|Scientific Name:||Anodonta nuttalliana Lea, I., 1838|
Anodon rostratus Sowerby, 1867
Anodonta californiensis Lea, 1852
Anodonta laosensis Fischer, 1891
Anodonta rotundovata Trask, 1855
Anodonta triangularis Trask, 1855
Anodonta wahlamatensis Lea, 1838
|Taxonomic Source(s):||Lea, I. 1838. Description of new freshwater and land shells. Transactions of the American Philosophical Society 6: 1-154.|
Lea (1838) originally described Anodonta nuttalliana and Anodonta wahlamatensis from the Wahlamat R. [Willamette River], Oregon. A. wahlamatensis was later synonymized under A. nuttalliana by Call (1884) and Turgeon et al. (1998). 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. nuttalliana Lea, 1838 and A. californiensis Lea, 1852. Mock et al. (2010) found that these two putative species as identified based on shell morphology, co-occurred in major western hydrologic basins. However, Anodonta specimens from the same populations, regardless of shell morphology, were more closely related to each other than to specimens having the same morphotype from other populations. Based on the findings of Chong et al. (2008), Bieler (2015) lists A. californiensis as a synonym of A. nuttalliana. Additionally, work by Mock et al. (2010; 2013) indicates that populations within major hydrologic basins across the west are distinct genetically. A detailed list of synonyms can be found at the Mussel Project Web Site: MUSSELp (Graf and Cummings 2015).
|Red List Category & Criteria:||Vulnerable A2c ver 3.1|
|Assessor(s):||Blevins, E., Jepsen, S., Brim Box, J. & Nez, D.|
|Contributor(s):||Barnhart, C., Fallon, C., Hatfield, R., Howard, J., LaBar, C., Maine, A., Mock, K., Myers, T., O’Brien, C., Smith, A., Tait, C. & Zarnoch, J.|
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; full list of contributors at http://www.xerces.org/western-freshwater-mussel-database-contributors/). 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 736 records dating prior to 1990 and 942 records dating 1990-2015, Anodonta nuttalliana has declined in EOO by 9% (208,031 km²) but in watershed area by 33% (120,427 km²). This analysis includes occurrence records for both A. nuttalliana and A. californiensis (Chong et al. 2008, Bieler 2015). Range contractions are evident in southern California and Arizona, as well as in other western states. These occurrence-based declines are reinforced by range-wide genetic research and regional and local abundance observations, especially observations of decline that have been reported since 1990, which are not reflected in the analysis. For example, Mock et al. (2004) has shown that population-level nuclear genetic diversity in Utah populations is low and that populations may now be isolated, two characteristics that may increase the risk of local extinctions. A population at Redden Spring in Utah may be of particular concern, as this site is isolated and contains incredibly low genetic diversity as compared even to other Utah populations (Mock et al. 2004, Mock et al. 2010). Mock et al. (2010) also found that populations within major hydrologic basins across the west are distinct enough to be considered evolutionarily significant units and possibly distinct management units. Several populations exhibit evidence of a recent genetic bottleneck; thus, even declines limited to certain hydrologic basins may have a disproportionate effect on future extinction risk in this species.
Populations in Nevada were once abundant (Call 1884), and though the species still persists, it now appears absent in the Lahontan and Humboldt basins in part of northwestern Nevada and scarce in other historic locations (reviewed in Jepsen et al. 2012, Hovingh 2004, Smith unpub. data 2009). Recent surveys in Wyoming also suggest that the species may be more imperilled than previously recognized. In a survey of 23 sites, only 13 total Anodonta were found, comprised of only larger, older individuals (Mathias and Edwards 2014). Indeed recent surveys by Howard et al. (2015) found that the species has been extirpated from all resurveyed historical southern California sites (n = 14; though the species was observed in the Bishop Creek Canal in Inyo County). Populations of Anodonta in northern California also appear to be declining in total population size and in number of populations (Howard et al. 2015).
Although a number of watersheds in the lower Colorado River Basin of Arizona indicate recent occupancy of Anodonta, work by Myers (2009) suggests that the species began its decline in Arizona circa 1960, following extensive habitat destruction and alteration. Since 1990, live Anodonta have been reported only from the Black River Basin; recent records from the Little Colorado basin are based on shells and shell fragments. Within the Black River Basin, surveys conducted more recently (post-2000) suggest that populations there have also declined (Myers 2009). This analysis is unable to detect declines that have occurred since 1990, since changes in extent of occurrence have been calculated using data before and after 1990, which may underestimate actual population declines. Portions of the Yaqui and Guzmán basins of southern Arizona and northern Mexico are still inhabited, but recent surveys of historical sites and observations by local residents indicate the species is no longer common (Myers, unpub. data 2008). Thus, decline in this region is likely higher than suggested by this analysis.
The status of the species in Idaho is unstudied, but anecdotal declines have been reported in both Oregon and Washington (reviewed in Jepsen et al. 2012), and state natural heritage programs consider the species critically imperilled in Washington and possibly Oregon and imperilled in Idaho (NatureServe 2015). Populations in British Columbia are listed as “apparently secure” (NatureServe 2015). Given observations of population declines and extirpations and the reduction in extent of occurrence and watershed area over the last 25 years, a decline in population equal to or greater than 30% over the past three generations (with generation length being estimated at eight years) is inferred, and this species should be considered Vulnerable.
Understanding of this species’ geographic range is confounded by difficulties associated with the identification of Anodonta species using shell morphology. Based on historic and recent collections and observations, it appears that this species is found from southern British Columbia south to northern Mexico (Sonora and Chihuahua) and east to Utah, Arizona, and western Wyoming. The species appears to now be extirpated from all of southern California (as defined by the southernmost 10 counties of the state) and most of the lower Colorado River Basin, which spans Arizona, Nevada, and California. Specimens of Anodonta from the Yaqui River Basin and Guzmán Basin of Sonora and Chihuahua, Mexico have been variously identified as Anodonta impura, A. dejecta, A. mearnsiana, A. exilior, A. coarctata, A. californiensis, and A. wahlametensis. However, recent research by Myers (2009, 2012) and Culver et al. (2012) suggests that Anodonta from these basins are most closely related to populations of Anodonta from the Owens and Black River basins of California and Arizona. Anodonta collected from other basins in Mexico appear to be more closely related to other species of Anodonta that do not occur in the U.S. (Culver et al. 2012). Thus, the records from the Yaqui River Basin and Guzmán Basin of Sonora and Chihuahua, Mexico likely represent the southern extent of this clade’s range.
Native:Canada (British Columbia); Mexico (Chihuahua, Sonora); United States (Arizona, California, Idaho, Nevada, Oregon, Utah, Washington, Wyoming)
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||As with geographic distribution, 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 (Brim Box et al. 2006, Hovingh 2004, Hegeman 2012, Davis et al. 2013). 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.|
Decline in watershed area is reinforced by more regional and local abundance observations, especially observations of decline that have been reported since 1990, which are not reflected in the analysis. Recent surveys in Wyoming suggest that the species may be more imperilled than previously recognised. In a survey of 23 sites, only 13 total Anodonta were found, comprised of only larger, older individuals (Mathias and Edwards 2014). Indeed recent surveys by Howard et al. (2015) found that the species has been extirpated from all resurveyed historical southern California sites (n = 14; though the species was observed in the Bishop Creek Canal in Inyo County). Populations of Anodonta in northern California also appear to be declining in total population size and in number of populations (Howard et al. 2015). In Arizona since 1990, live Anodonta have been reported only from the Black River Basin; recent records from the Little Colorado basin are based on shells and shell fragments. Within the Black River Basin, surveys conducted more recently (post-2000) suggest that populations there have also declined (Myers 2009).
|Current Population Trend:||Decreasing|
|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 oregonensis (Chong et al. 2008, Nedeau et al. 2009). In rivers, Anodonta may be found in both pools and runs (Hegeman 2012), although it is found almost solely in pools in the South Fork Eel River (Howard and Cuffey 2003).|
As with other unionids, A. nuttalliana requires a host fish to complete development. Anodonta glochidia (the larval stage) have been observed in northern California during all months of the year except September and October (Spring Rivers, 2007) and in June and July in Oregon (O’Brien et al. 2013) and are released in “a sticky, rust-colored, web-like mass” (O’Brien et al. 2013). Several species of host fish have been confirmed (i.e., glochidial infestation of the fish has been observed in the wild and metamorphosis of the glochidia has also been observed) or are considered potential hosts for Anodonta (either glochidia infestation has been observed only under artificial conditions or glochidial metamorphosis has not been observed; O’Brien and Brim Box 1999, O’Brien and Williams 2002, O’Brien et al. 2013), and this species appears to be a host-fish generalist (O’Brien et al. 2013). Confirmed native and non-native host fish reported for A. nuttalliana and synonymous species include Hardhead (Mylopharodon conocephalus), Pit Sculpin (Cottus pitensis), Redside Shiner (Richardsonius balteatus), Sacramento Pikeminnow (Ptychocheilus grandis), Speckled Dace (Rhinichthys osculus), Threespine Stickleback (Gasterosteus aculeatus), Torrent Sculpin (Cottus rhotheus), Tule Perch (Hysterocarpus traski), and Green Sunfish (Lepomis cyanellus) (Spring Rivers 2007, O’Brien et al. 2013, Maine et al. 2016). Potential native and non-native host fish reported for A. nuttalliana and synonymous species include Chiselmouth (Acrocheilus alutaceus), Longnose Dace (Rhinichthys cataractae), Margined Sculpin (Cottus marginatus), Northern Pikeminnow (Ptychocheilus oregonensis), Peamouth (Mylocheilus caurinus), Sucker (Catostomus sp.), and Mosquitofish (Gambusia affinis) (D'Eliscu 1972, Lang 1998, Spring Rivers 2007, O’Brien et al. 2013, Maine et al. 2016).
|Continuing decline in area, extent and/or quality of habitat:||Unknown|
|Generation Length (years):||8|
|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 to Anodonta nuttalliana and other species of 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. Several host fish species, such as sculpin and dace, are rather sedentary relative to host fish for other western freshwater mussel species (such as Margaritifera falcata, whose salmonid host fish may range hundreds of miles), and declines in host species’ population size and distribution may also have significant impacts on this species. Mock et al. (2010) also found that populations exhibit pronounced geographic structure with regard to hydrologic basin and some may have experienced recent genetic bottlenecks. Thus even threats limited to only a subset of populations or within a subset of hydrologic basins may have a disproportionate effect on future extinction risk in this species.
This species is easily confused with other western Anodonta, and protection of all Anodonta populations from known threats is recommended; remediation of known threats should be prioritized. Few abundance estimates are available for existing populations, and anecdotal declines have been reported across the range, although causes of these declines are not well understood. Additional surveys and monitoring of populations throughout the range to evaluate population trends should be prioritised. Methods to improve accurate identification of specimens to the species level should also be prioritised. More recent surveys of parts of the Humboldt Basin by Smith (2009) uncovered only a single old intact shell but no live specimens (unpub. data), and future extensive snorkel surveys are recommended in the basin to determine the species’ current status there.
|Errata reason:||This errata version of the assessment includes the assessment contributors, the distribution map (both were missing from the original assessment), and addresses some minor formatting issues.|
|Citation:||Blevins, E., Jepsen, S., Brim Box, J. & Nez, D. 2016. Anodonta nuttalliana. (errata version published in 2017) The IUCN Red List of Threatened Species 2016: e.T91149898A114130670.Downloaded on 20 October 2017.|
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