & attribution
Data and products from the PSEMP Marine Mammal Work Group are governed by a Creative Commons BY-NC-SA license. Attribution should be to: “PSEMP Marine Mammal Work Group” with a link back to https://psemp.net/mmwg.