Endangered and Threatened Wildlife and Plants; Endangered Species Status for Salina Mucket and Mexican Fawnsfoot and Designation of Critical Habitat, 47952-47988 [2023-15360]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 88, Number 141 (Tuesday, July 25, 2023)]
[Proposed Rules]
[Pages 47952-47988]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-15360]



[[Page 47951]]

Vol. 88

Tuesday,

No. 141

July 25, 2023

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 for Salina Mucket and Mexican Fawnsfoot and Designation of 
Critical Habitat; Proposed Rule

Federal Register / Vol. 88 , No. 141 / Tuesday, July 25, 2023 / 
Proposed Rules

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2023-0026; FF09E21000 FXES1111090FEDR 234]
RIN 1018-BG11


Endangered and Threatened Wildlife and Plants; Endangered Species 
Status for Salina Mucket and Mexican Fawnsfoot and Designation of 
Critical Habitat

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to 
list two mussel species, the Salina mucket (Potamilus metnecktayi) and 
Mexican fawnsfoot (Truncilla cognata) (which we collectively refer to 
as the Rio Grande mussels in this document), as endangered species 
under the Endangered Species Act of 1973, as amended (Act). This 
determination also serves as our 12-month findings on petitions to list 
the Salina mucket and Mexican fawnsfoot. After a review of the best 
available scientific and commercial information, we find that listing 
the Salina mucket and Mexican fawnsfoot is warranted. We also propose 
to designate critical habitat for the Salina mucket and Mexican 
fawnsfoot under the Act. For Salina mucket, approximately 200 river 
miles (rmi) (321 river kilometers (rkm)) in Brewster, Terrell, and Val 
Verde Counties, Texas, fall within the boundaries of the proposed 
critical habitat designation. For Mexican fawnsfoot, approximately 185 
rmi (299 rkm) in Maverick, Webb, and Zapata Counties, Texas, fall 
within the boundaries of the proposed critical habitat designation. We 
announce the availability of a draft economic analysis of the proposed 
designation of critical habitat for the Salina mucket and Mexican 
fawnsfoot. If we finalize this rule as proposed, it would add these 
species to the List of Endangered and Threatened Wildlife and extend 
the Act's protections to the species and their designated critical 
habitats.

DATES: We will accept comments received or postmarked on or before 
September 25, 2023. Comments submitted electronically using the Federal 
eRulemaking Portal (see ADDRESSES, below) must be received by 11:59 
p.m. eastern time on the closing date. We must receive requests for a 
public hearing, in writing, at the address shown in FOR FURTHER 
INFORMATION CONTACT by September 8, 2023.

ADDRESSES: You may submit comments by one of the following methods:
    (1) Electronically: Go to the Federal eRulemaking Portal: https://www.regulations.gov. In the Search box, enter FWS-R2-ES-2023-0026, 
which is the docket number for this rulemaking. Then, click on the 
Search button. On the resulting page, in the panel on the left side of 
the screen, under the Document Type heading, check the Proposed Rule 
box to locate this document. You may submit a comment by clicking on 
``Comment.''
    (2) By hard copy: Submit by U.S. mail to: Public Comments 
Processing, Attn: FWS-R2-ES-2023-0026, U.S. Fish and Wildlife Service, 
MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
    We request that you send comments only by the methods described 
above. We will post all comments on https://www.regulations.gov. This 
generally means that we will post any personal information you provide 
us (see Information Requested, below, for more information).
    Availability of supporting materials: Supporting materials, such as 
the species status assessment report, are available on the Service's 
website at https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot, at https://www.regulations.gov at Docket No. FWS-R2-ES-2023-0026, or both. For the 
proposed critical habitat designation, the coordinates or plot points 
or both from which the maps are generated are included in the decision 
file for this critical habitat designation and are available at https://www.regulations.gov at Docket No. FWS-R2-ES-2023-0026 and on the 
Service's website at https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot.

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 
Salina mucket (Potamilus metnecktayi) and Mexican fawnsfoot (Truncilla 
cognata) meet the Act's definition of endangered species; therefore, we 
are proposing to list both species as such and proposing a designation 
of critical habitat for both species. Both listing a species as an 
endangered or threatened species and designating critical habitat can 
be completed only by issuing a rule through the Administrative 
Procedure Act rulemaking process (5 U.S.C. 551 et seq.).
    What this document does. We propose to list the Salina mucket and 
Mexican fawnsfoot as endangered species under the Act, and we propose 
to designate critical habitat for both species.
    The basis for our action. Under the Act, we may determine that a 
species is an endangered or threatened species because of any of five 
factors: (A) The present or threatened destruction, modification, or 
curtailment of its habitat or range; (B) overutilization for 
commercial, recreational, scientific, or educational purposes; (C) 
disease or predation; (D) the inadequacy of existing regulatory 
mechanisms; or (E) other natural or manmade factors affecting its 
continued existence. We have determined that the Salina mucket and 
Mexican fawnsfoot are endangered due to the following threats: habitat 
loss through changes in water quality and quantity, and increased fine 
sediments (Factor A), all of which are exacerbated by the ongoing and 
expected effects of climate change (Factor E). Additionally, Mexican 
fawnsfoot is affected by in-stream barriers to fish movement (Factor 
E), which limits dispersal and prevents recolonization after stochastic 
events.
    Section 4(a)(3) of the Act requires the Secretary of the Interior 
(Secretary), to the maximum extent prudent and determinable, to 
designate critical habitat 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

[[Page 47953]]

species, at the time it is listed, on which are found those physical or 
biological features (I) essential to the conservation of the species 
and (II) which may require special management considerations or 
protections; and (ii) specific areas outside the geographical area 
occupied by the species at the time it is listed, upon a determination 
by the Secretary that such areas are essential for the conservation of 
the species. Section 4(b)(2) of the Act states that the Secretary must 
make the designation on the basis of the best scientific data available 
and after taking into consideration the economic impact, the impact on 
national security, and any other relevant impacts of specifying any 
particular area as critical habitat.

Information Requested

    We intend that any final action resulting from this proposed rule 
will be based on the best scientific and commercial data available and 
be as accurate and as effective as possible. Therefore, we request 
comments or information from other governmental agencies, Native 
American Tribes, the scientific community, industry, or any other 
interested parties concerning this proposed rule. We particularly seek 
comments concerning:
    (1) These species' biology, range, and population trends, 
including:
    (a) Biological or ecological requirements of the species, including 
habitat requirements for feeding, breeding, and sheltering;
    (b) Genetics and taxonomy;
    (c) Historical and current range, including distribution records 
and the locations of any additional populations of these species;
    (d) Historical and current population levels, and current and 
projected trends; and
    (e) Past and ongoing conservation measures for the species, their 
habitats, or both.
    (2) Threats and conservation actions affecting these species, 
including:
    (a) Factors that may be affecting the continued existence of the 
species, which may include habitat modification or destruction, 
overutilization, disease, predation, the inadequacy of existing 
regulatory mechanisms, or other natural or manmade factors;
    (b) Biological, commercial trade, or other relevant data concerning 
any threats (or lack thereof) to these species; and
    (c) Existing regulations or conservation actions that may be 
addressing threats to these species.
    (3) Additional information concerning the historical and current 
status of these species.
    (4) Specific information on:
    (a) The amount and distribution of Salina mucket and Mexican 
fawnsfoot habitat;
    (b) Any additional areas occurring within the range of these 
species, within the Rio Grande in Texas, that should be included in the 
designation because they (i) are occupied at the time of listing and 
contain the physical or biological features that are essential to the 
conservation of these species and that may require special management 
considerations, or (ii) are unoccupied at the time of listing and are 
essential for the conservation of these species;
    (c) Special management considerations or protection that may be 
needed in critical habitat areas we are proposing, including managing 
for the potential effects of climate change; and
    (d) Whether occupied areas are adequate for the conservation of 
these species, to help us evaluate the potential to include areas in 
the critical habitat designations that are not occupied at the time of 
listing. Please provide specific information regarding whether or not 
unoccupied areas would, with reasonable certainty, contribute to the 
conservation of these species and contain at least one physical or 
biological feature essential to the conservation of the species. We 
also seek comments or information regarding whether areas not occupied 
at the time of listing qualify as habitat for these species.
    (5) Land use designations and current or planned activities in the 
subject areas and their possible impacts on proposed critical habitat, 
including information regarding the types of Federal actions that may 
trigger an ESA section 7 consultation and potential conservation 
measures to avoid and minimize impacts to the critical habitat 
designation that are different from those to avoid and minimize impacts 
to the species.
    (6) Any probable economic, national security, or other relevant 
impacts of designating any area that may be included in the final 
designation, and the related benefits of including or excluding 
specific areas.
    (7) Information on the extent to which the description of probable 
economic impacts in the draft economic analysis is a reasonable 
estimate of the likely economic impacts and any additional information 
regarding probable economic impacts that we should consider, including:
    (a) Whether any data used in the economic analysis needs to be 
updated;
    (b) Additional costs arising specifically from the designation of 
critical habitat that have not been identified in the DEA or improved 
cost estimates for activities that are included in the DEA;
    (c) Information on the potential for incremental costs to occur 
outside of the section 7 consultation process. These types of costs may 
include triggering additional requirements or project modifications 
under other laws or regulations, and perceptional effects on markets; 
and,
    (d) Information on non-Federal entities that receive Federal 
funding, assistance, or permits, or that otherwise require approval or 
authorization from a Federal agency for an action, that may be 
indirectly impacted by the designation of critical habitat.
    (8) Whether any specific areas we are proposing for critical 
habitat designation should be considered for exclusion under section 
4(b)(2) of the Act, and whether the benefits of potentially excluding 
any specific area outweigh the benefits of including that area under 
section 4(b)(2) of the Act. If you think we should exclude any 
additional areas, please provide information supporting a benefit of 
exclusion.
    (9) Whether we could improve or modify our approach to designating 
critical habitat in any way to provide for greater public participation 
and understanding, or to better accommodate public concerns and 
comments.
    Please include sufficient information with your submission (such as 
scientific journal articles or other publications) to allow us to 
verify any scientific or commercial information you include.
    Please note that submissions merely stating support for, or 
opposition to, the action under consideration without providing 
supporting information, although noted, do not provide substantial 
information necessary to support a determination. Section 4(b)(1)(A) of 
the Act directs that determinations as to whether any species is an 
endangered or a threatened species must be made solely on the basis of 
the best scientific and commercial data available, and section 4(b)(2) 
of the Act directs that the Secretary shall designate critical habitat 
on the basis of the best scientific data available.
    You may submit your comments and materials concerning this proposed 
rule by one of the methods listed in ADDRESSES. We request that you 
send comments only by the methods described in ADDRESSES.
    If you submit information via https://www.regulations.gov, your 
entire submission--including any personal identifying information--will 
be posted

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on the website. If your submission is made via a hardcopy that includes 
personal identifying information, you may request at the top of your 
document that we withhold this information from public review. However, 
we cannot guarantee that we will be able to do so. We will post all 
hardcopy submissions on https://www.regulations.gov.
    Comments and materials we receive, as well as supporting 
documentation we used in preparing this proposed rule, will be 
available for public inspection on https://www.regulations.gov.
    Our final determination may differ from this proposal because we 
will consider all comments we receive during the comment period as well 
as any information that may become available after this proposal. Based 
on the new information we receive (and, if relevant, any comments on 
that new information), we may conclude that one or both of these 
species are threatened instead of endangered, or we may conclude that 
one or both of these species do not warrant listing as either an 
endangered species or a threatened species. For critical habitat, our 
final designations may not include all areas proposed, may include some 
additional areas that meet the definition of critical habitat, or may 
exclude some areas if we find the benefits of exclusion outweigh the 
benefits of inclusion and exclusion will not result in the extinction 
of the species. In our final rule, we will clearly explain our 
rationale and the basis for our final decision, including why we made 
changes, if any, that differ from this proposal.

Public Hearing

    Section 4(b)(5) of the Act provides for a public hearing on this 
proposal, if requested. Requests must be received by the date specified 
in DATES. Such requests must be sent to the address shown in FOR 
FURTHER INFORMATION CONTACT. We will schedule a public hearing on this 
proposal, if requested, and announce the date, time, and place of the 
hearing, as well as how to obtain reasonable accommodations, in the 
Federal Register and local newspapers at least 15 days before the 
hearing. We may hold the public hearing in person or virtually via 
webinar. We will announce any public hearing on our website, in 
addition to the Federal Register. The use of virtual public hearings is 
consistent with our regulations at 50 CFR 424.16(c)(3).

Previous Federal Actions

    On June 25, 2007, we received a petition dated June 18, 2007, from 
Forest Guardians (now WildEarth Guardians), requesting that we list 475 
species in the southwestern United States, including the Salina mucket, 
as endangered or threatened. On October 15, 2008, we received a 
petition dated October 9, 2008, from WildEarth Guardians, requesting 
that we list six species of freshwater mussels, including Mexican 
fawnsfoot, as endangered or threatened and designate critical habitat 
for them. On December 15, 2009, we published in the Federal Register 
(74 FR 66260) our 90-day finding that the above petitions presented 
substantial scientific information indicating that listing the Salina 
mucket and Mexican fawnsfoot may be warranted. This document 
constitutes our 12-month warranted petition finding for both species.

Peer Review

    A species status assessment (SSA) team prepared an SSA report for 
the Salina mucket and Mexican fawnsfoot (Service 2023, entire). 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 in 
listing actions under the Act, we solicited independent scientific 
review of the information contained in the Salina mucket and Mexican 
fawnsfoot SSA report (Service 2023, entire). We sent the SSA report to 
10 independent peer reviewers and received three responses. Results of 
this structured peer review process can be found at https://www.regulations.gov. In preparing this proposed rule, we incorporated 
the results of these reviews, as appropriate, into the SSA report, 
which is the foundation for this proposed rule.

Summary of Peer Reviewer Comments

    As discussed in Peer Review, above, we received comments from three 
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 information contained in the SSA report. The 
peer reviewers generally concurred with our methods and conclusions 
presented within the draft SSA report. They provided some additional 
information, suggestions regarding document structure, clarifications 
in terminology and sources, and feedback on threats. We incorporated 
the majority of the substantive comments into the SSA report (Service 
2023, entire) and this proposed rule. We outline the substantive 
comments that we did not incorporate, or fully incorporate, into the 
SSA report below.
    (1) Comment: A peer reviewer noted that the Intergovernmental Panel 
on Climate Change's (IPCC's) sixth assessment report had just been 
released (IPCC 2021, entire) and that although the reports are likely 
similar, the most recent report should have been included.
    Our response: When we were writing the SSA report and assigning the 
population condition for the Rio Grande mussels, the 2014 IPCC report 
(IPCC 2014, entire) was the most recent information. The climate 
projections in the newest report do not substantially deviate from the 
former report and the threat trajectories are similar to our 
projections. We have incorporated the latest IPCC report (IPCC 2021, 
entire) into this proposed rule, and we will incorporate any changes 
from the latest IPCC report into the SSA report before we make our 
final listing determinations for these species.
    (2) Comment: A peer reviewer noted that if hydrologic alteration is 
included in the ``flowing water'' factor, and hypolimnetic releases 
(low water temperatures) in the ``water quality'' factor, the current 
condition for the upstream population of Mexican fawnsfoot would most 
likely be ``low'' due to impacts to hydrology and temperature from 
releases from Amistad Reservoir.
    Our response: The populations of Mexican fawnsfoot and Salina 
mucket do not currently occur in stream reaches affected by the 
downstream effects of Amistad Reservoir. However, we agree that impacts 
to freshwater mussel populations are occurring due to altered hydrology 
and low stream temperatures caused by lake bottom releases from Amistad 
Reservoir. If we finalize these proposed listings, the alterations in 
habitat conditions in response to Amistad Reservoir operations would be 
considered during recovery planning efforts that focus on expanding the 
distribution of either, or both, species.
    (3) Comment: A peer reviewer requested clarification on how we 
arrived at the stream-length and abundance parameter delineations for 
distinguishing high, moderate, low, etc., conditions. They suggested 
that these criteria should be based on or connected to empirical 
relationships between these metrics and persistence probability.

[[Page 47955]]

    Our response: We understand that freshwater mussel populations that 
are more evenly distributed along longer stream reaches of a riverine 
system are more resilient to site-level stochastic and catastrophic 
events. In many instances, especially those concerning rare species in 
remote habitats, it would be nearly impossible to determine an exact 
length of stream necessary to provide the requested delineated levels 
of resiliency. Therefore, we relied on our best professional judgment 
to determine these condition levels for the identified habitat 
characteristics. These parameters represent our best assessment of 
resiliency for these species.
    (4) Comment: A peer reviewer stated that there is a contradiction 
in how range extent is being used to measure resiliency and how 
redundancy is being measured in the assessment. Specifically, all 
Salina mucket mussel beds within a hydrologically connected stream were 
grouped into a single population rather than as semi-connected 
populations within a metapopulation that provides redundancy within the 
metapopulation.
    Our response: For the purposes of this assessment, redundancy is 
measured at the species level. Redundancy is the ability of a species 
to withstand catastrophic events, such as no-flow or dry stream 
conditions or contaminant spills. A species with a single population is 
at higher risk of extinction if a catastrophic event occurs compared to 
a species with multiple, redundant populations. A species with a single 
population may still have limited redundancy, but if that population is 
sufficiently resilient and widespread (with multiple populations), then 
the species could have higher viability. We agree that the Salina 
mucket population exists somewhat as a metapopulation, where multiple 
mussel beds interact and provide a source of new individuals if some 
beds are extirpated. However, their connection to each other means they 
are not independent populations; redundant populations provide 
protection from extinction from large-scale, catastrophic events. Given 
there are no additional known populations outside of the one described 
in the SSA, the Salina mucket has no redundant populations and 
therefore limited redundancy. It is important to note that resiliency, 
redundancy, and representation inform our assessment of species' 
viability, and we analyze the overall risk of extinction regardless of 
whether we split or grouped Salina mucket into one or more populations. 
How we delineate populations, whether it is at the population or 
metapopulation scale, does not change the results of the overall 
viability assessment. Instead, our delineation of populations provides 
the basis upon which we analyze the species' status. The concept of 
redundancy includes consideration of a species' ability to withstand 
catastrophic events. Whether we called the range one population or 
multiple metapopulations would not change the fact that both species 
each only occur in one stream reach and have little to no capacity to 
withstand a catastrophic event within that stream reach.
    (6) Comment: A peer reviewer stated that representation should be 
assessed in the context of the species' entire historical ranges. There 
is no information on genetic variation between extant and extirpated 
populations, but if geography is a proxy for genetic variation, the 
major range contractions of both species (including total disappearance 
from whole systems) indicates that current representation is poor.
    Our response: We completed the assessment of representation in the 
context of the species' historical ranges. The loss of historical 
populations of both species means that any unique genotypes or 
phenotypes that may have existed historically are also lost. The 
individuals included within the small remaining populations for each 
species have likely adapted to the same suite of biological, physical, 
and chemical variables present within their respective geographic 
ranges. We agree that any additional genetic representation that 
historically occurred no longer exists, and we include this information 
in the SSA report.

I. Proposed Listing Determination

Background

General Mussel Biology

    Freshwater mussels, including these two Rio Grande mussels, have a 
complex life history involving parasitic larvae, called glochidia, 
which are wholly dependent on host fish. As freshwater mussels are 
generally immobile, dispersal is accomplished primarily through the 
behavior of host fish and their tendencies to travel upstream and 
against the current in rivers and streams. Mussels are broadcast 
spawners; males release sperm into the water column, which are taken in 
by the female through the incurrent siphon (the tubular structure used 
to draw water into the body of the mussel). The developing larvae 
remain with the female until they mature and are ready for release as 
glochidia, to attach on the gills, head, or fins of fishes (Vaughn and 
Taylor 1999, p. 913; Barnhart et al. 2008, pp. 371-373).
    Glochidia die if they fail to find a host fish, attach to the wrong 
species of host fish, attach to a fish that has developed immunity from 
prior infestations, or attach to the wrong location on a host fish 
(Neves 1991, p. 254; Bogan 1993, p. 599). Successful glochidia encyst 
(enclose in a cyst-like structure) on the host's tissue, draw nutrients 
from the fish, and develop into juvenile mussels (Arey 1932, pp. 214-
215). The glochidia will remain encysted for about a month through a 
transformation to the juvenile stage. Once transformed, the juveniles 
will excyst from the fish and drop to the substrate.
    Those juveniles that drop in unsuitable substrates die because 
their immobility prevents them from relocating to more favorable 
habitat. Juvenile freshwater mussels burrow into interstitial 
substrates and grow to a size that is less susceptible to predation and 
displacement from high-flow events (Yeager et al. 1994, p. 220). Adult 
mussels typically remain within the same general location where they 
dropped (excysted) from their host fish as juveniles.
    Host specificity can vary across mussel species, which may have 
specialized or generalized relationships with one or more taxa of fish. 
Mussels have evolved a wide variety of adaptations to facilitate 
transmission of glochidia to host fish, including: display/mantle lures 
mimicking fish or invertebrates; packages of glochidia (conglutinates) 
that mimic worms, insect larvae, larval fish, or fish eggs; and release 
of glochidia in mucous webs that entangle fish (Strayer et al. 2004, p. 
431). Polymorphism (existence of multiple forms) of mantle lures and 
conglutinates frequently exists within mussel populations (Barnhart et 
al. 2008, p. 383), representing important adaptive capacity in terms of 
genetic diversity and ecological representation.

Salina Mucket

    A thorough review of the taxonomy, life history, and ecology of the 
Salina mucket is presented in the SSA report (Service 2023, entire). 
Salina mucket (Potamilus metnecktayi) was formally described by Richard 
I. Johnson with the holotype specimen collected from the Rio Salado 
near Nuevo Laredo, Tamaulipas, Mexico (Johnson 1998, entire). 
Previously, the species was recognized as Lampsilis salinasensis from 
the Salinas River, Coahuila Mexico (Dall 1908, p. 181). Later, the 
species was referred to as Potamilus salinasensis, which appears to be 
the first attribution of the species to the

[[Page 47956]]

genus Potamilus (Neck and Metcalf 1988, p. 265). Six species of 
Potamilus were later recognized but did not include P. salinaensis or 
P. metnecktayi (Turgeon et al. 1998, p. 32). Salina mucket was 
classified as a member of the unionid subfamily Ambleminae in 2017 
(Williams et al. 2017, p. 51), which led to general consensus by the 
scientific community that P. metnecktayi is a valid taxon. The 
taxonomic validity of the Salina mucket was verified in 2020 (Smith et 
al. 2020, entire).
    The Salina mucket is a medium-sized freshwater mussel with a brown, 
tan, or black periostracum (outermost shell surface), an ovate outline, 
and a somewhat inflated shell (Howells et al. 1996, p. 93; Johnson 
1998, p. 430; Randklev et al. 2020a, entire). The species is sexually 
dimorphic with male shells being more pointed along the posterior end 
and females more broadly rounded and truncate. Younger individuals will 
occasionally have faint green rays (lines of color) on the periostracum 
(Johnson 1998, p. 430; Randklev et al. 2020a, entire). Mature adults 
can reach lengths of over 4.5 inches (120 millimeters (mm)) (Johnson 
1998, p. 4301). For a more detailed description of the morphological 
characteristics of Salina mucket, see Howells et al. 1996 (pp. 103-104) 
and Randklev et al. 2020a (entire).
    The Salina mucket historically occurred in the Texas portion of the 
Rio Grande drainage in the United States and Mexico. The species was 
described from the Rio Salado south of Nuevo Laredo in the State of 
Tamaulipas, Mexico, a tributary to the Rio Grande (Randklev et al. 
2017, p. 157; Johnson 1998, entire). However, the current status of the 
species at its type locality in Mexico is unknown and presumed 
extirpated based upon the lack of recent survey observations and 
records of no-flow conditions and inflows of untreated household waste 
pollutants (Strenth et al. 2004, p. 227). Currently, the species is 
known to occur in a single population upstream of Amistad Reservoir in 
the mainstem Rio Grande (Howells et al. 1996, p. 103; Burlakova et al. 
2019, p. 346; Randklev et al. 2017, pp. 157, 258).
    Little reproductive information is available for the Salina mucket. 
Based off closely related congener species (bleufer, P. purpuratus), 
spawning is believed to occur in the fall, brooding occurs over winter, 
and release of glochidia occurs the following spring (Williams et al. 
2008, p. 606; Haag 2012, p. 177). Therefore, the species is considered 
a long-term brooder (bradytictic). Host fish inoculation strategies are 
largely unknown for the species, but the Salina mucket may use 
conglutinates (packages of glochidia shaped as food items) to inoculate 
fish hosts similar to other Potamilus spp. (Barnhart et al. 2008, p. 
377).
    For Salina mucket, freshwater drum (Aplodinotus grunniens) have 
been identified as suitable host fish (Bosman et al. 2015, entire). 
However, this is the only fish species tested in laboratory 
experiments, and other species could serve as ecological hosts in the 
wild. The glochidia remain encysted for 13 to 28 days during 
transformation to the juvenile stage (Bosman et al. 2015, entire). Once 
transformed, the juveniles excyst from the fish and drop to the 
substrate. All species in the genus Potamilus have unique axe-head 
shaped glochidia which, unlike many other mussel species, grow in size 
while encysted on host fishes (Smith et al. 2020, pp. 2, 6, 10).
    Longevity is not known for the Salina mucket. However, bleufer, a 
closely related congener species, have been reported to have a maximum 
lifespan of 10 years and age of maturity at 0 to 2 years, with a mean 
fecundity of 417,407 glochidia (Haag 2012, pp. 196, 208; Haag 2013, p. 
750).
    Adult Salina mucket occur in medium to large rivers, generally in 
nearshore habitats and crevices, undercut riverbanks, travertine 
shelves, and under large boulders adjacent to runs (Howells et al. 
1996, pp. 103-104; Karatayev et al. 2012, p. 210; Randklev et al. 2017, 
pp. 157, 159; Randklev et al. 2020a, entire). Small-grained material, 
such as clay, silt, or sand, gathers in these crevices and provides 
suitable anchoring substrate. These areas are considered flow refugia 
from the large flood events that occur regularly in the rivers this 
species occupies. Salina mucket use these flow refugia to avoid being 
swept away as large volumes of water move through the system, as there 
is relatively little particle movement in the flow refugia, even during 
flooding (Strayer 1999, p. 472). Salina mucket need flowing water for 
survival and are not found in lakes, ponds, or reservoirs without flow, 
or in areas that are regularly dewatered. The absence of the species 
from lentic habitats suggests its inability to cope with impoundments 
and reservoirs (Randklev et al. 2020a, entire).
    Little is known about the specific feeding habits of the Salina 
mucket. Like all adult freshwater mussels, the Salina mucket is a 
filter feeder, siphoning suspended phytoplankton and detritus from the 
water column (Yeager et al. 1994, p. 221). Juvenile mussels live in the 
sediment and most likely feed interstitially rather than from the water 
column, using the large muscular foot to sweep organic and inorganic 
particles found among the substrate into the shell opening (Yeager et 
al. 1994, pp. 220-221).

Mexican Fawnsfoot

    A thorough review of the taxonomy, life history, and ecology of the 
Mexican fawnsfoot is presented in the SSA report (Service 2023, 
entire). The Mexican fawnsfoot was first described as Unio cognatus, 
from the Rio Salado, in Mexico (Lea 1860, p. 306). The species was 
moved to the subgenus Amygdalonaias by Simpson and then placed in the 
genus Truncilla by Frierson (Simpson 1900, p. 604; Frierson 1927, p. 
89). Johnson synonymized Truncilla cognata as Truncilla donaciformis 
(fawnsfoot) due to morphological similarities and the holotype specimen 
was a heavily weathered single valve (Johnson 1999, pp. 39-40). Mexican 
fawnsfoot is currently classified in the unionid subfamily Ambleminae 
and is considered a valid taxon by the scientific community (Turgeon et 
al. 1998, p. 33; Williams et al. 2017, pp. 35, 44; Burlakova et al. 
2019, entire; Smith et al. 2019, p. 7).
    Genetic studies have been conducted for species within the genus 
Truncilla. Most notably, Mexican fawnsfoot was recognized as 
genetically distinct from other Truncilla species (Smith et al 2019, p. 
7; Burlakova et al. 2019, entire). However, the genetic diversity 
within the species is unknown, as only a limited number of individuals 
have been analyzed.
    The Mexican fawnsfoot is a small-sized freshwater mussel with a 
yellow to green periostracum and faint chevron-like markings, an 
elongate outline, and laterally inflated shell (Lea 1860, pp. 368-369; 
Randklev et al. 2020b, entire). For a more detailed description of the 
morphological characteristics of Mexican fawnsfoot, see Howells et al. 
1996 (pp. 139-140).
    The Mexican fawnsfoot historically occurred in the lower Rio Grande 
drainage in Texas and Mexico. The holotype specimen was described from 
the Rio Salado, Mexico (State of Nuevo Le[oacute]n); however, the 
species is presumed extirpated in Mexico based on surveys conducted in 
the early 2000s and in 2017, which found suitable habitat but no live 
individuals or shell material of the species (Service 2023, pp. 25-26; 
Hein et al. 2017, entire).
    Mussels in the genus Truncilla have miniaturized glochidia and use 
molluscivorous freshwater drum as hosts (Barnhart et al. 2008, p. 373;

[[Page 47957]]

Smith et al. 2019, p. 6). The primary host fishes for the Mexican 
fawnsfoot are unknown; however, based on other species in the genus 
Truncilla, they are likely freshwater drum specialists (Haag 2012, pp. 
178-179; Sietman et al. 2018, pp. 1-2; Smith et al. 2019, p. 6). To 
date, no empirical laboratory studies have tested host fishes for the 
Mexican fawnsfoot.
    The Mexican fawnsfoot's reproductive strategy (e.g., mantle lures 
or conglutinates) is unknown. Some researchers have postulated that 
some female mussels of genus Truncilla allow themselves to be 
depredated (female self-sacrifice) by freshwater drum to infest the 
host fish (Haag 2012, pp. 178-179). However, this fails to explain the 
reproductive strategy of larger females that exceed the size range 
capable of being ingested by a freshwater drum or other potential host 
fish species (Sietman et al. 2018, p. 2). Therefore, it is possible 
that secondary reproductive strategies, such as broadcast of free 
glochidia or cryptic lures may become the primary method of glochidia 
dispersal (Haag 2012, p. 179).
    Longevity is not known for the Mexican fawnsfoot. However, congener 
species in the genus Truncilla from the southeastern United States have 
been reported to reach a maximum lifespan of 8 to 18 years (Haag and 
Rypel 2011, pp. 4-6; Sietman et al. 2018, p. 1). The Mexican fawnsfoot 
likely has a similar maximum lifespan.
    Adult Mexican fawnsfoot occur in medium to large rivers, in or 
adjacent to riffle and run habitats as well as in stream bank habitats 
(Karatayev et al. 2012, p. 211; Randklev et al. 2017, pp. 221-234; 
Randklev et al. 2020b, entire). Small-grained material, such as clay, 
silt, or sand, gathers in these crevices and provides suitable 
anchoring substrate. These areas are considered flow refugia from the 
large flood events that occur regularly in the rivers this species 
occupies. Mexican fawnsfoot use these flow refugia to avoid being swept 
away as large volumes of water move through the system, as there is 
relatively little particle movement in the flow refugia, even during 
flooding (Strayer 1999, p. 472). However, many of the riffle and near-
shore deposition areas occupied by Mexican fawnsfoot are bathymetric 
high points in a river system and are subject to exposure at reduced 
flow rates before the stream completely ceases to flow (Brewster 2015, 
p. 22). Mexican fawnsfoot need flowing water for survival and are not 
found in lakes, ponds, or reservoirs (Randklev et al. 2020b, entire).
    Little is known about the specific feeding habits of the Mexican 
fawnsfoot, but like the Salina mucket, it is a filter feeder, siphoning 
suspended phytoplankton and detritus from the water column (Yeager et 
al. 1994, p. 221).

Regulatory and Analytical Framework

Regulatory Framework

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

[[Page 47958]]

and should consider the timeframes applicable to the relevant threats 
and to the species' likely responses to those threats in view of its 
life-history characteristics. Data that are typically relevant to 
assessing the species' biological response include species-specific 
factors such as lifespan, reproductive rates or productivity, certain 
behaviors, and other demographic factors.

Analytical Framework

    The SSA report (Service 2023, entire) documents the results of our 
comprehensive biological review of the best scientific and commercial 
data regarding the status of these 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 proposed for listing 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 Salina mucket and Mexican fawnsfoot, 
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 the 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 each of the species 
arrived at its current condition. The final stage of the SSA involved 
making projections 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 
decisions.
    The following is a summary of the key results and conclusions from 
the SSA report; the full SSA report can be found at Docket No. FWS-R2-
ES-2023-0026 on https://www.regulations.gov and at https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot.

Summary of Biological Status and Threats

    In this discussion, we review the biological condition of the 
species and their resources, and the threats that influence the 
species' current and future conditions in order to assess the species' 
overall viability and the risks to that viability. We also considered a 
range of plausible future scenarios on the future viability of both 
species within the SSA report (Service 2023, pp. 60-86), but do not 
address them further in this proposed rule.

Historical Range and Distribution

Salina Mucket
    The Salina mucket is native to the Rio Grande (known in Mexico as 
the Rio Bravo) drainage in Texas and northern Mexico. The Salina mucket 
historically occupied approximately 734 river miles (rmi) (1,181 river 
kilometers (rkm)) in the United States and Mexico and is presumed 
extirpated from approximately 82 percent of the species' known 
historical distribution (Karatayev et al. 2015, p. 7).
    In the Rio Grande system, the Salina mucket historically occurred 
from the confluence of the Rio Conchos with the Rio Grande (Presidio 
County, Texas) to downstream just below the current location of Falcon 
Dam (Starr County, Texas). This stretch of occupied stream accounted 
for a total of approximately 686 rmi (1,104 rkm) in the mainstem Rio 
Grande (Johnson 1998, p. 433; Howells et al. 1996, pp. 103-104; 
Karatayev et al. 2012, pp. 210-211; Randklev et al. 2017, p. 157; 
Randklev et al. 2018, p. 135; Randklev et al. 2020a, entire). 
Additionally, the species historically occurred in the lower Pecos 
River to approximately 1 rmi (1.6 rkm) upstream of the river's 
confluence with the Rio Grande. However, the Pecos River population is 
now considered extirpated, as the last live individual was encountered 
in the 1960s and the lower portion of the Pecos River is now inundated 
by Amistad Reservoir. Possible recent reports of the species from the 
Pecos and Devils Rivers remain unconfirmed and are likely misidentified 
bleufer or Tampico pearlymussel (Cyrtonaias tampicoensis), which can 
have a similar appearance to Salina mucket.
    With no live collections from the Rio Grande having occurred since 
the early 1970s (Howells 2002, p. ii; Miller 2020, pers. comm.), Salina 
mucket were believed extirpated entirely from Texas until 2003, when 
the species was rediscovered upstream of Amistad Reservoir (Howells 
2003, p. ii; Randklev et al. 2017, p. 157). Long dead, sub-fossil 
shells have been encountered below Amistad Reservoir in the lower Rio 
Grande; however, no live individuals have ever been reported below 
Amistad Reservoir (Karatayev et al. 2012, p. 211; Randklev et al. 2017, 
p. 157; Miller 2020, pers. comm.).
    Based on the species' description (Johnson 1998, p. 429), we 
conclude the lower Rio Salado, a Rio Grande tributary partially located 
in the Mexican state of Tamaulipas, was historically occupied by Salina 
mucket in approximately the lower 48 rmi (77 rkm) before the river's 
confluence with the Rio Grande. The Don Martin dam project on the Rio 
Salado started in 1927 and was completed sometime in the early 1930s 
(Garza 2016, entire). This impoundment in the Mexican State of Coahuila 
would have likely extirpated or fragmented any historical populations 
farther upstream in the Rio Salado basin as the species is not found in 
still water. Surveys of the upper reaches of the Rio Salado and its 
tributaries in the north-central Coahuila completed in 2001, 2002, and 
2017 did not result in the collection of any live Salina mucket. No 
known records exist for Salina mucket from other tributaries to the Rio 
Grande in the United States or Mexico. As such, the historical range as 
described above is thought to be accurate.
    Rio Grande--Lower Canyons: The only known remaining population of 
Salina mucket is located in the Lower Canyons of the Rio Grande just 
downstream of Big Bend National Park, in Brewster, Terrell, and Val 
Verde Counties, Texas. Between 2003 and 2008, 19 live Salina mucket 
were found at one site near Dryden, Texas (Karatayev et al. 2012, p. 
210). Shell material from Salina mucket was found at an additional 7 
sites (n = 159 shells) (Karatayev et al. 2012, p. 210). Salina mucket 
was the rarest mussel species encountered during the study, which 
surveyed over 160 sites throughout the Rio Grande from Terrell County 
to Starr County (Karatayev et al. 2012, p. 210).

[[Page 47959]]

Subsequent surveys conducted in 2014 and 2015 confirmed the presence of 
Salina mucket in the same general reach of the Lower Canyons (n = 22 
sites) with 92 live individuals found at 22 of 114 sites (Randklev et 
al. 2017, pp. 154-174). The surveys in 2014 and 2015 were also the 
first live report of a Salina mucket in Brewster County, Texas, the 
farthest observed upstream locality for the species (Randklev et al. 
2017, p.159). Measured shell lengths of observed live Salina mucket 
indicated the presence of mostly older individuals. However, the 
presence of some smaller individuals indicated somewhat recent 
recruitment (Randklev et al. 2017, p. 159).
    Individual mussel beds in the Lower Canyons vary in density, with 
the densest sites near San Francisco Creek and Johns Marina in Terrell 
County, Texas, and sites with lower densities located upstream of the 
San Francisco Creek confluence and downstream of Johns Marina sites 
(Randklev et al. 2017, p. 168).
    The Lower Canyons reach extends for approximately 127 rmi (204 rkm) 
below Big Bend National Park through private lands along the U.S.-
Mexico border. This reach of the Rio Grande is largely spring-fed, with 
significant spring-flow inputs occurring upstream of the confluence of 
San Francisco Creek (Donnelly 2007, p. 3; Bennett et al. 2009, p. 1). 
The area was designated a National Wild and Scenic River in 1978 
(Garrett and Edwards 2004, p. 396), which affords some protection from 
Federal development projects, but the designation does not limit State, 
local, or private development (National Wild and Scenic Rivers System 
2021, p. 1). Urban and agricultural land use in the Lower Canyons reach 
is minimal, and most land in the watershed is undeveloped (Plateau 
Water Planning Group 2020, pp. 1-9-1-10; Far West Texas Water Planning 
Group 2020, pp.1-13-1-14). The Lower Canyons reach is characterized by 
swift rapids interspersed by pools, often bounded by high canyon walls 
(Garrett and Edwards 2004, p. 396), and transitions into slow-moving, 
impounded waters at the inflow areas to Amistad Reservoir, which was 
constructed in 1969.
    Rio Grande--Downstream of Amistad Reservoir: No live Salina mucket 
have been found in any surveys of the Rio Grande downstream of Amistad 
Reservoir (e.g., Howells et al. 1996, pp. 103-104; Karatayev et al. 
2012, pp. 210-211; Randklev et al. 2017, p. 157). However, Salina 
mucket sub-fossil shell material has been found in this portion of the 
basin, and that shell evidence suggests that, at one time, a large, 
widespread population of Salina mucket likely occurred there (Karatayev 
et al. 2012, pp. 210-211).
    Ongoing development and water management likely prohibit Salina 
mucket from occupying reaches downstream of Amistad Reservoir. The Rio 
Grande in the Laredo area is heavily influenced by development along 
the U.S.-Mexico border. Rapid human population growth, as well as 
industrialization on the Mexican side of the river, has stressed the 
existing wastewater treatment facilities, resulting in a high 
sedimentation load and impaired water quality in the Rio Grande (Texas 
Clean Rivers Program 2013, pp. 7-9). In addition, flows are regulated 
by releases from Amistad Reservoir based on hydropower generation and 
water deliveries for downstream irrigation needs (Texas Water 
Development Board 2021, p. 1). These water diversion and delivery 
projects have resulted in substantial daily variation in stream 
discharge and depth (Randklev et al. 2018, p. 734).
    Rio Salado Basin: The Salina mucket historically occurred in the 
Rio Salado basin in Mexico. Rio Salado and several of its tributaries 
were surveyed in the early 2000s, resulting in several recently dead 
mussel shells collected in 2001 and 2002 in the Rio Sabinas (Strenth et 
al. 2004, p. 225). The surveyed portions of the Rio Sabinas riverbed 
were reported to be dry with no evidence of recent water flow or live 
Salina mucket.
    In the mainstem Rio Salado, no living mussels or shells encountered 
during this survey were identified as Salina mucket (Strenth et al. 
2004, entire). As with the Rio Sabinas, the river exhibited no flow, 
and at one site, household waste was reported. These rivers, and many 
others in this region of Mexico, are losing flow and since the mid-
1990s have become dry or intermittent (Contreras-B. and Lozano-V. 1994, 
p. 381).
    In 2017, four sites in the Rio Salado system were visited, 
including the Rio Salado, Rio Sabinas, Rio San Rodrigo, and Rio 
Nadadores (Hein et al. 2017, entire). While these surveys focused on 
locating Texas hornshell (Popenaias popeii), the areas surveyed were 
within the Salina mucket's historical habitat. Several of the locations 
in the Rio Sabinas contained suitable habitat for the Salina mucket, 
including flowing water; however, these surveys provided no live or 
shell evidence of Salina mucket. Therefore, for the purposes of our 
analysis, Salina mucket is considered functionally extirpated from the 
Rio Salado and its tributaries.
Mexican Fawnsfoot
    The Mexican fawnsfoot is native to the Rio Grande drainage in Texas 
and northern Mexico. Mexican fawnsfoot historically occurred in the Rio 
Grande from approximately the confluence of the Pecos River with the 
Rio Grande (Val Verde County, Texas) to downstream just below the 
current location of Falcon Dam (Starr County, Texas). This represents 
approximately 340 rmi (547 rkm) of historically occupied river. The 
Mexican fawnsfoot may have occupied the lower section (approximately 1 
rmi (1.6 rkm)) of the Pecos River (Metcalf 1982, p. 52); however, 
inundation by Amistad Reservoir in the late 1960s, and subsequent 
changes in hydrology, temperature, and sedimentation, likely made that 
habitat unsuitable for Mexican fawsnfoot and extirpated any population 
there.
    Based on species' descriptions (Lea 1860, pp. 368-369; Johnson 
1999, pp. 38-40, 64), we infer the lower Rio Salado was historically 
occupied by the Mexican fawnsfoot in the Mexican State of Nuevo 
Le[oacute]n in the lower 48 rmi (77 rkm) before its confluence with the 
Rio Grande. However, the exact collection location of the holotype 
specimen is unknown. The Don Martin dam project in Coahuila and 
subsequent changes in hydrology, temperature, and sedimentation, as 
well as barriers to host fish passage, would have likely extirpated or 
fragmented any historical populations farther upstream in the Rio 
Salado basin. No other known records exist for Mexican fawnsfoot from 
other tributaries to the Rio Grande in the United States or Mexico. As 
such, the historical range, as described above, is thought to be 
accurate.
    Amistad Reservoir: There are very few reports of Mexican fawnsfoot 
in the reach of the Rio Grande near Del Rio, Texas (around the current 
location of Amistad Reservoir), likely due to upstream and downstream 
effects of Amistad Dam. Mexican fawnsfoot were collected from the Rio 
Grande near Del Rio, Texas, in 1972 (Howells et al. 1997, p. 123). 
However, subsequent surveys of that stream reach have yielded no 
Mexican fawnsfoot, live or dead, in either the upstream or downstream 
vicinity of Amistad Reservoir (Randklev et al. 2017, p. 221). 
Consequently, it is unlikely that this reach is inhabited by a 
substantial population of Mexican fawnsfoot, and any historical 
population that inhabited this reach was likely extirpated by either 
the construction and filling of Amistad Reservoir in the late 1960s or 
the subsequent changes in hydrology, temperature, and

[[Page 47960]]

sedimentation that occurred as a result of Amistad Dam.
    Rio Grande--Downstream of Amistad Reservoir: The only remaining 
Mexican fawnsfoot population occurs from approximately Eagle Pass, 
Texas, downstream to San Ygnacio, Texas (referred to below as the 
Laredo reach), for a total of approximately 184 rmi (296 rkm) (Randklev 
et al. 2017, p. 221). Falcon Dam, completed in 1954, likely caused the 
extirpation of Mexican fawnsfoot in the 40-rmi (64-rkm) length of river 
inundated by the impoundment due to changes in hydrology, temperature, 
and sedimentation (Randklev et al. 2017, p. 176). Mexican fawnsfoot 
were believed extirpated from Texas, as no live or dead individuals 
were found from 1972 to 2003, until a single live individual was 
located in Webb County, Texas, in 2003 (Howells 2001, entire; Howells 
2004, p. 35; Randklev et al. 2020b, entire). During extensive surveys 
between 2001 and 2011 throughout the Rio Grande drainage, only 19 live 
Mexican fawnsfoot were located from Laredo and Webb Counties, Texas. No 
live individuals were found downstream of the Laredo South Side 
wastewater treatment plant in Laredo, Texas; however, fresh dead (still 
containing soft tissue) Mexican fawnsfoot were located in Zapata 
County, Texas. Of the live individuals encountered, shell size ranged 
from 0.8 to 1.3 inches (20.5 to 33 mm) (Karatayev et al. 2012, p. 211). 
In another study, 213 live Mexican fawnsfoot were reported from 30 of 
114 sites surveyed in the Rio Grande basin (Randklev et al. 2017, p. 
223). Researchers noted that live individuals were found primarily in 
Webb and Zapata Counties and upstream of Falcon Lake (Randklev et al. 
2017, p. 224).
    As stated above under Rio Grande--Downstream of Amistad Reservoir 
for the Salina mucket, the Rio Grande in the Laredo area is influenced 
by development, high sedimentation, regulated flows, and water 
diversions, all of which have affected water quality and quantity and 
thus affected the Mexican fawnsfoot population in this reach.
    Rio Salado Basin: The Mexican fawnsfoot historically occurred in 
the Rio Salado basin; however, the current status of the population 
remains unknown and is likely extirpated (Burlakova et al. 2019, p. 
346). The Rio Salado, Rio Sabinas, and several other tributaries were 
surveyed in the early 2000s. The surveyed portions of river were 
reported to be dry with no indicators of recent stream flow. No 
evidence of Mexican fawnsfoot, either through the observation of live 
individuals or collection of shell material, was reported.
    In 2017, four sites in the Rio Salado system were visited, 
including the Rio Salado, Rio Sabinas, Rio San Rodrigo, and Rio 
Nadadores (Hein et al. 2017, entire). While several of the locations 
contained apparently suitable habitat, including flowing water, no live 
Mexican fawnsfoot or shell material were found at any location during 
these surveys. Therefore, for the purposes of our analysis, Mexican 
fawnsfoot is considered functionally extirpated from the Rio Salado and 
its tributaries.

Species Needs

Resiliency
    For the Rio Grande mussels to maintain viability, their populations 
or some portion thereof must be sufficiently resilient. Stochastic 
events that have the potential to affect their populations include 
high-flow events, drought, pollutant discharge, and accumulation of 
fine sediment. Multiple demographic factors, including occupied stream 
length, abundance, and recruitment, influence the resiliency of 
populations. Those factors, in turn, are influenced by the availability 
of important habitat features such as suitable substrate, flowing 
water, and good water quality. Both the demographic factors and the 
availability of important habitat features determine the resiliency of 
Salina mucket and Mexican fawnsfoot populations.
    Occupied Stream Length--Most freshwater mussels are found in 
aggregations, called mussel beds, that can vary in size from less than 
50 to greater than 5,000 square meters (m\2\), and are separated by 
stream reaches in which mussels are absent or rare (Vaughn 2012, p. 
983). For each of the Rio Grande mussels, a population is a collection 
of mussel beds within a hydrologically connected stream reach through 
which infested host fish may travel. This connection allows for ebbs 
and flows in mussel bed occupancy, distribution, and abundance 
throughout the stream reach. Therefore, sufficiently resilient 
populations must occupy stream reaches long enough such that stochastic 
events that affect individual mussel beds do not eliminate the entire 
population. Repopulation by infested fish from other source mussel beds 
within the reach can allow the population to recover from these events.
    Abundance--For populations to be adequately resilient, there must 
be many mussel beds of sufficient density such that local stochastic 
events do not necessarily eliminate all individuals from the bed(s), 
allowing the mussel bed(s) and the overall population in the stream 
reach to recover from any one event.
    Reproduction--Adequately resilient mussel populations must 
reproduce and recruit young individuals into the reproducing 
population. Population size and abundance reflect previous influences 
on the population and habitat and provide a current ``snapshot'' of the 
population, while reproduction and recruitment reflect stable, 
increasing, or decreasing population trends that reflect the future 
viability of the population. For example, a large, dense population of 
freshwater mussels that contains mostly older individuals and lacks 
younger individuals is not likely to remain large and dense into the 
future, as there are few young individuals to sustain the population 
over time. Conversely, a population that is less dense but has many 
young and/or gravid individuals may be likely to maintain or increase 
in density in the future as younger individuals mature and boost the 
reproductive capacity of the population. For the purposes of the SSA 
report (Service 2023, pp. 31-51), we considered populations with three 
or more distinct age classes highly resilient. Age classes are defined 
as multiple individuals within a similar shell size length, which 
indicates that multiple individuals are part of the same cohort or 
reproductive event.
    Substrate--Salina mucket occur in flow refuges such as crevices, 
undercut riverbanks, travertine shelves, large boulders, and near-shore 
deposition areas such as banks, point bars, and backwater pools. These 
refuges must have seams of clay or other fine sediments within which 
the mussels may anchor, but not so much excess sediment that the 
mussels are smothered.
    Mexican fawnsfoot occur primarily in riffles as well as near-shore 
depositional habitats. Habitats with clean-swept substrate with seams 
of fine sediments are considered to have suitable substrate, and those 
with copious fine sediment both in crevices and on the stream bottom 
are considered less suitable.
    Flowing Water--Freshwater mussels need flowing water for survival. 
The Rio Grande mussels are not found in lakes or in pools without flow, 
or in areas that are regularly dewatered (Randklev et al. 2020a, 
entire; Randklev et al. 2020b, entire). Therefore, stream reaches with 
continuous flow are considered suitable habitat, while those with 
little or no flow (caused either by dewatering or impoundment) are 
considered not suitable. Freshwater mussels are

[[Page 47961]]

sensitive to changes in flow rate. However, no empirical studies of 
flow requirements for the Rio Grande mussels have been conducted.
    Water Quality--Freshwater mussels, as a group, are sensitive to 
changes in water quality parameters such as dissolved oxygen, salinity, 
ammonia, and pollutants. Habitats within the unique tolerance limits of 
resident mussel species are considered suitable, while those habitats 
with levels outside of those tolerance limits are considered less 
suitable. No empirical studies of water quality tolerances for the Rio 
Grande mussels have been conducted.
Representation
    Maintaining representation in the form of genetic or ecological 
diversity is important to maintain the Rio Grande mussels' capacity to 
adapt to future environmental changes. Mussels need to maintain 
populations throughout their ranges to retain the genetic variability 
and life-history attributes that can buffer the species' response to 
environmental changes over time (Jones et al. 2006, p. 531). The Rio 
Grande mussels each have likely lost genetic diversity as populations 
have been extirpated throughout their ranges. Consequently, retaining 
the remaining representation in the form of genetic diversity is likely 
critical to the species' capacity to adapt to future environmental 
change.
Redundancy
    The Rio Grande mussels need multiple, sufficiently resilient 
populations distributed throughout their ranges to provide for 
redundancy. The more populations, and the wider the distribution of 
those populations, the more redundancy the species will exhibit. 
Redundancy reduces the risk that a large portion of the species' range 
will be negatively affected by a catastrophic natural or anthropogenic 
event at a given point in time. Species that are well-distributed 
across their historical range are less susceptible to extinction and 
more viable than species confined to a small portion of their range 
(Carroll et al. 2010, entire; Redford et al. 2011, entire). 
Historically, most Rio Grande mussel populations were likely connected 
by fish migration throughout the Rio Grande, upstream through the Pecos 
River, and throughout Rio Grande tributaries in the United States and 
Mexico. However, due to impoundments and river reaches with unsuitable 
water quality (e.g., high salinity), populations have become isolated 
from one another, and repopulation of extirpated locations is unlikely 
to occur without human assistance.

Threats

    We reviewed the potential threats that could be affecting the two 
Rio Grande mussel species now and in the future. In this proposed rule, 
we will discuss only those factors in detail that could meaningfully 
impact the status of the species. Those risks that are not known to 
have effects on Rio Grande mussel populations, such as disease, are not 
discussed here but are evaluated in the SSA report (Service 2023, 
entire). Many of the threats and risk factors are the same or similar 
for both species. Where the effects are expected to be similar, we 
present one discussion that applies to both species. Where the effects 
may be unique to or different for one species, we address that 
specifically. The primary threats affecting the status of the Rio 
Grande mussels are: Increased fine sediment (Factor A from the Act), 
changes in water quality (Factor A), altered hydrology in the form of 
loss of flow (Factor A), and specific to the Mexican fawnsfoot, 
barriers to fish movement (Factor E). These factors are all exacerbated 
by the ongoing and expected effects of climate change (Factor E). 
Finally, we also reviewed the conservation efforts being undertaken for 
the species.
Increased Fine Sediment
    Freshwater mussels require specific stream substrates (e.g., silt, 
sand, gravel, and larger cobbles) in order to anchor themselves into 
place in the streambed. Interstitial spaces (small openings between 
rocks and gravels) in the substrate 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 
rates and spaces may become reduced, thus reducing juvenile habitat 
availability and survivorship (Brim Box and Mossa 1999, p. 100). 
Excessive fine sediments can also embed in larger crevices, potentially 
causing a change in overall substrate composition and even leading to 
smothering of adult or juvenile mussels that occupy those spaces.
    Under natural conditions, fine sediments collect on the streambed 
and in crevices during low-flow events. Much of the accumulated 
sediment is dislodged and washed downstream during high-flow events 
(also known as cleansing flows). However, the increased frequency and 
duration of low-flow events (from groundwater extraction, instream 
surface flow diversions, or drought, such as drought caused by climate 
change) combined with a decrease in cleansing flows (from reservoir 
management and drought) and the presence of giant cane (Arundo donax), 
which can alter stream hydrology and morphology by retaining sediments 
and channeling flows (Yang et al. 2011, p. 1), have likely caused 
sediment to accumulate in excess of historical quantities in stream 
reaches occupied by both species of Rio Grande mussels, especially in 
bank habitats in areas occupied by Salina mucket. When water velocity 
decreases, which can occur from reduced streamflow or inundation, water 
loses its ability to mobilize sediment and carry it in suspension. This 
sediment can fall to the substrate and lead to the smothering of 
mussels that cannot adapt to softer or finer substrates (Watters 2000, 
p. 263). Furthermore, increased sediment accumulation resulting from 
altered hydrology can be exacerbated by a simultaneous increase in the 
number of sources of fine sediment in a watershed. In the range of the 
Rio Grande mussels, additional sources of fine sediment include, but 
are not limited to, streambank erosion from agricultural activities, 
livestock grazing, roads, border maintenance (e.g., boat ramp and road 
maintenance), and climate change.
    Potential changes in climate, like a higher frequency of drought 
with periodic intense rain events, can alter sediment load and sediment 
distribution (Allen et al. 2011, entire; EPA 2022, entire). Due to 
reduced vegetative cover and higher soil erodibility, high intensity 
rainfall during a drought period can more efficiently dislodge and 
transport sediment, which later settles in rivers and streambeds.
Water Quality Impairment
    Water quality can be impaired through contamination or by 
alteration of naturally occurring 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). Chemicals enter the 
environment through both point and nonpoint discharges, including 
spills, industrial sources, municipal effluents, and agricultural 
runoff. These sources contribute organic compounds, heavy metals, 
pesticides, herbicides, and a wide variety of newly emerging 
contaminants to the aquatic environment. Ammonia is of particular 
concern below agricultural areas and water treatment plant outfalls as 
freshwater mussels can be particularly sensitive to increased ammonia 
levels at all life stages; juveniles are especially

[[Page 47962]]

sensitive (Augspurger et al. 2003, p. 2569). Elevated levels of ammonia 
are likely the reason that Mexican fawnsfoot are not found for many 
miles downstream of multiple wastewater treatment plants that discharge 
into the Rio Grande from both the United States and Mexico near Nuevo 
Laredo (Karatayev et al. 2015, p. 9). Similarly, increased nutrients 
and heavy metals contained in inflows from the Rio Conchos, combined 
with reduced flow, have resulted in heavier concentrations of 
contaminants, which have influenced the distribution of Salina mucket 
(Rubio-Arias et al. 2010, pp. 2074-2081).
    An additional type of water quality impairment is alteration of 
water quality parameters like dissolved oxygen, temperature, or 
salinity. Because surface runoff or wastewater effluent frequently 
include decomposing organic materials, dissolved oxygen may be reduced 
by increased nutrient inputs from these sources (American Public Health 
Association 1992, entire). Juvenile freshwater mussels are particularly 
sensitive to low dissolved oxygen (Sparks and Strayer 1998, pp. 132-
133).
    Increases in water temperature due to climate change and low-flow 
conditions during drought can exacerbate the effects of low dissolved 
oxygen levels by further reducing dissolved oxygen within the waterbody 
and increasing freshwater mussel oxygen consumption rates. 
Additionally, elevated water temperatures can have their own direct 
metabolic effects on both juvenile and adult mussels by affecting their 
available energy for maintenance, growth, and reproduction (Ganser et 
al. 2013, p. 1169).
    Finally, salinity can also limit mussel abundance and distribution 
(Haag 2012, p. 330; Johnson et al. 2018, entire), including that of 
Salina mucket. Inflows from the Rio Conchos, Mexico, the primary source 
of instream flows entering the Rio Grande approximately 125 river miles 
(201 rkm) upstream of the known remaining population of Salina mucket, 
contribute significantly to base flow in the Rio Grande upstream of 
Amistad Reservoir. The Rio Grande average daily flow rate has been 
reported at 140 cubic feet per second (cfs) above the Rio Conchos 
confluence and 990 cfs downstream (Ward 2017, pp. 5-6). Spring inputs 
also account for some of the increases in riverine base flow. Based off 
U.S. International Boundary and Water Commission (USIBWC) gauge data, 
overall riverine flow increases as much as 60 percent due to spring 
water inputs throughout the Lower Canyons stretch of the Rio Grande 
(Brauch 2012, p. 4). This reach of the Rio Grande is occupied by the 
upstream portion of the known remaining population of Salina mucket. 
However, the spring inputs are often saline and thermal (hot water) and 
contribute to elevated salinity in the Lower Canyons of the Rio Grande 
(Urbanczyk and Bennett 2017, entire). Persistent inflows from the Rio 
Conchos are likely critical to maintaining appropriate salinity levels 
for the Salina mucket (Urbanczyk and Bennett 2017, p. 16). 
Additionally, aquifers have become increasingly saline due to salinized 
water recharge. Water management in the Pecos River, a Rio Grande 
tributary, has led to reduced flood frequency and magnitude, diminished 
stream flows, increased evapotranspiration, and increased prevalence of 
saline groundwater that has resulted in increased salinization 
(Hoagstrom 2009, entire). Irrigation return-flows exacerbate increasing 
salinity levels as salts build up on irrigated land and then are washed 
into the Rio Grande and its tributaries.
    A reduction in surface flow from drought, instream diversion, or 
groundwater extraction concentrates contaminant and salinity levels, 
increases water temperatures in streams, and exacerbates detrimental 
effects to the Rio Grande mussels.
Loss of Flowing Water
    The Rio Grande mussels need flowing water to survive. Low-flow 
events (including stream drying) and inundation can eliminate 
appropriate habitat conditions for both species, and while the species 
may survive these events if they are short in duration, populations 
will not persist if they experience these conditions frequently or 
continuously.
    Inundation has primarily occurred in the Rio Grande basin upstream 
of dams, both large (e.g., Amistad and Falcon) and small (e.g., water 
weir barriers built across the stream to control or slightly raise 
upstream water levels and diversion dams, such as those in the Rio 
Grande below Amistad). Inundation causes an increase in sediment 
deposition, eliminating interstitial spaces both mussel species need to 
anchor themselves and for juvenile growth. In large reservoirs, deep 
water is very cold and often devoid of oxygen and necessary nutrients. 
Cold water (less than 11 degrees Celsius ([deg]C) (52 degrees 
Fahrenheit ([deg]F))) has been shown to stunt mussel growth and delay 
or hinder spawning (Galbraith and Vaughn 2009, p. 45). Because 
glochidial release may be temperature dependent, it is likely that 
relict individuals living in the constantly cold hypolimnion (deepest 
portion of the reservoir) in these reservoirs may never reproduce or 
will reproduce less frequently (Khan et al. 2019, entire). Because 
inundation of occupied habitats is detrimental to the survival of both 
Rio Grande mussels from both a short-term survival perspective and a 
long-term reproductive potential perspective, neither species is 
considered tolerant of reservoir habitat (Randklev et al. 2020a entire; 
2020b, entire).
    Very low water levels are detrimental to the Rio Grande mussels as 
well. Recent droughts have led to extremely low flows in rivers across 
the desert Southwest. The areas inhabited by the Rio Grande mussels 
have some resiliency to drought because they are partially spring-fed 
(e.g., Salina mucket in the Lower Canyons of the Rio Grande), or have 
managed flow from major reservoirs (e.g., Mexican fawnsfoot downstream 
of Amistad). However, streamflow in the Rio Grande downstream of the 
confluence with the Rio Conchos (near the Lower Canyons of the Rio 
Grande) has been declining since the 1980s (Miyazono et al. 2015, p. A-
3). Overall river discharge for the Rio Grande is projected to continue 
to decline due to increased drought as a result of climate change 
(Nohara et al. 2006, p. 1087). In addition to increasingly common and 
extended low-flow conditions, climate change will also bring higher air 
temperatures and increased evaporation, which will further imbalance 
the supply and demand for water. Increased groundwater pumping and 
resultant aquifer shortages, as well as regulated reservoir releases, 
may lead to lower river flows of longer duration than have been 
recorded in the past.
    The Lower Canyons is very incised, and the Salina mucket occurs in 
crevices along the steep banks. Reductions in discharge in this area 
may lead to a higher proportion of the population being exposed than 
similar decreases experienced by other mussel species inhabiting the 
reach. Mexican fawnsfoot inhabits riffle and near-shore depositional 
areas; both areas are bathymetric high points in a river system. 
Therefore, decreased flows will likely lead to greater exposure of 
these habitats in both area and duration during drought and low flows. 
Since the habitats occupied by the Mexican fawnsfoot are high points in 
the river system, during periods of low flow, terrestrial predators 
have increased access to portions of the river that are otherwise too 
deep and inaccessible under normal flow conditions, which results in 
increased predation on the Mexican fawnsfoot.

[[Page 47963]]

    As spring and riverine flows decline due to drought or dropping 
water tables due to groundwater pumping, the habitat that can be 
occupied by the Rio Grande mussels could be further reduced and could 
eventually cease to exist. While these species may survive short 
periods of low-flow conditions, as low flows persist, mussels face 
increased risks due to oxygen deprivation, increased water temperature, 
and, ultimately, stranding, reducing survivorship, reproduction, and 
recruitment in the population.
Barriers to Fish Movement
    The natural ranges of the Rio Grande mussels historically extended 
throughout the mainstem Rio Grande and select major tributaries in 
Texas and Mexico. The overall distribution of mussels is, in part, a 
function of the dispersal of their host fish. Mussels colonize new 
areas through movement of infested host fish, and newly metamorphosed 
juveniles excysting from host fish into suitable habitats in new 
locations.
    Today, each mussel species has only a single remaining population, 
and mussels are distributed unevenly within each. This range 
restriction has greatly reduced the species' abilities to recolonize 
new areas, expand their current ranges, and maintain more distant 
mussel beds through fish host movement. The Rio Grande mussels do not 
have multiple, sufficiently resilient populations to provide redundancy 
and serve as sources to restore populations eliminated due to 
catastrophic events.
    Over time, by preventing fish passage, impoundments can lead to 
genetic isolation between individual populations throughout the 
species' ranges. These small, isolated populations are susceptible to 
genetic drift (random loss of genetic diversity) and inbreeding 
depression. This can make the species less adaptable and less resilient 
to changing environmental conditions. The Rio Grande mussels do not 
have additional populations to provide redundancy and serve as sources 
to restore genetic variability if the remaining population experiences 
genetic drift or inbreeding depression. Additionally, because each of 
the Rio Grande mussels only exists in a single, remaining population, 
any representation that historically occurred for each species through 
the existence of multiple populations in the Rio Grande and its 
tributaries has been lost.
    The Rio Grande mussels' primary host fish species, freshwater drum, 
are known to be a common and widespread species. We do not expect the 
distribution or abundance of the host fish itself to be a limiting 
factor for the Rio Grande mussels. There are no known fish host 
barriers within the range of the Salina mucket; therefore, we do not 
consider fish movement to be a stressor for that species. However, 
there are multiple low water weirs and other potential host fish 
barriers across the range of the Mexican fawnsfoot. In addition to 
existing barriers, new construction may further restrict host fish 
movement. One low-water weir has been proposed for construction near 
Laredo, Texas, which would likely restrict host fish passage between 
mussels on the up and downstream sides of the structure, resulting in 
genetic isolation. The low-water weir would also eliminate about 7 
percent of remaining occupied habitat for the Mexican fawnsfoot.
Climate Change
    Climate change has already begun, and continued greenhouse gas 
emissions at or above current rates will cause further warming 
(Intergovernmental Panel on Climate Change (IPCC) 2021, pp. 12-16). 
Warming in the Southwest is expected to be greatest in the summer, and 
annual mean precipitation is very likely to decrease in the Southwest 
(Ray et al. 2008, p. 1). In Texas, the number of extreme hot days (high 
temperatures exceeding 95 [deg]F) are expected to double by around 2050 
(Kinniburgh et al. 2015, p. 83). Texas is considered one of the 
``hotspots'' of climate change in North America with west Texas 
highlighted as an area that is expected to show greater responsiveness 
to the effects of climate change (Diffenbaugh et al. 2008, p. 3). Even 
if precipitation and groundwater recharge remain at current levels, 
increased groundwater pumping and resultant aquifer shortages due to 
increased temperatures are nearly certain (Loaiciga et al. 2000, p. 
193; Mace and Wade 2008, pp. 662, 664-665; Taylor et al. 2012, p. 3). 
Effects of climate change, such as air temperature increases and an 
increase in drought frequency and intensity, are occurring throughout 
the ranges of the Rio Grande mussels (Kinniburgh et al. 2015, p. 88). 
These effects are expected to exacerbate several of the stressors 
discussed above, such as water quality, water temperature, and loss of 
flowing water (Wuebbles et al. 2013, p. 16). In our analysis of the 
future condition of the Rio Grande mussels, we considered climate 
change to be an exacerbating factor in the increase of fine sediments, 
changes in water quality, and loss of flowing water.
Summary
    Our analysis of the past, current, and future influences on what 
the Rio Grande mussels need for long-term viability revealed that there 
are three influences that pose the largest risk to future viability of 
the species. These risks are primarily related to habitat changes: the 
accretion of fine sediments, the loss of flowing water, and impairment 
of water quality; all of these are anticipated to be exacerbated by 
climate change.
    Synergistic interactions are possible between the effects of 
climate change, the effects of threats (loss of stream flow, impairment 
of water quality, and accretion of fine sediments), and the activities 
that can lead to these threats, such as water development. Increases in 
temperature and changes in precipitation are likely to affect water 
quality, stream flows, and sediment accumulation rates in the Rio 
Grande. These threats could then be exacerbated by increases in water 
demand in the Rio Grande basin. However, it is difficult to project 
specifically how climate change will affect stream conditions because 
changes in stream conditions will also be directly tied to the 
management and water-use decisions made by both the United States and 
Mexico in the Rio Grande basin. Uncertainty regarding these management 
decisions in response to climate change, combined with uncertainty of 
future temperature and precipitation trends, make projecting possible 
synergistic effects of climate change speculative. However, we project 
that such synergistic effects will exist and will exacerbate the 
identified threats to the Salina mucket and Mexican fawnsfoot. Host 
fish availability and movement of glochidia are not anticipated to be 
key limiting factors that influence the future viability of Salina 
mucket; however, host fish availability and movement may affect the 
future viability of Mexican fawnsfoot.

Current Conditions

    Given each Rio Grande mussel species has only one extant 
population, we analyzed current condition by subdividing each current 
population into three stream segments (i.e., upstream, middle, and 
downstream) to capture variations in habitat and species' conditions 
within a population. We defined these stream segments by known changes 
in mussel habitat availability, water quality and quantity, and mussel 
abundance across each entire population.

[[Page 47964]]

Salina Mucket

    We subdivided the Salina mucket population, located upstream of 
Amistad Reservoir in the Rio Grande, into three segments based on 
population density and habitat conditions. We analyzed population and 
habitat factors for each segment based on the current information.
Upstream Segment
    This segment occurs in the upstream-most portion of the Salina 
mucket's current range for approximately 61 rmi (98 rkm) in Brewster 
County, Texas. The segment begins just downstream of the La Linda Texas 
International Bridge and ends at the Brewster and Terrell County line. 
The topography of this segment is dominated by steep canyon walls, 
predominantly bedrock streambed, and limited depositional areas. 
Outflows from the Rio Conchos and spring discharges from the Edwards-
Trinity Plateau Aquifer heavily influence riverine flow in this segment 
(Randklev et al. 2018, p. 734). Multiple springs throughout this 
segment contribute to base flow and incrementally increase water 
quality downstream (Bennett et al. 2009, entire; Urbanczyk and Bennett 
2017, p. 9). Species occurrence data in this segment, compiled from 
multiple sources, indicate that Salina mucket occur at an average 
abundance of 0.6 mussels per search hour (catch-per-unit-effort, CPUE). 
That is, one live Salina mucket is collected for roughly every 2 hours 
of search effort. The most recent comprehensive survey of this segment 
was conducted in 2015 and found 25 live Salina mucket from 11 of 24 
sites sampled (Randklev et al. 2017, p. 163).
Middle Segment
    This segment represents the approximate middle of the currently 
known population of the Salina mucket. The segment begins at the 
Brewster and Terrell County line and continues downstream for 22 rmi 
(35 rkm) to near Dryden, Texas (locally referred to as Johns Marina, a 
popular boat ramp). Riverine flows in this segment are typically higher 
velocity than upstream, and water quality appears to improve given the 
combined effects of spring inputs, Rio Conchos flows, and intermittent 
flows from San Francisco and Sanderson creeks. The river channel has 
greater access to the floodplain in this segment, resulting in 
hydrological changes including more depositional areas and bank 
habitats available for the Salina mucket (Miller 2020, pers. comm.). 
Salina mucket are more abundant, although still considered rare, in 
this segment. Sampling conducted in 2015 found 66 live Salina mucket 
from 11 of 14 sites sampled (Randklev et al. 2017, p. 163). Between 
2003 and 2008, 19 live Salina mucket were found at one site near 
Dryden, Texas, during basin-wide surveys (Karatayev et al. 2012, p. 
210). Shell material was also reported at an additional 7 sites (n = 
159 shells; Karatayev et al. 2012, p. 211). Overall, within this 
segment, the Salina mucket has an average CPUE of 1.35 live mussels per 
hour.
Downstream Segment
    The downstream segment begins at approximately Dryden, Texas, and 
extends downstream for 50 rmi (80 rkm) to Langtry, Texas, in Terrell 
and Val Verde Counties. Stream habitat and water quality are similar to 
that observed in the middle segment. However, the abundance of Salina 
mucket appears lower in this segment with an average CPUE of 0.6 live 
mussels per hour. Surveys conducted between 2013 and 2015 collected 
nine live Salina mucket found from three sites in this segment (Dascher 
et al. 2018, p. 318; Burlakova and Karatayev, 2013, unpaginated; 
Randklev et al. 2017, pp. 163-165; Randklev et al. 2020c, entire). 
Presumably, this reduced occupancy is due to a combination of effects, 
including inundation from Amistad Reservoir, irrigation, decreased 
flows due to a reduced number of spring inputs, and effects of 
evapotranspiration. Additional studies in this segment of the 
population are needed to better elucidate the species' occupancy 
(Karatayev et al. 2012, p. 214).
Resiliency
    The available information indicates that the Salina mucket is 
currently restricted to approximately 16 percent of its historical 
range in the United States and Mexico in the Lower Canyons of the Rio 
Grande, Texas. The species has been extirpated from a large portion of 
the Rio Grande, as well as the Pecos River (Texas) and the Rio Salado 
(Mexico). The single extant population of Salina mucket occurs in areas 
of relatively little development but of marginal habitat and water 
quality. As described above, the species' abundance varies throughout 
the population with the majority of live individuals located in the 
middle segment. This population shows some evidence of recent 
recruitment in the form of multiple age classes of individuals 
(Randklev et al. 2017, p. 156). However, given the degraded habitat 
quality and low numbers, this may not be sustainable over the long 
term. We consider this population to have low overall resiliency due to 
the low species abundance, limited evidence of recruitment, and 
degraded habitat, which limit the species' ability to recover following 
stochastic events.
Representation
    The Salina mucket only occupies one known population. We do not 
expect any significant differences in localized adaptations within this 
population, as the entire population occurs in similar habitat and 
faces similar stressors. As such, we consider this species to have 
representation consisting of a single population, limiting the species' 
ability to adapt to changes over time. Any representation that 
historically occurred throughout the Rio Grande or in Mexico has been 
lost.
Redundancy
    Within the Rio Grande basin, the Salina mucket does not have 
multiple sufficiently resilient populations. Only one extant population 
is known to occur in the Lower Canyons area between Big Bend National 
Park and Amistad Reservoir. No other extant populations are known to 
exist. Therefore, this species has little to no redundancy and is 
unlikely to recover from catastrophic events that could eliminate the 
one extant population.

Mexican Fawnsfoot

    We subdivided the Mexican fawnsfoot population, located between 
Eagle Pass and San Ygnacio, Texas, into three segments based on 
population density and habitat conditions. We analyzed population and 
habitat factors for each segment based on the current information.
Upstream Segment
    This segment begins about 6 miles upstream of Eagle Pass, Texas, 
and continues downstream for approximately 106 rmi (171 rkm) through 
Maverick and Webb Counties, Texas, to 3 miles upstream of the Laredo 
Columbia Solidarity International Bridge. The flows in this stretch of 
the Rio Grande are heavily influenced by releases from Amistad 
Reservoir (Schmandt et al. 2013, p. 82). This segment has significant 
diversions including the Maverick Canals, multiple low water weirs, and 
pumping for irrigation purposes. The habitat within the segment is 
largely degraded with a very low abundance of Mexican fawnsfoot. Only 
three live Mexican fawnsfoot were collected from 2 of 20 sites in 
Maverick County surveyed in 2015 (Randklev et al. 2017, p. 224). This 
represents the most recent live records

[[Page 47965]]

of the species within that segment from the last 30 years. The average 
CPUE for Mexican fawnsfoot in this segment is very low, at 0.35 live 
mussels per hour.
Middle Segment
    The middle segment begins about 3 miles upstream of the Laredo 
Colombia Solidarity International Bridge and continues downstream 
through Webb County, Texas, for 33 rmi (53 rkm) to the Interstate-35 
Juarez-Lincoln International Bridge in Laredo, Texas. Stream habitat 
improves marginally in this segment and is less influenced by flows 
from Amistad Reservoir. The average CPUE of Mexican fawnsfoot is 
highest in this segment at about 1.48 live mussels per hour. Several 
studies have documented the presence of Mexican fawnsfoot in this 
segment. Surveys conducted in 2014 and 2015 documented 160 live 
individuals from 13 sites (Randklev et al. 2017, pp. 227-232). During 
surveys in 2013 and 2014, a total of 69 live individuals and 241 
recently dead specimens from seven sites were collected (Brewster 2015, 
pp. 16-18). At a single site (near Pico Road, approximately the center 
of this segment), the surveyors discovered 35 live and 206 very 
recently dead individuals and noted that extremely low flows due to a 
major drought in July 2013 likely resulted in the elimination of the 
largest known Mexican fawnsfoot population (Brewster 2015, p. 30). 
Surveys between 2001 and 2011 collected 19 live individuals (Karatayev 
et al. 2012, p. 213).
Downstream Segment
    The downstream-most segment begins just upstream of the Juarez-
Lincoln International Bridge in Laredo, Texas, and continues through 
Webb and Zapata Counties, Texas, for 45 rmi (72 rkm) downstream to San 
Ygnacio, Texas, where impoundment effects of Falcon Lake begin. 
Historically, this segment most likely extended downstream farther into 
Zapata County and possibly Starr County; however, the completion and 
inundation of Falcon Lake in 1954 presumably extirpated any Mexican 
fawnsfoot occupying habitats underneath the current reservoir. 
Effluents from four wastewater treatment plants on the U.S. bank of the 
river and several on the Mexican bank of the river heavily influence 
this segment. The Texas Commission on Environmental Quality (TCEQ) has 
documented concentrations of fecal coliform and bacteria that exceed 
the established limits within this segment of the Rio Grande (TCEQ 
2002a, p. 1; TCEQ 2002b, p. 1). Historical collection data indicate a 
spike in bacteria concentration just upstream of the Juarez-Lincoln 
International Bridge, at the beginning of this population segment 
(USIBWC 2012, pp. 6-7, 9-10). It is likely that degraded water quality 
from point and non-point sources, coupled with hydrological alterations 
from urban runoff, diversions, and low-water weirs, has contributed to 
the decline of Mexican fawnsfoot in this segment. Currently, the 
average CPUE in this segment is very low at 0.37 live mussels per hour. 
During surveys in 2014 and 2015, 23 live Mexican fawnsfoot were found 
from 10 sites within this segment (Randklev et al. 2017, p. 229). A 
very small population of Mexican fawnsfoot has also been documented 
downstream of the confluence of Delores Creek near the Webb and Zapata 
County line (Miller 2020, pers. comm.). This population's persistence 
is likely attributed to cleaner inflows from Delores Creek, which 
improve water quantity and quality for a short distance in the mainstem 
of the Rio Grande.
Resiliency
    The available information indicates that the Mexican fawnsfoot is 
currently restricted to approximately 48 percent of its historical 
range in the United States and Mexico and is comprised of only one 
extant population in the Lower Rio Grande near Laredo, Texas. The 
species has been extirpated from a large portion of the Rio Grande near 
Amistad Reservoir (Texas) and presumably the Rio Salado (Mexico). The 
single extant population of Mexican fawnsfoot occurs in areas of 
significant development and hydrological alteration. The entire 
population has very limited abundance and only limited evidence of 
recruitment. As described above, the species' abundance varies 
throughout the population with the majority of the remaining live 
individuals located in the small, middle segment. This population shows 
some evidence of recent recruitment in the presence of multiple age 
classes of individuals, but these individuals are only found in the 
middle segment. However, given predicted human growth in this portion 
of the basin, this population will likely see increased threats. This 
population is considered to have low resiliency due to the very low 
species abundance, limited evidence of recruitment, and degraded 
habitat, which limit the species' ability to recover following 
stochastic events.
Representation
    The Mexican fawnsfoot occupies one known population. We do not 
expect any significant differences in localized adaptations within this 
population, as the entire population occurs in similar habitat and 
faces similar stressors. As such, we consider this species to have 
representation consisting of a single population, limiting the species' 
ability to adapt to changes over time. Any representation that 
historically occurred throughout the Rio Grande or in Mexico has been 
lost.
Redundancy
    Within the Rio Grande basin, the Mexican fawnsfoot has no redundant 
populations. Only one extant population is known to occur in the Rio 
Grande area between Amistad Reservoir and Laredo, Texas. No other known 
extant populations exist. Therefore, this species has little to no 
redundancy and is unlikely to recover from catastrophic events that 
could eliminate the one extant population.

Summary of Current Conditions

Salina Mucket
    The one remaining population of the Salina mucket has low 
resiliency due to degraded habitat quality, low abundance, and limited 
evidence of recruitment. These factors will limit the species' ability 
to recover following stochastic events. This species remains in only 
one contiguous population; therefore, we do not expect significant 
differences in localized adaptations that would provide adequate 
representation to adapt to changing conditions. Additionally, with only 
one remaining population, the Salina mucket has little to no redundancy 
to protect the species from extinction following catastrophic events. 
Therefore, we have determined that the Salina mucket has low 
resiliency, low representation, and no redundancy.
Mexican Fawnsfoot
    The one remaining population of the Mexican fawnsfoot has low 
resiliency due to very low species abundance, limited evidence of 
recruitment, and degraded habitat, which limit the species' ability to 
recover following stochastic events. This species remains in only one 
contiguous population; therefore, we do not expect significant 
differences in localized adaptations that would provide adequate 
representation to adapt to changing conditions. Additionally, with only 
one remaining population, the Mexican fawnsfoot has little to no 
redundancy to protect the species from extinction following 
catastrophic events. Therefore, we have determined that the Mexican 
fawnsfoot has low resiliency, low representation, and no redundancy.

[[Page 47966]]

    As part of the SSA, we also considered a range of plausible future 
scenarios to capture the range of uncertainties regarding future 
threats and the projected responses by the Salina mucket and Mexican 
fawnsfoot. Because we determined that the current conditions of the 
species are both consistent with an endangered species (see 
Determination of Status for the Salina Mucket and Mexican Fawnsfoot, 
below), we are not presenting the results of the future scenarios in 
this proposed rule. Please refer to the SSA report (Service 2023) for 
the full analysis of future scenarios.
    We note that, by using the SSA framework to guide our analysis of 
the scientific information documented in the SSA report, we have not 
only analyzed individual effects on the species, but we have also 
analyzed their potential cumulative effects. We incorporate the 
cumulative effects into our SSA analysis when we characterize the 
current and future condition of the species. To assess the current and 
future condition of the species, we undertake an iterative analysis 
that encompasses and incorporates the threats individually and then 
accumulates and evaluates the effects of all the factors that may be 
influencing the species, including threats and conservation efforts. 
Because the SSA framework considers not just the presence of the 
factors, but to what degree they collectively influence risk to the 
entire species, our assessment integrates the cumulative effects of the 
factors and replaces a standalone cumulative effects analysis.

Conservation Efforts and Regulatory Mechanisms

    Because we are considering the best available information and 
because the discussion above primarily addresses the viability of the 
Rio Grande mussels in relation to the threats and factors affecting 
their viability, here we will discuss regulatory mechanisms and 
conservation actions that potentially have influenced or will influence 
the current and future viability of the Rio Grande mussels.
    In Texas, the National Park Service manages lands and waterways 
under their purview in the Rio Grande Watershed for native plant and 
wildlife communities, including the Salina mucket. The large amount of 
land in conservation management in Big Bend National Park and the Rio 
Grande National Scenic River reduces risks to the Salina mucket from 
sediment inputs, habitat alterations, and contaminants.
    In other Texas reaches of the Rio Grande, we are not aware of any 
management actions for the Salina mucket or Mexican fawnsfoot.

Determination of Status for the Salina Mucket and Mexican Fawnsfoot

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

Status Throughout All of the Range

    After evaluating threats to the two Rio Grande mussel species and 
assessing the cumulative effect of the threats under the Act's section 
4(a)(1) factors, we find that both species of Rio Grande mussels have 
declined significantly in overall distribution and abundance throughout 
their ranges. Each species currently occurs in a single extant 
population, and the 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): increased fine 
sediments, water quality impairment, and the loss of flowing water, all 
of which are exacerbated by the effects of climate change (Factor E). 
Additionally, barriers to fish movement (Factor E) limit dispersal and 
prevent recolonization of Mexican fawnsfoot after stochastic events.
    Climate change has already begun to affect the Rio Grande basin of 
Texas and Mexico where theses mussels occur, resulting in higher air 
temperatures, increased evaporation, increased groundwater pumping, and 
changing precipitation patterns such that water levels have already 
reached historic lows rangewide (Dean and Schmidt 2011, p. 336; 
Sandoval-Solis et al. 2022, entire). These increasingly common and 
extended low-flow conditions put both species at elevated risk of 
habitat loss from increased fine sediments, poor water quality, loss of 
flowing water, and, specific to the Mexican fawnsfoot, increased risk 
of predation. Additionally, a low-water weir proposed for construction 
in the Lower Rio Grande in the upstream vicinity of Laredo, Texas, 
would eliminate the densest population segment of Mexican fawnsfoot, 
and about 7 percent of currently occupied habitat.
    These risks, individual or compounded, could result in the 
significant reduction or extirpation of the existing Rio Grande mussel 
populations, further reducing the overall resiliency and representation 
of the species or driving them to extinction. Historically, both 
species, with a larger range of interconnected populations, would have 
been sufficiently resilient to stochastic and catastrophic events such 
as sedimentation and drought because lost population segments could be 
recolonized over time by dispersal from nearby surviving populations. 
This connectivity made both Rio Grande mussels highly resilient 
overall. However, under current conditions, restoring that connectivity 
on a large scale is not feasible due to Amistad Reservoir, unsuitably 
low flows, and lack of redundant populations.

Salina Mucket

    Salina mucket has been extirpated from a large portion of the Rio 
Grande, as well as the Pecos River and the Rio Salado, and currently 
occupies only 16 percent of its historical range in the United States 
and Mexico. The last remaining population has low resiliency due to low 
species abundance, limited evidence of recruitment, and degraded 
habitat, which limit the species' ability to recover following 
stochastic events. Representation within the remaining Salina mucket 
population is extremely limited, impeding the species' ability to adapt 
to changes over time. With only one remaining population, a single 
catastrophic event has the potential to result in the extinction of the 
species. Additionally, this species is isolated from a large portion of 
its historical range due to the construction of reservoirs and 
unsuitable water quality, and, therefore, it is no longer able to 
recolonize other areas.
    Because the Salina mucket occurs in only one location, has low 
abundance and limited recruitment, and has no

[[Page 47967]]

ability to disperse into new areas, the species is extremely vulnerable 
to extinction. Our analysis of the species' current condition (which 
includes the threats of declining water quantity and impaired water 
quality inflows from the Rio Conchos and alterations to instream 
habitat caused by increased sedimentation), as well as the conservation 
efforts discussed above, shows that the Salina mucket is in danger of 
extinction throughout all of its range due to the severity and 
immediacy of threats currently impacting the species. We find that a 
threatened species status is not appropriate for the Salina mucket 
because the threats that the species is experiencing are already 
occurring across the species' extremely contracted range. Therefore, 
the species is currently in danger of extinction throughout its range.

Mexican Fawnsfoot

    Mexican fawnsfoot has been extirpated from a large portion of the 
Rio Grande near Amistad Reservoir and likely the Rio Salado, and 
currently occupies approximately 48 percent of its historical range in 
the United States and Mexico. The remaining population is considered to 
have low resiliency due to very low species abundance, limited evidence 
of recruitment, and degraded habitat, which limit the species' ability 
to recover following stochastic events. Representation within the 
remaining Mexican fawnsfoot population is extremely limited, impeding 
the species' ability to adapt to changes over time. With only one 
remaining population, a single catastrophic event has the potential to 
result in the extinction of the species. Additionally, this species is 
isolated from a large portion of its historical range due to the 
construction of reservoirs and unsuitable water quality, and, 
therefore, it is no longer able to recolonize other areas.
    Because the Mexican fawnsfoot occurs in only one location, has low 
abundance and limited recruitment, and has no ability to disperse into 
new areas, the species is extremely vulnerable to extinction. Our 
analysis of the species' current condition (which includes the threats 
of declining water quantity, impaired water quality, and the potential 
alteration of instream habitats by the construction of a weir in 
Laredo), as well as the conservation efforts discussed above, shows 
that the Mexican fawnsfoot is in danger of extinction throughout all of 
its range due to the severity and immediacy of threats currently 
impacting the species. We find that a threatened species status is not 
appropriate for the Mexican fawnsfoot because the threats that the 
species is experiencing are already occurring across the species' 
extremely contracted range. Therefore, the species is currently in 
danger of extinction throughout its range.

Status Throughout a Significant Portion of the Range

    Under the Act and our implementing regulations, a species may 
warrant listing if it is in danger of extinction or likely to become so 
in the foreseeable future throughout all or a significant portion of 
its range. We have determined that the Salina mucket and Mexican 
fawsnfoot are in danger of extinction throughout all of their ranges 
and accordingly did not undertake an analysis of any significant 
portion of the range for either species. Because the Salina mucket and 
Mexican fawnsfoot warrant listing as endangered throughout all of their 
ranges, our determination does not conflict with the decision in Center 
for Biological Diversity v. Everson, 435 F. Supp. 3d 69 (D.D.C. 2020) 
(Everson), which vacated the provision of the Final Policy on 
Interpretation of the Phrase ``Significant Portion of Its Range'' in 
the Endangered Species Act's Definitions of ``Endangered Species'' and 
``Threatened Species'' (79 FR 37578; July 1, 2014) providing that if 
the Services determine that a species is threatened throughout all of 
its range, the Services will not analyze whether the species is 
endangered in a significant portion of its range.

Salina Mucket and Mexican Fawnsfoot--Determination of Status

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

Available Conservation Measures

    Conservation measures provided to species listed as endangered or 
threatened species under the Act include recognition as a listed 
species, planning and implementation of recovery actions, requirements 
for Federal protection, and prohibitions against certain practices. 
Recognition through listing results in public awareness, and 
conservation by Federal, State, Tribal, and local agencies, private 
organizations, and individuals. The Act encourages cooperation with the 
States and other countries and calls for recovery actions to be carried 
out for listed species. The protection required by Federal agencies, 
including the Service, and the prohibitions against certain activities 
are discussed, in part, below.
    The primary purpose of the Act is the conservation of endangered 
and threatened species and the ecosystems upon which they depend. The 
ultimate goal of such conservation efforts is the recovery of these 
listed species, so that they no longer need the protective measures of 
the Act. Section 4(f) of the Act calls for the Service to develop and 
implement recovery plans for the conservation of endangered and 
threatened species. The goal of this process is to restore listed 
species to a point where they are secure, self-sustaining, and 
functioning components of their ecosystems.
    The recovery planning process begins with development of a recovery 
outline made available to the public soon after a final listing 
determination. The recovery outline guides the immediate implementation 
of urgent recovery actions while a recovery plan is being developed. 
Recovery teams (composed of species experts, Federal and State 
agencies, nongovernmental organizations, and stakeholders) may be 
established to develop and implement recovery plans. The recovery 
planning process involves the identification of actions that are 
necessary to halt and reverse the species' decline by addressing the 
threats to its survival and recovery. The recovery plan identifies 
recovery criteria for review of when a species may be ready for 
reclassification from endangered to threatened (``downlisting'') or 
removal from protected status (``delisting''), and methods for 
monitoring recovery progress. Recovery plans also establish a framework 
for agencies to coordinate their recovery efforts and provide estimates 
of the cost of implementing recovery tasks. Revisions of the plan may 
be done to address continuing or new threats to the species, as new 
substantive information becomes available. The recovery outline, draft 
recovery plan, final recovery plan, and any revisions will be available 
on our website as they are completed (https://www.fws.gov/program/endangered-species), or from our Austin Ecological Services Field 
Office (see FOR FURTHER INFORMATION CONTACT).
    Implementation of recovery actions generally requires the 
participation of a broad range of partners, including other Federal 
agencies, States, Tribes, nongovernmental organizations, businesses, 
and private landowners. Examples of recovery actions include habitat 
restoration (e.g., restoration of

[[Page 47968]]

native vegetation), research, captive propagation and reintroduction, 
and outreach and education. The recovery of many listed species cannot 
be accomplished solely on Federal lands because their range may occur 
primarily or solely on non-Federal lands. To achieve recovery of these 
species requires cooperative conservation efforts on private, State, 
and Tribal lands.
    If these species are listed, funding for recovery actions will be 
available from a variety of sources, including Federal budgets, State 
programs, and cost-share grants for non-Federal landowners, the 
academic community, and nongovernmental organizations. In addition, 
pursuant to section 6 of the Act, the State of Texas would be eligible 
for Federal funds to implement management actions that promote the 
protection or recovery of the Salina mucket and Mexican fawnsfoot. 
Information on our grant programs that are available to aid species 
recovery can be found at: https://www.fws.gov/service/financial-assistance.
    Although the Salina Mucket and Mexican fawnsfoot are only proposed 
for listing under the Act at this time, please let us know if you are 
interested in participating in recovery efforts for these species. 
Additionally, we invite you to submit any new information on these 
species whenever it becomes available and any information you may have 
for recovery planning purposes (see FOR FURTHER INFORMATION CONTACT, 
above).
    Section 7 of the Act is titled Interagency Cooperation and mandates 
all Federal action agencies to use their existing authorities to 
further the conservation purposes of the Act and to ensure that their 
actions are not likely to jeopardize the continued existence of listed 
species or adversely modify critical habitat. Regulations implementing 
section 7 are codified at 50 CFR part 402.
    Section 7(a)(2) states that each Federal action agency shall, in 
consultation with the Secretary, ensure that any action they authorize, 
fund, or carry out is not likely to jeopardize the continued existence 
of a listed species or result in the destruction or adverse 
modification of designated critical habitat. Each Federal agency shall 
review its action at the earliest possible time to determine whether it 
may affect listed species or critical habitat. If a determination is 
made that the action may affect listed species or critical habitat, 
formal consultation is required (50 CFR 402.14(a)), unless the Service 
concurs in writing that the action is not likely to adversely affect 
listed species or critical habitat. At the end of a formal 
consultation, the Service issues a biological opinion, containing its 
determination of whether the federal action is likely to result in 
jeopardy or adverse modification.
    In contrast, section 7(a)(4) of the Act requires Federal agencies 
to confer with the Service on any action which is likely to jeopardize 
the continued existence of any species proposed to be listed under the 
Act or result in the destruction or adverse modification of critical 
habitat proposed to be designated for such species. Although the 
conference procedures are required only when an action is likely to 
result in jeopardy or adverse modification, action agencies may 
voluntarily confer with the Service on actions that may affect species 
proposed for listing or critical habitat proposed to be designated. In 
the event that the subject species is listed or the relevant critical 
habitat is designated, a conference opinion may be adopted as a 
biological opinion and serve as compliance with section 7(a)(2).
    Examples of discretionary actions for the Rio Grande mussels that 
may be subject to conference and consultation procedures under section 
7 are land management or other landscape-altering activities on Federal 
lands administered by the National Park Service or the International 
Boundary and Water Commission as well as actions on State, Tribal, 
local, or private lands that require a Federal permit (such as a permit 
from the U.S. Army Corps of Engineers under section 404 of the Clean 
Water Act (33 U.S.C. 1251 et seq.) or a permit from the Service under 
section 10 of the Act) or that involve some other Federal action (such 
as funding from the Federal Highway Administration, Federal Aviation 
Administration, or the Federal Emergency Management Agency). Federal 
actions not affecting listed species or critical habitat--and actions 
on State, Tribal, local, or private lands that are not federally 
funded, authorized, or carried out by a Federal agency--do not require 
section 7 consultation. Federal agencies should coordinate with the 
local Service Field Office (see FOR FURTHER INFORMATION CONTACT, above) 
with any specific questions on section 7 consultation and conference 
requirements.
    The Act and its implementing regulations set forth a series of 
general prohibitions and exceptions that apply to endangered wildlife. 
The prohibitions of section 9(a)(1) of the Act, codified at 50 CFR 
17.21, make it illegal for any person subject to the jurisdiction of 
the United States to commit, to attempt to commit, to solicit another 
to commit or to cause to be committed any of the following: (1) import 
endangered wildlife to, or export from, the United States; (2) take 
(which includes harass, harm, pursue, hunt, shoot, wound, kill, trap, 
capture, or collect) endangered wildlife within the United States or on 
the high seas; (3) possess, sell, deliver, carry, transport, or ship, 
by any means whatsoever, any such wildlife that has been taken 
illegally; (4) deliver, receive, carry, transport, or ship in 
interstate or foreign commerce in the course of commercial activity; or 
(5) sell or offer for sale in interstate or foreign commerce. Certain 
exceptions to these prohibitions apply to employees or agents of the 
Service, the National Marine Fisheries Service, other Federal land 
management agencies, and State conservation agencies.
    We may issue permits to carry out otherwise prohibited activities 
involving endangered wildlife under certain circumstances. Regulations 
governing permits are codified at 50 CFR 17.22. With regard to 
endangered wildlife, a permit may be issued: for scientific purposes, 
for enhancing the propagation or survival of the species, or for take 
incidental to otherwise lawful activities. The statute also contains 
certain exemptions from the prohibitions, which are found in sections 9 
and 10 of the Act.
    It is the policy of the Services, as published in the Federal 
Register on July 1, 1994 (59 FR 34272), to identify, to the extent 
known at the time a species is listed, specific activities that will 
not be considered likely to result in violation of section 9 of the 
Act. To the extent possible, activities that will be considered likely 
to result in violation will also be identified in as specific a manner 
as possible. The intent of this policy is to increase public awareness 
of the effect of a proposed listing on proposed and ongoing activities 
within the range of the species proposed for listing.
    As discussed above, certain activities that are prohibited under 
section 9 may be permitted under section 10 of the Act. In addition, to 
the extent currently known, the following activities will not be 
considered likely to result in violation of section 9 of the Act:
    (1) Normal agricultural and silvicultural practices, including 
herbicide and pesticide use, that are carried out in accordance with 
any existing regulations, permit and label requirements, and best 
management practices; and
    (2) Normal residential landscaping activities.
    This list is intended to be illustrative and not exhaustive; 
additional activities that will not be considered likely to

[[Page 47969]]

result in violation of section 9 of the Act may be identified during 
coordination with the local field office, and in some instances (e.g., 
with new information), the Service may conclude that one or more 
activities identified here will be considered likely to result in 
violation of section 9.
    To the extent currently known, the following is a list of examples 
of activities that will be considered likely to result in violation of 
section 9 of the Act in addition to what is already clear from the 
descriptions of the prohibitions found at 50 CFR 17.21:
    (1) Unauthorized handling or collecting of the species;
    (2) Modification of the channel or water flow of any stream in 
which the Rio Grande mussels are known to occur;
    (3) Livestock grazing that results in direct or indirect 
destruction of stream habitat; and
    (4) Discharge of chemicals or fill material into any waters in 
which the Rio Grande mussels are known to occur.
    This list is intended to be illustrative and not exhaustive; 
additional activities that will be considered likely to result in 
violation of section 9 of the Act may be identified during coordination 
with the local field office, and in some instances (e.g., with new or 
site-specific information), the Service may conclude that one or more 
activities identified here will not be considered likely to result in 
violation of section 9. Questions regarding whether specific activities 
would constitute violation of section 9 of the Act should be directed 
to the Austin Ecological Services Field Office (see FOR FURTHER 
INFORMATION CONTACT, above).

II. Critical Habitat

Background

    Critical habitat is defined in section 3 of the Act as:
    (1) The specific areas within the geographical area occupied by the 
species, at the time it is listed in accordance with the Act, on which 
are found those physical or biological features
    (a) Essential to the conservation of the species, and
    (b) Which may require special management considerations or 
protection; and
    (2) Specific areas outside the geographical area occupied by the 
species at the time it is listed, upon a determination that such areas 
are essential for the conservation of the species.
    Our regulations at 50 CFR 424.02 define the geographical area 
occupied by the species as an area that may generally be delineated 
around species' occurrences, as determined by the Secretary (i.e., 
range). Such areas may include those areas used throughout all or part 
of the species' life cycle, even if not used on a regular basis (e.g., 
migratory corridors, seasonal habitats, and habitats used periodically, 
but not solely by vagrant individuals).
    Conservation, as defined under section 3 of the Act, means to use 
and the use of all methods and procedures that are necessary to bring 
an endangered or threatened species to the point at which the measures 
provided pursuant to the Act are no longer necessary. Such methods and 
procedures include, but are not limited to, all activities associated 
with scientific resources management such as research, census, law 
enforcement, habitat acquisition and maintenance, propagation, live 
trapping, and transplantation, and, in the extraordinary case where 
population pressures within a given ecosystem cannot be otherwise 
relieved, may include regulated taking.
    Critical habitat receives protection under section 7 of the Act 
through the requirement that Federal agencies ensure, in consultation 
with the Service, that any action they authorize, fund, or carry out is 
not likely to result in the destruction or adverse modification of 
critical habitat. The designation of critical habitat does not affect 
land ownership or establish a refuge, wilderness, reserve, preserve, or 
other conservation area. Such designation also does not allow the 
government or public to access private lands. Such designation does not 
require implementation of restoration, recovery, or enhancement 
measures by non-Federal landowners. Rather, designation requires that, 
where a landowner requests Federal agency funding or authorization for 
an action that may affect a listed species or critical habitat, the 
Federal agency consult with the Service under section 7(a)(2) of the 
Act. If the action may affect the listed species itself (such as for 
occupied critical habitat), the Federal agency would have already been 
required to consult with the Service even absent the designation 
because of the requirement to ensure that the action is not likely to 
jeopardize the continued existence of the species. Even if the Service 
were to conclude after consultation that the proposed activity is 
likely to result in destruction or adverse modification of the critical 
habitat, the Federal action agency and the landowner are not required 
to abandon the proposed activity, or to restore or recover the species; 
instead, they must implement ``reasonable and prudent alternatives'' to 
avoid destruction or adverse modification of critical habitat.
    Under the first prong of the Act's definition of critical habitat, 
areas within the geographical area occupied by the species at the time 
it was listed are included in a critical habitat designation if they 
contain physical or biological features (1) which are essential to the 
conservation of the species and (2) which may require special 
management considerations or protection. For these areas, critical 
habitat designations identify, to the extent known using the best 
scientific and commercial data available, those physical or biological 
features that are essential to the conservation of the species (such as 
space, food, cover, and protected habitat).
    Under the second prong of the Act's definition of critical habitat, 
we can designate critical habitat in areas outside the geographical 
area occupied by the species at the time it is listed, upon a 
determination that such areas are essential for the conservation of the 
species.
    Section 4 of the Act requires that we designate critical habitat on 
the basis of the best scientific data available. Further, our Policy on 
Information Standards Under the Endangered Species Act (published in 
the Federal Register on July 1, 1994 (59 FR 34271)), the Information 
Quality Act (section 515 of the Treasury and General Government 
Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R. 5658)), 
and our associated Information Quality Guidelines provide criteria, 
establish procedures, and provide guidance to ensure that our decisions 
are based on the best scientific data available. They require our 
biologists, to the extent consistent with the Act and with the use of 
the best scientific data available, to use primary and original sources 
of information as the basis for recommendations to designate critical 
habitat.
    When we are determining which areas should be designated as 
critical habitat, our primary source of information is generally the 
information from the SSA report and information developed during the 
listing process for the species. Additional information sources may 
include any generalized conservation strategy, criteria, or outline 
that may have been developed for the species; the recovery plan for the 
species; articles in peer-reviewed journals; conservation plans 
developed by States and counties; scientific status surveys and 
studies; biological assessments; other unpublished

[[Page 47970]]

materials; or experts' opinions or personal knowledge.
    Habitat is dynamic, and species may move from one area to another 
over time. We recognize that critical habitat designated at a 
particular point in time may not include all of the habitat areas that 
we may later determine are necessary for the recovery of the species. 
For these reasons, a critical habitat designation does not signal that 
habitat outside the designated area is unimportant or may not be needed 
for recovery of the species. Areas that are important to the 
conservation of the species, both inside and outside the critical 
habitat designation, will continue to be subject to: (1) Conservation 
actions implemented under section 7(a)(1) of the Act; (2) regulatory 
protections afforded by the requirement in section 7(a)(2) of the Act 
for Federal agencies to ensure their actions are not likely to 
jeopardize the continued existence of any endangered or threatened 
species; and (3) the prohibitions found in section 9 of the Act. 
Federally funded or permitted projects affecting listed species outside 
their designated critical habitat areas may still result in jeopardy 
findings in some cases. These protections and conservation tools will 
continue to contribute to recovery of the species. Similarly, critical 
habitat designations made on the basis of the best available 
information at the time of designation will not control the direction 
and substance of future recovery plans, habitat conservation plans 
(HCPs), or other species conservation planning efforts if new 
information available at the time of those planning efforts calls for a 
different outcome.

Physical or Biological Features Essential to the Conservation of the 
Species

    In accordance with section 3(5)(A)(i) of the Act and regulations at 
50 CFR 424.12(b), in determining which areas we will designate as 
critical habitat from within the geographical area occupied by the 
species at the time of listing, we consider the physical or biological 
features that are essential to the conservation of the species and 
which may require special management considerations or protection. The 
regulations at 50 CFR 424.02 define ``physical or biological features 
essential to the conservation of the species'' as the features that 
occur in specific areas and that are essential to support the life-
history needs of the species, including, but not limited to, water 
characteristics, soil type, geological features, sites, prey, 
vegetation, symbiotic species, or other features. A feature may be a 
single habitat characteristic or a more complex combination of habitat 
characteristics. Features may include habitat characteristics that 
support ephemeral or dynamic habitat conditions. Features may also be 
expressed in terms relating to principles of conservation biology, such 
as patch size, distribution distances, and connectivity. For example, 
physical features essential to the conservation of the species might 
include gravel of a particular size required for spawning, alkaline 
soil for seed germination, protective cover for migration, or 
susceptibility to flooding or fire that maintains necessary early-
successional habitat characteristics. Biological features might include 
prey species, forage grasses, specific kinds or ages of trees for 
roosting or nesting, symbiotic fungi, or absence of a particular level 
of nonnative species consistent with conservation needs of the listed 
species. The features may also be combinations of habitat 
characteristics and may encompass the relationship between 
characteristics or the necessary amount of a characteristic essential 
to support the life history of the species.
    In considering whether features are essential to the conservation 
of the species, we may consider an appropriate quality, quantity, and 
spatial and temporal arrangement of habitat characteristics in the 
context of the life-history needs, condition, and status of the 
species. These characteristics include, but are not limited to, space 
for individual and population growth and for normal behavior; food, 
water, air, light, minerals, or other nutritional or physiological 
requirements; cover or shelter; sites for breeding, reproduction, or 
rearing (or development) of offspring; and habitats that are protected 
from disturbance.
    We derive the specific physical or biological features essential to 
the conservation of the Salina mucket and Mexican fawnsfoot from 
studies of the species' habitat, ecology, and life history as described 
below. Additional information can be found in the SSA report (Service 
2023, entire; available on https://www.regulations.gov under Docket No. 
FWS-R2-ES-2023-0026).
    The primary physical and biological features that influence the 
resiliency of the Salina mucket and Mexican fawnsfoot include water 
quantity, availability of instream habitats, availability of and access 
to host fish, and adequate water quality. These features are described 
in further detail below, as well as above under Summary of Biological 
Status and Threats. Full descriptions of these habitat features are 
available in the SSA report (Service 2023, entire; available on https://www.regulations.gov under Docket No. FWS-R2-ES-2023-0026).

Water Quantity

    All life stages of the Salina mucket and Mexican fawnsfoot need 
flowing water for survival. They are not found in lakes, reservoirs, or 
pools without flow, or in areas that are regularly dewatered (Randklev 
et al., 2020a, entire). River reaches with continuous flow support all 
life stages of the Salina mucket and Mexican fawnsfoot, while those 
with little or no flow do not. Flow rates needed by the species will 
vary depending on the location, the size of the river at that location, 
and substrate type, but they must be adequate to provide inflows of 
algae, bacteria, and detritus for food and removal of waste (Yeager et 
al. 1994, pp. 220-221; Nichols and Garling 2000, p. 881).

Instream Habitats

Salina Mucket
    Salina mucket have specific habitat type and substrate needs. For 
juveniles, these include flow refugia, such as nearshore habitats, 
crevices, undercut riverbanks, travertine shelves, and large boulders 
(Randklev et al. 2017, p. 157). Adult Salina mucket also require stable 
areas of small-grained sediment, such as clay, silt, or sand, which 
provides suitable substrate for anchoring (Randklev et al. 2017, p. 
157).
Mexican Fawnsfoot
    Mexican fawnsfoot have specific habitat type and substrate needs. 
For juveniles, these include flow refugia such as riffle and run 
habitats, adjacent depositional areas, and banks (Karatayev et al. 
2012, p. 211). Adult Mexican fawnsfoot also require stable areas of 
small-grained sediment, such as clay, silt, or sand, which provides 
suitable substrate for anchoring, as well as soft, unconsolidated 
sediments in protected nearshore areas adjacent to riffles and 
backwater habitats (Randklev et al. 2017, pp. 221, 223, 234).

Host Fish

    As discussed earlier in this document, freshwater mussel larvae are 
parasites that must attach to a host fish to develop into juvenile 
mussels (Haag 2012, pp. 148, 178). The Salina mucket and Mexican 
fawnsfoot are believed to use the freshwater drum as a host fish 
(Bosman et al. 2015, entire; Sietman et al. 2018, pp. 1-2). The 
presence of this fish species, either singly or in combination with 
other yet-to-be-identified host fish species, supports the life-history 
needs of the Salina mucket and Mexican fawnsfoot.

[[Page 47971]]

Water Quality

    Freshwater mussels, as a group, are sensitive to changes in water-
quality parameters such as dissolved oxygen, salinity, ammonia, and 
pollutants. Habitats with appropriate levels of these parameters are 
considered suitable, while those habitats with levels outside of the 
appropriate ranges are considered less suitable. We have used 
information for the Salina mucket and Mexican fawnsfoot, where 
available, and data from other species when species-specific 
information is not available. Juvenile Salina mucket and Mexican 
fawnsfoot are expected to require low salinity (approximately 1.0 parts 
per thousand (ppt)) and low ammonia (approximately 0.7 milligrams per 
liter (mg/L)). Juvenile Salina mucket and Mexican fawnsfoot, like other 
juvenile freshwater mussels, are expected to be particularly 
susceptible to low dissolved oxygen levels. Juvenile mussels will 
reduce feeding behavior when dissolved oxygen is between 2-4 mg/L, and 
mortality has been shown to occur at dissolved oxygen levels below 1.3 
mg/L for juveniles and below 3 mg/L for adults. Juvenile mussels are 
also highly susceptible to heavy metal pollution and require low levels 
of copper and other contaminants in the substrates they occupy (Yeager 
et al. 1994, pp. 220-221).
    Finally, water temperature plays a critical role in the life 
history of freshwater mussels. High water temperatures can cause 
changes in clearance rates, valve closure, reduced reproductive output, 
and death (Chen et al. 2001, p. 214; Spooner and Vaughn 2008, pp. 308, 
315). Laboratory studies investigating the effects of thermal stress on 
glochidia and adults of other Texas freshwater mussel species have 
indicated thermal stress may occur around 29 [deg]C (84.2 [deg]F) 
(Bonner et al. 2018, p. 56; Khan et al. 2019, entire). As thermal 
studies have not been completed for the Salina mucket or Mexican 
fawnsfoot, we have used these data to indicate likely thermal stress 
limits for the Salina mucket.

Summary of Essential Physical or Biological Features

Salina Mucket
    We have determined that the physical or biological features 
essential to the conservation of the Salina mucket consist of a 
riverine system with habitat to support all life stages of the species, 
which includes:
    (a) Flowing water at rates high enough to support clean-swept 
substrate but not so high as to dislodge individuals;
    (b) Crevices beneath boulders, beneath shelves, and within undercut 
banks with seams of fine sediment;
    (c) The presence of freshwater drum (Aplodinotus grunniens) or 
other identified host fish; and
    (d) Water quality parameters within the following ranges:
    1. Salinity below approximately 1.0 ppt;
    2. Ammonia below 0.7 mg/L;
    3. Low levels of contaminants; and
    4. Dissolved oxygen levels within substrate greater than 1.3 mg/L.
Mexican Fawnsfoot
    We have determined that the physical or biological features 
essential to the conservation of the Mexican fawnsfoot consist of a 
riverine system with habitat to support all life stages of the species, 
which includes:
    (a) Flowing water at rates high enough to support clean-swept 
substrate but not so high as to dislodge individuals;
    (b) Stable areas of small-grained sediment, such as clay, silt, or 
sand;
    (c) Flow refugia such as riffle and run habitats, adjacent 
depositional areas, and banks;
    (d) The presence of freshwater drum (Aplodinotus grunniens) or 
other identified host fish; and
    (e) Water quality parameters within the following ranges:
    1. Salinity below approximately 1.0 ppt;
    2. Ammonia below 0.7 mg/L;
    3. Low levels of contaminants; and
    4. Dissolved oxygen levels within substrate greater than 1.3 mg/L.

Special Management Considerations or Protection

    When designating critical habitat, we assess whether the specific 
areas within the geographical area occupied by the species at the time 
of listing contain features which are essential to the conservation of 
the species and which may require special management considerations or 
protection. The features essential to the conservation of these species 
may require special management considerations or protection to reduce 
the following threats: Increased fine sediment, water quality 
impairment, loss of flowing water, and barriers to fish movement. 
Management activities that could ameliorate these threats and protect 
the integrity of the stream ecosystem include restoring or maintaining 
the natural hydrology of the stream, restoring or maintaining bank and 
riffle habitats, and appropriately maintaining bridges and other stream 
crossings to limit sediment input.

Criteria Used To Identify Critical Habitat

    As required by section 4(b)(2) of the Act, we use the best 
scientific data available to designate critical habitat. In accordance 
with the Act and our implementing regulations at 50 CFR 424.12(b), we 
review available information pertaining to the habitat requirements of 
the species and identify specific areas within the geographical area 
occupied by the species at the time of listing and any specific areas 
outside the geographical area occupied by the species to be considered 
for designation as critical habitat. For both the Salina mucket and 
Mexican fawnsfoot, we are proposing to designate critical habitat in 
areas within the geographical area occupied by the species at the time 
of listing. For the Salina mucket, we also are proposing to designate 
specific areas outside the geographical area occupied by the species 
because we have determined that a designation limited to occupied areas 
would be inadequate to ensure the conservation of the species given 
that it has only one extant population. We were able to identify an 
unoccupied area that qualifies as habitat because it contains the 
essential physical or biological features for the species, and we are 
reasonably certain that this area will contribute to the conservation 
of the Salina mucket because it contains suitable habitat, the riparian 
area is under Federal ownership and is managed by the National Park 
Service (NPS), and the subunit will provide a population expansion 
opportunity which will reduce the impact of site-level stochastic 
events on the sole remaining population. Although the current 
distributions of both Rio Grande mussels are much reduced from their 
historical distributions, we were unable to identify any unoccupied 
areas that are essential for the conservation of the Mexican fawnsfoot 
(i.e., unoccupied areas that contain at least one essential physical or 
biological feature for the Mexican fawnsfoot and have a reasonable 
certainty of contributing to the conservation of the species), and we 
are, therefore, not proposing to designate any unoccupied areas as 
critical habitat for this species. We anticipate that recovery will 
require continued protection of the existing populations and habitat, 
as well as ensuring that additional habitats are available, wherever 
possible, for the species to expand their populations.
    To determine and select appropriate areas that contain the physical 
or biological features essential to the conservation of the Salina 
mucket and

[[Page 47972]]

Mexican fawnsfoot, we developed a conservation strategy for these 
species. The goal of our conservation strategy is to recover the 
species to the point where the protections of the Act are no longer 
necessary. The role of critical habitat in achieving this conservation 
goal is to identify the specific areas within the species' range that 
provide essential physical or biological features, without which 
rangewide resiliency, redundancy, and representation could not be 
achieved. The current distributions of the Salina mucket and Mexican 
fawnsfoot are both reduced from their historical distributions to only 
one population each. We anticipate that recovery of these species will 
require not only continued protection of the last remaining extant 
populations and their habitats, but also reintroduction of populations 
in additional areas of the species' historical range. Reintroductions 
would ensure there are adequate numbers of mussels in stable 
populations and that these populations occur over a wide geographical 
area. This strategy will help to ensure that catastrophic events, such 
as drought, floods, or chemical spills, which can lead to the 
stranding, desiccation, or death of entire aggregations of mussels, 
cannot simultaneously affect all known populations.
    Guided by our conservation strategy goals, we determined which 
occupied and unoccupied areas to include as critical habitat for the 
Salina mucket and Mexican fawnsfoot by the criteria described below.

Areas Occupied at the Time of Listing

    To determine the general extent, location, and boundaries of 
critical habitat, we used Environmental Systems Research Institute, 
Inc. (Esri) ArcGIS mapping software for mapping and calculating areas 
along with spatial data layers, including historical and current 
records of Salina mucket's and Mexican fawnsfoot's occurrences, 
distribution, and habitat requirements found in publications, agency 
reports, and personal communications. We then identified stream 
segments occupied by the species through confirmed occupations from 
2000 to present. We determined that areas occupied within this time 
frame are likely to still support the species given survey recency and 
frequency in these areas. Given these species are both restricted to 
only one population each, we determined that all areas deemed to be 
occupied at the time of listing should be proposed for critical habitat 
designation.
    We delineated occupied critical habitat unit boundaries using the 
following criterion: First, we evaluated habitat suitability of stream 
segments within the geographical area occupied at the time of listing 
and delineated those segments that contain some or all of the physical 
and biological features to support life-history functions essential for 
conservation of these species. We then evaluated those occupied stream 
segments identified and refined the starting and ending points by 
evaluating the presence or absence of appropriate physical and 
biological features. We selected upstream and downstream cutoff points 
to omit areas that are highly degraded and are not likely to contain 
the physical or biological features to support the species. For 
example, permanently dewatered areas or areas in which there was a 
change to unsuitable parameters (e.g., water quality, water quantity, 
inadequate substrate) were used to mark the start or endpoint of a 
stream segment proposed for designation. Occupied critical habitat 
stream segments were then mapped using ArcMap version 10 (Environmental 
Systems Research Institute, Inc.), a Geographic Information Systems 
(GIS) program.
    We consider the following stream reach to be occupied by the Salina 
mucket at the time of proposed listing: Lower Canyons and Martin Canyon 
(see Proposed Critical Habitat Designation, below).
    We consider the following stream reach to be occupied by the 
Mexican fawnsfoot at the time of proposed listing: Laredo Reach (see 
Proposed Critical Habitat Designation, below).

Areas Unoccupied at the Time of Listing

Salina Mucket
    We have determined that a designation limited to the occupied areas 
would be inadequate to ensure the conservation of the Salina mucket. 
Therefore, we have also identified, and propose for designation as 
critical habitat, unoccupied areas that are essential for the 
conservation of the species. The Salina mucket is restricted to only 
one remaining population that has low resilience to stochastic events. 
This population has low abundance and reproduction, and it is affected 
by impairments to water quality and quantity. We consider this species 
functionally extirpated from the Rio Grande below Amistad Reservoir and 
from the Rio Salado in Mexico. Since there is only one remaining 
population of Salina mucket, the species has low representation and 
limited redundancy. Expanding the last remaining population farther 
upstream within the historical range of the species will increase 
viability of the Salina mucket and reduce the likelihood that a 
catastrophic event would result in the extinction of the species.
    The Rio Grande between the Talley Campground in Big Bend National 
Park and La Linda, Mexico, contains stream segments that maintain 
sufficient habitat to support adult and juvenile Salina mucket, as well 
as their host fish. Specifically, this reach of the Rio Grande contains 
habitat patches that contain appropriate water quantity and substrates 
to be occupied by Salina mucket, and a confirmed host fish, freshwater 
drum, has been collected in this stream reach. However, this reach of 
the Rio Grande is not currently known to be occupied by the Salina 
mucket. The Boquillas Canyon subunit lacks the recent, thorough survey 
efforts from 2000 through present that have been completed elsewhere 
within the historical range of the Salina mucket, and there is 
inadequate information in hand to deem the stream segment as currently 
occupied by the Salina mucket. This does not preclude the possibility 
that the species may occupy this segment, but we do not currently have 
adequate survey data available to make that determination at this time. 
Regardless of the current occupation status of the unit, we believe 
this subunit has retained the necessary physical or biological features 
that will allow for the occupation and maintenance of a Salina mucket 
population This unit is essential for the conservation of the species 
as it provides the only habitats into which the species can naturally 
expand its only remaining population, as habitats downstream of the 
occupied critical habitat unit cannot be restored to maintain the 
physical and biological features necessary to support the species. The 
proposed unoccupied critical habitat designation includes stream 
reaches known to have been occupied by the species historically, but 
they are currently not known to be occupied by the species.
Mexican Fawnsfoot
    We are not proposing to designate any areas outside the 
geographical area currently occupied by Mexican fawnsfoot because we 
could not identify any unoccupied areas that are essential for the 
conservation of the species. Although the Mexican fawnsfoot requires 
additional habitat for its recovery, we do not currently have 
information identifying additional unoccupied areas that could contain 
suitable habitat for adult and juvenile Mexican fawnsfoot and its host 
fish. Much of the historical range of the

[[Page 47973]]

Mexican fawnsfoot has been impacted by alterations to instream flows 
due to construction and operation of large impoundments, which have led 
to declines in habitat quality and the almost entire loss of freshwater 
mussel presence. Therefore, we do not have information at this time to 
allow us to determine which unoccupied areas may be essential for the 
conservation of the Mexican fawnsfoot.

Proposed Critical Habitat Designation

    We propose to designate as critical habitat stream reaches that we 
have determined are occupied at the time of listing (i.e., currently 
occupied) and that contain one or more of the physical or biological 
features that are essential to support life-history processes of the 
species. We have also identified, and propose for designation as 
critical habitat, unoccupied areas that are essential for the 
conservation of the Salina mucket.
    The proposed critical habitat designation is defined by the map or 
maps, as modified by any accompanying regulatory text, presented at the 
end of this document under Proposed Regulation Promulgation. We include 
more detailed information on the boundaries of the critical habitat 
designation in the preamble of this document. We will make the 
coordinates or plot points or both on which each map is based available 
to the public on https://www.regulations.gov at Docket No. FWS-R2-ES-
2023-0026.
    When determining proposed critical habitat boundaries, we made 
every effort to avoid including developed areas such as lands covered 
by buildings, pavement, and other structures because such lands lack 
physical or biological features necessary for the species. The scale of 
the maps we prepared under the parameters for publication within the 
Code of Federal Regulations may not reflect the exclusion of such 
developed lands. Any such lands inadvertently left inside critical 
habitat boundaries shown on the maps of this proposed rule have been 
excluded by text in the proposed rule and are not proposed for 
designation as critical habitat. Therefore, if the critical habitat is 
finalized as proposed, a Federal action involving these lands would not 
trigger section 7 consultation with respect to critical habitat and the 
requirement of no adverse modification unless the specific action would 
affect the physical or biological features in the adjacent critical 
habitat.
BILLING CODE 4333-15-P

[[Page 47974]]

[GRAPHIC] [TIFF OMITTED] TP25JY23.000

BILLING CODE 4333-15-C
    We present an index map of the proposed critical habitat for both 
mussel species:

Salina Mucket

    We are proposing a total of 199.6 river miles (rmi) (321.0 river 
kilometers (rkm)) in one unit, consisting of two subunits, as critical 
habitat for the Salina mucket. The critical habitat unit we describe 
below constitutes our current best assessment of areas that meet the 
definition of critical habitat for the Salina mucket. The area we 
propose as critical habitat for the Salina mucket is the Rio Grande 
unit (SM-1), along the Rio Grande from approximately 50 m downstream of 
the Talley Trail termination in Big Bend National Park to its 
confluence with Langtry Creek just upstream of Langtry, Texas. Table 1 
presents information on the proposed critical habitat unit, its 
subunits, and their approximate river miles.

[[Page 47975]]



                          Table 1--Proposed Critical Habitat Unit for the Salina Mucket
                    [Area estimates reflect all land within critical habitat unit boundaries]
----------------------------------------------------------------------------------------------------------------
                                                     Adjacent riparian     Size of unit in
     Critical habitat unit         Subunit name      land ownership by       river miles          Occupied?
                                                            type             (kilometers)
----------------------------------------------------------------------------------------------------------------
SM-1, Rio Grande..............  SM-1a, Lower       Federal (60.5 rmi;         136.8 (220.1)  Yes.
                                 Canyons and        97.3 rkm).
                                 Martin Canyon.    State (18.3 rmi; 29.5
                                                    rkm).
                                                   Private/Other (58.0
                                                    rmi: 93.3 rkm).
                                SM-1b, Boquillas   Federal (57.2 rmi;          62.8 (101.0)  No.
                                 Canyon.            92.0 rkm).
                                                   State (5.6 rmi; 9.0
                                                    rkm).
                                                                         ---------------------------------------
    Total.....................  .................  Federal (117.7 rmi;        199.6 (321.0)  ...................
                                                    189.3 rkm).
                                                   State (23.9 rmi; 38.4
                                                    rkm).
                                                   Private/Other (58.0
                                                    rmi; 93.3 rkm).
----------------------------------------------------------------------------------------------------------------
Note: River miles may not sum due to rounding.

    We present a brief description of the unit, and reasons why it 
meets the definition of critical habitat for Salina mucket, below.
Unit SM-1: Rio Grande
    Subunit SM-1a: Lower Canyons and Martin Canyon--This subunit 
consists of 136.8 rmi (220.1 rkm) of occupied habitat on the U.S. side 
of the Rio Grande in Terrell, Brewster, and Val Verde Counties, Texas. 
Most of this reach is part of the Rio Grande Wild and Scenic River, 
owned by the United States and managed by the National Park Service. A 
small portion of the subunit is owned by the State of Texas. It was 
designated a National Wild and Scenic River in 1978 (Garrett and 
Edwards 2004, p. 396), which affords some protection from Federal 
development projects but does not limit State, local, or private 
development (National Wild and Scenic Rivers System 2021, p. 1). 
Riverine flow in this segment is influenced by spring discharges from 
the Edwards-Trinity Plateau Aquifer, as well as outflows from the Rio 
Conchos and intermittent flows from San Francisco and Sanderson Creeks 
(Randklev et al. 2018, p. 734). Multiple springs throughout this 
segment contribute to base flow and incrementally increase water 
quality downstream (Bennett et al. 2009, entire; Urbanczyk and Bennett 
2017, p. 9). Increases in agricultural development in Rio Conchos or 
increased groundwater demands in the Edwards-Trinity Plateau Aquifer 
could decrease baseflows in this subunit and lead to loss of adequate 
flow and degraded water quality. Each of the identified physical or 
biological features essential to the conservation of the Salina mucket, 
including adequate stream flows, presence of appropriate instream 
habitats, adequate water quality, and access to host fish, are present 
in this subunit. Special management considerations may be required to 
maintain instream flows and adequate water quality in the river and to 
maintain bank habitats that can be occupied by the species.
    Subunit SM-1b: Boquillas Canyon--The Boquillas Canyon subunit 
consists of 62.8 rmi (101.0 rkm) of unoccupied habitat on the U.S. side 
of the Rio Grande in Brewster County, Texas. Most of this reach is part 
of Big Bend National Park and the Rio Grande Wild and Scenic River, 
both owned by the United States and managed by the National Park 
Service. Big Bend National Park was established in 1944, and the 
National Wild and Scenic River was designated in 1978 (Garrett and 
Edwards 2004, p. 396), which affords some protection from Federal 
development projects but does not limit State, local, or private 
development (National Wild and Scenic Rivers System 2021, p. 1).
    This unit is habitat for the Salina mucket because it contains 
appropriate water quantity and substrates for the species, and we are 
reasonably certain that this subunit will contribute to the 
conservation of the Salina mucket because the unit contains appropriate 
habitat, the riparian area is under Federal ownership and is managed by 
the NPS, and the subunit will provide a population expansion 
opportunity which will reduce the impact of site-level stochastic 
events on the sole remaining population.
    As with the Lower Canyons and Martin Canyon subunit, riverine flow 
in this segment is heavily influenced by outflows from the Rio Conchos 
and spring discharges from the Edwards-Trinity Plateau Aquifer 
(Randklev et al. 2018, p. 734). Multiple springs throughout this 
segment contribute to base flow and incrementally increase water 
quality downstream (Bennett et al. 2009, entire; Urbanczyk and Bennett 
2017, p. 9). Persistent inflows from the Rio Conchos are likely 
critical to maintaining appropriate salinity levels for the Salina 
mucket (Urbanczyk and Bennett 2017, p. 16). Increases in agricultural 
development in the Rio Conchos or increased groundwater demands in the 
Edwards-Trinity Plateau Aquifer could decrease baseflows in this 
subunit and lead to loss of adequate flow and degraded water quality. 
Each of the identified physical or biological features essential to the 
conservation of the Salina mucket, including adequate stream flows, 
adequate water quality, presence of appropriate instream habitats, and 
access to host fish, are present in this subunit.

Mexican Fawnsfoot

    We are proposing a total of 185.6 rmi (298.7 rkm) in one unit as 
critical habitat for the Mexican fawnsfoot. The critical habitat unit 
we describe below constitutes our current best assessment of areas that 
meet the definition of critical habitat for the Mexican fawnsfoot. The 
area we propose as critical habitat for Mexican fawnsfoot is the Laredo 
Reach unit (MXFF-1) along the Rio Grande from approximately Eagle Pass, 
Texas, to its confluence with the El Salado approximately 4.5 miles 
downstream of San Ygnacio, Texas. Table 2 shows the proposed critical 
habitat unit and the approximate river miles of the unit.

[[Page 47976]]



                          Table 2--Proposed Critical Habitat Unit for Mexican Fawnsfoot
                    [Area estimates reflect all land within critical habitat unit boundaries]
----------------------------------------------------------------------------------------------------------------
                                                                     Size of unit in
        Critical habitat unit            Adjacent riparian land        river miles             Occupied?
                                            ownership by type          (kilometers)
----------------------------------------------------------------------------------------------------------------
MXFF-1, Laredo Reach................  State/Local (3.7 rmi; 6.0         185.6 (298.7)  Yes.
                                       rkm).
                                      Tribal (0.7 rmi; 1.1 rkm)...
                                      Private (181.2 rmi;
                                       291.6rkm).
                                                                   ---------------------------------------------
    Total...........................  State/Local (3.7 rmi; 6.0         185.6 (298.7)  .........................
                                       rkm).
                                      Tribal (0.7 rmi; 1.1 rkm)...
                                      Private (181.2 rmi; 291.6
                                       rkm).
----------------------------------------------------------------------------------------------------------------
Note: River miles may not sum due to rounding.

    We present a brief description of the unit, and reasons why it 
meets the definition of critical habitat for Mexican fawnsfoot, below.
Unit MXFF-1: Laredo Reach
    This unit consists of 185.6 rmi (298.7 rkm) of the U.S. side of the 
Rio Grande between Eagle Pass in Maverick County, Texas; through Webb 
County, Texas; and to San Ygnacio in Zapata County, Texas. This unit is 
in State, local, Tribal, and private ownership. This unit is occupied 
and contains the last known remaining population of the Mexican 
fawnsfoot. This unit is heavily influenced by development along the 
U.S.-Mexico border. Rapid human population growth as well as 
industrialization on the Mexican side of the river has stressed the 
existing wastewater treatment facilities, and Rio Grande water quality 
is impaired as a result (Texas Clean Rivers Program 2013, p. 7). Flows 
in this unit are regulated by released from Amistad Reservoir based on 
hydropower generation and water deliveries for downstream irrigation 
needs in Texas (Texas Water Development Board 2016, pp. 7-8). Each of 
the identified physical or biological features essential to the 
conservation of the Mexican fawnsfoot, including adequate stream flows, 
adequate water quality, presence of appropriate instream habitats, and 
access to host fish, are present in part or in whole in this unit. 
Special management considerations to improve water quality and maintain 
instream flows in the river may be required.

Effects of Critical Habitat Designation

Section 7 Consultation

    Section 7(a)(2) of the Act requires Federal agencies, including the 
Service, to ensure that any action they authorize, fund, or carry out 
is not likely to jeopardize the continued existence of any endangered 
species or threatened species or result in the destruction or adverse 
modification of designated critical habitat of such species. In 
addition, section 7(a)(4) of the Act requires Federal agencies to 
confer with the Service on any agency action which is likely to 
jeopardize the continued existence of any species proposed to be listed 
under the Act or result in the destruction or adverse modification of 
proposed critical habitat.
    We published a final rule revising the definition of destruction or 
adverse modification on August 27, 2019 (84 FR 44976). Destruction or 
adverse modification means a direct or indirect alteration that 
appreciably diminishes the value of critical habitat as a whole for the 
conservation of a listed species.
    Compliance with the requirements of section 7(a)(2) is documented 
through our issuance of:
    (1) A concurrence letter for Federal actions that may affect, but 
are not likely to adversely affect, listed species or critical habitat; 
or
    (2) A biological opinion for Federal actions that may affect, and 
are likely to adversely affect, listed species or critical habitat.
    When we issue a biological opinion concluding that a project is 
likely to jeopardize the continued existence of a listed species and/or 
destroy or adversely modify critical habitat, we provide reasonable and 
prudent alternatives to the project, if any are identifiable, that 
would avoid the likelihood of jeopardy and/or destruction or adverse 
modification of critical habitat. We define ``reasonable and prudent 
alternatives'' (at 50 CFR 402.02) as alternative actions identified 
during formal consultation that:
    (1) Can be implemented in a manner consistent with the intended 
purpose of the action,
    (2) Can be implemented consistent with the scope of the Federal 
agency's legal authority and jurisdiction,
    (3) Are economically and technologically feasible, and
    (4) Would, in the Service Director's opinion, avoid the likelihood 
of jeopardizing the continued existence of the listed species or avoid 
the likelihood of destroying or adversely modifying critical habitat.
    Reasonable and prudent alternatives can vary from slight project 
modifications to extensive redesign or relocation of the project. Costs 
associated with implementing a reasonable and prudent alternative are 
similarly variable.
    Regulations at 50 CFR 402.16 set forth requirements for Federal 
agencies to reinitiate consultation if any of the following four 
conditions occur: (1) the amount or extent of taking specified in the 
incidental take statement is exceeded; (2) new information reveals 
effects of the action that may affect listed species or critical 
habitat in a manner or to an extent not previously considered; (3) the 
identified action is subsequently modified in a manner that causes an 
effect to the listed species or critical habitat that was not 
considered in the biological opinion or written concurrence; or (4) a 
new species is listed or critical habitat designated that may be 
affected by the identified action. The reinitiation requirement applies 
only to actions that remain subject to some discretionary Federal 
involvement or control. As provided in 50 CFR 402.16, the requirement 
to reinitiate consultations for new species listings or critical 
habitat designation does not apply to certain agency actions (e.g., 
land management plans issued by the Bureau of Land Management in 
certain circumstances).

Application of the ``Destruction or Adverse Modification'' Standard

    The key factor related to the destruction or adverse modification 
determination is whether implementation of the proposed Federal action 
directly or indirectly alters the designated critical habitat in a way 
that appreciably diminishes the value of the critical habitat as a 
whole for the conservation of the listed species. As discussed above, 
the role of critical

[[Page 47977]]

habitat is to support the physical or biological features essential to 
the conservation of a listed species and provide for the conservation 
of the species.
    Section 4(b)(8) of the Act requires us to briefly evaluate and 
describe, in any proposed or final regulation that designates critical 
habitat, activities involving a Federal action that may violate section 
7(a)(2) of the Act by destroying or adversely modifying such habitat, 
or that may be affected by such designation.
    Activities that we may, during a consultation under section 7(a)(2) 
of the Act, consider likely to destroy or adversely modify critical 
habitat include, but are not limited to:
    (1) Actions that would alter the existing flow regime. Such 
activities could include, but are not limited to, impoundment, water 
diversion, and water withdrawal. These activities could eliminate or 
reduce the habitat necessary for the growth and reproduction of the Rio 
Grande mussels.
    (2) Actions that would significantly alter water chemistry or 
temperature. Such activities could include, but are not limited to, 
release of chemicals, biological pollutants, or heated effluents into 
the surface water or connected groundwater at a point source or by 
dispersed release (non-point source). These activities could alter 
water conditions to levels that are beyond the tolerances of the Rio 
Grande mussels or their host fish and result in direct or cumulative 
adverse effects to these individuals and their life cycles.
    (3) Actions that would significantly increase sediment deposition 
within the stream channel. Such activities could include, but are not 
limited to, excessive sedimentation from livestock grazing, road 
construction, channel alteration, and other watershed and floodplain 
disturbances. These activities could eliminate or reduce the habitat 
necessary for the growth and reproduction of the Rio Grande mussels and 
their host fish by increasing the sediment deposition to levels that 
would adversely affect their ability to complete their life cycles.
    (4) Actions that would significantly alter instream habitats that 
could be occupied by the species. Such activities could include bank 
grading or other mechanical alterations of bank habitats, streambed 
grading, and gravel mining of instream riffle habitats.

Exemptions

Application of Section 4(a)(3) of the Act

    Section 4(a)(3)(B)(i) of the Act (16 U.S.C. 1533(a)(3)(B)(i)) 
provides that the Secretary shall not designate as critical habitat any 
lands or other geographical areas owned or controlled by the Department 
of Defense (DoD), or designated for its use, that are subject to an 
integrated natural resources management plan (INRMP) prepared under 
section 101 of the Sikes Improvement Act of 1997 (16 U.S.C. 670a), if 
the Secretary determines in writing that such plan provides a benefit 
to the species for which critical habitat is proposed for designation. 
No DoD lands with a completed INRMP are within the proposed critical 
habitat designation.

Consideration of Impacts Under Section 4(b)(2) of the Act

    Section 4(b)(2) of the Act states that the Secretary shall 
designate and make revisions to critical habitat on the basis of the 
best available scientific data after taking into consideration the 
economic impact, national security impact, and any other relevant 
impact of specifying any particular area as critical habitat. The 
Secretary may exclude an area from designated critical habitat based on 
economic impacts, impacts on national security, or any other relevant 
impacts. Exclusion decisions are governed by the regulations at 50 CFR 
424.19 and the Policy Regarding Implementation of Section 4(b)(2) of 
the Endangered Species Act (hereafter, the ``2016 Policy''; 81 FR 7226, 
February 11, 2016), both of which were developed jointly with the 
National Marine Fisheries Service (NMFS). We also refer to a 2008 
Department of the Interior Solicitor's opinion entitled, ``The 
Secretary's Authority to Exclude Areas from a Critical Habitat 
Designation under Section 4(b)(2) of the Endangered Species Act'' (M-
37016).
    In considering whether to exclude a particular area from the 
designation, we identify the benefits of including the area in the 
designation, identify the benefits of excluding the area from the 
designation, and evaluate whether the benefits of exclusion outweigh 
the benefits of inclusion. If the analysis indicates that the benefits 
of exclusion outweigh the benefits of inclusion, the Secretary may 
exercise discretion to exclude the area only if such exclusion would 
not result in the extinction of the species. In making the 
determination to exclude a particular area, the statute on its face, as 
well as the legislative history, are clear that the Secretary has broad 
discretion regarding which factor(s) to use and how much weight to give 
to any factor. In our final rules, we explain any decision to exclude 
areas, as well as decisions not to exclude, to make clear the rational 
basis for our decision. We describe below the process that we use for 
taking into consideration each category of impacts and any initial 
analyses of the relevant impacts.

Consideration of Economic Impacts

    Section 4(b)(2) of the Act and its implementing regulations require 
that we consider the economic impact that may result from a designation 
of critical habitat. To assess the probable economic impacts of a 
designation, we must first evaluate specific land uses or activities 
and projects that may occur in the area of the critical habitat. We 
then must evaluate the impacts that a specific critical habitat 
designation may have on restricting or modifying specific land uses or 
activities for the benefit of the species and its habitat within the 
areas proposed. We then identify which conservation efforts may be the 
result of the species being listed under the Act versus those 
attributed solely to the designation of critical habitat for this 
particular species. The probable economic impact of a proposed critical 
habitat designation is analyzed by comparing scenarios both ``with 
critical habitat'' and ``without critical habitat.''
    The ``without critical habitat'' scenario represents the baseline 
for the analysis, which includes the existing regulatory and socio-
economic burden imposed on landowners, managers, or other resource 
users potentially affected by the designation of critical habitat 
(e.g., under the Federal listing as well as other Federal, State, and 
local regulations). Therefore, the baseline represents the costs of all 
efforts attributable to the listing of the species under the Act (i.e., 
conservation of the species and its habitat incurred regardless of 
whether critical habitat is designated). The ``with critical habitat'' 
scenario describes the incremental impacts associated specifically with 
the designation of critical habitat for the species. The incremental 
conservation efforts and associated impacts would not be expected 
without the designation of critical habitat for the species. In other 
words, the incremental costs are those attributable solely to the 
designation of critical habitat, above and beyond the baseline costs. 
These are the costs we use when evaluating the benefits of inclusion 
and exclusion of particular areas from the final designation of 
critical habitat should we choose to conduct a discretionary 4(b)(2) 
exclusion analysis.
    Executive Orders (E.O.s) 12866 and 13563 direct Federal agencies to 
assess the costs and benefits of available regulatory alternatives in 
quantitative (to the extent feasible) and qualitative terms. Consistent 
with the E.O.

[[Page 47978]]

regulatory analysis requirements, our effects analysis under the Act 
may take into consideration impacts to both directly and indirectly 
affected entities, where practicable and reasonable. If sufficient data 
are available, we assess to the extent practicable the probable impacts 
to both directly and indirectly affected entities. Section 3(f) of E.O. 
12866 identifies four criteria when a regulation is considered a 
``significant regulatory action'' and requires additional analysis, 
review, and approval if met. The criterion relevant here is whether the 
designation of critical habitat may have an economic effect of $200 
million or more in any given year (section 3(f)(1)). Therefore, our 
consideration of economic impacts uses a screening analysis to assess 
whether the critical habitat designations for the Salina mucket and 
Mexican fawnsfoot are likely to exceed the economically significant 
threshold.
    For these particular designations, we developed an incremental 
effects memorandum (IEM) considering the probable incremental economic 
impacts that may result from the proposed designations of critical 
habitat. The information contained in our IEM was then used to develop 
a screening analysis of the probable effects of the critical habitat 
designations for the Salina mucket and Mexican fawnsfoot (IEc 2022, 
entire). We began by conducting a screening analysis of the proposed 
designations of critical habitat in order to focus our analysis on the 
key factors that are likely to result in incremental economic impacts. 
The purpose of the screening analysis is to filter out particular 
geographical areas of critical habitat that are already subject to such 
protections and are, therefore, unlikely to incur incremental economic 
impacts. In particular, the screening analysis considers baseline costs 
(i.e., absent critical habitat designation) and includes any probable 
incremental economic impacts where land and water use may already be 
subject to conservation plans, land management plans, best management 
practices, or regulations that protect the habitat area as a result of 
the Federal listing status of the species. Ultimately, the screening 
analysis allows us to focus our analysis on evaluating the specific 
areas or sectors that may incur probable incremental economic impacts 
as a result of the designations. The presence of the listed species in 
occupied areas of critical habitat means that any destruction or 
adverse modification of those areas is also likely to jeopardize the 
continued existence of the species. Therefore, designating occupied 
areas as critical habitat typically causes little if any incremental 
impacts above and beyond the impacts of listing the species. As a 
result, we generally focus the screening analysis on areas of 
unoccupied critical habitat (unoccupied units or unoccupied areas 
within occupied units). Overall, the screening analysis assesses 
whether designation of critical habitat is likely to result in any 
additional management or conservation efforts that may incur 
incremental economic impacts. This screening analysis combined with the 
information contained in our IEM constitute what we consider to be our 
draft economic analysis (DEA) of the proposed critical habitat 
designations for the Salina mucket and Mexican fawnsfoot; our DEA is 
summarized in the narrative below.
    As part of our screening analysis, we considered the types of 
economic activities that are likely to occur within the areas likely 
affected by the critical habitat designations. In our evaluation of the 
probable incremental economic impacts that may result from the proposed 
critical habitat designations for the Salina mucket and Mexican 
fawnsfoot, first we identified, in the IEM dated March 22, 2022, 
probable incremental economic impacts associated with the following 
categories of activities: (1) Federal (National Park Service) lands 
management; (2) roadway and bridge construction; (3) reservoir 
management; (4) instream dams and diversions; (5) instream projects or 
management; (6) border activities; (7) powerline or pipeline 
construction or maintenance; and (8) border protection. We considered 
each industry or category individually. Additionally, we considered 
whether the activities have any Federal involvement. Critical habitat 
designation generally will not affect activities that do not have any 
Federal involvement; under the Act, designation of critical habitat 
only affects activities conducted, funded, permitted, or authorized by 
Federal agencies. If we list the species, in areas where the Salina 
mucket and Mexican fawnsfoot are present, Federal agencies would be 
required to consult with the Service under section 7 of the Act on 
activities they authorize, fund, or carry out that may affect the 
species. If when we list the species, we also finalize these proposed 
critical habitat designations, Federal agencies would be required to 
consider the effects of their actions on the designated habitat, and if 
the Federal action may affect critical habitat, our consultations would 
include an evaluation of measures to avoid the destruction or adverse 
modification of critical habitat.
    In our IEM, we attempted to clarify the distinction between the 
effects that would result from the species being listed and those 
attributable to the critical habitat designations (i.e., difference 
between the jeopardy and adverse modification standards) for the Salina 
mucket and Mexican fawnsfoot. Because the critical habitat designations 
for the Salina mucket and Mexican fawnsfoot are being proposed 
concurrently with their listing, it has been our experience that it is 
more difficult to discern which conservation efforts are attributable 
to the species being listed and those which will result solely from the 
designation of critical habitat. However, the following specific 
circumstances in this case help to inform our evaluation: (1) The 
essential physical or biological features identified for each species' 
critical habitat are the same features essential for the life 
requisites of the species, and (2) any actions that would likely 
adversely affect the essential physical or biological features of 
occupied critical habitat are also likely to adversely affect the 
species itself. The IEM outlines our rationale concerning this limited 
distinction between baseline conservation efforts and incremental 
impacts of the critical habitat designations for these species. This 
evaluation of the incremental effects has been used as the basis to 
evaluate the probable incremental economic impacts of these proposed 
designations of critical habitat.
Salina Mucket
    The proposed critical habitat designation for the Salina mucket 
totals approximately 199.6 rmi (321.0 rkm), of which approximately 69 
percent is occupied by the species. In these areas, any actions that 
may affect the species or its habitat would also affect designated 
critical habitat, and it is unlikely that any additional conservation 
efforts would be recommended to address the adverse modification 
standard over and above those recommended as necessary to avoid 
jeopardizing the continued existence of the Salina mucket. Therefore, 
only administrative costs are expected in approximately 69 percent of 
the proposed critical habitat designation. While this additional 
analysis will require time and resources by both the Federal action 
agency and the Service, it is believed that, in most circumstances, 
these costs would predominantly be administrative in nature and would 
not be significant.
    The remaining 62.8 rmi (101.0 rkm) (31 percent of the total 
proposed critical

[[Page 47979]]

habitat designation) are currently unoccupied by the species but are 
essential for the conservation of the species. In these unoccupied 
areas, any conservation efforts or associated probable impacts would be 
considered incremental effects attributed to the critical habitat 
designation. Within the 62.8 rmi (101.0 rkm) of unoccupied critical 
habitat, few actions are expected to occur that will result in section 
7 consultation or associated project modifications. Unoccupied critical 
habitat for the Salina mucket is entirely within Subunit SM-1b, 
Boquillas Canyon, which is almost exclusively managed NPS. Based upon 
communications with the NPS, we expect to consult only on future 
activities related to invasive riparian vegetation management, which 
are likely to be covered under a programmatic consultation. Therefore, 
we do not anticipate more than a just a few consultations in this 
subunit, with minor conservation efforts that would likely result in 
relatively low probable economic impacts.
    A small portion (9 percent) of Subunit SM-1b is owned by the State 
of Texas. Although the entities most likely to incur incremental costs 
are Federal action agencies, such as NPS, in some cases, third parties, 
most frequently State agencies or municipalities, may also incur costs. 
However, based on coordination efforts with State and local agencies, 
we do not anticipate any cost to private entities within these sectors.
    The probable incremental economic impacts of the Salina mucket's 
critical habitat designation are expected to be limited to additional 
administrative effort and the minor costs of conservation efforts 
resulting from a small number of future section 7 consultations. This 
limitation is due to two factors: (1) A large portion of proposed 
critical habitat stream reaches are considered to be occupied by the 
species (69 percent), and incremental economic impacts of critical 
habitat designation, other than administrative costs, are unlikely; and 
(2) in proposed areas that are not occupied by Salina mucket (31 
percent), few actions are anticipated that would result in section 7 
consultation or associated project modifications. At approximately 
$10,000 or less per consultation, the burden resulting from the 
designation of critical habitat for the Salina mucket, based on the 
anticipated annual number of consultations and associated consultation 
costs, is not expected to exceed $32,600 in most years. The designation 
is unlikely to trigger additional requirements under State or local 
regulations. Thus, the annual administrative burden is relatively low. 
Although the exact cost of project modifications resulting from 
projects in unoccupied habitat for the Salina mucket is uncertain, it 
is estimated to be less than $32,600 in a given year and is therefore 
unlikely to exceed $200 million in a single year.
Mexican Fawnsfoot
    The proposed critical habitat designation for the Mexican fawnsfoot 
totals approximately 185.6 rmi (298.7 rkm), of which all is currently 
occupied by the species. In these areas, any actions that may affect 
the species or its habitat would also affect designated critical 
habitat, and it is unlikely that any additional conservation efforts 
would be recommended to address the adverse modification standard over 
and above those recommended as necessary to avoid jeopardizing the 
continued existence of the Mexican fawnsfoot. Therefore, only 
administrative costs are expected within the proposed critical habitat 
designation. While this additional analysis will require time and 
resources by both the Federal action agency and the Service, it is 
believed that, in most circumstances, these costs would predominantly 
be administrative in nature and would not be significant.
    The probable incremental economic impacts of the Mexican 
fawnsfoot's critical habitat designation are expected to be limited to 
additional administrative effort resulting from a small number of 
future section 7 consultations. This is because all of the proposed 
critical habitat stream reaches are considered to be occupied by the 
species, and incremental economic impacts of critical habitat 
designation, other than administrative costs, are unlikely. At 
approximately $10,000 or less per consultation, the burden resulting 
from the designation of critical habitat for the Mexican fawnsfoot, 
based on the anticipated annual number of consultations and associated 
consultation costs, is not expected to exceed $11,000 in most years. 
The designation is unlikely to trigger additional requirements under 
State or local regulations. Thus, the annual administrative burden is 
relatively low.
    While current development or other projects are not planned in 
proposed critical habitat areas, future planning efforts could be 
affected by proposed critical habitat designation. Any future probable 
incremental economic impacts are not likely to exceed $200 million in 
any single year, and impacts that are concentrated in any geographical 
area or sector are not likely as a result of this critical habitat 
designation.
    We are soliciting data and comments from the public on the DEA 
discussed above. During the development of the final designations, we 
will consider the information presented in the DEA and any additional 
information on economic impacts we receive during the public comment 
period to determine whether any specific areas should be excluded from 
the final critical habitat designations under authority of section 
4(b)(2) of the Act, our implementing regulations at 50 CFR 424.19, and 
the 2016 Policy. We may exclude an area from critical habitat if we 
determine that the benefits of excluding the area outweigh the benefits 
of including the area, provided the exclusion will not result in the 
extinction of this species.

Consideration of National Security Impacts

    Section 4(a)(3)(B)(i) of the Act may not cover all DoD lands or 
areas that pose potential national-security concerns (e.g., a DoD 
installation that is in the process of revising its INRMP for a newly 
listed species or a species previously not covered). If a particular 
area is not covered under section 4(a)(3)(B)(i), then national-security 
or homeland-security concerns are not a factor in the process of 
determining what areas meet the definition of ``critical habitat.'' 
However, the Service must still consider impacts on national security, 
including homeland security, on those lands or areas not covered by 
section 4(a)(3)(B)(i) because section 4(b)(2) requires the Service to 
consider those impacts whenever it designates critical habitat. 
Accordingly, if DoD, Department of Homeland Security (DHS), or another 
Federal agency has requested exclusion based on an assertion of 
national-security or homeland-security concerns, or we have otherwise 
identified national-security or homeland-security impacts from 
designating particular areas as critical habitat, we generally have 
reason to consider excluding those areas.
    However, we cannot automatically exclude requested areas. When DoD, 
DHS, or another Federal agency requests exclusion from critical habitat 
on the basis of national-security or homeland-security impacts, we must 
conduct an exclusion analysis if the Federal requester provides 
information, including a reasonably specific justification of an 
incremental impact on national security that would result from the 
designation of that specific area as critical habitat. That 
justification could include demonstration of probable impacts, such as 
impacts to ongoing border-security patrols and surveillance activities, 
or a delay in

[[Page 47980]]

training or facility construction, as a result of compliance with 
section 7(a)(2) of the Act. If the agency requesting the exclusion does 
not provide us with a reasonably specific justification, we will 
contact the agency to recommend that it provide a specific 
justification or clarification of its concerns relative to the probable 
incremental impact that could result from the designation. If we 
conduct an exclusion analysis because the agency provides a reasonably 
specific justification or because we decide to exercise the discretion 
to conduct an exclusion analysis, we will defer to the expert judgment 
of DoD, DHS, or another Federal agency as to: (1) Whether activities on 
its lands or waters, or its activities on other lands or waters, have 
national-security or homeland-security implications; (2) the importance 
of those implications; and (3) the degree to which the cited 
implications would be adversely affected in the absence of an 
exclusion. In that circumstance, in conducting a discretionary section 
4(b)(2) exclusion analysis, we will give great weight to national-
security and homeland-security concerns in analyzing the benefits of 
exclusion.
    In preparing this proposal, we have determined that the lands 
within the proposed critical habitat designations for the Salina mucket 
and Mexican fawnsfoot are not owned or managed by the DoD or DHS, and, 
therefore, we anticipate no impact on national security or homeland 
security.

Consideration of Other Relevant Impacts

    Under section 4(b)(2) of the Act, we consider any other relevant 
impacts, in addition to economic impacts and impacts on national 
security discussed above. To identify other relevant impacts that may 
affect the exclusion analysis, we consider a number of factors, 
including whether there are permitted conservation plans covering the 
species in the area--such as HCPs, safe harbor agreements (SHAs), or 
candidate conservation agreements with assurances (CCAAs)--or whether 
there are non-permitted conservation agreements and partnerships that 
may be impaired by designation of, or exclusion from, critical habitat. 
In addition, we look at whether Tribal conservation plans or 
partnerships, Tribal resources, or government-to-government 
relationships of the United States with Tribal entities may be affected 
by the designations. We also consider any State, local, social, or 
other impacts that might occur because of the designations.
Tribal Lands
    Several Executive Orders, Secretary's Orders, and policies concern 
working with Tribes. These guidance documents generally confirm our 
trust responsibilities to Tribes, recognize that Tribes have sovereign 
authority to control Tribal lands, emphasize the importance of 
developing partnerships with Tribal governments, and direct the Service 
to consult with Tribes on a government-to-government basis.
    A joint Secretary's Order that applies to both the Service and the 
National Marine Fisheries Service (NMFS)--Secretary's Order 3206, 
American Indian Tribal Rights, Federal-Tribal Trust Responsibilities, 
and the Endangered Species Act (June 5, 1997) (S.O. 3206)--is the most 
comprehensive of the various guidance documents related to Tribal 
relationships and Act implementation, and it provides the most detail 
directly relevant to the designation of critical habitat. In addition 
to the general direction discussed above, the appendix to S.O. 3206 
explicitly recognizes the right of Tribes to participate fully in any 
listing process that may affect Tribal rights or Tribal trust 
resources; this includes the designation of critical habitat. Section 
3(B)(4) of the appendix requires the Service to consult with affected 
Tribes ``when considering the designation of critical habitat in an 
area that may impact Tribal trust resources, Tribally-owned fee lands, 
or the exercise of Tribal rights.'' That provision also instructs the 
Service to avoid including Tribal lands within a critical habitat 
designation unless the area is essential to conserve a listed species, 
and it requires the Service to ``evaluate and document the extent to 
which the conservation needs of the listed species can be achieved by 
limiting the designation to other lands.''
    Our implementing regulations at 50 CFR 424.19 and the 2016 Policy 
are consistent with S.O. 3206. When we undertake a discretionary 
exclusion analysis under section 4(b)(2) of the Act, in accordance with 
S.O. 3206, we consult with any Tribe whose Tribal trust resources, 
tribally owned fee lands, or Tribal rights may be affected by including 
any particular areas in a critical habitat designation. We evaluate the 
extent to which the conservation needs of the species can be achieved 
by limiting the designation to other areas and give great weight to 
Tribal concerns in analyzing the benefits of exclusion.
    However, S.O. 3206 does not override the Act's statutory 
requirement of designation of critical habitat. As stated above, we 
must consult with any Tribe when a designation of critical habitat may 
affect Tribal lands or resources. The Act requires us to identify areas 
that meet the definition of ``critical habitat'' (i.e., areas occupied 
at the time of listing that contain the essential physical or 
biological features that may require special management considerations 
or protection and unoccupied areas that are essential to the 
conservation of a species), without regard to land ownership. While 
S.O. 3206 provides important direction, it expressly states that it 
does not modify the Secretary's statutory authority under the Act or 
other statutes.
    The proposed critical habitat designation for the Mexican fawnsfoot 
includes a portion of the Kickapoo Indian Reservation of Texas. This 
Tribe does not have a management or conservation plan for the Mexican 
fawnsfoot; however, we will consider any requests for exclusion we 
receive during the public comment period for this proposed rule (see 
DATES, above).
Federal Lands
    Federal land managers have unique obligations under the Act. First, 
Congress declared its policy that all Federal departments and agencies 
shall seek to conserve endangered species and threatened species and 
shall utilize their authorities in furtherance of the purposes of the 
Act (section 2(c)(1)). Second, all Federal agencies have 
responsibilities under section 7 of the Act to carry out programs for 
the conservation of listed species and to ensure their actions are not 
likely to jeopardize the continued existence of listed species or 
result in the destruction or adverse modification of critical habitat. 
Therefore, in general, we focus our exclusions on non-Federal lands. 
Our regulations at 50 CFR 424.19 and the 2016 Policy provide for the 
consideration of the exclusion of Federal lands in particular 
instances.
    We have not identified any areas to consider for exclusion from 
critical habitat based on other relevant impacts because there are no 
identified relevant impacts to Tribes, States, or local governments, 
and there are no permitted conservation plans covering the species. 
However, during the development of final designations, we will consider 
all information currently available or received during the public 
comment period on this proposed rule (see DATES, above) that we 
determine indicates that there is a potential for the benefits of 
exclusion to outweigh the benefits of inclusion. If we evaluate 
information regarding a request for an exclusion and we do not exclude, 
we will fully describe our rationale for not excluding

[[Page 47981]]

in the final critical habitat determinations. We may also exercise the 
discretion to undertake exclusion analyses for other areas as well, and 
we will describe all of our exclusion analyses as part of our final 
critical habitat determinations.

Summary of Exclusions Considered Under Section 4(b)(2) of the Act

    At this time, we are not considering any exclusions from the 
proposed designations based on economic impacts, national security 
impacts, or other relevant impacts--such as partnerships, management, 
or protection afforded by cooperative management efforts--under section 
4(b)(2) of the Act. We are not aware of any conservation plans, such as 
management plans or other large-scale habitat conservation plans, that 
would benefit the Rio Grande mussels within the proposed designations.
    However, if through the public comment period we receive 
information that we determine indicates that there are economic, 
national security, or other relevant impacts from designating 
particular areas as critical habitat, then as part of developing the 
final designations of critical habitat, we will evaluate that 
information and may conduct a discretionary exclusion analysis to 
determine whether to exclude those areas under the authority of section 
4(b)(2) of the Act and our implementing regulations at 50 CFR 424.19. 
If we receive a request for exclusion of a particular area and after 
evaluation of supporting information we do not exclude, we will fully 
explain our decision in the final rule for this action. (Please see 
ADDRESSES, above, for instructions on how to submit comments.)

Required Determinations

Clarity of the Rule

    We are required by E.O.s 12866 and 12988 and by the Presidential 
Memorandum of June 1, 1998, to write all rules in plain language. This 
means that each rule we publish must:
    (1) Be logically organized;
    (2) Use the active voice to address readers directly;
    (3) Use clear language rather than jargon;
    (4) Be divided into short sections and sentences; and
    (5) Use lists and tables wherever possible.
    If you feel that we have not met these requirements, send us 
comments by one of the methods listed in ADDRESSES. To better help us 
revise the rule, your comments should be as specific as possible. For 
example, you should tell us the numbers of the sections or paragraphs 
that are unclearly written, which sections or sentences are too long, 
the sections where you feel lists or tables would be useful, etc.

Regulatory Planning and Review--Executive Orders 12866, 13563, and 
14094

    Executive Order 14094 reaffirms the principles of E.O. 12866 and 
E.O. 13563 and states that regulatory analysis should facilitate agency 
efforts to develop regulations that serve the public interest, advance 
statutory objectives, and are consistent with E.O. 12866, E.O. 13563, 
and the Presidential Memorandum of January 20, 2021 (Modernizing 
Regulatory Review). Regulatory analysis, as practicable and 
appropriate, shall recognize distributive impacts and equity, to the 
extent permitted by law. E.O. 13563 emphasizes further that regulations 
must be based on the best available science and that the rulemaking 
process must allow for public participation and an open exchange of 
ideas. We have developed this final rule in a manner consistent with 
these requirements.
    E.O. 12866, as reaffirmed by E.O. 13563 and E.O. 14094, provides 
that the Office of Information and Regulatory Affairs (OIRA) in the 
Office of Management and Budget (OMB) will review all significant 
rules. OIRA has determined that this rule is not significant.

Regulatory Flexibility Act (5 U.S.C. 601 et seq.)

    Under the Regulatory Flexibility Act (RFA; 5 U.S.C. 601 et seq.), 
as amended by the Small Business Regulatory Enforcement Fairness Act of 
1996 (SBREFA; 5 U.S.C. 801 et seq.), whenever an agency is required to 
publish a notice of rulemaking for any proposed or final rule, it must 
prepare and make available for public comment a regulatory flexibility 
analysis that describes the effects of the rule on small entities 
(i.e., small businesses, small organizations, and small government 
jurisdictions). However, no regulatory flexibility analysis is required 
if the head of the agency certifies the rule will not have a 
significant economic impact on a substantial number of small entities. 
The SBREFA amended the RFA to require Federal agencies to provide a 
certification statement of the factual basis for certifying that the 
rule will not have a significant economic impact on a substantial 
number of small entities.
    According to the Small Business Administration, small entities 
include small organizations such as independent nonprofit 
organizations; small governmental jurisdictions, including school 
boards and city and town governments that serve fewer than 50,000 
residents; and small businesses (13 CFR 121.201). Small businesses 
include manufacturing and mining concerns with fewer than 500 
employees, wholesale trade entities with fewer than 100 employees, 
retail and service businesses with less than $5 million in annual 
sales, general and heavy construction businesses with less than $27.5 
million in annual business, special trade contractors doing less than 
$11.5 million in annual business, and agricultural businesses with 
annual sales less than $750,000. To determine whether potential 
economic impacts to these small entities are significant, we considered 
the types of activities that might trigger regulatory impacts under 
this designation as well as types of project modifications that may 
result. In general, the term ``significant economic impact'' is meant 
to apply to a typical small business firm's business operations.
    Under the RFA, as amended, and as understood in light of recent 
court decisions, Federal agencies are required to evaluate the 
potential incremental impacts of rulemaking on those entities directly 
regulated by the rulemaking itself; in other words, the RFA does not 
require agencies to evaluate the potential impacts to indirectly 
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 out by the agency is not 
likely to destroy or adversely modify critical habitat. Therefore, 
under section 7, only Federal action agencies are directly subject to 
the specific regulatory requirement (avoiding destruction and adverse 
modification) imposed by critical habitat designation. Consequently, it 
is our position that only Federal action agencies would be directly 
regulated if we adopt the proposed critical habitat designations. The 
RFA does not require evaluation of the potential impacts to entities 
not directly regulated. Moreover, Federal agencies are not small 
entities. Therefore, because no small entities would be directly 
regulated by this rulemaking, the Service certifies that, if made final 
as proposed, the proposed critical habitat designations will not have a 
significant economic impact on a substantial number of small entities.
    In summary, we have considered whether the proposed designations

[[Page 47982]]

would result in a significant economic impact on a substantial number 
of small entities. For the above reasons and based on currently 
available information, we certify that, if made final, the proposed 
critical habitat designations will not have a significant economic 
impact on a substantial number of small business entities. Therefore, 
an initial regulatory flexibility analysis is not required.

Energy Supply, Distribution, or Use--Executive Order 13211

    Executive Order 13211 (Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use) requires 
agencies to prepare Statements of Energy Effects when undertaking 
certain actions. In our DEA, we did not find that these proposed 
critical habitat designations would significantly affect energy 
supplies, distribution, or use. We did not find that these proposed 
critical habitat designations will have an annual effect on the economy 
of $200 million or more or significantly affect energy supplies, 
distribution, or use due to the lack of any energy supply or 
distribution lines within the proposed critical habitat designations. 
Therefore, this action is not a significant energy action, and no 
statement of energy effects is required.

Unfunded Mandates Reform Act (2 U.S.C. 1501 et seq.)

    In accordance with the Unfunded Mandates Reform Act (2 U.S.C. 1501 
et seq.), we make the following finding:
    (1) This proposed rule would not produce a Federal mandate. In 
general, a Federal mandate is a provision in legislation, statute, or 
regulation that would impose an enforceable duty upon State, local, or 
Tribal governments, or the private sector, and includes both ``Federal 
intergovernmental mandates'' and ``Federal private sector mandates.'' 
These terms are defined in 2 U.S.C. 658(5)-(7). ``Federal 
intergovernmental mandate'' includes a regulation that ``would impose 
an enforceable duty upon State, local, or Tribal governments'' with two 
exceptions. It excludes ``a condition of Federal assistance.'' It also 
excludes ``a duty arising from participation in a voluntary Federal 
program,'' unless the regulation ``relates to a then-existing Federal 
program under which $500,000,000 or more is provided annually to State, 
local, and Tribal governments under entitlement authority,'' if the 
provision would ``increase the stringency of conditions of assistance'' 
or ``place caps upon, or otherwise decrease, the Federal Government's 
responsibility to provide funding,'' and the State, local, or Tribal 
governments ``lack authority'' to adjust accordingly. At the time of 
enactment, these entitlement programs were: Medicaid; Aid to Families 
with Dependent Children work programs; Child Nutrition; Food Stamps; 
Social Services Block Grants; Vocational Rehabilitation State Grants; 
Foster Care, Adoption Assistance, and Independent Living; Family 
Support Welfare Services; and Child Support Enforcement. ``Federal 
private sector mandate'' includes a regulation that ``would impose an 
enforceable duty upon the private sector, except (i) a condition of 
Federal assistance or (ii) a duty arising from participation in a 
voluntary Federal program.''
    The designation of critical habitat does not impose a legally 
binding duty on non-Federal Government entities or private parties. 
Under the Act, the only regulatory effect is that Federal agencies must 
ensure that their actions are not likely to destroy or adversely modify 
critical habitat under section 7. While non-Federal entities that 
receive Federal funding, assistance, or permits, or that otherwise 
require approval or authorization from a Federal agency for an action, 
may be indirectly impacted by the designation of critical habitat, the 
legally binding duty to avoid destruction or adverse modification of 
critical habitat rests squarely on the Federal agency. Furthermore, to 
the extent that non-Federal entities are indirectly impacted because 
they receive Federal assistance or participate in a voluntary Federal 
aid program, the Unfunded Mandates Reform Act would not apply, nor 
would critical habitat shift the costs of the large entitlement 
programs listed above onto State governments.
    (2) We do not believe that this rule would significantly or 
uniquely affect small governments because the units do not occur within 
the jurisdiction of small governments. Therefore, a Small Government 
Agency Plan is not required.
    We do not believe that this rule will significantly or uniquely 
affect small governments because small governments will be affected 
only to the extent that any programs having Federal funds, permits, or 
other authorized activities must ensure that their actions will not 
adversely affect critical habitat. This rule will not produce a Federal 
mandate of $200 million or greater in any year; that is, it is not a 
``significant regulatory action'' under the Unfunded Mandates Reform 
Act. The designation of critical habitat imposes no obligations on 
State or local governments. By definition, Federal agencies are not 
considered small entities, although the activities they fund or permit 
may be proposed or carried out by small entities. Consequently, we do 
not find that the proposed critical habitat designations will 
significantly or uniquely affect small government entities. Therefore, 
a Small Government Agency Plan is not required.

Takings--Executive Order 12630

    In accordance with E.O. 12630 (Government Actions and Interference 
with Constitutionally Protected Private Property Rights), we have 
analyzed the potential takings implications of designating critical 
habitat for the Salina mucket and Mexican fawnsfoot in a takings 
implications assessment. The Act does not authorize the Service to 
regulate private actions on private lands or confiscate private 
property as a result of critical habitat designation. Designation of 
critical habitat does not affect land ownership, or establish any 
closures of, or restrictions on use of or access to, the designated 
areas. Furthermore, the designation of critical habitat does not affect 
landowner actions that do not require Federal funding or permits, nor 
does it preclude development of habitat conservation programs or 
issuance of incidental take permits to permit actions that do require 
Federal funding or permits to go forward. However, Federal agencies are 
prohibited from carrying out, funding, or authorizing actions that 
would destroy or adversely modify critical habitat. A takings 
implications assessment has been completed for the proposed designation 
of critical habitat for the Salina mucket and Mexican fawnsfoot, and it 
concludes that, if adopted, these critical habitat designations do not 
pose significant takings implications for lands within or affected by 
the designations.

Federalism--Executive Order 13132

    In accordance with E.O. 13132 (Federalism), this proposed rule does 
not have significant Federalism effects. A federalism summary impact 
statement is not required. In keeping with Department of the Interior 
and Department of Commerce policy, we requested information from, and 
coordinated development of these proposed critical habitat designations 
with, appropriate State resource agencies. 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, the proposed rule does 
not have

[[Page 47983]]

substantial direct effects either on the States, or on the relationship 
between the Federal government and the States, or on the distribution 
of powers and responsibilities among the various levels of government. 
The proposed designations may have some benefit to these governments 
because the areas that contain the features essential to the 
conservation of the species are more clearly defined, and the physical 
or biological features of the habitat necessary for the conservation of 
the species are specifically identified. This information does not 
alter where and what federally sponsored activities may occur. However, 
it may assist State and local governments in long-range planning 
because they no longer have to wait for case-by-case section 7 
consultations to occur.
    Where State and local governments require approval or authorization 
from a Federal agency for actions that may affect critical habitat, 
consultation under section 7(a)(2) of the Act would be required. While 
non-Federal entities that receive Federal funding, assistance, or 
permits, or that otherwise require approval or authorization from a 
Federal agency for an action, may be indirectly impacted by the 
designation of critical habitat, the legally binding duty to avoid 
destruction or adverse modification of critical habitat rests squarely 
on the Federal agency.

Civil Justice Reform--Executive Order 12988

    In accordance with E.O. 12988 (Civil Justice Reform), the Office of 
the Solicitor has determined that the rule would not unduly burden the 
judicial system and that it meets the requirements of sections 3(a) and 
3(b)(2) of the Order. We have proposed designating critical habitat in 
accordance with the provisions of the Act. To assist the public in 
understanding the habitat needs of the species, this proposed rule 
identifies the physical or biological features essential to the 
conservation of the species. The proposed areas of critical habitat are 
presented on maps, and the proposed rule provides several options for 
the interested public to obtain more detailed location information, if 
desired.

Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.)

    This rule does not contain information collection requirements, and 
a submission to the Office of Management and Budget (OMB) under the 
Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.) is not 
required. We may not conduct or sponsor and you are not required to 
respond to a collection of information unless it displays a currently 
valid OMB control number.

National Environmental Policy Act (42 U.S.C. 4321 et seq.)

    Regulations adopted pursuant to section 4(a) of the Act are exempt 
from the National Environmental Policy Act (NEPA; 42 U.S.C. 4321 et 
seq.) and do not require an environmental analysis under NEPA. We 
published a notice outlining our reasons for this determination in the 
Federal Register on October 25, 1983 (48 FR 49244). This includes 
listing, delisting, and reclassification rules, as well as critical 
habitat designations. In a line of cases starting with Douglas County 
v. Babbitt, 48 F.3d 1495 (9th Cir. 1995), the courts have upheld this 
position.

Government-to-Government Relationship With Tribes

    In accordance with the President's memorandum of April 29, 1994 
(Government-to-Government Relations with Native American Tribal 
Governments; 59 FR 22951), E.O. 13175 (Consultation and Coordination 
with Indian Tribal Governments), and the Department of the Interior's 
manual at 512 DM 2, we readily acknowledge our responsibility to 
communicate meaningfully with federally recognized Tribes on a 
government-to-government basis. In accordance with Secretary's Order 
3206 of June 5, 1997 (American Indian Tribal Rights, Federal-Tribal 
Trust Responsibilities, and the Endangered Species Act), we readily 
acknowledge our responsibilities to work directly with Tribes in 
developing programs for healthy ecosystems, to acknowledge that Tribal 
lands are not subject to the same controls as Federal public lands, to 
remain sensitive to Indian culture, and to make information available 
to Tribes. There are Tribal lands in Texas included in this proposed 
designation of critical habitat for the Mexican fawnsfoot. The Kickapoo 
Indian Reservation of Texas owns 0.7 rmi (1.1 rkm) adjacent to the Rio 
Grande in Unit MXFF-1, Laredo Reach. A notification letter was sent to 
the Kickapoo Indian Reservation of Texas as part of the SSA process, 
but no response was received at that time. However, we will continue to 
work with Tribal entities during the development of a final rule to 
designate critical habitat for the Mexican fawnsfoot. We have 
determined that no Tribal lands fall within the boundaries of the 
proposed critical habitat for the Salina mucket, so no Tribal lands 
would be affected by the designation for that species.

References Cited

    A complete list of references cited in this rulemaking is available 
on the internet at https://www.regulations.gov and upon request from 
the Austin Ecological Services Field Office (see FOR FURTHER 
INFORMATION CONTACT).

Authors

    The primary authors of this proposed rule are the staff members of 
the Fish and Wildlife Service's Species Assessment Team and the Austin 
Ecological Services Field Office.

List of Subjects in 50 CFR Part 17

    Endangered and threatened species, Exports, Imports, Plants, 
Reporting and recordkeeping requirements, Transportation, Wildlife.

Signing Authority

    Martha Williams, Director of the U.S. Fish and Wildlife Service, 
approved this action on June 21, 2023, for publication. On July 14, 
2023, Martha Williams authorized the undersigned to sign the document 
electronically and submit it to the Office of the Federal Register for 
publication as an official document of the U.S. Fish and Wildlife 
Service.

Proposed Regulation Promulgation

    Accordingly, we propose to amend part 17, subchapter B of chapter 
I, title 50 of the Code of Federal Regulations, as set forth below:

PART 17--ENDANGERED AND THREATENED WILDLIFE AND PLANTS

0
1. The authority citation for part 17 continues to read as follows:

    Authority:  16 U.S.C. 1361-1407; 1531-1544; and 4201-4245, 
unless otherwise noted.
0
2. In Sec.  17.11, in paragraph (h), amend the List of Endangered and 
Threatened Wildlife by adding entries for ``Fawnsfoot, Mexican'' and 
``Mucket, Salina'' in alphabetical order under CLAMS to read as 
follows:


Sec.  17.11  Endangered and threatened wildlife.

* * * * *
    (h) * * *

[[Page 47984]]



----------------------------------------------------------------------------------------------------------------
                                                                                           Listing citations and
          Common name              Scientific name      Where listed          Status         applicable rules
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                                      Clams
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Fawnsfoot, Mexican.............  Truncilla cognata.  Wherever found....               E   (Federal Register
                                                                                           citation when
                                                                                           published as a final
                                                                                           rule); 50 CFR
                                                                                           17.95(f).\CH\
 
                                                  * * * * * * *
Mucket, Salina.................  Potamilus           Wherever found....               E   (Federal Register
                                  metnecktayi.                                             citation when
                                                                                           published as a final
                                                                                           rule); 50 CFR
                                                                                           17.95(f).\CH\
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------

0
3. In Sec.  17.95, amend paragraph (f) by:
0
a. Adding an entry for ``Mexican Fawnsfoot (Truncilla cognata)'' before 
the entry for ``Carolina Heelsplitter (Lasmigona decorata)''; and
0
b. Adding an entry for ``Salina Mucket (Potamilus metnecktayi)'' 
following the entry for ``Carolina Heelsplitter (Lasmigona decorata)''.
    The additions read as follows.


Sec.  17.95  Critical habitat--fish and wildlife.

* * * * *
    (f) Clams and Snails.
* * * * *
    Mexican Fawnsfoot (Truncilla cognata)
    (1) Critical habitat units are depicted for Maverick, Webb, and 
Zapata Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Mexican fawnsfoot consist of a 
riverine system with habitat to support all life stages of the species, 
which includes:
    (i) Flowing water at rates high enough to support clean-swept 
substrate but not so high as to dislodge individuals;
    (ii) Stable areas of small-grained sediment, such as clay, silt, or 
sand;
    (iii) Flow refugia such as riffle and run habitats, adjacent 
depositional areas, and banks;
    (iv) The presence of freshwater drum (Aplodinotus grunniens) or 
other identified host fish; and
    (v) Water quality parameters within the following ranges:
    (A) Salinity below approximately 1.0 parts per thousand (ppt);
    (B) Ammonia below 0.7 milligrams per liter (mg/L);
    (C) Low levels of contaminants; and
    (D) Dissolved oxygen levels within substrate greater than 1.3 mg/L.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
the effective date of the final rule.
    (4) Data layers defining map units were created were created using 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and 
critical habitat units were then mapped using Universal Transverse 
Mercator (UTM) Zone 15N coordinates. The maps in this entry, as 
modified by any accompanying regulatory text, establish the boundaries 
of the critical habitat designation. The coordinates or plot points or 
both on which each map is based are available to the public at the 
Service's internet site at https://www.regulations.gov at Docket No. 
FWS-R2-ES-2023-0026 and at the field office responsible for this 
designation. You may obtain field office location information by 
contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Unit MXFF-1: Laredo Reach; Maverick, Webb, and Zapata Counties, 
Texas.
    (i) Unit MXFF-1 consists of 185.6 river miles (rmi) (298.7 river 
kilometers (rkm)) in Maverick, Webb, and Zapata Counties and is 
composed of lands in Tribal (0.7 rmi (1.1 rkm)), State/local (3.7 rmi 
(6.0 rkm)), and private (181.2 rmi (291.6 rkm)) ownership.
    (ii) Map of Unit MXFF-1 follows:

Figure 1 to Mexican Fawnsfoot (Truncilla cognata) paragraph (5)(ii)
BILLING CODE 4333-15-P

[[Page 47985]]

[GRAPHIC] [TIFF OMITTED] TP25JY23.001

* * * * *
Salina Mucket (Potamilus metnecktayi)
    (1) Critical habitat units are depicted for Brewster, Terrell, and 
Val Verde Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Salina mucket consist of a riverine 
system with habitat to support all life stages of the species, which 
includes:
    (i) Flowing water at rates high enough to support clean-swept 
substrate but not so high as to dislodge individuals;
    (ii) Crevices beneath boulders, beneath shelves, and within 
undercut banks with seams of fine sediment;

[[Page 47986]]

    (iii) The presence of freshwater drum (Aplodinotus grunniens) or 
other identified host fish; and
    (iv) Water quality parameters within the following ranges:
    (A) Salinity below approximately 1.0 parts per thousand (ppt);
    (B) Ammonia below 0.7 milligrams per liter (mg/L);
    (C) Low levels of contaminants; and
    (D) Dissolved oxygen levels within substrate greater than 1.3 mg/L.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
the effective date of the final rule.
    (4) Data layers defining map units were created using U.S. 
Geological Survey digital ortho-photo quarter-quadrangles, and critical 
habitat units were then mapped using Universal Transverse Mercator 
(UTM) Zones 13 and 14N coordinates. The maps in this entry, as modified 
by any accompanying regulatory text, establish the boundaries of the 
critical habitat designation. The coordinates or plot points or both on 
which each map is based are available to the public at the Service's 
internet site at https://www.regulations.gov at Docket No. FWS-R2-ES-
2023-0026 and at the field office responsible for this designation. You 
may obtain field office location information by contacting one of the 
Service regional offices, the addresses of which are listed at 50 CFR 
2.2.
    (5) Unit SM-1: Rio Grande; Brewster, Terrell, and Val Verde 
Counties, Texas.
    (i) Unit SM-1 consists of 199.6 river miles (rmi) (321.0 river 
kilometers (rkm)) in Brewster, Terrell, and Val Verde Counties and is 
composed of lands in Federal (117.7 rmi (189.33 rkm)), State (23.9 rmi 
(38.4 rkm)), and private (58.0 rmi (93.3 rkm)) ownership.
    (ii) Map of Unit SM-1 follows:

    Figure 1 to Salina Mucket (Potamilus metnecktayi) paragraph (5)(ii)

[[Page 47987]]

[GRAPHIC] [TIFF OMITTED] TP25JY23.002


[[Page 47988]]


* * * * *

Madonna Baucum,
Regulations and Policy Chief, Division of Policy, Economics, Risk 
Management, and Analytics of the Joint Administrative Operations, U.S. 
Fish and Wildlife Service.
[FR Doc. 2023-15360 Filed 7-24-23; 8:45 am]
BILLING CODE 4333-15-C