Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 85909 

amendment proposed, or specify the 

rule, regulation, or standard that the 

petitioner seeks to have repealed. 

(b) Explain the interest of the 

petitioner, and the need for the action 

requested. 

(c) Contain sufficient information to 

support the action sought including an 

evaluation of anticipated impacts of the 

action sought; each evaluation must 

include an estimate of resulting costs to 

the private sector, to consumers, and to 

Federal, State, and local governments as 

well as an evaluation of resulting 

benefits, quantified to the extent 

practicable. 

■ 6. Revise § 211.11 to read as follows: 

§ 211.11 Processing of petitions for 

rulemaking. 

(a) General. Each petition for 

rulemaking filed as prescribed in 

§§ 211.7 and 211.10 is referred to the 

head of the office responsible for the 

subject matter of the petition to review 

and recommend appropriate action to 

the Administrator. No public hearing or 

oral argument is held before the 

Administrator decides whether the 

petition should be granted. However, a 

notice may be published in the Federal 

Register inviting written comments 

concerning the petition. Each petition 

shall be granted or denied not later than 

six months after its receipt by the 

Docket Clerk. 

(b) Grants. If the Administrator 

determines that a rulemaking petition 

complies with the requirements of 

§ 211.10 and that rulemaking is 

justified, the Administrator initiates a 

rulemaking proceeding by publishing an 

advance notice or notice of proposed 

rulemaking in the Federal Register. 

(c) Denials. If the Administrator 

determines that a rulemaking petition 

does not comply with the requirements 

of § 211.10 or that rulemaking is not 

justified, the Administrator denies the 

petition. If the petition pertains to 

railroad safety, the Administrator may 

also initiate an informal safety inquiry 

under § 211.61. 

(d) Notification; closing of docket. 

Whenever the Administrator grants or 

denies a rulemaking petition, a notice of 

the grant or denial is sent to the 

petitioner. If the petition is denied, the 

proceeding is terminated and the docket 

for that petition is closed. 

■ 7. Revise § 211.13 to read as follows: 

§ 211.13 Initiation and completion of 

rulemaking proceedings. 

The Administrator initiates all 

rulemaking proceedings on the 

Administrator’s own motion by 

publishing an advance notice of 

proposed rulemaking or a notice of 

proposed rulemaking in the Federal 

Register. However, the Administrator 

may consider the recommendations of 

interested persons or other agencies of 

the United States. A separate docket is 

established and maintained for each 

rulemaking proceeding. Each 

rulemaking proceeding shall be 

completed not later than 12 months 

after the initial notice in that proceeding 

is published in the Federal Register. 

However, if it was initiated as the result 

of the granting of a rulemaking petition, 

the rulemaking proceeding shall be 

completed not later than 12 months 

after the petition was filed as prescribed 

in §§ 211.7 and 211.10. 

■ 8. Amend § 211.41 by revising 

paragraph (b) to read as follows: 

§ 211.41 Processing of petitions for waiver 

of safety rules. 

* * * * * 

(b) Notice and hearing. A notice is 

published in the Federal Register, an 

opportunity for public comment is 

provided (with a standard comment 

period of 60 days), and a hearing is held 

in accordance with § 211.25, before the 

petition is granted or denied. Any 

comment period shorter than 60 days 

must be authorized by the 

Administrator. 

* * * * * 

■ 9. Amend § 211.43 by revising 

paragraph (b) to read as follows: 

§ 211.43 Processing of other waiver 

petitions. 

* * * * * 

(b) Notice and hearing. A notice is 

published in the Federal Register, an 

opportunity for public comment is 

provided (with a standard comment 

period of 60 days), and a hearing is held 

in accordance with § 211.25, before the 

petition is granted or denied. Any 

comment period shorter than 60 days 

must be authorized by the 

Administrator. 

* * * * * 

Issued in Washington, DC. 

Amitabha Bose, 

Administrator. 

[FR Doc. 2024–24586 Filed 10–28–24; 8:45 am] 

BILLING CODE 4910–06–P 

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. 

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 


khammond on DSKJM1Z7X2PROD with PROPOSALS
85910 Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 

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 gianfranco_

basili@fws.gov. 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-ofcontact 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. 


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Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 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 ApalachicolaChattahoochee-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. 


khammond on DSKJM1Z7X2PROD with PROPOSALS
85912 Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 

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, 


khammond on DSKJM1Z7X2PROD with PROPOSALSEP29OC24.000</GPH>

ALABAMA· 

N 

A 

0 20. 40 60 Kili:imef&i'S f ·· i I ·1 I·· I • • 

o 20 40 60'Miles .. 

FLORIDA 

R ACF River Basin. 

0 River Basin 

D state Boundarv 

Figure 1. Large river basins within the Apalachicola Drainage of Alabama, Georgia, and 

Florida. The Apalachicola Basin is commonly referred to by the names of the three 

largest rivers, the Apalachicola, Chattahoochee, and Flint (ACF River Basin) (Service 

2021, p. 27). 
Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 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 freeliving 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 silttolerant species in stream bank habitats 

with slower currents, thus it has more 

available habitat than mid-channeldwelling 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 (°C) (75 degrees 

Fahrenheit (°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 


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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; ‘‘MOpinion,’’ available online at https://

www.doi.gov/sites/doi.opengov.

ibmcloud.com/files/uploads/M37021.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 


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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 roadstream 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 


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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 subbasins 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 


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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 °C (81 °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 


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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 


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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 humanfacilitated) 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 speciesrelevant 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). 


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TABLE 2—SUMMARY OF CONDITION CATEGORIES AND RESILIENCY FACTORS TO ASSESS CHIPOLA SLABSHELL’S CURRENT

RESILIENCY

Condition category 

Population factors 

(since 2005) 

Habitat 

factors 

Occupancy 

(proportion of occupied HUC–10s) 

Abundance & recruitment 

(# individuals and evidence 

of reproduction) 

Sedimentation index 

((a) Density of road crossings and 

transmission lines, percent nonnatural cover, and (b) soil loss 

potential) 

Canopy 

(% 200-ft 

buffer with 

≥50% 

canopy 

cover 

within 

assessed 

stream 

length) 

Excellent ............... Consistent occupation in addition 

to newly occupied.

>100 (live) during a given sampling 

event; suggests a healthy population (e.g., likely ongoing recruitment).

0–0.08: (a) minimal; (b) low ........... >90. 

Good ..................... Consistent occupancy .................... 10–100 (live or dead); more than 

one age class represented.

0.09–0.23: (a & b) low ................... 76 to 90. 

Fair ........................ <50% Decreased occupancy ......... <10 individuals (live or dead); potentially represented only by 

older individuals with limited recruitment.

0.24–0.36: (a & b) moderate ......... 50 to 75. 

Poor ...................... ≥50% Decreased occupancy ......... Only dead observed; population 

reduction likely not offset by recruitment.

0.37–0.76: (a) maximal; (b) moderate to high.<50. 

; ........................... No occupancy in HUC–10 ............. No records ..................................... N/A ................................................. N/A. 

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) 

MU HUC–10s 

Population factors Habitat factors 

Watershed score Overall MU 

resiliency Occupancy Abundance & 

reproduction 

Sedimentation 

index Canopy 

1 .......... River Styx & Douglas Slough.Excellent ................ Good ...................... Excellent ................ Excellent ................ High ........................ High. 

2 .......... Merritts Mill Pond— 

South.

Good ...................... Good ...................... Good ...................... Excellent ................ Moderate ................ Moderate. 

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 Pond— 

North.

Excellent ................ Fair ......................... Good ...................... Excellent ................ Moderate.

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 highranking 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 


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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

Condition 

category 

Population factors Habitat factors 

Abundance Recruitment Habitat occupancy Water quality Water quantity 

High ............... Recent density and population estimate at high 

end of known range (>1 

per square meter (m2); 

>1 million). Increasing or 

stable population trend.

Presence of multiple age 

classes (individuals > 

and <50 mm); small individuals (≤35 mm) detected using hydraulic 

dredge methods.

71–100% or maximal occupancy.No known or anticipated 

contaminant or sediment 

problems given the land 

cover.

Lower relative risk of direct 

and indirect impacts to 

the survival, health, or recruitment of species from 

low flow events. 

Moderate ........ Recent density and population estimate at lower 

end of known range (≤1/ 

m2 to 0.11/m2; >100k to 

1 million). Increasing or 

stable population trend.

Presence of multiple age 

classes (individuals > 

and <50 mm); but no 

small individuals (≤35 

mm) detected using hydraulic dredge methods.

31–70% or intermediate occupancy.Associated contaminant or 

sediment issues are likely in some areas.

N/A. 

Low ................ No population estimate, 

generally known to be 

present at low density 

(5–10 individuals minimum and/or ≤0.1/m2). 

Possible stable trend 

since 2000, but 

undetectable in the past.

Only one size class ≥50 

mm; no small individuals 

(≤35 mm) detected using 

hydraulic dredge methods.

<30% or minimal occupancy.Associated contaminant or 

sediment issues increases the risk of negative impacts throughout 

habitat.

Higher relative risk of direct 

and indirect impacts to 

the survival, health, or recruitment of species from 

low flow events. 

Very Low ........ Not assessed (N/A) ............ N/A ..................................... N/A ..................................... Associated contaminant or 

sediment levels pose the 

highest relative risk to 

habitat; Significant, widespread, or prolonged impacts likely occurring.

N/A. 

; .................... 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

Analysis unit 

Population factors Habitat factors 

Overall 

resiliency Abundance Evidence of 

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 


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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

MU Watershed 

(HUC–10) 

Current Lower range scenario Moderate range scenario Higher range scenario 

Watershed 

score 

Overall MU 

resiliency 

Watershed 

score 

Overall MU 

resiliency 

Watershed 

score 

Overall MU 

resiliency 

Watershed 

score 

Overall MU 

resiliency 

1 ................. River Styx & Douglas 

Slough.

High ............. High ............. High ............. High ............. High ............. High ............. Moderate ..... Moderate. 

2 ................. Merritts Mill Pond— 

South.

Mill Creek ......................

Tenmile Creek ...............

Dead Lake .....................

Moderate .....

Moderate 

High 

Moderate 

Moderate ..... Moderate .....

High 

High 

Moderate 

Moderate ..... Low .............

Moderate 

High 

Moderate 

Moderate ..... Very Low .....

Moderate 

High 

Moderate 

Low. 

3 ................. Marshall Creek ..............

Cowarts Creek ..............

Merritts Mill Pond— 

North.

Low .............

Moderate 

Moderate 

Low ............. Low .............

Moderate 

Moderate 

Low ............. Very Low .....

Very Low 

Low 

Very Low ..... Very Low .....

Very Low 

Low 

Very Low. 

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). 


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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 multifaceted 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 * 

Analysis 

unit 

Current 

resiliency 

Future 

intermediate sea level rise (SLR) 

Future 

high SLR 2

Future 

extreme SLR 2

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. 1Scenario 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. 


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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 


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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 subbasins (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 


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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 


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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 


khammond on DSKJM1Z7X2PROD with PROPOSALS
85928 Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 

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 postdelisting 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. 


khammond on DSKJM1Z7X2PROD with PROPOSALS
Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 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 

■ 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. 

§ 17.11 [Amended] 

■ 2. In § 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. 

■ 3. In § 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: 

§ 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) 


khammond on DSKJM1Z7X2PROD with PROPOSALS
85930 Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 

(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) 

Species Critical habitat units States 

Purple bankclimber (Elliptoideus sloatianus) ....................................................... Units 5, 6, 7, 8, 9, 10 ........................... AL, FL, GA. 

Gulf moccasinshell (Medionidus penicillatus) ...................................................... Units 1, 2, 4, 5, 6, 7 ............................. AL, FL, GA. 

Ochlockonee moccasinshell (Medionidus simpsonianus) ................................... Unit 9 ................................................... FL, GA. 

Oval pigtoe (Pleurobema pyriforme) ................................................................... Units 1, 2, 4, 5, 6, 7, 9, 11 .................. AL, FL, GA. 

Shinyrayed pocketbook (Hamiota subangulata) .................................................. Units 2, 3, 4, 5, 6, 7, 9 ........................ AL, FL, GA. 


khammond on DSKJM1Z7X2PROD with PROPOSALSEP29OC24.001</GPH>

Index Map: Five Listed Mussels Critical Habitat 
Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 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) 

* * * * * 

(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 


khammond on DSKJM1Z7X2PROD with PROPOSALSEP29OC24.002</GPH>

Unit 2: Chipola River, Alabama and Florida, for the Shinyrayed 

Pocketbook, Gulf Moccasinshell, and Oval Pigtoe 

ALABAMA 

FLORIDA l Marshall 

I 

r' 

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I 

( Russ MillC 

,---, 

I I 

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I 

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I 

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=-=-=-: Roads 

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I 

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I 

I 

I 

CALHOUN 

~--.;.;..;..""".;=; 

GULF 

N 

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I 

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85932 Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 

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) 

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 


khammond on DSKJM1Z7X2PROD with PROPOSALSEP29OC24.003</GPH>

Unit 7: Lower Flint River (Western), Georgia, for the Shinyrayed 

Pocketbook, Gulf Moccasinshell, Oval Pigtoe, and Purple Bank climber 

r----------

EARLY 

I 

I 

I 

--------'-

/\,/ Critical Habitat 

::-=-= Roads O 2•

5 

SEMINOLE 

N 

5 

Km + ,, ' " County --- -c::===:::i5 Miles 

I 

I 

l BAKER 

__ J - ... __ r, - r.r,_,-----

MILLER 

DECATUR 
Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 85933 

shinyrayed pocketbook (Hamiota 

subangulata) Paragraph (13)(ii) 

(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) 


khammond on DSKJM1Z7X2PROD with PROPOSALSEP29OC24.004</GPH>

Unit 7: Lower Flint River (Eastern), Georgia, for the Shinyrayed 

Pocketbook, GulfMoccasinshell, Oval Pigtoe, and Purple Bankclimber 

Bear • -

- Little.--, 

Pachitla 

Creek 

,:; CALHO 

DOUGHERTY 

} ---JL------

EARLY 1⁄2 1 

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I 

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J t.,,.. ""i ..r-·--- -·--- ~, 

I 

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I 

MILLER I 

I 

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I 

I 

J .J 

I DECATUR 

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I 

OO[eeTM 

Cree 

BAKER 

-~-----"-.,--------

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MITCHELL 

~ Critical Habitat 

=-::oc Roads 0 8 

--===::::iKm 

4 

N 

+ 

I 1 ,,, ',,, County 0 4 8 ---====:::i Miles 
85934 Federal Register / Vol. 89, No. 209 / Tuesday, October 29, 2024 / Proposed Rules 

* * * * * 

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 


khammond on DSKJM1Z7X2PROD with PROPOSALSEP29OC24.005</GPH>

Unit 8: Apalachicola River, Florida, for the Purple Bankclimber 

I 

I 

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l 

1 

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l 

I 

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I 

I 

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Chipola Cutoff 

GULF 

/\j' Critical Habitat 

=-::a:::a: Roads 

/'V State o 4 8 

Km 

N 

+ ,, ' ,, County o 4 s ---=====::i.Miles 

I 

I_ __ _ 

!..--, 

I 

I 

I 

GEORGIA 

FLORIDA 

GADSDEN 

, __ .....,. 

LIBERTY 

-K,innedy Creek 

FRANKLIN 

,......_Bloody Bluff Island ,., 

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