Endangered and Threatened Wildlife and Plants; Endangered Species Status With Critical Habitat for Guadalupe Fatmucket, Texas Fatmucket, Guadalupe Orb, Texas Pimpleback, Balcones Spike, 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

[Docket No. FWS-R2-ES-2019-0061; FXES1111090FEDR-245-FF09E21000]

RIN 1018-BD16

Endangered and Threatened Wildlife and Plants; Endangered Species Status With Critical Habitat for Guadalupe Fatmucket, Texas Fatmucket, Guadalupe Orb, Texas Pimpleback, Balcones Spike, 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:

Final rule.

SUMMARY:

We, the U.S. Fish and Wildlife Service (Service), determine endangered species status under the Endangered Species Act of 1973 (Act), as amended, for the Guadalupe fatmucket (

Lampsilis bergmanni

), Texas fatmucket (

Lampsilis bracteata

), Guadalupe orb (

Cyclonaias necki

), Texas pimpleback (

Cyclonaias

(=

Quadrula

)

petrina

), Balcones spike (

Fusconaia

(=

Quincuncina

)

iheringi

), and false spike (

Fusconaia

(=

Quincuncina

)

mitchelli

), and threatened species status for the Texas fawnsfoot (

Truncilla macrodon

), seven species of freshwater mussels from central Texas. We also issue a rule under section 4(d) of the Act for the Texas fawnsfoot that provides measures that are necessary and advisable to provide for the conservation of the Texas fawnsfoot. In addition, we designate critical habitat for all seven species. In total, approximately 1,577.5 river miles (2,538.7 river kilometers) in Blanco, Brown, Caldwell, Coleman, Comal, Concho, DeWitt, Gillespie, Gonzales, Guadalupe, Hays, Kendall, Kerr, Kimble, Lampasas, Llano, Mason, McCulloch, Menard, Mills, Palo Pinto, Parker, Runnels, San Saba, Shackelford, Stephens, Sutton, Throckmorton, Tom Green, Travis, and Victoria Counties, Texas, fall within the boundaries of the critical habitat designation. This rule applies the protections of the Act to these species and their designated critical habitats.

DATES:

This rule is effective July 5, 2024.

ADDRESSES:

This final rule is available on the internet at

https://www.regulations.gov

. Comments and materials we received, as well as supporting documentation we used in preparing this rule, are available for public inspection at

https://www.regulations.gov

at Docket No. FWS-R2-ES-2019-0061.

Availability of supporting materials:

Supporting materials we used in preparing this rule, such as the species status assessment report, are available for public inspection at

https://www.regulations.gov

at Docket No. FWS-R2-ES-2019-0061. 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.regulations.gov

at Docket No. FWS-R2-ES-2019-0061.

FOR FURTHER INFORMATION CONTACT:

Karen Myers, Field Supervisor, U.S. Fish and Wildlife Service, Austin Ecological Services Field Office, 1505 Ferguson Lane, Austin, TX 78754; telephone (512) 937-7371. Individuals in the United States who are deaf, deafblind, hard of hearing, or have a speech disability may dial 711 (TTY, TDD, or TeleBraille) to access telecommunications relay services. Individuals outside the United States should use the relay services offered within their country to make international calls to the point-of-contact in the United States.

SUPPLEMENTARY INFORMATION:

Executive Summary

Why we need to publish a rule.

Under the Act, a species warrants listing if it meets the definition of an endangered species (in danger of extinction throughout all or a significant portion of its range) or a threatened species (likely to become endangered within the foreseeable future throughout all or a significant portion of its range). If we determine that a species warrants listing, we must list the species promptly and designate the species' critical habitat to the maximum extent prudent and determinable. We have determined that the Guadalupe fatmucket (

Lampsilis bergmanni

), Texas fatmucket (

Lampsilis bracteata

), Guadalupe orb (

Cyclonaias necki

), Texas pimpleback (

Cyclonaias

(=

Quadrula

)

petrina

), Balcones spike (

Fusconaia

(=

Quincuncina

)

iheringi

), and false spike (

Fusconaia

(=

Quincuncina

)

mitchelli

) meet the Act's definition of endangered species, and the Texas fawnsfoot (

Truncilla macrodon

) meets the Act's definition of a threatened species; therefore, we are listing them as such, finalizing a rule under section 4(d) of the Act for the Texas fawnsfoot, and designating critical habitat. Both listing a species as an endangered or threatened species and designating critical habitat can be completed only by issuing a rule through the Administrative Procedure Act rulemaking process (5 U.S.C. 551

et seq.

).

What this document does.

This rule makes final the listing of the Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and false spike as endangered species, and the Texas fawnsfoot as a threatened species with a rule issued under section 4(d) of the Act (a “4(d) rule”). In addition, this rule designates critical habitat for all seven central Texas mussel species in 20 units (including 32 subunits) totaling 1,577.5 river miles (2,538.7 river kilometers (km)) on private, State, and Federal property within portions of 31 counties in Texas.

The basis for our action.

Under the Act, we may determine that a species is an endangered or threatened species because of any of five factors: (A) The present or threatened destruction, modification, or curtailment of its habitat or range; (B) overutilization for commercial, recreational, scientific, or educational purposes; (C) disease or predation; (D) the inadequacy of existing regulatory mechanisms; or (E) other natural or manmade factors affecting its continued existence; we also take into account conservation efforts, such as Candidate Conservation Agreements with Assurances (CCAAs). We have determined that increased fine sediment, changes in water quality, and altered hydrology in the form of inundation and loss of flow and scour of substrate (Factor A), collection (Factor B), predation (Factor C), and barriers to fish movement (Factor E) are the primary threats to these species. These factors are all exacerbated by the ongoing and expected effects of climate change.

Section 4(a)(3) of the Act requires the Secretary of the Interior (Secretary), to designate critical habitat, to the maximum extent prudent and determinable, concurrent with listing. Section 3(5)(A) of the Act defines critical habitat as (i) the specific areas within the geographical area occupied by the species, at the time it is listed, on which are found those physical or biological features (I) essential to the conservation of the species and (II) which may require special management considerations or protections; and (ii) specific areas outside the geographical area occupied by the species at the time it is listed, upon a determination by the Secretary that such areas are essential for the conservation of the species. Section 4(b)(2) of the Act states that the Secretary must make the designation on the basis of the best scientific data

available and after taking into consideration the economic impact, the impact on national security, and any other relevant impacts of specifying any particular area as critical habitat.

Previous Federal Actions

Please refer to the August 26, 2021, proposed rule (86 FR 47916) for a detailed description of previous Federal actions concerning these species.

Peer Review

A species status assessment (SSA) team prepared an SSA report for the Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe orb, Texas pimpleback, and false spike. This SSA report was competed prior to the taxonomic divergence of the false spike to reflect the recently described Balcones spike (

Fusconaia iheringi

) (Smith et al. 2020, entire) (see Summary of Changes from the Proposed Rule, below). The SSA team was composed of Service biologists, in consultation with other species experts. The SSA report represents a compilation of the best scientific and commercial data available concerning the status of the species, including the impacts of past, present, and future factors (both negative and beneficial) affecting the species.

In accordance with our joint policy on peer review published in the

Federal Register

on July 1, 1994 (59 FR 34270), and our August 22, 2016, memorandum updating and clarifying the role of peer review of listing actions under the Act, we solicited independent scientific review of the information contained in the SSA report. We sent the SSA report to eight independent peer reviewers and received six responses. Results of this structured peer review process can be found at

https://regulations.gov

. In preparing the proposed rule, we incorporated the results of these peer reviews, as appropriate, into version 1.1 of the SSA report, which was the foundation for the proposed rule and this final rule. A summary of the peer review comments and our responses can be found under Summary of Comments and Recommendations, below.

Summary of Changes From the Proposed Rule

Based upon our review of the public comments, State agency comments, peer review comments, and relevant information that became available since the August 26, 2021, proposed rule published, we updated information in our SSA report, including:

• Updating the taxonomy of false spike (

Fusconaia mitchelli

) to reflect the divergence from the recently described Balcones spike (

Fusconaia iheringi

) (Smith et al. 2020, entire).

• Updating text to clearly differentiate between the threat of sedimentation to freshwater mussels and naturally occurring turbidity in a river system; improve consistency in the use of “impaired” when discussing water quality; and further differentiate between the threat of sedimentation within a system and the presence of turbidity associated with fine organic or inorganic matter, soluble organic compounds, algae, or other microscopic organisms.

We made these and other changes as appropriate in this final rule. In addition to minor clarifying edits and incorporation of additional information on the species' biology, populations, and threats, this final determination differs from the August 26, 2021, proposed rule in the following ways:

(1) We add updated population data for the Texas fatmucket, including survey data made available by the Texas Department of Transportation since the publication of the proposed rule. Based on the presence of Texas fatmucket in Unit TXFM-6b (Upper Onion Creek), this unit has now changed from unoccupied to occupied, so we combine the Upper and Lower Onion Creek critical habitat units (TXFM-6b and TXFM-6a, respectively) into one occupied unit (TXFM-6). Therefore, this rule differs slightly from the proposed critical habitat designation (86 FR 47916; August 26, 2021) by unit numbering and occupancy.

(2) Both the Balcones spike and the false spike are included in this final listing rule because the entity known as false spike in the August 26, 2021, proposed rule was taxonomically divided into the two species. We rename and renumber critical habitat units to reflect the updated taxonomy and range of false spike and Balcones spike. We renumber proposed critical habitat unit FASP-4 (Guadalupe River Unit) as FASP-1; it is now the only critical habitat unit for the false spike. The remaining three proposed critical habitat units for the false spike are renamed and renumbered for the Balcones spike: unit FASP-1 (Little River Unit) is now BASP-1, FASP-2 (San Saba River Unit) is now BASP-2, and FASP-3 (Llano River Unit) is now BASP-3.

(3) For the critical habitat designation, we exclude proposed units TXFF-3, TXFF-4, and BASP-1 (previously FASP-1) based on the implementation of conservation measures completed by the Brazos River Authority (BRA) as part of their candidate conservation agreement with assurances (CCAA) for the Balcones spike and Texas fawnsfoot in the Brazos River Basin (BRA 2021, pp. 35-51; hereafter, the “BRA Agreement”). We also exclude proposed units TXFF-6 and TXPB-6 based upon the implementation of conservation measures completed by the Lower Colorado River Authority (LCRA) as part of their CCAA for the Texas pimpleback, Texas fawnsfoot, Texas fatmucket, and Balcones spike in the Lower Colorado River Basin below O.H. Ivie Reservoir (LCRA 2023, pp. 45-84; hereafter, the “LCRA Agreement”). In addition, we exclude proposed units TXFF-7 and TXFF-8 based upon the implementation of conservation measures completed by the Trinity River Authority (TRA) as part of their CCAA for six species in the Trinity River Basin (TRA 2023, pp. 47-66; hereafter, the “TRA Agreement”).

(4) We incorporate minor changes in the length of river miles (and kilometers) of occupied stream reaches. We also incorporate minor changes in the length of river miles (and kilometers) from the proposed critical habitat to reflect those included in the final critical habitat unit maps. While we use the same start and end points for all final critical habitat unit designations, these minor changes in critical habitat designation length are the result of geoprocessing tools used in ArcGIS.

(5) We include short textual descriptions of the designated units under Regulation Promulgation in this rule, as under 50 CFR 17.94, general descriptions of the location and boundaries of each area may be provided to clarify or refine what is included within the boundaries depicted on the map, or to explain the exclusion of sites (

e.g.,

paved roads, buildings) within the mapped area. These descriptions mirror information in the preamble of this rule, which reflects the unit description information presented in our August 26, 2021, proposed rule as amended by the changes described in this document.

(6) Based on public comments, we update language in the 4(d) rule for the Texas fawnsfoot to clarify and refine the specific prohibitions and exceptions to those prohibitions to minimize potential ambiguity. Specifically, to qualify for exceptions when conducting channel restoration projects, we clarify that the project must meet all applicable Federal, State, and local permitting requirements. In addition, to allow the Service to make arrangements for surveys and potential relocation of any mussels that might be adversely affected during channel restoration projects, we add that notice must be provided to the Service of the location and nature of the

proposed work at least 30 days prior to commencing actual construction within an area designated as critical habitat for the Texas fawnsfoot. In addition, to qualify for exceptions when conducting streambank stabilization projects, we specify that: (i) native live stakes, native live fascines, or native live brush must be used; (ii) methods that include the use of quarried rock (riprap) for more than 25 percent of the area within the streambanks or include the use of rock baskets or gabion structures do not qualify for this exception; (iii) work using these bioengineering methods must be performed at base flow or low water conditions and when significant rainfall likely to result in significant runoff is not predicted at or upstream of the area where work is proposed for a period of at least 3 days after the work is scheduled to be undertaken, in order to reduce streambank erosion and sedimentation; and (iv) the project must meet all applicable Federal, State, and local permitting requirements. Further, to qualify for exceptions when conducting soil and water conservation practices, and riparian and adjacent upland habitat management activities, we add that, to allow the Service to make arrangements for surveys and potential relocation of any mussels that might be adversely affected during channel restoration projects, notice must be provided to the Service of the location and nature of the proposed work at least 30 days prior to commencing actual construction within an area designated as critical habitat for Texas fawnsfoot.

(7) Based on public comments, we update language to include examples of discretionary actions for the central Texas mussels that may be subject to consultation procedures under section 7, and more clearly define the standards for avoiding jeopardizing the continued existence of the species for future section 7 conferences/consultations (see Available Conservation Measures, below). In addition, we update language to include protective regulations to address the threats to the Texas fawnsfoot under section 9, as well as what activities would and would not be likely to constitute a violation of section 9 take prohibition (see Provisions of the 4(d) Rule, below).

(8) Based on a public comments, we also make minor, nonsubstantive changes and corrections throughout this rule in response to public comments. However, the information we received during the public comment period on the proposed rule did not change our determination that the Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and false spike meet the Act's definition of endangered species, and the Texas fawnsfoot meets the Act's definition of a threatened species.

Summary of Comments and Recommendations

In the proposed rule published on August 26, 2021 (86 FR 47916), we requested that all interested parties submit written comments on the proposal by October 25, 2021. We also contacted appropriate Federal and State agencies, scientific experts and organizations, and other interested parties and invited them to comment on the proposal. Newspaper notices inviting general public comment were published in the Austin Statesman, and we held public hearings on September 14 and September 16, 2021. All substantive information we received during the comment period has either been incorporated directly into this final determination or is addressed below.

Peer Reviewer Comments

As discussed in Peer Review above, we received comments from six peer reviewers on the draft SSA report. We reviewed all comments we received from the peer reviewers for substantive issues and new information regarding the contents of the SSA report. Peer reviewer comments are addressed in the following summary. As discussed above, because we conducted this peer review prior to the publication of our proposed rule, we had already incorporated all applicable peer review comments into version 2.1 of the SSA report, which was the foundation for the proposed rule. The peer reviewers generally concurred with our methods and conclusions, and provided additional information, clarifications, and suggestions to improve the SSA report (Service 2019b, entire). Peer reviewer comments are addressed in the following summary and are incorporated into the SSA report as appropriate.

(1)

Comment:

One peer reviewer suggested that, in addition to the value limited by the population abundance factor in the overall current condition, the ranges used to assign values to the six condition factors after averaging should be included in the SSA report.

Our response:

The overall average current condition of the populations, not limited by the abundance condition, is not reflective of population condition. We chose to limit the overall current conditions so they could not exceed abundance because our information regarding habitat is not robust enough to outweigh abundance (

i.e.,

a mussel population with low abundance but indications of moderate or high habitat factors should not be rated to be in moderate or high condition). Therefore, reporting the unlimited averages would only cause reader confusion that could be derived from presenting multiple “overall condition” values for each population.

(2)

Comment:

One peer reviewer suggested, particularly for false spike, that the lack of knowledge of host fish could be a factor influencing central Texas mussel distribution and abundance if the host fish is in fact not a common species.

Our response:

Following the submission of the draft SSA for peer review, studies were completed identifying the red shiner (

Cyprinella lutrensis

) and blacktail shiner (

Cyprinella venusta

) as host fish for false spike, and both are common fish species in this area (Dudding et al. 2019, p. 16). Host fish for congeners of the mussel species that are the subjects of this rule are a suite of typically common fish species, and therefore it is unlikely that these mussel species rely exclusively on rare fish species to serve as the sole or primary fish hosts for reproduction.

(3)

Comment:

One peer reviewer and one State commenter stated concerns of using 35-millimeter (mm) length to define juveniles, especially the use of the threshold for the generally smaller Texas fawnsfoot, and they requested that the Service revisit the evidence of reproduction criteria, in particular for smaller species.

Our response:

We consulted with regional and national freshwater mussel experts from around the United States, and the 35-mm length was considered to be an appropriate delineating threshold to use when differentiating between adult and juvenile mussels. This conclusion was made based on the general consensus amongst those asked that individuals below 35 mm in length are not readily detectable during field surveys. Without species-specific data identifying the known size at age of sexual maturity for the subject species, we found it appropriate to consistently use the same cutoff for multiple species if no species-specific data were available. As these data become available, we will update these criteria as appropriate.

Comments From States

(4)

Comment:

One commenter requested that the Service emphasize desiccation study data completed at the San Marcos Aquatic Resources Center that demonstrate that Texas pimpleback is able to tolerate 32 days without water and the Texas fatmucket can tolerate about 3 days without water.

Our response:

The desiccation trials mentioned by the commenter were conducted in a laboratory growth chamber at 25 degrees Celsius (°C) (77 degrees Fahrenheit (°F)) and the relative humidity is not reported (Bonner et al. 2018, p. 193). Presumably, live freshwater mussels experiencing dewatering occurring in the natural environment would be exposed to temperatures greater than 25 °C (77 °F), especially during summer, when drying events are most likely to occur. Additionally, exposed animals would be susceptible to predation. Therefore, while we report the results of the desiccation study, emphasizing them could erroneously create an inaccurate representation of the conditions that exposed mussels would experience and artificially inflate the exposure time during which mussels could be expected to survive in the wild.

(5)

Comment:

The State of Texas disagrees with the finding that there are no federalism implications for the designation of critical habitat.

Our response:

Federalism is the division and sharing of power between the Federal Government and the individual State governments. In keeping with Department of the Interior and Department of Commerce policy, we requested information from, and coordinated development of, the proposed critical habitat designation with appropriate State resource agencies throughout central Texas. From a federalism perspective, the designation of critical habitat directly affects only the responsibilities of Federal agencies. The Act imposes no other duties with respect to critical habitat, either for States and local governments, or for anyone else. As a result, this final rule does not have substantial direct effects either on the States, or on the relationship between the national government and the States, or on the distribution of powers and responsibilities among the various levels of government. In accordance with Executive Order 13132 (Federalism), this rule does not have significant federalism effects, and a federalism summary impact statement is not required.

(6)

Comment:

The State of Texas requested clarification on whether the completion of an approved freshwater mussel identification and sampling course and proficiency testing will be required for scientists with a permit issued under section 10(a)(1)(a) of the Act (a “10(a)(1)(a) permit”), and whether the 4(d) rule will allow qualified individuals to relocate Texas fawnsfoot.

Our response:

The provision of the 4(d) rule that allows for Texas fawnsfoot surveys to be conducted by those who pass an approved Texas mussel identification and sampling course is intended for those who are sampling for freshwater mussels, in which mussels are collected, identified, and returned to the mussel bed from which they came. Surveyors who are trained in survey techniques and how to identify the various species that occur in Texas will not need a 10(a)(1)(a) permit because we expect the effects to the species to be negligible. This provision in the 4(d) rule is not intended to replace the 10(a)(1)(a) permit process, and those with a 10(a)(1)(a) permit will not be required to complete the course. Furthermore, relocation of Texas fawnsfoot from one mussel bed to another is not an excepted form of take under this 4(d) rule.

(7)

Comment:

The State of Texas suggested that naturally occurring ambient water quality should be considered in the context of historical water quality, and laboratory thresholds reported for temperature, salinity, chlorides, and dissolved oxygen should be considered when identifying essential water quality thresholds as components of critical habitat.

Our response:

The objective use of laboratory-based studies, in addition to in situ monitoring, is critical to the understanding of physiological and toxicological thresholds for freshwater mussels. Even though certain ambient water quality parameters are currently occurring in the presence of live freshwater mussels, there is no clear indication that these parameters are protective of freshwater mussels, as different life stages of the species are more sensitive to water quality changes than others (

i.e.,

glochidia and juveniles are more sensitive than adults). Freshwater mussel populations throughout the State of Texas have declined in recent decades, and the presence of reduced or restricted mussel populations should not be used as an indicator that instream conditions are adequate for the long-term persistence of the population. The completion of laboratory studies can provide objective thresholds for individual chemicals, temperatures, or other water quality parameters for both lethal and sublethal effects on individual freshwater mussel species. When identifying the physical or biological features related to water quality for the mussels, we set the thresholds at levels that have been objectively identified as protective of the mussels. Therefore, laboratory-derived values were selected when identifying these components rather than utilizing observed ambient values, which, as described above, may not be protective of all the covered species life stages.

(8)

Comment:

The State of Texas requested clarification on how increased extreme precipitation is projected to have divergent effects on future high stream flows in different rivers, as the Service has predicted for the Llano River and Middle Trinity River.

Our response:

Different river basins experience different conditions that affect the future of flows within those basins. For the Llano River, while there have been recent significant high flow events, recent trends in stream flows in the river have shown an overall reduction in flows in the basin. These reductions are expected to continue in response to climate change (reduced projected rainfall) and expanding development in Texas (groundwater pumping). Conversely, the Trinity River is anticipated to experience increases in flows in the future due to the growth of the Dallas-Fort Worth metroplex and its reliance on surface waters. Water resources that historically would have been distributed across the landscape in north Texas have been consolidated into an assortment of wastewater treatment and water supply system with many return flows feeding into the Trinity River. These return flows combine to elevate the baseflows of the Trinity River at all times (TRA 2023, pp. 23, 25-27) and can combine with rain events, leading to higher high flow events.

(9)

Comment:

The State of Texas provided recommendations for clarification of the physical or biological features (PBFs) essential to the conservation of the central Texas mussels, particularly the PBFs concerning the identification of specific elements of the flow regimes considered essential, adaptive flexibility in defining host fish for the subject mussel species, and the number of sample events required (single or multiple) to evaluate the ranges of water quality parameters.

Our response:

For the flowing water PBF, we welcome additional research on the identification of specific flow regime elements needed for the long-term conservation of these mussel species. However, this information does not currently exist, and so we could not use specific flow rates when developing the PBFs for the species. We are actively working with external partners who are researching the role of stream flows on Texas fatmucket growth and survival in the Colorado River Basin, and we will use these findings as we develop recovery plans for the species.

For the host fish PBF, we must use the best available information when

identifying essential PBFs, and the current science indicates that sunfishes (including bluegill (

Lepomis macrochirus

), green sunfish (

L. cyanellus

), Guadalupe bass (

Micropterus treculii

), and largemouth bass (

M. salmoides

)), freshwater drum (

Aplodinotus grunniens

), catfish (channel catfish (

Ictalurus punctatus

), flathead catfish (

Pylodictis olivarus

), and tadpole madtom (

Noturus gyrinus

)), minnows (family Cyprinidae), and shiners (blacktail shiner (

Cyprinella venusta

) and red shiner (

C. lutrensis

)) are hosts for the central Texas mussel species. Additional host fish species identified for these mussels will be incorporated into the recovery planning process.

Finally, for the PBF that relates to water quality, it can be challenging to provide specific thresholds for water quality parameters because effects to freshwater mussels can range from sublethal to lethal depending on the duration of the exposure to conditions as well as the time of year, flow rates, and other factors. Currently, species-specific toxicology studies have not been completed for the species included in this rule. Therefore, currently, the Service is using surrogate acute water quality standards from other freshwater mussel species in the United States to identify physical features for designated critical habitat. As the species-specific acute and chronic standards are developed for the covered species, the Service will revisit and refine the characteristics of these water quality features. Once these standards are developed, the Service will work with subject matter experts to identify the appropriate sampling techniques to evaluate the acceptable thresholds for water quality parameters, and work with project proponents to ensure that the most appropriate methods will be used to determine effects on listed freshwater mussels on a project-by-project basis.

(10)

Comment:

The State of Texas and several commenters requested that the Service more clearly identify the estimated probability of persistence (threshold) that would preclude a listing decision.

Our response:

The “probability of persistence” is just one small part of our SSA report that informed our analysis and listing decision, which also considered the factors identified by the Act (such as a species' life history, generation time, current and future threats, and trajectory of those threats). There is not a strict probability above which we would not list and below which we would list, particularly because the information we use to assess the species' persistence is of a general nature and does not pinpoint the likelihood of persistence to the degree we would require to provide certainty that that the species persistence was above or below such a threshold. Therefore, “probability of persistence” alone is not going to result in a decision that a species meets the definition of threatened or endangered.

(11)

Comment:

The State of Texas and several commenters are concerned about the economic impact that proposed critical habitat would have on private landowners, private property values, and wastewater treatment plants (WWTPs), suggesting that the incremental effects memo (IEM) only captures baseline costs, and not the total costs associated with critical habitat designation. The commenters requested that prior to publishing a final rule, the Service conduct a new economic analysis, using the coextensive approach.

Our response:

As stated in the economic analysis of the designation of critical habitat for the Central Texas mussels, guidelines issued by the U.S. Office of Management and Budget (OMB) for the economic analysis of regulations direct Federal agencies to measure the costs and benefits of a regulatory action against a baseline (

i.e.,

costs and benefits that are “incremental” to the baseline). The OMB defines the baseline as the “best assessment of the way the world would look absent the proposed action.” (Circular A-4, 2003). In other words, the baseline includes any existing regulatory and socio-economic burden imposed on landowners, managers, or other resource users affected by the designation of critical habitat. The baseline includes the economic impacts of listing the species under the Act, even if the listing occurs concurrently with critical habitat designation. Impacts that are incremental to the baseline (

i.e.,

occurring over and above existing constraints) are those that are solely attributable to the designation of critical habitat and are the focus of the economic analysis.

The Service acknowledges that significant debate has occurred regarding whether assessing the impact of critical habitat designations using the incremental approach is appropriate, with several courts issuing divergent opinions. Most recently, the U.S. Ninth Circuit Court of Appeals concluded that the incremental approach is appropriate, and the U.S. Supreme Court declined to hear the case (

Home Builders Association of Northern California

v.

United States Fish and Wildlife Service,

616 F.3d 983 (9th Cir. 2010), cert. denied, 179 L. Ed 2d 301, 2011 U.S. Lexis 1392, 79 U.S.L.W. 3475 (2011);

Arizona Cattle Growers

v.

Salazar,

606 F.3d 1160 (9th Cir. 2010), cert. denied, 179 L. Ed. 2d 300, 2011 U.S. Lexis 1362, 79 U.S. L.W. 3475 (2011)). Subsequently, on August 28, 2013, the Service revised its approach to conducting impact analyses for designations of critical habitat, specifying that the incremental approach should be used (78 FR 53062).

Public Comments

(12)

Comment:

A commenter suggested that the reliance on data regarding recently dead shell material that are up to 21 years old, combined with the difficulty to detect mussels at sites that are not visited multiple times, is insufficient to define areas occupied at the time of listing and designate those areas as critical habitat for the Texas fatmucket, Texas fawnsfoot, and Texas pimpleback.

Our response:

While the Service used the year 2000 as the oldest year for “recent” survey data, much of the survey data used during the review of the species that are the subjects of this rule were collected during the increase in sampling efforts following the 2010 State listing of these species as threatened by the Texas Parks and Wildlife Department (TPWD). Therefore, much of the data used for the SSA were closer to 10 years old when we were developing the August 26, 2021, proposed rule. However, in instances in which the data were in fact collected approximately 20 years ago, the time gap between the data collection and proposed rule would be between 1 and 3 generations for these species. Because the Service has not been notified of or witnessed rapid, substantial, permanent habitat changes or been provided evidence of recent mussel die-offs through the collection of large numbers of fresh-dead (shells still attached to soft tissue) or recent dead (shells lacking connection to soft tissue but still containing a shiny inner shell layer), it is reasonable to conclude that these occupied areas would still be occupied by the species at some level.

Much of the freshwater mussel sampling that has been completed in Texas to date has consisted of single, opportunistic surveys as part of larger research projects or environmental compliance surveys completed prior to some form of instream construction rather than monitoring events that would require multiple visits to individual sites. While multiple visits to a site will provide a clearer picture of population abundance and extent, a single visit is often sufficient to

determine occupancy if the species is present at that time.

(13)

Comment:

A commenter stated that the proposed critical habitat designation does not include an initial regulatory flexibility analysis to satisfy the requirements of the Regulatory Flexibility Act (RFA; 5 U.S.C. 601

et seq.

), and the Service has not prepared an environmental impact statement to satisfy the National Environmental Policy Act (NEPA; 42 U.S.C. 4321

et seq.

).

Our response:

When a species is proposed for listing, the Act's section 4(a)(3) requires the Secretary of the Interior (Secretary), to the maximum extent prudent and determinable, to designate critical habitat for that species. For more information about the considerations we must undertake when designating critical habitat, see and Consideration of Impacts under Section 4(b)(2) of the Act and

Regulatory Flexibility Act (5 U.S.C. 601 et seq.),

below.

Under the Regulatory Flexibility Act (RFA), Federal agencies are only required to evaluate the potential incremental impacts of a rulemaking on directly regulated entities. The regulatory mechanism through which critical habitat protections are realized is section 7 of the Act, which requires Federal agencies, in consultation with the Service, to ensure that any action authorized, funded, or carried by the Agency is not likely to adversely modify critical habitat. Therefore, only Federal action agencies are directly subject to the specific regulatory requirement (avoiding destruction and adverse modification) imposed by critical habitat designation. Under these circumstances, it is the Service's position that only Federal action agencies will be directly regulated by this designation. Therefore, because Federal agencies are not small entities, the Service may certify that the proposed critical habitat rule will not have a significant economic impact on a substantial number of small entities. Because certification is possible, no regulatory flexibility analysis is required.

Upon recommendation of the Council on Environmental Quality (CEQ), the Service determined that NEPA documents need not be prepared in connection with regulations finalizing the listing status for species pursuant to section 4(a) of the Act. This critical habitat designation is issued concurrently with the listing of the species under section 4(a). On October 25, 1983, the Service published in the

Federal Register

a notice explaining this decision (48 FR 49244). The Service subsequently interpreted this 1983 determination to apply to critical habitat designations, based on the decision delivered in a Sixth Circuit Court of Appeals case (

Pacific Legal Foundation

v.

Andrus,

657 F. 2d 829 (1981)) and CEQ's recommendation.

Based on this interpretation, the Service did not conduct NEPA analyses on critical habitat designations between 1983 and 1998. However, since the mid-1990s, the question of whether NEPA applies to the Federal action of designating critical habitat under the Act has been the subject of multiple lawsuits. In

Douglas County

v.

Babbitt,

48 F.3d 1495 (9th Cir. 1995), the U.S. Court of Appeals for the Ninth Circuit upheld the Service's conclusion that critical habitat actions are exempt from NEPA compliance. The Service was again challenged on this conclusion in

Catron County Board of Commissioners

v.

U.S. Fish and Wildlife Service,

75 F.3d 1429 (10th Cir. 1996) (

Catron County

); the U.S. Court of Appeals for the Tenth Circuit ordered the Secretary to comply with NEPA when completing critical habitat determinations. The DC District Court in

Cape Hatteras Access Pres. All.

v.

U.S. Dep't of Interior,

344 F. Supp. 2d 108 (D.D.C. 2004) similarly held that NEPA applied to critical habitat designations. However, more recently, the Fifth Circuit Court of Appeals agreed with the Ninth Circuit and held that NEPA does not apply to critical habitat designations under the Act (

Markle Interests

v.

FWS,

827 F.3d 452 (5th Cir. 2016),

rev'd on other grounds sub nom. Weyerhaeuser

v.

U.S. Fish and Wildlife Service,

139 S. Ct. 361 (2018)). Other district courts have applied this reasoning as well (

e.g., Otay Mesa Property, LP

v.

U.S. Department of the Interior,

144 F. Supp. 3d 35 (D.D.C. 2015)).

While the Service does not concede that NEPA applies to critical habitat designations or revisions under the Act, we agreed to address NEPA compliance for critical habitat designations when the range of the species occurs within the jurisdiction of the U.S. Court of Appeals for the Tenth Circuit, which includes the following States: Colorado, Kansas, New Mexico, Oklahoma, Utah, and Wyoming. The central Texas mussels' critical habitat designations do not occur within the jurisdiction of the U.S. Court of Appeals for the Tenth Circuit, so we did not prepare an environmental assessment under NEPA for this designation.

(14)

Comment:

A commenter requested that proposed critical habitat unit TXFM-2 (San Saba River) for the Texas fatmucket be limited to the upper section of the San Saba River, as it is the only segment of the river that has the PBFs essential to the conservation of the species. Because the middle reach of this critical habitat unit lacks an adequate hydrologic flow regime, which is an essential PBF, and this flow regime is not expected to improve under current predictions of increasing periods of drought, and the species does not currently exist in the lower reach of the San Saba River, they requested these middle and lower reaches of the San Saba River be removed from final critical habitat designation.

Our response:

Based on recent survey data, we consider this reach to be currently occupied by the species. Despite the anticipated future threats to water levels in the middle San Saba River and the Hill Country as a whole, live Texas fatmucket have been observed at multiple locations in the middle reach of the San Saba River in the last 10 years. Historical collection records provide evidence that the species has also occurred in the past in the lower reach of the San Saba River near San Saba, Texas. We acknowledge that the unique geology of the middle reach of the San Saba River presents conservation challenges concerning flowing water (an essential PBF) in the lower reach of the river, but this unit currently contains adequate flowing water, suitable substrate, appropriate host fish, and adequate water quality, and recovery will entail restoring the species to reaches of habitat long enough such that stochastic events do not eliminate the entire population. The lower reach of the San Saba does not present these geological challenges and contains the essential PBFs needed to support the species in this portion of the San Saba River. The middle and lower reaches of the San Saba River add approximately 69 river miles (mi) (111 river kilometers (km)) of habitat to the population, they would increase the overall resiliency of the population.

(15)

Comment:

A commenter stated that the Service lacks enough species-specific information to designate critical habitat, particularly in unoccupied areas, and that the proposed rule fails to show that designated critical habitat is determinable.

Our response:

We are required to designate critical habitat based on the best scientific data available at the time of designation. We considered the best scientific data available regarding the central Texas mussels to evaluate potential critical habitat under the Act. We have sufficient information to understand the habitat these species need and where the species occur, and we solicited peer review on our evaluation of that information. The

listing and critical habitat process does not require perfect information; it requires that we use the best available information to make our determinations. Therefore, we found that critical habitat was determinable in both occupied and unoccupied areas.

(16)

Comment:

Several commenters requested that critical habitat designation for endangered species be limited to occupied reaches.

Our response:

The Act defines critical habitat under section 3(5)(A) and allows for the designation of areas within and outside the geographical areas occupied by the species at the time of listing. There is no statutory requirement to limit critical habitat areas to only occupied areas. The Act requires that areas outside the geographical area occupied by the species be essential for the conservation of the species.

We have determined that unoccupied units are essential for the conservation of the Texas fatmucket and Texas pimpleback because they provide for the growth and expansion of the species within portions of their historical ranges. We identified areas outside the geographical areas currently occupied by the Texas fatmucket and Texas pimpleback as critical habitat in order to increase the stream length of critical habitat designations adjacent to existing small populations. These unoccupied areas are located immediately adjacent to currently occupied stream reaches, include one or more of the essential PBFs, and allow for expansion of existing populations necessary to improve population resiliency, extend physiographic representation, and reduce the risk of extinction for the species. The establishment of additional moderately healthy to healthy populations across the range of these species would reduce their risk of extinction. Improving the resiliency of populations in the currently occupied streams, and into identified unoccupied areas, will increase species viability. See Criteria Used to Identify Critical Habitat, below.

(17)

Comment:

Commenters requested that additional unoccupied areas be designated as critical habitat. These areas included the upstream portions of the Llano River in Edwards County, Texas, lower reaches of the Llano River, downstream of the City of Llano in Llano County, Texas, and Johnson Creek, which flows into the Guadalupe River in Kerr County, Texas.

Our response:

After identifying areas occupied by the species at the time of listing, we will identify specific areas outside the geographical area occupied by the species at the time of listing that the Secretary determines are essential for the conservation of the species. We evaluated the upstream portions of the South Llano River located in Edwards County and found that this reach of the river does not consistently remain wetted and does not provide suitable habitat through large portions of the stream in Edwards County and is not essential for the conservation of the species. Therefore, we did not designate the area as critical habitat. We evaluated the lower reaches of the Llano River near the river's confluence with the Little Llano River; these reaches are bookended by a dam in the City of Llano used for drinking water and a low-head dam which impounds Robinson Lake. Any suitable habitat between the two structures would be isolated from other existing populations due to stretches of unsuitable habitat and impairment of fish passage and therefore is not essential for the conservation of either Texas pimpleback or Texas fatmucket. Therefore, for the central Texas mussels, other than the unoccupied areas noted in this rule (TXFM-1c, TXFF-1b, TXPB-1a, and TXPB-5b),we are not designating additional areas outside the geographical area occupied by the species because we have not identified any additional unoccupied areas that meet the definition of critical habitat at this time.

(18)

Comment:

One commenter stated that proposed critical habitat unit TXFM-1 does not meet the criteria established for critical habitat since it does not contain all the PBFs described in the proposed rule as essential to the conservation of the species.

Our response:

In areas occupied at the time of listing a species as endangered or threatened, critical habitat is the specific areas on which are found the physical or biological features (PBFs) that are essential to the conservation of the species and that may require special management considerations or protection. It is not required that an area contain all PBFs in order to qualify as critical habitat. Unit TXFM-1 contains multiple PBFs (

e.g.,

presence of suitable substrates, connected instream habitats, and presence of host fish), and while the unit may need special management considerations to reduce sedimentation, improve water quality, maintain adequate flows, and improve habitat connectivity, it meets the definition of critical habitat for the Texas fatmucket.

(19)

Comment:

A commenter requested that the Service revise its discussion of water quality in the lower Colorado River mainstem below Austin to state that, according to the Texas Commission on Environmental Quality's (TCEQ's) 2020 Integrated Report (TCEQ 2020; entire), all water quality parameters being monitored are meeting the Texas Surface Water Quality Standards, and there are no impairments.

Our response:

Impairment, as defined through the Texas Surface Water Quality Standards, can differ from biological requirements for individual species. Because a stream reach meets legal standards for water quality parameters does not mean that the water quality meets the needs of the species. While we understand that the entire lower Colorado River mainstem below Austin may not experience conditions that are impacting freshwater mussel growth and survival, we feel that it is important to acknowledge that these conditions can exist at times in the reach of the river. For example, TCEQ produces an integrated report every 2 years that sets the ammonia criterion to denote impairment in segments of the Colorado River and includes any exceedances of this criteria (TCEQ 2022, entire). Chronic ammonia toxicity studies have shown that juvenile freshwater mussel species experience significant reductions in growth and survival when exposed to ammonia concentrations below these levels (Wang et al. 2007, p. 2054). Data presented in the TCEQ 2022 report would place the observed significant reductions in growth below the exceedance threshold of 0.33 milligrams per liter (mg/L) and reductions in survival near the observed exceedance mean value of 0.45 mg/L.

(20)

Comment:

Commenters requested more discussion of the threat of extended low-flow conditions in the lower Colorado River Basin.

Our response:

There are threats of extended low-flow conditions in the lower reaches of the lower Colorado River Basin, and we are actively working with the LCRA on the implementation of the LCRA Agreement, which includes conservation measures that would help further understand, avoid, and minimize the threat of low-flow conditions to freshwater mussels in this river basin.

The 2020 LCRA Water Management Plan (WMP) allocates a portion of its “firm water” supply to meet environmental flow needs within the lower Colorado River Basin (LCRA 2020, pp. ES-2-ES-3). These needs are determined through calculated monthly subsistence flow values and are based on results of an instream flow study in 2008 (Bio-West 2008, pp. 69-90) that investigated the flow relationships to aquatic habitat and the State-threatened blue sucker (

Cycleptus elongatus

), and they are consistent with the Texas Instream Flow Program methodology

(LCRA 2020, p. 2-2). While this 2008 study did not specifically focus on the habitat needs of freshwater mussels, a subsequent study in 2018 determined that the subsistence flows standards set by the WMP were adequate to protect instream freshwater mussel habitat during the periods expected to receive the lowest flow conditions (August; 107 cubic feet per second at the Wharton U.S. Geological Survey (USGS) gauge) (Bonner et al. 2018; entire). The LCRA Agreement states that an amendment to the 2020 WMP, which will consider additional information regarding flow or temperature needed for freshwater mussels or host fish, if available during that amendment process, is expected to occur not later than March 1, 2025 (LCRA 2023, pp. 60-63). While these flow assurances cannot entirely remove the threat of low flow conditions in the lower Colorado River, they can reduce the threat and ameliorate the instream conditions during these periods.

(21)

Comment:

A commenter stated that candidate conservation agreements with assurances (CCAAs) do not provide sufficient certainty of benefits to the species because they have limited authority, focus on a subset of the threats, allow permittees to withdraw at any time, and do not ensure future conditions. The commenter, therefore, requests that CCAAs not be used as a basis for critical habitat exclusions in the final rule.

Our response:

We evaluate whether an area should be excluded from critical habitat based on whether the benefits of exclusion outweigh the benefits of inclusion. As outlined in our Policy Regarding Implementation of Section 4(b)(2) of the Endangered Species Act (81 FR 7226), when we undertake a discretionary 4(b)(2) exclusion analysis, we will always consider areas covered by a permitted candidate conservation agreement with assurances (CCAA) and anticipate consistently excluding those areas from a critical habitat designation if incidental take caused by the activities in those areas is covered by the permit under section 10 of the Act and the CCAA meets all of the following conditions: the permittee is properly implementing the agreement and is expected to do so for the term of the agreement; the species for which critical habitat is being designated is a covered species in the agreement; and the agreement specifically addresses the habitat of the species for which critical habitat is being designated and meets the conservation needs of the species in the planning area.

We have determined that the BRA Agreement (BRA 2021, entire), LCRA Agreement (LCRA 2023, entire), and TRA Agreement (TRA 2023, entire) fulfill the above criteria, and we are excluding from this critical habitat designation some non-Federal lands covered by these three CCAAs that provide for the conservation of the Texas fawnsfoot, Texas pimpleback, and Balcones spike. The LCRA Agreement also provides for the conservation of Texas fatmucket. However, because no critical habitat units for the Texas fatmucket fall within reaches where the LCRA Agreement can directly reduce the primary threat of low water quantity, we have not excluded any proposed critical habitat for the Texas fatmucket based on the LCRA Agreement. Additionally, within the BRA and LCRA CCAAs, some non-Federal lands are included in the CCAAs' Covered Areas that we did not exclude from designated critical habitat (

i.e.,

river miles above Possum Kingdom Reservoir and river miles above the Highland lakes in the BRA and LCRA CCAAs respectively). These areas were not excluded because while the BRA and LCRA CCAAs provide overall net conservation benefits for the covered species, threat reduction efforts included as conservation measures within the agreements target other locations of their respective basins.

Possum Kingdom Reservoir represents the most upstream BRA-operated infrastructure in the Brazos River Basin. The BRA has no infrastructure and limited interests above Possum Kingdom reservoir, and therefore, has no way to directly influence freshwater mussel populations or their habitats in this portion of the basin (BRA 2021, p. 15). Regarding the LCRA CCAA, with the exception of two reservoirs LCRA owns and operates for purposes of power plant cooling which are not included in the critical habitat designation, LCRA does not own or operate any other water infrastructure on any tributaries or on the main stem of the Colorado River upstream of Lake Buchanan or on other tributaries or river segments that contribute flow to the Highland Lakes or the Colorado River within LCRA's broader service area.

The development and maintenance of effective working partnerships with non-Federal partners for the conservation of at-risk species is particularly important in areas such as Texas, a State with relatively little Federal landownership and many species of conservation concern. We find that excluding areas from critical habitat that are receiving long-term conservation and management for the purpose of protecting the habitat that supports the Texas fawnsfoot, Texas pimpleback, and Balcones spike will preserve our external partnerships in Texas and will encourage future collaboration towards conservation and recovery of listed species.

Because the agreements are voluntary, they demonstrate the commitment of the partners to the conservation actions; the CCAA process takes time and effort to put in place, and the agreement must result in a net conservation benefit to the species. The partnership benefits are significant and outweigh the potential regulatory, educational, and ancillary benefits of including the land in the final critical habitat designation for these three species; in addition, the subject areas are occupied by the species, so there is less incremental benefit to the unit being included in the critical habitat designation. Therefore, the BRA Agreement, LCRA Agreement, and TRA Agreement provide greater protection of habitat for the Texas fawnsfoot, Texas pimpleback, and Balcones spike than could be gained through the project-by-project analysis under a critical habitat designation.

(22)

Comment:

A commenter claimed that our proposed 4(d) rule was arbitrary and capricious because we did not assess the costs and benefits of the rule and therefore did not establish that the proposed 4(d) rule was necessary and advisable.

Our response:

The Act clearly prohibits the Service from considering economic or similar information when making listing, delisting, or reclassification decisions. Congress added this prohibition in the 1982 amendments to the Act when it introduced into section 4(b)(1) an explicit requirement that all decisions under section 4(a)(1) of the Act be based “solely on the basis of the best scientific and commercial data available.” Congress further explained this prohibition in the Conference Report accompanying the 1982 Amendments: “The principal purpose of these amendments is to ensure that decisions in every phase of the process pertaining to the listing or delisting of species are based solely upon biological criteria and to prevent non-biological considerations from affecting such decisions. These amendments are intended to expedite the decision-making process and to ensure prompt action in determining the status of the many species which may require the protections of the Act.” (H.R. Conf. Rep. No. 97-835, at 19 (1982).)

Therefore, following statutory framework and congressional intent, we do not conduct or develop economic impact analyses for classification decisions. Additionally, 4(d) rules concurrently issued with a classification rule are inherently a part of a

classification decision for a threatened species and therefore, a consideration of economic impacts does not apply. If we determine that a species meets the Act's definition of a threatened species, part of our consideration for completing the listing process is to consider what measures are necessary and advisable to provide for the conservation of the species under section 4(d) of the Act. We, therefore, consider a 4(d) rule to be a necessary phase of the listing process to put in place protections for threatened species.

(23)

Comment:

Commenters expressed concerns that threatened status may be insufficient for the Texas fawnsfoot and recommended it be assigned endangered status.

Our response:

The Act defines “endangered species” and “threatened species” and mandates five factors for consideration when determining a species' status under the Act. We have determined that endangered species status under the Act is not appropriate for the Texas fawnsfoot because the species maintains multiple, moderately resilient populations across its historical range with low risk of significant decline in the near term. Further, given its distribution and the health of its populations, the Texas fawnsfoot has sufficient redundancy and representation to withstand catastrophic events and novel changes in its environment in the near term. For these reasons, the Texas fawnsfoot is not currently in danger of extinction; it is, however, at risk of extinction in the foreseeable future because 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, within 25 to 50 years, 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 three populations are expected to become functionally extirpated, leaving no more than four unhealthy populations remaining after 25 years. See

Determination of Status: Texas Fawnsfoot,

below.

(24)

Comment:

A commenter requested that all species be listed as threatened to better promote voluntary habitat conservation.

Our response:

The Act requires us to make a listing determination using the best available scientific and commercial data after conducting a review of the status of the species. The primary difference between an endangered species and a threatened species is the timing of the risk of extinction. An “endangered species” is one that is in danger of extinction throughout all or a significant portion of its range. A “threatened species” is one that is likely to become endangered within the foreseeable future throughout all or a significant portion of its range; therefore, it is not currently in danger of extinction. After evaluating threats to the central Texas mussel species and assessing the cumulative effect of the threats under the Act's section 4(a)(1) factors, we found that Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and false spike have declined significantly in overall distribution and abundance. At present, most of their 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. We found that, for these six species, the threats are currently occurring and result in the species being in danger of extinction now. Therefore, a threatened status determination for these species would not be appropriate. The difference between endangered and threatened does not affect our ability to encourage voluntary conservation.

The listing of a species does not obstruct the development of conservation agreements or partnerships to conserve the species. Once a species is listed as either endangered or threatened, the Act provides many tools to advance the conservation of listed species. Conservation of listed species in many parts of the United States is dependent upon working partnerships with a wide variety of entities, including the voluntary cooperation of non-Federal landowners. Building partnerships and promoting cooperation with landowners are essential to understanding the status of species on non-Federal lands and may be necessary to implement recovery actions, such as reintroduction of listed species, habitat restoration, and habitat protection. Once a species is listed, for private or other non-Federal property owners, we offer voluntary safe harbor agreements that can contribute to the recovery of species, habitat conservation plans that allow activities (

e.g.,

grazing) to proceed while minimizing effects to species, funding through the Partners for Fish and Wildlife Program to help promote conservation actions, and grants to the States under section 6 of the Act.

(25)

Comment:

A commenter stated concerns that the Service focused on recent trends when modeling the impacts of climate change and disagreed that climate change will exacerbate identified threats in central Texas.

Our response:

Experts anticipate that climate change will lead to decreased water availability in Texas due to increased frequency and intensity of drought conditions in the State. During drought periods, pressure on freshwater resources, particularly increased evaporation in reservoirs and higher demands on groundwater pumping, in the State will lead to a decline in instream flows. Decreased instream flows correlate with increases in instream temperatures. In the SSA report, we relied upon numerous studies that have identified the effects of increased temperature on the growth, fitness, and survival of freshwater mussels (Bonner et al. 2018, p. 6; Ganser et al. 2015, p. 1712; Spooner and Vaughn 2008, pp. 312-313; Service 2022, p. 10). The combination of declines in instream flows and increasing temperatures of the remaining flows are anticipated to have a negative impact on remaining freshwater mussel populations.

(26)

Comment:

A commenter questioned whether mussels are actually declining due to human development and suggests that declines may have been occurring prior to human contact.

Our response:

While mussel populations surely ebbed and flowed prior to human development, it is well established that widespread declines of freshwater mussels have occurred in the last 50 to 75 years (Haag 2019, p. 43; Haag 2012, pp. 316-390). Through a combination of long-term monitoring and evidence in the historical record, it is clear that the decline of freshwater mussels is closely tied to advances in human infrastructure development (Haag 2012, pp. 316-390). In some cases, the ties can be closely pinpointed to the construction of a single structure (

e.g.,

large, power-generating hydrodam) and a resulting decline and eventual extirpation of an upstream freshwater mussel population (

e.g.,

extirpation of the elephant ear (

Elliptio crassidens

) population in the Upper Tennessee Basin following habitat fragmentation in tributaries of the Tennessee River (Johnson et al. 2012a, p. 89)). Regardless of whether declines occurred prior to human development, the declines of the central Texas mussel species in the recent past are well documented.

(27)

Comment:

A commenter requested clarification on whether the artificially sustained wastewater effluent flows are beneficial or detrimental to the central Texas mussels.

Our response:

Artificially sustained effluent flows can be beneficial to freshwater mussels by providing flow in low-flow and drying areas where mussels might otherwise desiccate. However, effluent flows can also be detrimental to freshwater mussels if the effluent water quality is poor. We consider both water quantity and quality when evaluating effluent and its impact on mussels. Parameters for healthy water quality and water quantity are defined in the SSA report (Service 2022, pp. 6-10), and we use these benchmarks as we evaluate the species' status now and in the future.

(28)

Comment:

A commenter disagreed that pesticides originating from agricultural sources are a pollutant of concern at levels experienced in the natural environment.

Our response:

Pesticides have been demonstrated to have both lethal and non-lethal effects on freshwater organisms, including freshwater mussels around the world (Milam et al. 2005, pp. 169-172; Bringolf et al. 2007a, p. 2099, 2007b, pp. 2105-2106, 2007c, p. 2092; Chmist et al. 2019, pp. 439-440). These studies have been completed for multiple, freshwater mussel life stages, including glochidia, juveniles, and adults, and have documented the harmful effects of a variety of herbicides, pesticides, and other chemical compounds. While we support and applaud agricultural producers' efforts to target applications and reduce run-off into adjacent waterways, it is still necessary to acknowledge the threat of the compounds to these mussels, as the specific lethal and non-lethal effects are not known for all mussel species, and spills, unregulated discharges, and errant applications are possible and would have significant negative effects on populations.

(29)

Comment:

A commenter claimed that the proposed listings are unnecessary as Texas already protects the central Texas mussels.

Our response:

In 2007 and 2008, we received petitions requesting that we list as endangered or threatened species and designate critical habitat for the Texas fatmucket, Texas fawnsfoot, Texas pimpleback, and false spike. (See Previous Federal Actions in the August 26, 2021, proposed rule (86 FR 47918-47919) for more information.) In 2009, the State of Texas listed the Texas fatmucket, Texas fawnsfoot, Texas pimpleback, and the false spike as threatened, launching an era of freshwater mussel conservation Statewide and bringing attention to this faunal group. However, once the Service is petitioned to list a species, we are required to complete our regulatory process which takes into account conservation efforts and State regulatory efforts in our listing determination. Under the requirements of the Act, we must conduct the required analysis and list the species if it is found to be warranted, and we cannot defer to any State listing. This rule codifies our listing determinations for the central Texas mussels.

I. Final Listing Determination

Background

A thorough review of the taxonomy, life history, and ecology of the Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe orb, Texas pimpleback, Balcones spike, and false spike, referred to as the central Texas mussels, is presented in the SSA report (Service 2022, pp. 4-44).

Guadalupe Fatmucket

The Guadalupe fatmucket (

Lampsilis bergmanni

) was recently discovered to be a separate and distinct species from Texas fatmucket (Inoue et al. 2018, pp. 5-6; Inoue et al. 2020, entire), and the Service now recognizes the Guadalupe fatmucket as a new species that occurs only in the Guadalupe River Basin. Because the Guadalupe fatmucket is so similar to the Texas fatmucket and better information is not yet available, we conclude the Guadalupe fatmucket has similar habitat needs (headwater habitats in gravel or bedrock fissures) and host fish (sunfishes) as the Texas fatmucket, below.

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; it 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 to 25 years (Haag and Rypel 2010, pp. 4-6), and we expect Guadalupe fatmucket to have a similar lifespan.

Guadalupe fatmucket is currently found in one population, which occurs in 52 miles (84 km) of the Guadalupe River Basin in Kendall and Kerr Counties, Texas (Randklev et al. 2017c, p. 4) (see table 1, below; see also figure 5.11 in Service 2022, p. 118).

Table 1—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

Kendall and Kerr Co., TX

52 (84)

2018 (22)

2019 (shells)

Texas Fatmucket

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. 2020, pp. 93-111); therefore, we now know the Texas fatmucket to only occur 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. 2012b, 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).

We expect Texas fatmucket has a similar lifespan to related species in the genus

Lampsilis

from the southeast United States, which reach a maximum age of 13 to 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. 2017c, p. 4) in five populations: lower Elm Creek, upper/middle San Saba River, Llano River, Pedernales River, and Onion Creek (see table 2, below; see also figure 5.5 in Service 2022, p. 91). Isolated individuals not considered part of larger functioning populations have been found in Cherokee Creek, Bluff Creek, and the North Llano River.

Table 2—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 (19)

2005 (no live animals)

2008 (1)

2019 (1)

Upper/Middle San Saba River

San Saba River

Mason, McCulloch, Menard, and San Saba Co., TX

62 (100)

2005 (2)

2012 (8)

2013 (5)

2016 (29)

2017 (87)

2017 (71)

Llano River

Llano River, South Llano River

Kimble, Llano, and Mason Co., TX

127 (204)

2016 (72)

2017 (47)

2017 (5)

2018 (635)

2019 (6)

2019 (18)

2021 (99)

Pedernales River

Pedernales River, Live Oak Creek

Blanco, Gillespie, and Hays Co., TX

79 (127)

2011 (1)

2012 (1)

2017 (18)

Onion Creek

Onion Creek

Travis Co., TX

24 (38)

2010 (3)

2018 (1)

2021 (5)

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 expect 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 to 18 years (Haag and Rypel 2010, pp. 4-6), and we expect the lifespan of Texas fawnsfoot to be similar.

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 occur 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 (see table 3, below; see also figure 5.7 in Service 2022, p. 101). Texas fawnsfoot was historically distributed throughout the Colorado and Brazos River basins (Howells 2014, pp. 111-112; 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 the Leon River, but they are currently extirpated (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.

Table 3—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

Anderson, Houston, Leon, Madison, and Navarro 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

Austin, Brazos, Burleson, Falls, Fort Bend, Grimes, McLennan, Milam, Robertson, Waller, and Washington Co., TX

346 (557)

2014 (188)

2017 (28)

2021 (1)

San Saba/Colorado Rivers

San Saba River, Colorado River

Mills and San Saba Co., TX

43 (69)

2017 (0)

2018 (2)

Lower Colorado River

Colorado River

Colorado, Matagorda, and Wharton Co., TX

109 (175)

2010 (52)

2015 (10)

2017 (9)

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 (

Ictalurus punctatus

), flathead catfish (

Pylodictis olivarus

), and tadpole madtom (

Noturus gyrinus

) 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 the reproduction, ecological interactions, and habitat requirements of Guadalupe orb are similar to those of the closely related Texas pimpleback.

The Guadalupe orb is only known to occur in the Guadalupe River Basin in two separate and isolated populations: the upper Guadalupe River and the lower Guadalupe River (see table 4, below; see also figure 5.13 in Service 2022, p. 125). 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).

Table 4—Current Guadalupe Orb Populations

Population

Streams included

Counties

Occupied

reach length

(mi (km))

Recent collection years

(numbers)

Upper Guadalupe River

Guadalupe River

Comal, Kendall, and Kerr Co., TX

95 (153)

2013 (1)

2017 (10)

2018 (2)

Lower Guadalupe River

Guadalupe River, San Marcos River

Caldwell, DeWitt, Gonzales, Guadalupe, and Victoria Co., TX

181 (291)

2014-2015 (893)

2017 (41)

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 are now considered to occur only in the Colorado River Basin of Texas. The 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, flathead catfish, and tadpole madtom are host fish for the Texas pimpleback (Dudding et al. 2019, p. 2). Related species have miniature glochidia and also 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 to 72 years (Haag and Rypel 2010, p. 10).

Texas pimpleback are known to occur 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 (see table 5, below; see also figure 5.9 in Service 2022, p. 110). 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. 2017c, pp. 109-110).

Table 5—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

Brown, Coleman, McCulloch, Mills, and San Saba Co., TX

178 (286)

2012 (247)

2014 (481)

2017 (20)

2017 (97)

2018 (42)

2019 (23)

Llano River

Llano River

Mason Co., TX

5 (8)

2012 (10)

2016 (1)

2017 (23)

2018 (1)

2021 (46)

Lower Colorado River

Colorado River

Colorado and Wharton Co., TX

98 (158)

2014 (49)

2017 (8)

2018 (30)

Balcones Spike

The Balcones spike (

Fusconaia iheringi

) was recently discovered to be a separate and distinct species from false spike (Smith et al. 2020, entire), and the Service now recognizes the Balcones spike as a new species that occurs in the Brazos and Colorado River basins. Because the Balcones spike has recently been split from false spike, species-specific data are not yet available, and so we expect the Balcones spike has similar habitat needs (larger creeks and rivers with sand, gravel, or cobble substrates, slow to moderate flows) and host fish (red shiner (

Cyprinella lutrensis

) and blacktail shiner (

Cyprinella venusta

)) as the false spike.

The Balcones spike is a small to medium-sized freshwater mussel (to approximately 3.8 inches (in) (96 millimeters (mm))) with a yellow-green to brown elongate shell, sometimes with greenish rays. While similar in appearance to false spike, Balcones spike usually has a sharper posterior ridge and shinier periostracum when compared to false spike. For a more detailed description, see Smith et al. 2020 (entire). Related species in the genus

Fusconaia

from the southeast United States reach a maximum age of 15 to 51 years (Haag and Rypel 2010, pp. 4-6). The closely related congener species, false spike, is thought to have a maximum age of 15 years (Dudding et al. 2019, p. 167) and to reach sexual maturity around 5 years of age (Dudding et al. 2019, p. 167).

Balcones spike is currently found in three populations in the Little River and some tributaries (Brazos River Basin), the lower San Saba River (Colorado River Basin), and the Llano River (Colorado River Basin) (see table 6, below; see also figure 5.3 in Service 2022, p. 85).

Table 6—Current Balcones Spike Populations

Population

Streams included

Counties

Occupied

reach length

(mi (km))

Recent collection years

(numbers collected)

Little River and tributaries

Little River, Brushy Creek, San Gabriel River

Milam and Williamson Co., TX

41 (66)

2015 (29)

2021 (13)

2021 (1)

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)

2021 (14)

False Spike

The false spike is native to the Guadalupe Basin 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). Recently, individuals that had been known as false spike in the Brazos and Colorado River basins were found to be a new species (Smith et al. 2020, entire); therefore, the false spike occurs only in the Guadalupe River Basin.

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 was 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 and red shiner (Dudding et al. 2019, p. 16).

Related species in the genus

Fusconaia

from the southeast United States reach a maximum age of 15 to 51 years (Haag and Rypel 2010, pp. 4-6). False spike is thought to have a maximum age of 15 years (Dudding et al. 2019, p. 167) and to reach sexual maturity around 5 years of age (Dudding et al. 2019, p. 167).

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 2010, p. 4; Randklev et al. 2011, p. 17). The patchy distribution of false spike could be related to host fish relationships (Dudding et al. (2019, pp. 16-17); that is, because their host fish have a small home range, have 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, there is only one known population of false spike in the lower Guadalupe River (Guadalupe River Basin) (see table 7, below; see also figure 5.2 in Service 2022, p. 81). For more information on this population, see the SSA report (Service 2022, pp. 75-82). False spike is estimated to have been extirpated from the remainder of its historical range throughout the Guadalupe Basin of central Texas (reviewed in Randklev et al. 2017c, pp. 12-13).

Table 7—Current False Spike Population

Population

Streams included

Counties

Occupied

reach length

(mi (km))

Recent collection years

(number collected)

Lower Guadalupe River

Guadalupe River

DeWitt, Gonzales, and Victoria Co., TX

102 (164)

2014-2015 (652)

Regulatory and Analytical Framework

Regulatory Framework

Section 4 of the Act (16 U.S.C. 1533) and the implementing regulations in title 50 of the Code of Federal Regulations set forth the procedures for determining whether a species is an endangered species or a threatened species, issuing protective regulations for threatened species, and designating critical habitat for endangered and species. On April 5, 2024, jointly with the National Marine Fisheries Service, the Service issued a final rule that revised the regulations in 50 CFR 424 regarding how we add, remove, and reclassify endangered and threatened species to the lists and the criteria for designating listed species' critical habitat (89 FR 24300). On the same day, the Service published a final rule revising our protections for endangered species and threatened species at 50 CFR 17 (89 FR 23919). These final rules are now in effect and are incorporated into the current regulations. Our analysis for this decision applied our current regulations. Given that we proposed listing and critical habitat for these species under our prior regulations (revised in 2019), we have also undertaken an analysis of whether our decision would be different if we had continued to apply the 2019 regulations and we concluded that the decision would be the same. The analyses under both the regulations currently in effect and the 2019 regulations are available on

https://www.regulations.gov

.

The Act defines an “endangered species” as a species that is in danger of extinction throughout all or a significant portion of its range, and a “threatened species” as a species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. The Act requires that we determine whether any species is an endangered species or a threatened species because of any of the following factors:

(A) The present or threatened destruction, modification, or curtailment of its habitat or range;

(B) Overutilization for commercial, recreational, scientific, or educational purposes;

(C) Disease or predation;

(D) The inadequacy of existing regulatory mechanisms; or

(E) Other natural or manmade factors affecting its continued existence.

These factors represent broad categories of natural or human-caused actions or conditions that could have an effect on a species' continued existence. In evaluating these actions and conditions, we look for those that may have a negative effect on individuals of the species, as well as other actions or conditions that may ameliorate any negative effects or may have positive effects.

We use the term “threat” to refer in general to actions or conditions that are known to or are reasonably likely to negatively affect individuals of a species. The term “threat” includes actions or conditions that have a direct impact on individuals (direct impacts), as well as those that affect individuals through alteration of their habitat or required resources (stressors). The term “threat” may encompass—either together or separately—the source of the action or condition or the action or condition itself.

However, the mere identification of any threat(s) does not necessarily mean that the species meets the statutory definition of an “endangered species” or a “threatened species.” In determining whether a species meets either definition, we must evaluate all identified threats by considering the species' expected response and the effects of the threats—in light of those actions and conditions that will ameliorate the threats—on an individual, population, and species level. We evaluate each threat and its expected effects on the species, then analyze the cumulative effect of all of the threats on the species as a whole. We also consider the cumulative effect of the threats in light of those actions and conditions that will have positive effects on the species, such as any

existing regulatory mechanisms or conservation efforts. The Secretary determines whether the species meets the definition of an “endangered species” or a “threatened species” only after conducting this cumulative analysis and describing the expected effect on the species now and in the foreseeable future.

The Act does not define the term “foreseeable future,” which appears in the statutory definition of “threatened species.” Our implementing regulations at 50 CFR 424.11(d) set forth a framework for evaluating the foreseeable future on a case-by-case basis which is further described in the 2009 Memorandum Opinion on the foreseeable future from the Department of the Interior, Office of the Solicitor (M-37021, January 16, 2009; “M- Opinion,” available online at

https://www.doi.gov/sites/doi.opengov.ibmcloud.com/files/uploads/M-37021.pdf

). The foreseeable future extends as far into the future as the U.S. Fish and Wildlife Service and National Marine Fisheries Service (hereafter, the Services) can make reasonably reliable predictions about the threats to the species and the species' responses to those threats. We need not identify the foreseeable future in terms of a specific period of time. We will describe the foreseeable future on a case-by-case basis, using the best available data and taking into account considerations such as the species' life-history characteristics, threat-projection timeframes, and environmental variability. In other words, the foreseeable future is the period of time over which we can make reasonably reliable predictions. “Reliable” does not mean “certain”; it means sufficient to provide a reasonable degree of confidence in the prediction, in light of the conservation purposes of the Act.

Analytical Framework

The SSA report documents the results of our comprehensive biological review of the best scientific and commercial data regarding the status of the species, including an assessment of the potential threats to the species. The SSA report does not represent our decision on whether the species should be listed as endangered or threatened species under the Act. However, it does provide the scientific basis that informs our regulatory decisions, which involve the further application of standards within the Act and its implementing regulations and policies.

To assess the viability of the seven central Texas mussels, we used the three conservation biology principles of resiliency, redundancy, and representation (Shaffer and Stein 2000, pp. 306-310). Briefly, resiliency is the ability of the species to withstand environmental and demographic stochasticity (for example, wet or dry, warm or cold years), redundancy is the ability of the species to withstand catastrophic events (for example, droughts, large pollution events), and representation is the ability of the species to adapt to both near-term and long-term changes in its physical and biological environment (for example, climate conditions, pathogens). In general, species viability will increase with increases in resiliency, redundancy, and representation (Smith et al. 2018, p. 306). Using these principles, we identified the species' ecological requirements for survival and reproduction at the individual, population, and species levels, and described the beneficial and risk factors influencing the species' viability.

The SSA process can be categorized into three sequential stages. During the first stage, we evaluated each 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. Throughout all of these stages, we used the best available information to characterize viability as the ability of a species to sustain populations in the wild over time. We use this information to inform our regulatory decision.

The following is a summary of the key results and conclusions from the SSA report; the full SSA report can be found at Docket FWS-R2-ES-2019-0061 on

https://www.regulations.gov

and at

https://www.fws.gov/office/austin-ecological-services

.

Summary of Biological Status and Threats

In this discussion, we review the biological condition of the species and its resources, and the threats that influence the species' current and future condition, 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 sufficiently resilient. A number of factors influence the resiliency of central Texas mussel populations, including occupied stream length, abundance, and recruitment. While some of the seven 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 are 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 more than 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, sufficiently resilient mussel populations must occupy stream reaches long enough such that stochastic events that affect individual mussel beds do not eliminate the entire population, and 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 mi (32 and 79 river km) have some resiliency to stochastic events, and populations occupying reaches less than 20 miles (32 km) have little resiliency.

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 the central Texas mussel species to be healthy (

i.e.,

sufficiently 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 the 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

Adequately 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, as sampling for these species involves tactile searches and mussels smaller than 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 (about 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 seven central Texas mussels now and in the future. In this 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 seven species. Where the effects are expected to be similar, we present one discussion that applies to all seven 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 B), 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 seven species of the 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). In this context, sedimentation explicitly is restricted to increased fine sediments entering a stream system at a rate beyond the naturally occurring losing rate and does not replace the use of the broader term of turbidity. In addition to increased levels of fine sediment, turbidity is also influenced by concentrations of fine organic and inorganic matter, soluble organic compounds, algae, and other microscopic organisms. Changes in stream turbidity are not inherently an indicator of increased sedimentation as turbidity can naturally vary from stream to stream in Texas due to unrelated factors (

e.g.,

stream primary productivity). 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). 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 the central Texas mussels face the risk of fine sediment accumulation to varying degrees. Multiple populations of the seven central Texas mussel species are experiencing increased sedimentation, including, in particular, the Clear Fork Brazos River (Texas fawnsfoot), middle and lower Brazos River (Balcones spike and Texas fawnsfoot), and lower Colorado River (Texas pimpleback and Texas fawnsfoot). In the future, we expect sediment deposition to continue to increase across the range of all seven 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 into the aquatic environment (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 rank lower in waters that are polluted or otherwise degraded by contaminants. Freshwater mussels are not generally found for many miles downstream of municipal WWTPs (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 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 WWTPs because freshwater mussels are particularly sensitive to increased ammonia levels (Augspurger et al. 2003, p. 2569). Elevated concentrations (greater than 0.2 parts per billion) of un-ionized ammonia (NH

3

) in the interstitial spaces of benthic habitats 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 = parts per million (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 pimpleback (

Cyclonaias pustulosa,

a species native to central Texas but not included in this listing), the revised Environmental Protection Agency 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 have yet to be experimentally investigated.

Municipal wastewater contains both ionized and un-ionized ammonia, and wastewater discharge permits issued by the 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. Approximately 480 discharge permits have been issued for the Brazos River watershed alone from its headwaters above Possum Kingdom Lake down to the Gulf of Mexico (TCEQ 2018, entire), and WWTP outfalls are numerous in other basins throughout the ranges of the central Texas mussels. 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).

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 (86 °F) and approaching 40 °C (104 °F)) 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 the 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 to 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). The behavioral response of valve closure to high salinity concentrations (greater than 2 ppt) is the likely mechanism for reduced metabolic rates, reduced feeding, and reduced reproductive success based on reported sublethal effects of salinity of more than 2 ppt for the Texas pimpleback (Bonner et al. 2018, pp. 155-156).

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 the central Texas mussels. Not only can temperature be a biological, physical, and chemical stressor, the toxicity of many pollutants (

e.g.,

ammonia, mercury) to aquatic organisms increases at higher temperatures. We foresee threats to water quality increasing into the future as demand and competition for limited water resources grows.

Altered Hydrology—Inundation

All seven 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 the 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 of the 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 the central Texas mussels. In large reservoirs, deep water is very cold and often devoid of oxygen and necessary nutrients. Cold water (less than 11 °C (52 °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 (TPWD 2007, p. ii), and are cold enough to support a recreational nonnative 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 riverbed (

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 the central Texas mussels. There are now 27 major reservoirs, 16 of which have more than 50,000 acre-feet of storage, in the Brazos River Basin (BBEST 2012, p. 33); 31 major reservoirs in the Colorado River Basin, including the Highland Lakes (TWDB 2018, p. 1); 9 major reservoirs on the Guadalupe River (BBEST 2011, 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 (see 83 FR 16061; April 13, 2018), 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 (LCRA 2018, 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 (BRA 2018a, 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—are threats to 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, impacts 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 (USGS 2019, unpaginated).

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 2008, pp. 812, 814, 848, 870, 878, 880), and overall river discharge for the Colorado River 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 2008, p. 892), Pedernales River at Fredericksburg (USGS 2008, p. 896), Onion Creek near Driftwood, and Onion Creek at Highway 183 (flows appear to become more erratic, characteristic of a developing watershed) (USGS 2008, pp. 930, 946). In the San Saba River, continuing or increasing surface and alluvial aquifer groundwater withdrawals in combination with drought are 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 2008, pp. 578, 600, 626, 638; BRA 2018b, p. 6), although baseflows are maintained somewhat due to releases from Lake Granbury and other reservoirs in the upper basin (USGS 2008, p. 644; BRA 2018b, 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 2008, pp. 652, 676, 766, 776; BRA 2018b, 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 2008, pp. 754, 766, 776; BRA 2018b, p. 6). Lake Limestone releases also appear to be contributing to higher base flows in the Lower Brazos (BRA 2018b, p. 6). Flows have declined in the upper Guadalupe River (USGS 2008, pp. 992, 994, 1000, 1018) but appear relatively unchanged at Comfort and Spring Branch and in the San Marcos River (USGS 2008, pp. 1004, 1006, 1022), and in the lower Guadalupe River (USGS 2008, 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 2008, pp. 964, 966). In the Trinity River, low flows are higher (elevated baseflows) than they were in the past (USGS 2008, 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 the central Texas mussels in the tributary streams is reduced and could eventually cease to exist (Randklev et al. 2018, pp. 13-14). While the 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 2018, entire). In 2017, Service, TPWD, and Texas Department of Transportation (TxDOT) biologists noted 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). Prior to the flooding events, this site held the highest mussel abundance (Bonner et al. 2018, pp. 242-243) and represented high-quality habitat within the Colorado River Basin. After 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 cubic feet per second (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) (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), which is occupied by the false spike and Guadalupe orb, in 2015 (Giardino and Rowley 2016, pp. 70-72). The usual drought/flood cycle in central Texas can be characterized by long periods of time without 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 20th 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 the 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 the 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 (Robertson 2023, entire).

Repeated collections and handling can cause disturbance to the growth of individual mussels. Freshwater mussels close their shell in response to handling, which can lead to the production of a disturbance ring in the shell. When closing its shell, it is possible for the mussel's mantle-shell margin connection to be disrupted as the mantle tissue is retracted. This can result in the production of a growth disturbance ring when this mantle-shell connection is re-established in a slightly differing location than the original collection causing a misalignment of the prismatic layer and periostracum (Haag 2012, p. 11). Additionally, the closure of the shell during handling can prevent feeding (Haag 2012, p. 29), alter respiration rate and heart patterns (Haag 2012, pp. 29-30), and require additional energy expenditure to retract and then re-establish the foot in substrate to prevent dislodgment when returned to stream substrates.

Handling of freshwater mussels can also have a detrimental impact on the reproductive efforts of individual mussels and possibly the overall population. It is commonly observed that short-term brooders will abort their glochidia due to disturbances or handling (Haag 2012, p. 199). In species or individuals that are not able to successfully produce multiple broods within a single breeding season, the abortion of these glochidia can cause the loss of reproductive output for that individual for the year. If many animals have their reproductive output curtailed at a single location due to widespread sampling of a site, the abortion of glochidia by multiple animals in response to handling can lead to an overall reduced reproductive output at a site. If this sampling effort is repeated multiple times during a breeding season and across multiple years, there is potential for the disturbance of multiple years of breeding efforts for many animals at a single location. This extended disturbance can lead to multiple years of failed recruitment and potentially the loss of multiple age-class cohorts within a population at the site.

Loss of reproductive effort due to handling could be compounded by the intentional collection of gravid individuals, especially the potential effects on the native populations if an excessive number of females are removed, for use as broodstock for propagation or research purposes (Jones et al. 2006, p. 531). For example, pulling many gravid females from a site may prevent in-situ reproduction from occurring due to essentially removing a large percentage of that year's reproducing portion of the population from the site.

Barriers to Fish Movement

The 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 common, widespread species in 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 the 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 is already taking 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 (Loáiciga 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 the 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 2018, 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 (Service 2022, pp. 142-145, 149, and appendix C).

Species Current 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 factors (occupied stream length, abundance, and reproduction) and three habitat factors (substrate, flowing water, and water quality) 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 estimated 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 with low abundance and little evidence of reproduction or recruitment. Very few individuals have been found in recent years. The upper Guadalupe River in this reach already experiences very low water levels, and these low water events are expected to continue into the future; the population is 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. 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 face threats from 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 the river gains streamflow from groundwater except for 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, including Texas fatmucket and Texas pimpleback, 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; TCEQ 2013, entire). 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, and collection of the species is frequent at this location, although there has been limited evidence that the population is successfully reproducing. We expect flows to continue to decline and the frequency of extreme flow events to increase, leading to increased sedimentation, decreased water quality, and scour. As a result, the population of Texas fatmucket is expected to decline.

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 very low Texas fatmucket abundance in the river result in a population that is likely to be extirpated and currently is unhealthy.

Onion Creek:

Few live individuals of Texas fatmucket have 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.

Guadalupe Orb

There are two known 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 Guadalupe orb populations are moderately healthy.

Upper Guadalupe River:

The Guadalupe orb population in the upper Guadalupe River occurs over approximately 95 river mi (153 river km), and water quantity and quality are in moderate condition. However, the population occurs in low numbers, with limited 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. Thus, the stream reach is vulnerable to ongoing and future hydrological alterations that reduce flows, and thereby result in substrate and water quality degradations, during critical conditions.

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's partners. These measures bolster 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 the population at risk of decline.

Texas Pimpleback

There are five known 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 in moderate condition.

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. Therefore, this population is moderately healthy.

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, and the population 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

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