Leptodea leptodon (scaleshell mussel) rangewide status assessment 1998

              Leptodea leptodon

(Scaleshell Mussel)

Rangewide Status Assessment

1998

Written by: Jennifer Szymanski

U.S. Fish & Wildlife Service

1 Federal Drive

Fort Snelling, Minnesota 55111

Acknowledgments: Numerous State and Federal agency personnel and interested individuals

provided information regarding L. leptodon’s status. The following individuals graciously

provided critical input and review on portions of the manuscript: Bob Anderson, Sue

Bruenderman, Al Buchanan, Cindy Chaffee, Kevin Cummings, John Harris, Andy Roberts,

and Caryn Vaughn.

Cover: Leptodea leptodon photograph provided by Kevin Cummings.

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LEPTODEA LEPTODON STATUS ASSESSMENT

Taxonomy and Physical Description

Leptodea leptodon was described by Rafinesque in 1820. Synonymy includes Unio velum (Say

1829), Sympnynota tenuissima (Lea 1829), Lampsilis blatchleyi (Daniels 1902), and Lampsilis

leptodon (Rafinesque 1820). Leptodea leptodon is commonly known as scaleshell.

A description of the species was provided by Buchanan (1980), Cummings and Mayer (1992),

Oesch (1984), and Watters (1995). The shell is typically one to four inches, elongate, and very

thin and compressed. The anterior end is rounded; the posterior end in males is bluntly pointed.

In females, the periostracum forms a wavy, fluted extension of the shell posteriorly. The dorsal

margin is straight; the ventral margin is gently rounded. Umbos are small and low, about even

with the hinge line. The beak sculpture is compressed and inconspicuous and consists of four or

five double-looped ridges. The periostracum is smooth, yellowish green or brown, with numerous

faint green rays. The pseudocardinal teeth are reduced to a small thickened ridge. The lateral

teeth are moderately long; two long, indistinct lateral teeth occur in the left valve, one fine tooth

in the right. The beak cavity is very shallow or absent. The nacre is pinkish white or light purple

and highly iridescent.

Distribution

Leptodea leptodon historically occurred throughout most of the eastern United States. Williams

et al. (1993) reported the historical range as Alabama, Arkansas, Illinois, Indiana, Iowa,

Kentucky, Michigan, Mississippi, Missouri, Ohio, Oklahoma, South Dakota, Tennessee, and

Wisconsin. Leptodea leptodon occurrence is also reported from the Minnesota River, Minnesota

(Clarke 1996). Gordon (1991), in describing L. leptodon’s distribution, included a portion of the

St. Lawrence drainage. However, the specimens that were the source of the St. Lawrence River

record were later identified as wingless examples of L. fragilis, which are often seen in New York

(David Strayer, Institute of Ecosystem Studies, in litt. 1995). Given this and that no other

authentic specimens have been found (David Stansbery, Ohio State University, in litt. 1995), the

historical occurrence of L. leptodon in St. Lawrence Basin is doubtful. Similarly, L. leptodon

occurrence has not been documented in Michigan and Mississippi. Currently, the species is

known from a few scattered populations within the Mississippi River System in Missouri,

Oklahoma, and Arkansas (Figure 1).

Population Trends

Historically, L. leptodon was broadly distributed but locally rare (Gordon 1991, Oesch 1984, Call

1900). Within the last 50 years, it has become increasingly rare and range restricted. Species

that persist at low abundances are difficult to census; thus, deriving population trend is nearly

impossible. However, reliable inferences can be made based on small population biology theory

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and observations from field investigations. First, population stability implies, at a minimum, that

recruitment exceeds mortality. The presence of juveniles serves as evidence for recruitment.

Rangewide surveys have failed to locate juvenile L. leptodon specimens in all rivers except for the

Meramec River Basin. Second, small populations are more susceptible to extinction due to

chance events. All known L. leptodon populations, except for populations within the Meramec

River Basin, are based on the collection of a few individuals and often only a single specimen.

Third, small populations must rely on movement among populations to remain genetically viable.

Existing L. leptodon occurrences, with the possible exception of those in the Meramec River, are

isolated from each other with very little potential for dispersal among them. The lack of evidence

for recruitment, the vulnerability of L. leptodon populations to chance events, and the isolation of

sites, strongly suggests that the L. leptodon throughout its range is declining.

To facilitate population comparisons across state lines, criteria for status and trend categories

were devised (Appendix 1 & Table 1). Based on these criteria, 13 of 53 known historical

populations persist today, i.e., have extant status (Table 2). Of these extant populations, three are

likely stable, two are declining, four are presumed declining, and four have unknown trend. An

additional six populations may also persist but their current status is uncertain due to lack of

recent collections or surveys. The population status for five of these occurrences is likely

extirpated and for the other the status is unknown (Table 2).

Upper Mississippi River System- Leptodea leptodon is documented from eight rivers and

tributaries within this river system (Table 3). However, L. leptodon has not been found in more

than 50 years and is believed extirpated from the Upper Mississippi River system (Kevin

Cummings, Illinois Natural History Survey, in litt. 1994).

Middle Mississippi River System- Historically, L. leptodon occurred in 25 rivers and

tributaries within this system (Table 3). Currently, the species is extant in four, possibly five,

rivers within the Meramec River and Missouri River drainages. Of the five populations, two are

likely stable, two are presumed declining, and one has unknown population trend (Table 2).

Ohio River Drainage- The species has been extirpated from the entire Ohio River system. The

most recent collection date from the Ohio River Basin is 1964 (from Green River, Wayne Davis,

Kentucky Dept. of Fish and Wildlife, in litt. 1994). All other records are pre-1950 (Cummings;

Catherine Gremillion-Smith, Indiana Dept. of Fish and Wildlife; Ron Cicerello, Kentucky Dept. of

Fish and Wildlife, in litt. 1994; Paul Parmelee, University of Tennessee, pers. comm. 1995)

Meramec River Drainage- During a 1979 survey of the Meramec River Basin, 198 sites were

searched and 14 sites had evidence of past or current L. leptodon presence (Buchanan 1980). Ten

of the sites had evidence (i.e., live or a freshdead shell ) of L. leptodon persistence. Seven of the

14 sites were in the lower 112 miles of the Meramec River, five in the lower 54 miles of the

Bourbeuse River, and two in the lower 10 miles of the Big River. In addition to being restricted

to only three rivers, L. leptodon is also locally rare. Buchanan found that the species comprised

less than 0.1 percent of the living naiades (with live specimens collected at four sites--three in the

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Meramec and one in the Bourbeuse) found in the Meramec River Basin. The Meramec River,

according to Buchanan, supports more freshwater mussel species (42 species) than any other

stream in the Meramec River basin. Although the lower 108 miles of the river had suitable habitat

for a number of rare species, only the lower 40 miles harbored live L. leptodon specimens

(Buchanan 1980). Both the Bourbeuse and Big rivers (especially the Big River) had lower

species diversity and less suitable habitat than the Meramec River. Suitable habitat was restricted

to the lower 54 miles of the Bourbeuse River and lower 10 miles of the Big River (Buchanan

1980). The lower species diversity and abundance of the Big River is attributed to the effects of

lead mining. Specifically, from 1978 and beyond, 81,000 cubic yards of mine tailing were

discharged into the Big River. As a result, 25 miles of stream was covered and the lower 80 miles

of the river were negatively impacted (Alan Buchanan, Missouri Dept. of Conservation, in litt.

1995).

An intensive resurvey of the Meramec River Basin occurred in 1997 (Sue Bruenderman, MDOC,

in litt. 1998). Similar to Buchanan’s findings, L. leptodon represented only 0.4 percent of the

living freshwater mussels, with specimens collected from the Meramec River proper (n=34 at 9

sites, comprising 20.9% of the sites surveyed), the Bourbeuse River (n=10 at 5 sites comprising

19.2% of the sites surveyed), and the Big River (n=2 at 1 site comprising 16.7% of the sites

surveyed). Leptodea leptodon presence was documented at four of the five sites where

Buchanan had collected specimens on the Meramec River (Andy Roberts pers. comm. 1998).

The site where L. leptodon occurrence was not reconfirmed contained only two live specimens of

any mussel species--Buchanan found 93 living individuals. This site no longer supports suitable

mussel habitat. Portions of the Meramec River continue to provide suitable habitat, although

above river mile 64, mussel species diversity and abundance declines noticeably. The Bourbeuse

River has undergone the greatest change with respect to mussel populations. This is especially

patent in the lower river. Buchanan found this part of the Bourbouese River to be the most

diverse stretch but the 1997 survey found that the mussel populations were decimated. The sites

resurveyed in the Big River, which has been the river most affected by past pollution spills, have

changed little since the early 1980s. Leptodea leptodon specimens were collected from a single,

new site. The mussel diversity in the upper portion of the river, as also observed for both the

Meramec and Bourbeuse rivers, appears to be declining.

Although the number of L. leptodon specimens collected in 1997 is greater than that reported by

Buchanan’s study, this is not proof of an increasing population. Deriving population trend from a

comparison of the studies is difficult because of the low population densities encountered.

However, the persistence of L. leptodon indicates (because the species is short-lived and thin-shelled)

recent recruitment has occurred, although it is unknown whether this recruitment is

sufficient to sustain continued survival. Nonetheless, the small number of specimens collected,

especially from the Bourbeuse and Big rivers, indicate that the long-term viability of these

populations is tenuous. Moreover, the limited mussel habitat available and the loss of mussel beds

since 1980 as a result of sedimentation, extreme enrichment and unstable substrates (Buchanan in

litt. 1997; Roberts pers. comm. 1998) indicate that L. leptodon populations within the Meramec

River basin are threatened.

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Missouri River Drainage- Within the Missouri River drainage, L. leptodon is reported from

Missouri, Gasconade, Big Piney and South Grand rivers and Auxvasse Creek (Buchanan 1980,

1994; Oesch 1984). Leptodea leptodon was last collected from Auxvasse Creek in the late 1960s

(Buchanan, in litt. 1997). Similarly, the last known collection date for the South Grand is the

early 1970s, and this collection site is now inundated by Truman Lake and is unsuitable for L.

leptodon inhabitance (Buchanan, in litt. 1997). The only specimen reported from the Missouri

River proper is from South Dakota very close to the Nebraska border (Hoke 1983). This

occurrence represents the westernmost record within the Upper Mississippi River system. A

subsequent survey failed to relocate live specimens or relict shells (Clarke 1996). A single, fresh

dead specimen was collected from Big Piney River in 1981(Bruenderman, in litt. 1998). No other

information is available on L. leptodon’s occurrence in this river.

The Gasconade River was surveyed in 1994 and was found to support 36 species of freshwater

mussels (Buchanan 1994). Leptodea leptodon specimens were collected at eight sites between

river miles 6 and 57.7. At two sites only dead shells were found and the remaining six sites had

a total of eight live specimens. Overall, L. leptodon comprised less than 0.1% of the mussels

collected. Several areas of the river were highly unstable, most likely a result of row-crop farming

near the bank in conjunction with the 1993 flood. These areas had high cut mud banks with fallen

trees into the river, unstable substrate, and contained very few mussels. Many of these areas will,

within the next five years, continue to degrade and the mussel fauna will be further impacted with

some species possibly disappearing (Buchanan 1994). Below river mile 6, only one stable bar

contained a diverse mussel fauna. High silt deposition from Missouri River limits the potential for

additional freshwater mussel habitat below this area. If populations still exist in any of the rivers

within the Missouri River drainage, their longterm persistence is undoubtably precarious.

Lower Mississippi River System- Leptodea leptodon is documented from 20 rivers and

tributaries (Table 3). Nine rivers, and possibly an additional five, support L. leptodon

populations today. Of the fourteen populations, one is likely stable, four are declining, four are

presumed declining, and for the remaining five population trend is unknown (Table 2).

St. Francis River- Several mussel surveys have been conducted in portions and throughout the

length of the St. Francis River (Bates and Dennis 1983, Ahlstedt and Jenkinson 1987, Clarke

1985, Harris 1986, Rust 1993). Records of dead mussels and relic shells indicate that at one time

mussels were distributed throughout the river (Bates and Dennis 1983). Leptodea leptodon

occurrence is documented at two sites by single specimens (Clarke 1985). Much of the St.

Francis River from the mouth above Helena, Arkansas to Wappapello Dam, Missouri has been

drastically altered by channelization, construction of levees, diversion ditches, and control

structures and floodways (Ahlstedt and Jenkinson 1987, Bates and Dennis 1983). Bates and

Dennis (1983) found that of the 54 sites sampled, 15 were productive, 10 marginal, and 29 had

either no shells or dead specimens only. Although L. leptodon was not collected, they noted that

three areas, comprising 48 miles, provided suitable mussel habitat: Wappapello Dam, MO to

Mingo Ditch, MO; Parkin, AR to Madison, AR; and Marianna to the confluence with the

Mississippi River at Helena, AR. The remaining river miles are unsuitable for mussel habitation.

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If L. leptodon is extant, it occurs in very small numbers and is confined to the remaining suitable

patches.

White River Drainage- Leptodea leptodon is documented from White River proper, James

River, Spring River, South Fork Spring, Strawberry River, Myatt Creek, and Middle Fork Little

Red River. The sole White River specimen was collected in 1902 near Garfield, Arkansas (Clarke

1996). A late 1970s survey of the White River between Beaver Reservoir and its headwaters

failed to relocate live or dead L. leptodon individuals (Gordon 1980). Municipal pollution, gravel

dredging, and dam construction have rendered this reach of the river unsuitable for mussels.

Bates and Dennis (1983) surveyed the White River from Newport, AR to the confluence of the

Mississippi River. In their report, they concluded that navigational maintenance activities

continue to destroy habitat. As a result, mussel populations have been relegated to a few refugial

sites, none of which support L. leptodon. Specimens have not been collected from the James

River, a tributary of the White River, since before 1950 (Clarke 1996). It is unlikely that either

river currently supports L. leptodon.

An eight-mile section of the Spring River supports a diverse assemblage of freshwater mussels

(Gordon et al. 1979 and 1984, Arkansas Highway and Transportation Dept 1984, Miller and

Hartfield 1986). Eight specimens of L. leptodon have been collected from this river (Cummings

in litt 1994, Clarke 1996, Arkansas State Hwy. and Transportation Dept. 1984, Miller and Nelson

1984). A 1984 (Gordon et al. 1984) survey found suitable mussel habitat between river miles 3.2

and 11.0, although species richness below river mile 9 (at the confluence of Eleven Point River)

declined markedly. Gordon and colleagues (1984), as well as Miller and Hartfield (1986),

reported that the lower three miles of river were completely depauperate of mussels and contained

no suitable habitat (Miller and Hartfield 1986, Gordon et al. 1984). Sand and gravel dredging,

cattle wading, siltation, and surface run-off of pesticide and fertilizer appear to be contributing

factors in the degradation of this river reach (Gordon et al. 1984). A 1993 survey of Spring River

failed to document L. leptodon presence (John Harris, Arkansas State University, in litt. 1997).

Leptodea leptodon was collected from the South Fork Spring River in 1983 and 1990. During

the 1983 survey (Harris in litt. 1997), four specimens near Saddle, Arkansas and one specimen

and one valve north of Hunt, Arkansas were collected. During a subsequent visit in 1990 (Harris

pers. comm. 1995) fairly young adults were collected. Although juveniles were not found, the

presence of young adults signifies that reproduction has occurred in recent years. South Fork

Spring and Meramec rivers appear to support the most robust L. leptodon populations.

The Strawberry River and the Myatt Creek occurrences are single specimen collections (Harris in

litt 1997). The Strawberry River specimen (collected live in 1996) was collected near the

confluence with Clayton Creek in Lawrence County. A single relict specimen was collected in

1996 from Myatt Creek in Fulton County (Harris in litt 1997).

The historical locality (near Shirley, Van Buren County, Arkansas) of the single, known specimen

from the Middle Fork of the Little Red River no longer supports mussel habitat. According to

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Clarke (1987), suitable mussel habitat exists for a six-mile stretch from the confluence of Tick

Creek upstream to the mouth of Meadow Creek. Below Tick Creek, only dead mussels were

found. Upstream of Meadow Creek, the river recedes to form a series of isolated pools during

dry summer months.

Arkansas River Drainage- Leptodea leptodon has been collected from the Arkansas River

system in Oklahoma and Arkansas. The species is reported from the Poteau River in Oklahoma

(Gordon 1991), Frog Bayou in Arkansas (Harris and Gordon 1987), the South Fourche La Fave

and Mulberry rivers in Arkansas (Gordon 1991 and Harris 1992). Despite several freshwater

mussel surveys of the Poteau River (Isely 1925, White 1977in Harris 1994, Branson 1984, and

Harris 1994), only a single, undated specimen has been collected (Gordon 1980). Leptodea

leptodon persistent in Poteau River is doubtful.

Leptodea leptodon is documented from the Frog Bayou by two specimens (Gordon 1980). One

of the specimens was collected at a site that is now inundated by the Beaver Reservoir. The most

recent collection was a fresh dead individual, accompanied by several other fresh dead mussel

species, during a 1979 survey (Gordon 1980). Gordon noted that this site and other nearby sites

were recently disturbed by streambank bulldozing upstream. He also reported in-stream gravel

mining activities at several sites. Within Frog Bayou, potential habitat is restricted to the area

between Rudy and the confluence of the Arkansas River. Above Rudy, the river is impacted by

the two reservoirs; one near Maddux Spring and the other at Mountainburg. At the confluence of

the Arkansas River, live mussels have not been found--likely due to dredging activities (Gordon

1980). The occurrence of L. leptodon is uncertain, but if present the population is in jeopardy due

to limited habitat and in-stream mining activities.

The South Fourche La Fave River is dominated by a few widely distributed and abundant species.

The only L. leptodon record from this river is a single, live specimen found in 1991 (Harris 1992).

The potential of additional mussels populations is unlikely due to the limited availability of

suitable substrate. Similarly, other major tributaries of the South Fourche La Fave River provide

little opportunity for mussel occurrence. Similar to the Frog Bayou, persistence of L. leptodon in

this river is in doubt.

Although Gordon (1991) indicated L. leptodon occurrence in the Mulberry River, documentation

is lacking (i.e., no written acknowledgment). A recent survey failed to obtain evidence of L.

leptodon presence as well (Craig Hilborne, U.S. Forest Service, pers. comm. 1995; Stoeckel et al.

1995). Leptodea leptodon existence in the Mulberry River is unlikely.

Red River Drainage- The historical distribution of L. leptodon in the Red River drainage

includes Kiamichi River (OK), Gates Creek (OK), Little River (OK and AR), Mountian Fork

(OK), Cossatot River (AR), Saline River (AR), and Ouachita River (AR).

A single, undated specimen was collected from Gates Creek, a tributary of the Kiamichi River

(Valentine and Stansbery 1971). The first collection date from the Kiamichi River is 1925 (Isley

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1925). From Isley’s work, it is obvious that the Kiamichi River supported a diverse and abundant

mussel fauna. He collected 36 specimens of L. leptodon at one of 22 stations visited. As recently

as 1987 (Clarke 1987), the Kiamichi River was described as “in remarkably good condition” and a

“faunal treasure”. However, despite extensive searches of the Kiamichi River over the last 11

years, only a single fresh dead shell (in 1987) has been collected (CarynVaughn, Oklahoma

Biological Survey, pers. comm. 1997; Charles Mather, University of Science and Arts of

Oklahoma, in litt. 1984 and 1995). Vaughn (pers. comm. 1997) failed to find even a L. leptodon

shell during three years (1993-1996) of surveys in the Red River system. However, the Kiamichi

River is in relatively good shape above the Hugo Reservoir, (Clarke 1987) and may still support a

remnant population of L. leptodon. A potential threat to the Kiamichi River is a proposed

reservoir at Tuskahoma (located above Hugo Reservoir). Although the U.S. Army Corps of

Engineers has authorized construction, the lack of a local sponsor has rendered the project

"inactive" (Martinez, pers comm. 1997). If constructed, the devastating effects associated with

reservoirs (e.g., increased siltation and altered temperature regime) are likely to destroy the

diverse mussel fauna that currently inhabits the Kiamichi River.

Unlike the Kiamichi River, the Little River continues to be greatly affected by sewage pollution,

gravel dredging, and reservoir effects. The mainstem of the river is impounded by the Pine Creek

Reservoir. Further downstream, a major tributary to the Little River, the Mountain Fork River, is

impounded by Broken Bow Reservoir. Although lacking evidence of L. leptodon persistence, the

Little River above the Pine Creek Reservoir supports healthy mussel populations (Vaughn in litt.

1997). Below Pine Creek Lake, the mussel fauna is severely depleted but recovers with

increasing distance from the impoundment (Vaughn in litt.1997). A L. leptodon specimen was

reported from Mountain Fork by Valentine and Stansbery (1971). Clarke (1987) believed that,

based on the presence of mussel populations at the confluence of Mountain Fork and beyond the

Arkansas border, damage to Mountain Fork from the Broken Bow Reservoir has not occurred.

However, Vaughn (in litt. 1997) indicated that these populations are now severely depleted with

most no longer containing live mussels. Although extensive surveys throughout the length of

Little River failed to collect L. leptodon, suitable habitat remains and L. leptodon individuals may

persist (Vaughn in litt. 1997). If L. leptodon does not occur there now, however, discharge of

hypolimnectic water from Pine Creek and periodic discharge of pollution from Rolling Fork Creek

prevents future recolonization (Clarke 1987).

If L. leptodon still occurs in the Red River drainage in Oklahoma, extant populations are small

and are likely restricted to the few remaining, isolated suitable areas in the Kiamichi and Mt. Fork

rivers. Given the extensive survey effort over the last decade, L. leptodon long-term persistence

in Oklahoma is tenuous.

The occurrence of L. Leptodon in the Cossatot and Saline rivers is attributed to single specimens

collected in 1983 (Harris in litt. 1997) and 1987 (Harris pers. comm. 1995), respectively. No

other information is available for either river. Leptodea leptodon occurrence in the Ouachita

River and its two tributaries, the Saline River and Little Missouri River, is sporadic as well. Both

the Little Missouri and Saline rivers records are from single specimens. The Saline River

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specimen was collected in 1946 (Clarke 1996), and the Little Missouri River collection record is

from 1995 (Harris in litt. 1997). Leptodea leptodon occurrence in the Ouachita River is

documented by four undated museum specimens from Arkadelphia, Clark County, Arkansas

(Clarke 1996). Ouachita River has been severely impacted by hydroelectric dams and artificial

lakes. The “Old River,” an oxbow system off the mainstem, is now essentially a series of muddy,

stagnant pools with water quality problems resulting from dumps, interspersed with small, isolated

pockets of suitable mussel habitat (Clarke 1987). Based on the small number of collections and

the limited habitat available, the long-term persistence in Cossatot, Saline, Little Missouri, and

Ouachita rivers is precarious.

Habitat

Although always somewhat rare, L. leptodon apparently was not habitat limited. According to

published accounts, the species occupied a wide variety of habitat types. For example, Buchanan

(1980, 1994) and Gordon (1991) reported L. leptodon from riffle areas with substrate

assemblages of gravel, cobble, boulder, and occasionally mud or sand. Oesch (1984) considered

L. leptodon a typical riffle species, occurring only in clear, unpolluted water with good current.

Conversely, Call (1900), Goodrich and Van der Schalie (1944), and Cummings and Mayer (1992)

reported collections from muddy bottoms of big rivers. The unifying characteristic appears to be

an intact system with good water quality. This is consistent with the current distribution of L.

leptodon. Most extant populations are restricted to river stretches that support a high diversity of

freshwater mussels (Buchanan 1980, Harris 1992) and that have maintained relatively good water

quality.

Ecology

Very little is known about the ecology of L. leptodon specifically. Baker (1928 in Buchanan 1980

and Oesch 1984) surmised that the breeding season is bradytictic (i.e., long-term breeder with

larvae held until the following spring or summer). This was based on reports of glochidia present

in the ectobranchous marsupia in September, October, November, and March (Gordon 1991).

Watters (1995) provides a overview of the unionid life cycle. The female stores the unfertilized

eggs in a region of the gills called marsupia. She takes up sperm liberated into the water by the

male. Over a period of days to months, the fertilized eggs develop into glochidia (i.e., larvae).

The female expels glochidia into the water which then attach to suitable hosts. Host fish

specificity is seemingly the rule rather than the exception for most of the mussel species (Neves

1993). Following proper infestation, glochidia transform into juveniles and excyst. The length of

time is dependent on water temperature. For further information on the life history of freshwater

mussels, see Gordon and Layzer (1989) and Watters (1995).

Threats

A. Present or threatened destruction, modification, or curtailment of habitat or range: The loss of

mussel diversity in the U.S. has been well documented and is a major concern for conservation

9

biologists. In a review of the conservation status of native freshwater fauna, the American

Fisheries Society found that of the 297 native freshwater mussels, 71 percent are imperiled

(Williams et al. 1993). Similarly, The Nature Conservancy recognizes 55 percent of North

America's mussel fauna as extinct or imperiled (Master 1990 in Williams et al. 1993). The current

status of L. leptodon exemplifies the loss of mussel diversity. The range of L. leptodon was once

expansive, spanning the Mississippi River Basin in at least 53 rivers and 13 States. Today, the

range is significantly reduced with known extant populations persisting in only 13 rivers in three

States.

Arguably, L. leptodon has suffered a greater range restriction than any other unionid. Leptodea

leptodon has been decimated from the entire Upper and most of the Middle Mississippi River

drainages. Much of the decline occurred before mid-century; having been last documented from

Alabama, Illinois, Indiana, Iowa, Kentucky, Ohio, Tennessee, and Wisconsin more than 30, and

for most more than 50, years ago (Thomas Watters, Ohio State University, in litt. 1995; Parmelee

and David Heath, Wisconsin Department of Natural Resources, pers. comm. 1995; Cummings,

Smith, and Cicerello, in litt.1994; Michael Hoggarth, Otterbein College and Patricia Jones, Ohio

Dept. of Natural Resources, in litt.1994; Stansbery 1976). As with most endangered mussels, the

principal cause of this decline is habitat destruction. Habitat degradation--as a result of physical,

chemical, and biological alteration--has and continues to threaten L. leptodon populations. The

major causes of such alteration are channelization, damming and impoundment, and nonpoint and

point source pollution. The most pernicious effects of these factors are contamination and

sedimentation (Fuller 1974, Myers et al. 1985, USSCS 1988). Freshwater mussels, because of

their sedentary nature and their filter-feeding habit, are very susceptible to degraded water quality.

Reports of wholesale destruction of mussel populations as a consequence of pollution and

sedimentation date back to the late 19th and early 20th centuries (Lewis 1868, Ortmann 1909 in

Fuller 1974), and continue to be implicated as the primary factors in the loss of mussel diversity

(Vaughn 1993, Goudreau et al. 1988; Coon et al. 1977).

Contamination

Contamination of waterways is a result of point and nonpoint source pollution. Point source

pollution refers to entry of material from a discrete, identifiable source (e.g., industrial effluents,

sewage treatment plants, solid waste disposal sites). Little information exists on the specific

toxicity of contaminants to mussels. However, freshwater mussel mortality from toxic spills and

chronic lethality of polluted water are well documented (Lewis 1868 in Neves 1993, Ortmann

1909, and Baker 1928 in Fuller 1974; Cairns et al. 1971 in Neves 1993; Goudreau et al. 1988). It

is generally accepted that contaminants are at least partially responsible for decreases in

population densities, ranges, and diversity of unionids. Decline and elimination of populations

may be due to acute and chronic toxic effects that result in direct mortality, reduced reproductive

success, or compromised health of the animal or host fish. Mussels, as filter-feeders, are exposed

to contaminants that dissolve in water and deposit in bottom substrate. The toxicity of pollutants

stored in mussel tissue can greatly exceed the levels found in surrounding water, i.e.,

bioaccumulate (USFWS in prep.). Furthermore, sediment and dissolved organic matter act

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synergistically with metallic pollution (USFWS in prep). As toxic metals are adsorbed onto

suspended particles (Tessier and Campbell 1987 in USFWS in prep.), they can accumulate and

directly affect filter-feeding animals (USFWS in prep.). This can lead to shell calcification

interference (Rosenberg and Henschen 1986). The sedentary nature of mussels predisposes L.

leptodon to chronic water quality problems. Although adult mussels are able to close their valves

for an extended period of time to avoid acute toxic effects (Holwerda and Veenhof 1984), this

mechanism is not effective for chronic toxic exposure (Neves 1993). Research indicates that

glochidia and juveniles are more sensitive to toxicants than adults (Goudreau et al. 1993, Neves

1993); yet the larval stage lacks valve closure capabilities. Thus, larvae are vulnerable to both

acute and chronic toxic effects.

Nonpoint source pollution is responsible for more than half of all water pollution (Chesters and

Schierow 1985). This type of pollution refers to entry of material into the environment from a

diffuse source. The major contributors of nonpoint source pollution include agricultural, urban,

construction, and silvicultural activities (Myers et al. 1985). The most pervasive source of

nonpoint contamination is agricultural operations (Thomas 1985). Fertilizers, manure and

pesticides are the primary derivations of these pollutants, which can be transported with sediment

(adsorbed pollutants) or in solution (soluble pollutants). Nitrogen and phosphorus are the major

pollutants associated with water quality degradation (Myers et al. 1985). These pollutants

accelerate eutrophication (i.e., organic enrichment) of water bodies (Fuller 1974). Freshwater

mussels are considered one of the most sensitive faunal groups to organic enrichment (Goudreau

et al. 1988). Although organic enrichment can be beneficial (i.e., increase in food production), it

can also be destructive through smothering and chemical alteration (Dance 1981in Wolcott and

Neves 1990). Organic enrichment increases aquatic plant productivity, which correlates to an

increase in decaying organic matter. As a result, oxygen is depleted, current slackens, carbon

dioxide production increases, and pH decreases--all of which are inimical to the survival of most

freshwater mussels (Fuller 1974).

Additionally, high concentrations of phosphorus, potassium, ammonium, bacteria, and organic

matter in manure can contaminate surface waters when animals are allowed direct access to

streams (Chesters and Schierow 1985, Myers et al. 1985) or when animal wastes are not properly

stored. In addition to causing organic enrichment, phosphorus can also hinder shell development

(Rosenberg and Henschen 1986 in Goudreau et al. 1988). Potassium at high concentrations can

be toxic to mussels and can be responsible for the loss of entire populations (Fuller 1974).

Ammonia has both lethal and sublethal effects. Toxic ammonia induces glochidial closure and thus

interferes with fish host infection (Goudreau et al. 1988). Pollutants from fertilizers applied

around homes, golf courses, and parks may also add to the degradation of water quality (Myers et

al. 1985). Likewise, construction sites can significantly degrade waterbodies. These areas

generate pollutants, including fertilizers, pesticides, petroleum products, and a variety of other

construction materials, that degrade water quality and are toxic to aquatic organisms (Myers et al.

1985).

Sedimentation

11

Sediment is material that is in suspension, is being transported, or has been moved as the result of

erosion (USSCS 1988). The water quality impacts caused by sedimentation are numerous. In

general, it affects aquatic biota by altering the substratum (Ellis 1936, USSCS 1988, Myers et al.

1985) and by altering the chemical and physical composition of the water (Ellis 1936, Myers et

al. 1985, USSCS 1988). Sedimentation directly affects freshwater mussel survival by interfering

with respiration and feeding. Having great difficulty in escaping smothering conditions (Imlay

1972), a sudden or slow blanketing of stream bottom with sediment can suffocate freshwater

mussels (Ellis 1936). Increased sediment levels may also cause reduced feeding efficiency--

empirical studies have found that mussels remain close 25-40 percent longer when exposed to

greater sedimentation concentrations than under normal conditions (Ellis 1936)--which can lead

to decreased growth and survival (Bayne et al. 1981 in Spacie and Chaney 1993).

Sedimentation also influences the physical and chemical composition of the water. Suspended

materials are very effective in limiting light penetration through the water column which reduces

the production of phytoplankton (a food source for mussels) and alters the water temperature.

Extreme fluctuations in water temperature can have lethal effects (Ray 1977 in Imlay 1982).

Decreases in temperature may induce egg mass abortion (with sudden decreases in temperature;

Matteson 1948 in Fuller 1974) and decrease reproductive success by dulling glochidial response

to opportunities for host fish infection (Arey 1921 in Fuller 1974). Conversely, increasing

temperature can result in increased oxygen demand, shorten excystment period (Young 1911 in

Fuller 1974), and increase toxic ammonia concentrations (Goudreau et al. 1988). Sedimentation

also causes retention of organic material and other substances. This alters the oxygen demand

and the pH of the water, and increases bacterial concentrations (Ellis 1936). Low levels of

dissolved oxygen impair mussel growth (Imlay and Paige 1972). Decreases in pH can induce

closure (Matteson 1955 in Fuller 1974) and permit suspended materials to remain in suspension,

both of which can interfere with mussel feeding activities (Fuller 1974). Moreover, when

sediment settles out of suspension, it may carry with it adsorbed organic materials. This can result

in increased and localized enrichment of the stream (Fuller 1974), which as previously discussed

can have adverse effects. In addition, pollutants stored in the soil can be carried by the sediment

(Myers et al. 1985). Thus, increased sediment loads can also facilitate contamination of water

bodies.

Although sedimentation is a natural process, agricultural encroachment, channelization and

damming, timber harvesting within riparian zones, heavy recreational use, urbanization, as well as

other landuse activities greatly accelerate erosion (Waters 1995, Myers et al. 1985, Chesters and

Schierow 1985). Agriculture is the primary source of sedimentation (Myers et al. 1985; USEPA

1990 in Waters 1995). This is not surprising given that more than half of all non-federal land is

used for agricultural purposes (based on a 1985 estimate, Myers et al. 1985). It has been long

recognized that adjacent landuse influences the stream sediment load and discharge (Waters 1995;

Myers et al. 1985; Sorensen et al. 1977). Striffler (1964 in Waters 1995) reported that streams

within forested or other well-vegetated idle land had stable flows and less sediment; whereas,

streams in cultivated or pastured watersheds had heavy sediment and variable flows.

12

Channelization and damming are also major sources of sedimentation. Channelization and other

dredging operations (e.g., sand and gravel mining) can bury, crush, or physically remove mussels

with the substrate (Watters 1995). It also causes loss of substrate stability (Hartfield 1993),

which results in the release of sediment and pollutants. In some instances, the mussel fauna and

habitat are severely diminished as documented in the Yellow and Kankakee rivers in Indiana, the

Big Vermillion River in Illinois, and the Ohio River (Fuller 1974). Dams have similar effects by

creating sediment traps upstream and powerful currents below. Resultant currents move sediment

over beds and smother mussels and erode streambanks (Fuller 1974). Impoundments also

increase sediment load by decreasing the water’s sediment carrying capacity (Bates 1962, Negus

1966 in Watters 1995). Beyond sedimentation impacts, impoundments affect downstream mussel

populations by inducing scouring, changing temperature regimes, and altering habitat, food, and

fish host availability (Vaughn, in litt. 1997). Scour is a major cause of mussel mortality below

dams (Layzer et al. 1993). Most detrimental, however, is the disruption of reproductive

processes (Fuller 1974). Impoundments, which interfere with fish movement, alter normal fish

behavior, reduce the amount of suitable substrate, and diminish recruitment success (Vaughn

1993). Layzer and colleagues (1993) found that the cold water releases associated with some

impoundments led to a 30 to 60 percent decrease of the mussel fauna. Other sublethal effects

include reduced growth and increased eutrophication (Watters 1995).

Urbanization and silvicultural activities are important contributors of sedimentation as well.

Construction, although representing a small fraction of the nationwide sediment load in receiving

waters, can have enormous, immediate impacts. Soil erosion rates are typically 10 to 20 times

those on agricultural land and run-off rates may be 100 times greater (Myers et al. 1985). Over

short periods of time, construction activities can contribute more sediment to streams than was

previously deposited over several decades. Likewise, silviculture operations, such as road

building and harvesting operations, can also generate substantial amounts of sediment (Myers et

al. 1985). Moreover, deforestation causes irregular stream flow, high water temperatures, and

lowered dissolved oxygen--all which can adversely affect freshwater mussel survival for years

after the timber harvest (Fuller 1974).

Leptodea leptodon appears to be especially susceptible to contamination and sedimentation.

Historically, the species was widespread and occurred in diverse habitat; whereas today, L.

leptodon no longer occurs at sites which still support other endangered unionids (i.e., at sites

which have not been terribly altered). This suggests that L. leptodon is especially sensitive to

changes that have occurred (e.g., degraded water quality). Given the pervasiveness of the sources

of pollution and sedimentation, it is apparent that these threats will continue to be problematic for

L. leptodon. Nonpoint and point source pollution is currently affecting the Spring River in

Arkansas (Gordon et al. 1984, Miller and Hartfield 1986) and the Little River in Oklahoma

(Clarke 1987, Vaughn 1994). Sedimentation is causing deleterious effects in the Meramec River,

MO (Roberts, pers. comm. 1998); Gasconade River, MO (Buchanan 1994); Frog Bayou, AR

(Gordon 1980); and Spring River, AR (Gordon et al. 1984). Sand and gravel mining are

eliminating important pool habitat (for both L. leptodon and potential fish hosts) in the Meramec

and Gasconade rivers in Missouri (Bruenderman pers. comm. 1998). Impoundments,

13

channelization, and other dredging activities (e.g., sand and gravel mining) are impairing water

quality in Frog Bayou, AR (Gordon 1980); St. Francis River, AR (Ahlstedt and Jenkinson 1987);

White River, AR (Bates and Dennis 1983); Spring River, AR (Gordon et al. 1984); and Ouachita

River, AR (Clarke 1987). The proposed Kiamichi River reservoir, if constructed, will

undoubtably have devastating impacts. Nearly all L. leptodon populations are now restricted to

small stretches of rivers with little, if any, potential for expansion or recolonization to other areas.

The Little River in Oklahoma, for example, is so degraded by sewage pollution, gravel dredging,

and reservoir construction that only a few, small stretches are able support mussel populations.

B. Overutilization for scientific or commercial purposes: It is unlikely that L. leptodon, because of

its small size and thin shell, was ever purposefully collected by commercial musselers. It is

plausible, however, that extirpated populations were subjected to over-harvesting activities. For

example, according to local fishermen, mussel beds in the Spring and Black rivers were severely

over-collected during a period of extended drought and most beds were completely destroyed

(Gordon et al. 1984). Thus, L. leptodon populations may have been indirectly impacted (e.g., by

habitat destruction, removal from the stream, and discarded or improper replacement). Today,

incidental collecting could potentially be detrimental to existing populations. In addition to

possibly destroying or modifying the stream bed, collection or improper replacement of only a few

individuals--given that L. leptodon now occurs in very small, isolated populations--could decimate

an entire population. Musseling techniques, such as brailling, are nonselective harvesting methods

that typically result in unwanted and juvenile individuals being discarded (Williams et al. 1993).

Even for those individuals that are returned to the stream, mortality can still occur (Williams et al.

1993). Furthermore, gravid females may abort when disturbed (Imlay 1972), resulting in a loss of

an individual’s entire reproductive effort.

C. Disease or predation: Although natural predation is not problematic for stable, healthy

populations, small mammal predation could potentially pose a problem for L. leptodon

populations (Gordon 1991). The extant L. leptodon populations in Arkansas and Oklahoma are

small, isolated and have very limited recolonization potential. Consequently, predation could

exacerbate ongoing population declines.

Bacteria and protozoans persist at unnaturally high concentrations in streams with high sediment

load or in waterbodies affected by point source pollution, such as sewage treatment plants

(Goudreau et al. 1988). At these densities, ova and glochidia are vulnerable to attack (Ellis 1929

in Fuller 1974) and mussel growth can be slowed (Imlay and Paige 1972).

D. Inadequacy of existing regulatory mechanisms:. The River and Harbors Act of 1899 was the

first of a sequence of federal laws to protect surface waters. This Act was promulgated to curb

refuse disposal. Although this law has had beneficial effects, the Water Pollution Control Act of

1948 was the first law that explicitly intended to abate water pollution and to assign responsibility

to the individual States. Subsequent amendments to the Act in 1956 and 1961 provided

construction grants for wastewater treatment plants and provided research funds to study

pollution effects and to develop improved methods of effluent treatment. The Wild and Scenic

14

Rivers Act of 1968 provided a mechanism to identify and protect river reaches by prohibition of

federal approval or assistance for water projects that would have adverse effects. However, the

legislation provided inadequate protection from private development (Neves 1993). The passage

of the Clean Water Act of 1972 (CWA) set the stage for the regulations and the water standards

that exist today. Goals of the CWA include protection and enhancement of fish, shellfish, and

wildlife; providing conditions suitable for recreation in surface waters; and eliminating the

discharge of pollutants in U.S. waters.

Although positive consequences (e.g., a decrease in lead and fecal coliform bacteria) have been

realized following the passage of these Acts, degraded water quality still presents problems for

sensitive aquatic organisms such as freshwater mussels. Specifically, nationwide sampling has

indicated increases in nitrate, chloride, arsenic, and cadmium concentrations (Neves 1993). Non-point

pollution sources appear to be the cause of increases in nitrogen trend. Agriculture is

recognized as the most prominent source of non-point source pollutants, affecting more than two-thirds

of the nation's river basins (Neves 1993). However, only a few regulations aimed at

controlling runoff have been imposed on the agricultural community. The programs that address

nonpoint source pollution are mostly voluntary, and unfortunately contamination and

sedimentation continue to threaten freshwater mussel survival.

Although recognized by species experts as threatened in Arkansas, L. leptodon is not afforded

state protection (Table 4). Missouri and Oklahoma afford State protective status for L. leptodon-

-listed as rare and species of concern, respectively (Bruenderman, in litt. 1998; Vaughn pers.

comm. 1995). State regulations, however, provide inadequate protection from direct take and

habitat destruction (Martinez; McKenzie; pers. comm. 1997). Without habitat protection, neither

slowing nor prevention of L. leptodon decline will occur.

E. Other manmade or natural factors: As a consequence of the above factors, the inherent

biological traits of freshwater mussels increase their vulnerability to extinction (Neves 1993). For

example, the larval stage (glochidium) of most mussels is dependent on a few or a specific host

fish (Neves 1993). Despite the tremendous fecundity of females, this trait greatly reduces the

likelihood of contact between glochidia and suitable hosts. Watters (1995) postulated that the

glochidia must acquire suitable hosts within 24 hours. Obviously, reduction or loss of host fish

populations will adversely impact L. leptodon populations. Once a larva successfully transforms

on a host, it is further challenged with dropping off (known as excystment) into suitable habitat.

Watters (1995) reported that estimated chances of successful transformation and excystment

range from 0.0001% (Jansen and Hanson 1991) and 0.000001% (Young and Williams 1984). As

a result of fish host-specificity and the difficulty of locating suitable habitat, freshwater mussel

population growth occurs very slowly. Furthermore, the sedentary nature of mussels limits their

dispersal capability. This trait coupled with low recruitment success translates into the need for

decades of immigration and recruitment for re-establishment of self-sustaining populations.

Thus, achieving longterm survival for species that have undergone population decline is an

protracted and ardous task. Accomplishing this task, however, is nearly impossible for those

species confronted habitat degradation as well.

15

The threats to L. leptodon survival posed by the above factors are exacerbated by the small

number of low density populations that remain. Although L. leptodon was always somewhat

rare, the current population densities are likely much lower (due to the previously identified

threats) than historical levels. Despite any evolutionary adaptations for rarity, habitat loss and

degradation increase a species vulnerability to extinction (Noss and Cooperrider 1994).

Numerous studies have shown that with decreasing habitat availability, the probability of

extinction increases. Similarly, as the number of occupied sites decreases, the likelihood of

extinction increases (Vaughn 1993). This increased vulnerability is the result of chance events.

Environmental variation, random or predictable, naturally causes fluctuations in populations.

However, populations with small numbers are more likely to fluctuate below the minimum viable

population (i.e., the minimum number of individuals needed in a population to survive). If

population levels stay below this minimum size, an inevitable, and often irreversible, slide toward

extinction will occur. Small populations are also more susceptible to inbreeding depression and

genetic drift. Populations subjected to either of these problems usually have low genetic diversity,

which reduces fertility and survivorship. Lastly, chance variation in age and sex ratios can affect

birth and deaths rates. Skewing of the demographics may lead to death rates exceeding the birth

rates, and when this occurs in small populations there is a higher risk of extinction.

Similarly, the fertilization success of mussels may be related to population density, with a

threshold density required for any reproductive success to occur (Downing et al. 1993 in Watters

1995). Small mussel populations may have individuals too scattered to reproduce effectively

(Wilson and Clark 1912 in Fuller 1974). Many of the remaining L. leptodon populations may be

at or below this threshold density. These populations will be, if one of the aforementioned threats

go unabated, forced below or forced to remain below the minimum threshold. As a result, the

current decline to extinction will be accelerated.

Furthermore, species that occur in low numbers must rely on dispersal and recolonization for

long-term persistence. In order to retain genetic viability and guard against chance extinction,

movement between local populations must occur (i.e., a functional metapopulation, Appendix 1).

Although L. leptodon naturally occurs in patches and necessarily possesses mechanisms to adapt

to such a population structure, anthropogenic influences have fragmented and furthered

lengthened the distance between populations. Empirical studies have shown that with increasing

isolation colonization rates decrease. Also as previously explained, natural recolonization of

mussels occurs at a very low rate (Vaughn 1993). Therefore, it is imperative for long-term

freshwater mussel survival that a metapopulation structure is preserved. Unfortunately, many of

the extant L. leptodon populations now occur as single, isolated sites. These insular populations

are very susceptible to chance events and extinction with no chance of recolonization.

Lastly, the invasion of the exotic zebra mussel (Dreissena polymorpha) threatens all native

unionids through suffocation and competition for space, food, and survival of glochidia.

Currently, the native freshwater mussel fauna of the Mississippi and Ohio rivers is being

decimated by the invasion of the zebra mussel (Clarke 1995). The natural history of zebra

mussels is not completely understood; therefore, effective control measures are not yet known.

16

Given that recreational and commercial vessels greatly facilitate zebra mussel movement and

because of the proliferation and spread that has occurred, invasion of the D. polymorpha into

portions of the lower Mississippi River Basin appears inevitable (Buchanan pers. comm. 1995). If

zebra mussel invasion does indeed occur, the continued survival of L. leptodon will be

jeopardized.

Conservation Efforts

Interest in the conservation of freshwater mussels dates back to the turn of the century and is even

more evident today. Government agencies, researchers, private organizations, and individuals are

working together to preserve North American native mussel fauna. Several of these efforts

directly and indirectly benefit L. leptodon. First, numerous studies aimed at investigating the

ecology (e.g., glochidial infections, habitat preferences, etc.) and efforts to develop management

protocols (e.g., monitoring, relocation and reintroduction techniques) for specific mussel species

are ongoing. Information garnered from these studies may provide insightful information for L.

leptodon conservation. Next, the rapid spread of the zebra mussel has precipitated the formation

of committees whose sole purposes are to address the zebra mussel control. The Ohio River

Zebra Mussel Group has developed a strategic plan that outlines the actions needed for

avoidance, minimization, and mitigation. Obviously, any action that thwarts zebra mussel

dispersal will aid in the conservation of L. leptodon. Finally, The Nature Conservancy has

initiated the development and the distribution of species databases which describe what is and is

not known for specific taxa. These databases facilitate species management and research. For

example, a 1991 TNC abstract was used as a source of distribution records for this assessment.

Efforts such as this will provide a forum for researchers, government agencies, and other

interested parties to easily and effectively communicate research findings and further conservation

needs.

APPENDIX 1 - DEFINITIONS

Population Terminology (Vaughn 1993):

Local population refers to an assemblage of individuals that more or less interact with each other

in the course of their routine feeding and breeding activities

Metapopulation or river population refers the species at a regional scale at which individuals

infrequently move from one local population to another, typically across unsuitable habitat and

with risk of failure to locate another suitable patch

Species or population at the geographic scale refers to the species entire range; individuals

typically have no possibility of moving to most parts of its range.

Table Definitions:

*Last Date Collected: Last collection date regardless of condition (live, fresh dead or weathered).

*Status: A qualitative assessment of the current existence of a local population. Due to the low

population densities of current L. leptodon occurrences, ascertaining existence is difficult. Thus,

status is assigned based on the following criteria.

Extant (E) status is assigned if at least one live or fresh dead specimen has been collected

since 1980, and no evidence of significant habitat destruction since last date of collection.

Likely Extirpated (LX) status (i.e., could be extant but likely extirpated) is assigned if live

or fresh dead specimens have not been collected since 1980 despite subsequent surveys

but suitable habitat patches remain.

Extirpated (X) status is assigned if: (1) thorough post 1980 surveys have failed to find any

evidence of L. leptodon’s occurrence; or (2)virtually all suitable habitat has been

eliminated; or (3) last date of collection was before 1967.

Unknown (UK) status is assigned if: (1) specimens not collected since 1980 and no other

information is available; or (2) post 1980 surveys lacking but suitable habitat patches

remain.

*Trend: A qualitative assessment of change in a local population’s numbers and its future

condition. Although ascertaining population trend is difficult, inferences are made based on

number and age of specimens collected, date of last collection, habitat availability, and threats.

Stable (S) trend (i.e, longterm persistence is probable) is assigned if post 1980 collections

of juveniles or young adults (i.e., less than 2 years of age), and optimal habitat is available,

and no evidence of immediate threats to habitat.

Likely Stable (LS) trend (i.e., longterm persistence is possible but unsure) was assigned if:

(1) post-1980 collections of relatively young adults and good habitat is available; or (2)

post 1980 surveys with only mature live or fresh dead individuals found and optimal or

good habitat available.

Declining (D) trend (i.e., longterm persistence is tenuous) is assigned if: (1) thorough

post-1980 surveys failed to collect at least one specimen; or (2) post 1980 survey lacking

and only a limited number of specimens collected during the previous survey, and habitat

is very restricted; or (3) only mature or dead individuals found despite thorough surveys

conducted over several years.

Presumed Declining (PD) trend (i.e., existing data suggests that longterm persistence is in

doubt) is assigned if: (1) post 1980 collections of specimens (including juveniles and

young adults) and habitat is very restricted; or (2) post 1980 surveys lacking and previous

collections consist of only a few and optimal or good habitat is available.

Unknown (UK) trend is assigned if: (1) individuals have been collected since 1980 and no

other information is available; or (2) post 1980 surveys lacking and habitat quality and

quantity unknown.

Table 1: Alternate Format for Trend Categories for Extant Populations and Those of Uncertain Status

Survey and Results

Habitat

Quality and

Abundance

Post 1980;

Juveniles or

young adults

collected

Post-1980;

mature live

or fresh dead

found

Pre-1980

only; Few

individ.

collected

previously

Thorough &

post-1980;

no live or

fresh dead

shells found

Post 1980,

thorough

surveys

spanning

sev.yrs;

mature or fd

shells only

Optimal S(no threats) LS(2) PD(3) D(1) D(3)

Good LS(1) LS(2) PD(3) D(1) D(3)

Vy. Restricted PD(1) PD(1) D(2) D(1) D(3)

Unknown UK UK UK D(1) D(3)

Table 2: Leptodea leptodon population status and trend.

River

Population

Last Date

Collected*1

Status * Trend * Threats **

UPPER

MISSISSIPPI

Mississippi River

proper

(IL, IA, WI)

pre-1958 X NA NA

Minnesota River

(MN)

1800s X NA NA

Burdett’s(?Binde

tte) Slough (IA)

1890 X NA NA

Iowa River (IA) pre-1944 X NA NA

Cedar River (IA) 1882 X NA NA

Illinois River (IL) pre-1887 X NA NA

Sangamon River

(IL)

pre-1944 X NA NA

Pecatonica River

(IL)

pre-1944 X NA NA

MIDDLE

MISSISSIPPI

Kaskaskia River

(IL)

1921 X NA NA

Ohio River

Proper (KY, OH)

1897 X NA NA

Wabash River

(IL,IN)

pre-1919 X NA NA

White River (IN) pre-1919 X NA NA

Sugar Creek (IN) 1925 X NA NA

Green River (KY) 1964 X NA NA

Licking River

(KY)

pre-1950 X NA NA

Scioto River

(OH)

1838 X NA NA

Table 2: Leptodea leptodon population status and trend.

River

Population

Last Date

Collected*1

Status * Trend * Threats **

St. Mary’s River

(OH)

1930 X NA NA

E. Fork Lt.

Miami River

(OH)

~1900 X NA NA

Cumberland

River (KY, TN)

1964 X NA NA

Beaver Creek

(KY)

1948 X NA NA

Caney Fork (TN) pre-1950 X NA NA

Tennessee River

(AL,TN)

pre-1950 X NA NA

Clinch River

(TN)

pre-1950 X NA NA

Holston River

(TN)

pre-1950 X NA NA

Duck River (TN) pre-1950 X NA NA

Meramec River

(MO)

1997 E LS

Big River (MO) 1997 E PD small pop., isolated and

restricted habitat

Bourbeuse River

(MO)

1997 E LS Small population

Auxvasse Creek

(MO)

late 1960s X NA

South Grand

(MO)

early 1970s X NA NA

Missouri River

Proper (SD)

1983 X NA NA

Gasconade River

(MO)

1994 E PD Sedimentation, Small

population

Big Piney River

(MO)

1981 UK UK

Table 2: Leptodea leptodon population status and trend.

River

Population

Last Date

Collected*1

Status * Trend * Threats **

LOWER

MISSISSIPPI

St. Francis River

(AR)

1985 E D Limited habitat, Small

population, Sedimentation

White River

(AR)

1902 X NA NA

James River

(AR)

pre-1950 X NA NA

Spring River

(AR)

1991 E PD In-stream mining,

Sedimentation, Nonpoint

source pollution

S. Fork Spring

(AR)

1990 E LS Unknown

Myatt Creek

(AR)

1996 LX UK Unknown, Suspect small

population if present

Strawberry

River (AR)

1996 E UK Unknown, Suspect small

population

Middle Fork Lt.

Red River (AR)

1967 X NA NA

Poteau River

(OK)

pre-1980 X NA NA

Frog Bayou

(AR)

1979 LX PD Reservoirs, In-stream

mining, Sedimentation

S. Fourche

LaFave River

(AR)

1991 E PD Limited habitat, Small

population

Kiamichi River

(OK)

1987 E D Small population, Proposed

reservoir

Gates Creek

(OK)

pre-1971 LX PD

Little River

(OK)

1960 LX D Reservoir Impacts

Table 2: Leptodea leptodon population status and trend.

River

Population

Last Date

Collected*1

Status * Trend * Threats **

Mountain Fork

(OK)

pre-1971 LX D Reservoir-potential, Suspect

small population

Cossatot River

(AR)

1983 E UK Small population

Saline River

(AR)

1987 E UK Small population

Ouachita River

(AR)

Old museum

record

X NA NA

Lt. Missouri

River (AR)

1995 E UK Suspect small population

Saline River,

Ouachita Trib.

(AR)

1946 X NA NA

*See Note on appendix page

**See text for citation and further discussion.

1 Citation for Date Last Collected are as follows: Illinois Natural History Survey records

(Mississippi River, Burdett’s Slough, Sanagamon River, Illinois River, Kaskaskia River, Pecatonia

River, Wabash River, White River, Sugar Creek, and Kiamichi River); Clarke 1995 (St. Francis

River); Clarke 1996 (Cedar River, Big Piney River, Meramec River, Big River, E. Fork Lt.

Miami River, Licking River, Beaver Creek, Caney Fork, Tennessee River, Clinch River, Holston

River, Duck River, White River, Middle Fork Lt. Red River, AR, James River, Little River,

Ouachita River, and Saline River); Hoke 1983 (Missouri River); Buchanan 1994 (Gasconade

River); Alan Buchanan, Missouri Dept. of Nat. Res., in litt. 1997 (South Grand River and

Auxvasse Creek); Buchanan 1980 (Bourbeus River); Patricia Jones, Ohio Dept. of Nat. Res., in

litt. 1994 (Ohio River, Scioto River, and St. Mary’s River); Wayne Davis, Kentucky Dept. of

Fish and Game, pers. comm. 1994 (Green River, Beaver Creek, and Cumberland River); John

Harris, Arkansas State, pers. comm. 1995, and in litt. 1996, 1997 (Spring River, S. Fork Spring,

Myatt Creek, Strawberry River, Casatot River, Lt. Missouri River, and Saline River); Harris

1992 (S. Forche Larve River); Valentine and Stansbery 1971 (Gates Creek and Mountain

Fork); Gordon 1980 (Frog Bayou); Gordon 1991 (Mulberry River and Poteau River)

Table 2: Leptodea leptodon population status and trend.

Table 2: Leptodea leptodon population status and trend.

RIVER

DRAINAGE

DRAINAGE

SUBDIVISION

RIVER

SUBDIVISION

TRIBUTARY STATE

Upper

Mississippi

River

Mississippi River

proper

IA,IL Carroll (IL), Hancock (IA), Clayton (IA), Minnesota River MN Dakota

Burdett’s Slough IA Muscatine

Iowa River Iowa proper IA Johnson

Cedar River IA Linn

Illinois River Illinois River IL Peoria

Sanagamon

River

IL Menard

Pecatonica River IL Stephenson

Middle

Mississippi

River

Kaskaskia River IL Washington

Ohio River Ohio River

proper

KY,OH Boone (KY), Kenton Washington (OH)

Wabash River

proper

IL,IN Posey (IN), Vigo Carroll (IN), White White River IN Marian

Sugar Creek IN Parke

Green River KY Hart

Licking River KY unknown

Scioto River OH unknown

St. Mary's River OH unknown

E. Fork Lt.

Miami River

OH unknown

Table 2: Leptodea leptodon population status and trend.

RIVER

DRAINAGE

DRAINAGE

SUBDIVISION

RIVER

SUBDIVISION

TRIBUTARY STATE

Cumberland

River proper

KY,TN, AL Cumberland (KY), Colbert (AL)

Beaver Creek KY Russell

Caney Fork TN Smith

Tennessee River

proper

AL,TN Colbert (AL), Knox Clinch River TN Anderson

Holston River TN Knox

Duck River TN Unknown

Meramec River Meramec River

proper

MO Crawford, Jefferson, Big River MO Jefferson

Bourbeus River MO St. Louis, Jefferson, Missouri River Missouri River

Proper

SD Yankton

Gasconade River MO Gasconade, Osage

Big Piney

River

MO Pulaski

South Grand MO Benton

Auxvasse Creek MO Callaway

Lower

Mississippi

St. Francis River St. Francis

proper

AR St. Francis, Cross, White River White River

proper

AR Benton

James River AR Stone

Spring River

proper

AR Sharpe, Randolph, S. Fork Spring AR Fulton

RIVER

DRAINAGE

DRAINAGE

SUBDIVISION

RIVER

SUBDIVISION

TRIBUTARY STATE

Myatt Creek AR Fulton

Strawberry

River

AR Lawrence

Middle Fork Lt.

Red River

AR Van Buren

Arkansas River

Mulberry River AR Unknown

Frog Bayou AR Sevier

Poteau River OK LeFlore

South Fourche

LaFave River

AR Perry

Red River

Kiamichi River OK Choctaw, Pushmataha.

Gates Creek OK Pushmataha

Little River OK McCurtain

Mountain Fork OK McCurtain

Casatot River AR Sevier

Saline River AR Sevier, Howard

Ouachita River AR Clark

Lt. Missouri

River

AR Clark

Saline River AR Cleveland

* The exact locations of Leptodea leptodon collections was not given (Clarke 1985).

Table 4: State Legal Status and Population Trend

STATE STATE LEGAL STATUS POPULATION STATUS

Alabama None (Extirpated1) Extirpated

Arkansas None (Threatened1) Extant

Illinois Extirpated Extirpated

Indiana Extirpated Extirpated

Iowa Extirpated Extirpated

Kentucky Extirpated Extirpated

Minnesota None (Extirpated) Extirpated

Missouri Rare2 Extant

Ohio Extirpated Extirpated

Oklahoma Species of Concern Extant

South Dakota None Extirpated

Tennessee Extirpated Extirpated

Wisconsin Extirpated Extirpated

1Species experts' unofficial designation

2 State considering elevating to endangered status (Sue Bruenderman, Missouri DOC, pers.

comm. 1998).

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CONTACT LIST

Steve Ahlstedt (1995) Tennessee Valley Authority,

Aquatic Biology Dept., P.O. Box 460

Norris, TN 37828 615/494-9800

Bob Anderson U.S. Geological Survey

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Pittsburg, PA 15222 412/644-2278

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