|Scientific Name:||Gonidea angulata|
|Species Authority:||(Lea, 1838)|
Anodon biangulata Sowerby, 1869
Anodon feminalis Gould, 1850
Anodonta angulata Lea, 1838
Anodonta randallii Trask, 1855
Gonidea coalingensis Arnold, 1909
Margaritana subangulata Cooper, 1894
|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 placed the species in the genus Anodonta and described a specimen from the type locality “Lewis R., Ore.” Gould (1850) later described Anodon feminalis, which Lea (1852) revised back to Anodonta angulata. Trask (1855) described Anodonta randallii from the Sacramento and San Joaquin rivers, which Lea (1856) also revised back to Anodonta angulata. Sowerby (1869) described Anodon biangulata, which Lea (1870) synonymized with Anodonta angulata. Cooper (1894) recognized Margaritana subangulata, and Arnold (1909) recognized Gonidea coalingensis and Gonidea coalingensis cooperi. Graf & Cummings (2015) list each of these as synonyms of Gonidea angulata. A list of synonyms can be found at the Mussel Project Web Site: MUSSELp (Graf & Cummings, 2015).
|Red List Category & Criteria:||Vulnerable A2c ver 3.1|
|Assessor(s):||Blevins, E., Jepsen, S., Brim Box, J. & Nez, D.|
|Reviewer(s):||Tait, C. & Mageroy, 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). 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 338 records dating prior to 1990 and 605 records dating 1990–2015, Gonidea angulata, the only extant member of the genus Gonidea, has declined in EOO by 28% (339,740 km²) and watershed area by 43% (77,647 km²). The range for this species appears to have always been smaller than other species of western freshwater mussels, comprising approximately 47% of the average historic EOO and watershed area for Anodonta oregonensis, Anodonta nuttalliana, and Margaritifera falcata.
G. angulata has been assessed as endangered in Canada (COSEWIC 2010) based on limited extent of occurrence, inferred continuing decline in populations at some sites and high risk of continuing decline in light of existing threats and future threats such as dreissenid mussel introduction (COSEWIC 2010, BCCDC 2015). Declines in the Okanagan Basin are suspected based on the extent of habitat modification dating as far back as the 1950s (COSEWIC 2010). Taylor (1981) and Coney (1993) have reported that G. angulata is likely extirpated from southern California and most of the Central Valley. While the species has been found in abundance at several sites in northern California, it appears to no longer be widespread throughout the state, as only a subset of historical sites are still occupied (Howard 2010, Davis et al. 2013). Indeed, more recent surveys (Howard et al. 2015; Howard 2010, Western Mollusk Sciences 2008) found no evidence that G. angulata still occurs in southern California. It is unknown whether this species is capable of recolonising historic habitat; additionally, Howard et al. (2015) report the loss of several California historical sites (now dry or relocated). Populations in Washington, Oregon, and Idaho are also believed to be in decline, although quantitative estimates of population size and trends are unavailable. The species has been extirpated from historical sites in the Snake and Columbia River basins (Brim Box et al. 2006, COSEWIC 2003, Frest and Johannes 1995), and other declines have been reported (reviewed in Jepsen and LaBar 2012). More recent surveys of parts of the Humboldt Basin by Smith (2009) uncovered only a single old intact shell but no live specimens (Smith 2009, unpublished data). Given observations of population declines and extirpations and the reduction in extent of occurrence and watershed area, a decline in population over the past three generations (generation length estimated to be 15 years) equal to or greater than 30% is inferred, and this species should be considered Vulnerable.
Museum records and historical observations indicate that this species formerly occurred from the Santa Ana River Basin of southern California north to southern British Columbia in the Okanagan Basin and east to the Snake River Basin in Idaho and northern Nevada. Historical references to Montana and Utah populations (Henderson 1924, 1929, 1936) have never been confirmed, despite many surveys (NatureServe 2015, Stagliano 2010). Possible Colorado records have since been recognised as mistaken California localities (NatureServe 2015). G. angulata is currently known from sites as far south as Napa County in northern California, north to the Okanagan and possibly Kootenay basins of British Columbia. It ranges from western Oregon and Washington east to the Snake River Basin of Idaho and Nevada and south to the Humboldt River Basin of Nevada. The range for this species appears to have always been smaller than other species of freshwater mussels, comprising approximately 47% of the average historic extent of occurrence and watershed area of other western freshwater mussel species: Anodonta oregonensis, Anodonta nuttalliana, and Margaritifera falcata.
Native:Canada (British Columbia); United States (California, Idaho, Nevada, Oregon, Washington)
|Range Map:||Click here to open the map viewer and explore range.|
This species can occur in beds as dense as ~575 mussels/m² (Middle Fork John Day River, Oregon, USA; Brim Box et al. 2006) or as sparse as 0.04 mussels/m² (Lower Granite Reservoir, Washington, USA; Frest unpublished data, cited in COSEWIC 2010). Recent surveys (2008-2011) in Okanagan Lake in British Columbia suggest a current population size of 4,000 individuals at one site and 1,000 at another, comprising one of five main sites within the lake (Stanton et al. 2012). Additional research in the Okanagan Basin documents juvenile recruitment, but suggests it is occurring at a level insufficient to support current population sizes in several of the studied populations. Densities there range from 0.23 to 3.46 mussels/m² (Mageroy 2015). Mussel counts elsewhere suggest the species is currently absent from certain drainages, but may be present in large numbers in others (5,623 individuals observed in the Middle Fork John Day River; Brim Box et al. 2006).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:|
This species is found in both lotic and lentic habitats, occurring on the bottom of streams, rivers and lakes with substrates that vary from gravel to firm mud, and include at least some sand, silt or clay (COSEWIC, 2003). It is generally associated with constant flow, shallow water (<3 m in depth), and well oxygenated substrates (COSEWIC, 2003). This species is often present in areas with seasonally turbid streams, but absent from areas with continuously turbid water (i.e. glacial melt water streams) (Frest & Johannes, 1992). In Idaho, G. angulata is abundant in areas with sand and gravel bars, and less abundant in more stable, boulder dominated reaches, suggesting that it can tolerate soft, fine sediments (Vannote & Minshall, 1982). In Okanagan Lake, the species is associated with sites having medium to high substrate embeddedness, substrate consisting mainly of sand, low boulder occurrence, and high effective fetch (Snook, 2015). The species generally occurs at low to mid elevations (Nedeau, et al., 2009) and may be more common at downstream sites than headwater sites, as seen in an eastern Oregon study (Brim Box, et al., 2006). Many sites where this species has been found lack dense macrophyte beds. Typically, individuals of this species are found buried to at least half their length in fine substrate, with the posterior end facing upstream (COSEWIC, 2003).
As with other unionids, G. angulata requires a host fish to complete development. Glochidia (the larval stage) are released from late March through early August in watery mucous; conglutinates are white and leaf-like (Spring Rivers, 2007; COSEWIC, 2003; Barnhart, et al., 2008). 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 (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 Hardhead (Mylopharodon conocephalus), Pit Sculpin (Cottus pitensis), and Tule Perch (Hysterocarpus traski) (Spring Rivers, 2007). Potential native and nonnative host fish include Leopard Dace (Rhinichthys falcatus), Longnose Dace (Rhinichthys cataractae), Margined Sculpin (Cottus marginatus), Northern Pikeminnow (Ptychocheilus oregonensis), Pit Roach (Lavinia symmetricus mitrulus), Prickly Sculpin (Cottus asper), Shorthead Sculpin (Cottus confusus), and Black Crappie (Pomoxis nigromaculatus) (Spring Rivers, 2007; O’Brien, et al., 2013; Mageroy, 2015; Brownlee, et al., in prep).
|Continuing decline in area, extent and/or quality of habitat:||Unknown|
|Generation Length (years):||15|
|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 Gonidea angulata 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. Declines in host species’ population size and distribution may also have significant impacts on this species.
Few abundance estimates are available for existing populations, and anecdotal declines and population extirpations have been reported across the range, although causes of these declines are not well understood. Additional surveys and monitoring of populations throughout the range should be prioritised, as should protection from and remediation of known threats. More recent surveys of parts of the Humboldt Basin by Smith (2009) uncovered only a single old intact shell but no live specimens, and future extensive snorkel surveys are recommended in the basin to determine the species’ current status there. In general, more surveys are needed to document the viability of extant populations throughout the range. Continued monitoring of populations considered nonviable is also recommended.
|Citation:||Blevins, E., Jepsen, S., Brim Box, J. & Nez, D. 2016. Gonidea angulata. The IUCN Red List of Threatened Species 2016: e.T173073A62905403.Downloaded on 23 January 2017.|
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