47916 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

DEPARTMENT OF THE INTERIOR 

Fish and Wildlife Service 

50 CFR Part 17 

[FWS–R2–ES–2019–0061; FF09E21000 

FXES11110900000 212] 

RIN 1018–BD16 

Endangered and Threatened Wildlife 

and Plants; Endangered Species 

Status With Critical Habitat for 

Guadalupe Fatmucket, Texas 

Fatmucket, Guadalupe Orb, Texas 

Pimpleback, and False Spike, and 

Threatened Species Status With 

Section 4(d) Rule and Critical Habitat 

for Texas Fawnsfoot 

AGENCY: Fish and Wildlife Service, 

Interior. 

ACTION: Proposed rule. 

SUMMARY: We, the U.S. Fish and 

Wildlife Service (Service or USFWS), 

propose to list six Central Texas mussel 

species: The Guadalupe fatmucket 

(Lampsilis bergmanni), Texas fatmucket 

(Lampsilis bracteata), Texas fawnsfoot 

(Truncilla macrodon), Guadalupe orb 

(Cyclonaias necki), Texas pimpleback 

(Cyclonaias (=Quadrula) petrina), and 

false spike (Fusconaia (=Quincuncina) 

mitchelli) as endangered or threatened 

under the Endangered Species Act of 

1973, as amended (Act). After review of 

the best available scientific and 

commercial information, we find that 

listing Guadalupe fatmucket, Texas 

fatmucket, Guadalupe orb, Texas 

pimpleback, and false spike as 

endangered species is warranted, and 

listing Texas fawnsfoot as a threatened 

species is warranted. We propose a rule 

issued under section 4(d) of the Act 

(‘‘4(d) rule’’) for the Texas fawnsfoot. If 

we finalize this rule as proposed, it 

would add these species to the List of 

Endangered and Threatened Wildlife 

and extend the Act’s protections to the 

species. We also propose to designate 

critical habitat for all six species under 

the Act. In total, approximately 1,944 

river miles (3,129 river kilometers) in 

Texas fall within the boundaries of the 

proposed critical habitat designations. 

We also announce the availability of a 

draft economic analysis (DEA) of the 

proposed designation of critical habitat. 

We also are notifying the public that we 

have scheduled two informational 

meetings followed by public hearings on 

the proposed rule. 

DATES: 

Comment submission: We will accept 

comments received or postmarked on or 

before October 25, 2021. Comments 

submitted electronically using the 

Federal eRulemaking Portal (see 

ADDRESSES, below) must be received by 

11:59 p.m. Eastern Time on the closing 

date. 

Public informational meeting and 

public hearing: We will hold public 

informational sessions from 5:00 p.m. to 

6:00 p.m., Central Time, followed by 

public hearings from 6:30 p.m. to 8:30 

p.m., Central Time, on September 14, 

2021, and September 16, 2021. 

ADDRESSES: You may submit comments 

by one of the following methods: 

(1) Electronically: Go to the Federal 

eRulemaking Portal: http://

www.regulations.gov. In the Search box, 

enter FWS–R2–ES–2019–0061, which is 

the docket number for this rulemaking. 

Then, in the Search panel on the left 

side of the screen, under the Document 

Type heading, check the Proposed Rules 

box to locate this document. You may 

submit a comment by clicking on 

‘‘Comment Now!’’ 

(2) By hard copy: Submit by U.S. mail 

to: Public Comments Processing, Attn: 

FWS–R2–ES–2019–0061, U.S. Fish and 

Wildlife Service, MS: JAO/1N, 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 http://

www.regulations.gov. This generally 

means that we will post any personal 

information you provide us (see 

Information Requested, below, for more 

information). 

Public informational meetings and 

public hearings: The public 

informational meetings and the public 

hearings will be held virtually using the 

Zoom platform. See Public Hearing, 

below, for more information. 

Availability of supporting materials: 

For the critical habitat designation, the 

coordinates or plot points or both from 

which the maps are generated are 

included in the decision file and are 

available at https://www.fws.gov/ 

southwest/es/AustinTexas/ESA_Sp_

Mussels.html and at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. Any 

additional tools or supporting 

information that we may develop for the 

critical habitat designation will also be 

available at the Service website set out 

above, and may also be included in the 

preamble and/or at http://

www.regulations.gov. 

FOR FURTHER INFORMATION CONTACT: 

Adam Zerrenner, Field Supervisor, U.S. 

Fish and Wildlife Service, Austin 

Ecological Services Field Office, 10711 

Burnet Rd., Suite 200, Austin, TX 

78758; telephone (512) 490–0057. 

Persons who use a telecommunications 

device for the deaf (TDD) may call the 

Federal Relay Service at 800–877–8339. 

SUPPLEMENTARY INFORMATION: 

Executive Summary 

Why we need to publish a rule. Under 

the Act, if we determine that a species 

may be an endangered or threatened 

species throughout all or a significant 

portion of its range, we are required to 

promptly publish a proposal in the 

Federal Register and make a 

determination on our proposal within 1 

year. To the maximum extent prudent 

and determinable, we must designate 

critical habitat for any species that we 

determine to be an endangered or 

threatened species under the Act. 

Listing a species as an endangered or 

threatened species and designation of 

critical habitat can only be completed 

by issuing a rule. 

What this document does. This 

document proposes the Guadalupe 

fatmucket (Lampsilis bergmanni), Texas 

fatmucket (Lampsilis bracteata), 

Guadalupe orb (Cyclonaias necki), 

Texas pimpleback (Cyclonaias 

(=Quadrula) petrina), and false spike 

(Fusconaia (=Quincuncina) mitchelli) as 

endangered species and Texas fawnsfoot 

(Truncilla macrodon) as a threatened 

species. This document also proposes 

the designation of critical habitat for all 

six species, as well as a 4(d) rule 

providing protective regulations for the 

Texas fawnsfoot. 

The basis for our action. Under the 

Act, we may determine that a species is 

an endangered or threatened species 

based on any of five factors: (A) The 

present or threatened destruction, 

modification, or curtailment of its 

habitat or range; (B) overutilization for 

commercial, recreational, scientific, or 

educational purposes; (C) disease or 

predation; (D) the inadequacy of 

existing regulatory mechanisms; or (E) 

other natural or manmade factors 

affecting its continued existence. We 

have determined habitat loss through 

changes in water quality and quantity, 

as well as increased fine sediments 

(Factor A), are the primary threats to 

these species. 

Under the Act, for any species that is 

determined to be threatened, we must 

provide protective regulations to 

provide for the conservation of that 

species. For the Texas fawnsfoot, we are 

proposing to prohibit take and 

possession. 

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

Secretary of the Interior (Secretary) to 

designate critical habitat concurrent 

with listing to the maximum extent 

prudent and determinable. Section 

4(b)(2) of the Act states that the 

Secretary must make the designation on 


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the basis of the best scientific data 

available and after taking into 

consideration the economic impact, the 

impact on national security, and any 

other relevant impacts of specifying any 

particular area as critical habitat. 

Section 3(5)(A) of the Act defines 

critical habitat as (i) the specific areas 

within the geographical area occupied 

by the species, at the time it is listed, 

on which are found those physical or 

biological features (I) essential to the 

conservation of the species and (II) 

which may require special management 

considerations or protections; and (ii) 

specific areas outside the geographical 

area occupied by the species at the time 

it is listed, upon a determination by the 

Secretary that such areas are essential 

for the conservation of the species. 

Supporting analyses. We prepared an 

analysis of the economic impacts of the 

proposed critical habitat designations 

and hereby announce the availability of 

the draft economic analysis for public 

review and comment. 

Our species status assessment report 

(SSA report) documents the results of 

the comprehensive biological status 

review for the central Texas mussels 

and provides an account of the species’ 

overall viability through forecasting of 

the species’ condition in the future 

(Service 2019a, entire). Additionally, 

the SSA report contains our analysis of 

required habitat and the existing 

conditions of that habitat. 

Peer review. In accordance with our 

joint policy on peer review published in 

the Federal Register on July 1, 1994 (59 

FR 34270), and our August 22, 2016, 

memorandum updating and clarifying 

the role of peer review of listing actions 

under the Act, we sought the expert 

opinions of eight appropriate specialists 

regarding the species status assessment 

report. We received responses from six 

specialists, which informed this 

proposed rule. The purpose of peer 

review is to ensure that our listing 

determinations, critical habitat 

designations, and 4(d) rules are based 

on scientifically sound data, 

assumptions, and analyses. The peer 

reviewers have expertise in the biology, 

habitat, and threats to the species. 

We sought comments from 

independent specialists on the SSA 

report to ensure that our proposal is 

based on scientifically sound data and 

analyses. We received feedback from six 

scientists with expertise in freshwater 

mussel biology, ecology, genetics, 

climate science, and hydrology as peer 

review of the SSA report. The reviewers 

were generally supportive of our 

approach and made suggestions and 

comments that strengthened our 

analysis. The SSA report and other 

materials relating to this proposal can be 

found at http://www.regulations.gov 

under Docket No. FWS–R2–ES–2019– 

0061. 

Because we will consider all 

comments and information received 

during the comment period, our final 

determinations may differ from this 

proposal. Based on the new information 

we receive (and any comments on that 

new information), we may conclude that 

any of these species are threatened 

instead of endangered, or endangered 

instead of threatened, or we may 

conclude that any of these species do 

not warrant listing as either an 

endangered species or a threatened 

species. Such final decisions would be 

a logical outgrowth of this proposal, as 

long as we: (a) Base the decisions on the 

best scientific and commercial data 

available after considering all of the 

relevant factors; (2) do not rely on 

factors Congress has not intended us to 

consider; and (3) articulate a rational 

connection between the facts found and 

the conclusions made, including why 

we changed our conclusion. 

Information Requested 

We intend that any final action 

resulting from this proposed rule will be 

based on the best scientific and 

commercial data available and be as 

accurate and as effective as possible. 

Therefore, we request comments or 

information from other 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) The species’ biology, range, and 

population trends, including: 

(a) Biological or ecological 

requirements of these species, including 

habitat requirements for feeding, 

breeding, and sheltering; 

(b) Genetics, genomics, systematics, 

and taxonomy; 

(c) Historical and current range, 

including distribution patterns; 

(d) Historical and current population 

levels, abundance, and current and 

projected trends; and 

(e) Past and ongoing conservation 

measures for these species, their 

habitats, or both. 

(2) Factors that may affect the 

continued existence of the species, 

which may include habitat modification 

or destruction, overutilization, disease, 

predation, the inadequacy of existing 

regulatory mechanisms, or other natural 

or manmade factors. 

(3) Biological, commercial trade, or 

other relevant data concerning any 

threats (or lack thereof) to these species 

and existing regulations that may be 

addressing those threats. 

(4) Additional information concerning 

the historical and current status, range, 

distribution, and population size of 

these species, including the locations of 

any additional populations of the 

Central Texas mussels. 

(5) Information on regulations that are 

necessary and advisable to provide for 

the conservation of the Texas fawnsfoot 

and that the Service can consider in 

developing a 4(d) rule for the species. In 

particular, information concerning the 

extent to which we should include any 

of the section 9 prohibitions in the 4(d) 

rule or whether any other forms of take 

should be excepted from the 

prohibitions in the 4(d) rule. 

(6) The reasons why we should or 

should not designate habitat as ‘‘critical 

habitat’’ under section 4 of the Act, 

including information to inform the 

following factors such that a designation 

of critical habitat may be determined to 

be not prudent: 

(a) The species is threatened by taking 

or other human activity and 

identification of critical habitat can be 

expected to increase the degree of such 

threat to the species; 

(b) The present or threatened 

destruction, modification, or 

curtailment of a species’ habitat or range 

is not a threat to the species, or threats 

to the species’ habitat stem solely from 

causes that cannot be addressed through 

management actions resulting from 

consultations under section 7(a)(2) of 

the Act; 

(c) Areas within the jurisdiction of the 

United States provide no more than 

negligible conservation value, if any, for 

a species occurring primarily outside 

the jurisdiction of the United States; 

(d) No areas meet the definition of 

critical habitat. 

(7) Specific information on: 

(a) The amount and distribution of 

habitat for all six Central Texas mussels; 

(b) What areas, that were occupied at 

the time of listing and that contain the 

physical or biological features essential 

to the conservation of the species, 

should be included in the designation 

and why; 

(c) Any additional areas occurring 

within the range of the species, i.e., 

Anderson, Austin, Bastrop, Bell, Blanco, 

Brazoria, Brazos, Brown, Burleson, 

Caldwell, Coleman, Colorado, Comal, 

Concho, Dallas, DeWitt, Edwards, Ellis, 

Falls, Fayette, Fort Bend, Freestone, 

Gillespie, Gonzales, Grimes, Guadalupe, 

Hays, Henderson, Houston, Kaufman, 

Kerr, Kendall, Kimble, Lampasas, Leon, 

Llano, Madison, Mason, Matagorda, 

McCulloch, McLennan, Menard, Milam, 

Mills, Navarro, Palo Pinto, Parker, 


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Robertson, Runnels, San Saba, 

Shackelford, Stephens, Sutton, Tom 

Green, Travis, Throckmorton, Waller, 

Washington, Victoria, Wharton, and 

Williamson Counties, Texas, that should 

be included in the designation because 

they (1) are occupied at the time of 

listing and contain the physical or 

biological features that are essential to 

the conservation of the species and that 

may require special management 

considerations, or (2) are unoccupied at 

the time of listing and are essential for 

the conservation of the species; 

(d) Special management 

considerations or protection that may be 

needed in critical habitat areas we are 

proposing, including managing for the 

potential effects of climate change; and 

(e) What areas not occupied at the 

time of listing are essential for the 

conservation of the species. We 

particularly seek comments: 

(i) Regarding whether occupied areas 

are inadequate for the conservation of 

the species; 

(ii) Providing specific information 

that supports the determination that 

unoccupied areas will, with reasonable 

certainty, contribute to the conservation 

of the species and contain at least one 

physical or biological feature essential 

to the conservation of the species; and 

(iii) Explaining whether or not 

unoccupied areas fall within the 

definition of ‘‘habitat’’ at 50 CFR 424.02 

and why. 

(8) Land use designations and current 

or planned activities in the subject areas 

and their possible impacts on proposed 

critical habitat. 

(9) Any probable economic, national 

security, or other relevant impacts of 

designating any area that may be 

included in the final designation, and 

the related benefits of including or 

excluding specific areas. 

(10) Information on the extent to 

which the description of probable 

economic impacts in the draft economic 

analysis is a reasonable estimate of the 

likely economic impacts and any 

additional information regarding 

probable economic impacts that we 

should consider. 

(11) Whether any specific areas we are 

proposing for critical habitat 

designation should be considered for 

exclusion under section 4(b)(2) of the 

Act, and whether the benefits of 

potentially excluding any specific area 

outweigh the benefits of including that 

area under section 4(b)(2) of the Act. If 

you think we should exclude any 

additional areas, please provide credible 

information regarding the existence of a 

meaningful economic or other relevant 

impact supporting a benefit of 

exclusion. 

(12) Whether we could improve or 

modify our approach to designating 

critical habitat in any way to provide for 

greater public participation and 

understanding, or to better 

accommodate public concerns and 

comments. 

Please include sufficient information 

with your submission (such as scientific 

journal articles or other publications) to 

allow us to verify any scientific or 

commercial information you include. 

Please note that submissions merely 

stating support for, or opposition to, the 

action under consideration without 

providing supporting information, 

although noted, will not be considered 

in making a determination, as section 

4(b)(1)(A) of the Act directs that 

determinations as to whether any 

species is an endangered or a threatened 

species must be made ‘‘solely on the 

basis of the best scientific and 

commercial data available.’’ 

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 http:// 

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. 

We will post all hardcopy submissions 

on http://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 http://www.regulations.gov. 

Public Hearing 

We have scheduled two public 

informational meetings and public 

hearings on this proposed rule to list the 

Central Texas mussels as endangered or 

threatened species with critical habitat. 

We will hold the public informational 

meetings and public hearings on the 

date and at the times listed above under 

Public informational meeting and public 

hearing in DATES. We are holding the 

public informational meetings and 

public hearings via the Zoom online 

video platform and via teleconference so 

that participants can attend remotely. 

For security purposes, registration is 

required. To listen and view the meeting 

and hearing via Zoom, listen to the 

meeting and hearing by telephone, or 

provide oral public comments at the 

public hearing by Zoom or telephone, 

you must register. For information on 

how to register, or if you encounter 

problems joining Zoom the day of the 

meeting, visit https://www.fws.gov/ 

southwest/. Registrants will receive the 

Zoom link and the telephone number 

for the public informational meetings 

and public hearings. If applicable, 

interested members of the public not 

familiar with the Zoom platform should 

view the Zoom video tutorials (https:// 

support.zoom.us/hc/en-us/articles/ 

206618765-Zoom-video-tutorials) prior 

to the public informational meetings 

and public hearings. 

The public hearings will provide 

interested parties an opportunity to 

present verbal testimony (formal, oral 

comments) regarding this proposed rule. 

While the public informational meetings 

will be opportunities for dialogue with 

the Service, the public hearings are not: 

They are a forum for accepting formal 

verbal testimony. In the event there is a 

large attendance, the time allotted for 

oral statements may be limited. 

Therefore, anyone wishing to make an 

oral statement at the public hearing for 

the record is encouraged to provide a 

prepared written copy of their statement 

to us through the Federal eRulemaking 

Portal, or U.S. mail (see ADDRESSES, 

above). There are no limits on the length 

of written comments submitted to us. 

Anyone wishing to make an oral 

statement at the public hearings must 

register before the hearing (https://

www.fws.gov/southwest/). The use of a 

virtual public hearing is consistent with 

our regulations at 50 CFR 424.16(c)(3). 

Previous Federal Actions 

Table 1, below, summarizes the 

petition history and proposed status of 

the Central Texas mussels under the 

Endangered Species Act. On June 25, 

2007, we received a formal petition 

dated June 18, 2007, from Forest 

Guardians (now WildEarth Guardians), 

for 475 species in the southwestern 

United States. The petitioned group of 

species included the Texas fatmucket. 

On October 15, 2008, we received a 

petition dated October 9, 2008, from 

WildEarth Guardians, requesting that 

the Service list as threatened or 

endangered and designate critical 

habitat for six species of freshwater 

mussels, including the Texas 

pimpleback, Texas fawnsfoot, and false 

spike. 

On December 15, 2009, we published 

our 90-day finding that the above 

petitions presented substantial scientific 

information indicating that listing the 

Texas fatmucket, Texas pimpleback, 

Texas fawnsfoot, and false spike may be 

warranted (74 FR 66260). As a result of 


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the finding, we initiated status reviews 

for these four species. On October 6, 

2011, we published a 12-month finding 

for five Texas mussels, including the 

Texas fatmucket, Texas fawnsfoot, and 

Texas pimpleback, that listing was 

warranted but precluded by higher 

priority actions, and these species were 

added to the candidate list (76 FR 

62166). Candidates are those fish, 

wildlife, and plants for which we have 

on file sufficient information on 

biological vulnerability and threats to 

support preparation of a listing 

proposal, but for which development of 

a listing rule is precluded by other 

higher priority listing activities. The 

Texas fatmucket, Texas fawnsfoot, and 

Texas pimpleback were included in all 

of our subsequent annual Candidate 

Notices of Review (77 FR 69993, 

November 21, 2012; 78 FR 70104, 

November 22, 2013; 79 FR 72450, 

December 5, 2014; 80 FR 80584, 

December 24, 2015; 81 FR 87246, 

December 2, 2016; and 84 FR 54732, 

October 10, 2019). 

The distribution of the newly 

described Guadalupe orb was 

previously fully contained within the 

distribution of the Texas pimpleback. 

Genetic information received in 2018 

(Burlakova et al. 2018, entire) confirmed 

that the Guadalupe orb is a separate 

species distinct from the Texas 

pimpleback, and the Guadalupe orb is 

now a newly described species. 

Similarly, the Guadalupe fatmucket was 

split from the Texas fatmucket in 2018 

(Inoue et al. 2018, entire) and described 

in 2019 (Inoue et al. 2019, in press). As 

both species were part of the original 

petitioned entities, we evaluated both of 

these new species as well as the four 

original species in our SSA, and all six 

species are included in this proposed 

rule. 

This document constitutes our 

concurrent 12-month warranted petition 

finding for the false spike and proposed 

listing rule and proposed critical habitat 

rule for all six Central Texas mussel 

species. 

TABLE 1—LIST OF THE PETITION FINDINGS FOR THE SIX CENTRAL TEXAS MUSSELS

Scientific name Common name River basins Petition received date 90-day finding date 12-month finding date 

Lampsilis bergmanni .. Guadalupe fatmucket Guadalupe ................ Previously included in Texas fatmucket. 

Lampsilis bracteata .... Texas fatmucket ....... Colorado ................... June 25, 2007 ........... December 15, 2009 .. October 6, 2011. 

Truncilla macrodon ..... Texas fawnsfoot ........ Trinity, Brazos, Colorado.October 15, 2008 ...... December 15, 2009 .. October 6, 2011. 

Cyclonaias necki ........ Guadalupe orb .......... Guadalupe ................ Previously included in Texas pimpleback. 

Cyclonaias petrina ...... Texas pimpleback ..... Colorado ................... October 15, 2008 ...... December 15, 2009 .. October 6, 2011. 

Fusconaia mitchelli ..... False spike ................ Brazos, Colorado, 

Guadalupe.

October 15, 2008 ...... December 15, 2009 .. This finding. 

I. Proposed Listing Determination 

Background 

General Mussel Biology 

Freshwater mussels, including the six 

Central Texas mussels, have a complex 

life history involving parasitic larvae, 

called glochidia, which are wholly 

dependent on host fish. As freshwater 

mussels are generally sessile 

(immobile), dispersal is accomplished 

primarily through the behavior of host 

fish and their tendencies to travel 

upstream and against the current in 

rivers and streams. Mussels are 

broadcast spawners; males release 

sperm into the water column, which is 

taken in by the female through the 

incurrent siphon (the tubular structure 

used to draw water into the body of the 

mussel). The developing larvae remain 

with the female until they mature and 

are ready for release as glochidia, to 

attach on the gills, head, or fins of fishes 

(Vaughn and Taylor 1999, p. 913; 

Barnhart et al. 2008, pp. 371–373). 

Glochidia die if they fail to find a host 

fish, attach to the wrong species of host 

fish, attach to a fish that has developed 

immunity from prior infestations, or 

attach to the wrong location on a host 

fish (Neves 1991, p. 254; Bogan 1993, p. 

599). Successful glochidia encyst 

(enclose in a cyst-like structure) on the 

host’s tissue, draw nutrients from the 

fish, and develop into juvenile mussels 

(Arey 1932, pp. 214–215). The glochidia 

will remain encysted for about a month 

through a transformation to the juvenile 

stage. Once transformed, the juveniles 

will excyst from the fish and drop to the 

substrate. 

Freshwater mussel species vary in 

both onset and duration of spawning, 

how long developing larvae are held in 

the marsupial gill chambers (gills used 

for holding eggs and glochidia), and 

which fish species serve as hosts. The 

mechanisms employed by mussel 

species to increase the likelihood of 

interaction between host fish and 

glochidia vary by species. 

Mussels are generally immobile; their 

primary opportunity for dispersal and 

movement within the stream comes 

when glochidia attach to a mobile host 

fish (Smith 1985, p. 105). Upon release 

from the host, newly transformed 

juveniles drop to the substrate on the 

bottom of the stream. Those juveniles 

that drop in unsuitable substrates die 

because their immobility prevents them 

from relocating to more favorable 

habitat. Juvenile freshwater mussels 

burrow into interstitial substrates and 

grow to a larger size that is less 

susceptible to predation and 

displacement from high flow events 

(Yeager et al. 1994, p. 220). Adult 

mussels typically remain within the 

same general location where they 

dropped off (excysted) from their host 

fish as juveniles. 

Host specificity can vary across 

mussel species, which may have 

specialized or generalized relationships 

with one or more taxa of fish. Mussels 

have evolved a wide variety of 

adaptations to facilitate transmission of 

glochidia to host fish including: 

Display/mantle lures mimicking fish or 

invertebrates; packages of glochidia 

(conglutinates) that mimic worms, 

insect larvae, larval fish, or fish eggs; 

and release of glochidia in mucous webs 

that entangle fish (Strayer et al. 2004, p. 

431). Polymorphism (existence of 

multiple forms) of mantle lures and 

conglutinates frequently exists within 

mussel populations (Barnhart et al. 

2008, p. 383), representing important 

adaptive capacity in terms of genetic 

diversity and ecological representation. 

Guadalupe Fatmucket 

The Guadalupe fatmucket (Lampsilis 

bergmanni) was recently discovered to 

be a separate and distinct species from 

Texas fatmucket (L. bracteata; Inoue et 

al. 2018, pp. 5–6; Inoue et al. 2019, in 

press), and the Service now recognizes 

the Guadalupe fatmucket as a new 


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species that occurs only in the 

Guadalupe River basin. Because the 

Guadalupe fatmucket has recently been 

split from Texas fatmucket, the species 

are very similar, and better information 

is not yet available, we believe the 

Guadalupe fatmucket has similar habitat 

needs (headwater habitats in gravel or 

bedrock fissures) and host fish 

(sunfishes) as the Texas fatmucket. 

The Guadalupe fatmucket is a small to 

medium-sized freshwater mussel (to 4 

inches (in) (100 millimeters (mm))) that 

exhibits sexual dimorphism and has a 

yellow-green-tan shell, and is similar in 

appearance to the Texas fatmucket (a 

more detailed description of the Texas 

fatmucket is found in Howells et al. 

2011, pp. 14–16). Related species in the 

genus Lampsilis from the southeast 

United States reach a maximum age of 

13–25 years (Haag and Rypel 2010, pp. 

4–6). 

Guadalupe fatmucket is currently 

found in one population, which occurs 

in 54 miles (87 km) of the Guadalupe 

River basin in Kerr and Kendall 

Counties, Texas (Randklev et al. 2017, 

p. 4) (table 2; figure 1). For more 

information on this population, see the 

SSA report. 

TABLE 2—CURRENT GUADALUPE FATMUCKET POPULATION

Population Streams included Counties 

Occupied 

reach length 

(mi (km)) 

Recent collection 

years 

(numbers) 

Guadalupe River ............................ Guadalupe River; North Fork, 

Guadalupe River; Johnson 

Creek.

Kerr and Kendall Co., TX ............. 54 (87) 2018 (22), 2019 

(shells). 

BILLING CODE 4333–15–P 


jbell on DSKJLSW7X2PROD with PROPOSALS3
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47921 

Texas Fatmucket 

A thorough review of the taxonomy, 

life history, and ecology of the Texas 

fatmucket is presented in the SSA 

report. Texas fatmucket has been 

characterized as a rare Texas endemic 

(Burlakova et al. 2011a, p. 158) and was 

originally described as the species Unio 

bracteatus by A.A. Gould in 1855 (p. 

228) from the ‘‘Llanos River’’ in 

‘‘Upper’’ Texas. The species is currently 

recognized as Lampsilis bracteata 

(Williams et al. 2017, pp. 35, 39). 

Recently, individuals that had been 

known as Texas fatmucket in the 

Guadalupe River basin were found to be 

a new species (Inoue et al. 2019, in 

press); therefore, the Texas fatmucket 

occurs only in the Colorado River basin. 

The Texas fatmucket is a small to 

medium-sized freshwater mussel (to 4 

in (100 mm)) that exhibits sexual 

dimorphism (males and females have 

different shapes) and has a yellowVerDate Sep<11>2014 21:39 Aug 25, 2021 Jkt 253001 PO 00000 Frm 00007 Fmt 4701 Sfmt 4702 E:\FR\FM\26AUP3.SGM 26AUP3

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J j 

\ 

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, 

Current Known Populations of Guadalupe Fatmucket 

.f 

uan_o.,.~ ___ ,--,, - .-1' ... 

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' 

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[ ] County Boundaries ~ Lakes 

= lnterstates El Cities 

Figure 1. Map showing location of known Guadalupe fatmucket population. 
47922 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

green-tan shell (Howells et al. 2011, pp. 

14–16). For a detailed morphological 

description see Howells et al. 1996 (p. 

61) and Howells 2014 (p. 41). 

Host fishes for Texas fatmucket are 

members of the Family Centrarchidae 

(sunfishes) including bluegill (Lepomis 

macrochirus), green sunfish (L. 

cyanellus), Guadalupe bass (Micropterus 

treculii), and largemouth bass (M. 

salmoides) (Howells 1997, p. 257; 

Johnson et al. 2012, p. 148; Howells 

2014, p. 41; Ford and Oliver 2015, p. 4; 

Bonner et al. 2018, p. 9). 

Related species can expel 

conglutinates (packets of glochidia) and 

are known to use mantle lures (Barnhart 

et al. 2008, pp. 377, 380) to attract sightfeeding fishes that attack and rupture 

the marsupium where the glochidia are 

held, thereby becoming infested by 

glochidia. These species are long-term 

brooders (bradytictic), spawning and 

becoming gravid in the fall and 

releasing glochidia in the spring 

(Barnhart et al. 2008, p. 384). 

Related species in the genus Lampsilis 

from the southeast United States reach 

a maximum age of 13–25 years (Haag 

and Rypel 2010; pp. 4–6). Texas 

fatmucket occur in firm mud, stable 

sand, and gravel bottoms, in shallow 

waters, sometimes in bedrock fissures or 

among roots of bald cypress (Taxodium 

distichum) and other aquatic vegetation 

(Howells 2014, p. 41). The species 

typically occurs in free-flowing rivers 

but can survive in backwater areas, such 

as in areas upstream of lowhead dams 

(e.g. Llano Park Lake (BioWest, Inc., 

2018, pp. 2–3)). 

Texas fatmucket currently occur only 

in the upper reaches of major tributaries 

within the Colorado River basin 

(Randklev et al. 2017, p. 4) in five 

populations: Lower Elm Creek, upper/ 

middle San Saba River, Llano River, 

Pedernales River, and lower Onion 

Creek (table 3; figure 2). Isolated 

individuals not considered part of larger 

functioning populations have been 

found in Cherokee Creek, Bluff Creek, 

and the North Llano River. For more 

information on these populations, see 

the SSA report. 

TABLE 3—CURRENT TEXAS FATMUCKET POPULATIONS

Population Streams included Counties 

Occupied 

reach length 

(mi (km)) 

Recent collection years 

(number collected) 

Lower Elm Creek ................... Elm Creek .............................. Runnels Co., TX .................... 12.5 (20) * 2005 

2008 (1) 

2019 (1) 

Upper/Middle San Saba River San Saba River ..................... Menard, Mason, San Saba, 

and McCulloch Co., TX.

62 (100) 2016 (29) 

2017 (87) 

2017 (71) 

Llano River ............................. Llano River, South Llano 

River.

Kimble, Mason, Llano Co., TX 127 (204) 2016 (72) 

2017 (47) 

2017 (5) 

Pedernales River .................... Pedernales River, Live Oak 

Creek.

Gillespie, Hays, and Blanco 

Co., TX.

79 (127) 2017 (17) 

Lower Onion Creek ................ Onion Creek ........................... Travis Co., TX ........................ 5 (8) 2010 (3) 

2018 (1) 

* No live animals. 


jbell on DSKJLSW7X2PROD with PROPOSALS3
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47923 

Texas Fawnsfoot 

The Texas fawnsfoot was originally 

described as Unio macrodon 1859 from 

a location near Rutersville, Fayette 

County, Texas (Lea 1859, pp. 154–155). 

Texas fawnsfoot is recognized by the 

scientific community as Truncilla 

macrodon (Williams et al. 2017, pp. 35, 

44). 

Texas fawnsfoot is a small- to 

medium-sized (2.4 in (60 mm)) mussel 

with an elongate oval shell (Howells 

2014, p. 111). For a detailed description, 

see Howells et al. 1996 (p. 143) and 

Howells 2014 (p. 111). 

Host fish species are not confirmed 

for the Texas fawnsfoot, but we 

conclude they use freshwater drum 

(Aplodinotus grunniens; Howells 2014, 

p. 111), like other Truncilla species 

occurring in Texas and elsewhere (Ford 

and Oliver 2015, p. 8). Freshwater drum 

are molluscivorous (mollusk-eating) and 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.026</GPH>

, 

, 

I 

' I 

Current Known Populations of 'lexas Fatmucket 

Mi O 10 

L__J 

tl 

KmO 10 

~/ 

,, 

J 

,, 

~ 

-Populations ~ -- - Rivers 

County Boundaries ffl lakes 

= Interstates I:J Cities 

Figure 2. Map showing locations of known Texas fatmucket populations. 
47924 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

become infested with glochidia when 

they consume gravid female mussels 

(Barnhart et al. 2008, p. 373). This 

strategy of host infestation may limit 

population size, as reproductively 

successful females are sacrificed (i.e., 

eaten by freshwater drum). Related 

species are bradytictic, brooding larvae 

over the winter instead of releasing 

them immediately (Barnhart et al. 2008, 

p. 384). Other species in the genus 

Truncilla from the Southeast and 

Midwest reach a maximum age ranging 

from 8–18 years (Haag and Rypel 2010, 

pp. 4–6). 

Texas fawnsfoot are found in 

medium- to large-sized streams and 

rivers with flowing waters and mud, 

sand, and gravel substrates (Howells 

2014, p. 111). Adults are most often 

found in bank habitats and occasionally 

in backwater, riffle, and point bar 

habitats, with low to moderate velocities 

that appear to function as flow refuges 

during high flow events (Randklev et al. 

2017c, p. 137). 

Texas fawnsfoot occurs in the lower 

reaches of the Colorado and Brazos 

Rivers, and in the Trinity River 

(Randklev et al. 2017b, p. 4) in seven 

populations: East Fork Trinity River, 

Middle Trinity River, Clear Fork Brazos 

River, Upper Brazos River, Middle/ 

Lower Brazos River, San Saba/Colorado 

Rivers, and Lower Colorado River (table 

4; figure 3). Texas fawnsfoot was 

historically distributed throughout the 

Colorado and Brazos River basins 

(Howells 2014, pp. 111–112; and 

reviewed in Randklev et al. 2017c, pp. 

136–137) and in the Trinity River basin 

(Randklev et al. 2017b, p. 11). Texas 

fawnsfoot historically occurred in, but is 

now absent from, the Leon River 

(Popejoy et al. 2016, p. 477). Randklev 

et al. (2017c, p. 135) surveyed the Llano, 

San Saba, and Pedernales Rivers and 

found neither live individuals nor dead 

shells of Texas fawnsfoot. Isolated 

individuals not considered part of 

functioning populations have been 

found in the Little River. For more 

information on Texas fawnsfoot 

populations, see the SSA report. 

TABLE 4—CURRENT TEXAS FAWNSFOOT POPULATIONS

Population Streams included Counties 

Occupied 

reach length 

(mi (km)) 

Recent 

collection 

years 

(numbers) 

East Fork Trinity River .................... East Fork Trinity River ................... Kaufman Co., TX ........................... 12 (19) 2017 (40) 

2018 (12) 

Middle Trinity River ......................... Trinity River .................................... Navarro, Anderson, Leon, Houston, and Madison Co., TX.140 (225) 2016—2017 

(59) 

Clear Fork Brazos River ................. Clear Fork Brazos River ................ Shackelford and Throckmorton 

Co., TX.

13 (21) 2010 (1) 

2018 (0) 

Upper Brazos River ........................ Brazos River .................................. Palo Pinto and Parker Co., TX ...... 62 (100) 2017 (23) 

Middle/Lower Brazos River ............ Brazos River .................................. McLennan, Falls, Robertson, 

Milam, Brazos, Burleson, 

Grimes, Washington, Waller, 

Austin, and Fort Bend Co., TX.

346 (557) 2014 (188) 

2017 (28) 

San Saba/Colorado Rivers ............. San Saba River, Colorado River ... San Saba and Mills Co., TX .......... 43 (69) 2017 (0) 

2018 (2) 

Lower Colorado River ..................... Colorado River ............................... Colorado, Wharton, and 

Matagorda Co., TX.

109 (175) 2010 (52) 

2015 (10) 

2017 (9) 


jbell on DSKJLSW7X2PROD with PROPOSALS3
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47925 

Guadalupe Orb 

Burlakova et al. (2018, entire) recently 

described the Guadalupe orb 

(Cyclonaias necki) from the Guadalupe 

River basin as a separate species distinct 

from Texas pimpleback. The Guadalupe 

orb occurs only in the Guadalupe basin 

and is a small-sized mussel with a shell 

length that reaches up to 2.5 in (63 mm) 

(Burlakova et al. 2018, p. 48). 

Guadalupe orb shells are thinner and 

more compressed but otherwise 

morphologically similar to the closely 

related Texas pimpleback. The posterior 

ridge is more distinct and prominent, 

and the umbo is more compressed than 

in Texas pimpleback (Burlakova et al. 

2018, p. 48). Individuals collected from 

the upper Guadalupe River (near 

Comfort, Texas) averaged 1.9 in (48 mm) 

(Bonner et al. 2018, p. 221). Channel 

catfish, flathead catfish, and tadpole 

madtom are host fish for the Guadalupe 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.027</GPH>

' , 

' 

' I 

Current Known Populations of Texas Fawnsfoot 

' "'..,r.- ............. ., 

e 

Mi 0 25 

II 

KmO 25 

, 

' t 

,, J 

' 

-Populations - -- - Rivers 

County Boundaries ~ Lakes 

Interstates G Cities 

Figure 3. Map showing locations of known Texas fawnsfoot populations. 
47926 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

orb (Dudding et al. 2019, p. 15). 

Dudding et al. (2019, p. 16) cautioned 

that the apparent clumped distribution 

of Guadalupe orb (and closely related 

species) in ‘‘strongholds’’ could be 

related to observed ongoing declines in 

native catfishes, including the small and 

rare tadpole madtom, a riffle specialist. 

The best available information leads us 

to believe that reproduction, ecological 

interactions and habitat requirements of 

Guadalupe orb are similar to those of 

the closely related Texas pimpleback. 

The Guadalupe orb occurs only in the 

Guadalupe River basin in two separate 

and isolated populations: The upper 

Guadalupe River and the lower 

Guadalupe River (table 5; figure 4). An 

isolated individual not considered part 

of a functioning population has been 

found in the Blanco River, a tributary to 

the San Marcos River (Johnson et al. 

2018, p. 7). For more information on 

these populations, see the SSA report. 

TABLE 5—CURRENT GUADALUPE ORB POPULATIONS

Population Streams included Counties 

Occupied 

reach length 

(mi (km)) 

Recent 

collection 

years 

(numbers) 

Upper Guadalupe River .................. Guadalupe River ............................ Kerr, Kendall, and Comal Co., TX 95 (153) 2013 (1) 

2017 (10) 

2018 (2) 

Lower Guadalupe River .................. Guadalupe River, San Marcos 

River.

Caldwell, Guadalupe, Gonzales, 

DeWitt, and Victoria Co., TX.

181 (291) 2014–2015 

(893) 

2017 (41) 


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Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47927 

Texas Pimpleback 

The Texas pimpleback was originally 

described as Unio petrinus from the 

‘‘Llanos River’’ in ‘‘Upper’’ Texas 

(Gould 1855, p. 228). The species is now 

recognized as Cyclonaias petrina by the 

scientific community (Williams et al. 

2017, pp. 35, 37). Burlakova et al. (2018, 

entire) recently described the 

Guadalupe orb (C. necki) from the 

Guadalupe River basin as a separate 

species distinct from Texas pimpleback. 

Texas pimpleback is now considered to 

occur only in the Colorado River basin 

of Texas. Texas pimpleback is a smallto medium-sized (up to 4 in (103 mm)) 

mussel with a moderately inflated, 

yellow, brown, or black shell, 

occasionally with vague green rays or 

concentric blotches (Howells 2014, p. 

93). 

Recent laboratory studies of the 

closely related Guadalupe orb suggest 

that channel catfish (Ictalurus 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.028</GPH>

Current Known Populations of Guadalupe Orb 

Q 

Mi O 10 

L__j 

II 

KmO 10 

-Populations - - - - Rivers 

County Boundaries ~ Lakes 

= Interstates G Cities 

Figure 4. Map showing locations of known Guadalupe orb populations. 
47928 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

punctatus), flathead catfish (Pylodictus 

olivarus) and tadpole madtom (Noturus 

gyrinus) are host fish for Texas 

pimpleback (Dudding et al. 2019, p. 2). 

Related species have miniature 

glochidia and use catfish as hosts 

(Barnhart et al. 2008, pp. 373, 379). 

Additionally, related species can also 

produce conglutinates (Barnhart et al. 

2008, p. 376) and tend to exhibit shortterm brooding (tachytictia; releasing 

glochidia soon after the larvae mature) 

(Barnhart et al. 2008, p. 384). Texas 

pimpleback are reproductively active 

between April and August (Randklev et 

al. 2017c, p. 110). Related species live 

as long as 15–72 years (Haag and Rypel 

2010, p. 10). 

Texas pimpleback occurs in the 

Colorado River basin in five isolated 

populations: Concho River, Upper San 

Saba River, Lower San Saba River/ 

Colorado River, Llano River, and the 

Lower Colorado River (table 6; figure 5). 

Only the Lower San Saba and Llano 

River populations are known to be 

successfully reproducing. Texas 

pimpleback was historically distributed 

throughout the Colorado River basin 

(Howells 2014, pp. 93–94; reviewed in 

Randklev et al. 2017, pp. 109–110). For 

more information on Texas pimpleback 

populations, see the SSA report. 

TABLE 6— CURRENT TEXAS PIMPLEBACK POPULATIONS

Population Streams included Counties 

Occupied 

reach length 

(mi (km)) 

Recent 

collection 

years 

(numbers) 

Concho River .................................. Concho River ................................. Concho Co., TX ............................. 14 (23) 2008 (47) 

2012 (1) 

Upper San Saba River ................... San Saba River .............................. Menard Co., TX ............................. 30 (48) 2017 (1) 

Lower San Saba/Colorado Rivers .. San Saba River, Colorado River ... San Saba, McCulloch, Mills, 

Brown, and Coleman Co., TX.

178 (286) 2012 (247) 

2014 (481) 

2017 (97) 

2018 (42) 

Llano River ..................................... Llano River ..................................... Mason Co., TX ............................... 5 (8) 2012 (10) 

2016 (1) 

2017 (23) 

Lower Colorado River ..................... Colorado River ............................... Colorado and Wharton Co., TX ..... 98 (158) 2014 (49) 

2017 (8) 

2018 (30) 


jbell on DSKJLSW7X2PROD with PROPOSALS3
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47929 

False Spike 

The false spike is native to the Brazos, 

Colorado, and Guadalupe basins in 

central Texas (Howells 2010, p. 4; 

Randklev et al. 2017c, p. 12). It was 

thought to have historically occurred in 

the Rio Grande based on the presence of 

fossil and subfossil shells there 

(Howells 2010, p. 4), but those 

specimens have now been attributed to 

Sphenonaias taumilapana Conrad 1855 

(no common name; Randklev et al. 

2017c, p. 12; Graf and Cummings 2007, 

p. 309). 

The false spike was originally 

described as Unio mitchelli by Charles 

T. Simpson in 1895 from the Guadalupe 

River in Victoria County, Texas (Dall 

1896, pp. 5–6). The species has been 

assigned as Quincuncina mitchelli by 

Turgeon et al. (1988, p. 33) and was 

recognized as such by Howells et al. 

(1996, p. 127), and it was referenced as 

Quadrula mitchelli by Haag (2012, p. 


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Current Known Populations of 'lexas Pimpleback 

Q 

Mi O 20 

I 

II 

KmO 20 

-Populations - -- - Rivers 

County Boundaries~ Lakes 

:= Interstates El Cities 

Figure 5. Map showing locations of known Texas pimpleback populations. 
47930 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

71). Finally, it was recognized as 

Fusconaia mitchelli, its current 

nomenclature, by Pfeiffer et al. (2016, p. 

289). False spike is considered a valid 

taxon by the scientific community 

(Williams et al. 2017, pp. 35, 39). 

The false spike is a medium-sized 

freshwater mussel (to 5.2 in (132 mm)) 

with a yellow-green to brown or black 

elongate shell, sometimes with greenish 

rays. For a detailed description see 

Howells et al. 1996 (pp. 127–128) and 

Howells 2014 (p. 85). 

Based on closely related species, false 

spike likely brood eggs and larvae from 

early spring to late summer and host 

fish are expected to be minnows (family 

Cyprinidae) (Pfeiffer et al. 2016, p. 287). 

Confirmed host fish for false spike 

include blacktail shiner (Cyprinella 

venusta) and red shiner (C. lutrensis; 

Dudding et al. 2019, p. 16). 

Related species in the genus 

Fusconaia from the southeast United 

States are reach a maximum age of 15– 

51 years (Haag and Rypel 2010, pp. 4– 

6). No information on age at maturity 

currently exists for false spike (Howells 

2010d, p. 3). In part because of their 

long lifespan and episodic recruitment 

strategy, populations may be slow to 

recover from disturbance. 

False spike occur in larger creeks and 

rivers with sand, gravel, or cobble 

substrates, and in areas with slow to 

moderate flows. The species is not 

known from impoundments, nor from 

deep waters (Howells 2014, p. 85). 

False spike was once considered 

common wherever it was found; 

however, beginning in the early 1970s, 

the species began to be regarded as rare 

throughout its range, based on 

collection information (Strecker 1931, 

pp. 18–19; Randklev et al. 2017c, p. 13). 

It was considered to be extinct until 

2011, when the discovery of seven live 

false spike in the Guadalupe River, near 

Gonzales, Texas, was the first report of 

living individuals in nearly four 

decades (Howells 2010d, p. 4; Randklev 

et al. 2011, p. 17). Dudding et al. (2019, 

pp. 16–17) cautioned that the patchy 

distribution of false spike could be 

related to host fish relationships; that is, 

because their host fish have a small 

home range, limited dispersal ability, 

and are sensitive to human impacts, 

distribution of false spike could be 

limited by access to, and movement of, 

host fish. 

Currently, the false spike occurs in 

four populations: In the Little River and 

some tributaries (Brazos River basin), 

the lower San Saba and Llano Rivers 

(Colorado River basin), and in the lower 

Guadalupe River (Guadalupe River 

Basin) (table 7; figure 6). For more 

information on these populations, see 

the SSA report. False spike is presumed 

to have been extirpated from the 

remainder of its historical range 

throughout the Brazos, Colorado, and 

Guadalupe Basins of central Texas 

(reviewed in Randklev et al. 2017c, pp. 

12–13). 

TABLE 7—CURRENT FALSE SPIKE POPULATIONS

Population Streams included Counties 

Occupied 

reach length 

(mi (km)) 

Recent 

collection 

years 

(number 

collected) 

Little River and tributaries .............. Little River ......................................

Brushy Creek, San Gabriel River ..

Milam and Williamson Co., TX ...... 41 (66) 2015 (29) 

Lower San Saba River ................... San Saba River .............................. San Saba Co., TX .......................... 42 (67) 2012 (3) 

Llano River ..................................... Llano River ..................................... Mason Co., TX ............................... <1 (∼1) 2017 (1) 

Lower Guadalupe River .................. Guadalupe River ............................ Gonzales, DeWitt, and Victoria 

Co., TX.

102 (164) 2014–2015 

(652) 


jbell on DSKJLSW7X2PROD with PROPOSALS3
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47931 

BILLING CODE 4333–15–C 

Regulatory and Analytical Framework 

Regulatory Framework 

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 is 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 any species is an 

‘‘endangered species’’ or a ‘‘threatened 

species’’ because of any of the following 

factors: 


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Current Known Populations of False Spike 

Mi O 10 

L__J 

n 

KmO 10 

- Populations - -- - Rivers 

County Boundaries m lakes 

=-= Interstates G Cities 

Figure 6. Map showing locations of known false spike populations. 
47932 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(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 (e.g. conservation measures). 

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 

expected response by the species, and 

the effects of the threats—in light of 

those actions and conditions that will 

ameliorate the threats—on an 

individual, population, and species 

level. We evaluate each threat and its 

expected effects on the species, then 

analyze the cumulative effect of all of 

the threats on the species as a whole. 

We also consider the cumulative effect 

of the threats in light of those actions 

and conditions that will have positive 

effects on the species, such as any 

existing regulatory mechanisms or 

conservation efforts. The Secretary 

determines whether the species meets 

the definition of an ‘‘endangered 

species’’ or a ‘‘threatened species’’ only 

after conducting this cumulative 

analysis and describing the expected 

effect on the species now and in the 

foreseeable future. 

The Act does not define the term 

‘‘foreseeable future,’’ which appears in 

the statutory definition of ‘‘threatened 

species.’’ Our implementing regulations 

at 50 CFR 424.11(d) set forth a 

framework for evaluating the foreseeable 

future on a case-by-case basis. The term 

foreseeable future extends only so far 

into the future as the Services can 

reasonably determine that both the 

future threats and the species’ responses 

to those threats are likely. In other 

words, the foreseeable future is the 

period of time in which we can make 

reliable predictions. ‘‘Reliable’’ does not 

mean ‘‘certain’’; it means sufficient to 

provide a reasonable degree of 

confidence in the prediction. Thus, a 

prediction is reliable if it is reasonable 

to depend on it when making decisions. 

It is not always possible or necessary 

to define foreseeable future as a 

particular number of years. Analysis of 

the foreseeable future uses the best 

scientific and commercial data available 

and should consider the timeframes 

applicable to the relevant threats and to 

the species’ likely responses to those 

threats in view of its life-history 

characteristics. Data that are typically 

relevant to assessing the species’ 

biological response include speciesspecific factors such as lifespan, 

reproductive rates or productivity, 

certain behaviors, and other 

demographic factors. 

Analytical Framework 

The SSA report documents the results 

of our comprehensive biological status 

review for the Guadalupe fatmucket, 

Texas fatmucket, Texas fawnsfoot, 

Guadalupe orb, Texas pimpleback, and 

false spike, including an assessment of 

the potential stressors to each species. 

The SSA report does not represent a 

decision by the Service on whether the 

species should be proposed for listing as 

endangered or threatened species under 

the Act. The SSA report provides the 

scientific basis that informs our 

regulatory decision, which involves the 

further application of standards within 

the Act and its implementing 

regulations and policies. The following 

is a summary of the key results and 

conclusions from the SSA report; the 

full SSA report can be found at Docket 

No. FWS–R2–ES–2019–0061 on http://

www.regulations.gov. 

To assess the viability of the six 

Central Texas mussels, we used the 

three conservation biology principles of 

resiliency, redundancy, and 

representation (Shaffer and Stein 2000, 

pp. 306–310). Briefly, resiliency 

supports the ability of the species to 

withstand environmental and 

demographic stochasticity (for example, 

wet or dry, warm or cold years), 

redundancy supports the ability of the 

species to withstand catastrophic events 

(for example, droughts, large pollution 

events), and representation supports the 

ability of the species to adapt over time 

to long-term changes in the environment 

(for example, climate changes). In 

general, the more resilient and 

redundant a species is and the more 

representation it has, the more likely it 

is to sustain populations over time, even 

under changing environmental 

conditions. Using these principles, we 

identified the species’ ecological 

requirements for survival and 

reproduction at the individual, 

population, and species levels, and 

described the beneficial and risk factors 

influencing the species’ viability. 

The SSA process can be categorized 

into three sequential stages. During the 

first stage, we evaluated individual 

species’ life-history needs. The next 

stage involved an assessment of the 

historical and current condition of the 

species’ demographics and habitat 

characteristics, including an 

explanation of how the species arrived 

at its current condition. The final stage 

of the SSA involved making predictions 

about the species’ responses to positive 

and negative environmental and 

anthropogenic influences. This process 

used the best available information to 

characterize viability as the ability of a 

species to sustain populations in the 

wild over time. We use this information 

to inform our regulatory decision. 

Summary of Biological Status and 

Threats 

In this discussion, we review the 

biological condition of the species and 

their resources, and the threats that 

influence the species’ current and future 

conditions, in order to assess the 

species’ overall viability and the risks to 

that viability. 

Using various timeframes and the 

current and projected future resiliency, 

redundancy, and representation, we 

describe the species’ levels of viability 

over time. For the Central Texas mussels 

to maintain viability, their populations 

or some portion thereof must be 

resilient. A number of factors influence 

the resiliency of Central Texas mussel 

populations, including occupied stream 

length, abundance, and recruitment. 

While some of the six species have lifehistory adaptations that help them 

tolerate dewatering and other stressors 

to some extent, each of these stressors 

diminishes the resiliency of populations 

to some degree and especially in 

combination. Elements of the species’ 

habitat that determine whether Central 

Texas mussel populations can grow to 

maximize habitat occupancy influence 

those factors, thereby increasing the 

resiliency of populations. These 


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resiliency factors and habitat elements 

are discussed in detail in the SSA report 

and summarized here. 

Species Needs 

Occupied Stream Length: Most 

freshwater mussels, including the 

Central Texas mussel species, are found 

in aggregations, called mussel beds, that 

vary in size from about 50 to >5,000 

square meters (m2), separated by stream 

reaches in which mussels are absent or 

rare (Vaughn 2012, p. 2). We define a 

mussel population at a larger scale than 

a single mussel bed; it is the collection 

of mussel beds within a stream reach 

between which infested host fish may 

travel, allowing for ebbs and flows in 

mussel bed density and abundance over 

time throughout the entirety of the 

population’s occupied reach. Therefore, 

resilient mussel populations must 

occupy stream reaches long enough 

such that stochastic events that affect 

individual mussel beds do not eliminate 

the entire population. Repopulation by 

infested fish from other mussel beds 

within the reach can allow the 

population to recover from these events. 

We consider populations extending 

more than 50 miles (80 kilometers (km)) 

to be highly resilient to stochastic 

events because a single event is unlikely 

to affect the entire population. 

Populations occupying reaches between 

20 and 49 river miles (32–79 km) have 

some resiliency to stochastic events, and 

populations occupying reaches less than 

20 miles (32 km) have little resiliency. 

Note that, by definition, an extirpated or 

functionally extirpated population 

occupies a stream length of 

approximately (or approaching) zero 

miles (0 km). 

Abundance: Mussel abundance in a 

given stream reach is a product of the 

number of mussel beds and the density 

of mussels within those beds. For 

populations of Central Texas mussel 

species to be healthy (i.e., resilient), 

there must be many mussel beds of 

sufficient density such that local 

stochastic events do not necessarily 

eliminate the bed(s), allowing the 

mussel bed and the overall local 

population within a stream reach to 

recover from any single event. Mussel 

abundance is indicated by the number 

of individuals found during a sampling 

event; mussel surveys rarely represent a 

complete census of the population. 

Instead, density is estimated by the 

number found during a survey event 

using various statistical techniques. 

Because we do not have population 

estimates for most populations of 

Central Texas mussels, nor are the 

techniques directly comparable (i.e., 

same area size searched, similar search 

time, etc.), we used the number of 

individuals captured as an index over 

time, presuming relatively similar levels 

of effort. While we cannot precisely 

determine population abundance at the 

sites using these numbers, we are able 

to determine if the species is dominant 

at the site or rare and examine this over 

time if those data are available. 

Reproduction: Resilient Central Texas 

mussel populations must also be 

reproducing and recruiting young 

individuals into the population. 

Population size and abundance reflects 

previous influences on the population 

and habitat, while reproduction and 

recruitment reflect population trends 

that may be stable, increasing, or 

decreasing over time. For example, a 

large, dense mussel population that 

contains mostly old individuals is not 

likely to remain large and dense into the 

future, as there are few young 

individuals to sustain the population 

over time (i.e., death rates exceed birth 

rates and subsequent recruitment of 

reproductive adults resulting in negative 

population growth). Conversely, a 

population that is less dense but has 

many young and/or gravid individuals 

may likely grow to a higher density in 

the future (i.e., birth rates and 

subsequent recruitment of reproductive 

adults exceeds death rates resulting in 

positive population growth). Detection 

rates of very young juvenile mussels 

during routine abundance and 

distribution surveys are extremely low 

due to sampling bias because sampling 

for these species involves tactile 

searches and mussels <35 mm are very 

difficult to detect (Strayer and Smith 

2003, pp. 47–48). 

Evidence of reproduction is 

demonstrated by repeated captures of 

small-sized individuals (juveniles and 

subadults near the low end of the 

detectable range size ∼35 mm; Randklev 

et al. 2013, p. 9) over time and by 

observing gravid (with eggs in the 

marsupium, gills, or gill pouches) 

females during the reproductively active 

time of year. While small-sized mussels 

and gravid females can be difficult to 

detect, it is important that surveyors 

attempt to detect them as reproduction 

and subsequent recruitment are 

important demographic parameters that 

affect growth rates in mussel 

populations (Berg et al. 2008, pp. 396, 

398–399; Matter et al. 2013, pp. 122– 

123, 134–135). 

Risk Factors for the Central Texas 

Mussels 

We reviewed the potential risk factors 

(i.e., threats, stressors) that could be 

affecting the six Central Texas mussels 

now and in the future. In this proposed 

rule, we will discuss only those factors 

in detail that could meaningfully impact 

the status of the species. Those risks 

that are not known to have effects on 

Central Texas mussel populations, such 

as disease, are not discussed here but 

are evaluated in the SSA report. Many 

of the threats and risk factors are the 

same or similar for each of the six 

species. Where the effects are expected 

to be similar, we present one discussion 

that applies to all six species. Where the 

effects may be unique or different to one 

species, we will address that 

specifically. The primary risk factors 

(i.e., threats) affecting the status of the 

Central Texas mussels are: (1) Increased 

fine sediment (Factor A from the Act), 

(2) changes in water quality (Factor A), 

(3) altered hydrology in the form of 

inundation (Factor A), (4) altered 

hydrology in the form of loss of flow 

and scour of substrate (Factor A), (5) 

predation and collection (Factor C), and 

(6) barriers to fish movement (Factor E). 

These factors are all exacerbated by the 

ongoing and expected effects of climate 

change. Finally, we also reviewed the 

conservation efforts being undertaken 

for the species. 

Increased Fine Sediment 

Juvenile and adult Central Texas 

mussels inhabit microsites that have 

abundant interstitial spaces, or small 

openings in an otherwise closed matrix 

of substrate, created by gravel, cobble, 

boulders, bedrock crevices, tree roots, 

and other vegetation. Inhabited 

interstitial spaces have some amount of 

fine sediment (i.e., clay and silt) 

necessary to provide appropriate 

shelter. However, excessive amounts of 

fine sediments can reduce the number 

of appropriate microsites in an 

otherwise suitable mussel bed by filling 

in these interstitial spaces and can 

smother mussels in place. All six 

species of Central Texas mussels 

generally require stable substrates, and 

loose silt deposits do not generally 

provide for substrate stability that can 

support mussels. Interstitial spaces 

provide essential habitat for juvenile 

mussels. Juvenile freshwater mussels 

burrow into interstitial substrates, 

making them particularly susceptible to 

degradation of this habitat feature. 

When clogged with sand or silt, 

interstitial flow may become reduced 

(Brim Box and Mossa 1999, p. 100), thus 

reducing juvenile habitat availability 

and quality. While adult mussels can be 

physically buried by excessive 

sediment, ‘‘the main impacts of excess 

sedimentation on unionids (freshwater 

mussels) are often sublethal’’ and 

include interference with feeding 

mediated by valve closure (Brim Box 


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and Mossa 1999, p. 101). Many land use 

activities can result in excessive 

erosion, sediment production, and 

channel instability, including, but not 

limited to: logging, crop farming, 

ranching, mining, and urbanization 

(Brim Box and Mossa 1999, p. 102). 

Under a natural flow regime, a 

stream’s sediment load is in equilibrium 

such that as sediments are naturally 

moved downstream from one microsite 

to another, the amount of sediment in 

the substrate is relatively stable, given 

that different reaches within a river or 

stream may be aggrading (gaining) or 

degrading (losing) sediment (Poff et al. 

1997, pp. 770–772). Current and past 

human activities result in enhanced 

sedimentation in river systems, and 

legacy sediment, resulting from past 

land disturbance and reservoir 

construction, continues to persist and 

influence river processes and sediment 

dynamics (Wohl 2015, p. 31) and these 

legacy effects can degrade mussel 

habitats. Fine sediments collect on the 

streambed and in crevices during low 

flow events, and much of the sediment 

is washed downstream during high flow 

events (also known as cleansing flows) 

and deposited elsewhere. However, 

increased frequency of low flow events 

(from groundwater extraction, instream 

surface flow diversions, and drought) 

combined with a decrease in cleansing 

flows (from reservoir management and 

drought) causes sediment to 

accumulate. Sediments deposited by 

large-scale flooding or other disturbance 

may persist for several years until 

adequate cleansing flows can 

redistribute that sediment downstream. 

When water velocity decreases, which 

can occur from reduced streamflow or 

inundation, water loses its ability to 

carry sediment in suspension, and 

sediment falls to the substrate, 

eventually smothering mussels not 

adapted to soft substrates (Watters 2000, 

p. 263). Sediment accumulation can be 

exacerbated when there is a 

simultaneous increase in the sources of 

fine sediments in a watershed. 

In the range of the Central Texas 

mussels, these sources include 

streambank erosion from development, 

agricultural activities, livestock and 

wildlife grazing and browsing, inchannel disturbances, roads, and 

crossings, among others (Poff et al. 

1997, p. 773). In areas with ongoing 

development, runoff can transport 

substantial amounts of sediment from 

ground disturbance related to 

construction activities with inadequate 

or absent sedimentation controls. While 

these construction impacts can be 

transient (lasting only during the 

construction phase), the long-term 

effects of development are long lasting 

and can result in hydrological 

alterations as increased impervious 

cover increases runoff and resulting 

shear stress causes streambank 

instability and additional 

sedimentation. 

All populations of Central Texas 

mussels face the risk of fine sediment 

accumulation to varying degrees. 

Multiple populations of the six Central 

Texas mussel species are experiencing 

increased sedimentation, including in 

particular the Clear Fork Brazos River 

(Texas fawnsfoot), middle and lower 

Brazos River (false spike and Texas 

fawnsfoot), and lower Colorado River 

(Texas pimpleback, Texas fawnsfoot). In 

the future, we expect sediment 

deposition to continue to increase 

across the range of all six species due to 

low water levels and decreasing 

frequency of cleansing flows at all 

populations and for longer periods due 

to climate change and additional human 

development in the watershed. 

Changes in Water Quality 

Freshwater mussels and their host 

fish require water in sufficient quantity 

and quality on a consistent basis to 

complete their life cycles. Urban growth 

and other anthropogenic activities 

across Texas are placing increased 

demands on limited freshwater 

resources that, in turn, can have 

deleterious effects on water quality. 

Water quality can be degraded through 

contamination or alteration of water 

chemistry. Chemical contaminants are 

ubiquitous throughout the environment 

and are a major reason for the current 

declining status of freshwater mussel 

species nationwide (Augspurger et al. 

2007, p. 2025). Immature mussels (i.e., 

juveniles and glochidia) are especially 

sensitive to water quality degradation 

and contaminants (Cope et al. 2008, 

p. 456, Wang et al. 2017, pp. 791–792; 

Wang et al. 2018, p. 3041). 

Chemicals enter the environment 

through both point and nonpoint source 

discharges, including hazardous spills, 

industrial wastewater, municipal 

effluents, and agricultural runoff. These 

sources contribute organic compounds, 

trace metals, pesticides, and a wide 

variety of newly emerging contaminants 

(e.g., pharmaceuticals) that comprise 

some 85,000 chemicals in commerce 

today that are released to the aquatic 

environment (Environmental Protection 

Agency (EPA) 2018, p. 1). The extent to 

which environmental contaminants 

adversely affect aquatic biota can vary 

depending on many variables such as 

concentration, volume, and timing of 

the release. Species diversity and 

abundance consistently ranks lower in 

waters that are polluted or otherwise 

impaired by contaminants. Freshwater 

mussels are not generally found for 

many miles downstream of municipal 

wastewater treatment plants (Gillis et al. 

2017, p. 460; Goudreau et al. 1993, p. 

211; Horne and McIntosh 1979, p. 119). 

For example, transplanted common 

freshwater mussels (including 

threeridge (Amblema plicata) and the 

nonnative Asian clam (Corbicula 

fluminea) showed reduced growth and 

survival below a wastewater treatment 

plant (WWTP) outfall relative to sites 

located upstream of the WWTP in 

Wilbarger Creek (a tributary to the 

Colorado River in Travis County, 

Texas); water chemistry was altered by 

the wastewater flows at downstream 

sites, with elevated constituents in the 

water column that included copper, 

potassium, magnesium, and zinc 

(Duncan and Nobles 2012, p. 8; Nobles 

and Zhang 2015, p. 11). Contaminants 

released during hazardous spills are also 

of concern. Although spills are 

relatively short-term localized events, 

depending on the types of substances 

and volume released, water resources 

nearby can be severely impacted and 

degraded for years following an 

incident. 

Ammonia is of particular concern 

below wastewater treatment plants 

because freshwater mussels are 

particularly sensitive to increased 

ammonia levels (Augspurger et al. 2003, 

p. 2569). Elevated concentrations of unionized ammonia (NH3) in the 

interstitial spaces of benthic habitats 

(>0.2 parts per billion) have been 

implicated in the reproductive failure of 

other freshwater mussel populations 

(Strayer and Malcom 2012, pp. 1787– 

1788), and sublethal effects (valve 

closures) have recently been described 

as total ammonia nitrogen approaches 

2.0 milligrams per liter (mg/L = ppm; 

Bonner et al. 2018, p. 186). Immature 

mussels (i.e., juveniles and glochidia) 

are especially sensitive to water quality 

degradation and contaminants, 

including ammonia (Wang et al. 2007, 

p. 2055). For smooth pimpleback 

(Cyclonaias houstonensis, a species 

native to central Texas but not included 

in this listing), the revised EPA 

ammonia benchmarks are sufficient to 

protect from short term effects of 

ammonia on the species’ physiological 

processes (Bonner et al. 2018, p. 151). 

However, the long-term effects of 

chronic exposure (i.e., years or decades) 

to freshwater mussels has yet to be 

experimentally investigated. 

Municipal wastewater contains both 

ionized and un-ionized ammonia, and 

wastewater discharge permits issued by 

Texas Commission on Environmental 


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Quality (TCEQ) do not always impose 

limits on ammonia, particularly for 

smaller volume dischargers. Therefore, 

at a minimum, concentrations of 

ammonia are likely to be elevated in the 

immediate mixing zone of some WWTP 

outfalls. To give some insight into the 

potential scope of WWTP related 

impacts, approximately 480 discharge 

permits are issued for the Brazos River 

watershed alone from its headwaters 

above Possum Kingdom Lake down to 

the Gulf of Mexico (TCEQ 2018c, 

entire). In addition, some industrial 

permits, such as animal processing 

facilities, have ammonia limits in the 

range of 3 to 4 mg/L or higher, which 

exceeds levels that inhibited growth in 

juvenile fatmucket (Lampsilis 

siliquoidea) and rainbow mussel 

(Villosa iris) (Wang et al. 2007, entire). 

Similar to the Brazos River, WWTP 

outfalls are numerous throughout the 

ranges of the Central Texas mussels. 

An additional type of water quality 

degradation that affects the Central 

Texas mussels is alteration of water 

quality parameters such as dissolved 

oxygen, temperature, and salinity levels. 

Dissolved oxygen levels may be reduced 

from increased nutrient inputs or other 

sources of organic matter that increase 

the biochemical oxygen demand in the 

water column as microorganisms 

decompose waste. Organic waste can 

originate from storm water or irrigation 

runoff or wastewater effluent, and 

juvenile mussels seem to be particularly 

sensitive to low dissolved oxygen (with 

sublethal effects evident at 2 ppm and 

lethal effects evident at 1.3 ppm; Sparks 

and Strayer 1998, pp. 132–133). 

Increased water temperature (over 30 °C 

and approaching 40 °C) from climate 

change and from low flows during 

drought can exacerbate low dissolved 

oxygen levels in addition to other 

drought-related effects on both juvenile 

and adult mussels (Sparks and Strayer 

1998, pp. 132–133). Finally, high 

salinity concentrations are an additional 

concern in certain watersheds, where 

dissolved salts can be particularly 

limiting to Central Texas mussels. 

Upper portions of the Brazos and 

Colorado Rivers, originating from the 

Texas High Plains, contain saline water, 

sourced from both natural geological 

formations, and from oil and gas 

development. Salinity in river water is 

diluted by surface flow and as surface 

flow decreases salt concentrations 

increase, resulting in adverse effects to 

freshwater mussels. Even low levels of 

salinity (2–4 parts per thousand (ppt)) 

have been demonstrated to have 

substantial negative effects on 

reproductive success, metabolic rates, 

and survival of freshwater mussels 

(Blakeslee et al. 2013, p. 2853). Bonner 

et al. (2018, pp. 155–156) suggest that 

the behavioral response of valve closure 

to high salinity concentrations (>2 ppt) 

is the likely mechanism for reduced 

metabolic rates, reduced feeding, and 

reduced reproductive success based on 

reported sublethal effects of salinity >2 

ppt for Texas pimpleback. 

Water quality and quantity are 

interdependent, so reductions in surface 

flow from drought, instream diversion, 

and groundwater extraction serve to 

concentrate contaminants by reducing 

flows that would otherwise dilute point 

and non-point source pollution. For 

example, salinity inherently poses a 

greater risk to aquatic biota under low 

flow conditions as salinity 

concentrations and water temperatures 

increase. Drought conditions can place 

additional stressors on stream systems 

beyond reduced flow by exacerbating 

contaminant-related effects to aquatic 

biota, including Central Texas mussels. 

Not only can temperature be a 

biological, physical, and chemical 

stressor, the toxicity of many pollutants 

to aquatic organisms increases at higher 

temperatures (e.g., ammonia, mercury). 

We foresee threats to water quality 

increasing into the future as demand 

and competition for limited water 

resources grows. 

Altered Hydrology—Inundation 

Central Texas mussels are adapted to 

flowing water (lotic habitats) rather than 

standing water (lentic habitats) and 

require free-flowing water to survive. 

Low flow events (including stream 

drying) and inundation can eliminate 

habitat appropriate for Central Texas 

mussels, and while these species can 

survive these events for a short 

duration, populations that experience 

prolonged drying events or repeated 

drying events will not persist over time. 

Inundation has primarily occurred 

upstream of dams, both large (such as 

the Highland Lakes on the Colorado 

River and other major flood control and 

water supply reservoirs) and small (low 

water crossings and diversion dams 

typical of the tributaries and occurring 

usually on privately owned lands 

throughout Central Texas). Inundation 

causes an increase in sediment 

deposition, eliminating the crevices that 

many Central Texas mussel species 

inhabit. Inundation also includes the 

effects of reservoir releases where 

frequent variation in surface water 

elevation acts to make habitats 

unsuitable for Central Texas mussels. In 

large reservoirs, deep water is very cold 

and often devoid of oxygen and 

necessary nutrients. Cold water (less 

than 11 °Celsius (C) or 52 °F (F)) stunts 

mussel growth and delays or hinders 

spawning. The Central Texas mussels 

do not tolerate inundation under large 

reservoirs. Further, deep-water 

reservoirs with bottom release (like 

Canyon Reservoir) can affect water 

temperatures several miles downriver. 

The water temperature remains below 

21.1 °C for the first 3.9 miles (6.3 km) 

of the 13.8-mile (22.2-km) Canyon 

Reservoir tailrace (Texas Parks and 

Wildlife Department (TPWD) 2007c, p. 

ii), cold enough to support a 

recreational non-native rainbow and 

brown trout fishery. 

The construction of dams, inundation 

of reservoirs, and management of water 

releases have significant effects on the 

natural hydrology of a river or stream. 

For example, dams trap sediment in 

reservoirs, and managed releases 

typically do not conform to the natural 

flow regime (i.e., higher baseflows, and 

peak flows of reduced intensity but 

longer duration). Rivers transport not 

only water but also sediment, which is 

transported mostly as suspended load 

(held by the water column), and most 

sediment transport occurs during floods 

as sediment transport increases as a 

power function (greater than linear) of 

flow (Kondolf 1997, p. 533). It follows 

that increased severity of flooding 

would result in greater sediment 

transport, with important effects on 

substrate stability and benthic habitats 

for freshwater mussels and other 

organisms dependent on stable benthic 

habitats. Further, water released by 

dams is usually clear and does not carry 

a sediment load and is considered 

‘‘hungry water because the excess 

energy is typically expended on erosion 

of the channel bed and banks . . . 

resulting in incision (downcutting of the 

bed) and coarsening of the bed material 

until a new equilibrium is reached’’ 

(Kondolf 1997, p. 535). Conversely, 

depending on how dam releases are 

conducted, reduced flood peaks can 

lead to accumulations of fine sediment 

in the river bed (i.e., loss of flushing 

flows, Kondolf 1997, pp. 535, 548). 

Operation of flood-control, watersupply, and recreation reservoirs results 

in altered hydrologic regimes, including 

an attenuation of both high- and lowflow events. Flood-control dams store 

floodwaters and then release them in a 

controlled manner; this extended 

release of flood waters can result in 

significant scour and loss of substrates 

that provide mussel habitat. Along with 

this change in the flow of water, 

sediment dynamics are affected as 

sediment is trapped above and scoured 

below major impoundments. These 

changes in water and sediment transport 


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have negatively affected freshwater 

mussels and their habitats. 

There are numerous dams throughout 

the range of Central Texas mussels. 

There are now 27 major reservoirs in the 

Brazos River basin (16 have >50,000 

acre-feet of storage) (Brazos River and 

Associated Bay Estuary System Basin 

and Bay Expert Science Team (BBEST) 

2012, p. 33); 31 major reservoirs in the 

Colorado River basin, including the 

Highland Lakes (Texas Water 

Development Board (TWDB) 2018d, p. 

1); 9 major reservoirs on the Guadalupe 

River (BBEST 2011b, p. 2.2); and 31 

major reservoirs in the Trinity River 

basin (BBEST 2009, p. 10). These 

reservoirs, subsequent inundation, and 

resulting fragmentation of mussel 

populations has been the primary driver 

of the current distribution of the Central 

Texas mussels. Additional reservoirs are 

planned for the future, including the 

Cedar Ridge Reservoir, proposed by the 

City of Abilene on the Clear Fork of the 

Brazos River near the town of Lueders, 

Texas (83 FR 16061), and more than one 

reservoir is proposed to be built off the 

main channel of the Lower Colorado 

River in Wharton and Colorado 

Counties, Texas (Lower Colorado River 

Authority (LCRA) 2018c, p. 1). The 

Allens Creek Reservoir is proposed for 

construction on Allens Creek near the 

City of Wallis, to provide water supply 

and storage for the City of Houston 

(Brazos River Authority (BRA) 2018b, p. 

1). Water that is planned to be pumped 

from the Brazos River during high flows 

will be stored and released back into the 

river to meet downstream needs during 

periods of low flow. 

Altered Hydrology—Flow Loss and 

Scour 

Extreme water levels—both low flows 

and high flows—threaten population 

persistence of the Central Texas 

mussels. The effects of population 

losses associated with excessively low 

flows are compounded by population 

losses associated with excessively high 

flows. Whereas persistent low flow 

during times of drought results in 

drying of mussel habitats and 

desiccation of exposed mussels, rapid 

increases in flows associated with largescale rain events and subsequent 

flooding results in scour of the 

streambed and physical displacement of 

mussels and appropriate substrates. 

Appropriately-sized substrates are 

moved during scouring high flow events 

and mussels are transported 

downstream to inappropriate sites or are 

buried by inappropriately sized 

materials. The Central Texas mussels 

are experiencing a repeating cycle of 

alternating droughts and flooding that, 

in combination with hydrological 

alterations, threatens population 

persistence. 

Droughts that have occurred in the 

recent past have led to extremely low 

flows in several Central Texas rivers. 

Many of these rivers have some 

resiliency to drought because they are 

spring-fed (Colorado River tributaries, 

Guadalupe River), are very large (lower 

Brazos and Colorado Rivers), or have 

significant return flows (Trinity River), 

but drought in combination with 

increased groundwater pumping may 

lead to lower river flows of longer 

duration than have been recorded in the 

past. Reservoir releases can be managed 

to some extent during drought 

conditions to prevent complete 

dewatering below many major 

reservoirs. During the months of July 

and August 2018, the Clear Fork Brazos, 

Concho, San Saba, Llano, Pedernales, 

and upper Colorado and upper 

Guadalupe Rivers all had very low flows 

(U.S. Geological Survey (USGS) 2019). 

Streamflow in the Colorado River 

above the Highland Lakes and 

downstream of the confluence with 

Concho River has been declining since 

the 1960s as evidenced by annual daily 

mean streamflow (USGS 2008b, pp. 812, 

814, 848, 870, 878, 880), and overall 

river discharge for each of the rivers can 

be expected to continue to decline due 

to increased drought as a result of 

climate change, absent significant return 

flows. There are a few exceptions 

including the Llano River at Llano 

(USGS 2008b, p. 892), Pedernales River 

at Fredericksburg (USGS 2008b, p. 896), 

Onion Creek near Driftwood, and Onion 

Creek at Highway 183 (flows appear to 

become more erratic, characteristic of a 

developing watershed; USGS 2008b, pp. 

930, 946). In the San Saba River, 

continuing or increasing surface and 

alluvial aquifer groundwater 

withdrawals in combination with 

drought is likely to result in reduced 

streamflow, affecting mussels in the 

future (Randklev et al. 2017c, pp. 10– 

11). 

Flows have declined due to drought 

in the Brazos River in recent years 

upstream of Lake Whitney (USGS 

2008b, pp. 578, 600, 626, 638; BRA 

2018e, p. 6), although baseflows are 

maintained somewhat due to releases 

from Lake Granbury and other reservoirs 

in the upper basin (USGS 2008b, p. 644; 

BRA 2018e, p. 6). In the middle Brazos, 

U.S. Army Corps of Engineers (USACE) 

dams have reduced the magnitude of 

floods on the mainstem of the Brazos 

River downstream of Lake Whitney 

(USGS 2008b, pp. 652, 676 766, 776; 

BRA 2018e, p. 6), while flows in the 

lower Brazos and Navasota Rivers 

appear to have higher baseflows due to 

water supply operations in the upper 

basin that deliver to downstream users 

(USGS 2008b, pp. 754, 766, 776; BRA 

2018e, p. 6). Lake Limestone releases 

also appear to be contributing to higher 

base flows in the Lower Brazos (BRA 

2018e, p. 6). Flows have declined in the 

upper Guadalupe River (USGS 2008b, 

pp. 992, 994, 1000, 1018) but appear 

relatively unchanged at Comfort and 

Spring Branch and in the San Marcos 

River (USGS 2008b, pp. 1004, 1006, 

1022), and in the lower Guadalupe River 

(USGS 2008b, pp. 1036, 1040). In the 

lower sections of the Colorado River, 

lower flows and reduced high flow 

events are more common now decades 

after major reservoirs were constructed 

(USGS 2008b, pp. 964, 966). In the 

Trinity River, low flows are higher 

(elevated baseflows) than they were in 

the past (USGS 2008b, pp. 370, 398, 

400, 430) because of substantial return 

flows from Dallas area wastewater 

treatment plants. 

Many of the tributary streams (i.e., 

Concho, San Saba, Llano, and 

Pedernales Rivers) historically received 

significant groundwater inputs from 

multiple springs associated with the 

Edwards and other aquifers. As spring 

flows decline due to drought or 

groundwater lowering from pumping, 

habitat for Central Texas mussels in the 

tributary streams is reduced and could 

eventually cease to exist (Randklev et al. 

2018, pp. 13–14). While Central Texas 

mussels may survive short periods of 

low flow, as low flows persist, mussels 

face oxygen deprivation, increased 

water temperature, increased predation 

risk, and ultimately stranding, all 

reducing survivorship, reproduction, 

and recruitment in the population. 

Low-flow events lead to increased risk 

of desiccation (physical stranding and 

drying) and exposure to elevated water 

temperature and other water quality 

degradations, such as contaminants, as 

well as to predation. For example, 

sections of the San Saba River, 

downstream of Menard, Texas, 

experienced very low flows during the 

summer of 2015, which led to 

dewatering of occupied habitats as 

evidenced by observations of recent 

dead shell material of Texas pimpleback 

and Texas fatmucket (TPWD 2015, pp. 

2–3; described in detail by Randklev et 

al. 2018, entire). Several USGS stream 

gauges reported very low flows during 

the 2017–2018 water year, including: 

the Clear Fork of the Brazos River, Elm 

Creek, Concho River at Paint Rock, San 

Saba River, Colorado River at San Saba, 

Llano River, Pedernales River, and 

upper Guadalupe River (USGS 2018a, 

entire). Service, TPWD, and Texas 


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Department of Transportation (TxDOT) 

biologists noted in 2017 that at one site 

on the Brazos River near Highbank, 

Texas, the presence of 42 dead to fresh 

dead (with tissue intact) Texas 

fawnsfoot that likely died as a result of 

recent drought or scouring events 

(Tidwell 2017, entire). 

High flow events lead to increased 

risk of physical removal, transport, and 

burial (entrainment) of mussels as 

unstable substrates are transported 

downstream by floodwaters and later 

redeposited in locations that may not be 

suitable. A site in the lower Colorado 

River near Altair, Texas, suffered 

significant changes in both mussel 

community structure and bathymetry 

(measurement of water depths) during 

extensive flooding (and resulting high 

flows) in August 2017, as a result of 

Hurricane Harvey (Bonner et al. 2018, p. 

266). This site previously held the 

highest mussel abundance (Bonner et al. 

2018, pp. 242–243) and represented 

high-quality habitat within the Colorado 

River basin, prior to the flooding events. 

Mussel abundance significantly 

decreased by nearly two orders of 

magnitude (Bonner et al. 2018, p. 266). 

This location had two of the Central 

Texas mussel species (Texas fawnsfoot 

and Texas pimpleback) present during 

initial surveys in 2017 (Bonner et al. 

2018, p. 242). Widespread flooding was 

reported in the Colorado and Guadalupe 

River basins of Central Texas in October 

2018. 

The distribution of mussel beds and 

their habitats is affected by large floods 

returning at least once during the 

typical life span of an individual mussel 

(generally from 3 to 30 years). The 

presence of flow refuges mediates the 

effects of these floods, as shear stress is 

relatively low in flow refuges and where 

sediments are relatively stable, and 

individual mussels ‘‘must either tolerate 

high-frequency disturbances or be 

eliminated, and can colonize areas that 

are infrequently disturbed between 

events’’ (Strayer 1999, pp. 468–469). 

Shear stress and relative substrate 

stability are limiting to mussel 

abundance and species richness 

(Randklev et al. 2017a, p. 7), and riffle 

habitats may be more resilient to high 

flow events than littoral (bank) habitats. 

The Central Texas mussels have 

historically been, and currently remain, 

exposed to extreme hydrological 

conditions, including severe drought 

leading to dewatering, and heavy rains 

leading to damaging scour events with 

movement of mussels and substrate (i.e., 

‘‘flash flooding’’). For example, in 2018, 

over the span of 69 days, the Llano 

River near Llano, Texas, experienced 

extreme low flows (0.08 cfs on August 

8, 2018), and extreme high flows leading 

to severe flooding, which resulted in 

substantial scour of streambed and 

riparian area habitats (278,000 cfs on 

October 16, 2018) (Llano River 

Watershed Alliance (LRWA) 2019, 

entire). Prolonged drought followed by 

severe flooding can result in failure and 

collapse of river banks and subsequent 

sedimentation, as demonstrated by 

slumping and undercutting on the lower 

Guadalupe River near Cuero, Texas, in 

2015 (Giardino and Rowley 2016, pp. 

70–72), which is occupied by the false 

spike and Guadalupe orb. The usual 

drought/flood cycle in Central Texas 

can be characterized by long periods of 

time absent of rain interrupted by short 

periods of heavy rain, resulting in often 

severe flooding. These same patterns led 

to the development of flood control and 

storage reservoirs throughout Texas in 

the twentieth century. It follows that, 

given the extreme and variable climate 

of Central Texas, mussels must have 

life-history strategies and other 

adaptations that allow them to persist 

by withstanding severe conditions and 

repopulating during more favorable 

conditions. However, it is also likely 

that there is a limit to how the mussels 

might respond to increasing variability, 

frequency, and severity of extreme 

weather events, combined with habitat 

fragmentation and population isolation. 

Sediment deposition may arise from 

human activities, as well. Sand and 

gravel can be mined from rivers or from 

adjacent alluvial deposits, and instream 

gravels often require less processing and 

are thus more attractive from a business 

perspective (Kondolf 1997, p. 541). 

Instream mining directly affects river 

habitats, and can indirectly affect river 

habitats through channel incision, bed 

coarsening, and lateral channel 

instability (Kondolf 1997, p. 541). 

Excavation of pits in or near to the 

channel can create a nickpoint, which 

can contribute to erosion (and 

mobilization of substrate) associated 

with head cutting (Kondolf 1997, p. 

541). Off-channel mining of floodplain 

pits can become involved during floods, 

such that the pits become hydrologically 

connected and thus can affect sediment 

dynamics in the stream (Kondolf 1997, 

p. 545). 

Predation and Collection 

Predation on freshwater mussels is a 

natural phenomenon. Raccoons, 

muskrats, snapping turtles, wading 

birds, and fish are known to prey upon 

Central Texas mussels. Under natural 

conditions, the level of predation 

occurring within Central Texas mussel 

populations is not likely to pose a 

significant risk to any given population. 

However, during periods of low flow, 

terrestrial predators and wading birds 

have increased access to portions of the 

river that are otherwise too deep under 

normal flow conditions. High levels of 

predation during drought have been 

observed on the Llano and San Saba 

Rivers. As drought and low flow are 

predicted to occur more often and for 

longer periods due to the effects of 

future climate change, the Hill Country 

tributaries (of the Colorado River) in 

particular are expected to experience 

additional predation pressure into the 

future, and this may become especially 

problematic in the Llano and San Saba 

Rivers. Predation is expected to be less 

of a problem for the lower portions of 

the mainstem river populations because 

the rivers are significantly larger than 

the tributary streams and Central Texas 

mussels are less likely to be found by 

predators in exposed or very shallow 

habitats. 

Certain mussel beds within some 

populations, due to ease of access, are 

vulnerable to overcollection and 

vandalism. These areas, primarily on 

the Llano and San Saba Rivers, have 

well-known and well-documented 

mussel beds that have been sampled 

repeatedly over the past few years by 

multiple researchers and others for a 

variety of projects. Given the additional 

stressors aforementioned in this section, 

these populations are being put at 

additional risk due to over-collection 

and over-harvest for scientific needs. 

Barriers to Fish Movement 

Central Texas mussels historically 

colonized new areas through movement 

of infested host fish, as newly 

metamorphosed juveniles would excyst 

from host fish in new locations. Today, 

the remaining Central Texas mussel 

populations are significantly isolated 

due to habitat fragmentation by major 

reservoirs such that recolonization of 

areas previously extirpated is extremely 

unlikely, if not impossible, due to 

existing dams creating permanent 

barriers to host fish movement. There is 

currently no opportunity for interaction 

among any of the extant Central Texas 

mussel populations, as they are isolated 

from one another by major reservoirs. 

The overall distribution of mussels is, 

in part, a function of host fish dispersal 

(Smith 1985, p. 105). There is limited 

potential for immigration and 

emigration between populations other 

than through the movement of infected 

host fish between mussel populations. 

Small populations are more affected by 

this limited immigration potential 

because they are susceptible to genetic 

drift, resulting from random loss of 

genetic diversity, and inbreeding 


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depression. At the species level, isolated 

populations that are eliminated due to 

stochastic events cannot be recolonized 

naturally due to barriers to host fish 

movement, leading to reduced overall 

redundancy and representation. 

Many of the Central Texas mussels’ 

known or assumed primary host fish 

species are known to be common, 

widespread species in the Central Texas 

river basins. We know that populations 

of mussels and their host fish have 

become fragmented and isolated over 

time following the construction of major 

dams and reservoirs throughout Central 

Texas. We do not currently have 

information demonstrating that the 

distribution of host fish is a factor 

currently limiting Central Texas mussels 

distribution. However, a recent study 

suggested that the currently restricted 

distribution of false spike, Guadalupe 

orb, and other related species could be 

related to declining abundance of their 

host fish, particularly those fish having 

small home ranges and specialized 

habitat affinities (Dudding et al. 2019, 

entire). Further research into the 

relationships between each of the 

Central Texas mussel species and their 

host fish is needed to more fully 

examine the possible role of declining 

host fish abundance in declining mussel 

populations. 

Effects of Climate Change 

Climate change has been documented 

to have already taken place, and 

continued greenhouse gas emissions at 

or above current rates will cause further 

warming (Intergovernmental Panel on 

Climate Change (IPCC) 2013, pp. 11–12). 

Warming in Texas is expected to be 

greatest in the summer (Maloney et al. 

2014, p. 2236). The number of extremely 

hot days (high temperatures exceeding 

95 °F) is expected to double by around 

2050 (Kinniburgh et al. 2015, p. 83). 

Western Texas, including portions of 

the ranges of the Central Texas mussels, 

is an area expected to show greater 

responsiveness to the effects of climate 

change (Diffenbaugh et al. 2008, p. 3). 

Changes in stream temperatures are 

expected to reflect changes in air 

temperature, at a rate of approximately 

0.6–0.8 °C increase in stream water 

temperature for every 1 °C increase in 

air temperature (Morrill et al. 2005, pp. 

1–2, 15) and with implications for 

temperature-dependent water quality 

parameters such as dissolved oxygen 

and ammonia toxicity. The Central 

Texas mussels exist at or near a climate 

and habitat gradient in North America, 

with the eastern United States having 

more rainfall and higher freshwater 

mussel diversity, and the western 

United States receiving less rainfall and 

having fewer species of freshwater 

mussels. As such, it is likely that the 

Central Texas mussels may be 

particularly vulnerable to future climate 

changes in combination with current 

and future stressors (Burlakova et al. 

2011a, pp. 156, 161, 163; Burlakova et 

al. 2011b, pp. 395, 403). 

While projected changes to rainfall in 

Texas are small (U.S. Global Change 

Research Program (USGCRP) 2017, p. 

217), higher temperatures caused by 

anthropogenic factors lead to increased 

soil water deficits because of higher 

rates of evapotranspiration. This is 

likely to result in increasing drought 

severity in future climate scenarios just 

as ‘‘extreme precipitation, one of the 

controlling factors in flood statistics, is 

observed to have generally increased 

and is projected to continue to do so 

across the United States in a warming 

atmosphere’’ (USGCRP 2017, p. 231). 

Even if precipitation and groundwater 

recharge remain at current levels, 

increased groundwater pumping and 

resultant aquifer shortages due to 

increased temperatures are nearly 

certain (Loaiciga et al. 2000, p. 193; 

Mace and Wade 2008, pp. 662, 664–665; 

Taylor et al. 2013, p. 325). Higher 

temperatures are also expected to lead 

to increased evaporative losses from 

reservoirs, which could negatively affect 

downstream releases and flows 

(Friedrich et al. 2018, p. 167). Effects of 

climate change, such as air temperature 

increases and an increase in drought 

frequency and intensity, have been 

shown to be occurring throughout the 

range of Central Texas mussels 

(USGCRP 2017, p. 188; Andreadis and 

Lettenmaier 2006, p. 3), and these 

effects are expected to exacerbate 

several of the stressors discussed above, 

such as water temperature and flow loss 

(Wuebbles et al. 2013, p. 16). 

A recent review of future climate 

projections for Texas concludes that 

both droughts and floods could become 

more common in Central Texas and 

projects that years like 2011 (the 

warmest on record) could be 

commonplace by the year 2100 (Mullens 

and McPherson 2017, pp. 3, 6). This 

trend toward more frequent drought is 

attributed to increases in hot 

temperatures, and the number of days at 

or above 100 °F are projected to 

‘‘increase in both consecutive events 

and the total number of days’’ (Mullens 

and McPherson 2017, pp. 14–15). 

Similarly, floods are projected to 

become more common and severe 

because of increases in the magnitude of 

extreme precipitation (Mullens and 

McPherson 2017, p. 20). Recent 

‘‘historic’’ flooding of the Llano River 

resulted in the transport of high levels 

of silt and debris to Lake Travis, so 

much so that the City of Austin’s ability 

to treat raw water was affected and the 

City issued a boil water notice and call 

for water conservation (City of Austin 

2018c, p. 3) 

In the analysis of the future condition 

of the Central Texas mussels, we 

considered climate change to be an 

exacerbating factor, contributing to the 

increase of fine sediments, changes in 

water quality, loss of flowing water, and 

predation. Due to the effects of ongoing 

climate change (represented by 

representative concentration pathway 

(RCP) 4.5), we expect the frequency and 

duration of cleansing flows to decrease, 

leading to the increase in fine sediments 

at all populations. Many populations 

will experience increased frequency of 

low flows. More extreme climate change 

projections (RCP 8.5 and beyond) lead 

to further increases in fine sediment 

within the populations. Similarly, as 

lower water levels concentrate 

contaminants and cause unsuitable 

temperature and dissolved oxygen 

levels, we expect water quality to 

decline to some degree in the future. 

The SSA report includes a detailed 

analysis of the species’ responses to 

both RCP 4.5 and 8.5. 

Conservation Actions and Regulatory 

Mechanisms 

Since 2011, when three of the Central 

Texas mussel species became 

candidates for listing under the 

Endangered Species Act, many agencies, 

non-governmental organizations, and 

other interested parties have been 

working to develop voluntary 

agreements with private landowners to 

restore or enhance habitats for fish and 

wildlife in the region, including in the 

watersheds where Central Texas 

mussels occur. These agreements 

provide voluntary conservation 

including upland habitat enhancements 

that will, if executed properly, reduce 

threats to the species while improving 

in-stream physical habitat and water 

quality, as well as adjacent riparian and 

upland habitats. Additionally, as many 

as three river authorities are developing 

(or have already developed) 

conservation plans that may lead to 

candidate conservation agreements with 

assurances to benefit one or more 

species of candidate mussels (including 

the Central Texas mussels) in their 

basins. Because these plans and 

agreements are not yet fully drafted and 

implemented, we are not considering 

the conservation actions in our 

evaluation of the status of the Central 

Texas mussels; however, we will 

evaluate any new information on these 


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actions prior to making our final listing 

determination for these species. 

Some publicly and privately owned 

lands in the watersheds occupied by 

Central Texas mussels are protected 

with conservation easements or are 

otherwise managed to support 

populations of native fish, wildlife, and 

plant populations. The Natural 

Resources Conservation Service (NRCS), 

along with the Service and State and 

local partners, are working with private 

landowners to develop and implement 

comprehensive conservation plans to 

address soil, water, and wildlife 

resource concerns in the lower Colorado 

River basin through a Working Lands for 

Wildlife project (NRCS 2019a, entire). 

The Service has been hosting annual 

mussel research and coordination 

meetings to help manage and monitor 

scientific collection of mussel 

populations and encourage 

collaboration among researchers and 

other conservation partners since 2018 

(USFWS 2018, p. 1, USFWS 2019a, p. 

1). Additionally, work is under way to 

evaluate methods of captive propagation 

for the Central Texas mussel species at 

the Service’s hatchery and research 

facilities (San Marcos Aquatic Research 

Center, Inks Dam National Fish 

Hatchery, and Uvalde National Fish 

Hatchery), including efforts to collect 

gravid females from the wild to infest 

host fish (Bonner et al. 2018, pp. 8, 9, 

11). 

Species Condition 

Here we discuss the current condition 

of each known population, taking into 

account the risks to those populations 

that are currently occurring, as well as 

management actions that are currently 

occurring to address those risks. We 

consider climate change to be currently 

occurring, resulting in changes to the 

timing and amount of rainfall affecting 

streamflow, increased stream 

temperatures, and increased 

accumulation of fine sediments. In the 

SSA report, for each species and 

population, we developed and assigned 

condition categories for three 

population and three habitat factors that 

are important for viability of each 

species. The condition scores for each 

factor were then used to determine an 

overall condition of each population: 

healthy, moderately healthy, unhealthy, 

or functionally extirpated. These overall 

conditions translate to our presumed 

probability of persistence of each 

population, with healthy populations 

having the highest probability of 

persistence over 20 years (greater than 

90 percent), moderately healthy 

populations having a probability of 

persistence that falls between 60 and 90 

percent, and unhealthy populations 

having the lowest probability of 

persistence (between 10 and 60 

percent). Functionally extirpated 

populations are not expected to persist 

over 20 years or are already extirpated. 

Guadalupe Fatmucket 

Overall, there is one known remaining 

population of Guadalupe fatmucket, in 

the Guadalupe River. Historically, 

Guadalupe fatmucket likely occurred 

through the Guadalupe River basin, but 

it currently only occurs in the upper 

Guadalupe River in an unhealthy 

population due to low abundance and 

little evidence of reproduction and 

recruitment. Very few individuals have 

been found in recent years, and the 

upper Guadalupe River in this reach 

already experiences very low water 

levels. These low water events are 

expected to continue into the future, 

and the population will be unlikely to 

rebound from any degraded habitat 

conditions. 

Texas Fatmucket 

Overall, there are five known 

remaining populations of Texas 

fatmucket, all limited to the headwater 

reaches of the Colorado River and its 

tributaries (see figure 2, above). 

Historically, most Texas fatmucket 

populations were likely connected by 

fish migration throughout the Colorado 

River basin, but due to impoundments 

and low water conditions in the 

Colorado River and tributaries they are 

currently isolated from one another, and 

repopulation of extirpated locations is 

unlikely to occur without human 

assistance. Two of the current 

populations are moderately healthy, two 

are unhealthy, and one is functionally 

extirpated. 

Lower Elm Creek: The Elm Creek 

population of Texas fatmucket is 

extremely small and isolated. This 

population will continue to be 

threatened by excessive sedimentation 

and deterioration of substrate, altered 

hydrology associated with 

anthropogenic activities and the effects 

of climate change, and water quality 

degradation. The poor habitat 

conditions and only a single individual 

found at this site more than a decade 

ago indicate a population that is 

unlikely to persist and may already be 

extirpated. 

Upper/Middle San Saba River: The 

population of Texas fatmucket in the 

upper/middle San Saba River is 

currently moderately healthy. Most of 

the flows in the Upper San Saba River 

(in Menard County, Texas) are from 

Edwards Formation springs, where it 

gains streamflow from groundwater 

except for, and due to a change in the 

underlying geology, a reach that loses 

flow to the aquifer (called a losing 

reach) near the Menard/Mason County 

line (LBG-Guyton 2002, p. 3). It is in 

this losing reach where drought effects 

are especially noticeable, as some flows 

may percolate downward to the aquifer. 

Much of the middle San Saba River 

below Menard is reported to have gone 

dry for 10 of the last 16 years by 

landowners downstream of Menard 

(Carollo Engineers 2015, p. 2). 

Regardless of the cause, low flows in the 

San Saba River have resulted in 

significant stream drying, and stranded 

Central Texas mussels have been 

identified following dewatering as 

recently as 2015 near and below the 

losing reach (TPWD 2015, p. 3). During 

the 2011–2013 drought, stream flows in 

the San Saba River were critically low, 

such that several water rights in 

Schleicher, Menard, and McCulloch 

Counties were suspended by the Texas 

Commission on Environmental Quality 

(TCEQ). These very low flow events are 

expected to continue into the future and 

put the upper/middle San Saba River 

population of Texas fatmucket at risk of 

extirpation. Even if the locations of 

Texas fatmucket do not become dry, 

water quality degradation and increased 

sedimentation associated with low 

flows is expected. 

Llano River: The Llano River 

population of Texas fatmucket is 

currently moderately healthy, although 

there has been limited evidence that the 

population is successfully reproducing, 

and collection of the species is frequent 

at this location. We expect flows to 

continue to decline and the frequency of 

extreme flow events to increase, leading 

to increased sedimentation and 

decreased water quality, and scour, and 

the population is expected to decline as 

a result. 

Pedernales River: The population of 

Texas fatmucket in the Pedernales River 

is very small and isolated. The 

Pedernales River is a flashy system, 

which experiences extreme high flow 

events, especially in the lower reaches 

in the vicinity of Pedernales Falls State 

Park and below. Occasional, intense 

thunderstorms can dramatically 

increase streamflow and mobilize large 

amounts of silt and organic debris 

(LCRA 2017, p. 82). The continued 

increasing frequency of high flow events 

combined with the very low abundances 

in the river result in a population that 

is likely to be extirpated and currently 

is unhealthy. 

Onion Creek: Only a single live 

individual of Texas fatmucket has been 

found in Onion Creek since 2010, and 

we consider this population to be 


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functionally extirpated with little 

chance of persistence. The upper 

reaches of Onion Creek frequently go 

dry, and several privately owned lowhead in-channel dams currently exist 

along upper and lower Onion Creek, 

which further provide barriers to fish 

passage and mussel dispersal, 

preventing recolonization after low 

water events. Onion Creek is in close 

proximity to the City of Austin, and 

continued development in the 

watershed is expected to continue to 

degrade habitat conditions. 

Texas Fawnsfoot 

There are seven remaining 

populations of Texas fawnsfoot, in the 

Trinity, Brazos, and Colorado River 

basins. Historically, Texas fawnsfoot 

occurred throughout each basin with 

populations connected by fish migration 

within each basin, but due to 

impoundments and low water 

conditions, they are currently isolated 

from one another, and repopulation of 

extirpated locations is unlikely to occur 

without human assistance. Four Texas 

fawnsfoot populations are moderately 

healthy, and three are unhealthy. 

East Fork Trinity River: The Texas 

fawnsfoot population in the East Fork 

Trinity River occupies a small stream 

reach (12 mi (19 km)), making it 

especially vulnerable to a single 

stochastic event such as a spill or flood 

and changes to water quality. Further, 

no evidence of reproduction exists for 

this population. The population is 

expected to decline as a result of the 

lack of reproduction. This population is 

small and isolated from the middle and 

lower Trinity River population by 

unsuitable habitat affected primarily by 

altered hydrology as flows from the 

Dallas-Fort Worth metro area are too 

flashy to provide suitable habitat for 

Texas fawnsfoot. Therefore, this 

population is unhealthy. 

Middle Trinity River: Texas fawnsfoot 

in the Trinity River have experienced 

improved water quality over the past 30 

years due to advancements in 

wastewater treatment technology and 

facilities, and streamflows have been 

subsidized by return flows originating 

in part from other basins, although 

water quality degradation and 

sedimentation are still of concern. 

Additionally, the middle Trinity River 

is a relatively long and unobstructed 

reach of river. While habitat may 

decline, we expect the population of 

Texas fawnsfoot to persist in the middle 

Trinity River, as we expect that flows 

will remain within a normal range of 

environmental variation in this reach. 

Clear Fork Brazos River: Texas 

fawnsfoot in the Clear Fork of the 

Brazos River is very small and isolated. 

This population likely experienced 

extensive mortality associated with 

prolonged dewatering during the 2011– 

2013 drought, combined with ambient 

water quality degradation associated 

with naturally occurring elevated 

salinity levels from the upper reaches of 

the river. This population is likely 

functionally extirpated, although more 

survey effort is needed to reach a 

definitive conclusion. Further, the 

proposed Cedar Ridge Reservoir, if 

constructed, will likely result in 

significant hydrologic alterations, all of 

which would not be expected to 

improve the overall condition of this 

population of Texas fawnsfoot. 

Upper Brazos River: The population 

of Texas fawnsfoot in the Upper Brazos 

River is characterized by low 

abundances and lack of reproduction, 

and reduced flows associated with 

continued drought and upstream dam 

operations. Further, water quality 

degradation associated with naturally 

occurring salinity is expected to 

continue. This population is at risk of 

extirpation due to its small population 

size and continued poor habitat 

conditions. 

Middle/Lower Brazos River: The 

population of Texas fawnsfoot in the 

middle and lower Brazos River occupies 

a fairly long reach of river (346 mi (557 

km)) and exhibits evidence of 

reproduction. The lack of major 

impoundments and diversions in the 

Brazos River below Waco, Texas, 

benefits this population through 

maintenance of a relatively natural 

hydrological regime. Even so, Texas 

fawnsfoot surveys have yet to yield the 

species in numbers that would indicate 

a healthy population, and future habitat 

degradation from reduced flows, 

increased temperatures, and decreased 

water quality will likely reduce the 

resiliency of this population. 

Lower San Saba: Texas fawnsfoot in 

the lower San Saba River are found in 

low abundance with little evidence of 

reproductive success and subsequent 

recruitment of new individuals to the 

population. Habitat factors are currently 

unhealthy overall, due primarily to 

degraded substrate conditions caused, 

in part, by reductions in flowing water 

over time due to a combination of 

increased water withdrawals and 

drought. We expect this population to 

become functionally extirpated due to 

lack of water and degradation of 

substrate. 

Lower Colorado River: The Texas 

fawnsfoot population in the lower 

Colorado River is expected to remain 

extant under current conditions, as this 

reach is expected to remain wetted but 

flowing at reduced amounts that reduce 

available habitat. Despite increasing 

demands for municipal water, we 

expect that the lower Colorado River 

will continue to provide water 

associated with priority downstream 

agricultural and industrial water rights. 

Similar to the lower Brazos River 

population, the Lower Colorado River is 

vulnerable to reduced flows and 

associated habitat degradation, because 

the Texas fawnsfoot occurs in bank 

habitats that are likely to become 

exposed to desiccation, predation, and 

increased water temperatures as river 

elevations decline while the river still 

flows in its main channel. Over time, we 

expect flows in the lower Colorado 

River to be reduced, negatively affecting 

substrate quality and water quality 

(through increased sediment load and 

water temperature) such that 

reproduction and abundance are 

negatively affected, resulting in overall 

unhealthy population conditions. 

Guadalupe Orb 

There are two remaining populations 

of the Guadalupe orb, all in the 

Guadalupe River basin. Historically, 

Guadalupe orb likely occurred 

throughout the basin with populations 

connected by fish migration, but due to 

impoundments and low water 

conditions, they are currently isolated 

from one another, and repopulation of 

extirpated locations is unlikely to occur 

without human assistance. Both of the 

Guadalupe orb populations are 

moderately healthy. 

Upper Guadalupe River: The 

Guadalupe orb population in the upper 

Guadalupe River occurs over 

approximately 95 river miles (153 river 

km), and water quantity and quality are 

in moderate condition. However, the 

population occurs in low numbers, and 

there appears to be a lack of 

reproduction; this population is 

unhealthy and is expected to become 

functionally extirpated in the near 

future. This stream reach is expected to 

be sensitive to potential changes in 

groundwater inputs to stream flow and 

thus is vulnerable to ongoing and future 

hydrological alterations that reduce 

flows during critical conditions, 

resulting in substrate quality 

degradations as well as water quality 

degradation. 

San Marcos/Lower Guadalupe Rivers: 

In the San Marcos and Lower 

Guadalupe River, the Guadalupe orb 

population currently occupies a 

relatively long stream length, is 

observed in relatively high abundances, 

and exhibits evidence of reproduction. 

Significant spring complexes contribute 

substantially to baseflow during dry 


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periods in this system and are expected 

to continue to contribute to baseflows 

for the next 50 years due to conservation 

measures implemented by the Edwards 

Aquifer Habitat Conservation Plan 

partners, bolstering the resiliency of this 

population. However, this population is 

subject to extreme high flow events that 

scour and mobilize the substrate, and 

water quality degradation and 

sedimentation are threats, putting it at 

risk of decline. 

Texas Pimpleback 

There are five remaining Texas 

pimpleback populations, all in the 

Colorado River basin. Historically, 

Texas pimpleback likely occurred 

throughout the basin with populations 

connected by fish migration, but due to 

impoundments and low water 

conditions, they are currently 

fragmented and isolated from one 

another and repopulation of extirpated 

locations is unlikely to occur without 

human assistance. Three of the 

remaining Texas pimpleback 

populations are unhealthy and are not 

reproducing, and two of the populations 

are moderately healthy. 

CONCHO RIVER: The Texas pimpleback 

population in the Concho River is 

limited by very low levels of flowing 

water (including periods of almost 

complete dewatering), poor water 

quality, and poor substrate quality 

associated with excessive 

sedimentation. The drought of 2011– 

2013 resulted in extremely low flows in 

this river, and only one live adult has 

been found since that time. This 

population may currently be 

functionally extirpated. 

Middle Colorado/Lower San Saba 

Rivers: The population of Texas 

pimpleback in the middle Colorado and 

lower San Saba River is the largest 

known. This population has relatively 

high abundance but little evidence of 

reproduction, so we expect this 

population to decline as old individuals 

die and very few young individuals are 

recruited into the reproducing 

population. The combination of reduced 

flows, degraded water quality, and 

substrate degradation will reduce the 

resiliency of this population and may 

cause it to become extirpated. 

Upper San Saba River: Similar to 

other populations of Texas pimpleback, 

the population in the Upper San Saba 

River is currently unhealthy and does 

not appear to be reproducing. 

Regardless of the high risk of low water 

levels, the very small population size 

and lack of reproduction will likely 

result in the extirpation of this 

population. Because of the losing reach 

near Hext, Texas, that serves to separate 

the upper and lower San Saba River 

populations, along with differences in 

substrate, this population is isolated and 

no longer connected to the lower San 

Saba River population. 

Llano River: The population of Texas 

pimpleback in the Llano River occupies 

a very short stream length, which is 

negatively affected by substrate 

degradation during periods of low 

flows. This population, due to ease of 

access to the location, is especially 

vulnerable to the threat of 

overcollection and vandalism. The 

small population size and frequency of 

low water levels, and flooding with 

scour, cause this population to be 

unhealthy. 

Lower Colorado River: Currently, the 

population of Texas pimpleback in the 

lower Colorado River is relatively 

abundant over a long stream length. 

However, because the species is a riffle 

specialist, the Texas pimpleback is 

especially sensitive to hydrological 

alterations leading to both extreme 

drying (dewatering) during low flow 

events, and to extreme high flow events 

leading to scouring of substrate and 

movement of mature individuals to sites 

that may or may not be appropriate (as 

evidenced by the August 2017 scouring 

flood event that substantially degraded 

the quality of the Altair Riffle in the 

lower Colorado River, a formerly robust 

mussel bed). We expect this population 

to be at risk of extirpation due to these 

extreme flow events. 

False Spike 

Overall, there are four known 

remaining populations of false spike 

(see figure 6, above), comprising less 

than 10 percent of the species’ known 

historical range. Historically, most false 

spike populations were likely connected 

by fish migration throughout each of the 

Brazos, Colorado, and Guadalupe river 

basins, but due to impoundments they 

are currently fragmented and isolated 

from one another and repopulation of 

extirpated locations is unlikely to occur 

without human assistance. Based on our 

analysis as described in the SSA Report, 

one population is moderately healthy, 

and three are unhealthy. 

Little River and tributaries: The Little 

River population is considered to have 

low resiliency currently due to the small 

size of the population. Development in 

the watershed has reduced water quality 

and substrate conditions currently, and 

habitat factors are expected to continue 

to decline because of alterations to flows 

and water quality associated primarily 

with increasing development in the 

watershed as the Austin-Round Rock 

(Texas) metropolitan area continues to 

expand. Low water levels remain a 

concern that is mediated somewhat by 

the likelihood that enhanced return 

flows associated with the development 

and use of alternative water supplies 

will bolster base flows somewhat. The 

small size of the population combined 

with continued habitat degradation put 

this population at high risk of 

extirpation. 

Lower San Saba River: The lower San 

Saba River population is currently small 

and isolated and therefore has low 

resiliency. The population has low 

abundance, and a lack of reproduction 

and subsequent recruitment, and we 

expect it to become functionally 

extirpated in the next 10 years. Future 

degradation of habitat factors is 

expected as flows continue to be 

diminished, most notably by altered 

precipitation patterns (that result in 

dewatering droughts and scouring 

floods) combined with enhanced 

evaporative demands and anthropogenic 

withdrawals to support existing and 

future demands for municipal and 

agricultural water. 

Llano River: The Llano River 

population is currently very small and 

isolated and therefore has low 

resiliency. The population occupies an 

extremely small area, and degradation of 

habitat is expected to continue as flows 

continue to decline due to altered 

precipitation patterns (dewatering 

droughts and scouring floods) combined 

with enhanced evaporative demands 

and anthropogenic withdrawals to 

support existing and future demands for 

municipal and agricultural water. 

Further, this population is well known 

and easy to access and therefore has 

experienced high collection pressure in 

recent years, and the population has not 

shown recent evidence of reproduction. 

Therefore, we expect the population to 

become extirpated. 

Lower Guadalupe River: The lower 

Guadalupe River population of false 

spike is the largest population of the 

species and the most resilient. This 

population has fairly high abundance 

over a long reach, and flow protections 

afforded by the Edwards Aquifer Habitat 

Conservation Plan have contributed 

substantially to the resiliency of this 

population by sustaining base flows 

above critical levels. However, despite 

these base flow protections, this 

population remains vulnerable to 

changes in water quality, sedimentation, 

and extreme high flow events, such as 

from hurricanes or other strong storms, 

which scour and deplete mussel beds 

(Strayer 1999, pp. 468–469). Overall, 

this population is moderately healthy. 

We note that, by using the SSA 

framework to guide our analysis of the 

scientific information documented in 


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the SSA report, we have not only 

analyzed individual effects on the 

species, but we have also analyzed their 

potential cumulative effects. We 

incorporate the cumulative effects into 

our SSA analysis when we characterize 

the current and future condition of the 

species. Our assessment of the current 

and future conditions encompasses and 

incorporates the threats individually 

and cumulatively. Our current and 

future condition assessment is iterative 

because it accumulates and evaluates 

the effects of all the factors that may be 

influencing the species, including 

threats and conservation efforts. 

Because the SSA framework considers 

not just the presence of the factors, but 

to what degree they collectively 

influence risk to the entire species, our 

assessment integrates the cumulative 

effects of the factors and replaces a 

standalone cumulative effects analysis. 

Determination of Status 

Section 4 of the Act (16 U.S.C. 1533) 

and its implementing regulations (50 

CFR part 424) set forth the procedures 

for determining whether a species meets 

the definition of ‘‘endangered species’’ 

or ‘‘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 

‘‘endangered species’’ or ‘‘threatened 

species’’ because of any of the following 

factors: (A) The present or threatened 

destruction, modification, or 

curtailment of its habitat or range; (B) 

Overutilization for commercial, 

recreational, scientific, or educational 

purposes; (C) Disease or predation; (D) 

The inadequacy of existing regulatory 

mechanisms; or (E) Other natural or 

manmade factors affecting its continued 

existence. 

Status Throughout All of Its Range 

After evaluating threats to the six 

Central Texas mussel species and 

assessing the cumulative effect of the 

threats under the section 4(a)(1) factors, 

we found that all six species of Central 

Texas mussels have declined 

significantly in overall distribution and 

abundance. At present, most of the 

known populations exist in very low 

abundances and show limited evidence 

of recruitment. Furthermore, existing 

available habitats are reduced in quality 

and quantity, relative to historical 

conditions. Our analysis revealed five 

primary threats that caused these 

declines and pose a meaningful risk to 

the viability of the species. These 

threats are primarily related to habitat 

changes (Factor A from the Act): The 

accumulation of fine sediments, altered 

hydrology, and impairment of water 

quality, all of which are exacerbated by 

the effects of climate change. Predation 

and collection (Factor C) are also 

affecting those populations already 

experiencing low stream flow, and 

barriers to fish movement (Factor E) 

limit dispersal and prevent 

recolonization after stochastic events. 

Because of historic and ongoing 

habitat destruction and fragmentation, 

remaining Central Texas mussel 

populations are now fragmented and 

isolated from one another, interrupting 

the once functional metapopulation 

dynamic that historically made mussel 

populations robust and very resilient to 

change. The existing fragmented and 

isolated mussel populations are largely 

in a state of chronic degradation due to 

a number of historical and ongoing 

stressors affecting flows, water quality, 

sedimentation, and substrate quality. 

Given the high risk of catastrophic 

events including droughts and floods, 

both of which are exacerbated by 

climate change, many Central Texas 

mussel populations are at a high risk of 

extirpation. 

Beginning around the turn of the 

twentieth century until 1970, over 100 

major dams had been constructed, 

creating reservoirs across Texas, 

including several reservoirs in the 

Brazos and Trinity basins, the chain of 

Highland Lakes on the Lower Colorado 

River, the Guadalupe Valley 

Hydroelectric Project, and the Canyon 

Reservoir on the Guadalupe River 

(Dowell 1964, pp. 3–8). The inundation 

and subsequent altered hydrology and 

sediment dynamics associated with 

operation of these flood-control, 

hydropower, and municipal water 

supply reservoirs have resulted in 

irreversible changes to the natural flow 

regime of these rivers. These changes 

have re-shaped and fragmented these 

aquatic ecosystems and fish and 

invertebrate communities, including 

populations of the six species of Central 

Texas mussels, which all depend on 

natural river flows. 

Water quality has benefited from 

dramatically improved wastewater 

treatment technology in recent years, 

such that fish populations have 

rebounded but not completely recovered 

(Perkin and Bonner 2016, p. 97). 

However, water quality degradation 

continues to affect mussels and their 

habitats, especially as low flow 

conditions and excessive sedimentation 

interact to diminish instream habitats, 

and substrate-mobilizing and musselscouring flood events have become more 

extreme and perhaps more frequent. 

Additionally, while host fish may still 

be adequately represented in 

contemporary fish assemblages, access 

to fish hosts can be reduced during 

critical reproductive times by barriers 

such as the many low-water crossings 

and low-head dams that now exist and 

fragment the landscape. Diminished 

access to host fish leads to reduced 

reproductive success just as barriers to 

fish passage impede the movement of 

fish, and thus compromise the ability of 

mussels to disperse and colonize new 

habitats following a disturbance 

(Schwalb et al. 2013, p. 447). 

Populations of each of the six Central 

Texas mussels face risks from declining 

water quantity in both large and small 

river segments. Low flows lead to 

dewatering of habitats and desiccation 

of individuals, elevated water 

temperatures, and other quality 

degradations, as well as increased 

exposure to predation. Future higher air 

temperatures, higher rates of 

evaporation and transpiration, and 

changing precipitation patterns are 

expected in central Texas (Jiang and 

Yang 2012, pp. 234–239, 242). Future 

climate changes are expected to lead to 

human responses, such as increased 

groundwater pumping and surface water 

diversions, associated with increasing 

demands for and decreasing availability 

of freshwater resources in the State 

(reviewed in Banner et al. 2010, entire). 

Finally, direct mortality due to 

predation and collection further limits 

population sizes of those populations 

already experiencing the stressors 

discussed above. 

These threats, alone or in 

combination, are expected to cause the 

extirpation of additional mussel 

populations, further reducing the 

overall redundancy and representation 

of each of the six species of Central 

Texas mussels. Historically, each 

species, with a large range of 

interconnected populations (i.e., having 

metapopulation dynamics), would have 

been resilient to stochastic events such 

as drought, excessive sedimentation, 

and scouring floods because even if 

some locations were extirpated by such 

events, they could be recolonized over 

time by dispersal from nearby survivors 

and facilitated by movements by 

‘‘affiliate species’’ of host fish (Douda et 

al. 2012, p. 536). This connectivity 

across potential habitats would have 

made for highly resilient species overall, 

as evidenced by the long and successful 

evolutionary history of freshwater 

mussels as a taxonomic group, and in 


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North America in particular. However, 

under present circumstances, 

restoration of that connectivity on a 

regional scale is not feasible. As a 

consequence of these current 

conditions, the viability of the six 

species of Central Texas mussels now 

primarily depends on maintaining and 

improving the remaining isolated 

populations and potentially restoring 

new populations where feasible. 

Guadalupe Fatmucket 

The Guadalupe fatmucket has only 

one remaining population, and very few 

individuals have been detected and 

reported in recent years. The upper 

Guadalupe River in this reach already 

experiences very low water levels, 

putting this population at high risk of 

extirpation. The species has very low 

viability, with a single population at 

high risk of extirpation, and no 

additional representation or 

redundancy. Our analysis of the species’ 

current and future conditions, as well as 

the conservation efforts discussed 

above, show that the Guadalupe 

fatmucket is in danger of extinction 

throughout all of its range due to the 

severity and immediacy of threats 

currently impacting the species. 

Texas Fatmucket 

Of the five remaining fragmented and 

isolated populations of Texas fatmucket, 

two are small in abundance and 

occupied stream length and have low to 

no resiliency (unhealthy), and one 

population is functionally extirpated. 

The other two current populations are 

moderately healthy. The upper/middle 

San Saba and Llano River populations 

are larger, with increased abundance 

and occupied stream length, but these 

populations are vulnerable to stream 

drying and overcollection. These very 

low flow events are expected to 

continue into the future, and both of 

these populations of Texas fatmucket 

are at risk of extirpation. Even if the 

locations of Texas fatmucket do not 

become dry, water quality degradation 

and increased sedimentation associated 

with low flows is expected. 

Additionally, the Llano River 

population does not appear to be 

successfully reproducing, further 

increasing the species’ risk of 

extirpation at this location. The Texas 

fatmucket has no populations that are 

currently considered healthy. Loss of 

populations at high risk of extirpation 

leads to low levels of redundancy and 

representation. Overall, these low levels 

of resiliency, redundancy, and 

representation result in the Texas 

fatmucket having low viability, and the 

species currently faces a high risk of 

extinction. Our analysis of the species’ 

current and future conditions shows 

that the Texas fatmucket is in danger of 

extinction throughout all of its range 

due to the severity and immediacy of 

threats currently impacting the species. 

Texas Fawnsfoot 

Seven populations of Texas fawnsfoot 

remain. Four populations are 

moderately healthy, and three are 

unhealthy or are functionally extirpated. 

Currently, two of the moderately 

healthy populations are not subject to 

flow declines similar to the remaining 

populations of this species, due to 

increased flow returns in the Trinity 

River from wastewater treatment 

facilities and a lack of impoundments 

on the mainstem of the lower Brazos 

River. In the future, however, as extreme 

flow events become more frequent as 

rainfall patterns change, and increased 

urbanization results in reduced 

groundwater levels, we expect even 

these populations to be at an increased 

risk of extirpation. Within 25 to 50 

years, even under the best conditions 

and with additional conservation efforts 

undertaken, given the ongoing effects of 

climate change and human activities on 

altered hydrology and habitat 

degradation, we expect only one 

population to be in healthy condition, 

one population to remain in moderately 

healthy condition, four populations to 

be in unhealthy condition, and one 

population to become functionally 

extirpated. Given the likelihood of 

increased climate and anthropogenic 

effects in the foreseeable future, as many 

as five populations are expected to 

become functionally extirpated, leaving 

no more than three unhealthy 

populations remaining after 50 years. In 

the future, we anticipate that the Texas 

fawnsfoot will have reduced viability, 

with no highly resilient populations and 

limited representation and redundancy. 

Thus, after assessing the best available 

information, we determine that the 

Texas fawnsfoot is not currently in 

danger of extinction but is likely to 

become in danger of extinction within 

the foreseeable future throughout all of 

its range. 

Guadalupe Orb 

Only two fragmented and isolated 

populations of Guadalupe orb remain, 

and one of these populations is 

functionally extirpated. The San 

Marcos/Lower Guadalupe River 

population is more resilient but is at 

risk of catastrophic events, such as 

hurricane flooding, that can scour and 

reduce the abundance and distribution 

of this population. The Guadalupe orb 

has no populations that are considered 

healthy. Loss of populations at high risk 

of extirpation leads to low levels of 

redundancy and representation, and 

results in overall low viability. The 

Guadalupe orb currently faces a high 

risk of extinction. Our analysis of the 

species’ current and future conditions, 

as well as the conservation efforts 

discussed above, show that the 

Guadalupe orb is in danger of extinction 

throughout all of its range due to the 

severity and immediacy of threats 

currently impacting the species. 

Texas Pimpleback 

Of the five remaining Texas 

pimpleback populations, three are 

unhealthy and are not reproducing, and 

two are moderately healthy. The 

populations that are not reproducing are 

considered functionally extirpated, and 

the two moderately healthy populations 

are expected to continue to decline. The 

population in the middle Colorado and 

lower San Saba Rivers has very little 

evidence of reproduction and is 

therefore likely to decline due to a lack 

of young individuals joining the 

population as the population ages. The 

lower Colorado River population has 

very recently experienced an extreme 

high flow event (i.e., associated with 

Hurricane Harvey flooding in August 

and September of 2017) that vastly 

changed the substrate and mussel 

composition of much of its length, 

putting this population at high risk of 

extirpation. The Texas pimpleback has 

no healthy populations, and all 

populations are expected to continue to 

decline. Loss of populations at high risk 

of extirpation leads to low levels of 

redundancy and representation. Overall, 

these low levels of resiliency, 

redundancy, and representation result 

in the Texas pimpleback having low 

viability, and the species currently faces 

a high risk of extinction. Our analysis of 

the species’ current and future 

conditions, as well as the conservation 

efforts discussed above, show that the 

Texas pimpleback is in danger of 

extinction throughout all of its range 

due to the severity and immediacy of 

threats currently impacting the species. 

False Spike 

Of the four remaining fragmented and 

isolated populations of false spike, three 

are small in abundance and occupied 

stream length, having low to no 

resiliency. The remaining lower 

Guadalupe River population is larger, 

with increased abundance and occupied 

stream length; however, the risk of 

extreme high flow events in this reach 

is high. Therefore, the false spike has no 

populations that are currently 

considered healthy (i.e., highly 


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resilient). Loss of populations at high 

risk of extirpation leads to low levels of 

redundancy (few populations will 

persist to withstand catastrophic events) 

and representation (little to no 

ecological or genetic diversity will 

persist to respond to changing 

environmental conditions). The threats 

identified above are occurring now and 

are expected to continue into the future. 

Overall, these low levels of resiliency, 

redundancy, and representation result 

in the false spike having low viability, 

and the species currently faces a high 

risk of extinction. Our analysis of the 

species’ current and future conditions 

demonstrate that the false spike is in 

danger of extinction throughout all of its 

range due to the severity and immediacy 

of threats currently impacting the 

species. 

Summary of Status Throughout All of 

Its Range: Guadalupe Fatmucket, Texas 

Fatmucket, Guadalupe Orb, Texas 

Pimpleback, and False Spike 

Our analysis of the species’ current 

and future conditions, as well as the 

conservation efforts discussed above, 

show that the Guadalupe fatmucket, 

Texas fatmucket, Guadalupe orb, Texas 

pimpleback, and false spike are in 

danger of extinction throughout all their 

ranges due to the severity and 

immediacy of threats currently 

impacting their populations. The risk of 

extinction is high because the remaining 

fragmented populations have a high risk 

of extirpation, are isolated, and have 

limited potential for recolonization. We 

find that a threatened species status is 

not appropriate for Guadalupe 

fatmucket, Texas fatmucket, Guadalupe 

orb, Texas pimpleback, and false spike 

because of their currently contracted 

ranges, because all populations are 

fragmented and isolated from one 

another, because the threats are 

occurring across the entire range of 

these species, and because the threats 

are ongoing currently and are expected 

to continue or worsen into the future. 

Because these species are already in 

danger of extinction throughout their 

ranges, a threatened status is not 

appropriate. 

Summary of Status Throughout All of 

Its Range: Texas Fawnsfoot 

After evaluating threats to the species 

and assessing the cumulative effect of 

the threats under the section 4(a)(1) 

factors, we find that that Texas 

fawnsfoot populations will continue to 

decline over the next 25 years so that 

this species is likely to become in 

danger of extinction throughout all or a 

significant portion of its range within 

the foreseeable future due to increased 

frequency of drought and extremely 

high flow events, decreased water 

quality, and decreased substrate 

suitability. We considered whether the 

Texas fawnsfoot is presently in danger 

of extinction and determined that 

endangered status is not appropriate. 

The current conditions as assessed in 

the SSA report show two of the 

populations in two of the representative 

units are not currently subject to 

declining flows or extreme flow events. 

While threats are currently acting on the 

species and many of those threats are 

expected to continue into the future, we 

did not find that the species is currently 

in danger of extinction throughout all of 

its range. According to our assessment 

of plausible future scenarios in the SSA 

report, the species is likely to become an 

endangered species in the foreseeable 

future of 25 years throughout all of its 

range. Twenty-five years encompasses 

about 5 generations of the Texas 

fawnsfoot; additionally, models of 

human demand for water (Texas Water 

Development Board 2017, p. 30) and 

climate change (e.g., Kinniburgh et al. 

2015, p. 83) project decreased water 

availability over 25 and 50 years, 

respectively. As a result, we expect 

increased incidences of low flows 

followed by scour events as well as 

persistent decreased water quality to be 

occurring in 25 years. Thus, after 

assessing the best available information, 

we determine that the Texas fawnsfoot 

is not currently in danger of extinction 

but is likely to become in danger of 

extinction within the foreseeable future 

throughout all of its range. 

Status Throughout a Significant Portion 

of Its Range: Guadalupe Fatmucket, 

Texas Fatmucket, Guadalupe Orb, 

Texas Pimpleback, and False Spike 

Under the Act and our implementing 

regulations, a species may warrant 

listing if it is in danger of extinction or 

likely to become so in the foreseeable 

future throughout all or a significant 

portion of its range. We have 

determined that the Guadalupe 

fatmucket, Texas fatmucket, Guadalupe 

orb, Texas pimpleback, and false spike 

are in danger of extinction throughout 

all of their ranges, and accordingly did 

not undertake an analysis of whether 

there are any significant portions of 

these species’ ranges. Because the 

Guadalupe fatmucket, Texas fatmucket, 

Guadalupe orb, Texas pimpleback, and 

false spike warrant listing as endangered 

throughout all of their ranges, our 

determination is consistent with the 

decision in Center for Biological 

Diversity v. Everson, 2020 WL 437289 

(D.D.C. Jan. 28, 2020), in which the 

court vacated the aspect of the 2014 

Significant Portion of its Range Policy 

that provided the Services do not 

undertake an analysis of significant 

portions of a species’ range if the 

species warrants listing as threatened 

throughout all of its range. 

Status Throughout a Significant Portion 

of Its Range: Texas Fawnsfoot 

Under the Act and our implementing 

regulations, a species may warrant 

listing if it is in danger of extinction or 

likely to become so within the 

foreseeable future throughout all or a 

significant portion of its range. The 

court in Center for Biological Diversity 

v. Everson, 2020 WL 437289 (D.D.C. Jan. 

28, 2020) (Center for Biological 

Diversity), vacated the aspect of the 

2014 Significant Portion of its Range 

Policy that provided that the Services 

do not undertake an analysis of 

significant portions of a species’ range if 

the species warrants listing as 

threatened throughout all of its range. 

Therefore, we proceed to evaluating 

whether the species is endangered 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 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. 

Following the court’s holding in 

Center for Biological Diversity, we now 

consider whether there are any 

significant portions of the species’ range 

where the species is in danger of 

extinction now (i.e., endangered). In 

undertaking this analysis for the Texas 

fawnsfoot, we choose to address the 

status question first—we consider 

information pertaining to the geographic 

distribution of both the species and the 

threats that the species faces to identify 

any portions of the range where the 

species is endangered. 

We considered whether any of the 

threats acting on the species are 

geographically concentrated in any 

portion of the range at a biologically 

meaningful scale. We examined the 

following threats throughout the range 

of the species: The accumulation of fine 

sediments, altered hydrology, and 

impairment of water quality (Factor A); 

predation and collection (Factor C); and 

barriers to fish movement (Factor E). 

We identified a portion of the range 

of Texas fawnsfoot, the upper Brazos 


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River (including the populations in the 

Upper Brazos River and Clear Fork 

Brazos River), that is experiencing a 

concentration of the following threats: 

Altered hydrology and impaired water 

quality. Although these threats are not 

unique to this area, they are acting at a 

greater intensity here (e.g., populations 

higher in the watershed and that receive 

less rainfall are more vulnerable to 

stream drying because there is a smaller 

volume of water in the river), either 

individually or in combination, than 

elsewhere in the range. In addition, the 

small sizes of each population, coupled 

with the current condition information 

in the SSA report suggesting the two 

populations in this area are unhealthy, 

leads us to find that this portion 

provides substantial information 

indicating the populations occurring 

here may be in danger of extinction 

now. 

We then proceeded to the significance 

question, asking whether there is 

substantial information indicating that 

this portion of the range (i.e., the Upper 

Brazos River and Clear Fork Brazos 

River) may be significant. As an initial 

note, the Service’s most recent 

definition of ‘‘significant’’ within 

agency policy guidance has been 

invalidated by court order (see Desert 

Survivors v. Dep’t of the Interior, No. 

16–cv–01165 (N.D. Cal. Aug. 24, 2018)). 

In undertaking this analysis for the 

Texas fawnsfoot, we considered 

whether the Upper Brazos River portion 

of the species’ range may be significant 

based on its biological importance to the 

overall viability of the Texas fawnsfoot. 

Therefore, for the purposes of this 

analysis, when considering whether this 

portion may be biologically significant, 

we considered whether the portion may 

(1) occur in a unique habitat or 

ecoregion for the species, (2) contain 

high quality or high value habitat 

relative to the remaining portions of the 

range, for the species’ continued 

viability in light of the existing threats, 

or (3) contain habitat that is essential to 

a specific life-history function for the 

species and that is not found in the 

other portions (for example, the 

principal breeding ground for the 

species). 

We evaluated the available 

information about the portion of the 

range of Texas fawnsfoot that occupies 

the upper Brazos River in this context, 

assessing its biological significance in 

terms of these three habitat criteria, and 

determined the information did not 

substantially indicate it may be 

significant. Texas fawnsfoot in these 

populations exhibit similar habitat and 

host fish use to Texas fawnsfoot in the 

remainder of its range; thus, there is no 

unique observable environmental usage 

or behavioral characteristics attributable 

to just this area’s populations. The 

Upper Brazos River is not essential to 

any specific life-history function of the 

Texas fawnsfoot that is not found 

elsewhere in the range. Further, the 

habitat in the Upper Brazos River does 

not contain higher quality or higher 

value than the remainder of the species’ 

range. The Upper Brazos River 

populations have a small number of 

individuals compared to most of the 

other populations throughout the range 

of Texas fawnsfoot (see Table 4, above). 

The Clear Fork Brazos River population 

may already be extirpated, and the 

Upper Brazos River population had 23 

individuals found in 2017. These 

populations do not interact with other 

populations of the species. 

Overall, we found no substantial 

information that would indicate the 

Upper Brazos River may be significant. 

While this area provides some 

contribution to the species’ overall 

ability to withstand catastrophic or 

stochastic events (redundancy and 

resiliency, respectively), the species has 

a larger population that occupies a 

larger area downstream in the Brazos 

River. The best scientific and 

commercial information available 

indicates that the Upper Brazos River 

population’s contribution is very 

limited in scope due to the small 

population sizes and isolation from 

other populations. Therefore, because 

we could not answer both the status and 

significance questions in the affirmative, 

we conclude that the Upper Brazos 

River portion of the range does not 

warrant further consideration as a 

significant portion of the range. 

We did not identify any portions of 

the Texas fawnsfoot’s range where: (1) 

The portion is significant; and, (2) the 

species is in danger of extinction in that 

portion. Therefore, we conclude that the 

Texas fawnsfoot is likely to become in 

danger of extinction within the 

foreseeable future throughout all of its 

range. This is consistent with the courts’ 

holdings in Desert Survivors v. 

Department of the Interior, No. 16-cv– 

01165–JCS, 2018 WL 4053447 (N.D. Cal. 

Aug. 24, 2018), and Center for Biological 

Diversity v. Jewell, 248 F. Supp. 3d, 946, 

959 (D. Ariz. 2017). 

Determination of Status: Guadalupe 

Fatmucket, Texas Fatmucket, 

Guadalupe Orb, Texas Pimpleback, and 

False Spike 

Our review of the best available 

scientific and commercial information 

indicates that the Guadalupe fatmucket, 

Texas fatmucket, Guadalupe orb, Texas 

pimpleback, and false spike meet the 

definition of endangered species. 

Therefore, we propose to list the 

Guadalupe fatmucket, Texas fatmucket, 

Guadalupe orb, Texas pimpleback, and 

false spike as endangered species in 

accordance with sections 3(6) and 

4(a)(1) of the Act. 

Determination of Status: Texas 

Fawnsfoot 

Our review of the best available 

scientific and commercial information 

indicates that the Texas fawnsfoot meets 

the definition of a threatened species. 

Therefore, we propose to list the Texas 

fawnsfoot as a threatened species in 

accordance with sections 3(20) and 

4(a)(1) of the Act. 

Available Conservation Measures 

Conservation measures provided to 

species listed as endangered or 

threatened species under the Act 

include recognition, recovery actions, 

requirements for Federal protection, and 

prohibitions against certain practices. 

Recognition through listing results in 

public awareness, and conservation by 

Federal, State, tribal, and local agencies, 

private organizations, and individuals. 

The Act encourages cooperation with 

the States and other countries and calls 

for recovery actions to be carried out for 

listed species. The protection required 

by Federal agencies and the prohibitions 

against certain activities are discussed, 

in part, below. 

The primary purpose of the Act is the 

conservation of endangered and 

threatened species and the ecosystems 

upon which they depend. The ultimate 

goal of such conservation efforts is the 

recovery of these listed species, so that 

they no longer need the protective 

measures of the Act. Section 4(f) of the 

Act calls for the Service to develop and 

implement recovery plans for the 

conservation of endangered and 

threatened species. The recovery 

planning process involves the 

identification of actions that are 

necessary to halt or reverse species’ 

decline by addressing the threats to 

survival and recovery. The goal of this 

process is to restore listed species to a 

point where they are secure, selfsustaining, and functioning components 

of their ecosystems. 

Recovery planning consists of 

preparing draft and final recovery plans, 

beginning with the development of a 

recovery outline and making it available 

to the public within 30 days of a final 

listing determination. The recovery 

outline guides the immediate 

implementation of urgent recovery 

actions and describes the process to be 

used to develop a recovery plan. 

Revisions of the plan may be done to 


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address continuing or new threats to the 

species, as new substantive information 

becomes available. The recovery plan 

also identifies recovery criteria for 

review of when a species may be ready 

for reclassification from endangered to 

threatened (‘‘downlisting’’) or removal 

from protected status (‘‘delisting’’), and 

methods for monitoring recovery 

progress. Recovery plans also establish 

a framework for agencies to coordinate 

their recovery efforts and provide 

estimates of the cost of implementing 

recovery tasks. Recovery teams 

(composed of species experts, Federal 

and State agencies, nongovernmental 

organizations, and stakeholders) are 

often established to develop recovery 

plans. When completed, the recovery 

outline, draft recovery plan, and the 

final recovery plan will be available on 

our website (http://www.fws.gov/ 

endangered). 

Implementation of recovery actions 

generally requires the participation of a 

broad range of partners, including other 

Federal agencies, States, Tribes, 

nongovernmental organizations, 

businesses, and private landowners. 

Examples of recovery actions include 

habitat restoration (e.g., restoration of 

native vegetation), research, captive 

propagation and reintroduction, and 

outreach and education. The recovery of 

many listed species cannot be 

accomplished solely on Federal lands 

because their range may occur primarily 

or solely on non-Federal lands. To 

achieve recovery of these species 

requires cooperative conservation efforts 

on private, State, and tribal lands. 

If these species are listed, funding for 

recovery actions will be available from 

a variety of sources, including Federal 

budgets, State programs, and cost-share 

grants for non-Federal landowners, the 

academic community, and 

nongovernmental organizations. In 

addition, pursuant to section 6 of the 

Act, the State of Texas would be eligible 

for Federal funds to implement 

management actions that promote the 

protection or recovery of the Central 

Texas mussels. Information on our grant 

programs that are available to aid 

species recovery can be found at: http:// 

www.fws.gov/grants. 

Although the Central Texas mussels 

are only proposed for listing under the 

Act at this time, please let us know if 

you are interested in participating in 

recovery efforts for these species. 

Additionally, we invite you to submit 

any new information on this species 

whenever it becomes available and any 

information you may have for recovery 

planning purposes (see FOR FURTHER

INFORMATION CONTACT). 

Section 7(a) of the Act requires 

Federal agencies to evaluate their 

actions with respect to any species that 

is proposed or listed as an endangered 

or threatened species and with respect 

to its critical habitat, if any is 

designated. Regulations implementing 

this interagency cooperation provision 

of the Act are codified at 50 CFR part 

402. Section 7(a)(4) of the Act requires 

Federal agencies to confer with the 

Service on any action that is likely to 

jeopardize the continued existence of a 

species proposed for listing or result in 

destruction or adverse modification of 

proposed critical habitat. If a species is 

listed subsequently, section 7(a)(2) of 

the Act requires Federal agencies to 

ensure that activities they authorize, 

fund, or carry out are not likely to 

jeopardize the continued existence of 

the species or destroy or adversely 

modify its critical habitat. If a Federal 

action may affect a listed species or its 

critical habitat, the responsible Federal 

agency must enter into consultation 

with the Service. 

Federal agency actions within the 

species’ habitat that may require 

conference or consultation or both as 

described in the preceding paragraph 

include management and any other 

landscape-altering activities on Federal 

lands administered by the National Park 

Service. 

The Act and its implementing 

regulations set forth a series of general 

prohibitions and exceptions that apply 

to endangered wildlife. The prohibitions 

of section 9(a)(1) of the Act, codified at 

50 CFR 17.21, make it illegal for any 

person subject to the jurisdiction of the 

United States to take (which includes 

harass, harm, pursue, hunt, shoot, 

wound, kill, trap, capture, or collect; or 

to attempt any of these) endangered 

wildlife within the United States or on 

the high seas. In addition, it is unlawful 

to import; export; deliver, receive, carry, 

transport, or ship in interstate or foreign 

commerce in the course of commercial 

activity; or sell or offer for sale in 

interstate or foreign commerce any 

species listed as an endangered species. 

It is also illegal to possess, sell, deliver, 

carry, transport, or ship any such 

wildlife that has been taken illegally. 

Certain exceptions apply to employees 

of the Service, the National Marine 

Fisheries Service, other Federal land 

management agencies, and State 

conservation agencies. 

We may issue permits to carry out 

otherwise prohibited activities 

involving endangered wildlife under 

certain circumstances. Regulations 

governing permits are codified at 50 

CFR 17.22. With regard to endangered 

wildlife, a permit may be issued for the 

following purposes: For scientific 

purposes, to enhance the propagation or 

survival of the species, and for 

incidental take in connection with 

otherwise lawful activities. There are 

also certain statutory exemptions from 

the prohibitions, which are found in 

sections 9 and 10 of the Act. 

It is our policy, as published in the 

Federal Register on July 1, 1994 (59 FR 

34272), to identify to the maximum 

extent practicable at the time a species 

is listed, those activities that would or 

would not constitute a violation of 

section 9 of the Act. The intent of this 

policy is to increase public awareness of 

the effect of a proposed listing on 

proposed and ongoing activities within 

the range of the species proposed for 

listing. The discussion below regarding 

protective regulations under section 4(d) 

of the Act for the Texas fawnsfoot 

complies with our policy. 

Based on the best available 

information, the following actions are 

unlikely to result in a violation of 

section 9, if these activities are carried 

out in accordance with existing 

regulations and permit requirements; 

this list is not comprehensive: 

(1) Normal agricultural and 

silvicultural practices, including 

herbicide and pesticide use, which are 

carried out in accordance with any 

existing regulations, permit and label 

requirements, and best management 

practices; and, 

(2) Normal residential landscape 

activities. 

Based on the best available 

information, the following activities 

may potentially result in a violation of 

section 9 of the Act if they are not 

authorized in accordance with 

applicable law; this list is not 

comprehensive: 

(1) Unauthorized handling or 

collecting of the species; 

(2) Modification of the channel or 

water flow of any stream in which the 

Central Texas mussels are known to 

occur; 

(3) Livestock grazing that results in 

direct or indirect destruction of stream 

habitat; and 

(4) Discharge of chemicals or fill 

material into any waters in which the 

Central Texas mussels are known to 

occur. 

Questions regarding whether specific 

activities would constitute a violation of 

section 9 of the Act should be directed 

to the Austin Ecological Services Field 

Office (see FOR FURTHER INFORMATION

CONTACT). 


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II. Proposed Rule Issued Under Section 

4(d) of the Act 

Background 

Section 4(d) of the Act contains two 

sentences. The first sentence states that 

the ‘‘Secretary shall issue such 

regulations as he deems necessary and 

advisable to provide for the 

conservation’’ of species listed as 

threatened. The U.S. Supreme Court has 

noted that statutory language like 

‘‘necessary and advisable’’ demonstrates 

a large degree of deference to the agency 

(see Webster v. Doe, 486 U.S. 592 

(1988)). Conservation is defined in the 

Act to mean ‘‘the use of all methods and 

procedures which are necessary to bring 

any endangered species or threatened 

species to the point at which the 

measures provided pursuant to [the Act] 

are no longer necessary.’’ Additionally, 

the second sentence of section 4(d) of 

the Act states that the Secretary ‘‘may by 

regulation prohibit with respect to any 

threatened species any act prohibited 

under section 9(a)(1), in the case of fish 

or wildlife, or section 9(a)(2), in the case 

of plants.’’ Thus, the combination of the 

two sentences of section 4(d) provides 

the Secretary with wide latitude of 

discretion to select and promulgate 

appropriate regulations tailored to the 

specific conservation needs of the 

threatened species. The second sentence 

grants particularly broad discretion to 

the Service when adopting the 

prohibitions under section 9. 

The courts have recognized the extent 

of the Secretary’s discretion under this 

standard to develop rules that are 

appropriate for the conservation of a 

species. For example, courts have 

upheld rules developed under section 

4(d) as a valid exercise of agency 

authority where they prohibited take of 

threatened wildlife, or include a limited 

taking prohibition (see Alsea Valley 

Alliance v. Lautenbacher, 2007 U.S. 

Dist. Lexis 60203 (D. Or. 2007); 

Washington Environmental Council v. 

National Marine Fisheries Service, 2002 

U.S. Dist. Lexis 5432 (W.D. Wash. 

2002)). Courts have also upheld 4(d) 

rules that do not address all of the 

threats a species faces (see State of 

Louisiana v. Verity, 853 F.2d 322 (5th 

Cir. 1988)). As noted in the legislative 

history when the Act was initially 

enacted, ‘‘once an animal is on the 

threatened list, the Secretary has an 

almost infinite number of options 

available to him with regard to the 

permitted activities for those species. He 

may, for example, permit taking, but not 

importation of such species, or he may 

choose to forbid both taking and 

importation but allow the transportation 

of such species’’ (H.R. Rep. No. 412, 

93rd Cong., 1st Sess. 1973). 

Exercising its authority under section 

4(d), the Service has developed a 

proposed rule that is designed to 

address the Texas fawnsfoot’s specific 

threats and conservation needs. 

Although the statute does not require 

the Service to make a ‘‘necessary and 

advisable’’ finding with respect to the 

adoption of specific prohibitions under 

section 9, we find that this rule as a 

whole satisfies the requirement in 

section 4(d) of the Act to issue 

regulations deemed necessary and 

advisable to provide for the 

conservation of the Texas fawnsfoot. As 

discussed in the Summary of Biological 

Status and Threats section, the Service 

has concluded that the Texas fawnsfoot 

is likely to become in danger of 

extinction within the foreseeable future 

primarily due to habitat changes such as 

the accumulation of fine sediments, 

altered hydrology, and impairment of 

water quality, predation and collection, 

and barriers to fish movement. The 

provisions of this proposed 4(d) rule 

would promote conservation of the 

Texas fawnsfoot by encouraging riparian 

landscape conservation while also 

meeting the conservation needs of Texas 

fawnsfoot. By streamlining those 

projects that follow best management 

practices and improve instream habitat 

(such as streambank stabilization, 

instream channel restoration, and 

upland restoration that improves 

instream habitat), conservation is more 

likely to occur for Texas fawnsfoot, 

improving the condition of populations 

in those reaches. The provisions of this 

proposed rule are one of many tools that 

the Service would use to promote the 

conservation of the Texas fawnsfoot. 

This proposed 4(d) rule would apply 

only if and when the Service makes 

final the listing of the Texas fawnsfoot 

as a threatened species. 

Provisions of the Proposed 4(d) Rule 

This proposed 4(d) rule would 

provide for the conservation of the 

Texas fawnsfoot by prohibiting the 

following activities, except as otherwise 

authorized or permitted: Take, 

possession, and import/export of 

unlawfully taken specimens. 

As discussed in the Summary of 

Biological Status and Threats (above), 

habitat loss, predation and collection, 

and barriers to fish movement are 

affecting the status of the Texas 

fawnsfoot. A range of activities have the 

potential to impact the Texas fawnsfoot, 

including: Instream construction, water 

withdrawals, flow releases from 

upstream dams, riparian vegetation 

removal, improper handling, and 

wastewater treatment facility outflows. 

Regulating these activities will help 

preserve the species’ remaining 

populations, slow their rate of decline, 

and decrease synergistic, negative 

effects from other stressors. 

Under the Act, ‘‘take’’ means to 

harass, harm, pursue, hunt, shoot, 

wound, kill, trap, capture, or collect, or 

to attempt to engage in any such 

conduct. Some of these provisions have 

been further defined in regulation at 50 

CFR 17.3. Take can result knowingly or 

otherwise, by direct and indirect 

impacts, intentionally or incidentally. 

Regulating incidental and intentional 

take will help preserve the species’ 

remaining populations, slow their rate 

of decline, and decrease synergistic, 

negative effects from other stressors. 

We have identified some exceptions 

to the prohibition on incidental and 

intentional take. Those exceptions 

include the following activities: 

(1) Channel restoration projects that 

create natural, physically stable 

(streambanks and substrate remaining 

relatively unchanging over time), 

ecologically functioning streams or 

stream and wetland systems (containing 

an assemblage of fish, mussels, other 

invertebrates, and plants) that are 

reconnected with their groundwater 

aquifers. These projects can be 

accomplished using a variety of 

methods, but the desired outcome is a 

natural channel with low shear stress 

(force of water moving against the 

channel); bank heights that enable 

reconnection to the floodplain; a 

reconnection of surface and 

groundwater systems, resulting in 

perennial flows in the channel; riffles 

and pools composed of existing soil, 

rock, and wood instead of large 

imported materials; low compaction of 

soils within adjacent riparian areas; and 

inclusion of riparian wetlands and 

woodland buffers. This exception to the 

proposed 4(d) rule for incidental take 

would promote conservation of Texas 

fawnsfoot by creating stable stream 

channels that are less likely to scour 

during high flow events, thereby 

increasing population resiliency. 

(2) Bioengineering methods such as 

streambank stabilization using live 

stakes (live, vegetative cuttings inserted 

or tamped into the ground in a manner 

that allows the stake to take root and 

grow), live fascines (live branch 

cuttings, usually willows, bound 

together into long, cigar-shaped 

bundles), or brush layering (cuttings or 

branches of easily rooted tree species 

layered between successive lifts of soil 

fill). These methods would not include 

the sole use of quarried rock (rip-rap) or 

the use of rock baskets or gabion 


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structures. In addition, to reduce 

streambank erosion and sedimentation 

into the stream, work using these 

bioengineering methods would be 

performed at base flow or low water 

conditions and when significant rainfall 

is not predicted. Further, streambank 

stabilization projects must keep all 

equipment out of the stream channels 

and water. Similar to channel 

restoration projects, this exception to 

the proposed 4(d) rule for incidental 

take would promote conservation of 

Texas fawnsfoot by creating stable 

stream channels that are less likely to 

scour during high flow events, thereby 

increasing population resiliency. 

(3) Soil and water conservation 

practices and riparian and adjacent 

upland habitat management activities 

that restore instream habitats for the 

species, restore adjacent riparian 

habitats that enhance stream habitats for 

the species, stabilize degraded and 

eroding stream banks to limit 

sedimentation and scour of the species’ 

habitats, and restore or enhance nearby 

upland habitats to limit sedimentation 

of the species’ habitats and comply with 

conservation practice standards and 

specifications and technical guidelines 

developed by the Natural Resources 

Conservation Service (NRCS) and 

available in the Field Office Technical 

Guide (FOTG). Soil and water 

conservation practices and aquatic 

species habitat restoration projects 

associated with NRCS conservation 

plans are designed to improve water 

quality and enhance fish and aquatic 

species habitats. This exception to the 

proposed 4(d) rule for incidental take 

would promote conservation of Texas 

fawnsfoot by creating stable stream 

channels and reducing sediment inputs 

to the stream, thereby increasing 

population resiliency. 

(4) Presence or abundance surveys for 

Texas fawnfoot conducted by 

individuals who successfully complete 

and show proficiency by passing the 

end-of-course test with a score equal to 

or greater than 90 percent, with 100 

percent accuracy in identification of 

mussel species listed under the 

Endangered Species Act, in an approved 

freshwater mussel identification and 

sampling course (specific to the species 

and basins in which the Texas 

fawnsfoot is known to occur), such as 

that administered by the Service, State 

wildlife agency, or qualified university 

experts. Those individuals exercising 

this exemption should provide reports 

to the Service annually on number, 

specific location (e.g. GPS coordinates), 

and date of encounter. This exemption 

does not apply if lethal take or 

collection is anticipated. This 

exemption only applies for 5 years from 

the date of successful completion of the 

course. This provision of the 4(d) rule 

for intentional take would promote 

conservation of Texas fawnsfoot by 

ensuring surveyors are proficient at 

identification of freshwater mussels and 

would add to the knowledge and 

understanding of the distribution of 

Texas fawnsfoot populations. 

We may issue permits to carry out 

otherwise prohibited activities, 

including those described above, 

involving threatened wildlife under 

certain circumstances. Regulations 

governing permits are codified at 50 

CFR 17.32. With regard to threatened 

wildlife, a permit may be issued for the 

following purposes: Scientific purposes, 

to enhance propagation or survival, for 

economic hardship, for zoological 

exhibition, for educational purposes, for 

incidental taking, or for special 

purposes consistent with the purposes 

of the Act. There are also certain 

statutory exemptions from the 

prohibitions, which are found in 

sections 9 and 10 of the Act. 

The Service recognizes the special 

and unique relationship with our State 

natural resource agency partners in 

contributing to conservation of listed 

species. State agencies often possess 

scientific data and valuable expertise on 

the status and distribution of 

endangered, threatened, and candidate 

species of wildlife and plants. State 

agencies, because of their authorities 

and their close working relationships 

with local governments and 

landowners, are in a unique position to 

assist the Services in implementing all 

aspects of the Act. In this regard, section 

6 of the Act provides that the Services 

shall cooperate to the maximum extent 

practicable with the States in carrying 

out programs authorized by the Act. 

Therefore, any qualified employee or 

agent of a State conservation agency that 

is a party to a cooperative agreement 

with the Service in accordance with 

section 6(c) of the Act, who is 

designated by his or her agency for such 

purposes, will be able to conduct 

activities designed to conserve Texas 

fawnsfoot that may result in otherwise 

prohibited take without additional 

authorization. 

Nothing in this proposed 4(d) rule 

would change in any way the recovery 

planning provisions of section 4(f) of the 

Act, the consultation requirements 

under section 7 of the Act, or the ability 

of the Service to enter into partnerships 

for the management and protection of 

the Texas fawnsfoot. However, 

interagency cooperation may be further 

streamlined through planned 

programmatic consultations for the 

species between Federal agencies and 

the Service. We ask the public, 

particularly State agencies and other 

interested stakeholders that may be 

affected by the proposed 4(d) rule, to 

provide comments and suggestions 

regarding additional guidance and 

methods that the Service could provide 

or use, respectively, to streamline the 

implementation of this proposed 4(d) 

rule (see Information Requested, above). 

III. Proposed Critical Habitat 

Designation 

Background 

Critical habitat is defined in section 3 

of the Act as: 

(1) The specific areas within the 

geographical area occupied by the 

species, at the time it is listed in 

accordance with the Act, on which are 

found those physical or biological 

features 

(a) Essential to the conservation of the 

species, and 

(b) Which may require special 

management considerations or 

protection; and 

(2) Specific areas outside the 

geographical area occupied by the 

species at the time it is listed, upon a 

determination that such areas are 

essential for the conservation of the 

species. 

Our regulations at 50 CFR 424.02 

define the geographical area occupied 

by the species as an area that may 

generally be delineated around species’ 

occurrences, as determined by the 

Secretary (i.e., range). Such areas may 

include those areas used throughout all 

or part of the species’ life cycle, even if 

not used on a regular basis (e.g., 

migratory corridors, seasonal habitats, 

and habitats used periodically, but not 

solely by vagrant individuals). 

Additionally, our regulations at 50 CFR 

424.02 define the word ‘‘habitat’’ as 

follows: ‘‘for the purposes of designating 

critical habitat only, habitat is the 

abiotic and biotic setting that currently 

or periodically contains the resources 

and conditions necessary to support one 

or more life processes of a species.’’ 

Conservation, as defined under 

section 3 of the Act, means to use and 

the use of all methods and procedures 

that are necessary to bring an 

endangered or threatened species to the 

point at which the measures provided 

pursuant to the Act are no longer 

necessary. Such methods and 

procedures include, but are not limited 

to, all activities associated with 

scientific resources management such as 

research, census, law enforcement, 

habitat acquisition and maintenance, 

propagation, live trapping, and 


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transplantation, and, in the 

extraordinary case where population 

pressures within a given ecosystem 

cannot be otherwise relieved, may 

include regulated taking. 

Critical habitat receives protection 

under section 7 of the Act through the 

requirement that Federal agencies 

ensure, in consultation with the Service, 

that any action they authorize, fund, or 

carry out is not likely to result in the 

destruction or adverse modification of 

critical habitat. The designation of 

critical habitat does not affect land 

ownership or establish a refuge, 

wilderness, reserve, preserve, or other 

conservation area. Designation also does 

not allow the government or public to 

access private lands, nor does 

designation require implementation of 

restoration, recovery, or enhancement 

measures by non-Federal landowners. 

Where a landowner requests Federal 

agency funding or authorization for an 

action that may affect a listed species or 

critical habitat, the Federal agency 

would be required to consult with the 

Service under section 7(a)(2) of the Act. 

However, even if the Service were to 

conclude that the proposed activity 

would result in destruction or adverse 

modification of the critical habitat, the 

Federal action agency and the 

landowner are not required to abandon 

the proposed activity, or to restore or 

recover the species; instead, they must 

implement ‘‘reasonable and prudent 

alternatives’’ to avoid destruction or 

adverse modification of critical habitat. 

Under the first prong of the Act’s 

definition of critical habitat, areas 

within the geographical area occupied 

by the species at the time it was listed 

are included in a critical habitat 

designation if they contain physical or 

biological features (1) which are 

essential to the conservation of the 

species and (2) which may require 

special management considerations or 

protection. For these areas, critical 

habitat designations identify, to the 

extent known using the best scientific 

and commercial data available, those 

physical or biological features that are 

essential to the conservation of the 

species (such as space, food, cover, and 

protected habitat). In identifying those 

physical or biological features that occur 

in specific occupied areas, we focus on 

the specific features that are essential to 

support the life-history needs of the 

species, including but not limited to, 

water characteristics, soil type, 

geological features, prey, vegetation, 

symbiotic species, or other features. A 

feature may be a single habitat 

characteristic, or a more-complex 

combination of habitat characteristics. 

Features may include habitat 

characteristics that support ephemeral 

or dynamic habitat conditions. Features 

may also be expressed in terms relating 

to principles of conservation biology, 

such as patch size, distribution 

distances, and connectivity. 

Under the second prong of the Act’s 

definition of critical habitat, we can 

designate critical habitat in areas 

outside the geographical area occupied 

by the species at the time it is listed, 

upon a determination that such areas 

are essential for the conservation of the 

species. The implementing regulations 

at 50 CFR 424.12(b)(2) further delineate 

unoccupied critical habitat by setting 

out three specific parameters: (1) When 

designating critical habitat, the 

Secretary will first evaluate areas 

occupied by the species; (2) the 

Secretary will only consider unoccupied 

areas to be essential where a critical 

habitat designation limited to 

geographical areas occupied by the 

species would be inadequate to ensure 

the conservation of the species; and (3) 

for an unoccupied area to be considered 

essential, the Secretary must determine 

that there is a reasonable certainty both 

that the area will contribute to the 

conservation of the species and that the 

area contains one or more of those 

physical or biological features essential 

to the conservation of the species. 

Section 4 of the Act requires that we 

designate critical habitat on the basis of 

the best scientific data available. 

Further, our Policy on Information 

Standards under the Endangered 

Species Act (published in the Federal 

Register on July 1, 1994 (59 FR 34271)), 

the Information Quality Act (section 515 

of the Treasury and General 

Government Appropriations Act for 

Fiscal Year 2001 (Pub. L. 106–554; H.R. 

5658)), and our associated Information 

Quality Guidelines, provide criteria, 

establish procedures, and provide 

guidance to ensure that our decisions 

are based on the best scientific data 

available. They require our biologists, to 

the extent consistent with the Act and 

with the use of the best scientific data 

available, to use primary and original 

sources of information as the basis for 

recommendations to designate critical 

habitat. 

When we are determining which areas 

should be designated as critical habitat, 

our primary source of information is 

generally the information from the SSA 

report and information developed 

during the listing process for the 

species. Additional information sources 

may include any generalized 

conservation strategy, criteria, or outline 

that may have been developed for the 

species; the recovery plan for the 

species; articles in peer-reviewed 

journals; conservation plans developed 

by States and counties; scientific status 

surveys and studies; biological 

assessments; other unpublished 

materials; or experts’ opinions or 

personal knowledge. 

As the regulatory definition of 

‘‘habitat’’ reflects (50 CFR 424.02), 

habitat is dynamic, and species may 

move from one area to another over 

time. We recognize that critical habitat 

designated at a particular point in time 

may not include all of the habitat areas 

that we may later determine are 

necessary for the recovery of the 

species. For these reasons, a critical 

habitat designation does not signal that 

habitat outside the designated area is 

unimportant or may not be needed for 

recovery of the species. Areas that are 

important to the conservation of the 

species, both inside and outside the 

critical habitat designation, will 

continue to be subject to: (1) 

Conservation actions implemented 

under section 7(a)(1) of the Act; (2) 

regulatory protections afforded by the 

requirement in section 7(a)(2) of the Act 

for Federal agencies to ensure their 

actions are not likely to jeopardize the 

continued existence of any endangered 

or threatened species; and (3) section 9 

of the Act’s prohibitions on taking any 

individual of the species, including 

taking caused by actions that affect 

habitat. Federally funded or permitted 

projects affecting listed species outside 

their designated critical habitat areas 

may still result in jeopardy findings in 

some cases. These protections and 

conservation tools will continue to 

contribute to recovery of these species. 

Similarly, critical habitat designations 

made on the basis of the best available 

information at the time of designation 

will not control the direction and 

substance of future recovery plans, 

habitat conservation plans (HCPs), or 

other species conservation planning 

efforts if new information available at 

the time of these planning efforts calls 

for a different outcome. 

Prudency Determinations 

Section 4(a)(3) of the Act, as 

amended, and implementing regulations 

(50 CFR 424.12), require that the 

Secretary shall designate critical habitat 

at the time the species is determined to 

be an endangered or threatened species 

to the maximum extent prudent and 

determinable. Our regulations (50 CFR 

424.12(a)(1)) state that the Secretary 

may, but is not required to, determine 

that a designation would not be prudent 

in the following circumstances: 

(i) The species is threatened by taking 

or other human activity and 

identification of critical habitat can be 


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expected to increase the degree of such 

threat to the species; 

(ii) The present or threatened 

destruction, modification, or 

curtailment of a species’ habitat or range 

is not a threat to the species, or threats 

to the species’ habitat stem solely from 

causes that cannot be addressed through 

management actions resulting from 

consultations under section 7(a)(2) of 

the Act; 

(iii) Areas within the jurisdiction of 

the United States provide no more than 

negligible conservation value, if any, for 

a species occurring primarily outside 

the jurisdiction of the United States; 

(iv) No areas meet the definition of 

critical habitat; or 

(v) The Secretary otherwise 

determines that designation of critical 

habitat would not be prudent based on 

the best scientific data available. 

As discussed in the proposed listing 

rule, above, while collection at certain 

locations has been identified as a threat 

to certain populations of Texas 

pimpleback, Texas fatmucket, and false 

spike in the Llano River, the location of 

these populations is well known and the 

identification and mapping of critical 

habitat is not expected to increase the 

degree of this threat. In our SSA report 

and proposed listing rule for the Central 

Texas mussels, we determined that the 

present or threatened destruction, 

modification, or curtailment of habitat 

or range is a threat to the Central Texas 

mussels and that those threats in some 

way can be addressed by section 7(a)(2) 

consultation measures. The species 

occurs wholly in the jurisdiction of the 

United States, and we are able to 

identify areas that meet the definition of 

critical habitat. Therefore, because none 

of the circumstances enumerated in our 

regulations at 50 CFR 424.12(a)(1) have 

been met and because there are no other 

circumstances the Secretary has 

identified for which this designation of 

critical habitat would be not prudent, 

we have determined that the 

designation of critical habitat is prudent 

for the Central Texas mussels. 

Critical Habitat Determinability 

Having determined that designation is 

prudent, under section 4(a)(3) of the Act 

we must find whether critical habitat for 

the Central Texas mussels is 

determinable. Our regulations at 50 CFR 

424.12(a)(2) state that critical habitat is 

not determinable when one or both of 

the following situations exist: 

(i) Data sufficient to perform required 

analyses are lacking, or 

(ii) The biological needs of the species 

are not sufficiently well known to 

identify any area that meets the 

definition of ‘‘critical habitat.’’ 

When critical habitat is not 

determinable, the Act allows the Service 

an additional year to publish a critical 

habitat designation (16 U.S.C. 

1533(b)(6)(C)(ii)). 

We reviewed the available 

information pertaining to the biological 

needs of the species and habitat 

characteristics where these species are 

located. This and other information 

represent the best scientific data 

available and led us to conclude that the 

designation of critical habitat is 

determinable for the Central Texas 

mussels. 

Physical or Biological Features 

Essential to the Conservation of the 

Species 

In accordance with section 3(5)(A)(i) 

of the Act and regulations at 50 CFR 

424.12(b), in determining which areas 

we will designate as critical habitat from 

within the geographical area occupied 

by the species at the time of listing, we 

consider the physical or biological 

features that are essential to the 

conservation of the species and that may 

require special management 

considerations or protection. The 

regulations at 50 CFR 424.02 define 

‘‘physical or biological features essential 

to the conservation of the species’’ as 

the features that occur in specific areas 

and that are essential to support the lifehistory needs of the species, including 

but not limited to, water characteristics, 

soil type, geological features, sites, prey, 

vegetation, symbiotic species, or other 

features. A feature may be a single 

habitat characteristic, or a more 

complex combination of habitat 

characteristics. Features may include 

habitat characteristics that support 

ephemeral or dynamic habitat 

conditions. Features may also be 

expressed in terms relating to principles 

of conservation biology, such as patch 

size, distribution distances, and 

connectivity. 

For example, physical features 

essential to the conservation of the 

species might include gravel of a 

particular size required for spawning, 

alkali soil for seed germination, 

protective cover for migration, or 

susceptibility to flooding or fire that 

maintains necessary early-successional 

habitat characteristics. Biological 

features might include prey species, 

forage grasses, specific kinds or ages of 

trees for roosting or nesting, symbiotic 

fungi, or a particular level of nonnative 

species consistent with conservation 

needs of the listed species. The features 

may also be combinations of habitat 

characteristics and may encompass the 

relationship between characteristics or 

the necessary amount of a characteristic 

essential to support the life history of 

the species. 

In considering whether features are 

essential to the conservation of the 

species, the Service may consider an 

appropriate quality, quantity, and 

spatial and temporal arrangement of 

habitat characteristics in the context of 

the life-history needs, condition, and 

status of the species. These 

characteristics include, but are not 

limited to, space for individual and 

population growth and for normal 

behavior; food, water, air, light, 

minerals, or other nutritional or 

physiological requirements; cover or 

shelter; sites for breeding, reproduction, 

or rearing (or development) of offspring; 

and habitats that are protected from 

disturbance. 

We derive the specific physical or 

biological features (PBFs) essential for 

Central Texas mussels from studies of 

these species’ habitat, ecology, and life 

history. The life histories of the six 

Central Texas mussel species are very 

similar—mussels need flowing water, 

suitable substrate, suitable water 

quality, flow refuges, and appropriate 

host fish—and so we will discuss their 

common habitat needs and then 

describe species-specific needs 

thereafter. 

Space for Individual and Population 

Growth and for Normal Behavior 

Most freshwater mussels, including 

the Central Texas mussels, are found in 

aggregations, called mussel beds, that 

vary in size from about 50 to greater 

than 5,000 square meters (m2), separated 

by stream reaches in which mussels are 

absent or rare (Vaughn 2012, p. 983). 

Freshwater mussel larvae (called 

glochidia) are parasites that must attach 

to a host fish. A population incorporates 

more than one mussel bed; it is the 

collection of mussel beds within a 

stream reach between which infested 

host fish may travel, allowing for ebbs 

and flows in mussel bed density and 

abundance over time throughout the 

population’s occupied reach. Therefore, 

resilient mussel populations must 

occupy stream reaches long enough so 

that stochastic events that affect 

individual mussel beds do not eliminate 

the entire population. Repopulation by 

infested host fish from other mussel 

beds within the reach can allow the 

population to recover from these events. 

Longer stream reaches are more likely to 

support populations of Central Texas 

mussels into the future than shorter 

stream reaches. Therefore, we determine 

that long stream reaches, over 50 miles 

(80.5 km), are an important component 

of a riverine system with habitat to 


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support all life stages of Central Texas 

mussels. 

All six species of Central Texas 

mussels need flowing water for survival. 

They are not found in lakes, reservoirs, 

or in pools without flow, or in areas that 

are regularly dewatered. River reaches 

with continuous flow support all life 

stages of Central Texas mussels, while 

those with little or no flow do not. Flow 

rates needed by each species will vary 

depending on the species and the river 

size, location, and substrate type. 

Additionally, each species of Central 

Texas mussel has specific substrate 

needs, including gravel/cobble 

(Guadalupe orb, Texas pimpleback, and 

false spike), gravel/sand/silt (Texas 

fawnsfoot), and bedrock crevices/ 

vegetated runs (Guadalupe fatmucket 

and Texas fatmucket). Except for 

habitats for Texas fawnsfoot, these 

locations must be relatively free of fine 

sediments such that the mussels are not 

smothered. 

Physiological Requirements: Water 

Quality Requirements 

Freshwater mussels, as a group, are 

sensitive to changes in water quality 

parameters such as dissolved oxygen, 

salinity, ammonia, and pollutants. 

Habitats with appropriate levels of these 

parameters are considered suitable, 

while those habitats with levels outside 

of the appropriate ranges are considered 

less suitable. We have used information 

for these six Central Texas mussel 

species, where available, and data from 

other species when species-specific 

information is not available. Juvenile 

freshwater mussels are particularly 

susceptible to low dissolved oxygen 

levels. Juveniles will reduce feeding 

behavior when dissolved oxygen is 

between 2–4 milligrams per liter (mg/L), 

and mortality has been shown to occur 

at dissolved oxygen levels below 1.3 

mg/L. Increased salinity levels may also 

be stressful to freshwater mussels, and 

additionally, Central Texas mussels 

show signs of stress at salinity levels of 

2 ppt or higher (Bonner et al. 2018; pp. 

155–156). 

The release of pollutants into streams 

from point and nonpoint sources have 

immediate impacts on water quality 

conditions and may make environments 

unsuitable for habitation by mussels. 

Early life stages of freshwater mussels 

are some of the most sensitive 

organisms of all species to ammonia and 

copper (Naimo 1995, pp. 351–352; 

Augsperger et al. 2007, p. 2025). 

Additionally, sublethal effects of 

contaminants over time can result in 

reduced feeding efficiency, reduced 

growth, decreased reproduction, 

changes in enzyme activity, and 

behavioral changes to all mussel life 

stages. Even wastewater discharges with 

low ammonia levels have been shown to 

negatively affect mussel populations. 

Finally, water temperature plays a 

critical role in the life history of 

freshwater mussels. High water 

temperatures can cause valve closure, 

reduced reproductive output, and death. 

The Central Texas mussels differ in 

their optimal temperature ranges, with 

some species much more tolerant of 

high temperatures than others. 

Laboratory studies investigating the 

effects of thermal stress on glochidia 

and adults has indicated thermal stress 

may occur at 29 °C (84.2) °F) (Bonner et 

al. 2018; Khan et al. 2019, entire)). 

Based on the above information, we 

determine that stream reaches with the 

following water quality parameters are 

suitable for the Guadalupe fatmucket, 

Texas fatmucket, Texas fawnsfoot, 

Guadalupe orb, Texas pimpleback, and 

false spike: 

• Low salinity (less than 2 ppt); 

• Low total ammonia (less than 0.77 

mg/L total ammonia nitrogen); 

• Low levels of contaminants; 

• Dissolved oxygen levels greater 

than 2 mg/L; 

• Water temperatures below 29 °C 

(84.2 °F). 

Sites for Development of Offspring 

As discussed above, freshwater 

mussel larvae are parasites that must 

attach to a host fish to develop into 

juvenile mussels. The Central Texas 

mussels use a variety of host fish, many 

of which are widely distributed 

throughout their ranges. The presence of 

these fish species, either singly or in 

combination, supports the life-history 

needs of the Central Texas mussels: 

• False spike: Blacktail shiner 

(Cyprinella venusta) and red shiner (C. 

lutrensis); 

• Texas fawnsfoot: Freshwater drum 

(Aplodinotus grunniens); 

• Texas pimpleback and Guadalupe 

orb: Channel catfish (Ictalurus 

punctatus), flathead catfish (Pylodictus 

olivaris), and tadpole madtom (Noturus 

gyrinus); 

• Texas fatmucket and Guadalupe 

fatmucket: Green sunfish (Lepomis 

cyanellus), bluegill (L. macrochirus), 

largemouth bass (Micropterus 

salmoides), and Guadalupe bass (M. 

treculii). 

Summary of Essential Physical or 

Biological Features 

In summary, we derive the specific 

PBFs essential to the conservation of 

Central Texas mussels from studies of 

these species’ habitat, ecology, and life 

history as described above. Additional 

information can be found in the SSA 

report available on http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. We have 

determined that the following PBFs are 

essential to the conservation of the 

Central Texas mussels: 

(1) Suitable substrates and connected 

instream habitats, characterized by 

geomorphically stable stream channels 

and banks (i.e., channels that maintain 

lateral dimensions, longitudinal 

profiles, and sinuosity patterns over 

time without an aggrading or degrading 

bed elevation) with habitats that support 

a diversity of freshwater mussel and 

native fish (such as stable riffle-run-pool 

habitats that provide flow refuges 

consisting of silt-free gravel and coarse 

sand substrates). 

(2) Adequate flows, or a hydrologic 

flow regime (which includes the 

severity, frequency, duration, and 

seasonality of discharge over time), 

necessary to maintain benthic habitats 

where the species are found and to 

maintain connectivity of streams with 

the floodplain, allowing the exchange of 

nutrients and sediment for maintenance 

of the mussels’ and fish hosts’ habitat, 

food availability, spawning habitat for 

native fishes, and the ability for newly 

transformed juveniles to settle and 

become established in their habitats. 

(3) Water and sediment quality 

(including, but not limited to, dissolved 

oxygen, conductivity, hardness, 

turbidity, temperature, pH, ammonia, 

heavy metals, and chemical 

constituents) necessary to sustain 

natural physiological processes for 

normal behavior, growth, and viability 

of all life stages. 

(4) The presence and abundance of 

fish hosts necessary for recruitment of 

the Central Texas mussels. 

Special Management Considerations or 

Protection 

When designating critical habitat, we 

assess whether the specific areas within 

the geographical area occupied by the 

species at the time of listing contain 

features which are essential to the 

conservation of the species and which 

may require special management 

considerations or protection. The 

features essential to the conservation of 

the Central Texas mussels may require 

special management considerations or 

protections to reduce the following 

threats: Increased fine sediment, 

changes in water quality impairment, 

altered hydrology from both inundation 

and flow loss/scour, predation and 

collection, and barriers to fish 

movement. 

Management activities that could 

ameliorate these threats include, but are 


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not limited to: Use of best management 

practices (BMPs) designed to reduce 

sedimentation, erosion, and bank side 

destruction; protection of riparian 

corridors and leaving sufficient canopy 

cover along banks; exclusion of 

livestock and nuisance wildlife (feral 

hogs, exotic ungulates); moderation of 

surface and ground water withdrawals 

to maintain natural flow regimes; 

increased use of stormwater 

management and reduction of 

stormwater flows into the systems; use 

of highest water quality standards for 

wastewater and other return flows, and 

reduction of other watershed and 

floodplain disturbances that release 

sediments, pollutants, or nutrients into 

the water. 

In summary, we find that the 

occupied areas we are proposing to 

designate as critical habitat contain the 

PBFs that are essential to the 

conservation of the species and that may 

require special management 

considerations or protection. Special 

management considerations or 

protection may be required of the 

Federal action agency to eliminate, or to 

reduce to negligible levels, the threats 

affecting the PBFs of each unit. 

Criteria Used To Identify Critical 

Habitat 

As required by section 4(b)(2) of the 

Act, we use the best scientific data 

available to designate critical habitat. In 

accordance with the Act and our 

implementing regulations at 50 CFR 

424.12(b), we review available 

information pertaining to the habitat 

requirements of the species and identify 

specific areas within the geographical 

area occupied by the species at the time 

of listing and any specific areas outside 

the geographical area occupied by the 

species to be considered for designation 

as critical habitat. 

We are proposing to designate critical 

habitat in areas within the geographical 

area that was occupied by the species at 

the time of listing. We also are 

proposing to designate specific areas 

outside the geographical area occupied 

by the species at the time of listing 

because we have determined that a 

designation limited to occupied areas 

would be inadequate to ensure the 

conservation of the species. The current 

distributions of all six of the Central 

Texas mussels are much reduced from 

their historical distributions. We 

anticipate that recovery will require 

continued protection of existing 

populations and habitat, as well as 

ensuring that there are adequate 

numbers of mussels in stable 

populations that occur over a wide 

geographic area. This strategy will help 

to ensure that catastrophic events, such 

as the effects of hurricanes (which can 

lead to flooding that causes excessive 

sedimentation, nutrients, and debris to 

disrupt stream ecology, etc.) and 

drought, cannot simultaneously affect 

all known populations. Rangewide 

recovery considerations, such as 

maintaining existing genetic diversity 

and striving for representation of all 

major portions of the species’ current 

ranges, were considered in formulating 

this proposed critical habitat. The 

unoccupied areas included in this 

designation all contain at least one PBF, 

fall within the regulatory definition of 

‘‘habitat’’ (50 CFR 424.02), and are 

reasonably certain to contribute to the 

conservation of the species, as discussed 

in the below unit descriptions. 

Sources of data for this proposed 

critical habitat include multiple 

databases maintained by universities 

and State agencies, scientific and agency 

reports, and numerous survey reports on 

streams throughout the species’ ranges 

(see SSA report). 

Areas Occupied at the Time of Listing 

The proposed critical habitat 

designations do not include all streams 

known to have been occupied by the 

species historically; instead, they focus 

on streams occupied at the time of 

listing that have retained the necessary 

PBFs that will allow for the 

maintenance and expansion of existing 

populations. A stream reach may not 

have all of the PBFs to be included as 

proposed critical habitat; in such 

reaches, our goal is to recover the 

species by restoring the missing PBFs. 

We defined ‘‘occupied’’ units as stream 

channels with observations of one or 

more live individuals. Specific habitat 

areas were delineated based on reports 

of live individuals and recently dead 

shells. We include ‘‘recent dead shell 

material’’ to delineate the boundaries of 

a unit because recently dead shell 

material at a site indicates the species is 

present in that area. Recently dead 

shells have tissue remaining on the 

shells or have retained a shiny nacre, 

indicating the animal died within days 

or weeks of finding the shell. It is highly 

unlikely that a dead individual 

represents the last remaining individual 

of the population, and recently dead 

shells are an accepted indicator of 

species’ presence (e.g., Howells 1996; 

Randklev et al. 2012). We are relying on 

evidence of occupancy from data 

collected in 2000 to the present. This is 

because freshwater mussels may be 

difficult to detect and some sites are not 

visited multiple times. Additionally, 

these species live at least 15—20 years. 

Because adults are less sensitive to 

habitat changes than juveniles, changes 

in population sizes usually occur over 

decades rather than years. As a result, 

areas where individuals were collected 

within the last 20 years are expected to 

remain occupied now. Additionally, any 

areas that were surveyed around 20 

years ago and do not have subsequent 

surveys were reviewed for any largescale habitat changes (i.e., major flood 

or scour event, drought) to confirm that 

general habitat characteristics remained 

constant over this time. None of the 

relatively few areas without more recent 

survey information had experienced 

changes to general habitat 

characteristics. Therefore, data from 

around 2000 would be considered a 

strong indicator a species remains 

extant at a site if general habitat 

characteristics have remained constant 

over that time. 

For occupied areas proposed as 

critical habitat, we delineated critical 

habitat unit boundaries using the 

following criterion: Evaluate habitat 

suitability of stream segments within 

the geographic area occupied at the time 

of listing, and retain those segments that 

contain some or all of the PBFs to 

support life-history functions essential 

for conservation of the species. 

As a final step, we evaluated those 

occupied stream segments retained 

through the above analysis and refined 

the starting and ending points by 

evaluating the presence or absence of 

appropriate PBFs. We selected upstream 

and downstream cutoff points to 

reference existing easily recognizable 

geopolitical features including 

confluences, highway crossings, and 

county lines. Using these features as end 

points allows the public to clearly 

understand the boundaries of critical 

habitat. Unless otherwise specified, any 

stream beds located directly beneath 

bridge crossings or other landmark 

features used to describe critical habitat 

spatially, such as stream confluences, 

are considered to be wholly included 

within the critical habitat unit. Critical 

habitat stream segments were then 

mapped using ArcMap version 10 (ESRI, 

Inc.), a Geographic Information Systems 

program. 

We consider the following streams to 

be occupied by the Guadalupe 

fatmucket at the time of proposed 

listing: Guadalupe River, North Fork 

Guadalupe River, and Johnson Creek 

(see Unit Descriptions, below). 

We consider the following streams to 

be occupied by the Texas fatmucket at 

the time of proposed listing: Bluff Creek, 

Elm Creek, San Saba River, Cherokee 

Creek, North Llano River, South Llano 

River, Llano River, James River, 

Threadgill Creek, Beaver Creek, 


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Pedernales River, Live Oak Creek, and 

Onion Creek (see Unit Descriptions, 

below). 

We consider the following streams to 

be occupied by the Texas fawnsfoot at 

the time of proposed listing: Clear Fork 

of the Brazos River, Upper Brazos River, 

Lower Brazos River, Navasota River, 

Little River, Lower San Saba River, 

Upper Colorado River, Lower Colorado 

River, East Fork of the Trinity River, and 

Middle Trinity River (see Unit 

Descriptions, below). 

We consider the following streams to 

be occupied by the Guadalupe orb at the 

time of proposed listing: Upper 

Guadalupe River, South Fork Guadalupe 

River, Lower Guadalupe River, and San 

Marcos River (see Unit Descriptions, 

below). 

We consider the following streams to 

be occupied by the Texas pimpleback at 

the time of proposed listing: Concho 

River, Upper Colorado River, Lower San 

Saba River, Upper San Saba River, Llano 

River, and Lower Colorado River (see 

Unit Descriptions, below). 

We consider the following streams to 

be occupied by false spike at the time 

of proposed listing: Little River, San 

Gabriel River, Brushy Creek, San Saba 

River, Llano River, San Marcos River, 

and Guadalupe River (see Unit 

Descriptions, below). 

Areas Outside the Geographic Area 

Occupied at the Time of Listing 

We are not proposing to designate any 

areas outside the geographical area 

currently occupied by the false spike, 

Guadalupe orb, and Guadalupe 

fatmucket because we did not find any 

unoccupied areas that contained the 

necessary PBFs and were essential for 

the conservation of the species. 

However, each species needs the 

establishment and protection of 

additional resilient populations across 

their historical ranges to reduce their 

risk of extinction. While the species 

need these areas, we do not currently 

have adequate information to identify 

where these populations could be 

located at this time. 

We have determined that a 

designation limited to the occupied 

units would be inadequate to ensure the 

conservation of the Texas fatmucket, 

Texas fawnsfoot, and Texas pimpleback. 

Of the five remaining fragmented and 

isolated populations of Texas fatmucket, 

two are small in abundance and 

occupied stream length and have low to 

no resiliency (i.e., are unhealthy), and 

one population is functionally 

extirpated. The other two current 

populations have moderate resiliency 

and remain at risk of extirpation. For 

Texas fawnsfoot, seven populations 

remain. Four populations have 

moderate resiliency, and three are 

unhealthy or are functionally extirpated. 

The populations with moderate 

resiliency are all in the mainstem of 

large rivers, subject to decreased water 

quality as urbanization increases. 

Increasing the size of populations in the 

upper portions of the watersheds will 

increase the redundancy and 

representation of the Texas fawnsfoot in 

areas that are not subject to similar 

water quality declines. Finally, of the 

five remaining Texas pimpleback 

populations, three are unhealthy and are 

not reproducing, and two have moderate 

resiliency. This species needs expanded 

populations across its range to increase 

the populations’ resiliency and the 

species’ redundancy and representation. 

In the SSA report, we defined 50 

miles (80 km) as a stream length long 

enough to sustain a highly resilient 

population of the Central Texas mussels 

because a single event is unlikely to 

affect the entire population, and the 

affected section may be repopulated by 

mussel beds up- or downstream. Where 

available, we identified areas outside 

the geographical area currently 

occupied by Texas fatmucket, Texas 

pimpleback, and Texas fawnsfoot as 

critical habitat in order to increase the 

occupied stream length of existing small 

populations. Not all small (less than 50 

miles) occupied stream reaches may 

have adjacent unoccupied reaches that 

are reasonably certain to contribute to 

the conservation of the species, and 

while these smaller reaches will 

inherently have a higher risk of 

extirpation, these smaller areas 

contribute to the conservation of the 

species through maintaining 

redundancy and representation. Special 

management within smaller occupied 

units can reduce the risk of extirpation. 

We are proposing to designate some 

areas outside the geographical area 

currently occupied by Texas fatmucket, 

Texas pimpleback, and Texas fawnsfoot 

we found to be essential for the 

conservation of each species. The 

proposed unoccupied subunits are 

essential to the conservation of the 

species because each provides for the 

growth and expansion of the species 

within portions of their historical 

ranges. The longer the reach occupied 

by a species, the more likely it is that 

the population can withstand stochastic 

events such as extreme flooding, 

dewatering, or water contamination. 

Therefore, the unoccupied subunits are 

each essential for the conservation of 

the species. These proposed areas are 

located immediately adjacent to 

currently occupied stream reaches, 

include one or more of the necessary 

PBFs, and would allow for expansion of 

existing populations necessary to 

improve population resiliency, extend 

physiographic representation, and 

reduce the risk of extinction for the 

species. The establishment of additional 

moderately healthy to healthy 

populations across the range of these 

species would sufficiently reduce their 

risk of extinction. Improving the 

resiliency of populations in the 

currently occupied streams, and into 

identified unoccupied areas, will 

increase species viability to the point 

that the protections of the Act are no 

longer necessary. The unoccupied 

reaches we are proposing for critical 

habitat designation are Elm Creek and 

Onion Creek for the Texas fatmucket; 

the Clear Fork Brazos River for the 

Texas fawnsfoot; and the Llano River 

and Concho River for the Texas 

pimpleback. 

General Information on the Maps of the 

Proposed Critical Habitat Designations 

When determining proposed critical 

habitat boundaries, we made every 

effort to avoid including developed 

areas such as lands covered by 

buildings, pavement, and other 

structures because such lands lack 

physical or biological features necessary 

for the Central Texas mussels. The scale 

of the maps we prepared under the 

parameters for publication within the 

Code of Federal Regulations may not 

reflect the exclusion of such developed 

lands. Any such lands inadvertently left 

inside critical habitat boundaries shown 

on the maps of this proposed rule have 

been excluded by text in the proposed 

rule and are not proposed for 

designation as critical habitat. 

Therefore, if the critical habitat is 

finalized as proposed, a Federal action 

involving these lands would not trigger 

section 7 consultation under the Act 

with respect to critical habitat and the 

requirement of no adverse modification 

unless the specific action would affect 

the physical or biological features in the 

adjacent critical habitat. 

We propose to designate as critical 

habitat lands that we have determined 

are occupied at the time of listing (i.e., 

currently occupied) and that contain 

one or more of the physical or biological 

features that are essential to support 

life-history processes of the species. We 

have determined that occupied areas are 

inadequate to ensure the conservation of 

the species. Therefore, we have also 

identified, and propose for designation 

as critical habitat, unoccupied areas that 

are essential for the conservation of the 

species. 

The proposed critical habitat 

designations are defined by the map or 


jbell on DSKJLSW7X2PROD with PROPOSALS3
47954 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

maps, as modified by any accompanying 

regulatory text, presented at the end of 

this document under Proposed 

Regulation Promulgation. We include 

more detailed information on the 

boundaries of the proposed critical 

habitat designations in the discussion of 

individual units below. We will make 

the coordinates or plot points or both on 

which each map is based available to 

the public on http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

Proposed Critical Habitat Designation 

In total, we are proposing to designate 

approximately 1,944 river mi (3,129 

river km), accounting for overlapping 

units, in 27 units (total of 50 subunits; 

Table 8) as critical habitat for one or 

more Central Texas mussel species: The 

false spike, Texas fatmucket, Guadalupe 

fatmucket, Texas pimpleback, 

Guadalupe orb, and Texas fawnsfoot. 

All but five of the subunits are currently 

occupied by one or more of the species, 

and each of the 50 subunits contains the 

physical and biological features 

essential to the conservation of each 

species. These proposed critical habitat 

areas, described below, constitute our 

current best assessment of areas that 

meet the definition of critical habitat for 

the six Central Texas mussel species. 

Each species historically occurred in a 

different subset of watersheds in Central 

Texas; therefore, there are large 

differences in the amount of critical 

habitat proposed for each species. For 

example, the Guadalupe fatmucket only 

occurred in the upper reaches of the 

Guadalupe River basin. As such, we 

have not proposed to designate areas 

outside of the very small historical 

range. In contrast, Texas fawnsfoot was 

historically widespread in three basins; 

therefore, to maintain the adaptive 

capacity of this species, we are 

proposing to designate a larger area for 

Texas fawnsfoot. Texas surface water is 

owned by the State, as are the beds of 

navigable streams; thus the actual 

critical habitat units (occupied waters 

and streambeds up to the ordinary highwater mark) are owned by the State of 

Texas (Texas Water Code Section 

11.021, 11.0235). Adjacent riparian 

areas are in most cases, privately 

owned, and are what is reported in the 

discussion that follows. In many cases, 

activities on adjacent private land 

would not trigger section 7 consultation 

under the Act if those activities do not 

affect instream habitat. 

TABLE 8—OVERALL PROPOSED CRITICAL HABITAT FOR THE CENTRAL TEXAS MUSSELS

[Note: Stream lengths will not sum due to overlapping units.] 

Species Basin/unit name Occupied 

Proposed critical 

habitat river mi 

(km) 

Guadalupe fatmucket .................... Guadalupe River: ................................................................................. Yes.

GUFM–1a: North Fork Guadalupe River ...................................... ................ 7.5 (12.1) 

GUFM–1b: Johnson Creek ........................................................... ................ 10.4 (16.7) 

GUFM–1c: Guadalupe River ........................................................ ................ 36.2 (58.3) 

Total: 54.1 (87.1) 

Texas fatmucket ............................ Colorado River: .................................................................................... Yes.

TXFM–1a: Bluff Creek .................................................................. ................ 11.8 (19.0) 

TXFM–1b: Lower Elm Creek ........................................................ ................ 12.5 (20.2) 

TXFM–2: San Saba River ............................................................ ................ 93.4 (150.3) 

TXFM–3: Cherokee Creek ............................................................ ................ 18.1 (29.2) 

TXFM–4a: North Llano River ........................................................ ................ 31.2 (50.1) 

TXFM–4b: South Llano River ....................................................... ................ 22.9 (36.8) 

TXFM–4c: Llano River .................................................................. ................ 90.4 (145.6) 

TXFM–4d: James River ................................................................ ................ 18.6 (30.1) 

TXFM–4e: Threadgill Creek ......................................................... ................ 8.3 (13.4) 

TXFM–4f: Beaver Creek ............................................................... ................ 12.9 (20.8) 

TXFM–5a: Pedernales River ........................................................ ................ 80.1 (128.9) 

TXFM–5b: Live Oak Creek ........................................................... ................ 2.6 (4.2) 

TXFM–6a: Lower Onion Creek ..................................................... ................ 5.2 (8.3) 

Total: 408.2 (656.8) 

Colorado River: .................................................................................... No.

TXFM–1c: Upper Elm Creek ........................................................ ................ 9.1 (14.7) 

TXFM–6b: Upper Onion Creek ..................................................... ................ 18.9 (30.4) 

Total: 28 (45.1) 

Texas fawnsfoot ............................ Brazos River: ....................................................................................... Yes.

TXFF–1a: Upper Clear Fork Brazos River ................................... ................ 27.9 (44.9) 

TXFF–2: Upper Brazos River ....................................................... ................ 79.9 (128.6) 

TXFF–3a: Lower Brazos River ..................................................... ................ 348.0 (560.0) 

TXFF–3b: Navasota River ............................................................ ................ 39.3 (63.2) 

Colorado River: 

TXFF–4: Little River ...................................................................... ................ 35.6 (57.3) 

TXFF–5a: San Saba River ........................................................... ................ 50.4 (81.1) 

TXFF–5b: Upper Colorado River .................................................. ................ 10.5 (16.9) 

TXFF–6: Lower Colorado River .................................................... ................ 124.4 (200.2) 

Trinity River: 

TXFF–7: East Fork Trinity River ................................................... ................ 15.6 (25.1) 

TXFF–8: Trinity River ................................................................... ................ 157.0 (252.7) 

Total: 888.6 (1,430.1) 


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TABLE 8—OVERALL PROPOSED CRITICAL HABITAT FOR THE CENTRAL TEXAS MUSSELS—Continued 

[Note: Stream lengths will not sum due to overlapping units.] 

Species Basin/unit name Occupied 

Proposed critical 

habitat river mi 

(km) 

Brazos River: ....................................................................................... No.

TXFF–1b: Lower Clear Fork Brazos River ................................... ................ 28.6 (46.0) 

Guadalupe orb .............................. Guadalupe River: ................................................................................. Yes.

GORB–1a: South Fork Guadalupe River ..................................... ................ 5.1 (8.3) 

GORB–1b: Upper Guadalupe River ............................................. ................ 99.4 (159.9) 

GORB–2a: San Marcos River ...................................................... ................ 65.3 (105.1) 

GORB–2b: Lower Guadalupe River ............................................. ................ 124.7 (200.7) 

294.5 (474.0) 

Texas pimpleback ......................... Colorado River: .................................................................................... Yes.

TXPB–1a: Bluff Creek .................................................................. ................ 11.8 (19.0) 

TXPB–1b: Lower Elm Creek ........................................................ ................ 12.5 (20.2) 

TXPB–2a: Lower Concho River ................................................... ................ 35.6 (57.2) 

TXPB–3a: Upper Colorado River ................................................. ................ 153.8 (247.6) 

TXPB–3b: Lower San Saba River ................................................ ................ 50.4 (81.1) 

TXPB–4: Upper San Saba River ......................................................... ................ 52.8 (85.0) 

TXPB–5a: Upper Llano River ....................................................... ................ 38.3 (61.6) 

TXPB–6: Lower Colorado River ................................................... ................ 111.3 (179.1) 

Total: 466.5 (750.8) 

Colorado River: .................................................................................... No.

TXPB–2b: Upper Concho River ................................................... ................ 16.0 (25.7) 

TXPB–5b: Lower Llano River ....................................................... ................ 12.2 (19.7) 

Total: 28.2 (45.4) 

False spike .................................... Brazos River: ....................................................................................... Yes.

FASP–1a: Little River ................................................................... ................ 35.6 (57.3) 

FASP–1b: San Gabriel River ........................................................ ................ 31.4 (50.5) 

FASP–1c: Brushy Creek ............................................................... ................ 14.0 (22.5) 

Colorado River: 

FASP–2: San Saba River ............................................................. ................ 50.4 (81.1) 

FASP–3: Llano River .................................................................... ................ 50.5 (81.3) 

Guadalupe River: 

FASP–4a: San Marcos River ....................................................... ................ 21.6 (34.8) 

FASP–4b: Guadalupe River ......................................................... ................ 124.7 (200.7) 

Total: 328.2 (528.2) 

Guadalupe Fatmucket 

We are proposing to designate 

approximately 54.1 river mi (87.1 river 

km) in a single unit (three subunits) as 

critical habitat for Guadalupe fatmucket. 

The critical habitat areas we describe 

below constitute our current best 

assessment of areas that meet the 

definition of critical habitat for 

Guadalupe fatmucket. The unit we 

propose as critical habitat is GUFM–1: 

Guadalupe River Unit. Table 9 shows 

the occupancy of the unit, the riparian 

ownership, and approximate length of 

the proposed designated areas for the 

Texas fatmucket. We present a brief 

description of the proposed unit, and 

reasons why it meets the definition of 

critical habitat for Guadalupe fatmucket, 

below. 

TABLE 9—PROPOSED CRITICAL HABITAT UNITS FOR THE GUADALUPE FATMUCKET

[Note: Lengths may not sum due to rounding.] 

Unit Subunit Riparian 

ownership Occupancy River miles (kilometers) 

GUFM–1: Guadalupe River ................................. GUFM–1a: North Fork Guadalupe River ............ Private ...... Occupied .. 7.5 (12.1) 

GUFM–1b: Johnson Creek .................................. Private ...... Occupied .. 10.4 (16.7) 

GUFM–1c: Guadalupe River ............................... Private ...... Occupied .. 36.2 (58.3) 

Total .............................................................. .............................................................................. ................... ................... 54.1 (87.1) 


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Guadalupe River Basin 

Unit GUFM–1: Guadalupe River 

Subunit GUFM–1a: North Fork 

Guadalupe River. The North Fork 

Guadalupe River subunit consists of 7.5 

river mi (12.1 river km) in Kerr County, 

Texas. The adjacent riparian areas of the 

subunit are privately owned. The entire 

subunit is currently occupied by the 

species. The North Fork Guadalupe 

River subunit extends from the FM 1340 

bridge crossing (just upstream of the 

Bear Creek Boy Scout camp) 

downstream to the confluence with the 

Guadalupe River. This subunit contains 

all of the PBFs essential to the 

conservation of the Guadalupe 

fatmucket. The North Fork Guadalupe 

River subunit is in a mostly rural 

setting; is influenced by drought, low 

flows, and flooding (leading to scour); 

and is being affected by ongoing 

agricultural activities and development 

resulting in excessive sedimentation, 

water quality degradation, and ground 

water withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management may be necessary to ensure 

adequate instream flow and water 

quality. 

Subunit GUFM–1b: Johnson Creek. 

The Johnson Creek subunit consists of 

10.4 river mi (16.7 river km) within Kerr 

County, Texas. The Johnson Creek 

subunit begins at the Byas Springs Road 

crossing downstream to the confluence 

with the Guadalupe River. The adjacent 

riparian area is privately owned. The 

subunit is occupied by the Guadalupe 

fatmucket. This site contains the 

majority of the PBFs essential to the 

conservation of the species. Certain 

PBFs, such as sufficient water flow, 

dissolved oxygen levels, and water 

temperature, may be missing or 

degraded during times of drought. The 

Johnson Creek subunit is in a mostly 

rural but urbanizing setting, is 

influenced by drought, low flows, and 

flooding (leading to scour), and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and groundwater 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit GUFM–1c: Guadalupe River. 

This unit consists of approximately 36.2 

river mi (58.3 river km) in Kerr and 

Kendall Counties, Texas. The 

Guadalupe River Subunit extends from 

the confluence of the North and South 

Fork Guadalupe Rivers downstream to 

the Interstate Highway 10 bridge 

crossing near Comfort, Texas. The 

adjacent riparian areas of this subunit 

are privately owned. The subunit is 

occupied by the Guadalupe fatmucket. 

This portion of the Guadalupe River 

basin is largely agricultural with several 

municipalities and multiple low-head 

dams originally built for a variety of 

purposes and now largely used for 

recreation (kayaking, fishing, camping, 

swimming, etc.). This subunit provides 

all of the PBFs essential to the 

conservation of the species. The 

Guadalupe River subunit is 

experiencing some urbanization and is 

influenced by drought, low flows, and 

flooding (leading to scour), and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by Guadalupe orb. 

Texas Fatmucket 

We are proposing to designate 

approximately 436.0 river mi (701.7 km) 

in 6 units (15 subunits) as critical 

habitat for Texas fatmucket. The critical 

habitat areas we describe below 

constitute our current best assessment of 

areas that meet the definition of critical 

habitat for Texas fatmucket. The six 

areas we propose as critical habitat are: 

TXFM–1: Elm Creek Unit; TXFM–2: San 

Saba River Unit; TXFM–3: Cherokee 

Creek Unit; TXFM–4: Llano River Unit; 

TXFM–5: Pedernales River Unit; and 

TXFM–6: Onion Creek Unit. Table 10 

shows the occupancy of the units, the 

riparian ownership, and approximate 

length of the proposed designated areas 

for the Texas fatmucket. We present 

brief descriptions of all proposed units, 

and reasons why they meet the 

definition of critical habitat for Texas 

fatmucket, below. 

TABLE 10—PROPOSED CRITICAL HABITAT UNITS FOR TEXAS FATMUCKET

[Note: Lengths may not sum due to rounding.] 

Unit Subunit Riparian 

ownership Occupancy River miles (kilometers) 

TXFM–1: Elm Creek ......................................... TXFM–1a: Bluff Creek ...................................... Private ........ Occupied .... 11.8 (19.0) 

TXFM–1b: Lower Elm Creek ............................ Private ........ Occupied .... 12.5 (20.2) 

TXFM–1c: Upper Elm Creek ............................ Private ........ Unoccupied 9.1 (14.7) 

TXFM–2: San Saba River ................................. ........................................................................... Private ........ Occupied .... 93.4 (150.3) 

TXFM–3: Cherokee Creek ................................ ........................................................................... Private ........ Occupied .... 18.1 (29.2) 

TXFM–4: Llano River ........................................ TXFM–4a: North Llano River ............................ Private ........ Occupied .... 31.2 (50.1) 

TXFM–4b: South Llano River ........................... Private ........ Occupied .... 22.9 (36.8) 

TXFM–4c: Llano River ...................................... Private ........ Occupied .... 90.4 (145.6) 

TXFM–4d: James River .................................... Private ........ Occupied .... 18.6 (30.1) 

TXFM–4e: Threadgill Creek ............................. Private ........ Occupied .... 8.3 (13.4) 

TXFM–4f: Beaver Creek ................................... Private ........ Occupied .... 12.9 (20.8) 

TXFM–5: Pedernales River .............................. TXFM–5a: Pedernales River ............................ Private, Federal.Occupied .... 80.1 (128.9) 

TXFM–5b: Live Oak Creek ............................... Private ........ Occupied .... 2.6 (4.2) 

TXFM–6: Onion Creek ...................................... TXFM–6a: Lower Onion Creek ......................... Private ........ Occupied .... 5.2 (8.3) 

TXFM–6b: Upper Onion Creek ......................... Private ........ Unoccupied 18.9 (30.4) 

Total ........................................................... ........................................................................... .................... .................... 436.0 (701.7) 


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Colorado River Basin 

Unit TXFM–1: Elm Creek 

Subunit TXFM–1a: Bluff Creek. This 

occupied critical habitat subunit 

consists of 11.8 river mi (19.0 km) of 

Bluff Creek, a tributary to Elm Creek, in 

Runnels County, Texas. The subunit 

extends from the County Road 153 

bridge crossing, near the town of 

Winters, Texas, downstream to the 

confluence of Bluff and Elm creeks. The 

riparian area of this subunit is privately 

owned. This subunit is currently 

occupied by Texas fatmucket. The Bluff 

Creek subunit is in a rural setting, is 

influenced by drought, low flows, and 

elevated chlorides, and is being affected 

by ongoing agricultural activities and 

development resulting in excessive 

sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by Texas pimpleback. 

Subunit TXFM–1b: Lower Elm Creek. 

This subunit consists of 12.5 river mi 

(20.2 km) of Elm Creek beginning at the 

confluence of Bluff Creek and 

continuing downstream to Elm Creek’s 

confluence with the Colorado River in 

Runnels County, Texas. The riparian 

lands adjacent to this subunit are 

privately owned. The Elm Creek 

watershed is relatively small and 

remains largely rural and dominated by 

agricultural practices. This stream 

regularly has extremely low or no flow 

during times of drought. Moreover, this 

stream has elevated chloride 

concentrations and sedimentation 

resulting in reduced habitat quality and 

availability, and decreased water 

quality. Lower Elm Creek is occupied by 

Texas fatmucket and contains some of 

the PBFs essential to the conservation of 

the species such as presence of host 

fish; others are in degraded condition 

and would benefit from management 

actions such as improving water quality 

and substrate. The Lower Elm Creek 

subunit is influenced by drought, low 

flows, and elevated chlorides, and is 

being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This unit is also 

occupied by Texas pimpleback. 

Subunit TXFM–1c: Upper Elm Creek. 

Because we have determined occupied 

areas are not adequate for the 

conservation of the species, we 

evaluated whether any unoccupied 

areas are essential for the conservation 

of Texas fatmucket and identified this 

area as essential for the conservation of 

the species. This subunit consists of 9.1 

river mi (14.7 km) from the County Road 

153 crossing, near the town of Winters, 

Texas, downstream to the confluence of 

Bluff and Elm creeks. The riparian area 

surrounding this subunit is privately 

owned. The entire Elm Creek watershed 

is dominated by agriculture and remains 

rural. Upper Elm Creek is not currently 

occupied by Texas fatmucket, but it is 

essential for the conservation of the 

species because it provides for the 

growth and expansion of the Texas 

fatmucket within a portion of its 

historical range on Elm Creek; the 

occupied segment of Elm Creek is too 

small to ensure conservation of the 

Texas fatmucket over the long term. 

This unit is important to the 

conservation of Texas fatmucket 

because it is the furthest upstream 

population; its loss would shrink the 

overall range of Texas fatmucket to the 

lower, larger tributaries of the Colorado 

River. Additionally, this population of 

Texas fatmucket is substantially far from 

the other population of the species, such 

that if a catastrophic event such as 

drought or extreme flooding were to 

occur it is likely that this population 

would be affected differently, increasing 

the chance of the species surviving such 

an event. 

The Upper Elm Creek subunit is in a 

rural setting, is influenced by drought, 

low flows, and elevated chlorides, and 

is being affected by ongoing agricultural 

activities. Although it is considered 

unoccupied, portions of this subunit 

contain some or all of the physical or 

biological features essential for the 

conservation of the species. As 

previously mentioned, flow rates in this 

subunit are typically not within the 

range required by the Texas fatmucket 

(PBF 1). This subunit is often 

characterized by small, isolated pools 

separated by short riffles over bedrock 

during low flow and when dam releases 

are minimal. During the last decade, 

lower Elm Creek has experienced both 

the lowest and highest flow rates on 

record (see SSA report for more 

information). This subunit will require 

management actions that address flow 

rate and associated stream habitat 

quality. 

Suitable stream habitat and 

hydrological connectivity (PBF 2) are 

unsupported throughout the entirety of 

this subunit. Specifically, low flows 

during times of drought punctuated by 

high flows are either scouring the 

stream habitat, or depositing stream 

sediments downstream. Because 

mussels are sedentary organisms, 

transportation of individuals during 

flooding events is often lethal. 

The Texas fatmucket uses predatory 

fish (e.g., bass and sunfishes) for its host 

infestation period of its lifecycle. These 

host fishes (PBF 3) are presumed to be 

common throughout the state of Texas 

and within the Upper Elm Creek 

subunit. While ongoing research may be 

necessary to confirm current abundance 

of host fishes are at suitable levels, we 

currently believe they are adequate. 

This subunit is not included in Texas 

Commission on Environmental Quality 

classified stream segments; therefore, 

we have no specific water quality 

information. During times of normal 

flow this subunit likely supports 

healthy water quality parameters (PBF 

4) for Texas fatmucket, but water quality 

is likely compromised during low flows, 

when water temperatures rise and 

dissolved oxygen drops. The Upper Elm 

Creek subunit will require additional 

management practices to ensure 

sufficient water quality standards are 

being met and maintained for Texas 

fatmucket. 

Because this reach of Elm Creek 

periodically contains the flowing water 

conditions and host fish species used by 

Texas fatmucket, it qualifies as habitat 

according to our regulatory definition 

(50 CFR 424.02). 

If the Texas fatmucket can be 

reestablished in this reach, it will 

expand the occupied reach length in 

Elm Creek to a length that will be more 

resilient to the stressors that the species 

is facing. The longer the reach occupied 

by a species, the more likely it is that 

the population can withstand stochastic 

events such as extreme flooding, 

dewatering, or water contamination. In 

the SSA report, we identified 50 miles 

(80.5 km) as a reach long enough for a 

population to be able to withstand 

stochastic events, and the addition of 

this 10.9-mile reach, as well as the 

adjacent tributary of Bluff Creek, would 

expand the existing Texas fatmucket 

population downstream in Lower Elm 

Creek and in Bluff Creek closer to 50 

miles. The addition of multiple 

tributaries increases the value of the 

overall critical habitat unit, providing 

protection for the population should a 

stochastic event occur in one tributary. 

If Texas fatmucket were to become 

reestablished throughout this unit, it 

would likely be a moderately to highly 

resilient population due to longer 

stream length and would increase the 

species’ future redundancy. This unit is 


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essential for the conservation of the 

species because it will provide habitat 

for range expansion in portions of 

known historical habitat that is 

necessary to increase viability of the 

species by increasing its resiliency, 

redundancy, and representation. 

We are reasonably certain that this 

unit will contribute to the conservation 

of the species, because the need for 

conservation efforts is recognized and is 

being discussed by our conservation 

partners, and methods for restoring and 

reintroducing the species into 

unoccupied habitat are being developed. 

The Texas fatmucket is listed as 

threatened by the State of Texas, and the 

Texas Comptroller of Public Accounts 

has funded research, surveys, 

propagation, and reintroduction studies 

for this species. State and Federal 

partners have shown interest in 

propagation and reintroduction efforts 

for the Texas fatmucket. As previously 

mentioned, efforts are underway 

regarding a captive propagation program 

for Texas fatmucket at the San Marcos 

Aquatic Resource Center and Inks Dam 

National Fish Hatchery. The State of 

Texas, San Marcos Aquatic Resource 

Center, Inks Dam National Fish 

Hatchery, and the Service’s Austin and 

Texas Coastal Field Offices collaborate 

regularly on conservation actions. 

Therefore, this unoccupied critical 

habitat subunit is essential for the 

conservation of the Texas fatmucket and 

is reasonably certain to contribute to 

such conservation. 

Unit TXFM–2: San Saba River 

This unit consists of 93.4 river mi 

(150.3 km) of the San Saba River in 

Menard, Mason, McCulloch, and San 

Saba Counties, Texas. This unit of the 

San Saba River extends from the 

Schleicher and Menard County line, 

near Fort McKavett, Texas, downstream 

to the San Saba River confluence with 

the Colorado River. The adjacent 

riparian areas are privately owned. This 

basin is largely rural and is dominated 

by mostly agricultural activities 

including cattle grazing and hay and 

pecan farming. This unit is affected by 

very low flows and drought during the 

summer, which is exacerbated by 

pumping. This unit contains all of the 

PBFs essential to the conservation of the 

Texas fatmucket and is currently 

occupied by the species. The San Saba 

River unit is influenced by drought, low 

flows, underlying geology resulting in a 

losing reach and is being affected by 

ongoing agricultural activities and 

development resulting in excessive 

sedimentation, water quality 

degradation, groundwater withdrawals 

and surface water diversions, and 

collection. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, improve 

habitat connectivity, and manage 

collection. Special management will be 

necessary to ensure adequate flow and 

prevent water quality degradation. This 

subunit is also occupied by Texas 

fawnsfoot, Texas pimpleback, and false 

spike. 

Unit TXFM–3: Cherokee Creek 

This unit consists of 18.1 river mi 

(29.2 km) of Cherokee Creek in San Saba 

County, Texas. The adjacent riparian 

lands are privately owned. The 

Cherokee Creek unit extends from the 

County Road 409 bridge crossing 

downstream to the confluence with the 

Colorado River. This unit is occupied by 

the Texas fatmucket and contains all of 

the PBFs essential to the conservation of 

the species. Even though this unit is 

smaller than 50 miles, which we had 

determined was the reach length long 

enough to withstand stochastic events, 

this population increases the species’ 

redundancy, making it more likely to 

withstand catastrophic events that may 

eliminate one or more of the other 

populations. The Cherokee Creek unit is 

in a rural setting, is influenced by 

drought and low flows, and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and groundwater 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management may be necessary to limit 

the effect of low flow and drought 

conditions. With this special 

management, the threats to the 

population may be reduced, increasing 

the resiliency of the population, and 

providing additional redundancy and 

representation for the species. 

Unit TXFM–4: Llano River 

Subunit TXFM–4a: North Llano River. 

This subunit consists of 31.2 river mi 

(50.1 km) in Sutton and Kimble 

Counties, Texas. The North Llano River 

subunit extends from the most upstream 

County Road 307 bridge crossing in 

Sutton County downstream for 31.2 

river mi (50.1 river km) into Kimble 

County at the confluence with the South 

Llano River near the city of Junction, 

Texas. The North Llano River is 

occupied by the Texas fatmucket and 

contains all of the PBFs essential to the 

conservation of the species. Riparian 

areas adjacent to this subunit are 

privately owned and largely dominated 

by rural agricultural operations. This 

subunit is not heavily influenced by 

spring inputs like some other tributaries 

to the Llano River, such as the South 

Llano River. During summertime low 

flows and extended periods of drought, 

this subunit often becomes a series of 

isolated pools separated by shallow 

flowing riffles over bedrock. These 

reduced flows can leave mussels 

stranded and dessicated in dry beds or 

isolated in shallow pools. Decreased 

flows can also result in decreased water 

quality, specifically in the form of 

reduced dissolved oxygen and increased 

temperature. Special management may 

be required to address ongoing concerns 

of low flows and subsequent water 

quality degradation. 

Subunit TXFM–4b: South Llano River. 

The South Llano River subunit extends 

from the Edwards and Kimble County 

line downstream 22.9 river mi (36.8 

river km) to the confluence with the 

North Llano River in Kimble County, 

Texas. Riparian areas adjacent to this 

subunit are privately owned. Major 

activities in this basin are farming, 

ranching, and other agricultural uses, as 

the watershed remains largely rural. The 

South Llano River subunit is occupied 

by the Texas fatmucket and contains all 

of the PBFs essential to the conservation 

of the species. The South Llano River 

subunit is influenced by flooding 

(leading to scour), drought, and low 

flows and is being affected by ongoing 

agricultural activities and development 

resulting in excessive sedimentation, 

water quality degradation, and 

groundwater withdrawals and surface 

water diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management will be required to address 

episodic low flows during summer 

drought and associated with reduced 

spring flow. 

Subunit TXFM–4c: Llano River. This 

subunit consists of 90.4 river mi (145.6 

km) in Kimble, Mason, and Llano 

Counties, Texas. The Llano River 

subunit begins at the confluence of the 

North and South Fork Llano River and 

continues downstream to the State 

Highway 16 bridge crossing in Llano 

County. The riparian land adjacent to 

the subunit is privately owned, and the 

watershed remains largely rural. The 

Llano River subunit is occupied by the 

Texas fatmucket and contains all of the 

PBFs essential to the conservation of the 

species. The Llano River subunit is in a 

rural setting; is influenced by flooding 

(leading to scour), drought, and low 

flows; and is being affected by ongoing 


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agricultural activities and development 

resulting in excessive sedimentation, 

water quality degradation, and 

groundwater withdrawals and surface 

water diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management may be necessary to 

prevent low-flow conditions due to 

drought and agricultural water use. This 

subunit is also occupied by Texas 

pimpleback and false spike. 

Subunit TXFM–4d: James River. The 

James River subunit consists of 18.6 

river mi (30.1 km) of the James River 

and begins at the Kimble and Mason 

county line and continues downstream 

to the Llano River confluence. Adjacent 

riparian areas are privately owned. The 

James River subunit is occupied by the 

Texas fatmucket and contains all of the 

PBFs essential to the conservation of the 

species. The James River subunit is in 

a rural setting; is influenced by flooding 

(leading to scour), drought, and low 

flows; and is being affected by ongoing 

agricultural activities and development 

resulting in excessive sedimentation, 

water quality degradation, and 

groundwater withdrawals and surface 

water diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit TXFM–4e: Threadgill Creek. 

The Threadgill Creek subunit consists of 

8.3 river mi (13.4 river km) extending 

from the Ranch Road 783 bridge 

crossing downstream to the confluence 

with Beaver Creek. Riparian lands 

adjacent to this subunit are privately 

owned. Threadgill Creek is occupied by 

the Texas fatmucket and contains all of 

the PBFs essential to the conservation of 

the species. The Threadgill Creek 

subunit is in a rural setting; is 

influenced by flooding (leading to 

scour), drought, and low flows; and is 

being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit TXFM–4f: Beaver Creek. The 

Beaver Creek Subunit consists of 12.9 

river mi (20.8 river km) and begins at 

the confluence with Threadgill Creek 

and continues downstream to the 

confluence with the Llano River. 

Adjacent riparian habitats are privately 

owned. This subunit contains all of the 

PBFs essential to the conservation of 

Texas fatmucket. The Beaver Creek 

subunit is in a rural setting; is 

influenced by flooding (leading to 

scour), drought, and low flows; and is 

being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

This subunit is connected to known 

populations of Texas fatmucket in 

Subunits TXFM–4c and TXFM–4e, but 

there are no recent surveys of Beaver 

Creek itself. There are no instream 

structures in subunits TXFM–4c and 

TXFM–4e that would impede water 

flow; the flow regime is the same as in 

those subunits; and the host fish may 

move between the subunits freely. 

Based on this information, it is 

reasonable to conclude that the 

populations in subunits TXFM–4c and 

TXFM–4e are unlikely to stop at the 

most up- or downstream survey 

location; therefore, we conclude that 

this subunit is occupied. 

However, due to the lack of recent 

surveys, we are analyzing this subunit 

against the second prong of the 

definition of critical habitat for 

unoccupied habitat out of an abundance 

of caution. If subunit TXFM–4f is not, 

in fact, occupied, it is essential to the 

conservation of the species because it 

provides for needed growth and 

expansion of the species in this portion 

of its historical range and connectivity 

between documented occupied reaches. 

Connecting occupied reaches increases 

the resiliency of the occupied reaches 

by allowing for gene flow and 

repopulation after stochastic events. The 

longer the occupied reach, the more 

likely it is that the Texas fatmucket 

population can rebound after stochastic 

events such as extreme flooding, 

dewatering, or water contamination. 

Therefore, subunit TXFM–4e is essential 

for the conservation of the species. 

Unit TXFM–5: Pedernales River 

Subunit TXFM–5a: Pedernales River. 

The Pedernales River subunit consists of 

80.1 river mi (128.9 river km) in 

Gillespie, Blanco, Hays, and Travis 

Counties, Texas. The Pedernales River 

subunit extends from the origination of 

the Pedernales River at the confluence 

of Bear and Wolf creeks in Gillespie 

County downstream to the FM 3238 

(Hamilton Pool Road) bridge crossing in 

Travis County. The riparian area of this 

subunit is primarily privately owned, 

although 1.5 river mi (2.4 river km) 

within Lyndon B. Johnson National 

Historical Park owned and managed by 

the National Park Service (NPS) in 

Gillespie County, Texas. The subunit is 

currently occupied by the Texas 

fatmucket and supports all of the PBFs 

essential to the conservation of the 

species. The watershed of the 

Pedernales River is characterized by 

agricultural uses including irrigated 

orchards and vineyards. Excess 

nutrients, sediment, and pollutants 

enter the Pedernales River from 

wastewater, agricultural runoff, and 

urban stormwater runoff, all of which 

reduces instream water quality. The 

Pedernales River geology, like many 

central Texas rivers, is predominately 

limestone outcroppings; therefore, this 

system is subject to flashy, episodic 

flooding during rain events that 

mobilize large amounts of sediment and 

wood materials. Special management 

may be required in this subunit to 

address low water levels as a result of 

water withdrawals and drought. 

Additionally, implementation of the 

highest levels of treatment of 

wastewater practicable would improve 

water quality in this subunit, and 

maintenance of riparian habitat and 

upland buffers would maintain or 

improve substrate quality. 

Subunit TXFM–5b: Live Oak Creek. 

The Live Oak Creek subunit consists of 

2.6 river mi (4.2 river km) in Gillespie 

County, Texas. Riparian ownership of 

lands adjacent to this subunit is private. 

The Live Oak Creek subunit originates 

at the FM 2093 bridge crossing 

downstream to its confluence with the 

Pedernales River. This subunit is 

currently occupied by Texas fatmucket 

and contains all of the PBFs essential to 

the conservation of the species. The 

Live Oak Creek subunit is in a mostly 

rural setting with some urbanization; is 

influenced by drought, low flows, and 

flooding (leading to scour); and is being 

affected by ongoing development and 

agricultural activities resulting in 

excessive sedimentation, water quality 

degradation, and groundwater 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management considerations may be 

required to address periods of low flow, 

increased sedimentation, and water 

quality degradation. 

Unit TXFM–6: Onion Creek 

Subunit TXFM–6a: Lower Onion 

Creek. The Lower Onion Creek subunit 

consists of 5.2 river mi (8.3 river km) in 


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Travis County, Texas. This subunit 

extends from the State Highway 130 

bridge crossing downstream to the 

confluence with the Colorado River. 

This subunit is in close proximity to the 

rapidly urbanizing city of Austin, Texas, 

and contains substantial municipal 

developments. The effects of such rapid 

and widespread urbanization have 

contributed to significantly altered 

flows in Onion Creek that have led to 

bank destabilization, increased 

sedimentation and streambed 

mobilization, and loss of stable 

substrate. Further, urban runoff 

pollutants are responsible for degraded 

water quality conditions. Even though 

this unit is smaller than 50 miles, which 

we had determined was the reach length 

long enough to withstand stochastic 

events, the population increases the 

species’ redundancy, making it more 

likely to withstand catastrophic events 

that may eliminate one or more of the 

other populations. Further, it is the 

easternmost population of Texas 

fatmucket and its loss would lessen the 

species’ distribution considerably. The 

Lower Onion Creek subunit is occupied 

by Texas fatmucket. The subunit occurs 

within private land and contains some 

of the PBFs essential to the conservation 

of Texas fatmucket, including host 

fishes. Several PBFs, such as water 

quality, sufficient flow rates, and 

sedimentation, are either missing in this 

subunit or minimally acceptable for the 

species. Special management is 

necessary to reduce sedimentation, 

improve water quality, maintain 

adequate flows, and improve habitat 

connectivity. 

Subunit TXFM–6b: Upper Onion 

Creek. Because we have determined 

occupied areas are not adequate for the 

conservation of the species, we have 

evaluated whether any unoccupied 

areas are essential for the conservation 

of Texas fatmucket and identified this 

area as essential for the conservation of 

the species. The Upper Onion Creek 

subunit consists of 18.9 river mi (30.4 

river km) of stream habitat with private 

riparian ownership. The subunit begins 

at the Interstate Highway 35 bridge 

crossing and extends downstream to the 

State Highway 130 bridge, where it is 

adjacent to subunit TXFM–6a. The 

Upper Onion Creek subunit is in a rural 

but urbanizing setting and is influenced 

by drought, low flows, and flooding 

(leading to scour). Riparian lands 

adjacent to this subunit are privately 

owned. 

This unit is essential to the 

conservation of Texas fatmucket 

because it would expand the 

easternmost population; its loss would 

diminish the distribution of Texas 

fatmucket. Additionally, this population 

of Texas fatmucket is substantially far 

from the other population of the species, 

such that if a catastrophic event such as 

drought or extreme flooding were to 

occur it is likely that this population 

would be affected differently, increasing 

the chance of the species surviving such 

an event. The subunit is being affected 

by ongoing agricultural and 

development activities resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. 

Although it is considered unoccupied, 

portions of this subunit contain some or 

all of the physical or biological features 

essential for the conservation of the 

species. Water quantity (PBF 1) is likely 

present only during portions of the year. 

This subunit is subjected to extreme 

high and extreme low flows during 

periods of flash flooding and prolonged 

drought. This subunit requires 

management actions that address these 

hydrological alterations leading to 

extreme high and low flow events. 

Suitable substrate and connected 

instream habitats (PBF 2) are not present 

through the majority of this reach. The 

Upper Onion Creek subunit’s watershed 

is highly urbanized and even minor 

precipitation events frequently result in 

elevated flows, which scour, mobilize, 

and redeposit stream bed materials. 

Management actions addressing 

overland flows and the frequency of 

elevated flows in this subunit are 

required. 

Access to host fishes (PBF 3) is the 

only physical or biological factor 

currently supported by this subunit 

because Texas fatmucket utilize 

common basses and sunfishes (see the 

SSA report for more details). Future 

management actions could focus on 

determining if the abundance and 

distribution of host fish are sufficient to 

support a robust Texas fatmucket 

population. 

Urban runoff and resulting inflows 

from tributary streams contributes to 

elevated levels of salts and decreased 

dissolved oxygen levels in Onion Creek. 

While these parameters may be present 

during periods of normal flows, we 

believe they are degraded overall. 

Management actions that contribute to 

increased quality of key water 

parameters (PBF 4) would benefit this 

stream subunit and allow for the 

reestablishment of Texas fatmucket. 

This subunit occurs within the Barton 

Springs segment of the Edwards Aquifer 

recharge zone, and the continued 

management of this aquifer may 

indirectly benefit Texas fatmucket 

through water quality improvements. 

Because this reach of Onion Creek 

periodically contains the flowing water 

conditions and host fish species used by 

Texas fatmucket, it qualifies as habitat 

according to our regulatory definition 

(50 CFR 424.02). 

If the Texas fatmucket becomes 

reestablished in this reach, it will 

expand the occupied reach length in 

Onion Creek to a length that will be 

more resilient to the stressors that the 

species is facing. The longer the reach 

occupied by a species, the more likely 

it is that the population can withstand 

stochastic events such as extreme 

flooding, dewatering, or water 

contamination. The addition of this 

18.9-mile reach to the 5.2-mile occupied 

section of Onion Creek would expand 

the existing Texas fatmucket population 

in Onion Creek to 25.1 miles. While this 

reach length is still less than 50 miles, 

(the stream length identified in the SSA 

report as a reach long enough for a 

population to be able to withstand 

stochastic events) the additional stream 

miles would substantially increase the 

resiliency of this population and 

dramatically reduce the likelihood of its 

extirpation. If this unit were established, 

it would likely be a moderately resilient 

population due to longer stream length 

and would increase the species’ future 

redundancy This unit is essential for the 

conservation of the species because it 

will provide habitat for range expansion 

in portions of known historical habitat 

that is necessary to increase viability of 

the species by increasing its resiliency, 

redundancy, and representation. 

We are reasonably certain that this 

unit will contribute to the conservation 

of the species because it is an extension 

of a currently occupied unit and it 

supports the host fish of the species 

(PBF 2), as well as the appropriate 

flowing water conditions (PBF 1) 

periodically. Additionally, the need for 

conservation efforts is recognized and is 

being discussed by our conservation 

partners, and methods for restoring and 

reintroducing the species into 

unoccupied habitat are being worked 

on. The Texas fatmucket is listed as 

threatened by the State of Texas, and the 

Texas Comptroller of Public Accounts 

has funded research, surveys, 

propagation, and reintroduction studies 

for this species. State and Federal 

partners have shown interest in 

propagation and reintroduction efforts 

for the Texas fatmucket. As previously 

mentioned, efforts are underway 

regarding a captive propagation program 

for Texas fatmucket at the San Marcos 

Aquatic Resource Center and Inks Dam 

National Fish Hatchery. The State of 

Texas, San Marcos Aquatic Resource 

Center, Inks Dam National Fish 


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Hatchery, and the Service’s Austin and 

Texas Coastal Field Offices collaborate 

regularly on conservation actions. 

Therefore, this unoccupied critical 

habitat subunit is essential for the 

conservation of the Texas fatmucket and 

is reasonably certain to contribute to 

such conservation. 

Texas Fawnsfoot 

We are proposing to designate 

approximately 917.2 river mi (1,476.1 

km) in eight units (11 subunits) as 

critical habitat for Texas fawnsfoot. The 

critical habitat areas we describe below 

constitute our current best assessment of 

areas that meet the definition of critical 

habitat for Texas fawnsfoot. The eight 

areas we propose as critical habitat are: 

TXFF–1: Clear Fork Brazos River Unit; 

TXFF–2: Upper Brazos River Unit; 

TXFF–3: Lower Brazos River Unit; 

TXFF–4: Little River; TXFF–5: Lower 

San Saba and Upper Colorado River 

Unit; TXFF–6: Lower Colorado River 

Unit; TXFF–7: East Fork Trinity River 

Unit; and TXFF–8: Trinity River Unit. 

Table 11 shows the occupancy of the 

units, the riparian ownership, and 

approximate length of the proposed 

designated areas for the Texas 

fawnsfoot. We present brief descriptions 

of all proposed units, and reasons why 

they meet the definition of critical 

habitat for Texas fawnsfoot, below. 

TABLE 11—PROPOSED CRITICAL HABITAT UNITS FOR THE TEXAS FAWNSFOOT (Truncilla macrodon) 

[Note: Lengths may not sum due to rounding.] 

Unit Subunit Riparian 

ownership Occupancy River miles (kilometers) 

TXFF–1: Clear Fork Brazos River .................. TXFF–1a: Upper Clear Fork Brazos River ..... Private ........ Occupied .... 27.9 (44.9) 

TXFF–1b: Lower Clear Fork Brazos River ..... Private ........ Unoccupied 28.6 (46.0) 

TXFF–2: Upper Brazos River ......................... ......................................................................... Private ........ Occupied .... 79.9 (128.6) 

TXFF–3: Lower Brazos River ......................... TXFF–3a: Lower Brazos River ....................... Private ........ Occupied .... 348.0 (560.0) 

TXFF–3b: Navasota River .............................. Private ........ Occupied .... 39.3 (63.2) 

TXFF–4: Little River ........................................ ......................................................................... Private ........ Occupied .... 35.6 (57.3) 

TXFF–5: Lower San Saba and Upper Colorado River.TXFF–5a. Lower San Saba River ..................

TXFF–5b. Upper Colorado River ...................

Private ........

Private ........

Occupied ....

Occupied ....

50.4 (81.1) 

10.5 (16.9) 

TXFF–6: Lower Colorado River ...................... ......................................................................... Private ........ Occupied .... 124.4 (200.2) 

TXFF–7: East Fork Trinity River ..................... ......................................................................... Private ........ Occupied .... 15.6 (25.1) 

TXFF–8: Trinity River ...................................... ......................................................................... Private ........ Occupied .... 157.0 (252.7) 

Total ......................................................... ......................................................................... .................... .................... 917.2 (1,476.1) 

Brazos River Basin 

Unit TXFF–1: Clear Fork of the Brazos 

River 

Subunit TXFF–1a: Upper Clear Fork 

of the Brazos River. The Upper Clear 

Fork of the Brazos River Subunit 

consists of approximately 27.9 river mi 

(44.9 river km) in Throckmorton and 

Shackelford Counties, Texas. The 

subunit begins at the confluence of 

Paint Creek and extends downstream to 

the US Highway 283 bridge, near Fort 

Griffin, Texas. Adjacent riparian lands 

are privately owned. This subunit is 

occupied by Texas fawnsfoot and 

contains some of the PBFs essential to 

the conservation of the species, such as 

appropriate fish hosts and appropriate 

flows during portions of the year. The 

Upper Clear Fork of the Brazos River 

does not currently have sufficient flow, 

and water quality is often inadequate for 

the Texas fawnsfoot in this subunit, 

largely due to ongoing low-flow 

conditions from summertime drought 

and continued pressure on already 

strained water resources for municipal 

and agricultural uses. 

The Upper Clear Fork Brazos River 

subunit is in a rural setting and is 

influenced by drought, low flows, and 

chlorides. The subunit is being affected 

by ongoing agricultural activities and 

development, resulting in excessive 

sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit TXFF–1b: Lower Clear Fork 

of the Brazos River. Because we have 

determined occupied areas are not 

adequate for the conservation of the 

species, we have evaluated whether any 

unoccupied areas are essential for the 

conservation of Texas fawnsfoot and 

identified this area as essential for the 

conservation of the species. The Lower 

Clear Fork of the Brazos River Subunit 

consists of 28.6 river mi (46.0 river km) 

in Shackelford and Stephens Counties, 

Texas. This subunit begins at the US 

Highway 283 bridge and continues 

downstream to the US Highway 183 

bridge in Stephens County, Texas. 

Adjacent riparian lands are privately 

owned. 

This unit is essential to the 

conservation of Texas fawnsfoot because 

it would expand the most northern 

population; its loss would reduce the 

distribution of Texas fawnsfoot to only 

mainstem, higher order streams. 

Additionally, this population of Texas 

fawnsfoot is geographically distant from 

the other populations of the species, 

such that if a catastrophic event were to 

occur within the range of Texas 

fawnsfoot, such as extreme flooding or 

drought, it is likely that this population 

would not be affected in the same way, 

increasing the chance of the species 

surviving such an event. The Lower 

Clear Fork Brazos River Subunit is in a 

rural setting; is influenced by drought, 

low flows, and chlorides; and is being 

affected by ongoing agricultural 

activities and development, resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. 

Although it is considered unoccupied, 

portions of this subunit contain some or 

all of the physical or biological features 

essential for the conservation of the 

species. Flowing water at rates needed 

by Texas fawnsfoot (PBF 1) is not 

adequate in this subunit throughout 

most of the year due to low 

precipitation, surface diversions, and 

groundwater withdrawals. In the SSA 

report, we noted that the Lower Clear 

Fork of the Brazos River experienced 

both the lowest flow rate (0 cfs) during 

the 2011 drought and the highest flow 

rate (approaching 4,000 cfs) during the 

2015 floods. This altered hydrological 

regime also degrades stream habitat 

(PBF 2) by either scouring out available 

substrate or depositing large amounts of 

sediment on top of otherwise suitable 

areas. Appropriate substrates are found 

only in isolated reaches. Management 


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actions that allow for improvement of 

degraded habitat areas within this 

subunit would allow Texas fawnsfoot 

populations to expand and increase the 

subunit’s resiliency. 

Freshwater drum, the Texas 

fawnsfoot’s host fish (PBF 3), is 

expected to be present in the Lower 

Clear Fork of the Brazos River. However, 

it remains unclear if the abundance of 

host fish for the Texas fawnsfoot is 

currently sufficient. Thus, management 

actions may be necessary to ensure 

appropriate populations of host fish are 

co-occurring with Texas fawnsfoot. 

Water quality (PBF 4) may not be 

sufficient in the Lower Clear Fork of the 

Brazos River. Elevated chloride levels 

from naturally occurring underground 

salt formations are exacerbated by 

reduced water flow. In order for Texas 

fawnsfoot populations to expand and 

occupy the Lower Clear Fork of the 

Brazos River subunit, management 

actions would be necessary to reduce 

chloride levels. 

Because this reach of the Clear Fork 

Brazos River periodically contains the 

flowing water conditions and host fish 

species used by Texas fawnsfoot, it 

qualifies as habitat according to our 

regulatory definition (50 CFR 424.02). 

If the Texas fawnsfoot can be 

reestablished in this reach, it will 

expand the occupied reach length in the 

Clear Fork Brazos River to a length that 

will be more resilient to the stressors 

that the species is experiencing. The 

longer the reach occupied by a species, 

the more likely it is that the population 

can withstand stochastic events such as 

extreme flooding, dewatering, or water 

contamination. In the SSA report, we 

identified 50 miles (80.5 km) as a reach 

long enough for a population to be able 

to withstand stochastic events, and the 

addition of this 28.6-mile reach to the 

27.9-mile occupied section of the Clear 

Fork Brazos River would expand the 

existing Texas fawnsfoot population in 

the Clear Fork Brazos River to 56.5 

miles, achieving a length that would 

allow for a highly resilient population to 

be reestablished, increasing the species’ 

future redundancy. This unit is essential 

for the conservation of the species 

because it will provide habitat for range 

expansion in portions of known 

historical habitat that is necessary to 

increase viability of the species by 

increasing its resiliency, redundancy, 

and representation. 

We are reasonably certain that this 

unit will contribute to the conservation 

of the species, because the need for 

conservation efforts is recognized and is 

being discussed by our conservation 

partners, and methods for restoring and 

reintroducing the species into 

unoccupied habitat are being developed. 

The Texas fawnsfoot is listed as 

threatened by the State of Texas, and the 

Texas Comptroller of Public Accounts 

has funded research, surveys, 

propagation, and reintroduction studies 

for this species. State and Federal 

partners have shown interest in 

propagation and reintroduction efforts 

for the Texas fawnsfoot. As previously 

mentioned, efforts are underway 

regarding a captive propagation program 

for Texas fawnsfoot at the San Marcos 

Aquatic Resource Center and Inks Dam 

National Fish Hatchery. The State of 

Texas, San Marcos Aquatic Resource 

Center, Inks Dam National Fish 

Hatchery, and the Service’s Austin, 

Arlington and Texas Coastal Field 

Offices collaborate regularly on 

conservation actions for Texas 

fawnsfoot. Therefore, this unoccupied 

critical habitat subunit is essential for 

the conservation of the Texas fawnsfoot 

and is reasonably certain to contribute 

to such conservation. 

Unit TXFF–2: Upper Brazos River 

The Upper Brazos River Unit consists 

of approximately 79.9 river mi (128.6 

km) of the Brazos River in Palo Pinto 

and Parker Counties, Texas. The Upper 

Brazos River Unit extends from the FM 

4 bridge crossing in Palo Pinto County, 

Texas, downstream to the FM 1189 

bridge in Parker County, Texas. The unit 

is currently occupied by the species, 

and adjacent riparian lands are privately 

owned. This unit currently supports 

some of the PBFs essential to the 

conservation of Texas fawnsfoot, such 

as presence of appropriate fish hosts 

and suitable flow conditions during 

portions of the year, but becomes 

unsuitable during times of drought. The 

PBFs for water quality and sufficient 

flow are degraded in this unit, as 

excessive chloride concentrations and 

persistent low flows diminish habitat 

quality in this unit. Elevated chloride 

concentrations in this portion of Central 

Texas are often a result of natural 

causes, such as saline water inputs from 

spring releases flowing through 

subterranean salt deposits. However, 

while the Texas fawnsfoot may be able 

to tolerate some minor increases in 

salinity, low-flow rates in this unit 

exacerbate the concentrations of 

chlorides. 

The Upper Brazos River Unit is in a 

rural setting with some urbanization; is 

influenced by drought, low flows, 

chlorides, and reservoir operations; and 

is being affected by rock, sand and 

gravel mining, ongoing agricultural 

activities and development, resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management may be required to 

improve the water quantity, water 

quality, and habitat connectivity in this 

unit. 

Unit TXFF–3: Lower Brazos River 

Subunit TXFF–3a: Lower Brazos 

River. The Lower Brazos River Subunit 

consists of approximately 348.0 river mi 

(560.0 km) in McLennan, Falls, 

Robertson, Milam, Burleson, Brazos, 

Washington, Grimes, Waller, Austin, 

and Fort Bend Counties, Texas. This 

subunit begins at the Texas State 

Highway 6 bridge crossing, downstream 

of Waco, Texas, to the Fort Bend and 

Brazoria county line. This subunit is 

occupied by Texas fawnsfoot and 

supports all of the PBFs essential to the 

conservation of the Texas fawnsfoot. 

Adjacent riparian lands are privately 

owned and include rural agricultural 

operations such as cattle grazing and 

row-crop agriculture. Because much of 

the historically forested floodplain has 

been deforested, bank sloughing and 

sedimentation is ongoing in this 

segment. 

The Lower Brazos River Subunit is in 

a rural setting with some urbanization; 

is influenced by drought, low flows, and 

reservoir operations; and is being 

affected by rock, sand and gravel 

mining, channel incision, ongoing 

agricultural activities and development, 

resulting in excessive sedimentation, 

water quality degradation, groundwater 

withdrawals and surface water 

diversions, and wastewater inputs. 

Therefore, special management is 

necessary to reduce sedimentation, 

improve water quality, maintain 

adequate flows, restore riparian 

vegetation, and improve habitat 

connectivity. The Brazos River 

Authority (BRA) owns and manages 

surface water rights throughout the 

Brazos River basin, and, through 

operations of the BRA system of 

reservoirs, the BRA is able to manage 

flows in this subunit to some degree. 

Subunit TXFF–3b: Navasota River. 

The Navasota River Subunit consists of 

39.3 river mi (63.2 river km) of the 

Navasota River in Brazos and Grimes 

Counties, Texas. This subunit extends 

from the State Highway 30 bridge 

downstream to the Brazos River 

confluence. Adjacent riparian lands to 

this subunit are primarily privately 

owned. The subunit is largely rural with 

agricultural practices dominating the 

surrounding landscape. This subunit is 


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occupied by the Texas fawnsfoot and 

supports the PBFs essential to the 

conservation of the species. The 

Navasota River has experienced water 

quality degradation (low dissolved 

oxygen and elevated bacteria) from 

adjacent land use practices, flow 

alterations associated with drought, and 

operation of the Lake Limestone 

reservoir. Additionally, this subunit has 

elevated levels of nitrate and 

phosphorus presumably from 

agricultural runoff. The Navasota River 

Subunit is in a rural setting with some 

urbanization; is influenced by drought, 

low flows, and reservoir operations; and 

is being affected by ongoing agricultural 

activities and development, resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, restore 

riparian vegetation, and improve habitat 

connectivity. 

Colorado River Basin 

Unit TXFF–4: Little River 

The Little River Unit consists of 35.6 

river miles (57.3 km) of the Little River 

in Milam County, Texas. This subunit 

begins at the Bell and Milam county line 

and continues downstream to the 

confluence of the Little and San Gabriel 

rivers. The lands adjacent to the critical 

habitat unit are privately owned. The 

unit is currently occupied by the species 

and supports all of the PBFs essential to 

the conservation of the species. The 

Little River subunit is in a mostly rural 

setting, is influenced by ongoing 

development in the upper reaches 

associated with the Austin-Round Rock 

metropolitan area, and is being affected 

by ongoing agricultural activities and 

development resulting in excessive 

sedimentation, water quality 

degradation, and groundwater 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. The Little River 

Unit is also occupied by false spike. 

Unit TXFF–5: Lower San Saba River and 

Upper Colorado River 

Subunit TXFF–5a: Lower San Saba 

River. The Lower San Saba River 

Subunit consists of approximately 50.4 

river mi (81.1 river km) in San Saba 

County, Texas. This subunit begins at 

the Brady Creek confluence and extends 

to the Colorado River confluence. 

Adjacent riparian lands are owned and 

are primarily in agricultural use. The 

river experiences periods of low flow 

due to drought and water withdrawals, 

and water withdrawals are expected to 

increase in the future. The subunit is 

occupied by Texas fawnsfoot and 

contains all of the PBFs essential to the 

conservation of the species. The Lower 

San Saba River Subunit is experiencing 

some urbanization and is influenced by 

drought, low flows, and wastewater 

discharges. The watershed is being 

affected by ongoing agricultural 

activities and development, resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by Texas pimpleback and 

false spike. 

Subunit TXFF–5b: Upper Colorado 

River. The Upper Colorado River 

Subunit consists of 10.5 river mi (16.9 

river km) of the Colorado River near its 

confluence with the San Saba River in 

San Saba, Mills, and Lampasas 

Counties, Texas. This subunit extends 

from the County Road 124 bridge and 

continues downstream to the US 

highway 190 bridge. Activities in the 

watershed are mostly agricultural. The 

river experiences periodic low flows 

from drought and upstream water 

withdrawals. The average daily flow 

rate of the upper Colorado River in this 

segment has been declining since the 

early 1920s. This subunit is currently 

occupied, and adjacent riparian lands 

are privately owned. All PBFs essential 

to the conservation of Texas fawnsfoot 

are present in this subunit, with the 

exception of appropriate flows 

throughout the year. 

The Upper Colorado River Subunit is 

influenced by reservoir operations and 

chlorides and is being affected by 

ongoing agricultural activities and 

development, resulting in excessive 

sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by the Texas pimpleback. 

Unit TXFF–6: Lower Colorado River 

The Lower Colorado River Unit 

consists of approximately 124.4 river mi 

(200.2 river km) of the Colorado River 

in Colorado, Wharton, and Matagorda 

Counties, Texas. This unit begins at the 

Fayette and Colorado county line and 

continues downstream to the Texas 

State Highway 35 bridge near Bay City, 

Texas. Adjacent riparian habitats are 

privately owned. This unit is currently 

occupied by Texas fawnsfoot, and all 

PBFs essential to the conservation of the 

species are present in the unit. 

Upstream reservoir operation and 

urbanization in the Austin, Texas, 

metropolitan area contribute to altered 

flows and degraded water quality 

downstream. 

The Lower Colorado River Unit is in 

a mostly rural setting with some 

urbanization downstream from an urban 

area; is influenced by reservoir 

operations, drought, low flows, flooding 

(leading to scour), and wastewater 

discharges; and is being affected by 

ongoing agricultural activities and 

development, resulting in excessive 

sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, 

wastewater inputs, and rock, sand and 

gravel mining. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by the Texas pimpleback. 

Trinity River Basin 

Unit TXFF–7: East Fork of the Trinity 

River 

This unit consists of approximately 

15.6 river mi (25.1 km) of the East Fork 

of the Trinity River in Kaufman County, 

Texas. The East Fork of the Trinity River 

Unit extends from the Dallas and 

Kaufman county line downstream to the 

Trinity River confluence. This unit is 

currently occupied, and adjacent 

riparian lands are privately owned. 

Even though this unit is smaller than 50 

miles, which we had determined was 

the reach length long enough to 

withstand stochastic events, the 

population increases the species’ 

redundancy, making it more likely to 

withstand catastrophic events that may 

eliminate one or more of the other 

populations. 

Some of the PBFs essential to the 

conservation of Texas fawnsfoot are 

present, such as host fishes and 

appropriate substrate. The East Fork 

Trinity River Unit is in an urban setting; 

is influenced by drought, low flows, 

wastewater discharges, and flooding 

(leading to scour); and is being affected 

by ongoing development activities, 

resulting in excessive sedimentation, 

water quality degradation, ground water 

withdrawals and surface water 

diversions, and wastewater inputs. 

Therefore, special management is 

necessary to reduce sedimentation, 


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improve water quality, maintain 

adequate flows, and improve habitat 

connectivity, which would reduce the 

threats to the population, increasing the 

resiliency of the population. 

Unit TXFF–8: Middle Trinity River 

The Middle Trinity River Unit 

consists of approximately 157.0 river mi 

(252.7 km) of the Trinity River in 

Navarro, Henderson, Freestone, 

Anderson, Leon, Houston, and Madison 

Counties, Texas. This unit extends from 

the State Highway 31 bridge, west of 

Trinidad, Texas, to the State Highway 

21 bridge in Madison County. This unit 

is occupied, and adjacent riparian lands 

are privately owned. This unit provides 

all of the PBFs essential to the 

conservation of Texas fawnsfoot, 

although flows in this portion of the 

Trinity River are elevated above natural 

levels due to altered hydrology within 

the basin and daily high mean discharge 

approaching 80,000 cubic feet per 

second. Runoff and wastewater effluent 

release in the Dallas-Fort Worth 

metropolitan area result in daily pulses 

of high and low flow moving through 

the Trinity basin. 

The Middle Trinity River Unit is in a 

rural setting with some urbanization; is 

influenced by drought, low flows, 

wastewater discharges, reservoir 

operations, and flooding (leading to 

scour); and is being affected by channel 

incision, ongoing agricultural activities 

and development, resulting in excessive 

sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, restore 

riparian vegetation, and improve habitat 

connectivity. 

Guadalupe Orb 

We are proposing to designate 

approximately 294.5 river mi (474.0 

river km) in two units (four subunits) as 

critical habitat for Guadalupe orb. The 

critical habitat areas we describe below 

constitute our current best assessment of 

areas that meet the definition of critical 

habitat for Guadalupe orb. The two 

areas we propose as critical habitat are: 

GORB–1: Upper Guadalupe River Unit 

and GORB–2: Lower Guadalupe River 

Unit. Table 12 shows the occupancy of 

the units, the riparian ownership, and 

approximate length of the proposed 

designated areas for the Guadalupe orb. 

We present brief descriptions of all 

proposed units, and reasons why they 

meet the definition of critical habitat for 

Guadalupe orb, below. 

TABLE 12—PROPOSED CRITICAL HABITAT UNITS FOR THE GUADALUPE ORB

[Note: Lengths may not sum due to rounding.] 

Unit Subunit Riparian 

ownership Occupancy River miles (kilometers) 

GORB–1: Upper Guadalupe River ..................... GORB–1a: South Fork Guadalupe River ........... Private ...... Occupied .. 5.1 (8.3) 

GORB–1b: Upper Guadalupe River ................... Private ...... Occupied .. 99.4 (159.9) 

GORB–2: Lower Guadalupe River ..................... GORB–2a: San Marcos River ............................ Private ...... Occupied .. 65.3 (105.1) 

GORB–2b: Lower Guadalupe River ................... Private ...... Occupied .. 124.7 (200.7) 

Total ............................................................. ............................................................................. ................... ................... 294.5 (474.0) 

Guadalupe River Basin 

Unit GORB–1: Upper Guadalupe River 

Subunit GORB–1a: South Fork 

Guadalupe River. The South Fork 

Guadalupe River Subunit consists of 5.1 

river mi (8.3 river km) of the South Fork 

Guadalupe River in Kerr County, Texas. 

This subunit extends from Griffin Road 

crossing just downstream of the Texas 

Highway 39 crossing in Kerr County, to 

its confluence with the North Fork 

Guadalupe River. This subunit is 

occupied by the Guadalupe orb, and the 

riparian area is privately owned. This 

subunit is mostly rural and agricultural, 

with organized recreational camps. 

These camps often operate very low 

dams that form small impoundments 

along the subunit. The South Fork 

Guadalupe River Subunit contains all of 

the PBFs essential to the conservation of 

the species. This subunit, combined 

with the Upper Guadalupe River 

subunit, results in a highly resilient 

population with presence in several 

tributaries, protecting the population 

from a single stochastic event 

eliminating the entire population. 

The South Fork Guadalupe River 

Subunit is in a mostly rural setting; is 

influenced by drought, low flows, and 

flooding (leading to scour); and is being 

affected by ongoing agricultural 

activities and development, resulting in 

excessive sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit GORB–1b: Upper Guadalupe 

River. The Upper Guadalupe River 

Subunit consists of 99.4 river mi (159.9 

river km) of the Guadalupe River in 

Kerr, Kendall, and Comal Counties, 

Texas. This subunit extends from the 

confluence of the North and South 

Forks of the Guadalupe River 

downstream to the US Highway 311 

bridge in Comal County, Texas. The 

Upper Guadalupe River is occupied by 

the Guadalupe orb, and adjacent 

riparian areas are privately owned. The 

subunit contains the PBFs essential to 

the conservation of the Guadalupe orb. 

In recent years, the Guadalupe orb in 

this reach have experienced some of the 

highest and lowest flows on record, as 

well as water quality degradation (high 

temperature and low dissolved oxygen). 

Extreme high flows removed needed 

gravel and cobble, while low flows 

caused suspended sediment to settle 

out, reducing substrate quality for the 

Guadalupe orb. 

The Upper Guadalupe River subunit 

is in a mostly rural setting with some 

urbanization; is influenced by drought, 

low flows, and flooding (leading to 

scour); and is being affected by ongoing 

agricultural activities and development, 

resulting in excessive sedimentation, 

water quality degradation, ground water 

withdrawals and surface water 

diversions, and wastewater inputs. 

Therefore, special management is 

necessary to reduce sedimentation, 

improve water quality, maintain 

adequate flows, and improve habitat 

connectivity. This subunit is also 

occupied by Guadalupe fatmucket. 

Unit GORB–2: Lower Guadalupe River 

Subunit GORB–2a: San Marcos River. 

The San Marcos River Subunit consists 

of approximately 65.3 river miles (105.1 

river km) in Caldwell, Guadalupe, and 

Gonzales Counties, Texas. The subunit 

extends from the FM 1977 bridge 

crossing in Caldwell County to the 


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Guadalupe River confluence. The 

subunit is currently occupied by the 

Guadalupe orb, and adjacent riparian 

areas are privately owned. The San 

Marcos River drains the City of San 

Marcos, including the campus of Texas 

State University, leading to impacts of 

urban runoff, waste water inputs, and 

altered hydrology. The large San Marcos 

springs complex, the second largest in 

Texas, contributes significantly to the 

flows in this river and the lower 

Guadalupe River. This segment contains 

all of the PBFs essential to the 

conservation of the species. 

The San Marcos River Subunit is in a 

mostly rural setting with some 

urbanization and downstream from an 

urban area; is influenced by drought, 

low flows, flooding (leading to scour), 

and wastewater discharges; and is being 

affected by ongoing agricultural 

activities and development, resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by the false spike. 

Subunit GORB–2b: Lower Guadalupe 

River. The Lower Guadalupe River 

Subunit consists of approximately 124.7 

river mi (200.7 river km) in Gonzales, 

DeWitt, and Victoria Counties, Texas. 

This subunit extends from the San 

Marcos River confluence downstream to 

the US Highway 59 bridge crossing near 

Victoria, Texas. The Lower Guadalupe 

River Subunit is currently occupied by 

the Guadalupe orb, and adjacent 

riparian areas are privately owned. This 

subunit contains all of the PBFs 

necessary for the Guadalupe orb and is 

the most resilient population known. 

Existing protections for the San Marcos 

and Comal Springs from the Edwards 

Aquifer Authority Habitat Conservation 

Plan provide some protection to spring 

flows and help ensure flow rates and 

water quality are generally believed to 

be suitable for downstream mussel beds 

during times of drought and low flows. 

The Lower Guadalupe River subunit 

is in a mostly rural setting with some 

urbanization downstream from some 

urban areas; is influenced by reservoir 

operations, drought, low flows, flooding 

(leading to scour), and wastewater 

discharges; and is being affected by 

ongoing agricultural activities and 

development, resulting in excessive 

sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by the false spike. 

Texas Pimpleback 

We are proposing to designate 

approximately 494.7 river mi (796.1 km) 

in six units (10 subunits) as critical 

habitat for Texas pimpleback. The 

critical habitat areas we describe below 

constitute our current best assessment of 

areas that meet the definition of critical 

habitat for Texas pimpleback. The five 

areas we propose as critical habitat are: 

TXPB–1: Elm Creek Unit; TXPB–2: 

Concho River Unit; TXPB–3: Upper 

Colorado River/Lower San Saba River 

Unit; TXPB–4: Upper San Saba River 

Unit; TXPB–5: Llano River Unit; and 

TXPB–6: Lower Colorado River Unit. 

Table 13 shows the occupancy of the 

units, the riparian ownership, and 

approximate length of the proposed 

designated areas for the Texas 

pimpleback. We present brief 

descriptions of all proposed units, and 

reasons why they meet the definition of 

critical habitat for Texas pimpleback, 

below. 

TABLE 13—PROPOSED CRITICAL HABITAT UNITS FOR THE TEXAS PIMPLEBACK

[Note: Lengths may not sum due to rounding.] 

Unit Subunit Riparian 

ownership Occupancy River miles (kilometers) 

TXPB–1: Elm Creek .......................................... TXPB–1a: Bluff Creek ...................................... Private ........ Occupied .... 11.8 (19.0) 

TXPB–1b: Lower Elm Creek ............................ Private ........ Occupied .... 12.5 (20.2) 

TXPB–2: Concho River ..................................... TXPB–2a: Lower Concho River ....................... Private ........ Occupied .... 35.6 (57.2) 

TXPB–2b. Upper Concho River ....................... Private ........ Unoccupied 16.0 (25.7) 

TXPB–3. Upper Colorado River/Lower San 

Saba River.

TXPB–3a. Upper Colorado River .....................

TXPB–3b. Lower San Saba River ....................

Private ........

Private ........

Occupied ....

Occupied ....

153.8 (247.6) 

50.4 (81.1) 

TXPB–4: Upper San Saba River ...................... Private ........ Occupied .... 52.8 (85.0) 

TXPB–5: Llano River ........................................ TXPB–5a: Upper Llano River ........................... Private ........ Occupied .... 38.3 (61.6) 

TXPB–5b: Lower Llano River ........................... Private ........ Unoccupied 12.2 (19.7) 

TXPB–6. Lower Colorado River ....................... ........................................................................... Private ........ Occupied .... 111.3 (179.1) 

Total ........................................................... ........................................................................... .................... .................... 494.7 (796.1) 

Colorado River Basin 

Unit TXPB–1: Elm Creek 

Subunit TXPB–1a: Bluff Creek. This 

occupied critical habitat subunit 

consists of 11.8 river mi (19.0 km) of 

Bluff Creek, a tributary to Elm Creek, in 

Runnels County, Texas. The subunit 

extends from the County Road 153 

bridge crossing, near the town of 

Winters, Texas, downstream to the 

confluences of Bluff and Elm creeks. 

The riparian area of this subunit is 

privately owned. This subunit is 

currently occupied by Texas 

pimpleback. The Bluff Creek subunit is 

in a rural setting, is influenced by 

drought, low flows, and elevated 

chlorides, and is being affected by 

ongoing agricultural activities and 

development resulting in excessive 

sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by Texas fatmucket. 

Subunit TXPB–1b: Lower Elm Creek. 

This subunit consists of 12.5 river mi 

(20.2 km) of Elm Creek beginning at the 

County Road 344 crossing downstream 

to Elm Creek’s confluence with the 

Colorado River in Runnels County, 

Texas. The riparian lands adjacent to 

this subunit are privately owned. The 

Elm Creek watershed is relatively small 

and remains largely rural and 

dominated by agricultural practices. 

This stream regularly has extremely low 

or no flow during times of drought. 

Moreover, this stream has elevated 

chloride concentrations and 


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sedimentation resulting in reduced 

habitat quality and availability, and 

decreased water quality. Lower Elm 

Creek is occupied by Texas pimpleback 

and contains some of the PBFs essential 

to the conservation of the species such 

as presence of host fish; others are in 

degraded condition and would benefit 

from management actions. The Lower 

Elm Creek subunit is influenced by 

drought, low flows, and elevated 

chlorides, and is being affected by 

ongoing agricultural activities and 

development resulting in excessive 

sedimentation, water quality 

degradation, and groundwater 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This unit is also 

occupied by Texas fatmucket. 

Unit TXPB–2: Concho River 

Subunit TXPB–2a: Lower Concho 

River. The Lower Concho River Subunit 

consists of approximately 35.6 river mi 

(57.2 river km) in Tom Green and 

Concho Counties, Texas. The Concho 

River subunit extends from the FM 1692 

bridge crossing downstream to the FM 

1929 crossing. This subunit is occupied, 

and its riparian area is privately owned. 

The Lower Concho River Subunit does 

not currently contain all of the PBFs 

essential to the conservation of the 

Texas pimpleback, as it does not 

currently have sufficient water quality 

(e.g., water temperature is high and 

dissolved oxygen is low) and instream 

flow is too low at certain times of the 

year. Upstream reservoirs, built for flood 

control and municipal water storage, 

have contributed to a downward trend 

in normal river base-flows in recent 

years. The Lower Concho River subunit 

is in a mostly rural setting downstream 

from an urban area, is influenced by 

reservoir operations and chlorides, and 

is being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit TXPB–2b: Upper Concho 

River. Because we have determined 

occupied areas are not adequate for the 

conservation of the species, we have 

evaluated whether any unoccupied 

areas are essential for the conservation 

of Texas pimpleback and identified this 

area as essential for the conservation of 

the species. The Upper Concho River 

subunit consists of 16.0 river mi (25.7 

river km) of the Concho River in Tom 

Green County, Texas, from the FM 380 

bridge crossing, downstream of San 

Angelo, Texas, to the FM 1692 bridge 

where it adjoins subunit TXPB–2a. The 

riparian lands adjacent to this subunit 

are privately owned. 

This subunit is essential to the 

conservation of Texas pimpleback 

because it would expand one of the 

smaller populations to a length that 

would be highly resilient to stochastic 

events; its loss would shrink the 

distribution of Texas pimpleback and 

reduce redundancy of the species, 

limiting its viability. The Upper Concho 

River subunit is in a mostly rural setting 

with some urbanization downstream 

from an urban area; is influenced by 

reservoir operations, wastewater 

discharges, and chlorides; and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, groundwater withdrawals 

and surface water diversions, and 

wastewater inputs. 

Although it is considered unoccupied, 

portions of this subunit contain some or 

all of the physical or biological features 

essential for the conservation of the 

species. Flowing water (PBF 1) is not at 

levels appropriate for Texas pimpleback 

in this subunit. Several upstream 

reservoirs divert the already limited 

flows, and reduced precipitation has 

resulted in an overall decrease in river 

flow rates. Management actions to 

increase stream flows in this subunit 

would be required for the Texas 

pimpleback population to be 

reestablished. 

Currently, appropriate substrates (PBF 

2) exist in isolated areas throughout this 

subunit. These isolated pockets of 

suitable habitat could allow for 

expansion and recolonization of Texas 

pimpleback. However, future 

management actions that focus on 

habitat restoration in this reach to 

improve connectivity between habitat 

patches would improve the resiliency of 

this population, once restored. 

Recent research on the closely related 

Guadalupe orb indicated that several 

species of catfishes are likely suitable 

host fishes for Texas pimpleback, as 

well. Currently, we believe appropriate 

host fishes (PBF 3) are occurring 

throughout the subunit and would allow 

for reproduction of Texas pimpleback 

when the species is reestablished. 

Management actions could address any 

deficit in the abundance and 

distribution of fish hosts in this area 

allowing for expansion and future 

reestablishment of this subunit from the 

adjacent occupied subunit TXPB–2a. 

Water quality (PBF 4) is degraded in 

this subunit. The Upper Concho River 

subunit, due in part to low flows and 

high water temperature, experiences 

decreased levels of dissolved oxygen at 

such a level that could preclude mussel 

occupancy. We believe these periods of 

low dissolved oxygen primarily occur 

during hot summer months when 

droughts are common. Therefore, 

management actions that increase flow 

rates would also improve water quality 

in this reach. 

Because this reach of the Concho 

River periodically contains the 

appropriate substrate conditions and 

host fish species used by Texas 

pimpleback, it qualifies as habitat 

according to our regulatory definition 

(50 CFR 424.02). 

If the Texas pimpleback can be 

reestablished in this reach, it will 

expand the occupied reach length in the 

Concho River to a length that will be 

more resilient to the stressors that the 

species is facing. The longer the reach 

occupied by a species, the more likely 

it is that the population can withstand 

stochastic events such as extreme 

flooding, dewatering, or water 

contamination. In the SSA report, we 

identified 50 miles (80.5 km) as a reach 

long enough for a population to be able 

to withstand stochastic events, and the 

addition of this 16.0-mile reach to the 

35.6-mile occupied section of the 

Concho River would expand the 

existing Texas fawnsfoot population in 

the Concho River to 51.6 miles, 

achieving a length that would allow for 

a highly resilient population to be 

reestablished, increasing the species’ 

future redundancy. This unit is essential 

for the conservation of the species 

because it will provide habitat for range 

expansion in portions of known 

historical habitat that is necessary to 

increase viability of the species by 

increasing its resiliency, redundancy, 

and representation. 

We are reasonably certain that this 

unit will contribute to the conservation 

of the species, because the need for 

conservation efforts is recognized and is 

being discussed by our conservation 

partners, and methods for restoring and 

reintroducing the species into 

unoccupied habitat are being worked 

on. The Texas pimpleback is listed as 

threatened by the State of Texas, and the 

Texas Comptroller of Public Accounts 

has funded research, surveys, 

propagation, and reintroduction studies 

for this species. State and Federal 

partners have shown interest in 

propagation and reintroduction efforts 

for the Texas pimpleback. As previously 

mentioned, efforts are underway 

regarding a captive propagation program 


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for Texas pimpleback at the San Marcos 

Aquatic Resource Center and Inks Dam 

National Fish Hatchery. The State of 

Texas, San Marcos Aquatic Resource 

Center, Inks Dam National Fish 

Hatchery, and the Service’s Austin and 

Texas Coastal Field Offices collaborate 

regularly on conservation actions. 

Therefore, this unoccupied critical 

habitat subunit is essential for the 

conservation of the Texas pimpleback 

and is reasonably certain to contribute 

to such conservation. 

Unit TXPB–3: Upper Colorado River 

and Lower San Saba River 

Subunit TXPB–3a: Upper Colorado 

River. The Upper Colorado River 

Subunit consists of approximately 153.8 

river mi (247.6 river km) in Coleman, 

McCulloch, Brown, San Saba, Mills, and 

Lampasas Counties, Texas. The subunit 

extends from the Coleman and 

McCulloch county line downstream to 

the confluence of the Colorado River 

and Cherokee Creek. The riparian area 

of this subunit is privately owned. The 

Upper Colorado River is occupied by 

Texas pimpleback and contains some of 

the PBFs essential to the conservation of 

the species, including host fishes in 

appropriate abundance and small areas 

of suitable substrate habitat, but not 

several PBFs, such as sufficient flow 

rate and sufficient water quality 

(dissolved oxygen is often low, and 

temperature reaches unsuitably high 

levels during summer drought). The 

Upper Colorado River subunit is in a 

mostly rural setting, is influenced by 

reservoir operations and chlorides, and 

is being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, groundwater withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by Texas fawnsfoot. 

Subunit TXPB–3b: Lower San Saba 

River. The Lower San Saba River 

Subunit consists of 50.4 river mi (81.1 

river km) of the San Saba River. This 

subunit is currently occupied by the 

species, and adjacent riparian areas are 

privately owned. The Lower San Saba 

Subunit extends from the Brady Creek 

confluence in San Saba County, Texas, 

downstream to the Colorado River 

confluence where it adjoins the Upper 

Colorado River subunit (TXPB–3a). This 

subunit contains all the PBFs essential 

to the conservation of the Texas 

pimpleback most of the year. This 

population contains evidence of recent 

Texas pimpleback reproduction, which 

is largely absent from the rest of the 

species’ range. 

This subunit is primarily rural, with 

cattle grazing and irrigated orchards. 

Summer drought and water withdrawals 

cause occasional periods of low flow, 

which results in water quality 

degradation as water temperatures are 

high and dissolved oxygen is low. 

Additionally, high-flow events during 

flooding can result in habitat scour and 

sedimentation. The Lower San Saba 

River Subunit is experiencing some 

urbanization; is influenced by drought, 

low flows, and wastewater discharges; 

and is being affected by ongoing 

agricultural activities and development, 

resulting in excessive sedimentation, 

water quality degradation, ground water 

withdrawals and surface water 

diversions, and wastewater inputs. 

Therefore, special management is 

necessary to reduce sedimentation, 

improve water quality, maintain 

adequate flows, and improve habitat 

connectivity. This subunit is also 

occupied by Texas fawnsfoot and false 

spike. 

Unit TXPB–4: Upper San Saba River 

The Upper San Saba River Unit 

consists of approximately 52.8 river mi 

(85.0 river km) of the San Saba River in 

Menard County, Texas. Adjacent 

riparian habitats are privately owned. 

The Upper San Saba River Unit extends 

from the Schleicher County line near 

Fort McKavett, Texas, downstream to 

the FM 1311 bridge crossing in Menard, 

County, Texas. Texas pimpleback 

occupies the Upper San Saba River Unit 

in low densities. The Upper San Saba 

River Unit contains the PBFs essential 

to the conservation of Texas pimpleback 

most of the year, although flows decline 

to low levels during summer drought. 

The PBFs of sufficient water flow and 

water quality are lacking during these 

times, as low-flow conditions lead to 

high water temperature and low 

dissolved oxygen. The Upper San Saba 

River unit is in a rural setting; is 

influenced by drought, low flows, and 

underlying geology resulting in a losing 

reach; and is being affected by ongoing 

agricultural activities and development 

resulting in excessive sedimentation, 

water quality degradation, groundwater 

withdrawals and surface water 

diversions, and collection. Therefore, 

special management is necessary to 

reduce sedimentation, improve water 

quality, maintain adequate flows, and 

improve habitat connectivity. This 

subunit is also occupied by Texas 

fatmucket. 

Unit TXPB–5: Llano River 

Subunit TXPB–5a: Upper Llano River. 

The Upper Llano River Subunit consists 

of approximately 38.3 river mi (61.6 

river km) in Kimble and Mason 

Counties, Texas. Adjacent riparian areas 

are privately owned. This subunit 

extends from the Ranch Road RR 385 

bridge crossing downstream to the US 

Highway 87 bridge. This reach of the 

Llano River is largely rural, with much 

of the land in agricultural use. The 

Upper Llano River Subunit is occupied 

by the Texas pimpleback and contains 

all the necessary PBFs essential to the 

conservation of the species most of the 

year. However, drought conditions and 

flooding in the Llano River can be 

extreme, causing the species to 

experience either extreme low-flow 

conditions with related reduced water 

quality or extreme high flows that 

mobilize substrate, eroding habitat or 

depositing sediment on Texas 

pimpleback populations. The Upper 

Llano River Subunit is in a rural setting; 

is influenced by drought, low flows, and 

flooding (leading to scour); and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

collection. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, improve 

habitat connectivity, and manage 

collection. This subunit is also occupied 

by Texas fatmucket. 

Subunit TXPB–5b: Lower Llano River. 

Because we have determined occupied 

areas are not adequate for the 

conservation of the species, we have 

evaluated whether any unoccupied 

areas are essential for the conservation 

of Texas pimpleback and identified this 

area as essential for the conservation of 

the species. The Lower Llano River 

Subunit consists of 12.2 river mi (19.7 

river km) of the Llano River. This 

subunit extends from the US Highway 

87 bridge in Mason County downstream 

to the Mason and Llano county line. 

Adjacent riparian lands are privately 

owned. 

This subunit is essential to the 

conservation of Texas pimpleback 

because it would expand one of the 

smaller populations to a length that 

would be highly resilient to stochastic 

events in a separate tributary; its loss 

would reduce the distribution of Texas 

pimpleback and reduce redundancy of 

the species, limiting its viability. The 

Lower Llano River Subunit is in a rural 

setting; is influenced by drought, low 

flows, and flooding (leading to scour); 


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and is being affected by ongoing 

agricultural activities and development, 

resulting in excessive sedimentation, 

water quality degradation, and ground 

water withdrawals and surface water 

diversions. 

Although it is considered unoccupied, 

portions of this subunit contain some or 

all of the physical or biological features 

essential for the conservation of the 

species. Flowing water (PBF 1) is 

generally sufficient in this subunit 

during portions of the year. However, in 

the past decade the Llano River has seen 

both the highest and lowest flow rates 

ever recorded, with extremely low water 

levels and stranding of mussels during 

low flow, and scour and entrainment of 

mussels with subsequent deposition 

over suitable habitat during floods. 

Spring inputs from the South Llano 

River help mitigate the effects of 

drought in the lower portions of the 

Llano River, although water 

withdrawals for agricultural operations 

contribute to decreased flows during 

drought. Ongoing management actions 

by resource management agencies and 

non-profit organizations are 

contributing to restoring a natural flow 

regime. 

In the Llano River, suitable substrates 

(PBF 2) exist as isolated riffles between 

larger pools. Given the hydrology of the 

Llano River basin, suitable substrates 

have been degraded in this reach and 

would need restoration. 

The Texas pimpleback uses similar 

host fishes as the closely related 

Guadalupe orb, including channel 

catfish, flathead catfish, and tadpole 

madtom. Sufficient abundance of host 

fishes (PBF 3) are present in the lower 

Llano River subunit to support a 

population of Texas pimpleback. 

Water quality in the lower Llano River 

subunit (PBF 4) are generally sufficient 

for the species during portions of the 

year. However, dissolved oxygen 

declines and water temperature 

increases during periods of low flow. 

Management to ensure sufficient flow 

rates in this reach will improve water 

quality as well. 

Because this reach of the Llano River 

periodically contains the flowing water 

conditions, suitable substrates, and host 

fish species used by Texas pimpleback, 

it qualifies as habitat according to our 

regulatory definition (50 CFR 424.02). 

If the Texas pimpleback can be 

reestablished in this reach, it will 

expand the occupied reach length in the 

Llano River to a length that will be more 

resilient to the stressors that the species 

is facing. The longer the reach occupied 

by a species, the more likely it is that 

the population can withstand stochastic 

events such as extreme flooding, 

dewatering, or water contamination. In 

the SSA report, we identified 50 miles 

(80.5 km) as a reach long enough for a 

population to be able to withstand 

stochastic events, and the addition of 

this 12.2-mile reach to the 38.3-mile 

occupied section of the Llano River 

would expand the existing Texas 

pimpleback population in the Llano 

River to 50.5 miles, achieving a length 

that would allow for a highly resilient 

population to be reestablished, 

increasing the species’ future 

redundancy. This unit is essential for 

the conservation of the species because 

it will provide habitat for range 

expansion in portions of known 

historical habitat that is necessary to 

increase viability of the species by 

increasing its resiliency, redundancy, 

and representation. 

We are reasonably certain that this 

unit will contribute to the conservation 

of the species, because the need for 

conservation efforts is recognized and is 

being discussed by our conservation 

partners, and methods for restoring and 

reintroducing the species into 

unoccupied habitat are being worked 

on. The Texas pimpleback is listed as 

threatened by the State of Texas, and the 

Texas Comptroller of Public Accounts 

has funded research, surveys, 

propagation, and reintroduction studies 

for this species. State and Federal 

partners have shown interest in 

propagation and reintroduction efforts 

for the Texas pimpleback. As previously 

mentioned, efforts are underway 

regarding a captive propagation program 

for Texas pimpleback at the San Marcos 

Aquatic Resource Center and Inks Dam 

National Fish Hatchery. The State of 

Texas, San Marcos Aquatic Resource 

Center, Inks Dam National Fish 

Hatchery, and the Service’s Austin and 

Texas Coastal Field Offices collaborate 

regularly on conservation actions. 

Therefore, this unoccupied critical 

habitat subunit is essential for the 

conservation of the Texas pimpleback 

and is reasonably certain to contribute 

to such conservation. This subunit is 

also occupied by Texas fatmucket and 

false spike. 

Unit TXPB–6: Lower Colorado River 

The Lower Colorado River Unit 

consists of approximately 111.3 river mi 

(179.1 river km) of the Colorado River 

in Colorado and Wharton Counties, 

Texas. The Lower Colorado River unit 

extends from the Fayette and Colorado 

County line downstream to the Wharton 

and Matagorda County line. The unit is 

currently occupied, and adjacent 

riparian lands are privately owned. This 

unit contains all of the PBFs essential to 

the conservation of Texas pimpleback. 

Periodic low flows due to drought and 

water management activities contribute 

to diminished and variable flows, 

dewatering, scour, and water quality 

decline from urban run-off, agricultural 

operations, and wastewater treatment 

effluent. The Lower Colorado River Unit 

is in a mostly rural setting with some 

urbanization downstream from an urban 

area and is influenced by reservoir 

operations, drought, low flows, flooding 

(leading to scour), and wastewater 

discharges. The unit is being affected by 

ongoing agricultural activities and 

development, resulting in excessive 

sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, 

wastewater inputs, and rock, sand and 

gravel mining. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by Texas fatmucket. 

False Spike 

We are proposing to designate 

approximately 328.2 river mi (528.2 km) 

in four units (seven subunits) as critical 

habitat for false spike. Each of the seven 

subunits is currently occupied by the 

species and contains all of the PBFs 

essential to the conservation of the 

species. The critical habitat areas we 

describe below constitute our current 

best assessment of areas that meet the 

definition of critical habitat for false 

spike. The four areas we propose as 

critical habitat are: FASP–1: Little River 

Unit; FASP–2: San Saba River Unit; 

FASP–3: Llano River Unit; and FASP– 

4: Guadalupe River Unit. Table 14 

shows the occupancy of the units, the 

riparian ownership, and approximate 

length of the proposed designated areas 

for the false spike. We present brief 

descriptions of all proposed units, and 

reasons why they meet the definition of 

critical habitat for false spike, below. 


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TABLE 14—PROPOSED CRITICAL HABITAT UNITS FOR FALSE SPIKE

[Note: Lengths may not sum due to rounding] 

Unit Subunit Riparian 

ownership Occupancy River miles (kilometers) 

FASP–1: Little River ........................................... FASP–1a: Little River ......................................... Private ...... Occupied .. 35.6 (57.3) 

FASP–1b: San Gabriel River ............................. Private ...... Occupied .. 31.4 (50.5) 

FASP–1c: Brushy Creek .................................... Private ...... Occupied .. 14.0 (22.5) 

FASP–2: San Saba River ................................... ............................................................................. Private ...... Occupied .. 50.4 (81.1) 

FASP–3: Llano River .......................................... ............................................................................. Private ...... Occupied .. 50.5 (81.3) 

FASP–4: Guadalupe River ................................. FASP–4a: San Marcos River ............................. Private ...... Occupied .. 21.6 (34.8) 

FASP–4b: Guadalupe River ............................... Private ...... Occupied .. 124.7 (200.7) 

Total ............................................................. ............................................................................. ................... ................... 328.2 (528.2) 

Brazos River Basin 

Unit FASP–1: Little River 

Subunit FASP–1a: Little River. This 

subunit consists of 35.6 river miles (57.3 

km) of the Little River in Milam County, 

Texas. This subunit begins at the Bell 

and Milam county line and continues 

downstream to the confluence of the 

Little and San Gabriel Rivers. The lands 

adjacent to the critical habitat unit are 

privately owned. The unit is currently 

occupied by the species and supports all 

of the PBFs essential to the conservation 

of the species. The Little River subunit 

is in a mostly rural setting, is influenced 

by ongoing development in the upper 

reaches associated with the AustinRound Rock metropolitan area, and is 

being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit is 

also occupied by the Texas fawnsfoot. 

Subunit FASP–1b: San Gabriel River. 

This subunit consists of 31.4 river mi 

(50.5 km) of the San Gabriel River in 

Williamson and Milam Counties, Texas. 

The subunit starts downstream of the 

Granger Lake dam (at the downstream 

edge of the Pecan Grove State Wildlife 

Management Area) and continues 

through Williamson County to the 

confluence of the San Gabriel and Little 

Rivers in Milam County. The land 

adjacent to this subunit is all privately 

owned. The San Gabriel River subunit is 

currently occupied by the species and 

currently supports all of the PBFs 

essential to the conservation of the 

species. The San Gabriel River subunit 

is in a rural setting, is influenced by 

releases from Granger Reservoir, and is 

being affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, and ground water 

withdrawals and surface water 

diversions. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. 

Subunit FASP–1c: Brushy Creek. The 

subunit consists of 14.0 river mi (22.5 

km) of Brushy Creek in Milam County, 

Texas. The subunit begins at the US 

Highway 79 bridge crossing and extends 

downstream to the confluence with 

Brushy Creek and the San Gabriel River. 

The unit is currently occupied by the 

species, and the adjacent riparian areas 

are privately owned. This stream drains 

a large portion of the City of Cedar Park, 

resulting in altered hydrology, altered 

flow regimes, and increased 

sedimentation. Brushy Creek contains 

some of the PBFs essential to the 

conservation of the false spike, such as 

adequate fish hosts, but other factors 

like water flow rates and water quality 

parameters may not be adequate during 

summer low-flow periods. The Brushy 

Creek subunit is in a rural but 

urbanizing setting, and it is influenced 

by wastewater discharges and ongoing 

development in the upper reaches 

associated with the Austin-Round Rock 

metropolitan area. It is also being 

affected by ongoing development and 

agricultural activities resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Additionally, 

hydrological alterations in this 

watershed result in scour and 

mobilization of sediment during times 

of high-flow rates, resulting in loss of 

appropriate mussel habitat. Special 

management considerations for this area 

could include the highest level of 

wastewater treatment, decreased 

pollutant inputs from surface flows, 

bank stabilization, and increased flows 

during low-flow periods. 

Colorado River Basin 

Unit FASP–2: San Saba River 

This unit consists of 50.4 river mi 

(81.1 km) of the San Saba River in San 

Saba County, Texas. The unit extends 

from the San Saba River and Brady 

Creek confluence and continues 

downstream to the confluence of the 

San Saba and Colorado Rivers. The 

riparian land adjacent to the critical 

habitat unit is privately owned. The unit 

is currently occupied by the species and 

contains all of the PBFs essential to the 

conservation of false spike. The San 

Saba River subunit is in a rural setting, 

is influenced by drought, low flows, and 

wastewater discharges, and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, groundwater withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Much of the land 

use in the watershed is agricultural, and 

special management considerations or 

protection may be required to address 

excess nutrients, sediment, and 

pollutants that enter the San Saba River 

and reduce instream water quality. 

Sources of these types of pollution are 

wastewater, agricultural runoff, and 

urban stormwater runoff. Additional 

special management considerations or 

protection may be required in this unit 

to address low water levels that result 

from water withdrawals and drought, as 

well as excessive erosion. This subunit 

is also occupied by Texas pimpleback. 

Unit FASP–3: Llano River 

This unit consists of 50.5 river mi 

(81.3 km) of the Llano River in Kimble 

and Mason Counties, Texas. The Llano 

River unit begins at the Ranch Road 385 

bridge crossing in Kimble County and 


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continues downstream to the Mason and 

Llano County line. The unit is occupied 

by the species, and surrounding riparian 

areas are privately owned. The majority 

of the Llano River basin is rural and 

composed of agricultural operations that 

were historically used for sheep and 

goat ranching. During 2018, the Llano 

River experienced some of the largest 

floods and most severe drought within 

the same year. Extreme floods and 

drought conditions result in both stream 

bed mobilization, sedimentation, and 

dewatering. The Llano River unit 

contains all the PBFs essential to the 

conservation of false spike. The Llano 

River unit is in a rural setting; is 

influenced by drought, low flows, and 

flooding (leading to scour); and is being 

affected by ongoing agricultural 

activities and development resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

collection. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, improve 

habitat connectivity, and manage 

collection. Additionally, special 

management may be required to address 

excess nutrients, sediment, and 

pollutants, as well as exceptionally low 

and high flows. This subunit is also 

occupied by Texas fatmucket, Texas 

fawnsfoot, and Texas pimpleback. 

Guadalupe River Basin 

Unit FASP–4: Guadalupe River 

Subunit FASP–4a: San Marcos River. 

This subunit consists of 21.6 river mi 

(34.8 km) of the San Marcos River in 

Gonzales County, Texas. The San 

Marcos River subunit begins at the 

Farm-to-Market (FM) 2091 bridge 

crossing within Palmetto State Park 

(Park Road 11) and continues for 21.7 

river miles downstream to the San 

Marcos River confluence with the 

Guadalupe River. The riparian lands 

adjacent to this subunit are primarily 

privately owned; Texas Parks and 

Wildlife Department’s Palmetto State 

Park occurs in the upstream reaches. 

The San Marcos River drains the City of 

San Marcos, including the campus of 

Texas State University, which causes 

the river to be impacted by urban runoff, 

wastewater inputs, and altered 

hydrology. The San Marcos springs 

complex, the second largest in Texas, 

contributes significantly to the flows in 

this river and the lower Guadalupe 

River. The lower San Marcos River 

watershed is characterized by 

agricultural land in the lower portion of 

the San Marcos River. The subunit is 

occupied by the false spike and contains 

all of the PBFs essential to the 

conservation of the species. Because the 

San Marcos River subunit is 

downstream from an urban area in a 

rural but urbanizing setting, it is 

influenced by wastewater discharges 

and ongoing development in the upper 

reaches associated with the AustinRound Rock metropolitan area. It is also 

being affected by ongoing development 

and agricultural activities resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. Special 

management considerations may be 

required to address riparian bank 

sloughing, increased sedimentation, and 

pollutants from upstream urbanization 

and agricultural practices. This subunit 

is also occupied by Guadalupe orb. 

Subunit FASP–4b: Guadalupe River. 

This subunit consists of 124.7 river mi 

(200.7 km) of the Guadalupe River in 

Gonzales, DeWitt, and Victoria 

Counties, Texas. The Guadalupe River 

subunit begins at the confluence of the 

Guadalupe and San Marcos Rivers and 

continues downstream for 124.7 river 

miles to the US highway 59 bridge near 

Victoria, Texas. Adjacent riparian areas 

within this subunit are privately owned. 

This subunit is occupied by the false 

spike and contains all of the PBFs 

essential to the conservation of the 

species. The Guadalupe River subunit is 

in a mostly rural but urbanizing setting, 

is influenced by reservoir releases (from 

Canyon and Guadalupe Valley) and 

flooding (leading to scour), and is being 

affected by ongoing development and 

agricultural activities resulting in 

excessive sedimentation, water quality 

degradation, ground water withdrawals 

and surface water diversions, and 

wastewater inputs. Therefore, special 

management is necessary to reduce 

sedimentation, improve water quality, 

maintain adequate flows, and improve 

habitat connectivity. This subunit 

contains the most resilient known 

population of false spike. During times 

of drought, spring water influence from 

the Comal and San Marcos Rivers can 

contribute as much as 50 percent of the 

flows to the lower Guadalupe River. 

Continued protections for these spring 

systems are imperative for protecting 

mussel beds in the lower Guadalupe 

River. Special management 

considerations may be required to 

ensure low flows, sedimentation, and 

degraded water quality parameters do 

not worsen and contribute to future 

population decline. This subunit is also 

occupied by Guadalupe orb. 

Effects of Critical Habitat Designation 

Section 7 Consultation 

Section 7(a) of the Act requires 

Federal agencies to evaluate their 

actions with respect to any species that 

is proposed or listed as an endangered 

or threatened species and with respect 

to its critical habitat, if any is 

designated. Section 7(a)(2) of the Act 

requires Federal agencies, including the 

Service, to ensure that any action they 

fund, authorize, or carry out is not likely 

to jeopardize the continued existence of 

any endangered species or threatened 

species or result in the destruction or 

adverse modification of designated 

critical habitat of such species. In 

addition, section 7(a)(4) of the Act 

requires Federal agencies to confer with 

the Service on any agency action that is 

likely to jeopardize the continued 

existence of any species proposed to be 

listed under the Act or result in the 

destruction or adverse modification of 

proposed critical habitat. 

We published a final regulation with 

a revised definition of destruction or 

adverse modification on August 27, 

2019 (84 FR 44976). Destruction or 

adverse modification means a direct or 

indirect alteration that appreciably 

diminishes the value of critical habitat 

as a whole for the conservation of a 

listed species. 

If a Federal action may affect a listed 

species or its critical habitat, the 

responsible Federal agency (action 

agency) must enter into consultation 

with us. Examples of actions that are 

subject to the section 7 consultation 

process are actions on State, tribal, 

local, or private lands that require a 

Federal permit or that involve some 

other Federal action. Federal agency 

actions within the species’ habitat that 

may require conference or consultation 

or both include management and any 

other landscape-altering activities on 

Federal lands administered by the U.S. 

Fish and Wildlife Service, Army 

National Guard, U.S. Forest Service, and 

National Park Service; issuance of 

section 404 Clean Water Act (33 U.S.C. 

1251 et seq.) permits by the U.S. Army 

Corps of Engineers; and construction 

and maintenance of roads or highways 

by the Federal Highway Administration. 

Federal actions not affecting listed 

species or critical habitat, and actions 

on State, tribal, local, or private lands 

that are not federally funded, 

authorized, or carried out by a Federal 

agency, do not require section 7 

consultation. 


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Compliance with the requirements of 

section 7(a)(2), is documented through 

our issuance of: 

(1) A concurrence letter for Federal 

actions that may affect, but are not 

likely to adversely affect, listed species 

or critical habitat; or 

(2) A biological opinion for Federal 

actions that may affect, and are likely to 

adversely affect, listed species or critical 

habitat. 

When we issue a biological opinion 

concluding that a project is likely to 

jeopardize the continued existence of a 

listed species and/or destroy or 

adversely modify critical habitat, we 

provide reasonable and prudent 

alternatives to the project, if any are 

identifiable, that would avoid the 

likelihood of jeopardy and/or 

destruction or adverse modification of 

critical habitat. We define ‘‘reasonable 

and prudent alternatives’’ (at 50 CFR 

402.02) as alternative actions identified 

during consultation that: 

(1) Can be implemented in a manner 

consistent with the intended purpose of 

the action, 

(2) Can be implemented consistent 

with the scope of the Federal agency’s 

legal authority and jurisdiction, 

(3) Are economically and 

technologically feasible, and 

(4) Would, in the Service Director’s 

opinion, avoid the likelihood of 

jeopardizing the continued existence of 

the listed species and/or avoid the 

likelihood of destroying or adversely 

modifying critical habitat. 

Reasonable and prudent alternatives 

can vary from slight project 

modifications to extensive redesign or 

relocation of the project. Costs 

associated with implementing a 

reasonable and prudent alternative are 

similarly variable. 

Regulations at 50 CFR 402.16 set forth 

requirements for Federal agencies to 

reinitiate formal consultation on 

previously reviewed actions. These 

requirements apply when the Federal 

agency has retained discretionary 

involvement or control over the action 

(or the agency’s discretionary 

involvement or control is authorized by 

law) and, if subsequent to the previous 

consultation: (1) If the amount or extent 

of taking specified in the incidental take 

statement is exceeded; (2) if new 

information reveals effects of the action 

that may affect listed species or critical 

habitat in a manner or to an extent not 

previously considered; (3) if the 

identified action is subsequently 

modified in a manner that causes an 

effect to the listed species or critical 

habitat that was not considered in the 

biological opinion; or (4) if a new 

species is listed or critical habitat 

designated that may be affected by the 

identified action. In such situations, 

Federal agencies sometimes may need to 

request reinitiation of consultation with 

us, but the regulations also specify some 

exceptions to the requirement to 

reinitiate consultation on specific land 

management plans after subsequently 

listing a new species or designating new 

critical habitat. See the regulations for a 

description of those exceptions. 

Application of the ‘‘Adverse 

Modification’’ Standard 

The key factor related to the 

destruction or adverse modification 

determination is whether 

implementation of the proposed Federal 

action directly or indirectly alters the 

designated critical habitat in a way that 

appreciably diminishes the value of the 

critical habitat as a whole for the 

conservation of the listed species. As 

discussed above, the role of critical 

habitat is to support physical or 

biological features essential to the 

conservation of a listed species and 

provide for the conservation of the 

species. 

Section 4(b)(8) of the Act requires us 

to briefly evaluate and describe, in any 

proposed or final regulation that 

designates critical habitat, activities 

involving a Federal action that may 

violate 7(a)(2) of the Act by destroying 

or adversely modifying such habitat, or 

that may be affected by such 

designation. 

Activities that the Service may, 

during a consultation under section 

7(a)(2) of the Act, find are likely to 

destroy or adversely modify critical 

habitat include, but are not limited to: 

(1) Actions that would alter the 

minimum flow or the existing flow 

regime. Such activities could include, 

but are not limited to, impoundment, 

channelization, water diversion, water 

withdrawal, and hydropower 

generation. These activities could 

eliminate or reduce the habitat 

necessary for the growth and 

reproduction of the Central Texas 

mussels and its fish host by decreasing 

or altering flows to levels that would 

adversely affect their ability to complete 

their life cycles. 

(2) Actions that would significantly 

alter water chemistry or temperature. 

Such activities could include, but are 

not limited to, release of chemicals 

(including pharmaceuticals, metals, and 

salts), biological pollutants, or heated 

effluents into the surface water or 

connected groundwater at a point 

source or by dispersed release (nonpoint source). These activities could 

alter water conditions to levels that are 

beyond the tolerances of the mussel or 

its host fish and result in direct or 

cumulative adverse effects to these 

individuals and their life cycles. 

(3) Actions that would significantly 

increase sediment deposition within the 

stream channel. Such activities could 

include, but are not limited to, excessive 

sedimentation from livestock grazing, 

road construction, channel alteration, 

timber harvest, off-road vehicle use, 

agricultural, industrial, and urban 

development, and other watershed and 

floodplain disturbances. These activities 

could eliminate or reduce the habitat 

necessary for the growth and 

reproduction of the mussel and its fish 

host by increasing the sediment 

deposition to levels that would 

adversely affect their ability to complete 

their life cycles. 

(4) Actions that would significantly 

alter channel morphology or geometry. 

Such activities could include, but are 

not limited to, channelization, 

impoundment, road and bridge 

construction, mining, dredging, and 

destruction of riparian vegetation. These 

activities may lead to changes in water 

flows and levels that would degrade or 

eliminate the mussel or its fish host 

and/or their habitats. These actions can 

also lead to increased sedimentation 

and degradation in water quality to 

levels that are beyond the tolerances of 

the mussel or its fish host. 

(5) Actions that result in the 

introduction, spread, or augmentation of 

nonnative aquatic species in occupied 

stream segments, or in stream segments 

that are hydrologically connected to 

occupied stream segments, even if those 

segments are occasionally intermittent, 

or introduction of other species that 

compete with or prey on the Central 

Texas mussels. Possible actions could 

include, but are not limited to, stocking 

of nonnative fishes, stocking of sport 

fish, or other related actions. These 

activities can introduce parasites or 

disease for host fish, and can result in 

direct predation, or affect the growth, 

reproduction, and survival, of Central 

Texas mussels. 

Exemptions 

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

Section 4(a)(3)(B)(i) of the Act (16 

U.S.C. 1533(a)(3)(B)(i)) provides that the 

Secretary shall not designate as critical 

habitat any lands or other geographical 

areas owned or controlled by the 

Department of Defense, or designated 

for its use, that are subject to an 

integrated natural resources 

management plan (INRMP) prepared 

under section 101 of the Sikes Act (16 

U.S.C. 670a), if the Secretary determines 

in writing that such plan provides a 


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benefit to the species for which critical 

habitat is proposed for designation. 

There are no Department of Defense 

(DoD) lands with a completed INRMP 

within the proposed critical habitat 

designation. 

Consideration of Impacts Under Section 

4(b)(2) of the Act 

Section 4(b)(2) of the Act states that 

the Secretary shall designate and make 

revisions to critical habitat on the basis 

of the best available scientific data after 

taking into consideration the economic 

impact, national security impact, and 

any other relevant impact of specifying 

any particular area as critical habitat. 

The Secretary may exclude an area from 

critical habitat if she determines that the 

benefits of such exclusion outweigh the 

benefits of specifying such area as part 

of the critical habitat, unless she 

determines, based on the best scientific 

data available, that the failure to 

designate such area as critical habitat 

will result in the extinction of the 

species. In making that determination, 

the statute on its face, as well as the 

legislative history, are clear that the 

Secretary has broad discretion regarding 

which factor(s) to use and how much 

weight to give to any factor. 

Under section 4(b)(2) of the Act, we 

may exclude an area from designated 

critical habitat based on economic 

impacts, impacts on national security, 

or any other relevant impacts. In 

considering whether to exclude a 

particular area from the designation, we 

identify the benefits of including the 

area in the designation, identify the 

benefits of excluding the area from the 

designation, and evaluate whether the 

benefits of exclusion outweigh the 

benefits of inclusion. If the analysis 

indicates that the benefits of exclusion 

outweigh the benefits of inclusion, the 

Secretary may exercise the discretion to 

exclude the area only if such exclusion 

would not result in the extinction of the 

species. We describe below the process 

that we undertook for taking into 

consideration each category of impacts 

and our analyses of the relevant 

impacts. 

The Service is aware of efforts 

currently under way by the Brazos River 

Authority, Trinity River Authority of 

Texas, and Lower Colorado River 

Authority (collectively the River 

Authorities) to develop comprehensive 

management plans for one or more 

species of Central Texas mussels. The 

Service is currently working with the 

River Authorities individually to 

develop Candidate Conservation 

Agreements with Assurances (CCAAs) 

that address activities conducted by the 

River Authorities and conservation 

measures specifically designed to 

provide a net conservation benefit to the 

covered species, including the Central 

Texas mussels, in the covered area for 

the term of the CCAA. The Brazos River 

Authority CCAA would cover the false 

spike and Texas fawnsfoot. The Trinity 

River Authority of Texas is developing 

a CCAA that would cover the Texas 

fawnsfoot. The Colorado River 

Authority is developing a CCAA that 

would cover the Texas fawnsfoot and 

Texas pimpleback. Finally, the 

Guadalupe-Blanco River Authority, in 

partnership with the Upper Guadalupe 

River Authority, has plans to develop a 

comprehensive Habitat Conservation 

Plan (HCP) for the entire Guadalupe 

River Basin that would cover the false 

spike, Guadalupe orb, and Guadalupe 

fatmucket, among other species. None of 

these plans have been approved or 

operationalized as of the time this 

proposal is published. While these 

agreements are not yet completed, if and 

when they are, we may consider 

excluding areas covered by the 

completed agreements from our critical 

habitat designations. 

Consideration of Economic Impacts 

Section 4(b)(2) of the Act and its 

implementing regulations require that 

we consider the economic impact that 

may result from a designation of critical 

habitat. To assess the probable 

economic impacts of a designation, we 

must first evaluate specific land uses or 

activities and projects that may occur in 

the area of the critical habitat. We then 

must evaluate whether a specific critical 

habitat designation may restrict or 

modify specific land uses or activities 

for the benefit of the species and its 

habitat within the areas proposed. We 

then identify which conservation efforts 

may be the result of the species being 

listed under the Act versus those 

attributed solely to the designation of 

critical habitat. The probable economic 

impact of a proposed critical habitat 

designation is analyzed by comparing 

scenarios both ‘‘with critical habitat’’ 

and ‘‘without critical habitat.’’ 

The ‘‘without critical habitat’’ 

scenario represents the baseline for the 

analysis, which includes the existing 

regulatory and socioeconomic burden 

imposed on landowners, managers, or 

other resource users potentially affected 

by the designation of critical habitat 

(e.g., under the Federal listing as well as 

other Federal, State, and local 

regulations). The baseline, therefore, 

represents the costs of all efforts 

attributable to the listing of the species 

under the Act (i.e., conservation of the 

species and its habitat incurred 

regardless of whether critical habitat is 

designated). The ‘‘with critical habitat’’ 

scenario describes the incremental 

impacts associated specifically with the 

designation of critical habitat for the 

species. The incremental conservation 

efforts and associated impacts would 

not be expected without the designation 

of critical habitat for the species. In 

other words, the incremental costs are 

those attributable solely to the 

designation of critical habitat, above and 

beyond the baseline costs. These are the 

costs we use when evaluating the 

benefits of inclusion and exclusion of 

particular areas from the final 

designation of critical habitat should we 

choose to conduct a discretionary 

4(b)(2) exclusion analysis. 

For these proposed designations, we 

developed an incremental effects 

memorandum (IEM) considering the 

probable incremental economic impacts 

that may result from these proposed 

designations of critical habitat. The 

information contained in our IEM was 

then used to develop a screening 

analysis of the probable effects of the 

designations of critical habitat for the 

Central Texas mussels (Industrial 

Economics, Inc. (IEc) 2019, entire). We 

began by conducting a screening 

analysis of the proposed designation of 

critical habitat in order to focus our 

analysis on the key factors that are 

likely to result in incremental economic 

impacts. The purpose of the screening 

analysis is to filter out particular 

geographic areas of critical habitat that 

are already subject to such protections 

and are, therefore, unlikely to incur 

incremental economic impacts. In 

particular, the screening analysis 

considers baseline costs (i.e., absent 

critical habitat designation) and 

includes probable incremental 

economic impacts where land and water 

use may be subject to conservation 

plans, land management plans, best 

management practices, or regulations 

that protect the habitat area as a result 

of the Federal listing status of the 

species. Ultimately, the screening 

analysis allows us to focus our analysis 

on evaluating the specific areas or 

sectors that may incur probable 

incremental economic impacts as a 

result of the designation. The screening 

analysis also assesses whether units are 

unoccupied by the species and thus may 

require additional management or 

conservation efforts as a result of the 

critical habitat designation for the 

species; these additional efforts may 

incur incremental economic impacts. 

This screening analysis, combined with 

the information contained in our IEM, 

constitute our draft economic analysis 

(DEA) of the proposed critical habitat 


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designations for the Central Texas 

mussels, and is summarized in the 

narrative below. 

Executive Orders (E.O.s) 12866 and 

13563 direct Federal agencies to assess 

the costs and benefits of available 

regulatory alternatives in quantitative 

(to the extent feasible) and qualitative 

terms. Consistent with the E.O. 

regulatory analysis requirements, our 

effects analysis under the Act may take 

into consideration impacts to both 

directly and indirectly affected entities, 

where practicable and reasonable. If 

sufficient data are available, we assess 

to the extent practicable the probable 

impacts to both directly and indirectly 

affected entities. As part of our 

screening analysis, we considered the 

types of economic activities that are 

likely to occur within the areas likely 

affected by the proposed critical habitat 

designations. In our December 4, 2019, 

IEM describing probable incremental 

economic impacts that may result from 

the proposed designations, we first 

identified probable incremental 

economic impacts associated with each 

of the following categories of activities: 

(1) Federal lands management (National 

Park Service, U.S. Forest Service, 

Department of Defense); (2) agriculture; 

(3) forest management/silviculture/ 

timber; (4) development; (5) recreation; 

(6) restoration activities; and (7) 

transportation. We considered each 

industry or category individually. 

Additionally, we considered whether 

the activities have any Federal 

involvement. Critical habitat 

designation generally will not affect 

activities that do not have any Federal 

involvement; under the Act, designation 

of critical habitat only affects activities 

conducted, funded, permitted, or 

authorized by Federal agencies. If we 

list any of the species, as proposed in 

this document, in areas where the 

Central Texas mussels are present, 

under section 7 of the Act, Federal 

agencies would be required to consult 

with the Service on activities they fund, 

permit, or implement that may affect the 

species. If we finalize this proposed 

critical habitat designation, 

consultations to avoid the destruction or 

adverse modification of critical habitat 

would be incorporated into the existing 

consultation process. 

In our IEM, we attempted to clarify 

the distinction between the effects that 

would result from the species being 

listed and those attributable to the 

critical habitat designations (i.e., 

difference between the jeopardy and 

adverse modification standards) for the 

Central Texas mussels. Because the 

designation of critical habitat is being 

proposed concurrently with the listing, 

it has been our experience that it is 

more difficult to discern which 

conservation efforts are attributable to 

the species being listed and those which 

would result solely from the designation 

of critical habitat. However, the 

following specific circumstances in this 

case help to inform our evaluation: (1) 

The essential physical or biological 

features identified for critical habitat are 

the same features essential for the life 

requisites of the species, and (2) any 

actions that would result in sufficient 

harm or harassment to constitute 

jeopardy to the Central Texas mussels 

would also likely adversely affect the 

essential physical or biological features 

of critical habitat. The IEM outlines our 

rationale concerning this limited 

distinction between baseline 

conservation efforts and incremental 

impacts of the designations of critical 

habitat for these species. This 

evaluation of the incremental effects has 

been used as the basis to evaluate the 

probable incremental economic impacts 

of these proposed designations of 

critical habitat. 

The proposed critical habitat 

designations for the Central Texas 

mussels totals approximately 1,944 river 

mi (3,129 river km) in 27 units with a 

combination of occupied and 

unoccupied areas. In occupied areas, 

any actions that may affect the species 

or their habitat would likely also affect 

proposed critical habitat, and it is 

unlikely that any additional 

conservation efforts would be required 

to address the adverse modification 

standard over and above those 

recommended as necessary to avoid 

jeopardizing the continued existence of 

the species. Therefore, the only 

additional costs that are expected in the 

occupied proposed critical habitat 

designations are administrative costs, 

due to the fact that this additional 

analysis will require time and resources 

by both the Federal action agency and 

the Service. However, it is believed that, 

in most circumstances, these costs 

would not reach the threshold of 

‘‘significant’’ under E.O. 12866. We 

anticipate incremental costs of section 7 

consultations in occupied critical 

habitat to total less than $75,000 per 

year. 

In unoccupied critical habitat, any 

costs of section 7 consultations would 

not be incurred due to the listing of the 

species. We are proposing to designate 

six subunits that are currently 

unoccupied by the Central Texas 

mussels. We anticipate approximately 

five new formal section 7 consultations 

to occur in the next 10 years in these 

subunits. Considering the costs of 

formal consultation as well as project 

modifications that arise from 

consultation, we project consultations 

in unoccupied critical habitat to cost 

approximately $15,000 per consultation. 

In total, in both occupied and 

unoccupied critical habitat, we expect 

the total cost of critical habitat 

designations not to exceed $82,500 per 

year. 

We are soliciting data and comments 

from the public on the DEA discussed 

above, as well as on all aspects of this 

proposed rule and our required 

determinations. During the development 

of a final designation, we will consider 

the information presented in the DEA 

and any additional information on 

economic impacts received during the 

public comment period to determine 

whether any specific areas should be 

excluded from the final critical habitat 

designation under authority of section 

4(b)(2) and our implementing 

regulations at 50 CFR 17.90. If we 

receive credible information regarding 

the existence of a meaningful economic 

or other relevant impact supporting a 

benefit of exclusion, we will conduct an 

exclusion analysis for the relevant area 

or areas. We may also exercise the 

discretion to evaluate any other 

particular areas for possible exclusion. 

Furthermore, when we conduct an 

exclusion analysis based on impacts 

identified by experts in, or sources with 

firsthand knowledge about, impacts that 

are outside the scope of the Service’s 

expertise, we will give weight to those 

impacts consistent with the expert or 

firsthand information unless we have 

rebutting information. We may exclude 

an area from critical habitat if we 

determine that the benefits of excluding 

the area outweigh the benefits of 

including the area, provided the 

exclusion will not result in the 

extinction of this species. 

Exclusions 

Exclusions Based on Economic Impacts 

The first sentence of section 4(b)(2) of 

the Act requires the Service to consider 

the economic impacts (as well as the 

impacts on national security and any 

other relevant impacts) of designating 

critical habitat. In addition, economic 

impacts may, for some particular areas, 

play an important role in the 

discretionary section 4(b)(2) exclusion 

analysis under the second sentence of 

section 4(b)(2). In both contexts, the 

Service will consider the probable 

incremental economic impacts of the 

designation. When the Service 

undertakes a discretionary section 

4(b)(2) exclusion analysis with respect 

to a particular area, we will weigh the 

economic benefits of exclusion (and any 


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other benefits of exclusion) against any 

benefits of inclusion (primarily the 

conservation value of designating the 

area). The conservation value may be 

influenced by the level of effort needed 

to manage degraded habitat to the point 

where it could support the listed 

species. 

The Service will use its discretion in 

determining how to weigh probable 

incremental economic impacts against 

conservation value. The nature of the 

probable incremental economic impacts 

and not necessarily a particular 

threshold level triggers considerations 

of exclusions based on probable 

incremental economic impacts. For 

example, if an economic analysis 

indicates high probable incremental 

impacts of designating a particular 

critical habitat unit of low conservation 

value (relative to the remainder of the 

designation), the Service may consider 

exclusion of that particular unit. 

Exclusions Based on National Security 

Impacts or Homeland Security Impacts 

Under section 4(b)(2) of the Act, we 

consider whether there are lands where 

a national security impact might exist. 

In preparing this proposal, we have 

determined that there are no lands 

within the proposed designations of 

critical habitat for the Central Texas 

mussels owned or managed by the 

Department of Defense or Department of 

Homeland Security. We anticipate no 

impact on national security because 

there are no lands owned or managed by 

the Department of Defense within this 

proposal, and we have not identified 

any national security or homeland 

security activities that would be affected 

by the proposed designations. However, 

if through the public comment period 

we receive credible information 

regarding impacts on national security 

or homeland security from designating 

particular areas as critical habitat, then 

as part of developing the final 

designation of critical habitat, we will 

conduct a discretionary exclusion 

analysis to determine whether to 

exclude those areas under authority of 

section 4(b)(2) and our implementing 

regulations at 50 CFR 17.90. 

Exclusions Based on Other Relevant 

Impacts 

Under section 4(b)(2) of the Act, we 

consider any other relevant impacts, in 

addition to economic impacts and 

impacts on national security. We 

consider a number of factors including 

whether there are permitted 

conservation plans covering the species 

in the area such as HCPs, safe harbor 

agreements, or candidate conservation 

agreements with assurances (CCAAs), or 

whether there are non-permitted 

conservation agreements and 

partnerships that would be encouraged 

by designation of, or exclusion from, 

critical habitat. In addition, we look 

whether there are Tribal conservation 

plans or parnerships, Tribal resources, 

or government-to-government 

relationships of the United States with 

Tribal entities that may be affected by 

the designation. We also consider any 

State, local, public health, community 

interest, environmental, or social 

impacts that might occur because of the 

designations. 

In preparing this proposal, we have 

determined that there are currently no 

HCPs or other management plans for the 

Central Texas mussels, and the 

proposed designations do not include 

any tribal lands or trust resources. We 

anticipate no impact on tribal lands, 

partnerships, or HCPs from these 

proposed critical habitat designations. 

We are aware of efforts currently under 

way by the River Authorities to develop 

CCAAs for the Central Texas mussels, as 

discussed above, and will take those 

efforts into account in a final 

designation. During the development of 

a final designation, we will consider any 

additional information received through 

the public comment period regarding 

other relevant impacts to determine 

whether any specific areas should be 

excluded from the final critical habitat 

designation under authority of section 

4(b)(2) and our implementing 

regulations at 50 CFR 17.90. 

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. 

Regulatory Planning and Review 

(Executive Orders 12866 and 13563) 

Executive Order 12866 provides that 

the Office of Information and Regulatory 

Affairs (OIRA) in the Office of 

Management and Budget will review all 

significant rules. OIRA has determined 

that this rule is not significant. 

Executive Order 13563 reaffirms the 

principles of E.O. 12866 while calling 

for improvements in the Nation’s 

regulatory system to promote 

predictability, to reduce uncertainty, 

and to use the best, most innovative, 

and least burdensome tools for 

achieving regulatory ends. The 

Executive order directs agencies to 

consider regulatory approaches that 

reduce burdens and maintain flexibility 

and freedom of choice for the public 

where these approaches are relevant, 

feasible, and consistent with regulatory 

objectives. E.O. 13563 emphasizes 

further that regulations must be based 

on the best available science and that 

the rulemaking process must allow for 

public participation and an open 

exchange of ideas. We have developed 

this rule in a manner consistent with 

these requirements. 

Regulatory Flexibility Act (5 U.S.C. 601 

et seq.) 

Under the Regulatory Flexibility Act 

(RFA; 5 U.S.C. 601 et seq.), as amended 

by the Small Business Regulatory 

Enforcement Fairness Act of 1996 

(SBREFA; 5 U.S.C. 801 et seq.), 

whenever an agency is required to 

publish a notice of rulemaking for any 

proposed or final rule, it must prepare 

and make available for public comment 

a regulatory flexibility analysis that 

describes the effects of the rule on small 

entities (i.e., small businesses, small 

organizations, and small government 

jurisdictions). However, no regulatory 

flexibility analysis is required if the 

head of the agency certifies the rule will 

not have a significant economic impact 

on a substantial number of small 

entities. The SBREFA amended the RFA 

to require Federal agencies to provide a 

certification statement of the factual 

basis for certifying that the rule will not 

have a significant economic impact on 

a substantial number of small entities. 

According to the Small Business 

Administration, small entities include 

small organizations such as 

independent nonprofit organizations; 

small governmental jurisdictions, 

including school boards and city and 

town governments that serve fewer than 

50,000 residents; and small businesses 

(13 CFR 121.201). Small businesses 

include manufacturing and mining 

concerns with fewer than 500 


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employees, wholesale trade entities 

with fewer than 100 employees, retail 

and service businesses with less than $5 

million in annual sales, general and 

heavy construction businesses with less 

than $27.5 million in annual business, 

special trade contractors doing less than 

$11.5 million in annual business, and 

agricultural businesses with annual 

sales less than $750,000. To determine 

if potential economic impacts to these 

small entities are significant, we 

considered the types of activities that 

might trigger regulatory impacts under 

this designation as well as types of 

project modifications that may result. In 

general, the term ‘‘significant economic 

impact’’ is meant to apply to a typical 

small business firm’s business 

operations. 

Under the RFA, as amended, and as 

understood in the light of recent court 

decisions, Federal agencies are required 

to evaluate the potential incremental 

impacts of rulemaking only on those 

entities directly regulated by the 

rulemaking itself and, therefore, are not 

required to evaluate the potential 

impacts to indirectly regulated entities. 

The regulatory mechanism through 

which critical habitat protections are 

realized is section 7 of the Act, which 

requires Federal agencies, in 

consultation with the Service, to ensure 

that any action authorized, funded, or 

carried out by the agency is not likely 

to destroy or adversely modify critical 

habitat. Therefore, under section 7, only 

Federal action agencies are directly 

subject to the specific regulatory 

requirement (avoiding destruction and 

adverse modification) imposed by 

critical habitat designation. 

Consequently, it is our position that 

only Federal action agencies would be 

directly regulated if we adopt the 

proposed critical habitat designations. 

There is no requirement under the RFA 

to evaluate the potential impacts to 

entities not directly regulated. 

Moreover, Federal agencies are not 

small entities. Therefore, because no 

small entities would be directly 

regulated by this rulemaking, the 

Service certifies that, if promulgated, 

the proposed critical habitat 

designations will not have a significant 

economic impact on a substantial 

number of small entities. 

In summary, we have considered 

whether the proposed designations 

would result in a significant economic 

impact on a substantial number of small 

entities. For the above reasons and 

based on currently available 

information, we certify that, if made 

final, the proposed critical habitat 

designations will not have a significant 

economic impact on a substantial 

number of small business entities. 

Therefore, an initial regulatory 

flexibility analysis is not required. 

Energy Supply, Distribution, or Use— 

Executive Order 13211 

Executive Order 13211 (Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use) requires agencies 

to prepare Statements of Energy Effects 

when undertaking certain actions. In 

our economic analysis, we did not find 

that the designations of this proposed 

critical habitat will significantly affect 

energy supplies, distribution, or use. 

Therefore, this action is not a significant 

energy action, and no Statement of 

Energy Effects is required. 

Unfunded Mandates Reform Act (2 

U.S.C. 1501 et seq.) 

In accordance with the Unfunded 

Mandates Reform Act (2 U.S.C. 1501 et 

seq.), we make the following findings: 

(1) This proposed rule would not 

produce a Federal mandate. In general, 

a Federal mandate is a provision in 

legislation, statute, or regulation that 

would impose an enforceable duty upon 

State, local, or tribal governments, or the 

private sector, and includes both 

‘‘Federal intergovernmental mandates’’ 

and ‘‘Federal private sector mandates.’’ 

These terms are defined in 2 U.S.C. 

658(5)–(7). ‘‘Federal intergovernmental 

mandate’’ includes a regulation that 

‘‘would impose an enforceable duty 

upon State, local, or tribal governments’’ 

with two exceptions. It excludes ‘‘a 

condition of Federal assistance.’’ It also 

excludes ‘‘a duty arising from 

participation in a voluntary Federal 

program,’’ unless the regulation ‘‘relates 

to a then-existing Federal program 

under which $500,000,000 or more is 

provided annually to State, local, and 

tribal governments under entitlement 

authority,’’ if the provision would 

‘‘increase the stringency of conditions of 

assistance’’ or ‘‘place caps upon, or 

otherwise decrease, the Federal 

Government’s responsibility to provide 

funding,’’ and the State, local, or tribal 

governments ‘‘lack authority’’ to adjust 

accordingly. At the time of enactment, 

these entitlement programs were: 

Medicaid; Aid to Families with 

Dependent Children work programs; 

Child Nutrition; Food Stamps; Social 

Services Block Grants; Vocational 

Rehabilitation State Grants; Foster Care, 

Adoption Assistance, and Independent 

Living; Family Support Welfare 

Services; and Child Support 

Enforcement. ‘‘Federal private sector 

mandate’’ includes a regulation that 

‘‘would impose an enforceable duty 

upon the private sector, except (i) a 

condition of Federal assistance or (ii) a 

duty arising from participation in a 

voluntary Federal program.’’ 

The designations of critical habitat do 

not impose a legally binding duty on 

non-Federal Government entities or 

private parties. Under the Act, the only 

regulatory effect is that Federal agencies 

must ensure that their actions do not 

destroy or adversely modify critical 

habitat under section 7. While nonFederal entities that receive Federal 

funding, assistance, or permits, or that 

otherwise require approval or 

authorization from a Federal agency for 

an action, may be indirectly impacted 

by the designation of critical habitat, the 

legally binding duty to avoid 

destruction or adverse modification of 

critical habitat rests squarely on the 

Federal agency. Furthermore, to the 

extent that non-Federal entities are 

indirectly impacted because they 

receive Federal assistance or participate 

in a voluntary Federal aid program, the 

Unfunded Mandates Reform Act would 

not apply, nor would critical habitat 

shift the costs of the large entitlement 

programs listed above onto State 

governments. 

(2) We do not believe that this 

proposed rule would significantly or 

uniquely affect small governments 

because the lands being proposed for 

critical habitat designation are owned 

by the State of Texas. This government 

entity does not fit the definition of 

‘‘small governmental jurisdiction.’’ 

Therefore, a Small Government Agency 

Plan is not required. 

Takings—Executive Order 12630 

In accordance with E.O. 12630 

(Government Actions and Interference 

with Constitutionally Protected Private 

Property Rights), we have analyzed the 

potential takings implications of 

designating critical habitat for the 

Central Texas mussels in a takings 

implications assessment. The Act does 

not authorize the Service to regulate 

private actions on private lands or 

confiscate private property as a result of 

critical habitat designation. Designation 

of critical habitat does not affect land 

ownership, or establish any closures or 

restrictions on use of or access to the 

designated areas. Furthermore, the 

designation of critical habitat does not 

affect landowner actions that do not 

require Federal funding or permits, nor 

does it preclude development of habitat 

conservation programs or issuance of 

incidental take permits to permit actions 

that do require Federal funding or 

permits to go forward. However, Federal 

agencies are prohibited from carrying 

out, funding, or authorizing actions that 

would destroy or adversely modify 


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critical habitat. A takings implications 

assessment has been completed and 

concludes that, if adopted, these 

designations of critical habitat for the 

Central Texas mussels does not pose 

significant takings implications for 

lands within or affected by the 

designations. 

Federalism—Executive Order 13132 

In accordance with E.O. 13132 

(Federalism), this proposed rule does 

not have significant federalism effects. 

A federalism summary impact statement 

is not required. In keeping with 

Department of the Interior and 

Department of Commerce policy, we 

requested information from, and 

coordinated development of these 

proposed critical habitat designations 

with, appropriate State resource 

agencies in Texas. From a federalism 

perspective, the designation of critical 

habitat directly affects only the 

responsibilities of Federal agencies. The 

Act imposes no other duties with 

respect to critical habitat, either for 

States and local governments, or for 

anyone else. As a result, the proposed 

rule does not have substantial direct 

effects either on the States, or on the 

relationship between the National 

Government and the States, or on the 

distribution of powers and 

responsibilities among the various 

levels of government. The proposed 

designations may have some benefit to 

these governments because the areas 

that contain the features essential to the 

conservation of the species are more 

clearly defined, and the physical or 

biological features of the habitat 

necessary to the conservation of the 

species are specifically identified. This 

information does not alter where and 

what federally sponsored activities may 

occur. However, it may assist these local 

governments in long-range planning 

(because these local governments no 

longer have to wait for case-by-case 

section 7 consultations to occur). 

Where State and local governments 

require approval or authorization from a 

Federal agency for actions that may 

affect critical habitat, consultation 

under section 7(a)(2) would be required. 

While non-Federal entities that receive 

Federal funding, assistance, or permits, 

or that otherwise require approval or 

authorization from a Federal agency for 

an action, may be indirectly impacted 

by the designation of critical habitat, the 

legally binding duty to avoid 

destruction or adverse modification of 

critical habitat rests squarely on the 

Federal agency. 

Civil Justice Reform—Executive Order 

12988 

In accordance with Executive Order 

12988 (Civil Justice Reform), the Office 

of the Solicitor has determined that the 

rule does not unduly burden the judicial 

system and that it meets the 

requirements of sections 3(a) and 3(b)(2) 

of the Order. We have proposed 

designating critical habitat in 

accordance with the provisions of the 

Act. To assist the public in 

understanding the habitat needs of the 

species, this proposed rule identifies the 

elements of physical or biological 

features essential to the conservation of 

the species. The proposed areas of 

designated critical habitat are presented 

on maps, and the proposed rule 

provides several options for the 

interested public to obtain more 

detailed location information, if desired. 

Paperwork Reduction Act of 1995 (44 

U.S.C. 3501 et seq.) 

This rule does not contain 

information collection requirements, 

and a submission to the Office of 

Management and Budget (OMB) under 

the Paperwork Reduction Act of 1995 

(44 U.S.C. 3501 et seq.) is not required. 

We may not conduct or sponsor and you 

are not required to respond to a 

collection of information unless it 

displays a currently valid OMB control 

number. 

National Environmental Policy Act (42 

U.S.C. 4321 et seq.) 

It is our position that, outside the 

jurisdiction of the U.S. Court of Appeals 

for the Tenth Circuit, we do not need to 

prepare environmental analyses 

pursuant to the National Environmental 

Policy Act (NEPA; 42 U.S.C. 4321 et 

seq.) in connection with designating 

critical habitat under the Act. We 

published a notice outlining our reasons 

for this determination in the Federal 

Register on October 25, 1983 (48 FR 

49244). This position was upheld by the 

U.S. Court of Appeals for the Ninth 

Circuit (Douglas County v. Babbitt, 48 

F.3d 1495 (9th Cir. 1995), cert. denied 

516 U.S. 1042 (1996)). 

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 

recognized Federal 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. 

We have determined that no tribal lands 

fall within the boundaries of the 

proposed critical habitat designations 

for the Central Texas mussels, so no 

tribal lands would be affected by the 

proposed designations. 

References Cited 

A complete list of references cited in 

this rulemaking is available on the 

internet at http://www.regulations.gov 

and upon request from the Austin 

Ecological Services Field Office (see FOR

FURTHER INFORMATION CONTACT). 

Authors 

The primary authors of this proposed 

rule are the staff members of the U.S. 

Fish and Wildlife Service’s Species 

Assessment Team and the Austin 

Ecological Services Field Office. 

List of Subjects in 50 CFR Part 17 

Endangered and threatened species, 

Exports, Imports, Reporting and 

recordkeeping requirements, 

Transportation. 

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. 

■ 2. Amend § 17.11(h) by adding entries 

for ‘‘Fatmucket, Guadalupe’’; 

‘‘Fatmucket, Texas’’; ‘‘Fawnsfoot, 

Texas’’; ‘‘Orb, Guadalupe’’; 

‘‘Pimpleback, Texas’’; and ‘‘Spike, false’’ 

to the List of Endangered and 

Threatened Wildlife in alphabetical 

order under Clams to read as follows: 

§ 17.11 Endangered and threatened 

wildlife. 

* * * * * 

(h) * * * 


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Common name Scientific name Where listed Status Listing citations and applicable rules 

*******

CLAMS

* * * * * * * 

Fatmucket, Guadalupe ... Lampsilis bergmanni ..... Wherever found ............ E [Federal Register citation when published as a 

final rule]; 50 CFR 17.95(f)CH. 

Fatmucket, Texas ........... Lampsilis bracteata ....... Wherever found ............ E [Federal Register citation when published as a 

final rule]; 50 CFR 17.95(f)CH. 

Fawnsfoot, Texas ........... Truncilla macrodon ....... Wherever found ............ T [Federal Register citation when published as a 

final rule]; 50 CFR 17.45(c)4d; 50 CFR 

17.95(f)CH. 

* * * * * * * 

Orb, Guadalupe .............. Cyclonaias necki ........... Wherever found ............ E [Federal Register citation when published as a 

final rule]; 50 CFR 17.95(f)CH. 

* * * * * * * 

Pimpleback, Texas ......... Cyclonaias petrina ........ Wherever found ............ E [Federal Register citation when published as a 

final rule]; 50 CFR 17.95(f)CH. 

* * * * * * * 

Spike, false ..................... Fusconaia mitchelli ....... Wherever found ............ E [Federal Register citation when published as a 

final rule]; 50 CFR 17.95(f)CH. 

* * * * * * * 

■ 3. As proposed to be added at 83 FR 

51570 (Oct. 11, 2018), and amended at 

85 FR 44821 (July 24, 2020) and 85 FR 

61384 (Sept. 29, 2020), § 17.45 is further 

amended by adding paragraph (c) to 

read as follows: 

§ 17.45 Special rules—snails and clams. 

* * * * * 

(c) Texas fawnsfoot (Truncilla 

macrodon)—(1) Prohibitions. The 

following prohibitions that apply to 

endangered wildlife also apply to the 

Texas fawnsfoot. Except as provided at 

paragraph (c)(2) of this section and 

§§ 17.4 and 17.5, it is unlawful for any 

person subject to the jurisdiction of the 

United States to commit, to attempt to 

commit, to solicit another to commit, or 

cause to be committed, any of the 

following acts in regard to the Texas 

fawnsfoot: 

(i) Import or export, as set forth at 

§ 17.21(b). 

(ii) Take, as set forth at § 17.21(c)(1). 

(iii) Possession and other acts with 

unlawfully taken specimens, as set forth 

at § 17.21(d)(1). 

(iv) Interstate or foreign commerce in 

the course of commercial activity, as set 

forth at § 17.21(e). 

(v) Sale or offer for sale, as set forth 

at § 17.21(f). 

(2) Exceptions from the prohibitions. 

With regard to this species, you may: 

(i) Conduct activities as authorized by 

a permit under § 17.32. 

(ii) Take, as set forth at § 17.21(c)(2) 

through (4) for endangered wildlife. 

(iii) Take, as set forth at § 17.31(b). 

(iv) Possess and engage in other acts 

with unlawfully taken Texas fawnsfoot, 

as set forth at § 17.21(d)(2). 

(v) Take incidental to an otherwise 

lawful activity caused by: 

(A) Channel restoration projects that 

create natural, physically stable, 

ecologically functioning streams (or 

stream and wetland systems) that are 

reconnected with their groundwater 

aquifers. 

(B) Bioengineering methods such as 

streambank stabilization using live 

stakes (live, vegetative cuttings inserted 

or tamped into the ground in a manner 

that allows the stake to take root and 

grow), live fascines (live branch 

cuttings, usually willows, bound 

together into long, cigar-shaped 

bundles), or brush layering (cuttings or 

branches of easily rooted tree species 

layered between successive lifts of soil 

fill). These methods would not include 

the sole use of quarried rock (rip-rap) or 

the use of rock baskets or gabion 

structures. In addition, to reduce 

streambank erosion and sedimentation 

into the stream, work using these 

bioengineering methods would be 

performed at base-flow or low-water 

conditions and when significant rainfall 

is not predicted. Further, streambank 

stabilization projects must keep all 

equipment out of the stream channels 

and water. 

(C) Soil and water conservation 

practices and riparian and adjacent 

upland habitat management activities 

that restore in-stream habitats for the 

species, restore adjacent riparian 

habitats that enhance stream habitats for 

the species, stabilize degraded and 

eroding stream banks to limit 

sedimentation and scour of the species’ 

habitats, and restore or enhance nearby 

upland habitats to limit sedimentation 

of the species’ habitats and comply with 

conservation practice standards and 

specifications, and technical guidelines 

developed by the Natural Resources 

Conservation Service. 

(D) Presence or abundance surveys for 

Texas fawnfoot conducted by 

individuals who successfully complete 

and show proficiency by passing the 

end-of-course test with a score equal to 

or greater than 90 percent, with 100 

percent accuracy in identification of 

mussel species listed under the 

Endangered Species Act, in an approved 

freshwater mussel identification and 

sampling course (specific to the species 

and basins in which the Texas 

fawnsfoot is known to occur), such as 

that administered by the Service, a State 

wildlife agency, or qualified university 

experts. Those individuals exercising 

the exemption in this paragraph 

(c)(2)(v)(D) should provide reports to the 

Service annually on number, location, 

and date of collection. The exemption in 

this paragraph (c)(2)(v)(D) does not 

apply if lethal take or collection is 

anticipated. The exemption in this 

paragraph (c)(2)(v)(D) only applies for 5 

years from the date of successful course 

completion. 

* * * * * 

■ 4. Amend § 17.95(f) by: 

■ a. Adding critical habitat entries for 

‘‘Guadalupe Fatmucket (Lampsilis 


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bergmanni)’’, ‘‘Texas Fatmucket 

(Lampsilis bracteata)’’, and ‘‘Texas 

Fawnsfoot (Truncilla macrodon)’’ 

immediately following the entry for 

‘‘Appalachian Elktoe (Alasmidonta 

raveneliana)’’; 

■ b. Adding an entry for ‘‘Guadalupe 

Orb (Cyclonaias necki)’’ immediately 

following the entry for ‘‘Carolina 

Heelsplitter (Lasmigona decorata)’’; and 

■ c. Adding entries for ‘‘Texas 

Pimpleback (Cyclonaias petrina)’’ and 

‘‘False Spike (Fusconaia mitchelli)’’ 

immediately following the entry for 

‘‘Georgia Pigtoe (Pleurobema 

hanleyianum)’’. 

The additions read as follows: 

§ 17.95 Critical habitat—fish and wildlife. 

* * * * * 

(f) * * * 

Guadalupe Fatmucket (Lampsilis 

bergmanni) 

(1) A critical habitat unit is depicted 

for Kendall and Kerr Counties, Texas, 

on the map in this critical habitat entry. 

(2) Within this area, the physical or 

biological features essential to the 

conservation of Guadalupe fatmucket 

consist of the following components 

within waters and streambeds up to the 

ordinary high-water mark: 

(i) Flowing water at moderate to high 

rates with sufficient depth to remain 

sufficiently cool and oxygenated during 

low-flow periods; 

(ii) Substrate including bedrock and 

boulder crevices, point bars, and 

vegetated run habitat comprising sand, 

gravel, and larger cobbles; 

(iii) Green sunfish (Lepomis 

cyanellus), bluegill (L. macrochirus), 

largemouth bass (Micropterus 

salmoides), and Guadalupe bass (M. 

treculii) present; and 

(iv) Water quality parameters within 

the following ranges: 

(A) Dissolved oxygen >2 mg/L; 

(B) Salinity <2 ppt; 

(C) Total ammonia <0.77 mg/L total 

ammonia nitrogen; 

(D) Water temperature <29 °C (84.2 

°F); and 

(E) Low levels of contaminants. 

(3) Critical habitat does not include 

manmade structures (such as buildings, 

aqueducts, runways, roads, and other 

paved areas) and the land on which they 

are located existing within the legal 

boundaries on [EFFECTIVE DATE OF 

THE FINAL RULE]. 

(4) The maps in this entry, as 

modified by any accompanying 

regulatory text, establish the boundaries 

of the critical habitat designation. The 

coordinates or plot points or both on 

which each map is based are available 

to the public at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

(5) Index map of critical habitat for 

the Central Texas mussels, which 

includes the Guadalupe fatmucket, 

follows: 

BILLING CODE 4333–15–P 


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jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.031</GPH>

Central Texas Mussels Critical Habitat 

All S cies Overview 

Q 

Mi 0 

I 

r--i 

KmO 25 

25 

! ., 

.... L--,....,_J_~-

.'t \ I ) '. 

___ __,..---

- Critical Habitat - Occupied - - - - Rivers 

~Critical Habitat- Unoccupied 8_88B: Lakes 

,--7 County Boundaries El Cities 

= Interstates 

(6) Map of Unit GUFM-1: Guadalupe River follows: 
47980 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

Texas Fatmucket (Lampsilis bracteata) 

(1) Critical habitat units are depicted 

for Blanco, Gillespie, Hays, Kimble, 

Llano, Mason, McCulloch, Menard, 

Runnels, San Saba, and Travis Counties, 

Texas, on the maps in this critical 

habitat entry. 

(2) Within these areas, the physical or 

biological features essential to the 

conservation of Texas fatmucket consist 

of the following components within 

waters and streambeds up to the 

ordinary high-water mark: 

(i) Flowing water at moderate to high 

rates with sufficient depth to remain 

sufficiently cool and oxygenated during 

low-flow periods; 

(ii) Substrate including bedrock and 

boulder crevices, point bars, and 

vegetated run habitat comprising sand, 

gravel, and larger cobbles; 

(iii) Green sunfish (Lepomis 

cyanellus), bluegill (L. macrochirus), 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.032</GPH>

~ Johnson Cr: ... -....... _,. ... 

, ' 

' 

Critical Habitat for Guadalupe Fatmucket 

Unit 1 • Guadalupe River 

Gillespie 

',, ~ 

El 

IFredericksburgj 

~, GUFM-1b:-Johns·orf'Cre·ek I 

' -~-~~-~~ar:~~~;,.,,i-...,,,_ ................ ' 'I ,,, ,' ~=;:------' 

Kendall 

GUFM-:t·a: ' North Fork 

, -~~Guadalupe River - - ' , I 'J • ,n8 ~ -~ ~lur S Fl< 01.10 

' ' , I 

....... -,.,,~, ....... ,'-...... ,J- .... ,, 1_._ ', 

1'xa~ 

Bandera 

' ' 

e 

Mi 0 

I 

r7 

KmO 4 

4 

I 

, 

' ) 

' 

' ' I 

Guadalupe 

-' I' 

, ... .., ....... 

/,/ 

/ 

Medina/t/ ,. 

./ 

,,... ... 1'\,.,_ 

\J ,,, 

Bexar 

- Critical Habitat - Occupied - '- - - Rivers 

County Boundaries ~ Lakes 

= Interstates El Cities 

I Subunit Divider 

TEXAS FATMUCKET (LAMPS/US BRACTEATA) 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47981 

largemouth bass (Micropterus 

salmoides), and Guadalupe bass (M. 

treculii) present; and 

(iv) Water quality parameters within 

the following ranges: 

(A) Dissolved oxygen >2 mg/L; 

(B) Salinity <2 ppt; 

(C) Total ammonia <0.77 mg/L total 

ammonia nitrogen; 

(D) Water temperature <29 °C (84.2 

°F); and 

(E) Low levels of contaminants. 

(3) Critical habitat does not include 

manmade structures (such as buildings, 

aqueducts, runways, roads, and other 

paved areas) and the land on which they 

are located existing within the legal 

boundaries on [EFFECTIVE DATE OF 

THE FINAL RULE]. 

(4) The maps in this entry, as 

modified by any accompanying 

regulatory text, establish the boundaries 

of the critical habitat designation. The 

coordinates or plot points or both on 

which each map is based are available 

to the public at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

(5) Note: An index map of the critical 

habitat designations for the Central 

Texas mussels, which includes the 

Texas fatmucket, can be found in this 

paragraph (f) at the entry for the 

Guadalupe fatmucket. An index map of 

critical habitat units for the Texas 

fatmucket follows: 


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Critical Habitat for Texas Fatmucket - Unit Overview 

Mi O 10 

L__J 

f"7 

KmO 10 

- Critical Habitat - Occupied = Interstates 

-====- Critical Habitat - Unoccupied - - - - Rivers 

County Boundaries ~ lakes 

Subunit Divider 3 Cities 
47982 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(6) Map of TXFM–1: Elm Creek 

follows: 


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Critical Habitat for Texas Fatmucket 

Unit 1 • Elm Creek 

I 

I 

:t.; 

: It:: 

!Winters I ; S 

E] I 

, 

I 

I 

' 

, 

I 

TXFM-1a: 

Bluff Creek TXFM-1 c: Upper Elm Creek 

I 

Runnels 

TXFM-1 b: Lower Elm Creek 

!Paint Rock I 

G 

e 

Mi O 3 

I 

r7 

KmO 3 

COletuan 

Concho 

- Critical Habitat - Occupied - - - - Rivers 

-=::aCritical Habitat- Unoccupied G Cities 

CJ County Boundaries 

I Subunit Divider 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47983 

(7) Map of Unit TXFM–2: San Saba 

River, Unit TXFM–3: Cherokee Creek, 

Unit TXFM–4: Llano River, and Unit 

TXFM–5: Pedernales River, follows: 


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Critical Habitat for Texas Fatmucket 

Units: 2-San Saba River, 3-Cherokee Creek, 4-Llano River, 5-Pedemales River 

Paint Rock 

El 

C-0ucb.o 

TXfM;;2: 

Real 

McCulloch 

(.,. ...... J"' .... _ .. t ...... 

' 

Mi O 10 

I 

ii 

KmO 10 

- Criticaf Habitat~ Occupied - - - - Rivers 

c:::J County Boundaries El Cities 

I Subunit Divider 
47984 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(8) Map of Unit TXFM–6: Onion 

Creek follows: 

Texas Fawnsfoot (Truncilla macrodon) 

(1) Critical habitat units are depicted 

for Anderson, Austin, Brazos, Burleson, 

Colorado, Falls, Fort Bend, Freestone, 

Grimes, Henderson, Houston, Kaufman, 

Lampasas, Leon, Madison, Matagorda, 

McLennan, Milam, Mills, Navarro, Palo 

Pinto, Parker, Robertson, San Saba, 

Shackelford, Stephens, Throckmorton, 

Waller, Washington, and Wharton 

Counties, Texas, on the maps in this 

critical habitat entry. 

(2) Within these areas, the physical or 

biological features essential to the 

conservation of Texas fawnsfoot consist 

of the following components within 

waters and streambeds up to the 

ordinary high-water mark: 

(i) Flowing water at rates suitable to 

prevent excess sedimentation but not so 

high as to dislodge individuals or 

sediment; 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.036</GPH>

Critical Habitat for Texas Fatmucket 

Unit 6 - Onion Creek 

e 

Mi 0 

I 

II 

KmO 2.5 

2.5 

Bastrop 

Caldwell 

- Critical Habitat - Occupied = Interstates 

-==- Critical Habitat - Unoccupied - - - - Rivers 

D County Boundaries ffi: Lakes 

I Subunit Divider 0 Cities 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47985 

(ii) Stable bank and riffle habitats 

with gravel, sand, silt, and mud 

substrates that are clean swept by 

flushing flows; 

(iii) Freshwater drum (Aplodinotus 

grunniens) present; and 

(iv) Water quality parameters within 

the following ranges: 

(A) Dissolved oxygen >2 mg/L; 

(B) Salinity <2 ppt; 

(C) Total ammonia <0.77 mg/L total 

ammonia nitrogen; 

(D) Water temperature <29 °C (84.2 

°F); and 

(E) Low levels of contaminants. 

(3) Critical habitat does not include 

manmade structures (such as buildings, 

aqueducts, runways, roads, and other 

paved areas) and the land on which they 

are located existing within the legal 

boundaries on [EFFECTIVE DATE OF 

THE FINAL RULE]. 

(4) The maps in this entry, as 

modified by any accompanying 

regulatory text, establish the boundaries 

of the critical habitat designation. The 

coordinates or plot points or both on 

which each map is based are available 

to the public at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

(5) Note: An index map of the critical 

habitat designations for the Central 

Texas mussels, which includes the 

Texas fawnsfoot, can be found in this 

paragraph (f) at the entry for the 

Guadalupe fatmucket. An index map of 

critical habitat units for the Texas 

fawnsfoot follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3
47986 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.037</GPH>

, ... ,_ __ ----i-··-~· --~ 

! 

Critical Habitat for Texas Fa'Mlsfoot - Unit Overview 

Mi O 25 

I 

r7 

KmO 25 

- Critical Habitat• Occupied.. Rivers 

c:::::::11 Critical Habitat - Unoccupred 2.8&s: lakes 

County Boundaries El Cities 

= Interstates 

Subunit Divider 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47987 

(6) Map of Unit TXFF–1: Clear Fork 

Brazos River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.038</GPH>

Haskell 

~ 

I ' 

I 

Jones ', 

' 

I ' 

I 

Taylor 

~~ 

' 

,,.._,,,. .... I 

Critical Habitat for Texas Fawnsfoot 

Unit 1 - Clear Fork Brazos River 

TI1foda:norton 

TXFF-1 a: Upper Clear Fork Young 

Brazos River 

TXFF-1 b: Lower Clear Fork 

Brazo~ River 

Shackelford !Breckenridge I 

Callahan 

e 

Mi O 5 

II 

KmO 5 

Stephens 

- Critical Habitat - Occupied = Interstates 

c:::::::11 Critical Habitat- Unoccupied - - - - Rivers 

I , County Boundaries El Cities 

I Subunit Divider 
47988 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(7) Map of Unit TXFF–2: Upper 

Brazos River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.039</GPH>

Young 

,.;.,. 

I c1.,.,.._ J I 

, ,, 

,~ ': ...... ,_/)- i'~ 

'✓ 'J5 Possum > 

KingdomL 

,.,,,, ~_.,.. ..,_.,.., I 

- ~ ' ~ ,,. ~ J.._J,.. l 

Palo Pinto 

Eastland 

~xa~ 

Critical Habitat for Texas Fawnsfoot 

Unit 2 - Upper Brazos River 

Jack 

Erath 

E) 

Mi 0 5 

I 

17 

KmO 5 

Wise 

Parker 

, 

I 

I 

' 

Somer\;-:eU ' 

- Critical Habitat - Occupied - - - - Rivers 

D County Boundaries ~ Lakes 

= Interstates El Cities 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47989 

(8) Map of Unit TXFF–3: Lower 

Brazos River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.040</GPH>

Critical Habitat for Texas Fawnsfoot 

Unit 3 • Lower Brazos River 

' \ 

Limestone 

Robertson 

e 

Mi O 10 

L__J 

17 

KmO 10 

LConroe ~~ 

' I 

' 

Montgomery [\, 

- Critical Habitat - Occupied - - - - Rivers 

D County Boundaries 28..88: lakes 

= Interstates El Cities 

I Subunit Divider 
47990 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(9) Map of Unit TXFF–4: Little River 

follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.041</GPH>

Burnet 

Hays 

Caldweli 

Critical Habitat for Texas Fawnsfoot 

Unit 4 • Little River 

e 

Mi 0 8 

I 

r-7 

KmO 8 

Fath 

, ....... I'• 

,_ I l _,- 1,,. , 

, ,,1 

' 

Robertson 

Bm!eson 

Washington 

Fayette 

- Critical Habitat - Occupied ., -- - Rivers 

D County Boundaries ~ Lakes 

= Interstates G Cities 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47991 

(10) Map of TXFF–5: Lower San Saba 

and Upper Colorado River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.042</GPH>

McCulloch 

Mas011 

Mason 

Critical Habitat for Texas Fawnsfoot 

Unit 5 - Lower San Saba River and Upper Colorado River 

Bwwn 

t ' , 

San Saba 

Mi O 5 

II 

KmO 5 

Hamilton 

Lrunpasas 

Burnet 

- Critical Habitat- Occupied - -- - Rivers 

D County Boundaries ~ Lakes 

I Subunit Divider 3 Cities 
47992 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(11) Map of Unit TXFF–6: Lower 

Colorado River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.043</GPH>

Fayette 

I 

, 

' ,-' Lavaca 

Victmfa 

Critical Habitat for Texas Fawnsfoot 

Unit 6 - Lower Colorado River 

Colorado 

I ' 

Jackson 

-, 

I 

/ 

,_ I 

' ' , I __ 

e 

Mi 0 

I 

17 

KmO 5 

5 

vVharton 

Matagorda 

J 

El 

IBavcitvl 

I 

I 

I 

' 

- Critical Habitat - Occupied - - - - Rivers 

D County Boundaries El Cities 

= Interstates 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47993 

(12) Map of Unit TXFF–7: East Fork 

Trinity River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.044</GPH>

Denton 

Critical Habitat for Texas Fawnsfoot 

Unit 7 - East Fork Trinity River 

Collin 

Dallas 

I 

I 

Q 

\, 

Mi O 5 

I 

II 

KmO 5 

Kaufimm 

!Kaufman I 

13 

TXFF-7: East Fork 

Trinity River 

~ 

I 

, 

Van 

- Critical Habitat- Occupied ~ - - - Rivers 

D County Boundaries ~ Lakes 

= Interstates 13 Cities 
47994 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(13) Map of Unit TXFF–8: Trinity 

River follows: 

* * * * * 

Guadalupe Orb (Cyclonaias necki) 

(1) Critical habitat units are depicted 

for Caldwell, Comal, DeWitt, Gonzales, 

Guadalupe, Kendall, Kerr, and Victoria 

Counties, Texas, on the maps in this 

critical habitat entry. 

(2) Within these areas, the physical or 

biological features essential to the 

conservation of Guadalupe orb consist 

of the following components within 

waters and streambeds up to the 

ordinary high-water mark: 

(i) Flowing water at rates suitable to 

keep riffle habitats wetted and welloxygenated and to prevent excess 

sedimentation or scour during high-flow 

events but not so high as to dislodge 

individuals; 

(ii) Stable riffles and runs with 

substrate composed of cobble, gravel, 

and fine sediments; 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.045</GPH>

\ 

' 

Navarro 

Robertson 

Critical Habitat for Texas Fawnsfoot 

Unit 8 - Trinity River 

Henderson 

Anderson 

Houston 

nmity 

Madison 

- Critical Habitat- Occupied - -- - Rivers 

Mi O 8 D County Boundaries El Cities 

Ii = Interstates 

KmO 8 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47995 

(iii) Channel catfish (Ictalurus 

punctatus), flathead catfish (Pylodictus 

olivaris), and tadpole madtom (Noturus 

gyrinus) present; and 

(iv) Water quality parameters within 

the following ranges: 

(A) Dissolved oxygen >2 mg/L; 

(B) Salinity <2 ppt; 

(C) Total ammonia <0.77 mg/L total 

ammonia nitrogen; 

(D) Water temperature <29 °C (84.2 

°F); and 

(E) Low levels of contaminants. 

(3) Critical habitat does not include 

manmade structures (such as buildings, 

aqueducts, runways, roads, and other 

paved areas) and the land on which they 

are located existing within the legal 

boundaries on [EFFECTIVE DATE OF 

THE FINAL RULE]. 

(4) The maps in this entry, as 

modified by any accompanying 

regulatory text, establish the boundaries 

of the critical habitat designation. The 

coordinates or plot points or both on 

which each map is based are available 

to the public at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

(5) Note: An index map of the critical 

habitat designations for the Central 

Texas mussels, which includes the 

Guadalupe orb, can be found in this 

paragraph (f) at the entry for the 

Guadalupe fatmucket. An index map of 

critical habitat units for the Guadalupe 

orb follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3
47996 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.046</GPH>

Critical Habitat for Guadalupe Orb - Unit Overview 

Q 

Mi O 10 

L__J 

r7 

KmO 10 

- Critical Habitat - Occupied - - - - Rivers 

County Boundaries ~ Lakes 

= Interstates 0 Citiea 

I Subunit Divider 

I 

' 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47997 

(6) Map of Unit GORB–1: Upper 

Guadalupe River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.047</GPH>

Nfrk 

GuadallJP9 

Critical Habitat for Guadalupe Orb 

Unit 1 - Upper Guadalupe River 

Gillespie 

!Fredericksburg I 

El 

,_;-~,i.t---~~L 

;-•- \ ,.- .... 

·GORB-1 a: South 

Fork-Guadalu~e River 

Kerr 

Bandera 1 ·"1- Medina R 

'.,, ... , .., ... ~,_;.,.,,,, '-

' , I~ // 

" / : / i---,--------------4- Medin;lL I' 

Medina 

,./ 

I 

, 

., ' ., 

I 

I 

,. < ~ 

,, 

_) 

Blanco 

e 

Mi O 5 

- Critical Habitat- Occupied - - - - Rivers 

D County Boundaries ~ lakes 

L__J 

r7 

KmO 5 

= Interstates 3 Cities 

I Subunit Divider 
47998 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(7) Map of Unit GORB–2: Lower 

Guadalupe River follows: 

* * * * * 

Texas Pimpleback (Cyclonaias petrina) 

(1) Critical habitat units are depicted 

for Brown, Coleman, Colorado, Concho, 

Kimble, Lampasas, Mason, McCulloch, 

Menard, Mills, San Saba, Tom Green, 

and Wharton Counties, Texas, on the 

maps in this critical habitat entry. 

(2) Within these areas, the physical or 

biological features essential to the 

conservation of Texas pimpleback 

consist of the following components 

within waters and streambeds up to the 

ordinary high-water mark: 

(i) Flowing water at rates suitable to 

keep riffle habitats wetted and welloxygenated and to prevent excess 

sedimentation or scour during high-flow 

events but not so high as to dislodge 

individuals; 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.048</GPH>

', ~TilSon J 

'I 

Critical Habitat for Guadalupe Orb 

Unit 2 - Lower Guadalupe River 

Karnes I 

' 

Mio 8 

I 

II 

KmO 8 

DeWitt 

• !Victoria I 

- Critical Habitat - Occupied - - - - Rivers 

D County Boundaries ffi Lakes 

= Interstates 0 Cites 

I Subunit Divider 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 47999 

(ii) Stable riffles and runs with 

substrate composed of cobble, gravel, 

and fine sediments; 

(iii) Channel catfish (Ictalurus 

punctatus), flathead catfish (Pylodictus 

olivaris), and tadpole madtom (Noturus 

gyrinus) present; and 

(iv) Water quality parameters within 

the following ranges: 

(A) Dissolved oxygen >2 mg/L; 

(B) Salinity <2 ppt; 

(C) Total ammonia <0.77 mg/L total 

ammonia nitrogen; 

(D) Water temperature <29 °C (84.2 

°F); and 

(E) Low levels of contaminants. 

(3) Critical habitat does not include 

manmade structures (such as buildings, 

aqueducts, runways, roads, and other 

paved areas) and the land on which they 

are located existing within the legal 

boundaries on [EFFECTIVE DATE OF 

THE FINAL RULE]. 

(4) The maps in this entry, as 

modified by any accompanying 

regulatory text, establish the boundaries 

of the critical habitat designation. The 

coordinates or plot points or both on 

which each map is based are available 

to the public at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

(5) Note: An index map of the critical 

habitat designations for the Central 

Texas mussels, which includes the 

Texas pimpleback, can be found in this 

paragraph (f) at the entry for the 

Guadalupe fatmucket. An index map of 

critical habitat units for the Texas 

pimpleback follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3
48000 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.049</GPH>

Critical Habitat for Texas Pimpleback - Unit Overview 

Mi O 20 

L__J 

17 

KmO 20 

- Critical Habitat - Occupied = Interstates 

c:::::1 Critical Habitat - Unoccupied - - - - Rivers 

County Boundaries El Cities 

Subunit Divider 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 48001 

(6) Map of Unit TXPB–1: Elm Creek 

follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.050</GPH>

,, -\ 

I 

l 

l 

' 

Critical Habitat for Texas Pimpleback 

Unit 1 - Elm Creek 

TXPB-1a: Bluff Creek 

Runnels 

' /1 

' ' f 

\ \--; 1 ... , --~-.;........, 

~ ~ ' 

, I I I , , ~ ' - - ' ... lo . __ , , I Ball' 1nger I -... '\ .,- Colorado R' 

I , 

I 

, 

' 

, , 

, 

I 

I 

I 

I 

I 

I ' 

I 

I 

I 

TXPB-1 b: Lower Elm Creek 

I , 

............ 

' I 

I ,, 

0 - Critical Habitat - Occupied - - - - Rivers 

Mi O .2 

I County Boundaries 13 Cities 

II 

KmO 2 Subunit Divider 
48002 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(7) Map of Unit TXPB–2: Concho 

River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.051</GPH>

Coke 

ISan Angelo I 

[:] ,' 

Critical Habitat for Texas Pimpleback 

Unit 2 - Concho River 

TXPB-2b: Upper 

Concho River 

Runnels 

I 

<-, 

Colanllll 

Tom Green 

Mi O 4 

I 

II 

KmO 4 

,.,,._,,..,,. ..... - ....... __ ,,.--- .... 

Brady Cr/~ .,..;I ... - ........... _..__.,, ....... 

- Critical Habitat - Occupied - - - - Rivers 

c:::::::11 Critical Habitat - Unoccupied [:] Cities 

County Boundaries 

I Subunit Divider 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 48003 

(8) Map of Unit TXPB–3: Upper 

Colorado River and Lower San Saba 

River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.052</GPH>

Critical Habitat for Texas Pimpleback 

Unit 3 - Upper Colorado River and Lower San Saba River 

Coleman 

!Brownwood I 

El 

Brmvn 

/,) 

/ 

//-

TXPB-Ja: Upper Colorado River .,,.,, Mills 

McCulloch 

TXPB-4 

TXPBiJb: Lower 

San Saba River:..-· 111111.,. .. w,1 

Mason 

, 

I 

Sari Saba 

Llano LBuchanan 

IMasonl LlanoR ~--, El ,- -- ,,- ____ ,- , 

-,,..,. ........ 

- Critical Habitat ;.; Occupied - - - Rivers 

Mi O 6 D County Boundaries 1®:ii Lakes 

I 

II I Subunit Divider S Cities 

KmO 6 
48004 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(9) Map of Unit TXPB–4: Upper San 

Saba River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.053</GPH>

Tom Green 

Schleicher 

N Valley Prong 

Sutton 

Critical Habitat for Texas Pimpleback 

Unit 4 - Upper San Saba River 

Menard 

TXPB-4: Upper 

San Saba River 

Kimble 

, , Brady 

-, ~, Reservoir 

..... - .... ' 

McCulloch 

Mi O 4 

- Critical Habitat- Occupied - - ""' " Rivers 

D County Boundaries m Lakes 

I 

II = Interstates El Cities 

KmO 4 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 48005 

(10) Map of Unit TXPB–5: Llano River 

follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.054</GPH>

Menard 

,- .... ,. 

-.. . ..-, I 

Critical Habitat for Texas Pimpleback 

Unit 5 - Llano River 

Mason 

IMasonl 

El 

i1XPB-5a: Upper 

Llano River 

TX.PB-Sb: Lower 

Llano River .,. .,,. ---

Llano 

Kimble 

Kerr 

e 

Mi 0 

I 

r-7 

KmO 4 

Gillespie 

!Fredericksburg I 

El 

- Critical Habitat- Occupied = Interstates 

4 ic::=:::a Critical Habiat - Unoccupied - - - - Rivers 

I I County Boundaries El Cities 

I Subunit Divider 
48006 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(11) Map of Unit TXPB–6: Lower 

Colorado River follows: 

False Spike (Fusconaia mitchelli) 

(1) Critical habitat units are depicted 

for DeWitt, Gonzales, Kimble, Mason, 

Milam, San Saba, Victoria, and 

Williamson Counties, Texas, on the 

maps in this critical habitat entry. 

(2) Within these areas, the physical or 

biological features essential to the 

conservation of false spike consist of the 

following components within waters 

and streambeds up to the ordinary highwater mark: 

(i) Flowing water at rates suitable to 

keep riffle habitats wetted and well 

oxygenated, and to prevent excess 

sedimentation but not so high as to 

dislodge individuals; 

(ii) Stable riffles and runs with cobble, 

gravel, and fine sediments; 

(iii) Blacktail shiner (Cyprinella 

venusta) and red shiner (Cyprinella 

lutrensis) present; and 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.055</GPH>

I 

I 

\i;L_ Fayette 

Ila Grange! r - J 

\ 

' 

-rLavaca 

Critical Habitat for Texas Pimpleback 

Unit 6 - Lower Colorado River 

Colorado 

\Vharton 

Bend 

Jackson ' 

'l,..._Ba-v -Cit~vl 

\ ' I 

e 

Mi 0 

r-7 

KmO 6 

6 

:G Matagorda : 

J 

I ' 

- Critical Habitat - Occupied - - - - Rivers 

County Boundaries 

= Interstates 

G Cities 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 48007 

(iv) Water quality parameters within 

the following ranges: 

(A) Dissolved oxygen >2 mg/L; 

(B) Salinity <2 ppt; 

(C) Total ammonia <0.77 mg/L total 

ammonia nitrogen; 

(D) Water temperature <29 °C (84.2 

°F); and 

(E) Low levels of contaminants. 

(3) Critical habitat does not include 

manmade structures (such as buildings, 

aqueducts, runways, roads, and other 

paved areas) and the land on which they 

are located existing within the legal 

boundaries on [EFFECTIVE DATE OF 

THE FINAL RULE]. 

(4) The maps in this entry, as 

modified by any accompanying 

regulatory text, establish the boundaries 

of the critical habitat designation. The 

coordinates or plot points or both on 

which each map is based are available 

to the public at http://

www.regulations.gov under Docket No. 

FWS–R2–ES–2019–0061. 

(5) Note: An index map of the critical 

habitat designations for the Central 

Texas mussels, which includes the false 

spike, can be found in this paragraph (f) 

at the entry for the Guadalupe 

fatmucket. An index map of critical 

habitat units for the false spike follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.056</GPH>

Critical Habitat for False Spike - Unit Overview 

Mi O 10 

L__J. 

r7· 

KmO 10 

-critical Habitat - Occupied - - - - Rivers 

County Boundaries ffi lakes 

= Interstates G Cities· 

Subunit Divider 
48008 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(6) Map of Unit FASP–1: Little River 

follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.057</GPH>

BeH 

----

~x~ 

Mi 

Critical Habitat for False Spike 

Unit 1 - little River 

/ 

/ 

\ l.jttleR .._.,, -'-·) 

!Holland j 

G 

' \ 

I 

I 

I 

Milm.n 

e - Critical Habitat - Occupied - -- - Rivers 

0 4 

I 

[~=l County Boundaries ~ Lakes 

"~·-'=- Interstates G Cities 

ii Subunit Divider 

KmO 4 

I 

.. 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 48009 

(7) Map of Unit FASP–2: San Saba 

River follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.058</GPH>

McCulloch 

Mason 

Critical Habitat for False Spike 

Unit 2 - San Saba River 

El 

!Brownwood I 

Brown Hamilton 

Mills 

Lampasas 

San 

Burnet 

Llano 

- Critical Habitat - Occupied ·m: lakes 

Mi O 5 

I County Boundaries El Cities 

II - -- - Rivers 

KmO 5 
48010 Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 

(8) Map of Unit FASP–3: Llano River 

follows: 


jbell on DSKJLSW7X2PROD with PROPOSALS3EP26AU21.059</GPH>

IMe~~rdl 

-a- -,, 

Critical Habitat for False Spike 

Unit 3 - Uano River 

McCulloch San Saba 

,_ ,- .......... J.._.,..' ... -

Menard 

Mason 

Llano 

FASP-3: Llano River 

Kirnble 

Gillespie 

!Fredericksburg! 

G 

Kerr 

- Critical Habitat- Occupied - - - - Rivers 

Mi O 5 I I County Boundaries G Cities 

II = Interstates 

KrnO 5 
Federal Register / Vol. 86, No. 163 / Thursday, August 26, 2021 / Proposed Rules 48011 

(9) Map of Unit FASP–4: Guadalupe 

River follows: 

* * * * * 

Martha Williams, 

Principal Deputy Director, Exercising the 

Delegated Authority of the Director U.S. Fish 

and Wildlife Service. 

[FR Doc. 2021–18012 Filed 8–25–21; 8:45 am] 

BILLING CODE 4333–15–C 


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