Anodonta californiensis 

Scope: Global

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Bivalvia Unionoida Unionidae

Scientific Name: Anodonta californiensis
Species Authority: I. Lea, 1852
Common Name(s):
English California Floater
Taxonomic Notes: Recently, Zanatta et al. (2007) supported the monophyly of both Pyganodon and Utterbackia using mutation coding of allozyme data, but also resolved the Eurasian Anodonta cygnea to Pyganodon, Utterbackia, and North American Anodonta. This indicates that futher phylogenetic analysis of the Anodontinae is required including both North American and Eurasian species. Since the time of Call (1884) there has been much confusion regarding the taxonomic status of this and other floaters (Anodonta) of western North America. Isaac Lea (1838) described Anodonta wahlametensis, Anodonta nuttalliana, and Anodonta oregonensis from the same site ("Wahlamet [Willamette River], near its junction with the Columbia River [Oregon]") all in the same publication. Under the Rule of First Revisor (ICZN), Call (1884) considered Anodonta nuttalliana to include, as synonyms, Anodonta wahlametensis, Anodonta oregonensis, and Anodonta californiensis. Recent authors (e.g., Burch 1975, Clarke 1981, Turgeon et al. 1998), however, have considered A. californiensis, A. nuttalliana, and A. oregonensis to be distinct. Some authors even continue to recognize Anodonta wahlamatensis as a distinct species (Frest and Johannes 1995, Taylor 1981, Henderson 1929) while most place it in the synonymy of A. nuttalliana (Burch 1975, Turgeon et al. 1998). Whether A. wahlamatensis should be removed from the synonymy of A. nuttalliana will depend on future anatomical and genetic work on western Anodonta. Considerable taxonomic confusion surrounds this species complex. Mock et al. (2004, 2005) found a lack of resolution (very little nuclear diversity) in phylogenetic reconstructions of Anodonta (A. californiensis, A. oregonensis, A. wahlamatensis) populations in the Bonneville Basin, Utah, but there was a tendency for the Bonneville Basin Anodonta (tentatively A. californiensis) to cluster with A. oregonensis from the adjacent Lahontan Basin in Nevada. Other taxonomic issues surrounding this and other members of western North American anodontines can be found in Chong et al. (2008).

A list of synonyms for this species can be found on The MUSSEL project web site (Graf and Cummings 2011).

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2011
Date Assessed: 2011-07-22
Assessor(s): Cummings, K. & Cordeiro, J.
Reviewer(s): Böhm, M. & Collen, B.
Contributor(s): Dyer, E., Soulsby, A.-M., Whitton, F., McGuinness, S., De Silva, R., Milligan, H.T., Kasthala, G., Thorley, J., Herdson, R., McMillan, K. & Collins, A.
Anodonta californiensis has been assessed as Least Concern due to its widespread distribution. This species was once thought to have been widespread in the Pacific Drainage from British Columbia into Mexico, but there is considerable taxonomic confusion as to the placement of the western North American Anodonta species. The current range however is patchy, and it has apparently disappeared from the Central Valley in California. Extant occurrences in the Columbia and Snake river systems are threatened by river impoundment. If this species turns out to be a composite, its conservation status would require reassessment.
Previously published Red List assessments:

Geographic Range [top]

Range Description:The range of this species is unclear due to taxonomic uncertainty with the Pacific Drainage members of this genus. In the broadest view, it once ranged from southern British Columbia south to northernmost Baja California, eastward to western Wyoming, eastern Arizona and Chihuahua (Mexico), but this distribution probably includes records for other species (Taylor 1981, Nedeau et al. 2005) such as Anodonta nuttalliana. Taylor (1987) lists the species in 4 inch or greater depth pools in a spring complex above the North Fork of the East Fork of the Black River, Apache Co., Arizona. Clarke and Hovingh (1993) state that "as presently understood this species occurs in California, Nevada, Utah, and Arizona." and that the closely related Anodonta nuttalliana occurs in Oregon, Washington, and British Columbia. Preliminary analysis (K. Mock pers. comm. 2010) indicates Utah Anodonta are distinct from Anodonta oregonensis of the Pacific northwest and should tentatively be assigned to Anodonta californiensis pending future taxonomic work. Presently, Frest and Johannes (1995) report  that the range has been reduced and extant populations are currently found in the following areas: the Middle Snake River in Idaho; the Fall and Pit rivers in Shasta County, California; the Okanogan river in Chelan County, Washington; and Roosevelt and Curlew lakes in Ferry County, Washington. No living specimens were found in the Willamette and lower Columbia rivers in searches by Frest and Johannes conducted from 1988-1990. Taylor (1981) reports that most of the natural populations in California have been eradicated and it is probably extinct in most of the Central Valley of southern California. In Utah, the only recent records are in two widely-spaced locations, Big Creek and Reddin Spring pond, but it may still be extant in the Raft River and portions of the Bear River drainage (Clarke and Hovingh 1993). It is extirpated from Utah Lake. Hovingh (2004) found it widely distributed in the Humboldt River drainage (Lahontan Basin) in northern Nevada, in the Bonneville Basin in Utah, Nevada, and Wyoming, and in the Malheur and Warner Basins in Oregon. Mock et al. (2005) list six sites in the Bonneville basin of Utah tentatively assigned to this species.
Countries occurrence:
Canada (British Columbia); Mexico (Chihuahua); United States (Arizona, California, Idaho, Nevada, Oregon, Utah, Washington, Wyoming)
Additional data:
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Due to taxonomic uncertainty, it is difficult to determine the number of occurrences for this species (probably more than twenty but less than 100). Beetle (1989) lists the Bear River in Uinta Co., Wyoming. In Utah, occurrences (between two and six) are known from Utah, Millard, Rich, Tooele, and Box Elder Cos. (Oliver and Bosworth 1999). These sites were resurveyed recently and extant populations (tentatively Anodonta californiensis) were found in Bear River, Redden Spring, Pruess Lake, Piute Reservoir, Otter Creek Reservoir, and Burriston Ponds, all in Utah (Mock et al. 2004). Mock et al. (2004) also cite specimens tentatively identified as A. californiensis from the Black River, Apache, Arizona. Frest and Johannes (1995) report that the range has been reduced and extant populations are found in: the Middle Snake River in Idaho; the Fall and Pit Rivers in Shasta Co., California; the Okanogan river in Chelan Co., Washington; and Roosevelt and Curlew Lakes in Ferry Co., Washington. No living specimens were found in the Willamette and lower Columbia rivers in searches by Frest and Johannes from 1988-1990. Frest and Johannes (2000) list it as common locally in the Snake River and major tributaries. Taylor (1981) reports most California populations as eradicated and the species is probably extinct in most of the Central Valley. It was once distributed throughout six major drainages in Arizona (including Lake Mead, Grand Canyon, Lower Colorado-Marble Canyon, Lower Lake Powell), but today is only in portions of the Black River drainage and Little Colorado River (Nedeau et al. 2005). In Utah, the only recent records are widely spaced, in Big Creek and Reddin Spring Pond, but it may still be extant in the Raft River and portions of the Bear River drainage (Clarke and Hovingh 1993). Hovingh (2004) found it widely distributed in the Humboldt River drainage (Lahontan Basin) in northern Nevada, the Bonneville Basin in Utah, Nevada, and Wyoming, and the Malheur and Warner Basins in Oregon. Other Nevada occurrences are in the Great Salt Lake, North Fork Humboldt, Truckee, and Carson Desert basins (NV NHP pers. comm. 2007). Mock et al. (2004), in an analysis of genetic diversity, found the Bonneville Basin (Utah) population cluster with Anodonta oregonensis from the adjacent Lahontan Basin (surveyed in Elko, Nevada) and the Middle Snake/Powder basin (Baker Co., Oregon). Mock et al. (2004) further differentiated Glenn and Solano Co., California, specimens as Anodonta wahlamatensis, thereby limiting Anodonta californiensis populations to Utah (see above) and Arizona (Black River in Apache). In Oregon, several populations were recently found in the Middle Fork John Day River and the lower main stem Umatilla River, but due to taxonomic confusion, identification beyond genus was not possible (Brim Box et al. 2006); however, preliminary evidence indicates the John Day River population includes the A. californiensis/nuttalliana clade and the Umatilla River population include both A. oregonensis/kennerlyi and A. californiensis/nuttalliana clades in sympatry (K. Mock, Utah State University, pers. comm. 2007). Chong et al. (2008) utilized specimens from the East Fork Black River, Arizona, in their phylogenetic study. Recent Washington records are mainly from the Columbia and Okanogan Rivers and some ponds adjacent to the Columbia River (Nedeau et al. 2005). In Arizona, Bequaert and Miller (1973) list the Lower Colorado, San Pedro-Wilcox, Chevelon, and Little Colorado drainages as historical with the only recent occurrence in the Black River drainage. Historically in Arizona, it was found in most drainages including the Black, Salt, Santa Cruz, Verde, Gila and Colorado Rivers, but today it is only found in the upper Black River in the the Apache-Sitgreaves National Forest to at least the White Mountain Apache Reservation (AZ NHP pers. comm. 2007). A population may be extant on Chevelon Creek according to Landye (1981).

In a survey of streams in California, approximately 8,000 individuals were found in the upper reaches of the Eel River (none in Ten Mile, Elder, or Fox Creeks), restricted to the lower 2 km of the upper portion of the river (Cuffey 2002).

Frest and Johannes (1995) report that the species is declining in terms of area occupied and the number of sites and individuals, and local declines have been observed throughout the range (Mock et al. 2010). It is generally widely distributed, though scarce; it is likely extirpated from the Colorado River basin in Arizona and Death Valley Basin, Los Angeles Basin, and Central Valley in Caifornia (Hovingh 2004). A recent survey of 115 sites in the Plumas, Tahoe, and Eldorado National Forests plus Lake Tahoe Basin management unit found no Anodonta specimens (in 70+ streams) except a few whole shells at 15 m depth in Donner Lake despite historical occurrences there (Howard 2008). The species is declining (possibly extirpated) in Utah with historic populations only in the Raft River (Box Elder Co.), Utah Lake (Utah Co.), and Bear Lake (Rich Co.) (Oliver and Bosworth, 1999). It is nearly extirpated from Arizona and has disappeared from the Sacramento River system. In Canada, this species occurs in British Columbia where it is declining (Metcalfe-Smith and Cudmore-Vokey 2004). Regardless of the taxonomic outcome of analysis of Anodonta molecular phylogeny, it is widely recognized that Anodonta in the western U.S. are in decline (Mock et al. 2004).
Current Population Trend:Decreasing
Additional data:
Population severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:This is a low elevation species that is found in both lakes and lake-like stream environments (Frest and Johannes 1995).
Congregatory:Congregatory (and dispersive)

Threats [top]

Major Threat(s): Threats to this species includes pollution; diversion of rivers for irrigation, hydroelectric, and water supply projects; elimination of natural fish hosts; eutrophication due to agricultural run-off and urbanization; impoundments. The species can tolerate some water pollution, but not heavy nutrient enhancement (Frest and Johannes 1995).

Mock et al. (2004) found that populations of Anodonta (tentatively Anodonta californiensis but further taxonomic study could reveal them to be Anodonta oregonensis or Anodonta wahlamatensis) from the Bonneville Basin of Utah were strongly structured with little or no recent gene flow among extant populations which are currently hydrologically separated. This fragmentation makes the populations vulnerable to threats.

Conservation Actions [top]

Conservation Actions: This species breaks into eight conservation units based on available genetic data. These subclades can be considered evolutionarily significant units and all populations (with the exception of AOC and APR) could be considered distinct management units (Mock et al. 2010). However, no specific conservation actions have been undertaken. Some conservation units would potentially require careful monitoring (A.Bogan pers. comm. 2010). Further research is necessary regarding this species' taxonomy, population trends, ecology and impacting threats. Future monitoring of population trends and the implementation of conservation policies are required in order to protect this species from future declines. Ex-situ conservation could play a part in species recovery.

Citation: Cummings, K. & Cordeiro, J. 2011. Anodonta californiensis. The IUCN Red List of Threatened Species 2011: e.T1311A3409492. . Downloaded on 24 October 2016.
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