Anodonta oregonensis 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Bivalvia Unionoida Unionidae

Scientific Name: Anodonta oregonensis
Species Authority: Lea, 1838
Common Name(s):
English Oregon Floater
Anodon cognata Gould, 1850
Taxonomic Source(s): Lea, I. 1838. Description of new freshwater and land shells. Transactions of the American Philosophical Society 6: 1-154.
Taxonomic Notes:

Lea (1838) originally described Anodonta oregonensis from the Wahlamat R. [Willamette River], Oregon. Simpson (1900) subsequently synonymized Anodon cognata Gould, 1850 (Locality: Oregon). Work by Chong, et al. (2008) revealed that western North American Anodonta species are comprised of three genetically distinct lineages. One of these clades includes two of Lea's described species, A. oregonensis Lea, 1838 and A. kennerlyi Lea, 1860. Based on this work, Bieler (2015) lists A. kennerlyi as a synonym of A. oregonensis. A detailed list of synonyms can also be found at the Mussel Project Web Site: MUSSELp (Graf & Cummings, 2015).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2016
Date Assessed: 2016-03-14
Assessor(s): Blevins, E., Jepsen, S., Brim Box, J. & Nez, D.
Reviewer(s): Tait, C.

We used a dataset of western freshwater mussel occurrence records (shells and/or live animals) from nearly 300 sources spanning the 1830s to 2015 (Xerces/CTUIR 2015). This analysis examined change in extent of occurrence (EOO) and area of watershed occupancy from occurrence (presence) data prior to 1990, and from 1990–2015. Based on 371 records dating prior to 1990 and 758 records dating 1990–2015, Anodonta oregonensis has declined in EOO by 9% (231,834 km²) but in watershed area by 26% (69,474 km²). This analysis includes occurrence records for both A. oregonensis and A. kennerlyi (Chong, et al., 2008; Bieler, 2015). Estimates are also dependent on a number of assumptions regarding historical and recent distribution. Based on a review of 235 historical museum specimens or photos of specimens (Blevins et al., unpublished data, 2015) using morphological analyses to differentiate western Anodonta (Chong, 2006; Hegeman, et al. unpublished manuscript, 2015), historic records for this species in Utah, Nevada, and southern California were considered in error; no measured specimens were identified as A. oregonensis based on measures of both length to height ratio and anterior slope angle. Healthy reproducing populations have been reported in the lower Columbia Basin in Washington and Oregon. Additionally, compared with A. nuttalliana, which is distributed across more arid watersheds, A. oregonensis is believed to be less threatened by the impacts of climate change and dewatering. Therefore, this species is currently considered of Least Concern. 

Previously published Red List assessments:

Geographic Range [top]

Range Description:

Understanding of this species’ geographic range is confounded by difficulties associated with the identification of Anodonta species using shell morphology and the overlap in species’ ranges (Chong, 2006). In Canada, this species is found in British Columbia. Museum records are reported from Atlantic and Arctic river basins in Alberta and the Northwest Territories, but the species’ current presence in these basins is unverified. In the United States, the species is found in Oregon, Washington, Idaho, northern California, and Alaska, and based on morphological evidence (Blevins et al., unpublished data, 2015) from 235 historical museum specimens or photos of specimens using measures described by Chong (2006) and Hegeman, et al. (unpublished manuscript, 2015), Anodonta oregonensis did not historically occur in southern California (as defined by the southernmost 10 counties of the state), Utah, or Nevada no measured specimens were identified as A. oregonensis based on measures of both length to height ratio and anterior slope angle. More than twice as many observations of this species have been reported since 1990 compared to pre-1990. 

Countries occurrence:
Canada (British Columbia); United States (California, Idaho, Oregon, Washington)
Additional data:
Continuing decline in area of occupancy (AOO):Unknown
Extreme fluctuations in area of occupancy (AOO):UnknownEstimated extent of occurrence (EOO) - km2:2406376
Continuing decline in extent of occurrence (EOO):UnknownExtreme fluctuations in extent of occurrence (EOO):Unknown
Continuing decline in number of locations:Unknown
Extreme fluctuations in the number of locations:Unknown
Range Map:Click here to open the map viewer and explore range.

Population [top]


Knowledge of population abundance and trend is confounded by the identification of Anodonta species using shell morphology. Where found, populations of Anodonta may be locally common or abundant (Howard, et al., 2015; Xerces/CTUIR, 2015; Brim Box, et al., 2006) or sparsely distributed or rare (Hegeman, 2012; Davis, et al., 2013; Starkey, 2015). Anodonta density has been reported as low as 0.52 mussels/m² (Hegeman, 2012) and as high as ~275 individuals/m² (Brim Box, et al., 2006) in the Middle Fork John Day River, Oregon. Healthy reproducing populations have been reported in the lower Columbia Basin in Washington and Oregon.

Current Population Trend:Unknown
Additional data:
Continuing decline of mature individuals:Unknown
Extreme fluctuations:UnknownPopulation severely fragmented:No
Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:

This species has been reported from many types of habitats, including low elevation ponds, reservoirs, lakes, creeks, and rivers and may co-occur with Anodonta nuttalliana (Chong, et al., 2008; Nedeau, et al., 2009). In rivers, Anodonta may be found in both pools and runs (Hegeman, 2012). As with other unionids, A. oregonensis requires a host fish to complete development. Host fish species may be confirmed (i.e., glochidial infestation of the fish has been observed in the wild and metamorphosis of the glochidia has also been observed) or may be considered potential hosts (either glochidia infestation has been observed only under artificial conditions or glochidial metamorphosis has not been observed; O’Brien & Brim Box, 1999; O’Brien & Williams, 2002; O’Brien, et al., 2013). Confirmed native and nonnative host fish include Prickly Sculpin (Cottus asper) and Threespine Stickleback (Gasterosteus aculeatus) (Martel & Lauzon-Guay, 2005). Potential native and nonnative host fish include Chinook Salmon (Oncorhynchus tshawytscha), Coho Salmon (Oncorhynchus kisutch), Cutthroat Trout (Oncorhynchus clarkii), Dolly Varden (Salvelinus malma), Margined Sculpin (Cottus marginatus), Rainbow Trout (Oncorhynchus mykiss), Redside Shiner (Richardsonius balteatus), and Speckled Dace (Rhinichthys osculus) (Moles, 1983; Martel & Lauzon-Guay, 2005; Maine & O’Brien, unpublished data, 2016).

Continuing decline in area, extent and/or quality of habitat:Unknown
Generation Length (years):8

Use and Trade [top]

Use and Trade: Freshwater mussels have cultural significance for First Nations and Tribes in western North America, including as a traditional food resource (COSEWIC 2003; CTUIR 2015).

Threats [top]

Major Threat(s):

Threats to freshwater mussels in North America include: impoundments and loss or decline of host fish, channel modification from channelisation, dredging and mining, restoration activities that impact streambanks or streambeds or dewater channels, contamination, sedimentation and scouring, nutrient enrichment, water withdrawal and diversion, thermal pollution, livestock grazing in riparian areas, shoreline development, and the introduction of non-native plant, fish and invertebrate species (Jepsen, et al., 2012). Many of these impacts, especially a reduction in stream flow and thermal pollution in arid areas, are being exacerbated by climate change.

Conservation Actions [top]

Conservation Actions:

Because this species is easily confused with other western Anodonta that are Vulnerable, protection of all Anodonta populations from known threats is recommended and remediation of known threats should be prioritised. Methods to improve accurate identification of specimens to the species level should be prioritized, as should additional surveys and long term monitoring to evaluate population trends. The species’ range in Alaska, which overlaps with genetically distinct Anodonta beringiana, should be assessed. Observations in Alberta and one in the Northwest Territories should be further explored and specimens collected in order to determine whether or not A. oregonensis occurs in these areas.

Citation: Blevins, E., Jepsen, S., Brim Box, J. & Nez, D. 2016. Anodonta oregonensis. The IUCN Red List of Threatened Species 2016: e.T189487A69491650. . Downloaded on 23 January 2017.
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