Endangered and Threatened Wildlife and Plants; Critical Habitat for Five Endangered and Two Threatened Mussels in Four Northeast Gulf of Mexico Drainages, 32746-32796 [06-5075]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 71, Number 108 (Tuesday, June 6, 2006)]
[Proposed Rules]
[Pages 32746-32796]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-5075]



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Part III





Department of the Interior





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Fish and Wildlife Service



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50 CFR Part 17



Endangered and Threatened Wildlife and Plants; Critical Habitat for 
Five Endangered and Two Threatened Mussels in Four Northeast Gulf of 
Mexico Drainages; Proposed Rule

Federal Register / Vol. 71, No. 108 / Tuesday, June 6, 2006 / 
Proposed Rules

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

RIN 1018-AU87


Endangered and Threatened Wildlife and Plants; Critical Habitat 
for Five Endangered and Two Threatened Mussels in Four Northeast Gulf 
of Mexico Drainages

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to 
designate critical habitat for the endangered fat threeridge, 
shinyrayed pocketbook, Gulf moccasinshell, Ochlockonee moccasinshell, 
and oval pigtoe, and the threatened Chipola slabshell and purple 
bankclimber (collectively referred to as the seven mussels), pursuant 
to the Endangered Species Act of 1973, as amended (Act). We propose to 
designate 11 units encompassing approximately 1,864 kilometers (1,158 
miles) of river and stream channels as critical habitat. Proposed 
critical habitat includes portions of the Econfina Creek drainage in 
Florida, the Apalachicola--Chattahoochee--Flint River drainage in 
Alabama, Florida, and Georgia, the Ochlockonee River drainage in 
Florida and Georgia, and the Suwannee River drainage in Florida.

DATES: We will accept comments from all interested parties until August 
7, 2006. We must receive requests for public hearings, in writing, at 
the address shown in the ADDRESSES section by July 21, 2006.

ADDRESSES: If you wish to comment, you may submit your comments and 
materials concerning this proposal by any one of the following methods:
    1. You may submit written comments and information to the Field 
Supervisor, U.S. Fish and Wildlife Service, 1601 Balboa Avenue, Panama 
City, Florida 32405.
    2. You may hand-deliver written comments to our office, at the 
above address.
    3. You may send comments by electronic mail (e-mail) to 
FW4ESFRPanamaCity@FWS.gov. Please see the ``Public Comments Solicited'' 
section under SUPPLEMENTARY INFORMATION for file format and other 
information about electronic filing.
    4. You may fax your comments to 850-763-2177.
    5. Federal eRulemaking Portal: https://www.regulations.gov. Follow 
the instructions for submitting comments.
    Comments and materials received, as well as supporting 
documentation used in the preparation of this proposed rule, will be 
available for public inspection, by appointment, during normal business 
hours at U.S. Fish and Wildlife Service, 1601 Balboa Avenue, Panama 
City, Florida 32405 (telephone 850-769-0552).

FOR FURTHER INFORMATION CONTACT: Jerry Ziewitz at the address above 
(telephone 850-769-0552 ext. 223; facsimile 850-763-2177).

SUPPLEMENTARY INFORMATION:

Public Comments Solicited

    We intend that any final action resulting from this proposal will 
be as accurate and as effective as possible. Therefore, comments or 
suggestions from the public, other concerned governmental agencies, the 
scientific community, industry, or any other interested party 
concerning this proposed rule are hereby solicited. We particularly 
seek comments concerning:
    (1) The reasons any habitat should or should not be determined to 
be critical habitat as provided by section 4 of the Act (16 U.S.C. 1531 
et seq.), including whether the benefit of designation will outweigh 
any threats to the species due to designation;
    (2) Specific information on the amount and distribution of habitat 
for the seven mussels, including areas occupied by the seven mussels at 
the time of listing and containing the features essential to the 
conservation of the species, and areas not occupied at the time of 
listing that are essential to the conservation of the species;
    (3) Whether the middle section of the Flint River complex, between 
the confluence of Gum Creek and the confluence of Auchumpkee/
Ulcohatchee Creek, has the Primary Constituent Elements for the 
mussels, is occupied by the mussels, or is essential to the 
conservation of the mussels;
    (4) Land use designations and current or planned activities in the 
subject areas and their possible impacts on proposed critical habitat;
    (5) Any foreseeable economic, national security, or other potential 
impacts resulting from the proposed designation and, in particular, any 
impacts on small entities; and
    (6) Whether our approach to designating critical habitat could be 
improved or modified in any way to provide for greater public 
participation and understanding, or to assist us in accommodating 
public concerns and comments.
    If you wish to comment, you may submit your comments and materials 
concerning this proposal by any one of several methods (see ADDRESSES 
section). Please submit e-mail comments to FW4ESFRPanamaCity@FWS.gov in 
ASCII file format and avoid the use of special characters or any form 
of encryption. Please also include ``Attn: 7 mussels--RIN 1018-AU87'' 
in your e-mail subject header, and your name and return address in the 
body of your message. If you do not receive a confirmation from the 
system that we have received your message, contact us directly by 
calling our Panama City, Florida, Fish and Wildlife Office at phone 
number 850-769-0552. Please note that the e-mail address 
FW4ESFRPanamaCity@FWS.gov will be closed out at the termination of the 
public comment period.
    Our practice is to make comments, including names and home 
addresses of respondents, available for public review during regular 
business hours. Individual respondents may request that we withhold 
their home addresses from the rulemaking record, which we will honor to 
the extent allowable by law. There also may be circumstances in which 
we would withhold from the rulemaking record a respondent's identity, 
as allowable by law. If you wish us to withhold your name or address, 
you must state this prominently at the beginning of your comment, but 
you should be aware that the Service may be required to disclose your 
name and address pursuant to the Freedom of Information Act. However, 
we will not consider anonymous comments. We will make all submissions 
from organizations or businesses, and from individuals identifying 
themselves as representatives or officials of organizations or 
businesses, available for public inspection in their entirety. Comments 
and materials received will be available for public inspection, by 
appointment, during normal business hours at the above address.

Role of Critical Habitat in Actual Practice of Administering and 
Implementing the Act

    Attention to and protection of habitat is paramount to successful 
conservation actions. The role that designation of critical habitat 
plays in protecting habitat of listed species, however, is often 
misunderstood. There are significant limitations on the regulatory 
effect of designation under Act section 7(a)(2). In brief, (1) 
designation provides additional protection to habitat only where there 
is a Federal nexus; (2) the protection is relevant only when, in the

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absence of designation, destruction or adverse modification of the 
critical habitat would in fact take place (in other words, other 
statutory or regulatory protections, policies, or other factors 
relevant to agency decision-making would not prevent the destruction or 
adverse modification); and (3) designation of critical habitat triggers 
the prohibition of destruction or adverse modification of that habitat, 
but it does not require specific actions to restore or improve habitat.
    Currently, only 475 species, or 36 percent of the 1,311 listed 
species in the U.S. under the jurisdiction of the Service, have 
designated critical habitat. We address the habitat needs of all 1,311 
listed species through conservation mechanisms such as listing, section 
7 consultations, the section 4 recovery planning process, the section 9 
protective prohibitions of unauthorized take, section 6 funding to the 
States, the section 10 incidental take permit process, and cooperative, 
non-regulatory efforts with private landowners. The Service believes 
that it is these measures that may make the difference between 
extinction and survival for many species.
    In considering exclusions of areas proposed for designation, we 
evaluated the benefits of designation in light of Gifford Pinchot Task 
Force v. United States Fish and Wildlife Service (378 F. 3d 1059 (9th 
Cir 2004). In that case, the Ninth Circuit invalidated the Service's 
regulation defining ``destruction or adverse modification of critical 
habitat.'' In response, on December 9, 2004, the Director issued 
guidance to be considered in making section 7 adverse modification 
determinations. This proposed critical habitat designation does not use 
the invalidated regulation in our consideration of the benefits of 
including areas in this final designation. Rather, it relies on the 
guidance issued by the Director in response to the Gifford Pinchot 
decision (see ``Adverse Modification Standard'' discussion below). The 
Service will carefully manage future consultations that analyze impacts 
to designated critical habitat, particularly those that appear to be 
resulting in an adverse modification determination. Such consultations 
will be reviewed by the Regional Office prior to finalizing to ensure 
that an adequate analysis has been conducted that is informed by the 
Director's guidance.
    On the other hand, to the extent that designation of critical 
habitat provides protection, that protection can come at significant 
social and economic cost. In addition, the mere administrative process 
of designation of critical habitat is expensive, time-consuming, and 
controversial. The current statutory framework of critical habitat, 
combined with past judicial interpretations of the statute, make 
critical habitat the subject of excessive litigation. As a result, 
critical habitat designations are driven by litigation and courts 
rather than biology, and made at a time and under a time frame that 
limits our ability to obtain and evaluate the scientific and other 
information required to make the designation most meaningful.
    In light of these circumstances, the Service believes that 
additional agency discretion would allow our focus to return to those 
actions that provide the greatest benefit to the species most in need 
of protection.

Procedural and Resource Difficulties in Designating Critical Habitat

    We have been inundated with lawsuits for our failure to designate 
critical habitat, and we face a growing number of lawsuits challenging 
critical habitat determinations once they are made. These lawsuits have 
subjected the Service to an ever-increasing series of court orders and 
court-approved settlement agreements, compliance with which now 
consumes nearly the entire listing program budget. This leaves the 
Service with little ability to prioritize its activities to direct 
scarce listing resources to the listing program actions with the most 
biologically urgent species conservation needs.
    The consequence of the critical habitat litigation activity is that 
limited listing funds are used to defend active lawsuits, to respond to 
Notices of Intent (NOIs) to sue relative to critical habitat, and to 
comply with the growing number of adverse court orders. As a result, 
listing petition responses, the Service's own proposals to list 
critically imperiled species, and final listing determinations on 
existing proposals are all significantly delayed.
    The accelerated schedules of court-ordered designations have left 
the Service with limited ability to provide for public participation or 
to ensure a defect-free rulemaking process before making decisions on 
listing and critical habitat proposals, due to the risks associated 
with noncompliance with judicially imposed deadlines. This in turn 
fosters a second round of litigation in which those who fear adverse 
impacts from critical habitat designations challenge those 
designations. The cycle of litigation appears endless and is expensive, 
thus diverting resources from conservation actions that may provide 
relatively more benefit to imperiled species.
    The costs resulting from the designation include legal costs, the 
cost of preparation and publication of the designation, the analysis of 
the economic effects and the cost of requesting and responding to 
public comment, and in some cases the costs of compliance with the 
National Environmental Policy Act (NEPA; 42 U.S.C. 4371 et seq.). These 
costs, which are not required for many other conservation actions, 
directly reduce the funds available for direct and tangible 
conservation actions.

Background

    In this proposed rule, we intend to discuss only information about 
the seven mussels that is directly relevant to the designation of 
critical habitat. For more information about these seven mussels, 
please refer to our final rule listing fat threeridge, shinyrayed 
pocketbook, Gulf moccasinshell, Ochlockonee moccasinshell, and oval 
pigtoe as endangered, and Chipola slabshell and purple bankclimber as 
threatened published in the Federal Register on March 16, 1998 (63 FR 
12664) and to our final recovery plan, which is available from the 
Panama City, Florida Fish and Wildlife Office or online at https://
www.fws.gov/endangered/recovery/#plans. The purple 
bankclimber (Elliptoideus sloatianus), Gulf moccasinshell (Medionidus 
penicillatus), Ochlockonee moccasinshell (Medionidus simpsonianus), 
oval pigtoe (Pleurobema pyriforme), shinyrayed pocketbook (Lampsilis 
subangulata), Chipola slabshell (Elliptio chipolaensis), and fat 
threeridge (Amblema neislerii) are variously distributed in four river 
basins that flow into the northeast Gulf of Mexico: Econfina Creek, 
Apalachicola River (a large basin generally labeled with the names of 
its major tributaries, the Chattahoochee and Flint rivers, as the ACF 
River Basin), Ochlockonee River, and Suwannee River.
    The endangered fat threeridge is a medium-sized to large, 
subquadrate, inflated, solid, and heavy-shelled mussel that reaches a 
length of 10.2 centimeters (cm) (4.0 inches (in)). Large specimens are 
so inflated that the width approximates the height. The umbos (bulges 
near the hinge of the shell) are in the anterior quarter of the shell. 
The dark brown to black shell is strongly sculptured with seven or 
eight prominent horizontal parallel plications (ridges).
    The endangered shinyrayed pocketbook is a medium-sized mussel that 
reaches approximately 8.4 cm (3.3 in) in length. The shell is generally 
elongated, with broad, somewhat inflated umbos and a rounded posterior 
ridge. The shell is thin but solid. The

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surface is smooth and shiny and ranges from straw-yellow to chestnut-
brown with a variable number of black to bright emerald-green rays, 
which emanate from the umbo across the disk.
    The shinyrayed pocketbook was listed as federally endangered under 
the scientific name Lampsilis subangulata. The shinyrayed pocketbook 
and three other Lampsilis species that are not federally listed are now 
assigned to the newly recognized genus Hamiota (Roe and Hartfield 2005, 
p. 1). Several characteristics, including glochidia packaging in a 
superconglutinate, placement and shape of the marsupia, and glochidia 
release through the excurrent siphon, support recognition of these 
species as a distinct genus (Roe and Hartfield 2005, p. 1), and we plan 
to implement the name change in a separate rule-making.
    The endangered Gulf moccasinshell is a small mussel that reaches a 
length of about 5.6 cm (2.2 in), is elongate-elliptical or rhomboidal 
in outline, fairly inflated, and has relatively thin valves. The 
ventral margin is nearly straight or slightly rounded. The posterior 
ridge is rounded to slightly angled and intersects the end of the shell 
at the base line. Females tend to have the posterior point above the 
ventral margin and are more inflated than males.
    The endangered Ochlockonee moccasinshell is small, generally under 
5.6 cm (2.2 in) long. It is slightly elongate-elliptical in outline, 
the posterior end obtusely rounded at the median line, and the ventral 
margin broadly curved. The posterior ridge is moderately angular and 
covered in its entire length with well-developed, irregular plications. 
Sculpturing may also extend onto the disk below the ridge. The 
periostracum (outside surface of the shell) is smooth. The color is 
light brown to yellowish green, with dark green rays formed by a series 
of connected chevrons or undulating lines across the length of the 
shell.
    The endangered oval pigtoe is a small-to-medium-sized mussel that 
attains a length of about 6.1 cm (2.4 in). The shell is suboviform and 
compressed. The periostracum is shiny smooth; yellowish, chestnut, or 
dark brown; rayless; and with distinct growth lines. The posterior 
slope is biangulate and forms a blunt point on the posterior margin. 
The umbos are slightly elevated above the hingeline.
    The endangered oval pigtoe is the only species among the seven 
mussels of this proposed rule that occurs in all four Gulf of Mexico 
river basins comprising their collective range: Econfina Creek, ACF, 
Ochlockonee, and Suwannee. Morphological variation across this broad 
range has led to the description of several nominal species since it 
was originally described as Unio pyriformis (Lea 1857, p. 169-172). 
Williams and Butler (1994, p. 111) recognized the form distributed in 
the Ochlockonee and Suwannee River systems as the Florida pigtoe, 
Pleurobema reclusum (Wright 1898, p. 111-112), consistent with Simpson 
(1914, p. 1-1540). However, Turgeon et al. (1998, p. 36) recognized the 
forms from all four basins as one species, P. pyriforme, which was the 
taxonomic classification upon which we relied on for the 1998 final 
rule listing this species as endangered. A recent study using molecular 
genetic techniques compared tissue samples from three of the four 
basins (Econfina Creek, ACF, and Suwannee), and concluded that the 
Suwannee samples were distinctive and warranted specific status as P. 
reclusum (Kandl et al. 2001, p. 10). We acknowledged these findings in 
our 2003 final recovery plan, but have deferred any revisions to the 
listing taxonomy pending review of an analysis that includes samples 
from the Ochlockonee Basin as well. Peer review and publication of a 
genetic analysis of samples from all four basins is expected sometime 
in 2006 (J.D. Williams, USGS, pers. comm. 2005).
    The threatened Chipola slabshell is a medium-sized species reaching 
a length of about 8.4 cm (3.3 in). The shell is ovate to subelliptical, 
somewhat inflated, and with the posterior ridge starting out rounded 
but flattening to form a prominent biangulate margin. The periostracum 
is smooth and chestnut-colored. Dark brown coloration may appear in the 
umbo region, and the remaining surface may exhibit alternating light 
and dark bands.
    The threatened purple bankclimber is a large, heavy-shelled, 
strongly sculptured mussel reaching lengths of 20.5 cm (8.0 in). A 
well-developed posterior ridge extends from the umbo to the posterior 
ventral margin of the shell. The posterior slope and the disk just 
anterior to the posterior ridge are sculptured by several irregular 
plications that vary greatly in development. The umbos are low, 
extending just above the dorsal margin of the shell.

Life History

    The seven mussels are all bivalve mollusks (clams) of the family 
Unionidae. Unionid mussels generally live embedded in the bottom of 
rivers, streams, and other bodies of water. They siphon water into 
their shells and across four gills that are specialized for respiration 
and food collection. Known food items include detritus (disintegrated 
organic debris), diatoms, phytoplankton, zooplankton, and other 
microorganisms (Coker et al. 1921, p. 88; Churchill and Lewis 1924, p. 
462; Fuller 1974, p. 221). Adults are filter feeders and generally 
orient themselves on or near the substrate surface to take food and 
oxygen from the water above them (Kraemer 1979, p. 1085-1096). 
Juveniles typically burrow completely beneath the substrate surface and 
are pedal (foot) feeders (bringing food particles inside the shell for 
ingestion that adhere to the foot while it is extended outside the 
shell) until the structures for filter feeding are more fully developed 
(Gatenby et al. 1996, p. 604; Yeager et al. 1994, p. 221).
    Sexes in unionid mussels are usually separate. Males release sperm 
into the water, which females take in through their siphons during 
feeding and respiration. Eggs are fertilized and retained in the gills 
of the female until the larvae (glochidia) fully develop. The glochidia 
of most unionid species, including all seven species addressed in this 
proposed rule, require a parasitic stage on the fins, gills, or skin of 
a fish to transform into juvenile mussels (for species-specific 
information, see ``Primary Constituent Elements--Fish Hosts''). Females 
release glochidia either separately or in masses termed conglutinates, 
depending on the mussel species. Exceptionally large conglutinates, 
such as those of the shinyrayed pocketbook, are termed 
superconglutinates. The duration of the parasitic stage varies by 
mussel species, water temperature, and perhaps host fish species. When 
the transformation is complete, juvenile mussels normally detach from 
their fish host and sink to the stream bottom where, given suitable 
conditions, they grow and mature to the adult form.

Distribution

    The historical and current range of the seven mussels includes 
portions of four river basins of the northeast Gulf of Mexico in 
Alabama, Florida, and Georgia: Econfina Creek, ACF, Ochlockonee, and 
Suwannee. Of these four basins, the ACF is the largest and the only one 
that extends beyond the Coastal Plain physiographic province into the 
Piedmont of Georgia and Alabama. Two or more of the seven mussels occur 
in each of the four basins, except the Suwannee, in which only the oval 
pigtoe is found. Because large reservoirs are unsuitable as habitat for 
these mussels and the dams that impound them are barriers to the 
movement of their host fishes, their

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range within two of the basins (ACF and Ochlockonee) is divided into 
two or more sub-basins that likely represent the maximum spatial extent 
of potentially interbreeding populations. We estimate that the five 
species listed as endangered are each extirpated from over half of 
their historical ranges, and the two threatened species are extirpated 
from about one-third of their historical ranges (USFWS 2003, p. 77).

Summary of Threats to Surviving Populations

    The declining range and abundance of the seven mussels is due 
mostly to changes in their riverine habitats resulting from dams, 
dredging, mining, channelization, pollution, sedimentation, and water 
withdrawals, and possibly also the introduction of nonnative species, 
such as the Asian clam. Each of these threats affect one or more of the 
physical and biological habitat features that we have identified as 
essential to the conservation of the seven mussels, which we discuss in 
detail under ``Primary Constituent Elements.''
    More than 350 kilometers (km) (217 miles (mi)) of large and small 
river habitat in the ACF and Ochlockonee basins within the current 
range of the seven mussels is inundated by reservoirs. None of the 
seven species are known to persist in impoundments, although a single 
purple bankclimber was found in an impounded portion of the 
Chattahoochee River (C. Stringfellow, Columbus State University, pers. 
comm. 2000). Obligate riverine fishes, some of which may serve as hosts 
for larvae of the seven mussels, are also eliminated by dams and 
impoundments. Several populations of the seven species persist in 
relatively small fragments of the four major river basins that are 
isolated from other populations by impoundments or other large patches 
of unsuitable habitat and by dams or other barriers to dispersal via 
their fish hosts. Habitat fragmentation reduces the probability of 
population persistence (Wilcox and Murphy 1985, p. 879-884), because 
smaller, more isolated populations are less able to rebound from chance 
adverse environmental, demographic, and genetic events (Shaffer 1981, 
p. 131; Lande 1988, p. 1455).
    A variety of activities may induce channel instability that 
adversely affects habitat conditions for mussels. Because impoundments 
block the natural downstream movement of sediment, channel degradation 
is commonly observed in the tailwaters of dams (Williams and Wolman 
1984, p. 14; Lignon et al. 1995, p. 187). The mean bed elevation of the 
Apalachicola River downstream of Jim Woodruff Lock and Dam, which is 
located at the confluence of the Chattahoochee and Flint rivers, has 
degraded about 1.2 to 1.5 meters (m) (4 to 5 feet (ft)) since its 
construction in the late 1950s (Light et al. 1998, p. 21). The main 
channel of the river widened at a rate of about 0.45 m (1.5 ft) per 
year, based on cross sections measured by the U.S. Army Corps of 
Engineers (USACE) between 1980 and 2001 (USACE 2002, p. 1.1-8.3). The 
Apalachicola River near the Chattahoochee-Flint confluence once 
supported a particularly rich mussel bed, which included large numbers 
of fat threeridge and purple bankclimber, but this bed had declined 
substantially in diversity and numbers by the early 1970s (Heard 1975, 
p. 1-31). Although the purple bankclimber persists, the fat threeridge 
is now rare in the upper river (Brim Box and Williams 2000, p. 89). 
Quantitative sampling using substrate sieves at two locations in the 
upper river failed to detect juveniles of any unionid mussels 
(Richardson and Yokley 1996, p. 137). The decline of the rich mussel 
fauna of the Chattahoochee River was attributed partly to erosion from 
intensive farming before the Civil War (van der Schalie 1938, p. 56; 
Clench 1955, p. 96), although substantial erosion continued for several 
more decades (Glenn 1911, p. 1-137; Trimble 1972, p. 454-457). The most 
striking example of this erosion and resulting stream channel 
instability is in the headwaters of Turner Creek, a Chattahoochee River 
tributary in Stewart County, Georgia. The massive amount of sediment 
that washed away was conveyed via Turner Creek over time to the 
Chattahoochee River.

Channelization

    Channelization (straightening a stream course by artificial cutoffs 
and other means for flood control and navigation), dredging, snagging 
(removal of large woody debris), in-stream gravel mining, and other 
forms of direct stream channel modifications may induce channel 
instability. A well-documented example of how direct modifications to a 
stream induced substantial instability is the Homochitto River in 
Mississippi, which incised 5 m (16.4 ft) and widened 450 percent 
following channelization (Kesel and Yodis 1992, p. 99). Hartfield 
(1993, p. 131-141) and Neves et al. (1997, p. 71-72) reviewed the 
adverse effects of channel modifications on freshwater mollusks. 
Dredging in the Apalachicola River to maintain navigability may be 
contributing to observed channel instability in that system (letter 
from G. Carmody, Service, to R. Keyser, USACE, dated August 8, 2003). 
Channel instability induced by gravel mining has probably played a 
significant role in extirpating the Gulf moccasinshell and oval pigtoe 
from the Uchee Creek system (Howard 1997, p. 157), where a small 
population of the shinyrayed pocketbook persists. A recent Service 
stream habitat condition survey in the Ochlockonee Basin found evidence 
of substantial channel instability (actively eroding banks) at only 9 
of 181 sites surveyed, but classified over half of the sites (99) as 
having a moderate risk of bank erosion (H. Blalock-Herod, Service, 
pers. comm. 2006).

Sedimentation

    Sedimentation is widely reported as a contributing factor in the 
decline of stream mussel populations (Kunz 1898, p. 328; Ellis 1931, p. 
5; 1936, p. 29; Imlay 1972, p. 76; Coon et al. 1977, p. 279; Marking 
and Bills 1979, p. 204; Dennis 1985, p. 1-171; Aldridge et al. 1987, p. 
17; Schuster et al. 1989, p. 84; Wolcott and Neves 1990, p. 74; Houp 
1993, p. 93-97; Richter et al. 1997a, p. 1090; Brim Box 1999, p. 1-
108). Sedimentation is the process by which water detaches, transports, 
and deposits soil materials on the substrates of streams, lakes, and 
wetlands. In geomorphically stable stream reaches, sediment input is 
balanced by sediment output, resulting in no net accumulation or loss 
of sediment from the stream bed. Sediment input is increased by a 
variety of human activities that are common in the range of the seven 
mussels. Substantial sediment accumulation is one factor that may 
induce channel instability. Lesser amounts may also adversely affect 
substrate quality for mussels by altering its texture (usually by 
increasing the percentage of fine materials) and by introducing harmful 
pollutants.
    Waters (1995, p. 173-176) reviewed the biological effects of 
sediments in streams, and Mount (1995, p. 1-359) provided an overview 
of the effects of various land uses on stream systems. Brim Box and 
Mossa (1999, p. 99-117) reviewed the effects of sediments and land uses 
specifically on mussels. They identified several activities that may 
affect mussels through sedimentation, including logging, farming, 
ranching, mining, and urbanization. Without adequate measures to 
control erosion, these activities may deliver sediment to streams via 
upland gullies, unpaved roads, road-side ditches, construction sites, 
and other areas of soil disturbance. All of these activities are 
widespread in the current range of the seven mussels.
    Sediment samples from several ACF Basin streams contained elevated

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concentrations of two heavy metals that are harmful to mussels: Copper 
(found throughout the Piedmont) and cadmium (found in large Coastal 
Plain tributaries of the Flint River) (Frick et al. 1998, p. 19). 
Elevated concentrations of heavy metals (such as chromium and cadmium) 
were measured in Asian clams and in sediment samples collected 
downstream of two abandoned battery salvage operations on the Chipola 
River (Winger et al. 1985, p. 141, 144). Farther downstream in the 
Chipola River, the chromium concentrations found in the sediments of 
Dead Lake (Winger et al. 1985, p. 141, 144) are toxic to mussels 
(Havlik and Marking 1987, p. 1-20).

Impoundments

    The operations of several dams and withdrawals of surface and 
groundwater may alter flow regimes to a degree that adversely affects 
mussels. Four portions of the range of the seven mussels are 
immediately downstream of major mainstem dams. The Apalachicola River 
is downstream of Jim Woodruff Lock and Dam (JWLD), which impounds Lake 
Seminole, a large but shallow reservoir in the southwest corner of 
Georgia with a storage capacity of about 86 million meters\3\ (70,000 
acre-feet). Seminole is the downstream-most reservoir in a series of 
much larger reservoirs on the Chattahoochee River with a cumulative 
capacity of about 2.2 billion m\3\ (1.8 million ac-ft), which 
represents about 11 percent of the average annual discharge from JWLD 
(USACE 1998, p. 4.10, 4.48, 4.56). During extended periods without 
substantial rainfall, however, as during 1999 to 2002, the flow of the 
Apalachicola River may consist mostly of releases from storage in the 
Chattahoochee reservoirs.
    The Flint River is impounded by two mainstem reservoirs, Lake 
Blackshear and Lake Worth. By impeding passage of host fishes, these 
dams separate individuals of the shinyrayed pocketbook, Gulf 
moccasinshell, oval pigtoe, and purple bankclimber into at least three 
populations within the basin. Both dams are used for hydropower and are 
licensed to operate generally in a run-of-river mode (releases 
approximately equal reservoir inflow) (USACE 1998, p. 4.48, 4.56), but 
short-term alterations of river flow may occur. A mainstem dam on the 
Ochlockonee River creates Lake Talquin, which is licensed and operated 
in a similar fashion. No dams have been constructed on Econfina Creek 
or the Suwannee River and its major tributaries within the range of the 
seven mussels.

Water Withdrawals

    Water withdrawals for agricultural, municipal, and industrial use 
may reduce stream flow and affect mussels. In the Dougherty Plain of 
the lower Flint River Basin and upper Chipola River Basin, irrigated 
agriculture is the largest consumptive water use (Marella et al. 1993, 
p. 6, 13, 29, 42). Major crops in the region include cotton, peanuts, 
corn, and soybeans, with the largest acreage irrigated by groundwater 
using center pivot sprinkler systems. Due to the porous limestone 
underlying this area, ground and surface waters are highly connected, 
and the base flow of many streams is supported by the discharge of 
springs (Torak et al. 1996, p. 1-106). This area is also the center of 
the current range of several of the seven mussels. Approximately 
172,125 hectares (ha) (425,000 acres (ac)) of cropland were irrigated 
using center pivot systems in a 16-county area of Georgia in the lower 
Flint River Basin, with an additional 30,375 ha (75,000 ac) irrigated 
with surface waters (Litts et al. 2001, p. 23). Using models 
representing surface water--groundwater dynamics in the lower Flint-
upper Chipola area, Albertson and Torak (2002, p. 22) found that 8 of 
37 streams examined (7 of these 37 support listed mussels) were highly 
sensitive to groundwater withdrawal and that during droughts these 
streams may go dry.
    Water supply for municipal and industrial needs are greatest in the 
areas of greatest human population. Several large urban areas 
(population greater than 100,000) are near or within the current range 
of the seven mussels, including Dothan, Alabama; Panama City and 
Tallahassee, Florida; and Albany, Atlanta, and Columbus, Georgia. The 
largest of these is the Atlanta metro area, which extends into the 
headwaters of the Flint River Basin. Population in the 16-county metro 
area is forecast to increase from about 4 million people in 2000 to 
about 8 million in 2030, when regional water planning authorities 
predict water demand will equal available water supply from existing 
and presently planned sources (Ashley 2005, p. 1). Water use will 
likely increase along with increasing human population in each of the 
four basins that support the seven mussels.

Water Quality

    Water quality is reported as impaired or potentially impaired in 
some portions of all four river basins within the current range of the 
seven mussels, according to the water quality agencies of the three 
States in their periodic assessments under Section 305(b) of the Clean 
Water Act (CWA). Although water quality in the smallest of the four 
basins, Econfina Creek, is generally good, mercury accumulation in fish 
populations was cited as a potential impairment in Florida's most 
recent basin status report (FDEP 2003a, p. 71). Barrios and Chelette 
(2004, p. 7) described the hydrologic setting of Econfina Creek, which 
strongly influences its water quality characteristics. Except during 
periods of high rainfall, most of the flow in Econfina Creek derives 
from the discharge of a series of at least 39 spring vents from the 
Floridan Aquifer in the middle section of the creek. The ground water 
contribution zone for these springs is large and encompasses a 
significant portion of the creek's surface water basin. Water quality 
in the Floridan Aquifer is vulnerable to land use activities in this 
contribution zone.
    Water quality in the largest of the four basins, the ACF, varies 
considerably. Two small portions of the seven mussels' current range in 
the ACF are within the State of Alabama: The entire Uchee Creek 
watershed (a Chattahoochee River tributary) and the headwaters of the 
Chipola River watershed (an Apalachicola River tributary). In the 
latter, the Alabama Department of Environmental Management (2004, p. 7) 
reports that Cypress Creek is impaired due to organic enrichment and 
low dissolved oxygen (DO). We have no records of the seven mussels in 
Cypress Creek; however, three of the species are known to occur within 
a few miles downstream of its mouth. In the Florida portion of the ACF, 
several stream segments that support one or more of the seven mussels 
in the Chipola and Apalachicola watersheds are potentially impaired due 
to excessive coliform bacteria, nutrients, un-ionized ammonia, or 
turbidity (FDEP 2003b, p. 1-208). Mercury-based fish advisories apply 
to one or more segments of both watersheds. The current range of the 
seven mussels in the Flint River Basin includes 131 km (81 mi) that are 
reported as not supporting or partially supporting designated uses due 
to departures from Georgia's standards for DO or biological integrity, 
or are under mercury-based fish consumption advisories (GDNR-EPD 2002, 
p. 1/1-9/2). The streams listed include such Flint River tributaries as 
Spring Creek and Kinchafoonee Creek, but not the mainstem. The 
conditions in an additional 58 km (36 mi) of Flint River tributaries 
occupied by the mussels violate the coliform bacteria standard.

[[Page 32751]]

    Water quality is considered impaired in a majority of the mussels' 
range in the Ochlockonee River Basin of Florida and Georgia. In both 
States, the entire mainstem length of the river is impaired or 
potentially impaired by excessive coliform bacteria or nutrients, low 
DO, or is under mercury-based fish consumption advisories (FDEP 2003c, 
p. 1-141; GDNR--EPD 2002, p. 1/1-9/2). A study of water and sediment 
quality in the basin in relation to mussels found that sites with low 
DO or elevated levels of lead, manganese, or ammonia no longer 
supported their historical mussel assemblages, including the listed 
species (Hemming et al. 2005, p. 2).
    The range of the seven mussels in the Suwannee River Basin is 
limited to one species (the oval pigtoe), to the Florida portion of the 
basin, and to one watershed within that portion (the Santa Fe River 
watershed). The oval pigtoe is currently known only from the New River 
and a short segment of Santa Fe itself downstream of the mouth of the 
New River. Most of the New River was listed as impaired due to 
excessive coliform bacteria, excessive nutrients, and low DO in 1998, 
and remains potentially impaired under Florida's current standards 
(FDEP 2003d, p. 1-159).
    Agricultural sources of contaminants in the ACF and Suwannee basins 
include nutrient enrichment from poultry farms and livestock feedlots, 
and pesticides and fertilizers from row crop agriculture (Couch et al. 
1996, p. 1-58; Frick et al. 1998, p. 1-36; Berndt et al. 1998, p. 1-
32). A study by the U.S. Soil Conservation Service (1993, p. 26) (now 
the Natural Resources Conservation Service) in the Flint River system 
determined that between 72 and 75 percent of the nutrients entering 
Lake Blackshear were derived from agricultural sources. Organochlorine 
pesticides were found at levels in ACF Basin streams that often 
exceeded chronic exposure criteria for the protection of aquatic life 
(Buell and Couch 1995, p. 1; Frick et al. 1998, p. 11). Cotton is 
raised in much of the region inhabited by these mussels. One of the 
most important pesticides used in cotton farming, malathion, affects 
mussels physiologically and may decrease respiration and feeding 
ability (Kabeer et al. 1979, p. 71-73). Within the Suwannee River 
basin, nutrient concentrations were greater in agricultural areas and 
nitrates were found to exceed U.S. Environmental Protection Agency 
(USEPA) drinking water standards in 20 percent of the surficial aquifer 
groundwater samples (Berndt et al. 1998, p. 6). Mostly in urban areas, 
pesticide concentrations were found to exceed criteria for protection 
of aquatic life.
    Many pollutants in the ACF Basin originate from urban stormwater 
runoff, developmental activities, and municipal waste water facilities, 
primarily upstream of the fall line (the line marking the relatively 
abrupt elevation transition between the Piedmont physiographic province 
and the coastal plain) (Frick et al. 1998, p. 1-36). Urban catchments 
in Piedmont drainages have higher concentrations of nutrients, heavy 
metals, pesticides, and organic compounds than do agricultural or 
forested ones (Lenat and Crawford 1994, p. 185; Frick et al. 1998, p. 
1-36), and at levels sufficient to affect fish health (Ostrander et al. 
1995, p. 213). Couch et al. (1996, p. 50) counted 137 municipal 
wastewater treatment facilities in the ACF Basin.

Host Fish

    Collectively, eight species of fish are now considered probable 
primary hosts for the larval life stage of four of the seven mussels: 
Largemouth bass, spotted bass, bluegill, redear sunfish, weed shiner, 
sailfin shiner, blackbanded darter, and brown darter (O'Brien and Brim 
Box 1999, p. 136; O'Brien and Williams 2002, p. 150-152) (see ``PCEs--
Fish Hosts''). According to Lee et al. (1980, p. 1-854), the range of 
each of these fishes encompasses the range of the respective mussel(s) 
that successfully parasitized each species in laboratory tests, with 
the possible exception of the sailfin shiner--oval pigtoe association. 
The sailfin shiner does not occur far upstream of the fall line in the 
ACF basin (B. Albanese, GA DNR Wildlife Division, pers. comm. 2006), 
but the oval pigtoe does; therefore, at least one more fish likely 
serves as a host for this species. None of the eight fishes is 
protected under the Act or considered imperiled rangewide (Williams et 
al. 1989, p. 2-20); however, Georgia recognizes the sailfin shiner as a 
species of special concern (State rank ``S3''; rare or uncommon in 
State). The four centrarchid fishes (the two basses, bluegill, and 
redear sunfish) are each classified as game species by the three 
States. Riverine fish populations in the southeast generally have been 
adversely affected by a variety of the same habitat alterations that 
have contributed to the decline of the region's mussel fauna (Etnier 
1997, p. 91; Neves et al. 1997, p. 60; Warren et al. 1997, p. 106, 123-
125, 127, 131).

Non-Native Species

Asian Clam

    The invasion of non-native aquatic species has contributed to the 
decline of several North American mussel species (Neves et al. 1977, p. 
72-75; Strayer 1999, p. 74). Some native mussels may go extinct due to 
the continued spread of the zebra mussel (Dreissena polymorpha), a 
species not yet established in the southeast (Ricciardi et al. 1998, p. 
618). Another non-native bivalve, the Asian clam (Corbicula fluminea), 
is well-established and almost ubiquitous in the range of the seven 
mussels. Reports of Asian clam density vary considerably, from 9 per 
square foot (Flint River, Sickel 1973, p. 11) to over 195 per square 
foot (Santa Fe River, Bass and Hitt 1974, p. 16). In the New River 
(Suwannee River drainage), Blalock and Herod (1999, p. 145-151) found 
an overall density of 8 Asian clams per square foot in an area where 
oval pigtoe density was 0.003 per square foot (Blalock-Herod 2000, p. 
1-72). In one reach of the Apalachicola River immediately downstream of 
Jim Woodruff Lock and Dam, the stream bed is almost entirely covered 
with a layer of live and dead Asian clams several inches deep (J. 
Ziewitz, personal observation). Several researchers have suggested that 
the Asian clam competes with native mussels for food, nutrients, and 
space (Heard 1977, p. 1-177; Kraemer 1979, p. 1094; Clarke 1986, p. 8), 
particularly with juvenile unionids (Neves and Widlak 1987, p. 6). 
Yeager et al. (2000, p. 257) determined that high densities of Asian 
clams reduced survival and growth of newly metamorphosed juvenile 
mussels. However, Asian clams are present at almost all locations where 
the seven mussels for which we are proposing critical habitat in this 
proposed rule are currently found, and the specific impact of this 
species upon native mussels is largely unresolved (Leff et al. 1990, p. 
415; Strayer 1999, p. 90).

Black Carp

    The black carp (Mylopharyngodon piceus) is another introduced 
species that may pose a threat to the seven mussels. Largest of the 
Asiatic carp species, the black carp eats mollusks (snails and 
mussels), and sterile fish are sometimes used in catfish aquaculture to 
control snails that are the intermediate hosts of a catfish parasite 
(Nico et al. 2001, p. 1-124). Escape of substantial numbers of the 
sterile fish could significantly reduce numbers of native mussels where 
the escape occurs, and the establishment of non-sterile black carp in 
the wild could

[[Page 32752]]

conceivably extirpate entire mussel populations.

Previous Federal Actions

    We listed the seven mussels under the Act on March 16, 1998 (63 FR 
12664), and approved a final recovery plan for the seven species on 
September 19, 2003 (68 FR 56647; October 1, 2003). In the final 1998 
rule, we determined that designation of critical habitat was not 
prudent. On March 15, 2004, the Center for Biological Diversity 
(Center) filed a lawsuit in the U.S. District Court for the Northern 
District of Georgia (Civil Action No. 1:04 CV-0729-GET) alleging that 
we violated the Act by failing to designate critical habitat for the 
seven mussels. We entered a settlement agreement with the Center on 
August 31, 2004, which stipulates that the Service would submit for 
publication in the Federal Register, on or before May 30, 2006, a new 
prudency determination, and if designation was determined to be 
prudent, a proposed rule designating critical habitat. This publication 
is our new prudency determination and our proposed rule designating 
critical habitat for the seven mussels.

Critical Habitat

    Critical habitat is defined in section 3 of the Act 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 
geographical 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, as defined under section 3 of the Act, means 
to use and the use of all methods and procedures which are necessary to 
bring any endangered species or threatened species to the point at 
which the measures provided pursuant to the Act are no longer 
necessary.
    Critical habitat receives protection under section 7 of the Act 
through the prohibition against destruction or adverse modification of 
critical habitat with regard to actions carried out, funded, or 
authorized by a Federal agency. Section 7 requires consultation on 
Federal actions that are likely to result in the destruction or adverse 
modification of critical habitat. The designation of critical habitat 
does not affect land ownership or establish a refuge, wilderness, 
reserve, preserve, or other conservation area. Such designation does 
not allow government or public access to private lands.
    To be included in a critical habitat designation, the habitat 
within the area occupied by the species must first have features that 
are essential to the conservation of the species. Critical habitat 
designations identify, to the extent known using the best scientific 
data available, habitat areas that provide essential life cycle needs 
of the species (areas on which are found the primary constituent 
elements, as defined at 50 CFR 424.12(b)).
    Habitat occupied at the time of listing may be included in critical 
habitat only if the essential features thereon may require special 
management or protection. Thus, we do not include areas where existing 
management is sufficient to conserve the species. Accordingly, when the 
best available scientific data do not demonstrate that the conservation 
needs of the species so require, we will not designate critical habitat 
in areas outside the geographical area occupied by the species at the 
time of listing. An area currently occupied by the species but was not 
known to be occupied at the time of listing is likely, but not always, 
essential to the conservation of the species and is typically included 
in the critical habitat designation.
    The Service's Policy on Information Standards Under the Endangered 
Species Act, published in the Federal Register on July 1, 1994 (59 FR 
34271), and Section 515 of the Treasury and General Government 
Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R. 5658) 
and the associated Information Quality Guidelines issued by the 
Service, provide criteria, establish procedures, and provide guidance 
to ensure that decisions made by the Service represent the best 
scientific data available. They require Service biologists to the 
extent consistent with the Act and with the use of the best scientific 
data available, to use primary and original sources of information as 
the basis for recommendations to designate critical habitat. When 
determining which areas are critical habitat, a primary source of 
information is generally the listing package for the species. 
Additional information sources include the recovery plan for the 
species, articles in peer-reviewed journals, conservation plans 
developed by States and counties, scientific status surveys and 
studies, biological assessments, or other unpublished materials and 
expert opinion or personal knowledge. All information is used in 
accordance with the provisions of Section 515 of the Treasury and 
General Government Appropriations Act for Fiscal Year 2001 (Pub. L. 
106-554; H.R. 5658) and the associated Information Quality Guidelines 
issued by the Service.
    Section 4 of the Act requires that we designate critical habitat on 
the basis of the best scientific data available. Habitat is often 
dynamic, and species may move from one area to another over time. 
Furthermore, we recognize that designation of critical habitat may not 
include all of the habitat areas that may eventually be determined to 
be necessary for the recovery of the species. For these reasons, 
critical habitat designations do not signal that habitat outside the 
designation is unimportant or may not be required for recovery.
    Areas that support populations, but are outside the critical 
habitat designation, will continue to be subject to conservation 
actions implemented under section 7(a)(1) of the Act and to the 
regulatory protections afforded by the section 7(a)(2) jeopardy 
standard, as determined on the basis of the best available information 
at the time of the action. Federally funded or permitted projects 
affecting listed species outside their designated critical habitat 
areas may still result in jeopardy findings in some cases. Similarly, 
critical habitat designations made on the basis of the best available 
information at the time of designation will not control the direction 
and substance of future recovery plans, habitat conservation plans, or 
other species conservation planning efforts, if new information 
available to these planning efforts calls for a different outcome.

Prudency Determination

    Section 4(a)(3) of the Act and its implementing regulations (50 CFR 
424.12) require that, to the maximum extent prudent and determinable, 
we designate critical habitat at the time a species is listed as 
endangered or threatened. Our regulations at 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 activity and the 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. In our March 16, 1998, final rule (63 FR 12664), we determined 
that designating critical habitat was not prudent for the seven mussels 
because it would result in no known benefit to the species and could 
further pose a threat to them through publication of their site-
specific localities. However, several of our determinations that the

[[Page 32753]]

designation of critical habitat would not be prudent have been 
overturned by court decisions (for example, Conservation Council for 
Hawaii v. Babbitt (2 F. Supp. 2d 1280 [D. Hawaii 1998]); and Natural 
Resources Defense Council v. U.S. Department of the Interior (113 F. 3d 
1121, 1125 [9th Cir. 1997])).
    We are already working with Federal and State agencies, private 
individuals, and organizations in carrying out conservation activities 
for the seven mussels, conducting surveys for additional occurrences, 
and assessing habitat conditions. However, critical habitat designation 
may provide additional information to individuals, local and State 
governments, and other entities engaged in long-range planning, since 
areas with features essential to the conservation of the species are 
clearly delineated and, to the extent currently feasible, the primary 
constituent elements of the habitat necessary to the survival of the 
subspecies are specifically identified. Furthermore, although the low 
numbers of these mussels make it unlikely that their populations could 
withstand even moderate collecting pressure or vandalism, we do not 
have specific evidence of taking, collection, vandalism, trade, or 
unauthorized human disturbance.
    Accordingly, we withdraw our previous determination that the 
designation of critical habitat will not benefit the seven mussels and 
will increase the degree of threat to the species. We determine that 
the designation of critical habitat is prudent for these species. At 
this time, we have sufficient information necessary to identify 
specific areas that meet the definition of critical habitat and are, 
therefore, proposing critical habitat for the seven mussels.

Methods

    As required by section 4(b)(1) of the Act, we used the best 
scientific and commercial data available in determining areas that 
contain the physical and biological features essential to the 
conservation of the seven mussels. We reviewed the available 
information pertaining to their historical and current distributions, 
life histories, host fishes, habitats, threats to mussels in general, 
and threats to the seven mussels in particular. This information 
includes our own site-specific species and habitat data; unpublished 
survey reports; notes and communications with other qualified 
biologists or experts; peer-reviewed scientific publications; the final 
listing rule for the seven mussels; and our final recovery plan for the 
seven mussels.
    Our principal sources of information for identifying the specific 
areas within the occupied range of the seven mussels on which are found 
those features essential to their conservation were: the collective 
database of locality records for the seven mussels, which is tabulated 
in our 2003 final recovery plan and has been supplemented with surveys 
completed since then, and the peer-reviewed scientific literature on 
mussels' life history and habitat requirements. Our 1998 final listing 
rule relied extensively upon data obtained in a rangewide status survey 
of the seven mussels commissioned by the Service and conducted in 1991 
and 1992 (cited as Butler (1993, p. 1-30) in the final listing). Most 
of these data were taken in the ACF basin and have since been published 
by Brim Box and Williams (2000, p. 3). Although mussel surveys have 
been conducted since publication of the final listing rule at various 
locations in the four river basins that encompass their known range, 
the 1991-1992 status survey still provides a majority of the most 
recent distributional records for these seven mussels. For purposes of 
this proposed rule, the Service considers the most recent post-1990 
survey data at a particular location as representing a species' current 
presence or absence at that location, and we consider pre-1990 survey 
data as representing historical distribution. We must extend the 
definition of current distribution back to 1990 because mussels are 
sedentary, long-lived animals, some species attaining maximum life 
spans of 100 to 200 years (Neves and Moyer 1988, p. 185; Bauer 1992, p. 
425; Mutvei et al. 1994, p. 163-186). It was rare in the 1991-1992 
survey, and is still rare, to find juveniles of the seven mussels.
    We relied on a variety of information sources for identifying 
occupied areas in which the features essential to the conservation of 
the seven mussels may require special management considerations or 
protection, including land and water management plans of State and 
regional government agencies, surveys of stream channel condition, 
water quality assessments, and distributional information for host 
fishes. We used the sources cited in our final recovery plan's summary 
of known threats to the seven mussels to identify which essential 
features may be most vulnerable in certain portions of the occupied 
range.

Primary Constituent Elements

    In accordance with section 3(5)(A)(i) of the Act and regulations at 
50 CFR 424.12, we are required to base critical habitat determinations 
on the best scientific and commercial data available and to consider 
within areas occupied by the species at the time of listing those 
physical and biological features that are essential to the conservation 
of the species (PCEs), and that may require special management 
considerations or protection. These include, but are not limited to: 
Space for individual and population growth and for normal behavior; 
food, water, air, light, minerals, or other nutritional or 
physiological requirements; cover or shelter; sites for breeding, 
reproduction, and rearing (or development) of offspring; and habitats 
that are protected from disturbance or are representative of the 
historic geographical and ecological distributions of a species.
    The specific PCEs essential for the seven mussels are derived from 
their biological needs as described in the Background section of this 
proposal. Space for individual and population growth and normal 
behavior, and sites for reproduction and development of offspring are 
provided for the seven mussels on and within the streambed of stable 
channels with a suitable substrate, which we have captured in the PCEs 
regarding channel stability, substrate quality, and flow regime. 
Because the seven mussels are dependent on fish to complete their 
larval life stage, the PCE regarding fish hosts is a further 
requirement for successful reproduction. Various nutritional and 
physiological requirements are captured in the PCEs regarding flow 
regime and water quality. These PCEs are explained in additional detail 
below.

Channel Stability

    Unstable channels do not favor mussels in part because adults and 
juveniles are relatively sedentary animals. They are unable to move 
quickly or across great distances from unsuitable to suitable 
microhabitats on and in the stream bed. Several researchers have 
reported direct adverse effects to mussels in aggrading (filling) and 
degrading (scouring) channels (Vannote and Minshall 1982, p. 4106; 
Kanehl and Lyons 1992, p. 7; Hartfield 1993, p. 133; Brim Box and Mossa 
1999, p. 99-117). In degrading channels, mussels lose the substrate 
sediment in which they anchor themselves against the current. Mussels 
have been extirpated from streams experiencing a ``headcut'' (stream 
bed degradation progressing in an upstream direction) and from 
degrading reaches immediately downstream of dams. In aggrading channels 
or in channels with

[[Page 32754]]

actively eroding stream banks, excess sediment fouls the gills of 
mussels, which reduces feeding and respiratory efficiency, disrupts 
metabolic processes, reduces growth rates, and physically smothers 
mussels (Ellis 1936, p. 39; Stansbery and Stein 1971, p. 2178; Marking 
and Bills 1979, p. 209-210; Kat 1982, p. 123; Vannote and Minshall 
1982, p. 4105-4106; Aldridge et al. 1987, p. 18; Waters 1995, p. 173-
176; Brim Box 1999, p. 65).
    In addition to the direct effects above, channel instability 
indirectly affects mussels and their fish hosts in several ways. 
Channels becoming wider and shallower via bank erosion develop more 
extreme daily and seasonal temperature regimes, which affects DO levels 
and many other temperature-regulated physical and biological processes. 
Mussels in wider and shallower channels are likely more susceptible to 
predation. Erosive channels lose the habitat complexity provided by 
mature bankside vegetation, which reduces diversity and abundance of 
fish species. Fewer fish means lower probability of mussel recruitment 
(see ``Fish Hosts''). The many direct and indirect adverse effects of 
channel instability on mussels and their fish hosts strongly suggest 
that channel stability is a habitat feature essential to their 
conservation.

Substrate Quality

    Adult unionid mussels are generally found in localized patches 
(beds) almost completely burrowed in the substrate with only the area 
around their siphons exposed (Balfour and Smock 1995, p. 255-268). The 
composition and abundance of adult mussels have been linked to bed 
sediment distributions (Neves and Widlak 1987, p. 5; Leff et al. 1990, 
p. 415). Substrate texture (particle size distribution) affects the 
ability of mussels to burrow in the substrate and anchor themselves 
against stream currents (Lewis and Riebel 1984, p. 2025). Texture and 
other aspects of substrate composition, including bulk density (ratio 
of mass to volume), porosity (ratio of void space to volume), and 
sediment sorting may also influence mussel densities (Brim Box 1999, p. 
1-86; Brim Box and Mossa 1999, p. 99-117). Although several studies 
have reported adult habitat selection by substrate composition, most 
species are found in a relatively broad range of substrate types 
(Tevesz and McCall 1979, p. 114; Strayer 1981, p. 411; Hove and Neves 
1994, p. 36; Strayer and Ralley 1993, p. 255), with few exceptions 
(Stansbery 1966, p. 29-30). The seven mussels for which we are 
proposing critical habitat in this proposed rule are found in a variety 
of substrates, ranging from pockets of sand on bedrock to sandy mud, 
but not in substrates composed of predominantly fine materials (more 
than 50 percent silt or clay by dry weight) (Brim Box and Williams 
2000, p. 1-143; Blalock-Herod 2000, p. 1-72).
    Interstitial spaces (pores) in coarse stream substrates may become 
clogged when fine sediment input to streams is excessive (Gordon et al. 
1992, p. 1-444). Reduced pore space and pore flow rates reduce habitat 
for juvenile mussels, which tend to burrow entirely beneath the 
substrate surface, and for some adult mussels as well (Brim Box and 
Mossa 1999, p. 99-117). At least some species of juvenile unionids feed 
primarily on particles associated with sediments and pore water during 
their early development (Yeager et al. 1994, p. 221). Fine sediments 
act as vectors in delivering contaminants such as nutrients, heavy 
metals, and pesticides to streams (Salomons et al. 1987, p. 13). Most 
toxicity data for freshwater mussels is from tests with water-only 
exposures, despite reports that contaminated sediments have contributed 
to mussel declines (Newton 2003, p. 2543; Wilson et al. 1995, p. 213-
218).
    Because the juveniles and adults of the seven mussels live in 
relatively coarse and not predominantly fine-grained substrates, and 
the introduction of fine-grained sediments and various pollutants is 
likely detrimental to one or more of their life stages, we have 
determined that substrate quality is a habitat feature essential to 
their conservation.

Flow Regime

    The species that are the subject of this proposed rule are all 
riverine unionid mussels and are not found in natural or manmade ponds 
and lakes. One known exception is a