Endangered and Threatened Wildlife and Plants; Endangered Species Status for Texas Hornshell, 52796-52809 [2016-18816]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 81, Number 154 (Wednesday, August 10, 2016)]
[Proposed Rules]
[Pages 52796-52809]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-18816]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2016-0077; 4500030113]
RIN 1018-BB34


Endangered and Threatened Wildlife and Plants; Endangered Species 
Status for Texas Hornshell

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to 
list the Texas hornshell (Popenaias popeii), a freshwater mussel 
species from New Mexico and Texas, as an endangered species under the 
Endangered Species Act (Act). If we finalize this rulemaking as 
proposed, it would extend the Act's protections to this species.

DATES: We will accept comments received or postmarked on or before 
October 11, 2016. Comments submitted electronically using the Federal 
eRulemaking Portal (see ADDRESSES, below) must be received by 11:59 
p.m. Eastern Time on the closing date. We must receive requests for 
public hearings, in writing, at the address shown in FOR FURTHER 
INFORMATION CONTACT by September 26, 2016.

ADDRESSES: You may submit comments by one of the following methods:
    (1) Electronically: Go to the Federal eRulemaking Portal: https://www.regulations.gov. In the Search box, enter FWS-R2-ES-2016-0077, 
which is the docket number for this rulemaking. Then, in the Search 
panel on the left side of the screen, under the Document Type heading, 
click on the Proposed Rules link to locate this document. You may 
submit a comment by clicking on ``Comment Now!''
    (2) By hard copy: Submit by U.S. mail or hand-delivery to: Public 
Comments Processing, Attn: FWS-R2-ES-2016-0077, U.S. Fish and Wildlife 
Service, MS: BPHC, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
    We request that you send comments only by the methods described 
above. We will post all comments on https://www.regulations.gov. This 
generally means that we will post any personal information you provide 
us (see Public Comments, below, for more information).

FOR FURTHER INFORMATION CONTACT: Chuck Ardizzone, U.S. Fish and 
Wildlife Service, Texas Coastal Ecological Services Field Office, 17629 
El Camino Real #211, Houston, TX 77058; by telephone 281-286-8282; or 
by facsimile 281-488-5882. Persons who use a telecommunications device 
for the deaf (TDD) may call the Federal Information Relay Service 
(FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION: 

Executive Summary

    Why we need to publish a rule. Under the Act, if a species is 
determined to be an endangered or threatened species throughout all or 
a significant portion of its range, we are required to promptly publish 
a proposal in the Federal Register and make a determination on our 
proposal within 1 year. Critical habitat shall be designated, to the 
maximum extent prudent and determinable, for any species determined to 
be an endangered or threatened species under the Act. Listing a species 
as an endangered or threatened species and designations and revisions 
of critical habitat can only be completed by issuing a rule.
    This rulemaking proposes the listing of the Texas hornshell 
(Popenaias popeii) as an endangered species. The Texas hornshell is a 
candidate species for which we have on file sufficient information on 
biological vulnerability and threats to support preparation of a 
listing proposal, but for which development of a listing regulation has 
been precluded by other higher priority listing activities. This 
proposed rule reassesses all available information regarding the status 
of and threats to the Texas hornshell.
    The basis for our action. Under the Act, we can determine that a 
species is an endangered or threatened species based on any of five 
factors, acting alone or in combination: (A) The present or threatened 
destruction, modification, or curtailment of its habitat or range; (B) 
overutilization for commercial, recreational, scientific, or 
educational purposes; (C) disease or predation; (D) the inadequacy of 
existing regulatory mechanisms; or (E) other natural or manmade factors 
affecting its continued existence. We have determined that the Texas 
hornshell is in danger of extinction due to habitat loss from loss of 
water flow, decreased water quality, and increased accumulation of fine 
sediments (Factor A) and predation (Factor C).
    We will seek peer review. We will seek comments from independent 
specialists to ensure that our determination is based on scientifically 
sound data, assumptions, and analyses. We will invite these peer 
reviewers to comment on our listing proposal. Because we will consider 
all comments and information we receive during the comment period, our 
final determination may differ from this proposal.
    We prepared a species status assessment report (SSA report) for the 
Texas hornshell. The SSA report documents the results of the 
comprehensive biological status review for the Texas hornshell and 
provides an account of the species' overall viability through 
forecasting of the species' condition in the future (Service 2016, 
entire). We received feedback from four scientists with expertise in 
freshwater mussel biology, ecology, and genetics as peer review of the 
SSA report. The reviewers were generally supportive of our approach and 
made suggestions and comments that strengthened our analysis. The SSA 
report and other materials relating to this proposal can be found at 
https://www.regulations.gov under Docket No. FWS-R2-ES-2016-0077.

Information Requested

Public Comments

    We intend that any final action resulting from this proposed rule 
will be based on the best scientific and commercial data available and 
be as accurate and as effective as possible. Therefore, we request 
comments or information from other concerned governmental agencies, 
Native American tribes, the scientific community, industry, or any 
other interested parties concerning this proposed rule. We particularly 
seek comments concerning:

[[Page 52797]]

    (1) The Texas hornshell's biology, range, and population trends, 
including:
    (a) Biological or ecological requirements of the species, including 
habitat requirements for feeding and spawning;
    (b) Genetics and taxonomy;
    (c) Historical and current range, including distribution patterns;
    (d) Historical and current population levels, and current and 
projected trends; and
    (e) Past and ongoing conservation measures for the species, its 
habitat, or both.
    (2) Factors that may affect the continued existence of the species, 
which may include habitat modification or destruction, overutilization, 
disease, predation, the inadequacy of existing regulatory mechanisms, 
or other natural or manmade factors.
    (3) Biological, commercial trade, or other relevant data concerning 
any threats (or lack thereof) to this species and existing regulations 
that may be addressing those threats.
    (4) Additional information concerning the historical and current 
status, range, distribution, and population size of this species, 
including the locations of any additional populations of this species, 
particularly in Mexico.
    (5) Information related to climate change within the range of the 
Texas hornshell and how it may affect the species' habitat.
    (6) The reasons why areas should or should not be designated as 
critical habitat as provided by section 4 of the Act (16 U.S.C. 1531 et 
seq.)
    (7) Specific information on:
    (a) The amount and distribution of habitat for the Texas hornshell;
    (b) What areas, that are currently occupied and that contain the 
physical and biological features essential to the conservation of the 
Texas hornshell, should be included in a critical habitat designation 
and why;
    (c) Special management considerations or protection that may be 
needed for the essential features in potential critical habitat areas, 
including managing for the potential effects of climate change; and
    (d) What areas not occupied at the time of listing are essential 
for the conservation of the species and why.
    Please include sufficient information with your submission (such as 
scientific journal articles or other publications) to allow us to 
verify any scientific or commercial information you include.
    Please note that submissions merely stating support for or 
opposition to the action under consideration without providing 
supporting information, although noted, will not be considered in 
making a determination, as section 4(b)(1)(A) of the Act directs that 
determinations as to whether any species is an endangered or threatened 
species must be made ``solely on the basis of the best scientific and 
commercial data available.''
    You may submit your comments and materials concerning this proposed 
rule by one of the methods listed in ADDRESSES. We request that you 
send comments only by the methods described in ADDRESSES.
    If you submit information via https://www.regulations.gov, your 
entire submission--including any personal identifying information--will 
be posted on the Web site. If your submission is made via a hardcopy 
that includes personal identifying information, you may request at the 
top of your document that we withhold this information from public 
review. However, we cannot guarantee that we will be able to do so. We 
will post all hardcopy submissions on https://www.regulations.gov.
    Comments and materials we receive, as well as supporting 
documentation we used in preparing this proposed rule, will be 
available for public inspection on https://www.regulations.gov, or by 
appointment, during normal business hours, at the U.S. Fish and 
Wildlife Service, Texas Coastal Ecological Services Field Office (see 
FOR FURTHER INFORMATION CONTACT).

Public Hearing

    Section 4(b)(5) of the Act provides for one or more public hearings 
on this proposal, if requested. Requests must be received within 45 
days after the date of publication of this proposed rule in the Federal 
Register (see DATES, above). Such requests must be sent to the address 
shown in FOR FURTHER INFORMATION CONTACT. We will schedule public 
hearings on this proposal, if any are requested, and announce the 
dates, times, and places of those hearings, as well as how to obtain 
reasonable accommodations, in the Federal Register and local newspapers 
at least 15 days before the hearing.

Peer Review

    In accordance with our joint policy on peer review published in the 
Federal Register on July 1, 1994 (59 FR 34270), we will seek the expert 
opinions of five appropriate and independent specialists regarding this 
proposed rule. The purpose of peer review is to ensure that our listing 
determination is based on scientifically sound data, assumptions, and 
analyses. We invite comment from the peer reviewers during the public 
comment period on this proposed rule.

Previous Federal Actions

    We identified the Texas hornshell as a Category 2 candidate species 
in our January 6, 1989, Review of Vertebrate Wildlife (54 FR 554). 
Category 2 candidates were defined as species for which we had 
information that proposed listing was possibly appropriate, but 
conclusive data on biological vulnerability and threats were not 
available to support a proposed rule at the time. The species remained 
a Category 2 candidate in subsequent annual candidate notices of review 
(CNOR) (56 FR 58804, November 21, 1991, and 59 FR 58982, November 15, 
1994). In the February 28, 1996, CNOR (61 FR 7596), we discontinued the 
designation of Category 2 species as candidates; therefore, the Texas 
hornshell was no longer a candidate species.
    Subsequently, in 2001, the Texas hornshell was added to the 
candidate list (66 FR 54808, October 30, 2001). Candidates are those 
fish, wildlife, and plants for which we have on file sufficient 
information on biological vulnerability and threats to support 
preparation of a listing proposal, but for which development of a 
listing rule is precluded by other higher priority listing activities. 
The Texas hornshell was included in all of our subsequent annual CNORs 
(67 FR 40657, June 13, 2002; 69 FR 24876, May 4, 2004; 70 FR 24870, May 
11, 2005; 71 FR 53756, September 12, 2006; 72 FR 69034, December 6, 
2007; 73 FR 75176, December 10, 2008; 74 FR 57804, November 9, 2009; 75 
FR 69222, November 10, 2010; 76 FR 66370, October 26, 2011; 77 FR 
69994, November 21, 2012; 78 FR 70104; November 22, 2013; 79 FR 72450, 
December 5, 2014; and 80 FR 80584, December 24, 2015). On May 11, 2004, 
we were petitioned to list the Texas hornshell, although no new 
information was provided in the petition. Because we had already found 
the species warranted listing, no further action was taken on the 
petition.
    On September 9, 2011, the Service entered into two settlement 
agreements regarding species on the candidate list at that time 
(Endangered Species Act Section 4 Deadline Litigation, No. 10-377 
(EGS), MDL Docket No. 2165 (D.D.C. May 10, 2011)). This proposed 
listing rule fulfills the requirements of those settlement agreements 
for the Texas hornshell.

Background

    A thorough review of the taxonomy, life history, ecology, and 
overall viability of the Texas hornshell

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(Popenaias popeii) is presented in the Species Status Assessment Report 
for the Texas Hornshell (SSA report) (Service 2016; available at https://www.regulations.gov). The SSA report documents the results of the 
comprehensive biological status review for the Texas hornshell and 
provides an account of the species' overall viability through 
forecasting of the species' condition in the future (Service 2016, 
entire). In the SSA report, we summarized the relevant biological data 
and a description of past, present, and likely future stressors and 
conducted an analysis of the viability of the species. The SSA report 
provides the scientific basis that informs our regulatory decision 
regarding whether this species should be listed as an endangered or 
threatened species under the Act. This decision involves the 
application of standards within the Act, its implementing regulations, 
and Service policies (see Determination, below). The SSA report 
contains the risk analysis on which this determination is based, and 
the following discussion is a summary of the results and conclusions 
from the SSA report. We solicited peer review of the draft SSA report 
from five qualified experts. We received responses from four of the 
reviewers, and we modified the SSA report as appropriate.

Species Description

    The Texas hornshell is a medium sized (3 to 4 inches long) 
freshwater mussel with a dark brown to green, elongate, laterally 
compressed shell (Howells et al. 1996, p. 93; Carman 2007, p. 2). The 
Texas hornshell was described by Lea (1857, p. 102) from the Devils 
River in Texas and Rio Salado in Mexico. Currently, the Texas hornshell 
is classified in the unionid subfamily Ambleminae (Campbell et al. 
2005, pp. 140, 144) and is considered a valid taxon by the scientific 
community (Turgeon et al. 1998, p. 36).
    Freshwater mussels, including the Texas hornshell, have a complex 
life history. Males release sperm into the water column, which are 
taken in by the female through the incurrent siphon (the tubular 
structure used to draw water into the body of the mussel). The sperm 
fertilizes the eggs, which are held during maturation in an area of the 
gills called the marsupial chamber. The developing larvae remain in the 
gill chamber until they mature and are ready for release. These mature 
larvae, called glochidia, are obligate parasites (cannot live 
independently of their hosts) on the gills, head, or fins of fishes 
(Vaughn and Taylor 1999, p. 913). Glochidia die if they fail to find a 
host fish, attach to a fish that has developed immunity from prior 
infestations, or attach to the wrong location on a host fish (Neves 
1991, p. 254; Bogan 1993, p. 599). Glochidia encyst (enclose in a cyst-
like structure) on the host's tissue, draw nutrients from the fish, and 
develop into juvenile mussels weeks or months after attachment (Arey 
1932, pp. 214-215).
    For the Texas hornshell, spawning generally occurs from March 
through August (Smith et al. 2003, p. 335), and fertilized eggs are 
held in the marsupial chambers of females for 4 to 6 weeks (Smith et 
al. 2003, p. 337). Glochidia are released in a sticky mucous net or 
string (Carman 2007, p. 9); the host fish likely swim into the nets, 
and the glochidia generally attach to the face or gills of the fish and 
become encysted in its tissue (Levine et al. 2012, pp. 1858). The 
glochidia will remain encysted for about a month through transformation 
to the juvenile stage. Once transformed, the juveniles will excyst from 
the fish and drop to the substrate. The known primary host fishes for 
the Texas hornshell are river carpsucker (Carpiodes carpio), grey 
redhorse (Moxostoma congestum), and red shiner (Cyprinella lutrensis) 
(Levine et al. 2012, pp. 1857-1858).
    Mussels are generally immobile but experience their primary 
opportunity for dispersal and movement within the stream as glochidia 
attached to a mobile host fish (Smith 1985, p. 105). Upon release from 
the host, newly transformed juveniles drop to the substrate on the 
bottom of the stream. Those juveniles that drop in unsuitable 
substrates die because their immobility prevents them from relocating 
to more favorable habitat. Juvenile freshwater mussels burrow into 
interstitial substrates and grow to a larger size that is less 
susceptible to predation and displacement from high flow events (Yeager 
et al. 1994, p. 220). Throughout the rest of their life cycle, mussels 
generally remain within the same small area where they excysted from 
the host fish.
    Life span is not known for the Texas hornshell, although two adult 
individuals were captured and marked in the Black River in New Mexico 
in 1997, and were recaptured 15 years later (Inoue et al. 2014, p. 5). 
Species in the subfamily Ambleminae, which includes Texas hornshell, 
commonly live more than 20 years (Carman 2007, p. 9), so we assume the 
Texas hornshell can live at least 20 years.
    Little is known about the specific feeding habits of Texas 
hornshell. Like all adult freshwater mussels, Texas hornshell are 
filter feeders, siphoning suspended phytoplankton and detritus from the 
water column (Yeager et al. 1994, p. 221; Carman 2007, p. 8).

Habitat and Range

    Adult Texas hornshell occur in medium to large rivers, in habitat 
not typical for most mussel species: In crevices, undercut riverbanks, 
travertine shelves, and under large boulders adjacent to runs (Carman 
2007, p. 6; Randklev et al. 2015, p. 8), although in the Devils River, 
the species is found in gravel beds at the heads of riffles and rapids 
(Randklev et al. 2015, p. 8). Small-grained material, such as clay, 
silt, or sand, gathers in these crevices and provides suitable 
anchoring substrate. These crevices are considered to be flow refuges 
from the large flood events that occur regularly in the rivers this 
species occupies. Texas hornshell are able to use these flow refuges to 
avoid being swept away as large volumes of water move through the 
system, as there is relatively little particle movement in the flow 
refuges, even during flooding (Strayer 1999, p. 472). Texas hornshell 
are not known from lakes, ponds, or reservoirs.
    The Texas hornshell historically ranged throughout the Rio Grande 
drainage in the United States (New Mexico and Texas) and Mexico as well 
as Mexican Gulf Coast streams south to the northern Mexican state of 
Veracruz (Johnson 1999, p. 23). Currently, five known populations of 
Texas hornshell remain in the United States: Black River (Eddy County, 
New Mexico), Pecos River (Val Verde County, Texas), Devils River (Val 
Verde County, Texas), Lower Canyons of the Rio Grande (Brewster and 
Terrell Counties, Texas), and Lower Rio Grande near Laredo (Webb 
County, Texas) (Map 1). They are described briefly below.

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[GRAPHIC] [TIFF OMITTED] TP10AU16.000

    Black River: The Black River, in Eddy County, New Mexico, 
originates from several groundwater-fed springs and flows approximately 
30 miles (mi) (48 kilometers (km)) through the Chihuahuan Desert until 
its confluence with the Pecos River (Inoue et al. 2014, p. 3) near 
Malaga, New Mexico. Extensive population monitoring (Lang 2001, entire; 
2006, entire; 2010, entire; 2011, entire) and a long-term mark-
recapture study (Inoue et al. 2014, entire) have yielded significant 
information about the population size and extent. Texas hornshell occur 
in approximately 8.7 mi (14.0 km) of the middle Black River, between 
two low-head (small) dams (Lang 2001, p. 20). The total population size 
has been estimated at approximately 48,000 individuals (95 percent 
confidence interval: 28,849-74,127) (Inoue et al. 2014, p. 7), with a 
diversity of size classes, primarily aggregated in flow refuges within 
narrow riffles. The population remained relatively stable over the 15 
year study period from 1997 to 2012 (Inoue et al. 2014, p. 6).
    Pecos River: In the Pecos River, inundation from Amistad Reservoir 
has resulted in the extirpation of Texas hornshell from the lower 
reaches of the river. Additionally, salinity levels are too high for 
freshwater mussel habitation in much of the Pecos River from the 
confluence with the Black River in New Mexico, downstream to the 
confluence with Independence Creek. However, three live Texas hornshell 
were collected from a small section of the Pecos River downstream of 
the confluence with Independence Creek and upstream of Amistad 
Reservoir near Pandale in Val Verde County, Texas, as well as 37 shells 
(Bosman et al. 2016, p. 6; Randklev et al. 2016, p. 9). Farther 
downstream, only dead shells were found in 2016, although they were 
numerous (Bosman et al. 2016, p. 6; Randklev et al. 2016, p. 9). Live 
individuals had not been collected at this location since 1973 
(Randklev et al. 2016, p. 4).
    Because the sample size of live individuals is so small (three live 
individuals found in recent months), it is difficult to draw many 
conclusions about the population. The population appears to be 
extremely small, and no evidence of reproduction was noted.
    Devils River: Texas hornshell were historically found in the Devils 
River and were known to occupy only the lower reaches of the river, 
which are currently inundated by Amistad Reservoir (Neck 1984, p. 11; 
Johnson 1999, p. 23; Burlakova and Karatayev 2014, p. 19). In recent 
years, 11 individuals were collected from upstream in the Devils River 
between 2008 and 2014 (Burlakova and Karatayev 2014, p. 16; Karatayev 
et al. 2015, p. 4). More intensive surveys conducted in 2014 and 2015, 
including 11 sites, have yielded 48 individuals at two sites: All from 
The Nature Conservancy's Dolan Falls Preserve except for a singleton at 
the Devils River State Natural Area's Dan A. Hughes Unit (formerly 
known as the Big Satan Unit) (Randklev et al. 2015, pp. 6-7). Because 
of the increased number of individuals collected in 2014 and 2105, it 
is likely that the Devils River population is more numerous than 
previously thought, although we do not expect that this

[[Page 52800]]

population is particularly large based on the limited number of 
collections to date. Interestingly, Texas hornshell in the Devils River 
occupy different habitats than those in the rest of the range; instead 
of being found under rock slabs and in travertine shelves, they occupy 
gravel beds at the heads of riffles or in clean-swept pools with 
bedrock (Randklev et al. 2015, p. 8). Even though the number of 
collected individuals is small, several young individuals were found, 
as well as females brooding glochidia (gravid females) (Randklev et al. 
2015, p. 8), indicating reproduction and recruitment (offspring survive 
to join the reproducing population) are occurring in the Devils River 
population.
    Rio Grande--Lower Canyons: One of two remaining populations of 
Texas hornshell in the Rio Grande is found in the Lower Canyons, just 
downstream of Big Bend National Park, in Terrell County, Texas. 
Burlakova and Karatayev (2014, p. 16) found the species in low density 
(approximately 40 individuals per km) in this region of the Rio Grande. 
Subsequent surveys by Randklev et al. (2015, entire) confirmed the 
presence of Texas hornshell in approximately 18.5 mi (30 km) of the 
Lower Canyons in two sections, finding that the species occupies 
approximately 63 percent of sites with suitable (rocky) habitat. For 
purposes of this analysis, we presume the entire section between these 
collections, approximately 62 mi (100 km), is occupied. Sites in the 
Rio Grande--Lower Canyons reach vary in density, with the densest sites 
near Sanderson Canyon, Terrell County, Texas, and decreasing downstream 
(Randklev et al. 2015, p. 13); the average density of Texas hornshell 
at each site is lower compared to the Black River and Rio Grande--
Laredo (5  14 individuals per site). Texas hornshell may 
occur between the known occupied sections, near the confluence with San 
Francisco Creek (Howells 2001a, p. 6), but limited access has prevented 
recent surveys from determining current occupancy of this reach. Young 
individuals and gravid females have been found throughout the Lower 
Canyons reach, indicating recruitment is occurring (Randklev et al. 
2015, p. 8).
    Rio Grande--Laredo: The largest Texas hornshell population occurs 
from Laredo, Texas (near La Bota Ranch just northwest of Laredo), 
upstream approximately 56 mi (90 km) (Randklev et al. 2015, p. 7). The 
density in this reach is high, with some habitat patches containing 
more than 8,000 individuals (Karatayev et al. 2015, p. 4) and 100 
percent of surveyed patches of suitable habitat containing Texas 
hornshell (Randklev et al. 2015, p. 7). Throughout this reach, the 
density of Texas hornshell is estimated 170  131 
individuals per suitable (rocky) habitat site (Randklev et al. 2015, p. 
7). Young individuals and gravid females have been found throughout the 
Laredo reach, indicating reproduction and recruitment are occurring 
(Randklev et al. 2015, p. 8). No live Texas hornshell have been found 
downstream of the city of Laredo in recent years.
    Mexico: A large portion of the Texas hornshell's estimated 
historical range is in Mexico. The species occurred in the Rio Salado 
basin, which is a tributary to the Rio Grande in Mexico, and in 
approximately 15 rivers that flow into the Gulf of Mexico. At one time, 
one-half to two-thirds of the species' range may have been in Mexico. 
Unfortunately, the most recent live collections of Texas hornshell in 
Mexico occurred in the 1980s (Mussel Project 2015, entire), and we have 
very few records of surveys with positive or negative collection data 
since that time. We have no information on population size or extent 
during those times of collection, and we also have no information on 
whether populations of Texas hornshell still occur in one or more of 
these streams; therefore, we have very low confidence in the species' 
current condition throughout most of the Mexican range. One or more of 
these populations may still be extant, or they may all be extirpated.

Species Needs

    Texas hornshell need seams of fine sediment in crevices, undercut 
riverbanks, travertine shelves, and large boulders in riverine 
ecosystems with flowing water and periodic cleansing flows to keep the 
substrate free of fine sediment accumulation. They need water quality 
parameters to be within a suitable range (i.e., dissolved oxygen above 
3 milligrams/liter (mg/L), salinity below 0.9 parts per thousand, and 
ammonia below 0.7 mg/L (Sparks and Strayer 1998, p. 132; Augspurger et 
al. 2003, p. 2574; Augspurger et al. 2007, p. 2025; Carman 2007, p. 6)) 
and phytoplankton as food. Finally, Texas hornshell need host fish to 
be present during times of spawning.
    We describe the Texas hornshell's viability by characterizing the 
status of the species in terms of its resiliency (ability of the 
populations to withstand stochastic events), redundancy (ability of the 
species to withstand large-scale, catastrophic events), and 
representation (the ability of the species to adapt to changing 
environmental conditions). Using various time frames and the current 
and projected resiliency, redundancy, and representation, we describe 
the species' level of viability over time. For the Texas hornshell to 
maintain viability, its populations or some portion thereof must be 
resilient. A number of factors influence the resiliency of Texas 
hornshell populations, including occupied stream length, abundance, and 
recruitment. Elements of Texas hornshell habitat that determine whether 
Texas hornshell populations can grow to maximize habitat occupancy 
influence those factors, thereby increasing the resiliency of 
populations. These resiliency factors and habitat elements are 
discussed here.
    Occupied Stream Length: Most freshwater mussels, including Texas 
hornshell, are found in aggregations, called mussel beds, that vary in 
size from about 50 to greater than 5,000 square meters (m\2\) (540 to 
greater than 53,800 square feet (ft\2\)), separated by stream reaches 
in which mussels are absent or rare (Vaughn 2012, p. 983). Resilient 
Texas hornshell populations must occupy stream reaches sufficient in 
length such that stochastic events that affect individual mussel beds 
do not eliminate the entire population. Repopulation by fish infested 
with Texas hornshell glochidia from other mussel beds within the reach, 
if present and connected, can allow the population to recover from 
these events.
    Abundance: Mussel abundance in a given stream reach is a product of 
the number of mussel beds times the density of mussels within those 
beds. For populations of Texas hornshell to be resilient, there must be 
many mussel beds of sufficient density (~200 individuals per 150 m\2\ 
(1,614 ft\2\); see SSA report for more discussion) such that local 
stochastic events do not necessarily eliminate the bed(s), allowing the 
mussel bed and the overall population in the stream reach to recover 
from any one event. We measure Texas hornshell abundance by the number 
of beds within the population, and the estimated density of Texas 
hornshell within each.
    Reproduction: Resilient Texas hornshell populations must also be 
reproducing and recruiting young individuals into the reproducing 
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. Detection of very young juvenile mussels during routine 
abundance and distribution surveys happens extremely rarely due to 
sampling bias; sampling for this species involves tactile searches, and 
mussels below about 35 millimeters (mm) (1.4

[[Page 52801]]

inches (in)) are very hard to detect. Therefore, reproduction is 
verified by repeatedly capturing small-sized individuals near the low 
end of the detectable range size (about 35 mm (1.4 in)) over time and 
by capturing gravid females during the reproductively active time of 
year (generally, March through August (Smith et al. 2003, p. 335)).
    Substrate: Texas hornshell occur in flow refuges such as crevices, 
undercut riverbanks, travertine shelves, and large boulders. These 
refuges must have seams of clay or other fine sediments within which 
the mussels may anchor, but not so much excess sediment that the 
mussels are smothered. Those areas with clean-swept substrate with 
seams of fine sediments are considered to have suitable substrate, and 
those with copious fine sediment both in crevices and on the stream 
bottom are considered less suitable.
    Flowing Water: Texas hornshell need flowing water for survival. 
They are not found in lakes or in pools without flow, or in areas that 
are regularly dewatered. River reaches with continuous flow are 
considered suitable habitat, while those with little or no flow are 
considered not suitable.
    Water Quality: Freshwater mussels, as a group, are sensitive to 
changes in water quality parameters such as dissolved oxygen, salinity, 
ammonia, and pollutants (i.e., dissolved oxygen above 3 mg/L, salinity 
below 0.9 parts per thousand, and ammonia below 0.7 mg/L (Sparks and 
Strayer 1998, p. 132; Augspurger et al. 2003, p. 2574; Augspurger et 
al. 2007, p. 2025; Carman 2007, p. 6)). Habitats with appropriate 
levels of these parameters are considered suitable, while those 
habitats with levels outside of the appropriate ranges are considered 
less suitable.
    Maintaining representation in the form of genetic or ecological 
diversity is important to maintain the Texas hornshell's capacity to 
adapt to future environmental changes. Texas hornshell populations in 
the Rio Grande and Devils River (and, presumably, the Pecos River, due 
to its proximity to Rio Grande populations) have distinct variation in 
allele frequencies from those in the Black River (Inoue et al. 2015, p. 
1916). We expect additional variation was present in Mexican 
populations. Mussels, like Texas hornshell, need to retain populations 
throughout their range to maintain the overall potential genetic and 
life-history attributes that can buffer the species' response to 
environmental changes over time (Jones et al. 2006, p. 531). The Texas 
hornshell has likely lost genetic diversity as populations have been 
extirpated. As such, maintaining the remaining representation in the 
form of genetic diversity may be important to the capacity of the Texas 
hornshell to adapt to future environmental change.
    Finally, the Texas hornshell needs to have multiple resilient 
populations distributed throughout its range to provide for redundancy, 
the ability of the species to withstand catastrophic events. The more 
populations, and the wider the distribution of those populations, the 
more redundancy the species will exhibit. Redundancy reduces the risk 
that a large portion of the species' range will be negatively affected 
by a catastrophic natural or anthropogenic event at a given point in 
time. Species that are well-distributed across their historical range 
are considered less susceptible to extinction and have higher viability 
than species confined to a small portion of their range (Carroll et al. 
2010, entire; Redford et al. 2011, entire).

Summary of Biological Status and Threats

    The Act directs us to determine whether any species is an 
endangered species or a threatened species because of any factors 
affecting its continued existence. We completed a comprehensive 
assessment of the biological status of the Texas hornshell, and 
prepared a report of the assessment, which provides a thorough account 
of the species' overall viability. In this section, we summarize the 
conclusions of that assessment, which can be accessed at Docket No. 
FWS-R2-ES-2016-0077 on https://www.regulations.gov.

Risk Factors

    We reviewed the potential risk factors (i.e., threats, stressors) 
that could be affecting the Texas hornshell now and in the future. In 
this proposed rule, we will discuss only those factors in detail that 
could meaningfully impact the status of the species. Those risks that 
are not known to have effects on Texas hornshell populations, such as 
collection and disease, are not discussed here. The primary risk 
factors (i.e., threats) affecting the status of the Texas hornshell 
are: (1) Increased fine sediment (Factor A from the Act), (2) water 
quality impairment (Factor A), (3) loss of flowing water (Factor A), 
(4) barriers to fish movement (Factor E), and (5) increased predation 
(Factor C). These factors are all exacerbated by climate change. 
Finally, we reviewed the conservation efforts being undertaken for the 
species.
Increased Fine Sediment
    Texas hornshell require seams of fine sediment under boulders and 
bedrock and in streambanks in order to anchor themselves into place on 
the stream bottom; however, too much fine sediment can fill in these 
crevices and smother any mussels within those spaces. Under natural 
conditions, fine sediments collect on the streambed and in crevices 
during low flow events, and they are washed downstream during high flow 
events (also known as cleansing flows). However, the 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), has caused 
sediment to accumulate to some degree at all populations. When water 
velocity decreases, which can occur from reduced streamflow or 
inundation, water loses its ability to carry sediment in suspension; 
sediment falls to the substrate, eventually smothering mussels that 
cannot adapt 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 Texas 
hornshell, these sources include streambank erosion from agricultural 
activities, livestock grazing, and roads, among others.
    Interstitial spaces (small openings between rocks and gravels) in 
the substrate 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 rates and spaces may 
become reduced (Brim Box and Mossa 1999, p. 100), thus reducing 
juvenile habitat availability.
    All populations of Texas hornshell face the risk of fine sediment 
accumulation to varying degrees. Elimination of Texas hornshell from 
mussel beds due to large amounts of sediment deposition has been 
documented on the Black River in two locations in recent years. In the 
future, we expect this may continue to occur sporadically. Fine 
sediments are also accumulating at the Rio Grande--Laredo population. 
Low water levels on the Devils River will likely lead to additional 
sediment accumulation at this population, as well. In the future, we 
expect lower flows to occur more often at all populations and for 
longer periods due to climate change.

[[Page 52802]]

Water Quality Impairment
    Water quality can be impaired 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). 
Chemicals enter the environment through both point and nonpoint 
discharges, including spills, industrial sources, municipal effluents, 
and agricultural runoff. These sources contribute organic compounds, 
heavy metals, pesticides, herbicides, and a wide variety of newly 
emerging contaminants to the aquatic environment. Ammonia is of 
particular concern below water treatment plants because freshwater 
mussels have been shown to be particularly sensitive to increased 
ammonia levels (Augspurger et al. 2003, p. 2569). It is likely for this 
reason that Texas hornshell are not found for many miles downstream of 
two wastewater treatment plants that discharge into the Rio Grande: at 
Nuevo Laredo, Mexico, and at Eagle Pass, Texas (Karatayev et al. 2015, 
p. 14).
    An additional type of water quality impairment is alteration of 
water quality parameters such as dissolved oxygen, temperature, and 
salinity levels. Dissolved oxygen levels may be reduced from increased 
nutrients in the water column from runoff or wastewater effluent, and 
juveniles seem to be particularly sensitive to low dissolved oxygen 
(Sparks and Strayer 1998, pp. 132-133). Increased water temperature 
from climate change and from low flows during drought can exacerbate 
low dissolved oxygen levels as well as have its own effects on both 
juvenile and adult mussels. Finally, salinity appears to be 
particularly limiting to Texas hornshell. The aquifer near Malaga, New 
Mexico, contains saline water. As the saline water emerges from the 
ground, it is diluted by surface flow. As surface flow decreases, 
however, the concentration of salinity in the river increases. 
Additionally, aquifers have become increasingly saline due to salinized 
water recharge (Hoagstrom 2009, p. 35). Irrigation return flows 
exacerbate salinity levels as salts build up on irrigated land and then 
are washed into the riverway. The Pecos River from the confluence with 
the Black River to the confluence with Independence Creek has become 
particularly saline in the past few decades, with levels at 7 parts per 
million (ppm) or higher, which is too high for freshwater mussel 
habitation. Additionally, the Black River downstream of the Texas 
hornshell population has had salinity levels in the range of 6 ppm, 
which may be one reason the population has been extirpated from the 
downstream reach.
    Contaminant spills are also a concern. In particular, the Black 
River population is vulnerable to spills from the high volume of truck 
traffic crossing the river at low water access points (Bren School of 
Environmental Management 2014, p. 26). Due to the topography and steep 
slopes of these areas, spilled contaminants and contaminated soils 
could directly enter the surface water of the river and negatively 
impact the species (Boyer 1986, p. 300) and downstream habitat. For the 
smaller populations (Black, Devils, Pecos rivers), a single spill could 
eliminate the entire population.
    A reduction in surface flow from drought, instream diversion, or 
groundwater extraction concentrates contaminant and salinity levels, 
increases water temperatures in streams, and exacerbates effects to 
Texas hornshell.
    Poor water quality affects most Texas hornshell populations 
currently to some degree, and future water quality is expected to 
decrease due to decreasing river flow and increasing temperatures. The 
Pecos River experiences very high salinity levels upstream of the 
existing population, and we expect that the observed high mortality of 
the Pecos River population is due to salinity pulses. Rangewide, as 
water flow is expected to decrease due to climate change, water quality 
will decline.
Loss of Flowing Water
    Texas hornshell populations need flowing water in order to survive. 
Low flow events (including stream drying) and inundation can eliminate 
appropriate habitat for Texas hornshell, and while the species can 
survive these events if they last for a short time, populations that 
experience these events regularly will not persist.
    Inundation has primarily occurred upstream of dams, both large 
(such as Amistad, Falcon, and Red Bluff Dams) and small (low water 
crossings and diversion dams, such as those on the Black River). 
Inundation causes an increase in sediment deposition, eliminating the 
crevices this species inhabits. In large reservoirs, deep water is very 
cold and often devoid of oxygen and necessary nutrients. Cold water 
(less than 11 degrees Celsius ([deg]C) (52 degrees Fahrenheit 
([deg]F))) has been shown to stunt mussel growth (Hanson et al. 1988, 
p. 352). Because glochidial release may be temperature dependent, it is 
likely that relict individuals living in the constantly cold 
hypolimnion (deepest portion of the reservoir) in these reservoirs may 
never reproduce, or reproduce less frequently. Additionally, the 
effects of these reservoirs extend beyond inundation and fragmentation 
of populations; the reservoirs are managed for flood control and water 
delivery, and the resultant downstream releases rarely mimic natural 
flow regimes, tempering the natural fluctuations in flow that flush 
fine sediments from the substrate.
    At the Rio Grande--Laredo population, a low-water weir has been 
proposed for construction (Rio Grande Regional Water Planning Group 
2016, p. 8-8). The dam would be located just downstream of the La Bota 
area, which contains the largest known and most dense Texas hornshell 
bed within the Rio Grande--Laredo population and rangewide. The 
impounded area would extend approximately 14 mi (22.5 km) upstream, 
effectively eliminating habitat for Texas hornshell from 25 percent of 
the currently occupied area and likely leading to extirpation of the 
densest sites within this population.
    Very low water levels are detrimental to Texas hornshell 
populations, as well. Effects of climate change have already begun to 
affect the regions of Texas and New Mexico where the Texas hornshell 
occurs, resulting in higher air temperatures, increased evaporation, 
increased groundwater pumping, and changing precipitation patterns such 
that water levels rangewide have already reached historic lows (Dean 
and Schmidt 2011, p. 336; Bren School of Environmental Management 2014, 
p. 50). The rivers inhabited by Texas hornshell have some resiliency to 
drought because they are spring-fed (Black and Devils Rivers) and very 
large (Rio Grande), but drought in combination with increased 
groundwater pumping and regulated reservoir releases may lead to lower 
river flows of longer duration than have been recorded in the past. 
Streamflow in the Rio Grande downstream of the confluence with the Rio 
Conchos (near the Rio Grande-Lower Canyons population) has been 
declining since the 1980s (Miyazono et al. 2015, p. A-3), and overall 
river discharge for the Rio Grande is projected to continue to decline 
due to increased drought as a result of climate change (Nohara et al. 
2006, p. 1087). The Rio Conchos contributes more than 90 percent of the 
flow of the lower Rio Grande (Dean and Schmidt 2011, p. 4). However, 
during times of drought (such as between 1994 and 2003), Mexico has 
fallen short of its water delivery commitments, and so the contribution 
of the Rio Conchos has fallen to as low as 40 percent (Carter et

[[Page 52803]]

al. 2015, p. 15). The Rio Grande--Lower Canyons population is 
downstream of the confluence with the Rio Conchos and is at risk from 
these reduced deliveries. The Rio Grande--Lower Canyons is very incised 
(in other words, has vertical banks), and the population occurs in 
crevices along the steep banks. Due to the habitat characteristics of 
this population, reductions in discharge in this area may lead to a 
higher proportion of the Texas hornshell population being exposed than 
would be found in other populations experiencing similar flow 
decreases.
    In the Black River, surface water is removed from the river for 
irrigation, including the Carlsbad Irrigation District's Black River 
Canal at the diversion dam. Studies have shown that flows in the river 
are affected by groundwater withdrawals, particularly those from the 
Black River Valley. Groundwater in the Black River watershed is also 
being used for hydraulic fracturing for oil and gas activities. Between 
4.3 acre-feet (187,308 ft\3\ (5,304 m\3\)) and 10.7 acre-feet (466,091 
ft\3\ (13,198 m3)) of water is used for each hydraulic fracturing job 
(Bren School of Environmental Management 2014, p. 91). Overall, mean 
monthly discharge has already declined since the mid-1990s, and mean 
monthly temperatures have increased over the past 100 years (Inoue et 
al. 2014, p. 7). In the Black River, survivorship is positively 
correlated with discharge (Inoue et al. 2014, p. 9); as mean monthly 
discharge decreases, we expect Texas hornshell survivorship to 
decrease, as well. The Black River is expected to lose streamflow in 
the future due to air temperature increases, groundwater extraction, 
and reduced precipitation.
    In the Devils River, future water withdrawals from aquifers that 
support spring flows in the range of the Texas hornshell could result 
in reduction of critical spring flows and river drying. In particular, 
there have been multiple proposals to withdraw water from the nearby 
aquifer and deliver the water to municipalities (e.g., Val Verde Water 
Company 2013, pp. 1-2). To date, however, none have been approved.
    As spring flows decline due to drought or groundwater lowering from 
pumping, habitat for the Texas hornshell is reduced and could 
eventually cease to exist. While Texas hornshell may survive short 
periods of low flow, as low flows persist, mussels face oxygen 
deprivation, increased water temperature, and, ultimately, stranding.
Barriers to Fish Movement
    Two of the Texas hornshell's primary host fish species (river 
carpsucker and red shiner) are known to be common, widespread species. 
We do not expect the distribution of host fish to be a limiting factor 
in Texas hornshell distribution. However, the barriers that prevent 
fish movement upstream and downstream affect the viability of Texas 
hornshell.
    Texas hornshell were likely historically distributed throughout the 
Rio Grande, Pecos River, Devils River, and Black River in Texas and New 
Mexico, as well as throughout the rivers draining to the Gulf of Mexico 
from which the species was known when few natural barriers existed to 
prevent migration (via host species) among suitable habitats. The 
species colonized new areas through movement of infested host fish, and 
newly metamorphosed juveniles would excyst from host fish in new 
locations. Today, the remaining populations are significantly isolated 
from one another such that recolonization of areas previously 
extirpated is extremely unlikely if not impossible due to existing 
contemporary barriers to host fish movement. The primary reason for 
this isolation is reservoir construction and unsuitable water quality. 
The Black River is isolated from the rest of the populations by high 
salinity reaches of the Pecos River, as well as Red Bluff Reservoir, 
and is hundreds of river miles from the nearest extant population. 
Amistad Reservoir separates the three Texas populations from each 
other, isolating the Rio Grande--Lower Canyons, Devils River, and Rio 
Grande--Laredo populations. There is currently no opportunity for 
interaction among any of the five extant U.S. populations.
    The overall distribution of mussels is, in part, a function of the 
dispersal of their host fish. Small populations are more affected by 
this limited immigration potential because they are susceptible to 
genetic drift (random loss of genetic diversity) and inbreeding 
depression. At the species level, populations that are eliminated due 
to stochastic events cannot be recolonized naturally, leading to 
reduced overall redundancy and representation.
Increased Predation
    Predation on freshwater mussels is a natural ecological 
interaction. Raccoons, snapping turtles, and fish are known to prey 
upon Texas hornshell. Under natural conditions, the level of predation 
occurring within Texas hornshell populations is not likely to pose a 
significant risk to any given population. However, during periods of 
low flow, terrestrial predators 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 
Devils River, and muskrat predation has also been reported on the Black 
River. As drought and low flow conditions are predicted to occur more 
often and for longer periods due to the effects of climate change, the 
Black and Devils Rivers are expected to experience additional predation 
pressure into the future. Predation is expected to be less of a concern 
for the Rio Grande populations, as the river is significantly larger 
than the Black and Devils Rivers and Texas hornshell are less likely to 
be found in exposed or very shallow portions of the stream.
Effects of Climate Change
    Climate change in the form of the change in timing and amount of 
precipitation and air temperature increase is occurring, 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 the Southwest is expected to be greatest in the summer 
(IPCC 2013, pp. 11-12), and annual mean precipitation is very likely to 
decrease in the Southwest (Ray et al. 2008, p. 1; IPCC 2013, pp. 11-
12). In Texas, the number of extreme hot days (high temperatures 
exceeding 95 [deg]F (35 [deg]C) are expected to double by around 2050 
(Kinniburgh et al. 2015, p. 83), and Texas is considered one of the 
``hotspots'' of climate change in North America; west Texas is an area 
expected to show greater responsiveness to the effects of climate 
change (Diffenbaugh et al. 2008, p. 3). Even if precipitation and 
groundwater recharge remain at current levels, increased groundwater 
pumping and resultant aquifer shortages due to increased temperatures 
are nearly certain (Loaiciga et al. 2000, p. 193; Mace and Wade 2008, 
pp. 662, 664-665; Taylor et al. 2012, p. 3). Increased water 
temperature can cause stress to individuals, decrease dissolved oxygen 
levels, and increase toxicity of contaminants. 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 Texas hornshell (Kinniburgh et al. 2015, p. 88), and these 
effects are expected to exacerbate several of the stressors discussed 
above, such as water temperature and flow loss (Wuebbles et

[[Page 52804]]

al. 2013, p. 16). As we projected the future condition of the Texas 
hornshell and which stressors are likely to occur, we considered 
climate change to be an exacerbating factor in the increase of fine 
sediments, changes in water quality, and loss of flowing water.
    Due to the effects of ongoing climate change, we expect the 
frequency and duration of cleansing flows to decrease, leading to the 
increase in fine sediments and reduced water levels at all populations. 
More extreme climate change projections 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.

Conservation Actions and Regulatory Mechanisms

    About 7 percent of known occupied habitat for the Texas hornshell 
is in New Mexico, and the Service is collaborating with water users, 
oil and gas developers, landowners, and other partners to develop 
candidate conservation agreements (CCAs) for the species on State, 
Federal, and private lands. These agreements are currently under 
development, and the potential purpose is to provide voluntary 
conservation that would reduce threats to the species while improving 
physical habitat and water quality. The key conservation measures in 
the agreements will be designed to limit oil and gas development to 
areas outside of the Black and Delaware River floodplains, minimize 
erosion, and maintain minimum water flows in the rivers. Along with 
these measures, the partners to the agreement are evaluating 
alternatives to the multiple low water crossings on the Black River. 
Partners are considering alternate crossing locations, which could 
include bridges designed to allow host fishes to pass through in 
addition to decreasing potential contamination events. Because these 
agreements have not been completed, we are not considering the 
conservation actions in our present evaluation of the status of Texas 
hornshell.
    The New Mexico Department of Game and Fish has begun Texas 
hornshell reintroduction efforts into the Delaware River, which is 
within the historical range of the species. Adults and infested host 
fish were released in suitable habitat in the Delaware River in 2013 
and 2015. Many of the released adults have been subsequently located, 
and success of the reintroduction will be determined in the coming 
years. We expect the reintroduction effort to continue over the next 
several years, but we are not considering the action to have been 
successful to date.
    In Texas, The Nature Conservancy and Texas Parks and Wildlife 
Department manage lands under their purview in the Devils River 
watershed for native communities, including Texas hornshell. The large 
amount (over 200,000 acres) of land in conservation management in the 
Devils River watershed reduces the risks to Texas hornshell from 
sediment inputs and contaminants.
    In the Rio Grande, we are not aware of any management actions for 
Texas hornshell. The Texas Comptroller of Public Accounts has 
established an Endangered Species Task Force and has funded much of the 
recent research in Texas on Texas hornshell, which has led to greater 
understanding of the species' distribution in the State.

Current Condition

    Overall, there are five known remaining populations of Texas 
hornshell, comprising approximately 15 percent of the species' 
historical range in the United States (see Map 1, above). Historically, 
most Texas hornshell populations were likely connected by fish 
migration throughout the Rio Grande, upstream through the Pecos River, 
and throughout the tributaries, but due to impoundments and river 
reaches with unsuitable water quality (for example, high salinity) they 
are currently isolated from one another, and repopulation of extirpated 
locations is unlikely to occur without human assistance. 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 low levels of climate change to be currently 
occurring, resulting in reduced timing and amount of streamflow, 
increased stream temperatures, and increased accumulation of fine 
sediments.
    Black River: The Black River population is quite dense and 
recruitment appears to be high, but the short size (8.7 mi (14.0 km)) 
of the occupied reach limits this population's resiliency. Accumulation 
of fine sediment in the substrate has already occurred due to increased 
sediment input into the river from road crossings, culverts, and cattle 
grazing, combined with a decreased frequency of cleansing river flows. 
The current level of climate change will continue to reduce flow in the 
river from groundwater extraction and drought, resulting in fewer 
cleansing flows and increased fine sediments. The distribution of Texas 
hornshell in the Black River will remain small, and the risk of a 
contaminant spill will remain high, resulting in a high likelihood that 
water quality will become unsuitable and reduce abundance of Texas 
hornshell significantly. Therefore, taking into account the current 
threats to the population and its distribution within the river, the 
Texas hornshell population in the Black River has low resiliency.
    Pecos River: The Pecos River population is extremely small and 
exhibits no evidence of reproduction. The few number of live 
individuals among the very high number of dead shells indicates a 
population in severe decline; this is likely due to high salinity 
levels in the river upstream of the population. There is a high 
likelihood this population will be extirpated in the near future due to 
water quality alone. Therefore, the Pecos River population of Texas 
hornshell has very low resiliency.
    Devils River: The Devils River population has low abundance and has 
exhibited some evidence of reproduction. The current level of climate 
change will continue to reduce flow in the Devils River due to 
groundwater extraction and drought. The low flows this population 
experiences during dry times will continue to become more frequent and 
prolonged. Because Texas hornshell in the Devils River occur at the 
heads of riffles, they are vulnerable to complete flow loss when water 
levels drop. The reduction in cleansing flows will also result in the 
accumulation of fine sediments, reducing substrate quality. Low flows 
will also affect water quality parameters such as temperature and 
dissolved oxygen, causing them to become unsuitable for Texas 
hornshell. Additionally, the species is already vulnerable to predation 
from terrestrial predators during times of low flow; predation will 
occur more frequently as periods of low flow become more common. 
Overall, because the population is currently small and would be 
unlikely to grow, the Devils River population has low resiliency.
    Rio Grande--Lower Canyons: The Lower Canyons population has 
relatively high abundance and evidence of recruitment. Drought and 
groundwater extraction resulting from currently observed levels of 
climate change will continue to lower water levels in the Rio Grande--
Lower Canyons population of Texas hornshell. We expect that Mexico's 
management of the Rio Conchos will continue to be an

[[Page 52805]]

unreliable source of water. This section of the Rio Grande is 
relatively deep and incised, and the population of Texas hornshell 
primarily occurs in crevices along the banks. Water flow reductions 
would expose a high proportion of the existing population; therefore, 
this reduction in flow will likely have a larger effect on the 
population size than in other populations, although at a small to 
moderate decrease in water flow we still expect abundance to be 
maintained at moderate levels. Overall, the Rio Grande--Lower Canyons 
population exhibits moderate resiliency.
    Rio Grande--Laredo: Similar to the Lower Canyons population, the 
Laredo population has numerous mussel beds with high Texas hornshell 
abundance and evidence of reproduction. However, drought and upstream 
water management will continue to reduce flows in the Rio Grande. Water 
quality will continue to decrease due to lower flows, and fine 
sediments will accumulate. Declining water flow will cause fine 
sediments to accumulate and water quality to decline, leading to a 
decline in population abundance. Overall, the Rio Grande--Laredo has 
moderate resiliency.
    Mexico: We have low confidence in the species' current condition 
throughout most of the Mexican range. One or more of these populations 
may still be extant, or they may all be extirpated. We have no recent 
data on the species' occurrence in Mexico; the last live recordings are 
from the mid-1980s. Because of this uncertainty, we did not rely on the 
Texas hornshell's distribution in Mexico when evaluating the viability 
of the species.

Future Condition

    As part of the SSA, we also developed multiple future condition 
scenarios to capture the range of uncertainties regarding future 
threats and the projected responses by the Texas hornshell. Our 
scenarios included a status quo scenario, which incorporated the 
current risk factors continuing on the same trajectory that they are on 
now. We also evaluated four additional future scenarios that 
incorporated varying levels of increasing risk factors with elevated 
negative effects on hornshell populations. However, because we 
determined that the current condition of the Texas hornshell and the 
associated status quo projections were consistent with an endangered 
species (see Determination, below), we are not presenting the results 
of the other future scenarios in this proposed rule. The additional 
future scenarios project conditions that are worse for the Texas 
hornshell. Since the status quo scenario was determined to be 
endangered, other projected scenarios would also be endangered, as they 
forecast conditions that are more at risk of extinction than the status 
quo. Please refer to the SSA report (Service 2016) for the full 
analysis of future scenarios.

Determination

    Section 4 of the Act, and its implementing regulations at 50 CFR 
part 424, set forth the procedures for adding species to the Federal 
Lists of Endangered and Threatened Wildlife and Plants. Under section 
4(b)(1)(a), the Secretary is to make endangered or threatened 
determinations required by subsection 4(a)(1) solely on the basis of 
the best scientific and commercial data available to her after 
conducting a review of the status of the species and after taking into 
account conservation efforts by States or foreign nations. The 
standards for determining whether a species is endangered or threatened 
are provided in section 3 of the Act. An endangered species is any 
species that is ``in danger of extinction throughout all or a 
significant portion of its range.'' A threatened species is any species 
that is ``likely to become an endangered species within the foreseeable 
future throughout all or a significant portion of its range.'' Per 
section 4(a)(1) of the Act, in reviewing the status of the species to 
determine if it meets the definition of endangered or of threatened, we 
determine whether any species is an endangered species or a threatened 
species because of any of the following 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; and (E) other natural or manmade 
factors affecting its continued existence. Listing actions may be 
warranted based on any of the above threat factors, singly or in 
combination.
    The fundamental question before the Service is whether the species 
warrants protection as an endangered or threatened species under the 
Act. To make this determination, we evaluated extinction risk, 
described in terms of the current condition of populations and their 
distribution (taking into account the risk factors (i.e., threats, 
stressors) and their effects on those populations). For any species, as 
population conditions decline and distribution shrinks, the species' 
overall viability declines and extinction risk increases.
    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
to the Texas hornshell. Our analysis of the past, current, and future 
influences on what the Texas hornshell needs for long-term viability 
revealed that there are five influences that may pose a meaningful risk 
to the viability of the species. These are primarily related to habitat 
changes (Factor A from the Act): The accumulation of fine sediments, 
the loss of flowing water, and impairment of water quality, all of 
which are exacerbated by the effects of climate change. Predation 
(Factor C) is also affecting those populations already experiencing low 
stream flow, and barriers to fish movement (Factor E) prevent 
recolonization after stochastic events.
    The Texas hornshell has declined significantly in overall 
distribution and abundance, with the species currently occupying 
approximately 15 percent of its historical range in the United States. 
Between one-half and two-thirds of the Texas hornshell's historical 
range occurred in Mexico; we have very low confidence in the species' 
current condition throughout most of the Mexican range. The resulting 
remnant populations occupy shorter reaches compared to presumed 
historical populations, and they are all isolated from one another.
    The primary historical reason for this reduction in range was 
reservoir construction and unsuitable water quality. Large reservoirs 
have been constructed on the Rio Grande and Pecos River, and much of 
the Pecos River upstream of the confluence with Independence Creek now 
has salinity levels too high for mussel habitation (Hoagstrom 2009, p. 
28). The effects of these reservoirs extend beyond fragmentation of 
populations; the resultant downstream water releases do not mimic 
natural flow regimes, and the change in timing and frequency of 
cleansing flows results in increases in fine sediments, increases in 
predation, and decreases in water quality. Add to this the exacerbating 
effects of climate change--increased temperature and decreased stream 
flow--and the remaining Texas hornshell populations face moderate to 
high levels of risk of extirpation currently. For the populations 
occupying the smaller reaches (such as the Black River, Devils River, 
and Pecos River populations), a single stochastic event such as 
contaminant spill or drought could eliminate an entire population of 
Texas hornshell. These effects are heightened at the species level 
because the isolation of the populations prohibits natural 
recolonization from host fish carrying Texas hornshell glochidia, which 
likely

[[Page 52806]]

happened in the past and allowed for the species to ebb and flow from 
suitable areas.
    Populations in both large and small reaches face risks from natural 
and anthropogenic sources. Climate change has already begun to affect 
the regions of Texas and New Mexico where Texas hornshell occurs, 
resulting in higher air temperatures, increased evaporation, increased 
groundwater pumping, and changing precipitation patterns such that 
water levels rangewide have already reached historic lows. These low 
water levels put the populations at risk of habitat loss from increased 
fine sediments, poor water quality, and increased predation risk.
    These risks, alone or in combination, are expected to result in the 
extirpation of additional populations, further reducing the overall 
redundancy and representation of the species. Historically, the 
species, with a large range of interconnected populations, would have 
been resilient to stochastic events such as drought and sedimentation 
because even if some populations were extirpated by such events, they 
could be recolonized over time by dispersal from nearby surviving 
populations. This connectivity would have made for a highly resilient 
species overall. However, under current conditions, connectivity is 
prevented due to large reservoirs and unsuitably high salinity levels 
between populations. As a consequence of these current conditions, the 
viability of the Texas hornshell now primarily depends on maintaining 
the remaining isolated populations.
    Of the five remaining isolated populations, three are small in 
abundance and occupied stream length and have low to no resiliency. The 
remaining two are larger, with increased abundance and occupied stream 
length; however, flow reduction, water quality decline, and habitat 
loss from sedimentation reduce the abundance and distribution of those 
populations. We have no information on population status in Mexico. 
Therefore, the Texas hornshell has no populations that are currently 
considered highly resilient. The high risk of extirpation of these 
populations leads to low levels of redundancy (few populations will 
persist to withstand catastrophic events) and representation (little to 
no ecological or genetic diversity will persist to respond to changing 
environmental conditions). Overall, these low levels of resiliency, 
redundancy, and representation result in the Texas hornshell having low 
viability, and the species currently faces a high risk of extinction.
    The Act defines an endangered species as any species that is ``in 
danger of extinction throughout all or a significant portion of its 
range'' and a threatened species as any species ``that is likely to 
become endangered throughout all or a significant portion of its range 
within the foreseeable future.'' We find that the Texas hornshell is 
presently in danger of extinction throughout its entire range based on 
the severity and immediacy of threats currently impacting the species. 
The overall range has been significantly reduced, and the remaining 
habitat and populations are threatened by a multitude of factors acting 
in combination to reduce the overall viability of the species. The risk 
of extinction is high because the remaining populations have a high 
risk of extirpation, are isolated, and have limited potential for 
recolonization. Therefore, on the basis of the best available 
scientific and commercial information, we propose listing the Texas 
hornshell as endangered in accordance with sections 3(6) and 4(a)(1) of 
the Act. We find that a threatened species status is not appropriate 
for the Texas hornshell because of the currently contracted range (loss 
of 85 percent of its historic range in the United States, and likely 
more in Mexico), because the threats are occurring across the entire 
range of the species, and because the threats are ongoing currently and 
are expected to continue or worsen into the future. Because the species 
is already in danger of extinction throughout its range, a threatened 
status is not appropriate.
    Under the Act and our implementing regulations, a species may 
warrant listing if it is endangered or threatened throughout all or a 
significant portion of its range. Because we have determined that the 
Texas hornshell is endangered throughout all of its range, no portion 
of its range can be ``significant'' for purposes of the definitions of 
``endangered species'' and ``threatened species.'' See the Final Policy 
on Interpretation of the Phrase ``Significant Portion of Its Range'' in 
the Endangered Species Act's Definitions of ``Endangered Species'' and 
``Threatened Species'' (79 FR 37578; July 1, 2014).

Available Conservation Measures

    Conservation measures provided to species listed as endangered or 
threatened species under the Act include recognition, recovery actions, 
requirements for Federal protection, and prohibitions against certain 
practices. Recognition through listing results in public awareness, and 
conservation by Federal, State, Tribal, and local agencies; private 
organizations; and individuals. The Act encourages cooperation with the 
States and other countries and calls for recovery actions to be carried 
out for listed species. The protection required by Federal agencies and 
the prohibitions against certain activities are discussed, in part, 
below.
    The primary purpose of the Act is the conservation of endangered 
and threatened species and the ecosystems upon which they depend. The 
ultimate goal of such conservation efforts is the recovery of these 
listed species, so that they no longer need the protective measures of 
the Act. Subsection 4(f) of the Act calls for the Service to develop 
and implement recovery plans for the conservation of endangered and 
threatened species. The recovery planning process involves the 
identification of actions that are necessary to halt or reverse the 
species' decline by addressing the threats to its survival and 
recovery. The goal of this process is to restore listed species to a 
point where they are secure, self-sustaining, and functioning 
components of their ecosystems.
    Recovery planning includes the development of a recovery outline 
shortly after a species is listed and preparation of a draft and final 
recovery plan. The recovery outline guides the immediate implementation 
of urgent recovery actions and describes the process to be used to 
develop a recovery plan. Revisions of the plan may be done to address 
continuing or new threats to the species, as new substantive 
information becomes available. The recovery plan also identifies 
recovery criteria for review of when a species may be ready for 
downlisting or delisting, and methods for monitoring recovery progress. 
Recovery plans also establish a framework for agencies to coordinate 
their recovery efforts and provide estimates of the cost of 
implementing recovery tasks. Recovery teams (composed of species 
experts, Federal and State agencies, nongovernmental organizations, and 
stakeholders) are often established to develop recovery plans. When 
completed, the recovery outline, draft recovery plan, and the final 
recovery plan will be available on our Web site (https://www.fws.gov/endangered), or from our Texas Coastal Ecological Services Field Office 
(see FOR FURTHER INFORMATION CONTACT).
    Implementation of recovery actions generally requires the 
participation of a broad range of partners, including other Federal 
agencies, States, Tribes, nongovernmental organizations, businesses, 
and private landowners. Examples of recovery actions include

[[Page 52807]]

habitat restoration (e.g., restoration of native vegetation), research, 
captive propagation and reintroduction, and outreach and education. The 
recovery of many listed species cannot be accomplished solely on 
Federal lands because their ranges may occur primarily or solely on 
non-Federal lands. To achieve recovery of these species requires 
cooperative conservation efforts on private, State, and Tribal lands. 
If this species is listed, funding for recovery actions will be 
available from a variety of sources, including Federal budgets, State 
programs, and cost share grants for non-Federal landowners, the 
academic community, and nongovernmental organizations. In addition, 
pursuant to section 6 of the Act, the States of Texas and New Mexico 
would be eligible for Federal funds to implement management actions 
that promote the protection or recovery of the Texas hornshell. 
Information on our grant programs that are available to aid species 
recovery can be found at: https://www.fws.gov/grants.
    Although the Texas hornshell is only proposed for listing under the 
Act at this time, please let us know if you are interested in 
participating in recovery efforts for this species. Additionally, we 
invite you to submit any new information on this species whenever it 
becomes available and any information you may have for recovery 
planning purposes (see FOR FURTHER INFORMATION CONTACT).
    Section 7(a) of the Act requires Federal agencies to evaluate their 
actions with respect to any species that is proposed or listed as an 
endangered or threatened species and with respect to its critical 
habitat, if any is designated. Regulations implementing this 
interagency cooperation provision of the Act are codified at 50 CFR 
part 402. Section 7(a)(4) of the Act requires Federal agencies to 
confer with the Service on any action that is likely to jeopardize the 
continued existence of a species proposed for listing or result in 
destruction or adverse modification of proposed critical habitat. If a 
species is listed subsequently, section 7(a)(2) of the Act requires 
Federal agencies to ensure that activities they authorize, fund, or 
carry out are not likely to jeopardize the continued existence of the 
species or destroy or adversely modify its critical habitat. If a 
Federal action may affect a listed species or its critical habitat, the 
responsible Federal agency must enter into consultation with the 
Service.
    Federal agency actions within the species' habitat that may require 
conference or consultation or both as described in the preceding 
paragraph include management and any other landscape-altering 
activities on Federal lands administered by the Bureau of Land 
Management, Bureau of Reclamation, and National Park Service; issuance 
of section 404 Clean Water Act (33 U.S.C. 1251 et seq.) permits by the 
U.S. Army Corps of Engineers; and construction and maintenance of roads 
or highways by the Federal Highway Administration.
    The Act and its implementing regulations set forth a series of 
general prohibitions and exceptions that apply to endangered wildlife. 
The prohibitions of section 9(a)(1) of the Act, codified at 50 CFR 
17.21, make it illegal for any person subject to the jurisdiction of 
the United States to take (which includes harass, harm, pursue, hunt, 
shoot, wound, kill, trap, capture, or collect; or to attempt any of 
these) endangered wildlife within the United States or on the high 
seas. In addition, it is unlawful to import; export; deliver, receive, 
carry, transport, or ship in interstate or foreign commerce in the 
course of commercial activity; or sell or offer for sale in interstate 
or foreign commerce any listed species. It is also illegal to possess, 
sell, deliver, carry, transport, or ship any such wildlife that has 
been taken illegally. Certain exceptions apply to employees of the 
Service, the National Marine Fisheries Service, other Federal land 
management agencies, and State conservation agencies.
    We may issue permits to carry out otherwise prohibited activities 
involving endangered wildlife under certain circumstances. Regulations 
governing permits are codified at 50 CFR 17.22. With regard to 
endangered wildlife, a permit may be issued for the following purposes: 
For scientific purposes, to enhance the propagation or survival of the 
species, and for incidental take in connection with otherwise lawful 
activities. There are also certain statutory exemptions from the 
prohibitions, which are found in sections 9 and 10 of the Act.
    It is our policy, as published in the Federal Register on July 1, 
1994 (59 FR 34272), to identify to the maximum extent practicable at 
the time a species is listed, those activities that would or would not 
constitute a violation of section 9 of the Act. The intent of this 
policy is to increase public awareness of the effect of a proposed 
listing on proposed and ongoing activities within the range of the 
species proposed for listing. Based on the best available information, 
if we list this species, the following actions are unlikely to result 
in a violation of section 9, if these activities are carried out in 
accordance with existing regulations and permit requirements; this list 
is not comprehensive:
    (1) Normal agricultural and silvicultural practices, including 
herbicide and pesticide use, which are carried out in accordance with 
any existing regulations, permit and label requirements, and best 
management practices; and
    (2) Normal residential landscape activities.
    Based on the best available information, if we list this species, 
the following activities may potentially result in a violation of 
section 9 of the Act; this list is not comprehensive:
    (1) Unauthorized handling or collecting of the species;
    (2) Modification of the channel or water flow of any stream in 
which the Texas hornshell is known to occur;
    (3) Livestock grazing that results in direct or indirect 
destruction of stream habitat; and
    (4) Discharge of chemicals or fill material into any waters in 
which the Texas hornshell is known to occur.
    Questions regarding whether specific activities would constitute a 
violation of section 9 of the Act should be directed to the Texas 
Coastal Ecological Services Field Office (see FOR FURTHER INFORMATION 
CONTACT).

Critical Habitat for the Texas Hornshell

Background

    Critical habitat is defined in section 3 of the Act as:
    (1) The specific areas within the geographical area occupied by the 
species, at the time it is listed in accordance with the Act, on which 
are found those physical or biological features:
    (a) Essential to the conservation of the species, and
    (b) Which may require special management considerations or 
protection; and
    (2) Specific areas outside the geographical area occupied by the 
species at the time it is listed, upon a determination that such areas 
are essential for the conservation of the species.
    Conservation, as defined under section 3 of the Act, means to use 
and the use of all methods and procedures that are necessary to bring 
an endangered or threatened species to the point at which the measures 
provided pursuant to the Act are no longer necessary. Such methods and 
procedures include, but are not limited to, all activities associated 
with scientific resources management such as research, census, law 
enforcement,

[[Page 52808]]

habitat acquisition and maintenance, propagation, live trapping, and 
transplantation, and, in the extraordinary case where population 
pressures within a given ecosystem cannot be otherwise relieved, may 
include regulated taking.
    Critical habitat receives protection under section 7 of the Act 
through the requirement that Federal agencies ensure, in consultation 
with the Service, that any action they authorize, fund, or carry out is 
not likely to result in the destruction or adverse modification of 
critical habitat. The designation of critical habitat does not affect 
land ownership or establish a refuge, wilderness, reserve, preserve, or 
other conservation area. Such designation does not allow the government 
or public to access private lands. Such designation does not require 
implementation of restoration, recovery, or enhancement measures by 
non-Federal landowners. Where a landowner requests Federal agency 
funding or authorization for an action that may affect a listed species 
or critical habitat, the consultation requirements of section 7(a)(2) 
of the Act would apply, but even in the event of a destruction or 
adverse modification finding, the obligation of the Federal action 
agency and the landowner is not to restore or recover the species, but 
to implement reasonable and prudent alternatives to avoid destruction 
or adverse modification of critical habitat.
    Section 4 of the Act requires that we designate critical habitat on 
the basis of the best scientific data available. Further, our Policy on 
Information Standards Under the Endangered Species Act (published in 
the Federal Register on July 1, 1994 (59 FR 34271)), the Information 
Quality Act (section 515 of the Treasury and General Government 
Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R. 5658)), 
and our associated Information Quality Guidelines, provide criteria, 
establish procedures, and provide guidance to ensure that our decisions 
are based on the best scientific data available. They require our 
biologists, to the extent consistent with the Act and with the use of 
the best scientific data available, to use primary and original sources 
of information as the basis for recommendations to designate critical 
habitat.

Prudency Determination

    Section 4(a)(3) of the Act, as amended, and implementing 
regulations (50 CFR 424.12), require that, to the maximum extent 
prudent and determinable, the Secretary designate critical habitat at 
the time the species is determined to be endangered or threatened. Our 
regulations (50 CFR 424.12(a)(1)) state that the designation of 
critical habitat is not prudent when one or both of the following 
situations exist: (1) The species is threatened by taking or other 
human activity, and identification of critical habitat can be expected 
to increase the degree of threat to the species, or (2) such 
designation of critical habitat would not be beneficial to the species.
    There is currently no imminent threat of take attributed to 
collection or vandalism under Factor B for the Texas hornshell, and 
identification and mapping of critical habitat is not likely to 
increase any such threat. In the absence of finding that the 
designation of critical habitat would increase threats to a species, if 
there are any benefits to a critical habitat designation, then a 
prudent finding is warranted. The potential benefits of designation 
include: (1) Triggering consultation under section 7 of the Act in new 
areas for actions in which there may be a Federal nexus where it would 
not otherwise occur because, for example, it is or has become 
unoccupied or the occupancy is in question; (2) focusing conservation 
activities on the most essential features and areas; (3) providing 
educational benefits to State or county governments or private 
entities; and (4) preventing people from causing inadvertent harm to 
the species. Therefore, because we have determined that the designation 
of critical habitat will not likely increase the degree of threat to 
these species and may provide some measure of benefit, we find that 
designation of critical habitat is prudent for the Texas hornshell.

Critical Habitat Determinability

    Having determined that designation is prudent, under section 
4(a)(3) of the Act we must find whether critical habitat for the 
species is determinable. Our regulations at 50 CFR 424.12(a)(2) state 
that critical habitat is not determinable when one or both of the 
following situations exist: (1) Information sufficient to perform 
required analyses of the impacts of the designation is lacking, or (2) 
the biological needs of the species are not sufficiently well known to 
permit identification of an area as critical habitat.
    As discussed above, we have reviewed the available information 
pertaining to the biological needs of this species and habitat 
characteristics where this species is located. Because the biological 
needs are not sufficiently well known to permit identification of 
critical habitat, we are seeking additional information regarding 
updated occurrence records for the Texas hornshell, future climate 
change effects on the species' habitat, and other analyses. Therefore, 
we conclude that the designation of critical habitat is not 
determinable for the Texas hornshell at this time. We will make a 
determination on critical habitat no later than 1 year following any 
final listing determination.

Required Determinations

Clarity of the Rule

    We are required by Executive Orders 12866 and 12988 and by the 
Presidential Memorandum of June 1, 1998, to write all rules in plain 
language. This means that each rule we publish must:
    (1) Be logically organized;
    (2) Use the active voice to address readers directly;
    (3) Use clear language rather than jargon;
    (4) Be divided into short sections and sentences; and
    (5) Use lists and tables wherever possible.
    If you feel that we have not met these requirements, send us 
comments by one of the methods listed in ADDRESSES. To better help us 
revise the rule, your comments should be as specific as possible. For 
example, you should tell us the numbers of the sections or paragraphs 
that are unclearly written, which sections or sentences are too long, 
the sections where you feel lists or tables would be useful, etc.

National Environmental Policy Act (42 U.S.C. 4321 et seq.)

    We have determined that environmental assessments and environmental 
impact statements, as defined under the authority of the National 
Environmental Policy Act (NEPA; 42 U.S.C. 4321 et seq.), need not be 
prepared in connection with listing a species as an endangered or 
threatened species under the Endangered Species Act. We published a 
notice outlining our reasons for this determination in the Federal 
Register on October 25, 1983 (48 FR 49244).

References Cited

    A complete list of references cited is available in Appendix A of 
the SSA Report (U.S. Fish and Wildlife Service. 2016. Species status 
assessment report for the Texas hornshell (Popenaias popeii), Version 
1.0. Albuquerque, NM), available online at https://www.regulations.gov, 
under Docket Number FWS-R2-ES-2016-0077.

[[Page 52809]]

Authors

    The primary authors of this proposed rule are the staff members of 
the Texas Coastal Ecological Services Field Office.

List of Subjects in 50 CFR Part 17

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

Proposed Regulation Promulgation

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

PART 17--ENDANGERED AND THREATENED WILDLIFE AND PLANTS

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

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

0
2. Amend Sec.  17.11(h) by adding an entry for ``Hornshell, Texas'' to 
the List of Endangered and Threatened Wildlife in alphabetical order 
under Clams:


Sec.  17.11  Endangered and threatened wildlife.

* * * * *
    (h) * * *

----------------------------------------------------------------------------------------------------------------
                                                                                              Listing citations
           Common name                Scientific name        Where listed         Status        and applicable
                                                                                                    rules
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
              Clams
 
                                                  * * * * * * *
Hornshell, Texas.................  Popenaias popeii....  Wherever found.....  E              [Federal Register
                                                                                              citation when
                                                                                              published as a
                                                                                              final rule.]
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------


    Dated: July 21, 2016.
 Stephen Guertin,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 2016-18816 Filed 8-9-16; 8:45 am]
 BILLING CODE P