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Proposed Rule2023-05107

Endangered and Threatened Wildlife and Plants; Endangered Species Status With Critical Habitat for Texas Heelsplitter, and Threatened Status With Section 4(d) Rule and Critical Habitat for Louisiana Pigtoe

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Published

March 20, 2023

Issuing agencies

Interior DepartmentFish and Wildlife Service

Abstract

We, the U.S. Fish and Wildlife Service (Service), propose to list the Texas heelsplitter (Potamilus amphichaenus) as an endangered species and the Louisiana pigtoe (Pleurobema riddellii) as a threatened species under the Endangered Species Act of 1973, as amended (Act). Both species are freshwater mussels. This document serves as our 12- month finding on a petition to list the Texas heelsplitter and Louisiana pigtoe. For the Louisiana pigtoe, we also propose a rule issued under section 4(d) of the Act (a "4(d) rule") to provide for the conservation of the species. In addition, we propose to designate critical habitat for the Texas heelsplitter and Louisiana pigtoe under the Act. In total, approximately 831.8 river miles (1,338.6 river kilometers) in 31 counties in Texas fall within the boundaries of the proposed critical habitat designation for the Texas heelsplitter, and approximately 1,028.2 river miles (1,654.3 river kilometers) in 3 counties in Arkansas, 6 parishes in Louisiana, 2 counties in Mississippi, 1 county in Oklahoma, and 21 counties in Texas fall within the boundaries of the proposed critical habitat designation for the Louisiana pigtoe. We announce the availability of a draft economic analysis of the proposed designation of critical habitat for the Texas heelsplitter and Louisiana pigtoe. Finally, we announce an informational meeting followed by a public hearing on this proposed rule. If we finalize this rule as proposed, it would extend the Act's protections to these species and their critical habitats.

Full Text

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[Federal Register Volume 88, Number 53 (Monday, March 20, 2023)]
[Proposed Rules]
[Pages 16776-16832]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2023-05107]

[[Page 16775]]

Vol. 88

Monday,

No. 53

March 20, 2023

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; Endangered Species
Status With Critical Habitat for Texas Heelsplitter, and Threatened
Status With Section 4(d) Rule and Critical Habitat for Louisiana
Pigtoe; Proposed Rule

Federal Register / Vol. 88, No. 53 / Monday, March 20, 2023 /
Proposed Rules

[[Page 16776]]

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2022-0026; FF09E21000 FXES1111090FEDR 234]
RIN 1018-BE46

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
list the Texas heelsplitter (Potamilus amphichaenus) as an endangered
species and the Louisiana pigtoe (Pleurobema riddellii) as a threatened
species under the Endangered Species Act of 1973, as amended (Act).
Both species are freshwater mussels. This document serves as our 12-
month finding on a petition to list the Texas heelsplitter and
Louisiana pigtoe. For the Louisiana pigtoe, we also propose a rule
issued under section 4(d) of the Act (a ``4(d) rule'') to provide for
the conservation of the species. In addition, we propose to designate
critical habitat for the Texas heelsplitter and Louisiana pigtoe under
the Act. In total, approximately 831.8 river miles (1,338.6 river
kilometers) in 31 counties in Texas fall within the boundaries of the
proposed critical habitat designation for the Texas heelsplitter, and
approximately 1,028.2 river miles (1,654.3 river kilometers) in 3
counties in Arkansas, 6 parishes in Louisiana, 2 counties in
Mississippi, 1 county in Oklahoma, and 21 counties in Texas fall within
the boundaries of the proposed critical habitat designation for the
Louisiana pigtoe. We announce the availability of a draft economic
analysis of the proposed designation of critical habitat for the Texas
heelsplitter and Louisiana pigtoe. Finally, we announce an
informational meeting followed by a public hearing on this proposed
rule. If we finalize this rule as proposed, it would extend the Act's
protections to these species and their critical habitats.

DATES: We will accept comments received or postmarked on or before May
19, 2023. Comments submitted electronically using the Federal
eRulemaking Portal (see ADDRESSES, below) must be received by 11:59
p.m. eastern time on the closing date.
Public informational meeting and public hearing: We will hold a
public informational session from 5 p.m. to 6 p.m., central time,
followed by a public hearing from 6:30 p.m. to 8 p.m., central time, on
May 2, 2023.

ADDRESSES: You may submit comments by one of the following methods:
(1) Electronically: Go to the Federal eRulemaking Portal: <a href="https://www.regulations.gov">https://www.regulations.gov</a>. In the Search box, enter FWS-R2-ES-2022-0026,
which is the docket number for this rulemaking. Then, click on the
Search button. On the resulting page, in the panel on the left side of
the screen, under the Document Type heading, check the Proposed Rule
box to locate this document. You may submit a comment by clicking on
``Comment.''
(2) By hard copy: Submit by U.S. mail to: Public Comments
Processing, Attn: FWS-R2-ES-2022-0026, U.S. Fish and Wildlife Service,
MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
We request that you send comments only by the methods described
above. We will post all comments on <a href="https://www.regulations.gov">https://www.regulations.gov</a>. This
generally means that we will post any personal information you provide
us (see Information Requested, below, for more information).
Availability of supporting materials: For the proposed critical
habitat designation, the coordinates or plot points or both from which
the maps are generated are included in the decision file and are
available at <a href="https://www.fws.gov/southwest/es/arlingtontexas/">https://www.fws.gov/southwest/es/arlingtontexas/</a>, at
<a href="https://www.regulations.gov">https://www.regulations.gov</a> under Docket No. FWS-R2-ES-2022-0026, and
at the Arlington Ecological Services Field Office (see FOR FURTHER
INFORMATION CONTACT). Additional supporting information that we
developed for this critical habitat designation will be available on
the Service's website, at <a href="https://www.regulations.gov">https://www.regulations.gov</a>, or both.
Public informational meeting and public hearing: The public
informational meeting and the public hearing will be held virtually
using the Zoom online video platform and via teleconference. See Public
Hearing, below, for more information.

FOR FURTHER INFORMATION CONTACT: Debra Bills, Field Supervisor, U.S.
Fish and Wildlife Service, Arlington Ecological Services Field Office,
501 West Felix Street, Suite 1105, Fort Worth, Texas 76115; telephone
817-277-1100. Individuals in the United States who are deaf, deafblind,
hard of hearing, or have a speech disability may dial 711 (TTY, TDD, or
TeleBraille) to access telecommunications relay services. Individuals
outside the United States should use the relay services offered within
their country to make international calls to the point-of-contact in
the United States.

SUPPLEMENTARY INFORMATION:

Executive Summary

Why we need to publish a rule. Under the Act, a species warrants
listing if it meets the definition of an endangered species (in danger
of extinction throughout all or a significant portion of its range) or
a threatened species (likely to become endangered within the
foreseeable future throughout all or a significant portion of its
range). If we determine that a species warrants listing, we must list
the species promptly and designate the species' critical habitat to the
maximum extent prudent and determinable. We have determined that the
Texas heelsplitter meets the definition of an endangered species and
that the Louisiana pigtoe meets the definition of a threatened species;
therefore, we are proposing to list them as such and proposing a
designation of critical habitat for both species. Both listing a
species as an endangered or threatened species and designating critical
habitat can be completed only by issuing a rule through the
Administrative Procedure Act rulemaking process.
What this document does. We propose to list the Texas heelsplitter
as an endangered species and to list the Louisiana pigtoe as a
threatened species with a 4(d) rule. We also propose to designate
critical habitat for both species.
The basis for our action. Under the Act, we may determine that a
species is an endangered or threatened species because of any of five
factors: (A) The present or threatened destruction, modification, or
curtailment of its habitat or range; (B) overutilization for
commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) the inadequacy of existing regulatory
mechanisms; or (E) other natural or manmade factors affecting its
continued existence. We have determined that habitat loss through
changes in water quality, the gradual accumulation of additional layers
of fine sediments, and altered hydrology (Factor A) are the primary
threats to these species, all of which are exacerbated by the ongoing
and expected future effects of climate change (Factor E). Additionally,
predation (Factor C) and collection (Factor B), as well as other
natural or human-induced events/activities that result in direct
mortality, are also

[[Page 16777]]

affecting those populations already experiencing low stream flow, and
reservoirs and other instream barriers to fish movement (Factor E) that
limit dispersal and prevent recolonization after stochastic events.
Section 4(a)(3) of the Act requires the Secretary of the Interior
(Secretary) to designate critical habitat concurrent with listing to
the maximum extent prudent and determinable. Section 3(5)(A) of the Act
defines critical habitat as (i) the specific areas within the
geographical area occupied by the species, at the time it is listed, on
which are found those physical or biological features (I) essential to
the conservation of the species and (II) which may require special
management considerations or protections; and (ii) specific areas
outside the geographical area occupied by the species at the time it is
listed, upon a determination by the Secretary that such areas are
essential for the conservation of the species. Section 4(b)(2) of the
Act states that the Secretary must make the designation on the basis of
the best scientific data available and after taking into consideration
the economic impact, the impact on national security, and any other
relevant impacts of specifying any particular area as critical habitat.

Information Requested

We intend that any final action resulting from this proposed rule
will be based on the best scientific and commercial data available and
be as accurate and as effective as possible. Therefore, we request
comments or information from other governmental agencies, Native
American Tribes, the scientific community, industry, or any other
interested parties concerning this proposed rule. We particularly seek
comments concerning:
(1) The species' biology, range, and population trends, including:
(a) Biological or ecological requirements of the species, including
habitat requirements for feeding, breeding, and sheltering;
(b) Genetics and taxonomy;
(c) Historical and current ranges, including distribution patterns
and the locations of any additional populations of these species;
(d) Historical and current population levels, and current and
projected trends; and
(e) Past and ongoing conservation measures for the species, their
habitats, or both.
(2) Threats and conservation actions affecting these species,
including:
(a) Factors that may affect the continued existence of the species,
which may include habitat modification or destruction, overutilization,
disease, predation, the inadequacy of existing regulatory mechanisms,
or other natural or manmade factors.
(b) Biological, commercial trade, or other relevant data concerning
any threats (or lack thereof) to these species.
(c) Existing regulations or conservation actions that may be
addressing threats to these species.
(3) Additional information concerning the historical and current
status of these species.
(4) Information on regulations that are necessary and advisable to
provide for the conservation of the Louisiana pigtoe and that we can
consider in developing a 4(d) rule for the species. We particularly
seek information concerning the extent to which we should include any
of the section 9 prohibitions in the 4(d) rule or whether we should
consider any additional exceptions from the prohibitions in the 4(d)
rule.
(5) Specific information on:
(a) The amount and distribution of Texas heelsplitter and Louisiana
pigtoe habitat;
(b) Any additional areas occurring within the range of the
Louisiana pigtoe, i.e., Howard, Little River, and Sevier Counties,
Arkansas; Allen, Beauregard, Rapides, St. Tammany, Vernon, and
Washington parishes, Louisiana; Marion and Pearl River Counties,
Mississippi; McCurtain County, Oklahoma; and Anderson, Angelina,
Cherokee, Gregg, Hardin, Harrison, Houston, Jasper, Jefferson, Liberty,
Montgomery, Nacogdoches, Orange, Panola, Polk, Rusk, Smith, Trinity,
Tyler, Upshur, and Wood Counties, Texas, and Texas heelsplitter, i.e.,
Anderson, Angelina, Cherokee, Ellis, Freestone, Gregg, Grimes, Hardin,
Harrison, Henderson, Houston, Jasper, Jefferson, Kaufman, Leon,
Madison, Navarro, Orange, Panola, Polk, Rains, Rusk, Sabine, Shelby,
Smith, Trinity, Tyler, Upshur, Van Zandt, Walker, and Wood Counties,
Texas, that should be included in the designation because they (i) are
occupied at the time of listing and contain the physical or biological
features that are essential to the conservation of the species and that
may require special management considerations, or (ii) are unoccupied
at the time of listing and are essential for the conservation of the
species; and
(c) Special management considerations or protection that may be
needed in critical habitat areas we are proposing, including managing
for the potential effects of climate change; and
(d) To evaluate the potential to include areas not occupied at the
time of listing, we particularly seek comments regarding whether
occupied areas are adequate for the conservation of the species.
Additionally, please provide specific information regarding whether or
not unoccupied areas would, with reasonable certainty, contribute to
the conservation of the species and contain at least one physical or
biological feature essential to the conservation of the species. We
also seek comments or information regarding whether areas not occupied
at the time of listing qualify as ``habitat'' for the species.
(7) Land use designations and current or planned activities in the
subject areas and their possible impacts on proposed critical habitat.
(8) Any probable economic, national security, or other relevant
impacts of designating any area that may be included in the final
designation, and the related benefits of including or excluding
specific areas.
(9) Information on the extent to which the description of probable
economic impacts in the draft economic analysis is a reasonable
estimate of the likely economic impacts and any additional information
regarding probable economic impacts that we should consider.
(10) Whether any specific areas we are proposing for critical
habitat designation should be considered for exclusion under section
4(b)(2) of the Act, and whether the benefits of potentially excluding
any specific area outweigh the benefits of including that area under
section 4(b)(2) of the Act. If you think we should exclude any
additional areas, please provide information supporting a benefit of
exclusion.
(11) Whether we could improve or modify our approach to designating
critical habitat in any way to provide for greater public participation
and understanding, or to better accommodate public concerns and
comments.
Please include sufficient information with your submission (such as
scientific journal articles or other publications) to allow us to
verify any scientific or commercial information you include.
Please note that submissions merely stating support for, or
opposition to, the action under consideration without providing
supporting information, although noted, do not provide substantial
information necessary to support a determination. Section 4(b)(1)(A) of
the Act directs that determinations as to whether any species is an
endangered or a threatened species must be made solely on the basis of
the best scientific and commercial data available and section

[[Page 16778]]

4(b)(2) of the Act directs that the Secretary shall designate critical
habitat on the basis of the best scientific information available.
You may submit your comments and materials concerning this proposed
rule by one of the methods listed in ADDRESSES. We request that you
send comments only by the methods described in ADDRESSES.
If you submit information via <a href="https://www.regulations.gov">https://www.regulations.gov</a>, your
entire submission--including any personal identifying information--will
be posted on the website. If your submission is made via a hardcopy
that includes personal identifying information, you may request at the
top of your document that we withhold this information from public
review. However, we cannot guarantee that we will be able to do so. We
will post all hardcopy submissions on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Comments and materials we receive, as well as supporting
documentation we used in preparing this proposed rule, will be
available for public inspection on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Because we will consider all comments and information we receive
during the comment period, our final determinations may differ from
this proposal. Based on the new information we receive (and any
comments on that new information), we may conclude that Texas
heelsplitter is threatened instead of endangered or that Louisiana
pigtoe is endangered instead of threatened, or we may conclude that one
or both species do not warrant listing as either an endangered species
or a threatened species. For critical habitat, our final designations
may not include all areas proposed, may include some additional areas
that meet the definition of critical habitat, or may exclude some areas
if we find the benefits of exclusion outweigh the benefits of
inclusion. In addition, we may change the parameters of the
prohibitions or the exceptions to those prohibitions in the 4(d) rule
if we conclude it is appropriate in light of comments and new
information we receive. For example, we may expand the prohibitions to
include prohibiting additional activities if we conclude that those
additional activities are not compatible with conservation of the
species. Conversely, we may establish additional exceptions to the
prohibitions in the final rule if we conclude that the activities would
facilitate or are compatible with the conservation and recovery of the
species.

Public Hearing

We have scheduled a public informational meeting and public hearing
on this proposed rule. We will hold the public informational meeting
and public hearing on the date and at the times provided above under
Public informational meeting and public hearing in DATES. We are
holding the public informational meeting and public hearing via the
Zoom online video platform and via teleconference so that participants
can attend remotely. For security purposes, registration is required.
You must register in order to listen and view the meeting and hearing
via Zoom, listen to the meeting and hearing by telephone, or provide
oral public comments at the public hearing by Zoom or telephone. For
information on how to register, or if you encounter problems joining
Zoom the day of the meeting, visit <a href="https://www.fws.gov/office/arlington-ecological-services">https://www.fws.gov/office/arlington-ecological-services</a>. Registrants will receive the Zoom link
and the telephone number for the public informational meeting and
public hearing. If applicable, interested members of the public not
familiar with the Zoom platform should view the Zoom video tutorials
(<a href="https://support.zoom.us/hc/en-us/articles/206618765-Zoom-video-tutorials">https://support.zoom.us/hc/en-us/articles/206618765-Zoom-video-tutorials</a>) prior to the public informational meeting and public
hearing.
The public hearing will provide interested parties an opportunity
to present verbal testimony (formal, oral comments) regarding this
proposed rule. The public informational meeting will be an opportunity
for dialogue with the Service. The public hearing is a forum for
accepting formal verbal testimony. In the event there is a large
attendance, the time allotted for oral statements may be limited.
Therefore, anyone wishing to make an oral statement at the public
hearing for the record is encouraged to provide a prepared written copy
of their statement to us through the Federal eRulemaking Portal, or
U.S. mail (see ADDRESSES, above). There are no limits on the length of
written comments submitted to us. Anyone wishing to make an oral
statement at the public hearing must register before the hearing
(<a href="https://www.fws.gov/office/arlington-ecological-services">https://www.fws.gov/office/arlington-ecological-services</a>). The use of
a virtual public hearing is consistent with our regulations at 50 CFR
424.16(c)(3).

Previous Federal Actions

The Texas heelsplitter was identified as a category 2 candidate
species on January 6, 1989 (54 FR 554). The category 2 designation was
assigned to taxa for which information indicated that proposing to list
as endangered or threatened was possibly warranted, but for which
conclusive data on biological vulnerability and threats were not
currently available to support proposed rules. The species remained so
designated in subsequent candidate notices of review (CNORs) (56 FR
58804, November 21, 1991; 59 FR 58982, November 15, 1994). In the
February 28, 1996, CNOR (61 FR 7596), we discontinued the designation
of category 2 species as candidates; therefore, with the publication of
that CNOR, the Texas heelsplitter was no longer a candidate species.
On June 25, 2007, we were petitioned to list both the Texas
heelsplitter and Louisiana pigtoe. We published a substantial 90-day
finding for Texas heelsplitter on December 15, 2009 (74 FR 66260), and
for Louisiana pigtoe on December 16, 2009 (74 FR 66866).
This document constitutes our 12-month warranted petition finding,
our proposed listing rule, and our proposed critical habitat rule for
the Texas heelsplitter and Louisiana pigtoe.

Supporting Documents

A species status assessment (SSA) team prepared an SSA report for
the Texas heelsplitter and Louisiana pigtoe. The SSA team was composed
of Service biologists, in consultation with other species experts. The
SSA report represents a compilation of the best scientific and
commercial data available concerning the status of the species,
including the impacts of past, present, and future factors (both
negative and beneficial) affecting the species. In accordance with our
joint policy on peer review published in the Federal Register on July
1, 1994 (59 FR 34270), and our August 22, 2016, memorandum updating and
clarifying the role of peer review of listing actions under the Act, we
sought the expert opinions of 11 appropriate specialists regarding the
SSA. We received 6 responses.

I. Proposed Listing Determination

Background

General Mussel Biology

A thorough review of the taxonomy, life history, and ecology of the
Texas heelsplitter and Louisiana pigtoe is presented in the SSA report
(USFWS 2022, entire), and briefly summarized here.
Freshwater mussels, including the Texas heelsplitter and Louisiana
pigtoe, have a complex life history involving parasitic larvae, called
glochidia, which are wholly dependent on host fish. As freshwater
mussels are generally sessile (immobile), dispersal is accomplished
primarily through the behavior of host fish and their tendencies to
travel upstream and against the current in rivers and streams. Mussels
are broadcast spawners; males release

[[Page 16779]]

sperm into the water column, which is taken in by the female through
the incurrent aperture (the tubular structure used to draw water into
the body of the mussel). The developing larvae remain with the female
until they mature and are ready for release as glochidia, to attach on
the gills, head, or fins of fishes (Vaughn and Taylor 1999, p. 913;
Barnhart et al. 2008, pp. 371-373).
Glochidia die if they fail to find a host fish, attach to the wrong
species of host fish, attach to a fish that has developed immunity from
prior infestations, or attach to the wrong location on a host fish
(Neves 1991, p. 254; Bogan 1993, p. 599). Successful glochidia encyst
(enclose in a cyst-like structure) on the host's tissue, draw nutrients
from the fish, and develop into juvenile mussels (Arey 1932, pp. 214-
215). The glochidia will remain encysted for about a month through a
transformation to the juvenile stage. Once transformed, the juveniles
will excyst from the fish and drop to the substrate.
Freshwater mussel species vary in both onset and duration of
spawning, how long developing larvae are held in the marsupial gill
chambers (gills used for holding eggs and glochidia), and which fish
species serve as hosts. The mechanisms employed by mussel species to
increase the likelihood of interaction between host fish and glochidia
vary by species.
Mussels are generally immobile; their primary opportunity for
dispersal and movement within the stream comes when glochidia attach to
a mobile host fish (Smith 1985, p. 105). Upon release from the host,
newly transformed juveniles drop to the substrate on the bottom of the
stream. Those juveniles that drop in unsuitable substrates die because
their immobility prevents them from relocating to more favorable
habitat. Juvenile freshwater mussels burrow into interstitial
substrates and grow to a larger size that is less susceptible to
predation and displacement from high-flow events (Yeager et al. 1994,
p. 220). Adult mussels typically remain within the same general
location where they dropped off (excysted) from their host fish as
juveniles.
Host specificity can vary across mussel species, which may have
specialized or generalized relationships with one or more taxa of fish.
Mussels have evolved a wide variety of adaptations to facilitate
transmission of glochidia to host fish, including mantle displays
(lures) mimicking fish or invertebrates; packages of glochidia
(conglutinates) that mimic worms, insect larvae, larval fish, or fish
eggs; and release of glochidia in mucous webs that entangle fish
(Strayer et al. 2004, p. 431). Polymorphism (existence of multiple
forms) of mantle lures and conglutinates frequently exists within
mussel populations (Barnhart et al. 2008, p. 383), representing
important adaptive capacity in terms of genetic diversity and
ecological representation.

Texas Heelsplitter

The Texas heelsplitter was first described as the species Unio
amphichaenus by Frierson (1898, p. 109) from the Sabine River near
Logansport, Louisiana. The current recognized scientific name for Texas
heelsplitter is Potamilus amphichaenus (Williams et al. 2017a, pp. 35,
42). The Texas heelsplitter is a medium- to large-sized freshwater
mussel (up to 177 millimeters (mm) (7 inches (in)) shell length) that
has a tan to brown or black elliptical shell, with lighter coloration
on the beaks, and a relatively straight hinge line. Texas heelsplitters
exhibit slight sexual dimorphism; females have a broadly rounded
posterior margin and males are more pointed (Howells 2010b, p. 2). The
base of the anterior margin exhibits a long, narrow gape, while a
shorter, much wider gape is located along the posterior margin,
presumably to accommodate the incurrent and excurrent apertures (Neck
and Howells 1995, p. 4).
Although information specific to Texas heelsplitter reproduction is
unavailable, other species from the tribe Lampsilini release glochidia
in packets, called conglutinates, and are known to use mantle lures to
attract sight feeding fishes that attack and rupture the marsupium,
thereby becoming infested by glochidia (Barnhart et al. 2008, pp. 377,
380). Related species are long-term brooders (bradytictic), spawning
and becoming gravid in the fall and releasing glochidia in the spring
(Barnhart et al. 2008, p. 384). Freshwater drum (Aplodinotus grunniens)
have been confirmed as host fish for the Texas heelsplitter (Bosman et
al. 2015, p. 15).
A related freshwater mussel species, bleufer (Potamilus
purpuratus), from the southeastern United States was reported to reach
a maximum age of 9-26 years, and other related species ranged from 4-50
years with a higher growth rate compared to other species (Haag and
Rypel 2011, pp. 229, 234, 239). The Texas heelsplitter has been
reported mature at approximately 60 mm (2.4 in) (Ford et al. 2016, p.
31).
Texas heelsplitters occur in streams and rivers of the Trinity,
Neches, and Sabine drainages in east Texas and in the Sabine River at
the western border of Louisiana on substrates consisting of ``firm mud,
sand, or finer gravels bottoms, in still to moderate flows'' and
sometimes associated with fallen timber (Howells 2014, p. 69; Howells
2010b, p. 3 and table 2.3). Additionally, Texas heelsplitters can
tolerate manmade impoundments and have been found in several East Texas
reservoirs (Howells 2010b, p. 3).

Louisiana Pigtoe

The Louisiana pigtoe was originally described as the species Unio
riddellii (Lea 1862, p. 228) from the Trinity River near the City of
Dallas, Dallas County, Texas. The current recognized scientific name
for Louisiana pigtoe is Pleurobema riddellii (Williams et al. 2017a,
pp. 35, 42). The Louisiana pigtoe is a medium-sized freshwater mussel
(shell lengths to greater than 62 mm (2.4 in)) with a brown to black,
triangular to subquadrate shell without external sculpturing, sometimes
with greenish rays. For a detailed description, see Howells et al. 1996
(pp. 91-92) and Howells 2014 (p. 65). Other native mussel species
(e.g., pimpleback (Cyclonaias pustulosa), Texas pigtoe (Fusconaia
askewi), Trinity pigtoe (F. chunii), and Wabash pigtoe (F. flava)) can
easily be mistaken for Louisiana pigtoe when identified by shell
morphology alone.
Louisiana pigtoe are bradytictic (i.e., long-term brooders;
spawning occurs during the summer, and glochidia are held by the female
over winter and released the following spring); however, gravid females
have been observed in July (Marshall 2014, pp. 46-47). A closely
related congener, the rough pigtoe (Pleurobema plenum), is known to
utilize the tachytictic reproductive cycle (i.e., short-term brooders;
fertilization occurs in the spring, and glochidia are expelled during
the summer or early fall) (EPA 2007, p. 37).
The primary host fish for Louisiana pigtoe has not been confirmed.
Bullhead minnow (Pimephales vigilax), blacktail shiner (Cyprinella
venusta), and red shiner (Cyprinella lutrensis) have been suggested as
potential fish hosts based on a fish host distribution modeling effort
(Marshall 2014, pp. 59-60).
A single juvenile Louisiana pigtoe from the Neches River, Texas,
was reported to grow 15 mm (0.6 in) during its first year from an
initial shell length of 2 mm (0.08 in) (Ford et al. 2016, p. 30).
Sexual maturity is achieved at shell lengths around 40 mm (1.6 in)
(Ford et al. 2016, pp. 28, 30), and Louisiana pigtoe could reach
maturity in 3 to 4 years. Based on egg production, sexually mature
females were estimated by external annuli to be between 4 and 12 years
of age with shell lengths ranging

[[Page 16780]]

from 29-59 mm (1.1-2.3 in) (Hinkle 2018, p. 19).
Louisiana pigtoes occur in medium- to large-sized streams
throughout portions of east Texas, Louisiana, west Mississippi,
southeast Oklahoma, and southwest Arkansas (Vidrine 1993, p. 66;
Howells et al. 1997, p. 22; Randklev et al. 2013, p. 269; Randklev
2018, entire) in flowing waters (0.3-1.4 meters per second (m/s)) over
substrates of cobble and rock or sand, gravel, cobble, and woody
debris; they are often associated with riffle, run, and sometimes
larger backwater tributary habitats (Ford et al. 2016, pp. 42, 52;
Howells 2010a, pp. 3-4; Williams et al. 2017b, p. 21). Specimens are
typically found in shallower waters (0.1-1.2 m (0.3-3.9 feet (ft) in
depth; Howells 2010a, p. 3)); however, recent surveys found Louisiana
pigtoe as deep as 3.33 m (10.9 ft) in the lower Neches River (Corbett
2020, pp. 2, 4).

Regulatory and Analytical Framework

Regulatory Framework

Section 4 of the Act (16 U.S.C. 1533) and the implementing
regulations in title 50 of the Code of Federal Regulations set forth
the procedures for determining whether a species is an endangered
species or a threatened species, issuing protective regulations for
threatened species, and designating critical habitat for endangered and
threatened species. In 2019, jointly with the National Marine Fisheries
Service, the Service issued a final rule that revised the regulations
in 50 CFR part 424 regarding how we add, remove, and reclassify
endangered and threatened species and the criteria for designating
listed species' critical habitat (84 FR 45020; August 27, 2019). On the
same day, the Service also issued final regulations that, for species
listed as threatened species after September 26, 2019, eliminated the
Service's general protective regulations automatically applying to
threatened species the prohibitions that section 9 of the Act applies
to endangered species (84 FR 44753; August 27, 2019).
The Act defines an ``endangered species'' as a species that is in
danger of extinction throughout all or a significant portion of its
range, and a ``threatened species'' as a species that is likely to
become an endangered species within the foreseeable future throughout
all or a significant portion of its range. The Act requires that we
determine whether any species is an endangered species or a threatened
species because of any of the following factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
These factors represent broad categories of natural or human-caused
actions or conditions that could have an effect on a species' continued
existence. In evaluating these actions and conditions, we look for
those that may have a negative effect on individuals of the species, as
well as other actions or conditions that may ameliorate any negative
effects or may have positive effects.
We use the term ``threat'' to refer in general to actions or
conditions that are known to or are reasonably likely to negatively
affect individuals of a species. The term ``threat'' includes actions
or conditions that have a direct impact on individuals (direct
impacts), as well as those that affect individuals through alteration
of their habitat or required resources (stressors). The term ``threat''
may encompass--either together or separately--the source of the action
or condition or the action or condition itself.
However, the mere identification of any threat(s) does not
necessarily mean that the species meets the statutory definition of an
``endangered species'' or a ``threatened species.'' In determining
whether a species meets either definition, we must evaluate all
identified threats by considering the expected response by the species,
and the effects of the threats--in light of those actions and
conditions that will ameliorate the threats--on an individual,
population, and species level. We evaluate each threat and its expected
effects on the species, then analyze the cumulative effect of all of
the threats on the species as a whole. We also consider the cumulative
effect of the threats in light of those actions and conditions that
will have positive effects on the species, such as any existing
regulatory mechanisms or conservation efforts. The Secretary determines
whether the species meets the definition of an ``endangered species''
or a ``threatened species'' only after conducting this cumulative
analysis and describing the expected effect on the species now and in
the foreseeable future.
The Act does not define the term ``foreseeable future,'' which
appears in the statutory definition of ``threatened species.'' Our
implementing regulations at 50 CFR 424.11(d) set forth a framework for
evaluating the foreseeable future on a case-by-case basis. The term
``foreseeable future'' extends only so far into the future as the
Services can reasonably determine that both the future threats and the
species' responses to those threats are likely. In other words, the
foreseeable future is the period of time in which we can make reliable
predictions. ``Reliable'' does not mean ``certain''; it means
sufficient to provide a reasonable degree of confidence in the
prediction. Thus, a prediction is reliable if it is reasonable to
depend on it when making decisions.
It is not always possible or necessary to define foreseeable future
as a particular number of years. Analysis of the foreseeable future
uses the best scientific and commercial data available and should
consider the timeframes applicable to the relevant threats and to the
species' likely responses to those threats in view of its life-history
characteristics. Data that are typically relevant to assessing the
species' biological response include species-specific factors such as
lifespan, reproductive rates or productivity, certain behaviors, and
other demographic factors.

Analytical Framework

The SSA report documents the results of our comprehensive
biological review of the best scientific and commercial data regarding
the status of the species, including an assessment of the potential
threats to the species. The SSA report does not represent a decision by
the Service on whether the species should be proposed for listing as an
endangered or threatened species under the Act. It does, however,
provide the scientific basis that informs our regulatory decisions,
which involve the further application of standards within the Act and
its implementing regulations and policies. The following is a summary
of the key results and conclusions from the SSA report; the full SSA
report can be found at Docket No. FWS-R2-ES-2022-0026 on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
To assess the viability of the Texas heelsplitter and Louisiana
pigtoe, we used the three conservation biology principles of
resiliency, redundancy, and representation (Shaffer and Stein 2000, pp.
306-310). Briefly, resiliency supports the ability of the species to
withstand environmental and demographic stochasticity (for example, wet
or dry, warm or cold years), redundancy supports the ability of the
species to withstand catastrophic events (for example, droughts, large
pollution events), and representation supports the

[[Page 16781]]

ability of the species to adapt over time to long-term changes in the
environment (for example, climate changes). In general, the more
resilient and redundant a species is and the more representation it
has, the more likely it is to sustain populations over time, even under
changing environmental conditions. Using these principles, we
identified the species' ecological requirements for survival and
reproduction at the individual, population, and species levels, and
described the beneficial and risk factors influencing the species'
viability.
The SSA process can be categorized into three sequential stages.
During the first stage, we evaluated each individual species' life-
history needs. The next stage involved an assessment of the historical
and current condition of each species' demographics and habitat
characteristics, including an explanation of how the species arrived at
its current condition. The final stage of the SSA involved making
predictions about each species' responses to positive and negative
environmental and anthropogenic influences. Throughout all of these
stages, we used the best available information to characterize
viability as the ability of a species to sustain populations in the
wild over time. We use this information to inform our regulatory
decision.

Summary of Biological Status and Threats

In this discussion, we review the biological condition of the
species and their resources, and the threats that influence the
species' current and future condition, in order to assess the species'
overall viability and the risks to that viability. We analyze these
factors both individually and cumulatively to determine the current
condition of the species and project the future condition of the
species under several plausible future scenarios.
Using various timeframes and the current and projected future
resiliency, redundancy, and representation, we describe the species'
levels of viability over time. For the Texas heelsplitter and Louisiana
pigtoe to maintain viability, their populations or some portion thereof
must be sufficiently resilient. A number of factors influence the
resiliency of their populations, including occupied stream length,
abundance, and recruitment. Elements of the species' habitat that
determine whether Texas heelsplitter and Louisiana pigtoe populations
can grow to maximize habitat occupancy influence those factors, thereby
increasing the resiliency of populations. These resiliency factors and
habitat elements are discussed in detail in the SSA report and
summarized here.

Species Needs

Occupied Stream Length
Most freshwater mussels, including the Texas heelsplitter and
Louisiana pigtoe, are found in aggregations called mussel beds that
vary in size from about 50 to over 5,000 square meters (m\2\),
separated by stream reaches in which mussels are absent or rare (Vaughn
2012, p. 2). Mussel populations in streams are highly patchy,
especially at a small scale (less than 100 stream meters) (Strayer
1999, p. 468). We define a mussel population at a larger scale than a
single mussel bed; it is the collection or series of mussel beds within
a stream reach between that infested host fish may travel, allowing for
ebbs and flows in mussel bed density and abundance over time throughout
the population's occupied reach. Therefore, adequately resilient mussel
populations must occupy stream reaches that are long enough such that
stochastic events that adversely affect individual mussel beds do not
eliminate the entire population. Repopulation by glochidia-infested
fish from other mussel beds within the reach, if present and connected,
allow the population to recover from the temporary loss of individuals
due to occasional disruptive events.
For our analysis, we consider populations extending greater than 50
river miles (river mi) (80 kilometers (km)) to have a high probability
of persistence to stochastic events because a single event is unlikely
to affect the entire population. Populations occupying reaches between
20 and 50 river mi (32 and 80 km) have moderate resiliency to
stochastic events, while populations occupying reaches less than 20 mi
(32.19 km) have low resiliency. Note that we define populations
occupying a stream length at or approaching zero miles as being
functionally extirpated (populations with abundance that is currently
at such low levels that we expect them to become extirpated in the near
future) or extirpated.
Abundance
Populations require a minimum number of individuals to ensure
stability and persistence. This threshold is often referred to as the
minimum viable population and is generally calculated through a
population viability analysis that estimates extinction risk given a
number of input variables. There are no published minimum viable
population estimates for the Texas heelsplitter or Louisiana pigtoe;
therefore, it is unknown how many individuals are required to sustain
populations of these mussels. However, population health is dependent
on species abundance as well as water availability and the ability for
mussels to meet life-history needs within their habitats, which were
evaluated as part of the SSA.
It is important to recognize that Louisiana pigtoe observations
used to determine abundance in the SSA report may include misidentified
individuals. Without genetic confirmation, identification of Louisiana
pigtoe in the field based on shell morphology is questionable, with
seasoned experts accurately identifying the species only 76 percent of
the time (Inoue 2018, p. 1). Unfortunately, genetic testing was not
available for the majority of reported Louisiana pigtoe historical
observations, which relied solely on shell morphological
characteristics for species identification (Randklev 2018, entire).
Since there is no way to know the margin of error or to otherwise
account for potential misidentifications, we determined abundance for
Louisiana pigtoe based on reported observations (as is) and did not
adjust or modify the survey data to compensate for potential
misidentifications. We do not consider misidentification to be an issue
for Texas heelsplitter observations, since they are recognizable based
on morphological characteristics observed in the field and not easily
confused with other species.
Mussel abundance in a given stream reach is a product of the number
of mussel beds and the density of mussels within those beds. For
populations of Texas heelsplitter and Louisiana pigtoe to be healthy
(i.e., adequately resilient), mussel beds of sufficient number and
density must be present to allow recovery from natural and local
stochastic events, allowing the mussel bed to persist and the overall
local population to survive within a stream reach. Mussel abundance is
indicated by the number of individuals found during a sample event.
Mussel surveys are rarely a complete census of the population, but
density can be estimated by the number of individuals found during a
survey effort using various statistical techniques (i.e., estimate the
total population from a subset of surveyed individuals). Population
estimates are not available for all Texas heelsplitter and Louisiana
pigtoe populations, and techniques for available surveys are not always
directly comparable (i.e., same area size searched, similar search
time, etc.). When available, we used the number of

[[Page 16782]]

individuals captured relative to the amount of time surveys were
conducted to estimate population abundance, hereafter referred to as
overall catch per unit effort (CPUE). Although overall CPUE was the
preferred metric to estimate population abundance, when overall CPUE
was not available, the number of individuals detected during the most
recent comprehensive survey effort was used as a surrogate metric.
Calculation of abundance in this manner is intended to be an estimate
and is considered the best available information when population trend
data do not exist and precise population abundance cannot be
determined. Using CPUE, we are able to estimate if the species is
currently (since year 2000) common or rare within populations.
Abundance for each population is rated from ``high'' to ``low'' (or
functionally extirpated/extirpated) based on overall CPUE (or number of
individuals found when survey effort is not reported) according to live
or recent dead found during surveys since the year 2000, as follows:
``high'' is overall CPUE of greater than or equal to 4.0 (or 100 or
more individuals); ``moderate'' is overall CPUE greater than or equal
to 2.0 and less than 4.0 (or between 25 individuals and 99
individuals); ``low'' is overall CPUE greater than or equal to 0.5 and
less than 2.0 (or between 3 and 24 individuals); and ``functionally
extirpated/extirpated'' is overall CPUE less than 0.5 (or fewer than 3
individuals).
Reproduction/Recruitment
Sufficiently resilient Texas heelsplitter and Louisiana pigtoe
populations must also be reproducing and recruiting young individuals
into the population to replace individuals lost to old age, disease, or
predation. Population size and abundance are a reflection of habitat
conditions, environmental stressors, and other past influences on the
population. The ability of populations to successfully reproduce and
recruit will determine if a population may be stable, increasing, or
decreasing over time. For example, a large, dense mussel population
that contains mostly old individuals is not likely to remain large and
dense into the future if there are few young individuals to sustain the
population over time (i.e., death rates exceed birth rates resulting in
negative population growth). Conversely, a population that is less
dense but has many young and/or gravid individuals is likely to grow,
becoming more densely populated in the future (i.e., birth rates, and
subsequent recruitment of reproductive adults, exceed death rates,
resulting in positive population growth). Detection rates of very young
juvenile mussels during routine abundance and distribution surveys are
extremely low due to sampling bias because sampling involves tactile
searches and mussels less than 35 mm (1.4 in) can be difficult to
detect (Strayer and Smith 2003, pp. 47-48). For this evaluation, we
concluded there was evidence of reproduction/recruitment for a
population when surveys detected small-sized individuals (near the low
end of the detectable range or approximately 35 mm (1.4 in) in size)
since the year 2000 or gravid females (eggs and/or glochidia visible)
were observed during the reproductively active time of year.

Risk Factors for Texas Heelsplitter and Louisiana Pigtoe

We reviewed the potential risk factors (i.e., threats, stressors)
that could be affecting the Texas heelsplitter and Louisiana pigtoe now
and in the future. In this proposed rule, we will discuss only those
factors in detail that could meaningfully impact the status of the
species. Many of the threats and risk factors are the same or similar
for both species. Where the effects are expected to be similar, we
present one discussion that applies to both species. Where the effects
may be unique to one species, we will address that specifically. The
primary risk factors (i.e., threats) affecting the status of the Texas
heelsplitter and Louisiana pigtoe all fall under Factor A of the Act
and are: (1) Water quality changes, (2) altered hydrology, (3) changes
to habitat structure and substrate, and (4) habitat fragmentation.
These factors are all exacerbated by the ongoing and expected effects
of climate change (Factor E). Additionally, predation (Factor C) and
collection (Factor B), as well as other natural or human induced
events/activities that result in direct mortality, are also affecting
those populations already experiencing low stream flow, and reservoirs
and instream barriers to fish movement (Factor E) limit dispersal and
prevent recolonization after stochastic events.
Changes to Water Quality
Freshwater mussels require water in sufficient quantity and quality
on a consistent basis to complete their life cycles and those of their
host fishes. Water quality can be degraded through contamination or
alteration of water chemistry. Environmental contaminants include a
broad array of natural, synthetic, and chemical substances introduced
to the environment that can be hazardous to living organisms. Chemical
contaminants are ubiquitous throughout the environment and are a major
contributor to the current declining status of freshwater mussel
species nationwide (Augspurger et al. 2007, p. 2025). Contaminants
enter the environment through both point (e.g., hazardous spills,
industrial wastewater, municipal effluents) and non-point (e.g., urban
stormwater and agricultural runoff) sources. These sources contribute
organic compounds, trace metals, pesticides, plastics, petroleum
hydrocarbons, flame retardants, and a wide variety of emerging
contaminants (e.g., pharmaceuticals and personal care products).
Ammonia is of particular concern below wastewater treatment plant
outfalls because freshwater mussels have been shown to be particularly
sensitive to increases in ammonia levels (Augspurger et al. 2003, p.
2569). The extent to which environmental contaminants adversely affect
aquatic biota can vary depending on many site-specific variables, but
species diversity and abundance consistently ranks lower in waters that
are known to be polluted or otherwise impaired by contaminants. For
example, freshwater mussels are not generally found for many miles
downstream of municipal wastewater treatment plants (treatment plants)
(Gillis et al. 2017, p. 460; Goudreau et al. 1993, p. 211; Horne and
McIntosh 1979, p. 119).
There are approximately 386 treatment plant discharge permits
issued for the Trinity River Basin from its headwaters above the
Dallas-Fort Worth metroplex down to the Gulf of Mexico (Texas
Commission on Environmental Quality (TCEQ) 2018, entire). The San
Jacinto Basin, although geographically smaller than most other basins
in Texas, has approximately 1,052 treatment plant outfalls, while the
Neches and Sabine rivers have 218 and 191 outfalls, respectively. In
addition, some industrial permits can discharge millions of gallons per
day and have ammonia limits that exceed levels that inhibited growth in
juvenile fatmucket (Lampsilis siliquoidea) and rainbow mussel (Villosa
iris) during 28-day chronic tests (Wang et al. 2007, entire). Immature
mussels (juveniles and glochidia) are especially sensitive to water
quality degradation and contaminants (Cope et al. 2008, p. 456; Wang et
al. 2017, pp. 791-792; Wang et al. 2018, p. 3041).
An additional type of water quality impairment is the alteration of
water quality parameters such as dissolved oxygen, temperature, total
dissolved solids (TDS), and salinity levels. Dissolved oxygen levels
may be reduced from increased nutrients in the water

[[Page 16783]]

from runoff or wastewater effluent, and juveniles seem to be
particularly sensitive to low dissolved oxygen (Sparks and Strayer
1998, pp. 132-133). Increases in water temperature from water
diversions, climate change, or low flows during droughts can exacerbate
low dissolved oxygen levels as well as have its own effects on juvenile
and adult mussels.
Total dissolved solids, a measure of the mineral content of water
(i.e., inorganic salts, metals, cations, or anions dissolved in water,
including calcium, magnesium, potassium, sodium, bicarbonates,
chlorides, and sulfates), is commonly elevated in watersheds impacted
by a variety of industrial, commercial, urban, and agricultural
activities and has been associated with acute and chronic toxicity to
aquatic organisms. Watersheds with increasing trends in conductivity or
TDS are experiencing declines in water quality that can be harmful to
mussels and other aquatic organisms. Increasing trends in TDS are
common in watersheds impacted by anthropogenic activities.
Contaminant spills are also a concern. Texas leads the nation in
crude oil and natural gas production, and various chemicals, refined
fuels, and wastewater related to oil and natural gas exploration are
routinely transported along highways. These facilities and equipment
used for extraction, transportation, and refinement of hazardous
materials are all potential sources of hazardous spills, and can
originate from human error, equipment failure, or catastrophic events
like industrial accidents, fires, or floods. Although spills are
relatively short-term events and may be localized, water resources
nearby can be severely impacted and degraded for years after the
incident along with the biological resources that inhabit the area. A
reduction in surface flow drought, instream diversions, or groundwater
extraction serve to concentrate contaminant and salinity levels,
increases water temperatures in streams, and exacerbates effects to
Texas heelsplitter and Louisiana pigtoe.
Poor water quality affects most Texas heelsplitter and Louisiana
pigtoe populations currently to some degree, and future water quality
is expected to decrease due to decreasing stream flow and increasing
temperatures. We foresee threats to water quality increasing into the
future due to the effects of climate change as demand and competition
for limited water resources grows (USFWS 2022, pp. 61-62).
Altered Hydrology
Altered hydrology, through changes to historical flow regimes,
leads to inundation, or low- or high-flow conditions that may reduce
the quality of affected habitats to the point where they are no longer
suitable for freshwater mussels. While Texas heelsplitter and Louisiana
pigtoe have adapted to survive natural fluctuations in flows,
populations that experience sustained higher than normal flows,
prolonged flooding, or unnatural fluctuations in the frequency or
intensity of high/low flows or extended (or repeated) drying events
will not persist. Virtually every watershed within the range of these
two freshwater mussels has experienced some level of alteration, a
trend that has continued into the 21st century, particularly in areas
with rapid population growth.
Inundation of previously free-flowing rivers and streams by
impoundments has arguably had the single largest human-related impact
on the distribution of freshwater mussels. The construction of
reservoirs and other impoundments permanently alters the hydrology and,
hence, the ecology of rivers, often with deleterious effects to water
quality, water quantity, host fish movement, and dispersal of mussel
glochidia, nutrient cycling, sediment deposition, fate and transport of
contaminants, and numerous other changes to the physical, chemical, and
biological characteristics of affected areas (upstream and downstream).
The close relationship of flow to mussels makes them uniquely
vulnerable to hydrology changes.
Both mussel species are adapted to flowing water (lotic habitats)
rather than standing water (lentic habitats). Louisiana pigtoe require
free-flowing water to survive. The Texas heelsplitter has also been
observed in lentic habitats and appears to be tolerant of reservoir
conditions; this species may occur in higher densities in areas of
reservoirs that are influenced by stream inflows where conditions more
closely resemble their preferred riverine habitat (Whisenant 2019, p.
1; Neck and Howells 1995, p. 15).
Inundation of mussel habitat has primarily occurred upstream of
dams, including major flood control and water supply reservoirs, such
as Toledo Bend Reservoir, and smaller structures like low water vehicle
crossings and diversion dams typically found along tributaries on
privately owned land. These structures alter the hydrology of rivers by
slowing, impeding, or diverting normal flow patterns, and increasing
deposition in some areas and eliminating the interstitial spaces that
juvenile Texas heelsplitters and Louisiana pigtoes inhabit.
Large reservoirs that release water from the hypolimnion, the
deeper water is cold and often devoid of oxygen and necessary
nutrients, can adversely affect mussel survival, as cold water can
stunt mussel growth and delay or hinder spawning (Vaughn and Taylor
1999, p. 917). Cold water releases from reservoirs like Broken Bow Lake
in southeast Oklahoma can affect water temperatures for miles
downstream. These cold releases create an extinction gradient, where
freshwater mussels are absent or presence is low near the dam, and
abundance does not rebound until some distance downstream where ambient
conditions raise the water temperature to within the tolerance limits
of mussels (Davidson et al. 2014, p. 29; Vaugh and Taylor 1999, pp.
915, 916).
The construction of dams for flood control and drinking water
supply, and the subsequent management of water releases from those
reservoirs (e.g., timing, intensity, and duration), often resulting in
higher base flows and peak flows of reduced intensity but longer
duration, has significant impacts on the natural function and hydrology
of rivers and streams. The additional shear stress caused by these
sustained high base flows can incise channels, erode river banks, scour
mussel beds, and remove substrate preferred by mussels. Over time, the
physical force of these higher base flows can dislodge mussels from the
sediment and permanently alter the geomorphology of rivers.
During flood events, along with water, rivers transport sediment,
mostly as solids, suspended in the water column. The increase in
flooding severity results in greater sediment transport, with important
effects to substrate stability and benthic habitats for freshwater
mussels, as well as other organisms that are dependent on stable
benthic habitats. Further, water released by dams is usually clear due
to reduced sediment load and results in incision (downcutting of the
bed) and coarsening of the bed material until a new equilibrium is
reached (Kondolf 1997, p. 535). The extent to which downcutting and
erosion occurs as a result of dam releases varies, but in some cases
leads to bank collapse, burial of mussel beds, and mortality.
Conversely, depending on how dam releases are conducted, reduced flood
peaks can lead to accumulations of fine sediment in the river bed
(i.e., loss of flushing flows; Kondolf 1997, pp. 535, 548).
Operation of reservoirs for flood control, water supply, and
recreation results in altered hydrologic regimes,

[[Page 16784]]

including an attenuation of both high- and low-flow events. The changes
to flood flows alters sediment dynamics, as sediments are trapped above
and scoured below major impoundments, and negatively affect freshwater
mussels and their habitats (Gascho Landis and Stoeckel 2016, p. 234;
Ford 2013, p. 3). Evidence that the Texas heelsplitter is able to
tolerate reservoir conditions leads us to believe the overall impacts
of reservoirs may be more pronounced for the Louisiana pigtoe (Howells
2010b, p. 3).
Very low flows and low water levels are also detrimental to Texas
heelsplitter and Louisiana pigtoe populations. Droughts that occurred
in the recent past led to extremely low flows in several east Texas
rivers. Some rivers, or portions thereof, are resilient to drought
because they are spring-fed (Calcasieu, Neches rivers), contain large
volumes of water (Trinity River), have large reservoirs in the upper
reaches that release water for downstream users (all, excluding
Calcasieu River), or have significant return flows (Pearl, Sabine,
Trinity rivers); however, drought in combination with increasing trends
in groundwater extraction may lead to lower river flows of longer
duration than previously recorded. Reservoir releases can be managed to
some extent, but in many cases dam operators must stop releases during
droughts to conserve water and protect water supplies, or to maximize
flood releases during major floods to protect public safety and
property, both can negatively affect mussels downstream.
Streamflow and overall discharge for rivers inhabited by the Texas
heelsplitter and Louisiana pigtoe are expected to decline due to
climate change and projected increases in temperatures and evaporation
rates, resulting in more frequent and intense droughts (Lafontaine et
al. 2019, entire) (Factor E). Return flows, consisting primarily of
treated municipal wastewater, are projected to continue to increase in
areas with population growth and may serve to ameliorate some of the
effects of climate change downstream of metropolitan areas, albeit with
notable impacts to water quality; however, these benefits may become
less significant as municipalities increase wastewater reuse as a
conservation measure. The Trinity River, for example, has been a
significantly modified, highly controlled, and highly regulated system
since the 1960s, with low flows steadily increasing as the population
has grown, resulting in base flows that are significantly higher
compared to historical flows (Clark and Mangham 2019, p. 9). The
increase in base flows can be attributed to substantial return flows
from Dallas/Fort Worth metropolitan area wastewater treatment plants
and are projected to continue to increase in the future. Surface and
alluvial aquifer groundwater withdrawals will likely increase in the
future due to the effects of more intense droughts, with reductions in
stream flows putting an additional strain on aquatic resources.
However, with the exception of stream segments where municipal effluent
return flows supplement base flows, most streams experience lower base
flows and reduced high-flow events after major reservoirs are
constructed (U.S. Geological Survey (USGS) 2008, pp. 964, 966).
Many streams within the range of these two freshwater mussel
species receive significant groundwater inputs from multiple springs
associated with aquifers. As spring flows decline due to drought,
climate change, or groundwater pumping, habitat for freshwater mussels
in affected streams is reduced and could eventually cease to exist.
While the Texas heelsplitter and Louisiana pigtoe may survive short
periods of low flow, as low flows persist, mussels can be subjected to
oxygen deprivation, increased water temperature, stranding, increased
predation, and, ultimately, desiccation which leads to reduced
survivorship, reproduction, and recruitment to the population. High-
flow events can lead to increased risk of mortality through physical
removal, transport, or burial of mussels as unstable substrates are
transported downstream by flood waters (entrainment) and dislodged
mussels are later redeposited in locations that may not be suitable
habitat.
The distribution of mussel communities and their habitats is
affected by large floods returning at least once during the typical
life span of an individual mussel (generally from 3-30 years), as
mediated by the presence of flow refuges, where shear stress is
relatively low, sediments are relatively stable, and mussels must
either tolerate high-frequency disturbances or be eliminated and can
colonize only areas that are infrequently disturbed between events
(Strayer 1999, pp. 468-469). Shear stress and relative shear stress are
limiting to mussel abundance and species richness (Randklev et al.
2017, p. 7), and riffle habitats may be more resilient to high-flow
events than bank habitats.
The Texas heelsplitter and Louisiana pigtoe undoubtedly evolved in
the presence of extreme hydrological conditions, including severe
droughts leading to dewatering, and heavy rains leading to damaging
scour events and movement of mussels and substrate, although the
frequency, duration, and intensity of these events may be different
from what is observed today. These same patterns led to the development
of flood control and storage reservoirs throughout Texas in the 20th
century. The increasing variability, frequency, and severity of extreme
weather events is a contributing factor to the contraction of
populations for both species.
Another source of alteration to hydrology is from sand and gravel
mining directly from rivers or from adjacent alluvial deposits (Kondolf
1997, p. 541). Instream mining directly impacts river habitats by
removal of substrates used by mussels, and can indirectly affect river
habitats through channel incision, bed coarsening, and lateral channel
instability (Kondolf 1997, p. 541). Excavation of pits in or near to
the channel can create a knickpoint, which can contribute to erosion
(and mobilization of substrate) associated with head cutting (Kondolf
1997, p. 541). Pits associated with off-channel mining of the
floodplain can become involved during floods, such that the pits become
hydrologically connected, and thus can affect sediment dynamics in the
stream or river (Kondolf 1997, p. 545). Sand and gravel mines occurred
historically and continue to operate in some basins throughout the
ranges of the Texas heelsplitter and Louisiana pigtoe.
Specifically, a change to the number of days with zero flow was
limiting for the Louisiana pigtoe, and the number of high pulses was
limiting for the Texas heelsplitter. In summary, results to date
indicate natural flow regimes have been altered in east Texas rivers,
as was expected, which has led to modification of instream habitats and
contributed to declines in freshwater mussels (Khan and Randklev 2019,
entire). These findings agree with the estimate of many experts, who
based on their research believe: (1) Portions of the Trinity River have
been significantly modified and may no longer support mussels
(particularly in the upper basin where stream hydrology and
geomorphology have been permanently altered), and (2) the Neches River
is the least altered and has some of the best remaining mussel habitat,
along with the most abundant and diverse mussel populations, in east
Texas.
Changes to Habitat Structure/Substrate
Texas heelsplitters and Louisiana pigtoes inhabit microhabitat
along river stream beds that have abundant

[[Page 16785]]

interstitial spaces or small openings in an otherwise closed matrix of
stable substrates created by gravel, cobble, boulders, bedrock
crevices, tree roots, and other vegetation, with some amount of fine
sediment (i.e., clay and silt) necessary to provide appropriate
shelter. Excessive amounts of fine sediments can reduce available
microhabitat by filling in these interstitial spaces, effectively
smothering mussels in place. Interstitial spaces provide essential
habitat for juvenile mussels, offering protection from predation and
vital nutrients. While adult mussels can be physically buried by
excessive sediment, the main impacts of excess sedimentation on
freshwater mussels are often sublethal and include interference with
feeding mediated by valve closure (Box and Mossa 1999, p. 101).
Under a natural flow regime, sediments are naturally washed away
from one microhabitat to another, the amount of sediment in the
substrate is relatively stable, and different reaches within a river or
stream may be aggrading or degrading sediment at any given time (Poff
et al. 1997, pp. 770-772). Current (and past) human activities often
result in enhanced sedimentation in river systems, including legacy
sediment from past land disturbances and reservoir construction. These
activities continue in many basins occupied by the Texas heelsplitter
and Louisiana pigtoe, and influence river processes and sediment
dynamics (Wohl 2015, pp. 31, 39), with legacy effects that can result
in degradation of mussel habitat. Sediments deposited by large-scale
flooding or other disturbance may persist for several years until
adequate cleansing flows can redistribute that sediment downstream.
Conversely, when water velocity decreases from reduced streamflow or
inundation, water loses its ability to carry sediment in suspension and
sediment falls to the substrate, eventually smothering mussels not
adapted to soft substrates (Watters 2000, p. 263).
Sediment accumulation can be exacerbated when there is a
simultaneous increase in the sources of fine sediments in a watershed,
including streambank erosion from development, agricultural activities,
livestock and wildlife grazing, in-channel disturbances, roads, and
crossings, among others (Poff et al. 1997, p. 773). In areas with
ongoing development, runoff can transport substantial amounts of
sediment from ground disturbance related to construction activities
with inadequate or absent sedimentation controls. While these
construction impacts can be transient (lasting only during the
construction phase), the long-term effects of development on water
quantity and quality are long lasting and can result in hydrological
alterations as increased impervious cover increases run off and
resulting shear stress causes streambank instability and additional
sedimentation.
Habitat Fragmentation
Historically, the Texas heelsplitter and Louisiana pigtoe were
likely distributed in areas with suitable habitat throughout the river
basins described above under Background. Today, the remaining Texas
heelsplitter and Louisiana pigtoe populations are isolated from one
another by major reservoirs, habitat alterations, and de-watering
events, prolonged drought, among other reasons, such that natural
recolonization of areas previously extirpated is extremely unlikely, if
not impossible, due to barriers to host fish movement. With the
exception of the Louisiana pigtoe populations in the Red River Basin in
Arkansas and Oklahoma, there is currently no opportunity for
substantial interaction among extant Texas heelsplitter and Louisiana
pigtoe populations, resulting in genetic isolation.
The impacts of reservoirs are significant, causing permanent
changes to fish movement, water quality, and hydrology, with cascading
effects to river ecology and aquatic species that utilize areas
downstream. Small populations are more affected by limited host fish
immigration potential because they are susceptible to genetic drift
(random loss of genetic diversity) and inbreeding depression. At the
species level, populations that are eliminated due to stochastic events
cannot be recolonized naturally, leading to reduced overall redundancy
and representation.
The confirmed or assumed primary host fish species for both the
Texas heelsplitter and Louisiana pigtoe are known to be common and
widespread throughout the range of both mussel species and are
therefore not believed to be a limiting factor to dispersal at this
time (Nico and Sturtevant 2022, entire; Nico et al. 2022, entire; Nico
and Fuller 2022, entire; Fuller et al. 2022, entire). Each of the
identified fish hosts are known to tolerate lake environments and may
utilize impoundments as corridors to facilitate migration between
hydrologically connected tributaries, thus aiding mussel dispersal. If
fish host species are indeed abundant, existing dams, the construction
of new major dams and reservoirs, and other barriers to fish movement
are the primary mechanism through which remaining populations are
isolated. Furthermore, reservoir impacts to river ecosystems can be
difficult and costly to manage or minimize.
Most reservoirs function primarily to provide water supply and/or
flood control, and meeting those objectives typically involves holding
on to as much water as possible (i.e., not releasing); this may limit
the ability of reservoir managers to modify releases for the purpose of
meeting wildlife conservation or recovery goals. Although dams have
been managed to allow fish passage for spawning, to our knowledge, fish
passage has not been facilitated specifically to allow movement of host
fish for the benefit of freshwater mussels, nor would this be cost-
effective considering host fish for the Texas heelsplitter and
Louisiana pigtoe are believed to be abundant. Nevertheless, reservoirs
represent a permanent barrier to freshwater mussel dispersal. The
overall impact of reservoirs is believed to be greater for the
Louisiana pigtoe than for the Texas heelsplitter, which is able to
persist in reservoir conditions although questions remain about their
reproductive success in lake environments.
Direct Mortality
Direct mortality includes any activity or event, whether human-
induced or natural, that results in the death of mussels within a
localized area due to removal, crushing, burying, consumption,
desiccation, or poisoning. Potential activities or events causing
direct mortality include, but are not limited to, development projects
(such as bridge replacement, stream channelization, and impoundment
construction), undeveloped low-water crossings with vehicular traffic
that intersect mussel beds, bank collapse, accidental release of
hazardous materials, predation, vandalism, and collection (whether for
scientific purposes or recreation) (USFWS 2022, pp. 57-58). The
frequency, intensity, and magnitude of these impacts likely vary in
time and by location and are difficult to quantify with any certainty
other than to acknowledge that they exist and negatively affect mussel
survival to some degree.
Predation on freshwater mussels is a natural ecological
interaction. Raccoons, feral hogs, muskrats, snapping turtles, and fish
are known to prey upon mussels (East et al. 2013, p. 692; Walters and
Ford 2013, p. 480; Kaller et al. 2007, p. 174; Neves and Odom 1989, p.
939). Under natural conditions, the level of predation occurring is not
likely to pose

[[Page 16786]]

a significant risk to any given population; however, during periods of
low flow, terrestrial predators have increased access to portions of
the river that are otherwise too deep under normal flow conditions,
resulting in unnaturally high levels of predation that can decimate
mussel populations. Predation during drought has been observed for the
Texas heelsplitter on the Sabine River (Walters and Ford 2013, p. 479).
Drought, low-flow conditions, and reductions in minimum summer base
flows are predicted to occur more often and for longer periods due to
the effects of future climate change; therefore, the tributaries and
upper portions of focal areas for the Texas heelsplitter and Louisiana
pigtoe are expected to experience increased predation pressure into the
future (Lafontaine et al. 2019, entire).
Additionally, certain mussel beds within some populations, due to
ease of access, are vulnerable to over-collection and vandalism. These
areas have well known and well documented mussel beds that are often
sampled multiple times annually by various researchers for various
scientific projects. Populations subjected to repeated sampling or
monitoring may experience increased stress or higher rates of
mortality. Mortality may also occur in areas where local fishing
enthusiasts have been observed using freshwater mussels as bait. The
risk of direct mortality from recreation or over-collection for
scientific purposes are compounded by the additional stressors
discussed in this section, which can influence mussel survival in a
cumulative manner. Because collection of Louisiana pigote is localized
and could affect populations, we carried this risk factor forward as a
population-level threat. Service biologists recently hosted a meeting
with State biologists, consultants, and academia who are involved in
mussel research to discuss ongoing monitoring and scientific
collections and to reduce the likelihood of over-harvesting mussels
from any given population (USFWS 2018, p. 1), and we anticipate this
collaboration among researchers will continue into the future with
ongoing coordination and annual meetings.
Invasive Species
Invasive species, such as Asian clam (Corbicula fluminea), zebra
mussel (Dreissena polymorpha), feral hog (Sus scrofa), floating water
hyacinth (Eichhornia crassipes), giant salvinia (Salvinia molesta), and
hydrilla (Hydrilla verticillata), occur throughout the ranges of the
Texas heelsplitter and Louisiana pigtoe and can negatively impact
mussel survival. These impacts include predation (feral hog), habitat
destruction or modification (feral hog, floating water hyacinth, giant
salvinia, hydrilla), changes to water quality (feral hog, zebra
mussel), increased resource competition (Asian clam, zebra mussel), or
physical impairment (zebra mussel, hydrilla) (Kaller and Kelso 2006,
pp. 172-174; Howells 2010a, p. 13; Howells 2010b, pp. 14-15).
Although zebra mussel infestations occur in several Texas
reservoirs, including Lewisville Lake and Lake Livingston, populations
have not yet become established in nearby river habitats occupied by
the Texas heelsplitter and Louisiana pigtoe (Ford et al. 2016, p. 47;
Texas Parks and Wildlife Department (TPWD) 2019, entire; USGS 2019e,
entire).
Feral hogs occur throughout the range of both mussel species and
are known to engage in a variety of activities that cause bank and
streambed damage, contribute to erosion and increased sedimentation,
and their presence appears to cause native mussel diversity and
abundance to decrease through organic enrichment of the water and
unfavorable changes to microbial community composition (Kaller et al.
2007, p. 174; Howells 2010b, p. 10).
Invasive macrophyte infestations of floating water hyacinth,
hydrilla, and giant salvinia negatively impact native mussels and their
host fish throughout the southern half of the ranges of the Texas
heelsplitter and Louisiana pigtoe by creating hypoxic conditions
through respiration and during decay (Karatayev and Burlakova 2007, p.
298; USGS 2019b, entire; USGS 2019c, entire; USGS 2019d, entire). Dense
mats of hydrilla can also impede native mussel movement during periods
of fluctuating surface water levels, leaving them stranded as water
levels recede.
Climate Change
Climate change in the form of the change in timing and amount of
precipitation and air temperature increase is occurring, and continued
greenhouse gas emissions at or above current rates will cause further
warming (Intergovernmental Panel on Climate Change (IPCC) 2021, pp. 1-
13-1-15). Warming in Texas is expected to be greatest in the summer
(Maloney et al. 2014, p. 2236, figure 3), with the number of extremely
hot days (high temperatures exceeding 35 [deg]C (95 [deg]F)) projected
to double by around 2050 (Kinniburgh et al. 2015, p. 83). Changes in
stream temperatures are expected to reflect changes in air temperature,
at a rate of an approximately 0.6-0.8 [deg]C (33 [deg]F) increase in
stream water temperature for every 1 [deg]C (33 [deg]F) increase in air
temperature (Morrill et al. 2005, pp. 1-2, 15), with implications for
temperature-dependent water quality parameters such as dissolved oxygen
and ammonia toxicity. Given that freshwater mussels in Texas exist at
or near the ecophysiological edge of climate and habitat gradients of
freshwater mussel biogeography in North America, they may be
particularly vulnerable to future climate changes in combination with
current and future stressors (Burlakova et al. 2011a, pp. 156, 161,
163; Burlakova et al. 2011b, pp. 395, 403).
While projected changes to rainfall in Texas may seem relatively
small (U.S. Global Change Research Program (USGCRP) 2017, p. 217),
higher temperatures caused by anthropogenic activity will lead to
increased soil water deficits because of higher rates of
evapotranspiration. In turn, higher evapotranspiration rates will
likely result in increasing drought severity in future climate
scenarios, and the warming atmosphere is projected to continue across
the United States (USGCRP 2017, p. 231). Even if precipitation and
groundwater recharge remain at current levels, increased groundwater
pumping and resulting aquifer shortages due to increased temperatures
are nearly certain (Loaiciga et al. 2000, p. 193; Mace and Wade 2008,
pp. 662, 664-665; Taylor et al. 2013, p. 3).
Effects of climate change, such as changes to seasonal rainfall
patterns, air temperature increases, and increases in drought frequency
and intensity, have been shown to be occurring throughout the ranges of
the Texas heelsplitter and Louisiana pigtoe (Andreadis and Lettenmaier
2006, p. 3; USGCRP 2017, p. 188); these effects are expected to
exacerbate several of the stressors discussed above, such as water
temperature and flow loss (Wuebbles et al. 2013, p. 16). A recent
review of future climate projections for Texas concludes that both
droughts and floods could become more common in east Texas, with
droughts like 2011 (the driest on record) becoming commonplace by the
year 2100 (Mullens and McPherson 2017, pp. 3, 6). This trend of more
frequent droughts is driven by increases in hot temperatures (e.g.,
daily maximum) and the number of days projected to be at or above 37.8
[deg]C (100 [deg]F), which is set to ``increase in both consecutive
events and the total number of days'' (Mullens and McPherson 2017, pp.
14-15). Similarly, floods and extreme runoff are projected to become
more common and severe in the 21st century as the frequency,

[[Page 16787]]

magnitude, and intensity of heavy precipitation events increase
(Mullens and McPherson 2017, p. 20; USGCRP 2017, p. 224).
In the analysis of the future condition for the Texas heelsplitter
and Louisiana pigtoe, climate change is considered further under
various plausible future scenarios, serving to exacerbate already
deteriorating conditions through an increase of fine sediments, changes
to water quality, loss of flowing water, and predation, among others.
Summary of Risk Factors for Texas Heelsplitter and Louisiana Pigtoe
Our analysis of the past, current, and future influences on the
needs of the Texas heelsplitter and Louisiana pigtoe for long-term
viability revealed that there are four that pose the greatest impact on
current condition and future viability: degradation of water quality,
altered hydrology, substrate changes, and habitat fragmentation, all of
which are exacerbated by climate change.

Conservation Efforts and Regulatory Mechanisms

The level of interest among stakeholders, regulatory agencies, and
partners to better understand the status, threats, and conservation of
freshwater mussels in Texas has increased significantly since 2017,
when the Service initiated reviews of several Texas mussel species for
possible listing under the Act. This led to improved communication
among interested parties and multiple partnerships seeking to conduct
research and improve our understanding of the health and distribution
of mussel populations across Texas, as well as increased efforts to
protect and conserve known populations. Although there are currently no
formal conservation agreements in place designed to specifically
provide benefits to the Texas heelsplitter or Louisiana pigtoe, we are
in discussions with multiple stakeholders who are interested in
strengthening partnerships to conserve rare species, including several
river authorities that are in the process of developing candidate
conservation agreements with assurances (CCAAs). The CCAAs, if
finalized, would implement voluntary conservation actions in river
basins that would result in a net conservation benefit for the species.
Additionally, several stakeholders have voluntarily funded research to
ensure that we have the best available information upon which to base a
listing decision, and we commend them for their efforts to improve the
science of freshwater mussels in Texas. Interested stakeholders and
potential future conservation partners include the Trinity River
Authority, Lower Neches Valley Authority, North Texas Municipal Water
District, Sabine River Authority, the Cities of Dallas and Fort Worth,
Tarrant Regional Water District, Texas Department of Transportation,
Texas Parks and Wildlife Department, U.S. Army Corps of Engineers,
Texas Comptroller of Public Accounts, Texas A&M University, Texas State
University, and others.
With regard to silvicultural operations that occur on forested
areas across the range of the species, we recognize that private timber
companies routinely implement State-approved best management practices
(BMPs; as reviewed by Cristan et al. 2018, entire). Adherence to these
BMPs, such as citing river crossings away from sensitive areas and
leaving intact habitat as buffers for areas adjacent to streams,
broadly protects water quality by reducing timber harvest-related
impacts, particularly erosion and sedimentation (as reviewed by Cristan
et al. 2018; Warrington et al. 2017, entire; and Schilling et al. 2021,
entire). However, it is important to recognize that while BMPs reduce
timber harvest impacts, they do not eliminate impacts; therefore,
sensitive species and their habitats may still be impacted even when
BMP guidelines are followed.
Some voluntary habitat restoration projects have been completed on
private lands within the river basins currently known to be occupied by
one or both species. These restoration projects include upland and
riparian habitat enhancements coordinated by our State, Federal, and
nongovernmental partners, as well as our Partners for Fish and Wildlife
Program. There are also regulatory mechanisms in place to protect water
quality and quantity, such as protections afforded by the Clean Water
Act (33 U.S.C. 1251 et seq.), that are implemented by the States with
oversight by the EPA. While these regulations are in place and provide
some level of protection, population declines continue to be documented
in some species of freshwater mussels, indicating that existing
regulations may not be sufficient to prevent extinction.

Species Condition

Here we discuss the current and future condition of each known
population, taking into account the risks to those populations that are
currently occurring, as well as management actions that are currently
occurring to address those risks. We consider climate change to be
currently occurring, resulting in changes to the timing and amount of
rainfall affecting streamflow, which can alter stream characteristics
such as an increase in stream temperatures, erosion, and the
accumulation of fine sediments. The current condition of each species
and population is based upon the cumulative effects of these factors.
In the SSA report, for each species and population, we developed and
assigned condition categories for three population factors (occupied
stream length, abundance, reproduction/recruitment; see Species Needs,
above) and three habitat factors (habitat structure/substrate,
hydrological regime, and water quality; see Risk Factors for Texas
Heelsplitter and Louisiana Pigtoe, above) that are important for the
viability of each species. The summation of all six condition scores
assigned to each factor were then used to determine the overall
condition of each population: high (healthy), moderate (moderately
healthy), low (unhealthy), or functionally extirpated/extirpated. All
six factors were weighted equally in importance except abundance, which
was viewed as the most relevant and direct measure of current
biological condition; therefore, overall condition was capped by the
abundance score such that no population's overall condition could
exceed the abundance score. These overall conditions translate to our
presumed probability of persistence of each population, with healthy
populations having the highest probability of persistence over 20 years
(greater than 90 percent), moderately healthy populations having a
probability of persistence that falls between 60 and 90 percent,
unhealthy populations having the lowest probability of persistence
(between 10 and 60 percent). Functionally extirpated populations (less
than 10 percent) are not expected to persist over 20 years or are
already extirpated.
Texas Heelsplitter
There are five remaining Texas heelsplitter populations, occurring
in three adjacent river basins (Neches, Sabine, and Trinity River
basins) in east Texas and on the Sabine River to the western border of
Louisiana. Historically, populations likely occurred throughout the
entirety of each basin where connectivity was not an issue and
conditions were suitable. Based on our analysis, three populations are
considered to have a low current condition, and two populations are
considered functionally extirpated/extirpated (see Table 1, below).
Neches River Basin: There are two Texas heelsplitter populations in
the

[[Page 16788]]

Neches River Basin, one in the Neches River/B.A. Steinhagen Reservoir
and the other in the Lower Neches River; these populations are
fragmented and isolated from each other by the dam that forms B.A.
Steinhagen Reservoir. The Neches River/B.A. Steinhagen Reservoir
population occurs in habitat on a fairly long reach (240.9 river mi
(387.6 km)) of the Neches River that extends from just below Lake
Palestine to B.A. Steinhagen Reservoir and includes the portion of
mainstem Angelina River between B.A. Steinhagen and Sam Rayburn
reservoirs. This population is characterized by low abundance and a
lack of evidence of reproductive success, resulting in low recruitment
of new individuals. Further, water quality in tributaries and segments
of the occupied habitat is affected by a variety of point and non-point
source pollution, and infrequent but substantial drawdowns of the B.A.
Steinhagen Reservoir have resulted in direct mortality of Texas
heelsplitters. The Lower Neches River population extends 74.2 river mi
(119.4 km) downstream from Lake B.A. Steinhagen Reservoir's Town Bluff
Dam to approximately 4.5 river mi (7.2 km) downstream of the Village
Creek confluence. This population is also characterized by low
abundance and lack of evidence of reproductive success, with subsequent
low recruitment of new individuals. Further, hydrology and water
quality in this reach are affected by water releases from the B.A.
Steinhagen Reservoir. The Neches River/B.A. Steinhagen Reservoir
population and the Lower Neches River population have a low overall
current condition, resulting in low resiliency for both populations.
Sabine River Basin: This Texas heelsplitter population occurs in a
fairly long reach (245.8 river mi (395.5 km)) of the Sabine River
Basin, that includes the Toledo Bend Reservoir, Sabine River upstream
to Lake Tawakoni's Iron Bridge Dam, a portion of Lake Fork Creek
upstream from its confluence with the Sabine River, and a portion of
Patroon Bayou upstream from its confluence with Toledo Bend Reservoir.
While the overall water quality, habitat structure/substrate, and
occupied habitat reach length are in high condition, construction of
Lake Tawakoni and Toledo Bend Reservoir have altered the natural
hydrologic conditions through dam releases causing substrate scouring
and elimination of habitat downstream. Due to lack of evidence of
reproduction and recruitment, as well as extremely low abundance (CPUE
= 0.14) based on 99 surveys since 2000, this population of Texas
heelsplitter is considered functionally extirpated/extirpated.
Trinity River Basin: There are two populations of the Texas
heelsplitter in the Trinity River Basin, one within Grapevine Lake and
another within the Trinity River/Lake Livingston, that are
hydrologically isolated from one another by the dam that forms
Grapevine Lake. The habitat structure/substrate rating for the
Grapevine Lake population is in high condition, with stormwater runoff
and the discharge of municipal wastewater and associated pollutants
limiting water quality to moderate condition. Reservoir-related changes
to natural flow regimes likewise limited the hydrology rating to
moderate condition. However, with only two individuals found during
population surveys, abundance is extremely low, this combined with the
lack of juveniles and gravid females, the Grapevine Lake population is
considered to be functionally extirpated. The Trinity River population
is characterized by high current condition for the relatively large
habitat reach length currently occupied, while habitat structure/
substrate is affected by unnaturally elevated base flows and is in
moderate current condition. Large daily volumes of municipal wastewater
discharge and associated pollutants are impacting water quality and
hydrology, which are in low current condition. This population is also
characterized by low abundance and lack of evidence of reproductive
success, with subsequent low recruitment of new individuals. The
Trinity River/Lake Livingston population has a low overall current
condition and low resiliency.

Table 1--Estimated Current Overall Condition of Texas Heelsplitter
Populations
[USFWS 2022, pp. 40-44]
------------------------------------------------------------------------
Overall current
River basin Population condition
------------------------------------------------------------------------
Sabine.......................... Sabine River/ FE/E.\1\ \2\
Toledo Bend.
Neches.......................... Neches River/B.A. Low.\2\
Steinhagen. Low.\2\
Lower Neches River
Trinity......................... Grapevine Lake.... FE/E.\1\ \2\
Trinity River/Lake Low.\2\
Livingston.
------------------------------------------------------------------------
\1\ FE/E = Functionally extirpated/extirpated.
\2\ Indicates representation areas where overall condition was capped by
abundance.

Redundancy describes the ability of a species to withstand and
recover from catastrophic events. High redundancy is achieved through
multiple populations that serve to spread risk, thereby reducing the
impact that any one event might have in terms of overall loss to the
species. Redundancy is characterized by having multiple healthy,
resilient populations distributed across the range of the species. It
can be measured by population number, resiliency, spatial extent, and
degree of connectivity. Our analysis explored the influence of the
number, distribution, and connectivity of populations on the species'
ability to withstand catastrophic events.
Within the identified representation areas (Neches, Sabine, and
Trinity River basins), only the Neches and Trinity River basins
currently have at least one known population (the Sabine River/Toledo
Bend population in the Sabine River Basin and Grapevine Lake in the
Trinity River Basin are considered functionally extirpated). The Neches
River Basin currently has two populations (Neches River and Lower
Neches River populations); however, these populations are
hydrologically isolated, and therefore provide only minimal redundancy.
Representation describes the ability of a species to adapt to
changing environmental conditions over time. It is characterized by the
breadth of genetic and environmental diversity within and among
populations. Our analysis explores the relationship between the species
life history and the influence of genetic and ecological diversity and
the species ability to adapt to changing environmental conditions over
time.
We consider the Texas heelsplitter to have representation in the
form of genetic, geographic, and ecological diversity in the three
currently occupied river basins. Because there are no freshwater
connections between the three basins, we treated each river basin as
separate areas of representation.
Louisiana Pigtoe
Overall, there are 13 remaining populations of Louisiana pigtoe in
multiple river drainages throughout portions of east Texas (Big
Cypress-Sulphur, Neches-Angelina, Sabine, and San Jacinto river
basins), Louisiana (Calcasieu, Sabine, and Pearl river systems), west
Mississippi (Pearl River), southeast Oklahoma (Little River), and
southwest Arkansas (Cossatot, Saline, Rolling Fork, and Little rivers).
Because reported populations from the Ouachita River system in Arkansas
were determined to be phylogenetically distinct (a separate species)
from Louisiana pigtoe, they were not considered in the SSA. In 2019, an
additional population was discovered within the Lower Neches Valley
River

[[Page 16789]]

Authority canal system in Beaumont, Texas (Bio-West 2021, p. 1).
Because this population occupies artificially maintained habitat that
may not persist without active operational management by the Lower
Neches Valley River Authority, it was not considered for analysis in
the SSA.
Historically, the Louisiana pigtoe likely occurred throughout each
basin wherever conditions were suitable and connectivity was not an
issue, with populations connected by fish migration; however, due
primarily to impoundments, the populations are currently isolated from
one another, and repopulation of functionally extirpated/extirpated
locations is unlikely to occur without human assistance. Two
populations are currently considered to be in high condition, four
populations are in moderate condition, five populations are in low
condition, and two populations are considered functionally extirpated/
extirpated (see Table 2, below).
Big Cypress-Sulphur Basin: Although Louisiana pigtoes have not been
genetically confirmed and observations may be misidentified as Wabash
pigtoe (Fusconaia flava), past surveys indicated Louisiana pigtoe
presence (Randklev 2018, entire) in this basin. Therefore, we included
this population in this assessment. The Louisiana pigtoe population in
Big Cypress Bayou includes approximately 32.0 river mi (51.5 km) of Big
Cypress Bayou and Little Cypress Bayou upstream of their confluence.
This population is characterized by moderate condition for occupied
habitat stream length, abundance, habitat structure/substrate,
hydrology, and water quality; the habitat factors are influenced by a
variety of anthropogenic activities that vary by watershed, including
stormwater runoff and discharges from multiple wastewater treatments
plants. However, there has been a lack of reported juveniles or gravid
females, so this population is in low condition for reproduction and
recruitment.
Calcasieu River Basin: Louisiana pigtoe has a single population in
the Calcasieu-Mermentau Basin that occurs along an approximately 134-
river-mi (216-km) section of hydrologically connected portions of the
mainstem Calcasieu River, and the Whisky Chitto and Tenmile creeks
located in Allen, Rapides, and Vernon parishes, Louisiana. This
population is characterized as being in high condition for occupied
habitat reach length and habitat structure/substrate, while hydrology
and water quality are in moderate condition due to fluctuations in flow
rates and municipal wastewater effluent discharges, among other sources
of pollution. However, abundance, reproduction, and recruitment are in
low condition, which corresponds to low resiliency.
Neches River Basin: The Neches River Basin in Texas has three
populations of Louisiana pigtoe, one each in the Angelina (above Sam
Rayburn Reservoir), Neches (above B.A. Steinhagen Reservoir), and Lower
Neches rivers (below B.A. Steinhagen Reservoir). These three
populations combined extend over 400 river mi (644 km) in a basin that
many experts believe contains some of the best remaining habitat and
most diverse populations of freshwater mussels in Texas. The Neches
River and Lower Neches River populations are hydrologically isolated
from each other by the Town Bluff Dam that forms B.A. Steinhagen
Reservoir, and the Angelina River population is isolated from the
Neches River population by Sam Rayburn Dam and Reservoir. The Neches
River population's current condition is characterized as high condition
for the occupied habitat reach length (203 river mi (326.7 km)),
abundance, habitat structure/substrate, and hydrology, and moderate
condition for reproduction/recruitment and water quality. The Lower
Neches River population is characterized by high current condition for
occupied habitat reach length (160.4 river mi (258.1 km)) and habitat
structure/substrate, and a moderate current condition for hydrology,
water quality, and reproduction/recruitment due to the impacts of
fluctuating stream flows, pollution loading from point and non-point
sources, and few reports of gravid females or juvenile mussels. In
addition, few individuals have been observed, resulting in a low
current condition for population abundance. The Angelina River
population is in high condition for occupied habitat reach length (53.2
river mi (85.6 km)), habitat structure/substrate, and hydrology;
however, water quality impacts such as elevated bacteria, fecal
coliform, and ammonia resulted in a moderate current condition for
water quality. Like the Lower Neches River population, due to the few
numbers of individuals observed and a lack of juvenile or gravid female
presence, abundance and reproduction/recruitment are in low condition
for the Angelina River population. The Neches River population has a
high overall current condition, and the Lower Neches River and Angelina
River populations have a low overall current condition (primarily due
to being capped by low abundance).
Pearl River Basin: The Pearl River Basin in Louisiana and
Mississippi has a single population of the Louisiana pigtoe within the
main stem that extends approximately 280 river mi (450 km) below Ross
Barnett Dam near Jackson to Picayune, Mississippi (upstream of
Interstate 59). A new impoundment proposed by the Rankin-Hinds Pearl
River Flood and Drainage Control District, located 9 mi (14.5 km)
downstream of Ross Barnett Reservoir, intended for flood control, is
still under review. For the Pearl River population, we determined that
occupied habitat reach length is in high condition, and habitat
structure/substrate, hydrology, and water quality are in moderate
condition due to erratic flows and pollutants from urban areas and
industry wastewater discharge. Because few individuals have been
reported and there is a lack of juvenile or gravid female presence,
abundance and reproduction/recruitment are in low condition. The Pearl
River population has an estimated overall low current condition and low
resiliency.
Red River Basin: The Red River Basin contains four distinct
populations of the Louisiana pigtoe that extend along 88.3 river mi
(142.1 km) within the Little River drainage in Arkansas and Oklahoma,
including populations in the Cossatot River, Little River/Rolling Fork,
Lower Little River, and Saline River. Millwood Lake, located in
southwest Arkansas, hydrologically separates the Cossatot River, Saline
River, and Little River/Rolling Fork populations from the Lower Little
River population. The current condition evaluation for the Cossatot
River population determined that abundance, reproduction/recruitment,
and habitat structure/substrate are in high condition, and occupied
habitat reach length, hydrology, and water quality are in moderate
condition due to fluctuations of stream flows from Gillham Lake, as
well as pollutant discharges from agriculture and other sources. No
habitat or population factors are determined to be in low condition.
The Little River/Rolling Fork population's current condition evaluation
determined occupied habitat reach length and reproduction/recruitment
are in high condition. All other population and habitat factors are in
moderate condition due to lower abundance, fluctuations in instream
flow (which affect benthic habitat, substrate, and stream hydrology),
and increased levels of zinc, lead, and salinity (among other
pollutants), leading to moderate water quality. The Saline River
population's current condition evaluation found

[[Page 16790]]

occupied habitat reach length, abundance, hydrology, and water quality
in moderate condition caused by prolonged high water levels and low
levels of dissolved oxygen. Due to the lack of evidence of reproductive
success and subsequent recruitment of new individuals, and altered flow
conditions downstream of Dierks Lake, reproduction/recruitment and
habitat structure/substrate are in low condition. The Lower Little
River population's current condition evaluation determined that
reproduction/recruitment and all habitat factors are in low condition
primarily because of its short reach length (8.5 river mi (14.16 km)),
altered flow regime, and paucity of survey data. This population is
located downstream of Millwood Lake and Dam, a flood control reservoir,
and is subject to altered hydrology that further impacts habitat
structure and substrates during flood events. Agricultural runoff
associated with the lower section of this reach impacts water quality.
Due to the extremely low numbers of individuals observed (abundance),
this population is considered functionally extirpated/extirpated. In
summary, the Cossatot River population has a high overall current
condition and high resiliency, the Little River/Rolling Fork and Saline
River populations have a moderate overall current condition and
moderate resiliency, and the Lower Little River population is
considered functionally extirpated/extirpated.
Sabine River: There are two known populations of the Louisiana
pigtoe within the Sabine River, one located along 87 river mi (140 km)
between Hawkins and Tatum, Texas, and a second population within a 9-
river-mi (15-km) segment of Bayou Anacoco in Louisiana. These
populations are hydrologically separated by Toledo Bend Dam and
Reservoir. The Sabine River population's current condition evaluation
determined that occupied habitat reach length and habitat structure/
substrate are in high condition. Dam releases from Lake Tawakoni and
Toledo Bend Reservoir, wastewater releases, and water quality
degradation (including elevated levels of bacteria) are primary causes
for moderate current conditions for hydrology and water quality. Due to
an extremely low number of individuals detected during surveys, and the
lack of juveniles or gravid females observed, abundance and
reproduction/recruitment are in low condition, and this population is
considered functionally extirpated/extirpated. The Bayou Anacoco
population's current condition evaluation found habitat structure/
substrate is high condition, and abundance, hydrology, and water
quality are in moderate condition. However, the occupied habitat reach
length and reproduction/recruitment are in low condition due to the
distribution of observed individuals and lack of reported juveniles or
gravid females. The Bayou Anacoco population is in moderate current
overall condition and has moderate resiliency.
East Fork San Jacinto River: There is one known population of
Louisiana pigtoe that occurs within a short (1.3-river-mi (2-km))
segment of the East Fork San Jacinto River near Plum Grove, Texas. The
population's current condition evaluation determined that hydrology and
water quality are in moderate condition, whereas sand and gravel mining
are affecting the habitat structure/substrate, which is in low
condition. Due to a low number of individuals detected and lack of
juveniles or gravid females observed, population abundance and
reproduction/recruitment are in low condition. The East Fork San
Jacinto River population is determined to be in overall low condition
and has low resiliency.

Table 2--Estimated Current Overall Condition of Known Louisiana Pigtoe
Populations
[USFWS 2022, pp. 34-40]
------------------------------------------------------------------------
Overall current
River basin Population condition
------------------------------------------------------------------------
Red............................. Little River/ Moderate.
Rolling Fork. High.
Cossatot River.... Moderate.
Saline River...... FE/E. \1\ \2\
Lower Little River
Big Cypress-Sulphur............. Big Cypress Bayou. Moderate.
Calcasieu-Mermentau............. Calcasieu River... Low. \2\
Pearl........................... Pearl River....... Low. \2\
Sabine.......................... Sabine River...... FE/E. \1\ \2\
Bayou Anacoco..... Moderate.
Neches.......................... Angelina River.... Low. \2\
Neches River...... High.
Lower Neches River Low.\2\
San Jacinto..................... East Fork San Low.
Jacinto River.
------------------------------------------------------------------------
\1\ FE/E = Functionally extirpated/extirpated.
\2\ Indicates representation areas where overall condition was capped by
abundance.

Within identified representation areas, the Big Cypress-Sulphur,
Calcasieu-Mermentau, Pearl, and San Jacinto River basins each have only
one known current population, and therefore lack redundancy should
catastrophic events occur that cause extirpation of one or a few
populations. The Sabine River Basin has two separate populations
(Sabine River and Bayou Anacoco populations) but lacks redundancy due
to the Sabine River population being functionally extirpated. The
Neches and Red River basins each currently have three known populations
(the Lower Little River population in the Red River Basin is considered
functionally extirpated), however each population is hydrologically
isolated within their respective river basins and are, therefore,
considered to provide only limited redundancy.
We consider Louisiana pigtoe to have representation in the form of
genetic, ecological, and geographical diversity between each of seven
river basins: Big Cypress-Sulphur, Calcasieu-Mermentau, Neches, Pearl,
Red, Sabine, and San Jacinto. Because there are no un-impounded,
freshwater connections that allow movement between the seven basins,
each river was considered a separate area of representation.

Future Conditions

As part of the SSA, we developed multiple future condition
scenarios to capture the range of uncertainties

[[Page 16791]]

regarding future threats and the projected responses by the Texas
heelsplitter and Louisiana pigtoe. Our scenarios included a status quo
scenario, which incorporated the current risk factors continuing on the
same trajectory that they are on now. We also evaluated two future
scenarios that incorporated varying levels of increasing risk factors
with elevated negative effects on Texas heelsplitter and Louisiana
pigtoe populations. However, because we determined that the current
condition of the Texas heelsplitter is consistent with an endangered
species (see Texas Heelsplitter: Determination of Status, below), we
are not presenting the results of the future scenarios in this proposed
rule. Please refer to the SSA report (Service 2022) for the full
analysis of future scenarios.
We forecasted the Louisiana pigtoe's responses to two plausible
future scenarios of environmental conditions projected across the next
10, 25, and 50 years. Ten years represents one to two generations of
mussels, assuming an average reproductive life span of five to 10
years. Twenty-five years similarly represents at least two to four
mussel generations and 50 years represents at least five or more
generations of mussels. The scenarios project the threats into the
future and consider the impacts those threats could have on the
viability of the Louisiana pigtoe. We apply the concepts of resiliency,
redundancy, and representation to the future scenarios to describe
possible future conditions of the Louisiana pigtoe. The scenarios
described in the SSA report represent only two possible future
conditions. Uncertainty is inherent in any projection of future
condition, so we must consider plausible scenarios to make our
determinations. When assessing the future, viability is not a specific
state, but rather a continuous measure of the likelihood that the
species will sustain populations over time.
We included climate change in our future scenarios as a factor that
would add to the negative impacts of the primary threats on the
species' habitat. Climate change is expected to alter the natural flow
regime through increased drought and flooding worsening desiccation,
scour, and sedimentation. Global climate models project changes in
global temperature and other associated climatic changes based on
potential future scenarios of greenhouse gas concentrations in the
atmosphere (i.e., Representative Concentration Pathways, or RCPs). RCP
4.5 assumes major near-future cuts to carbon dioxide emissions, and RCP
8.5 assumes that current emissions practices continue with no
significant change (Terando et al. 2020, p. 10). Thus, these RCPs
represent conditions in the upper and lower ends of the range of what
can reasonably be expected for the future effects of climate change
(Terando et al. 2020, p. 17).
Scenario 1 assesses the species' responses to moderate increases in
stressors influencing Louisiana pigtoe populations. Scenario 1 is based
on RCP 4.5 emission trajectory and associated model projections, and
represents medium-term increases in emissions followed by a decline
through the rest of the century. Scenario 2 assesses the species'
responses to severe increases in stressors and is based on RCP 8.5
projections. Scenario 2 also includes anthropogenic actions, such as
the construction of new reservoirs, wastewater treatment plants, and
other currently proposed projects, and manifests as a future where the
hydrological conditions of many of the rivers and streams currently
occupied by Louisiana pigtoe are altered such that base flows are
diminished, floods are more severe if not more frequent, and mussels
and their habitats are adversely affected through degradation of water
quality and quantity. These altered hydrological conditions are
primarily caused by a combination of increasing anthropogenic stressors
and climate change. Due to a lack of resolution of the available data,
we were unable to distinguish any meaningful difference between a
moderate increase in stressors and a moderate decrease in stressors. As
a result, we limited the future forecasts to these two scenarios, which
we projected over a 50-year period. We restricted our evaluation to 50
years primarily due to limitations projecting non-modeled, extrapolated
future conditions for water quality, road density, and habitat
fragmentation. Fifty years encompasses about 5 generations of the
Louisiana pigtoe; additionally, projected human population growth and
the limitations of existing resources are expected to increase and
interact with climate effects to exacerbate the effects of drought
which is likely to impact water quality and quantity (i.e., the ability
to provide the minimum flow needed by the Louisiana pigtoe). A full
description of the future scenarios and our methods is available in the
SSA report (USFWS 2022, pp. 63-73).
Under Scenario 1, populations of the Louisiana pigtoe decline in
resiliency, redundancy, and representation over time as conditions
moderately decline from current conditions. One population will remain
in moderate condition, seven in low condition, and five functionally
extirpated in 50 years. This species will lose two areas of
representation, diminishing the overall adaptive capacity to future
environmental change in the next 50 years (see Table 3).

Table 3--Future Condition of Louisiana Pigtoe Populations With a Moderate Increase in Stressors
[Scenario 1]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Scenario 1 future condition
Species River basin Population --------------------------------------------------------------------
10 years 25 years 50 years
--------------------------------------------------------------------------------------------------------------------------------------------------------
Louisiana Pigtoe................... Red Little River/ Moderate.............. Low.................. Low..................
Rolling Fork. High.................. High................. Moderate.............
Cossatot River........ Moderate.............. Moderate............. Low..................
Saline River.......... FE/E \1\.............. FE/E \1\............. FE/E.\1\.............
Lower Little River....
Big Cypress-Sulphur... Big Cypress Bayou..... Moderate............. Moderate............. Low.
Calcasieu............. Calcasieu River....... Low.................. Low.................. FE/E.\1\
Pearl................. Pearl River........... Low.................. Low.................. Low.
Sabine................ Sabine River.......... FE/E \1\............. FE/E \1\............. FE/E.\1\
Bayou Anacoco......... Low.................. Moderate............. Low.
Neches................ Angelina River........ Low.................. Low.................. FE/E.\1\
Neches River.......... High................. Low.................. Low.
Lower Neches River.... Low.................. Low.................. Low.

[[Page 16792]]

San Jacinto........... East Fork San Jacinto Low.................. Low.................. FE/E. \1\
River.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ FE/E = Functionally extirpated/extirpated.

Under Scenario 2, populations of the Louisiana pigtoe further
decline in resiliency, redundancy, and representation over time as the
effects of climate change impact populations through extremely low
stream flows, severe increases in sedimentation, reductions in water
quality, and an increase in potential for desiccation of habitat. Eight
populations of Louisiana pigtoe are expected to become either
functionally extirpated or extirpated within 50 years, with the
remaining five populations in low condition. The Louisiana pigtoe is
projected to lose four of the seven current representation areas in 50
years, with eight populations remaining or becoming extirpated;
therefore, the adaptive capacity of this species is projected to be
severely reduced in the future (see Table 4).

Table 4--Future Condition of Louisiana Pigtoe Populations With a Severe Increase in Stressors
[Scenario 2]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Scenario 2 future condition
Species River basin Population --------------------------------------------------------------------
10 years 25 years 50 years
--------------------------------------------------------------------------------------------------------------------------------------------------------
Louisiana Pigtoe................... Red................... Little River/Rolling Moderate............. Low.................. Low.
Fork. High................. High................. Low.
Cossatot River........ Moderate............. Low.................. Low.
Saline River.......... FE/E \1\............. FE/E \1\............. FE/E.\1\
Lower Little River....
Big Cypress-Sulphur... Big Cypress Bayou..... Moderate............. Moderate............. Low.
Calcasieu-Mermentau... Calcasieu River....... Low.................. Low.................. FE/E.\1\
Pearl................. Pearl River........... Low.................. Low.................. FE/E.\1\
Sabine................ Sabine River.......... FE/E \1\............. FE/E \1\............. FE/E.\1\
Bayou Anacoco......... Low.................. Moderate............. FE/E.\1\
Neches................ Angelina River........ Low.................. Low.................. FE/E.\1\
Neches River.......... High................. Low.................. Low
Lower Neches River.... Low.................. Low.................. FE/E.\1\
San Jacinto........... East Fork San Jacinto Low.................. FE/E \1\............. FE/E.\1\
River.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ FE/E = Functionally extirpated/extirpated.

We note that, by using the SSA framework to guide our analysis of
the scientific information documented in the SSA report, we have not
only analyzed individual effects on the species, but we have also
analyzed their potential cumulative effects. We incorporate the
cumulative effects into our SSA analysis when we characterize the
current and future condition of the species. To assess the current and
future condition of the species, we undertake an iterative analysis
that encompasses and incorporates the threats individually and then
accumulates and evaluates the effects of all the factors that may be
influencing the species, including threats and conservation efforts.
Water quality degradation, altered hydrology, changes to habitat
structure/substrate, habitat fragmentation, invasive species, climate
change, and collecting are all factors that influence or could
influence the viability of these two freshwater mussel species. These
factors also have the potential to act cumulatively to impact Texas
heelsplitter and Louisiana pigtoe viability and their cumulative
impacts were considered in our characterization of the species' current
and future condition in the SSA. Because the SSA framework considers
not just the presence of the factors, but to what degree they
collectively influence risk to the entire species, our assessment
integrates the cumulative effects of the factors and replaces a
standalone cumulative effects analysis.

Determination of Status

Section 4 of the Act (16 U.S.C. 1533) and its implementing
regulations (50 CFR part 424) set forth the procedures for determining
whether a species meets the definition of an endangered species or a
threatened species. The Act defines an ``endangered species'' as a
species in danger of extinction throughout all or a significant portion
of its range, and a ``threatened species'' as a species likely to
become an endangered species within the foreseeable future throughout
all or a significant portion of its range. The Act requires that we
determine whether a species meets the definition of an endangered
species or a threatened species because of any of the following
factors: (A) The present or threatened destruction, modification, or
curtailment of its habitat or range; (B) overutilization for
commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) the inadequacy of existing regulatory
mechanisms; or (E) other natural or manmade factors affecting its
continued existence.

Status Throughout All of Its Range

After evaluating threats to the Texas heelsplitter and Louisiana
pigtoe and

[[Page 16793]]

assessing the cumulative effect of the threats under the Act's section
4(a)(1) factors, we found that both species of freshwater mussels have
declined significantly in overall distribution and abundance. At
present, most of the known populations exist in very low abundances and
show limited evidence of recruitment. Furthermore, existing available
habitats are reduced in quality and quantity, relative to historical
conditions. Our analysis revealed six primary threats that caused these
declines and pose a meaningful risk to the viability of the species.
These threats are primarily related to habitat changes (Factor A):
impairment of water quality, altered hydrology, the accumulation of
fine sediments, and habitat fragmentation, all of which are exacerbated
by the effects of climate change (Factor E). Predation (Factor C) and
collection (Factor B), as well as other natural or human-induced
events/activities that result in direct mortality, are also affecting
those populations already experiencing low stream flow, and reservoirs
and instream barriers to fish movement (Factor E) limit dispersal and
prevent recolonization after stochastic events.
Populations of the Texas heelsplitter and Louisiana pigtoe are
faced with a myriad of stressors from natural and anthropogenic sources
that pose a risk to their survival in both large and small river
segments. Climate change has the noteworthy distinction of being able
to directly or indirectly exacerbate the most relevant stressors to
freshwater mussels wherever they occur. Climate projections suggest
persistent droughts over the continental United States that are longer,
cover more area, and are more intense than what has been experienced in
the 20th century (APA 2019, p. 4; Terando et al. 2018, p. 786; Wehner
et al. 2017, p. 237). Humans are likely to respond to climate change in
predictable ways to meet their needs, such as increased groundwater
pumping and surface water diversions, and increased use of reverse
osmosis to treat sources of water that are of poor quality (thereby
generating increasing volumes of wastewater). These activities will
increase overall demand for freshwater resources at a time when those
very resources are strained and less abundant (reviewed in Banner et
al. 2010, entire). We expect climate change impacts to occur throughout
the range of both the Texas heelsplitter and the Louisiana pigtoe.
The threats to the species, acting alone or in combination with
each other and climate change, could result in the extirpation of
additional mussel populations, further reducing the overall redundancy
and representation of the Texas heelsplitter and Louisiana pigtoe.
Historically, each species, bolstered by large, interconnected
populations (i.e., with meta-population dynamics), would have been more
resilient to stochastic events such as drought, excessive
sedimentation, and scouring floods. As locations became extirpated by
catastrophic events, they could be recolonized over time by dispersal
from nearby surviving populations, facilitated by movements of host
fish. This connectivity across potential habitats made for highly
resilient species overall, as evidenced by the long and successful
evolutionary history of freshwater mussels as a taxonomic group, and in
North America in particular. However, under current conditions,
restoration of that connectivity on a regional scale is not feasible.
Because of these current conditions, the viability of the Texas
heelsplitter and Louisiana pigtoe now primarily depends on maintaining
the remaining isolated populations and potentially restoring new
populations where feasible.

Texas Heelsplitter: Status Throughout All of Its Range

The Texas heelsplitter has declined significantly in overall
distribution and abundance over the past 100 or more years. Most known
populations of the Texas heelsplitter are isolated and currently exist
in very low numbers (low abundance), have limited evidence of
recruitment, and are believed to occupy much less habitat than in the
past (range contraction). Of the five remaining populations of Texas
heelsplitter, three are small in abundance and have low resiliency, and
two are considered functionally extirpated/extirpated. While the three
low resiliency populations (Neches River/B.A. Steinhagen Reservoir,
Lower Neches River, and Trinity River/Lake Livingston) have habitat in
high or moderate current condition, all three have very little evidence
of reproduction and are therefore likely to decline due to a lack of
young individuals joining the population as the population ages. Low
abundance, combined with the lack of evidence of reproduction and
recruitment, results in populations with very little population
resiliency. Overall, these low levels of resiliency, redundancy, and
representation currently result in the Texas heelsplitter having a high
risk of extinction.
Our analysis of the species' current condition, as well as the
conservation efforts discussed above, show that the Texas heelsplitter
is in danger of extinction throughout all of its range due to the
severity and immediacy of threats currently impacting their
populations. The risk of extinction is high because the remaining
fragmented populations have a high risk of extirpation, are isolated,
and have limited potential for recolonization. We find that a
threatened species status is not appropriate for the Texas heelsplitter
because its current range is already contracted, all populations are
fragmented and isolated from one another, the threats are occurring
across the entire range of this species, and the species currently
exhibits low resiliency, redundancy, and representation. Because these
conditions place the species already in danger of extinction throughout
its range, a threatened status is not appropriate.

Texas Heelsplitter: Status Throughout a Significant Portion of Its
Range

Under the Act and our implementing regulations, a species may
warrant listing if it is in danger of extinction or likely to become so
in the foreseeable future throughout all or a significant portion of
its range. We have determined that the Texas heelsplitter is in danger
of extinction throughout all of its range and accordingly did not
undertake an analysis of any significant portion of its range. Because
the Texas heelsplitter warrants listing as endangered throughout all of
its range, our determination does not conflict with the decision in
Center for Biological Diversity v. Everson, 2020 WL 437289 (D.D.C. Jan.
28, 2020), because that decision related to significant portion of the
range analyses for species that warrant listing as threatened, not
endangered, throughout all of their range.

Texas Heelsplitter: Determination of Status

Our review of the best available scientific and commercial
information indicates that the Texas heelsplitter meets the Act's
definition of an endangered species. Therefore, we propose to list the
Texas heelsplitter as an endangered species in accordance with sections
3(6) and 4(a)(1) of the Act.

Louisiana Pigtoe: Status Throughout All of Its Range

Many Louisiana pigtoe populations are relatively abundant, but
populations are isolated from one another; therefore, the species is
unable to recolonize following stochastic events that may reduce or
eliminate populations. Additionally, many populations occur in degraded
habitats. Although some

[[Page 16794]]

conservation efforts are underway, they are not sufficient to prevent
the decline of the species. Thirteen populations of Louisiana pigtoe
remain. Two populations are in high condition, four in moderate
condition, five are in low condition, and two are functionally
extirpated/extirpated. The Red River Basin has four populations, and
only one is in high condition (Cossatot River), two are in moderate
overall condition, and one (Lower Little River) is functionally
extirpated/extirpated. The Neches River is the only other population
with a high overall current condition. Only two populations, Little
River/Rolling Fork and Cossatot River (both within the Red River
Basin), have strong evidence of reproduction and recruitment as
indicated by presence of fish hosts, juveniles, and gravid females; two
(Neches and Lower Neches rivers) have moderate evidence of reproduction
and recruitment; the remaining nine populations have low evidence of
reproduction and recruitment. Two populations have high abundance
(Cossatot and Neches rivers) four populations have moderate abundance
(Little River/Rolling Rock, Saline River, Big Cypress Bayou, and Bayou
Anacoco), and five populations have extremely low abundance (Calcasieu,
Pearl, Angelina, Lower Neches, and East Fork San Jacinto rivers), and
population abundance is too low to support resiliency of two
populations (Lower Little River (tributary to the Red River) and Sabine
River), which are functionally extirpated/extirpated
We considered whether the Louisiana pigtoe is presently in danger
of extinction throughout all of its range and determined that
endangered status is not appropriate. The current conditions as
assessed in the SSA report show two of the populations in two of the
representative units are in high current condition, and four are in
moderate current condition; they are not currently subject to declining
flows or extreme flow events. While threats are currently acting on the
species and many of those threats are expected to continue into the
future, we did not find that the species is currently in danger of
extinction throughout all of its range.
In the future, as extreme flow events become more frequent as
rainfall patterns change, and increased urbanization results in reduced
groundwater levels, we expect even these populations to be at an
increased risk of extirpation. Given the likelihood of climate change
and other anthropogenic effects in the foreseeable future, within 50
years we estimate at least five populations will become (or remain)
functionally extirpated/extirpated, seven will be in low condition, and
one population will be in moderate condition. In the future, we
anticipate that the Louisiana pigtoe will have reduced viability, with
no highly resilient populations and limited representation and
redundancy.
According to our assessment of plausible future scenarios in the
SSA report, the species is likely to become an endangered species in
the foreseeable future of 50 years throughout all of its range. Fifty
years encompasses about 5 generations of the Louisiana pigtoe;
additionally, projected human population growth and the limitations of
existing resources are expected to increase and interact with climate
effects to exacerbate the effects of drought on surface water resources
throughout all of its range. These effects are likely to impact the
ability to provide the minimum flow needed by the Louisiana pigtoe. As
a result, we expect increased incidences of low flows followed by scour
events, as well as persistent decreased water quality, to be occurring
in 50 years.
After evaluating threats to the species and assessing the
cumulative effect of the threats under the Act's section 4(a)(1)
factors, we find that the Louisiana pigtoe populations will continue to
decline over the next 50 years so that this species is likely to become
in danger of extinction throughout all of its range within the
foreseeable future due to increased frequency of drought and extremely
high-flow events, decreased water quality, and decreased substrate
suitability.
Thus, after assessing the best available information, we determine
that the Louisiana pigtoe is not currently in danger of extinction but
is likely to become in danger of extinction within the foreseeable
future throughout all of its range.

Louisiana Pigtoe: Status Throughout a Significant Portion of Its Range

Under the Act and our implementing regulations, a species may
warrant listing if it is in danger of extinction or likely to become so
in the foreseeable future throughout all or a significant portion of
its range. The court in Center for Biological Diversity v. Everson,
2020 WL 437289 (D.D.C. Jan. 28, 2020) (Everson), vacated the aspect of
the Final Policy on Interpretation of the Phrase ``Significant Portion
of Its Range'' in the Endangered Species Act's Definitions of
``Endangered Species'' and ``Threatened Species'' (Final Policy) (79 FR
37578; July 1, 2014) that provided that the Service does not undertake
an analysis of significant portions of a species' range if the species
warrants listing as threatened throughout all of its range. Therefore,
we proceed to evaluating whether the species is endangered in a
significant portion of its range--that is, whether there is any portion
of the species' range for which both (1) the portion is significant;
and (2) the species is in danger of extinction in that portion.
Depending on the case, it might be more efficient for us to address the
``significance'' question or the ``status'' question first. We can
choose to address either question first. Regardless of which question
we address first, if we reach a negative answer with respect to the
first question that we address, we do not need to evaluate the other
question for that portion of the species' range.
Following the court's holding in Everson, we now consider whether
there are any significant portions of the species' range where the
species is in danger of extinction now (i.e., endangered). In
undertaking this analysis for the Louisiana pigtoe, we choose to
address the status question first--we consider information pertaining
to the geographic distribution of both the species and the threats that
the species faces to identify any portions of the range where the
species may be endangered.
For the Louisiana pigtoe, we consider abundance to be the most
direct measure of the health and status of the species (see Species
Condition, above). Measures like water quality and hydrology may rank
moderate or high, indicating higher quality habitat--but that does not
necessarily indicate the presence of Louisiana pigtoe, only presence of
suitable habitat. All six factors were weighted equally in importance
except abundance, which was viewed as the most relevant and direct
measure of current biological condition; therefore, overall condition
was capped by the abundance score such that no population's overall
condition could exceed the abundance score. By capping abundance, we
ensured that the overall current condition score is based on species-
specific information. There are five populations that are considered to
be in low overall current condition (with between 3-25 individuals
found per population survey) and two that are considered functionally
extirpated/extirpated (with less than 3 individuals found per
population survey). In addition to low abundance, there was a lack of
evidence of reproduction in 9 of the 13 populations; these two
population factors are similar in scope, scale, and distribution across
the range of the species (See Reproduction/

[[Page 16795]]

Recruitment in Species Needs above). We then considered whether these
populations that are at higher risk of extirpation are geographically
concentrated in any portion of the species' range at a biologically
meaningful scale.
We examined the range of Louisiana pigtoe for biologically
meaningful portions that may be at higher risk of extirpation, as
reflected by current population resiliency. The range of Louisiana
pigtoe is relatively large, and populations are distributed in varying
conditions across the range. Therefore, we examined the range based on
accepted mussel faunal provinces (i.e., Haag 2010, p. 18), which
reflect phylogenetic relationships as well as physiogeographical
differences in stream habitat. The faunal provinces germane to the
range of the Louisiana pigtoe are Interior Highlands (includes the
Little River and tributaries), Mississippi Embayment (includes Big
Cypress Bayou), Sabine-Trinity (includes Upper Calcasieu, Sabine,
Angelina, Neches, and East Fork San Jacinto Rivers, and Bayou Anacoco),
and Pontchartrain-Pearl-Pascagoula (includes Pearl River). Of these
faunal provinces, the Interior Highlands, Sabine-Trinity, and
Pontchartrain-Pearl-Pascagoula faunal provinces contain populations in
low condition or that are functionally extirpated and therefore are at
higher risk of extirpation.
The Interior Highlands faunal province is characterized by upland
streams in the Ozark and Ouachita mountains. This province has numerous
endemic aquatic species of both fish and freshwater mussels, due to the
isolation of the river systems within the province from each other and
from other upland river systems (Haag 2012, pp. 82-83). In this faunal
province, the Lower Little River is functionally extirpated, with the
remaining populations in moderate (Little River and Saline River) or
high (Cossatot River) condition. While the populations in this faunal
province are subject to threats such as erratic flows capable of
causing bed movement or dislocation of mussels, increased
sedimentation, altered water chemistry (e.g., low temperatures), and
decreased water quality due to higher pollutant loads from urban areas
and industrial wastewater discharges, the threats are primarily
occurring in the future. Under a moderate increase in stressors based
on the lower greenhouse gas emissions trajectory (RCP 4.5), model
projections expect an increase in global mean surface temperatures that
will alter precipitation events resulting in drought and flooding in
the next 25-50 years, this combined with future human demand for water
resources indicate an overall decline in populations in the future.
Louisiana pigtoe within the Interior Highlands faunal province are not
currently in danger of extinction; therefore, they do not have a
different status from the remainder of the species' range.
The Sabine-Trinity faunal province is located in the central Gulf
Coast of Texas, and characterized by lowland streams and rivers, with
lentic and wetland habitats bordering the main channels (Haag 2012, pp.
86-87). In this faunal province, the Upper Calcasieu River, Angelina
River, Lower Neches River, and the East Fork San Jacinto River are in
low condition, the Sabine River is functionally extirpated, with the
remaining populations in moderate (Big Cypress Bayou) or high condition
(Neches River). While the populations in this faunal province are being
affected by impoundments resulting in threats such as excessive
sedimentation and water quality degradation, as well as ongoing
agricultural activities, groundwater withdrawals, and surface water
diversions, these threats are primarily occurring in the future. Under
a moderate increase in stressors based on the lower greenhouse gas
emissions trajectory (RCP 4.5), model projections expect an increase in
global mean surface temperatures that will alter precipitation events
resulting in more extreme drought and flooding conditions that reduces
water quality, mobilizes substrates, eroded habitat or deposits
sentiments on Louisiana pigtoe populations in the next 25-50 years. The
Sabine-Trinity faunal province are not currently in danger of
extinction; therefore, they do not have a different status from the
remainder of the species' range.
The Pontchartrain-Pearl-Pascagoula faunal province lies entirely
within the Coastal Plain and is characterized by lowland streams filled
with sandy and fine sediments, with lentic and wetland habitats
alongside the main stream channels (Haag 2012, p. 87.). This province
has numerous endemic aquatic species of both fish and freshwater
mussels, the majority of which are shared with the Mobile Basin
province (Haag 2012, pp. 87-89), and includes the Pearl River
population in an overall low condition. The Pearl River population in
this faunal province is subject to threats such as erratic flows from
water releases from the Ross Barrett Dam that are capable of causing
bed movement or dislocation of mussels, increased sedimentation, and
altered water chemistry (e.g., low temperatures), the threats are
primarily occurring in the future. Under a moderate greenhouse gas
emission trajectory (RCP 4.5), model projections no changes from
current condition are expected within 10-years. Within 25-years,
hydrologic conditions would be negatively affected by the construction
of a flood control reservoir proposed for the upper portion of the
focal area, resulting in a moderate decline in substrate condition as
sediments accumulate on mussel beds from a lack or cleansing flows, and
water quality degradation. Although these threats are not unique to
this area, they may be acting at a greater intensity here, either
individually or in combination, than elsewhere in the range, given the
low abundance of Louisiana pigtoe in this reach. The small size of this
population, coupled with the current condition information in the SSA
report suggesting the population in this area has low resiliency,
indicates the populations in the Pontchartrain-Pearl-Pascagoula faunal
province may be in danger of extinction now.
We evaluated the available information about this portion of the
range of Louisiana pigtoe that occupies the upper Pearl River in this
context, assessing its biological significance in terms of the three
habitat criteria (habitat/structure, hydrology, and water quality; see
Species Condition) used to assign the current condition of Louisiana
Pigtoe populations, and determined the information did not indicate it
may be significant. Louisiana pigtoe in this population exhibit similar
habitat and host fish use to Louisiana pigtoe in the remainder of its
range; thus, there is no unique observable environmental usage or
behavioral characteristics attributable to just this area's population.
The Pearl River is not essential to any specific life-history function
of the Louisiana pigtoe that is not found elsewhere in the range.
Further, the habitat in the Pearl River does not contain higher quality
or higher value than the remainder of the species' range of the
Louisiana pigtoe (see Table 3). Additionally, this population does not
interact with other populations of the species. Overall, we found no
substantial information that would indicate the population in the Pearl
River may be significant. While this reach provides some contribution
to the species' overall ability to withstand catastrophic or stochastic
events (redundancy and resiliency, respectively), the species has
larger populations in adjacent faunal provinces. The best scientific
and commercial information available indicate that this populations'
contribution is very limited in scope

[[Page 16796]]

due to small population size and isolation from other populations.
Therefore, because we could not answer both the status and significance
questions in the affirmative, we conclude that the Pearl River does not
warrant further consideration as a significant portion of the range of
the Louisiana pigtoe.
Therefore, no portion of the species' range provides a basis for
determining that the species is in danger of extinction in a
significant portion of its range, and we determine that the species is
likely to become in danger of extinction within the foreseeable future
throughout all of its range. This does not conflict with the courts'
holdings in Desert Survivors v. Department of the Interior, 321 F.
Supp. 3d 1011, 1070-74 (N.D. Cal. 2018), and Center for Biological
Diversity v. Jewell, 248 F. Supp. 3d, 946, 959 (D. Ariz. 2017) because,
in reaching this conclusion, we did not need to consider whether any
portions are significant and, therefore, did not apply the aspects of
the Final Policy's definition of ``significant'' that those court
decisions held were invalid.

Louisiana Pigtoe: Determination of Status

Our review of the best available scientific and commercial
information indicates that the Louisiana pigtoe meets the Act's
definition of a threatened species. Therefore, we propose to list the
Louisiana pigtoe as a threatened species in accordance with sections
3(20) and 4(a)(1) of the Act.

Available Conservation Measures

Conservation measures provided to species listed as endangered or
threatened species under the Act include recognition as a listed
species, planning and implementation of recovery actions, requirements
for Federal protection, and prohibitions against certain practices.
Recognition through listing results in public awareness, and
conservation by Federal, State, Tribal, and local agencies, private
organizations, and individuals. The Act encourages cooperation with the
States and other countries and calls for recovery actions to be carried
out for listed species. The protection required by Federal agencies,
including the Service, and the prohibitions against certain activities
are discussed, in part, below.
The primary purpose of the Act is the conservation of endangered
and threatened species and the ecosystems upon which they depend. The
ultimate goal of such conservation efforts is the recovery of these
listed species, so that they no longer need the protective measures of
the Act. Section 4(f) of the Act calls for the Service to develop and
implement recovery plans for the conservation of endangered and
threatened species. The goal of this process is to restore listed
species to a point where they are secure, self-sustaining, and
functioning components of their ecosystems.
The recovery planning process begins with development of a recovery
outline made available to the public soon after a final listing
determination. The recovery outline guides the immediate implementation
of urgent recovery actions while a recovery plan is being developed.
Recovery teams (composed of species experts, Federal and State
agencies, nongovernmental organizations, and stakeholders) may be
established to develop and implement recovery plans. The recovery
planning process involves the identification of actions that are
necessary to halt and reverse the species' decline by addressing the
threats to its survival and recovery. The recovery plan identifies
recovery criteria for review of when a species may be ready for
reclassification from endangered to threatened (``downlisting'') or
removal from protected status (``delisting''), and methods for
monitoring recovery progress. Recovery plans also establish a framework
for agencies to coordinate their recovery efforts and provide estimates
of the cost of implementing recovery tasks. Revisions of the plan may
be done to address continuing or new threats to the species, as new
substantive information becomes available. The recovery outline, draft
recovery plan, final recovery plan, and any revisions will be available
on our website as they are completed (<a href="https://www.fws.gov/program/endangered-species">https://www.fws.gov/program/endangered-species</a>).
Implementation of recovery actions generally requires the
participation of a broad range of partners, including other Federal
agencies, States, Tribes, nongovernmental organizations, businesses,
and private landowners. Examples of recovery actions include habitat
restoration (e.g., restoration of native vegetation), research, captive
propagation and reintroduction, and outreach and education. The
recovery of many listed species cannot be accomplished solely on
Federal lands because their ranges may occur primarily or solely on
non-Federal lands. To achieve recovery of these species requires
cooperative conservation efforts on private, State, and Tribal lands.
If these species are listed, funding for recovery actions will be
available from a variety of sources, including Federal budgets, State
programs, and cost-share grants for non-Federal landowners, the
academic community, and nongovernmental organizations. In addition,
pursuant to section 6 of the Act, the States of Arkansas, Oklahoma,
Louisiana, Mississippi, and Texas would be eligible for Federal funds
to implement management actions that promote the protection or recovery
of the Texas heelsplitter and Louisiana pigtoe. Information on our
grant programs that are available to aid species recovery can be found
at: <a href="https://www.fws.gov/service/financial-assistance">https://www.fws.gov/service/financial-assistance</a>.
Although the Texas heelsplitter and Louisiana pigtoe are only
proposed for listing under the Act at this time, please let us know if
you are interested in participating in recovery efforts for these
species. Additionally, we invite you to submit any new information on
these species whenever it becomes available and any information you may
have for recovery planning purposes (see FOR FURTHER INFORMATION
CONTACT).
Section 7(a) of the Act requires Federal agencies to evaluate their
actions with respect to any species that is proposed or listed as an
endangered or threatened species and with respect to its critical
habitat, if any is designated. Regulations implementing this
interagency cooperation provision of the Act are codified at 50 CFR
part 402. Section 7(a)(4) of the Act requires Federal agencies to
confer with the Service on any action that is likely to jeopardize the
continued existence of a species proposed for listing 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 the
species or 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 consultation with the
Service.
Federal agency actions within the species' habitat that may require
conference or consultation or both as described in the preceding
paragraph include management and any other landscape-altering
activities on Federal lands administered by the Federal Emergency
Management Agency (related to disaster recovery projects), National
Park Service, Natural Resources Conservation Service, National Wildlife
Refuge System, U.S. Army, U.S. Army Corps of Engineers, and the U.S.
Forest Service.

[[Page 16797]]

The Act and its implementing regulations set forth a series of
general prohibitions and exceptions that apply to endangered wildlife.
The prohibitions of section 9(a)(1) of the Act, codified at 50 CFR
17.21, make it illegal for any person subject to the jurisdiction of
the United States to take (which includes harass, harm, pursue, hunt,
shoot, wound, kill, trap, capture, or collect; or to attempt any of
these) endangered wildlife within the United States or on the high
seas. In addition, it is unlawful to import; export; deliver, receive,
carry, transport, or ship in interstate or foreign commerce in the
course of commercial activity; or sell or offer for sale in interstate
or foreign commerce any species listed as an endangered species. It is
also illegal to possess, sell, deliver, carry, transport, or ship any
such wildlife that has been taken illegally. Certain exceptions apply
to employees of the Service, the National Marine Fisheries Service,
other Federal land management agencies, and State conservation
agencies.
We may issue permits to carry out otherwise prohibited activities
involving endangered wildlife under certain circumstances. Regulations
governing permits are codified at 50 CFR 17.22. With regard to
endangered wildlife, a permit may be issued for the following purposes:
For scientific purposes, to enhance the propagation or survival of the
species, and for incidental take in connection with otherwise lawful
activities. The statute also contains certain exemptions from the
prohibitions, which are found in sections 9 and 10 of the Act.
It is our policy, as published in the Federal Register on July 1,
1994 (59 FR 34272), to identify to the maximum extent practicable at
the time a species is listed, those activities that would or would not
constitute a violation of section 9 of the Act. The intent of this
policy is to increase public awareness of the effect of a proposed
listing on proposed and ongoing activities within the range of the
species proposed for listing. The Act allows the Secretary to
promulgate protective regulations for threatened species pursuant to
section 4(d) of the Act. The discussion in the following section,
Proposed Rule Issued Under Section 4(d) of the Act, regarding
protective regulations under section 4(d) of the Act for the Louisiana
pigtoe complies with our policy.
For the Texas heelsplitter, based on the best available
information, the following actions are unlikely to result in a
violation of section 9, if these activities are carried out in
accordance with existing regulations and permit requirements; this list
is not comprehensive:
(1) Normal agricultural and silvicultural practices, including
herbicide and pesticide use, that are carried out in accordance with
any existing regulations, permit and label requirements, and best
management practices; and
(2) Normal residential landscaping activities.
Based on the best available information, the following activities
may potentially result in a violation of section 9 of the Act, if they
are not authorized in accordance with applicable law; this list is not
comprehensive:
(1) Unauthorized handling or collecting of the species;
(2) Unauthorized destruction or alteration of Texas heelsplitter
habitat by dredging, channelization, impoundment, diversion,
recreational vehicle operation within the stream channel, sand or
gravel removal, or other activities that result in the destruction or
significant degradation of channel or bank stability, streamflow/water
quantity, substrate composition, and water quality used by the species
for foraging, cover, and reproduction;
(3) Modification of the channel or water flow of any stream,
including the withdrawal (decrease) or supplementation (increase) of
surface or ground waters where the Texas heelsplitter is known to
occur;
(4) Livestock grazing that results in direct or indirect
destruction of riparian or instream habitat; and
(5) Unauthorized discharge of chemicals (including pesticides and
fertilizers in violation of label restrictions), household waste, silt,
sediments, fill material, or other pollutants (e.g., sewage, oil and
gasoline, heavy metals), into any waters or their adjoining riparian
areas where the Texas heelsplitter is known to occur.
Questions regarding whether specific activities would constitute a
violation of section 9 of the Act should be directed to the Arlington
Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT).

II. Proposed Rule Issued Under Section 4(d) of the Act

Background

Section 4(d) of the Act contains two sentences. The first sentence
states that the Secretary shall issue such regulations as she deems
necessary and advisable to provide for the conservation of species
listed as threatened. The U.S. Supreme Court has noted that statutory
language similar to the language in section 4(d) of the Act authorizing
the Secretary to take action that she ``deems necessary and advisable''
affords a large degree of deference to the agency (see Webster v. Doe,
486 U.S. 592 (1988)). Conservation is defined in the Act to mean 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.
Additionally, the second sentence of section 4(d) of the Act states
that the Secretary may by regulation prohibit with respect to any
threatened species any act prohibited under section 9(a)(1), in the
case of fish or wildlife, or section 9(a)(2), in the case of plants.
Thus, the combination of the two sentences of section 4(d) provides the
Secretary with wide latitude of discretion to select and promulgate
appropriate regulations tailored to the specific conservation needs of
the threatened species. The second sentence grants particularly broad
discretion to the Service when adopting the prohibitions under section
9.
The courts have recognized the extent of the Secretary's discretion
under this standard to develop rules that are appropriate for the
conservation of a species. For example, courts have upheld, as a valid
exercise of agency authority, rules developed under section 4(d) that
included limited prohibitions against takings (see Alsea Valley
Alliance v. Lautenbacher, 2007 U.S. Dist. Lexis 60203 (D. Or. 2007);
Washington Environmental Council v. National Marine Fisheries Service,
2002 WL 511479 (W.D. Wash. 2002)). Courts have also upheld 4(d) rules
that do not address all of the threats a species faces (see State of
Louisiana v. Verity, 853 F.2d 322 (5th Cir. 1988)). As noted in the
legislative history when the Act was initially enacted, ``once an
animal is on the threatened list, the Secretary has an almost infinite
number of options available to [her] with regard to the permitted
activities for those species. [She] may, for example, permit taking,
but not importation of such species, or [she] may choose to forbid both
taking and importation but allow the transportation of such species''
(H.R. Rep. No. 412, 93rd Cong., 1st Sess. 1973).
The provisions of this proposed 4(d) rule would promote
conservation of the Louisiana pigtoe by encouraging riparian landscape
conservation while also meeting the conservation needs of the Louisiana
pigtoe. By streamlining those projects that follow best management
practices and improve instream habitat (such as streambank

[[Page 16798]]

stabilization, instream channel restoration, and upland restoration
that improves instream habitat), conservation is more likely to occur
for Louisiana pigtoe, improving the condition of populations in those
reaches. The provisions of this proposed rule are several of many tools
that we would use to promote the conservation of the Louisiana pigtoe.
This proposed 4(d) rule would apply only if and when we make final the
listing of the Louisiana pigtoe as a threatened species.
As mentioned previously in Available Conservation Measures, section
7(a)(2) of the Act requires Federal agencies, including the Service, to
ensure that any action they fund, authorize, or carry out is not likely
to jeopardize the continued existence of any endangered species or
threatened species or result in the destruction or adverse modification
of designated critical habitat of such species. In addition, section
7(a)(4) of the Act requires Federal agencies to confer with the Service
on any agency action that is likely to jeopardize the continued
existence of any species proposed to be listed under the Act or result
in the destruction or adverse modification of proposed critical
habitat.
If a Federal action may affect a listed species or its critical
habitat, the responsible Federal agency (action agency) must enter into
consultation with us. Examples of Federal actions that are subject to
the section 7 consultation process are actions on State, Tribal, local,
or private lands that require a Federal permit (such as a permit from
the U.S. Army Corps of Engineers under section 404 of the Clean Water
Act (33 U.S.C. 1251 et seq.) or a permit from the Service under section
10 of the Act) or that involve some other Federal action (such as
funding from the Federal Highway Administration, Federal Aviation
Administration, or the Federal Emergency Management Agency). Federal
actions not affecting listed species or critical habitat--and actions
on State, Tribal, local, or private lands that are not federally
funded, authorized, or carried out by a Federal agency--do not require
section 7 consultation.
These requirements are the same for a threatened species with a
species-specific 4(d) rule. For example, a Federal agency's
determination that an action is ``not likely to adversely affect'' a
threatened species will require the Service's written concurrence.
Similarly, a Federal agency's determination that an action is ``likely
to adversely affect'' a threatened species will require formal
consultation and the formulation of a biological opinion.

Provisions of the Proposed 4(d) Rule

Exercising the Secretary's authority under section 4(d) of the Act,
we have developed a proposed rule that is designed to address the
Louisiana pigtoe's specific conservation needs. As discussed previously
in Summary of Biological Status and Threats, we have concluded that the
Louisiana pigtoe is likely to become in danger of extinction within the
foreseeable future primarily due to habitat changes such as the
accumulation of fine sediments, altered hydrology, and impairment of
water quality; predation and collection; and barriers to fish movement.
Section 4(d) requires the Secretary to issue such regulations as she
deems necessary and advisable to provide for the conservation of each
threatened species and authorizes the Secretary to include among those
protective regulations any of the prohibitions that section 9(a)(2) of
the Act prescribes for endangered species. We find that, if finalized,
the protections, prohibitions, and exceptions in this proposed rule as
a whole satisfy the requirement in section 4(d) of the Act to issue
regulations deemed necessary and advisable to provide for the
conservation of the Louisiana pigtoe.
The protective regulations we are proposing for the Louisiana
pigtoe incorporate prohibitions from section 9(a)(1) to address the
threats to the species. Section 9(a)(1) prohibits the following
activities for endangered wildlife: importing or exporting; take;
possession and other acts with unlawfully taken specimens; delivering,
receiving, transporting, or shipping in interstate or foreign commerce
in the course of commercial activity; or selling or offering for sale
in interstate or foreign commerce. This protective regulation includes
most of these prohibitions for the Louisiana pigtoe because the
Louisiana pigtoe is at risk of extinction in the foreseeable future and
putting these prohibitions in place will help to preserve the species'
remaining populations, slow its rate of decline, and decrease
synergistic, negative effects from other stressors.
In particular, this proposed 4(d) rule would provide for the
conservation of the Louisiana pigtoe by prohibiting the following
activities, unless they fall within specific exceptions or are
otherwise authorized or permitted: Importing or exporting; take;
possession and other acts with unlawfully taken specimens; delivering,
receiving, transporting, or shipping in interstate or foreign commerce
in the course of commercial activity; or selling or offering for sale
in interstate or foreign commerce.
Under the Act, ``take'' means to harass, harm, pursue, hunt, shoot,
wound, kill, trap, capture, or collect, or to attempt to engage in any
such conduct. Some of these provisions have been further defined in
regulations at 50 CFR 17.3. Take can result knowingly or otherwise, by
direct and indirect impacts, intentionally or incidentally. Regulating
incidental and intentional take would help preserve the species'
remaining populations, slow their rate of decline, and decrease
synergistic, negative effects from other stressors. Therefore, we
propose to prohibit take of the Louisiana pigtoe, except for take
resulting from those actions and activities specifically excepted by
the 4(d) rule.
Exceptions to the prohibition on take would include most of the
general exceptions to the prohibition against take of endangered
wildlife, as set forth in 50 CFR 17.21 and certain other specific
activities that we propose for exception, as described below.
The proposed 4(d) rule would also provide for the conservation of
the species by allowing exceptions that incentivize conservation
actions or that, while they may have some minimal level of take of the
Louisiana pigtoe, are not expected to rise to the level that would have
a negative impact (i.e., would have only de minimis impacts) on the
species' conservation. The proposed exceptions to these prohibitions
include the following activities that are expected to have negligible
impacts to the Louisiana pigtoe and its habitat:
(1) Channel restoration projects that create natural, physically
stable (streambanks and substrate remaining relatively unchanging over
time), ecologically functioning streams or stream and wetland systems
(containing an assemblage of fish, mussels, other invertebrates, and
plants) that are reconnected with their groundwater aquifers. These
projects can be accomplished using a variety of methods, but the
desired outcome is a natural channel with low shear stress (force of
water moving against the channel); bank heights that enable
reconnection to the floodplain; a reconnection of surface and
groundwater systems, resulting in perennial flows in the channel;
riffles and pools composed of existing soil, rock, and wood instead of
large imported materials; low compaction of soils within adjacent
riparian areas; and inclusion of riparian wetlands and woodland
buffers. This exception to the

[[Page 16799]]

proposed 4(d) rule for incidental take would promote conservation of
Louisiana pigtoe by creating stable stream channels that are less
likely to scour during high-flow events, thereby increasing population
resiliency.
(2) Bioengineering methods such as streambank stabilization using
live native stakes (live, vegetative cuttings inserted or tamped into
the ground in a manner that allows the stake to take root and grow),
live native fascines (live branch cuttings, usually willows, bound
together into long, cigar-shaped bundles), or native brush layering
(cuttings or branches of easily rooted tree species layered between
successive lifts of soil fill). These methods must not include the sole
use of quarried rock (rip-rap) or the use of rock baskets or gabion
structures. In addition, to reduce streambank erosion and sedimentation
into the stream, work using these bioengineering methods must be
performed at base flow or low water conditions and when significant
rainfall is not predicted. Further, streambank stabilization projects
must keep all equipment out of the stream channels and water. Similar
to channel restoration projects, this exception to the proposed 4(d)
rule for incidental take would promote conservation of Louisiana pigtoe
by creating stable stream channels that are less likely to scour during
high-flow events, thereby increasing population resiliency.
(3) Soil and water conservation practices and riparian and adjacent
upland habitat management activities that restore instream habitats for
the species, restore adjacent riparian habitats that enhance stream
habitats for the species, stabilize degraded and eroding stream banks
to limit sedimentation and scour of the species' habitats, and restore
or enhance nearby upland habitats to limit sedimentation of the
species' habitats. We recommend that these practices and activities
comply with specifications and technical guidelines developed by the
U.S. Department of Agriculture's Natural Resources Conservation Service
(NRCS), as soil and water conservation practices and aquatic species
habitat restoration projects associated with NRCS conservation plans
are designed to improve water quality and enhance fish and aquatic
species habitats. This exception to the proposed 4(d) rule for
incidental take would promote conservation of Louisiana pigtoe by
creating stable stream channels and reducing sediment inputs to the
stream, thereby increasing population resiliency.
We include other standard exceptions to the prohibitions in the
proposed 4(d) rule for the Louisiana pigtoe.
Despite these prohibitions regarding threatened species, we may
under certain circumstances issue permits to carry out one or more
otherwise-prohibited activities, including those described above. The
regulations that govern permits for threatened wildlife state that the
Director may issue a permit authorizing any activity otherwise
prohibited with regard to threatened species. These include permits
issued for the following purposes: for scientific purposes, to enhance
propagation or survival, for economic hardship, for zoological
exhibition, for educational purposes, for incidental taking, or for
special purposes consistent with the purposes of the Act (50 CFR
17.32). The statute also contains certain exemptions from the
prohibitions, which are found in sections 9 and 10 of the Act.
We recognize the special and unique relationship with our State
natural resource agency partners in contributing to conservation of
listed species. State agencies often possess scientific data and
valuable expertise on the status and distribution of endangered,
threatened, and candidate species of wildlife and plants. State
agencies, because of their authorities and their close working
relationships with local governments and landowners, are in a unique
position to assist us in implementing all aspects of the Act. In this
regard, section 6 of the Act provides that we must cooperate to the
maximum extent practicable with the States in carrying out programs
authorized by the Act. Therefore, any qualified employee or agent of a
State conservation agency that is a party to a cooperative agreement
with us in accordance with section 6(c) of the Act, who is designated
by his or her agency for such purposes, would be able to conduct
activities designed to conserve Louisiana pigtoe that may result in
otherwise prohibited take without additional authorization.
Nothing in this proposed 4(d) rule would change in any way the
recovery planning provisions of section 4(f) of the Act, the
consultation requirements under section 7 of the Act, or our ability to
enter into partnerships for the management and protection of the
Louisiana pigtoe. However, interagency cooperation may be further
streamlined through planned programmatic consultations for the species
between us and other Federal agencies, where appropriate. We ask the
public, particularly State agencies and other interested stakeholders
that may be affected by the proposed 4(d) rule, to provide comments and
suggestions regarding additional guidance and methods that we could
provide or use, respectively, to streamline the implementation of this
proposed 4(d) rule (see Information Requested, above).

III. Critical Habitat

Background

Critical habitat is defined in section 3 of the Act as:
(1) The specific areas within the geographical area occupied by the
species, at the time it is listed in accordance with the Act, on which
are found those physical or biological features
(a) Essential to the conservation of the species, and
(b) Which may require special management considerations or
protection; and
(2) Specific areas outside the geographical area occupied by the
species at the time it is listed, upon a determination that such areas
are essential for the conservation of the species.
Our regulations at 50 CFR 424.02 define the geographical area
occupied by the species as an area that may generally be delineated
around species' occurrences, as determined by the Secretary (i.e.,
range). Such areas may include those areas used throughout all or part
of the species' life cycle, even if not used on a regular basis (e.g.,
migratory corridors, seasonal habitats, and habitats used periodically,
but not solely by vagrant individuals).
Conservation, as defined under section 3 of the Act, means to use
and the use of all methods and procedures that are necessary to bring
an endangered or threatened species to the point at which the measures
provided pursuant to the Act are no longer necessary. Such methods and
procedures include, but are not limited to, all activities associated
with scientific resources management such as research, census, law
enforcement, habitat acquisition and maintenance, propagation, live
trapping, and transplantation, and, in the extraordinary case where
population pressures within a given ecosystem cannot be otherwise
relieved, may include regulated taking.
Critical habitat receives protection under section 7 of the Act
through the requirement that Federal agencies ensure, in consultation
with the Service, that any action they authorize, fund, or carry out is
not likely to result in the destruction or adverse modification of
critical habitat. The designation of critical habitat does not affect
land

[[Page 16800]]

ownership or establish a refuge, wilderness, reserve, preserve, or
other conservation area. Such designation also does not allow the
government or public to access private lands. Such designation does not
require implementation of restoration, recovery, or enhancement
measures by non-Federal landowners. Where a landowner requests Federal
agency funding or authorization for an action that may affect a listed
species or critical habitat, the Federal agency would be required to
consult with the Service under section 7(a)(2) of the Act. However,
even if the Service were to conclude that the proposed activity would
likely result in destruction or adverse modification of the critical
habitat, the Federal action agency and the landowner are not required
to abandon the proposed activity, or to restore or recover the species;
instead, they must implement ``reasonable and prudent alternatives'' to
avoid destruction or adverse modification of critical habitat.
Under the first prong of the Act's definition of critical habitat,
areas within the geographical area occupied by the species at the time
it was listed are included in a critical habitat designation if they
contain physical or biological features (1) which are essential to the
conservation of the species and (2) which may require special
management considerations or protection. For these areas, critical
habitat designations identify, to the extent known using the best
scientific and commercial data available, those physical or biological
features that are essential to the conservation of the species (such as
space, food, cover, and protected habitat).
Under the second prong of the Act's definition of critical habitat,
we can designate critical habitat in areas outside the geographical
area occupied by the species at the time it is listed, upon a
determination that such areas are essential for the conservation of the
species.
Section 4 of the Act requires that we designate critical habitat on
the basis of the best scientific data available. Further, our Policy on
Information Standards Under the Endangered Species Act (published in
the Federal Register on July 1, 1994 (59 FR 34271)), the Information
Quality Act (section 515 of the Treasury and General Government
Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R. 5658)),
and our associated Information Quality Guidelines provide criteria,
establish procedures, and provide guidance to ensure that our decisions
are based on the best scientific data available. They require our
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 we are determining which areas should be designated as
critical habitat, our primary source of information is generally the
information from the SSA report and information developed during the
listing process for the species. Additional information sources may
include any generalized conservation strategy, criteria, or outline
that may have been developed for the species; 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; other unpublished materials; or
experts' opinions or personal knowledge.
Habitat is dynamic, and species may move from one area to another
over time. We recognize that critical habitat designated at a
particular point in time may not include all of the habitat areas that
we may later determine are necessary for the recovery of the species.
For these reasons, a critical habitat designation does not signal that
habitat outside the designated area is unimportant or may not be needed
for recovery of the species. Areas that are important to the
conservation of the species, both inside and outside the critical
habitat designation, will continue to be subject to: (1) Conservation
actions implemented under section 7(a)(1) of the Act; (2) regulatory
protections afforded by the requirement in section 7(a)(2) of the Act
for Federal agencies to ensure their actions are not likely to
jeopardize the continued existence of any endangered or threatened
species; and (3) the prohibitions found in section 9 of the Act.
Federally funded or permitted projects affecting listed species outside
their designated critical habitat areas may still result in jeopardy
findings in some cases. These protections and conservation tools will
continue to contribute to recovery of this species. 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
(HCPs), or other species conservation planning efforts if new
information available at the time of these planning efforts calls for a
different outcome.

Prudency Determination

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, the Secretary shall designate critical habitat at the
time the species is determined to be an endangered or threatened
species. Our regulations (50 CFR 424.12(a)(1)) state that the Secretary
may, but is not required to, determine that a designation would not be
prudent in the following circumstances:
(i) The species is threatened by taking or other human activity and
identification of critical habitat can be expected to increase the
degree of such threat to the species;
(ii) The present or threatened destruction, modification, or
curtailment of a species' habitat or range is not a threat to the
species, or threats to the species' habitat stem solely from causes
that cannot be addressed through management actions resulting from
consultations under section 7(a)(2) of the Act;
(iii) Areas within the jurisdiction of the United States provide no
more than negligible conservation value, if any, for a species
occurring primarily outside the jurisdiction of the United States;
(iv) No areas meet the definition of critical habitat; or
(v) The Secretary otherwise determines that designation of critical
habitat would not be prudent based on the best scientific data
available.
As discussed earlier in this document, there are well documented
beds of Louisiana pigtoe that are sampled for scientific projects, and
to a lesser degree collected by fishing enthusiasts for use as bait.
Because these areas are already well known, and they are not being
collected for private collections, there is currently no additional
imminent threat of collection or vandalism identified under Factor B
for these species, and identification and mapping of critical habitat
is not expected to initiate any such threat. In our SSA and proposed
listing determination for the Texas heelsplitter and Louisiana pigtoe,
we determined that the present or threatened destruction, modification,
or curtailment of habitat or range is a threat to these species and
that those threats in some way can be addressed by section 7(a)(2)
consultation measures. These species occur wholly in the jurisdiction
of the United States, and we are able to identify areas that meet the
definition of critical habitat. Therefore, because none of the
circumstances enumerated in our regulations at 50 CFR 424.12(a)(1) have
been met and because

[[Page 16801]]

the Secretary has not identified other circumstances for which this
designation of critical habitat would be not prudent, we have
determined that the designation of critical habitat is prudent for the
Texas heelsplitter and Louisiana pigtoe.

Critical Habitat Determinability

Having determined that designation is prudent, under section
4(a)(3) of the Act we must find whether critical habitat for the Texas
heelsplitter and Louisiana pigtoe is determinable. Our regulations at
50 CFR 424.12(a)(2) state that critical habitat is not determinable
when one or both of the following situations exist:
(i) Data sufficient to perform required analyses are lacking, or
(ii) The biological needs of the species are not sufficiently well
known to identify any area that meets the definition of ``critical
habitat.'' When critical habitat is not determinable, the Act allows
the Service an additional year to publish a critical habitat
designation (16 U.S.C. 1533(b)(6)(C)(ii)).
We reviewed the available information pertaining to the biological
needs of the species and habitat characteristics where these species
are located. This and other information represent the best scientific
data available and led us to conclude that the designation of critical
habitat is determinable for the Texas heelsplitter and Louisiana
pigtoe.

Physical or Biological Features Essential to the Conservation of the
Species

In accordance with section 3(5)(A)(i) of the Act and regulations at
50 CFR 424.12(b), in determining which areas we will designate as
critical habitat from within the geographical area occupied by the
species at the time of listing, we consider the physical or biological
features that are essential to the conservation of the species and that
may require special management considerations or protection. The
regulations at 50 CFR 424.02 define ``physical or biological features
essential to the conservation of the species'' as the features that
occur in specific areas and that are essential to support the life-
history needs of the species, including, but not limited to, water
characteristics, soil type, geological features, sites, prey,
vegetation, symbiotic species, or other features. A feature may be a
single habitat characteristic or a more complex combination of habitat
characteristics. Features may include habitat characteristics that
support ephemeral or dynamic habitat conditions. Features may also be
expressed in terms relating to principles of conservation biology, such
as patch size, distribution distances, and connectivity.
For example, physical features essential to the conservation of the
species might include gravel of a particular size required for
spawning, alkaline soil for seed germination, protective cover for
migration, or susceptibility to flooding or fire that maintains
necessary early-successional habitat characteristics. Biological
features might include prey species, forage grasses, specific kinds or
ages of trees for roosting or nesting, symbiotic fungi, or a particular
level of nonnative species consistent with conservation needs of the
listed species. The features may also be combinations of habitat
characteristics and may encompass the relationship between
characteristics or the necessary amount of a characteristic essential
to support the life history of the species.
In considering whether features are essential to the conservation
of the species, we may consider an appropriate quality, quantity, and
spatial and temporal arrangement of habitat characteristics in the
context of the life-history needs, condition, and status of the
species. These characteristics 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, or
rearing (or development) of offspring; and habitats that are protected
from disturbance.
We derive the specific physical or biological features (PBFs)
essential for the conservation of the Texas heelsplitter and Louisiana
pigtoe from studies of these species' habitat, ecology, and life
history. The life histories of these two freshwater mussel species are
very similar--mussels need suitable water quality, flowing water,
suitable substrate, flow refuges, and appropriate host fish--and so we
will discuss their common habitat needs and then describe their
species-specific needs.

Physiological Requirements: Water Quality Requirements

Freshwater mussels, as a group, are sensitive to changes in water
quality, including parameters such as dissolved oxygen, salinity,
ammonia, and environmental pollutants (e.g., pesticides and trace
metals). Habitats with appropriate levels of these parameters that are
pollutant-free or have low levels of pollutants are considered
suitable, while those habitats with levels outside of the appropriate
ranges or that contain elevated pollutants are considered less
suitable. We have used information for the Texas heelsplitter and
Louisiana pigtoe, where available, and data from other species when
species-specific information is not available. Juvenile freshwater
mussels are particularly susceptible to low dissolved oxygen levels.
Juveniles will reduce feeding behavior when dissolved oxygen is between
2-4 milligrams per liter (mg/L), and mortality has been shown to occur
at dissolved oxygen levels below 1.3 mg/L. Increased salinity levels
may also be stressful to freshwater mussels, with some species showing
signs of stress at salinity levels of 2 ppt or higher (Bonner et al.
2018; pp. 155-156).
The release of pollutants into streams from point and nonpoint
sources have immediate impacts on water quality conditions and may make
environments unsuitable for habitation by mussels. Early life stages of
freshwater mussels are some of the most sensitive organisms of all
species to ammonia and copper (Augspurger et al. 2007, p. 2025).
Additionally, sublethal effects of contaminants over time can result in
reduced feeding efficiency, reduced growth, decreased reproduction,
changes in enzyme activity, and behavioral changes to all mussel life
stages. Even wastewater discharges with low ammonia levels have been
shown to negatively affect mussel populations.
Finally, water temperature plays a critical role in the life
history of freshwater mussels. High water temperatures can cause valve
closure, reduced reproductive output, and death. Laboratory studies
investigating the effects of thermal stress on glochidia and adults
have indicated thermal stress may occur at 27 [deg]C (80.6 [deg]F)
(Bonner et al. 2018; Khan et al. 2019, entire)).
Based on the above information, we determine that stream reaches
with the following water quality parameters are suitable for the Texas
heelsplitter and Louisiana pigtoe:
<bullet> Water temperature below 27 [deg]C (80.6 [deg]F);
<bullet> Dissolved oxygen levels greater than 3 mg/L;
<bullet> Low salinity (less than 2 ppt) and total dissolved solids;
<bullet> Low total ammonia and nitrogen (below 0.3-0.7 mg/L total
ammonia nitrogen);
<bullet> Low levels of copper, nickel, and other trace metals;
<bullet> Low levels of pesticides, sulfate, chloride, potassium,
and other harmful constituents; and
<bullet> Low pollutants and environmental contaminants common to
wastewater.

[[Page 16802]]

Space for Individual and Population Growth and for Normal Behavior

Most freshwater mussels, including the Texas heelsplitter and
Louisiana pigtoe, are found in aggregations, called mussel beds, that
vary in size from about 50 to greater than 5,000 square meters (m\2\),
separated by stream reaches in which mussels are absent or rare (Vaughn
2012, p. 983). Freshwater mussel larvae (called glochidia) are
parasites that must attach to a host fish. A population incorporates
more than one mussel bed; it is the collection of mussel beds within a
stream reach between which infested host fish may travel, allowing for
ebbs and flows in mussel bed density and abundance over time throughout
the population's occupied reach. Accordingly, sufficiently resilient
mussel populations must occupy stream reaches long enough so that
stochastic events that affect individual mussel beds do not eliminate
the entire population. Repopulation by infested host fish from other
mussel beds within the reach can allow the population to recover from
these events. Longer stream reaches are more likely to support
populations of the Texas heelsplitter and Louisiana pigtoe into the
future than shorter stream reaches. Therefore, we determine that long
stream reaches, over 50 river miles (80.5 km), are an important
component of a riverine system with habitat to support all life stages
of the Texas heelsplitter and Louisiana pigtoe. Populations occupying
reaches shorter than 50 miles can still provide population redundancy
and, if habitat factors are of sufficiently high quality, can be an
important component of the recovery of Texas heelsplitter and Louisiana
pigtoe.
The Texas heelsplitter needs low to moderately flowing streams, and
tolerates impoundments (lakes, reservoirs, or pools without flow). All
life stages of the Texas heelsplitter require substrates consisting of
firm mud, sand, finer gravels, and mixtures of those with high organic
matter content. The Louisiana pigtoe needs flowing water for survival
and occurs in medium- to large-sized streams and rivers associated with
riffle, run, and sometimes larger backwater tribut

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