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

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

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,

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

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

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

EP26AU21.025

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 yellow-

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 sight-feeding 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.

EP26AU21.026

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

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)

EP26AU21.027

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

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)

EP26AU21.028

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 small- to 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

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 short-term 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)

EP26AU21.029

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.

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)

EP26AU21.030

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:

(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 species-specific 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 life-history 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

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 (m

2

), 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

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, in-channel 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 un-ionized ammonia (NH

3

) 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

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, water-supply, and recreation reservoirs results in altered hydrologic regimes, including an attenuation of both high- and low-flow 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

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 large-scale 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

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

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

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

functionally extirpated with little chance of persistence. The upper reaches of Onion Creek frequently go dry, and several privately owned low-head 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

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

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 mussel-scouring 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

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

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

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, self-sustaining, 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

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 s

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