Leptodea leptodon - (Rafinesque, 1820)
Scaleshell
Other English Common Names: Scale Shell
Taxonomic Status: Accepted
Related ITIS Name(s): Leptodea leptodon (Rafinesque, 1820) (TSN 80185)
Unique Identifier: ELEMENT_GLOBAL.2.115603
Element Code: IMBIV24020
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Leptodea
Genus Size: B - Very small genus (2-5 species)
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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: Leptodea leptodon
Conservation Status
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NatureServe Status

Global Status: G1G2
Global Status Last Reviewed: 05May2009
Global Status Last Changed: 06Feb2007
Rounded Global Status: G1 - Critically Imperiled
Reasons: This species has experienced a severe reduction in extant occurrences (approximately 75% reduction in number of streams) that has reduced this species from a fairly widespread species to a "regional endemic" in the Interior Highlands region. Subnational extirpations have occurred in Alabama, Iowa, Illinois, Indiana, Kentucky, Minnesota, Ohio, Tennessee, and Wisconsin. While it exists in 14 streams, only three or four populations are thought to be stable and most occurrences are widely disjunct.
Nation: United States
National Status: N1N2 (06Feb2007)

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 (SX), Arkansas (S2), Illinois (S1), Indiana (SX), Iowa (SX), Kentucky (SX), Michigan (SU), Minnesota (SX), Missouri (S1), Nebraska (S1), Ohio (SX), Oklahoma (S1), South Dakota (S1), Tennessee (SX), Wisconsin (SX)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (09Oct2001)
U.S. Fish & Wildlife Service Lead Region: R3 - North Central
IUCN Red List Category: NT - Near threatened
American Fisheries Society Status: Endangered (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 1000-5000 square km (about 400-2000 square miles)
Range Extent Comments: Historically this species was distributed through 55 streams in much of the Interior Basin and a portion of the St. Lawrence drainage, including 13 states (USFWS, 2004). Within the latter, records are primarily from the Lake Erie basin incorporating portions of western New York, southern Ontario, and southern Michigan. Records from New York are doubtful, however and are likely attributed to wingless examples of Leptodea fragilis (Szymanski, 1998). Interior Basin records are from streams in Ohio, Kentucky, Tennessee, Indiana, Illinois, southern Wisconsin, Iowa, Missouri, Kansas, Arkansas, and Oklahoma. Extensive surveys for the species in Minnesota have revealed no extant populations and only one historical record (MN DNR, 2004; Sietman, 2003). The only known extant populations are now restricted 13 streams in the Interior Highland divisions in Missouri, Arkansas, and Oklahoma (see Oesch, 1984; 1995; Gordon, 1985; Harris and Gordon, 1987; Clarke, 1987; Cummings and Mayer, 1992; Parmalee and Bogan, 1998; Szymanski, 1998; and USFWS, 1999). An additional site in the lower Missouri River near St. Louis, was discovered in 1990 (Hoke, 2000) bringing the total to 14. The species has not reported from Alabama since ompoundment of the Tennessee River (Mirarchi et al., 2004). Extensive surveys for the species in Minnesota have revealed no extant populations and only one historical record (MN DNR, 2004). Fresh dead shell were recently discovered below Lewis and Clark Lake, Nebraska in the Missouri River (Hoke, 2005).

Area of Occupancy: 126-2,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 6 - 20
Number of Occurrences Comments: Historically, this species was known from 55 streams; but is currently restricted to 14 streams of which only three probably contain viable populations or occurrences (USFWS, 1999; 2004; Szymanski, 1998). Extant populations exist in the Meramec, Missouri, St. Francis, White, Arkansas, and Red River drainages though only the Meramec and Missouri River drainage populations seem viable. With the exception of the Meramec, Bourbeuse, and Gasconade Rivers in Missouri, all rivers listed as supporting the scaleshell are based on a few or a single specimen (USFWS, 2004). In Arkansas, it occurs in widely disjunct occurrences in the northern (White, Strawberry, Spring, Mulberry, Myatt Rivers) and southwestern parts of the state (South Fork Fourche La Fave River, Saline River, Cossatot River, Ouachita River) but all with low viability and few specimens found (Harris and Gordon, 1987; Harris et al., 1997); and Frog Bayou (Gordon, 1985). In South Dakota it is known from the Missouri River along the Nebraska/South Dakota border (Backlund, 2000). In Missouri, it has been reported from only the Auxvasse Creek, Big River, Gasconade River, and Meramec River (Oesch, 1995). An additional site in the lower Missouri River between the Gavin's Point Dam and the mouth near St. Louis, was discovered in 1990 (Hoke, 2000). Fresh dead shell were recently discovered below Lewis and Clark Lake, Nebraska in the Missouri River (Hoke, 2005). In the Red River drainage in Oklahoma, it occurs in the Kiamichi River drainage historically although may still be holding on currently (Vaughn, 2000) as fresh dead shells were found recently at three sites (Galbraith et al., 2008).

Population Size: Unknown
Population Size Comments: In surveys since 1980 it has never comprised more than 0.1% of the mussels collected and was only found in 14 of 198 sites surveyed in the Meramec River drainage (in 3 rivers) (Buchanan, 1980). A resurvey of these sites in 1997 revealed a similar 0.4% composition with specimens collected from three rivers (n=34 at 9 sites, n=10 at 5 sites, n=2 at 1 site). The species was present at 4 of 5 sites where buchanan (1980) had collected it while the fifth site no longer supports the species (Szymanski, 1998; USFWS, 2004). See U.S. Fish and Wildlife Service (1999; 2004) and Szymanski (1998) for a detailed account of collections.

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: Historically, this species was known from 55 streams; but is currently restricted to 14 streams of which only three probably contain viable populations or occurrences (USFWS, 1999; 2004; Szymanski, 1998). Extant populations exist in the Meramec, Missouri, St. Francis, White, Arkansas, and Red River drainages though only the Meramec and Missouri River drainage populations seem viable. With the exception of the Meramec, Bourbeuse, and Gasconade Rivers in Missouri, all rivers listed as supporting the scaleshell are based on a few or a single specimen (USFWS, 2004). Only three of the 14 populations (Meramec River drainage primarily) are thought to be stable (USFWS, 1999; 2004). Missouri River drainage sites are mostly unstable with populations tenuous, at best (Szymanski, 1998). The few remaining populations in Arkansas do not appear to be viable with no evidence of reproduction recently (Anderson, 2006).

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: This species is severely impacted by alteration and inundation of channels, siltation from agriculture and clear-cutting, chemical and organic pollution. The decline of scaleshell is primarily due to threats that cause habitat loss and degradation from construction activities and intensive land use (USFWS, 2004). The most viable sites on the Meramec River drainage are affected by lead mining (Szymanski, 1998) and have a small populations with declining bed habitat from sedimenatation, extreme enrichment, and unstable substrates.

Szymanski (1998) lists the following threats:
(1) destruction, modification, or curtailment of habitat or range: This species has suffered one of the greatest range restrictions in North America. Degradation continues to threaten populations. Major causes are channelization, damming and impoundment, sedimentation, and nonpoint and point source pollution.
(2) overutilization for scientific or commercial purposes: This is unlikely due to the small size of this species. Extirpated populations may have been subjected to overharvesting and today incidental collecting may be a problem.
(3) disease and predation: Small mammal predation could potentially pose a problem for populations especially for small populations in Arkansas and Oklahoma.
(4) inadequacy of existing regulatory mechanisms: The species is not afforded state protection in Arkansas but Missouri and Oklahoma afford state protective status.

Short-term Trend: Decline of >70%
Short-term Trend Comments: Much of the decline occurred before 1950, however some populations are still declining. Of the remaining 14 populations, three are thought to be stable, two are declining, four are presumed to be declining, and the status of four is unknown (USFWS, 1999; 2004). Resurvey of Buchanan's (1980) sites in the Meramec River drainage in 1997 revealed a similar 0.4% composition with specimens collected from three riversand the species was present at 4 of 5 sites where Buchanan (1980) had collected it while the fifth site no longer supports the species (Szymanski, 1998; USFWS, 2004). Although the species is persisting in this area, the limited number of specimens collected, limited habitat available, and loss of beds since 1980 indicate populations are declining. Wabash River drainage, Indiana, occurrences were extirpated many years ago (Fisher, 2006). Only dead shells have been found recently in the Kiamichi River, Oklahoma (Galbraith et al., 2008).

Long-term Trend: Decline of 70-90%
Long-term Trend Comments: Current range for this species is much reduced from its historic extent. Of the 53 locales in which the scaleshell has been collected historically, only 13 or 14 are believed to contain extant populations (USFWS, 1999; Szymanski, 1998). The species is considered extirpated from Minnesota with the only specimen collected in the Minnesota River at Pike Island in the late 1800s (Sietman, 2003). It has probably been extirpated from Tennessee rivers for at least several decades (Parmalee and Bogan, 1998). It has been extirpated from the Upper Mississippi River system for over 50 years where it historically occurred in eight rivers and tributaries in the system (Szymanski, 1998). It is also nearly extirpated from the previously known 25 rivers and tributaries within the Middle Mississippi River system with only about 4 or 5 rivers in the Missouri and Meramec River drainages currently containing populations (Szymanski, 1998). It is extirpated from Alabama, probably during the 1900s; but probably once occurred in the Tennessee River across northern Alabama however all records are from Muscle Shoals (Williams et al., 2008). It is extirpated from Ohio with historical occurrences in the Ohio River at Cincinnati and Marietta, lower Muskingum River, and Scioto River at Columbus and Circleville (Watters et al., 2009).

Intrinsic Vulnerability: Not intrinsically vulnerable
Intrinsic Vulnerability Comments: A sample of 33 dead specimens and 2 living individuals collected in 2000 from a Gasconade River site did not contain any individuals exceeding approximately seven years old based on counts of external annuli (Barnhart, 2001). Likewise, no individuals over approximately six years old were observed out of 44 living individuals collected in 1997 from the Meramec Basin (Roberts and Bruenderman, 2000). Based on these collections, it appears that the life expectancy of the scaleshell is less than 10 years.

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity Comments: This species occurs in riffles with moderate to high gradients in creeks to large rivers. It is typically associated with riffles, relatively strong currents, and substrate of mud, sand , or assemblages of gravel, cobble, and boulder. It has been found completely buried in the substrate down to depths of 15 cm (Oesch, 1984; 1995). It occurs in medium to large rivers with low to moderate gradients in a variety of stream habitats including gravel, cobble, boulders, and occasionally mud or sand substrates (Buchanan, 1980; 1994; Oesch, 1995). Although always somewhat rare, this species historically was not habitat limited and once occupied a wide variety of habitats including riffle areas with assemblages of gravel, cobble, boulder, and occasionally mud or sand; as well as big rivers with muddy bottoms (Szymanski, 1998). Currently it is more restricted to rivers with relatively good water quality (Oesch, 1995) in stretches with stable channels (Buchanan, 1980).

Other NatureServe Conservation Status Information

Inventory Needs: Determine the extent of existing populations, continue surveys for additional EOs, and assess potential reintroduction sites.

Protection Needs: All populations should receive protection through aquisition, easement, registry, and working with local, state, and federal government agencies on issues relating to development, water quality, river designations, etc. Watershed management plans to promote conservation of aquatic resources and recovery of impacted habitats are essential. Critical habitat not currently designated but necessary. Because only a small number of populations exist, it is essential that they all be protected, and recovery cannot be achieved without habitat restoration

Distribution
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Global Range: (1000-5000 square km (about 400-2000 square miles)) Historically this species was distributed through 55 streams in much of the Interior Basin and a portion of the St. Lawrence drainage, including 13 states (USFWS, 2004). Within the latter, records are primarily from the Lake Erie basin incorporating portions of western New York, southern Ontario, and southern Michigan. Records from New York are doubtful, however and are likely attributed to wingless examples of Leptodea fragilis (Szymanski, 1998). Interior Basin records are from streams in Ohio, Kentucky, Tennessee, Indiana, Illinois, southern Wisconsin, Iowa, Missouri, Kansas, Arkansas, and Oklahoma. Extensive surveys for the species in Minnesota have revealed no extant populations and only one historical record (MN DNR, 2004; Sietman, 2003). The only known extant populations are now restricted 13 streams in the Interior Highland divisions in Missouri, Arkansas, and Oklahoma (see Oesch, 1984; 1995; Gordon, 1985; Harris and Gordon, 1987; Clarke, 1987; Cummings and Mayer, 1992; Parmalee and Bogan, 1998; Szymanski, 1998; and USFWS, 1999). An additional site in the lower Missouri River near St. Louis, was discovered in 1990 (Hoke, 2000) bringing the total to 14. The species has not reported from Alabama since ompoundment of the Tennessee River (Mirarchi et al., 2004). Extensive surveys for the species in Minnesota have revealed no extant populations and only one historical record (MN DNR, 2004). Fresh dead shell were recently discovered below Lewis and Clark Lake, Nebraska in the Missouri River (Hoke, 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 ALextirpated, AR, IAextirpated, IL, INextirpated, KYextirpated, MI, MNextirpated, MO, NE, OHextirpated, OK, SD, TNextirpated, WIextirpated

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
AL Lauderdale (01077)*
AR Crawford (05033), Fulton (05049), Jackson (05067), Lawrence (05075), Perry (05105), Sevier (05133), St. Francis (05123)
IN Posey (18129)*, Tippecanoe (18157)*, Vigo (18167)*
KY Boone (21015)*, Campbell (21037)*, Cumberland (21057)*, Hart (21099)*, Kenton (21117)*, Pendleton (21191)*, Russell (21207)*, Wayne (21231)*, Woodford (21239)*
MI Kent (26081)*
MN Dakota (27037)*, Ramsey (27123)*
MO Crawford (29055)*, Franklin (29071), Gasconade (29073), Jefferson (29099), Laclede (29105), Maries (29125), Osage (29151), Phelps (29161), Pulaski (29169), St. Louis (29189), Wright (29229)
NE Cedar (31027)
OK LeFlore (40079), McCurtain (40089)*, Pushmataha (40127)
SD Yankton (46135)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
04 Lower Grand (04050006)+*
05 Muskingum (05040004)*, Upper Scioto (05060001)*, Lower Scioto (05060002)*, Ohio Brush-Whiteoak (05090201)+*, Middle Ohio-Laughery (05090203)+*, Licking (05100101)+*, Lower Kentucky (05100205)+*, Upper Green (05110001)+*, Middle Wabash-Deer (05120105)*, Middle Wabash-Little Vermilion (05120108)+*, Middle Wabash-Busseron (05120111)+*, Lower Wabash (05120113)+*, Upper White (05120201)*, Upper Cumberland-Lake Cumberland (05130103)+*, Obey (05130105)*
06 Holston (06010104)*, Watts Bar Lake (06010201)*, Lower Clinch (06010207)*, Pickwick Lake (06030005)+*, Upper Duck (06040002)*
07 Twin Cities (07010206)+*, Lower Minnesota (07020012)+*, Turkey (07060004)*, Copperas-Duck (07080101)*, Flint-Henderson (07080104)*, Middle Cedar (07080205)*, Lower Iowa (07080209)*, Pecatonica (07090003)*, Lower Rock (07090005)*, Kishwaukee (07090006)*, Green (07090007)*, Lower Illinois-Senachwine Lake (07130001)*, Upper Sangamon (07130006)*, South Fork Sangamon (07130007)*, Lower Sangamon (07130008)*, Salt (07130009)*, Lower Illinois (07130011)*, Macoupin (07130012)*, Meramec (07140102)+, Bourbeuse (07140103)+, Big (07140104)+, Upper Kaskaskia (07140201)*, Middle Kaskaskia (07140202)*, Lower Kaskaskia (07140204)*
08 Upper St. Francis (08020202)*, Lower St. Francis (08020203)+, Upper Ouachita (08040102)*, Little Missouri (08040103)*, Lower Ouachita-Bayou De Loutre (08040202)*, Upper Saline (08040203)*, Lower Saline (08040204)*
10 Lewis and Clark Lake (10170101)+, South Grand (10290108)*, Upper Gasconade (10290201)+, Big Piney (10290202), Lower Gasconade (10290203)+, Lower Missouri-Moreau (10300102)*
11 Beaver Reservoir (11010001)*, James (11010002)*, Bull Shoals Lake (11010003)*, Spring (11010010)+, Strawberry (11010012)+, Upper White-Village (11010013)+, Little Red (11010014)*, Elk (11070208), Frog-Mulberry (11110201)+, Fourche La Fave (11110206)+, Kiamichi (11140105)+, Upper Little (11140107)*, Mountain Fork (11140108)+*, Lower Little (11140109)+
+ 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 elongated-elliptical, compressed, thin, translucent shell with a rounded anterior margin.
General Description: Shell small to medium-sized, elongated-elliptical, compressed, thin, tramslucent; anterior margin rounded; ventral margin convex; posterior of male bluntly pointed, obliquely convex; posterior of female truncated, membraneous, margin wavy; dorsal margin fairly straight to slightly convex, anterio-dorsal junction angular; beak low, depressed, positioned in anterior quarter of shell length, sculpted by 4-5 very fine double-looped ridges; posterior ridge rounded; posterior slope slightly convex becoming concave and compressed near shell margin, expanded into a low wing which may be obliterated; periostracum yellowish or greenish to olive brown, often with numerous faint green rays, annual growth lines rather distinct. Pseudocardinal teeth rudimentary, single, compressed; interdentum absent; lateral teeth short, low, lamellar, single; anterior muscle scars impressed, smooth, distinct; posterior muscle scars apparent; pallial line apparent anteriorly, may be obscure posteriorly; beak cavity very shallow; nacre bluish to purple, occasionally with copper or salmon overcast, highly iridescent (FWS, 2001).
Diagnostic Characteristics: This species is rather distinct with its extremely thin shell, poorly developed hinge definition, elongate shape with low wing, and the highly iridescent purplish nacre. Leptodea fragilis (Rafinesque, 1820) and Proptera ohiensis (Rafinesque, 1820) are also very thin but are considerably larger, broader shells with relatively large wings. Hemistena lata (Rafinesque, 1820) also resembles Leptodea leptodon but completely lacks hinge definition and is not as iridescent or translucent. Height: 60mm (FWS, 2001).
Reproduction Comments: From USFWS (2004):
"Baker (1928) surmised that scaleshell is a long-term brooder. Recent observations support Baker's conclusion. Gordon (1991) reported observations of gravid scaleshell in September, October, November, and March (location unknown). In Missouri, gravid specimens have been observed in the Meramec and Gasconade rivers in August, September, October, April, and June (Barnhart 2001, data from Roberts and Bruenderman 2000). Additionally, Barnhart (1998) observed scaleshell in the Meramec River brooding undeveloped eggs in early August. The only known report of scaleshell collected in a non-gravid condition is July from the Big River, Missouri (Data from Roberts and Bruenderman 2000). Based on these observations, scaleshell spawns and begins brooding in early August and glochidia are released the following June in Missouri. Formal studies are needed to better define the breeding season of scaleshell. These studies should be based on water temperature, in addition to season, as a controlling factor of its reproductive cycle."

Embryonic stages and glochidia have been reported in echtobranchous marsupia for this species in September, October, November, and March, indicating that it is a long-term brooder (USFWS, 2001); supporting Baker's (1928) original observations. Studies by Barnhart et al. (1998) found the drum, Aplodinotus grunniens, to be an effective glochidial host among tests of 24 potential species. How a scaleshell infects its host and the intricacy of this relationship is unknown. A further reproduction summary can be found in USFWS (2004).

Ecology Comments: No specific studies have examined the ecology of this species. Oesch (1984) notes that it requires quite clear, unpolluted water, indicating a rather low tolerance to disterbance. Its adaptations to withstand the physical forces inherent to riffles resemble those of Hemistena lata (shell completely burried in a vertical position with the foot extended as an anchor) (Gordon and Layzer 1989).
Habitat Type: Freshwater
Non-Migrant: N
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 mussles are displaced from the substrate during floods. Major dispersal occurs while glochidia are encysted on their hosts (FWS, 2001).
Riverine Habitat(s): BIG RIVER, CREEK, High gradient, MEDIUM RIVER, Moderate gradient, Riffle
Special Habitat Factors: Benthic
Habitat Comments: This species occurs in riffles with moderate to high gradients in creeks to large rivers. It is typically associated with riffles, relatively strong currents, and substrate of mud, sand , or assemblages of gravel, cobble, and boulder. It has been found completely buried in the substrate down to depths of 15 cm (Oesch, 1984; 1995). It occurs in medium to large rivers with low to moderate gradients in a variety of stream habitats including gravel, cobble, boulders, and occasionally mud or sand substrates (Buchanan, 1980; 1994; Oesch, 1995). Although always somewhat rare, this species historically was not habitat limited and once occupied a wide variety of habitats including riffle areas with assemblages of gravel, cobble, boulder, and occasionally mud or sand; as well as big rivers with muddy bottoms (Szymanski, 1998). Currently it is more restricted to rivers with relatively good water quality (Oesch, 1995) in stretches with stable channels (Buchanan, 1980).
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 trophic guilds such as postulated for the Sphaeriidae (see Lopez and Holopaien 1987, Gordon 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 expectedly be greatly reduced during cold-temperature months.
Length: 11.7 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: This species was listed as federally endangered in the U.S. in 2001 and a recovery plan has been drafted (USFWS, 2004). Recovery narrative: (1) Establish a working group to implement the recovery actions outlined in this plan, (2) Protect, restore, and maintain existing populations and habitat, (3) Improve understanding of the biology and ecology of scaleshell, (4) Identify suitable reintroduction sites and develop and implement habitat restoration strategies for those areas, (5) Reintroduce scaleshell into portions of its former range, (6) Initiate educational and public outreach actions to heighten awareness of the scaleshell as an endangered species and solicit help with recovery actions, (7) Conduct periodic reviews and track recovery.
Biological Research Needs: Determine habitat preferences and environmental tolerances, tolerance to various pollutants and siltation, and reproductive biology/glochidial hosts.
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: 05May2009
NatureServe Conservation Status Factors Author: Cordeiro, J. (2009); Gordon, M.E. (1992); Morrison, M. (1999)
Management Information Edition Date: 02Aug2007
Management Information Edition Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 08Nov2006
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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  • Minnesota Department of Natural Resources Natural Heritage and Nongame Research Program. 2004. Minnesota scaleshell mussel (Leptodea leptodon) survey. Final report for Federal Aid Project E-6-R to the U.S. Fish and Wildlife Service. January 2004. 9 pp.

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  • Oesch, R.D. 1995. Missouri Naiades. A Guide to the Mussels of Missouri. Second edition. Missouri Department of Conservation: Jefferson City, Missouri. viii + 271 pp.

  • Parmalee, P.W. and A.E. Bogan. 1998. The Freshwater Mussels of Tennessee. University of Tennessee Press: Knoxville, Tennessee. 328 pp.

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  • ROBERTS, ANDY, 2001. DETERMINATION OF ENDANGERED STATUS FOR THE SCALESHELL MUSSEL, U.S. FISH & WILDLIFE SERVICE, FINAL RULE. FEDERAL REGISTER 66 (195), OCTOBER 9, 2001, PP 51322-51323.

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  • Strayer, D.L. 1999a. Use of flow refuges by unionid mussels in rivers. Journal of the North American Benthological Society 18(4):468-476.

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  • 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.

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References for Watershed Distribution Map
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  • Cummings, K.S. and C.A. Mayer. 1997. Distributional checklist and status of Illinois freshwater mussels (Mollusca: Unionacea). Pages 129-145 in: K.S. Cummings, A.C. Buchanan, C.A. Mayer, and T.J. Naimo (eds.) Conservation and management of freshwater mussels II: initiatives for the future. Proceedings of a UMRCC Symposium, October 1995, St. Louis, Missouri. Upper Mississippi River Conservation Committee, Rock Island, Illinois.

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  • Harris, J.L., P.J. Rust, A.C. Christian, W.R. Posey II, C.L. Davidson, and G.L. Harp. 1997. Revised status of rare and endangered Unionacea (Mollusca: Margaritiferidae, Unionidae) in Arkansas. Journal of the Arkansas Academy of Science, 51: 66-89.

  • Hoke, E. 2005a. The freshwater mussels (Mollusca: Bivalvia: Unionidea) of northern Nebraska: the Missouri, Niobrara, and White River basins. American Malacological Bulletin, 20: 27-35.

  • Szymanski, J. 1998. Leptodea leptodon (scaleshell mussel) rangewide status assessment. Report prepared for U.S. Fish and Wildlife Service, Fort Snelling, Minnesota. 16 pp. + app.

  • U.S. Fish and Wildlife Service (USFWS). 2004. Scaleshell mussel draft recovery plan (Leptodea leptodon). U.S. Fish and Wildlife Service, Fort Snelling, Minnesota. 90 pp.

  • Vaughn, C.C. 2000. Changes in the mussel fauna of the middle Red River drainage: 1910 - present. Pages 225-232 in R.A. Tankersley, D.I. Warmolts, G.T. Watters, B.J. Armitage, P.D. Johnson, and R.S. Butler (eds.). Freshwater Mollusk Symposia Proceedings. Ohio Biological Survey, Columbus, Ohio. 274 pp.

  • Watters, G.T., M.A. Hoggarth, and D.H. Stansbery. 2009b. The Freshwater Mussels of Ohio. Ohio State University Press: Columbus, Ohio. 421 pp.

  • Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater Mussels of Alabama & the Mobile Basin in Georgia, Mississippi & Tennessee. University of Alabama Press: Tuscaloosa, Alabama. 908 pp.

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