Pleurobema clava - (Lamarck, 1819)
Clubshell
Other English Common Names: Club Naiad, Clubshell Pearly Mussel
Taxonomic Status: Accepted
Related ITIS Name(s): Pleurobema clava (Lamarck, 1819) (TSN 80092)
Unique Identifier: ELEMENT_GLOBAL.2.902145
Element Code: IMBIV35060
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Pleurobema
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
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Concept Reference: Watters, G.T., M.A. Hoggarth, and D.H. Stansbery. 2009b. The Freshwater Mussels of Ohio. Ohio State University Press: Columbus, Ohio. 421 pp.
Concept Reference Code: B09WAT01EHUS
Name Used in Concept Reference: Pleurobema clava
Taxonomic Comments: The relationship between Pleurobema oviforme and Pleurobema clava is a matter of debate as P. oviforme replaces P. clava in headwaters of the Tennessee River, and it has been suggested that they are conspecific (Williams et al., 2008).

In the latest treatment of freshwater mussels of Ohio, Watters et al. (2009) treat Pleurobema bournianum (known only from the type locality of the Scioto River and not collected in over 150 years) as a synonym of Pleurobema clava.
Conservation Status
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NatureServe Status

Global Status: G1G2
Global Status Last Reviewed: 05Aug2010
Global Status Last Changed: 05Aug2010
Rounded Global Status: G1 - Critically Imperiled
Reasons: This species has been extirpated from most of its range in this century (probably less than 20% of historical range remains). Continued loss of habitat and water quality deterioration threaten remaining populations.
Nation: United States
National Status: N1N2 (05Aug2010)

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), Illinois (S1), Indiana (S1), Kentucky (S1), Michigan (S1), Nebraska (SX), New York (S1), Ohio (S1), Pennsylvania (S1S2), Tennessee (SH), West Virginia (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE, XN: Listed endangered, nonessential experimental population (22Jan1993)
Comments on USESA: On January 22, 1993, the clubshell was listed Endangered throughout its range, except where listed as an Experimental Population. On June 14, 2001, the clubshell was designated as Experimental Population, Non-Essential in the U.S.A. (AL;The free-flowing reach of the Tennessee R. from the base of Wilson Dam downstream to the backwaters of Pickwick Reservoir [about 12 RM (19 km)] and the lower 5 RM [8 km] of all tributaries to this reach in Colbert and Lauderdale Cos.
U.S. Fish & Wildlife Service Lead Region: R5 - Northeast
IUCN Red List Category: CR - Critically endangered
Convention on International Trade in Endangered Species Protection Status (CITES): Appendix II
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, it was distributed across nine states in the Wabash, Ohio, Kanawha, Kentucky (Danglade, 1922; Clarke, 1987), Green, Monongahela, and Allegheny Rivers and their tributaries. It has been recorded from most of the tributaries in Kentucky, Illinois, Indiana, and Ohio, as well as from more isolated systems in Michigan, Pennsylvania, and West Virginia. Records from Nebraska, Minnesota, and Iowa (Simpson, 1900) ar eroneous (USFWS, 1994). Listed as occurring in the St. Peter's River in Minnesota and from Nebraska by Simpson (1914), however these records are probably in error. Somne records from the Cumberland River appear to be authentic, but others may represent Pleurobema oviforme (Gordon and Layzer, 1989). It is currently known from 12 streams in six states: Tippecanoe River in Indiana; Fish Creek in Ohio and Indiana; West Branch of the St. Josephs River in Ohio and Michigan; Walhonding River in Ohio; East Fork of the West Branch of the St. Josephs River in Michigan; Little Darby Creek in Madison County, Ohio; French Creek in Pennsylvania, in small numbers in the Green River in Kentucky, and the Elk River and Hackers Creek of the West Fork River in West Virginia (USFWS, 1994). It is extirpated from Alabama (Mirarchi et al., 2004), Illinois, Tennessee (U.S. Fish and Wildlife Service) and was recently thought to be extirpated from New York (Strayer and Jirka, 1997) but a population was recently rediscovered in the Allegheny River watershed (Smith and Horn, 2006).

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

Number of Occurrences: 6 - 20
Number of Occurrences Comments: Known from short reaches of 12 streams (USFWS, 1993; 1994) including small populations in the headwater tributaries of the St. Joseph River (Indiana/Ohio) (Grabarkiewicz and Crail, 2006). It is known from the St. Joseph and Maumee (Pror, 2005) and Tippecanoe Rivers, Indiana (Cummings and Berlocher, 1990; Fisher, 2006). Weathered shells are known from Sugar Creek (east fork White River drainage) in central Indiana (Harmon, 1992). A single specimen was collected from the Middle Branch of the North Fork Vermillion River in Illinois (Szafoni et al., 2000). More recently, this species was found in 5 sites (4 with living specimen) in Pymatuning Creek in Ashtabula County, Ohio (Huehner and Corr, 1994). Matter et al. (2006) failed to find this species in surveys of Ohio Brush Creek, Ohio, despite reports of a weathered specimen in 1987 (Watters, 1992) indicating it may be extirpated from that locale. Populations in Ohio are also known from the Walhonding River (OH NHP, pers. comm., 2006). Recently this species was rediscovered in Cassadaga Creek in the Allegheny River watershed in New York (Smith and Horn, 2006). In Pennsylvania it is extant in the Shenango drainage (Bursey, 1987); French (Mohler et al., 2006) and Middle Allegheny-Redbank drainages (PA NHP, pers. comm., 2006) and historical in the Conemaugh, Connoquenessing, Kiskiminetas, Mahoning, and Lower Monongahela drainages (Ortmann, 1919). A few sites are known in northwestern drainages in West Virginia (WV NHP, pers. comm., 2007) possibly in the Ohio and Kanawha Rivers (Taylor and Horn, 1983). In Kentucky it is rare in the upper Green River (Cicerello and Schuster, 2003) including Rough River (Gordon, 1991) and may still be holding on in the lower Ohio (Blue-Sinking section) (KY NHP, pers. comm., 2004).

Population Size: Unknown
Population Size Comments: Due to problems obtaining a unbiased and complete sample, abundance in mussels is always difficult to estimate. Few detailed abundance estimates have been done on this species. Surveys in 1992 and 1993 of the Tippecanoe River in Indiana found living individuals at nine sites from the mouth upstream 150 miles. Fresh dead individuals were found at another 10 sites with weathered shells at 97% of sites studied. It was also found as weathered shells at 8 sites and fresh dead at another site in the Mississinewa River in Indiana in 1994 as well as weathered shells from two sites in Indiana's Salamonie River (USFWS, 1994). Smith and Crabtree (2010) found this species at 2 of 32 sites (1 with recruitment) along the entire length of Pennsylvania's French Creek.

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: The largest population is likely in the Tippecanoe River, Indiana (USFWS, 1994). Reproducing population is known from the French Creek drainage in Pennsylvania (Mohler et al., 2006).

Overall Threat Impact: High
Overall Threat Impact Comments: This species is threatened by domestic and industrial waste and navigation developments in the upper Ohio and Wabash river watersheds. Stansbery (pers. comm.) believed that various pesticides were at least partially responsible for the overall decrease in the fauna of areas in which Pleurobema clava was present. Proposed coal mining in the Elk River watershed may threaten that population. The introduced zebra mussel could also pose a significant threat. The species is particularly vulnerable to siltation, which clogs the substrate interstices and suffocates the animal. USFWS (1994) lists the following reasons for decline: siltation (from agriculture, construction, and forestry runoff), impoundment (including dam constructon and maintenance), instream sand and gravel mining (for channelization), pollutants (pesticides and fertilizers, heavy metals, ammonia from wastewater, acid-mine runoff, and invasive species (zebra mussel, quagga mussel).

Short-term Trend: Decline of >70%
Short-term Trend Comments: The U.S. Fish and Wildlife Service (1993) estimate at least a 95% reduction in range as this species was much more widespread historically. For example, it was formerly widely distributed in the Vermillion and Wabash River drainages in Illinois and Ohio (Clarke, 1987) but is now extirpated from the state of Illinois (Cummings and Mayer, 1997) except for the North Fork Vermillion River (Szafoni et al., 2000) and was also formerly distributed in the lower Tennessee River and Cumberland River in Tennessee, but it is also likely extirpated in that state (Parmalee and Bogan, 1998). Much of its former range in south central Ohio has been reduced or eliminated (Watters, 1992) including the Scioto River, near Chillicothe, Ohio (as P. bournianum- Watters, 1995; Watters et al., 2009) where it has not been seen in over 150 years. It is nearly extirpated from New York (Strayer and Jirka, 1997).

Long-term Trend: Decline of 70-90%
Long-term Trend Comments: In Pennsylvania it is extant in the Shenango drainage (Bursey, 1987); French and Middle Allegheny-Redbank drainages (PA NHP, pers. comm., 2006) and historical in the Conemaugh, Connoquenessing, Kiskiminetas, Mahoning, and Lower Monongahela drainages (Ortmann, 1919). In Alabama it occurred in the Tennessee River across the northern part of the state but si now extirpated with the most recent known collections of live individuals in tailwaters of Wilson Dam in 1966 (Williams et al., 2008). It is extirpated from the McAlpine dam pool in the Ohio River at Louisville, Kentucky (and Indiana) (Watters and Flaute, 2010).

Intrinsic Vulnerability: Unknown

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity Comments: This species is generally found in clean, coarse sand and gravel in runs, often just downstream of a riffle, and cannot tolerate mud or slackwater conditions (USFWS, 1994).

Other NatureServe Conservation Status Information

Distribution
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Global Range: (1000-5000 square km (about 400-2000 square miles)) Historically, it was distributed across nine states in the Wabash, Ohio, Kanawha, Kentucky (Danglade, 1922; Clarke, 1987), Green, Monongahela, and Allegheny Rivers and their tributaries. It has been recorded from most of the tributaries in Kentucky, Illinois, Indiana, and Ohio, as well as from more isolated systems in Michigan, Pennsylvania, and West Virginia. Records from Nebraska, Minnesota, and Iowa (Simpson, 1900) ar eroneous (USFWS, 1994). Listed as occurring in the St. Peter's River in Minnesota and from Nebraska by Simpson (1914), however these records are probably in error. Somne records from the Cumberland River appear to be authentic, but others may represent Pleurobema oviforme (Gordon and Layzer, 1989). It is currently known from 12 streams in six states: Tippecanoe River in Indiana; Fish Creek in Ohio and Indiana; West Branch of the St. Josephs River in Ohio and Michigan; Walhonding River in Ohio; East Fork of the West Branch of the St. Josephs River in Michigan; Little Darby Creek in Madison County, Ohio; French Creek in Pennsylvania, in small numbers in the Green River in Kentucky, and the Elk River and Hackers Creek of the West Fork River in West Virginia (USFWS, 1994). It is extirpated from Alabama (Mirarchi et al., 2004), Illinois, Tennessee (U.S. Fish and Wildlife Service) and was recently thought to be extirpated from New York (Strayer and Jirka, 1997) but a population was recently rediscovered in the Allegheny River watershed (Smith and Horn, 2006).

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, IL, IN, KY, MI, NEextirpated, NY, OH, PA, TN, WV

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
AL Colbert (01033)*, Lauderdale (01077)*
IL Cumberland (17035)*, Vermilion (17183)*
IN Adams (18001), Allen (18003), Bartholomew (18005), Carroll (18015), Cass (18017)*, Clay (18021)*, Clinton (18023)*, Crawford (18025), Daviess (18027), De Kalb (18033), Dearborn (18029), Decatur (18031), Delaware (18035), Dubois (18037)*, Fountain (18045)*, Fulton (18049), Gibson (18051)*, Grant (18053), Greene (18055), Hamilton (18057), Hancock (18059), Harrison (18061), Howard (18067), Huntington (18069), Jackson (18071), Jay (18075)*, Johnson (18081)*, Knox (18083), Kosciusko (18085), Lawrence (18093), Madison (18095), Marion (18097), Marshall (18099), Martin (18101)*, Miami (18103), Monroe (18105), Montgomery (18107)*, Morgan (18109), Ohio (18115), Owen (18119), Parke (18121), Pike (18125)*, Posey (18129)*, Pulaski (18131), Randolph (18135), Ripley (18137), Rush (18139), Shelby (18145), Starke (18149), Steuben (18151), Sullivan (18153)*, Tippecanoe (18157), Vermillion (18165), Vigo (18167), Wabash (18169), Warren (18171)*, Washington (18175)*, Wells (18179), White (18181), Whitley (18183)
KY Allen (21003)*, Bath (21011)*, Boone (21015)*, Boyle (21021)*, Bracken (21023)*, Bullitt (21029)*, Butler (21031)*, Campbell (21037)*, Edmonson (21061), Gallatin (21077)*, Garrard (21079)*, Grant (21081)*, Grayson (21085)*, Green (21087), Hardin (21093)*, Harrison (21097)*, Hart (21099), Jefferson (21111)*, Kenton (21117)*, Larue (21123)*, Lincoln (21137)*, Livingston (21139)*, Lyon (21143)*, Marshall (21157)*, McCreary (21147)*, Meade (21163), Mercer (21167)*, Nelson (21179)*, Owen (21187)*, Pendleton (21191)*, Robertson (21201)*, Spencer (21215)*, Taylor (21217), Warren (21227)*, Wayne (21231)*, Woodford (21239)*
MI Hillsdale (26059)
NY Chautauqua (36013)
OH Adams (39001), Allen (39003), Ashland (39005), Ashtabula (39007), Athens (39009), Champaign (39021), Coshocton (39031), Defiance (39039), Delaware (39041)*, Fairfield (39045), Fayette (39047)*, Franklin (39049), Greene (39057)*, Hancock (39063), Hocking (39073), Knox (39083)*, Madison (39097), Pickaway (39129), Putnam (39137), Ross (39141)*, Tuscarawas (39157), Union (39159), Williams (39171)
PA Armstrong (42005), Beaver (42007)*, Butler (42019)*, Clarion (42031), Crawford (42039), Erie (42049), Fayette (42051)*, Forest (42053), Greene (42059)*, Indiana (42063)*, Lawrence (42073)*, Mercer (42085), Venango (42121), Warren (42123), Westmoreland (42129)*
TN DeKalb (47041)*, Hardin (47071)*, Humphreys (47085)*, Montgomery (47125)*, Putnam (47141)*, Smith (47159)*
WV Calhoun (54013), Doddridge (54017), Kanawha (54039), Lewis (54041), Ritchie (54085)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
04 St. Joseph (04100003)+, St. Marys (04100004)+, Upper Maumee (04100005)+, Tiffin (04100006)+, Auglaize (04100007)+, Blanchard (04100008)+, Lower Maumee (04100009)*
05 Upper Allegheny (05010001)+, Conewango (05010002)+, Middle Allegheny-Tionesta (05010003)+, French (05010004)+, Middle Allegheny-Redbank (05010006)+, Conemaugh (05010007)+*, Kiskiminetas (05010008)+*, Lower Allegheny (05010009)+*, West Fork (05020002)+, Cheat (05020004)+*, Lower Monongahela (05020005)+*, Upper Ohio (05030101)+*, Shenango (05030102)+, Mahoning (05030103)+*, Beaver (05030104)+*, Connoquenessing (05030105)+*, Little Muskingum-Middle Island (05030201)+, Upper Ohio-Shade (05030202)*, Little Kanawha (05030203)+, Hocking (05030204)+, Tuscarawas (05040001)+, Mohican (05040002)+, Walhonding (05040003)+, Muskingum (05040004)*, Elk (05050007)+, Upper Scioto (05060001)+, Lower Scioto (05060002)+, Paint (05060003)*, Upper Great Miami (05080001)*, Ohio Brush-Whiteoak (05090201)+, Little Miami (05090202)+, Middle Ohio-Laughery (05090203)+, Licking (05100101)+*, South Fork Licking (05100102)+*, Lower Kentucky (05100205)+*, Upper Green (05110001)+, Barren (05110002)+*, Rough (05110004)+, Upper Wabash (05120101)+, Salamonie (05120102)+, Mississinewa (05120103)+, 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)+, Upper White (05120201)+, Lower White (05120202)+, Eel (05120203)+*, Driftwood (05120204)+, Flatrock-Haw (05120205)+, Upper East Fork White (05120206)+, Lower East Fork White (05120208)+, Patoka (05120209)+*, South Fork Cumberland (05130104)+*, Caney (05130108)+*, Lower Cumberland (05130205)+*, Silver-Little Kentucky (05140101)+*, Salt (05140102)+*, Rolling Fork (05140103)+*, Blue-Sinking (05140104)+, Lower Ohio-Bay (05140203)+*
06 Pickwick Lake (06030005)+*, Lower Tennessee-Beech (06040001)+*, Lower Duck (06040003)+*, Lower Tennessee (06040006)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A small (up to 2 inches), thick, freshwater mussel with a tan colored shell with green rays.
General Description: SHELL: To 90 mm, small stream specimens considerably smaller. Elongate, triangular, distinctly wedge-shaped, the umbos placed anteriorly. No observable sexual dimorphism in shell. The majority of specimens have the umbos placed just posterior to the anterior margin; occasional examples have the umbo projecting past this margin. Individuals become increasingly more elongate with the umbos placed progressively forward with age. Anterior portion inflated, posterior portion compressed and tapering to an acute posterior margin. Shell sculptureless except for growth lines and a weak posterior ridge. Sulcus present on juvenile shell but may not persist into adult stages. Shell thickened anteriorly, posterior margin thin and fragile, even in large specimens. The beaks are sculptured with two to three microscopic, undulating ridges set obliquely to the umbo. Periostracum yellow in juveniles, becoming darker with age, with growth annuli dark and pronounced. Very old individuals may be nearly black. Shells patterned with dark green rays, particularly in juveniles. The typical pattern is of many fine rays anteriorly and one or more broad rays over the region of the sulcus. All rays are interrupted by the growth annuli creating a checkerboard pattern in many examples. Hinge plate moderately thick, the umbonal cavity shallow and wide. Left valve with two pseudolateral and pseudocardinal teeth each; right valve with one each. Teeth coarsely serrate. Nacre white, iridescent posteriorly, occasionally with a golden tinge to the teeth. Anterior adductor scar deeply set near anterior margin; posterior adductor scar at posterior end of hinge plate. Retractor muscle scars prominent.

ANIMAL: White to pale orange (unpreserved). The inner gill is somewhat larger than the outer in the male and nongravid female. In gravid females the outer is used as the brood pouch (Pennack, 1978) erroneously states that the inner gill is the brood pouch). The water tubes and placentae are lanceolate and the eggs pale in color. Incurrent opening coarsely papillose, excurrent finely papillose.

The shell has been illustrated by Call (1900, plate 62), Clench (1959) as PLEUROBEMA MYTILOIDES (figure 43.72), and by Parmalee (1967, plate 30A), Burch (1975, figure 62), and Stansbery (1976).

Diagnostic Characteristics: Despite shell variation there should be no difficulty in identifying this species. Superficially similar species such as P. DECISUM and P. CHATTANOOGAENSE are more southern in distribution. The fragile posterior portion of the shell is usually broken away in all but the freshest specimens, but the small size and anteriorly placed umbos are usually sufficient for identification.
Reproduction Comments: Virtually nothing is known specifically for Pleurobema clava. Ortmann (1919) reported that it bred from mid-May to late July.

Based upon counts of annular growth lines, Pleurobema clava may reach 30+ years of age. It is not known at what ages reproductive maturity begins and ends. Because of the rarity of live material, it is not known if existing populations are reproductively active. Because of their small size, it is not known if juveniles are present in any of the populations. It must be emphasized that existing populations may be large, healthy, and reproductively active and still be in imminent danger of extinction if the host fish is not present in the range. Laboratory studies by Watters and O'Dee (1997)and O'Dee and Watters (2000) identified the striped shiner (Luxilus chrysocephalus), blackside darter (Percina maculata), central stoneroller (Campostoma anomalum) and logperch (Perca caprodes) as potential fish hosts.

Ecology Comments: Virtually nothing is known specifically for P. CLAVA. Refer to the General Freshwater Mussel ESA for more information on the general biology-ecology of mussels.
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): BIG RIVER, CREEK, MEDIUM RIVER, Riffle
Special Habitat Factors: Benthic
Habitat Comments: Despite the type locality of Lake Erie (apparently in error), this is a species of small to medium-sized rivers and streams. Ortmann (1919) remarked that it was "a rare shell, and never found in great numbers. It is found mostly in sand and fine gravel, and is deeply buried." Hoggarth (pers. comm.) and Watters (unpublished) have found live individuals completely buried with the posterior shell margin facing up in sand/gravel substrate in riffle/run situations in less than 1.5 feet of water. This seems to be the habitat of choice. Because it buries itself beneath the substrate, it is rarely found alive even in places where it is believed to occur in some numbers. Although now considered a creek or small river species, many records from larger rivers such as the Wabash and Tennessee show that this is a recent misconception. This species is generally found in clean, coarse sand and gravel in runs, often just downstream of a riffle, and cannot tolerate mud or slackwater conditions (USFWS, 1994).
Length: 9 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: This subspecies was listed as federally endangered in the U.S. in 1993 and a recovery plan created (USFWS, 1994).
Restoration Potential: The original range includes waterfront on such cities as Indianapolis, Toledo, Cincinnati, Columbus, Charleston, and Pittsburg. It is doubtful that the range of P. CLAVA can ever be recovered based upon the present water quality of the rivers serving these cities. At this time the reasons for the extirpation of P. CLAVA from most of its range are unknown; this reduces any conservation plans to save it to mere guesswork.
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: 12May2009
NatureServe Conservation Status Factors Author: Cordeiro, J. (2009); Watters, T. G.; Morrison, M. (1998)
Management Information Edition Date: 01Aug1986
Management Information Edition Author: Watters, Thomas G.
Element Ecology & Life History Edition Date: 06Dec2006
Element Ecology & Life History Author(s): Cordeiro, J. (2006); 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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