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Rule2024-11645

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

Primary source

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Published

June 4, 2024

Effective

July 5, 2024

Issuing agencies

Interior DepartmentFish and Wildlife Service

Abstract

We, the U.S. Fish and Wildlife Service (Service), determine endangered species status under the Endangered Species Act of 1973 (Act), as amended, for the Guadalupe fatmucket (Lampsilis bergmanni), Texas fatmucket (Lampsilis bracteata), Guadalupe orb (Cyclonaias necki), Texas pimpleback (Cyclonaias (=Quadrula) petrina), Balcones spike (Fusconaia (=Quincuncina) iheringi), and false spike (Fusconaia (=Quincuncina) mitchelli), and threatened species status for the Texas fawnsfoot (Truncilla macrodon), seven species of freshwater mussels from central Texas. We also issue a rule under section 4(d) of the Act for the Texas fawnsfoot that provides measures that are necessary and advisable to provide for the conservation of the Texas fawnsfoot. In addition, we designate critical habitat for all seven species. In total, approximately 1,577.5 river miles (2,538.7 river kilometers) in Blanco, Brown, Caldwell, Coleman, Comal, Concho, DeWitt, Gillespie, Gonzales, Guadalupe, Hays, Kendall, Kerr, Kimble, Lampasas, Llano, Mason, McCulloch, Menard, Mills, Palo Pinto, Parker, Runnels, San Saba, Shackelford, Stephens, Sutton, Throckmorton, Tom Green, Travis, and Victoria Counties, Texas, fall within the boundaries of the critical habitat designation. This rule applies the protections of the Act to these species and their designated critical habitats.

Full Text

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[Federal Register Volume 89, Number 108 (Tuesday, June 4, 2024)]
[Rules and Regulations]
[Pages 48034-48130]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2024-11645]

[[Page 48033]]

Vol. 89

Tuesday,

No. 108

June 4, 2024

Part II

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, Balcones Spike, and False Spike, and
Threatened Species Status With Section 4(d) Rule and Critical Habitat
for Texas Fawnsfoot; Final Rule

Federal Register / Vol. 89 , No. 108 / Tuesday, June 4, 2024 / Rules
and Regulations

[[Page 48034]]

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2019-0061; FXES1111090FEDR-245-FF09E21000]
RIN 1018-BD16

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine
endangered species status under the Endangered Species Act of 1973
(Act), as amended, for the Guadalupe fatmucket (Lampsilis bergmanni),
Texas fatmucket (Lampsilis bracteata), Guadalupe orb (Cyclonaias
necki), Texas pimpleback (Cyclonaias (=Quadrula) petrina), Balcones
spike (Fusconaia (=Quincuncina) iheringi), and false spike (Fusconaia
(=Quincuncina) mitchelli), and threatened species status for the Texas
fawnsfoot (Truncilla macrodon), seven species of freshwater mussels
from central Texas. We also issue a rule under section 4(d) of the Act
for the Texas fawnsfoot that provides measures that are necessary and
advisable to provide for the conservation of the Texas fawnsfoot. In
addition, we designate critical habitat for all seven species. In
total, approximately 1,577.5 river miles (2,538.7 river kilometers) in
Blanco, Brown, Caldwell, Coleman, Comal, Concho, DeWitt, Gillespie,
Gonzales, Guadalupe, Hays, Kendall, Kerr, Kimble, Lampasas, Llano,
Mason, McCulloch, Menard, Mills, Palo Pinto, Parker, Runnels, San Saba,
Shackelford, Stephens, Sutton, Throckmorton, Tom Green, Travis, and
Victoria Counties, Texas, fall within the boundaries of the critical
habitat designation. This rule applies the protections of the Act to
these species and their designated critical habitats.

DATES: This rule is effective July 5, 2024.

ADDRESSES: This final rule is available on the internet at <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Comments and materials we received, as well as
supporting documentation we used in preparing this rule, are available
for public inspection at <a href="https://www.regulations.gov">https://www.regulations.gov</a> at Docket No. FWS-
R2-ES-2019-0061.
Availability of supporting materials: Supporting materials we used
in preparing this rule, such as the species status assessment report,
are available for public inspection at <a href="https://www.regulations.gov">https://www.regulations.gov</a> at
Docket No. FWS-R2-ES-2019-0061. 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.regulations.gov">https://www.regulations.gov</a> at Docket No. FWS-R2-ES-2019-0061.

FOR FURTHER INFORMATION CONTACT: Karen Myers, Field Supervisor, U.S.
Fish and Wildlife Service, Austin Ecological Services Field Office,
1505 Ferguson Lane, Austin, TX 78754; telephone (512) 937-7371.
Individuals in the United States who are deaf, deafblind, hard of
hearing, or have a speech disability may dial 711 (TTY, TDD, or
TeleBraille) to access telecommunications relay services. Individuals
outside the United States should use the relay services offered within
their country to make international calls to the point-of-contact in
the United States.

SUPPLEMENTARY INFORMATION:

Executive Summary

Why we need to publish a rule. Under the Act, a species warrants
listing if it meets the definition of an endangered species (in danger
of extinction throughout all or a significant portion of its range) or
a threatened species (likely to become endangered within the
foreseeable future throughout all or a significant portion of its
range). If we determine that a species warrants listing, we must list
the species promptly and designate the species' critical habitat to the
maximum extent prudent and determinable. We have determined that the
Guadalupe fatmucket (Lampsilis bergmanni), Texas fatmucket (Lampsilis
bracteata), Guadalupe orb (Cyclonaias necki), Texas pimpleback
(Cyclonaias (=Quadrula) petrina), Balcones spike (Fusconaia
(=Quincuncina) iheringi), and false spike (Fusconaia (=Quincuncina)
mitchelli) meet the Act's definition of endangered species, and the
Texas fawnsfoot (Truncilla macrodon) meets the Act's definition of a
threatened species; therefore, we are listing them as such, finalizing
a rule under section 4(d) of the Act for the Texas fawnsfoot, and
designating critical habitat. Both listing a species as an endangered
or threatened species and designating critical habitat can be completed
only by issuing a rule through the Administrative Procedure Act
rulemaking process (5 U.S.C. 551 et seq.).
What this document does. This rule makes final the listing of the
Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback,
Balcones spike, and false spike as endangered species, and the Texas
fawnsfoot as a threatened species with a rule issued under section 4(d)
of the Act (a ``4(d) rule''). In addition, this rule designates
critical habitat for all seven central Texas mussel species in 20 units
(including 32 subunits) totaling 1,577.5 river miles (2,538.7 river
kilometers (km)) on private, State, and Federal property within
portions of 31 counties in Texas.
The basis for our action. Under the Act, we may determine that a
species is an endangered or threatened species because of any of five
factors: (A) The present or threatened destruction, modification, or
curtailment of its habitat or range; (B) overutilization for
commercial, recreational, scientific, or educational purposes; (C)
disease or predation; (D) the inadequacy of existing regulatory
mechanisms; or (E) other natural or manmade factors affecting its
continued existence; we also take into account conservation efforts,
such as Candidate Conservation Agreements with Assurances (CCAAs). We
have determined that increased fine sediment, changes in water quality,
and altered hydrology in the form of inundation and loss of flow and
scour of substrate (Factor A), collection (Factor B), predation (Factor
C), and barriers to fish movement (Factor E) are the primary threats to
these species. These factors are all exacerbated by the ongoing and
expected effects of climate change.
Section 4(a)(3) of the Act requires the Secretary of the Interior
(Secretary), to designate critical habitat, to the maximum extent
prudent and determinable, concurrent with listing. Section 3(5)(A) of
the Act defines critical habitat as (i) the specific areas within the
geographical area occupied by the species, at the time it is listed, on
which are found those physical or biological features (I) essential to
the conservation of the species and (II) which may require special
management considerations or protections; and (ii) specific areas
outside the geographical area occupied by the species at the time it is
listed, upon a determination by the Secretary that such areas are
essential for the conservation of the species. Section 4(b)(2) of the
Act states that the Secretary must make the designation on the basis of
the best scientific data

[[Page 48035]]

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.

Previous Federal Actions

Please refer to the August 26, 2021, proposed rule (86 FR 47916)
for a detailed description of previous Federal actions concerning these
species.

Peer Review

A species status assessment (SSA) team prepared an SSA report for
the Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe
orb, Texas pimpleback, and false spike. This SSA report was competed
prior to the taxonomic divergence of the false spike to reflect the
recently described Balcones spike (Fusconaia iheringi) (Smith et al.
2020, entire) (see Summary of Changes from the Proposed Rule, below).
The SSA team was composed of Service biologists, in consultation with
other species experts. The SSA report represents a compilation of the
best scientific and commercial data available concerning the status of
the species, including the impacts of past, present, and future factors
(both negative and beneficial) affecting the species.
In accordance with our joint policy on peer review published in the
Federal Register on July 1, 1994 (59 FR 34270), and our August 22,
2016, memorandum updating and clarifying the role of peer review of
listing actions under the Act, we solicited independent scientific
review of the information contained in the SSA report. We sent the SSA
report to eight independent peer reviewers and received six responses.
Results of this structured peer review process can be found at <a href="https://regulations.gov">https://regulations.gov</a>. In preparing the proposed rule, we incorporated the
results of these peer reviews, as appropriate, into version 1.1 of the
SSA report, which was the foundation for the proposed rule and this
final rule. A summary of the peer review comments and our responses can
be found under Summary of Comments and Recommendations, below.

Summary of Changes From the Proposed Rule

Based upon our review of the public comments, State agency
comments, peer review comments, and relevant information that became
available since the August 26, 2021, proposed rule published, we
updated information in our SSA report, including:
<bullet> Updating the taxonomy of false spike (Fusconaia mitchelli)
to reflect the divergence from the recently described Balcones spike
(Fusconaia iheringi) (Smith et al. 2020, entire).
<bullet> Updating text to clearly differentiate between the threat
of sedimentation to freshwater mussels and naturally occurring
turbidity in a river system; improve consistency in the use of
``impaired'' when discussing water quality; and further differentiate
between the threat of sedimentation within a system and the presence of
turbidity associated with fine organic or inorganic matter, soluble
organic compounds, algae, or other microscopic organisms.
We made these and other changes as appropriate in this final rule.
In addition to minor clarifying edits and incorporation of additional
information on the species' biology, populations, and threats, this
final determination differs from the August 26, 2021, proposed rule in
the following ways:
(1) We add updated population data for the Texas fatmucket,
including survey data made available by the Texas Department of
Transportation since the publication of the proposed rule. Based on the
presence of Texas fatmucket in Unit TXFM-6b (Upper Onion Creek), this
unit has now changed from unoccupied to occupied, so we combine the
Upper and Lower Onion Creek critical habitat units (TXFM-6b and TXFM-
6a, respectively) into one occupied unit (TXFM-6). Therefore, this rule
differs slightly from the proposed critical habitat designation (86 FR
47916; August 26, 2021) by unit numbering and occupancy.
(2) Both the Balcones spike and the false spike are included in
this final listing rule because the entity known as false spike in the
August 26, 2021, proposed rule was taxonomically divided into the two
species. We rename and renumber critical habitat units to reflect the
updated taxonomy and range of false spike and Balcones spike. We
renumber proposed critical habitat unit FASP-4 (Guadalupe River Unit)
as FASP-1; it is now the only critical habitat unit for the false
spike. The remaining three proposed critical habitat units for the
false spike are renamed and renumbered for the Balcones spike: unit
FASP-1 (Little River Unit) is now BASP-1, FASP-2 (San Saba River Unit)
is now BASP-2, and FASP-3 (Llano River Unit) is now BASP-3.
(3) For the critical habitat designation, we exclude proposed units
TXFF-3, TXFF-4, and BASP-1 (previously FASP-1) based on the
implementation of conservation measures completed by the Brazos River
Authority (BRA) as part of their candidate conservation agreement with
assurances (CCAA) for the Balcones spike and Texas fawnsfoot in the
Brazos River Basin (BRA 2021, pp. 35-51; hereafter, the ``BRA
Agreement''). We also exclude proposed units TXFF-6 and TXPB-6 based
upon the implementation of conservation measures completed by the Lower
Colorado River Authority (LCRA) as part of their CCAA for the Texas
pimpleback, Texas fawnsfoot, Texas fatmucket, and Balcones spike in the
Lower Colorado River Basin below O.H. Ivie Reservoir (LCRA 2023, pp.
45-84; hereafter, the ``LCRA Agreement''). In addition, we exclude
proposed units TXFF-7 and TXFF-8 based upon the implementation of
conservation measures completed by the Trinity River Authority (TRA) as
part of their CCAA for six species in the Trinity River Basin (TRA
2023, pp. 47-66; hereafter, the ``TRA Agreement'').
(4) We incorporate minor changes in the length of river miles (and
kilometers) of occupied stream reaches. We also incorporate minor
changes in the length of river miles (and kilometers) from the proposed
critical habitat to reflect those included in the final critical
habitat unit maps. While we use the same start and end points for all
final critical habitat unit designations, these minor changes in
critical habitat designation length are the result of geoprocessing
tools used in ArcGIS.
(5) We include short textual descriptions of the designated units
under Regulation Promulgation in this rule, as under 50 CFR 17.94,
general descriptions of the location and boundaries of each area may be
provided to clarify or refine what is included within the boundaries
depicted on the map, or to explain the exclusion of sites (e.g., paved
roads, buildings) within the mapped area. These descriptions mirror
information in the preamble of this rule, which reflects the unit
description information presented in our August 26, 2021, proposed rule
as amended by the changes described in this document.
(6) Based on public comments, we update language in the 4(d) rule
for the Texas fawnsfoot to clarify and refine the specific prohibitions
and exceptions to those prohibitions to minimize potential ambiguity.
Specifically, to qualify for exceptions when conducting channel
restoration projects, we clarify that the project must meet all
applicable Federal, State, and local permitting requirements. In
addition, to allow the Service to make arrangements for surveys and
potential relocation of any mussels that might be adversely affected
during channel restoration projects, we add that notice must be
provided to the Service of the location and nature of the

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proposed work at least 30 days prior to commencing actual construction
within an area designated as critical habitat for the Texas fawnsfoot.
In addition, to qualify for exceptions when conducting streambank
stabilization projects, we specify that: (i) native live stakes, native
live fascines, or native live brush must be used; (ii) methods that
include the use of quarried rock (riprap) for more than 25 percent of
the area within the streambanks or include the use of rock baskets or
gabion structures do not qualify for this exception; (iii) work using
these bioengineering methods must be performed at base flow or low
water conditions and when significant rainfall likely to result in
significant runoff is not predicted at or upstream of the area where
work is proposed for a period of at least 3 days after the work is
scheduled to be undertaken, in order to reduce streambank erosion and
sedimentation; and (iv) the project must meet all applicable Federal,
State, and local permitting requirements. Further, to qualify for
exceptions when conducting soil and water conservation practices, and
riparian and adjacent upland habitat management activities, we add
that, to allow the Service to make arrangements for surveys and
potential relocation of any mussels that might be adversely affected
during channel restoration projects, notice must be provided to the
Service of the location and nature of the proposed work at least 30
days prior to commencing actual construction within an area designated
as critical habitat for Texas fawnsfoot.
(7) Based on public comments, we update language to include
examples of discretionary actions for the central Texas mussels that
may be subject to consultation procedures under section 7, and more
clearly define the standards for avoiding jeopardizing the continued
existence of the species for future section 7 conferences/consultations
(see Available Conservation Measures, below). In addition, we update
language to include protective regulations to address the threats to
the Texas fawnsfoot under section 9, as well as what activities would
and would not be likely to constitute a violation of section 9 take
prohibition (see Provisions of the 4(d) Rule, below).
(8) Based on a public comments, we also make minor, nonsubstantive
changes and corrections throughout this rule in response to public
comments. However, the information we received during the public
comment period on the proposed rule did not change our determination
that the Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas
pimpleback, Balcones spike, and false spike meet the Act's definition
of endangered species, and the Texas fawnsfoot meets the Act's
definition of a threatened species.

Summary of Comments and Recommendations

In the proposed rule published on August 26, 2021 (86 FR 47916), we
requested that all interested parties submit written comments on the
proposal by October 25, 2021. We also contacted appropriate Federal and
State agencies, scientific experts and organizations, and other
interested parties and invited them to comment on the proposal.
Newspaper notices inviting general public comment were published in the
Austin Statesman, and we held public hearings on September 14 and
September 16, 2021. All substantive information we received during the
comment period has either been incorporated directly into this final
determination or is addressed below.

Peer Reviewer Comments

As discussed in Peer Review above, we received comments from six
peer reviewers on the draft SSA report. We reviewed all comments we
received from the peer reviewers for substantive issues and new
information regarding the contents of the SSA report. Peer reviewer
comments are addressed in the following summary. As discussed above,
because we conducted this peer review prior to the publication of our
proposed rule, we had already incorporated all applicable peer review
comments into version 2.1 of the SSA report, which was the foundation
for the proposed rule. The peer reviewers generally concurred with our
methods and conclusions, and provided additional information,
clarifications, and suggestions to improve the SSA report (Service
2019b, entire). Peer reviewer comments are addressed in the following
summary and are incorporated into the SSA report as appropriate.
(1) Comment: One peer reviewer suggested that, in addition to the
value limited by the population abundance factor in the overall current
condition, the ranges used to assign values to the six condition
factors after averaging should be included in the SSA report.
Our response: The overall average current condition of the
populations, not limited by the abundance condition, is not reflective
of population condition. We chose to limit the overall current
conditions so they could not exceed abundance because our information
regarding habitat is not robust enough to outweigh abundance (i.e., a
mussel population with low abundance but indications of moderate or
high habitat factors should not be rated to be in moderate or high
condition). Therefore, reporting the unlimited averages would only
cause reader confusion that could be derived from presenting multiple
``overall condition'' values for each population.
(2) Comment: One peer reviewer suggested, particularly for false
spike, that the lack of knowledge of host fish could be a factor
influencing central Texas mussel distribution and abundance if the host
fish is in fact not a common species.
Our response: Following the submission of the draft SSA for peer
review, studies were completed identifying the red shiner (Cyprinella
lutrensis) and blacktail shiner (Cyprinella venusta) as host fish for
false spike, and both are common fish species in this area (Dudding et
al. 2019, p. 16). Host fish for congeners of the mussel species that
are the subjects of this rule are a suite of typically common fish
species, and therefore it is unlikely that these mussel species rely
exclusively on rare fish species to serve as the sole or primary fish
hosts for reproduction.
(3) Comment: One peer reviewer and one State commenter stated
concerns of using 35-millimeter (mm) length to define juveniles,
especially the use of the threshold for the generally smaller Texas
fawnsfoot, and they requested that the Service revisit the evidence of
reproduction criteria, in particular for smaller species.
Our response: We consulted with regional and national freshwater
mussel experts from around the United States, and the 35-mm length was
considered to be an appropriate delineating threshold to use when
differentiating between adult and juvenile mussels. This conclusion was
made based on the general consensus amongst those asked that
individuals below 35 mm in length are not readily detectable during
field surveys. Without species-specific data identifying the known size
at age of sexual maturity for the subject species, we found it
appropriate to consistently use the same cutoff for multiple species if
no species-specific data were available. As these data become
available, we will update these criteria as appropriate.

Comments From States

(4) Comment: One commenter requested that the Service emphasize
desiccation study data completed at the San Marcos Aquatic Resources
Center that demonstrate that Texas pimpleback is able to tolerate 32
days without water and the Texas fatmucket can tolerate about 3 days
without water.

[[Page 48037]]

Our response: The desiccation trials mentioned by the commenter
were conducted in a laboratory growth chamber at 25 degrees Celsius
([deg]C) (77 degrees Fahrenheit ([deg]F)) and the relative humidity is
not reported (Bonner et al. 2018, p. 193). Presumably, live freshwater
mussels experiencing dewatering occurring in the natural environment
would be exposed to temperatures greater than 25 [deg]C (77 [deg]F),
especially during summer, when drying events are most likely to occur.
Additionally, exposed animals would be susceptible to predation.
Therefore, while we report the results of the desiccation study,
emphasizing them could erroneously create an inaccurate representation
of the conditions that exposed mussels would experience and
artificially inflate the exposure time during which mussels could be
expected to survive in the wild.
(5) Comment: The State of Texas disagrees with the finding that
there are no federalism implications for the designation of critical
habitat.
Our response: Federalism is the division and sharing of power
between the Federal Government and the individual State governments. In
keeping with Department of the Interior and Department of Commerce
policy, we requested information from, and coordinated development of,
the proposed critical habitat designation with appropriate State
resource agencies throughout central Texas. From a federalism
perspective, the designation of critical habitat directly affects only
the responsibilities of Federal agencies. The Act imposes no other
duties with respect to critical habitat, either for States and local
governments, or for anyone else. As a result, this final rule does not
have substantial direct effects either on the States, or on the
relationship between the national government and the States, or on the
distribution of powers and responsibilities among the various levels of
government. In accordance with Executive Order 13132 (Federalism), this
rule does not have significant federalism effects, and a federalism
summary impact statement is not required.
(6) Comment: The State of Texas requested clarification on whether
the completion of an approved freshwater mussel identification and
sampling course and proficiency testing will be required for scientists
with a permit issued under section 10(a)(1)(a) of the Act (a
``10(a)(1)(a) permit''), and whether the 4(d) rule will allow qualified
individuals to relocate Texas fawnsfoot.
Our response: The provision of the 4(d) rule that allows for Texas
fawnsfoot surveys to be conducted by those who pass an approved Texas
mussel identification and sampling course is intended for those who are
sampling for freshwater mussels, in which mussels are collected,
identified, and returned to the mussel bed from which they came.
Surveyors who are trained in survey techniques and how to identify the
various species that occur in Texas will not need a 10(a)(1)(a) permit
because we expect the effects to the species to be negligible. This
provision in the 4(d) rule is not intended to replace the 10(a)(1)(a)
permit process, and those with a 10(a)(1)(a) permit will not be
required to complete the course. Furthermore, relocation of Texas
fawnsfoot from one mussel bed to another is not an excepted form of
take under this 4(d) rule.
(7) Comment: The State of Texas suggested that naturally occurring
ambient water quality should be considered in the context of historical
water quality, and laboratory thresholds reported for temperature,
salinity, chlorides, and dissolved oxygen should be considered when
identifying essential water quality thresholds as components of
critical habitat.
Our response: The objective use of laboratory-based studies, in
addition to in situ monitoring, is critical to the understanding of
physiological and toxicological thresholds for freshwater mussels. Even
though certain ambient water quality parameters are currently occurring
in the presence of live freshwater mussels, there is no clear
indication that these parameters are protective of freshwater mussels,
as different life stages of the species are more sensitive to water
quality changes than others (i.e., glochidia and juveniles are more
sensitive than adults). Freshwater mussel populations throughout the
State of Texas have declined in recent decades, and the presence of
reduced or restricted mussel populations should not be used as an
indicator that instream conditions are adequate for the long-term
persistence of the population. The completion of laboratory studies can
provide objective thresholds for individual chemicals, temperatures, or
other water quality parameters for both lethal and sublethal effects on
individual freshwater mussel species. When identifying the physical or
biological features related to water quality for the mussels, we set
the thresholds at levels that have been objectively identified as
protective of the mussels. Therefore, laboratory-derived values were
selected when identifying these components rather than utilizing
observed ambient values, which, as described above, may not be
protective of all the covered species life stages.
(8) Comment: The State of Texas requested clarification on how
increased extreme precipitation is projected to have divergent effects
on future high stream flows in different rivers, as the Service has
predicted for the Llano River and Middle Trinity River.
Our response: Different river basins experience different
conditions that affect the future of flows within those basins. For the
Llano River, while there have been recent significant high flow events,
recent trends in stream flows in the river have shown an overall
reduction in flows in the basin. These reductions are expected to
continue in response to climate change (reduced projected rainfall) and
expanding development in Texas (groundwater pumping). Conversely, the
Trinity River is anticipated to experience increases in flows in the
future due to the growth of the Dallas-Fort Worth metroplex and its
reliance on surface waters. Water resources that historically would
have been distributed across the landscape in north Texas have been
consolidated into an assortment of wastewater treatment and water
supply system with many return flows feeding into the Trinity River.
These return flows combine to elevate the baseflows of the Trinity
River at all times (TRA 2023, pp. 23, 25-27) and can combine with rain
events, leading to higher high flow events.
(9) Comment: The State of Texas provided recommendations for
clarification of the physical or biological features (PBFs) essential
to the conservation of the central Texas mussels, particularly the PBFs
concerning the identification of specific elements of the flow regimes
considered essential, adaptive flexibility in defining host fish for
the subject mussel species, and the number of sample events required
(single or multiple) to evaluate the ranges of water quality
parameters.
Our response: For the flowing water PBF, we welcome additional
research on the identification of specific flow regime elements needed
for the long-term conservation of these mussel species. However, this
information does not currently exist, and so we could not use specific
flow rates when developing the PBFs for the species. We are actively
working with external partners who are researching the role of stream
flows on Texas fatmucket growth and survival in the Colorado River
Basin, and we will use these findings as we develop recovery plans for
the species.
For the host fish PBF, we must use the best available information
when

[[Page 48038]]

identifying essential PBFs, and the current science indicates that
sunfishes (including bluegill (Lepomis macrochirus), green sunfish (L.
cyanellus), Guadalupe bass (Micropterus treculii), and largemouth bass
(M. salmoides)), freshwater drum (Aplodinotus grunniens), catfish
(channel catfish (Ictalurus punctatus), flathead catfish (Pylodictis
olivarus), and tadpole madtom (Noturus gyrinus)), minnows (family
Cyprinidae), and shiners (blacktail shiner (Cyprinella venusta) and red
shiner (C. lutrensis)) are hosts for the central Texas mussel species.
Additional host fish species identified for these mussels will be
incorporated into the recovery planning process.
Finally, for the PBF that relates to water quality, it can be
challenging to provide specific thresholds for water quality parameters
because effects to freshwater mussels can range from sublethal to
lethal depending on the duration of the exposure to conditions as well
as the time of year, flow rates, and other factors. Currently, species-
specific toxicology studies have not been completed for the species
included in this rule. Therefore, currently, the Service is using
surrogate acute water quality standards from other freshwater mussel
species in the United States to identify physical features for
designated critical habitat. As the species-specific acute and chronic
standards are developed for the covered species, the Service will
revisit and refine the characteristics of these water quality features.
Once these standards are developed, the Service will work with subject
matter experts to identify the appropriate sampling techniques to
evaluate the acceptable thresholds for water quality parameters, and
work with project proponents to ensure that the most appropriate
methods will be used to determine effects on listed freshwater mussels
on a project-by-project basis.
(10) Comment: The State of Texas and several commenters requested
that the Service more clearly identify the estimated probability of
persistence (threshold) that would preclude a listing decision.
Our response: The ``probability of persistence'' is just one small
part of our SSA report that informed our analysis and listing decision,
which also considered the factors identified by the Act (such as a
species' life history, generation time, current and future threats, and
trajectory of those threats). There is not a strict probability above
which we would not list and below which we would list, particularly
because the information we use to assess the species' persistence is of
a general nature and does not pinpoint the likelihood of persistence to
the degree we would require to provide certainty that that the species
persistence was above or below such a threshold. Therefore,
``probability of persistence'' alone is not going to result in a
decision that a species meets the definition of threatened or
endangered.
(11) Comment: The State of Texas and several commenters are
concerned about the economic impact that proposed critical habitat
would have on private landowners, private property values, and
wastewater treatment plants (WWTPs), suggesting that the incremental
effects memo (IEM) only captures baseline costs, and not the total
costs associated with critical habitat designation. The commenters
requested that prior to publishing a final rule, the Service conduct a
new economic analysis, using the coextensive approach.
Our response: As stated in the economic analysis of the designation
of critical habitat for the Central Texas mussels, guidelines issued by
the U.S. Office of Management and Budget (OMB) for the economic
analysis of regulations direct Federal agencies to measure the costs
and benefits of a regulatory action against a baseline (i.e., costs and
benefits that are ``incremental'' to the baseline). The OMB defines the
baseline as the ``best assessment of the way the world would look
absent the proposed action.'' (Circular A-4, 2003). In other words, the
baseline includes any existing regulatory and socio-economic burden
imposed on landowners, managers, or other resource users affected by
the designation of critical habitat. The baseline includes the economic
impacts of listing the species under the Act, even if the listing
occurs concurrently with critical habitat designation. Impacts that are
incremental to the baseline (i.e., occurring over and above existing
constraints) are those that are solely attributable to the designation
of critical habitat and are the focus of the economic analysis.
The Service acknowledges that significant debate has occurred
regarding whether assessing the impact of critical habitat designations
using the incremental approach is appropriate, with several courts
issuing divergent opinions. Most recently, the U.S. Ninth Circuit Court
of Appeals concluded that the incremental approach is appropriate, and
the U.S. Supreme Court declined to hear the case (Home Builders
Association of Northern California v. United States Fish and Wildlife
Service, 616 F.3d 983 (9th Cir. 2010), cert. denied, 179 L. Ed 2d 301,
2011 U.S. Lexis 1392, 79 U.S.L.W. 3475 (2011); Arizona Cattle Growers
v. Salazar, 606 F.3d 1160 (9th Cir. 2010), cert. denied, 179 L. Ed. 2d
300, 2011 U.S. Lexis 1362, 79 U.S. L.W. 3475 (2011)). Subsequently, on
August 28, 2013, the Service revised its approach to conducting impact
analyses for designations of critical habitat, specifying that the
incremental approach should be used (78 FR 53062).

Public Comments

(12) Comment: A commenter suggested that the reliance on data
regarding recently dead shell material that are up to 21 years old,
combined with the difficulty to detect mussels at sites that are not
visited multiple times, is insufficient to define areas occupied at the
time of listing and designate those areas as critical habitat for the
Texas fatmucket, Texas fawnsfoot, and Texas pimpleback.
Our response: While the Service used the year 2000 as the oldest
year for ``recent'' survey data, much of the survey data used during
the review of the species that are the subjects of this rule were
collected during the increase in sampling efforts following the 2010
State listing of these species as threatened by the Texas Parks and
Wildlife Department (TPWD). Therefore, much of the data used for the
SSA were closer to 10 years old when we were developing the August 26,
2021, proposed rule. However, in instances in which the data were in
fact collected approximately 20 years ago, the time gap between the
data collection and proposed rule would be between 1 and 3 generations
for these species. Because the Service has not been notified of or
witnessed rapid, substantial, permanent habitat changes or been
provided evidence of recent mussel die-offs through the collection of
large numbers of fresh-dead (shells still attached to soft tissue) or
recent dead (shells lacking connection to soft tissue but still
containing a shiny inner shell layer), it is reasonable to conclude
that these occupied areas would still be occupied by the species at
some level.
Much of the freshwater mussel sampling that has been completed in
Texas to date has consisted of single, opportunistic surveys as part of
larger research projects or environmental compliance surveys completed
prior to some form of instream construction rather than monitoring
events that would require multiple visits to individual sites. While
multiple visits to a site will provide a clearer picture of population
abundance and extent, a single visit is often sufficient to

[[Page 48039]]

determine occupancy if the species is present at that time.
(13) Comment: A commenter stated that the proposed critical habitat
designation does not include an initial regulatory flexibility analysis
to satisfy the requirements of the Regulatory Flexibility Act (RFA; 5
U.S.C. 601 et seq.), and the Service has not prepared an environmental
impact statement to satisfy the National Environmental Policy Act
(NEPA; 42 U.S.C. 4321 et seq.).
Our response: When a species is proposed for listing, the Act's
section 4(a)(3) requires the Secretary of the Interior (Secretary), to
the maximum extent prudent and determinable, to designate critical
habitat for that species. For more information about the considerations
we must undertake when designating critical habitat, see and
Consideration of Impacts under Section 4(b)(2) of the Act and
Regulatory Flexibility Act (5 U.S.C. 601 et seq.), below.
Under the Regulatory Flexibility Act (RFA), Federal agencies are
only required to evaluate the potential incremental impacts of a
rulemaking on directly regulated entities. The regulatory mechanism
through which critical habitat protections are realized is section 7 of
the Act, which requires Federal agencies, in consultation with the
Service, to ensure that any action authorized, funded, or carried by
the Agency is not likely to adversely modify critical habitat.
Therefore, only Federal action agencies are directly subject to the
specific regulatory requirement (avoiding destruction and adverse
modification) imposed by critical habitat designation. Under these
circumstances, it is the Service's position that only Federal action
agencies will be directly regulated by this designation. Therefore,
because Federal agencies are not small entities, the Service may
certify that the proposed critical habitat rule will not have a
significant economic impact on a substantial number of small entities.
Because certification is possible, no regulatory flexibility analysis
is required.
Upon recommendation of the Council on Environmental Quality (CEQ),
the Service determined that NEPA documents need not be prepared in
connection with regulations finalizing the listing status for species
pursuant to section 4(a) of the Act. This critical habitat designation
is issued concurrently with the listing of the species under section
4(a). On October 25, 1983, the Service published in the Federal
Register a notice explaining this decision (48 FR 49244). The Service
subsequently interpreted this 1983 determination to apply to critical
habitat designations, based on the decision delivered in a Sixth
Circuit Court of Appeals case (Pacific Legal Foundation v. Andrus, 657
F. 2d 829 (1981)) and CEQ's recommendation.
Based on this interpretation, the Service did not conduct NEPA
analyses on critical habitat designations between 1983 and 1998.
However, since the mid-1990s, the question of whether NEPA applies to
the Federal action of designating critical habitat under the Act has
been the subject of multiple lawsuits. In Douglas County v. Babbitt, 48
F.3d 1495 (9th Cir. 1995), the U.S. Court of Appeals for the Ninth
Circuit upheld the Service's conclusion that critical habitat actions
are exempt from NEPA compliance. The Service was again challenged on
this conclusion in Catron County Board of Commissioners v. U.S. Fish
and Wildlife Service, 75 F.3d 1429 (10th Cir. 1996) (Catron County);
the U.S. Court of Appeals for the Tenth Circuit ordered the Secretary
to comply with NEPA when completing critical habitat determinations.
The DC District Court in Cape Hatteras Access Pres. All. v. U.S. Dep't
of Interior, 344 F. Supp. 2d 108 (D.D.C. 2004) similarly held that NEPA
applied to critical habitat designations. However, more recently, the
Fifth Circuit Court of Appeals agreed with the Ninth Circuit and held
that NEPA does not apply to critical habitat designations under the Act
(Markle Interests v. FWS, 827 F.3d 452 (5th Cir. 2016), rev'd on other
grounds sub nom. Weyerhaeuser v. U.S. Fish and Wildlife Service, 139 S.
Ct. 361 (2018)). Other district courts have applied this reasoning as
well (e.g., Otay Mesa Property, LP v. U.S. Department of the Interior,
144 F. Supp. 3d 35 (D.D.C. 2015)).
While the Service does not concede that NEPA applies to critical
habitat designations or revisions under the Act, we agreed to address
NEPA compliance for critical habitat designations when the range of the
species occurs within the jurisdiction of the U.S. Court of Appeals for
the Tenth Circuit, which includes the following States: Colorado,
Kansas, New Mexico, Oklahoma, Utah, and Wyoming. The central Texas
mussels' critical habitat designations do not occur within the
jurisdiction of the U.S. Court of Appeals for the Tenth Circuit, so we
did not prepare an environmental assessment under NEPA for this
designation.
(14) Comment: A commenter requested that proposed critical habitat
unit TXFM-2 (San Saba River) for the Texas fatmucket be limited to the
upper section of the San Saba River, as it is the only segment of the
river that has the PBFs essential to the conservation of the species.
Because the middle reach of this critical habitat unit lacks an
adequate hydrologic flow regime, which is an essential PBF, and this
flow regime is not expected to improve under current predictions of
increasing periods of drought, and the species does not currently exist
in the lower reach of the San Saba River, they requested these middle
and lower reaches of the San Saba River be removed from final critical
habitat designation.
Our response: Based on recent survey data, we consider this reach
to be currently occupied by the species. Despite the anticipated future
threats to water levels in the middle San Saba River and the Hill
Country as a whole, live Texas fatmucket have been observed at multiple
locations in the middle reach of the San Saba River in the last 10
years. Historical collection records provide evidence that the species
has also occurred in the past in the lower reach of the San Saba River
near San Saba, Texas. We acknowledge that the unique geology of the
middle reach of the San Saba River presents conservation challenges
concerning flowing water (an essential PBF) in the lower reach of the
river, but this unit currently contains adequate flowing water,
suitable substrate, appropriate host fish, and adequate water quality,
and recovery will entail restoring the species to reaches of habitat
long enough such that stochastic events do not eliminate the entire
population. The lower reach of the San Saba does not present these
geological challenges and contains the essential PBFs needed to support
the species in this portion of the San Saba River. The middle and lower
reaches of the San Saba River add approximately 69 river miles (mi)
(111 river kilometers (km)) of habitat to the population, they would
increase the overall resiliency of the population.
(15) Comment: A commenter stated that the Service lacks enough
species-specific information to designate critical habitat,
particularly in unoccupied areas, and that the proposed rule fails to
show that designated critical habitat is determinable.
Our response: We are required to designate critical habitat based
on the best scientific data available at the time of designation. We
considered the best scientific data available regarding the central
Texas mussels to evaluate potential critical habitat under the Act. We
have sufficient information to understand the habitat these species
need and where the species occur, and we solicited peer review on our
evaluation of that information. The

[[Page 48040]]

listing and critical habitat process does not require perfect
information; it requires that we use the best available information to
make our determinations. Therefore, we found that critical habitat was
determinable in both occupied and unoccupied areas.
(16) Comment: Several commenters requested that critical habitat
designation for endangered species be limited to occupied reaches.
Our response: The Act defines critical habitat under section
3(5)(A) and allows for the designation of areas within and outside the
geographical areas occupied by the species at the time of listing.
There is no statutory requirement to limit critical habitat areas to
only occupied areas. The Act requires that areas outside the
geographical area occupied by the species be essential for the
conservation of the species.
We have determined that unoccupied units are essential for the
conservation of the Texas fatmucket and Texas pimpleback because they
provide for the growth and expansion of the species within portions of
their historical ranges. We identified areas outside the geographical
areas currently occupied by the Texas fatmucket and Texas pimpleback as
critical habitat in order to increase the stream length of critical
habitat designations adjacent to existing small populations. These
unoccupied areas are located immediately adjacent to currently occupied
stream reaches, include one or more of the essential PBFs, and allow
for expansion of existing populations necessary to improve population
resiliency, extend physiographic representation, and reduce the risk of
extinction for the species. The establishment of additional moderately
healthy to healthy populations across the range of these species would
reduce their risk of extinction. Improving the resiliency of
populations in the currently occupied streams, and into identified
unoccupied areas, will increase species viability. See Criteria Used to
Identify Critical Habitat, below.
(17) Comment: Commenters requested that additional unoccupied areas
be designated as critical habitat. These areas included the upstream
portions of the Llano River in Edwards County, Texas, lower reaches of
the Llano River, downstream of the City of Llano in Llano County,
Texas, and Johnson Creek, which flows into the Guadalupe River in Kerr
County, Texas.
Our response: After identifying areas occupied by the species at
the time of listing, we will identify specific areas outside the
geographical area occupied by the species at the time of listing that
the Secretary determines are essential for the conservation of the
species. We evaluated the upstream portions of the South Llano River
located in Edwards County and found that this reach of the river does
not consistently remain wetted and does not provide suitable habitat
through large portions of the stream in Edwards County and is not
essential for the conservation of the species. Therefore, we did not
designate the area as critical habitat. We evaluated the lower reaches
of the Llano River near the river's confluence with the Little Llano
River; these reaches are bookended by a dam in the City of Llano used
for drinking water and a low-head dam which impounds Robinson Lake. Any
suitable habitat between the two structures would be isolated from
other existing populations due to stretches of unsuitable habitat and
impairment of fish passage and therefore is not essential for the
conservation of either Texas pimpleback or Texas fatmucket. Therefore,
for the central Texas mussels, other than the unoccupied areas noted in
this rule (TXFM-1c, TXFF-1b, TXPB-1a, and TXPB-5b),we are not
designating additional areas outside the geographical area occupied by
the species because we have not identified any additional unoccupied
areas that meet the definition of critical habitat at this time.
(18) Comment: One commenter stated that proposed critical habitat
unit TXFM-1 does not meet the criteria established for critical habitat
since it does not contain all the PBFs described in the proposed rule
as essential to the conservation of the species.
Our response: In areas occupied at the time of listing a species as
endangered or threatened, critical habitat is the specific areas on
which are found the physical or biological features (PBFs) that are
essential to the conservation of the species and that may require
special management considerations or protection. It is not required
that an area contain all PBFs in order to qualify as critical habitat.
Unit TXFM-1 contains multiple PBFs (e.g., presence of suitable
substrates, connected instream habitats, and presence of host fish),
and while the unit may need special management considerations to reduce
sedimentation, improve water quality, maintain adequate flows, and
improve habitat connectivity, it meets the definition of critical
habitat for the Texas fatmucket.
(19) Comment: A commenter requested that the Service revise its
discussion of water quality in the lower Colorado River mainstem below
Austin to state that, according to the Texas Commission on
Environmental Quality's (TCEQ's) 2020 Integrated Report (TCEQ 2020;
entire), all water quality parameters being monitored are meeting the
Texas Surface Water Quality Standards, and there are no impairments.
Our response: Impairment, as defined through the Texas Surface
Water Quality Standards, can differ from biological requirements for
individual species. Because a stream reach meets legal standards for
water quality parameters does not mean that the water quality meets the
needs of the species. While we understand that the entire lower
Colorado River mainstem below Austin may not experience conditions that
are impacting freshwater mussel growth and survival, we feel that it is
important to acknowledge that these conditions can exist at times in
the reach of the river. For example, TCEQ produces an integrated report
every 2 years that sets the ammonia criterion to denote impairment in
segments of the Colorado River and includes any exceedances of this
criteria (TCEQ 2022, entire). Chronic ammonia toxicity studies have
shown that juvenile freshwater mussel species experience significant
reductions in growth and survival when exposed to ammonia
concentrations below these levels (Wang et al. 2007, p. 2054). Data
presented in the TCEQ 2022 report would place the observed significant
reductions in growth below the exceedance threshold of 0.33 milligrams
per liter (mg/L) and reductions in survival near the observed
exceedance mean value of 0.45 mg/L.
(20) Comment: Commenters requested more discussion of the threat of
extended low-flow conditions in the lower Colorado River Basin.
Our response: There are threats of extended low-flow conditions in
the lower reaches of the lower Colorado River Basin, and we are
actively working with the LCRA on the implementation of the LCRA
Agreement, which includes conservation measures that would help further
understand, avoid, and minimize the threat of low-flow conditions to
freshwater mussels in this river basin.
The 2020 LCRA Water Management Plan (WMP) allocates a portion of
its ``firm water'' supply to meet environmental flow needs within the
lower Colorado River Basin (LCRA 2020, pp. ES-2-ES-3). These needs are
determined through calculated monthly subsistence flow values and are
based on results of an instream flow study in 2008 (Bio-West 2008, pp.
69-90) that investigated the flow relationships to aquatic habitat and
the State-threatened blue sucker (Cycleptus elongatus), and they are
consistent with the Texas Instream Flow Program methodology

[[Page 48041]]

(LCRA 2020, p. 2-2). While this 2008 study did not specifically focus
on the habitat needs of freshwater mussels, a subsequent study in 2018
determined that the subsistence flows standards set by the WMP were
adequate to protect instream freshwater mussel habitat during the
periods expected to receive the lowest flow conditions (August; 107
cubic feet per second at the Wharton U.S. Geological Survey (USGS)
gauge) (Bonner et al. 2018; entire). The LCRA Agreement states that an
amendment to the 2020 WMP, which will consider additional information
regarding flow or temperature needed for freshwater mussels or host
fish, if available during that amendment process, is expected to occur
not later than March 1, 2025 (LCRA 2023, pp. 60-63). While these flow
assurances cannot entirely remove the threat of low flow conditions in
the lower Colorado River, they can reduce the threat and ameliorate the
instream conditions during these periods.
(21) Comment: A commenter stated that candidate conservation
agreements with assurances (CCAAs) do not provide sufficient certainty
of benefits to the species because they have limited authority, focus
on a subset of the threats, allow permittees to withdraw at any time,
and do not ensure future conditions. The commenter, therefore, requests
that CCAAs not be used as a basis for critical habitat exclusions in
the final rule.
Our response: We evaluate whether an area should be excluded from
critical habitat based on whether the benefits of exclusion outweigh
the benefits of inclusion. As outlined in our Policy Regarding
Implementation of Section 4(b)(2) of the Endangered Species Act (81 FR
7226), when we undertake a discretionary 4(b)(2) exclusion analysis, we
will always consider areas covered by a permitted candidate
conservation agreement with assurances (CCAA) and anticipate
consistently excluding those areas from a critical habitat designation
if incidental take caused by the activities in those areas is covered
by the permit under section 10 of the Act and the CCAA meets all of the
following conditions: the permittee is properly implementing the
agreement and is expected to do so for the term of the agreement; the
species for which critical habitat is being designated is a covered
species in the agreement; and the agreement specifically addresses the
habitat of the species for which critical habitat is being designated
and meets the conservation needs of the species in the planning area.
We have determined that the BRA Agreement (BRA 2021, entire), LCRA
Agreement (LCRA 2023, entire), and TRA Agreement (TRA 2023, entire)
fulfill the above criteria, and we are excluding from this critical
habitat designation some non-Federal lands covered by these three CCAAs
that provide for the conservation of the Texas fawnsfoot, Texas
pimpleback, and Balcones spike. The LCRA Agreement also provides for
the conservation of Texas fatmucket. However, because no critical
habitat units for the Texas fatmucket fall within reaches where the
LCRA Agreement can directly reduce the primary threat of low water
quantity, we have not excluded any proposed critical habitat for the
Texas fatmucket based on the LCRA Agreement. Additionally, within the
BRA and LCRA CCAAs, some non-Federal lands are included in the CCAAs'
Covered Areas that we did not exclude from designated critical habitat
(i.e., river miles above Possum Kingdom Reservoir and river miles above
the Highland lakes in the BRA and LCRA CCAAs respectively). These areas
were not excluded because while the BRA and LCRA CCAAs provide overall
net conservation benefits for the covered species, threat reduction
efforts included as conservation measures within the agreements target
other locations of their respective basins.
Possum Kingdom Reservoir represents the most upstream BRA-operated
infrastructure in the Brazos River Basin. The BRA has no infrastructure
and limited interests above Possum Kingdom reservoir, and therefore,
has no way to directly influence freshwater mussel populations or their
habitats in this portion of the basin (BRA 2021, p. 15). Regarding the
LCRA CCAA, with the exception of two reservoirs LCRA owns and operates
for purposes of power plant cooling which are not included in the
critical habitat designation, LCRA does not own or operate any other
water infrastructure on any tributaries or on the main stem of the
Colorado River upstream of Lake Buchanan or on other tributaries or
river segments that contribute flow to the Highland Lakes or the
Colorado River within LCRA's broader service area.
The development and maintenance of effective working partnerships
with non-Federal partners for the conservation of at-risk species is
particularly important in areas such as Texas, a State with relatively
little Federal landownership and many species of conservation concern.
We find that excluding areas from critical habitat that are receiving
long-term conservation and management for the purpose of protecting the
habitat that supports the Texas fawnsfoot, Texas pimpleback, and
Balcones spike will preserve our external partnerships in Texas and
will encourage future collaboration towards conservation and recovery
of listed species.
Because the agreements are voluntary, they demonstrate the
commitment of the partners to the conservation actions; the CCAA
process takes time and effort to put in place, and the agreement must
result in a net conservation benefit to the species. The partnership
benefits are significant and outweigh the potential regulatory,
educational, and ancillary benefits of including the land in the final
critical habitat designation for these three species; in addition, the
subject areas are occupied by the species, so there is less incremental
benefit to the unit being included in the critical habitat designation.
Therefore, the BRA Agreement, LCRA Agreement, and TRA Agreement provide
greater protection of habitat for the Texas fawnsfoot, Texas
pimpleback, and Balcones spike than could be gained through the
project-by-project analysis under a critical habitat designation.
(22) Comment: A commenter claimed that our proposed 4(d) rule was
arbitrary and capricious because we did not assess the costs and
benefits of the rule and therefore did not establish that the proposed
4(d) rule was necessary and advisable.
Our response: The Act clearly prohibits the Service from
considering economic or similar information when making listing,
delisting, or reclassification decisions. Congress added this
prohibition in the 1982 amendments to the Act when it introduced into
section 4(b)(1) an explicit requirement that all decisions under
section 4(a)(1) of the Act be based ``solely on the basis of the best
scientific and commercial data available.'' Congress further explained
this prohibition in the Conference Report accompanying the 1982
Amendments: ``The principal purpose of these amendments is to ensure
that decisions in every phase of the process pertaining to the listing
or delisting of species are based solely upon biological criteria and
to prevent non-biological considerations from affecting such decisions.
These amendments are intended to expedite the decision-making process
and to ensure prompt action in determining the status of the many
species which may require the protections of the Act.'' (H.R. Conf.
Rep. No. 97-835, at 19 (1982).)
Therefore, following statutory framework and congressional intent,
we do not conduct or develop economic impact analyses for
classification decisions. Additionally, 4(d) rules concurrently issued
with a classification rule are inherently a part of a

[[Page 48042]]

classification decision for a threatened species and therefore, a
consideration of economic impacts does not apply. If we determine that
a species meets the Act's definition of a threatened species, part of
our consideration for completing the listing process is to consider
what measures are necessary and advisable to provide for the
conservation of the species under section 4(d) of the Act. We,
therefore, consider a 4(d) rule to be a necessary phase of the listing
process to put in place protections for threatened species.
(23) Comment: Commenters expressed concerns that threatened status
may be insufficient for the Texas fawnsfoot and recommended it be
assigned endangered status.
Our response: The Act defines ``endangered species'' and
``threatened species'' and mandates five factors for consideration when
determining a species' status under the Act. We have determined that
endangered species status under the Act is not appropriate for the
Texas fawnsfoot because the species maintains multiple, moderately
resilient populations across its historical range with low risk of
significant decline in the near term. Further, given its distribution
and the health of its populations, the Texas fawnsfoot has sufficient
redundancy and representation to withstand catastrophic events and
novel changes in its environment in the near term. For these reasons,
the Texas fawnsfoot is not currently in danger of extinction; it is,
however, at risk of extinction in the foreseeable future because 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, within 25 to
50 years, 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 three populations are
expected to become functionally extirpated, leaving no more than four
unhealthy populations remaining after 25 years. See Determination of
Status: Texas Fawnsfoot, below.
(24) Comment: A commenter requested that all species be listed as
threatened to better promote voluntary habitat conservation.
Our response: The Act requires us to make a listing determination
using the best available scientific and commercial data after
conducting a review of the status of the species. The primary
difference between an endangered species and a threatened species is
the timing of the risk of extinction. An ``endangered species'' is one
that is in danger of extinction throughout all or a significant portion
of its range. A ``threatened species'' is one that is likely to become
endangered within the foreseeable future throughout all or a
significant portion of its range; therefore, it is not currently in
danger of extinction. After evaluating threats to the central Texas
mussel species and assessing the cumulative effect of the threats under
the Act's section 4(a)(1) factors, we found that Guadalupe fatmucket,
Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and
false spike have declined significantly in overall distribution and
abundance. At present, most of their 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. We found that, for these six
species, the threats are currently occurring and result in the species
being in danger of extinction now. Therefore, a threatened status
determination for these species would not be appropriate. The
difference between endangered and threatened does not affect our
ability to encourage voluntary conservation.
The listing of a species does not obstruct the development of
conservation agreements or partnerships to conserve the species. Once a
species is listed as either endangered or threatened, the Act provides
many tools to advance the conservation of listed species. Conservation
of listed species in many parts of the United States is dependent upon
working partnerships with a wide variety of entities, including the
voluntary cooperation of non-Federal landowners. Building partnerships
and promoting cooperation with landowners are essential to
understanding the status of species on non-Federal lands and may be
necessary to implement recovery actions, such as reintroduction of
listed species, habitat restoration, and habitat protection. Once a
species is listed, for private or other non-Federal property owners, we
offer voluntary safe harbor agreements that can contribute to the
recovery of species, habitat conservation plans that allow activities
(e.g., grazing) to proceed while minimizing effects to species, funding
through the Partners for Fish and Wildlife Program to help promote
conservation actions, and grants to the States under section 6 of the
Act.
(25) Comment: A commenter stated concerns that the Service focused
on recent trends when modeling the impacts of climate change and
disagreed that climate change will exacerbate identified threats in
central Texas.
Our response: Experts anticipate that climate change will lead to
decreased water availability in Texas due to increased frequency and
intensity of drought conditions in the State. During drought periods,
pressure on freshwater resources, particularly increased evaporation in
reservoirs and higher demands on groundwater pumping, in the State will
lead to a decline in instream flows. Decreased instream flows correlate
with increases in instream temperatures. In the SSA report, we relied
upon numerous studies that have identified the effects of increased
temperature on the growth, fitness, and survival of freshwater mussels
(Bonner et al. 2018, p. 6; Ganser et al. 2015, p. 1712; Spooner and
Vaughn 2008, pp. 312-313; Service 2022, p. 10). The combination of
declines in instream flows and increasing temperatures of the remaining
flows are anticipated to have a negative impact on remaining freshwater
mussel populations.
(26) Comment: A commenter questioned whether mussels are actually
declining due to human development and suggests that declines may have
been occurring prior to human contact.
Our response: While mussel populations surely ebbed and flowed
prior to human development, it is well established that widespread
declines of freshwater mussels have occurred in the last 50 to 75 years
(Haag 2019, p. 43; Haag 2012, pp. 316-390). Through a combination of
long-term monitoring and evidence in the historical record, it is clear
that the decline of freshwater mussels is closely tied to advances in
human infrastructure development (Haag 2012, pp. 316-390). In some
cases, the ties can be closely pinpointed to the construction of a
single structure (e.g., large, power-generating hydrodam) and a
resulting decline and eventual extirpation of an upstream freshwater
mussel population (e.g., extirpation of the elephant ear (Elliptio
crassidens) population in the Upper Tennessee Basin following habitat
fragmentation in tributaries of the Tennessee River (Johnson et al.
2012a, p. 89)). Regardless of whether declines occurred prior to human
development, the declines of the central Texas mussel species in the
recent past are well documented.
(27) Comment: A commenter requested clarification on whether the
artificially sustained wastewater effluent flows are beneficial or
detrimental to the central Texas mussels.

[[Page 48043]]

Our response: Artificially sustained effluent flows can be
beneficial to freshwater mussels by providing flow in low-flow and
drying areas where mussels might otherwise desiccate. However, effluent
flows can also be detrimental to freshwater mussels if the effluent
water quality is poor. We consider both water quantity and quality when
evaluating effluent and its impact on mussels. Parameters for healthy
water quality and water quantity are defined in the SSA report (Service
2022, pp. 6-10), and we use these benchmarks as we evaluate the
species' status now and in the future.
(28) Comment: A commenter disagreed that pesticides originating
from agricultural sources are a pollutant of concern at levels
experienced in the natural environment.
Our response: Pesticides have been demonstrated to have both lethal
and non-lethal effects on freshwater organisms, including freshwater
mussels around the world (Milam et al. 2005, pp. 169-172; Bringolf et
al. 2007a, p. 2099, 2007b, pp. 2105-2106, 2007c, p. 2092; Chmist et al.
2019, pp. 439-440). These studies have been completed for multiple,
freshwater mussel life stages, including glochidia, juveniles, and
adults, and have documented the harmful effects of a variety of
herbicides, pesticides, and other chemical compounds. While we support
and applaud agricultural producers' efforts to target applications and
reduce run-off into adjacent waterways, it is still necessary to
acknowledge the threat of the compounds to these mussels, as the
specific lethal and non-lethal effects are not known for all mussel
species, and spills, unregulated discharges, and errant applications
are possible and would have significant negative effects on
populations.
(29) Comment: A commenter claimed that the proposed listings are
unnecessary as Texas already protects the central Texas mussels.
Our response: In 2007 and 2008, we received petitions requesting
that we list as endangered or threatened species and designate critical
habitat for the Texas fatmucket, Texas fawnsfoot, Texas pimpleback, and
false spike. (See Previous Federal Actions in the August 26, 2021,
proposed rule (86 FR 47918-47919) for more information.) In 2009, the
State of Texas listed the Texas fatmucket, Texas fawnsfoot, Texas
pimpleback, and the false spike as threatened, launching an era of
freshwater mussel conservation Statewide and bringing attention to this
faunal group. However, once the Service is petitioned to list a
species, we are required to complete our regulatory process which takes
into account conservation efforts and State regulatory efforts in our
listing determination. Under the requirements of the Act, we must
conduct the required analysis and list the species if it is found to be
warranted, and we cannot defer to any State listing. This rule codifies
our listing determinations for the central Texas mussels.

I. Final Listing Determination

Background

A thorough review of the taxonomy, life history, and ecology of the
Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe orb,
Texas pimpleback, Balcones spike, and false spike, referred to as the
central Texas mussels, is presented in the SSA report (Service 2022,
pp. 4-44).

Guadalupe Fatmucket

The Guadalupe fatmucket (Lampsilis bergmanni) was recently
discovered to be a separate and distinct species from Texas fatmucket
(Inoue et al. 2018, pp. 5-6; Inoue et al. 2020, entire), and the
Service now recognizes the Guadalupe fatmucket as a new species that
occurs only in the Guadalupe River Basin. Because the Guadalupe
fatmucket is so similar to the Texas fatmucket and better information
is not yet available, we conclude the Guadalupe fatmucket has similar
habitat needs (headwater habitats in gravel or bedrock fissures) and
host fish (sunfishes) as the Texas fatmucket, below.
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; it 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 to 25 years (Haag and Rypel 2010, pp. 4-6), and we
expect Guadalupe fatmucket to have a similar lifespan.
Guadalupe fatmucket is currently found in one population, which
occurs in 52 miles (84 km) of the Guadalupe River Basin in Kendall and
Kerr Counties, Texas (Randklev et al. 2017c, p. 4) (see table 1, below;
see also figure 5.11 in Service 2022, p. 118).

Table 1--Current Guadalupe Fatmucket Population
----------------------------------------------------------------------------------------------------------------
Occupied reach
Population Streams included Counties length (mi Recent collection
(km)) years (numbers)
----------------------------------------------------------------------------------------------------------------
Guadalupe River.................. Guadalupe River; Kendall and Kerr 52 (84) 2018 (22)
North Fork, Co., TX. 2019 (shells)
Guadalupe River;
Johnson Creek.
----------------------------------------------------------------------------------------------------------------

Texas Fatmucket

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.
2020, pp. 93-111); therefore, we now know the Texas fatmucket to only
occur 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-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. 2012b, 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

[[Page 48044]]

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).
We expect Texas fatmucket has a similar lifespan to related species
in the genus Lampsilis from the southeast United States, which reach a
maximum age of 13 to 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. 2017c, p.
4) in five populations: lower Elm Creek, upper/middle San Saba River,
Llano River, Pedernales River, and Onion Creek (see table 2, below; see
also figure 5.5 in Service 2022, p. 91). Isolated individuals not
considered part of larger functioning populations have been found in
Cherokee Creek, Bluff Creek, and the North Llano River.

Table 2--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 (19) 2005 (no live
animals)
2008 (1)
2019 (1)
Upper/Middle San Saba River..... San Saba River..... Mason, McCulloch, 62 (100) 2005 (2)
Menard, and San 2012 (8)
Saba Co., TX. 2013 (5)
2016 (29)
2017 (87)
2017 (71)
Llano River..................... Llano River, South Kimble, Llano, and 127 (204) 2016 (72)
Llano River. Mason Co., TX. 2017 (47)
2017 (5)
2018 (635)
2019 (6)
2019 (18)
2021 (99)
Pedernales River................ Pedernales River, Blanco, Gillespie, 79 (127) 2011 (1)
Live Oak Creek. and Hays Co., TX. 2012 (1)
2017 (18)
Onion Creek..................... Onion Creek........ Travis Co., TX..... 24 (38) 2010 (3)
2018 (1)
2021 (5)
----------------------------------------------------------------------------------------------------------------

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
expect 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 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 to 18 years (Haag and Rypel 2010,
pp. 4-6), and we expect the lifespan of Texas fawnsfoot to be similar.
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 occur 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 (see table 3, below;
see also figure 5.7 in Service 2022, p. 101). Texas fawnsfoot was
historically distributed throughout the Colorado and Brazos River
basins (Howells 2014, pp. 111-112; 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 the Leon River, but they
are currently extirpated (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.

[[Page 48045]]

Table 3--Current Texas Fawnsfoot Populations
----------------------------------------------------------------------------------------------------------------
Occupied reach
Population Streams included Counties length (mi Recent collection
(km)) years (numbers)
----------------------------------------------------------------------------------------------------------------
East Fork Trinity River.......... East Fork Trinity Kaufman Co., TX.... 12 (19) 2017 (40)
River. 2018 (12)
Middle Trinity River............. Trinity River....... Anderson, Houston, 140 (225) 2016-2017 (59)
Leon, Madison, and
Navarro Co., TX.
Clear Fork Brazos River.......... Clear Fork Brazos Shackelford and 13 (21) 2010 (1)
River. Throckmorton Co., 2018 (0)
TX.
Upper Brazos River............... Brazos River........ Palo Pinto and 62 (100) 2017 (23)
Parker Co., TX.
Middle/Lower Brazos River........ Brazos River........ Austin, Brazos, 346 (557) 2014 (188)
Burleson, Falls, 2017 (28)
Fort Bend, Grimes, 2021 (1)
McLennan, Milam,
Robertson, Waller,
and Washington
Co., TX.
San Saba/Colorado Rivers......... San Saba River, Mills and San Saba 43 (69) 2017 (0)
Colorado River. Co., TX. 2018 (2)
Lower Colorado River............. Colorado River...... Colorado, 109 (175) 2010 (52)
Matagorda, and 2015 (10)
Wharton Co., TX. 2017 (9)
----------------------------------------------------------------------------------------------------------------

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 (Ictalurus punctatus), flathead catfish (Pylodictis olivarus),
and tadpole madtom (Noturus gyrinus) are host fish for the Guadalupe
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 the reproduction, ecological
interactions, and habitat requirements of Guadalupe orb are similar to
those of the closely related Texas pimpleback.
The Guadalupe orb is only known to occur in the Guadalupe River
Basin in two separate and isolated populations: the upper Guadalupe
River and the lower Guadalupe River (see table 4, below; see also
figure 5.13 in Service 2022, p. 125). 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).

Table 4--Current Guadalupe Orb Populations
----------------------------------------------------------------------------------------------------------------
Occupied reach
Population Streams included Counties length (mi Recent collection
(km)) years (numbers)
----------------------------------------------------------------------------------------------------------------
Upper Guadalupe River............ Guadalupe River..... Comal, Kendall, and 95 (153) 2013 (1)
Kerr Co., TX. 2017 (10)
2018 (2)
Lower Guadalupe River............ Guadalupe River, San Caldwell, DeWitt, 181 (291) 2014-2015 (893)
Marcos River. Gonzales, 2017 (41)
Guadalupe, and
Victoria Co., TX.
----------------------------------------------------------------------------------------------------------------

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 are now considered to occur only in the
Colorado River Basin of Texas. The 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, flathead catfish, and tadpole madtom are
host fish for the Texas pimpleback (Dudding et al. 2019, p. 2). Related
species have miniature glochidia and also 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 to 72 years
(Haag and Rypel 2010, p. 10).
Texas pimpleback are known to occur 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 (see table 5, below; see also figure 5.9 in Service 2022, p.
110). Only the Lower San Saba and Llano River populations are known to
be successfully reproducing. Texas

[[Page 48046]]

pimpleback was historically distributed throughout the Colorado River
Basin (Howells 2014, pp. 93-94; reviewed in Randklev et al. 2017c, pp.
109-110).

Table 5--Current Texas Pimpleback Populations
----------------------------------------------------------------------------------------------------------------
Occupied reach
Population Streams included Counties length (mi Recent collection
(km)) years (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, Brown, Coleman, 178 (286) 2012 (247)
Colorado River. McCulloch, Mills, 2014 (481)
and San Saba Co., 2017 (20)
TX. 2017 (97)
2018 (42)
2019 (23)
Llano River...................... Llano River......... Mason Co., TX...... 5 (8) 2012 (10)
2016 (1)
2017 (23)
2018 (1)
2021 (46)
Lower Colorado River............. Colorado River...... Colorado and 98 (158) 2014 (49)
Wharton Co., TX. 2017 (8)
2018 (30)
----------------------------------------------------------------------------------------------------------------

Balcones Spike

The Balcones spike (Fusconaia iheringi) was recently discovered to
be a separate and distinct species from false spike (Smith et al. 2020,
entire), and the Service now recognizes the Balcones spike as a new
species that occurs in the Brazos and Colorado River basins. Because
the Balcones spike has recently been split from false spike, species-
specific data are not yet available, and so we expect the Balcones
spike has similar habitat needs (larger creeks and rivers with sand,
gravel, or cobble substrates, slow to moderate flows) and host fish
(red shiner (Cyprinella lutrensis) and blacktail shiner (Cyprinella
venusta)) as the false spike.
The Balcones spike is a small to medium-sized freshwater mussel (to
approximately 3.8 inches (in) (96 millimeters (mm))) with a yellow-
green to brown elongate shell, sometimes with greenish rays. While
similar in appearance to false spike, Balcones spike usually has a
sharper posterior ridge and shinier periostracum when compared to false
spike. For a more detailed description, see Smith et al. 2020 (entire).
Related species in the genus Fusconaia from the southeast United States
reach a maximum age of 15 to 51 years (Haag and Rypel 2010, pp. 4-6).
The closely related congener species, false spike, is thought to have a
maximum age of 15 years (Dudding et al. 2019, p. 167) and to reach
sexual maturity around 5 years of age (Dudding et al. 2019, p. 167).
Balcones spike is currently found in three populations in the
Little River and some tributaries (Brazos River Basin), the lower San
Saba River (Colorado River Basin), and the Llano River (Colorado River
Basin) (see table 6, below; see also figure 5.3 in Service 2022, p.
85).

Table 6--Current Balcones Spike Populations
----------------------------------------------------------------------------------------------------------------
Occupied reach Recent collection
Population Streams included Counties length (mi years (numbers
(km)) collected)
----------------------------------------------------------------------------------------------------------------
Little River and tributaries..... Little River, Brushy Milam and 41 (66) 2015 (29)
Creek, San Gabriel Williamson Co., TX. 2021 (13)
River. 2021 (1)
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)
2021 (14)
----------------------------------------------------------------------------------------------------------------

False Spike

The false spike is native to the Guadalupe Basin 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). Recently, individuals that had been known as false spike
in the Brazos and Colorado River basins were found to be a new species
(Smith et al. 2020, entire); therefore, the false spike occurs only in
the Guadalupe River Basin.
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 was 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. 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).

[[Page 48047]]

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 and red
shiner (Dudding et al. 2019, p. 16).
Related species in the genus Fusconaia from the southeast United
States reach a maximum age of 15 to 51 years (Haag and Rypel 2010, pp.
4-6). False spike is thought to have a maximum age of 15 years (Dudding
et al. 2019, p. 167) and to reach sexual maturity around 5 years of age
(Dudding et al. 2019, p. 167).
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 2010, p. 4; Randklev et al.
2011, p. 17). The patchy distribution of false spike could be related
to host fish relationships (Dudding et al. (2019, pp. 16-17); that is,
because their host fish have a small home range, have 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, there is only one known population of false spike in the
lower Guadalupe River (Guadalupe River Basin) (see table 7, below; see
also figure 5.2 in Service 2022, p. 81). For more information on this
population, see the SSA report (Service 2022, pp. 75-82). False spike
is estimated to have been extirpated from the remainder of its
historical range throughout the Guadalupe Basin of central Texas
(reviewed in Randklev et al. 2017c, pp. 12-13).

Table 7--Current False Spike Population
----------------------------------------------------------------------------------------------------------------
Occupied reach Recent collection
Population Streams included Counties length (mi years (number
(km)) collected)
----------------------------------------------------------------------------------------------------------------
Lower Guadalupe River............ Guadalupe River..... DeWitt, Gonzales, 102 (164) 2014-2015 (652)
and Victoria Co.,
TX.
----------------------------------------------------------------------------------------------------------------

Regulatory and Analytical Framework

Regulatory Framework

Section 4 of the Act (16 U.S.C. 1533) and the implementing
regulations in title 50 of the Code of Federal Regulations set forth
the procedures for determining whether a species is an endangered
species or a threatened species, issuing protective regulations for
threatened species, and designating critical habitat for endangered and
species. On April 5, 2024, jointly with the National Marine Fisheries
Service, the Service issued a final rule that revised the regulations
in 50 CFR 424 regarding how we add, remove, and reclassify endangered
and threatened species to the lists and the criteria for designating
listed species' critical habitat (89 FR 24300). On the same day, the
Service published a final rule revising our protections for endangered
species and threatened species at 50 CFR 17 (89 FR 23919). These final
rules are now in effect and are incorporated into the current
regulations. Our analysis for this decision applied our current
regulations. Given that we proposed listing and critical habitat for
these species under our prior regulations (revised in 2019), we have
also undertaken an analysis of whether our decision would be different
if we had continued to apply the 2019 regulations and we concluded that
the decision would be the same. The analyses under both the regulations
currently in effect and the 2019 regulations are available on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
The Act defines an ``endangered species'' as a species that is in
danger of extinction throughout all or a significant portion of its
range, and a ``threatened species'' as a species that is likely to
become an endangered species within the foreseeable future throughout
all or a significant portion of its range. The Act requires that we
determine whether any species is an endangered species or a threatened
species because of any of the following factors:
(A) The present or threatened destruction, modification, or
curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or
educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued
existence.
These factors represent broad categories of natural or human-caused
actions or conditions that could have an effect on a species' continued
existence. In evaluating these actions and conditions, we look for
those that may have a negative effect on individuals of the species, as
well as other actions or conditions that may ameliorate any negative
effects or may have positive effects.
We use the term ``threat'' to refer in general to actions or
conditions that are known to or are reasonably likely to negatively
affect individuals of a species. The term ``threat'' includes actions
or conditions that have a direct impact on individuals (direct
impacts), as well as those that affect individuals through alteration
of their habitat or required resources (stressors). The term ``threat''
may encompass--either together or separately--the source of the action
or condition or the action or condition itself.
However, the mere identification of any threat(s) does not
necessarily mean that the species meets the statutory definition of an
``endangered species'' or a ``threatened species.'' In determining
whether a species meets either definition, we must evaluate all
identified threats by considering the species' expected response 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

[[Page 48048]]

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 which is
further described in the 2009 Memorandum Opinion on the foreseeable
future from the Department of the Interior, Office of the Solicitor (M-
37021, January 16, 2009; ``M- Opinion,'' available online at <a href="https://www.doi.gov/sites/doi.opengov.ibmcloud.com/files/uploads/M-37021.pdf">https://www.doi.gov/sites/doi.opengov.ibmcloud.com/files/uploads/M-37021.pdf</a>).
The foreseeable future extends as far into the future as the U.S. Fish
and Wildlife Service and National Marine Fisheries Service (hereafter,
the Services) can make reasonably reliable predictions about the
threats to the species and the species' responses to those threats. We
need not identify the foreseeable future in terms of a specific period
of time. We will describe the foreseeable future on a case-by-case
basis, using the best available data and taking into account
considerations such as the species' life-history characteristics,
threat-projection timeframes, and environmental variability. In other
words, the foreseeable future is the period of time over which we can
make reasonably reliable predictions. ``Reliable'' does not mean
``certain''; it means sufficient to provide a reasonable degree of
confidence in the prediction, in light of the conservation purposes of
the Act.

Analytical Framework

The SSA report documents the results of our comprehensive
biological review of the best scientific and commercial data regarding
the status of the species, including an assessment of the potential
threats to the species. The SSA report does not represent our decision
on whether the species should be listed as endangered or threatened
species under the Act. However, it does provide the scientific basis
that informs our regulatory decisions, which involve the further
application of standards within the Act and its implementing
regulations and policies.
To assess the viability of the seven central Texas mussels, we used
the three conservation biology principles of resiliency, redundancy,
and representation (Shaffer and Stein 2000, pp. 306-310). Briefly,
resiliency is the ability of the species to withstand environmental and
demographic stochasticity (for example, wet or dry, warm or cold
years), redundancy is the ability of the species to withstand
catastrophic events (for example, droughts, large pollution events),
and representation is the ability of the species to adapt to both near-
term and long-term changes in its physical and biological environment
(for example, climate conditions, pathogens). In general, species
viability will increase with increases in resiliency, redundancy, and
representation (Smith et al. 2018, p. 306). Using these principles, we
identified the species' ecological requirements for survival and
reproduction at the individual, population, and species levels, and
described the beneficial and risk factors influencing the species'
viability.
The SSA process can be categorized into three sequential stages.
During the first stage, we evaluated each individual species' life-
history needs. The next stage involved an assessment of the historical
and current condition of 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. Throughout all of these
stages, we used the best available information to characterize
viability as the ability of a species to sustain populations in the
wild over time. We use this information to inform our regulatory
decision.
The following is a summary of the key results and conclusions from
the SSA report; the full SSA report can be found at Docket FWS-R2-ES-
2019-0061 on <a href="https://www.regulations.gov">https://www.regulations.gov</a> and at <a href="https://www.fws.gov/office/austin-ecological-services">https://www.fws.gov/office/austin-ecological-services</a>.

Summary of Biological Status and Threats

In this discussion, we review the biological condition of the
species and its resources, and the threats that influence the species'
current and future condition, in order to assess the species' overall
viability and the risks to that viability.
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
sufficiently resilient. A number of factors influence the resiliency of
central Texas mussel populations, including occupied stream length,
abundance, and recruitment. While some of the seven 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
resiliency factors and habitat elements are discussed in detail in the
SSA report and are 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 more than 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, sufficiently
resilient mussel populations must occupy stream reaches long enough
such that stochastic events that affect individual mussel beds do not
eliminate the entire population, and 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 mi (32 and 79
river km) have some resiliency to stochastic events, and populations
occupying reaches less than 20 miles (32 km) have little resiliency.
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 the central Texas mussel species to be healthy (i.e.,
sufficiently resilient), there must be many mussel beds of sufficient
density such that local stochastic events do not necessarily eliminate
the bed(s),

[[Page 48049]]

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 the 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
Adequately 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, as
sampling for these species involves tactile searches and mussels
smaller than 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 (about 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 seven central Texas mussels now and in the
future. In this 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 seven species. Where the effects are expected to be similar, we
present one discussion that applies to all seven 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 B), 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 seven species
of the 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 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). In this context, sedimentation explicitly is
restricted to increased fine sediments entering a stream system at a
rate beyond the naturally occurring losing rate and does not replace
the use of the broader term of turbidity. In addition to increased
levels of fine sediment, turbidity is also influenced by concentrations
of fine organic and inorganic matter, soluble organic compounds, algae,
and other microscopic organisms. Changes in stream turbidity are not
inherently an indicator of increased sedimentation as turbidity can
naturally vary from stream to stream in Texas due to unrelated factors
(e.g., stream primary productivity). 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). 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)

[[Page 48050]]

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 the central Texas mussels face the risk of fine
sediment accumulation to varying degrees. Multiple populations of the
seven central Texas mussel species are experiencing increased
sedimentation, including, in particular, the Clear Fork Brazos River
(Texas fawnsfoot), middle and lower Brazos River (Balcones spike and
Texas fawnsfoot), and lower Colorado River (Texas pimpleback and Texas
fawnsfoot). In the future, we expect sediment deposition to continue to
increase across the range of all seven 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 into the aquatic
environment (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 rank lower in waters that
are polluted or otherwise degraded by contaminants. Freshwater mussels
are not generally found for many miles downstream of municipal WWTPs
(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
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 WWTPs because freshwater
mussels are particularly sensitive to increased ammonia levels
(Augspurger et al. 2003, p. 2569). Elevated concentrations (greater
than 0.2 parts per billion) of un-ionized ammonia (NH<INF>3</INF>) in
the interstitial spaces of benthic habitats 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 = parts per million (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 pimpleback
(Cyclonaias pustulosa, a species native to central Texas but not
included in this listing), the revised Environmental Protection Agency
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 have yet to be experimentally
investigated.
Municipal wastewater contains both ionized and un-ionized ammonia,
and wastewater discharge permits issued by the Texas Commission on
Environmental 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. Approximately 480 discharge permits
have been issued for the Brazos River watershed alone from its
headwaters above Possum Kingdom Lake down to the Gulf of Mexico (TCEQ
2018, entire), and WWTP outfalls are numerous in other basins
throughout the ranges of the central Texas mussels. 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).
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

[[Page 48051]]

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
(86 [deg]F) and approaching 40 [deg]C (104 [deg]F)) 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 the
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
to 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).
The behavioral response of valve closure to high salinity
concentrations (greater than 2 ppt) is the likely mechanism for reduced
metabolic rates, reduced feeding, and reduced reproductive success
based on reported sublethal effects of salinity of more than 2 ppt for
the Texas pimpleback (Bonner et al. 2018, pp. 155-156).
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 the central
Texas mussels. Not only can temperature be a biological, physical, and
chemical stressor, the toxicity of many pollutants (e.g., ammonia,
mercury) to aquatic organisms increases at higher temperatures. We
foresee threats to water quality increasing into the future as demand
and competition for limited water resources grows.
Altered Hydrology--Inundation
All seven 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 the
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 of
the 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 the 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]C (52
[deg]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 (TPWD 2007, p. ii), and are cold enough to support a
recreational nonnative 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 riverbed (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 have negatively affected freshwater mussels and their
habitats.
There are numerous dams throughout the range of the central Texas
mussels. There are now 27 major reservoirs, 16 of which have more than
50,000 acre-feet of storage, in the Brazos River Basin (BBEST 2012, p.
33); 31 major reservoirs in the Colorado River Basin, including the
Highland Lakes (TWDB 2018, p. 1); 9 major reservoirs on the Guadalupe
River (BBEST 2011, 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 (see 83 FR
16061; April 13, 2018), 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 (LCRA 2018, 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 (BRA 2018a,
p. 1). Water that is planned to be pumped from the Brazos River during
high flows will be

[[Page 48052]]

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--are threats to
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, impacts 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 (USGS 2019,
unpaginated).
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 2008, pp.
812, 814, 848, 870, 878, 880), and overall river discharge for the
Colorado River 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
2008, p. 892), Pedernales River at Fredericksburg (USGS 2008, p. 896),
Onion Creek near Driftwood, and Onion Creek at Highway 183 (flows
appear to become more erratic, characteristic of a developing
watershed) (USGS 2008, pp. 930, 946). In the San Saba River, continuing
or increasing surface and alluvial aquifer groundwater withdrawals in
combination with drought are 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 2008, pp. 578, 600, 626, 638; BRA
2018b, p. 6), although baseflows are maintained somewhat due to
releases from Lake Granbury and other reservoirs in the upper basin
(USGS 2008, p. 644; BRA 2018b, 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 2008,
pp. 652, 676, 766, 776; BRA 2018b, 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 2008, pp. 754, 766, 776; BRA 2018b, p. 6). Lake Limestone
releases also appear to be contributing to higher base flows in the
Lower Brazos (BRA 2018b, p. 6). Flows have declined in the upper
Guadalupe River (USGS 2008, pp. 992, 994, 1000, 1018) but appear
relatively unchanged at Comfort and Spring Branch and in the San Marcos
River (USGS 2008, pp. 1004, 1006, 1022), and in the lower Guadalupe
River (USGS 2008, 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 2008,
pp. 964, 966). In the Trinity River, low flows are higher (elevated
baseflows) than they were in the past (USGS 2008, 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 the central Texas mussels in the tributary streams
is reduced and could eventually cease to exist (Randklev et al. 2018,
pp. 13-14). While the 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 2018, entire). In 2017, Service, TPWD, and Texas Department
of Transportation (TxDOT) biologists noted 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). Prior to the
flooding events, this site held the highest mussel abundance (Bonner et
al. 2018, pp. 242-243) and represented high-quality habitat within the
Colorado River Basin. After 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.

[[Page 48053]]

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 cubic feet
per second (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) (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), which is occupied by the false spike and Guadalupe
orb, in 2015 (Giardino and Rowley 2016, pp. 70-72). The usual drought/
flood cycle in central Texas can be characterized by long periods of
time without 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 20th
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 the 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 the 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 (Robertson
2023, entire).
Repeated collections and handling can cause disturbance to the
growth of individual mussels. Freshwater mussels close their shell in
response to handling, which can lead to the production of a disturbance
ring in the shell. When closing its shell, it is possible for the
mussel's mantle-shell margin connection to be disrupted as the mantle
tissue is retracted. This can result in the production of a growth
disturbance ring when this mantle-shell connection is re-established in
a slightly differing location than the original collection causing a
misalignment of the prismatic layer and periostracum (Haag 2012, p.
11). Additionally, the closure of the shell during handling can prevent
feeding (Haag 2012, p. 29), alter respiration rate and heart patterns
(Haag 2012, pp. 29-30), and require additional energy expenditure to
retract and then re-establish the foot in substrate to prevent
dislodgment when returned to stream substrates.
Handling of freshwater mussels can also have a detrimental impact
on the reproductive efforts of individual mussels and possibly the
overall population. It is commonly observed that short-term brooders
will abort their glochidia due to disturbances or handling (Haag 2012,
p. 199). In species or individuals that are not able to successfully
produce multiple broods within a single breeding season, the abortion
of these glochidia can cause the loss of reproductive output for that
individual for the year. If many animals have their reproductive output
curtailed at a single location due to widespread sampling of a site,
the abortion of glochidia by multiple animals in response to handling
can lead to an overall reduced reproductive output at a site. If this
sampling effort is repeated multiple times during a breeding season and
across multiple years, there is potential for the disturbance of
multiple years of breeding efforts for many animals at a single
location. This extended disturbance can lead to multiple years of
failed recruitment and potentially the loss of multiple age-class
cohorts within a population at the site.
Loss of reproductive effort due to handling could be compounded by
the intentional collection of gravid individuals, especially the
potential effects on the native populations if an excessive number of
females are removed, for use as broodstock for propagation or research
purposes (Jones et al. 2006, p. 531). For example, pulling many gravid
females from a site may prevent in-situ reproduction from occurring due
to essentially removing a large percentage of that year's reproducing
portion of the population from the site.

[[Page 48054]]

Barriers to Fish Movement
The 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 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 common, widespread species in 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 the 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 is already taking 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
(Lo[aacute]iciga 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 the 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 2018, 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 (Service 2022, pp. 142-145, 149, and appendix C).

Species Current Condition

Here we discuss the current condition of each known population,
taking into

[[Page 48055]]

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
factors (occupied stream length, abundance, and reproduction) and three
habitat factors (substrate, flowing water, and water quality) 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 estimated
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
with low abundance and little evidence of reproduction or recruitment.
Very few individuals have been found in recent years. The upper
Guadalupe River in this reach already experiences very low water
levels, and these low water events are expected to continue into the
future; the population is 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. 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 face
threats from 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 the river gains streamflow from
groundwater except for 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, including Texas fatmucket and Texas pimpleback,
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; TCEQ
2013, entire). 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, and collection of the species is frequent
at this location, although there has been limited evidence that the
population is successfully reproducing. We expect flows to continue to
decline and the frequency of extreme flow events to increase, leading
to increased sedimentation, decreased water quality, and scour. As a
result, the population of Texas fatmucket is expected to decline.
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 very low Texas fatmucket abundance in the river result in
a population that is likely to be extirpated and currently is
unhealthy.
Onion Creek: Few live individuals of Texas fatmucket have been
found in Onion Creek since 2010, and we consider this population to be
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.
Guadalupe Orb
There are two known 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 Guadalupe
orb populations are moderately healthy.
Upper Guadalupe River: The Guadalupe orb population in the upper
Guadalupe River occurs over approximately 95 river mi (153 river km),
and water quantity and quality are in moderate condition. However, the
population occurs in low numbers, with limited reproduction; this
population is unhealthy and is expected to become functionally
extirpated in the near

[[Page 48056]]

future. This stream reach is expected to be sensitive to potential
changes in groundwater inputs to stream flow. Thus, the stream reach is
vulnerable to ongoing and future hydrological alterations that reduce
flows, and thereby result in substrate and water quality degradations,
during critical conditions.
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 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's partners. These measures
bolster 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 the population at risk of decline.
Texas Pimpleback
There are five known 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 in moderate
condition.
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. Therefore, this
population is moderately healthy.
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, and the population 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. While this population is in moderate
condition, we expect this population to be at risk of extirpation due
to these extreme flow events.
Balcones Spike
Overall, there are three known remaining populations of Balcones
spike, comprising less than 3 percent of the species' known historical
range. Historically, most Balcones spike populations were likely
connected by fish migration throughout each of the Brazos and Colorado
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, the three populations 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; this
population is unhealthy.
Lower San Saba River: The lower San Saba River population is
currently small and isolated, and therefore has low resiliency and is
considered unhealthy. 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, has
experienced high collection pressure in recent years, and has not shown
recent evidence of reproduction. Therefore, this population is
unhealthy, and we expect the population to become extirpated.

[[Page 48057]]

False Spike
Overall, there is one known remaining population of false spike,
comprising approximately 20 percent of the species' known historical
range. Historically, most false spike populations were likely connected
by fish migration throughout the Guadalupe River Basin, but due to
impoundments, the false spike is currently isolated in the lower
portion of the Guadalupe River and repopulation of extirpated locations
is unlikely to occur without human assistance. Based on our analysis as
described in the SSA report, the population is moderately healthy.
Lower Guadalupe River: The lower Guadalupe River population of
false spike is the only remaining population of the species and
considered to have low resiliency. The 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.
Texas Fawnsfoot
There are seven known 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 observations
of recent reproduction exist for this population; all observed Texas
fawnsfoot individuals are adults, greater than 35 mm. This population
is small and isolated from the middle and lower Trinity River
population by habitat that is unsuitable primarily because of 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 moderately healthy.
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
streamflow has been subsidized by return flows originating in part from
other basins, although water quality degradation and sedimentation are
still affecting Texas fawnsfoot in this reach. Additionally, the middle
Trinity River is a relatively long and unobstructed reach of river.
While habitat may decline, this population is in moderate condition,
and, therefore, 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. Therefore,
this population is moderately healthy.
Clear Fork Brazos River: The Texas fawnsfoot population 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, would result in
significant hydrologic alterations, which would further degrade the
overall condition of this population of Texas fawnsfoot. Therefore,
this population is unhealthy.
Upper Brazos River: The population of Texas fawnsfoot in the Upper
Brazos River is characterized by low abundance and lack of evidence of
reproduction. This reach of the river experiences 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.
Therefore, this population is unhealthy.
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, results in the 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.
Therefore, this population is moderately healthy.
Lower San Saba River: 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.
Sedimentation is high, due in part to 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 increased sedimentation. Therefore, this population is
unhealthy.
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, although with reduced flow.
Despite increasing demands for municipal water, we expect that the
lower Colorado River will continue to flow due to priority downstream
agricultural and industrial water rights. Similar to the lower Brazos
River population, Texas fawnsfoot in the Lower Colorado River are
vulnerable to reduced flows and associated habitat degradation due to
reductions in flow from upstream tributaries; because the species
occurs in bank habitats that are likely to become exposed, the species
will be subjected to desiccation, predation, and increased water
temperatures as river elevations decline while the river still flows in
its main channel. Currently, the Lower Colorado River Authority is
implementing a water management plan that is alleviating this threat by
providing consistent subsistence flows to the lower Colorado River
Basin. Therefore, this population is moderately healthy.

Future-Condition Scenarios for the Texas Fawnsfoot

Because of significant uncertainty regarding if and when flow loss,
water quality degradations, extreme flooding and scour/substrate
mobilizing events, or impoundment construction may occur, we have
forecasted future viability for the Texas fawnsfoot in terms of
resiliency, redundancy, and representation under four plausible future
scenarios. Each scenario is projected across up to three time steps

[[Page 48058]]

and considers the biological status of this species' populations and
habitats in ten, twenty-five, and fifty years. Ten years represents one
to two generations of mussels, assuming an average reproductive life
span of five to ten years. Twenty-five years similarly represents two
to four mussel generations. Fifty years represents five or more
generations of mussels and corresponds with the current planning
horizon of the State Water Plans (from 2020 to 2070), a period of time
for which the human population of the State of Texas is expected to
grow 88% from 27 million to 51 million (TWDB 2017, p. 3) with much of
the growth of human population occurring in the watersheds these seven
species of mussels currently occupy (TWDB 2017, pp. 50-51). Below, we
provide a brief summary of each plausible future scenario; for more
detailed information on these models and their projections, please see
the SSA report (Service 2022, chapter 7).
Under Scenario 1, which considers a future where the current levels
of existing degradation as well as existing conservation, current as of
the preparation of the SSA report, continue for the next 50 years, a
loss of resiliency, representation, and redundancy is expected. Under
this scenario, we predicted that the effects of current levels of
climate change continue to result in low streamflow, which lead to
increased sedimentation, reduced water quality, and occasional
desiccation. One population of Texas fawnsfoot remains in moderate
condition, three populations are considered unhealthy, and three
populations are functionally extirpated. Those populations in unhealthy
condition are particularly vulnerable to extirpation.
Under Scenario 2, which considers a future where ``feasible and
appropriate conservation plans'' are implemented over the next 50
years, including Candidate Conservation Agreements with Assurances in
the Brazos and Colorado River basins that provide coverage for the
species, Texas fawnsfoot populations generally maintain, or slightly
improve, resiliency, redundancy, and representation over time as
conservation measures are implemented to counteract existing stressors.
Under this scenario, we predict that the effects of current levels of
climate change continue to result in low stream flows, which lead to
increased sedimentation, reduced water quality, and occasional
desiccation, but water conservation measures and riparian improvements
aid some populations. One population of Texas fawnsfoot is considered
healthy, three are in moderate condition, two populations are
considered unhealthy, and one population is functionally extirpated.
Those populations in unhealthy condition are particularly vulnerable to
extirpation.
Under Scenario 3, which considers a future where conditions are no
better for the species than the status quo Current Conditions, a loss
of resiliency, representation, and redundancy is expected for the Texas
fawnsfoot. Under this scenario we predict that intermediate climate
effects, including more frequent and intense droughts, combined with
increased ground- and surface-water demands associated with increased
human demand, reductions in streamflow are expected to occur in all
streams and rivers, and those effects will be more pronounced in the
upper basins. Scenario 3 considers additional water projects, such as
wastewater treatment plant outfalls, only if currently proposed or
planned. Four populations of Texas fawnsfoot are considered unhealthy,
three are in moderate condition, two populations are considered
unhealthy, and three populations are functionally extirpated. Those
populations in unhealthy condition are particularly vulnerable to
extirpation.
Under Scenario 4, which considers a future where conditions are not
better for the species than the status quo Current Conditions under
severe climate effects. This scenario considers sever climate effects,
and we predict more frequent and intense droughts, increased ground-
and surface-water demands associated with increased human demand,
additional water projects, like wastewater treatment plant outfalls, as
well as possible new reservoirs and other construction projects. The
effects of strong levels of climate change result in even lower stream
flows, which lead to increased sedimentation, reduced water quality,
and desiccation. Three populations of Texas fawnsfoot are considered
unhealthy, and four populations are considered functionally extirpated.
Those populations in unhealthy condition are particularly vulnerable to
extirpation.
As part of the SSA, we also developed three future-condition
scenarios to capture the range of uncertainties regarding future
threats and the projected responses by the Guadalupe fatmucket, Texas
fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and false
spike. Our scenarios assumed a moderate or enhanced probability of
severe drought, and either propagation or no propagation of the
species. Because we determined that the current condition of these six
central Texas mussels is consistent with an endangered species (see
Determination of Status, below), we are not presenting the results of
the future scenarios in this final rule. Please refer to the SSA report
(Service 2022) for the full analysis of future scenarios for these six
species.
We note that, by using the SSA framework to guide our analysis of
the scientific information documented in the SSA report, we have
analyzed the cumulative effects of identified threats and conservation
actions on the species. To assess the current and future condition of
the species, we evaluate the effects of all the relevant 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
each entire species, our assessment integrates the cumulative effects
of the factors and replaces a standalone cumulative effects analysis.

Conservation Efforts and Regulatory Mechanisms

Since 2011, when three of the central Texas mussel species became
candidates for listing under the Act, many agencies, nongovernmental
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 the 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 instream physical habitat and water quality, as well as
adjacent riparian and upland habitats. Additionally, the Brazos, Lower
Colorado, and Trinity river authorities have each developed and
implemented candidate conservation agreements with assurances to
benefit one or more species of candidate mussels, including the Texas
fatmucket, Texas fawnsfoot, Texas pimpleback, and Balcones spike in
their basins (see Private or Other Non-Federal Conservation Plans
Related to Permits Under Section 10 of the Act, below). Some publicly
and privately owned lands in the watersheds occupied by the central
Texas mussels are protected with conservation easements or are
otherwise managed to support populations of native fish, wildlife, and
plant populations. The U.S. Department of Agriculture's Natural
Resources Conservation Service

[[Page 48059]]

(NRCS), along with the Service and State and local partners, is 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 no date, entire).
There are active efforts to protect, maintain, and improve existing
water quantity in waters known to be important for mussel populations
and to reduce threats of flow loss. These efforts include the
establishment of the Texas Instream Flow Program by the Texas
Legislature as part of Senate Bill 2 in 2001, and the creation of a
``comprehensive, statewide process to protect environmental flows'' in
Senate Bill 3 (SB3) in 2007. Senate Bill 3 also directs the
Environmental Flows Advisory Group (EFAG) to develop a schedule for
development of environmental flow regime recommendations and the
adoption of environmental flow standards within the State. This process
allows for other groups to develop information on environmental flow
needs and ways in which those needs can be met for basins for which the
EFAG has not yet established environmental flow standard schedules
(Loeffler 2015, entire). The Hydrology-based Environmental Flow Regime
(HEFR; Opdyke et al. 2014, entire) tool was developed during the SB3
process and describes flow regimes in terms of subsistence flows, base
flows, pulse flows, and overbank floods, and it applies the
``indicators of hydrologic assessment'' (IHA; TNC 2009, entire) to
determine hydrologic separation and then inform an environmental flow
recommendation. Environmental flow recommendations have been set for
each of the river basins occupied by the species that are the subjects
of this rule.
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 (Service 2018, p. 1; Service
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).

Determination of Status

Section 4 of the Act (16 U.S.C. 1533) and its implementing
regulations (50 CFR part 424) set forth the procedures for determining
whether a species meets the definition of an endangered species or a
threatened species. The Act defines an ``endangered species'' as a
species in danger of extinction throughout all or a significant portion
of its range, and a ``threatened species'' as a species likely to
become an endangered species within the foreseeable future throughout
all or a significant portion of its range. The Act requires that we
determine whether a species meets the definition of 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 these seven species and assessing the
cumulative effect of the threats under the Act's section 4(a)(1)
factors, we found that all seven species of the 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. Collection (Factor B), and predation (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 historical 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 20th century until 1970, more than
100 major dams were 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 seven 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 seven 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

[[Page 48060]]

water temperatures, other quality degradations, and increased exposure
to predation. Finally, direct mortality due to predation and collection
further limits population sizes of those populations, which are 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 seven 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 ev

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