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Proposed Rule2021-18012

Endangered and Threatened Wildlife and Plants; Endangered Species Status With Critical Habitat for Guadalupe Fatmucket, Texas Fatmucket, Guadalupe Orb, Texas Pimpleback, and False Spike, and Threatened Species Status With Section 4(d) Rule and Critical Habitat for Texas Fawnsfoot

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Published

August 26, 2021

Issuing agencies

Interior DepartmentFish and Wildlife Service

Abstract

We, the U.S. Fish and Wildlife Service (Service or USFWS), propose to list six Central Texas mussel species: The Guadalupe fatmucket (Lampsilis bergmanni), Texas fatmucket (Lampsilis bracteata), Texas fawnsfoot (Truncilla macrodon), Guadalupe orb (Cyclonaias necki), Texas pimpleback (Cyclonaias (=Quadrula) petrina), and false spike (Fusconaia (=Quincuncina) mitchelli) as endangered or threatened under the Endangered Species Act of 1973, as amended (Act). After review of the best available scientific and commercial information, we find that listing Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, and false spike as endangered species is warranted, and listing Texas fawnsfoot as a threatened species is warranted. We propose a rule issued under section 4(d) of the Act ("4(d) rule") for the Texas fawnsfoot. If we finalize this rule as proposed, it would add these species to the List of Endangered and Threatened Wildlife and extend the Act's protections to the species. We also propose to designate critical habitat for all six species under the Act. In total, approximately 1,944 river miles (3,129 river kilometers) in Texas fall within the boundaries of the proposed critical habitat designations. We also announce the availability of a draft economic analysis (DEA) of the proposed designation of critical habitat. We also are notifying the public that we have scheduled two informational meetings followed by public hearings on the proposed rule.

Full Text

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[Federal Register Volume 86, Number 163 (Thursday, August 26, 2021)]
[Proposed Rules]
[Pages 47916-48011]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2021-18012]

[[Page 47915]]

Vol. 86

Thursday,

No. 163

August 26, 2021

Part IV

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 Guadalupe Fatmucket, Texas Fatmucket,
Guadalupe Orb, Texas Pimpleback, and False Spike, and Threatened
Species Status With Section 4(D) Rule and Critical Habitat for Texas
Fawnsfoot; Proposed Rule

Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 /
Proposed Rules

[[Page 47916]]

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[FWS-R2-ES-2019-0061; FF09E21000 FXES11110900000 212]
RIN 1018-BD16

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service or USFWS),
propose to list six Central Texas mussel species: The Guadalupe
fatmucket (Lampsilis bergmanni), Texas fatmucket (Lampsilis bracteata),
Texas fawnsfoot (Truncilla macrodon), Guadalupe orb (Cyclonaias necki),
Texas pimpleback (Cyclonaias (=Quadrula) petrina), and false spike
(Fusconaia (=Quincuncina) mitchelli) as endangered or threatened under
the Endangered Species Act of 1973, as amended (Act). After review of
the best available scientific and commercial information, we find that
listing Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas
pimpleback, and false spike as endangered species is warranted, and
listing Texas fawnsfoot as a threatened species is warranted. We
propose a rule issued under section 4(d) of the Act (``4(d) rule'') for
the Texas fawnsfoot. If we finalize this rule as proposed, it would add
these species to the List of Endangered and Threatened Wildlife and
extend the Act's protections to the species. We also propose to
designate critical habitat for all six species under the Act. In total,
approximately 1,944 river miles (3,129 river kilometers) in Texas fall
within the boundaries of the proposed critical habitat designations. We
also announce the availability of a draft economic analysis (DEA) of
the proposed designation of critical habitat. We also are notifying the
public that we have scheduled two informational meetings followed by
public hearings on the proposed rule.

DATES:
Comment submission: We will accept comments received or postmarked
on or before October 25, 2021. 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
public informational sessions from 5:00 p.m. to 6:00 p.m., Central
Time, followed by public hearings from 6:30 p.m. to 8:30 p.m., Central
Time, on September 14, 2021, and September 16, 2021.

ADDRESSES: You may submit comments by one of the following methods:
(1) Electronically: Go to the Federal eRulemaking Portal: <a href="http://www.regulations.gov">http://www.regulations.gov</a>. In the Search box, enter FWS-R2-ES-2019-0061,
which is the docket number for this rulemaking. Then, in the Search
panel on the left side of the screen, under the Document Type heading,
check the Proposed Rules box to locate this document. You may submit a
comment by clicking on ``Comment Now!''
(2) By hard copy: Submit by U.S. mail to: Public Comments
Processing, Attn: FWS-R2-ES-2019-0061, U.S. Fish and Wildlife Service,
MS: JAO/1N, 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="http://www.regulations.gov">http://www.regulations.gov</a>. This
generally means that we will post any personal information you provide
us (see Information Requested, below, for more information).
Public informational meetings and public hearings: The public
informational meetings and the public hearings will be held virtually
using the Zoom platform. See Public Hearing, below, for more
information.
Availability of supporting materials: For the 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/AustinTexas/ESA_Sp_Mussels.html">https://www.fws.gov/southwest/es/AustinTexas/ESA_Sp_Mussels.html</a> and at
<a href="http://www.regulations.gov">http://www.regulations.gov</a> under Docket No. FWS-R2-ES-2019-0061. Any
additional tools or supporting information that we may develop for the
critical habitat designation will also be available at the Service
website set out above, and may also be included in the preamble and/or
at <a href="http://www.regulations.gov">http://www.regulations.gov</a>.

FOR FURTHER INFORMATION CONTACT: Adam Zerrenner, Field Supervisor, U.S.
Fish and Wildlife Service, Austin Ecological Services Field Office,
10711 Burnet Rd., Suite 200, Austin, TX 78758; telephone (512) 490-
0057. Persons who use a telecommunications device for the deaf (TDD)
may call the Federal Relay Service at 800-877-8339.

SUPPLEMENTARY INFORMATION:

Executive Summary

Why we need to publish a rule. Under the Act, if we determine that
a species may be an endangered or threatened species throughout all or
a significant portion of its range, we are required to promptly publish
a proposal in the Federal Register and make a determination on our
proposal within 1 year. To the maximum extent prudent and determinable,
we must designate critical habitat for any species that we determine to
be an endangered or threatened species under the Act. Listing a species
as an endangered or threatened species and designation of critical
habitat can only be completed by issuing a rule.
What this document does. This document proposes the Guadalupe
fatmucket (Lampsilis bergmanni), Texas fatmucket (Lampsilis bracteata),
Guadalupe orb (Cyclonaias necki), Texas pimpleback (Cyclonaias
(=Quadrula) petrina), and false spike (Fusconaia (=Quincuncina)
mitchelli) as endangered species and Texas fawnsfoot (Truncilla
macrodon) as a threatened species. This document also proposes the
designation of critical habitat for all six species, as well as a 4(d)
rule providing protective regulations for the Texas fawnsfoot.
The basis for our action. Under the Act, we may determine that a
species is an endangered or threatened species based on 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 habitat loss through changes in
water quality and quantity, as well as increased fine sediments (Factor
A), are the primary threats to these species.
Under the Act, for any species that is determined to be threatened,
we must provide protective regulations to provide for the conservation
of that species. For the Texas fawnsfoot, we are proposing to prohibit
take and possession.
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 4(b)(2) of the Act
states that the Secretary must make the designation on

[[Page 47917]]

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. 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.
Supporting analyses. We prepared an analysis of the economic
impacts of the proposed critical habitat designations and hereby
announce the availability of the draft economic analysis for public
review and comment.
Our species status assessment report (SSA report) documents the
results of the comprehensive biological status review for the central
Texas mussels and provides an account of the species' overall viability
through forecasting of the species' condition in the future (Service
2019a, entire). Additionally, the SSA report contains our analysis of
required habitat and the existing conditions of that habitat.
Peer review. 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 eight appropriate specialists regarding the species status
assessment report. We received responses from six specialists, which
informed this proposed rule. The purpose of peer review is to ensure
that our listing determinations, critical habitat designations, and
4(d) rules are based on scientifically sound data, assumptions, and
analyses. The peer reviewers have expertise in the biology, habitat,
and threats to the species.
We sought comments from independent specialists on the SSA report
to ensure that our proposal is based on scientifically sound data and
analyses. We received feedback from six scientists with expertise in
freshwater mussel biology, ecology, genetics, climate science, and
hydrology as peer review of the SSA report. The reviewers were
generally supportive of our approach and made suggestions and comments
that strengthened our analysis. The SSA report and other materials
relating to this proposal can be found at <a href="http://www.regulations.gov">http://www.regulations.gov</a>
under Docket No. FWS-R2-ES-2019-0061.
Because we will consider all comments and information received
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 any of these
species are threatened instead of endangered, or endangered instead of
threatened, or we may conclude that any of these species do not warrant
listing as either an endangered species or a threatened species. Such
final decisions would be a logical outgrowth of this proposal, as long
as we: (a) Base the decisions on the best scientific and commercial
data available after considering all of the relevant factors; (2) do
not rely on factors Congress has not intended us to consider; and (3)
articulate a rational connection between the facts found and the
conclusions made, including why we changed our conclusion.

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 concerned 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 these species,
including habitat requirements for feeding, breeding, and sheltering;
(b) Genetics, genomics, systematics, and taxonomy;
(c) Historical and current range, including distribution patterns;
(d) Historical and current population levels, abundance, and
current and projected trends; and
(e) Past and ongoing conservation measures for these species, their
habitats, or both.
(2) 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.
(3) Biological, commercial trade, or other relevant data concerning
any threats (or lack thereof) to these species and existing regulations
that may be addressing those threats.
(4) Additional information concerning the historical and current
status, range, distribution, and population size of these species,
including the locations of any additional populations of the Central
Texas mussels.
(5) Information on regulations that are necessary and advisable to
provide for the conservation of the Texas fawnsfoot and that the
Service can consider in developing a 4(d) rule for the species. In
particular, information concerning the extent to which we should
include any of the section 9 prohibitions in the 4(d) rule or whether
any other forms of take should be excepted from the prohibitions in the
4(d) rule.
(6) The reasons why we should or should not designate habitat as
``critical habitat'' under section 4 of the Act, including information
to inform the following factors such that a designation of critical
habitat may be determined to be not prudent:
(a) 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;
(b) 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;
(c) 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;
(d) No areas meet the definition of critical habitat.
(7) Specific information on:
(a) The amount and distribution of habitat for all six Central
Texas mussels;
(b) What areas, that were occupied at the time of listing and that
contain the physical or biological features essential to the
conservation of the species, should be included in the designation and
why;
(c) Any additional areas occurring within the range of the species,
i.e., Anderson, Austin, Bastrop, Bell, Blanco, Brazoria, Brazos, Brown,
Burleson, Caldwell, Coleman, Colorado, Comal, Concho, Dallas, DeWitt,
Edwards, Ellis, Falls, Fayette, Fort Bend, Freestone, Gillespie,
Gonzales, Grimes, Guadalupe, Hays, Henderson, Houston, Kaufman, Kerr,
Kendall, Kimble, Lampasas, Leon, Llano, Madison, Mason, Matagorda,
McCulloch, McLennan, Menard, Milam, Mills, Navarro, Palo Pinto, Parker,

[[Page 47918]]

Robertson, Runnels, San Saba, Shackelford, Stephens, Sutton, Tom Green,
Travis, Throckmorton, Waller, Washington, Victoria, Wharton, and
Williamson Counties, Texas, that should be included in the designation
because they (1) 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 (2) are unoccupied at the time of listing and are essential for the
conservation of the species;
(d) 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
(e) What areas not occupied at the time of listing are essential
for the conservation of the species. We particularly seek comments:
(i) Regarding whether occupied areas are inadequate for the
conservation of the species;
(ii) Providing specific information that supports the determination
that unoccupied areas will, 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; and
(iii) Explaining whether or not unoccupied areas fall within the
definition of ``habitat'' at 50 CFR 424.02 and why.
(8) Land use designations and current or planned activities in the
subject areas and their possible impacts on proposed critical habitat.
(9) 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.
(10) 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.
(11) 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 credible information regarding the
existence of a meaningful economic or other relevant impact supporting
a benefit of exclusion.
(12) 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, will not be considered in
making a determination, as 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.''
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="http://www.regulations.gov">http://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="http://www.regulations.gov">http://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="http://www.regulations.gov">http://www.regulations.gov</a>.

Public Hearing

We have scheduled two public informational meetings and public
hearings on this proposed rule to list the Central Texas mussels as
endangered or threatened species with critical habitat. We will hold
the public informational meetings and public hearings on the date and
at the times listed above under Public informational meeting and public
hearing in DATES. We are holding the public informational meetings and
public hearings via the Zoom online video platform and via
teleconference so that participants can attend remotely. For security
purposes, registration is required. 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, you must register. 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/southwest/">https://www.fws.gov/southwest/</a>. Registrants will receive the Zoom link
and the telephone number for the public informational meetings and
public hearings. 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 meetings and public
hearings.
The public hearings will provide interested parties an opportunity
to present verbal testimony (formal, oral comments) regarding this
proposed rule. While the public informational meetings will be
opportunities for dialogue with the Service, the public hearings are
not: They are 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 hearings must register
before the hearing (<a href="https://www.fws.gov/southwest/">https://www.fws.gov/southwest/</a>). The use of a
virtual public hearing is consistent with our regulations at 50 CFR
424.16(c)(3).

Previous Federal Actions

Table 1, below, summarizes the petition history and proposed status
of the Central Texas mussels under the Endangered Species Act. On June
25, 2007, we received a formal petition dated June 18, 2007, from
Forest Guardians (now WildEarth Guardians), for 475 species in the
southwestern United States. The petitioned group of species included
the Texas fatmucket.
On October 15, 2008, we received a petition dated October 9, 2008,
from WildEarth Guardians, requesting that the Service list as
threatened or endangered and designate critical habitat for six species
of freshwater mussels, including the Texas pimpleback, Texas fawnsfoot,
and false spike.
On December 15, 2009, we published our 90-day finding that the
above petitions presented substantial scientific information indicating
that listing the Texas fatmucket, Texas pimpleback, Texas fawnsfoot,
and false spike may be warranted (74 FR 66260). As a result of

[[Page 47919]]

the finding, we initiated status reviews for these four species. On
October 6, 2011, we published a 12-month finding for five Texas
mussels, including the Texas fatmucket, Texas fawnsfoot, and Texas
pimpleback, that listing was warranted but precluded by higher priority
actions, and these species were added to the candidate list (76 FR
62166). Candidates are those fish, wildlife, and plants for which we
have on file sufficient information on biological vulnerability and
threats to support preparation of a listing proposal, but for which
development of a listing rule is precluded by other higher priority
listing activities. The Texas fatmucket, Texas fawnsfoot, and Texas
pimpleback were included in all of our subsequent annual Candidate
Notices of Review (77 FR 69993, November 21, 2012; 78 FR 70104,
November 22, 2013; 79 FR 72450, December 5, 2014; 80 FR 80584, December
24, 2015; 81 FR 87246, December 2, 2016; and 84 FR 54732, October 10,
2019).
The distribution of the newly described Guadalupe orb was
previously fully contained within the distribution of the Texas
pimpleback. Genetic information received in 2018 (Burlakova et al.
2018, entire) confirmed that the Guadalupe orb is a separate species
distinct from the Texas pimpleback, and the Guadalupe orb is now a
newly described species. Similarly, the Guadalupe fatmucket was split
from the Texas fatmucket in 2018 (Inoue et al. 2018, entire) and
described in 2019 (Inoue et al. 2019, in press). As both species were
part of the original petitioned entities, we evaluated both of these
new species as well as the four original species in our SSA, and all
six species are included in this proposed rule.
This document constitutes our concurrent 12-month warranted
petition finding for the false spike and proposed listing rule and
proposed critical habitat rule for all six Central Texas mussel
species.

Table 1--List of the Petition Findings for the Six Central Texas Mussels
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Petition received
Scientific name Common name River basins date 90-day finding date 12-month finding date
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Lampsilis bergmanni................ Guadalupe fatmucket... Guadalupe............. Previously included in Texas fatmucket.
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Lampsilis bracteata................ Texas fatmucket....... Colorado.............. June 25, 2007........ December 15, 2009.... October 6, 2011.
Truncilla macrodon................. Texas fawnsfoot....... Trinity, Brazos, October 15, 2008..... December 15, 2009.... October 6, 2011.
Colorado.
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Cyclonaias necki................... Guadalupe orb......... Guadalupe............. Previously included in Texas pimpleback.
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Cyclonaias petrina................. Texas pimpleback...... Colorado.............. October 15, 2008..... December 15, 2009.... October 6, 2011.
Fusconaia mitchelli................ False spike........... Brazos, Colorado, October 15, 2008..... December 15, 2009.... This finding.
Guadalupe.
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I. Proposed Listing Determination

Background

General Mussel Biology

Freshwater mussels, including the six Central Texas mussels, 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 sperm into the water column, which is
taken in by the female through the incurrent siphon (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: Display/mantle 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.

Guadalupe Fatmucket

The Guadalupe fatmucket (Lampsilis bergmanni) was recently
discovered to be a separate and distinct species from Texas fatmucket
(L. bracteata; Inoue et al. 2018, pp. 5-6; Inoue et al. 2019, in
press), and the Service now recognizes the Guadalupe fatmucket as a new

[[Page 47920]]

species that occurs only in the Guadalupe River basin. Because the
Guadalupe fatmucket has recently been split from Texas fatmucket, the
species are very similar, and better information is not yet available,
we believe the Guadalupe fatmucket has similar habitat needs (headwater
habitats in gravel or bedrock fissures) and host fish (sunfishes) as
the Texas fatmucket.
The Guadalupe fatmucket is a small to medium-sized freshwater
mussel (to 4 inches (in) (100 millimeters (mm))) that exhibits sexual
dimorphism and has a yellow-green-tan shell, and is similar in
appearance to the Texas fatmucket (a more detailed description of the
Texas fatmucket is found in Howells et al. 2011, pp. 14-16). Related
species in the genus Lampsilis from the southeast United States reach a
maximum age of 13-25 years (Haag and Rypel 2010, pp. 4-6).
Guadalupe fatmucket is currently found in one population, which
occurs in 54 miles (87 km) of the Guadalupe River basin in Kerr and
Kendall Counties, Texas (Randklev et al. 2017, p. 4) (table 2; figure
1). For more information on this population, see the SSA report.

Table 2--Current Guadalupe Fatmucket Population
----------------------------------------------------------------------------------------------------------------
Occupied reach
Population Streams included Counties length (mi Recent collection
(km)) years (numbers)
----------------------------------------------------------------------------------------------------------------
Guadalupe River.................. Guadalupe River; Kerr and Kendall 54 (87) 2018 (22), 2019
North Fork, Co., TX. (shells).
Guadalupe River;
Johnson Creek.
----------------------------------------------------------------------------------------------------------------

BILLING CODE 4333-15-P

[[Page 47921]]

[GRAPHIC] [TIFF OMITTED] TP26AU21.025

Texas Fatmucket

A thorough review of the taxonomy, life history, and ecology of the
Texas fatmucket is presented in the SSA report. Texas fatmucket has
been characterized as a rare Texas endemic (Burlakova et al. 2011a, p.
158) and was originally described as the species Unio bracteatus by
A.A. Gould in 1855 (p. 228) from the ``Llanos River'' in ``Upper''
Texas. The species is currently recognized as Lampsilis bracteata
(Williams et al. 2017, pp. 35, 39). Recently, individuals that had been
known as Texas fatmucket in the Guadalupe River basin were found to be
a new species (Inoue et al. 2019, in press); therefore, the Texas
fatmucket occurs only in the Colorado River basin.
The Texas fatmucket is a small to medium-sized freshwater mussel
(to 4 in (100 mm)) that exhibits sexual dimorphism (males and females
have different shapes) and has a yellow-

[[Page 47922]]

green-tan shell (Howells et al. 2011, pp. 14-16). For a detailed
morphological description see Howells et al. 1996 (p. 61) and Howells
2014 (p. 41).
Host fishes for Texas fatmucket are members of the Family
Centrarchidae (sunfishes) including bluegill (Lepomis macrochirus),
green sunfish (L. cyanellus), Guadalupe bass (Micropterus treculii),
and largemouth bass (M. salmoides) (Howells 1997, p. 257; Johnson et
al. 2012, p. 148; Howells 2014, p. 41; Ford and Oliver 2015, p. 4;
Bonner et al. 2018, p. 9).
Related species can expel conglutinates (packets of glochidia) and
are known to use mantle lures (Barnhart et al. 2008, pp. 377, 380) to
attract sight-feeding fishes that attack and rupture the marsupium
where the glochidia are held, thereby becoming infested by glochidia.
These 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).
Related species in the genus Lampsilis from the southeast United
States reach a maximum age of 13-25 years (Haag and Rypel 2010; pp. 4-
6). Texas fatmucket occur in firm mud, stable sand, and gravel bottoms,
in shallow waters, sometimes in bedrock fissures or among roots of bald
cypress (Taxodium distichum) and other aquatic vegetation (Howells
2014, p. 41). The species typically occurs in free-flowing rivers but
can survive in backwater areas, such as in areas upstream of lowhead
dams (e.g. Llano Park Lake (BioWest, Inc., 2018, pp. 2-3)).
Texas fatmucket currently occur only in the upper reaches of major
tributaries within the Colorado River basin (Randklev et al. 2017, p.
4) in five populations: Lower Elm Creek, upper/middle San Saba River,
Llano River, Pedernales River, and lower Onion Creek (table 3; figure
2). Isolated individuals not considered part of larger functioning
populations have been found in Cherokee Creek, Bluff Creek, and the
North Llano River. For more information on these populations, see the
SSA report.

Table 3--Current Texas Fatmucket Populations
----------------------------------------------------------------------------------------------------------------
Occupied reach Recent collection
Population Streams included Counties length (mi years (number
(km)) collected)
----------------------------------------------------------------------------------------------------------------
Lower Elm Creek.................. Elm Creek.......... Runnels Co., TX.... 12.5 (20) * 2005
2008 (1)
2019 (1)
Upper/Middle San Saba River...... San Saba River..... Menard, Mason, San 62 (100) 2016 (29)
Saba, and 2017 (87)
McCulloch Co., TX. 2017 (71)
Llano River...................... Llano River, South Kimble, Mason, 127 (204) 2016 (72)
Llano River. Llano Co., TX. 2017 (47)
2017 (5)
Pedernales River................. Pedernales River, Gillespie, Hays, 79 (127) 2017 (17)
Live Oak Creek. and Blanco Co., TX.
Lower Onion Creek................ Onion Creek........ Travis Co., TX..... 5 (8) 2010 (3)
2018 (1)
----------------------------------------------------------------------------------------------------------------
* No live animals.

[[Page 47923]]

[GRAPHIC] [TIFF OMITTED] TP26AU21.026

Texas Fawnsfoot

The Texas fawnsfoot was originally described as Unio macrodon 1859
from a location near Rutersville, Fayette County, Texas (Lea 1859, pp.
154-155). Texas fawnsfoot is recognized by the scientific community as
Truncilla macrodon (Williams et al. 2017, pp. 35, 44).
Texas fawnsfoot is a small- to medium-sized (2.4 in (60 mm)) mussel
with an elongate oval shell (Howells 2014, p. 111). For a detailed
description, see Howells et al. 1996 (p. 143) and Howells 2014 (p.
111).
Host fish species are not confirmed for the Texas fawnsfoot, but we
conclude they use freshwater drum (Aplodinotus grunniens; Howells 2014,
p. 111), like other Truncilla species occurring in Texas and elsewhere
(Ford and Oliver 2015, p. 8). Freshwater drum are molluscivorous
(mollusk-eating) and

[[Page 47924]]

become infested with glochidia when they consume gravid female mussels
(Barnhart et al. 2008, p. 373). This strategy of host infestation may
limit population size, as reproductively successful females are
sacrificed (i.e., eaten by freshwater drum). Related species are
bradytictic, brooding larvae over the winter instead of releasing them
immediately (Barnhart et al. 2008, p. 384). Other species in the genus
Truncilla from the Southeast and Midwest reach a maximum age ranging
from 8-18 years (Haag and Rypel 2010, pp. 4-6).
Texas fawnsfoot are found in medium- to large-sized streams and
rivers with flowing waters and mud, sand, and gravel substrates
(Howells 2014, p. 111). Adults are most often found in bank habitats
and occasionally in backwater, riffle, and point bar habitats, with low
to moderate velocities that appear to function as flow refuges during
high flow events (Randklev et al. 2017c, p. 137).
Texas fawnsfoot occurs in the lower reaches of the Colorado and
Brazos Rivers, and in the Trinity River (Randklev et al. 2017b, p. 4)
in seven populations: East Fork Trinity River, Middle Trinity River,
Clear Fork Brazos River, Upper Brazos River, Middle/Lower Brazos River,
San Saba/Colorado Rivers, and Lower Colorado River (table 4; figure 3).
Texas fawnsfoot was historically distributed throughout the Colorado
and Brazos River basins (Howells 2014, pp. 111-112; and reviewed in
Randklev et al. 2017c, pp. 136-137) and in the Trinity River basin
(Randklev et al. 2017b, p. 11). Texas fawnsfoot historically occurred
in, but is now absent from, the Leon River (Popejoy et al. 2016, p.
477). Randklev et al. (2017c, p. 135) surveyed the Llano, San Saba, and
Pedernales Rivers and found neither live individuals nor dead shells of
Texas fawnsfoot. Isolated individuals not considered part of
functioning populations have been found in the Little River. For more
information on Texas fawnsfoot populations, see the SSA report.

Table 4--Current Texas Fawnsfoot Populations
----------------------------------------------------------------------------------------------------------------
Recent
Occupied reach collection
Population Streams included Counties length (mi years
(km)) (numbers)
----------------------------------------------------------------------------------------------------------------
East Fork Trinity River........... East Fork Trinity Kaufman Co., TX...... 12 (19) 2017 (40)
River. 2018 (12)
Middle Trinity River.............. Trinity River........ Navarro, Anderson, 140 (225) 2016--2017
Leon, Houston, and (59)
Madison Co., TX.
Clear Fork Brazos River........... Clear Fork Brazos Shackelford and 13 (21) 2010 (1)
River. Throckmorton Co., TX. 2018 (0)
Upper Brazos River................ Brazos River......... Palo Pinto and Parker 62 (100) 2017 (23)
Co., TX.
Middle/Lower Brazos River......... Brazos River......... McLennan, Falls, 346 (557) 2014 (188)
Robertson, Milam, 2017 (28)
Brazos, Burleson,
Grimes, Washington,
Waller, Austin, and
Fort Bend Co., TX.
San Saba/Colorado Rivers.......... San Saba River, San Saba and Mills 43 (69) 2017 (0)
Colorado River. Co., TX. 2018 (2)
Lower Colorado River.............. Colorado River....... Colorado, Wharton, 109 (175) 2010 (52)
and Matagorda Co., 2015 (10)
TX. 2017 (9)
----------------------------------------------------------------------------------------------------------------

[[Page 47925]]

[GRAPHIC] [TIFF OMITTED] TP26AU21.027

Guadalupe Orb

Burlakova et al. (2018, entire) recently described the Guadalupe
orb (Cyclonaias necki) from the Guadalupe River basin as a separate
species distinct from Texas pimpleback. The Guadalupe orb occurs only
in the Guadalupe basin and is a small-sized mussel with a shell length
that reaches up to 2.5 in (63 mm) (Burlakova et al. 2018, p. 48).
Guadalupe orb shells are thinner and more compressed but otherwise
morphologically similar to the closely related Texas pimpleback. The
posterior ridge is more distinct and prominent, and the umbo is more
compressed than in Texas pimpleback (Burlakova et al. 2018, p. 48).
Individuals collected from the upper Guadalupe River (near Comfort,
Texas) averaged 1.9 in (48 mm) (Bonner et al. 2018, p. 221). Channel
catfish, flathead catfish, and tadpole madtom are host fish for the
Guadalupe

[[Page 47926]]

orb (Dudding et al. 2019, p. 15). Dudding et al. (2019, p. 16)
cautioned that the apparent clumped distribution of Guadalupe orb (and
closely related species) in ``strongholds'' could be related to
observed ongoing declines in native catfishes, including the small and
rare tadpole madtom, a riffle specialist. The best available
information leads us to believe that reproduction, ecological
interactions and habitat requirements of Guadalupe orb are similar to
those of the closely related Texas pimpleback.
The Guadalupe orb occurs only in the Guadalupe River basin in two
separate and isolated populations: The upper Guadalupe River and the
lower Guadalupe River (table 5; figure 4). An isolated individual not
considered part of a functioning population has been found in the
Blanco River, a tributary to the San Marcos River (Johnson et al. 2018,
p. 7). For more information on these populations, see the SSA report.

Table 5--Current Guadalupe Orb Populations
----------------------------------------------------------------------------------------------------------------
Recent
Occupied reach collection
Population Streams included Counties length (mi years
(km)) (numbers)
----------------------------------------------------------------------------------------------------------------
Upper Guadalupe River............. Guadalupe River...... Kerr, Kendall, and 95 (153) 2013 (1)
Comal Co., TX. 2017 (10)
2018 (2)
Lower Guadalupe River............. Guadalupe River, San Caldwell, Guadalupe, 181 (291) 2014-2015
Marcos River. Gonzales, DeWitt, (893)
and Victoria Co., TX. 2017 (41)
----------------------------------------------------------------------------------------------------------------

[[Page 47927]]

[GRAPHIC] [TIFF OMITTED] TP26AU21.028

Texas Pimpleback

The Texas pimpleback was originally described as Unio petrinus from
the ``Llanos River'' in ``Upper'' Texas (Gould 1855, p. 228). The
species is now recognized as Cyclonaias petrina by the scientific
community (Williams et al. 2017, pp. 35, 37). Burlakova et al. (2018,
entire) recently described the Guadalupe orb (C. necki) from the
Guadalupe River basin as a separate species distinct from Texas
pimpleback. Texas pimpleback is now considered to occur only in the
Colorado River basin of Texas. Texas pimpleback is a small- to medium-
sized (up to 4 in (103 mm)) mussel with a moderately inflated, yellow,
brown, or black shell, occasionally with vague green rays or concentric
blotches (Howells 2014, p. 93).
Recent laboratory studies of the closely related Guadalupe orb
suggest that channel catfish (Ictalurus

[[Page 47928]]

punctatus), flathead catfish (Pylodictus olivarus) and tadpole madtom
(Noturus gyrinus) are host fish for Texas pimpleback (Dudding et al.
2019, p. 2). Related species have miniature glochidia and use catfish
as hosts (Barnhart et al. 2008, pp. 373, 379). Additionally, related
species can also produce conglutinates (Barnhart et al. 2008, p. 376)
and tend to exhibit short-term brooding (tachytictia; releasing
glochidia soon after the larvae mature) (Barnhart et al. 2008, p. 384).
Texas pimpleback are reproductively active between April and August
(Randklev et al. 2017c, p. 110). Related species live as long as 15-72
years (Haag and Rypel 2010, p. 10).
Texas pimpleback occurs in the Colorado River basin in five
isolated populations: Concho River, Upper San Saba River, Lower San
Saba River/Colorado River, Llano River, and the Lower Colorado River
(table 6; figure 5). Only the Lower San Saba and Llano River
populations are known to be successfully reproducing. Texas pimpleback
was historically distributed throughout the Colorado River basin
(Howells 2014, pp. 93-94; reviewed in Randklev et al. 2017, pp. 109-
110). For more information on Texas pimpleback populations, see the SSA
report.

Table 6-- Current Texas Pimpleback Populations
----------------------------------------------------------------------------------------------------------------
Recent
Occupied reach collection
Population Streams included Counties length (mi years
(km)) (numbers)
----------------------------------------------------------------------------------------------------------------
Concho River...................... Concho River......... Concho Co., TX....... 14 (23) 2008 (47)
2012 (1)
Upper San Saba River.............. San Saba River....... Menard Co., TX....... 30 (48) 2017 (1)
Lower San Saba/Colorado Rivers.... San Saba River, San Saba, McCulloch, 178 (286) 2012 (247)
Colorado River. Mills, Brown, and 2014 (481)
Coleman Co., TX. 2017 (97)
2018 (42)
Llano River....................... Llano River.......... Mason Co., TX........ 5 (8) 2012 (10)
2016 (1)
2017 (23)
Lower Colorado River.............. Colorado River....... Colorado and Wharton 98 (158) 2014 (49)
Co., TX. 2017 (8)
2018 (30)
----------------------------------------------------------------------------------------------------------------

[[Page 47929]]

[GRAPHIC] [TIFF OMITTED] TP26AU21.029

False Spike

The false spike is native to the Brazos, Colorado, and Guadalupe
basins in central Texas (Howells 2010, p. 4; Randklev et al. 2017c, p.
12). It was thought to have historically occurred in the Rio Grande
based on the presence of fossil and subfossil shells there (Howells
2010, p. 4), but those specimens have now been attributed to
Sphenonaias taumilapana Conrad 1855 (no common name; Randklev et al.
2017c, p. 12; Graf and Cummings 2007, p. 309).
The false spike was originally described as Unio mitchelli by
Charles T. Simpson in 1895 from the Guadalupe River in Victoria County,
Texas (Dall 1896, pp. 5-6). The species has been assigned as
Quincuncina mitchelli by Turgeon et al. (1988, p. 33) and was
recognized as such by Howells et al. (1996, p. 127), and it was
referenced as Quadrula mitchelli by Haag (2012, p.

[[Page 47930]]

71). Finally, it was recognized as Fusconaia mitchelli, its current
nomenclature, by Pfeiffer et al. (2016, p. 289). False spike is
considered a valid taxon by the scientific community (Williams et al.
2017, pp. 35, 39).
The false spike is a medium-sized freshwater mussel (to 5.2 in (132
mm)) with a yellow-green to brown or black elongate shell, sometimes
with greenish rays. For a detailed description see Howells et al. 1996
(pp. 127-128) and Howells 2014 (p. 85).
Based on closely related species, false spike likely brood eggs and
larvae from early spring to late summer and host fish are expected to
be minnows (family Cyprinidae) (Pfeiffer et al. 2016, p. 287).
Confirmed host fish for false spike include blacktail shiner
(Cyprinella venusta) and red shiner (C. lutrensis; Dudding et al. 2019,
p. 16).
Related species in the genus Fusconaia from the southeast United
States are reach a maximum age of 15-51 years (Haag and Rypel 2010, pp.
4-6). No information on age at maturity currently exists for false
spike (Howells 2010d, p. 3). In part because of their long lifespan and
episodic recruitment strategy, populations may be slow to recover from
disturbance.
False spike occur in larger creeks and rivers with sand, gravel, or
cobble substrates, and in areas with slow to moderate flows. The
species is not known from impoundments, nor from deep waters (Howells
2014, p. 85).
False spike was once considered common wherever it was found;
however, beginning in the early 1970s, the species began to be regarded
as rare throughout its range, based on collection information (Strecker
1931, pp. 18-19; Randklev et al. 2017c, p. 13). It was considered to be
extinct until 2011, when the discovery of seven live false spike in the
Guadalupe River, near Gonzales, Texas, was the first report of living
individuals in nearly four decades (Howells 2010d, p. 4; Randklev et
al. 2011, p. 17). Dudding et al. (2019, pp. 16-17) cautioned that the
patchy distribution of false spike could be related to host fish
relationships; that is, because their host fish have a small home
range, limited dispersal ability, and are sensitive to human impacts,
distribution of false spike could be limited by access to, and movement
of, host fish.
Currently, the false spike occurs in four populations: In the
Little River and some tributaries (Brazos River basin), the lower San
Saba and Llano Rivers (Colorado River basin), and in the lower
Guadalupe River (Guadalupe River Basin) (table 7; figure 6). For more
information on these populations, see the SSA report. False spike is
presumed to have been extirpated from the remainder of its historical
range throughout the Brazos, Colorado, and Guadalupe Basins of central
Texas (reviewed in Randklev et al. 2017c, pp. 12-13).

Table 7--Current False Spike Populations
----------------------------------------------------------------------------------------------------------------
Recent
Occupied reach collection
Population Streams included Counties length (mi years (number
(km)) collected)
----------------------------------------------------------------------------------------------------------------
Little River and tributaries...... Little River......... Milam and Williamson 41 (66) 2015 (29)
Brushy Creek, San Co., TX.
Gabriel River.
Lower San Saba River.............. San Saba River....... San Saba Co., TX..... 42 (67) 2012 (3)
Llano River....................... Llano River.......... Mason Co., TX........ <1 (~1) 2017 (1)
Lower Guadalupe River............. Guadalupe River...... Gonzales, DeWitt, and 102 (164) 2014-2015
Victoria Co., TX. (652)
----------------------------------------------------------------------------------------------------------------

[[Page 47931]]

[GRAPHIC] [TIFF OMITTED] TP26AU21.030

BILLING CODE 4333-15-C

Regulatory and Analytical Framework

Regulatory Framework

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 is an ``endangered species'' or a ``threatened
species.'' 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:

[[Page 47932]]

(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 (e.g. conservation measures).
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 status review for the Guadalupe fatmucket, Texas fatmucket,
Texas fawnsfoot, Guadalupe orb, Texas pimpleback, and false spike,
including an assessment of the potential stressors to each species. The
SSA report does not represent a decision by the Service on whether the
species should be proposed for listing as endangered or threatened
species under the Act. The SSA report provides the scientific basis
that informs our regulatory decision, which involves 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-2019-0061 on <a href="http://www.regulations.gov">http://www.regulations.gov</a>.
To assess the viability of the six Central Texas mussels, 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 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 individual species' life-history
needs. The next stage involved an assessment of the historical and
current condition of the 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 the species' responses to positive and negative
environmental and anthropogenic influences. This process 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 conditions, in order to assess the species'
overall viability and the risks to that viability.
Using various timeframes and the current and projected future
resiliency, redundancy, and representation, we describe the species'
levels of viability over time. For the Central Texas mussels to
maintain viability, their populations or some portion thereof must be
resilient. A number of factors influence the resiliency of Central
Texas mussel populations, including occupied stream length, abundance,
and recruitment. While some of the six species have life-history
adaptations that help them tolerate dewatering and other stressors to
some extent, each of these stressors diminishes the resiliency of
populations to some degree and especially in combination. Elements of
the species' habitat that determine whether Central Texas mussel
populations can grow to maximize habitat occupancy influence those
factors, thereby increasing the resiliency of populations. These

[[Page 47933]]

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
Central Texas mussel species, are found in aggregations, called mussel
beds, that vary in size from about 50 to >5,000 square meters (m\2\),
separated by stream reaches in which mussels are absent or rare (Vaughn
2012, p. 2). We define a mussel population at a larger scale than a
single 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
entirety of the population's occupied reach. Therefore, resilient
mussel populations must occupy stream reaches long enough such that
stochastic events that affect individual mussel beds do not eliminate
the entire population. Repopulation by infested fish from other mussel
beds within the reach can allow the population to recover from these
events. We consider populations extending more than 50 miles (80
kilometers (km)) to be highly resilient to stochastic events because a
single event is unlikely to affect the entire population. Populations
occupying reaches between 20 and 49 river miles (32-79 km) have some
resiliency to stochastic events, and populations occupying reaches less
than 20 miles (32 km) have little resiliency. Note that, by definition,
an extirpated or functionally extirpated population occupies a stream
length of approximately (or approaching) zero miles (0 km).
Abundance: 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 Central Texas mussel species to be healthy (i.e.,
resilient), there must be many mussel beds of sufficient density such
that local stochastic events do not necessarily eliminate the bed(s),
allowing the mussel bed and the overall local population within a
stream reach to recover from any single event. Mussel abundance is
indicated by the number of individuals found during a sampling event;
mussel surveys rarely represent a complete census of the population.
Instead, density is estimated by the number found during a survey event
using various statistical techniques. Because we do not have population
estimates for most populations of Central Texas mussels, nor are the
techniques directly comparable (i.e., same area size searched, similar
search time, etc.), we used the number of individuals captured as an
index over time, presuming relatively similar levels of effort. While
we cannot precisely determine population abundance at the sites using
these numbers, we are able to determine if the species is dominant at
the site or rare and examine this over time if those data are
available.
Reproduction: Resilient Central Texas mussel populations must also
be reproducing and recruiting young individuals into the population.
Population size and abundance reflects previous influences on the
population and habitat, while reproduction and recruitment reflect
population trends that 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, as there are few young individuals to sustain the population
over time (i.e., death rates exceed birth rates and subsequent
recruitment of reproductive adults resulting in negative population
growth). Conversely, a population that is less dense but has many young
and/or gravid individuals may likely grow to a higher density in the
future (i.e., birth rates and subsequent recruitment of reproductive
adults exceeds 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 for these species involves tactile searches and mussels <35 mm
are very difficult to detect (Strayer and Smith 2003, pp. 47-48).
Evidence of reproduction is demonstrated by repeated captures of
small-sized individuals (juveniles and subadults near the low end of
the detectable range size ~35 mm; Randklev et al. 2013, p. 9) over time
and by observing gravid (with eggs in the marsupium, gills, or gill
pouches) females during the reproductively active time of year. While
small-sized mussels and gravid females can be difficult to detect, it
is important that surveyors attempt to detect them as reproduction and
subsequent recruitment are important demographic parameters that affect
growth rates in mussel populations (Berg et al. 2008, pp. 396, 398-399;
Matter et al. 2013, pp. 122-123, 134-135).

Risk Factors for the Central Texas Mussels

We reviewed the potential risk factors (i.e., threats, stressors)
that could be affecting the six Central Texas mussels 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. Those
risks that are not known to have effects on Central Texas mussel
populations, such as disease, are not discussed here but are evaluated
in the SSA report. Many of the threats and risk factors are the same or
similar for each of the six species. Where the effects are expected to
be similar, we present one discussion that applies to all six species.
Where the effects may be unique or different to one species, we will
address that specifically. The primary risk factors (i.e., threats)
affecting the status of the Central Texas mussels are: (1) Increased
fine sediment (Factor A from the Act), (2) changes in water quality
(Factor A), (3) altered hydrology in the form of inundation (Factor A),
(4) altered hydrology in the form of loss of flow and scour of
substrate (Factor A), (5) predation and collection (Factor C), and (6)
barriers to fish movement (Factor E). These factors are all exacerbated
by the ongoing and expected effects of climate change. Finally, we also
reviewed the conservation efforts being undertaken for the species.
Increased Fine Sediment
Juvenile and adult Central Texas mussels inhabit microsites that
have abundant interstitial spaces, or small openings in an otherwise
closed matrix of substrate, created by gravel, cobble, boulders,
bedrock crevices, tree roots, and other vegetation. Inhabited
interstitial spaces have some amount of fine sediment (i.e., clay and
silt) necessary to provide appropriate shelter. However, excessive
amounts of fine sediments can reduce the number of appropriate
microsites in an otherwise suitable mussel bed by filling in these
interstitial spaces and can smother mussels in place. All six species
of Central Texas mussels generally require stable substrates, and loose
silt deposits do not generally provide for substrate stability that can
support mussels. Interstitial spaces provide essential habitat for
juvenile mussels. Juvenile freshwater mussels burrow into interstitial
substrates, making them particularly susceptible to degradation of this
habitat feature. When clogged with sand or silt, interstitial flow may
become reduced (Brim Box and Mossa 1999, p. 100), thus reducing
juvenile habitat availability and quality. While adult mussels can be
physically buried by excessive sediment, ``the main impacts of excess
sedimentation on unionids (freshwater mussels) are often sublethal''
and include interference with feeding mediated by valve closure (Brim
Box

[[Page 47934]]

and Mossa 1999, p. 101). Many land use activities can result in
excessive erosion, sediment production, and channel instability,
including, but not limited to: logging, crop farming, ranching, mining,
and urbanization (Brim Box and Mossa 1999, p. 102).
Under a natural flow regime, a stream's sediment load is in
equilibrium such that as sediments are naturally moved downstream from
one microsite to another, the amount of sediment in the substrate is
relatively stable, given that different reaches within a river or
stream may be aggrading (gaining) or degrading (losing) sediment (Poff
et al. 1997, pp. 770-772). Current and past human activities result in
enhanced sedimentation in river systems, and legacy sediment, resulting
from past land disturbance and reservoir construction, continues to
persist and influence river processes and sediment dynamics (Wohl 2015,
p. 31) and these legacy effects can degrade mussel habitats. Fine
sediments collect on the streambed and in crevices during low flow
events, and much of the sediment is washed downstream during high flow
events (also known as cleansing flows) and deposited elsewhere.
However, increased frequency of low flow events (from groundwater
extraction, instream surface flow diversions, and drought) combined
with a decrease in cleansing flows (from reservoir management and
drought) causes sediment to accumulate. Sediments deposited by large-
scale flooding or other disturbance may persist for several years until
adequate cleansing flows can redistribute that sediment downstream.
When water velocity decreases, which can occur 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.
In the range of the Central Texas mussels, these sources include
streambank erosion from development, agricultural activities, livestock
and wildlife grazing and browsing, 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 are long
lasting and can result in hydrological alterations as increased
impervious cover increases runoff and resulting shear stress causes
streambank instability and additional sedimentation.
All populations of Central Texas mussels face the risk of fine
sediment accumulation to varying degrees. Multiple populations of the
six Central Texas mussel species are experiencing increased
sedimentation, including in particular the Clear Fork Brazos River
(Texas fawnsfoot), middle and lower Brazos River (false spike and Texas
fawnsfoot), and lower Colorado River (Texas pimpleback, Texas
fawnsfoot). In the future, we expect sediment deposition to continue to
increase across the range of all six species due to low water levels
and decreasing frequency of cleansing flows at all populations and for
longer periods due to climate change and additional human development
in the watershed.
Changes in Water Quality
Freshwater mussels and their host fish require water in sufficient
quantity and quality on a consistent basis to complete their life
cycles. Urban growth and other anthropogenic activities across Texas
are placing increased demands on limited freshwater resources that, in
turn, can have deleterious effects on water quality. Water quality can
be degraded through contamination or alteration of water chemistry.
Chemical contaminants are ubiquitous throughout the environment and are
a major reason for the current declining status of freshwater mussel
species nationwide (Augspurger et al. 2007, p. 2025). Immature mussels
(i.e., 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).
Chemicals enter the environment through both point and nonpoint
source discharges, including hazardous spills, industrial wastewater,
municipal effluents, and agricultural runoff. These sources contribute
organic compounds, trace metals, pesticides, and a wide variety of
newly emerging contaminants (e.g., pharmaceuticals) that comprise some
85,000 chemicals in commerce today that are released to the aquatic
environment (Environmental Protection Agency (EPA) 2018, p. 1). The
extent to which environmental contaminants adversely affect aquatic
biota can vary depending on many variables such as concentration,
volume, and timing of the release. Species diversity and abundance
consistently ranks lower in waters that are polluted or otherwise
impaired by contaminants. Freshwater mussels are not generally found
for many miles downstream of municipal wastewater treatment plants
(Gillis et al. 2017, p. 460; Goudreau et al. 1993, p. 211; Horne and
McIntosh 1979, p. 119). For example, transplanted common freshwater
mussels (including threeridge (Amblema plicata) and the nonnative Asian
clam (Corbicula fluminea) showed reduced growth and survival below a
wastewater treatment plant (WWTP) outfall relative to sites located
upstream of the WWTP in Wilbarger Creek (a tributary to the Colorado
River in Travis County, Texas); water chemistry was altered by the
wastewater flows at downstream sites, with elevated constituents in the
water column that included copper, potassium, magnesium, and zinc
(Duncan and Nobles 2012, p. 8; Nobles and Zhang 2015, p. 11).
Contaminants released during hazardous spills are also of concern.
Although spills are relatively short-term localized events, depending
on the types of substances and volume released, water resources nearby
can be severely impacted and degraded for years following an incident.
Ammonia is of particular concern below wastewater treatment plants
because freshwater mussels are particularly sensitive to increased
ammonia levels (Augspurger et al. 2003, p. 2569). Elevated
concentrations of un-ionized ammonia (NH<INF>3</INF>) in the
interstitial spaces of benthic habitats (>0.2 parts per billion) have
been implicated in the reproductive failure of other freshwater mussel
populations (Strayer and Malcom 2012, pp. 1787-1788), and sublethal
effects (valve closures) have recently been described as total ammonia
nitrogen approaches 2.0 milligrams per liter (mg/L = ppm; Bonner et al.
2018, p. 186). Immature mussels (i.e., juveniles and glochidia) are
especially sensitive to water quality degradation and contaminants,
including ammonia (Wang et al. 2007, p. 2055). For smooth pimpleback
(Cyclonaias houstonensis, a species native to central Texas but not
included in this listing), the revised EPA ammonia benchmarks are
sufficient to protect from short term effects of ammonia on the
species' physiological processes (Bonner et al. 2018, p. 151). However,
the long-term effects of chronic exposure (i.e., years or decades) to
freshwater mussels has yet to be experimentally investigated.
Municipal wastewater contains both ionized and un-ionized ammonia,
and wastewater discharge permits issued by Texas Commission on
Environmental

[[Page 47935]]

Quality (TCEQ) do not always impose limits on ammonia, particularly for
smaller volume dischargers. Therefore, at a minimum, concentrations of
ammonia are likely to be elevated in the immediate mixing zone of some
WWTP outfalls. To give some insight into the potential scope of WWTP
related impacts, approximately 480 discharge permits are issued for the
Brazos River watershed alone from its headwaters above Possum Kingdom
Lake down to the Gulf of Mexico (TCEQ 2018c, entire). In addition, some
industrial permits, such as animal processing facilities, have ammonia
limits in the range of 3 to 4 mg/L or higher, which exceeds levels that
inhibited growth in juvenile fatmucket (Lampsilis siliquoidea) and
rainbow mussel (Villosa iris) (Wang et al. 2007, entire). Similar to
the Brazos River, WWTP outfalls are numerous throughout the ranges of
the Central Texas mussels.
An additional type of water quality degradation that affects the
Central Texas mussels is alteration of water quality parameters such as
dissolved oxygen, temperature, and salinity levels. Dissolved oxygen
levels may be reduced from increased nutrient inputs or other sources
of organic matter that increase the biochemical oxygen demand in the
water column as microorganisms decompose waste. Organic waste can
originate from storm water or irrigation runoff or wastewater effluent,
and juvenile mussels seem to be particularly sensitive to low dissolved
oxygen (with sublethal effects evident at 2 ppm and lethal effects
evident at 1.3 ppm; Sparks and Strayer 1998, pp. 132-133). Increased
water temperature (over 30 [deg]C and approaching 40 [deg]C) from
climate change and from low flows during drought can exacerbate low
dissolved oxygen levels in addition to other drought-related effects on
both juvenile and adult mussels (Sparks and Strayer 1998, pp. 132-133).
Finally, high salinity concentrations are an additional concern in
certain watersheds, where dissolved salts can be particularly limiting
to Central Texas mussels. Upper portions of the Brazos and Colorado
Rivers, originating from the Texas High Plains, contain saline water,
sourced from both natural geological formations, and from oil and gas
development. Salinity in river water is diluted by surface flow and as
surface flow decreases salt concentrations increase, resulting in
adverse effects to freshwater mussels. Even low levels of salinity (2-4
parts per thousand (ppt)) have been demonstrated to have substantial
negative effects on reproductive success, metabolic rates, and survival
of freshwater mussels (Blakeslee et al. 2013, p. 2853). Bonner et al.
(2018, pp. 155-156) suggest that the behavioral response of valve
closure to high salinity concentrations (>2 ppt) is the likely
mechanism for reduced metabolic rates, reduced feeding, and reduced
reproductive success based on reported sublethal effects of salinity >2
ppt for Texas pimpleback.
Water quality and quantity are interdependent, so reductions in
surface flow from drought, instream diversion, and groundwater
extraction serve to concentrate contaminants by reducing flows that
would otherwise dilute point and non-point source pollution. For
example, salinity inherently poses a greater risk to aquatic biota
under low flow conditions as salinity concentrations and water
temperatures increase. Drought conditions can place additional
stressors on stream systems beyond reduced flow by exacerbating
contaminant-related effects to aquatic biota, including Central Texas
mussels. Not only can temperature be a biological, physical, and
chemical stressor, the toxicity of many pollutants to aquatic organisms
increases at higher temperatures (e.g., ammonia, mercury). We foresee
threats to water quality increasing into the future as demand and
competition for limited water resources grows.
Altered Hydrology--Inundation
Central Texas mussels are adapted to flowing water (lotic habitats)
rather than standing water (lentic habitats) and require free-flowing
water to survive. Low flow events (including stream drying) and
inundation can eliminate habitat appropriate for Central Texas mussels,
and while these species can survive these events for a short duration,
populations that experience prolonged drying events or repeated drying
events will not persist over time.
Inundation has primarily occurred upstream of dams, both large
(such as the Highland Lakes on the Colorado River and other major flood
control and water supply reservoirs) and small (low water crossings and
diversion dams typical of the tributaries and occurring usually on
privately owned lands throughout Central Texas). Inundation causes an
increase in sediment deposition, eliminating the crevices that many
Central Texas mussel species inhabit. Inundation also includes the
effects of reservoir releases where frequent variation in surface water
elevation acts to make habitats unsuitable for Central Texas mussels.
In large reservoirs, deep water is very cold and often devoid of oxygen
and necessary nutrients. Cold water (less than 11 [deg]Celsius (C) or
52 [deg]F (F)) stunts mussel growth and delays or hinders spawning. The
Central Texas mussels do not tolerate inundation under large
reservoirs. Further, deep-water reservoirs with bottom release (like
Canyon Reservoir) can affect water temperatures several miles
downriver. The water temperature remains below 21.1 [deg]C for the
first 3.9 miles (6.3 km) of the 13.8-mile (22.2-km) Canyon Reservoir
tailrace (Texas Parks and Wildlife Department (TPWD) 2007c, p. ii),
cold enough to support a recreational non-native rainbow and brown
trout fishery.
The construction of dams, inundation of reservoirs, and management
of water releases have significant effects on the natural hydrology of
a river or stream. For example, dams trap sediment in reservoirs, and
managed releases typically do not conform to the natural flow regime
(i.e., higher baseflows, and peak flows of reduced intensity but longer
duration). Rivers transport not only water but also sediment, which is
transported mostly as suspended load (held by the water column), and
most sediment transport occurs during floods as sediment transport
increases as a power function (greater than linear) of flow (Kondolf
1997, p. 533). It follows that increased severity of flooding would
result in greater sediment transport, with important effects on
substrate stability and benthic habitats for freshwater mussels and
other organisms dependent on stable benthic habitats. Further, water
released by dams is usually clear and does not carry a sediment load
and is considered ``hungry water because the excess energy is typically
expended on erosion of the channel bed and banks . . . resulting in
incision (downcutting of the bed) and coarsening of the bed material
until a new equilibrium is reached'' (Kondolf 1997, p. 535).
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 flood-control, water-supply, and recreation reservoirs
results in altered hydrologic regimes, including an attenuation of both
high- and low-flow events. Flood-control dams store floodwaters and
then release them in a controlled manner; this extended release of
flood waters can result in significant scour and loss of substrates
that provide mussel habitat. Along with this change in the flow of
water, sediment dynamics are affected as sediment is trapped above and
scoured below major impoundments. These changes in water and sediment
transport

[[Page 47936]]

have negatively affected freshwater mussels and their habitats.
There are numerous dams throughout the range of Central Texas
mussels. There are now 27 major reservoirs in the Brazos River basin
(16 have >50,000 acre-feet of storage) (Brazos River and Associated Bay
Estuary System Basin and Bay Expert Science Team (BBEST) 2012, p. 33);
31 major reservoirs in the Colorado River basin, including the Highland
Lakes (Texas Water Development Board (TWDB) 2018d, p. 1); 9 major
reservoirs on the Guadalupe River (BBEST 2011b, p. 2.2); and 31 major
reservoirs in the Trinity River basin (BBEST 2009, p. 10). These
reservoirs, subsequent inundation, and resulting fragmentation of
mussel populations has been the primary driver of the current
distribution of the Central Texas mussels. Additional reservoirs are
planned for the future, including the Cedar Ridge Reservoir, proposed
by the City of Abilene on the Clear Fork of the Brazos River near the
town of Lueders, Texas (83 FR 16061), and more than one reservoir is
proposed to be built off the main channel of the Lower Colorado River
in Wharton and Colorado Counties, Texas (Lower Colorado River Authority
(LCRA) 2018c, p. 1). The Allens Creek Reservoir is proposed for
construction on Allens Creek near the City of Wallis, to provide water
supply and storage for the City of Houston (Brazos River Authority
(BRA) 2018b, p. 1). Water that is planned to be pumped from the Brazos
River during high flows will be stored and released back into the river
to meet downstream needs during periods of low flow.
Altered Hydrology--Flow Loss and Scour
Extreme water levels--both low flows and high flows--threaten
population persistence of the Central Texas mussels. The effects of
population losses associated with excessively low flows are compounded
by population losses associated with excessively high flows. Whereas
persistent low flow during times of drought results in drying of mussel
habitats and desiccation of exposed mussels, rapid increases in flows
associated with large-scale rain events and subsequent flooding results
in scour of the streambed and physical displacement of mussels and
appropriate substrates. Appropriately-sized substrates are moved during
scouring high flow events and mussels are transported downstream to
inappropriate sites or are buried by inappropriately sized materials.
The Central Texas mussels are experiencing a repeating cycle of
alternating droughts and flooding that, in combination with
hydrological alterations, threatens population persistence.
Droughts that have occurred in the recent past have led to
extremely low flows in several Central Texas rivers. Many of these
rivers have some resiliency to drought because they are spring-fed
(Colorado River tributaries, Guadalupe River), are very large (lower
Brazos and Colorado Rivers), or have significant return flows (Trinity
River), but drought in combination with increased groundwater pumping
may lead to lower river flows of longer duration than have been
recorded in the past. Reservoir releases can be managed to some extent
during drought conditions to prevent complete dewatering below many
major reservoirs. During the months of July and August 2018, the Clear
Fork Brazos, Concho, San Saba, Llano, Pedernales, and upper Colorado
and upper Guadalupe Rivers all had very low flows (U.S. Geological
Survey (USGS) 2019).
Streamflow in the Colorado River above the Highland Lakes and
downstream of the confluence with Concho River has been declining since
the 1960s as evidenced by annual daily mean streamflow (USGS 2008b, pp.
812, 814, 848, 870, 878, 880), and overall river discharge for each of
the rivers can be expected to continue to decline due to increased
drought as a result of climate change, absent significant return flows.
There are a few exceptions including the Llano River at Llano (USGS
2008b, p. 892), Pedernales River at Fredericksburg (USGS 2008b, p.
896), Onion Creek near Driftwood, and Onion Creek at Highway 183 (flows
appear to become more erratic, characteristic of a developing
watershed; USGS 2008b, pp. 930, 946). In the San Saba River, continuing
or increasing surface and alluvial aquifer groundwater withdrawals in
combination with drought is likely to result in reduced streamflow,
affecting mussels in the future (Randklev et al. 2017c, pp. 10-11).
Flows have declined due to drought in the Brazos River in recent
years upstream of Lake Whitney (USGS 2008b, pp. 578, 600, 626, 638; BRA
2018e, p. 6), although baseflows are maintained somewhat due to
releases from Lake Granbury and other reservoirs in the upper basin
(USGS 2008b, p. 644; BRA 2018e, p. 6). In the middle Brazos, U.S. Army
Corps of Engineers (USACE) dams have reduced the magnitude of floods on
the mainstem of the Brazos River downstream of Lake Whitney (USGS
2008b, pp. 652, 676 766, 776; BRA 2018e, p. 6), while flows in the
lower Brazos and Navasota Rivers appear to have higher baseflows due to
water supply operations in the upper basin that deliver to downstream
users (USGS 2008b, pp. 754, 766, 776; BRA 2018e, p. 6). Lake Limestone
releases also appear to be contributing to higher base flows in the
Lower Brazos (BRA 2018e, p. 6). Flows have declined in the upper
Guadalupe River (USGS 2008b, pp. 992, 994, 1000, 1018) but appear
relatively unchanged at Comfort and Spring Branch and in the San Marcos
River (USGS 2008b, pp. 1004, 1006, 1022), and in the lower Guadalupe
River (USGS 2008b, pp. 1036, 1040). In the lower sections of the
Colorado River, lower flows and reduced high flow events are more
common now decades after major reservoirs were constructed (USGS 2008b,
pp. 964, 966). In the Trinity River, low flows are higher (elevated
baseflows) than they were in the past (USGS 2008b, pp. 370, 398, 400,
430) because of substantial return flows from Dallas area wastewater
treatment plants.
Many of the tributary streams (i.e., Concho, San Saba, Llano, and
Pedernales Rivers) historically received significant groundwater inputs
from multiple springs associated with the Edwards and other aquifers.
As spring flows decline due to drought or groundwater lowering from
pumping, habitat for Central Texas mussels in the tributary streams is
reduced and could eventually cease to exist (Randklev et al. 2018, pp.
13-14). While Central Texas mussels may survive short periods of low
flow, as low flows persist, mussels face oxygen deprivation, increased
water temperature, increased predation risk, and ultimately stranding,
all reducing survivorship, reproduction, and recruitment in the
population.
Low-flow events lead to increased risk of desiccation (physical
stranding and drying) and exposure to elevated water temperature and
other water quality degradations, such as contaminants, as well as to
predation. For example, sections of the San Saba River, downstream of
Menard, Texas, experienced very low flows during the summer of 2015,
which led to dewatering of occupied habitats as evidenced by
observations of recent dead shell material of Texas pimpleback and
Texas fatmucket (TPWD 2015, pp. 2-3; described in detail by Randklev et
al. 2018, entire). Several USGS stream gauges reported very low flows
during the 2017-2018 water year, including: the Clear Fork of the
Brazos River, Elm Creek, Concho River at Paint Rock, San Saba River,
Colorado River at San Saba, Llano River, Pedernales River, and upper
Guadalupe River (USGS 2018a, entire). Service, TPWD, and Texas

[[Page 47937]]

Department of Transportation (TxDOT) biologists noted in 2017 that at
one site on the Brazos River near Highbank, Texas, the presence of 42
dead to fresh dead (with tissue intact) Texas fawnsfoot that likely
died as a result of recent drought or scouring events (Tidwell 2017,
entire).
High flow events lead to increased risk of physical removal,
transport, and burial (entrainment) of mussels as unstable substrates
are transported downstream by floodwaters and later redeposited in
locations that may not be suitable. A site in the lower Colorado River
near Altair, Texas, suffered significant changes in both mussel
community structure and bathymetry (measurement of water depths) during
extensive flooding (and resulting high flows) in August 2017, as a
result of Hurricane Harvey (Bonner et al. 2018, p. 266). This site
previously held the highest mussel abundance (Bonner et al. 2018, pp.
242-243) and represented high-quality habitat within the Colorado River
basin, prior to the flooding events. Mussel abundance significantly
decreased by nearly two orders of magnitude (Bonner et al. 2018, p.
266). This location had two of the Central Texas mussel species (Texas
fawnsfoot and Texas pimpleback) present during initial surveys in 2017
(Bonner et al. 2018, p. 242). Widespread flooding was reported in the
Colorado and Guadalupe River basins of Central Texas in October 2018.
The distribution of mussel beds and their habitats is affected by
large floods returning at least once during the typical life span of an
individual mussel (generally from 3 to 30 years). The presence of flow
refuges mediates the effects of these floods, as shear stress is
relatively low in flow refuges and where sediments are relatively
stable, and individual mussels ``must either tolerate high-frequency
disturbances or be eliminated, and can colonize areas that are
infrequently disturbed between events'' (Strayer 1999, pp. 468-469).
Shear stress and relative substrate stability are limiting to mussel
abundance and species richness (Randklev et al. 2017a, p. 7), and
riffle habitats may be more resilient to high flow events than littoral
(bank) habitats.
The Central Texas mussels have historically been, and currently
remain, exposed to extreme hydrological conditions, including severe
drought leading to dewatering, and heavy rains leading to damaging
scour events with movement of mussels and substrate (i.e., ``flash
flooding''). For example, in 2018, over the span of 69 days, the Llano
River near Llano, Texas, experienced extreme low flows (0.08 cfs on
August 8, 2018), and extreme high flows leading to severe flooding,
which resulted in substantial scour of streambed and riparian area
habitats (278,000 cfs on October 16, 2018) (Llano River Watershed
Alliance (LRWA) 2019, entire). Prolonged drought followed by severe
flooding can result in failure and collapse of river banks and
subsequent sedimentation, as demonstrated by slumping and undercutting
on the lower Guadalupe River near Cuero, Texas, in 2015 (Giardino and
Rowley 2016, pp. 70-72), which is occupied by the false spike and
Guadalupe orb. The usual drought/flood cycle in Central Texas can be
characterized by long periods of time absent of rain interrupted by
short periods of heavy rain, resulting in often severe flooding. These
same patterns led to the development of flood control and storage
reservoirs throughout Texas in the twentieth century. It follows that,
given the extreme and variable climate of Central Texas, mussels must
have life-history strategies and other adaptations that allow them to
persist by withstanding severe conditions and repopulating during more
favorable conditions. However, it is also likely that there is a limit
to how the mussels might respond to increasing variability, frequency,
and severity of extreme weather events, combined with habitat
fragmentation and population isolation.
Sediment deposition may arise from human activities, as well. Sand
and gravel can be mined from rivers or from adjacent alluvial deposits,
and instream gravels often require less processing and are thus more
attractive from a business perspective (Kondolf 1997, p. 541). Instream
mining directly affects river habitats, 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 nickpoint, which can contribute to erosion
(and mobilization of substrate) associated with head cutting (Kondolf
1997, p. 541). Off-channel mining of floodplain pits can become
involved during floods, such that the pits become hydrologically
connected and thus can affect sediment dynamics in the stream (Kondolf
1997, p. 545).
Predation and Collection
Predation on freshwater mussels is a natural phenomenon. Raccoons,
muskrats, snapping turtles, wading birds, and fish are known to prey
upon Central Texas mussels. Under natural conditions, the level of
predation occurring within Central Texas mussel populations is not
likely to pose a significant risk to any given population. However,
during periods of low flow, terrestrial predators and wading birds have
increased access to portions of the river that are otherwise too deep
under normal flow conditions. High levels of predation during drought
have been observed on the Llano and San Saba Rivers. As drought and low
flow are predicted to occur more often and for longer periods due to
the effects of future climate change, the Hill Country tributaries (of
the Colorado River) in particular are expected to experience additional
predation pressure into the future, and this may become especially
problematic in the Llano and San Saba Rivers. Predation is expected to
be less of a problem for the lower portions of the mainstem river
populations because the rivers are significantly larger than the
tributary streams and Central Texas mussels are less likely to be found
by predators in exposed or very shallow habitats.
Certain mussel beds within some populations, due to ease of access,
are vulnerable to overcollection and vandalism. These areas, primarily
on the Llano and San Saba Rivers, have well-known and well-documented
mussel beds that have been sampled repeatedly over the past few years
by multiple researchers and others for a variety of projects. Given the
additional stressors aforementioned in this section, these populations
are being put at additional risk due to over-collection and over-
harvest for scientific needs.
Barriers to Fish Movement
Central Texas mussels historically colonized new areas through
movement of infested host fish, as newly metamorphosed juveniles would
excyst from host fish in new locations. Today, the remaining Central
Texas mussel populations are significantly isolated due to habitat
fragmentation by major reservoirs such that recolonization of areas
previously extirpated is extremely unlikely, if not impossible, due to
existing dams creating permanent barriers to host fish movement. There
is currently no opportunity for interaction among any of the extant
Central Texas mussel populations, as they are isolated from one another
by major reservoirs.
The overall distribution of mussels is, in part, a function of host
fish dispersal (Smith 1985, p. 105). There is limited potential for
immigration and emigration between populations other than through the
movement of infected host fish between mussel populations. Small
populations are more affected by this limited immigration potential
because they are susceptible to genetic drift, resulting from random
loss of genetic diversity, and inbreeding

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depression. At the species level, isolated populations that are
eliminated due to stochastic events cannot be recolonized naturally due
to barriers to host fish movement, leading to reduced overall
redundancy and representation.
Many of the Central Texas mussels' known or assumed primary host
fish species are known to be common, widespread species in the Central
Texas river basins. We know that populations of mussels and their host
fish have become fragmented and isolated over time following the
construction of major dams and reservoirs throughout Central Texas. We
do not currently have information demonstrating that the distribution
of host fish is a factor currently limiting Central Texas mussels
distribution. However, a recent study suggested that the currently
restricted distribution of false spike, Guadalupe orb, and other
related species could be related to declining abundance of their host
fish, particularly those fish having small home ranges and specialized
habitat affinities (Dudding et al. 2019, entire). Further research into
the relationships between each of the Central Texas mussel species and
their host fish is needed to more fully examine the possible role of
declining host fish abundance in declining mussel populations.
Effects of Climate Change
Climate change has been documented to have already taken place, and
continued greenhouse gas emissions at or above current rates will cause
further warming (Intergovernmental Panel on Climate Change (IPCC) 2013,
pp. 11-12). Warming in Texas is expected to be greatest in the summer
(Maloney et al. 2014, p. 2236). The number of extremely hot days (high
temperatures exceeding 95 [deg]F) is expected to double by around 2050
(Kinniburgh et al. 2015, p. 83). Western Texas, including portions of
the ranges of the Central Texas mussels, is an area expected to show
greater responsiveness to the effects of climate change (Diffenbaugh et
al. 2008, p. 3). Changes in stream temperatures are expected to reflect
changes in air temperature, at a rate of approximately 0.6-0.8 [deg]C
increase in stream water temperature for every 1 [deg]C increase in air
temperature (Morrill et al. 2005, pp. 1-2, 15) and with implications
for temperature-dependent water quality parameters such as dissolved
oxygen and ammonia toxicity. The Central Texas mussels exist at or near
a climate and habitat gradient in North America, with the eastern
United States having more rainfall and higher freshwater mussel
diversity, and the western United States receiving less rainfall and
having fewer species of freshwater mussels. As such, it is likely that
the Central Texas mussels 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 are small (U.S. Global
Change Research Program (USGCRP) 2017, p. 217), higher temperatures
caused by anthropogenic factors lead to increased soil water deficits
because of higher rates of evapotranspiration. This is likely to result
in increasing drought severity in future climate scenarios just as
``extreme precipitation, one of the controlling factors in flood
statistics, is observed to have generally increased and is projected to
continue to do so across the United States in a warming atmosphere''
(USGCRP 2017, p. 231). Even if precipitation and groundwater recharge
remain at current levels, increased groundwater pumping and resultant
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. 325). Higher temperatures are also expected to
lead to increased evaporative losses from reservoirs, which could
negatively affect downstream releases and flows (Friedrich et al. 2018,
p. 167). Effects of climate change, such as air temperature increases
and an increase in drought frequency and intensity, have been shown to
be occurring throughout the range of Central Texas mussels (USGCRP
2017, p. 188; Andreadis and Lettenmaier 2006, p. 3), and 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 Central Texas
and projects that years like 2011 (the warmest on record) could be
commonplace by the year 2100 (Mullens and McPherson 2017, pp. 3, 6).
This trend toward more frequent drought is attributed to increases in
hot temperatures, and the number of days at or above 100 [deg]F are
projected to ``increase in both consecutive events and the total number
of days'' (Mullens and McPherson 2017, pp. 14-15). Similarly, floods
are projected to become more common and severe because of increases in
the magnitude of extreme precipitation (Mullens and McPherson 2017, p.
20). Recent ``historic'' flooding of the Llano River resulted in the
transport of high levels of silt and debris to Lake Travis, so much so
that the City of Austin's ability to treat raw water was affected and
the City issued a boil water notice and call for water conservation
(City of Austin 2018c, p. 3)
In the analysis of the future condition of the Central Texas
mussels, we considered climate change to be an exacerbating factor,
contributing to the increase of fine sediments, changes in water
quality, loss of flowing water, and predation. Due to the effects of
ongoing climate change (represented by representative concentration
pathway (RCP) 4.5), we expect the frequency and duration of cleansing
flows to decrease, leading to the increase in fine sediments at all
populations. Many populations will experience increased frequency of
low flows. More extreme climate change projections (RCP 8.5 and beyond)
lead to further increases in fine sediment within the populations.
Similarly, as lower water levels concentrate contaminants and cause
unsuitable temperature and dissolved oxygen levels, we expect water
quality to decline to some degree in the future. The SSA report
includes a detailed analysis of the species' responses to both RCP 4.5
and 8.5.
Conservation Actions and Regulatory Mechanisms
Since 2011, when three of the Central Texas mussel species became
candidates for listing under the Endangered Species Act, many agencies,
non-governmental organizations, and other interested parties have been
working to develop voluntary agreements with private landowners to
restore or enhance habitats for fish and wildlife in the region,
including in the watersheds where Central Texas mussels occur. These
agreements provide voluntary conservation including upland habitat
enhancements that will, if executed properly, reduce threats to the
species while improving in-stream physical habitat and water quality,
as well as adjacent riparian and upland habitats. Additionally, as many
as three river authorities are developing (or have already developed)
conservation plans that may lead to candidate conservation agreements
with assurances to benefit one or more species of candidate mussels
(including the Central Texas mussels) in their basins. Because these
plans and agreements are not yet fully drafted and implemented, we are
not considering the conservation actions in our evaluation of the
status of the Central Texas mussels; however, we will evaluate any new
information on these

[[Page 47939]]

actions prior to making our final listing determination for these
species.
Some publicly and privately owned lands in the watersheds occupied
by Central Texas mussels are protected with conservation easements or
are otherwise managed to support populations of native fish, wildlife,
and plant populations. The Natural Resources Conservation Service
(NRCS), along with the Service and State and local partners, are
working with private landowners to develop and implement comprehensive
conservation plans to address soil, water, and wildlife resource
concerns in the lower Colorado River basin through a Working Lands for
Wildlife project (NRCS 2019a, entire).
The Service has been hosting annual mussel research and
coordination meetings to help manage and monitor scientific collection
of mussel populations and encourage collaboration among researchers and
other conservation partners since 2018 (USFWS 2018, p. 1, USFWS 2019a,
p. 1). Additionally, work is under way to evaluate methods of captive
propagation for the Central Texas mussel species at the Service's
hatchery and research facilities (San Marcos Aquatic Research Center,
Inks Dam National Fish Hatchery, and Uvalde National Fish Hatchery),
including efforts to collect gravid females from the wild to infest
host fish (Bonner et al. 2018, pp. 8, 9, 11).

Species Condition

Here we discuss the current 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, increased stream temperatures, and increased
accumulation of fine sediments. In the SSA report, for each species and
population, we developed and assigned condition categories for three
population and three habitat factors that are important for viability
of each species. The condition scores for each factor were then used to
determine an overall condition of each population: healthy, moderately
healthy, unhealthy, or functionally extirpated. 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, and unhealthy populations having the lowest probability
of persistence (between 10 and 60 percent). Functionally extirpated
populations are not expected to persist over 20 years or are already
extirpated.
Guadalupe Fatmucket
Overall, there is one known remaining population of Guadalupe
fatmucket, in the Guadalupe River. Historically, Guadalupe fatmucket
likely occurred through the Guadalupe River basin, but it currently
only occurs in the upper Guadalupe River in an unhealthy population due
to low abundance and little evidence of reproduction and recruitment.
Very few individuals have been found in recent years, and the upper
Guadalupe River in this reach already experiences very low water
levels. These low water events are expected to continue into the
future, and the population will be unlikely to rebound from any
degraded habitat conditions.
Texas Fatmucket
Overall, there are five known remaining populations of Texas
fatmucket, all limited to the headwater reaches of the Colorado River
and its tributaries (see figure 2, above). Historically, most Texas
fatmucket populations were likely connected by fish migration
throughout the Colorado River basin, but due to impoundments and low
water conditions in the Colorado River and tributaries they are
currently isolated from one another, and repopulation of extirpated
locations is unlikely to occur without human assistance. Two of the
current populations are moderately healthy, two are unhealthy, and one
is functionally extirpated.
Lower Elm Creek: The Elm Creek population of Texas fatmucket is
extremely small and isolated. This population will continue to be
threatened by excessive sedimentation and deterioration of substrate,
altered hydrology associated with anthropogenic activities and the
effects of climate change, and water quality degradation. The poor
habitat conditions and only a single individual found at this site more
than a decade ago indicate a population that is unlikely to persist and
may already be extirpated.
Upper/Middle San Saba River: The population of Texas fatmucket in
the upper/middle San Saba River is currently moderately healthy. Most
of the flows in the Upper San Saba River (in Menard County, Texas) are
from Edwards Formation springs, where it gains streamflow from
groundwater except for, and due to a change in the underlying geology,
a reach that loses flow to the aquifer (called a losing reach) near the
Menard/Mason County line (LBG-Guyton 2002, p. 3). It is in this losing
reach where drought effects are especially noticeable, as some flows
may percolate downward to the aquifer. Much of the middle San Saba
River below Menard is reported to have gone dry for 10 of the last 16
years by landowners downstream of Menard (Carollo Engineers 2015, p.
2). Regardless of the cause, low flows in the San Saba River have
resulted in significant stream drying, and stranded Central Texas
mussels have been identified following dewatering as recently as 2015
near and below the losing reach (TPWD 2015, p. 3). During the 2011-2013
drought, stream flows in the San Saba River were critically low, such
that several water rights in Schleicher, Menard, and McCulloch Counties
were suspended by the Texas Commission on Environmental Quality (TCEQ).
These very low flow events are expected to continue into the future and
put the upper/middle San Saba River population of Texas fatmucket at
risk of extirpation. Even if the locations of Texas fatmucket do not
become dry, water quality degradation and increased sedimentation
associated with low flows is expected.
Llano River: The Llano River population of Texas fatmucket is
currently moderately healthy, although there has been limited evidence
that the population is successfully reproducing, and collection of the
species is frequent at this location. We expect flows to continue to
decline and the frequency of extreme flow events to increase, leading
to increased sedimentation and decreased water quality, and scour, and
the population is expected to decline as a result.
Pedernales River: The population of Texas fatmucket in the
Pedernales River is very small and isolated. The Pedernales River is a
flashy system, which experiences extreme high flow events, especially
in the lower reaches in the vicinity of Pedernales Falls State Park and
below. Occasional, intense thunderstorms can dramatically increase
streamflow and mobilize large amounts of silt and organic debris (LCRA
2017, p. 82). The continued increasing frequency of high flow events
combined with the very low abundances in the river result in a
population that is likely to be extirpated and currently is unhealthy.
Onion Creek: Only a single live individual of Texas fatmucket has
been found in Onion Creek since 2010, and we consider this population
to be

[[Page 47940]]

functionally extirpated with little chance of persistence. The upper
reaches of Onion Creek frequently go dry, and several privately owned
low-head in-channel dams currently exist along upper and lower Onion
Creek, which further provide barriers to fish passage and mussel
dispersal, preventing recolonization after low water events. Onion
Creek is in close proximity to the City of Austin, and continued
development in the watershed is expected to continue to degrade habitat
conditions.
Texas Fawnsfoot
There are seven remaining populations of Texas fawnsfoot, in the
Trinity, Brazos, and Colorado River basins. Historically, Texas
fawnsfoot occurred throughout each basin with populations connected by
fish migration within each basin, but due to impoundments and low water
conditions, they are currently isolated from one another, and
repopulation of extirpated locations is unlikely to occur without human
assistance. Four Texas fawnsfoot populations are moderately healthy,
and three are unhealthy.
East Fork Trinity River: The Texas fawnsfoot population in the East
Fork Trinity River occupies a small stream reach (12 mi (19 km)),
making it especially vulnerable to a single stochastic event such as a
spill or flood and changes to water quality. Further, no evidence of
reproduction exists for this population. The population is expected to
decline as a result of the lack of reproduction. This population is
small and isolated from the middle and lower Trinity River population
by unsuitable habitat affected primarily by altered hydrology as flows
from the Dallas-Fort Worth metro area are too flashy to provide
suitable habitat for Texas fawnsfoot. Therefore, this population is
unhealthy.
Middle Trinity River: Texas fawnsfoot in the Trinity River have
experienced improved water quality over the past 30 years due to
advancements in wastewater treatment technology and facilities, and
streamflows have been subsidized by return flows originating in part
from other basins, although water quality degradation and sedimentation
are still of concern. Additionally, the middle Trinity River is a
relatively long and unobstructed reach of river. While habitat may
decline, we expect the population of Texas fawnsfoot to persist in the
middle Trinity River, as we expect that flows will remain within a
normal range of environmental variation in this reach.
Clear Fork Brazos River: Texas fawnsfoot in the Clear Fork of the
Brazos River is very small and isolated. This population likely
experienced extensive mortality associated with prolonged dewatering
during the 2011-2013 drought, combined with ambient water quality
degradation associated with naturally occurring elevated salinity
levels from the upper reaches of the river. This population is likely
functionally extirpated, although more survey effort is needed to reach
a definitive conclusion. Further, the proposed Cedar Ridge Reservoir,
if constructed, will likely result in significant hydrologic
alterations, all of which would not be expected to improve the overall
condition of this population of Texas fawnsfoot.
Upper Brazos River: The population of Texas fawnsfoot in the Upper
Brazos River is characterized by low abundances and lack of
reproduction, and reduced flows associated with continued drought and
upstream dam operations. Further, water quality degradation associated
with naturally occurring salinity is expected to continue. This
population is at risk of extirpation due to its small population size
and continued poor habitat conditions.
Middle/Lower Brazos River: The population of Texas fawnsfoot in the
middle and lower Brazos River occupies a fairly long reach of river
(346 mi (557 km)) and exhibits evidence of reproduction. The lack of
major impoundments and diversions in the Brazos River below Waco,
Texas, benefits this population through maintenance of a relatively
natural hydrological regime. Even so, Texas fawnsfoot surveys have yet
to yield the species in numbers that would indicate a healthy
population, and future habitat degradation from reduced flows,
increased temperatures, and decreased water quality will likely reduce
the resiliency of this population.
Lower San Saba: Texas fawnsfoot in the lower San Saba River are
found in low abundance with little evidence of reproductive success and
subsequent recruitment of new individuals to the population. Habitat
factors are currently unhealthy overall, due primarily to degraded
substrate conditions caused, in part, by reductions in flowing water
over time due to a combination of increased water withdrawals and
drought. We expect this population to become functionally extirpated
due to lack of water and degradation of substrate.
Lower Colorado River: The Texas fawnsfoot population in the lower
Colorado River is expected to remain extant under current conditions,
as this reach is expected to remain wetted but flowing at reduced
amounts that reduce available habitat. Despite increasing demands for
municipal water, we expect that the lower Colorado River will continue
to provide water associated with priority downstream agricultural and
industrial water rights. Similar to the lower Brazos River population,
the Lower Colorado River is vulnerable to reduced flows and associated
habitat degradation, because the Texas fawnsfoot occurs in bank
habitats that are likely to become exposed to desiccation, predation,
and increased water temperatures as river elevations decline while the
river still flows in its main channel. Over time, we expect flows in
the lower Colorado River to be reduced, negatively affecting substrate
quality and water quality (through increased sediment load and water
temperature) such that reproduction and abundance are negatively
affected, resulting in overall unhealthy population conditions.
Guadalupe Orb
There are two remaining populations of the Guadalupe orb, all in
the Guadalupe River basin. Historically, Guadalupe orb likely occurred
throughout the basin with populations connected by fish migration, but
due to impoundments and low water conditions, they are currently
isolated from one another, and repopulation of extirpated locations is
unlikely to occur without human assistance. Both of the Guadalupe orb
populations are moderately healthy.
Upper Guadalupe River: The Guadalupe orb population in the upper
Guadalupe River occurs over approximately 95 river miles (153 river
km), and water quantity and quality are in moderate condition. However,
the population occurs in low numbers, and there appears to be a lack of
reproduction; this population is unhealthy and is expected to become
functionally extirpated in the near future. This stream reach is
expected to be sensitive to potential changes in groundwater inputs to
stream flow and thus is vulnerable to ongoing and future hydrological
alterations that reduce flows during critical conditions, resulting in
substrate quality degradations as well as water quality degradation.
San Marcos/Lower Guadalupe Rivers: In the San Marcos and Lower
Guadalupe River, the Guadalupe orb population currently occupies a
relatively long stream length, is observed in relatively high
abundances, and exhibits evidence of reproduction. Significant spring
complexes contribute substantially to baseflow during dry

[[Page 47941]]

periods in this system and are expected to continue to contribute to
baseflows for the next 50 years due to conservation measures
implemented by the Edwards Aquifer Habitat Conservation Plan partners,
bolstering the resiliency of this population. However, this population
is subject to extreme high flow events that scour and mobilize the
substrate, and water quality degradation and sedimentation are threats,
putting it at risk of decline.
Texas Pimpleback
There are five remaining Texas pimpleback populations, all in the
Colorado River basin. Historically, Texas pimpleback likely occurred
throughout the basin with populations connected by fish migration, but
due to impoundments and low water conditions, they are currently
fragmented and isolated from one another and repopulation of extirpated
locations is unlikely to occur without human assistance. Three of the
remaining Texas pimpleback populations are unhealthy and are not
reproducing, and two of the populations are moderately healthy.
Concho River: The Texas pimpleback population in the Concho River
is limited by very low levels of flowing water (including periods of
almost complete dewatering), poor water quality, and poor substrate
quality associated with excessive sedimentation. The drought of 2011-
2013 resulted in extremely low flows in this river, and only one live
adult has been found since that time. This population may currently be
functionally extirpated.
Middle Colorado/Lower San Saba Rivers: The population of Texas
pimpleback in the middle Colorado and lower San Saba River is the
largest known. This population has relatively high abundance but little
evidence of reproduction, so we expect this population to decline as
old individuals die and very few young individuals are recruited into
the reproducing population. The combination of reduced flows, degraded
water quality, and substrate degradation will reduce the resiliency of
this population and may cause it to become extirpated.
Upper San Saba River: Similar to other populations of Texas
pimpleback, the population in the Upper San Saba River is currently
unhealthy and does not appear to be reproducing. Regardless of the high
risk of low water levels, the very small population size and lack of
reproduction will likely result in the extirpation of this population.
Because of the losing reach near Hext, Texas, that serves to separate
the upper and lower San Saba River populations, along with differences
in substrate, this population is isolated and no longer connected to
the lower San Saba River population.
Llano River: The population of Texas pimpleback in the Llano River
occupies a very short stream length, which is negatively affected by
substrate degradation during periods of low flows. This population, due
to ease of access to the location, is especially vulnerable to the
threat of overcollection and vandalism. The small population size and
frequency of low water levels, and flooding with scour, cause this
population to be unhealthy.
Lower Colorado River: Currently, the population of Texas pimpleback
in the lower Colorado River is relatively abundant over a long stream
length. However, because the species is a riffle specialist, the Texas
pimpleback is especially sensitive to hydrological alterations leading
to both extreme drying (dewatering) during low flow events, and to
extreme high flow events leading to scouring of substrate and movement
of mature individuals to sites that may or may not be appropriate (as
evidenced by the August 2017 scouring flood event that substantially
degraded the quality of the Altair Riffle in the lower Colorado River,
a formerly robust mussel bed). We expect this population to be at risk
of extirpation due to these extreme flow events.
False Spike
Overall, there are four known remaining populations of false spike
(see figure 6, above), comprising less than 10 percent of the species'
known historical range. Historically, most false spike populations were
likely connected by fish migration throughout each of the Brazos,
Colorado, and Guadalupe river basins, but due to impoundments they are
currently fragmented and isolated from one another and repopulation of
extirpated locations is unlikely to occur without human assistance.
Based on our analysis as described in the SSA Report, one population is
moderately healthy, and three are unhealthy.
Little River and tributaries: The Little River population is
considered to have low resiliency currently due to the small size of
the population. Development in the watershed has reduced water quality
and substrate conditions currently, and habitat factors are expected to
continue to decline because of alterations to flows and water quality
associated primarily with increasing development in the watershed as
the Austin-Round Rock (Texas) metropolitan area continues to expand.
Low water levels remain a concern that is mediated somewhat by the
likelihood that enhanced return flows associated with the development
and use of alternative water supplies will bolster base flows somewhat.
The small size of the population combined with continued habitat
degradation put this population at high risk of extirpation.
Lower San Saba River: The lower San Saba River population is
currently small and isolated and therefore has low resiliency. The
population has low abundance, and a lack of reproduction and subsequent
recruitment, and we expect it to become functionally extirpated in the
next 10 years. Future degradation of habitat factors is expected as
flows continue to be diminished, most notably by altered precipitation
patterns (that result in dewatering droughts and scouring floods)
combined with enhanced evaporative demands and anthropogenic
withdrawals to support existing and future demands for municipal and
agricultural water.
Llano River: The Llano River population is currently very small and
isolated and therefore has low resiliency. The population occupies an
extremely small area, and degradation of habitat is expected to
continue as flows continue to decline due to altered precipitation
patterns (dewatering droughts and scouring floods) combined with
enhanced evaporative demands and anthropogenic withdrawals to support
existing and future demands for municipal and agricultural water.
Further, this population is well known and easy to access and therefore
has experienced high collection pressure in recent years, and the
population has not shown recent evidence of reproduction. Therefore, we
expect the population to become extirpated.
Lower Guadalupe River: The lower Guadalupe River population of
false spike is the largest population of the species and the most
resilient. This population has fairly high abundance over a long reach,
and flow protections afforded by the Edwards Aquifer Habitat
Conservation Plan have contributed substantially to the resiliency of
this population by sustaining base flows above critical levels.
However, despite these base flow protections, this population remains
vulnerable to changes in water quality, sedimentation, and extreme high
flow events, such as from hurricanes or other strong storms, which
scour and deplete mussel beds (Strayer 1999, pp. 468-469). Overall,
this population is moderately healthy.
We note that, by using the SSA framework to guide our analysis of
the scientific information documented in

[[Page 47942]]

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. Our
assessment of the current and future conditions encompasses and
incorporates the threats individually and cumulatively. Our current and
future condition assessment is iterative because it accumulates and
evaluates the effects of all the factors that may be influencing the
species, including threats and conservation efforts. 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 ``endangered species'' or
``threatened species.'' 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 a species meets the
definition of ``endangered species'' or ``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 six Central Texas mussel species
and assessing the cumulative effect of the threats under the section
4(a)(1) factors, we found that all six species of Central Texas 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 five 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 from the Act): The accumulation of fine sediments, altered hydrology,
and impairment of water quality, all of which are exacerbated by the
effects of climate change. Predation and collection (Factor C) are also
affecting those populations already experiencing low stream flow, and
barriers to fish movement (Factor E) limit dispersal and prevent
recolonization after stochastic events.
Because of historic and ongoing habitat destruction and
fragmentation, remaining Central Texas mussel populations are now
fragmented and isolated from one another, interrupting the once
functional metapopulation dynamic that historically made mussel
populations robust and very resilient to change. The existing
fragmented and isolated mussel populations are largely in a state of
chronic degradation due to a number of historical and ongoing stressors
affecting flows, water quality, sedimentation, and substrate quality.
Given the high risk of catastrophic events including droughts and
floods, both of which are exacerbated by climate change, many Central
Texas mussel populations are at a high risk of extirpation.
Beginning around the turn of the twentieth century until 1970, over
100 major dams had been constructed, creating reservoirs across Texas,
including several reservoirs in the Brazos and Trinity basins, the
chain of Highland Lakes on the Lower Colorado River, the Guadalupe
Valley Hydroelectric Project, and the Canyon Reservoir on the Guadalupe
River (Dowell 1964, pp. 3-8). The inundation and subsequent altered
hydrology and sediment dynamics associated with operation of these
flood-control, hydropower, and municipal water supply reservoirs have
resulted in irreversible changes to the natural flow regime of these
rivers. These changes have re-shaped and fragmented these aquatic
ecosystems and fish and invertebrate communities, including populations
of the six species of Central Texas mussels, which all depend on
natural river flows.
Water quality has benefited from dramatically improved wastewater
treatment technology in recent years, such that fish populations have
rebounded but not completely recovered (Perkin and Bonner 2016, p. 97).
However, water quality degradation continues to affect mussels and
their habitats, especially as low flow conditions and excessive
sedimentation interact to diminish instream habitats, and substrate-
mobilizing and mussel-scouring flood events have become more extreme
and perhaps more frequent.
Additionally, while host fish may still be adequately represented
in contemporary fish assemblages, access to fish hosts can be reduced
during critical reproductive times by barriers such as the many low-
water crossings and low-head dams that now exist and fragment the
landscape. Diminished access to host fish leads to reduced reproductive
success just as barriers to fish passage impede the movement of fish,
and thus compromise the ability of mussels to disperse and colonize new
habitats following a disturbance (Schwalb et al. 2013, p. 447).
Populations of each of the six Central Texas mussels face risks
from declining water quantity in both large and small river segments.
Low flows lead to dewatering of habitats and desiccation of
individuals, elevated water temperatures, and other quality
degradations, as well as increased exposure to predation. Future higher
air temperatures, higher rates of evaporation and transpiration, and
changing precipitation patterns are expected in central Texas (Jiang
and Yang 2012, pp. 234-239, 242). Future climate changes are expected
to lead to human responses, such as increased groundwater pumping and
surface water diversions, associated with increasing demands for and
decreasing availability of freshwater resources in the State (reviewed
in Banner et al. 2010, entire). Finally, direct mortality due to
predation and collection further limits population sizes of those
populations already experiencing the stressors discussed above.
These threats, alone or in combination, are expected to cause the
extirpation of additional mussel populations, further reducing the
overall redundancy and representation of each of the six species of
Central Texas mussels. Historically, each species, with a large range
of interconnected populations (i.e., having metapopulation dynamics),
would have been resilient to stochastic events such as drought,
excessive sedimentation, and scouring floods because even if some
locations were extirpated by such events, they could be recolonized
over time by dispersal from nearby survivors and facilitated by
movements by ``affiliate species'' of host fish (Douda et al. 2012, p.
536). This connectivity across potential habitats would have made for
highly resilient species overall, as evidenced by the long and
successful evolutionary history of freshwater mussels as a taxonomic
group, and in

[[Page 47943]]

North America in particular. However, under present circumstances,
restoration of that connectivity on a regional scale is not feasible.
As a consequence of these current conditions, the viability of the six
species of Central Texas mussels now primarily depends on maintaining
and improving the remaining isolated populations and potentially
restoring new populations where feasible.

Guadalupe Fatmucket

The Guadalupe fatmucket has only one remaining population, and very
few individuals have been detected and reported in recent years. The
upper Guadalupe River in this reach already experiences very low water
levels, putting this population at high risk of extirpation. The
species has very low viability, with a single population at high risk
of extirpation, and no additional representation or redundancy. Our
analysis of the species' current and future conditions, as well as the
conservation efforts discussed above, show that the Guadalupe fatmucket
is in danger of extinction throughout all of its range due to the
severity and immediacy of threats currently impacting the species.

Texas Fatmucket

Of the five remaining fragmented and isolated populations of Texas
fatmucket, two are small in abundance and occupied stream length and
have low to no resiliency (unhealthy), and one population is
functionally extirpated. The other two current populations are
moderately healthy. The upper/middle San Saba and Llano River
populations are larger, with increased abundance and occupied stream
length, but these populations are vulnerable to stream drying and
overcollection. These very low flow events are expected to continue
into the future, and both of these populations of Texas fatmucket are
at risk of extirpation. Even if the locations of Texas fatmucket do not
become dry, water quality degradation and increased sedimentation
associated with low flows is expected. Additionally, the Llano River
population does not appear to be successfully reproducing, further
increasing the species' risk of extirpation at this location. The Texas
fatmucket has no populations that are currently considered healthy.
Loss of populations at high risk of extirpation leads to low levels of
redundancy and representation. Overall, these low levels of resiliency,
redundancy, and representation result in the Texas fatmucket having low
viability, and the species currently faces a high risk of extinction.
Our analysis of the species' current and future conditions shows that
the Texas fatmucket is in danger of extinction throughout all of its
range due to the severity and immediacy of threats currently impacting
the species.

Texas Fawnsfoot

Seven populations of Texas fawnsfoot remain. Four populations are
moderately healthy, and three are unhealthy or are functionally
extirpated. Currently, two of the moderately healthy populations are
not subject to flow declines similar to the remaining populations of
this species, due to increased flow returns in the Trinity River from
wastewater treatment facilities and a lack of impoundments on the
mainstem of the lower Brazos River. In the future, however, 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.
Within 25 to 50 years, even under the best conditions and with
additional conservation efforts undertaken, given the ongoing effects
of climate change and human activities on altered hydrology and habitat
degradation, we expect only one population to be in healthy condition,
one population to remain in moderately healthy condition, four
populations to be in unhealthy condition, and one population to become
functionally extirpated. Given the likelihood of increased climate and
anthropogenic effects in the foreseeable future, as many as five
populations are expected to become functionally extirpated, leaving no
more than three unhealthy populations remaining after 50 years. In the
future, we anticipate that the Texas fawnsfoot will have reduced
viability, with no highly resilient populations and limited
representation and redundancy. Thus, after assessing the best available
information, we determine that the Texas fawnsfoot 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.

Guadalupe Orb

Only two fragmented and isolated populations of Guadalupe orb
remain, and one of these populations is functionally extirpated. The
San Marcos/Lower Guadalupe River population is more resilient but is at
risk of catastrophic events, such as hurricane flooding, that can scour
and reduce the abundance and distribution of this population. The
Guadalupe orb has no populations that are considered healthy. Loss of
populations at high risk of extirpation leads to low levels of
redundancy and representation, and results in overall low viability.
The Guadalupe orb currently faces a high risk of extinction. Our
analysis of the species' current and future conditions, as well as the
conservation efforts discussed above, show that the Guadalupe orb is in
danger of extinction throughout all of its range due to the severity
and immediacy of threats currently impacting the species.

Texas Pimpleback

Of the five remaining Texas pimpleback populations, three are
unhealthy and are not reproducing, and two are moderately healthy. The
populations that are not reproducing are considered functionally
extirpated, and the two moderately healthy populations are expected to
continue to decline. The population in the middle Colorado and lower
San Saba Rivers has very little evidence of reproduction and is
therefore likely to decline due to a lack of young individuals joining
the population as the population ages. The lower Colorado River
population has very recently experienced an extreme high flow event
(i.e., associated with Hurricane Harvey flooding in August and
September of 2017) that vastly changed the substrate and mussel
composition of much of its length, putting this population at high risk
of extirpation. The Texas pimpleback has no healthy populations, and
all populations are expected to continue to decline. Loss of
populations at high risk of extirpation leads to low levels of
redundancy and representation. Overall, these low levels of resiliency,
redundancy, and representation result in the Texas pimpleback having
low viability, and the species currently faces a high risk of
extinction. Our analysis of the species' current and future conditions,
as well as the conservation efforts discussed above, show that the
Texas pimpleback is in danger of extinction throughout all of its range
due to the severity and immediacy of threats currently impacting the
species.

False Spike

Of the four remaining fragmented and isolated populations of false
spike, three are small in abundance and occupied stream length, having
low to no resiliency. The remaining lower Guadalupe River population is
larger, with increased abundance and occupied stream length; however,
the risk of extreme high flow events in this reach is high. Therefore,
the false spike has no populations that are currently considered
healthy (i.e., highly

[[Page 47944]]

resilient). Loss of populations at high risk of extirpation leads to
low levels of redundancy (few populations will persist to withstand
catastrophic events) and representation (little to no ecological or
genetic diversity will persist to respond to changing environmental
conditions). The threats identified above are occurring now and are
expected to continue into the future. Overall, these low levels of
resiliency, redundancy, and representation result in the false spike
having low viability, and the species currently faces a high risk of
extinction. Our analysis of the species' current and future conditions
demonstrate that the false spike is in danger of extinction throughout
all of its range due to the severity and immediacy of threats currently
impacting the species.

Summary of Status Throughout All of Its Range: Guadalupe Fatmucket,
Texas Fatmucket, Guadalupe Orb, Texas Pimpleback, and False Spike

Our analysis of the species' current and future conditions, as well
as the conservation efforts discussed above, show that the Guadalupe
fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, and false
spike are in danger of extinction throughout all their ranges 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 Guadalupe fatmucket,
Texas fatmucket, Guadalupe orb, Texas pimpleback, and false spike
because of their currently contracted ranges, because all populations
are fragmented and isolated from one another, because the threats are
occurring across the entire range of these species, and because the
threats are ongoing currently and are expected to continue or worsen
into the future. Because these species are already in danger of
extinction throughout their ranges, a threatened status is not
appropriate.

Summary of Status Throughout All of Its Range: Texas Fawnsfoot

After evaluating threats to the species and assessing the
cumulative effect of the threats under the section 4(a)(1) factors, we
find that that Texas fawnsfoot populations will continue to decline
over the next 25 years so that this species is likely to become in
danger of extinction throughout all or a significant portion 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. We considered whether the Texas
fawnsfoot is presently in danger of extinction 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 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. 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 25 years throughout all
of its range. Twenty-five years encompasses about 5 generations of the
Texas fawnsfoot; additionally, models of human demand for water (Texas
Water Development Board 2017, p. 30) and climate change (e.g.,
Kinniburgh et al. 2015, p. 83) project decreased water availability
over 25 and 50 years, respectively. 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 25 years. Thus, after
assessing the best available information, we determine that the Texas
fawnsfoot 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.

Status Throughout a Significant Portion of Its Range: Guadalupe
Fatmucket, Texas Fatmucket, Guadalupe Orb, Texas Pimpleback, and False
Spike

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 Guadalupe fatmucket, Texas
fatmucket, Guadalupe orb, Texas pimpleback, and false spike are in
danger of extinction throughout all of their ranges, and accordingly
did not undertake an analysis of whether there are any significant
portions of these species' ranges. Because the Guadalupe fatmucket,
Texas fatmucket, Guadalupe orb, Texas pimpleback, and false spike
warrant listing as endangered throughout all of their ranges, our
determination is consistent with the decision in Center for Biological
Diversity v. Everson, 2020 WL 437289 (D.D.C. Jan. 28, 2020), in which
the court vacated the aspect of the 2014 Significant Portion of its
Range Policy that provided the Services do not undertake an analysis of
significant portions of a species' range if the species warrants
listing as threatened throughout all of its range.

Status Throughout a Significant Portion of Its Range: Texas Fawnsfoot

Under the Act and our implementing regulations, a species may
warrant listing if it is in danger of extinction or likely to become so
within 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) (Center for Biological
Diversity), vacated the aspect of the 2014 Significant Portion of its
Range Policy that provided that the Services do 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 Center for Biological Diversity,
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 Texas fawnsfoot, 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 is endangered.
We considered whether any of the threats acting on the species are
geographically concentrated in any portion of the range at a
biologically meaningful scale. We examined the following threats
throughout the range of the species: The accumulation of fine
sediments, altered hydrology, and impairment of water quality (Factor
A); predation and collection (Factor C); and barriers to fish movement
(Factor E).
We identified a portion of the range of Texas fawnsfoot, the upper
Brazos

[[Page 47945]]

River (including the populations in the Upper Brazos River and Clear
Fork Brazos River), that is experiencing a concentration of the
following threats: Altered hydrology and impaired water quality.
Although these threats are not unique to this area, they are acting at
a greater intensity here (e.g., populations higher in the watershed and
that receive less rainfall are more vulnerable to stream drying because
there is a smaller volume of water in the river), either individually
or in combination, than elsewhere in the range. In addition, the small
sizes of each population, coupled with the current condition
information in the SSA report suggesting the two populations in this
area are unhealthy, leads us to find that this portion provides
substantial information indicating the populations occurring here may
be in danger of extinction now.
We then proceeded to the significance question, asking whether
there is substantial information indicating that this portion of the
range (i.e., the Upper Brazos River and Clear Fork Brazos River) may be
significant. As an initial note, the Service's most recent definition
of ``significant'' within agency policy guidance has been invalidated
by court order (see Desert Survivors v. Dep't of the Interior, No. 16-
cv-01165 (N.D. Cal. Aug. 24, 2018)). In undertaking this analysis for
the Texas fawnsfoot, we considered whether the Upper Brazos River
portion of the species' range may be significant based on its
biological importance to the overall viability of the Texas fawnsfoot.
Therefore, for the purposes of this analysis, when considering whether
this portion may be biologically significant, we considered whether the
portion may (1) occur in a unique habitat or ecoregion for the species,
(2) contain high quality or high value habitat relative to the
remaining portions of the range, for the species' continued viability
in light of the existing threats, or (3) contain habitat that is
essential to a specific life-history function for the species and that
is not found in the other portions (for example, the principal breeding
ground for the species).
We evaluated the available information about the portion of the
range of Texas fawnsfoot that occupies the upper Brazos River in this
context, assessing its biological significance in terms of these three
habitat criteria, and determined the information did not substantially
indicate it may be significant. Texas fawnsfoot in these populations
exhibit similar habitat and host fish use to Texas fawnsfoot in the
remainder of its range; thus, there is no unique observable
environmental usage or behavioral characteristics attributable to just
this area's populations. The Upper Brazos River is not essential to any
specific life-history function of the Texas fawnsfoot that is not found
elsewhere in the range. Further, the habitat in the Upper Brazos River
does not contain higher quality or higher value than the remainder of
the species' range. The Upper Brazos River populations have a small
number of individuals compared to most of the other populations
throughout the range of Texas fawnsfoot (see Table 4, above). The Clear
Fork Brazos River population may already be extirpated, and the Upper
Brazos River population had 23 individuals found in 2017. These
populations do not interact with other populations of the species.
Overall, we found no substantial information that would indicate
the Upper Brazos River may be significant. While this area provides
some contribution to the species' overall ability to withstand
catastrophic or stochastic events (redundancy and resiliency,
respectively), the species has a larger population that occupies a
larger area downstream in the Brazos River. The best scientific and
commercial information available indicates that the Upper Brazos River
population's contribution is very limited in scope due to the small
population sizes and isolation from other populations. Therefore,
because we could not answer both the status and significance questions
in the affirmative, we conclude that the Upper Brazos River portion of
the range does not warrant further consideration as a significant
portion of the range.
We did not identify any portions of the Texas fawnsfoot's range
where: (1) The portion is significant; and, (2) the species is in
danger of extinction in that portion. Therefore, we conclude that the
Texas fawnsfoot is likely to become in danger of extinction within the
foreseeable future throughout all of its range. This is consistent with
the courts' holdings in Desert Survivors v. Department of the Interior,
No. 16-cv-01165-JCS, 2018 WL 4053447 (N.D. Cal. Aug. 24, 2018), and
Center for Biological Diversity v. Jewell, 248 F. Supp. 3d, 946, 959
(D. Ariz. 2017).

Determination of Status: Guadalupe Fatmucket, Texas Fatmucket,
Guadalupe Orb, Texas Pimpleback, and False Spike

Our review of the best available scientific and commercial
information indicates that the Guadalupe fatmucket, Texas fatmucket,
Guadalupe orb, Texas pimpleback, and false spike meet the definition of
endangered species. Therefore, we propose to list the Guadalupe
fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, and false
spike as endangered species in accordance with sections 3(6) and
4(a)(1) of the Act.

Determination of Status: Texas Fawnsfoot

Our review of the best available scientific and commercial
information indicates that the Texas fawnsfoot meets the definition of
a threatened species. Therefore, we propose to list the Texas fawnsfoot
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, 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 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 recovery planning process involves the
identification of actions that are necessary to halt or reverse
species' decline by addressing the threats to survival and recovery.
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.
Recovery planning consists of preparing draft and final recovery
plans, beginning with the development of a recovery outline and making
it available to the public within 30 days of a final listing
determination. The recovery outline guides the immediate implementation
of urgent recovery actions and describes the process to be used to
develop a recovery plan. Revisions of the plan may be done to

[[Page 47946]]

address continuing or new threats to the species, as new substantive
information becomes available. The recovery plan also 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. Recovery teams (composed of
species experts, Federal and State agencies, nongovernmental
organizations, and stakeholders) are often established to develop
recovery plans. When completed, the recovery outline, draft recovery
plan, and the final recovery plan will be available on our website
(<a href="http://www.fws.gov/endangered">http://www.fws.gov/endangered</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 range 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 State of Texas would be eligible
for Federal funds to implement management actions that promote the
protection or recovery of the Central Texas mussels. Information on our
grant programs that are available to aid species recovery can be found
at: <a href="http://www.fws.gov/grants">http://www.fws.gov/grants</a>.
Although the Central Texas mussels 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 this 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 National Park Service.
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. There are also certain statutory 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 discussion below regarding protective
regulations under section 4(d) of the Act for the Texas fawnsfoot
complies with our policy.
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, which are carried out in accordance with
any existing regulations, permit and label requirements, and best
management practices; and,
(2) Normal residential landscape 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) Modification of the channel or water flow of any stream in
which the Central Texas mussels are known to occur;
(3) Livestock grazing that results in direct or indirect
destruction of stream habitat; and
(4) Discharge of chemicals or fill material into any waters in
which the Central Texas mussels are known to occur.
Questions regarding whether specific activities would constitute a
violation of section 9 of the Act should be directed to the Austin
Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT).

[[Page 47947]]

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 he deems
necessary and advisable to provide for the conservation'' of species
listed as threatened. The U.S. Supreme Court has noted that statutory
language like ``necessary and advisable'' demonstrates 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 rules
developed under section 4(d) as a valid exercise of agency authority
where they prohibited take of threatened wildlife, or include a limited
taking prohibition (see Alsea Valley Alliance v. Lautenbacher, 2007
U.S. Dist. Lexis 60203 (D. Or. 2007); Washington Environmental Council
v. National Marine Fisheries Service, 2002 U.S. Dist. Lexis 5432 (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 him with regard to the permitted activities for those species. He
may, for example, permit taking, but not importation of such species,
or he 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).
Exercising its authority under section 4(d), the Service has
developed a proposed rule that is designed to address the Texas
fawnsfoot's specific threats and conservation needs. Although the
statute does not require the Service to make a ``necessary and
advisable'' finding with respect to the adoption of specific
prohibitions under section 9, we find that this rule as a whole
satisfies the requirement in section 4(d) of the Act to issue
regulations deemed necessary and advisable to provide for the
conservation of the Texas fawnsfoot. As discussed in the Summary of
Biological Status and Threats section, the Service has concluded that
the Texas fawnsfoot 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.
The provisions of this proposed 4(d) rule would promote conservation of
the Texas fawnsfoot by encouraging riparian landscape conservation
while also meeting the conservation needs of Texas fawnsfoot. By
streamlining those projects that follow best management practices and
improve instream habitat (such as streambank stabilization, instream
channel restoration, and upland restoration that improves instream
habitat), conservation is more likely to occur for Texas fawnsfoot,
improving the condition of populations in those reaches. The provisions
of this proposed rule are one of many tools that the Service would use
to promote the conservation of the Texas fawnsfoot. This proposed 4(d)
rule would apply only if and when the Service makes final the listing
of the Texas fawnsfoot as a threatened species.

Provisions of the Proposed 4(d) Rule

This proposed 4(d) rule would provide for the conservation of the
Texas fawnsfoot by prohibiting the following activities, except as
otherwise authorized or permitted: Take, possession, and import/export
of unlawfully taken specimens.
As discussed in the Summary of Biological Status and Threats
(above), habitat loss, predation and collection, and barriers to fish
movement are affecting the status of the Texas fawnsfoot. A range of
activities have the potential to impact the Texas fawnsfoot, including:
Instream construction, water withdrawals, flow releases from upstream
dams, riparian vegetation removal, improper handling, and wastewater
treatment facility outflows. Regulating these activities will help
preserve the species' remaining populations, slow their rate of
decline, and decrease synergistic, negative effects from other
stressors.
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
regulation at 50 CFR 17.3. Take can result knowingly or otherwise, by
direct and indirect impacts, intentionally or incidentally. Regulating
incidental and intentional take will help preserve the species'
remaining populations, slow their rate of decline, and decrease
synergistic, negative effects from other stressors.
We have identified some exceptions to the prohibition on incidental
and intentional take. Those exceptions include the following
activities:
(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 proposed 4(d) rule for incidental take
would promote conservation of Texas fawnsfoot 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 stakes (live, vegetative cuttings inserted or tamped into the
ground in a manner that allows the stake to take root and grow), live
fascines (live branch cuttings, usually willows, bound together into
long, cigar-shaped bundles), or brush layering (cuttings or branches of
easily rooted tree species layered between successive lifts of soil
fill). These methods would not include the sole use of quarried rock
(rip-rap) or the use of rock baskets or gabion

[[Page 47948]]

structures. In addition, to reduce streambank erosion and sedimentation
into the stream, work using these bioengineering methods would 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 Texas fawnsfoot
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 and comply with conservation practice standards and
specifications and technical guidelines developed by the Natural
Resources Conservation Service (NRCS) and available in the Field Office
Technical Guide (FOTG). 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 Texas fawnsfoot
by creating stable stream channels and reducing sediment inputs to the
stream, thereby increasing population resiliency.
(4) Presence or abundance surveys for Texas fawnfoot conducted by
individuals who successfully complete and show proficiency by passing
the end-of-course test with a score equal to or greater than 90
percent, with 100 percent accuracy in identification of mussel species
listed under the Endangered Species Act, in an approved freshwater
mussel identification and sampling course (specific to the species and
basins in which the Texas fawnsfoot is known to occur), such as that
administered by the Service, State wildlife agency, or qualified
university experts. Those individuals exercising this exemption should
provide reports to the Service annually on number, specific location
(e.g. GPS coordinates), and date of encounter. This exemption does not
apply if lethal take or collection is anticipated. This exemption only
applies for 5 years from the date of successful completion of the
course. This provision of the 4(d) rule for intentional take would
promote conservation of Texas fawnsfoot by ensuring surveyors are
proficient at identification of freshwater mussels and would add to the
knowledge and understanding of the distribution of Texas fawnsfoot
populations.
We may issue permits to carry out otherwise prohibited activities,
including those described above, involving threatened wildlife under
certain circumstances. Regulations governing permits are codified at 50
CFR 17.32. With regard to threatened wildlife, a permit may be issued
for the following purposes: 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. There are also certain
statutory exemptions from the prohibitions, which are found in sections
9 and 10 of the Act.
The Service recognizes 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 the Services in implementing all aspects of the Act.
In this regard, section 6 of the Act provides that the Services shall
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 the Service in accordance with section 6(c)
of the Act, who is designated by his or her agency for such purposes,
will be able to conduct activities designed to conserve Texas fawnsfoot
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 the ability of
the Service to enter into partnerships for the management and
protection of the Texas fawnsfoot. However, interagency cooperation may
be further streamlined through planned programmatic consultations for
the species between Federal agencies and the Service. 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 the Service
could provide or use, respectively, to streamline the implementation of
this proposed 4(d) rule (see Information Requested, above).

III. Proposed Critical Habitat Designation

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). Additionally, our regulations
at 50 CFR 424.02 define the word ``habitat'' as follows: ``for the
purposes of designating critical habitat only, habitat is the abiotic
and biotic setting that currently or periodically contains the
resources and conditions necessary to support one or more life
processes of a species.''
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

[[Page 47949]]

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 ownership or establish a refuge, wilderness, reserve, preserve, or
other conservation area. Designation also does not allow the government
or public to access private lands, nor does designation 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 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). In identifying those
physical or biological features that occur in specific occupied areas,
we focus on the specific features that are essential to support the
life-history needs of the species, including but not limited to, water
characteristics, soil type, geological features, 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.
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. The implementing regulations at 50 CFR 424.12(b)(2) further
delineate unoccupied critical habitat by setting out three specific
parameters: (1) When designating critical habitat, the Secretary will
first evaluate areas occupied by the species; (2) the Secretary will
only consider unoccupied areas to be essential where a critical habitat
designation limited to geographical areas occupied by the species would
be inadequate to ensure the conservation of the species; and (3) for an
unoccupied area to be considered essential, the Secretary must
determine that there is a reasonable certainty both that the area will
contribute to the conservation of the species and that the area
contains one or more of those physical or biological features essential
to 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.
As the regulatory definition of ``habitat'' reflects (50 CFR
424.02), 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) section 9 of the Act's prohibitions on taking any
individual of the species, including taking caused by actions that
affect habitat. 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 these
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 Determinations

Section 4(a)(3) of the Act, as amended, and implementing
regulations (50 CFR 424.12), require that the Secretary shall designate
critical habitat at the time the species is determined to be an
endangered or threatened species to the maximum extent prudent and
determinable. 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

[[Page 47950]]

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 in the proposed listing rule, above, while collection
at certain locations has been identified as a threat to certain
populations of Texas pimpleback, Texas fatmucket, and false spike in
the Llano River, the location of these populations is well known and
the identification and mapping of critical habitat is not expected to
increase the degree of this threat. In our SSA report and proposed
listing rule for the Central Texas mussels, we determined that the
present or threatened destruction, modification, or curtailment of
habitat or range is a threat to the Central Texas mussels and that
those threats in some way can be addressed by section 7(a)(2)
consultation measures. The species occurs 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 there are no other circumstances the Secretary has
identified for which this designation of critical habitat would be not
prudent, we have determined that the designation of critical habitat is
prudent for the Central Texas mussels.

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
Central Texas mussels 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 Central Texas mussels.

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 t

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