Epioblasma torulosa rangiana - (I. Lea, 1838)
Northern Riffleshell
Synonym(s): Dysnomia torulosa rangiana (I. Lea, 1838)
Taxonomic Status: Accepted
Related ITIS Name(s): Epioblasma torulosa rangiana (I. Lea, 1838) (TSN 80343)
French Common Names: Úpioblasme ventrue
Unique Identifier: ELEMENT_GLOBAL.2.118738
Element Code: IMBIV16184
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Epioblasma
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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: Epioblasma torulosa rangiana
Taxonomic Comments: Epioblasma is comprised of several recognized forms (torulosa, gubernaculum, rangiana, and cincinnatiensis), but it is not clear whether these forms represent ecophenotypic variation, true subspecies, or a species complex. The entire species group exhibits considerable ecophenotypic variation. Epioblasma was formerly placed in the genera Unio, Truncilla, and Dysnomia. It is not clear if Epioblasma rangiana is genetically distinct from Epioblasma torulosa at the species level, or at the subspecies level. Cummings and Berlocher (1990) provide good evidence for separation at the species level, but there is still the possibility that it is the headwaters form of torulosa in the Cumberland River system. Other common nams include: white-mouth riffleshell. Similar species include the tubercled blossom, Epioblasma torulosa. Bogan (1997) established the identity of Epioblasma biloba as the rangiana form of E. torulosa and although biloba Rafinesque, 1831, has priority over rangiana Lea, 1838, rangiana is retained as the subspecies name (Williams et al., 2008). Zanatta and Murphy (2007) found mt DNA sequence data did not indicate significant geographic structure among populations rangewide, but allelic data from microsatellite loci revealed highly significant population structuring such that individuals of E. torulosa rangiana can be assigned to their own river of origin with 98.6% accuracy.
Conservation Status
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NatureServe Status

Global Status: G2T2
Global Status Last Reviewed: 07Nov2007
Global Status Last Changed: 30Jan1998
Rounded Global Status: T2 - Imperiled
Reasons: Historically occurred throughout much of the Ohio River watershed but range has been dramatically reduced to eight to ten populations scattered over four states and one province with only three that are considered viable.
Nation: United States
National Status: N2 (22Jul2003)
Nation: Canada
National Status: N1 (24Sep2014)

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 Illinois (SNR), Indiana (S1), Kentucky (S1), Michigan (S1), Ohio (S1), Pennsylvania (S2), West Virginia (S1)
Canada Ontario (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE: Listed endangered (22Jan1993)
U.S. Fish & Wildlife Service Lead Region: R5 - Northeast
Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: E (05Jun2003)
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Endangered (25Apr2010)
Comments on COSEWIC: Reason for designation: This small freshwater mussel is restricted to two rivers in southern Ontario. Since the original COSEWIC assessment (2000), a small, possibly reproducing population was discovered in the Ausable River although only 16 live individuals, including one juvenile, have been found over the last 10 years. Recruitment is occurring at several sites along the Sydenham River and the population appears to be stable, but the perceived recovery could be due to increased sampling effort over the past 12 years. The main limiting factor is the availability of shallow, silt-free riffle habitat. Both riverine populations are in areas of intense agriculture and urban and industrial development, subject to siltation and pollution. Only four populations in the world, including the two in Canada, show signs of recruitment.

Status history: Designated Endangered in April 1999. Status re-examined and confirmed in May 2000 and April 2010.

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: 250-5000 square km (about 100-2000 square miles)
Range Extent Comments: This entity replaces Epioblasma torulosa torulosa in the headwaters of the Ohio River drainage; its counterpart in the headwaters of the Tennessee River System is Epioblasma torulosa gubernaculum. As with most naiads, its present range is a remnant of its former distribution. Historically, this entity was recorded from the mainstem of the Ohio River (Stansbery and Cooney, 1985) but has apparently been extirpated from there. The Ohio State University Museum of Zoology has records for the White and Wabash Rivers in Indiana but it has not been collected there in recent times (Clark, 1976; Cummings et al., 1991). Taylor and Hughart (1981) presumed that it was no longer present in the Elk River of West Virginia. Currently extant in only seven streams; the Green River in Kentucky, French and LeBoeuf Creeks and the Allegheny River in Pennsylvania, the Detroit River in Michigan (possibly extirpated- see below), and Big Darby Creek in Ohio (USFWS, 1993), and recently discovered in at least one additional river in Ontario (Metcalfe-Smith et al., 1998). Staton et al. (2000) lists historical and present distribution. Recently found in Conewanto Creek near Warren, Warren Co., Pennsylvania, where it was previously thought to be extirpated (Evans and Smith, 2005). In Illinois, it formerly occupied the Vermilion, Wabash, and Ohio Rivers but is now extirpated in the state (Cummings and Mayer, 1997). Recently this species has been confirmed to be likely extirpated from the main channel of the Detroit River between Lake St. Clair and Lake Erie, Michigan/Ontario; due to zebra mussel invasion (Schloesser et al., 2006).

Area of Occupancy: Unknown 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 6 - 20
Number of Occurrences Comments: Epioblasma torulosa rangiana, the only remaining extant subspecies, was formerly widespread in the Ohio River basin (including Ohio River system in Ohio River at Cincinnati, Little Miami, Scioto and tribs., Muskingham, Auglaize, Sandusy, and Olentangy Rivers, and Big Darby Creek- a tributary of the Scioto; Beaver River in Ohio and Pennsylvania; Lake Erie drainage in Fish Creek, and Kanawha River, West Virginia; Wabash River and tributaries-Tippecanoe River and the Eel, Blue, and White Rivers) (Parmalee and Bogan, 1998) as well as having been collected historically from the Allegheny River drainage in Pennsylvania above Pittsburgh and from the West Fork River (Ortmann, 1913), a tributary of the Monongahela River, Harrison Co., West Virginia (Parmalee and Bogan, 1998; USFWS, 1994). This subspecies now exists in eight to ten isolated populations, most of which are small and peripheral and with little signs of reproduction. It is known from the Kentucky, Licking, and Green River drainages in Kentucky (Johnson, 1978), but is likely only still extant in the Upper Green. In the Maumee River drainage, it was last seen in Fish Creek (St. Joseph drainage) in Ohio and Indiana and Big Darby Creek in Ohio (Watters et al., 2009), where live individuals were very rare (Watters, 1995; Grabarkiewicz and Crail, 2006). Recently found in Conewango Creek near Warren, Warren Co., Pennsylvania, where it was previously thought to be extirpated (Evans and Smith, 2005). It also occurs in the Allegheny River, Pennsylvania (Jones, 2004). Epioblasma torulosa rangiana occurs in Muddy Creek (French Creek drainage) in the Erie NWR in Crawford Co., Pennsylvania (Mohler et al., 2006) and elsewhere in the French Creek drainage. Weathered shells are reported from the Tippecanoe River (shell only- Cummings and Berlocher, 1990), Sugar Creek (east fork White River drainage) in central Indiana (Harmon, 1992) as well as throughout most central Indiana drainages but no living specimens are known recently (USFWS, 1994) and Fisher (2006) lists it as extirpated from the Wabash drainage. As such, it is likely extirpated from the rest of Indiana (IN NHP, pers. comm., 2009) with the last remaining population in the Tippecanoe drainage (USFWS, 1994). Specimens from the Black River (St. Clair drainage), Michigan, were relocated to the Detroit River in 1992 (Trdan and Hoeh, 1993). It is historically known from the Clinton River drainage in Michigan (Strayer, 1980). In Canada, it historically occurred in the Cedar River and currently occurs in the Sydenham River in the Northern Lake Erie drainage (Metcalfe-Smith et al., 2003) and also the Ausable River in the Eastern Lake Huron drainage (Staton et al., 2000).

Population Size: 1000 - 10,000 individuals
Population Size Comments: Smith and Crabtree (2010) found this species at 7 of 32 sites (7 with recruitment) along the entire length of Pennsylvania's French Creek. Densities in French Creek, Pennsylvania, ranged from 0.009-6.668 per sq. m (Crabtree and Smith, 2009).

Number of Occurrences with Good Viability/Integrity: Few (4-12)
Viability/Integrity Comments: The only populations with evidence of recruitment are two in Pennsylvania and the Sydenham River population in Ontario (Staton et al., 2000). Epioblasma torulosa rangiana occurs and is viable in Muddy Creek (French Creek drainage) in the Erie NWR in Crawford Co., Pennsylvania (Mohler et al., 2006). Four (of 12) sites in French Creek, Pennsylvania, show evidence of sustained recruitment (Crabtree and Smith, 2009).

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: Members of the genus Epioblasma seem to be particularly sensitive to impoundment; most species are riffle/run inhabitants and cannot tolerate other habitats. Impoundment of the Clinch River in Tennessee by the Norris Reservoir has resulted in the extirpation of the majority of species below the dam (Ahlstedt, 1984). The construction of the Wilson Dam on the Tennessee River has eliminated 20 of the original 22 Cumberlandian naiad species (Stansbery, 1971). Smith (1971) ranked the causes of extirpation or declines in fish species as follows: siltation, drainage of bottomland lakes, swamps, and prairie marshes, desiccation during drought, species introductions, pollution, impoundments, and increased water temperatures. All of these factors render habitats unsuitable, cause extirpations, and lead to the isolation of populations thereby increasing their vulnerability to extirpation for many aquatic species (including mussels) throughout North America. Zebra mussels Dreissena polymorpha have destroyed mussel populations in the Great Lakes and significantly reduced mussels in many of the large rivers of the eastern North America and has the potential to severely threaten and other populations especially if it makes its way into smaller streams. Pollution through point (industrial and residential discharge) and non-point (siltation, herbicide and fertilizer run-off) sources is perhaps the greatest on-going threat to this species and most freshwater mussels. Lowered dissolved oxygen content and elevated ammonia levels (frequently associated with agricultural runoff and sewage discharge) have been shown to be lethal to some species of freshwater naiads (Horne and McIntosh, 1979). Residential, mineral and industrial development also pose a significant threat. Destruction of habitat through stream channelization and maintenance and the construction of dams although slowed in recent years is still a threat in some areas. Impoundments reduce currents that are necessary for the most basic physiological activities such as feeding, waste removal and reproduction. In addition, reduced water flow typically results in a reduction in water oxygen levels and a settling out of suspended solids (silt, etc.), both of which are detrimental. Dredging of streams has an immediate effect on existing populations by physically removing and destroying individuals. Dredging also affects the long-term recolonization abilities by destroying much of the potential habitat, making the substrates and flow rates uniform throughout the system. Rotenone, a toxin used to kill fish in bodies of water for increased sport fishery quality, has been shown to be lethal to mussels as well (Heard, 1970). Natural predators include raccoons, otter, mink, muskrats, turtles and some birds, which feed heavily upon freshwater mussels (Simpson, 1899; Boepple and Coker, 1912; Evermann and Clark, 1918; Coker, et al. 1921; Parmalee, 1967; Snyder and Snyder, 1969). Domestic animals such as hogs can root mussel beds to pieces (Meek and Clark, 1912). Fishes, particularly catfish, Ictalurus spp. and Amierus spp.. and freshwater drum, Aplodinotus grunniens also consume large numbers of unionids. USFWS (1994) lists the following reasons for decline: siltation (from agriculture, construction, and forestry runoff), impoundment (including dam construction 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 subspecies Epioblasma torulosa rangiana (the only extant subspecies) has experienced greater than a 95% range reduction (USFWS, 1993; 1994; Staton et al., 2000). The other two subspecies, Epioblasma torulosa gubernaculum and Epioblasma torulosa torulosa have declined to extinction (USFWS, 1984; 1984; 1993; 1994). The northern riffleshell was listed as a federally endangered species in February of 1993. It was also considered to be Endangered by the freshwater mussel subcommittee of the endangered species committee of the American Fisheries Society (Williams et al., 1993). In the Midwest, the northern riffleshell was widely distributed and relatively common in some of the headwater streams in the Wabash and Ohio river drainages. Endangered in Michigan, and Ohio. Extirpated from Illinois and Indiana. See Staton et al. (2000) for trend information. In Illinois, it formerly occupied the Vermilion, Wabash, and Ohio Rivers but is now extirpated in the state (Cummings and Mayer, 1997). It historically occurred in the Ohio River in several places including the Smithland dam pool in Illinois, Meldahl dam pool in Ohio/Kentucky, and as far as the Upper Ohio just into Pennsylvania (Watters and Flaute, 2010).

Long-term Trend: Decline of >90%

Intrinsic Vulnerability: Highly vulnerable
Intrinsic Vulnerability Comments: Due to slow growth and relative immobility, establishment of sustainable, viable populations requires decades of immigration and recruitment, even where suitable habitat exists (Neves, 1993). Mussel recruitment is typically low and sporadic, with population stability and viability maintained by numerous slow-growing cohorts and occasional good year classes (Neves and Widlak, 1987).

Environmental Specificity: Very narrow. Specialist or community with key requirements scarce.
Environmental Specificity Comments: The decline in the overall range of this species suggests that it is not tolerant of poor water quality. Individuals are sensitive to pollution, siltation, habitat perturbation, inundation, and loss of glochidial hosts.

Other NatureServe Conservation Status Information

Inventory Needs: Historical records exist from the Mahoning and Little Mahoning rivers in Ohio and Pennsylvania and may still harbor populations and should be investigated. Additional work needs to be done on the Tippecanoe River in Indiana, the Elk River in West Virginia, and the Green River in Kentucky where fresh-dead shells have been found in recent years (Watters, 1994). An inventory of existing museum records should be compiled to provide information on historical sites and potential new ones.

Distribution
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Global Range: (250-5000 square km (about 100-2000 square miles)) This entity replaces Epioblasma torulosa torulosa in the headwaters of the Ohio River drainage; its counterpart in the headwaters of the Tennessee River System is Epioblasma torulosa gubernaculum. As with most naiads, its present range is a remnant of its former distribution. Historically, this entity was recorded from the mainstem of the Ohio River (Stansbery and Cooney, 1985) but has apparently been extirpated from there. The Ohio State University Museum of Zoology has records for the White and Wabash Rivers in Indiana but it has not been collected there in recent times (Clark, 1976; Cummings et al., 1991). Taylor and Hughart (1981) presumed that it was no longer present in the Elk River of West Virginia. Currently extant in only seven streams; the Green River in Kentucky, French and LeBoeuf Creeks and the Allegheny River in Pennsylvania, the Detroit River in Michigan (possibly extirpated- see below), and Big Darby Creek in Ohio (USFWS, 1993), and recently discovered in at least one additional river in Ontario (Metcalfe-Smith et al., 1998). Staton et al. (2000) lists historical and present distribution. Recently found in Conewanto Creek near Warren, Warren Co., Pennsylvania, where it was previously thought to be extirpated (Evans and Smith, 2005). In Illinois, it formerly occupied the Vermilion, Wabash, and Ohio Rivers but is now extirpated in the state (Cummings and Mayer, 1997). Recently this species has been confirmed to be likely extirpated from the main channel of the Detroit River between Lake St. Clair and Lake Erie, Michigan/Ontario; due to zebra mussel invasion (Schloesser et al., 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: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States IL, IN, KY, MI, OH, PA, WV
Canada ON

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
IL Champaign (17019), Vermilion (17183)
IN Allen (18003)*, Bartholomew (18005)*, Carroll (18015)*, Cass (18017)*, De Kalb (18033), Delaware (18035), Fulton (18049), Grant (18053), Greene (18055)*, Hamilton (18057)*, Howard (18067)*, Huntington (18069)*, Johnson (18081), Knox (18083)*, Kosciusko (18085), Madison (18095)*, Marion (18097)*, Marshall (18099), Martin (18101), Miami (18103), Morgan (18109), Pulaski (18131), Putnam (18133)*, Randolph (18135), Shelby (18145), Tippecanoe (18157), Vigo (18167)*, Wabash (18169), Wells (18179)*, White (18181)
KY Bath (21011)*, Boone (21015)*, Campbell (21037)*, Edmonson (21061), Franklin (21073)*, Grayson (21085)*, Green (21087)*, Hardin (21093)*, Hart (21099), Kenton (21117)*, Larue (21123)*, Mercer (21167)*, Nelson (21179)*, Pendleton (21191)*, Rowan (21205)*, Spencer (21215)*, Taylor (21217)*, Warren (21227), Woodford (21239)*
MI Bay (26017)*, Lenawee (26091)*, Monroe (26115)*, Oakland (26125)*, Sanilac (26151), Wayne (26163)
OH Defiance (39039)*, Franklin (39049), Knox (39083)*, Madison (39097), Ottawa (39123)*, Pickaway (39129), Williams (39171), Wyandot (39175)*
PA Armstrong (42005), Clarion (42031), Crawford (42039), Erie (42049), Forest (42053), Lawrence (42073)*, Mercer (42085), Venango (42121), Warren (42123)
WV Fayette (54019)*, Kanawha (54039)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
04 Saginaw (04080206)+*, St. Clair (04090001)+, Lake St. Clair (04090002)+, Clinton (04090003)+*, Detroit (04090004)+, Huron (04090005)+*, Raisin (04100002)+*, St. Joseph (04100003)+, Upper Maumee (04100005)+*, Tiffin (04100006)+*, Cedar-Portage (04100010)+*, Sandusky (04100011)+*
05 Upper Allegheny (05010001)+, Conewango (05010002)+, Middle Allegheny-Tionesta (05010003)+, French (05010004)+, Middle Allegheny-Redbank (05010006)+, Shenango (05030102)+*, Walhonding (05040003)+*, Upper Kanawha (05050006)+*, Elk (05050007)+, Upper Scioto (05060001)+, Lower Scioto (05060002)+*, Ohio Brush-Whiteoak (05090201)+*, Middle Ohio-Laughery (05090203)+*, Licking (05100101)+*, Lower Kentucky (05100205)+*, Upper Green (05110001)+, Barren (05110002)+, Upper Wabash (05120101)+*, Salamonie (05120102)+*, Mississinewa (05120103)+, Eel (05120104)+, Middle Wabash-Deer (05120105)+, Tippecanoe (05120106)+, Wildcat (05120107)+, Vermilion (05120109)+, Middle Wabash-Busseron (05120111)+*, Upper White (05120201)+, Lower White (05120202)+*, Eel (05120203)+*, Driftwood (05120204)+, Flatrock-Haw (05120205)+*, Lower East Fork White (05120208)+, Salt (05140102)+*, Rolling Fork (05140103)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: A freshwater mussel with males and females yellowish brown or green but much different in shape. Males oblong with a sulcus running along the posterior ridge from the umbo to the ventral margin. Females with a large expanded posterior end. Both without knobs.
General Description: SHELL: Shell elongate, thick anteriorly, much thinner posteriorly, and compressed. Anterior margin rounded, posterior-ventral margin broadly rounded in females, indented in males. Umbos low, somewhat turned forward. Tubercles or knobs on the lateral surface absent. A wide, shallow sulcus or depression present between the posterior and medial ridges. Periostracum yellowish brown with numerous fine green rays, obscure in older shells. Adult size to 2 inches. Pseudocardinal teeth triangular, divergent, and roughened; two in the left valve, one in the right, with two smaller teeth on either side. Lateral teeth moderately long, straight, and roughened; two in the left valve, one in the right with a much smaller tooth below. Beak cavity moderate to shallow. Nacre white, iridescent posteriorly (Cummings and Mayer, 1992).

ANIMAL: Unknown.

Reproduction Comments: Ortmann (1912: 358) reported Epioblasma torulosa rangiana to be gravid in September and Clarke (1981: 352) said it was a "longterm breeder, gravid from late summer to following spring". The female uses the posterior portion of the outer gill as marsupia. It is widely believed that the "brood pouch" swellings of the female shell are caused by the expanded gravid gills, but Stansbery (pers. comm.) and Hoggarth (pers. comm.) do not believe this to be the case.

Watters (1996) reports the following fish as suitable glochidial hosts: the mottled sculpin (Cottus bairdi), banded darter (Etheostoma zonale), bluebreast darter (Etheostoma camurum), and brown trout (Salmo trutta).

Based upon counts of annular growth lines, this species may reach 15+ years of age. It is not known at what ages reproductive maturity begins and ends. Because of the rarity of live material (and their enforced protection), 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.

Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): CREEK, High gradient, MEDIUM RIVER, Riffle
Special Habitat Factors: Benthic
Habitat Comments: Ortmann (1919: 334) reported that this species was "always found...on riffles, on a bottom of firmly packed and rather fine gravel, in swiftly flowing, shallow water or coarse gravel" and Clarke (1981: 362) gave its habitat as "highly oxygenated riffle". Preferred habitat appears to require swiftly moving water. The high oxygen concentrations in swift streams may be necessary for survival. It is a species of riffle areas of smaller streams, and as such has fared better than larger river species, which have been heavily impacted by dredging and impoundment. Of the eleven or so species of naiads thought to be extinct in 1971 by Stansbery, most were from this latter type of habitat and all were species of Epioblasma.
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: Although extirpated from much of its original range, several apparently healthy populations still exist. These populations should be carefully monitored to ensure that the existing condition of the habitat does not deteriorate.
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.
Biological Research Needs: In order to effectively manage mussel species it is necessary to work out certain life history characteristics first. Because of their unusual life-cycle and dependence on fish for completion of that cycle, it is imperative that the host species for the northern riffleshell be ascertained. Work needs to be done to identify age and size at sexual maturity, recruitment success, age class structure, and other important life history parameters.

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

Population/Occurrence Delineation
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Group Name: Freshwater Mussels

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

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

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

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

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

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 25Jul2007
NatureServe Conservation Status Factors Author: Cordeiro, J. (2007); Bier, C.; Watters, T. G; Cummings, K.S. (1998)
Management Information Edition Date: 01Aug1986
Management Information Edition Author: Watters, G. Thomas
Element Ecology & Life History Edition Date: 31Jan1991
Element Ecology & Life History Author(s): WATTERS, T. G.

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

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