[Federal Register: October 9, 2001 (Volume 66, Number 195)]
[Rules and Regulations]               
[Page 51322-51339]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]



Fish and Wildlife Service

50 CFR Part 17

RIN 1018-AF57

Endangered and Threatened Wildlife and Plants; Determination of 
Endangered Status for the Scaleshell Mussel

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.


SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine 
the scaleshell mussel (Leptodea leptodon) to be an endangered species 
under the Endangered Species Act of 1973, as amended (Act). The 
scaleshell mussel historically occurred in 55 rivers in 13 states in 
the eastern United States. Currently, the species is known to exist in 
14 rivers (and may occur in 6 others) within the Mississippi River 
Basin in Missouri, Oklahoma, and Arkansas. Its abundance and 
distribution have decreased markedly due to habitat loss and adverse 
effects associated with water quality degradation, sedimentation, 
channelization, sand and gravel mining, dredging, and reservoir 

DATES: This final rule is effective on November 8, 2001.

ADDRESSES: The complete file for this rule is available for inspection, 
by appointment, during normal business hours at the Columbia Field 
Office, U.S. Fish and Wildlife Service, 608 East Cherry Street, Room 
200, Columbia, Missouri 65201.

FOR FURTHER INFORMATION CONTACT: Andy Roberts (at the above address or 
telephone 573-876-1911, ext. 110; fax 573-876-1914). TTY users may 
contact us through the Federal Relay Service at 1-800-877-8339.



    Buchanan (1980), Cummings and Mayer (1992), Oesch (1995), and 
Watters (1995) provide descriptions of the scaleshell mussel. The shell 
grows to approximately three to ten centimeters (one to four inches) in 
length. The shells are elongate, very thin, and compressed. The 
anterior (front) end is rounded. In males, the posterior (rear) end is 
bluntly pointed. In females, the periostracum (the outside layer or 
covering of the shell) forms a wavy, fluted extension of the posterior 
end of the shell. The dorsal (top) margin is straight and the ventral 
(bottom) margin is gently rounded. Beaks (the raised or domed part of 
the dorsal margin of the shell) are small and low, and nearly even with 
the hinge line. The beak sculpture is inconspicuously compressed 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 (the triangular, often serrated, teeth located on 
the upper part of the shell) are reduced to a small thickened ridge. 
The lateral teeth (the elongated teeth along the hinge line of the 
shell) are moderately long with two indistinct teeth occurring in the 
left valve (shell) and one fine tooth in the right. The beak cavity (a 
cavity located inside the shell that extends into the beak) is very 
shallow. The nacre (the interior layer of the shell) is pinkish white 
or light purple and highly iridescent.

Life History

    The biology of the scaleshell mussel is similar to the biology of 
other bivalved mollusks belonging to the family Unionidae. Adult 
unionids are filter-feeders, spending their entire lives partially or 
completely buried in the stream bottom (Murray and Leonard 1962). The 
posterior margin of the shell is usually exposed and the siphons 
extended to facilitate feeding. During periods of activity, movement is 
accomplished by extending and contracting a single muscular foot 
between the valves. Extension of the foot also enables the mussel to 
wedge itself into the river bottom. Their food includes detritus 
(disintegrated organic material), plankton, and other microorganisms 
(Fuller 1974). Some freshwater mussel species are long-lived. 
Individuals of many species live more than 10 years and some have been 
reported to live over 100 years (Cummings and Mayer 1992).
    Unionids have an unusual and complex mode of reproduction, which 
includes a brief, obligatory parasitic

[[Page 51323]]

stage on fish. Males release sperm into the water column in the spring, 
summer, or early fall, and females using the incurrent water flow draw 
in the sperm. Fertilization takes place in the shell of the female. 
Fertilized eggs develop into microscopic larvae (glochidia) and are 
brooded within special gill chambers of the female. Once the glochidia 
are mature, they are expelled into the water where they must quickly 
attach to the gills or the fins of an appropriate fish host to complete 
development. Following proper host infestation, glochidia transform 
into juveniles and excyst (drop off). Juveniles must drop off into 
suitable habitat to survive. Host fish specificity varies among 
unionids. Some mussel species appear to require a single host species, 
while others can transform their glochidia into juvenile mussels on 
several fish species. For further information on the life history of 
freshwater mussels, see Gordon and Layzer (1989) and Watters (1995).
    Mussel biologists know relatively little about the specific life 
history requirements of the scaleshell mussel. Baker (1928) surmised 
that the scaleshell mussel is a long-term brooder (spawns in fall 
months and females brood the larvae in their gills until the following 
spring or summer). Glochidia found in the gill chambers in September, 
October, November, and March support that conclusion (Gordon 1991). The 
scaleshell mussel uses the freshwater drum (Aplodinotus grunniens) as 
the fish host for its larvae (Chris Barnhart, Southwest Missouri State 
University, pers. comm. 1998). Other species in the genus Leptodea and 
a closely related genus Potamilus are also known to use freshwater drum 
exclusively as a host (Watters 1994).
    Little is known about the life expectancy of the scaleshell mussel. 
However, recent collections from Missouri indicate that it is 
relatively short-lived compared to other species. A sample of 33 dead 
specimens and 2 living individuals collected in 2000 from a Gasconade 
River site did not contain any individuals exceeding seven years old 
(Chris Barnhart, pers. comm. 2000). Likewise, no individuals over six 
years old were observed out of 44 living individuals collected in 1997 
from the Meramec Basin (Roberts and Bruenderman 2000). Based on these 
collections, it appears that the life expectancy of the scaleshell 
mussel may be less than 10 years. In addition, the sex ratio of the 
above collections are significantly different from a 50/50 ratio (Chi-
Square Test, P 0.05). The Gasconade collection only contained eight 
females (including one living) out of 35 individuals, and the Meramec 
Basin collection only contained 15 females out of 44 living 
individuals. The reason females appear to be less common than males in 
the Gasconade River and Meramec Basin is unknown.

Habitat Characteristics

    The scaleshell mussel occurs in medium to large rivers with low to 
moderate gradients in a variety of stream habitats. Buchanan (1980, 
1994) and Gordon (1991) reported the scaleshell mussel from riffle 
areas with substrate consisting of gravel, cobble, boulder, and 
occasionally mud or sand. Oesch (1995) considered the scaleshell mussel 
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 medium-sized and large rivers. Roberts and Bruenderman 
(2000) collected the scaleshell mussel primarily from mussel beds 
(areas with a high concentration of mussels that contain more than one 
species) with stable, gravel substrates. The characteristic common to 
these sites appears to be a stable stream bed and good water quality. 
These habitat observations are consistent with the current distribution 
of the scaleshell mussel. The scaleshell mussel is restricted to rivers 
that have maintained relatively good water quality (Oesch 1995) and to 
river stretches with stable channels (Buchanan 1980, Harris 1992). The 
scaleshell mussel is also usually collected in mussel beds in 
association with a high diversity of other mussel species.

Distribution and Abundance

    The scaleshell mussel historically occurred in 13 states in the 
eastern United States. While the scaleshell mussel had a broad 
distribution, it appears that it was a rare species locally (Gordon 
1991, Oesch 1995, Call 1900). Williams et al. (1993) reported the 
historical range as Alabama, Arkansas, Illinois, Indiana, Iowa, 
Kentucky, Missouri, Ohio, Oklahoma, South Dakota, Tennessee, and 
Wisconsin. Historical records also exist for the Minnesota River, 
Minnesota (Clarke 1996). Williams et al. (1993) also listed Michigan 
and Mississippi as part of the scaleshell mussel's range, but no valid 
records exist in these states. Therefore, its presence cannot be 
confirmed (Bob Jones, Mississippi Wildlife Fisheries and Parks, Museum 
of Natural Science, pers. comm. 2000; Szymanski 1998). Gordon (1991) 
included a portion of the St. Lawrence drainage in describing the 
distribution of the scaleshell mussel. However, the specimens that were 
the source of the St. Lawrence River record were later identified as 
wingless examples of Leptodea fragilis (fragile papershell), which are 
often seen in New York (David Strayer, Institute of Ecosystem Studies, 
New York, in litt. 1995). Given this and that no other authentic 
specimens have been found (David Stansbery, Ohio State Museum, in litt. 
1995), the historical occurrence of the species in St. Lawrence Basin 
is doubtful.
    Within the last 50 years the scaleshell mussel has become 
increasingly rare and its range greatly restricted. Historically, the 
scaleshell mussel occurred in 55 rivers. Today, the species is known 
from only 14 rivers including the Meramec, Bourbeuse, Big, Gasconade, 
and Osage Rivers in Missouri; Frog Bayou and the St. Francis, Spring, 
South Fork Spring, South Fourche LaFave, and White Rivers in Arkansas; 
and the Little, Mountain Fork, and Kiamichi Rivers in Oklahoma. An 
additional six rivers (Cossatot, Little Missouri, Saline, and 
Strawberry Rivers, and Myatt and Gates Creeks) in Arkansas and Oklahoma 
may support the scaleshell mussel, but the existence of the species in 
these rivers is uncertain. With the exception of the Meramec, 
Bourbeuse, and Gasconade Rivers, all rivers listed as supporting the 
scaleshell mussel are based on the collection of a few or a single 
individual specimen.

Assessment of the Presumed Health of Individual Populations

    For the purposes of this rule, the term ``population'' is used in a 
geographical sense and, unless otherwise indicated, is defined as all 
individuals living in one river or stream. By using this term we do not 
imply that a scaleshell mussel population is currently reproducing or 
that it is a distinct genetic unit. Using the term in this way allows 
the status, trends, and threats to be discussed separately for each 
river where the scaleshell mussel occurs, improving the clarity of the 
    Due to the low densities of current scaleshell mussel populations, 
ascertaining status (an assessment of the current existence of a 
population) and trends (an assessment of change in a population's 
numbers and its probable future condition) is difficult. To facilitate 
population comparisons, a single classification system was devised to 
evaluate the probable current health of individual populations. The 
indicators of (or criteria for) the presumed health of scaleshell 
mussel populations are as follows. The

[[Page 51324]]

presumed health of a population is considered ``stable'' if (1) there 
is no evidence of significant habitat loss or degradation, and (2) 
there has been post-1980 collection of live or fresh dead mussels and, 
if surveys were thorough, evidence of recruitment was found. The 
presumed health of a population is considered ``declining'' if (1) 
habitat is limiting due to its small size, or a significant decrease in 
habitat quality or quantity has occurred, (2) there is no evidence of 
recruitment despite one or more thorough surveys, or (3) a significant 
decline in number of individual mussels has occurred. The presumed 
health of a population is considered ``extirpated'' if (1) despite one 
or more thorough post-1980 surveys, no scaleshell mussels, or only old 
dead shells, have been found, or (2) all known suitable habitat has 
been destroyed. The presumed health of a population is considered 
``unknown'' if the available information is inadequate to place the 
population in one of the above categories. In a few cases, additional 
biological information not listed above was used to categorize a 
population that otherwise would have been called ``unknown'' or which 
appeared to fit into multiple categories.
    Based on the above criteria, 14 scaleshell mussel populations are 
considered extant. Of these populations, the presumed health of 1 is 
thought to be stable and 13 are believed to be declining. Six other 
populations may also be extant, but their health is unknown due to lack 
of recent collections or surveys. The 14 extant populations and 6 
potentially extant populations are listed in Table 1 and included in 
the discussions below.

  Table 1.--Presumed Population Health of Extant and Potentially Extant
 Scaleshell Mussel Populations. S = stable, D = declining, UK = unknown
                 Population                        Presumed health
Big (MO)...................................  D
Bourbeuse (MO).............................  D
Cossatot (AR)..............................  UK
Frog Bayou (AR)............................  D
Gates Creek (OK)...........................  UK
Gasconade (MO).............................  D
Kiamichi (OK)..............................  D
Little Missouri (AR).......................  UK
Little (OK)................................  D
Meramec (MO)...............................  D
Mountain Fork (OK).........................  D
Myatt Creek (AR)...........................  UK
Osage River (MO)...........................  D
St. Francis (AR)...........................  D
Saline (AR)................................  UK
South Fork Spring (AR).....................  S
South Fourche LaFave (AR)..................  D
Spring River (AR)..........................  D
Strawberry (AR)............................  UK
White River (AR)...........................  D

River Basin Specific Discussion of the Scaleshell Mussel Status

Upper Mississippi River Basin

    The scaleshell mussel formerly occurred in eight rivers and 
tributaries within the upper Mississippi River Basin, including the 
Mississippi River in Illinois, Iowa, and Wisconsin; the Minnesota River 
in Minnesota; Burdett's Slough in Iowa; the Iowa and Cedar Rivers in 
Iowa; and the Illinois, Sangamon, and Pecatonica Rivers in Illinois. 
However, the scaleshell mussel has not been found for more than 50 
years in the upper Mississippi River Basin and is believed extirpated 
from that basin (Kevin Cummings, Illinois Natural History Survey, in 
litt. 1994).

Middle Mississippi River Basin

    Historically, the scaleshell mussel occurred in 26 rivers and 
tributaries within the middle Mississippi River Basin including the 
Kaskaskia River in Illinois; the mainstem Ohio River in Kentucky and 
Ohio; the Wabash River in Illinois and Indiana; the White River and 
Sugar Creek in Indiana; the Green and Licking Rivers in Kentucky; the 
Scioto, St. Mary's, and East Fork Little Miami Rivers in Ohio; the 
Cumberland River in Kentucky and Tennessee; Beaver Creek in Kentucky; 
Caney Fork in Tennessee; the Tennessee River in Alabama and Tennessee; 
the Clinch, Holston, and Duck Rivers in Tennessee; Auxvasse Creek in 
Missouri; the Meramec, Bourbeuse, South Grand, Gasconade, Big, Osage, 
and Big Piney Rivers in Missouri; and the mainstem Missouri River in 
South Dakota and Missouri. The scaleshell mussel has been extirpated 
from most of the middle Mississippi River Basin. Currently, the 
scaleshell mussel is extant in five rivers within the Meramec River 
basin and tributaries of the Missouri River drainages in Missouri.
    Ohio River Drainage--The scaleshell mussel has been extirpated from 
the entire Ohio River system. The most recent collection date from the 
Ohio River Basin is 1964 from the Greene River (Wayne Davis, Kentucky 
Department of Fish and Wildlife, in litt. 1994). All other records are 
pre-1950 (Kevin Cummings, in litt. 1994; Catherine Gremillion-Smith, 
Indiana Department of Natural Resources, in litt. 1994; Ron Cicerello, 
Kentucky Department of Fish and Wildlife, in litt., 1994; Paul 
Parmelee, University of Tennessee, pers. comm. 1995).
    Meramec River Basin (Missouri)--In 1979, Buchanan surveyed for 
mussels at 198 sites within the Meramec River Basin (Buchanan 1980). Of 
these sites, 14 had evidence of live or dead scaleshell mussels. Seven 
of the 14 sites were in the lower 180 kilometers (km) (112 miles (mi)) 
of the Meramec River, five in the lower 87 km (54 mi) of the Bourbeuse 
River, and two in the lower 16 km (10 mi) of the Big River. Buchanan 
found that the species comprised less than 0.1 percent of the 20,589 
living mussels he examined in the basin. He collected live scaleshell 
mussels at only four sites, three in the Meramec and one in the 
Bourbeuse. Although the lower 174 km (108 mi) of the Meramec River had 
suitable habitat for many rare species, live scaleshell mussels were 
found only in the lower 64 km (40 mi) (Buchanan 1980). Both the 
Bourbeuse and Big Rivers had lower species diversity and less suitable 
habitat than the Meramec River. Suitable habitat occurs only in the 
lower 87 km (54 mi) of the Bourbeuse River and lower 16 km (10 mi) of 
the Big River (Buchanan 1980).
    The Missouri Department of Conservation (MDC) sampled 78 sites in 
an intensive resurvey of the Meramec River basin in 1997 (Roberts and 
Bruenderman 2000). Similar to Buchanan's findings (1980), scaleshell 
mussels represented only 0.4 percent of the living mussels. Live 
specimens were collected from the mainstem Meramec River (34 specimens 
from 9 sites), the Bourbeuse River (10 specimens from 5 sites), and the 
Big River (2 specimens from 1 site). In addition to the nine sites 
surveyed by Buchanan (1979), new sites were included in the 1997 
survey. Living or dead scaleshell mussels were found at four of the 
five sites in the Meramec River and two of the four sites in the 
Bourbeuse River. The three sites where the presence of scaleshell 
mussels was not reconfirmed no longer support suitable mussel habitat 
due to stream bed degradation. Other species that were found in mussel 
beds at those sites in the earlier surveys were no longer present in 
1997. Although portions of the Meramec River basin continue to provide 
suitable habitat, mussel species diversity and abundance have declined 
noticeably since 1980 and

[[Page 51325]]

significant losses of mussel habitat have occurred (Roberts and 
Bruenderman 2000).
    The number of scaleshell mussel specimens the MDC collected in 1997 
is greater than that reported by Buchanan's study (Buchanan 1980); 
however, the small number of specimens collected, especially from the 
Bourbeuse and Big Rivers, indicates that the long-term viability of 
these populations is tenuous. Moreover, the long-term persistence of 
populations in the Meramec Basin is in question because of the limited 
availability of mussel habitat and the loss of mussel beds since 1980 
from bank and channel degradation, sedimentation, and eutrophication 
(excessive fertilization caused by pollution of plant nutrients) 
(Roberts and Bruenderman 2000; Alan Buchanan, MDC, in litt. 1997; Sue 
Bruenderman, MDC, pers. comm. 1998).
    Missouri River drainage (South Dakota and Missouri)--Within the 
Missouri River drainage, Buchanan (1980, 1994) and Oesch (1995) 
reported scaleshell mussels from the Missouri, Gasconade, Big Piney, 
South Grand, Osage Rivers, and Auxvasse Creek. The last collection of 
scaleshell mussels from Auxvasse Creek was in the late 1960s (Alan 
Buchanan, in litt. 1997). Similarly, the last known collection date for 
the South Grand is the early 1970s. This collection site is now 
inundated by Truman Lake and is unsuitable for the scaleshell mussel 
(Alan Buchanan, in litt. 1997). A single, fresh dead specimen was 
collected from Big Piney River in 1981 (Sue Bruenderman, in litt. 
1998). However, the scaleshell mussel has not been found in recent 
surveys of this river. Between 1994 and 1996, 70 sites were sampled in 
the Big Piney River from the mouth to the headwaters. While 3,331 
mussels of 26 species were collected, no evidence of scaleshell mussels 
were found (Janet Sternberg, MDC, pers. comm. 2000). Another survey was 
conducted in 1998, in which 10 sites were sampled between river miles 
53.6 and 96.0. Over 1,000 living mussels were collected representing 15 
species, but no living or dead scaleshell mussels were found (Sue 
Bruenderman, pers. comm. 2000).
    Only two records (both single dead shells) of scaleshell mussels 
exist for the mainstem of the Missouri River. In 1981 and 1982, the 
Missouri River was surveyed from Santee to Omaha, Nebraska (Hoke 1983). 
A single fresh dead shell was found during this study just below 
Gavin's Point Dam, South Dakota. This occurrence represents the 
westernmost record of the scaleshell mussel in North America. However, 
this species has not been found in subsequent surveys on the Missouri 
River just below Gavin's Point dam. In 1995, Clarke (1996) found no 
evidence of scaleshell mussels in a survey conducted from Gavin's Point 
Dam to 48 river km (30 mi) downstream. However, high water conditions 
limited Clark's search efforts, and only 10 individual mussels were 
found. In 1999, the Omaha District of the U.S. Army Corps of Engineers 
(Corps) funded a mussel survey between Gavin's Point Dam and Ponca, 
Nebraska, a distance of 96 river km (60 mi). In all, 355 live and 1,709 
dead individual mussels were collected representing 16 species, but no 
living or dead scaleshell mussels were found (Candace M. Gordon, Corps, 
Omaha District, in litt. 2000). The second scaleshell mussel record 
from the mainstem of the Missouri River is a single fresh dead 
individual that was collected in 1990 from Gasconade County, Missouri. 
This specimen was found during an extensive survey conducted from 
Gavin's Point Dam to St. Louis (Hoke 2000). However, the site of this 
collection was subsequently destroyed.
    Since no living scaleshell mussel has been found in the Missouri 
River, its habitat cannot be determined. However, both dead shells were 
collected from areas shielded from the main flow of the river in 
relatively stable, sandy bottoms with moderate current (Hoke 2000). 
Hoke (2000) described scaleshell mussel as ``extremely rare'' and its 
habitat ``very uncommon * * * and existing in only widely separated 
locals'' in the Missouri River. Based on the criteria used to assign 
presumed health to scaleshell mussel populations (Table 1), we consider 
this potential population to be extirpated at this time. Of the two 
known Missouri River records for scaleshell mussel, one locality has 
been destroyed and recent surveys have not found any evidence of this 
species at or in the vicinity of the other site. Further, no other 
scaleshell mussel specimens were found during Hoke's survey from 
Gavin's Point Dam to St. Louis. More information is needed on the 
existence of the scaleshell mussel and its habitat in the Missouri 
River. Furthermore, more information is needed on the location of 
sampling sites, distribution and habitat use of mussels, etc. from 
Hoke's survey work on the Missouri River, which is unavailable at this 
    Buchanan (1994) surveyed the lower 137 km (85 mi) of the Gasconade 
River, and documented 36 species of freshwater mussels. He collected 
scaleshell mussel specimens at eight sites between river miles 6.0 and 
57.7. Buchanan found only dead shells at two sites and eight live 
specimens from the remaining six sites. Overall, scaleshell mussels 
comprised less than 0.1 percent of the mussels collected. In 1998-99, 
the Gasconade River was surveyed at 46 sites from mile 92.0 to 256.0. 
At sites where scaleshell mussels were collected, living individuals 
represented less than 0.5 percent of the total number of mussels found. 
A total of 12 living scaleshell mussels were found at 9 sites, and dead 
shells were found at an additional 10 sites between river miles 92.0 
and 230.3 (Sue Bruenderman, pers. comm. 2000).
    A scaleshell mussel has recently been discovered in the lower Osage 
River in Osage County, Missouri. On July 16, 2001, one live male 
specimen was found at river mile 20 (Heidi Dunn, pers. comm.). This 
individual was found during a mussel survey that is currently underway 
in the lower 80 miles of the Osage River and its tributaries. To date, 
33 sites have been surveyed including 24 in the mainstem. A total of 
3,904 living mussels have been found representing 29 living species. No 
other evidence of scaleshell mussels were found during the survey, but 
more intensive sampling is planned for these same sites in the near 
    Until this recent discovery, the scaleshell mussel had never been 
reported from the Osage system in past surveys. Utterback (1917) found 
34 species in the basin. No other information is available because his 
notes and collections have since been lost. Oesch (1995) collected 
mussels in the 1970s at a number of sites in the basin and reported 39 
species. In 1980, a detailed study of mussel distribution was conducted 
by Grace and Buchanan (1981) of the Lower 80 miles of the Osage River 
and two tributaries below Bagnell Dam. A total of 43 sites were 
surveyed and 21,593 living mussels were found representing 36 species. 
No evidence of scaleshell mussels was found in any of these surveys.
    This new record of the scaleshell mussel does not significantly 
increase its range or lessen its risk of extinction. Similar to other 
records for the species, the one individual found indicates that a 
small population is present. No other evidence of the species was found 
during the 2001 survey. If a significant population of scaleshell 
mussels existed in the Osage River, dead shells would have been found. 
This is because dead shells accumulate over time, which makes them 
easier to detect than live specimens. Additionally, there are 
significant threats to scaleshell mussel in the Osage River from the 
operation of Bagnell Dam and instream gravel mining. Due to these 
habitat conditions, we categorized the Osage River

[[Page 51326]]

scaleshell mussel population's presumed health as declining.
    Middle Mississippi River Basin summary--Of the 26 rivers and 
tributaries in the middle Mississippi River Basin that historically 
supported scaleshell mussels, the species is still present in 5 
including the Meramec, Bourbeuse, Big, Osage, and Gasconade Rivers. The 
presumed health of all of these populations is thought to be declining.

Lower Mississippi River Basin

    The scaleshell mussel historically occupied 21 rivers and 
tributaries in the lower Mississippi River Basin. These include the St. 
Francis, White, James, Spring, Little Missouri, Middle Fork Little Red, 
Saline (of the Ouachita River), Ouachita, Cossatot, Saline (of the 
Little River), South Fourche LaFave, Mulberry, and Strawberry Rivers in 
Arkansas; South Fork Spring, Frog Bayou, and Myatt Creek in Arkansas; 
Poteau, Little, and Kiamichi Rivers in Oklahoma; and Gates Creek and 
Mountain Fork in Oklahoma. These rivers are organized and discussed 
below according to drainage (St. Francis, White, Arkansas, and Red 
River drainages).
    St. Francis River drainage (Arkansas)--Bates and Dennis (1983), 
Clarke (1985), and Ahlstedt and Jenkinson (1987) conducted mussel 
surveys on the St. Francis River in Arkansas and Missouri. Of these 
surveys, scaleshell mussels were only documented from two sites, both 
of which are single-specimen records (Clarke 1985). Records of dead 
shells of various species indicate that at one time freshwater mussels 
occurred throughout the river (Bates and Dennis 1983). Bates and Dennis 
(1983) determined that of the 54 sites sampled, 15 were productive, 10 
marginal, and 29 had either no shells or dead specimens only; 
scaleshell mussels were not documented at any of the 54 sites. They 
identified 77 km (48 mi.) of habitat generally suitable for mussels: 
Wappapello Dam to Mingo Ditch, Missouri; Parkin to Madison, Arkansas; 
and Marianna to the confluence with the Mississippi River at Helena, 
Arkansas. They indicated that the remaining portions of the river were 
no longer suitable for mussels. If the scaleshell mussel is extant in 
the St. Francis River, it is restricted to the few patches of suitable 
    White River drainage (Arkansas)--Clarke (1996) noted a 1902 
collection of a single specimen from the White River near Garfield, 
Arkansas. A late 1970s survey of the White River between Beaver 
Reservoir and its headwaters failed to relocate live or dead scaleshell 
mussel individuals. However, in 1999, a single live specimen was 
collected from the White River near Newport by John Harris (John 
Harris, Arkansas Department of Transportation, pers. comm. 2000). 
Navigation maintenance activities have relegated the mussel fauna to a 
few refugial sites (Bates and Dennis 1983). Specimens have not been 
collected from the James River, a tributary of the White River, since 
before 1950 (Clarke 1996).
    An eight-mile section of the Spring River in Arkansas supports a 
diverse assemblage of freshwater mussels (Gordon et al. 1984, Arkansas 
Highway and Transportation Dept 1984, Miller and Hartfield 1986). The 
collections from this river total eight scaleshell mussel specimens 
(Kevin Cummings, in litt. 1994; Clarke 1996, Arkansas State Highway and 
Transportation Department, 1984). Gordon et al. (1984) surveyed the 
river and reported suitable mussel habitat between river miles 3.2 and 
11.0, although species richness below river mile 9 had declined 
markedly compared to past surveys. Gordon et al. (1984), as well as 
Miller and Hartfield (1986), reported that the lower 5.0 km (3.0 mi) of 
river were completely depleted of mussels and contained no suitable 
habitat. Harris did not find scaleshell mussels in a 1993 survey of the 
Spring River (John Harris, in litt. 1997).
    Scaleshell mussels were collected from the South Fork of the Spring 
River in 1983 and 1990. During the 1983 survey, Harris (in litt. 1997) 
collected four specimens near Saddle, Arkansas, and one specimen and 
one valve north of Hunt, Arkansas. During a subsequent visit in 1990, 
Harris collected young adults (Harris, pers. comm. 1995). Although 
juveniles were not found, the presence of young adults suggests that 
reproduction recently occurred.
    Records of scaleshell mussels from the Strawberry River and the 
Myatt Creek are based on single specimen collections, both made in 1996 
(John Harris, in litt. 1997). Harris collected a live specimen from the 
Strawberry River near the confluence with Clayton Creek in Lawrence 
County. He also collected a single relict (a weathered shell that has 
been dead a long period of time) specimen from Myatt Creek in Fulton 
County (John Harris, in litt. 1997). Comprehensive surveys have not 
been conducted in these rivers since 1996.
    The historical locality (near Shirley, Van Buren County, Arkansas) 
where a single scaleshell mussel specimen was collected from the Middle 
Fork of the Little Red River no longer provides mussel habitat. Clarke 
(1987) stated that suitable mussel habitat was restricted to a 9.6 km 
(6.0 mi) stretch from the confluence of Tick Creek upstream to the 
mouth of Meadow Creek.
    Arkansas River drainage (Oklahoma and Arkansas)--The scaleshell 
mussel has been collected from the following streams from the Arkansas 
River drainage: Poteau River in Oklahoma (Gordon 1991), Frog Bayou in 
Arkansas (Harris and Gordon 1987), and the South Fourche LaFave and 
Mulberry Rivers in Arkansas (Gordon 1991; Harris 1992). A single 
scaleshell mussel specimen was collected in the Poteau River (Gordon 
1980). However, it has not been documented in subsequent surveys of 
this river (Branson 1984; Harris 1994). The existence of scaleshell 
mussels in Poteau River is doubtful.
    Gordon (1980) collected two scaleshell mussel specimens from Frog 
Bayou. Beaver Reservoir now inundates one of the Frog Bayou collection 
sites. The most recent collection was a fresh dead individual during a 
1979 survey (Gordon 1980). Gordon noted that stream bank bulldozing 
upstream recently disturbed this site and other nearby sites. 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, two reservoirs 
impact the river; one near Maddux Spring and the other at Mountainburg. 
Live mussels have not been found at the confluence of the Arkansas 
River, likely due to dredging activities (Gordon 1980). Although the 
current status of the scaleshell mussel in Frog Bayou is uncertain, any 
remaining individuals are in potential jeopardy due to limited habitat 
and in-stream mining activities.
    The only scaleshell mussel record from the South Fourche LaFave 
River is based on a single live specimen found in 1991 (Harris 1992). 
An 86-acre reservoir is approved for construction on Bear Creek 
approximately six miles upstream from this site. However, the effect of 
this impoundment on scaleshell mussels is uncertain. The potential for 
discovering additional scaleshell mussel sites in this river is 
unlikely due to the limited availability of suitable substrate. 
Similarly, other major tributaries of the South Fourche LaFave River 
provide little mussel habitat. Like Frog Bayou, the persistence of 
scaleshell mussels in this river is in doubt.
    Although Gordon (1991) reported scaleshell mussels from the 
Mulberry River, documentation is lacking. Recent surveys did not find 
the species in the Mulberry River (Craig Hilborne, U.S. Forest Service, 
pers. comm. 1995;

[[Page 51327]]

Stoeckel et al. 1995). The existence of scaleshell mussels in the 
Mulberry River is unlikely.
    Red River drainage (Oklahoma and Arkansas)--The scaleshell mussel 
has been documented from the following streams in the Red River 
drainage: the Kiamichi River, Gates Creek, Little River, Mountain Fork; 
and the Cossatot, Ouachita, Little Missouri, and Saline Rivers. Isley 
(1925) first collected scaleshell mussels from the Kiamichi River in 
1925. Based on his account, the Kiamichi River historically supported a 
diverse and abundant mussel fauna. He collected 36 scaleshell mussel 
specimens at one of 22 stations visited. A single specimen was also 
collected from Gates Creek, a tributary of the Kiamichi River, by 
Valentine and Stansbery (1971). As recently as 1987, Clarke described 
the Kiamichi River as ``in remarkably good condition'' and a ``faunal 
treasure'' (Clarke 1987). However, despite extensive searches of the 
Kiamichi River over the last 11 years, only a single fresh dead shell 
of scaleshell mussel (in 1987) has been collected (Caryn Vaughn, 
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 dead shell during three 
years (1993-1996) of surveys in the Red River Basin. However, the 
mussel habitat in the Kiamichi River is in relatively good condition 
above the Hugo Reservoir (Clarke 1987) and may still support a remnant 
population of scaleshell mussels.
    Although there is no evidence of scaleshell mussels persisting in 
the Little River, healthy mussel beds exist above the Pine Creek 
Reservoir (Caryn Vaughn, in litt. 1997). Below Pine Creek Reservoir, 
the mussel fauna is severely depleted but recovers with increasing 
distance from the impoundment (Caryn Vaughn, in litt. 1997). Although 
scaleshell mussels have not been documented during extensive surveys 
throughout the length of the Little River, suitable habitat remains and 
the species may persist (Caryn Vaughn, in litt. 1997). However, the 
discharge of reservoir water from Pine Creek and periodic discharge of 
pollution from Rolling Fork Creek may seriously impact any remaining 
viable scaleshell mussel populations and prohibit any future 
recolonization (Clarke 1987). Valentine and Stansbery (1971) reported a 
single specimen from Mountain Fork. Clarke (1987) hypothesized that, 
based on the presence of mussels 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 areas have been severely depleted with most no longer 
containing live mussels.
    If scaleshell mussels still occur in the Red River drainage in 
Oklahoma, extant populations are probably small and are likely 
restricted to isolated areas of suitable habitat in the Kiamichi and 
Mountain Fork Rivers. Given the extensive survey effort over the last 
decade, long-term survival of the scaleshell mussel in Oklahoma is 
    Harris collected single scaleshell mussel specimens from the 
Cossatot and Saline Rivers in Arkansas in 1983 (John Harris, in litt. 
1997) and 1987 (John Harris, pers. comm. 1995), respectively. No other 
information is available for either river.
    The existence of scaleshell mussels in the Ouachita River and its 
two tributaries, the Saline River and Little Missouri River, is 
questionable as well. Both the Little Missouri and Saline Rivers 
records are based on single specimens. The Saline River specimen was 
collected in 1964 (Clarke 1996), and the Little Missouri River 
collection record is from 1995 (John Harris, in litt. 1997). Four 
undated museum specimens of scaleshell mussels from the Ouachita River 
in Arkadelphia, Clark County, Arkansas are listed in Clarke (1996), but 
details are unavailable. Based on the few collections and the limited 
habitat available, the long-term persistence of scaleshell mussel in 
Cossatot, Saline, Little Missouri, and Ouachita Rivers appears 
    Lower Mississippi River Basin summary--Of these 21 rivers and 
tributaries in the lower Mississippi River Basin that historically 
supported scaleshell mussels, nine, and possibly an additional six, 
support the species today. Of these populations, the South Fork Spring 
River could possibly be stable; the St. Francis River, Kiamichi River, 
Little River, Mountain Fork, Spring River, Frog Bayou, South Fourche 
LaFave River, and White River are presumed to be declining; and the 
status of the Myatt and Gates Creeks and the Strawberry, Cossatot, 
Saline, and Little Missouri Rivers populations are unknown.

Previous Federal Action

    We had identified the scaleshell mussel as a Category 2 candidate 
species in a notice of review published in the Federal Register on May 
22, 1984 (49 FR 21664). The scaleshell mussel remained a Category 2 
candidate species in subsequent notices including January 6, 1989 (54 
FR 554), November 21, 1991 (56 FR 58804), and November 15, 1994 (59 FR 
58982). Prior to 1996, a Category 2 candidate species was one that we 
were considering for possible addition to the Federal List of 
Endangered and Threatened Wildlife, but for which conclusive data on 
biological vulnerability and threats were not available to support a 
proposed rule. We discontinued designating Category 2 species in the 
February 28, 1996, Notice of Review (61 FR 7596). We now define a 
candidate species as a species for which we have on file sufficient 
information on biological vulnerability and threats to support issuance 
of a proposed rule. We designated the scaleshell mussel as a candidate 
species on October 16, 1998.
    On August 13, 1999 (64 FR 44171), we published a proposal to list 
the scaleshell mussel as an endangered species and opened a 60-day 
comment period on the proposal. On November 29, 1999 (64 FR 66600), we 
reopened the comment period for 39 days in order to hold a public 
hearing. The hearing was held in Jefferson City, Missouri, on December 
8, 1999.

Summary of Comments and Recommendations

    In the August 13, 1999, proposed rule, and through associated 
notifications, we requested all interested parties to submit factual 
reports or information that might contribute to the development of a 
final rule. We contacted appropriate Federal and State agencies, County 
governments, scientific organizations, and interested parties and 
requested their comments. We published notices inviting public comment 
in the following newspapers in 1999: The Chicago Sun Times, The Chicago 
Tribune, The Peoria Journal Star, State Journal-Register, The Journal 
Gazette Co., The Indianapolis Star, The Columbia Daily Tribune, The 
Kansas City Star, The St. Louis Post-Dispatch, The South Bend Tribune, 
The Cedar Rapids Gazette, Quad City Times, The Des Moines Register, The 
Cincinnati Post, The Cleveland Plain Dealer,
The Columbus Dispatch, Cuba Free Press, Steelville Star-Crawford 
Mirror, Jefferson County Journal, Jefferson County Leader, Jefferson 
County News Democrat Journal, Meramec Journal, Jefferson County 
Watchman, TriCounty Journal, County Star Journal West, Chesterfield 
Journal, Clayton-St. Louis County Watchman, North County Journal-West, 
Florissant Valley Reporter, North County Journal-East, North Side 
Journal, County Star Journal-East, Concord Call, Mid-County Journal, 
Oakville Call, Oakville/Mehlville Journal, St. Louis Countian, South

[[Page 51328]]

County Journal, South County Times, Southwest County Journal, Webster-
Kirkwood Times, West County Journal, Citizen Journal, Webster/Kirkwood 
Journal, South County News-Times, Press Journal, New Haven Leader, St. 
Clair Missourian, Sullivan Independent-News, Franklin County Watchman, 
Union Missourian, Washington Missourian, Bland Courier, Advertiser-
Courier, Gasconade County Republican, Unterrified Democrat, Dixon 
Pilot, The Richland Mirror, Fort Leonard Wood Essayons, and The Daily 
    The Service hosted a public hearing (December 8, 1999, in Jefferson 
City, Missouri) at the request of Two Rivers Levee and Drainage 
Association, Law Offices of John C. Franken, Howard/Cooper County 
Regional Port Authority, and 180 private citizens. To accommodate this 
request, we reopened the comment period from November 29, 1999, to 
January 7, 2000, to allow for consideration of, and to provide an 
opportunity for, further comments. A notice of the hearing and 
reopening of the comment period was published in the Federal Register 
on November 29, 1999 (64 FR 66600), and in legal notices in the 
newspapers listed above.
    We received 26 letters providing comments and information during 
the comment periods. Additionally, six individuals provided oral 
statements at the public hearing. We have updated this rule to reflect 
any changes in information concerning distribution, status, and threats 
since the publication of the proposed rule. All pertinent comments have 
been considered in the formulation of this final rule. Written comments 
received during the comment periods and written comments and oral 
statements presented at the public hearings are addressed in the 
following summary. Comments of a similar nature or point are grouped 
together (referred to as ``Issues'' for the purpose of this summary) 
below, along with the Service's response to each.
    Issue 1: One respondent was unsure of what this listing would 
accomplish beyond the recovery efforts of other mussel species already 
federally listed in Missouri.
    Response: This action will extend the Act's protection to this 
species. Federal listing results in an increased awareness of this 
species' status and its need for conservation attention. It also 
provides for opportunities for funding research, management activities, 
and conservation actions specifically targeted for this species. In 
addition to better funding opportunities, Federal endangered status 
encourages scientists and natural resource managers to focus research 
and conservation actions specifically for the scaleshell mussel.
    There are currently four federally listed mussel species in 
Missouri (Missouri Natural Heritage Database 1999). These are the pink 
mucket (Lampsilis abrupta), Curtis pearlymussel (Epioblasma florentina 
curtisi), Higgins' eye (Lampsilis higginsii), and fat pocketbook 
(Potamilus capax). We agree that where overlap of listed mussels 
occurs, the prohibitions of the Act will provide little additional 
protection of habitat. However, the current range of scaleshell mussel 
extends to areas where there are no federally listed species. The Act 
will provide protection from further habitat loss and degradation in 
these areas.
    Issue 2: One respondent was concerned that the public will not know 
what impacts this listing will have on activities on private property 
until after the recovery plan is completed. The respondent was 
referring to potential impacts of recovery actions on private land in 
    Response: While recovery plans are not developed until after a 
species is listed, there is opportunity for public input in the 
recovery planning stage. The purpose of the recovery plan is to set 
recovery objectives (goals) and identify the tasks needed to meet those 
objectives before a species can be downlisted or delisted. As the draft 
recovery plan is announced in the Federal Register, we will solicit 
comment from species experts, natural resource managers, and other 
interested parties. To ensure broad participation in the review of the 
recovery plan, we will notify all interested parties that were 
identified during the listing process (for example, those that provided 
comments or requested to be on our mailing list).
    Although actions that could be affected by the listing were 
identified in the proposed rule, we acknowledge that impact upon 
private actions cannot be fully assessed until a recovery plan is 
developed. However, in ascertaining whether a species warrants Federal 
protection under the Act, we may consider only biological factors. In 
accordance with 16 U.S.C. sec. 1533(b)(1)(A) and 50 CFR 424.11, listing 
decisions are made solely on the basis of the best scientific and 
commercial data available. The legislative history of the 1982 Act 
amendments states: ``The addition of the word ``solely'' is intended to 
remove from the process of the listing or delisting of species any 
factor not related to the biological status of the species. The 
Committee strongly believes that economic considerations have no 
relevance to determinations regarding the status of the species. * * 
*'' H.R. Rep. No. 567, Part I, 97th Congress, 2nd Session 20 (1982). 
Thus, the impact of listing on private activities, although of great 
interest and importance to the public, is not a factor we may consider 
in our listing determination.
    Issue 3: One respondent questioned whether the range of the 
scaleshell mussel, particularly in the Missouri River, is based on 
records that were identified correctly. Scaleshell mussels can be 
easily confused with the fragile papershell (Leptodea fragilis) or the 
pink papershell (Potamilus ohioensis), which are more common and 
    Response: We acknowledge that scaleshell mussels may be confused 
with other species by the casual observer. Freshwater mussels are often 
difficult to identify by shell shape alone. However, to malacologists 
(a person who studies mollusks) and other properly trained biologists, 
there are no ambiguities in distinguishing scaleshell mussels from 
other species. Female scaleshell mussels are unique and unlikely to be 
mistaken with any other species. Females are small, very elongated, and 
the posterior edge is ruffled. Male scaleshell mussels can possibly be 
confused with other species, particularly the fragile papershell. 
However, several external characteristics distinguish male scaleshell 
mussels from the fragile papershell, the pink papershell, and other 
species. These characteristics include the presence of green rays, 
light brown periostracum, pointed posterior end, absence of dorsal 
wings, elongated shell, straight dorsal margin, and rounded ventral 
margin (Parmalee and Bogan 1998, Oesch 1995, Watters 1995).
    While it is possible that a small number of scaleshell mussel 
specimens have been misidentified, we are confident that the range of 
this species is based on valid specimens because many records are 
represented by voucher specimens that are housed in museums. The 
identification of these specimens has been verified by expert 
malacologists. In particular, the records of scaleshell mussel from the 
Missouri River were identified by Dr. David H. Stansbery, who is a 
leading authority in North America on freshwater mussel identification 
at the Ohio State Museum located at Ohio State University in Columbus, 
    Issue 4: The proposed rule states that gravel mining has recently 
become a more serious threat for scaleshell mussel range-wide because 
the Corps' authority to regulate instream gravel mining has been 
reduced. One respondent stated that this issue will probably not be

[[Page 51329]]

overlooked by the State agencies. In other words, gravel mining will 
probably be regulated by State agencies now that the Corps has less 
authority to regulate this activity.
    Response: Section 404 of the Clean Water Act of 1972 (CWA) provides 
regulations for discharge of dredged and fill materials in surface 
waters, including a permit program to ensure that such discharges 
comply with other State and Federal environmental regulations. The 
Corps is the Federal agency responsible for implementing this section 
of the CWA. Until 1997, instream mining was more strictly regulated, 
because incidental fallback of material during a dredging action was 
considered fill in surface waters, and thus triggered section 404 
compliance. Due to a 1997 Federal court decision, however, incidental 
fallback of material is no longer considered fill. Consequently, only 
activities that result in discharge of fill material greater than 
incidental fallback are regulated under section 404 (see factors A and 
D under the ``Summary of Factors Affecting the Species'' section for 
further information on this issue).
    As discussed in Issue 1, federally listed species frequently 
coexist with scaleshell mussels. Section 7 of the Act requires all 
Federal agencies, including the Corps, to consult with the Service 
regarding any action that may adversely affect listed species. Through 
this consultation process, the Service identifies conservation 
measures, which minimize adverse impacts to listed species. With 
incidental fallback no longer requiring a Corps section 404 permit, the 
section 7 consultation process is no longer applicable for many 
instream gravel mining activities.
    Some State agencies have authority to regulate gravel mining within 
their state. In Arkansas, instream gravel mining is regulated by the 
Arkansas Open-Cut Mining and Land Reclamation Code, which contains 
guidelines to reduce impacts (Roell 1999). The Missouri Department of 
Natural Resources (MDNR) also has the authority to regulate gravel 
mining in Missouri under the Land Reclamation Act. However, their 
regulatory authority is limited. First, only commercial operators are 
required to obtain a permit to remove gravel from streams and rivers. 
City, county, and state operators using their own equipment and private 
operations are not required to obtain a permit from MDNR. Also, these 
operators are not obligated to comply with permit conditions that are 
crucial in avoiding adverse impacts to the stream environment. Second, 
MDNR's conditions for gravel mining permits are less stringent than 
those required previously by the Corps (Mike Larson, Missouri 
Department of Natural Resources, pers. comm. 2000). For example, the 
MDNR permit does not prohibit the modification of water conveyance, 
limit excavation to unconsolidated areas, require bank and water buffer 
strips, or minimize the removal of aquatic and terrestrial vegetation. 
All of these factors could adversely affect the scaleshell mussel and 
its habitat.
    Issue 5: Several respondents are concerned that this listing will 
impact activities on private property. One respondent was concerned 
that impoundments will be more difficult to construct after the 
    Response: This listing will protect scaleshell mussels from take 
under section 9 (Prohibited Acts) of the Act. Take is defined by the 
Act as ``harass, harm, pursue, hunt, shoot, wound, capture, collect, or 
attempt to engage in any such conduct.'' Take is further defined by 
regulation to include ``significant habitat modification or degradation 
that actually kills or injures wildlife,'' (50 CFR 17.3 ``Harm''). Non-
Federal property owners, such as private landowners, corporations, or 
State or local governments, wishing to conduct activities on their land 
that might result in the incidental take of scaleshell mussels can 
obtain an incidental take permit from the U.S. Fish and Wildlife 
Service. Section 10 of the Act provides for the issuance of permits to 
conduct otherwise prohibited activities. Through section 10, there is 
an opportunity to provide species protection and habitat conservation 
for non-Federal development and land use activities that may result in 
incidental take of a listed species. For landowners and local 
governments, these incidental take permits, and their associated 
habitat conservation plans (HCP), provide long-term assurances that 
their activities will be in compliance with the requirements of the 
Act. Biologically, they provide the Service with a tool to offset the 
incidental take of listed species by reconciling species conservation 
with economic development. The HCP process allows private development 
to proceed while promoting listed species conservation.
    The No Surprises policy provides assurances to non-Federal 
landowners participating in HCP efforts through the section 10(a)(1)(B) 
process. Essentially, landowners are assured that if ``unforeseen 
circumstances'' arise, the Services will not require, without the 
consent of the permittee, the commitment of additional land, water or 
financial compensation or additional restrictions on the use of land, 
water, or other natural resources beyond the level otherwise agreed to 
in the HCP. The government will honor these assurances as long as a 
permittee is implementing the terms and conditions of the HCP, permit, 
and other associated documents in good faith. In effect, this 
regulation states that the government will honor its commitment as long 
as HCP permittees honor theirs.
    An activity on private land could also possibly be affected by this 
listing if that project (1) would need to be authorized, permitted, or 
funded by the Federal government, (2) would be located in habitat 
occupied by the scaleshell mussel or in designated critical habitat for 
the species, and (3) would have a direct or indirect effect on the 
species or its designated critical habitat. Federal programs and 
activities of this nature would usually require consultation with the 
Service under section 7 of the Act to evaluate the nature and extent of 
the adverse impacts and determine if project modification is necessary 
to reduce those impacts. Proposed impoundments within currently 
occupied streams and rivers are one type of activity that will require 
consultation. See the ``Available Conservation Measures'' section for 
additional examples of activities that will and will not require 
    While certain activities may require consultation, projects are 
rarely terminated due to the presence of a federally listed species, 
and private landowners are usually not affected. The consultation 
process is the responsibility of the Federal agencies involved. The 
majority of section 7 consultations are resolved informally. For 
example, consultation is ended at an early stage if the potential 
impacts of a proposed project are expected to be discountable, 
insignificant, or beneficial to the species. Even if a significant 
adverse effect is expected, the consultation can usually be concluded 
by developing minor modifications to project plans or designs that 
avoid those impacts. If potential impacts are of such nature that a 
federally listed species is likely to be adversely affected and such 
effects cannot be removed, formal consultation would be required. 
However, section 7(b)(4) of the Act allows incidental take of the 
listed species resulting from Federal actions if such take is not 
likely to jeopardize the continued existence of the species and if 
reasonable and prudent measures are implemented to minimize the adverse 
impacts of such take. A General Accounting Office audit (1992), which 
found that 99.9 percent of all projects reviewed between 1988 and 1992 

[[Page 51330]]

forward unchanged or with only minor modifications as a result of the 
section 7 consultation, attests to the regulatory flexibility afforded 
by the Act.
    Issue 6: One commenter stated that the same threats (i.e., water 
pollution, sedimentation, channelization, and impoundments) listed as 
impacting scaleshell mussel in the past (prior to 1950) are stated for 
present and future populations. The commenter stated that these 
conditions have improved. In Missouri, most of the channelization was 
established before the 1930s. Since 1950 land management practices have 
also evolved to more effectively control erosion and runoff, and the 
impacts of water pollution and sedimentation have been reduced.
    Response: The Service recognizes that some of these factors have 
improved, particularly land management practices to reduce erosion and 
runoff. In fact, the reason scaleshell mussels continue to persist 
could possibly be due to these improvements. However, the same threats 
that contributed to scaleshell mussels' decline before 1950, are still 
being observed and continue to impact scaleshell mussels. 
Channelization and new impoundments are currently proposed within the 
range of the scaleshell mussel, and water quality degradation and 
siltation has recently been documented as a serious threat in areas 
still occupied by scaleshell mussels. These threats are ongoing and 
qualify the scaleshell mussel for listing (See factor A in the 
``Summary of Factors Affecting the Species'' section). The small number 
and low density of the remaining populations exacerbate threats and 
adverse effects of chance events on the species.
    Issue 7: The data cited in the notice of proposed listing provide 
inadequate support for listing the scaleshell mussel as an endangered 
species. The decline of the scaleshell mussel is not serious enough to 
warrant listing. The six potential additional populations (status 
unknown), which would increase the current number of populations by 
almost 50 percent, merit further investigation before the listing 
decision is made.
    Response: Under section 4(b)(1)(A) of the Act, a listing 
determination must be based solely on the best scientific and 
commercial data available regarding the species' biological status and 
threats to its existence. Endangered status is assigned to species 
which are in danger of extinction throughout all or significant portion 
of their range. A species may be determined to be an endangered or 
threatened species due to one or more of the five factors described in 
section 4(a)(1) of the Act. These factors include (1) the present or 
threatened destruction, modification, or curtailment of its habitat or 
range; (2) overutilization for commercial, recreational, scientific, or 
educational purposes; (3) disease or predation; (4) the inadequacy of 
existing regulatory mechanisms; and (5) other natural or manmade 
factors affecting its continued existence.
    The scaleshell mussel has undergone one of the most extensive range 
reductions of all the federally listed freshwater mussel species. It is 
considered extirpated from ten states and from 39 of the 55 rivers 
within its historical range. Although 14 populations, and possibly six 
others, persist, the long-term viability of these populations is 
threatened by a variety of ongoing threats (see ``Summary of Factors 
Affecting the Species'' discussion). Given the extent of range 
reduction that has occurred and the persistence of threats to the 
remaining populations, we believe the scaleshell mussel is in danger of 
extinction throughout a significant portion of its range.
    Issue 8: Detecting population changes by using available data for a 
rare species is speculative. Specifically, the proposed rule states 
that the long-term viability of scaleshell mussel populations in the 
Meramec basin is tenuous. In a recent survey on the Meramec River, more 
scaleshell mussels were found than in a past survey. The respondent did 
not understand how those data could support a conclusion that the 
species is declining.
    Response: The Service acknowledges that rare species are difficult 
to census, and thus, deriving population trends based on counts of 
individuals is difficult and sometimes impossible. It is a common 
problem in rare species conservation that, as numbers of a rare species 
continue to decline, it becomes increasingly difficult to find and 
count the individuals in order to ``prove'' the decline is continuing. 
However, reliable inferences on the status and long-term viability of 
individual populations, as well as for a species as a whole, can be 
made based on ecological principles, small population biology theory, 
and observations of threats and habitat loss from field investigations. 
For example, population stability implies that recruitment exceeds 
mortality. For freshwater mussels, the presence of juveniles serves as 
the best evidence for recruitment. Thus, failure to collect juvenile 
specimens suggests that the population is declining. Similarly, small 
populations are more susceptible to extinction due to chance events, 
such as disease, drought, accidental spills of contaminants, or other 
fluctuations in local environmental conditions. Thus, even without 
multiple years of survey data, we know that low density mussel 
populations are vulnerable. Small populations must also rely on 
movement of individuals among populations to remain genetically viable. 
Thus, mussel populations that are isolated are threatened. In addition 
to these biological factors, the presence of threats, regardless of 
population size, can substantially influence the conservation status of 
a population. Using these factors, the health of individual populations 
and the species can be determined.
    To ensure consistency and objectivity, Szymanski (1998) developed 
criteria based on the aforementioned factors to assign status and trend 
categories to each scaleshell mussel population. These criteria were 
utilized in the proposed rule. However, a discussion of status and 
trends using the same set of limited data was confusing and redundant 
to readers. Therefore, in this final rule, we devised a single 
classification system (i.e., combined status and trend categories) to 
assess population health (Table 1). The revised classification system 
differs only in the presentation of the data and the results of its 
application are similar to those derived from the Szymanski (1998) 
methodology. As a result of additional information that was obtained 
during the public comment period, the status or trends reported in the 
proposed rule for a few populations differs from those reported herein. 
For example, the status of the White River population changed from 
extirpated to presumed declining as new information documented a 1999 
live scaleshell mussel collection from this river. A discussion of the 
criteria used for this classification system is provided in the 
``Distribution and Abundance'' section.
    With respect to the recent survey work in the Meramec River, the 
greater number of scaleshell mussels found in the 1997 survey was 
likely due to two aspects of the survey, and not a result of a 
population increase (Roberts and Brunderman 2000). First, a special 
effort was made to collect this species (i.e., raking the top layer of 
the substrate by hand) because it often lies buried in the substrate. 
This method likely increased the probability of finding the species 
compared to past surveys. Second, lower water levels from drought 
conditions exposed a mussel bed at one site, causing scaleshell mussels 
to actively crawl on top of the substrate. The collection of only 19 
scaleshell mussels, when viewed in light of the modified survey 
techniques and the

[[Page 51331]]

high visibility of individual mussels at one mussel bed, is strong 
evidence of the extreme rarity of this species.
    When attempting to monitor rare species, for which surveys usually 
locate only one or several surviving individuals, it is not uncommon 
for variations in survey methodology, weather conditions, and even time 
of day to affect the results of the survey. For species of extreme 
rarity, the effects of these factors can easily obscure the true 
population trend for the species. For this reason, we usually use 
criteria, in addition to population or density estimates, to evaluate 
the health of individual populations and the species as a whole.
    Based on the criteria described earlier, the three scaleshell 
mussel populations in the Meramec Basin (the Meramec, Bourbeuse, and 
Big Rivers) are believed to be declining at the present time. The long-
term persistence of these populations is considered questionable 
because of marked habitat loss and other existing threats. Furthermore, 
the small number of individuals and low density of these populations 
exacerbate the magnitude and adverse impacts of threats (see ``Summary 
of Factors Affecting the Species''). Thus, despite the fact that more 
scaleshell mussels were collected from the Meramec River in a recent 
survey than in the past, other factors indicate that these populations 
are threatened and are declining.
    Issue 9: One respondent requested clarification of references to 
historical and existing distribution and abundance of scaleshell 
mussels. The respondent asked if the terms ``populations'' and 
``occurrences'' are equivalent and if populations are equal in size and 
other qualities.
    Response: A ``historical record'' is any site where the scaleshell 
mussel has been documented regardless of when it was collected. The 
Service believes that recently discovered sites do not represent areas 
that have been colonized recently, but rather, they are sites that have 
existed historically (i.e., in historical times) and have not been 
previously known or sampled by collectors. A description of the 
historical range of the scaleshell mussel includes all known records. 
In contrast, a description of the existing distribution of the 
scaleshell mussel would include only its extant (that is, currently 
existing) range.
    An ``occurrence'' refers to a site where a scaleshell mussel 
specimen has been collected. An occurrence, which may be represented by 
one or more specimens, usually indicates the species is present or once 
existed in that area, depending on whether the specimen(s) is living or 
    In the context of this rule, the term ``population'' refers to all 
the current and historical occurrences of scaleshell mussels within a 
single river.
    It is impossible to determine if past and present scaleshell mussel 
populations are equal in size (in terms of number of individuals or 
length of stream inhabited), because many surveys conducted near the 
turn of the century were not thorough. However, it is believed that 
scaleshell mussels historically have always been rare relative to many 
other mussel species. Inferences regarding population trend can be made 
from existing data (e.g., age-structure, historical vs. current 
collections, habitat availability and condition, and threats). For 
example, scaleshell mussels were locally abundant in the Kiamichi River 
in the past (with 36 specimens collected from one sampling station). 
Today, however, no living scaleshell mussel specimens and only 1 fresh 
dead specimen were found during exhaustive survey efforts. It is 
apparent that scaleshell mussels, although always rare, occur today at 
lower densities than in the past in the Kiamichi River (see Issue 8 for 
further discussion regarding assessing conservation status). Within 
this final rule, populations that were assigned to the same 
conservation status do not necessarily have similar population size 
(although all populations persist at very low densities) or habitat 
    Issue 10: The proposed rule states that scaleshell mussels have not 
been found in the Upper Mississippi River basin in over 50 years. One 
respondent asked how often sampling has been conducted in the Upper 
Mississippi River basin, and what is the likelihood of detecting a 
locally rare species.
    Response: The historical range of the scaleshell mussel in the 
Upper Mississippi River basin includes the states of Illinois, Iowa, 
Minnesota, and Wisconsin. Natural resource agencies in these states are 
confident enough to consider the scaleshell mussel extirpated since it 
has not been collected in over 50 years despite a considerable number 
of surveys. Rivers with documented scaleshell mussel occurrences in the 
Upper Mississippi River basin include the Mississippi, Minnesota, Iowa, 
Cedar, Illinois, Sangamon, and Pecatonica Rivers, and Burdett's Slough 
of the Mississippi River (see ``Distribution and Abundance''). All of 
these rivers have been surveyed in the last 10-15 years. Surveys 
considered here are formal mussel surveys published in technical 
reports and scientific journals. Numerous other surveys, which are not 
discussed here, also have been conducted in these streams at selected 
sites for various Federal projects (e.g., proposed bridges, pipelines, 
channelization, etc.). Surveys have been conducted on the Minnesota 
River in 1977 and 1999 (Marian Havlik, Malacological Consultants, in 
litt. 2000; Tim Yager, Corps, St. Paul District, in litt. 2000). The 
Mississippi River mainstem, in particular, has been surveyed 
extensively since 1950. The Illinois, Sanagamon, and Pecatonica Rivers 
have also been surveyed extensively in the last 15 years (Kevin 
Cummings, pers. comm. 2000).
    The likelihood of detecting a locally rare species depends on the 
amount of time spent searching and the search methods employed. The 
most common method used for surveys is timed searches, which produce a 
measurement of the number of mussels collected per unit of time spent 
searching. Timed searches produce the most complete list of species 
(including rare species) at a given site (Strayer et al. 1997, Vaughn 
et al. 1997).
    Furthermore, the deficiency of suitable mussel habitat, both in 
quality and quantity, remaining in this drainage also suggest that 
scaleshell mussel persistence is highly unlikely. This is not to say 
individuals may not persist in the Upper Mississippi River drainage, 
but that the best available scientific information indicates that 
population viability is doubtful.
    Issue 11: One respondent believes that water turbulence produced by 
jet boat motors may be adversely affecting scaleshell mussels and other 
freshwater mussels in the Meramec River in Missouri.
    Response: The Service recognizes that jet boats, which can produce 
powerful water turbulence, could potentially have adverse affects on 
freshwater mussels including scaleshell mussels. Jet wash from motors 
may contribute to substrate destabilization and/or could dislodge adult 
and juvenile mussels from suitable habitat, particularly from shallow 
riffles where mussels typically occur. The magnitude and extent to 
which this factor may threaten populations, however, is unknown.

Peer Review

    In accordance with our July 1, 1994, Interagency Policy on Peer 
Review (59 FR 34270) we requested the expert opinions of independent 
specialists regarding pertinent scientific or commercial data and 
assumptions relating to the supportive biological and ecological 
information in the proposed rule. The purpose of such review is to

[[Page 51332]]

ensure that the listing decision is based on scientifically sound data, 
assumptions, and analyses, including input of appropriate experts and 
    We requested a formal scientific peer review from four 
malacologists who possess expertise on the scaleshell mussel. We 
received a written response and comments from two of these experts 
within the open comment periods. These experts strongly supported the 
listing proposal and agreed with the Service that this species is in 
need of Federal protection as an endangered species. One reviewer 
stated that the Service was thorough in reviewing this species and that 
the status and threats are accurately described. This reviewer felt 
that the threats posed by the zebra mussel to the scaleshell mussel, as 
discussed in the proposed rule, should not be underestimated. 
Additionally, more information was provided in one response regarding 
the extant distribution of the scaleshell mussel and threats to its 
existence. That information is incorporated into this final rule.

Summary of Factors Affecting the Species

    After a thorough review and consideration of all information 
available, we determine that the scaleshell mussel should be classified 
as an endangered species. We followed the procedures found at section 
4(a)(1) of the Act (16 U.S.C. 1531 et seq.) and regulations (50 CFR 
part 424) implementing the listing provisions of the Act. We may 
determine a species to be endangered or threatened due to one or more 
of the five factors described in section 4(a)(1). These factors and 
their application to the scaleshell mussel (Leptodea leptodon) are as 

A. The Present or Threatened Destruction, Modification, or Curtailment 
of its Habitat or Range.

    Arguably, the scaleshell mussel has suffered a greater range 
reduction than any other unionid. The range of this species was once 
expansive, spanning the Mississippi River Basin in at least 55 rivers 
in 13 states (Szymanski 1998). Today, the range is significantly 
reduced with known extant populations persisting in only 14, 
potentially 20, rivers in three states. The scaleshell mussel has been 
eliminated from the entire upper and most of the middle Mississippi 
River drainages. Although much of the decline occurred before 1950, 
population declines continue in most portions of the species' range, 
and numerous threats are impacting the few remaining extant 
populations. Water pollution, sedimentation, channelization, sand and 
gravel mining, dredging, and impoundments contribute to the decline of 
the scaleshell mussel throughout its range and continue to affect 
existing populations. A general description of how these factors affect 
mussels is given below, followed by specific examples of how these 
threats are affecting scaleshell mussels in its extant range. Refer to 
Szymanski (1998) for a more detailed discussion of threats to 
freshwater mussels.
    Mussel biologists generally agree that contaminants are partially 
responsible for the decline of mussels (Havlik and Marking 1987, 
Williams et al. 1993, Biggins et al. 1996). Mussels are sedentary 
filter feeders and are vulnerable to contaminants that are dissolved in 
water, associated with suspended particles, or deposited in bottom 
sediments (Naimo et al. 1992).
    Contaminants enter streams from point and nonpoint sources. Point 
source pollution is the entry of material from a discrete, identifiable 
source such as industrial effluents, sewage treatment plants, and solid 
waste disposal sites. Freshwater mussel mortality from toxic spills and 
polluted water is well documented (Ortmann 1909, Baker 1928, Cairns et 
al. 1971, Goudreau et al. 1988). 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.
    Nonpoint source pollution is the entry of material into the 
environment from a diffuse source such as runoff from cultivated 
fields, pastures, private wastewater effluents, agricultural feed-lots 
and poultry houses, active and abandoned mines, construction, and 
highway and road drainage. Stream discharge from these sources may 
accelerate eutrophication (i.e., organic enrichment), decrease oxygen 
concentration, increase acidity and conductivity, and cause other 
changes in water chemistry that are detrimental to the survival of most 
mussel species and may impact host fishes (Goudreau et al. 1988, Dance 
1981, Fuller 1974).
    Sediment is material that is suspended in the water, and is being 
transported, or has been moved, as the result of erosion (USSCS 1988). 
Although sedimentation is a natural process, agricultural encroachment, 
channelization, impoundments, timber harvesting within riparian zones, 
heavy recreational use, urbanization, and other land use activities can 
accelerate erosion (Waters 1995, Myers et al. 1985, Chesters and 
Schierow 1985). The water quality impacts caused by sedimentation are 
numerous. Generally, it affects aquatic biota by altering the 
substratum 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. Due to their difficulty in escaping smothering 
conditions (Imlay 1972, Aldridge et al. 1987), a sudden or slow 
blanketing of stream bottom with sediment can suffocate freshwater 
mussels (Ellis 1936). Sediment particles may carry contaminants toxic 
to mussels (Naimo et al. 1992). Increased sediment levels may also 
reduce feeding efficiency (Ellis 1936), which can lead to decreased 
growth and survival (Bayne et al. 1981).
    Channelization, sand and gravel mining, and dredging operations 
physically remove mussels from the water and may also bury or crush 
mussels (Watters 1995). Other effects of these activities extend 
upstream and downstream of the excavated area. Headcutting, the 
upstream progression of stream bed destabilization and accelerated bank 
erosion, can affect an area much larger than the dredging site 
(Hartfield 1993). In severe cases, this erosional process can extend 
for several miles upstream. As relatively immobile bottom-dwelling 
invertebrates, mussels are particularly vulnerable to channel 
degradation (Hartfield 1993). Accelerated erosion also releases 
sediment and pollutants, and in some instances, diminishes mussel 
diversity and habitat as documented in the Yellow and Kankakee Rivers 
in Indiana, the Big Vermillion River in Illinois, and the Ohio River 
(Fuller 1974).
    Gravel mining has recently become a more serious threat for 
scaleshell mussels range-wide. In 1997, a court ruling changed the 
interpretation of the CWA as it applies to the regulation of gravel 
mining (Roell 1999). Previously, gravel mining was more strictly 
regulated because ``incidental fallback'' (the incidental soil movement 
from excavation, such as the soil that is disturbed when dirt is 
shoveled, or back-spill that comes off a bucket and falls into the same 
place from which it was removed) was considered fill in surface waters, 
thus triggering section 404 of the CWA and the permitting process of 
the Corps. Prior to the 1997 ruling, gravel mining operators were 
required to obtain a Corps section 404 permit and follow several 
conditions outlined on the permit. Except in very small tributaries, 
the Corps required all operators to establish a streamside and riparian 
buffer and prohibited removing gravel from flowing water (i.e., no in-
stream mining) or from below the water

[[Page 51333]]

table (Danny McKlendon, Corps, St. Louis District, pers. comm. 1998). 
These requirements avoided most adverse effects to mussels including 
headcutting, channel modification, and the physical crushing or removal 
of mussels. Furthermore, the Corps' permit process included 
consultation with the Service concerning the presence of federally 
listed species at each proposed mining site. However, the 1997 ruling 
eliminated the Corps authority to regulate most instream gravel mining 
activities, thereby eliminating the section 404 permit and the 
conditions that protected mussel beds. Therefore, the scaleshell mussel 
has lost much of its protection from gravel mining. Only activities 
resulting in discharge of fill material greater than incidental 
fallback (such as instream gravel stockpiling, stream crossings, and 
select removal methods) are regulated. However, many gravel mining 
operations may not fall under this category.
    Impoundments negatively affect mussels both upstream and downstream 
by inducing scouring, changing water temperature regimes, and altering 
habitat, food, and fish host availability (Caryn Vaughn, in litt. 
1997). Impoundments permanently flood stream channels and eliminate 
flowing water that is essential habitat for most unionids, including 
scaleshell mussels (Fuller 1974, Oesch 1995). Scouring is a major cause 
of mussel mortality below dams (Layzer et al. 1993). Most detrimental, 
however, is the disruption of reproductive processes. Impoundments 
interfere with movement of host fishes, alter fish host assemblages, 
and isolate mussel beds from each other and from host fishes (Stansbery 
1973, Fuller 1974, Vaughn 1993, Williams et al. 1993). The result is 
diminished recruitment (Layzer et al. 1993). Dams are effective 
barriers to fish host movement and migration that unionids depend on 
for dispersal. Mussels living upstream from the dam can become 
reproductively isolated from those living downstream causing a decrease 
in genetic diversity. Even small, lowhead dams can hinder fish movement 
and isolate mussel beds from fish hosts and from each other. For 
example, Watters (1996) determined that the upstream distribution of 
two mussel species, the fragile papershell (Leptodea fragilis) and pink 
heelsplitter (Potamilus alatus) stopped at lowhead dams. These species, 
like the scaleshell mussel, are believed to use the freshwater drum as 
a sole host.
    The same threats that caused the extirpation of historical 
populations of scaleshell mussel still exist and continue to threaten 
extant populations. This species appears to be especially susceptible 
to contamination and sedimentation. Historically, the species was 
widespread and occurred in diverse habitats. Today, scaleshell mussels 
no longer occur at disturbed sites that still support other endangered 
unionids (Szymanski 1998). This suggests that scaleshell mussels are 
especially sensitive to degraded water quality. Given the pervasiveness 
of the sources of pollution and sedimentation, it is apparent that 
these threats continue to be problematic for the remaining scaleshell 
mussel populations.

Upper Mississippi River Basin

    The scaleshell mussel formerly occurred in eight rivers and 
tributaries within the Upper Mississippi Basin. However, this species 
has not been found in more than 50 years and is believed extirpated 
from this region (Kevin Cummings, in litt. 1994). We believe the same 
factors that have caused declines and extirpations of other mussel 
species including impoundments, pollution, sedimentation, and 
channelization and dredging activities, have caused the disappearance 
of scaleshell mussels from the Upper Mississippi River Basin.

Middle Mississippi River Basin

    Similar to the Upper Mississippi River Basin, impoundments, 
pollution, sedimentation, and channelization and dredging activities 
are believed to have led to the extirpation of the scaleshell mussel 
from the entire Ohio River Basin. These same threats continue to 
adversely affect extant populations in the middle Mississippi River 
Basin. Scaleshell mussel habitat in the Meramec River Basin has been 
reduced in recent years. In 1979, Buchanan found living or dead 
scaleshell mussels in the lower 180 km (112 mi) of the Meramec River 
(Buchanan 1980). In 1997, living or dead scaleshell mussels were 
collected only in the lower 96 km (60 mi) of the river (Roberts and 
Bruenderman 2000). While portions of the lower reach continue to 
provide suitable habitat, mussel species diversity and abundance above 
mile 60 have declined noticeably in the last 20 years and 9 mussel beds 
are no longer present between river mile 21.5 and 145.7. Roberts and 
Bruenderman (2000) attributed this decline primarily to the loss of 
channel stability. Within the Meramec Basin, the Bourbeuse River has 
undergone the greatest change with respect to mussel populations. In 
particular, mussel populations have declined in the lower river. 
Whereas Buchanan (1980) found this section of the Bourbeuse River to 
have the greatest mussel diversity, this stretch was nearly devoid of 
mussels when resurveyed in 1997. Additionally, five mussel beds are no 
longer present between miles 0.4 and 137. Buchanan (in litt. 1997) and 
Roberts and Bruenderman (2000) attributed this decline to habitat loss 
from sedimentation, eutrophication, and substrate destabilization.
    The Big River has the lowest species diversity and abundance in the 
Meramec River Basin. Buchanan (1980) attributed this to the effects of 
lead and barite mining. While most mining operations have ceased, 45 
dams retaining mine waste and numerous waste piles remain in the Big 
River Basin. Most of those dams were improperly constructed or 
maintained. The Corps found that only one of the 45 dams was safe and 
27 received the worst possible rating and could fail during a flood. 
The poor condition of the dams has led to large influxes of mine waste 
into the Big River from dam collapse (MDC 1997). For example, since 
1978, a ruptured tailings dam has discharged 63,000 cubic meters 
(81,000 cubic yards) of mine tailings into the Big River covering 40 km 
(25 mi) of stream bottom and negatively impacting the lower 129 km (80 
mi) of the river (Alan Buchanan, in litt. 1995), making it less 
suitable for mussels.
    While no major impoundments exist in the Meramec River Basin, 
several old mill dams (low-head dams) affect the mainstem of the Big 
and Bourbeuse Rivers. Five dams are still in place along the lower 48 
km (30 mi) of the Big River, and one dam exists in the lower Bourbeuse 
River. These structures are barriers to host fish movement during 
normal flows (MDC 1997) and thus, continue to depress reproductive 
rates of scaleshell and other mussels.
    Gravel mining poses an imminent threat to scaleshell mussel 
populations in the Meramec River Basin due to the high, and increasing, 
level of interest in gravel mining in the basin (Roberts and Brunderman 
2000). For example, between 1994 and 1998, the Corps issued permits for 
230 sites. Additional sites were mined without a permit, but the number 
of these unauthorized operations is unknown. (Danny McKlendon, Corps, 
St. Louis District, in litt. 1998).
    In 1994, several areas of the Gasconade River channel were highly 
unstable, possibly a result of riparian vegetation removal in 
conjunction with the 1993 flood. These areas had high cut mud banks 
with trees fallen into the river, unstable substrate, and contained 
very few mussels. Buchanan (1994) predicted that habitat degradation on 
this river would continue and

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postulated that the mussel fauna would be further impacted with some 
species possibly disappearing. He noted that below river mile 6, only 
one stable gravel bar contained a diverse mussel fauna. High silt 
deposition from the Missouri River prohibits the formation of mussel 
habitat below this area.
    The majority of the Osage River system has been impounded and is no 
longer suitable for freshwater mussels. The majority of remaining 
mussel habitat occurs below Bagnell dam in the lower 80 miles of the 
Osage River proper. This river reach is affected by the operation of 
Bagnell dam, which alters flow and temperature regimes, lowers 
dissolved oxygen levels, and causes channel scouring and accelerated 
bank erosion. Several instream gravel mining operations currently exist 
in the Osage River that physically remove mussels from the water and 
cause headcutting and siltation.

Lower Mississippi River Basin

    Channelization, levee construction, diversion ditches, control 
structures, and floodways have drastically altered much of the St. 
Francis River from the mouth above Helena, Arkansas, to Wa the St.