Quadrula fragosa - (Conrad, 1835)
Winged Mapleleaf
Other English Common Names: Rough Maple Leaf Pearlymussel
Taxonomic Status: Accepted
Related ITIS Name(s): Quadrula fragosa (Conrad, 1835) (TSN 80075)
Unique Identifier: ELEMENT_GLOBAL.2.111959
Element Code: IMBIV39050
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Quadrula
Genus Size: D - Medium to large genus (21+ 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: Quadrula fragosa
Taxonomic Comments: This species was recognized as valid, although apparently often confused with Quadrula quadrula, until Neel (1941) synonymized it and several other species under Quadrula quadrula. Neel's (1941) "Q. quadrula" is a composite species representing a complex of closely related species rather than one highly polymorphic entity.
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 06Nov2006
Global Status Last Changed: 26May1998
Rounded Global Status: G1 - Critically Imperiled
Reasons: This species was once extremely widespread and now is limited to just 3 or 4 occurrences all of which are disjunct and the species is imminently threatened with extinction. The excessive loss of occurrences due to habitat alteration threatens this species with extinction. Due to the mistaken synonomy of it under Quadrula quadrula by Neel (1941) and its relative rarity compared to the latter species, the declines in its populations were not recognized until recently. It apparently persists in a short section of the lower St. Croix River along the Minnesota/Wisconsin border and the Kiamichi River in Oklahoma.
Nation: United States
National Status: N1 (26May1998)

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

Other Statuses

U.S. Endangered Species Act (USESA): LE, XN: Listed endangered, nonessential experimental population (20Jun1991)
U.S. Fish & Wildlife Service Lead Region: R3 - North Central
IUCN Red List Category: CR - Critically endangered
American Fisheries Society Status: Endangered (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 100-250 square km (about 40-100 square miles)
Range Extent Comments: Because of misidentifications, published records cannot be relied upon to accurately reflect the historic distribution of this species. Museum records indicate that it was distributed throughout a considerable portion of the Interior Basin: Ohio and Sciota rivers (Ohio), Wabash and White rivers (Indiana), Sangamon River (Illinois), Tennessee and Duck rivers (Tennessee), St. Croix and Wisconsin rivers (Wisconsin), Cedar, Iowa, Mississippi, and Racoon rivers (Iowa), Little Fox River (Missouri), and Fall and Neosho rivers (Kansas). Records from the Kiamichi River, Oklahoma, were previously considered uncertain (USFWS, 1997) but recently Hove et al. (2003) confirmed its presence there. All museum vouchers from the Cumberland River (including those of Wilson and Clarck, 1914) are misidentified Quadrula quadrula. Records reported from Alabama (e.g. Ortmann, 1925) are misidentifications of Quadrula quadrula (Williams et al., 2008). There is also a specimen labeled only as "Louisiana", but the identity of the shell and the locality are questionable; Vidrine (1993) lists Quadrula quadrula from Louisiana but includes Quadrula fragosa as a synonym. A single specimen tentatively identified as Q. fragosa recently has been collected from the Ohio River adjacent to Kentucky (Cicerello, Kentucky Nature Preserves Commision, personal communication), but the condition of the shell and any possible population is not known. Hove et al. (2003) have determined that the historical range of this species is greater than once thought; with a historic range of at least 50 linear km in the St. Croix River mostly downstream of the St. Croix Dam (the present range is much less). The only known viable populations are from one section of the lower St. Croix River in Wisconsin/Minnesota and the Ouachita River in Arkansas. Hove et al. (2003) also note the Kiamachi River in Oklahoma.

Area of Occupancy: 3-125 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 1 - 5
Number of Occurrences Comments: Extant occurrences are only known from one ten mile section of the lower St. Croix River between Minnesota and Wisconsin (Sietman, 2003; USFWS, 1997) and the Ouachita River in Arkansas upstream of Camden in Ouachita Co. as well as the Little Missouri River near its confluence with Ouachita (Harris et al., 1997), and likely one small population in Oklahoma in the Kiamichi River (Hove et al., 2003). Recently specimens were found at four adjoining sites on the Little River, Oklahoma (Galbraith et al., 2008). Specimens have also been reported from a single site in Franklin Co., Missouri (MO NHP, pers. comm., 2006). Subfossil shells were recently reported from the Upper St. Croix River by Hove et al. (2000; 2002). In the Little Blue River basin it is known from subfossil shells only in the Kansas portion (Hoke, 2004). A thorough review of literature, museum specimens, and recent survey work in the Big Blue River system of southeastern Nebraska and northeastern Kansas revealed this species was represented by sub-fossil material only at a single site in Big Sandy Creek in Kansas and is likely extirpated from the basin (Hoke, 2005). A relic valve was collected from the Harpeth River in Davidson Co., Tennessee in 1988 (Parmalee and Bogan, 1998) but it is likely extirpated from that state.

Population Size: 50 - 1000 individuals
Population Size Comments: Surveys by the Wisconsin Deptartment of Natural Resources in 1997 observed evidence of successful reproduction from the one extant occurrence, which was formerly thought to have been extirpated though it was known since the early 1900s. Individuals observed at this site ranged from 49 specimens in 1988 and 1989 (Minnesota) to 10 specimens (+ 24 dead shells) in 1990-1991 (Wisconsin), 1 in 1991, and 26 from 1992-1995 (USFWS, 1997). Population size of the Oklahoma population is not known though it is considered not very viable (Hove et al, 2003). Recent population on the Little River in Oklahoma had densities of 0.13 to 0.53 per square meter (Galbraith et al., 2008). Fewer than 10 recent specimens are known from Arkansas (Harris et al., 1997). Viability of a recent occurrence in Missouri is not known.

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: Only one reproducing population ramains along a 10 km stretch of the St. Croix River, Minnesota (Hove et al., 2002), which is probably the largest remaining population globally (Sietman, 2003). Other remaining populations, such as those in Arkansas (Harris et al., 1997), and Missouri if any, are not viable, except perhaps recent specimens in Oklahoma (Hove et al., 2003). Recent population on the Little River in Oklahoma had densities of 0.13 to 0.53 per square meter (Galbraith et al., 2008). The Wisconsin population of the St. Croix River may also be viable.

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: Chemical and organic pollution, alteration and inundation of river channels and siltation have, and continue to have, a severe negative impact on this species. Commercial harvest of shells may also be a threat. A single catastrophic event could possibly cause the extinction of this species. Six of 12 municipal and industrial facilities with wastewater discharge permits into the Croix River are within the reach containing Quadrula fragosa. Stream flow in the relevant stretch of the St. Croix River is influenced, in part, by a hydroelectric dam at St. Croix Falls, Wisconsin. The availability of suitabile habitat is a major concern for the continued existence of this species. The species is vulnerable to stochastic events and, as a result of its small, fragmented distribution, has difficulty with recruitment. Changes in land use practices in the watershed are anticipated because the watershed is close to a major and growing metropolitan area. Recreational use in the area is heavy and potentially damaging (USFWS, 1997).

Short-term Trend: Decline of >70%
Short-term Trend Comments: Extant occurrences have declined to a critical level. The species is so rare that it had not been generally recognized as a valid species for approximately 50 years. Though formerly known from 6 drainages in Illinois, it has not been found alive in that state in over 50 years and is state extirpated (Cummings and Mayer, 1997). Oklahoma is reduced to a single population in the Kiamichi River (Hove et al., 2003). It was last seen in Ohio in Raccoon Creek and previously the Scioto River but is likely extirpated from the state (Watters, 1995), A relic valve was collected from the Harpeth River in Davidson Co., Tennessee in 1988 (Parmalee and Bogan, 1998) but it is likely extirpated from that state.

Long-term Trend: Decline of >90%
Long-term Trend Comments: This species was formerly very widespread occurring in the Mississippi, Tennessee, Cumberland, and Ohio River basins. Although formerly distributed in the Duck and Harpeth Rivers in Tennessee prior to 1960, and from the Cumberland and lower Tennessee Rivers, this species is likely extirpated from Tennessee today (Parmalee and Bogan, 1998). Literature records and recently collected weathered shells indicae this species once lived in Kansas in Soldier Creek, the Big Blue and Little Blue Rivers (Kansas River drainage), Walnut (Whitewater) River (Arkansas River drainage), Fall and Verdigris Rivers (Verdigris River drainage), and Neosho River (Couch, 1997; Hoke, 2005). Well over 50 years ago, it occurred in Illinois in the Spoon, Sangamon, Kaskaskia, Mississippi, Ohio, and Wabash drainages but is now extirpated from the state (Cummings and Mayer, 1997). This species is nearly extirpated from its entire historic range (including Alabama, Iowa, Illinois, Indiana, likely Kentucky, Nebraska, Ohio, Tennessee) except a few remnant populations (USFWS, 1997). Total historic distribution (most extirpated) includes much of the Mississippi River from Missouri to Wisconsin; the Red, Kiamichi, Boggy, and Little Rivers in Oklahoma; the Whitewater, Verdigris, fall, and Neosho Rivers in Kansas, the Ohio River in Ohio and Indiana; the Licking River in Kentucky; the Tennessee, Duck, Cumberland, and Harpeth Rivers in Tennessee; the Wabash and White Rivers in Indiana; the Scioto River at Columbus and Cincinnati and Raccoon Creek in Ohio (Watters et al., 2009), the Kaskaskia, Illinois, Spoon, and Sangamon Rivers in Illinois, Soldier Creek in Kansas and the Blue River and Bow Creek in Nebraska; the Des Moines, Raccoon, Iowa, and Cedar Rivers in Iowa; and the Wisconsin, Baraboo, and St. Croix Rivers in Wisconsin (USFWS, 1997). Perkins and Backlund (2003) cite relict shells from the James River and Skadsen and Perkins (2000) documented relict shells in the Big Sioux River in South Dakota.

Intrinsic Vulnerability: Highly vulnerable
Intrinsic Vulnerability Comments: The species is vulnerable to stochastic events and, as a result of its small, fragmented distribution, has difficulty with recruitment (USFWS, 1997).

Environmental Specificity: Narrow. Specialist or community with key requirements common.
Environmental Specificity Comments: The remnant population in the St. Croix River is found in riffles with clean gravel, sand, or rubble substrates and in clear water of high water quality but this may not reflect ideal habitat (USFWS, 1997).

Other NatureServe Conservation Status Information

Inventory Needs: Determine extent of existing populations and continue surveys for additional EOs, particularly outside the St. Croix system.

Protection Needs: All populations should receive protection through acquisition, easement, registry, and working with local, state, and federal government agencies on issues relating to development, water quality, river designation, etc. 35 juveniles collected in lab from 20 channel catfish released to downstream most edge of range in St. Croix River, Wisconsin (Hove et al., 2002). As outlined by the recovery plan (1997): (1) preserve the St. Croix population, (2) improve understanding of biology and ecology, (3) increase the St. Croix population; (4) re-establish the population in its historic range; (5) determine reclassification and delisting

Distribution
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Global Range: (100-250 square km (about 40-100 square miles)) Because of misidentifications, published records cannot be relied upon to accurately reflect the historic distribution of this species. Museum records indicate that it was distributed throughout a considerable portion of the Interior Basin: Ohio and Sciota rivers (Ohio), Wabash and White rivers (Indiana), Sangamon River (Illinois), Tennessee and Duck rivers (Tennessee), St. Croix and Wisconsin rivers (Wisconsin), Cedar, Iowa, Mississippi, and Racoon rivers (Iowa), Little Fox River (Missouri), and Fall and Neosho rivers (Kansas). Records from the Kiamichi River, Oklahoma, were previously considered uncertain (USFWS, 1997) but recently Hove et al. (2003) confirmed its presence there. All museum vouchers from the Cumberland River (including those of Wilson and Clarck, 1914) are misidentified Quadrula quadrula. Records reported from Alabama (e.g. Ortmann, 1925) are misidentifications of Quadrula quadrula (Williams et al., 2008). There is also a specimen labeled only as "Louisiana", but the identity of the shell and the locality are questionable; Vidrine (1993) lists Quadrula quadrula from Louisiana but includes Quadrula fragosa as a synonym. A single specimen tentatively identified as Q. fragosa recently has been collected from the Ohio River adjacent to Kentucky (Cicerello, Kentucky Nature Preserves Commision, personal communication), but the condition of the shell and any possible population is not known. Hove et al. (2003) have determined that the historical range of this species is greater than once thought; with a historic range of at least 50 linear km in the St. Croix River mostly downstream of the St. Croix Dam (the present range is much less). The only known viable populations are from one section of the lower St. Croix River in Wisconsin/Minnesota and the Ouachita River in Arkansas. Hove et al. (2003) also note the Kiamachi River in Oklahoma.

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 AR, IAextirpated, ILextirpated, INextirpated, KSextirpated, KYextirpated, MN, MO, OHextirpated, OK, SDextirpated, TN, WI

Range Map
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U.S. Distribution by County Help
State County Name (FIPS Code)
AL Jackson (01071)*
AR Ashley (05003), Bradley (05011), Calhoun (05013), Clark (05019), Cleveland (05025), Ouachita (05103)
KY Campbell (21037)*, Kenton (21117)*, Lyon (21143)*, Oldham (21185)*, Pendleton (21191)*, Trigg (21221)*
MN Blue Earth (27013), Carver (27019), Chisago (27025), Dakota (27037), Goodhue (27049)*, Hennepin (27053), Nicollet (27103), Ramsey (27123)*, Scott (27139), Sibley (27143), Washington (27163)
MO Franklin (29071)
OH Ross (39141)*
OK LeFlore (40079), Pushmataha (40127)
SD Lincoln (46083)*, Union (46127)*, Yankton (46135)*
WI Dunn (55033), Polk (55095), St. Croix (55109)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
05 Lower Scioto (05060002)+*, Raccoon-Symmes (05090101)*, Ohio Brush-Whiteoak (05090201)*, Middle Ohio-Laughery (05090203)+*, Licking (05100101)+*, Middle Wabash-Little Vermilion (05120108)*, Middle Wabash-Busseron (05120111)*, Lower Wabash (05120113)*, Lower White (05120202)*, Harpeth (05130204)*, Lower Cumberland (05130205)+*, Silver-Little Kentucky (05140101)+*, Lower Ohio-Bay (05140203)*, Lower Ohio (05140206)*
06 Guntersville Lake (06030001)+*, Upper Duck (06040002)*
07 Twin Cities (07010206)+*, Hawk-Yellow Medicine (07020004)*, Middle Minnesota (07020007)+, Lower Minnesota (07020012)+, Upper St. Croix (07030001)*, Lower St. Croix (07030005)+, Rush-Vermillion (07040001)+*, Buffalo-Whitewater (07040003)*, La Crosse-Pine (07040006)*, Lower Chippewa (07050005)+, Coon-Yellow (07060001)*, Grant-Little Maquoketa (07060003)*, Apple-Plum (07060005)*, Upper Wisconsin (07070001)*, Lake Dubay (07070002)*, Castle Rock (07070003)*, Baraboo (07070004)*, Lower Wisconsin (07070005)*, Copperas-Duck (07080101)*, Flint-Henderson (07080104)*, Upper Cedar (07080201)*, Middle Cedar (07080205)*, Lower Cedar (07080206)*, Upper Iowa (07080207)*, Middle Iowa (07080208)*, Lower Iowa (07080209)*, Upper Des Moines (07100002)*, Middle Des Moines (07100004)*, South Raccoon (07100007)*, Lower Des Moines (07100009)*, Bear-Wyaconda (07110001)*, The Sny (07110004)*, Peruque-Piasa (07110009)*, Upper Illinois (07120005)*, Lower Illinois-Senachwine Lake (07130001)*, Lower Illinois-Lake Chautauqua (07130003)*, Spoon (07130005)*, Upper Sangamon (07130006)*, South Fork Sangamon (07130007)*, Lower Sangamon (07130008)*, Salt (07130009)*, La Moine (07130010)*, Lower Illinois (07130011)*, Bourbeuse (07140103)+, Upper Kaskaskia (07140201)*, Middle Kaskaskia (07140202)*, Shoal (07140203)*, Lower Kaskaskia (07140204)*
08 Upper Ouachita (08040102)+, Little Missouri (08040103)+, Lower Ouachita-Smackover (08040201)+, Lower Saline (08040204)+
10 Lower James (10160011)+*, Lower Big Sioux (10170203)+*, Middle Kansas (10270102)*, Lower Big Blue (10270205)*, Lower Little Blue (10270207)*, Pomme De Terre (10290107)*, Lower Osage (10290111)*
11 Upper Walnut River (11030017)*, Lower Walnut River (11030018)*, Upper Verdigris (11070101)*, Fall (11070102)*, Upper Neosho (11070204)*, Middle Neosho (11070205)*, Muddy Boggy (11140103)*, Clear Boggy (11140104)*, Kiamichi (11140105)+, Upper Little (11140107)*, 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
General Description: Shell subcircular to pentagonal, solid, inflated; anterior end broadly rounded from dorsum to terminus of medial ridge; ventral margin between termini of medial and posterior ridges concave; posterio-ventral junction bluntly biangulate; posterior margin truncated, may be a slight concavity above the posterio-ventral biangulation; dorsal margin generally straight, concave lunule before beak; beak subcentral, elevated, relatively narrow, inclined anteriorly, sculpted by fine irregularly arched ridges and pustules; anterior third of shell surface generally lacks pustules, termini of annual growth increments elevated; maximum shell inflation along a medial ridge, sculpted by a narrow row of medium-sized pustules; medial and posterior ridges separated by a narrow sulcus; posterior ridge relatively low, bluntly angular, sculpted by a single row of prominent, widely spaced pustules; posterior slope concave, broad, expanded into moderately-developed wing, transversed by relatively heavy costations curved posterio-dorsally, a faint radial ridge and sulcus posterior to posterior ridge; periostracum with a cloth-like texture, greenish to brown, occasionly with wide, indistinct green rays. Pseudocardinal teeth heavy, serrated, triangular, double in left valve, single in right but with lamellar denticle adjacent to contiguous sulci; interdentum short, moderately wide; lateral teeth rather lamellar, roughened with striations, double in left valve, single in right but accessary lamella may develop ventrally; anterior muscle scars distinct, rather small, impressed, smooth; pallial line impressed, lighter posteriorly; posterior muscle scars lightly impressed, confluent; beak cavaties deep, compressed; nacre white, somewhat iridescent posteriorly.
Diagnostic Characteristics: This species is quite similar to and has often been confused with Quadrula quadrula. In outline, Q. fragosa more resembles the shape of Q. nodulata. With respect to Q. quadrula, Q. fragosa is more rounded and pentagonal in outline, the medial sulcus is narrower and more centrally positioned, the beak is narrower and appears more elevated, beak sculpture is finer and less developed, and the posterior slope is broader and more alate. The costations across the posterior slope are relatively thick, fairly smooth, and well-separated. In Q. quadrula, costations are more closely packed and tend to be composed of small pustules. Additionally, Q. quadrula is more quadrate in appearance, tends to be posteriorly elongated, has a yellowish and shiny periostracum, and may be highly rayed. Height: 84mm.
Reproduction Comments: Heath et al. (2000) observed winged mapleleaf in the St. Croix River for 3 years before they described it as a late season, short-term (~5 weeks) brooder that typically released its glochidia as water temperature decreased to ~15 C in early autumn. Most other Quadrula species are reported to brood and release glochidia over longer periods during spring and summer (Oesch, 1995; Heath et al., 2000). Steingraeber et al. (2007) provided evidence for a thermal cue (17-20 C) that presumably is needed to trigger peak juvenile excystment with glochidial metamorphosis time ranging from 28 to 37 d at constant 19C, 70 d in varied 12-19C, and 260-262 d in simulated natural thermal 0-21C. Therefore, the winged mapleleaf may be a host overwintering mussel (Watters and O'Dee, 2000) throughout much of its range. The channel catfish, Ictalurus punctatus, may be a suitable glochidial host (Hove et. al., 2000; 2001). Recently, channel catfish, Ictalurus punctatus, has been confirmed as the host fish for this species (Schwebach et al., 2003). Steingraeber et al. (2004; 2007) have confirmed blue catfish (Ictalurus furcatus) and channel catfish (Ictalurus punctatus) as suitable fish hosts, but blue catfish are a more prolific host. Oetker et al. (2005) also successfully reared this species on channel catfish.
Ecology Comments: Other than what was listed by Baker (1928) and the above speculation on habitat, nothing is known of this species.
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 mussels are displaced from the substrate during flooods. Major dispersal occurs while glochidia are encysted on their hosts.
Riverine Habitat(s): BIG RIVER, High gradient, MEDIUM RIVER, Moderate gradient, Riffle
Special Habitat Factors: Benthic
Habitat Comments: This species appears to have inhabited medium-sized and large rivers. Baker (1928) lists its habitat as "mud bottom in water 2m or more in depth". Locality records indicate that it also inhabited riffle areas with substantially shallower water depths and substrates ranging from sand and gravel to mixture including some cobble and boulder sized particles. The remnant population in the St. Croix River is found in riffles with clean gravel, sand, or rubble substrates and in clear water of high water quality but this may not reflect ideal habitat (USFWS, 1997). Information on substrate, flow, current, sediment, temperature, oxygen, alkalinity, nitrogen, phosphorus, conductivity, and toxics in the St. Croix River can be found in USFWS (1997).
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 trophic studies have been conducted on this species. General literature claims that mussels are filter-feeders that remove phytoplankton from the water column. These assumptions are based on casual observations on 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 observed microhabitat utilization. This suggests that mussels may occupy a variety of guilds such as postulated for the Sphaeriidae (see Lopez and Holopaien, 1987; Gordon and Layzer, 1989).
Phenology Comments: Glochidia brood in September and October.
Length: 10.2 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: This species was designated as U.S. federally endangered in 1991 (USFWS, 1991) and a recovery plan (USFWS, 1997) was drafted and reintroduction efforts are underway (Hove et al., 2002; 2003). Dams on the St. Croix River are currently managed for maximum protection of the species (USFWS, 1997). The U.S. Fish and Wildlife Service has developed and is apparently instigating the provisions of a recovery plan (USFWS, 1997). Portions of the river have been incorporated into the St. Croix National Scenic River. However, this does not protect occurrences from events in the rest of the watershed and outside the boundaries of the scenic river designation.
Biological Research Needs: Habitat preferences and environmental tolerances, particularly tolerance to various pollutants and siltation, need to be determined. Research on reproductive biology, including glochidial host identification are critical.
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: 06Nov2006
NatureServe Conservation Status Factors Author: Cordeiro, J. (2006); Gordon, M. 1992; Whittaker J. C. 1994
Element Ecology & Life History Edition Date: 12Jun2007
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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