Simpsonaias ambigua - (Say, 1825)
Salamander Mussel
Other English Common Names: Mudpuppy Mussel
Taxonomic Status: Accepted
Related ITIS Name(s): Simpsonaias ambigua (Say, 1825) (TSN 80145)
French Common Names: Mulette du Necture
Unique Identifier: ELEMENT_GLOBAL.2.114652
Element Code: IMBIV41010
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Simpsonaias
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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: Simpsonaias ambigua
Conservation Status
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NatureServe Status

Global Status: G3
Global Status Last Reviewed: 06Mar2007
Global Status Last Changed: 25Nov1996
Rounded Global Status: G3 - Vulnerable
Reasons: Although widely distributed and abundant in some areas, this species is still considered rare in all states where it is found and recently local extirpations have been occurring across nearly its range to the point where declines in area of occupancy have occurred.
Nation: United States
National Status: N3 (11May2006)
Nation: Canada
National Status: N1 (01Aug2017)

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 Arkansas (S1), Illinois (S1), Indiana (S2), Iowa (SX), Kentucky (S2S3), Michigan (S1), Minnesota (S1), Missouri (S1), New York (SH), Ohio (S3), Pennsylvania (S1), Tennessee (S1), West Virginia (S2), Wisconsin (S2)
Canada Ontario (S1)

Other Statuses

Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: E (05Jun2003)
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Endangered (06May2011)
Comments on COSEWIC: Reason for designation: This freshwater mussel was reported from two rivers in southern Ontario in 1998. Surveys since the original COSEWIC assessment (2001) have found live individuals still along the Sydenham River. Despite extensive additional sampling, the half-shell found in 1998 is the only evidence of this species along the Thames River. Habitat quality continues to decline from intense agriculture, urban development, and pollution from point and non-point sources. In addition, this mussel only uses the Mudpuppy, a salamander, as its host; threats to the salamander are also threats to the mussel.

Status history: Designated Endangered in May 2001. Status re-examined and confirmed in May 2011.

IUCN Red List Category: VU - Vulnerable
American Fisheries Society Status: Special Concern (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: Historically, this species occurred throughout the upper Mississippi River drainage and as far south as the Cumberland River drainage of Tennessee. Clarke (1985) gave the geographical records for this species. It is known from the Lake St. Clair, Lake Huron, and Lake Erie drainages; and from the Ohio River System, the Cumberland River System (Red River, Kentucky), and the upper Mississippi River System (Illinois, Iowa, Wisconsin, Missouri and Arkansas). In Minnesota, it is present only in the lower St. Croix River where it is rare and localized (Sietman, 2003). Its distribution in part is apparently related to the distribution of its glochidial host, the mudpuppy. In Canada, it is known from the Sydenham River and a potentially extant occurrence in the Thames River in London, Ontario (Cudmore et al., 2004).

Area of Occupancy: 2,501 to >12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 21 - 80
Number of Occurrences Comments: In Wisconsin, Mathiak (1979) reported this species from the Wolf River in Shawano Co. and a historical specimen taken near Prairie du Chien. Additional Wisconsin records include the Lower Chippewa, Lower Wisconsin, Eau Claire, Castle Rock, Grant-Little Maquoketa, Lower St. Croix, and South Fork Flambeau (WI NHP, pers. comm., 2007). In Minnesota, it is present only in the lower St. Croix River where it is rare and localized (Sietman, 2003). Clarke (1985) gave the geographical records for this species in Michigan: the Lake St. Clair, Lake Huron, and Lake Erie drainages but it is likely only still extant in Lake St. Clair; with recent occurrences in the Black River (Sanillac Co.), Pine River (St. Clair Co.), near Belle Isle (Wayne Co.), and Macon Creek (Monroe Co.). Parmalee and Bogan (1998) reported this species occurred from the Stones River in the Cumberland River drainage in Tennessee but reported it extirpated in the state as no new specimens had been found since 1965 (see Athearn, 1992). In 2003, a single fresh-dead specimen was collected along the shoreline of the Duck River in Humphreys Co., Tennessee (P. Johnson, pers. comm., 2006). Subsequent visits in 2005 uncovered another complete shell and several fragments. It is easy to overlook due to its small size and the fact that it can be hidden under large flat rocks. It is considered rare (but widespread) in Ohio (Watters, 1995) and is known from the Grand, St. Joseph, Big Darby Creek, Little Miami, Ohio Brush Creek, lower Little Scioto River and from Salt Creek (Watters, 1992; Watters et al., 2009); and Symmes Creek (Raccon basin) (Hoggarth et al., 2007). In Pennsylvania, it was historically known (with a recent newly discovered population) from the Middle Allegheny-Redbank drainage (Clarke, 1985),and is expanding in the upper Ohio basin in Greene (Dunkard Creek- tributary to Monongahela River), Armstrong (Allegheny River Pools 1, 3, 5, 6, and 7), and Crawford (French Creek) Cos. (Bogan and Locy, 2009). It has been documented historically in the Monongahela in West Virginia (Ortmann, 1919). In Missouri, it is known only from the Bourbeuse River (Oesch, 1995). In Illinois, it may still be holding on in the Kankakee and Vermillion River drainage but has not been collected in the state in over 30 years (Cummings and Mayer, 1997). In Kentucky, it is sporadic in the upper Green River and eastward (Cicerello and Schuster, 2003) and occurs in the Red River drainage (north fork) (Clarke, 1988). In Indiana, it still occurs in Wabash tributaries (Fisher, 2006); and Harmon (1989) reported it from six of 12 sites surveyed in Graham Creek in the southeast portion of the state; and weathered shells are reported from Sugar Creek (east fork White River drainage) in central Indiana (Harmon, 1992). Athearn (1992) also reports occurrences in Indiana in the Maumee River in Allen Co., Indiana; and Cummings and Berlocher (1990) cite the Tippecanoe. In Arkansas, midden specimens were collected in the 1980s from the Spring River at Imboden and the Black River at Black Rock (Harris and Gordon, 1987; Harris et al., 1997) as well as a Little Red River locality at Clinton noted by Johnson (1980). In Canada, the only remaining population is in the Sydenham River in southwestern Ontario (Metcalfe-Smith et al., 2003; Metcalfe-Smith and Cudmore-Vokey, 2004; Athearn, 1992), although one small population could still be present in the upper reaches of the Thames River based on a single fresh valve found in London in 1998 (Cudmore et al., 2004; Watson et al., 2000).

Population Size: >1,000,000 individuals
Population Size Comments: This species may be locally abundant where found. Call (1900: 527) reported over 200 individuals from a single square foot under a rock. Frierson (1927) remarked that it was "rarely found, but in abundance whenever found; a hundred have been taken from a square foot." Baker (1898) reported similar numbers

Number of Occurrences with Good Viability/Integrity: Unknown
Viability/Integrity Comments: Although widely distributed and at times abundant in some areas, it is rare throughout most of its range.

Overall Threat Impact: Unknown

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: While this species is easily overlooked, intense searches in areas where the species has previously been indicate decline (Stansbery, 1970; Clarke, 1985). Sietman (2003) reports it extirpated from the Mississippi River below St. Anthony Falls and portions of the Minnesota River drainage in Minnesota. Cummings and Mayer (1997) report it may be extirpated in Illinois. Some expansion has occurred in western Pennsylvania where it was not known historically in the upper Ohio River basin (Bogan and Locy, 2009). In Canada, it has been extirpated from the Cedar and Detroit Rivers by the zebra mussel and only a single population remains in the Sydenham River in Ontario (Metcalfe-Smith and Cudmore-Vokey, 2004) and possibly Lower Thames (Watson et al., 2000; Cudmore et al., 2004).

Long-term Trend: Decline of <50% to Relatively Stable
Long-term Trend Comments: In the 19th Century, it was collected from several sites near Buffalo including Lake Erie, Buffalo Creek [River], and Cayuga Creek at Lancaster in New York (Strayer and Jirka, 1997). In Ohio it is historically recorded from the Ohio Canal at New Philadelphia, Tuscarawas River, Scioto River at Columbus, and Sandusky Bay, upper Scioto River, Licking River, and weathered shells (recently) in the Muskingum River at Marietta (Watters et al., 2009).

Intrinsic Vulnerability: Moderately vulnerable
Intrinsic Vulnerability Comments: Dispersal is limited to the dispersal capability of its host, the mudpuppy.

Environmental Specificity: Broad. Generalist or community with all key requirements common.
Environmental Specificity Comments: Although occasionally found elsewhere, there is little doubt the preferred habitat is in sand or silt under large, flat stones in areas of a swift current (Call, 1900; Howard, 1915; Buchanan, 1980; Clarke, 1985; Oesch, 1984; 1995; Parmalee and Bogan, 1998). Its presence is presumably linked to the mudpuppy, Necturus maculosus. Cudmore et al. (2004) provides the following habitat information for Canada: found in all types of clear, freshwater habitat, including creeks, streams, rivers and lakes; it is found on a variety of substrates (mud, silt, sand, gravel, cobble or boulder) in areas of swift current.

Other NatureServe Conservation Status Information

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) Historically, this species occurred throughout the upper Mississippi River drainage and as far south as the Cumberland River drainage of Tennessee. Clarke (1985) gave the geographical records for this species. It is known from the Lake St. Clair, Lake Huron, and Lake Erie drainages; and from the Ohio River System, the Cumberland River System (Red River, Kentucky), and the upper Mississippi River System (Illinois, Iowa, Wisconsin, Missouri and Arkansas). In Minnesota, it is present only in the lower St. Croix River where it is rare and localized (Sietman, 2003). Its distribution in part is apparently related to the distribution of its glochidial host, the mudpuppy. In Canada, it is known from the Sydenham River and a potentially extant occurrence in the Thames River in London, Ontario (Cudmore et al., 2004).

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: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AR, IAextirpated, IL, IN, KY, MI, MN, MO, NY, OH, PA, TN, WI, WV
Canada ON

Range Map
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U.S. Distribution by County Help
State County Name (FIPS Code)
AR Lawrence (05075), Sharp (05135), Van Buren (05141)
IA Clayton (19043)*
IL Champaign (17019)*, Kankakee (17091)*, Vermilion (17183), Will (17197)
IN Cass (18017), Clinton (18023), Crawford (18025), Daviess (18027)*, De Kalb (18033), Dearborn (18029), Fountain (18045), Fulton (18049), Harrison (18061), Jefferson (18077), Jennings (18079), Johnson (18081), Kosciusko (18085), Martin (18101), Ohio (18115), Parke (18121), Pike (18125)*, Posey (18129)*, Pulaski (18131), Putnam (18133), Shelby (18145), Tippecanoe (18157), Warren (18171), Washington (18175), White (18181)*
KY Bath (21011), Boyd (21019), Breathitt (21025)*, Breckinridge (21027), Bullitt (21029), Butler (21031)*, Campbell (21037), Carroll (21041), Carter (21043), Casey (21045), Fleming (21069), Franklin (21073), Gallatin (21077), Grant (21081), Green (21087)*, Harrison (21097), Hart (21099)*, Henry (21103), Jefferson (21111), Kenton (21117), Leslie (21131), Lewis (21135), Lincoln (21137), Livingston (21139)*, Marion (21155), Menifee (21165), Metcalfe (21169), Morgan (21175), Nelson (21179), Nicholas (21181), Owen (21187), Pendleton (21191), Powell (21197), Robertson (21201), Shelby (21211), Spencer (21215), Warren (21227)*, Washington (21229), Wolfe (21237)
MI Lenawee (26091)*, Monroe (26115)*, Sanilac (26151), St. Clair (26147), Wayne (26163)
MN Blue Earth (27013), Chippewa (27023), Chisago (27025), Dakota (27037), Nicollet (27103), Pine (27115), Washington (27163), Yellow Medicine (27173)
MO Cedar (29039), Gasconade (29073)*, St. Louis (29189)
OH Adams (39001)*, Ashtabula (39007), Brown (39015), Clermont (39025), Coshocton (39031)*, Delaware (39041)*, Franklin (39049), Hancock (39063), Lake (39085), Morgan (39115)*, Pickaway (39129)*, Ross (39141), Scioto (39145), Trumbull (39155), Washington (39167)*, Williams (39171)
PA Armstrong (42005), Crawford (42039), Greene (42059)
TN Davidson (47037)*, Humphreys (47085), Rutherford (47149)*, Warren (47177)
WI Buffalo (55011), Burnett (55013), Columbia (55021), Crawford (55023), Dunn (55033), Eau Claire (55035), Grant (55043), Iowa (55049), Jackson (55053), Juneau (55057), La Crosse (55063), Lincoln (55069), Outagamie (55087), Pepin (55091), Polk (55095), Price (55099), Richland (55103), Sauk (55111), Sawyer (55113), Shawano (55115), St. Croix (55109), Trempealeau (55121), Waukesha (55133), Waupaca (55135)
WV Monongalia (54061), Putnam (54079)*
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
04 Wolf (04030202)+, Saginaw (04080206)*, Lake Huron (04080300)*, St. Clair (04090001)+, Lake St. Clair (04090002)+, Detroit (04090004)*, Ottawa-Stony (04100001)+*, Raisin (04100002)+*, St. Joseph (04100003)+, Upper Maumee (04100005), Tiffin (04100006)+*, Blanchard (04100008)+, Cedar-Portage (04100010), Ashtabula-Chagrin (04110003)*, Grand (04110004)+, Chautauqua-Conneaut (04120101)+, Buffalo-Eighteenmile (04120103)*, Lake Erie (04120200)*
05 French (05010004)+, Middle Allegheny-Redbank (05010006)+, West Fork (05020002)*, Lower Monongahela (05020005)+, Little Muskingum-Middle Island (05030201), Upper Ohio-Shade (05030202), Little Kanawha (05030203), Tuscarawas (05040001)*, Mohican (05040002)*, Walhonding (05040003)+*, Muskingum (05040004)+, Upper Kanawha (05050006)*, Lower Kanawha (05050008)+*, Upper Scioto (05060001)+, Lower Scioto (05060002)+, Lower Guyandotte (05070102)*, Raccoon-Symmes (05090101), Twelvepole (05090102), Little Scioto-Tygarts (05090103)+, Little Sandy (05090104)+, Ohio Brush-Whiteoak (05090201)+, Little Miami (05090202)+, Middle Ohio-Laughery (05090203)+, Licking (05100101)+, South Fork Licking (05100102)+, North Fork Kentucky (05100201)+*, Middle Fork Kentucky (05100202)+, Upper Kentucky (05100204)+, Lower Kentucky (05100205)+, Upper Green (05110001)+, Rough (05110004)+, Upper Wabash (05120101)*, Eel (05120104)+, Middle Wabash-Deer (05120105), Tippecanoe (05120106)+, Wildcat (05120107)+, Middle Wabash-Little Vermilion (05120108)+, Vermilion (05120109)+, Sugar (05120110)+, Middle Wabash-Busseron (05120111), Embarras (05120112), Lower Wabash (05120113)+*, Lower White (05120202), Eel (05120203)+, Driftwood (05120204)+, Flatrock-Haw (05120205)+, Muscatatuck (05120207)+, Lower East Fork White (05120208)+, Upper Cumberland (05130101)*, Collins (05130107)+, Stones (05130203)+*, Red (05130206), Silver-Little Kentucky (05140101)+, Salt (05140102)+, Rolling Fork (05140103)+, Blue-Sinking (05140104)+, Lower Ohio-Bay (05140203)+, Saline (05140204), Tradewater (05140205)
06 Lower Duck (06040003)+
07 Twin Cities (07010206)+, Hawk-Yellow Medicine (07020004)+, Chippewa (07020005)+, Middle Minnesota (07020007)+, Upper St. Croix (07030001)+, Lower St. Croix (07030005)+, Rush-Vermillion (07040001), Black (07040007)+, South Fork Flambeau (07050003)+, Lower Chippewa (07050005)+, Eau Claire (07050006)+, Coon-Yellow (07060001)+, Grant-Little Maquoketa (07060003)+, Apple-Plum (07060005)+*, Lake Dubay (07070002)+, Castle Rock (07070003)+, Lower Wisconsin (07070005)+, Copperas-Duck (07080101), Upper Rock (07090001)+, Peruque-Piasa (07110009), Kankakee (07120001)+, Des Plaines (07120004), Lower Illinois-Senachwine Lake (07130001), Upper Sangamon (07130006)+*, Meramec (07140102)+, Bourbeuse (07140103)+
10 Sac (10290106)+
11 Lower Black (11010009)+, Spring (11010010)+, Little Red (11010014)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
U.S. Distribution by Watershed (based on multiple information sources) Help
Ecology & Life History
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Basic Description: a freshwater mussel
General Description: Clarke (1985, p 61-3) gives the following description. "Shell lenticular-ovate, moderately inflated, unsculptured, with only rudimentary hinge teeth; up to about 48 mm long, 22 mm high, and 16 mm wide. Much thicker (2.9 mm) anteriorly than posteriorly (0.5 mm). Anterior margin more or less evenly rounded; ventral margin flatly rounded, flat, or slightly concave just posterior of center; posterior margin also more or less evenly rounded and similar to anterior margin or a little broader; and dorsal parallel with ventral margin except indented in front of the umbones. Maximum inflation (and maximum height) both behind the middle of the shell. Beaks somewhat pointed, directed inwardly and toward the anterior, not inflated, located about 24% to 26% the distance from anterior to posterior, and projecting only a little above the hinge line. Area of posterior ridge convex and inflated but no distinct posterior ridge is discernable in most species. Area of posterior slope slightly concave near margin. Growth increments indicated by dark concentric periostracal bands covering barely discernable concentric grooves. Additional post-juvenile sculpturing consisting only of concentric threads (especially anteriorly), a few obscure radial lines posteriorly, and low lines and grooves of growth. Periostracum predominately brown or yellowish brown but blackish posteriorly in some specimens. Rarely one sees faint traces of narrow rays over the center of the shell, but most specimens, including juveniles, are entirely unrayed. Ligament rather long or of medium length, of moderate thickness, brown, and fragile when dry. Hinge teeth unusual, small, and incomplete. The right valve has a single, small, low, rounded, slightly elongated pseudocardinal tooth that arises from the shell wall (not from a thickened hinge plate as in other specimens) just in front of the umbone. The left valve of some specimens has an even smaller tooth that arises below and posterior to the umbone, i.e., in the same position as the interdental projection in LASMIGONA species. This tooth, where present, is low, short, somewhat flange-like, rounded, and irregular. There are no articulating lateral hinge teeth, although the edge of the shell is a little thickened below the ligament and, in some specimens, a poorly defined lateral ridge may be present. Beak cavities somewhat excavated but not deep, and with a variable number of small, irregular muscle scars within. Major anterior muscle scars small and shallow but well marked; pallial band well marked, located quite far from the margin (and more clearly defined) anteriorly but closer to the margin posteriorly, and in some specimens with several tiny, parallel, collabral ridges within the anterior portion; and posterior muscle scars very lightly etched and located distinctly forward of the most posterior portion of the pallial band loop. Nacre bluish white, iridescent posteriorly, with yellowish, salmon, or purplish suffusions in the center and near the beak cavities, and thin in a narrow band around the edge of the shell with the periostracal color showing through. Beak sculpture composed of about six parallel, predominately inverted, V-shaped ridges, apparently corresponding to the middle portions of the double-looped ridges in LASMIGONA. The earliest two ridges ore obscure in available material: they appear to be single-looped and especially expanded anteriorly. Later ridges are inverted V- shaped, with anterior arms short and directed ventrally in their proximal portions but curving anteriorly distally, and with posterior arms also short and more or less straight and parallel with the ligament or slightly curved upward. In some specimens the bars are in the shape of shallow V's and the later bars are simple undulating ridges but in most specimens the bars are deeply indented centrally."
Reproduction Comments: Howard (1915; 1951) demonstrated that the host is the Mudpuppy, Necturus maculosus. He suspected "that necturus eats the adult mussel and in seeking food visits one rock after another. In satisfying its appetite it becomes infected with the mussel glochidia, nourishing them, and when they have matured serves as a transporting and distributing agent for the young mussels". Glochidia were found deeply imbedded in the external gills of the mudpuppy, which was confirmed as a host by Bequaert et al. (1998). There is some evidence that the glochidia are released in the fall (Clarke, 1985).

Simpson (1914) described gravid specimens; "Brood pouch filling the entire outer gills and forming enormously thickened pads, the upper part finely vertically striate, the lower part of different texture, lighter colored, wrinkled and granular on the surface: embryos very large; outer and inner gills nearly alike in size, the latter free from the abdominal sac, all united to the mantle to their posterior ends..."

Ecology Comments: Refer to the General Freshwater Mussel ESA for general ecology of mussels.
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): BIG RIVER, CREEK, MEDIUM RIVER, Moderate gradient
Lacustrine Habitat(s): Shallow water
Special Habitat Factors: Benthic
Habitat Comments: Although occasionally found elsewhere, there is little doubt the preferred habitat is in sand or silt under large, flat stones in areas of a swift current in medium to large rivers and lakes (Call, 1900; Howard, 1915; Buchanan, 1980; Clarke, 1985; Oesch, 1984; 1995; Parmalee and Bogan, 1998). Its presence is presumably linked to the mudpuppy, Necturus maculosus, and it is usually rare though can be abundant in patches. Cudmore et al. (2004) provides the following habitat information for Canada: found in all types of clear, freshwater habitat, including creeks, streams, rivers and lakes; it is found on a variety of substrates (mud, silt, sand, gravel, cobble or boulder) in areas of swift current.
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Refer to the General Freshwater Mussel ESA.
Restoration Potential: The broad distribution of this species in streams, smaller rives, and lakes suggests that its potential for recovery may be greater than that of many other rare naiads. It is possible that specimens could be introduced to areas that once supported this species if the quality of that area has been improved. The host is known and can be monitored at the same time as the naiad.
Preserve Selection & Design Considerations: Refer to the General Freshwater Mussel ESA.
Management Requirements: Refer to the General Freshwater Mussel ESA.
Monitoring Requirements: Refer to the General Freshwater Mussel ESA.
Management Research Needs: Refer to the General Freshwater Mussel ESA.
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: 29Aug2006
NatureServe Conservation Status Factors Author: Cordeiro, J. (2006); Whittaker, J.C. (1998)
Management Information Edition Date: 01Aug1986
Management Information Edition Author: Watters, G. Thomas
Element Ecology & Life History Edition Date: 29Jan2007
Element Ecology & Life History Author(s): Cordeiro, J. (2007); WATTERS, T. G. (1991)

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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