Proposed Rule2023-15360
Endangered and Threatened Wildlife and Plants; Endangered Species Status for Salina Mucket and Mexican Fawnsfoot and Designation of Critical Habitat
Primary source
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Published
July 25, 2023
Issuing agencies
Interior DepartmentFish and Wildlife Service
Abstract
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.
Full Text
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[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 [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[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
[[Page 47952]]
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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: <a href="https://www.regulations.gov">https://www.regulations.gov</a>. 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a>. This
generally means that we will post any personal information you provide
us (see Information Requested, below, for more information).
Availability of supporting materials: Supporting materials, such as
the species status assessment report, are available on the Service's
website at <a href="https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot">https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot</a>, at <a href="https://www.regulations.gov">https://www.regulations.gov</a> 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> at Docket No. FWS-R2-ES-2023-0026 and on the
Service's website at <a href="https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot">https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot</a>.
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 <a href="https://www.regulations.gov">https://www.regulations.gov</a>, your
entire submission--including any personal identifying information--will
be posted
[[Page 47954]]
on the website. If your submission is made via a hardcopy that includes
personal identifying information, you may request at the top of your
document that we withhold this information from public review. However,
we cannot guarantee that we will be able to do so. We will post all
hardcopy submissions on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
Comments and materials we receive, as well as supporting
documentation we used in preparing this proposed rule, will be
available for public inspection on <a href="https://www.regulations.gov">https://www.regulations.gov</a>.
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 <a href="https://www.regulations.gov">https://www.regulations.gov</a>. 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> and at <a href="https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot">https://www.fws.gov/library/collections/proposed-endangered-species-status-salina-mucket-and-mexican-fawnsfoot</a>.
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 (<a href="https://www.fws.gov/program/endangered-species">https://www.fws.gov/program/endangered-species</a>), 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: <a href="https://www.fws.gov/service/financial-assistance">https://www.fws.gov/service/financial-assistance</a>.
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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> 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
[…truncated; see source link]Indexed from Federal Register on July 25, 2023.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.