Plethobasus cyphyus - (Rafinesque, 1820)
Sheepnose
Other English Common Names: Bullhead, Clear Profit
Taxonomic Status: Accepted
Related ITIS Name(s): Plethobasus cyphyus (Rafinesque, 1820) (TSN 80229)
Unique Identifier: ELEMENT_GLOBAL.2.113633
Element Code: IMBIV34030
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Plethobasus
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Concept Reference
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Concept Reference: Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.
Concept Reference Code: B98TUR01EHUS
Name Used in Concept Reference: Plethobasus cyphyus
Taxonomic Comments: Ortmann (1918) noted a "subspecies" from the upper Tennessee river basin, Plethobasus cyphyus compertus (Frierson, 1911). This form differs from typical specimens by a more elongated shell, weak development of the medial row of knobs and sulcus, and the pale color (instead of orange) of the tissues. Ortmann (1918) speculated that compertus might be a local race but also reported that the two forms were sympatric. An in-depth systematic examination (morphological and electrophoretic) of these two forms should be performed to determine if any taxonomic significance is warranted. The specific epithet of this species has been variably spelled cyphya, scyphius, cyphius, cyphia, cyphyum, and ultimately as cyphyus. The sheepnose or its synonyms have been placed in the genera Unio, Pleurobema, Margarita, and Margaron. It was ultimately placed in the genus Plethobasus by Ortmann (1919), where it remains today (Turgeon et al., 1998).
Conservation Status
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NatureServe Status

Global Status: G3
Global Status Last Reviewed: 07May2009
Global Status Last Changed: 17Mar1998
Rounded Global Status: G3 - Vulnerable
Reasons: The sheepnose has been extirpated throughout much of its former range or reduced to several dozen isolated populations. This species has been eliminated from two-thirds of the total number of streams from which it was historically known although it still has a very wide distribution with dozens of occurrences in the Mississippi and Ohio basins (over two dozen streams in 14 states). The majority of the remaining populations are small and geographically isolated.
Nation: United States
National Status: N3 (17Mar1998)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (S1), Illinois (S1), Indiana (S1), Iowa (S1), Kansas (SNR), Kentucky (S1), Minnesota (S1), Mississippi (S1), Missouri (S2), Ohio (S1), Oklahoma (S4?), Pennsylvania (S1), Tennessee (S2S3), Virginia (S1), West Virginia (S2), Wisconsin (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (13Mar2012)
U.S. Fish & Wildlife Service Lead Region: R3 - North Central
IUCN Red List Category: NT - Near threatened
American Fisheries Society Status: Threatened (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 5000-20,000 square km (about 2000-8000 square miles)
Range Extent Comments: Butler (2003) summarized the historic distribution. Historically, the sheepnose occurred throughout much of the Mississippi River system with the exception of the upper Missouri River system and most lowland tributaries in the lower Mississippi River system. This species is known from the Mississippi, Ohio, Cumberland, Tennessee, and Ohio main stems, and scores of tributary streams rangewide. The sheepnose was historically known from 77 streams (including 1 canal) in 15 states and 3 Service regions (3, 4, and 5). These states are Minnesota, Wisconsin, Iowa, Illinois, Missouri, Ohio, West Virginia, Indiana, Kentucky, Tennessee, Alabama, Mississippi, Pennsylvania, Virginia, and Arkansas (see U.S. Fish and Wildlife Service, 2003). In Big Black (archaeological remains only) and Big Sunflower River (Yazoo River drainage) in Mississippi (Jones et al., 2005).

Area of Occupancy: 501-12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 21 - 80
Number of Occurrences Comments: Butler (2003) summarized the extant distribution. Extant populations of the sheepnose are known from 26 streams in the following 14 states (listed with streams): Alabama (Tennessee River), Illinois (Mississippi, Kankakee- Sietman et al., 2001, Ohio [contra Cummings and Mayer, 1997], Wabash Rivers), Indiana (Ohio, Wabash, Tippecanoe, Eel Rivers- see Fisher, 2006), Iowa (Mississippi River), Kentucky (Ohio, Licking, Kentucky, Green, Cumberland Rivers), Minnesota (Mississippi, St. Croix Rivers), Mississippi (Big Sunflower River), Missouri (Mississippi, Meramec, Bourbeuse, Osage Fork Gasconade Rivers), Ohio (Ohio, Muskingum Rivers), Pennsylvania (Allegheny River), Tennessee (Tennessee, Holston, Clinch, Powell Rivers), Virginia (Clinch, Powell Rivers), West Virginia (Ohio, Kanawha Rivers- Zeto et al., 1987), and Wisconsin (Mississippi, St. Croix, Chippewa, Flambeau, Wisconsin Rivers) (see U.S. Fish and Wildlife Service, 2003; Cummings and Berlocher, 1990). Ahlstedt et al. (2004) recently reported a single live individual from the Duck River just downstream from the old Columbia Dam (the first occurrence in the river in over a century). In Alabama, it only remains in tailwaters of Guntersville and Wilson Dams (Williams et al., 2008). The only remaining population in Mississippi is Big Sunflower River in Yazoo River drainage (Jones et al., 2005). In Missouri, it is limited to the east-central part of the state commonly found only in the Meramec River (Oesch, 1995). It has been collected in Kentucky in the Middle Green River (Cochran and Layzer, 1993). Taylor and Horn (1983) cite the Kanawha River in West Virginia and formerly in the Ohio River. In Ohio, it is extant on the Muskingum River and lower Scioto River plus som eoccurrences on the Ohio River mainstem (Watters et al., 2009).

Population Size: 2500 - 100,000 individuals
Population Size Comments: Wide historical distribution and occurrences in very large rivers makes a qualitative estimate difficult. Sharp declines in population densities have been noted and it is a very rare component of the fauna when present. Densities of 0.03 - 0.02 mussels/square meter (Jenkinson and Ahlstedt, 1988) are representative of surviving populations. Very rarely are more than a few individuals found at a particular site. Increasing rarity has been noted by qualitative sampling and by absence from commercial shell harvests.

Number of Occurrences with Good Viability/Integrity: Few (4-12)
Viability/Integrity Comments: Barr et al. (1994) determined (based on 1981 survey data) that viable populations exist in the Clinch and Powell Rivers. All populations of sheepnose face serious threats to their continued existence. Only four populations appear to be viable and at least one of these appears to be shrinking within its reach. None of these populations have been found to harbor much more than 50 individuals except one site. On the Holston River in Tennessee, 206 individuals were found in 2002, but signs of recruitment were absent (see USFWS, 2003). Parmalee and Bogan (1998) cite the most viable populations in Tennessee are in the upper Clinch River, Hancock Co., and in the Tennessee River below Pickwick Landing Dam, Hardin Co.

Overall Threat Impact: High
Overall Threat Impact Comments: Smith (1971) ranked the causes of extirpation or declines in fish species as follows: siltation, drainage of bottomland lakes, swamps, and prairie marshes, desiccation during drought, species introductions, pollution, impoundments, and increased water temperatures. All of these factors render habitats unsuitable, cause extirpations, and lead to the isolation of populations thereby increasing their vulnerability to extirpation for many aquatic species (including mussels) throughout North America. Zebra mussels, Dreissena polymorpha, have destroyed mussel populations in the Great Lakes and significantly reduced mussels in many of the large rivers of eastern North America. Zebra mussels have the potential to severely threaten other populations especially if they make their way into smaller streams. Pollution through point (industrial and residential discharge) and non-point (siltation, herbicide and fertilizer run-off) sources is perhaps the greatest on-going threat to this species and most freshwater mussels. Lowered dissolved oxygen content and elevated ammonia levels (frequently associated with agricultural runoff and sewage discharge) have been shown to be lethal to some species of freshwater naiads (Horne and McIntosh, 1979). Residential, mineral and industrial development also pose a significant threat. Rotenone, a toxin used to kill fish in bodies of water for increased sport fishery quality, has been shown to be lethal to mussels as well (Heard, 1970). Destruction of habitat through stream channelization and maintenance and the construction of dams is still a threat in some areas. Impoundments reduce currents that are necessary for basic physiological activities such as feeding, waste removal and reproduction. In addition, reduced water flow typically results in a reduction in water oxygen levels and a settling out of suspended solids (silt, etc.), both of which are detrimental. Dredging of streams has an immediate effect on existing populations by physically removing and destroying individuals. Dredging also affects the long-term recolonization abilities by destroying much of the potential habitat, making the substrates and flow rates uniform throughout the system. Natural predators include raccoons, otter, mink, muskrats, turtles and some birds (Simpson, 1899; Boepple and Coker, 1912; Evermann and Clark, 1918; Coker et al., 1921; Parmalee, 1967; Snyder and Snyder, 1969). Domestic animals such as hogs can root mussel beds to pieces (Meek and Clark, 1912). Fishes, particularly catfish, Ictalurus spp. and Ameirus spp., and freshwater drum, Aplodinotus grunniens, also consume large numbers of unionids. The decline of the sheepnose in the Mississippi River system and other mussel species in the eastern United States (described by Butler, 2003) is primarily the result of habitat loss and degradation. These losses have been well documented since the mid-19th century (Higgins, 1858). Chief among the causes of decline are impoundments (probably the greatest contributing factor to decline), channelization, chemical contaminants, mining, and sedimentation. Impoundments result in the dramatic modification of riffle and shoal habitats and the resulting loss of mussel resources, especially in larger rivers (Neves et al., 1997; Watters, 2000). Channelization impacts a stream's physical characteristics (e.g., accelerated erosion, reduced depth, decreased habitat diversity, geomorphic instability, riparian canopy loss) and biological composition (e.g., decreased fish and mussel diversity, changed species composition and abundance, decreased biomass, and reduced growth rates) (Hartfield, 1993; Hubbard et al., 1993). Contaminants contained in point and non-point discharges can degrade water and substrate quality and adversely impact, if not destroy, mussel populations (especially juveniles). Heavy metal-rich drainage from coal mining and associated sedimentation have adversely impacted portions of the upper Tennessee River system in Virginia. Sedimentation is a pervasive problem in streams and has been implicated in the decline of stream mussel populations (Ellis, 1936; Marking and Bills, 1979; Vannote and Minshall, 1982; Dennis, 1984; Brim Box, 1999; Fraley and Ahlstedt, 2000). Less serious threats include: (1) over-exploitation for commercial, scientific, or educational purposes although this is unlikely; (2) disease or predation (little known); (3) inadequacy of existing regulatory mechanisms; (4) population fragmentation and genetic isolation; (5) invasive species (Asiatic clam, zebra mussel, black carp) (see U.S. Fish and Wildlife Service, 2003; Williams et al., 1993; Neves, 1993; Neves et al., 1997; Watters, 2000).

Short-term Trend: Decline of 30-70%
Short-term Trend Comments: The sheepnose has been eliminated from two-thirds of the total number of streams from which it was historically known (26 streams currently compared to 77 streams historically). This species has also been eliminated from long reaches of former habitat in hundreds of miles of rivers such as the Illinois and Cumberland, and from several reaches of the Mississippi and Tennessee Rivers. In addition, the species is no longer known to occur in the State of Arkansas (see USFWS, 2003; Butler, 2003; Cummings and Mayer, 1997; Parmalee and Bogan, 1998). Sietman (2003) reports it extirpated from the lower Minnesota River in Minnesota.

Long-term Trend: Decline of 50-70%
Long-term Trend Comments: During historical times, it was fairly widespread in many Mississippi River system streams, although rarely very common. Archaeological evidence on relative abundance indicates it has been uncommon or rare in many streams for centuries. The sheepnose was last reported from some streams decades ago (e.g., Minnesota, Rock, Iowa, Illinois, Des Plaines, Fox, Mackinaw, Spoon, Castor, Little Sioux, Little Blue, Monongahela, Beaver, Scioto, Little Miami, Salt, Mississenewa, Vermilion, Embarras, White, Obey, Harpeth, North Fork Holston, French Broad, North Fork Clinch Rivers; Caney Fork) (Butler, 2003). According to Parmalee and Bogan (1998) and Neves (1991), the sheepnose has been extirpated throughout much of its former range or reduced to isolated populations. The last extant records for other streams are from several decades ago. The only records known from some streams are archeological specimens (e.g., Little Pigeon, Big Black, Yazoo Rivers; Saline Creek). It is extirpated from the Sangamon basin in Illinois (Schanzle and Cummings, 1991). Branson (1966) recorded it (valves only) from the Spring River in Missouri and alive in the Spring River in Kansas. It occurred historically across northern Alabama but now remains below Guntersville and Wilson Dams only (Williams et al., 2008).

Intrinsic Vulnerability: Highly to moderately vulnerable.
Intrinsic Vulnerability Comments: The majority of the remaining populations of sheepnose are small and geographically isolated. The likelihood is high that some populations of the sheepnose are below the effective population size (Soulé, 1980) required to maintain long-term genetic and population viability. The patchy distributional pattern of populations in short river reaches makes them much more susceptible to extirpation from single catastrophic events, such as toxic chemical spills. Furthermore, this level of isolation makes natural repopulation of any extirpated population virtually impossible without human intervention. Population isolation prohibits the natural interchange of genetic material between populations, and small population size reduces the reservoir of genetic diversity within populations, which can lead to inbreeding depression (see Butler, 2002; U.S. Fish and Wildlife Service, 2003).

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity Comments: Although it does inhabit medium-sized rivers, this mussel generally has been considered a large-river species. It may be associated with riffles and gravel/cobble substrates but usually has been reported from deep water (>2 m) with slight to swift currents and mud, sand, or gravel bottoms (Gordon and Layzer, 1989). It also appears capable of surviving in reservoirs, such as upper Chickamauga Reservoir immediately below Watts Bar Dam (Ahlstedt, 1989). Specimens in larger rivers may occur in deep runs (Parmalee and Bogan, 1998).

Other NatureServe Conservation Status Information

Inventory Needs: Monitor status of existing populations. Continue surveys for additional EOs, and assess potential reintroduction sites. Periodic status surveys are needed to monitor changes in the remaining populations of this species. Monitor spread of zebra mussels.

Protection Needs: All populations should receive protection through acquisition, easement, registry, and working with local, state, and federal government agencies on issues relating to development, water quality, river designation, etc. Propogation technology should be developed. A national wildlife refuge on the Clinch River is under consideration. This non traditional fish and wildlife refuge is planned to be slowly implemented over time. Other refuges may be established in other stream systems harboring sheepnose populations in the future. Reservoir releases from TVA dams have been modified in recent years to improve water quality and habitat conditions in many tailwaters. Improvements have enabled partners to attempt the reintroduction of extirpated species. Numerous experimental populations of federally listed species are now in various stages of planning and implementation. (see U.S. Fish and Wildlife Service, 2003)

Distribution
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Global Range: (5000-20,000 square km (about 2000-8000 square miles)) Butler (2003) summarized the historic distribution. Historically, the sheepnose occurred throughout much of the Mississippi River system with the exception of the upper Missouri River system and most lowland tributaries in the lower Mississippi River system. This species is known from the Mississippi, Ohio, Cumberland, Tennessee, and Ohio main stems, and scores of tributary streams rangewide. The sheepnose was historically known from 77 streams (including 1 canal) in 15 states and 3 Service regions (3, 4, and 5). These states are Minnesota, Wisconsin, Iowa, Illinois, Missouri, Ohio, West Virginia, Indiana, Kentucky, Tennessee, Alabama, Mississippi, Pennsylvania, Virginia, and Arkansas (see U.S. Fish and Wildlife Service, 2003). In Big Black (archaeological remains only) and Big Sunflower River (Yazoo River drainage) in Mississippi (Jones et al., 2005).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single nation

U.S. & Canada State/Province Distribution
United States AL, IA, IL, IN, KS, KY, MN, MO, MS, OH, OK, PA, TN, VA, WI, WV

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
AL Colbert (01033), Jackson (01071)*, Lauderdale (01077), Limestone (01083), Madison (01089), Marshall (01095)*, Morgan (01103)*
IA Clayton (19043), Johnson (19103), Muscatine (19139), Scott (19163), Webster (19187)
IL Adams (17001)*, Fayette (17051)*, Hancock (17067)*, Kankakee (17091), Lawrence (17101)*, Massac (17127)*, Mercer (17131)*, Rock Island (17161), Shelby (17173)*, Whiteside (17195), Will (17197)
IN Carroll (18015), Cass (18017), Fountain (18045)*, Fulton (18049), Gibson (18051)*, Hamilton (18057)*, Harrison (18061), Jasper (18073)*, Jefferson (18077), Knox (18083), Lake (18089)*, Lawrence (18093), Madison (18095)*, Marion (18097), Marshall (18099), Martin (18101)*, Miami (18103), Morgan (18109), Newton (18111)*, Parke (18121)*, Perry (18123), Porter (18127)*, Posey (18129)*, Pulaski (18131), Spencer (18147), Starke (18149), Switzerland (18155), Tippecanoe (18157), Vanderburgh (18163), Vermillion (18165)*, Vigo (18167)*, Warren (18171)*, Warrick (18173), White (18181)
KY Ballard (21007), Bath (21011), Boone (21015)*, Bracken (21023), Butler (21031), Campbell (21037), Carroll (21041), Cumberland (21057)*, Daviess (21059), Edmonson (21061), Fleming (21069), Garrard (21079), Greenup (21089), Hancock (21091), Hart (21099), Henderson (21101)*, Jefferson (21111), Jessamine (21113), Kenton (21117)*, Lewis (21135), Livingston (21139), Lyon (21143)*, Marshall (21157), Mason (21161), McCracken (21145), Meade (21163)*, Monroe (21171)*, Nicholas (21181), Oldham (21185), Pendleton (21191), Rowan (21205), Russell (21207)*, Trigg (21221)*, Trimble (21223), Union (21225)*, Warren (21227), Wayne (21231)*
MN Carver (27019), Dakota (27037), Goodhue (27049)*, Houston (27055)*, Mower (27099), Ramsey (27123), Scott (27139), Wabasha (27157), Washington (27163), Winona (27169)
MO Crawford (29055)*, Franklin (29071), Jefferson (29099), Laclede (29105), Lewis (29111), Marion (29127), Pike (29163), Ralls (29173), St. Louis (29189)
MS Sunflower (28133)
OH Brown (39015)*, Clermont (39025), Coshocton (39031), Gallia (39053), Hamilton (39061)*, Lawrence (39087), Licking (39089)*, Morgan (39115), Pike (39131)*, Scioto (39145), Washington (39167)
PA Allegheny (42003)*, Armstrong (42005)*, Beaver (42007)*, Forest (42053), Lawrence (42073)*, Venango (42121), Washington (42125)*, Westmoreland (42129)*
TN Claiborne (47025), DeKalb (47041)*, Decatur (47039)*, Grainger (47057), Hancock (47067), Hardin (47071), Jefferson (47089), Knox (47093), Loudon (47105), Maury (47119), Putnam (47141)*, Rhea (47143), Roane (47145), Sevier (47155)*, Smith (47159)*
VA Lee (51105), Russell (51167)*, Scott (51169)
WI Adams (55001), Buffalo (55011), Columbia (55021), Crawford (55023), Dane (55025), Dunn (55033), Eau Claire (55035), Grant (55043), Iowa (55049), La Crosse (55063), Pepin (55091), Pierce (55093)*, Richland (55103), Rusk (55107), Sauk (55111), Sawyer (55113)
WV Cabell (54011), Jackson (54035), Wood (54107)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
05 Middle Allegheny-Tionesta (05010003)+, Middle Allegheny-Redbank (05010006)+*, Lower Allegheny (05010009)*, Lower Monongahela (05020005)+*, Upper Ohio (05030101)+*, Beaver (05030104)+*, Little Muskingum-Middle Island (05030201)+, Upper Ohio-Shade (05030202)+, Tuscarawas (05040001)*, Mohican (05040002)+, Walhonding (05040003)+, Muskingum (05040004)+, Licking (05040006)+, Upper Kanawha (05050006), Lower Scioto (05060002)+*, Raccoon-Symmes (05090101)+, Little Scioto-Tygarts (05090103)+, Ohio Brush-Whiteoak (05090201)+, Little Miami (05090202)*, Middle Ohio-Laughery (05090203)+, Licking (05100101)+, Upper Kentucky (05100204)*, Lower Kentucky (05100205)+, Upper Green (05110001)+, Barren (05110002)+, Middle Green (05110003)+, Lower Green (05110005)+, Upper Wabash (05120101)*, Mississinewa (05120103)*, Eel (05120104)+, Middle Wabash-Deer (05120105)+*, Tippecanoe (05120106)+, Middle Wabash-Little Vermilion (05120108)+, Vermilion (05120109)*, Middle Wabash-Busseron (05120111)+, Embarras (05120112)*, Lower Wabash (05120113)+, Upper White (05120201)+, Lower White (05120202)+*, Upper East Fork White (05120206)*, Lower East Fork White (05120208)+, Upper Cumberland (05130101)*, Upper Cumberland-Lake Cumberland (05130103)+*, South Fork Cumberland (05130104)*, Obey (05130105)*, Upper Cumberland-Cordell Hull (05130106)*, Caney (05130108)+, Lower Cumberland-Old Hickory Lake (05130201)*, Lower Cumberland-Sycamore (05130202)*, Harpeth (05130204)*, Lower Cumberland (05130205)+, Silver-Little Kentucky (05140101)+, Salt (05140102)*, Blue-Sinking (05140104)+, Lower Ohio-Little Pigeon (05140201)+, Highland-Pigeon (05140202)+, Lower Ohio-Bay (05140203)+*, Lower Ohio (05140206)+
06 North Fork Holston (06010101)*, Holston (06010104)+, Pigeon (06010106), Lower French Broad (06010107)+, Watts Bar Lake (06010201), Lower Little Tennessee (06010204)*, Upper Clinch (06010205)+, Powell (06010206)+, Lower Clinch (06010207)+, Middle Tennessee-Chickamauga (06020001)+, Hiwassee (06020002)*, Guntersville Lake (06030001)+*, Wheeler Lake (06030002)+, Lower Elk (06030004)*, Pickwick Lake (06030005)+, Lower Tennessee-Beech (06040001)+, Lower Duck (06040003)+, Kentucky Lake (06040005)*, Lower Tennessee (06040006)+
07 Twin Cities (07010206)+, Chippewa (07020005), Lower Minnesota (07020012)+, Lower St. Croix (07030005)+, Rush-Vermillion (07040001)+, Cannon (07040002)+, Buffalo-Whitewater (07040003)+, Zumbro (07040004), La Crosse-Pine (07040006)+, Root (07040008)+*, Upper Chippewa (07050001)+, Flambeau (07050002)+, Lower Chippewa (07050005)+, Eau Claire (07050006)+, Red Cedar (07050007)+, Coon-Yellow (07060001)+*, Grant-Little Maquoketa (07060003)+, Turkey (07060004)+, Apple-Plum (07060005), Upper Wisconsin (07070001)*, Lake Dubay (07070002)*, Castle Rock (07070003)+, Baraboo (07070004)+, Lower Wisconsin (07070005)+, Copperas-Duck (07080101)+, Flint-Henderson (07080104)+, Upper Cedar (07080201)+, Lower Iowa (07080209)+, Upper Rock (07090001)*, Lower Rock (07090005)+, Middle Des Moines (07100004)+, Lower Des Moines (07100009)*, Bear-Wyaconda (07110001)+, The Sny (07110004)+, Salt (07110007)+, Kankakee (07120001)+, Des Plaines (07120004), Upper Illinois (07120005), Upper Fox (07120006), Lower Fox (07120007)*, Lower Illinois-Senachwine Lake (07130001), Lower Illinois-Lake Chautauqua (07130003), Mackinaw (07130004)*, Spoon (07130005)*, Upper Sangamon (07130006)*, South Fork Sangamon (07130007), Lower Sangamon (07130008), Salt (07130009), Meramec (07140102)+, Bourbeuse (07140103)+, Big (07140104)+, Upper Mississippi-Cape Girardeau (07140105)*, Whitewater (07140107)*, Cache (07140108)*, Upper Kaskaskia (07140201)+, Middle Kaskaskia (07140202)+, Lower Kaskaskia (07140204)*
08 Lower Mississippi-Memphis (08010100)*, Upper Hatchie (08010207)*, Lower Hatchie (08010208)*, Big Sunflower (08030207)+, Lower Yazoo (08030208)*, Deer-Steele (08030209)*, Black (08040305)*, Upper Big Black (08060201), Lower Big Black (08060202)
10 Little Sioux (10230003)*, Upper Gasconade (10290201)+, Lower Gasconade (10290203)
11 Spring (11070207)*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A freshwater mussel with an oblong shell, surface smooth except for a single row of bumps or knobs running from the umbo to the ventral margin.
General Description: SHELL EXTERIOR: Shell thick, oval or oblong, somewhat elongate, and slightly inflated. Anterior end rounded, posterior end bluntly pointed. Dorsal margin straight, ventral margin curved anteriorly, straight posteriorly. Umbos slightly elevated above the hinge line. Beak sculpture of two heavy ridges, visible only in young shells. Shell smooth, except for a row of knobs or tubercles on the center of the valve, running from the umbo to the ventral margin (sometimes obscure). A shallow sulcus or furrow present between the row of tubercles and the posterior ridge. Periostracum yellow or light brown in juveniles, becoming chestnut to dark brown in adults. Length to 12.7 cm.

SHELL INTERIOR: Pseudocardinal teeth rather small relative to overall shell size; two in the left valve, one in the right (occasionally with a smaller tubercular tooth on either side). Lateral teeth long, straight or slightly curved; two in the left valve, one in the right Beak cavity shallow. Nacre white, occasionally tinged with pink or salmon. (see Butler, 2003; Cummings and Mayer, 1992; Oesch, 1995; U.S. Fish and Wildlife Service, 2003)

Diagnostic Characteristics: This species is rather distinctive with its oval shape and flattened posterio-ventral margin, its knobby medial ridge, wide sulcus between the medial and posterior ridges, and shiny yellow priostracum. Obliquaria reflexa (Rafinesque, 1820) is similarly shaped but is a smaller, more inflated shell with medial knobs which alternate in position between the right and left valves, a costate posterior slope, and a brownish periostracum. it also superficially resembles Epioblasma torrulosa s.s. (Rafinesque, 1820) but that shell was highly rayed and apparently is now extinct. Butler (2003) lists key distinguishing characters as shell color, occurrences of central tubercles, and its outline.
Reproduction Comments: Plethobasus cyphyus is a short-termed brooder with ectobranchous marsupia. Gravid females have been found between May and July (Gordon and Layzer, 1989). Surber (1913) and Wilson (1916) found partially transformed glochidia on Stizostedion canadense (sauger) indicating that it serves as a glochidial host. Glochidia are released in conglutinates and mimic fish food organisms (Butler, 2003). New host fish confirmation from Watters et al. (2005): central stoneroller (Campostoma anomalum). Guenther et al. (2009) identified the following species as potential hosts for this mussel: blackspotted topminnow, blacktail shiner, bleeding shiner, bluntnose minnow, brassy minnow, bullhead minnow, central stoneroller, common shiner, eastern blacknose dace, fathead minnow, longnose dace, mimic shiner, Ozark minnow, pearl dace, red shiner, river shiner, silver chub, southern redbelly dace, spotfin shiner, steelcolor shiner, striped shiner, suckermouth minnow, western mosquitofish, whitetail shiner.
Ecology Comments: No specific studies have considered this species. Densities have been determined in a few surveys (e.g., Jenkinson and Ahlstedt, 1988; Layzer and Gordon, 1990).
Habitat Type: Freshwater
Non-Migrant: Y
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: This species is probably rather sessile with only limited movement through the substrate. Passive downstream movement may occur when mussels are displaced from the substrate during floods. Major dispersal occurs when glochidia are encysted on their hosts.
Riverine Habitat(s): BIG RIVER, Low gradient, MEDIUM RIVER, Moderate gradient, Riffle
Special Habitat Factors: Benthic
Habitat Comments: Although it does inhabit medium-sized rivers, this mussel generally has been considered a large-river species. It may be associated with riffles and gravel/cobble substrates but usually has been reported from deep water (>2 m) with slight to swift currents and mud, sand, or gravel bottoms (Gordon and Layzer, 1989). It also appears capable of surviving in reservoirs, such as upper Chickamauga Reservoir immediately below Watts Bar Dam (Ahlstedt, 1989). Specimens in larger rivers may occur in deep runs (Parmalee and Bogan, 1998).
Adult Food Habits: Detritivore
Immature Food Habits: Parasitic
Food Comments: Larvae (glochidia) of freshwater mussels generally are parasitic on fish and display varying degrees of host specificity. No specific tropic studies have been conducted on this species. General literature claims that mussels are filter-feeders which remove phytoplankton from the water column. These assumptions appear to be based on casual observations of mussels in situ and a few examinations of rectal contents. Baker (1928) speculated that detritus was the primary energy source. This has been substantiated by James (1987) and correlates well with microhabitats observed in the field. This suggests that mussels may occupy a variety of guilds such as postulated for the Sphaeriidae (see Lopez and Layzer, 1989).
Phenology Comments: Little is known concerning the phenology of mussels other than when eggs/glochidia are held in the branchial marsupia. Being poikilotherms, activity levels would expectly be greatly reduced during cold-temperature months.
Length: 12.7 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: This species was listed as a U.S. Federal candidate species (USFWS, 2003).

Recovery Objectives:
1) Maintain high quality habitat, consisting of flowing water sites in medium-to-large rivers with good water quality (new national wildlife refuge on Clinch River planned; modified reservoir releases from some dams to improve water quality by Tennessee Valley Authority may allow for potential reintroduction). 2) Monitor and regulate land use upstream to minimize erosion of silt to rivers. Maintain ongoing conservation outreach program focused on the St. Croix River and its mussel fauna (including The St. Croix River Research Rendezvous group and public outreach programs). 3) Relocation of a mussel communities can be used to minimize the impact of specific development-related projects (e.g., highway crossings, channel dredging, mooring cells) on important mussel resources, including listed species (beware of failed relocation attempts resulting in increased mortality of resident populations).

Biological Research Needs: Determine habitat preferences and environmental tolerances, particularly tolerance to various pollutants and siltation. Research is needed on reproductive biology, and identification of glochidial hosts should be reassessed.

In order to effectively manage mussel species it is necessary to work out certain life history characteristics first. Because of their unusual life-cycle and dependence on fish for completion of that cycle, it is imperative that the host species for the sheepnose be ascertained. Life history studies need to be done to identify age and size at sexual maturity, recruitment success, age class structure, and other important life history parameters.

Research is needed to assess the success of watershed protection on mussel populations. Abundance and distribution of selected species needs to be monitored in order to ascertain how species abundances change over time. From that we can assess what land-use changes, conservation practices, and physical/chemical parameters are correlated with, and possibly responsible for, the biological changes.

Population/Occurrence Delineation
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Group Name: Freshwater Mussels

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance.

Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls.
Separation Distance for Unsuitable Habitat: 2 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: None
Separation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence.

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 07May2009
NatureServe Conservation Status Factors Author: Cordeiro, J. (2009); Cummings, K.S. (2000); Whittaker, J.C. (1998)
Management Information Edition Date: 08May2007
Management Information Edition Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 08May2007
Element Ecology & Life History Author(s): Cordeiro, J.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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References for Watershed Distribution Map
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