[Federal Register: August 13, 1999 (Volume 64, Number 156)]
[Proposed Rules]               
[Page 44171-44182]
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; Proposed Rule To 
List the Scaleshell Mussel as Endangered

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule.


SUMMARY: We, the U.S. Fish and Wildlife Service, propose endangered 
status pursuant to the Endangered Species Act of 1973, as amended 
(Act), for the scaleshell mussel (Leptodea leptodon). This species 
historically occurred in 13 states in the eastern United States. 
Currently, the species is known from a few scattered populations within 
the Mississippi River Basin in Missouri, Oklahoma, and Arkansas. 
Scaleshell inhabits medium-sized to large rivers with stable channels 
and good water quality. The abundance and

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distribution of scaleshell have decreased due to habitat loss and 
adverse effects associated with water quality degradation, reservoir 
construction, sedimentation, channelization, and dredging. These 
habitat changes have resulted in significant extirpations, restricted 
and fragmented distributions, and poor recruitment. This proposed rule, 
if made final, would extend the Act's protection to the scaleshell 

DATES: Send your comments to reach us on or before October 12, 1999. We 
will not consider comments received after the above date in making our 
decision on the proposed rule. We must receive requests for public 
hearings by September 27, 1999.

ADDRESSES: The complete administrative file for this rule is available 
for inspection, by appointment, during normal business hours at the 
U.S. Fish and Wildlife Service, Bishop Henry Whipple Federal Building, 
1 Federal Drive, Fort Snelling, MN 55111-4056, (telephone 612-713-

FOR FURTHER INFORMATION CONTACT: Andy Roberts at the U.S. Fish and 
Wildlife Service, Columbia Field Office, 608 East Cherry Street, Room 
200, Columbia, Missouri 65201, (telephone 573-876-1911, ext. 110).



    The scaleshell mussel (Leptodea leptodon) was described by 
Rafinesque in 1820. Synonymy includes Unio velum (Say), Sympnynota 
tenuissima (Lea), Lampsilis blatchleyi (Daniels), and Lampsilis 
leptodon (Rafinesque).
    Buchanan (1980), Cummings and Mayer (1992), Oesch (1995), and 
Watters (1995) provide descriptions of the scaleshell mussel 
(scaleshell). The shell grows to about three to ten centimeters (one to 
four inches) in length. The shells are elongate, very thin, and 
compressed. The anterior end is rounded. In males, the posterior 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 margin is straight and the ventral margin 
is gently rounded. Beaks (the raised or domed part of the dorsal margin 
of the shell) are small and low, 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 and one fine 
tooth in the right. The beak cavity is very shallow. The nacre (the 
interior layer of the shell) is pinkish white or light purple and 
highly iridescent.

Life History

    The general biology of scaleshell is similar to other bivalved 
mollusks belonging to the family Unionidae. Adults are filter-feeders, 
spending their entire lives partially or completely buried within the 
substrate (Murray and Leonard 1962). Their food includes detritus, 
plankton, and other microorganisms (Fuller, 1974). Unionids have an 
unusual mode of reproduction. Their life cycle includes a brief, 
obligatory parasitic stage on fish. Eggs develop into microscopic 
larvae (glochidia) within special gill chambers (ectobranchous 
marsupia) of the female. The female expels the mature glochidia and 
they must attach to the gills or the fins of an appropriate fish host 
to complete development. Host fish specificity varies among unionids. 
Some species appear to use a single host, while others can transform on 
several host species. Following proper infestation, glochidia transform 
into juveniles and excyst (drop off). 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 scaleshell. Baker (1928) surmised that 
scaleshell is a long-term brooder (spawns in fall months and females 
brood the larvae in their gills until the following spring or summer). 
Glochidia present in the ectobranchous marsupia 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 (Roe and Lydeard 1997, Watters 1994).

Habitat Characteristics

    The scaleshell occurs in a variety of river habitats. For example, 
Buchanan (1980, 1994) and Gordon (1991) reported scaleshell from riffle 
areas with substrate assemblages of gravel, cobble, boulder, and 
occasionally mud or sand. Oesch (1995) considered scaleshell 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. The unifying characteristic appears 
to be an intact system (stable channels) with good water quality. This 
is consistent with the current distribution of scaleshell. Most extant 
populations are restricted to river stretches with stable channels 
(Buchanan 1980, Harris 1992) and that have maintained relatively good 
water quality (Oesch 1995). Scaleshell is usually collected in 
association with a high diversity of other freshwater mussels.

Distribution and Abundance

    Scaleshell historically occurred across most of the eastern United 
States. While the scaleshell had a broad distribution, locally it was a 
rare species (Gordon 1991, Oesch 1995, Call 1900). 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. Clarke (1996) also 
reported scaleshell occurrence from the Minnesota River, Minnesota. 
Within the last 50 years, this species has become increasingly rare and 
its range greatly restricted. Of the 53 historical populations, 13 
remain scattered within the Mississippi River Basin, including the 
Meramec, Bourbeuse, Big, and Gasconade Rivers in Missouri; the South 
Spring, St. Francis, Little, Mountain Fork, Spring, and South LaFave 
Rivers and Frog Bayou and Gates Creek in Arkansas; and the Kiamichi 
River in Oklahoma.
    Of the 13 extant scaleshell populations, three are thought to be 
stable (long term persistence is possible but unsure), two are 
declining, four are presumed to be declining (long term persistence is 
in doubt), and the status of four are unknown. Six additional 
populations may also persist but their current status is uncertain due 
to lack of recent collections or surveys (Szymanski 1998).

Upper Mississippi River Basin

    Scaleshell 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 has not been found in more

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than 50 years in the Upper Mississippi Basin and is believed extirpated 
from that basin (Kevin Cummings, Illinois Natural History Survey, in 
litt. 1994).

Middle Mississippi River Basin

    Historically, scaleshell occurred in 25 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, and Big Piney Rivers in 
Missouri; and the mainstem Missouri River in South Dakota. The 
scaleshell has been extirpated from most of the middle Mississippi 
River Basin. Currently, the scaleshell is extant in four, possibly 
five, rivers within the Meramec River and Missouri River drainages in 
Missouri as described below.
    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. 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, 
scaleshell is also locally rare. Buchanan found that the species 
comprised less than 0.1 percent of the 20,589 living naiades found in 
the basin. He collected live specimens at four sites, three in the 
Meramec and one in the Bourbeuse. Although the lower 108 miles of the 

Meramec River had suitable habitat for many rare species, live 
scaleshell were found only in the lower 40 miles (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 54 miles of the Bourbeuse River and lower 10 miles 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 (Sue 
Bruenderman, Missouri Department of Conservation, in litt. 1998). 
Similar to Buchanan's findings (1980), scaleshell represented only 0.4 
percent of the living mussels, with specimens 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). The MDC documented live scaleshell at four of the five sites 
where Buchanan previously collected live specimens on the Meramec River 
(Sue Bruenderman, pers. comm. 1998). One site where they did not 
reconfirm scaleshell had only two live mussels where Buchanan had 
previously observed 93 living individuals. This site no longer supports 
suitable mussel habitat. Although portions of the Meramec River 
continue to provide suitable habitat, mussel species diversity and 
abundance have declined noticeably above mile 64 since 1980.
    The number of scaleshell specimens 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 limited availability of mussel habitat and 
the loss of mussel beds since 1980 from sedimentation, eutrophication, 
and unstable substrates (Buchanan in litt. 1997; Sue Bruenderman pers. 
comm. 1998) indicate that scaleshell populations within the Meramec 
River Basin are threatened.
    Missouri River drainage (South Dakota, Missouri)--Within the 
Missouri River drainage, Buchanan (1980, 1994) and Oesch (1995) 
reported scaleshell from Missouri, Gasconade, Big Piney and South Grand 
Rivers and Auxvasse Creek. The last collection of Scaleshell from 
Auxvasse Creek was 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, now inundated by Truman Lake, is 
unsuitable for scaleshell (Buchanan, in litt. 1997). The only specimen 
reported from the mainstem Missouri River is from South Dakota adjacent 
to the Nebraska border (Hoke 1983). This occurrence represents the 
westernmost record within the Upper Mississippi River Basin. A 
subsequent survey failed to relocate live specimens or relict shells 
(Clarke 1996). However, high water conditions limited Clarke's survey 
and it is uncertain if scaleshell is still present below Gavin's Point 
Dam (Nell McPhillips, U.S. Fish and Wildlife Service, in litt. 1998). A 
single, fresh dead specimen was collected from Big Piney River in 1981 
(Bruenderman, in litt. 1998). No other specimens of scaleshell have 
been documented from this river.
    Buchanan (1994) surveyed the Gasconade River, and he found it to 
support 36 species of freshwater mussels. He collected scaleshell 
specimens at eight sites between river miles 6 and 57.7. Buchanan found 
only dead shells at two sites and eight live specimens at the remaining 
six sites. Overall, scaleshell comprised less than 0.1% of the mussels 
collected. If populations still exist in any of the rivers within the 
Missouri River drainage, their long-term persistence is undoubtably 
    Middle Mississippi River Basin summary--Of the 25 rivers and 
tributaries in the middle Mississippi River Basin, four, and possibly 
five, support scaleshell populations today. While populations in the 
Meramec and Bourbeuse Rivers are likely stable, numbers in the Big and 
Gasconade Rivers are presumed declining, and the status of populations 
in the Big Piney River are unknown (Szymanski 1998).

Lower Mississippi River Basin

    Scaleshell historically occupied 20 rivers and tributaries in the 
lower Mississippi River Basin. These include the St. Francis, White, 
James, Spring, Little Missouri, Middle Fork Little Red, Saline, 
Ouachita, Cossatot, South Fourche LaFave, 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.
    St. Francis River (Arkansas and Missouri)--Bates and Dennis (1983), 
Ahlstedt and Jenkinson (1987), Clarke (1985), and Rust (1993) conducted 
mussel surveys on the St. Francis River in Arkansas and Missouri. 
Records of dead mussels and relict shells indicate that at one time 
mussels were distributed throughout the river (Bates and Dennis 1983). 
Clarke (1985) documented scaleshell at two sites by single specimens. 
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. Although scaleshell was not collected, they identified 
48 miles of probable suitable mussel habitat: 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 river miles were unsuitable for mussels. 
If scaleshell is extant in the St. Francis River, it will be restricted 
to the few patches of suitable habitat.
    White River (Arkansas)--Clarke (1996) noted the collection, in 
1902, of

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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 individuals. 
Navigation maintenance activities have relegated mussel populations to 
a few refugial sites, none of which support scaleshell (Bates and 
Dennis 1983). 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 scaleshell.
    Spring River (Arkansas)--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 
specimens (Cummings in litt. 1994, Clarke 1996, Arkansas State Highway 
and Transportation Dept. 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 three miles of river were 
completely depleted of mussels and contained no suitable habitat. 
Harris did not document scaleshell in a 1993 survey of the Spring River 
(John Harris, Arkansas State University, in litt. 1997).
    Scaleshell was 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.
    Strawberry River and Myatt Creek (Arkansas)--Records of scaleshell 
from the Strawberry River and the Myatt Creek are based on single 
specimen collections (Harris in litt. 1997). In 1996, Harris collected 
a live specimen from the Strawberry River near the confluence with 
Clayton Creek in Lawrence County. He also collected a single relict 
specimen from Myatt Creek in Fulton County in 1996 (Harris in litt. 
    Little Red River (Arkansas)--The historical locality (near Shirley, 
Van Buren County, Arkansas) where a single, specimen of scaleshell 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 six-mile stretch from the confluence of 
Tick Creek upstream to the mouth of Meadow Creek.
    Arkansas River Basin (Oklahoma and Arkansas)--Scaleshell has been 
collected from the Arkansas River Basin in Oklahoma and Arkansas. The 
species is reported from the Poteau River in Oklahoma (Gordon 1991), 
Frog Bayou in Arkansas (Harris and Gordon 1987), and 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, Branson 1984, Harris 1994), only a single, undated specimen has 
been collected (Gordon 1980). The persistence of scaleshell in Poteau 
River is doubtful.
    Frog Bayou (Arkansas)--Gordon (1980) collected two scaleshell 
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 scaleshell in Frog Bayou 
is uncertain, any remaining individuals are in potential jeopardy due 
to limited habitat and in-stream mining activities.
    South Fork La Fave River (Arkansas)--The only scaleshell record 
from the South Fork La Fave River is based on a single live specimen 
found in 1991 (Harris 1992). The potential of discovering additional 
populations in this river is unlikely due to the limited availability 
of suitable substrate. Similarly, other major tributaries of the South 
Fourche La Fave River provide little mussel habitat. Like Frog Bayou, 
the persistence of scaleshell in this river is in doubt.
    Mulberry River (Arkansas)--Although Gordon (1991) reported 
scaleshell from the Mulberry River, documentation is lacking (no 
written acknowledgment). A recent survey did not find the species in 
the Mulberry River (Craig Hilborne, U.S. Forest Service, pers. comm. 
1995; Stoeckel et al. 1995). Persistence of scaleshell in the Mulberry 
River is unlikely.
    Red River Drainage (Oklahoma)--In the Red River drainage, Valentine 
and Stansbery (1971) reported the collection of a single, undated 
specimen from Gates Creek, a tributary of the Kiamichi River. Isley 
(1925) first collected scaleshell from the Kiamichi River in 1925. 
Based on his account, the Kiamichi River historically supported a 
diverse and abundant mussel fauna. He collected 36 specimens of 
scaleshell at one of 22 stations visited. 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 (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 
Kiamichi River is in relatively good shape above the Hugo Reservoir, 
(Clarke 1987) and may still support a remnant population of scaleshell.
    Little River, Red River Drainage (Oklahoma)--Although there is no 
evidence of scaleshell persisting in the Little River, above the Pine 
Creek Reservoir a healthy mussel population persists (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). Valentine and Stansbery (1971) reported a single specimen from 
Mountain Fork. Clarke (1987) hypothesized 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 have been severely depleted with most no longer containing 
live mussels. Although extensive surveys throughout the length of the 
Little River have not documented scaleshell, suitable habitat remains 
and scaleshell individuals may persist (Vaughn in litt. 1997). However, 
the discharge of reservoir water from Pine Creek and periodic discharge 
of pollution from Rolling Fork Creek would seriously impact any 
remaining viable populations and prohibit any future recolonization 
(Clarke 1987).
    If scaleshell still occurs in the Red River drainage in Oklahoma, 
extant populations are probably small and are

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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 in Oklahoma is 
    Cossatot and Saline Rivers (Arkansas)--Harris collected single 
specimens of scaleshell from the Cossatot and Saline Rivers in Arkansas 
in 1983 (Harris in litt. 1997) and 1987 (Harris pers. comm. 1995), 
respectively. No other information is available for either river. The 
existence of scaleshell 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 based on single 
specimens. The Saline River specimen was collected in 1946 (Clarke 
1996), and the Little Missouri River collection record is from 1995 
(Harris in litt. 1997). Four undated museum specimens taken from 
Arkadelphia, Clark County, Arkansas document the occurrence of 
scaleshell in the Ouachita River (Clarke 1996). Based on the few 
collections and the limited habitat available, the long-term 
persistence of scaleshell in Cossatot, Saline, Little Missouri, and 
Ouachita Rivers is precarious.
    Lower Mississippi River Basin summary--Of these 20 rivers and 
tributaries in the lower Mississippi River Basin, nine, and possibly an 
additional five, support scaleshell populations today. Of these 
populations, the South Spring River is likely stable; the St. Francis 
River, Kiamichi River, Little River, and Mountain Fork are declining; 
the Spring River, Frog Bayou, South Fourche LaFave River, and Gates 
Creek are presumed declining; and the status of populations in Mayatt 
Creek, Strawberry River, Cossatot River, Saline River and Little 
Missouri River are unknown (Szymanski 1998).

Previous Federal Action

    We had identified the scaleshell as a Category 2 species in notices 
of review published in the Federal Register on May 22, 1984 (49 FR 
21664). Scaleshell remained a Category 2 in subsequent notices 
including January 6, 1989 (54 FR 554), November 21, 1991 (56 FR 58804), 
November 15, 1994 (59 FR 58982). Prior to 1996, a Category 2 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 threat were not available to 
support a proposed rule. We stopped 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 to propose it for protection under the Act. We designated 
scaleshell as a candidate species on October 16, 1998.
    On May 8, 1998, we published Listing Priority Guidance for Fiscal 
Years 1998 and 1999 (63 FR 25502). The guidance clarifies the order in 
which we will process rulemakings, giving highest priority (Tier 1) to 
processing emergency rules to add species to the Lists of Endangered 
and Threatened Wildlife and Plants (Lists); second priority (Tier 2) to 
processing final determinations on proposals to add species to the 
Lists, processing new proposals to add species to the Lists, processing 
administrative findings on petitions (to add species to the Lists, 
delist species, or reclassify listed species), and processing a limited 
number of proposed or final rules to delist or reclassify species; and 
third priority (Tier 3) to processing proposed or final rules 
designating critical habitat. The processing of this proposed rule 
falls under Tier 2.

Summary of Factors Affecting the Species

    Section 4 of the Act and regulations (50 CFR Part 424) promulgated 
to implement the listing provisions of the Act set forth the procedures 
for adding species to the Federal lists. 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 
scaleshell (Leptodea leptodon) are as follows:
    A. The Present or Threatened Destruction, Modification, or 
Curtailment of its Habitat or Range. The loss of mussel diversity in 
the United States has been well documented and is a major concern for 
conservation 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 
LaRoe et al. 1995). Habitat loss and degradation are the primary causes 
of the precipitous decline of unionids (Neves 1993).
    Arguably, the scaleshell has suffered a greater range restriction 
than any other unionid. The range of this species 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. Scaleshell 
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 some portions of the 
species' range and numerous threats are likely to impact the few 
remaining viable extant populations. Water pollution, sedimentation, 
channelization, and impoundments contributed to the decline of 
scaleshell throughout its range. A general description of how these 
factors affect mussels is given below. Refer to Szymanski (1998) for a 
more detailed discussion.
    Mussel biologists generally accept that contaminants are partially 
responsible for the decline of mussels (Havlik and Marking 1987, 
Williams et al. 1993, Biggins et al. 1996). Because mussels are 
sedentary, they are extremely vulnerable to toxic effluents and changes 
in water chemistry from point and nonpoint source pollution. 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 are 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 in suspension, 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,

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Chesters and Schierow 1985). The water quality impacts caused by 
sedimentation are numerous. Generally, 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. 
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). 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 other dredging 
operations physically remove mussels along with the dredged material 
and may also bury or crush mussels (Watters 1995). Other effects of 
dredging extend beyond the excavated area. Headcutting, the upstream 
progression of substrate 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 throughout an entire 
system (Smith and Patrick 1991). As relatively immobile benthic 
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).
    Impoundments affect both upstream and downstream mussel populations 
by inducing scouring, changing temperature regimes, and altering 
habitat, food, and fish host availability (Vaughn, in litt. 1997). 
Impoundments permanently flood stream channels and eliminate flowing 
water that are essential habitat for most unionids including scaleshell 
(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 populations from each other and from host fishes (Stansbery 
1973, Fuller 1974, Vaughn 1993, Williams et al. 1993). The result of 
these factors is diminished recruitment success (Layzer et al. 1993). 
Dams are effective barriers to fish host movement and migration that 
unionids depend on for dispersal. Upstream populations can become 
reproductively isolated causing a decrease in genetic diversity. Even 
small, lowhead dams can hinder fish movement and isolate mussel 
populations from fish hosts. For example, Watters (1996) determined 
that the upstream distribution of two mussel species, the fragile 
papershell (Leptodea fragilis) and pink heelsplitter (Potamilus 
alatus), which like scaleshell are also believed to use the freshwater 
drum as a sole host, stopped at lowhead dams.
    Many of the same threats that caused the extirpation of historical 
populations of scaleshell 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 habitat. Today, scaleshell no longer 
occurs at disturbed sites that still support other endangered unionids 
(Szymanski 1998). This suggests that scaleshell is especially sensitive 
to 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 the remaining scaleshell populations.

Upper Mississippi River Basin

    Scaleshell 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, Illinois Natural History Survey, 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 from the Upper Mississippi River Basin.

Middle Mississippi River Basin

    Similar to the Upper Mississippi River Basin, threats have lead to 
the extirpation of scaleshell from the entire Ohio River Basin. Many of 
these threats continue to adversely affect extant populations in the 
middle Mississippi River Basin. Scaleshell habitat in the Meramec River 
Basin has been reduced in recent years. Buchanan (1980) found 
scaleshell in the lower 112 miles of the Meramec River. In 1997, 
scaleshell was collected only in the lower 60 miles of the river. 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. Bruenderman (pers. comm. 1998) 
attributed this decline primarily to the loss of channel stability. 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 void of mussels when resurveyed in 1997. Buchanan (in litt. 
1997) and Bruenderman (pers. comm. 1998) attributed this decline to 
several factors, including sedimentation, eutrophication, and unstable 
    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 U.S. Army Corps of Engineers 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 (Missouri 
Department of Conservation 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 25 miles of stream and 
negatively impacting the lower 80 miles of the river (Alan Buchanan, 
Missouri Department of Conservation, in litt. 1995).
    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 30 
miles of the Big River, and one dam exists in the lower Bourbeuse 
River. These structures are barriers to fish movement during normal 
flows (Missouri Department of Conservation 1997).
    Gravel mining poses an imminent threat to scaleshell populations in 
the Meramec River Basin. In 1998, a court ruling deauthorized the Army 
Corps of Engineers (Corps) from regulating gravel mining in the basin. 
Prior to that ruling, the Corps required operators to obtain a permit 
and follow several guidelines, which avoided adverse effects to 
mussels. 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 table. There are many gravel mining

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operations in the Meramec River Basin. Between 1994 and 1998, the Corps 
issued permits for 230 sites (excluding undocumented events). Existing 
and future mining operations will not need to obtain a permit or follow 
guidelines and may legally mine gravel directly from the Meramec River 
and all tributaries (Danny McKlendon, U.S. Army Corps of Engineers, St. 
Louis District, pers. comm. 1998).
    In 1994, several areas of the Gasconade River were highly unstable, 
possibly a result of row-crop farming near the bank 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 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. If populations still exist in any of 
the rivers within the Missouri River drainage, their long-term 
persistence is undoubtably precarious.

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 Wappapello Dam, 
Missouri (Ahlstedt and Jenkinson 1987, 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. They identified 48 miles that may still provide suitable mussel 
habitat, but did not collect scaleshell. All the remaining river miles 
are unsuitable for mussels. If the scaleshell is extant in the St. 
Francis River, it occurs in very small numbers and is restricted to the 
remaining few patches of suitable habitat.
    The White River between Beaver Reservoir and its headwaters, due to 
municipal pollution, gravel dredging, and dam construction, is no 
longer suitable for mussels (Gordon 1980). Navigational maintenance 
activities continue to destroy habitat from Newport to the confluence 
of the Mississippi River (Bates and Dennis 1983). This habitat 
destruction has relegated mussel populations to a few refugial sites, 
none of which support scaleshell.
    Species richness in the Spring River below river mile 9 has 
declined markedly from past surveys, with the lower three miles of 
river completely depleted of mussels and no longer supporting suitable 
habitat (Miller and Hartfield 1986, Gordon et al. 1984). Sand and 
gravel dredging, livestock movements (i.e., destruction of stream 
banks, disturbance of mussel beds, deposition of wastes, etc.), 
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).
    Within Frog Bayou, potential habitat is restricted to the area 
between Rudy and the confluence of the Arkansas River. Within this 
area, streambank modifications and in-stream gravel mining are 
degrading scaleshell habitat. Two reservoirs, one near Maddux Spring 
and the other at Mountainburg, impact the river above Rudy. Below the 
confluence of the Arkansas River, Gordon (1980) did not find live 
mussels, likely due to dredging activities (Gordon 1980). Although the 
current status of scaleshell in Frog Bayou is uncertain, any remaining 
individuals are probably in jeopardy due to limited habitat and in-
stream mining activities.
    The proposed Tuskahoma Reservoir (located above Hugo Reservoir) is 
a potential threat to mussels in the Kiamichi River. Although the U.S. 
Army Corps of Engineers has authorized construction, the lack of a 
local sponsor has rendered the project ``inactive'' (David Martinez, 
U.S. Fish and Wildlife Service, pers. comm. 1997). If constructed, the 
adverse effects associated with reservoirs (including permanent 
flooding of the channel and disruption of reproduction) are likely to 
destroy the mussel fauna.
    Sewage pollution, gravel dredging, and reservoirs continue to 
impact the Little River. Pine Creek Reservoir impounds the mainstem of 
the river. Further downstream, Broken Bow Reservoir impounds a major 
tributary to the Little River, the Mountain Fork River. Below Pine 
Creek Lake, the mussel fauna is severely depleted but recovers with 
increasing distance from the impoundment (Vaughn in litt. 1997). The 
discharge of reservoir water from Pine Creek and periodic discharge of 
pollution from Rolling Fork Creek, however, would seriously impact any 
remaining viable populations and prohibit any future recolonization 
(Clarke 1987).
    Hydroelectric dams and artificial lakes have impacted the Ouachita 
River. The ``Old River'' (an oxbow system off the mainstem), is now 
essentially a series of muddy, stagnant pools with water quality 
problems resulting from surrounding dumps (Clarke 1987).
    In summary, many of the same threats that caused the extirpation of 
historical populations of scaleshell still exist and continue to 
threaten extant populations. 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 and Bourbeuse Rivers, MO (Sue Bruenderman, pers. comm. 1998); 
Gasconade River, MO (Buchanan 1994); Frog Bayou, AR (Gordon 1980); and 
Spring River, AR (Gordon et al. 1984). Unregulated sand and gravel 
mining are eliminating important pool habitat (for both scaleshell and 
potential fish hosts) in the Meramec, Bourbeuse, Big, and Gasconade 
rivers in Missouri (Bruenderman pers. comm. 1998). Impoundments, 
channelization, and other dredging activities (e.g., sand and gravel 
mining) are destroying mussel populations and 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 have adverse 
impacts on any remaining populations in Oklahoma. Nearly all scaleshell 
populations are now restricted to small stretches of rivers with 
little, if any, potential for expansion or recolonization to other 
areas. For example, sewage pollution, gravel dredging, and reservoir 
construction have so degraded the Little River in Oklahoma that only a 
few small stretches are able to support mussel populations.
    B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes. It is unlikely that commercial mussel collectors 
ever purposefully collected scaleshell because of its small size and 
thin shell. It is probable, however, that over-harvesting activities 
that removed entire mussel beds impacted scaleshell populations. For 
example, according to local fishermen, during a period of extended 
drought mussel harvesters severely over-collected mussel beds in the 
Spring and Black rivers and completely destroyed most beds (Gordon et 
al. 1984). Thus, habitat destruction, removal of individuals from the 
stream and improper replacement may have indirectly impacted scaleshell 
populations. Today, incidental collecting could adversely affect

[[Page 44178]]

existing populations. In addition to disturbance of the stream bed, 
collection or improper replacement of only a few individuals, given 
that scaleshell now occurs in very small, isolated populations, could 
decimate an entire population. Even for mussels returned to the stream, 
mortality can still occur (Williams et al. 1993).
    As scaleshell becomes more uncommon, the interest of scientific and 
shell collectors will increase. Populations considered in this rule are 
generally localized, easily accessible, exposed during low flow 
periods, and are vulnerable to take for fish bait, curiosity, or 
vandalism. Up to five freshwater mussels per day, including scaleshell, 
may be legally collected in Missouri and used for bait (Sue 
Bruenderman, pers. comm. 1998).
    C. Disease or Predation. Although natural predation is not a factor 
for stable, healthy mussel populations, small mammal predation could 
potentially pose a problem for scaleshell populations (Gordon 1991). 
While the large size and/or thick shells of some species afford 
protection from small mammal predators, the small size and fragile 
shell of scaleshell makes it an easy and desirable prey species. A 
freshwater mussel survey of the Meramec and Bourbeuse Rivers found 
fresh scaleshell shells at several active racoon feeding areas (Sue 
Bruenderman pers. comm. 1998). Extant scaleshell 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 subject to infection 
(Ellis 1929) and mussel growth can be slowed (Imlay and Paige 1972). 
Disease and parasites may have caused major die-offs of freshwater 
mussels in the late 1970's throughout the eastern United States (Neves 
1986). For example, significant die-offs of freshwater mussels occurred 
in 1977 and 1978 in the Meramec and Bourbeuse Rivers. Large numbers of 
mussels of all species, including scaleshell were lost. Buchanan (1986) 
presumed an epizootic or other disease caused the die-off since no 
environmental impact was reported or could be found.
    D. The Inadequacy of Existing Regulatory Mechanisms. 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 into U.S. waters.
    Although the passage of these Acts has resulted in positive 
consequences (including a decrease in lead and fecal coliform 
bacteria), 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). Nonpoint pollution sources appear 
to be the cause of increases in nitrogen. Many of the impacts discussed 
above occurred in the past as unintended consequences of human 
development. Improved understanding of these consequences has led to 
regulatory (e.g., Clean Water Act) and voluntary measures (e.g., best 
management practices for agriculture and silviculture) and improved 
land use practices that are generally compatible with the continued 
existence of scaleshell. Nonetheless, scaleshell is highly restricted 
in numbers and distribution and shows little evidence of recovering 
from historic habitat losses.
    Although recognized by species experts as threatened in Arkansas, 
the scaleshell is not afforded State protection. Missouri and Oklahoma 
list the scaleshell as a species of conservation concern (Bruenderman, 
in litt. 1998; Caryn Vaughn pers. comm. 1995). However, these 
designations are used primarily for planning and communication purposes 
and do not afford State protective status from direct take and habitat 
destruction (David Martinez; Paul McKenzie; U.S. Fish and Wildlife 
Service, pers. comm. 1997). Without habitat protection, populations of 
scaleshell will continue to decline.
    E. Other Natural or Manmade Factors Affecting Its Continued 
Existence. 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). The scaleshell is believed to use freshwater drum as a sole 
host. Despite the tremendous fecundity of female mussels, 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 scaleshell populations. 
Once a larva successfully transforms on a host, it is further 
challenged with dropping off onto suitable habitat. Watters (1995) 
reported that estimated chances of successful transformation and 
excystment range between 0.0001 percent (Jansen and Hanson 1991) and 
0.000001 percent (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.
    The small number and low density of the remaining scaleshell 
populations exacerbate the threats to its survival posed by the above 
factors. Although the scaleshell was always locally rare if broadly 
distributed, the widespread loss of populations and the limited number 
of collections in recent years indicates that the current population 
densities are 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, low density 
populations are more likely to fluctuate below the minimum viable 
population (i.e., the minimum number of individuals needed in a 
population to persist). 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

[[Page 44179]]

required for any reproductive success to occur (Downing et al. 1993). 
Small mussel populations may have individuals too scattered to 
reproduce effectively. Many of the remaining scaleshell populations may 
be at or below this threshold density. These populations will be, if 
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. Although the scaleshell naturally 
occurs in patches and necessarily possesses mechanisms to adapt to such 
a population structure, anthropogenic influences have fragmented and 
further 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, preservation of a 
metapopulation (interconnected subpopulations) structure is imperative 
for long-term freshwater mussel survival. Unfortunately, many of the 
extant scaleshell 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 recent invasion of the exotic zebra mussel (Dreissena 
polymorpha) poses a substantial threat to native unionids (Herbert et 
al. 1989). The introduction of Dreissena into North America probably 
resulted from an ocean-crossing vessel that discharged freshwater 
ballast from Europe containing free-swimming larvae of the zebra mussel 
(Griffiths et al. 1991). The spread of this species has caused severe 
declines in native freshwater mussel species. Currently, the zebra 
mussel invasion of the Mississippi and Ohio rivers threaten native 
freshwater mussel fauna (Clarke 1995). Zebra mussels starve and 
suffocate native mussels by attaching to their shells in large numbers. 
The natural history of zebra mussels is not completely understood; 
therefore, effective control measures are not yet known. Given that 
recreational and commercial vessels greatly facilitate zebra mussel 
movement, and because of the proliferation and spread that has 
occurred, invasion of the zebra mussel into portions of the middle and 
lower Mississippi Basin is likely (Buchanan pers. comm. 1995). Massive 
unionid mortality and extinctions are expected in some areas colonized 
by zebra mussels (Biggins 1992). If zebra mussel invasion does occur, 
the continued survival of scaleshell will be further jeopardized.


    Significant habitat loss, range restriction, and population 
fragmentation and size reduction have rendered the scaleshell mussel 
vulnerable to extinction. The scaleshell has disappeared from the 
entire upper and most of the middle Mississippi River drainages. Of the 
53 known historical populations, 13 remain. Although much of the 
decline occurred before 1950, population declines continue in some 
portions of the species' range and numerous threats are likely to 
impact the few remaining viable extant populations. The small number 
and low density of the remaining scaleshell populations exacerbate the 
threats and effects of chance events to scaleshell. The survival of all 
scaleshell populations is threatened by water quality degradation, 
impoundments, sedimentation, channelization, or dredging. The recent 
deregulation of gravel mining is a significant threat to scaleshell 
populations in three rivers within the Meramec River Basin, Missouri.
    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
faced by the scaleshell in determining to make this proposed rule. The 
present distribution and abundance of the scaleshell is at risk given 
the potential for these impacts to continue. Federal listing under 
authority of the Endangered Species Act is the only mechanism we can 
presently identify that ensures protection to scaleshell. Therefore, 
based on this evaluation, the preferred action is to list the 
scaleshell mussel as an endangered species. The Act defines an 
endangered species as one that is in danger of extinction throughout 
all or a significant portion of its range. A threatened species is one 
that is likely to become an endangered species in the foreseeable 
future throughout all or a significant portion of its range. Endangered 
status is appropriate for the scaleshell due to habitat loss, range 
restriction, and population fragmentation.

Critical Habitat

    Section 3 of the Act defines critical habitat as: (i) the specific 
areas within the geographical area occupied by a species, at the time 
it is listed in accordance with the Act, on which are found those 
physical or biological features (I) essential to the conservation of 
the species and (II) that may require special management considerations 
or protection; and (ii) specific areas outside the geographic area 
occupied by a species at the time it is listed, upon a determination 
that such areas are essential for the conservation of the species. 
``Conservation'' means the use of all methods and procedures needed to 
bring the species to the point at which listing under the Act is no 
longer necessary.
    Section 4(a)(3) of the Act, as amended, and implementing 
regulations (50 CFR 424.12) require that, to the maximum extent prudent 
and determinable, we designate critical habitat at the time the species 
is determined to be endangered or threatened. Our regulations (50 CFR 
424.12(a)(1)) state that the designation of critical habitat is not 
prudent when one or both of the following situations exist--(1) the 
species is threatened by taking or other human activity, and 
identification of critical habitat can be expected to increase the 
degree of threat to the species, or (2) such designation of critical 
habitat would not be beneficial to the species. We find that 
designation of critical habitat is not prudent for scaleshell for both 
reasons stated above.
    Potential benefits of critical habitat designation derive from 
section 7(a)(2) of the Act, which requires Federal agencies, in 
consultation with us, to ensure that their actions are not likely to 
jeopardize the continued existence of listed species or to result in 
the destruction or adverse modification of critical habitat of such 
species. Critical habitat designation, by definition, directly affects 
only Federal agency actions. Since the scaleshell is aquatic, Federal 
actions that might affect this species and its habitat include those 
with impacts on stream channel geometry, bottom substrate composition, 
water quantity and quality, and stormwater runoff. Such activities that 
impact scaleshell habitat would be subject to review under section 
7(a)(2) of the Act, whether or not critical habitat was designated. The 
scaleshell has become so restricted in distribution that any 
significant adverse modification or destruction of occupied habitats 
would likely jeopardize the continued existence of this species. 
Additionally, our regulations (50 CFR part 402) specify that the 
jeopardy analysis, like the adverse modification or destruction of 
critical habitat analysis, consider the detrimental effect to both 
survival and recovery. Therefore, even as the species recovers

[[Page 44180]]

and its numbers increase, the jeopardy analysis would continue to 
protect scaleshell habitat. As part of the outreach from this proposed 
rule, we will notify the State and Federal agencies of this species' 
general distribution, and request that they provide data on proposed 
Federal actions that might adversely affect the species. Should any 
future projects be proposed in areas inhabited by this mussel, the 
involved Federal agency will have the distributional data needed to 
determine if their action may impact the species, and if needed, we 
will provide more specific distributional information. Therefore, 
habitat protection for the scaleshell can be accomplished through the 
implementation of section 7 jeopardy standard and there is no benefit 
in designating currently occupied habitat of this species as critical 
    Recovery of this species may require the identification of 
unoccupied stream and river reaches appropriate for reintroduction. 
Critical habitat designation of unoccupied stream and river reaches 
might benefit this species by alerting permitting agencies to potential 
sites for reintroduction and allowing them the opportunity to evaluate 
projects that may affect these areas. We are currently working with 
state and other Federal agencies to periodically survey and assess 
habitat potential of stream and river reaches for listed and candidate 
aquatic species. This process provides up to date information on 
instream habitat conditions in response to land use changes within 
watersheds. We distribute the information generated from river surveys 
and assessments through our coordination with other agencies. We will 
continue to work with State and Federal agencies, as well as private 
property owners and other affected parties, through the recovery 
process to identify stream reaches and potential sites for 
reintroduction of this species. Thus, any benefit that might be 
provided by designation of unoccupied habitat as critical will be 
accomplished more effectively with the current coordination process, 
and is preferable for aquatic habitats which change rapidly in response 
to watershed land use practices. In addition, we believe that any 
potential benefits to critical habitat designation on occupied and 
unoccupied habitats are outweighed by additional threats to the species 
that would result from such designation, as discussed below.
    All known populations of scaleshell occur in streams flowing 
through private lands, and if unoccupied habitat is needed for 
recovery, private lands may also be involved. One threat to all 
surviving populations appears to be pollutants in stormwater runoff 
that originate from private land activities. Therefore, the survival 
and recovery of this species will be highly dependent on landowner 
cooperation in reducing land use impacts. Controversy resulting from 
critical habitat designation has been known to reduce private landowner 
cooperation in the management of species listed under the Act. Critical 
habitat designation could affect landowner cooperation within 
watersheds occupied by the scaleshell and in areas unoccupied that 
might be needed for recovery.
    Though critical habitat designation directly affects only Federal 
agency actions, this process can arouse concern and resentment on the 
part of private landowners and other interested parties. The 
publication of critical habitat maps in the Federal Register and local 
newspapers, and other publicity or controversy accompanying critical 
habitat designation may increase the potential for vandalism as well as 
other collection threats. Scaleshell populations are especially 
vulnerable to vandalism. This species is found in shallow shoals or 
riffles in restricted stream and river segments and is relatively 
immobile and unable to escape collectors or vandals. It inhabits remote 
but easily accessed areas, and they are sensitive to a variety of 
easily obtained commercial chemicals and products. Because of these 
factors, vandalism or collecting could be undetectable and 
    We believe that the potential for taking represents a significant 
threat to scaleshell populations. The rarity of this species increases 
the likelihood that it will be sought by shell collectors and for 
scientific purposes. The publication of critical habitat, maps, and 
other publicity accompanying critical habitat designation could 
increase that threat. The locations of populations of this species have 
consequently been described only in general terms for purposes of this 
rulemaking action.
    Based on the above analysis, we have concluded that critical 
habitat designation would provide little additional benefit for this 
species beyond those that would accrue from listing under the Act. We 
also conclude that any potential benefit from such a designation would 
be offset by an increased level of vulnerability to vandalism or 
collecting and by a possible reduction in landowner cooperation to 
manage and recover this species. We have concluded therefore that the 
designation of critical habitat for scaleshell is not prudent.

Available Conservation Measures

    Conservation measures provided to species listed as endangered or 
threatened under the Act include recognition, recovery actions, 
requirements for Federal protection, and prohibitions against certain 
practices. Recognition through listing encourages and results in 
conservation actions by Federal, State, and local agencies, private 
organizations, and individuals. The Act provides for possible land 
acquisition and cooperation with the States and requires that recovery 
actions be carried out for all listed species. The protection required 
of Federal agencies and the prohibitions against taking and harm are 
discussed, in part, below.
    Section 7(a) of the Act, as amended, requires Federal agencies to 
evaluate their actions with respect to any species that is proposed or 
listed as endangered or threatened and with respect to its critical 
habitat, if any is being designated. Regulations implementing this 
interagency cooperation provision of the Act are codified at 50 CFR 
Part 402. Section 7(a)(4) requires Federal agencies to confer 
informally with us on any action that is likely to jeopardize the 
continued existence of a proposed species or result in destruction or 
adverse modification of proposed critical habitat. If a species is 
listed subsequently, Section 7(a)(2) of the Act requires Federal 
agencies to ensure that activities they authorize, fund, or carry out 
are not likely to jeopardize the continued existence of such a species 
or to destroy or adversely modify its critical habitat. If a Federal 
action may affect a listed species or its critical habitat, the 
responsible Federal agency must enter into formal consultation with us.
    Federal agency actions that may require conference and/or 
consultation as described in the preceding paragraph include the 
issuance of permits for reservoir construction, stream alterations, 
waste water facility development, water withdrawal projects, pesticide 
registration, agricultural assistance programs, mining, road and bridge 
construction, Federal loan programs, water allocation, and hydropower 
relicensing. In our experience, nearly all section 7 consultations 
result in protecting the species and meeting the project's objectives.
    The Act and implementing regulations set forth a series of general 
prohibitions and exceptions that apply to all endangered wildlife. The 
prohibitions, codified at 50 CFR 17.21, in part, make it illegal for 
any person subject to the jurisdiction of the United

[[Page 44181]]

States to take (includes harass, harm, pursue, hunt, shoot, wound, 
kill, trap, capture, or collect; or to attempt any of these), import or 
export, ship in interstate commerce in the course of commercial 
activity, or sell or offer for sale in interstate or foreign commerce 
any listed species. It also is illegal to possess, sell, deliver, 
carry, transport, or ship any such wildlife that has been taken 
illegally. Certain exceptions apply to our agents and agents of State 
conservation agencies.
    We may issue permits to carry out otherwise prohibited activities 
involving endangered wildlife under certain circumstances. We codified 
the regulations governing permits for endangered species at 50 CFR 
17.22. Such permits are available for scientific purposes, to enhance 
the propagation or survival of the species, and/or for incidental take 
in the course of otherwise lawful activities.
    It is our policy, published in the Federal Register on July 1, 1994 
(59 FR 34272), to identify, to the maximum extent practicable, those 
activities that are or are not likely to constitute a violation of 
section 9 of the Act. The intent of this policy is to increase public 
awareness as to the potential effects of this proposed listing on 
future and ongoing activities within a species' range. We believe that 
the following activities are unlikely to result in a violation of 
section 9:
    (1) Existing discharges into waters supporting these species, 
provided these activities are carried out in accordance with existing 
regulations and permit requirements (e.g., activities subject to 
sections 402, 404, and 405 of the Clean Water Act and discharges 
regulated under the National Pollutant Discharge Elimination System).
    (2) Actions that may affect the scaleshell and are authorized, 
funded or carried out by a Federal agency when the action is conducted 
in accordance with any reasonable and prudent measures we have 
specified in accordance with section 7 of the Act.
    (3) Development and construction activities designed and 
implemented pursuant to Federal, State, and local water quality 
    (4) Existing recreational activities such as swimming, wading, 
canoeing, and fishing.
    We believe the following activities would be likely to result in a 
violation of section 9; however, possible violations are not limited to 
these actions alone:
    (1) Unauthorized collection or capture of the species;
    (2) Unauthorized destruction or alteration of the species habitat 
(e.g., in-stream dredging, channelization, discharge of fill material);
    (3) violation of any discharge or water withdrawal permit within 
the species' occupied range; and
    (4) illegal discharge or dumping of toxic chemicals or other 
pollutants into waters supporting the species.
    We will review other activities not identified above on a case-by-
case basis to determine whether they may be likely to result in a 
violation of section 9 of the Act. We do not consider these lists to be 
exhaustive and provide them as information to the public.
    You should direct questions regarding whether specific activities 
may constitute a future violation of section 9 to the Field Supervisor 
of the Service's Columbia Field office (see ADDRESSES section). You may 
request copies of the regulations regarding listed wildlife from and 
address questions about prohibitions and permits to the U.S. Fish and 
Wildlife Service, Ecological Services Division, Henry Whipple Federal 
Building, 1 Federal Drive, Fort Snelling, MN 55111 (Phone 612/713-5350; 
Fax 612/713-5292).
    We intend that any final action resulting from this proposal will 
be as accurate and as effective as possible. Therefore, we request 
comments or suggestions from the public, other concerned governmental 
agencies, the scientific community, industry, or any other interested 
party concerning this proposed rule. Comments particularly are sought 
    (1) Biological, commercial trade, or other relevant data concerning 
any threat (or lack thereof) to this species;
    (2) The location of any additional populations of this species and 
the reasons why any habitat should or should not be determined to be 
critical habitat as provided by Section 4 of the Act;
    (3) Additional information concerning the range, distribution, and 
population size of this species;
    (4) Current or planned activities in the subject area and their 
possible impacts on this species.
    We will take into consideration your comments and any additional 
information received on this species when making a final determination 
regarding this proposal. We will also submit the available scientific 
data and information to appropriate, independent specialists for 
review. We will summarize the opinions of these reviewers in the final 
decision document. The final determination may differ from this 
proposal based upon the information we receive.
    The Act provides for a public hearing on this proposal, if 
requested. We must receive requests within 45 days of the date of 
publication of the proposal in the Federal Register. Such requests must 
be made in writing and addressed to Field Supervisor, U.S. Fish and 
Wildlife Service, Ecological Services Field Office, 608 East Cherry 
Street Room 200, Columbia, Missouri 65201.

Executive Order 12866

    Executive Order 12866 requires each agency to write regulations 
that are easy to understand. We invite your comments on how to make 
this rule easier to understand including answers to the following: (1) 
Are the requirements of the rule clear? (2) Is the discussion of the 
rule in the Supplementary Information section of the preamble helpful 
in understanding the rule? (3) What else could we do to make the rule 
easier to understand?
    Send a copy of any comments that concern how we could make this 
rule easier to understand to the office identified in the ADDRESSES 
section at the beginning of this document.

National Environmental Policy Act

    We have determined that we do not need to prepare an Environmental 
Assessment, as defined under the authority of the National 
Environmental Policy Act of 1969, in connection with regulations 
adopted pursuant to section 4(a) of the Act. We published a notice 
outlining our reasons for this determination in the Federal Register on 
October 25, 1983 (48 FR 49244).

Paperwork Reduction Act

    This rule does not contain any new collections of information other 
than those already approved under the Paperwork Reduction Act, 44 
U.S.C. 3501 et seq., and assigned Office of Management and Budget 
clearance number 1018-0094. An agency may not conduct or sponsor, and a 
person is not required to respond to a collection of information, 
unless it displays a currently valid control number. For additional 
information concerning permit and associated requirements for 
threatened species, see 50 CFR 17.22.

References Cited

    A complete list of all references cited herein, as well as others, 
is available upon request from the Field Supervisor (see ADDRESSES 
    Authors: The primary authors of this proposed rule are Mr. Andy 
Roberts (see FOR FURTHER INFORMATION CONTACT section) and Ms. Jennifer 
Szymanski (see ADDRESSES section).

[[Page 44182]]

List of Subjects in 50 CFR Part 17

    Endangered and threatened species, Exports, Imports, Reporting and 
record keeping requirements, Transportation.

Regulation Promulgation

    Accordingly, the Service amends part 17, subchapter B of chapter I, 
title 50 of the Code of Federal Regulations, as set forth below:


    1. The authority citation for part 17 continues to read as follows:

    Authority: 16 U.S.C. 1361-1407; 16 U.S.C. 1531-1544; 16 U.S.C. 
4201-4245; Pub. L. 99-625, 100 Stat. 3500; unless otherwise noted.

    2. Section 17.11(h) is amended by adding the following, in 
alphabetical order, under Clams to the List of Endangered and 
Threatened Wildlife:

Sec. 17.11  Endangered and threatened wildlife.

* * * * *
    (h) * * *

                        Species                                                    Vertebrate
--------------------------------------------------------                        population where                                  Critical     Special
                                                            Historic range       endangered or         Status      When listed    habitat       rules
           Common name                Scientific name                              threatened

       *                   *                   *                   *                   *                   *                   *

       *                   *                   *                   *                   *                   *                   *
Mussel, Scaleshell...............  Leptodea leptodon...  U.S.A. (AL, AR, IL,  NA.................  E                                     NA           NA
                                                          IN, IA, KY, MN,
                                                          MO, OH, OK, SD,
                                                          TN, WI).

       *                   *                   *                   *                   *                   *                   *

    Dated: July 29, 1999.
John G. Rogers,
Acting Director, Fish and Wildlife Service.
[FR Doc. 99-20965 Filed 8-12-99; 8:45 am]