Endangered and Threatened Wildlife and Plants; Removing Chipola Slabshell and Fat Threeridge From the Federal List of Endangered and Threatened Wildlife, 85909-85934 [2024-23929]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 89, Number 209 (Tuesday, October 29, 2024)]
[Proposed Rules]
[Pages 85909-85934]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-23929]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R4-ES-2024-0051; FXES1113090FEDR-245-FF09E22000]
RIN 1018-BF55


Endangered and Threatened Wildlife and Plants; Removing Chipola 
Slabshell and Fat Threeridge From the Federal List of Endangered and 
Threatened Wildlife

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 
remove the Chipola slabshell (Elliptio chipolaensis) and fat threeridge 
(Amblema neislerii), both freshwater mussels, from the Federal List of 
Endangered and Threatened Wildlife due to recovery. These species occur 
in the Apalachicola-Chattahoochee-Flint River Basin of Alabama, 
Georgia, and Florida. Our review of the best available scientific and 
commercial data indicates that the threats to the Chipola slabshell and 
fat threeridge have been eliminated or reduced to the point that both 
species have recovered and no longer meet the definition of an 
endangered or threatened species under the Endangered Species Act of 
1973, as amended (Act). Accordingly, we propose to delist the Chipola 
slabshell and the fat threeridge. If we finalize this rule as proposed, 
the prohibitions and conservation measures provided by the Act, 
particularly through sections 4 and 7 for the Chipola slabshell and 
sections 7 and 9 for the fat threeridge, would no longer apply to these 
species. This proposed rule also serves as the completed status review 
initiated under section 4(c)(2) of the Act.

DATES: We will accept comments received or postmarked on or before 
December 30, 2024. We must receive requests for public hearings, in 
writing, at the address shown in FOR FURTHER INFORMATION CONTACT by 
December 13, 2024.

ADDRESSES: 
    Written comments: You may submit comments by one of the following 
methods:
    (1) Electronically: Go to the Federal eRulemaking Portal: https://www.regulations.gov. In the Search box, enter FWS-R4-ES-2024-0051, 
which is the docket number for this rulemaking. Then, click on the 
Search button. On the resulting page, in the Search panel on

[[Page 85910]]

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.'' Comments must be received by 11:59 p.m. 
Eastern Time on the closing date listed in the DATES section.
    (2) By hard copy: Submit by U.S. mail to: Public Comments 
Processing, Attn: FWS-R4-ES-2024-0051, U.S. Fish and Wildlife Service, 
MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
    We request that you send comments only by the methods described 
above. We will post all comments on https://www.regulations.gov. This 
generally means that we will post any personal information you provide 
us (see Information Requested, below, for more information).
    Availability of supporting materials: This proposed rule and 
supporting documents, including the recovery plans, 5-year review, and 
species status assessment (SSA) reports, are available at https://ecos.fws.gov/ecp/ and at https://www.regulations.gov under Docket No. 
FWS-R4-ES-2024-0051.

FOR FURTHER INFORMATION CONTACT: Gian Basili, Deputy State Supervisor, 
Florida Ecological Services Office, 7915 Baymeadows Way, Suite 200, 
Jacksonville, FL 32256-7517; telephone 904-731-3079; email 
[email protected]. 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. Please see Docket No. FWS-
R4-ES-2024-0051 on https://www.regulations.gov for a document that 
summarizes this proposed rule.

SUPPLEMENTARY INFORMATION:

Executive Summary

    Why we need to publish a rule. Under the Act, a species warrants 
delisting if it no longer 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 an endangered species 
in the foreseeable future throughout all or a significant portion of 
its range). The Chipola slabshell is listed as a threatened species and 
the fat threeridge is listed as an endangered species, and we are 
proposing to delist them. We have determined the Chipola slabshell and 
fat threeridge do not meet the Act's definition of an endangered or 
threatened species. Delisting a species can be completed only by 
issuing a rule through the Administrative Procedure Act rulemaking 
process (5 U.S.C. 551 et seq.).
    What this document does. This rule proposes the removal of the 
Chipola slabshell and fat threeridge from the List of Endangered and 
Threatened Wildlife based on their recovery; if we finalize this rule 
as proposed, the prohibitions and conservation measures provided by the 
Act, particularly through sections 4 and 7 for the Chipola slabshell 
and sections 7 and 9 for the fat threeridge, would no longer apply to 
these 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. The determination to delist a species must be 
based on an analysis of the same factors.
    Under the Act, we must review the status of all listed species at 
least once every five years. We must delist a species if we determine, 
on the basis of the best available scientific and commercial data, that 
the species is neither a threatened species nor an endangered species. 
Our regulations at 50 CFR 424.11 identify four reasons why we might 
determine a species shall be delisted: (1) The species is extinct; (2) 
the species has recovered to the point at which it no longer meets the 
definition of an endangered species or a threatened species; (3) new 
information that has become available since the original listing 
decision shows the listed entity does not meet the definition of an 
endangered species or a threatened species; or (4) new information that 
has become available since the original listing decision shows the 
listed entity does not meet the definition of a species. Here, we have 
determined that the Chipola slabshell and fat threeridge have recovered 
to the point at which they no longer meet the definition of an 
endangered species or a threatened species; therefore, we are proposing 
to delist them.

Information Requested

    We intend that any final action resulting from this proposal will 
be based on the best scientific and commercial data available and be as 
accurate and as effective as possible. Therefore, we request comments 
or information from other concerned governmental agencies, Native 
American Tribes, the scientific community, industry, or any other 
interested parties concerning this proposed rule.
    We particularly seek comments concerning:
    (1) Reasons we should or should not remove Chipola slabshell or fat 
threeridge from the List of Endangered and Threatened Wildlife.
    (2) Relevant data concerning any threats (or lack thereof) to the 
Chipola slabshell or fat threeridge, particularly any data on the 
possible effects of climate change as it relates to habitat, as well as 
the extent of State protection and management that would be provided to 
these mussels as delisted species;
    (3) Current or planned activities within the geographic range of 
Chipola slabshell and fat threeridge that may have adverse or 
beneficial impacts on these species; and
    (4) Considerations for post-delisting monitoring, including 
monitoring protocols and length of time monitoring is needed, as well 
as triggers for reevaluation.
    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 actions 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 species or a threatened species must be made solely on the 
basis of the best scientific and commercial data available.
    You may submit your comments and materials concerning this proposed 
rule by one of the methods listed in ADDRESSES. We request that you 
send comments only by the methods described in ADDRESSES.
    If you submit information via https://www.regulations.gov, your 
entire submission--including any personal identifying information--will 
be posted on the website. If your submission is made via a hardcopy 
that includes personal identifying information, you may request at the 
top of your document that we withhold this information from public 
review. However, we cannot guarantee that we will be able to do so.

[[Page 85911]]

We will post all hardcopy submissions on https://www.regulations.gov.
    Comments and materials we receive, as well as supporting 
documentation we used in preparing this proposed rule, will be 
available for public inspection on https://www.regulations.gov.
    Our final determinations 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. For 
example, based on the new information we receive (and if relevant, any 
comments on that new information), we may conclude that Chipola 
slabshell should remain listed as a threatened species, or we may 
conclude that Chipola slabshell should be reclassified from a 
threatened species to an endangered species. We may conclude that the 
fat threeridge should remain listed as an endangered species, or we may 
conclude that the fat threeridge should be reclassified from an 
endangered species to a threatened species. 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 these virtual public 
hearings is consistent with our regulations at 50 CFR 424.16(c)(3).

Peer Review

    Species status assessment (SSA) teams prepared separate SSA reports 
for the Chipola slabshell and fat threeridge. The SSA teams were 
composed of Service biologists and staff from Texas A&M Natural 
Resource Institute, who consulted with subject area experts for both 
species. Each SSA report represents a compilation of the best 
scientific and commercial data available concerning the status of these 
species, including the impacts of past, present, and future factors 
(both negative and beneficial) affecting the species.
    In accordance with our joint policy on peer review published in the 
Federal Register on July 1, 1994 (59 FR 34270), and our August 22, 
2016, memorandum updating and clarifying the role of peer review of 
listing and recovery actions under the Act, we solicited independent 
scientific reviews of the information contained in each of the SSA 
reports. We sent the Chipola slabshell SSA report to three independent 
peer reviewers and received two responses. We sent the fat threeridge 
SSA report to four independent peer reviewers and received two 
responses. Results of these structured peer review processes can be 
found at https://www.regulations.gov. In preparing this proposed rule, 
we incorporated the results of these reviews, as appropriate, into the 
final SSA report for each species, which are the foundation for this 
proposed rule.

Summary of Peer Reviewer Comments

    As discussed in Peer Review above, we received comments from two 
peer reviewers on each of the draft SSA reports. We reviewed all 
comments we received from the peer reviewers for substantive issues and 
new information regarding the information contained in the SSA reports. 
The peer reviewers generally concurred with our methods and 
conclusions, and provided additional information, clarifications, and 
suggestions, including clarifications in terminology and discussions of 
survey information related to detection versus no detection, and other 
editorial suggestions. Otherwise, no substantive changes to our 
analysis and conclusions within either of the SSA reports were deemed 
necessary, and peer reviewer comments are addressed in versions 1.0 of 
each SSA report (Service 2020, entire; Service 2021, entire).

Previous Federal Actions

    On March 16, 1998, the Chipola slabshell was listed as a threatened 
species (63 FR 12664) and the fat threeridge as an endangered species 
(63 FR 12664) under the Act. On October 1, 2003, we completed a 
recovery plan for both species (68 FR 56647). A 5-year review of 37 
Southeastern species, including Chipola slabshell and fat threeridge, 
was completed on September 27, 2006 (71 FR 56545). Critical habitat was 
designated for the Chipola slabshell in the Chipola River main stem and 
seven tributaries comprising a stream length of approximately 228 km 
(142 mi) (72 FR 64286; November 15, 2007). Critical habitat was 
designated for the fat threeridge in the lower Flint River system (397 
km (247 mi)), the Apalachicola River system (161 km (100 mi)), and the 
Chipola River system (228 km (142 mi)) (72 FR 64286; November 15, 
2007). We published notices of initiation of periodic status reviews 
for both species as required under section 4(c)(2) of the Act in 2018 
(83 FR 38320, August 6, 2018); this proposed rule serves as completion 
of those status reviews. Recovery plan revisions were completed for 
both species on August 6, 2019 (84 FR 38284). The referenced documents 
and additional details can be found using our Environmental 
Conservation Online System (ECOS): https://ecos.fws.gov/.

Background

Species Information

    Both the Chipola slabshell and fat threeridge are members of the 
family Unionidae, a large group of freshwater mussels represented by 
298 species in North America. Both species are endemic to the 
Apalachicola-Chattahoochee-Flint River (ACF) River Basin of Alabama, 
Georgia, and Florida. The ACF River Basin extends approximately 620 
kilometers (km) (385 miles (mi)) and spans 50 counties in Georgia, 8 in 
Florida, and 10 in Alabama (see figure 1, below). For more details 
about the ACF River Basin, refer to the SSA reports (Service 2020, pp. 
12-15; Service 2021, pp. 26-50).
    The Chipola slabshell occurs in the mainstem of the Chipola River 
and several large tributaries. The fat threeridge occurs in the 
mainstems of the Flint River, Chipola River, and Apalachicola River. 
Neither species has known occurrences within the Chattahoochee River 
basin.

[[Page 85912]]

[GRAPHIC] [TIFF OMITTED] TP29OC24.000

General Mussel Biology

    Freshwater mussels, including Chipola slabshell and fat threeridge, 
have a complex reproduction process involving parasitic larvae, called 
glochidia, that are wholly dependent on host fish. Mussels release 
sperm into the water column, which is taken in by the female, wherein 
fertilization and development of glochidia occurs in a restricted 
portion of the gills, called the brood pouch or marsupium. When mature, 
the glochidia are released to the water column to attach on the gills, 
head, or fins of fishes. Glochidia die if they fail to attach to a host 
fish, attach to an incompatible fish species, or attach to the wrong 
location on a host fish (Neves 1991, p. 254; Bogan 1993, p. 599). Once 
attached to the host, glochidia draw nutrients from the fish's tissue 
as they develop (Arey 1932, pp. 214-215). Time to development, from 
attachment of glochidia to maturation,

[[Page 85913]]

ranges from just over 1 week to 6 weeks or more (Parmalee and Bogan 
1998, p. 8).
    Depending on the species, mussels are either short-term or long-
term brooders. In short-term brooders, such as Chipola slabshell and 
fat threeridge, fertilization occurs in the spring or summer and 
glochidia are released shortly after they are fully developed. In long-
term brooders, fertilization occurs in late summer or fall, and 
developed glochidia are held over winter and released in the following 
spring or summer (Haag 2012, pp. 39-40). Mature glochidia drop off 
their hosts and, if they settle in suitable habitat on the stream 
bottom, continue the remainder of their existence as free-living 
mussels. Newly released glochidia are juveniles that are reproductively 
immature but otherwise resemble adults, with both halves (valves) of 
the shell developed and poised for growth.
    Freshwater mussels are relatively sedentary and, under their own 
power, capable of moving only short horizontal distances, typically up 
to a few yards or less in a year (Haag 2012, pp. 34-35). Given mussels' 
limited mobility, host fish are their primary mode of dispersal, and 
the hosts are essential for maintaining population connectivity. Host 
specificity varies, with some mussel species being compatible with a 
few fish species while others can transform from glochidia to juveniles 
on several fish species.

Chipola Slabshell

    A thorough review of the taxonomy, life history, and ecology of the 
Chipola slabshell is presented in chapter 1 of the SSA report (Service 
2020, pp. 3-24).
    The Chipola slabshell is a freshwater mussel that does not exhibit 
sexual dimorphism in shell characters (Service 2020, p. 4). The species 
can attain a length of 85 millimeters (mm) (3.35 inches (in)), but 
typical length is between 47 to 76 mm (1.85 to 2.99 in). The Chipola 
slabshell has a chestnut colored periostracum (outer shell) with 1 to 4 
dark annuli (growth) bands (Service 2020, p. 4). Within its range, 
Chipola slabshell is the only species with light and dark bands on 
periostracum and with salmon-colored nacre (inner layer of shell) 
inside the shell. The umbos (shell protrusions near the hinge) are 
prominent, well above the hingeline, thus inside the umbo cavity is 
deep.
    Based on the size, shell characteristics, and traits from similar 
species in the genus Elliptio, the Chipola slabshell is thought to 
reach sexual maturity within 3-5 years and has an average lifespan of 
15-20 years (Service 2020, p. 8). The Chipola slabshell is a short-term 
brooder (tachytictic), meaning immature mussels (i.e., glochidia) are 
carried in the female's gills for a short time following spawning and 
released that same season. Females are gravid from early June to early 
July. The Chipola slabshell is a host-fish specialist, requiring a 
Centrarchid (i.e., sunfish) host.
    Currently, the Chipola slabshell is widespread within its range and 
common at some localities. A lack of consistent survey methods across 
observers and through time limits the discussion of abundance trends 
for Chipola slabshell, however historical data indicate approximately 
32 records whereas current records (from 2005 onward) indicate 
approximately 138 (Service 2020, p. 62). The species' distribution is 
primarily continuous in one river system, including the Chipola River 
and its tributaries. The species inhabits silty sand substrates of 
large creeks and the main channel of the Chipola River, in slow to 
moderate current. Chipola slabshell appears to be more tolerant of soft 
sediments than other mussel species in the ACF River Basin. It co-
occurs with more silt-tolerant species in stream bank habitats with 
slower currents, thus it has more available habitat than mid-channel-
dwelling species (Service 2020, p. 15).

Fat Threeridge

    A thorough review of the taxonomy, life history, and ecology of the 
fat threeridge mussel is presented in chapter 2 of the SSA report 
(Service 2021, pp. 14-25).
    The fat threeridge is an almost square, inflated, solid, and heavy 
shelled freshwater mussel that typically reaches up to 102 mm (4 in) in 
length. Older, larger individuals are quite inflated, where their width 
approximates their height. The dark brown to black shell is strongly 
sculptured with seven to eight prominent horizontal parallel ridges. 
The prominent, parallel ridges and inflated shell (older specimens, 
especially) distinguish this species from other mussels within its 
range (Service 2021, p. 15).
    The glochidia of fat threeridge, like most freshwater mussels, are 
obligate parasites on fish, and must attach to a host to transform into 
juvenile mussels; this parasitism serves as the primary dispersal 
mechanism for this relatively immobile group of organisms. To 
facilitate attachment, fat threeridge hookless glochidia are broadcast 
in a web-like mass that expands and wraps around a host. This method 
often is seen in host generalists because passive entanglement is 
nonselective. Reproductive studies confirm that fat threeridge is a 
host generalist, completing transformation on 23 species of fishes 
(Service 2021, p. 17). The fat threeridge is a short-term summer 
brooder. Females appear to be gravid when water temperatures reach 23.9 
degrees Celsius ([deg]C) (75 degrees Fahrenheit ([deg]F)), usually in 
late May and June.
    Because freshwater mussels are relatively long-lived and have 
limited mobility, habitat stability is a requirement shared by all 
unionids. Fat threeridge appears to be sensitive to the effects of 
sediment instability and completely reliant on stable fine sediment 
habitat patches. Excessive amounts of sediment and particulate matter 
can interfere with key aspects of mussel biology. The availability of 
stable sediment patches may help explain the restricted distribution in 
mainstem versus tributary environments, as the fat threeridge has never 
been found in a tributary stream. By their nature, tributaries are 
smaller in size than mainstems and have more dynamic flows and sediment 
transport (Fritz et al. 2018, p. 6). Thus, the fat threeridge is 
ecologically restricted/isolated to large river systems in low gradient 
areas with stable, very fine sediment patches (Service 2021, pp. 22-
23).
    Within its range in the ACF River Basin, fat threeridge is found in 
mainstem habitats in the Flint, Apalachicola, and Chipola rivers; there 
are no known collections from the Chattahoochee River (Service 2021, p. 
26). At the time the fat threeridge was listed in 1998, there were very 
few existing records of the species, with the most seen at a site being 
6 individuals (63 FR 12666). Current estimates in the middle 
Appalachicola alone are upwards of 7.7 million individuals (Service 
2021, p. 47).

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. On April 5, 2024, 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 what criteria we

[[Page 85914]]

apply when designating listed species' critical habitat (89 FR 24300). 
This final rule is now in effect. 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. The determination to delist a 
species must be based on an analysis of the same five factors.
    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 which is 
further described in the 2009 Memorandum Opinion on the foreseeable 
future from the Department of the Interior, Office of the Solicitor (M-
37021, January 16, 2009; ``M- Opinion,'' available online at https://www.doi.gov/sites/doi.opengov.ibmcloud.com/files/uploads/M-37021.pdf). 
The foreseeable future extends as far into the future as the U.S. Fish 
and Wildlife Service and National Marine Fisheries Service (hereafter, 
the Services) can make reasonably reliable predictions about the 
threats to the species and the species' responses to those threats. We 
need not identify the foreseeable future in terms of a specific period 
of time. We will describe the foreseeable future on a case-by-case 
basis, using the best available data and taking into account 
considerations such as the species' life-history characteristics, 
threat-projection timeframes, and environmental variability. In other 
words, the foreseeable future is the period of time over which we can 
make reasonably reliable predictions. ``Reliable'' does not mean 
``certain''; it means sufficient to provide a reasonable degree of 
confidence in the prediction, in light of the conservation purposes of 
the Act.

Analytical Framework

    The SSA reports document the results of our comprehensive 
biological review of the best scientific and commercial data regarding 
the status of the Chipola slabshell and fat threeridge, including 
assessments of the potential threats to these species. The SSA reports 
do not represent our decisions on whether these species should be 
proposed for delisting. However, they do 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 Chipola slabshell and fat threeridge viability, 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 each species' ecological requirements for survival and 
reproduction at the individual, population, and species levels, and 
described the beneficial and risk factors influencing these species' 
viability.
    The SSA process can be categorized into three sequential stages. 
During the first stage, we evaluated individual species' life-history 
needs. The next stage involved an assessment of the historical and 
current condition of these species' demographics and habitat 
characteristics, including an explanation of how these species arrived 
at their current condition. The final stage of the SSA involved making 
predictions about each species' responses to positive and negative 
environmental and anthropogenic influences. Throughout all of these 
stages, we used the best available information to characterize 
viability as the ability of these 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 reports; the full SSA reports can be found at Docket No. FWS-
R4-ES-2024-0051 on https://www.regulations.gov.

Summary of Biological Status and Threats

    In this discussion, we review the biological condition of each 
species and their resources, and the threats that influence these 
species' current and future conditions, in order to assess both 
species' overall viability and the risks to that viability. In 
addition, the SSA reports (Service 2020, entire; Service 2021, entire) 
document our comprehensive biological status review

[[Page 85915]]

for each species, including an assessment of the potential threats to 
each species. The following is a summary of these status reviews and 
the best available information gathered since that time that have 
informed these decisions.

Species Needs

    Both Chipola slabshell and fat threeridge share similar habitat 
needs, including stable stream channels; permanently flowing water to 
adequately deliver oxygen, enable passive reproduction, support host 
fish, deliver food items to the sedentary juvenile and adult life 
stages, and remove wastes; and good water quality (i.e., free from 
harmful toxicants (such as chlorine, unionized ammonia, heavy metals, 
salts, pesticides), or at low enough concentrations to avoid adverse 
effects). The Chipola slabshell prefers predominantly sand, gravel, 
and/or cobble stream substrate with low to moderate amounts of silt and 
clay (Service 2020, pp. 15-16), whereas the fat threeridge prefers 
stable fine sediment habitat patches (Service 2021, p. 22).

Analysis Units

    The Chipola slabshell consists of a single, panmictic population 
within the Chipola River basin; we delineated three subpopulations 
(i.e., management units, MUs) to account for the two natural breaks in 
connectivity (Service 2020, pp. 64-65). Although these breaks do not 
prevent dispersal of infected host fish between subpopulations of the 
Chipola slabshell, we delineated the MUs based on the potential 
barriers to dispersal and genetic exchange. Since our knowledge of the 
level of genetic diversity is limited, it is possible MUs exhibit some 
natural variation in genetic diversity. Each subpopulation was broken 
into U.S. Geological Survey (USGS) 10-digit hydrologic unit codes (HUC-
10s) as MUs (see table 1, below). These units reflect a spatial scale 
for which mussel survey data were available.

    Table 1--HUC-10s for Each Chipola Slabshell Management Unit (MU)
------------------------------------------------------------------------
                    MU                                 HUC-10s
------------------------------------------------------------------------
1.........................................  River Styx & Douglas Slough.
2.........................................  Merritts Mill Pond-South.
                                            Mill Creek.
                                            Tenmile Creek.
                                            Dead Lake.
3.........................................  Marshall Creek.
                                            Cowarts Creek.
                                            Merritts Mill Pond-North.
------------------------------------------------------------------------

    The fat threeridge also consists of a single population; we 
delineated six analysis units (HUC-10s) within the Flint, Chipola, and 
Apalachicola Rivers, based on potential reproductive isolation and/or 
unique geomorphology, available current occurrence records, and expert 
input (Service 2021, pp. 51-52).

Threats

    The primary threats affecting viability of both mussel species are 
predominantly related to historical land use practices resulting in the 
destruction, modification, or curtailment of these species' habitat or 
range (Factor A), ultimately affecting water quality and flow regime 
(i.e., water quantity). They are: (1) sedimentation; (2) impoundments; 
(3) agriculture; and (4) urbanization. Existing regulatory mechanisms 
(Factor D) and conservation actions have benefited the species, thus 
ameliorating many threats. Other threats such as invasive species 
(Factor C) likely have had some negative effects on the two mussel 
species, as described in the SSA reports, but were not considered 
primary threats that affect the species' overall viability (Service 
2020, pp. 40-41; Service 2021, p. 76). Our analyses also considered the 
effects of climate change (Factor E), but sea level rise (SLR) was only 
examined for fat threeridge based upon the potential of SLR to affect 
the lower portion of its range.
Sedimentation
    The primary listing factor for both the Chipola slabshell and fat 
threeridge was related to habitat modification, specifically the issue 
of increased sedimentation which causes turbidity from erosion (Service 
2020, p. 27; Service 2021, p. 76). Sedimentation is one of the most 
significant pollution sources for aquatic organisms and is a major 
factor in overall mussel declines (Service 2020, p. 31), as excessive 
amounts of sediment and particulate matter can interfere with key 
aspects of mussel biology (Service 2021, p. 24).
    Canopy, or riparian buffers, provide the conditions for stable 
stream channels, delivery of food items, and improved overall water 
quality because of their ability to filter runoff. Activities related 
to dredging, snag removal, agriculture, logging, and urban development 
are usually common sources of erosion and sedimentation. Dredging was a 
widespread, intensive, and frequent disturbance within the Apalachicola 
River that was detrimental to both species at the time of listing. 
However, over the past 20 years, dredging practices have been 
restricted through regulations such that very little dredging has 
occurred, and future dredging activities are expected to be limited. 
Following the cessation of widespread dredging, signs of habitat 
recovery have been observed, indicating improved habitat stability for 
fat threeridge and other freshwater mussels (including Chipola 
slabshell) in the Apalachicola River (Service 2021, pp. 58-59).
    In 2009, we conducted a basin threats assessment for the Chipola 
River in order to identify and reduce sedimentation risks to aquatic 
life. Unpaved roads were identified as primary contributors of sandy 
materials that are easily eroded and transported to stream corridors. 
All unpaved road-stream crossing sites were ranked and prioritized for 
subsequent restoration practices, and proximity to sites of listed 
species and their habitat was a primary consideration (Service 2020, p. 
55). We began unpaved stream crossing restoration efforts in 2013, in 
partnership with the Florida Fish and Wildlife Commission (FWC), and 
several projects have reduced sediment inputs (Service 2020, p. 56).
    Partnerships and programs have had success in restoring and 
reducing sediment inputs in priority stream reaches that have been 
identified as highly erodible. We and our partners, including but not 
limited to the University of Florida's Institute of Food and 
Agricultural Sciences Extension, Northwest Florida's Water Management 
District, Florida Department of Agriculture and Conserver Services, 
Natural Resources Conservation Service, FWC, the U.S. Forest Service, 
and many landowners (National Fish Habitat Partnership 2020, 
unpaginated), have successfully restored over 8 km (5 mi) of streams in 
the Chipola River Basin and continue to implement stream restoration 
projects (for example, bank stabilization, solar wells, livestock 
exclusion fencing, riparian restoration, low-water crossings, and 
reshaping of spring-fed tributaries) to reduce sediment inputs. The 
Southeast Aquatic Resources Partnership continues to use a Chipola 
River Basin threats assessment to reduce sedimentation in the basin and 
identify potential barriers to fish passage (Service 2020 pp. 55-56).
Impoundments
    Impoundments can alter downstream water quality and riverine 
habitat (Service 2020, p. 28). The most consequential direct effects to 
Chipola slabshell and fat threeridge from impoundments include upstream 
and downstream flow effects, as well as the

[[Page 85916]]

loss of and fragmentation of riverine habitat. Pre-existing dams that 
fragment and inundate habitat and alter natural flow are part of 
existing baseline conditions for these species and are unlikely to 
change substantially in the near future (Service 2020, pp. 33-36; 
Service 2021, p. 112). Impoundments remain within tributaries of the 
Chipola River, but the mainstem, which contains the majority of Chipola 
slabshell, as well as critical habitat for fat threeridge, is 
unobstructed (Service 2020, p. 28; Service 2021, p. 107). The main stem 
of the Chipola River formerly contained one impoundment, the Dead Lake 
Dam, which was removed in 1987. The final obstructions to natural flow 
in the channel were removed in 1989. The dam removal returned 
connectivity and natural flow conditions to the river, but the local 
sediment and detritus load is likely still high (Service 2021, p. 81). 
However, even with the accumulated detritus, the number of fish species 
almost doubled after the dam was removed, with anadromous fish able to 
travel through the lake to spawn or seek critical thermal refugia in 
the upper Chipola River (Service 2020, p. 34).
    Following the return of connectivity and natural flow regime of 
Dead Lakes, habitat conditions are anticipated to become more stable 
over time. Stable stream habitats are formed and maintained by natural 
flow regimes, channel features (dimension, pattern, and profile), and 
natural sediment input to the system through periodic flooding. These 
events help maintain connectivity and interaction with the floodplain, 
and consistently transport sediment load over time, such that the 
stream bed neither degrades nor aggrades (Service 2021, p. 22).
Agriculture
    Agriculture is the largest groundwater consumer in the ACF River 
Basin accounting for 35 percent of all water withdrawals in 2010. Of 
the groundwater withdrawn in the ACF River Basin, 89 percent was 
withdrawn in Georgia, and about 11 percent was withdrawn in Alabama and 
Florida during 2010 to provide irrigation for approximately 736,200 
acres (ac) (297,930 hectares (ha)) (Service 2021, p. 87). These 
groundwater withdrawals exacerbate drought conditions during dry years, 
which can affect both tributaries and main river channels (Service 
2021, p. 86).
    Water pollutants associated with agricultural activity may also 
adversely affect mussels. Ammonia is associated with nitrogenous 
fertilizers, wastewater from animal feedlots (livestock waste), and the 
effluents of older municipal wastewater treatment plants. While 
nitrogen from wastewater inputs originating from septic and sewer 
sources are also associated with urban centers, other forms of 
pollution are unique to these agricultural areas (Service 2020, p. 30). 
Properly implemented agricultural best management practices (BMPs) have 
improved the water quality in several basins where Chipola slabshell 
and fat threeridge occur. Implementing BMPs has reduced thousands of 
pounds of agricultural nitrogen inputs from fertilizers and livestock 
waste (Service 2020, p. 51).
    Agricultural land use is highest in the Lower Flint River, so 
impacts from stressors associated with agricultural activity could 
limit fat threeridge in the future. However, land use in the sub-basins 
with fat threeridge present has remained relatively stable from 2000-
2016. A large portion of each sub-basin is also forested, which 
provides an effective buffer for maintaining sufficient river 
baseflows, permeability, and reducing overall flooding impacts (Service 
2021, p. 87). Fat threeridge will likely maintain resiliency in larger 
river and mainstem habitats in the ACF River Basin, including the Lower 
Flint, if adequate water quality and quantity continue at current 
levels (Service 2021, pp. 129-130).
Urbanization
    Urban development not only causes habitat loss and fragmentation, 
but it also contributes to habitat degradation through storm water 
runoff and nonpoint source pollution. The term ``development'' refers 
to urbanization of the landscape, including (but not limited to) land 
conversion for residential, commercial, and industrial uses and the 
accompanying infrastructure. Urbanization effects may include 
alterations to water quality, water quantity, and instream and 
streamside habitat (Ren et al. 2003, p. 649; Wilson 2015, p. 424). The 
effects on habitat also include variability in streamflow, typically 
increasing the extent and volume of water entering a stream after a 
storm and decreasing the time it takes for the water to travel over the 
land before entering the stream (Giddings et al. 2009, p. 1). 
Freshwater mussel populations experience reduced abundance, species 
richness, reproduction, growth, and survival stemming from the impacts 
of urbanization on water and habitat quality (Diamond and Serveiss 
2001, p. 4716; Gangloff et al. 2009, p. 198; Cao et al. 2013, pp. 1212-
1214; Gillis et al. 2017, pp. 674-679). While there are some parts of 
both the Chipola slabshell's range and the fat threeridge's range that 
are affected by urbanization, it does not rise to the level that it is 
affecting current viability (see Current Conditions below).
Additional Water Quality and Quantity Considerations
    Influences on the viability of the Chipola slabshell and fat 
threeridge include habitat factors such as water quantity (flow) 
(Service 2020, p. 28). Flow impacts are varied between low flow and 
high flow conditions. When water flows decrease, the concentration of 
water pollutants increases, thus increasing the adverse effects that 
can negatively impact the freshwater mussels, such as Chipola slabshell 
and fat threeridge, and their habitat (Service 2020, p. 32; Service 
2021, p. 21).
    High-flow volumes can be both harmful and beneficial for freshwater 
mussels. Floods are often associated with habitat destruction and 
direct mortality, both to juveniles and adults that are stranded in 
unsuitable habitats (Service 2020, p. 32; Service 2021, p. 65). Floods 
can also increase the potential for shear stress events to occur. Shear 
stress is a critical factor in affecting displacement during high-flow 
events where substrates are unstable, conditions are generally poor for 
mussel habitation. However, floods can also help remove accumulated 
silt deposits, algal growth and harmful organic material from 
sediments, improving habitat for juvenile mussels. It is likely that 
large woody debris can also help to potentially stabilize sediments in 
the Coastal Plains ecoregion where Chipola slabshell and fat threeridge 
occur, and as a result these areas are expected to be the most stable 
during high flows (Service 2020, p. 32).
    Water quantity can become limited by withdrawals and be exacerbated 
during extreme drought events and periods of low flow. Groundwater 
recharge provides water to aquifers and springsheds, and alterations to 
groundwater removal can alter surface water flow impacting spring flow 
and available surface water (Service 2020, p. 41). Under moderate-flow 
conditions, groundwater makes up the majority of the Chipola River's 
discharge and the quality of water discharged from the Chipola River 
springs is predominantly determined by the quality of groundwater in 
the Floridan Aquifer (Service 2020, p. 19). The Chipola River's 
baseflow is derived principally from aquifers, therefore it is not as 
susceptible to drought conditions. In addition, Chipola slabshell has 
been found to occupy areas 1 to 2 meters (m) (3.3 to 6.6 feet (ft)) 
below the water

[[Page 85917]]

surface, providing a buffer against the effects of low flow conditions. 
Fat threeridge has also persisted and arguably increased in abundance 
through these periods of low flow (Service 2021, pg. 103).
    For more information regarding threats, see chapter 3 of the 
Chipola slabshell SSA report and chapter 5 of the fat threeridge SSA 
report (Service 2020, pp. 27-140; Service 2021, pp. 76-130).
Climate Change
    Impacts of climate changes can have direct effects or be driven by 
one or more factors working synergistically as indirect effects on 
species. These effects may be neutral, positive, or negative and they 
may change over time. Despite the recognition of potential climate 
effects on ecosystem processes, there is uncertainty about what the 
exact climate future for the southeastern United States will be and how 
ecosystems and species in this region will respond. The greatest threat 
from climate change may come from synergistic effects. That is, factors 
associated with a changing climate may act as risk multipliers by 
increasing the risk and severity of more imminent threats, especially 
for rivers in wide flood plains where stream channels have room to 
migrate (Elliot et al. 2014, pp. 67-68). As a result, impacts from land 
use change might be exacerbated under even a mild to moderate climate 
future. A suite of potential hydrological impacts to waters of the 
southeastern United States is possible under conditions of climate 
change, but climate models generally predict increases in extreme 
rainfall events and droughts of greater duration and intensity (Carter 
et al. 2018, pp. 745-746).

Flooding

    Tropical storms occur across the range of Chipola slabshell and fat 
threeridge, and they have become more intense during the past 20 years. 
The wind speeds and rainfall associated with hurricanes are likely to 
increase as the climate continues to warm (United States Environmental 
Protection Agency (USEPA) 2016b, p. 1, USEPA 2016c, p. 1). In October 
2018, Hurricane Michael substantially impacted northwest Florida. 
According to a report by the Florida Forest Service (FFS), more than 
2.8 million ac (1.13 million ha) of forest land were damaged by storm 
winds. The Chipola River experienced severe impacts, where 75 percent 
of upland and bottomland trees were damaged (FFS 2018, pp. 1, 4-5). 
However, high woody debris loading has greatly contributed to the 
formation of stable, fine sediment habitat in the Lower Chipola River 
(Kaeser et al. 2019, p. 667), resulting in net positive effects of 
blowdown for Chipola slabshell and fat threeridge assuming forest cover 
regenerates.
    The increased intensity of hurricanes as well as more frequent 
high-intensity precipitation events could also increase inland 
flooding. The precipitation received during heavy storms has increased 
by 27 percent in the Southeast with the trend for increasingly heavy 
rainfall events likely to continue into the future (USEPA 2016b, p. 2). 
With these heavy rainfall events comes flooding, as rivers overtop 
their banks more frequently, and more water accumulates in low-lying 
areas that drain slowly. Restoring and preserving flood protection and 
nutrient reduction capabilities of forested lands along the Chipola 
River is vital (Northwest Florida Water Management District (NWFWMD) 
2018, p. 6).

Drought

    Long-term climate records suggest that decade-long ``mega-
droughts'' have occurred periodically during the past 700 years in the 
southeastern United States, including in the ACF River Basin (Stahle et 
al. 2007, p. 147). Projections for the ACF watershed indicate that 
future droughts are likely to be more intense (Yao and Georgakakos 
2011, entire). This suggests that while the recently observed droughts 
in 2006-2008 and 2010-2012 were exceptional based on our recent <100-
year period of record, they may not be exceptional compared to historic 
episodes (Pederson et al. 2012, entire).
    The duration and severity of droughts may vary within the ranges of 
Chipola slabshell and fat threeridge. Droughts are likely to be more 
severe in some locations as periods without rain may be longer and very 
hot days will be more frequent. Dry spells are expected to be up to 20 
days shorter during the cold season in the southern half of Florida, 
and up to 20 days longer for the same season in Alabama (Keellings and 
Engstrom 2019, p. 1). While more intense cold season droughts might not 
be as stressful for mussels as intensification of droughts during the 
warm season would be, a cool season drought may limit recharge and 
storage of water in both natural and anthropogenic reservoirs (Engstrom 
and Keellings 2018, p. 261; Keellings and Engstrom 2019, p. 3). More 
frequent or severe droughts may reduce streamflow in some areas. In 
Alabama, the total amount of water running off into rivers or 
recharging ground water is likely to decline 2.5 to 5 percent, as 
increased evaporation offsets the greater rainfall (USEPA 2016b, p. 2). 
Low flows have decreased in the southeastern United States between 1940 
and 2019, meaning streams are carrying less water at low flow than 
historically recorded (USEPA 2016a, p. 2). Low flows have not gone 
below 200 cubic feet per second (cfs) in the Chipola River in the 
recent past (1986 to 2019; USGS National Water Resources, 2019, 
entire), but may in the future.
    The Chipola River is a spring-fed river with baseflow derived 
principally from aquifers, and therefore is not as susceptible to 
drought conditions derived from changes in precipitation patterns as it 
is to alterations in groundwater withdrawals. Mussel sites in the 
Chipola River generally have slopes greater than 20 percent, which 
helps to limit mussel mortality to less than 1 percent of the local 
population during low flow events (Service 2016b, p. 125). In addition, 
Chipola slabshell have been found to occupy areas 1 to 2 m (3.3 to 6.6 
ft) below the water surface, providing a buffer against the effects of 
low flow conditions (Service 2016b, p. 129). Even during severe drought 
conditions in 2007, Cowarts Creek (which joins Marshall Creek to form 
the Chipola River) did not exhibit signs of mussel mortality (Garner et 
al. 2009, p. 693). Cowarts Creek retained adequate dissolved oxygen 
(6.5 milligrams per liter (mg/L) (81.5 percent saturation)) and 
temperature (27 [deg]C (81 [deg]F), though the flow was sluggish and 
phytoplankton seemed elevated (Garner et al. 2009, p. 688).

Sea Level Rise

    Most freshwater mussels are intolerant of saline conditions. The 
potential for sea level rise (SLR), and thus intrusion of saline 
conditions, is considered for the fat threeridge range; however, the 
Chipola slabshell's range is not likely to be affected. Exposure to 
saline conditions (salt at 3 to 6 parts per trillion (ppt)) can 
decrease the reproduction and survival of freshwater mussels (Blakeslee 
et al. 2013, p. 2849). The upper limit for exposure of most adult 
unionid mussels to long-term salinity stress is < 6 ppt, which may be 
consistent with fat threeridge tolerances. Fat threeridge is not known 
to occur below the point of tidal influence in the Apalachicola River, 
where salt exposure is expected to be lethal. An increase in salinity 
of fresh waters through the intrusion of seawater associated with sea 
level rise will likely modify community composition of unionids in 
affected areas, eliminating or at least reducing the abundance of 
species that

[[Page 85918]]

are less adapted to increased salinity (Johnson et al. 2018, p. 67).
    Climatic changes, including SLR and shifts in seasonal 
precipitation, temperature, and storm cycles, are major threats to 
south Florida. Various studies (University of Florida Geoplan 2015, p. 
13; The Nature Conservancy 2011, p. 4-6; Sweet et al. 2017, p. 22-23) 
have developed scenarios that range from less than 0.3 m to 3.2 m (1 to 
10.4 ft) of SLR in the south Florida by 2100. Tidal gauges around 
Florida have shown 25 cm (10 in) of SLR since 1913, with an increase in 
SLR of 2.56 mm/year (0.1 inch/year) from 1967 to 2019, equivalent to 25 
cm (9.8 inches) in 100 years more locally (NOAA 2021, n.p.). This 
recent acceleration suggests that the intermediate to high SLR 
scenarios are more likely to occur than the low and intermediate-low 
scenarios (Sweet et al. 2022, pp. 20-21). Sea level rise since 2000 has 
generally been within the trajectory of the Intermediate-High scenario, 
but it is important to note the trajectory could change throughout the 
century. Rapid ice sheet collapse in Antarctica could move SLR from the 
intermediate to the high scenario by the end of the century (Sweet et 
al. 2022, p. 26). Under the high scenario, some areas supporting fat 
threeridge (e.g., the Lower Apalachicola) will likely become partially 
inundated (i.e., under water) at some point during this century 
(Service 2021, p. 102).

Conservation Efforts and Regulatory Mechanisms

    Since the listing of Chipola slabshell as an endangered species and 
fat threeridge as a threatened species under the Act in 1998, Federal 
agencies have been required under section 7 of the Act to coordinate 
with us to ensure actions that they carry out, fund, or authorize will 
not jeopardize either species' continued existence or destroy or 
adversely modify the critical habitat designated for these species in 
2007. This requirement has protected both Chipola slabshell and fat 
threeridge throughout most of their ranges. Both Federal and State 
regulations are relevant to the maintenance of water quality where 
Chipola slabshell and fat threeridge occur.
    Water quantity can become limited by agricultural, irrigation, 
municipal, and industrial withdrawals. Such withdrawals can be 
exacerbated during extreme drought events and periods of low flow. 
Groundwater recharge provides water to aquifers and springsheds, and 
alterations to groundwater removal can alter surface water flow 
impacting spring flow and available surface water. The State of Florida 
establishes minimum flow limits (MFLs) to identify the limit at which 
withdrawals would be significantly harmful to the water resources or 
ecology of an area. Water reservation is a legal mechanism in Florida 
that functions to set aside water from consumptive uses for the 
protection of fish and wildlife or public health and safety (2023 
Florida Statutes at section 373.223). Water reservations and MFLs are 
both important tools to ensure an adequate supply of water for citizens 
and environment. There is no known comparable mechanism to protect 
flows in Alabama. Water reservations were established for the Chipola 
and Apalachicola rivers in 2006 (Florida Administrative Code, rule 40A-
2.223). The magnitude, duration and frequency of observed flows are 
reserved, essentially in total, for the protection of fish and wildlife 
of the Chipola River, Apalachicola River, associated floodplains, and 
Apalachicola Bay.
    Federal guidelines are in place to minimize alterations to flow 
regimes. The Service and USEPA proposed instream flow guidelines for 
protecting riverine ecosystems under a possible interstate water 
allocation formula between Alabama, Florida, and Georgia for the ACF 
Basin. Although the three States failed to agree upon an allocation 
formula and the ACF compact authorizing their negotiations expired in 
2003, the Service has applied the instream flow guidelines in 
consultations with Federal agencies on actions affecting the species 
addressed in this proposed rule. At minimum, the Environmental Resource 
Permit Program within the USEPA regulates the construction, alteration, 
maintenance, removal, modification and operation of all activities in 
uplands, wetlands and all other surface waters that alter, divert and 
change the flow of surface waters. Both State and Federal permits may 
be required to alter wetlands and other surface waters.
    Future water quantity models in the Chipola River Basin have 
projected adequate water supply for citizens and the environment 
through 2045, even in drought years (NWFWMD 2023, p. ix). Water flows 
for most of the Chipola slabshell's and fat threeridge's occupied range 
are protected through consumptive uses by water reservation (legal 
protection), while other areas are supported by ground water 
contributions from springs during drought (Service 2020, pp. 96-139; 
Service 2021, p. 112). Water quantity models are updated every 5 years 
to ensure sufficient supply planning.
    Regional water plans in Georgia are developed in accordance with 
the Georgia Comprehensive State-wide Water Management Plan (State water 
plan), which was adopted by the General Assembly in January 2008. The 
State water plan requires the preparation of regional water development 
and conservation plans to manage water resources in a sustainable 
manner through 2050. A water conservation plan is required of all 
permit holders operating in the Flint River basin. This requirement 
will benefit fat threeridge resiliency in the future by ensuring 
permits are sufficiently protective of necessary water quantity and 
quality. These plans detail best water management practices to be 
followed, provide direction for funding conservation practices, 
describe permit conditions for withdrawal permits, and provide guidance 
for how to minimize and control water loss (Georgia Department of 
Natural Resources (GADNR) 2006, pp. 161-163).
    Minimum water quality standards have been set by Federal agencies 
both through the Clean Water Act (CWA; 33 U.S.C. 1251 et seq.) and 
other initiatives. The CWA is a Federal law that regulates the 
discharge of pollutants into surface waters, including lakes, rivers, 
streams, wetlands, and coastal areas. USEPA and the Service and 
National Marine Fisheries Service agreed to a national consultation on 
the CWA Section 304(a) aquatic life criteria as part of a Memorandum of 
Agreement regarding interagency coordination under the CWA and the Act 
(66 FR 11202; February 2, 2001). In 2013, the USEPA released new 
ammonia criteria that included acute and chronic toxicity testing for 
13 freshwater mussels, thus leading to an improved understanding of 
ammonia toxicity and setting a more protective ammonia criteria value 
for freshwater mussels (USEPA 2013, p. xi). In 2016, the Florida 
Department of Environmental Protection (FDEP) adopted the chronic 
criteria for ammonia as both the acute and chronic values (1.408 mg/L), 
therefore improving the ammonia standard even further for the 
conservation of freshwater mussels statewide (USEPA 2016a, entire). 
Georgia Department of Natural Resources' (GADNR) Environmental 
Protection Division (EPD) also implements the 2013 ammonia criteria as 
part of their National Pollutant Discharge Elimination System (NPDES) 
permitting process (GADNR 2022, pp. A-16-17).
    Florida has established water classifications that promote water 
quality standards that are more stringent than those of the CWA. The 
Florida

[[Page 85919]]

Department of Environmental Protection (FDEP) designates Outstanding 
Florida Waters (OFWs) under 2023 Florida Statutes section 403.061(27). 
An OFW is defined by FDEP as a waterbody worthy of special protection 
because of its natural attributes. In general, FDEP cannot issue 
permits for direct discharges to OFWs that would lower ambient 
(existing) water quality. FDEP also may not issue permits for indirect 
discharges that would significantly degrade a nearby waterbody 
designated as an OFW. The majority of waterbodies and segments in the 
range of Chipola slabshell and fat threeridge receive regulatory 
protection through designation as OFWs in addition to protections under 
their surface water classification as class III waterbodies, which 
include designated uses for fish consumption, recreation, and 
propagation and maintenance of a healthy, well-balanced population of 
fish and wildlife (Service 2020, appendix B). Further, the Florida 
Springs and Aquifer Protection Act of 2016 (2023 Florida Statutes at 
section 373.801-373.813) established Outstanding Florida Springs (OFSs) 
that require additional protections to ensure their conservation and 
restoration. Under this act, the State of Florida designated the 
Jackson Blue Spring within the Chipola River Basin as an OFS.
    Section 303(d) of the CWA (33 U.S.C. 1251 et seq.) requires states 
to identify waters that do not fully support their designated use 
classification, and so are deemed impaired. The most recent assessments 
within the range of Chipola slabshell and fat threeridge were completed 
by the FDEP and Alabama Department of Environmental Management (ADEM) 
as of 2018 and GDNR in 2022. Impaired water bodies are placed on each 
State's 303(d) list, and a total maximum daily load (TMDL) must be 
developed for the pollutant of concern. A TMDL is an estimate of the 
total load of pollutants that a segment of water can receive without 
exceeding applicable water quality criteria. There are several reasons 
why an impaired waterbody may be delisted, including but not limited 
to: a subsequent assessment determining that a waterbody-parameter is 
no longer impaired based on current water quality standards, if there 
has been a TMDL completed for the verified impaired parameter; or if a 
flaw in a previous assessment has been determined.
    Impaired waterbodies within watersheds occupied by Chipola 
slabshell and fat threeridge are largely impacted by fecal coliform. 
The standards for fecal coliform (e.g., Escherichia coli) relate to 
human health and do not necessarily reflect levels that would be 
harmful to mussels. While some waters are impaired due to nutrients or 
organic enrichment, these standards are in place to protect human 
health and do not relate directly to the potential effects of nutrients 
such as nitrogen on mussels. Monitoring results in Georgia indicate 
that approximately 60 percent of the streams are impaired for fecal 
coliform bacteria, with less than 2 percent for ammonia toxicity, which 
would adversely affect mussels, and those ammonia-impaired streams are 
not within the range of fat threeridge (GADNR 2022, p. 3-3). The 
numeric nutrient criteria (NNC) and ammonia standard in Florida reflect 
nutrient impact thresholds for mussels. This criterion includes total 
nitrogen (TN) and total phosphorus (TP) for flowing freshwaters. The TN 
NNC threshold concentrations are 0.67 mg/L for the Chipola River 
(Panhandle West), which is well below the newly adopted 1.408 mg/L 
ammonia concentration in Florida (Service 2016a, p. 6). Alabama also 
has a nitrate/nitrite nitrogen and ammonia standard in addition to 
other standards that are more representative of the potential harm to 
mussels than the nutrient or organic enrichment standard, which are no 
longer used as part of the water quality assessment process (ADEM 2018, 
pp. 11-14). Many of the delisted waterbodies were previously impaired 
due to elevated mercury levels in fish, which is also a human-health 
related standard (FDEP 2013, p. ii) that does not reflect levels that 
would be harmful to mussels. Given the parameters resulting in 
impairment and the establishment of TMDLs, water quality within the 
range of Chipola slabshell and fat threeridge is considered unimpaired 
in regards to freshwater mussel water quality thresholds.

Current Conditions

    Under the SSA framework, we assessed current resiliency, 
redundancy, and representation for Chipola slabshell and fat 
threeridge. Resiliency reflects a species' ability to withstand 
stochastic events (arising from random factors). Resiliency is measured 
at the population-level using metrics that characterize population 
health such as demographic rates and population size. We also consider 
the nature and extent of stressors to a species that could limit 
resiliency. Populations demonstrating resiliency are better able to 
withstand perturbations associated with demographic stochasticity 
(e.g., fluctuations in birth or mortality rates), environmental 
stochasticity (e.g., variation in precipitation or temperature), and 
anthropogenic activities. For the species to be considered viable, 
there must be adequate redundancy (suitable number, distribution, and 
connectivity of populations to allow the species to withstand 
catastrophic events). Redundancy improves with increasing numbers of 
populations distributed across the species range, and connectivity 
(either natural or human-facilitated) that allows connected populations 
to ``rescue'' each other after catastrophes. We can best gauge 
redundancy by analyzing the number and distribution of populations 
relative to the scale of anticipated species-relevant catastrophic 
events. Representation refers to the genetic and environmental 
diversity within and among populations that contributes to the ability 
of the species to respond and adapt to changing environmental 
conditions over time. The more representation, or diversity, a species 
has, the more it can adapt to changes (natural or human caused) in its 
environment. We can best gauge representation by examining the breadth 
of genetic, phenotypic, and ecological diversity found within a species 
and its ability to disperse and colonize new areas. For more 
information, see chapter 4 in each of the SSA reports (Service 2020, 
pp. 61-92; Service 2021, pp. 51-75).
Chipola Slabshell
    Our current condition analysis for the singular Chipola slabshell 
population describes the conditions of each of the three MUs (see table 
1, above). The magnitude and scale of potential impacts to Chipola 
slabshell or its habitat by a given threat are considered based on the 
condition of the watershed. Each HUC-10 watershed within the three MUs 
was rated as currently being in poor, fair, good, or excellent 
condition for each of the resiliency factors. Resiliency measures 
included two population factors (occupancy and abundance/recruitment) 
and two habitat factors (sedimentation and canopy) that were scored to 
provide overall MU resiliency (table 2, below). The four condition 
categories were then converted to numerical ranks and then a weighted 
average of the factor scores was calculated to generate an overall 
resiliency score. See the SSA report for details on the scoring 
methodology (Service 2020, pp. 89-91).

[[Page 85920]]



Table 2--Summary of Condition Categories and Resiliency Factors To Assess Chipola Slabshell's Current Resiliency
----------------------------------------------------------------------------------------------------------------
                                     Population factors (since 2005)                  Habitat factors
                              ----------------------------------------------------------------------------------
                                                                            Sedimentation index
                                                          Abundance &      ((a) Density of road   Canopy (% 200-
      Condition category             Occupancy          recruitment (#         crossings and      ft buffer with
                                  (proportion of        individuals and     transmission lines,  =50%
                                 occupied HUC-10s)        evidence of       percent non-natural    canopy cover
                                                         reproduction)      cover, and (b) soil  within assessed
                                                                              loss potential)     stream length)
----------------------------------------------------------------------------------------------------------------
Excellent....................  Consistent            >100 (live) during a  0-0.08: (a) minimal;  >90.
                                occupation in         given sampling        (b) low.
                                addition to newly     event; suggests a
                                occupied.             healthy population
                                                      (e.g., likely
                                                      ongoing
                                                      recruitment).
Good.........................  Consistent occupancy  10-100 (live or       0.09-0.23: (a & b)    76 to 90.
                                                      dead); more than      low.
                                                      one age class
                                                      represented.
Fair.........................  <50% Decreased        <10 individuals       0.24-0.36: (a & b)    50 to 75.
                                occupancy.            (live or dead);       moderate.
                                                      potentially
                                                      represented only by
                                                      older individuals
                                                      with limited
                                                      recruitment.
Poor.........................  >=50% Decreased       Only dead observed;   0.37-0.76: (a)        <50.
                                occupancy.            population            maximal; (b)
                                                      reduction likely      moderate to high.
                                                      not offset by
                                                      recruitment.
[Oslash].....................  No occupancy in HUC-  No records..........  N/A.................  N/A.
                                10.
----------------------------------------------------------------------------------------------------------------

    Within the single population for Chipola slabshell, there are 
currently two MUs that demonstrate moderate to high resiliency and one 
that has low resiliency (table 3, below). MU 1 has only one watershed, 
whereas MU 2 and MU 3 are each comprised of several watersheds. 
Although the range is narrow (i.e., solely within the Chipola River), 
current occupancy of the entire range is evident. Sedimentation, a risk 
to all mussels, is not a threat in the Chipola River Basin, as 
indicated by good to excellent indices in all but two areas of MU 3. 
Although the resiliency of MU 3 is overall low, we note that occupancy 
is excellent throughout this MU. The SSA report noted that the species 
is thought to occur in relatively low densities naturally, and the 
northern part of the range in MU 3 is considered marginal habitat for 
the slabshell (Service 2020, p. 92). Thus, Chipola slabshell exhibits 
sufficient resiliency throughout its current range, contributing to 
overall species viability.

                                   Table 3--Summary of Current Resiliency for Chipola Slabshell Management Units (MUs)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                         Population factors                   Habitat factors
                                                -----------------------------------------------------------------------                     Overall MU
              MU                    HUC-10s                           Abundance &      Sedimentation                    Watershed score     resiliency
                                                     Occupancy       reproduction          index            Canopy
--------------------------------------------------------------------------------------------------------------------------------------------------------
1............................  River Styx &      Excellent.......  Good............  Excellent.......  Excellent......  High...........  High.
                                Douglas Slough.
2............................  Merritts Mill     Good............  Good............  Good............  Excellent......  Moderate.......  Moderate.
                                Pond--South.
                               Mill Creek......  Good............  Excellent.......  Good............  Good...........  Moderate.......
                               Tenmile Creek...  Good............  Excellent.......  Excellent.......  Good...........  High...........
                               Dead Lake.......  Good............  Good............  Excellent.......  Good...........  Moderate.......
3............................  Marshall Creek..  Excellent.......  Fair............  Fair............  Good...........  Low............  Low.
                               Cowarts Creek...  Excellent.......  Good............  Fair............  Good...........  Moderate.......
                               Merritts Mill     Excellent.......  Fair............  Good............  Excellent......  Moderate.......
                                Pond--North.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    High redundancy for Chipola slabshell is defined as multiple 
resilient MUs distributed throughout the species' range. Two-thirds of 
the species' range has moderate to high levels of resiliency. We 
considered all three MUs as contributing to redundancy, thus enabling 
the species to withstand catastrophic events. Most of the population is 
not currently at risk from habitat modification, indicated by high-
ranking habitat factors and watershed scores (table 3, above), and 
there is a high degree of land protection where the Chipola slabshell 
habitat is buffered by forested public lands, protecting water quality 
and ensuring the viability of the population and ultimately the species 
as a whole.
    Representation, which refers to the breadth of genetic and 
environmental diversity within and among populations, reflects the 
species' adaptive capacity. Currently, there is limited information 
pertaining to genetic variation and no evidence to support delineating 
multiple representation units for Chipola slabshell (Service 2020, p. 
74). However, the breadth of environmental diversity within the range 
(e.g., the north-south gradient with headwater streams to mainstems of 
the Chipola River and the Apalachicola River) is currently occupied. 
Our knowledge of the level of genetic diversity for Chipola slabshell 
is

[[Page 85921]]

limited; however, it is possible subpopulations exhibit some natural 
variation in genetic diversity. Chipola slabshell representation has 
not likely changed over time, but as a narrow endemic, the species' 
adaptive potential is limited.
Fat Threeridge
    Current condition for fat threeridge describes the condition of the 
six analysis units. Characteristics of resiliency for fat threeridge 
include evidence of stable or increasing population trends, and 
evidence of reproduction (either direct observation of juveniles, or of 
multiple age classes as inferred by length data). An adequate number of 
resilient populations should be distributed throughout the species 
range to both protect adaptive capacity of the species, and protect 
from catastrophic events. We analyzed the resilience of units within 
the range of fat threeridge slightly differently than we did for 
Chipola slabshell due to differences in habitat use and perceived 
stressors. We assessed demographic resiliency factors including 
abundance, recruitment, and occupancy which inform population trends 
within the population, and we evaluated habitat resiliency factors 
related to water quality and water quantity to establish a baseline 
from which to project future condition (table 4, below).

                     Table 4--Summary of Condition Categories and Resiliency Factors To Assess Current Resiliency for Fat Threeridge
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                               Population factors                                          Habitat factors
         Condition category         --------------------------------------------------------------------------------------------------------------------
                                            Abundance              Recruitment         Habitat occupancy        Water quality          Water quantity
--------------------------------------------------------------------------------------------------------------------------------------------------------
High...............................  Recent density and      Presence of multiple    71-100% or maximal     No known or            Lower relative risk
                                      population estimate     age classes             occupancy.             anticipated            of direct and
                                      at high end of known    (individuals > and                             contaminant or         indirect impacts to
                                      range (>1 per square    <50 mm); small                                 sediment problems      the survival,
                                      meter (m\2\); >1        individuals (<=35 mm)                          given the land cover.  health, or
                                      million). Increasing    detected using                                                        recruitment of
                                      or stable population    hydraulic dredge                                                      species from low
                                      trend.                  methods.                                                              flow events.
Moderate...........................  Recent density and      Presence of multiple    31-70% or              Associated             N/A.
                                      population estimate     age classes             intermediate           contaminant or
                                      at lower end of known   (individuals > and      occupancy.             sediment issues are
                                      range (<=1/m\2\ to      <50 mm); but no small                          likely in some areas.
                                      0.11/m\2\; >100k to 1   individuals (<=35 mm)
                                      million). Increasing    detected using
                                      or stable population    hydraulic dredge
                                      trend.                  methods.
Low................................  No population           Only one size class     <30% or minimal        Associated             Higher relative risk
                                      estimate, generally     >=50 mm; no small       occupancy.             contaminant or         of direct and
                                      known to be present     individuals (<=35 mm)                          sediment issues        indirect impacts to
                                      at low density (5-10    detected using                                 increases the risk     the survival,
                                      individuals minimum     hydraulic dredge                               of negative impacts    health, or
                                      and/or <=0.1/m\2\).     methods.                                       throughout habitat.    recruitment of
                                      Possible stable trend                                                                         species from low
                                      since 2000, but                                                                               flow events.
                                      undetectable in the
                                      past.
Very Low...........................  Not assessed (N/A)....  N/A...................  N/A..................  Associated             N/A.
                                                                                                             contaminant or
                                                                                                             sediment levels pose
                                                                                                             the highest relative
                                                                                                             risk to habitat;
                                                                                                             Significant,
                                                                                                             widespread, or
                                                                                                             prolonged impacts
                                                                                                             likely occurring.
[Oslash]...........................  None..................  None..................  None.................  N/A..................  Intermittent flow; no
                                                                                                                                    survival.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    For each population and habitat factor, we considered whether the 
analysis units were currently in high, moderate, low, or very low 
condition (table 5, below). None of the analysis units are extirpated 
or in very low condition. The average of factor rankings was used to 
generate an overall resiliency score. For more details on the scoring 
methodology, see chapter 4 of the SSA report (Service 2021, pp. 56-70).

                                            Table 5--Fat Threeridge Resiliency Factors and Overall Resiliency
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                      Population factors                                  Habitat factors
                                 ----------------------------------------------------------------------------------------------------
          Analysis unit                                   Evidence of                                                                 Overall resiliency
                                       Abundance          recruitment         Occupation         Water quality      Water quantity
--------------------------------------------------------------------------------------------------------------------------------------------------------
Lower Flint.....................  Low...............  High..............  High..............  Low...............  High..............  Moderate.
Upper Apalachicola..............  Moderate..........  High..............  Low...............  Moderate..........  High..............  Moderate.
Middle Apalachicola.............  High..............  High..............  High..............  High..............  High..............  High.
Lower Apalachicola..............  Moderate..........  High..............  Moderate..........  High..............  High..............  High.
Lower Chipola...................  High..............  High..............  High..............  Moderate..........  High..............  High.
Chipola NDL *...................  Low...............  High..............  High..............  Moderate..........  High..............  Moderate.
--------------------------------------------------------------------------------------------------------------------------------------------------------
* North of Dead Lakes.

    Overall, fat threeridge is more abundant (currently estimated at 
approximately 12 million individuals) and more widely distributed than 
when the species was listed (Service 2021, p. 47). When the species was 
listed in 1998, the most individuals seen at a site was 6 (63 FR 
12666); current estimates across 164 sites in the middle Appalachicola 
alone are over 7.7 million individuals (Service 2021, p. 47). The 
positive trends for both population and habitat factors, including 
relatively large population sizes, are indicative of populations that 
are resilient to stochastic factors. Redundancy for the fat threeridge 
is moderate to high, as currently all analysis units in the species 
range exhibit moderate to high resiliency. Each unit contributes to 
overall species

[[Page 85922]]

redundancy, or the ability of the species to withstand catastrophic 
events. Further, the species currently has not had a contraction or 
disruption of connectivity (such as from an impoundment) within its 
range and this connectivity corresponds to a lowered risk of 
extirpation from catastrophic events (Service 2021, p. 72).
    The available genetic data for fat threeridge suggests little 
variation across the species range. This is supported by the absence of 
notable behavioral, morphological, or life history variation. This 
suggests genetic variation within the species is low. However, the 
species maintains ecological diversity in its occupancy of different 
river ``types'' (e.g., small and large river systems) and ecoregions 
(e.g., Southeastern Plains and Southern Coastal Plain). Overall, 
representation or adaptive capacity of fat threeridge is limited, as 
supported by little genetic variation within a narrow geographic range.

Future Conditions

    The main factor influencing the viability of both Chipola slabshell 
and fat threeridge is habitat degradation or loss through land use 
change (e.g., urbanization, agriculture). Land use change can lead to 
direct impacts on viability through increases in sedimentation and 
contaminants within waters occupied by each mussel species. Predicting 
future stream-channel conditions, particularly sedimentation, in the 
ACF River Basin remains a challenge, as the ongoing remobilization of 
sediments is difficult to separate from the cumulative effects of 
climate and land-use change (Elliott et al. 2014, p. 66). An increase 
in the contaminant load from incompatible land uses is expected to 
continue in varying degrees, depending on a combination of factors 
including the impacts of climate change across the landscape, with 
habitat degradation or loss likely to be more significant in some MUs/
analysis units compared to others. We attempted to discern this 
variance by analyzing spatially explicit models of future land use and 
climate change as indicators of associated water quality and water 
quantity conditions.
    We identified the main drivers of change for the future scenario 
analyses to be human population growth and subsequent urbanization and 
land use change. Land use change may have synergistic effects with 
climate change, so several common climate projections are considered in 
the assessment of future condition. Species and ecosystems are impacted 
by the habitat degradation and loss associated with population growth, 
including impacts to water pollution, local climate conditions, and 
disturbance dynamics.
Chipola Slabshell
    Future conditions of the Chipola slabshell were assessed under 
three plausible future scenarios (lower, moderate, and higher) 
incorporating a range of conditions associated with climate and land 
use change (Service 2020, pp. 96-125). The future scenarios were based, 
in part, on the results of climate-informed land use change (USGS's 
FOREcasting SCEnarios of Land-use Change (FORE-SCE)), with special 
report emissions scenario (SRES) B1 for the lower range, SRES A1B for 
moderate, and SRES A2 for the higher range, combined with 
Intergovernmental Panel on Climate Change (IPCC) climate models, with 
representative concentration pathway (RCP) 4.5 for the lower range, RCP 
6.0 for moderate, and RCP 8.5 for higher range, that projected general 
changes in habitat used by the Chipola slabshell. The factors that 
influence resiliency in the species (e.g., occupancy, abundance, 
sediment, canopy) either change minimally from the current condition 
(lower range scenario) or worsen to a moderate (moderate range 
scenario) or greater degree (higher range scenario) based on potential 
future climate and land use and their impacts on water quality and 
quantity. The expected future resiliency of each MU was forecasted 
based on events that were projected to occur under each scenario 
(Service 2020, pp. 208-133). All scenarios assumed that current 
conservation efforts, which are in place regardless of listing status, 
would remain in place but that no new actions would be taken. As with 
current condition estimates, estimates were scaled up to MU and the 
population levels (table 6, below).
    The three scenarios project Chipola slabshell viability 20 and 40 
years into the future, with each timestep representing approximately 
two generations. This projection was chosen to represent a time frame 
where climate change impacts may become apparent, while effects of 
management actions can be implemented and realized on the landscape. 
The 40-year timeframe, which includes approximately 4 to 5 generations, 
is also reasonable for this relatively long-lived (15 to 20 years) 
species, with relatively low fecundity, to respond to potential changes 
on the landscape.

   Table 6--Resiliency Summary for Chipola Slabshell MUs Including Current Condition, and Each of Three Future Scenarios (Lower, Moderate, Higher Range) at the End of the 40-Year Assessment
                                                                                             Period
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                Current                      Lower range scenario               Moderate range scenario              Higher range scenario
                                 Watershed (HUC- -----------------------------------------------------------------------------------------------------------------------------------------------
              MU                       10)                             Overall MU                          Overall MU                          Overall MU                          Overall MU
                                                   Watershed score     resiliency      Watershed score     resiliency      Watershed score     resiliency      Watershed score     resiliency
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.............................  River Styx &      High............  High............  High............  High............  High............  High............  Moderate........  Moderate.
                                 Douglas Slough.
2.............................  Merritts Mill     Moderate........  Moderate........  Moderate........  Moderate........  Low.............  Moderate........  Very Low........  Low.
                                 Pond--South.     Moderate........                    High............                    Moderate........                    Moderate........
                                Mill Creek......  High............                    High............                    High............                    High............
                                Tenmile Creek...  Moderate........                    Moderate........                    Moderate........                    Moderate........
                                Dead Lake.......
3.............................  Marshall Creek..  Low.............  Low.............  Low.............  Low.............  Very Low........  Very Low........  Very Low........  Very Low.
                                Cowarts Creek...  Moderate........                    Moderate........                    Very Low........                    Very Low........
                                Merritts Mill     Moderate........                    Moderate........                    Low.............                    Low.............
                                 Pond--North.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

    In the lower range scenario, we project no loss in MU resiliency 
and redundancy compared to the current condition. Management units 1 
and 2 would retain resiliency (in high or moderate resiliency), and MU 
3 would remain at low resiliency. For this scenario, the Chipola 
slabshell population is expected to persist in much the same condition 
as it is found currently, with some increases in watershed resilience 
through time given positive trends (e.g., future forest cover, recent 
population expansions).

[[Page 85923]]

    In the moderate range scenario, a loss of some resiliency and 
redundancy is expected. Management units 1 and 2 retain resiliency, but 
MU 3 may become extirpated given its overall very low resiliency. The 
one watershed in MU 1 is expected to retain high resiliency. The 
condition of MU 2 is expected to decrease slightly, with reduced 
resiliency in one (of four) watersheds by 2060. Management unit 2 is 
expected to retain more than one watershed with moderate or high 
resiliency, while MU 3 is expected to retain only one occupied 
watershed (Merritts Mill Pond--North), in low resiliency.
    In the higher range scenario, we anticipate impacts to resiliency 
in all management units. Management unit 1 has moderate resiliency with 
a reduced capacity to mitigate stochastic events. Management units 2 
and 3 exhibit reduced resiliency (low and very low, respectively), with 
MU 3 likely extirpated. Management unit 2 retains resiliency in the 
center of the Chipola slabshell range within the Mill Creek and Tenmile 
Creek watersheds, with sparse to no observable presence in the Merritts 
Mill Pond--South and Dead Lake watersheds. Similar to the moderate 
range scenario, redundancy would be reduced to three watersheds with 
likely extirpation in three of eight currently extant watersheds. Only 
MU 2 retains more than one watershed with resiliency, and MU 3 retains 
only one occupied watershed (Merritts Mill Pond--North) with low 
resiliency.
    The northern portion of the species range comprising the Chipola 
River headwaters (MU 3) was the most susceptible to change through 
time; MU 3 has low resiliency for current condition and is projected to 
have very low resiliency under the higher range scenario. It is 
important to note that the habitat in MU 3 is thought to be inherently 
variable with regards to sedimentation and has overall low suitability 
for Chipola slabshell. With the exception of small portions of MUs 1 
and 3, almost the entirety of the Chipola slabshell population is 
contained within the Chipola River mainstem in MU 2. Management unit 2 
is projected to retain moderate resiliency to 2060 under the lower and 
moderate range scenarios, but resiliency is reduced by 2060 under the 
higher range scenario. Management unit 2 retains one watershed (Tenmile 
Creek) at high resiliency through all scenarios and projection periods. 
Management unit 1 is also projected to retain high to moderate 
resiliency under all scenarios, benefitting from the presence of 
extensive protected areas and more suitable large stream habitats for 
Chipola slabshell.
Fat Threeridge
    Based on our review of factors affecting viability of fat 
threeridge, we focused our evaluation of future conditions on projected 
habitat degradation associated with two prevalent land uses in the ACF 
River Basin, agricultural and urban development, and their associated 
stressors to water quality and quantity. We also assessed potential 
impacts of SLR in lower portions of the Apalachicola and Chipola Rivers 
through removal of suitable habitat from projected saltwater 
inundation. We assessed resiliency, redundancy, and representation for 
fat threeridge under three SLR threat levels (intermediate, high, and 
extreme) and two multi-faceted scenarios incorporating variations in 
future land and water use. We summarized changes in land use within 
each of the fat threeridge analysis subwatersheds to assess future 
changes in nonpoint source pollution. We assessed both the change in 
the percent forested area in riparian buffers, and also the degree of 
urbanization and agricultural land use within subwatersheds, similar to 
what we assessed in current condition. To assess future water quantity, 
we used the same modeling outputs as in current condition, which 
provided annual predictions for the time frame 2045-2075. We extracted 
results for two climate scenarios, RCP 4.5 and RCP 8.5, to bound 
plausible future outcomes and compared these against a historical 
simulated state (1950-2005). Annual inputs of both historical and 
potential future land-cover type and percent impervious area were used 
to incorporate the effects of changing vegetation and impervious area.
    Scenario 1 assumes that conditions in the ACF River Basin continue 
for the next 50 years along their current trajectory, with climate 
change trajectories for SRES A2 and RCP 8.5 incorporated. Scenario 2 
assumes that conditions in the ACF River Basin continue for the next 50 
years along a modified trajectory, with climate change trajectories for 
SRES B1 and RCP 4.5 incorporated. We analyzed these future threats and 
their effects on habitat as indicators of directional change in 
resiliency compared to the current condition (table 7, below). We 
modeled threats 50 years into the future to project the conditions of 
analysis units in 2070. This timeframe is biologically appropriate 
(representing two or three generations) and within the available and 
reliable modeling timeframe for projecting future threats. The 50-year 
timeframe, which includes approximately 4 to 5 generations, is also 
reasonable for this relatively long-lived (15 to 40 years) species, 
with relatively low fecundity, to respond to potential changes on the 
landscape. Timeframes earlier than 2070 may be too short to observe a 
species response (based on a lifespan of at least 30 years) or change 
in threats, and beyond 2070 were considered too far into the future to 
reliably account for either. The land and water use threat assessment 
was completed within the six analysis units.

                                   Table 7--Summary of Fat Threeridge Current and Future Resiliency by Analysis Unit *
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                 Future intermediate sea level rise         Future high SLR \2\              Future extreme SLR \2\
                                    Current                     (SLR)               --------------------------------------------------------------------
        Analysis unit             resiliency    ------------------------------------
                                                  Scenario 1 \1\      Scenario 2        Scenario 1        Scenario 2       Scenario 1       Scenario 2
--------------------------------------------------------------------------------------------------------------------------------------------------------
Lower Flint..................  Mod.............  Mod.............  Mod.............  Mod.............  Mod............  Mod............  Mod.
Upper Apalachicola...........  Mod.............  Mod.............  Mod.............  Mod.............  Mod............  Mod............  Mod.
Middle Apalachicola..........  High............  Mod.............  High............  Mod.............  High...........  Mod............  High.
Lower Apalachicola...........  High............  High............  High............  Low.............  Low............  Low............  Low.
Lower Chipola................  High............  High............  High............  High............  High...........  Low............  Low.
Chipola NDL..................  Mod.............  Mod.............  Mod.............  Mod.............  Mod............  Mod............  Mod.
--------------------------------------------------------------------------------------------------------------------------------------------------------
* Changes in water quality and quantity inform degree of habitat degradation for scenarios 1 and 2, while NOAA SLR projections (intermediate and high)
  influence habitat removal by 2070.
\1\ Scenario 1 includes changes in water quality for the Middle Apalachicola that result in partial habitat degradation.
\2\ High and Extreme SLR involves partial removal of Lower Apalachicola.


[[Page 85924]]

    Future habitat degradation associated with land use change is not 
expected to impact fat threeridge significantly. No analysis units are 
projected to become extirpated under any scenario, but one high 
resiliency unit (Lower Apalachicola) may transition to low resiliency 
in the future primarily due to SLR effects. Redundancy is maintained in 
the future, regardless of scenario, as most (four of six) analysis 
units retain moderate to high resiliency under the most severe 
projections. Even under high SLR, fat threeridge is projected to 
maintain representation in each river system (i.e., Apalachicola, 
Chipola, and Flint) and in each ecoregion (i.e., Southeastern Plains 
and Southern Coastal Plain).
    By using the SSA framework to guide our analyses of scientific 
information documented in the SSA reports, we have analyzed both 
individual and cumulative effects on each species through 
characterizing species condition currently and under various plausible 
future scenarios. We assumed in our modeling of future conditions for 
both species that increased habitat degradation could result from 
increased land use or from climate change, or a combination. The 
impacts of climate change, along with habitat degradation or loss, are 
likely to be more significant in some MUs/analysis units than others, 
however, our projections indicate that both species maintain 
resiliency. Both species are projected to maintain a broad distribution 
throughout the ACF River Basin, across a variety of habitats and under 
both continuation and increased threat scenarios, meaning 
representation and redundancy are not expected to change.
    We note that, by using the SSA framework to guide our analysis of 
the scientific information documented in the SSA reports, we have 
analyzed the cumulative effects of identified threats and conservation 
actions on these species. To assess the current and future condition of 
each species, we evaluate the effects of all the relevant factors that 
may be influencing the species, including threats and conservation 
efforts. Because the SSA framework considers not just the presence of 
the factors, but to what degree they collectively influence risk to the 
entire species, our assessment integrates the cumulative effects of the 
factors and replaces a standalone cumulative-effects analysis.

Recovery Criteria

    Section 4(f) of the Act directs us to develop and implement 
recovery plans for the conservation and survival of endangered and 
threatened species unless we determine that such a plan will not 
promote the conservation of the species. Under section 4(f)(1)(B)(ii), 
recovery plans must, to the maximum extent practicable, include 
objective, measurable criteria which, when met, would result in a 
determination, in accordance with the provisions of section 4 of the 
Act, that the species be removed from the Lists of Endangered and 
Threatened Wildlife and Plants.
    Recovery plans provide a roadmap for us and our partners on methods 
of enhancing conservation and minimizing threats to listed species, as 
well as measurable criteria against which to evaluate progress towards 
recovery and assess the species' likely future condition. However, they 
are not regulatory documents and do not substitute for the 
determinations and promulgation of regulations required under section 
4(a)(1) of the Act. A decision to revise the status of a species or to 
delist a species is ultimately based on an analysis of the best 
scientific and commercial data available to determine whether a species 
is no longer an endangered species or a threatened species, regardless 
of whether that information differs from the recovery plan.
    There are many paths to accomplishing recovery of a species, and 
recovery may be achieved without all of the criteria in a recovery plan 
being fully met. For example, one or more criteria may be exceeded 
while other criteria may not yet be accomplished. In that instance, we 
may determine that the threats are minimized sufficiently and that the 
species is robust enough that it no longer meets the definition of an 
endangered species or a threatened species. In other cases, we may 
discover new recovery opportunities after having finalized the recovery 
plan. Parties seeking to conserve the species may use these 
opportunities instead of methods identified in the recovery plan. 
Likewise, we may learn new information about the species after we 
finalize the recovery plan. The new information may change the extent 
to which existing criteria are appropriate for identifying recovery of 
the species. The recovery of a species is a dynamic process requiring 
adaptive management that may, or may not, follow all of the guidance 
provided in a recovery plan.
    In 2003, we published a recovery plan for seven mussel species, 
including the Chipola slabshell and fat threeridge (Service 2003, 
entire). In 2019, we amended the Chipola slabshell and fat threeridge 
recovery plans to revise the recovery criteria and site-specific 
recovery actions (Service 2019a, entire; Service 2019b, entire). Both 
recovery plans for the Chipola slabshell and fat threeridge provide 
three criteria for delisting.

Chipola Slabshell

    For Chipola slabshell, the criteria to delist are: (1) the one 
existing population must exhibit a stable or increasing trend, natural 
recruitment, and multiple age classes; (2) the population from 
criterion 1 occupies each of the three delineated units to protect 
against extinction from catastrophic events and maintain adaptive 
potential; and (3) threats are addressed and/or managed to the extent 
that the species will remain viable into the foreseeable future.
Criterion 1
    Criterion 1 states that the one existing population must exhibit a 
stable or increasing trend, natural recruitment, and multiple age 
classes. Currently, the Chipola slabshell is known from one panmictic 
population within the Chipola River Basin. It is currently widespread 
throughout its range and common at some localities. The comparison 
between historical and current distribution shows an expansion north, 
south, and east of the species' previously known range. Occupancy has 
increased over time, although the magnitude of this estimate varies 
with spatial scale. Prior to 1991, the Chipola slabshell occupied 46 km 
(29 mi) in 6 U.S. Geological Survey (USGS) 10-digit hydrologic unit 
codes (HUC-10s) watersheds, and its current range has expanded to 
occupy 112 km (69 mi) in 7 HUC-10 watersheds. This increase in 
occupancy suggests a robust distribution throughout the known range 
(Service 2020, p. 62).
    Our current condition resiliency analysis examined abundance and 
reproduction across the range. Currently two HUC-10 watersheds have 
excellent abundance and reproduction, four HUC-10 watersheds have good 
abundance and reproduction, and two HUC-10 watersheds have fair 
abundance and reproduction. While there are some portions of the range 
with lower abundances and levels of recruitment, overall the Chipola 
slabshell population has multiple age classes showing natural 
recruitment, and the species has an expanded range. Thus, we conclude 
that this criterion has been met for Chipola slabshell.
Criterion 2
    Criterion 2 states the population (as identified in criterion 1) 
occupies each of the three delineated units to protect against 
extinction from catastrophic

[[Page 85925]]

events and maintain adaptive potential. All three delineated units, or 
subpopulations, of Chipola slabshell are currently occupied, with two 
of the three having moderate to high resiliency. Thus, we conclude that 
this criterion has been met for Chipola slabshell.
Criterion 3
    Criterion 3 for consideration of delisting Chipola slabshell states 
that threats have been addressed or managed to the extent that the 
species will remain viable into the foreseeable future. At the time of 
listing, Chipola slabshell faced a variety of threats from declines in 
water quality, loss of stream flow, riparian and instream 
fragmentation, and deterioration of instream habitats. Additionally, 
these threats were expected to be exacerbated by climate change and 
urbanization.
    Future water quantity models (updated every 5 years) in the Chipola 
River Basin have projected adequate water supply for citizens and the 
environment through 2045, even in drought years (NFWMD 2023, p. ix). 
Water flows for most of the Chipola slabshell's occupied range are 
protected through consumptive uses by water reservation (legal 
protection), while other areas are supported by ground water 
contributions from springs during drought (Service 2020, pp. 96-139). 
Urbanization models have projected little growth in the river basin 
through 2060 (Service 2020, pp. 27-60 and pp. 95-138).
    During the most recent status review, there was no documentation of 
any significant threats to the species or its habitat, as well as no 
evidence that the species has experienced curtailment of range or 
habitat, or is affected by disease or predation, commercial or 
recreational harvest, the inadequacy of existing regulatory mechanisms, 
or any other natural or manmade factor (Service 2020, p. 140). Thus, we 
conclude that this criterion has been met for Chipola slabshell.

Fat Threeridge

    For fat threeridge, the criteria to delist are: (1) at least four 
populations exhibit a stable or increasing trend, evidenced by natural 
recruitment and multiple age classes; (2) at last one population from 
criterion 1 occupies each of the Flint and Chipola Rivers sub-basins, 
and one population occupies two of the three delineated units in the 
Apalachicola River sub-basin for fat threeridge; (3) threats have been 
addressed or managed to the extent that each species will remain viable 
into the foreseeable future (Service 2019a, pg. 4, and Service 2019b, 
pg. 6).
Criterion 1
    Criterion 1 states that at least four populations exhibit a stable 
or increasing trend, evidenced by natural recruitment and multiple age 
classes. Since the last 5-year review in 2007, our knowledge of fat 
threeridge has increased substantially in all three river systems, 
including what we know about distribution, habitat use, and life 
history characteristics relevant to species recovery. As a result, we 
now consider the fat threeridge to consist of one population, with six 
analysis units. Further, we know that the species occupies most 
watersheds where it was found historically, and our resiliency analysis 
indicates that the species maintains moderate to high resiliency in the 
six analysis units. One of the population factors for resiliency is 
evidence of recruitment, and all six units exhibit recruitment through 
observation of small size classes. Its range has expanded in the 
Chipola and Apalachicola Rivers in Florida. Furthermore, fat threeridge 
is more abundant and widely distributed among mesohabitats than 
previously thought, including within deep habitats (Service 2021, pp. 
54-55). Thus, fat threeridge has stable trends in all six units, and 
high levels of recruitment, with an overall indication that multiple 
age classes exist in each unit throughout the population. For these 
reasons, we conclude that fat threeridge has met this criterion.
Criterion 2
    Criterion 2 for consideration of delisting fat threeridge states 
that at least one population occupies each of the Flint and Chipola 
Rivers sub-basins and in the Apalachicola River sub-basin at least one 
population occupies two of the three delineated units (Service 2019b, 
p. 6). As described in the SSA report, there are six subpopulations 
(also referred to as analysis units): one in the Flint, three in the 
Apalachicola, and two in the Chipola Rivers sub-basins (Service 2021, 
p. 52). Resiliency is moderate in the Lower Flint, Upper Apalachicola, 
and Chipola North of Dead Lakes analysis units; it is high in the 
Middle Apalachicola, Lower Apalachicola, and Lower Chipola analysis 
units (Service 2021, p. 69). Based on this, we conclude that criterion 
2 has been met for fat threeridge.
Criterion 3
    Criterion 3 for consideration of delisting fat threeridge states 
that threats have been addressed or managed to the extent that the 
species will remain viable into the foreseeable future. The primary 
threats to fat threeridge include land use change resulting in reduced 
water quality and quantity, and effects associated with climate change, 
including sea level rise (SLR). Our future conditions analysis 
indicates that at the watershed scale, the amount of land development 
through 2070 is projected to be low across all scenarios (Service 2021, 
pp. 115-116). No analysis units are expected to become extirpated, but 
two high resiliency units (Lower Apalachicola, Lower Chipola) may 
transition to low resiliency in the future as a result of SLR effects 
as projected in the high SLR scenarios (Service 2021, p.127).
    Redundancy is maintained under future scenarios, as most (four of 
six) analysis units retain resiliency under the most severe 
projections, and no change from the current condition is expected under 
intermediate SLR. Even under extreme SLR, ecoregion and river 
representation for fat threeridge is maintained.
    Increased sampling efforts and a better understanding of the 
species' habitat associations indicate a wider distribution of the fat 
threeridge than previously understood. In general, fat threeridge is 
more abundant and widely distributed among habitats than previously 
thought. Habitat mapping and species distribution modeling in the 
Apalachicola and Lower Chipola Rivers indicates sufficient abundance of 
habitat for the fat threeridge in these populations; similar habitat 
mapping has not been done at that scale for the Flint River, but 
habitat for the population at Newton, Georgia has supported the fat 
threeridge since 2006 (Service 2021, pp. 41-50). For these reasons, we 
conclude that this criterion has been met for fat threeridge.

Determinations of Chipola Slabshell and Fat Threeridge Status

    Section 4 of the Act (16 U.S.C. 1533) and its implementing 
regulations (50 CFR part 424) set forth the procedures for determining 
whether a species meets the definition of an endangered species or a 
threatened species. The Act defines an ``endangered species'' as a 
species that is in danger of extinction throughout all or a significant 
portion of its range, and a ``threatened species'' as a species that is 
likely to become an endangered species within the foreseeable future 
throughout all or a significant portion of its range. The Act requires 
that we determine whether a species meets the definition of an 
endangered species or a threatened

[[Page 85926]]

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 Their Range

    After evaluating the threats to these species and assessing the 
cumulative effects of the threats under the Act's section 4(a)(1) 
factors, we find that both the Chipola slabshell and fat threeridge 
have expanded distributions with nearly all populations having moderate 
to high resiliency and projections to maintain resiliency into the 
future. The primary threat at the time of listing was habitat loss and 
destruction. Based on our analyses of the current and future condition 
for the Chipola slabshell and fat threeridge, each species currently 
has sufficient resiliency and is projected to maintain resiliency into 
the future such that each species can withstand stochastic and 
catastrophic effects from existing and future threats. Together the 
current and future conditions analyses informed our determination as to 
whether each species is in danger of extinction throughout all of its 
range (i.e., whether each species meets the definition of an endangered 
species under the Act) or whether each species is in danger of 
extinction throughout all of its range in the foreseeable future (i.e., 
whether each species meets the definition of a threatened species under 
the Act). Our determinations for each species are discussed below.

Chipola Slabshell--Status Throughout All of Its Range

    The Chipola slabshell is currently widespread throughout its range 
and considered common at some localities. Since the time of listing, 
surveys indicate expansion of its previously known range. Two-thirds of 
the range have moderate to high resiliency, and the one MU, or sub-
population, that has low resiliency (MU 3) has a high proportion of 
marginal habitat for the species, and naturally low numbers of Chipola 
slabshell. Despite this, occupancy is good to excellent throughout the 
range. To summarize the species' current condition, the Chipola 
slabshell has sufficient resiliency to withstand stochastic events, as 
well as sufficient redundancy in the distribution of subpopulations 
with moderate to high resiliency such that the species can withstand 
catastrophic events.
    Potential threats to the species, including habitat degradation 
which led to the species being listed, appear to be well managed or 
minimized to the greatest extent possible either through protection, 
implementation of BMPs, and regulations in CWA or State OFW 
designations. Sedimentation, which is usually a major threat for mussel 
species, is not a current threat to Chipola slabshell in the Chipola 
River Basin. Thus, after assessing the best available information, we 
determine that Chipola slabshell is not in danger of extinction 
throughout all of its range.
    We next evaluate whether the Chipola slabshell is likely to be in 
danger of extinction throughout its range within the foreseeable 
future. We considered climate change and land use change as primary 
stressors influencing habitat degradation and loss, and we developed 
three scenarios that project Chipola slabshell viability 40 years into 
the future. This 40-year foreseeable future includes a time frame where 
both climate change and land use change effects will become apparent on 
the landscape. The timeframe also includes up to five generations which 
we consider reasonable for this relatively long-lived (15 to 20 years), 
low fecundity species to respond to potential changes on the landscape. 
We are able to reliably predict both the threats to the species and the 
species' response to those threats within this timeframe.
    Almost the entirety of the Chipola slabshell population is 
contained within the Chipola River mainstem. The core of the population 
(MU 2) is projected to retain moderate resiliency to 2060 under the 
Lower and Moderate Range Scenarios, but resiliency could be reduced by 
2060 under the higher range scenario. Despite this, two thirds of the 
watersheds that make up MU 2 retain moderate to high resiliency through 
all scenarios and projection periods. In addition, MU 1 is also 
projected to retain moderate to high resiliency under all scenarios, 
benefitting from the presence of extensive protected areas and 
available suitable large stream habitats for Chipola slabshell. Thus, 
species' viability is sustained within two of the three MUs into the 
future. The species' ability to retain resiliency 40 years into the 
future supports the determination that the Chipola slabshell is not in 
danger of extinction throughout all of its range in the foreseeable 
future.
    Thus, after assessing the best available information, we conclude 
that Chipola slabshell is not in danger of extinction now or likely to 
become so in the foreseeable future throughout all of its range.

Chipola Slabshell--Status Throughout a Significant Portion of Its Range

    Under the Act and our implementing regulations, a species may 
warrant listing if it is in danger of extinction or likely to become so 
in the foreseeable future throughout all or a significant portion of 
its range. Having determined that the Chipola slabshell is not in 
danger of extinction or likely to become so in the foreseeable future 
throughout all of its range, we now consider whether it may be in 
danger of extinction (i.e., endangered) or likely to become so in the 
foreseeable future (i.e., threatened) in a significant portion of its 
range--that is, whether there is any portion of the species' range for 
which both (1) the portion is significant; and, (2) the species is in 
danger of extinction or likely to become so in the foreseeable future 
in that portion. Depending on the case, it might be more efficient for 
us to address the ``significance'' question or the ``status'' question 
first. We can choose to address either question first. Regardless of 
which question we address first, if we reach a negative answer with 
respect to the first question that we address, we do not need to 
evaluate the other question for that portion of the species' range.
    In undertaking this analysis for the Chipola slabshell, we choose 
to address the status question first. We began by identifying portions 
of the range where the biological status of the species may be 
different from its biological status elsewhere in its range. For this 
purpose, we considered information pertaining to the geographic 
distribution of (a) individuals of the species, (b) the threats that 
the species faces, and (c) the resiliency condition of populations.
    We evaluated the range of the Chipola slabshell to determine if the 
species is in danger of extinction now or likely to become so in the 
foreseeable future in any portion of its range. The range of a species 
can theoretically be divided into portions in an infinite number of 
ways. We focused our analysis on portions of the species' range that 
may meet the definition of an endangered species or a threatened 
species. For the Chipola slabshell, we considered whether the threats 
or their effects on the species are greater in any biologically 
meaningful portion of the species' range than in other portions such 
that the species is in danger of extinction now or likely to become so 
in the foreseeable future in that portion.
    The Chipola slabshell is found solely in the ACF River Basin, which 
extends approximately 620 km (385 mi). This

[[Page 85927]]

species is a narrow endemic functioning as single, contiguous 
population and the MUs used do not represent biological populations, 
rather they were delineated as analysis units. However, these MUs could 
be considered portions, and one MU (MU 3) may represent a portion of 
the range that could have a different status. Management unit 3, 
comprised of marginal habitat and located in the Chipola River 
headwaters, currently has low resiliency and could possibly become 
extirpated (projected to have very low resiliency) in the foreseeable 
future. Thus, this could be a portion of the range that may be in 
danger of extinction now or within the foreseeable future. Having 
answered the status question affirmatively for MU 3, we then considered 
whether this unit is significant.
    To assess whether MU 3 is significant, we considered whether the 
area occupies a relatively large or particularly high-quality or unique 
habitat. Management unit 3 is not large, as it comprises less than one 
third of the known range of the species. We also examined whether the 
unit or characteristics within the unit make the species less 
susceptible to certain threats than other portions of the species' 
range, such that it could provide important population refugia in the 
event of extirpations elsewhere in the species' range. Although MU 3 
contributes to the overall species-level representation and redundancy, 
it does not contain high quality nor high value habitat or any habitat 
or resources unique to that area. For these reasons, we do not find 
this portion to be significant. Therefore, this unit does not represent 
a significant portion of the range, and we find that the species is not 
in danger of extinction now or likely to become so in the foreseeable 
future in any significant portion of its range. This does not conflict 
with the courts' holdings in Desert Survivors v. Department of the 
Interior, 321 F. Supp. 3d 1011, 1070-74 (N.D. Cal. 2018), and Center 
for Biological Diversity v. Jewell, 248 F. Supp. 3d 946, 959 (D. Ariz. 
2017) because, in reaching this conclusion, we did not apply the 
aspects 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), including the definition of ``significant'' that 
those court decisions held to be invalid.

Determination of Status--Chipola Slabshell

    Our review of the best scientific and commercial data available 
indicates that the Chipola slabshell does not meet the definition of an 
endangered species or a threatened species in accordance with sections 
3(6) and 3(20) of the Act. In accordance with our regulations at 50 CFR 
424.11(e)(2) currently in effect, the species has recovered to the 
point at which it no longer meets the definition of an endangered 
species or a threatened species. Therefore, we propose to remove the 
Chipola slabshell from the Federal List of Endangered and Threatened 
Wildlife.

Fat Threeridge--Status Throughout All of Its Range

    Fat threeridge is more abundant and widely distributed than 
previously thought. Current positive trends for both population and 
habitat factors, including relatively large population sizes with 
evidence of recruitment, are indicative of populations that are 
resilient to stochastic factors. All six analysis units across the 
species range exhibit moderate to high resiliency. The distribution of 
each resilient unit contributes to the species' ability to withstand 
catastrophic events. Further, the species has not experienced a change 
in connectivity--such as an impoundment--within its range, which is 
what generally corresponds to a lowered risk of extirpation from 
catastrophic events. For these reasons, we determined that the fat 
threeridge is not currently in danger of extinction throughout its 
range.
    We then considered whether the species may be likely to become in 
danger of extinction within the foreseeable future throughout its 
range. We considered threats 50 years into the future to project the 
conditions of the six analysis units to 2070. For fat threeridge, this 
timeframe is biologically appropriate (representing two or three 
generations) and within the available and reliable modeling timeframe 
for projecting future water quality and quantity, threats of 
urbanization and SLR. Timeframes earlier than 2070 were considered too 
short to observe a species response (based on a lifespan of at least 30 
years) or noticeable change in threats, and beyond 2070 were considered 
too far into the future to reliably account for species response.
    Future water quality and quantity degradation associated with land 
use change is not expected to impact fat threeridge. Over the 50-year 
timeframe, no analysis units are projected to become extirpated. Two 
currently high resiliency units (Lower Apalachicola, Lower Chipola) may 
transition to low resiliency in the future under the most extreme SLR 
effects. Species' redundancy is maintained in the future, regardless of 
scenario, as most (four of six) analysis units retain moderate to high 
resiliency under the most severe projections. Even under extreme SLR, 
fat threeridge is projected to maintain moderate to high resiliency in 
all but one analysis unit, thus representation is projected to be 
maintained in each river system (i.e., Apalachicola, Chipola, and Flint 
Rivers) and in each ecoregion (i.e., Southeastern Plains and Southern 
Coastal Plain). For these reasons, we conclude that the fat threeridge 
is not in danger of extinction now or likely to become so in the 
foreseeable future throughout all of its range.

Fat Threeridge--Status Throughout a Significant Portion of Range

    In undertaking this analysis for fat threeridge, we choose to 
address the status question first. We began by identifying portions of 
the range where the biological status of the species may be different 
from its biological status elsewhere in its range. For this purpose, we 
considered information pertaining to the geographic distribution of (a) 
individuals of the species, (b) the threats that the species faces, and 
(c) the resiliency condition of populations.
    We evaluated the range of the fat threeridge to determine if the 
species is in danger of extinction now or likely to become so in the 
foreseeable future in any portion of its range. The range of a species 
can theoretically be divided into portions in an infinite number of 
ways. We focused our analysis on portions of the species' range that 
may meet the definition of an endangered species or a threatened 
species. For fat threeridge, we considered whether the threats or their 
effects on the species are greater in any biologically meaningful 
portion of the species' range than in other portions such that the 
species is in danger of extinction now or likely to become so in the 
foreseeable future in that portion.
    The fat threeridge is found solely in the ACF River Basin, which 
extends approximately 620 km (385 mi). This species is a single, 
contiguous population and the units delineated for our analysis do not 
represent biological populations. We determined that two units 
together, representing the lower portion of the species' range (Lower 
Apalachicola and Lower Chipola) are a portion of the range that may 
have a different status due to effects related to SLR. Current 
resiliency for this portion is high, therefore the fat threeridge is 
not in danger of extinction now in this portion of the range, but 
future projections indicate that this portion could change from high 
resiliency to low resiliency under the high and extreme SLR scenarios 
within the

[[Page 85928]]

foreseeable future. Thus, we considered this a portion of the range 
that could become in danger of extinction in the foreseeable future.
    We next considered whether this portion constitutes a significant 
portion of the fat threeridge's range. To assess its significance, we 
evaluated whether the area is relatively large or particularly high-
quality, unique habitat. We also examined whether the characteristics 
within the lower portion of the range make the species less susceptible 
to certain threats than other portions of the species' range, such that 
it could provide important population refugia in the event of 
extirpations elsewhere in the species' range. The Lower Apalachicola 
and Lower Chipola do not constitute a large geographic area (less than 
20 percent of range) nor do they contain habitat of high quality 
relative to the rest of the range. This portion also does not 
constitute habitat or resources unique to that area for the species, as 
similar habitat is found throughout the range. For these reasons, we do 
not find this portion to be significant. Therefore, the lower portion 
of the fat threeridge range does not represent a significant portion of 
the range, and we find that the species is not in danger of extinction 
now or likely to become so in the foreseeable future in any significant 
portion of its range. This does not conflict with the courts' holdings 
in Desert Survivors v. Department of the Interior, 321 F. Supp. 3d 
1011, 1070-74 (N.D. Cal. 2018), and Center for Biological Diversity v. 
Jewell, 248 F. Supp. 3d 946, 959 (D. Ariz. 2017) because, in reaching 
this conclusion, we did not apply the aspects 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), including the 
definition of ``significant'' that those court decisions held to be 
invalid.

Determination of Status--Fat Threeridge

    Our review of the best scientific and commercial data available 
indicates that the fat threeridge does not meet the definition of an 
endangered species or a threatened species in accordance with sections 
3(6) and 3(20) of the Act. In accordance with our regulations at 50 CFR 
424.11(e)(2) currently in effect, the species has recovered to the 
point at which it no longer meets the definition of an endangered 
species or a threatened species. Therefore, we propose to remove the 
fat threeridge from the Federal List of Endangered and Threatened 
Wildlife.

Effects of This Rule

    This proposed rule, if made final, would revise 50 CFR 17.11(h) by 
removing both the Chipola slabshell mussel (Elliptio chipolaensis) and 
the fat threeridge mussel (Amblema neislerii) from the Federal List of 
Endangered and Threatened Wildlife. The prohibitions and conservation 
measures provided by the Act, particularly through sections 7 and 9, 
would no longer apply to these species. Federal agencies would no 
longer be required to consult with the Service under section 7 of the 
Act in the event that activities they authorize, fund, or carry out may 
affect these species.
    Critical habitat for Chipola slabshell and fat threeridge at 50 CFR 
17.95(f) would be removed if this proposal is made final.

Post-Delisting Monitoring

    Section 4(g)(1) of the Act requires us, in cooperation with the 
States, to implement a monitoring program for not less than 5 years for 
all species that have been recovered. Post-delisting monitoring (PDM) 
refers to activities undertaken to verify that a species delisted due 
to recovery remains secure from the risk of extinction after the 
protections of the Act no longer apply. The primary goal of PDM is to 
monitor the species to ensure that its status does not deteriorate, and 
if a decline is detected, to take measures to halt the decline so that 
proposing it as endangered or threatened is not again needed. If at any 
time during the monitoring period data indicate that protective status 
under the Act should be reinstated, we can initiate listing procedures, 
including, if appropriate, emergency listing.
    We will coordinate with other Federal agencies, State resource 
agencies, interested scientific organizations, and others as 
appropriate to develop and implement effective PDM plans for the 
Chipola slabshell and fat threeridge. The PDM plans will build upon 
current research and effective management practices that have improved 
the status of each of the species since listing. Ensuring continued 
implementation of proven management strategies that have been developed 
to sustain each of the species will be a fundamental goal for the PDM 
plans. The PDM plans will identify measurable management thresholds and 
responses for detecting and reacting to significant changes in Chipola 
slabshell and fat threeridge numbers, distribution, and persistence. If 
declines are detected equaling or exceeding these thresholds, the 
Service, in combination with other PDM participants, will investigate 
causes of these declines. The investigation will be to determine if the 
Chipola slabshell or fat threeridge warrants expanded monitoring, 
additional research, additional habitat protection, or resumption of 
Federal protection under the Act.
    We appreciate any information on what should be included in post-
delisting monitoring strategies for these species (see Information 
Requested, above).

Required Determinations

Clarity of the Rule

    We are required by Executive Orders 12866 and 12988 and by the 
Presidential Memorandum of June 1, 1998, to write all rules in plain 
language. This means that each rule we publish must:

    (1) Be logically organized;
    (2) Use the active voice to address readers directly;
    (3) Use clear language rather than jargon;
    (4) Be divided into short sections and sentences; and
    (5) Use lists and tables wherever possible.

    If you feel that we have not met these requirements, send us 
comments by one of the methods listed in ADDRESSES. To better help us 
revise the rule, your comments should be as specific as possible. For 
example, you should tell us the numbers of the sections or paragraphs 
that are unclearly written, which sections or sentences are too long, 
the sections where you feel lists or tables would be useful, etc.

Government-to-Government Relationship With Tribes

    In accordance with the President's memorandum of April 29, 1994 
(Government-to-Government Relations with Native American Tribal 
Governments; 59 FR 22951), Executive Order 13175 (Consultation and 
Coordination with Indian Tribal Governments), and the Department of the 
Interior's manual at 512 DM 2, we readily acknowledge our 
responsibility to communicate meaningfully with federally recognized 
Tribes on a government-to-government basis. In accordance with 
Secretarial Order 3206 of June 5, 1997 (American Indian Tribal Rights, 
Federal-Tribal Trust Responsibilities, and the Endangered Species Act), 
we readily acknowledge our responsibilities to work directly with 
Tribes in developing programs for healthy ecosystems, to acknowledge 
that Tribal lands are not subject to the same controls as Federal 
public lands, to remain sensitive to Indian culture, and to make 
information available to Tribes.

[[Page 85929]]

There are no Tribal lands associated with this proposed rule.

References Cited

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

Authors

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

List of Subjects in 50 CFR Part 17

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

Proposed Regulation Promulgation

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

PART 17--ENDANGERED AND THREATENED WILDLIFE AND PLANTS

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

    Authority:  16 U.S.C. 1361-1407; 1531-1544; and 4201-4245, 
unless otherwise noted.


Sec.  17.11  [Amended]

0
2. In Sec.  17.11, amend paragraph (h) by removing the entries for 
``Slabshell, Chipola'' and ``Threeridge, fat'' under CLAMS from the 
List of Endangered and Threatened Wildlife.
0
3. In Sec.  17.95, in paragraph (f), amend the entry for ``Seven mussel 
species (in four northeast Gulf of Mexico drainages): Purple 
bankclimber (Elliptoideus sloatianus), Gulf moccasinshell (Medionidus 
penicillatus), Ochlockonee moccasinshell (Medionidus simpsonianus), 
oval pigtoe (Pleurobema pyriforme), shinyrayed pocketbook (Hamiota 
subangulata), Chipola slabshell (Elliptio chipolaensis), and fat 
threeridge (Amblema neislerii)'' by revising the entry's heading, the 
introductory text of paragraph (2), paragraph (5), the table in 
paragraph (6), the introductory text of paragraph (8), paragraph 
(8)(ii), the introductory text of paragraph (13), paragraph (13)(ii), 
the introductory text of paragraph (14), and paragraph (14)(ii) to read 
as follows:


Sec.  17.95   Critical habitat--fish and wildlife.

* * * * *
    (f) Clams and Snails.
* * * * *
Five mussel species (in four northeast Gulf of Mexico drainages): 
Purple bankclimber (Elliptoideus sloatianus), Gulf moccasinshell 
(Medionidus penicillatus), Ochlockonee moccasinshell (Medionidus 
simpsonianus), oval pigtoe (Pleurobema pyriforme), and shinyrayed 
pocketbook (Hamiota subangulata)
* * * * *
    (2) The primary constituent elements of critical habitat for the 
purple bankclimber (Elliptoideus sloatianus), Gulf moccasinshell 
(Medionidus penicillatus), Ochlockonee moccasinshell (Medionidus 
simpsonianus), oval pigtoe (Pleurobema pyriforme), and shinyrayed 
pocketbook (Hamiota subangulata), are:
* * * * *
    (5) Index map of critical habitat units in the States of Alabama, 
Florida, and Georgia for the five mussels follows:

Figure 1 to Five mussel species (in four northeast Gulf of Mexico 
drainages): Purple bankclimber (Elliptoideus sloatianus), Gulf 
moccasinshell (Medionidus penicillatus), Ochlockonee moccasinshell 
(Medionidus simpsonianus), oval pigtoe (Pleurobema pyriforme), and 
shinyrayed pocketbook (Hamiota subangulata) Paragraph (5)

[[Page 85930]]

[GRAPHIC] [TIFF OMITTED] TP29OC24.001

    (6) * * *

Table 1 to Five mussel species (in four northeast Gulf of Mexico 
drainages): Purple bankclimber (Elliptoideus sloatianus), Gulf 
moccasinshell (Medionidus penicillatus), Ochlockonee moccasinshell 
(Medionidus simpsonianus), oval pigtoe (Pleurobema pyriforme), and 
shinyrayed pocketbook (Hamiota subangulata) Paragraph (6)

------------------------------------------------------------------------
                                   Critical habitat
             Species                     units              States
------------------------------------------------------------------------
Purple bankclimber (Elliptoideus  Units 5, 6, 7, 8,   AL, FL, GA.
 sloatianus).                      9, 10.
Gulf moccasinshell (Medionidus    Units 1, 2, 4, 5,   AL, FL, GA.
 penicillatus).                    6, 7.
Ochlockonee moccasinshell         Unit 9............  FL, GA.
 (Medionidus simpsonianus).
Oval pigtoe (Pleurobema           Units 1, 2, 4, 5,   AL, FL, GA.
 pyriforme).                       6, 7, 9, 11.
Shinyrayed pocketbook (Hamiota    Units 2, 3, 4, 5,   AL, FL, GA.
 subangulata).                     6, 7, 9.
------------------------------------------------------------------------


[[Page 85931]]

* * * * *
    (8) Unit 2. Chipola River and Dry, Rocky, Waddells Mill, Baker, 
Marshall, Big, and Cowarts Creeks in Houston County, Alabama, and in 
Calhoun, Gulf, and Jackson Counties, Florida. This is a critical 
habitat unit for the shinyrayed pocketbook, Gulf moccasinshell, and 
oval pigtoe.
* * * * *
    (ii) Unit 2 map follows:

Figure 3 to Five mussel species (in four northeast Gulf of Mexico 
drainages): Purple bankclimber (Elliptoideus sloatianus), Gulf 
moccasinshell (Medionidus penicillatus), Ochlockonee moccasinshell 
(Medionidus simpsonianus), oval pigtoe (Pleurobema pyriforme), and 
shinyrayed pocketbook (Hamiota subangulata) Paragraph (8)(ii)
[GRAPHIC] [TIFF OMITTED] TP29OC24.002

* * * * *
    (13) Unit 7. Lower Flint River and Spring, Aycocks, Dry, 
Ichawaynochaway, Mill, Pachitla, Little Pachitla, Chickasawhatchee, and 
Cooleewahee creeks in Baker, Calhoun, Decatur, Dougherty, Early, 
Miller, Mitchell, and Terrell Counties, Georgia. This is a critical 
habitat unit for the

[[Page 85932]]

shinyrayed pocketbook, Gulf moccasinshell, oval pigtoe, and purple 
bankclimber.
* * * * *
    (ii) Two maps of Unit 7--western part of unit 7 and eastern part of 
unit 7--follow:

Figure 10 to Five mussel species (in four northeast Gulf of Mexico 
drainages): Purple bankclimber (Elliptoideus sloatianus), Gulf 
moccasinshell (Medionidus penicillatus), Ochlockonee moccasinshell 
(Medionidus simpsonianus), oval pigtoe (Pleurobema pyriforme), and 
shinyrayed pocketbook (Hamiota subangulata) Paragraph (13)(ii)
[GRAPHIC] [TIFF OMITTED] TP29OC24.003

Figure 11 to Five mussel species (in four northeast Gulf of Mexico 
drainages): Purple bankclimber (Elliptoideus sloatianus), Gulf 
moccasinshell (Medionidus penicillatus), Ochlockonee moccasinshell 
(Medionidus simpsonianus), oval pigtoe (Pleurobema pyriforme), and

[[Page 85933]]

shinyrayed pocketbook (Hamiota subangulata) Paragraph (13)(ii)
[GRAPHIC] [TIFF OMITTED] TP29OC24.004

    (14) Unit 8. Apalachicola River, Chipola Cutoff, Swift Slough, 
River Styx, Kennedy Slough, and Kennedy Creek in Calhoun, Franklin, 
Gadsden, Gulf, Jackson, and Liberty Counties, Florida. This is a 
critical habitat unit for the purple bankclimber.
* * * * *
    (ii) Unit 8 map follows:

Figure 12 to Five mussel species (in four northeast Gulf of Mexico 
drainages): Purple bankclimber (Elliptoideus sloatianus), Gulf 
moccasinshell (Medionidus penicillatus), Ochlockonee moccasinshell 
(Medionidus simpsonianus), oval pigtoe (Pleurobema pyriforme), and 
shinyrayed pocketbook (Hamiota subangulata) Paragraph (14)(ii)

[[Page 85934]]

[GRAPHIC] [TIFF OMITTED] TP29OC24.005

* * * * *

Martha Williams,
Director, U.S. Fish and Wildlife Service.
[FR Doc. 2024-23929 Filed 10-28-24; 8:45 am]
BILLING CODE 4333-15-P