Endangered and Threatened Wildlife and Plants; Endangered Species Status for Texas Hornshell, 5720-5735 [2018-02672]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 83, Number 28 (Friday, February 9, 2018)]
[Rules and Regulations]
[Pages 5720-5735]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-02672]


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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: Final rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine 
endangered species status under the Endangered Species Act of 1973 
(Act), as amended, for the Texas hornshell (Popenaias popeii), a 
freshwater mussel species from New Mexico, Texas, and Mexico. The 
effect of this regulation will be to add this species to the List of 
Endangered and Threatened Wildlife.

DATES: This rule becomes effective March 12, 2018.

ADDRESSES: This final rule is available on the internet at https://www.regulations.gov in Docket No. FWS-R2-ES-2016-0077 and in https://www.fws.gov/southwest/es/TexasCoastal/. Comments and materials we 
received, as well as supporting documentation we used in preparing this 
rule, are available for public inspection at https://www.regulations.gov. Comments, materials, and documentation that we 
considered in this rulemaking will be available by appointment, during 
normal business hours at the address shown in FOR FURTHER INFORMATION 
CONTACT.

FOR FURTHER INFORMATION CONTACT: Charles Ardizzone, U.S. Fish and 
Wildlife Service, Texas Coastal Ecological Services Field Office, 17629 
El Camino Real #211, Houston, TX 77058; or by telephone 281-286-8282. 
Persons who use a telecommunications device for the deaf (TDD) may call 
the Federal Relay Service at 800-877-8339. Website: https://www.fws.gov/southwest/es/TexasCoastal/.

SUPPLEMENTARY INFORMATION: 

Executive Summary

    Why we need to publish a rule. Under the Endangered Species Act, a 
species is added to the Federal List of Endangered and Threatened 
Wildlife if it is endangered or threatened throughout all or a 
significant portion of its range. Listing a species as an endangered or 
threatened species can only be completed by issuing a rule. The Lists 
of Endangered and Threatened Wildlife and Plants are located in title 
50 of the Code of Federal Regulations (CFR) in part 17.
    What this rule does. This rule finalizes the listing of the Texas 
hornshell (Popenaias popeii) as an endangered species. The species will 
be added to the List of Endangered and Threatened Wildlife at 50 CFR 
17.11(h).
    The basis for our action. Under the Endangered Species Act, we can 
determine that a species is an endangered or threatened species based 
on any of the following factors: (A) The present or threatened 
destruction, modification, or curtailment of its habitat or range; (B) 
Overutilization for commercial, recreational, scientific, or 
educational purposes; (C) Disease or predation; (D) The inadequacy of 
existing regulatory mechanisms; or (E) Other natural or manmade factors 
affecting its continued existence.
    The Texas hornshell is an endangered species based on impairment of 
water quality, loss of flowing water, and accumulation of fine sediment 
(Factor A), predation (Factor C), and barriers to host fish movement 
and the effects of climate change (Factor E).
    Peer review and public comment. 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 2018, entire). We sought comments on the SSA report from 
independent specialists to ensure that our analysis was based on 
scientifically sound data, assumptions, and analyses. We received 
feedback from four scientists with expertise in freshwater mussel 
biology, ecology, and genetics. During the comment period for the 
proposed rule, we reached out to an additional five peer reviewers, and 
we received responses from three. We incorporated peer review 
suggestions and comments into the SSA report and the final listing 
rule. 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.

Previous Federal Actions

    On August 10, 2016, we published a proposed rule (81 FR 52796) to 
list the Texas hornshell as an endangered species under the Endangered 
Species Act of 1973, as amended (Act; 16 U.S.C. 1531 et seq.). The 
publication of this proposed rule complied with a deadline established 
in a court-approved settlement agreement (Endangered Species Act 
Section 4 Deadline Litigation, No. 10-377 (EGS), MDL Docket No. 2165 
(D.D.C. May 10, 2011)). That proposal had a 60-day comment period, 
ending October 11, 2016. We reopened the comment period for 30 days on 
May 30, 2017 (82 FR 24654), in order to hold two public hearings on the 
proposed rule. We then extended the final listing determination for 6 
months due to substantial scientific disagreement about the species' 
status in Mexico and reopened the comment period for an additional 30 
days (82 FR 37397). For a description of previous Federal actions 
concerning the Texas hornshell, please refer to the August 10, 2016, 
proposed listing rule (81 FR 52796).

Background

    A thorough review of the taxonomy, life history, and ecology of 
Texas hornshell (Popenaias popeii) is presented in the SSA report 
(Service 2018, entire).

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 (Williams et al. 2017, p. 42).
    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 
fertilize the eggs, which are held during maturation in an area of the 
gills called the marsupial chamber. The

[[Page 5721]]

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, p. 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.
    The actual lifespan 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 
believe 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 to occur in lakes, ponds, or reservoirs.
    The Texas hornshell historically ranged throughout the Rio Grande 
drainage in the United States (New Mexico and Texas) and Mexico. 
Individuals that had previously been identified as Texas hornshell in 
Mexican Gulf Coastal streams (Johnson 1999, p. 23), including in our 
proposed rule to list the species, have recently been determined to 
belong to a different, undescribed species (Inoue 2017, p. 1). 
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.

[[Page 5722]]

[GRAPHIC] [TIFF OMITTED] TR09FE18.004

    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, in 2016, researchers 
collected three old, live Texas hornshell and 37 shells 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 (Bosman et al. 2016, p. 6; Randklev et al. 
2016, p. 9). Numerous dead shells were found farther downstream in the 
Pecos River in 2016 (Bosman et al. 2016, p. 6; Randklev et al. 2016, p. 
9). Prior to this collection, live individuals had not been collected 
in the Pecos River since 1973 (Randklev et al. 2016, p. 4).
    Because the number of live individuals detected is so small (three 
live individuals found in 2016), it is difficult to draw many 
conclusions about the overall abundance and health of the population. 
The population appears to be extremely small, the live individuals were 
old, and no evidence of reproduction such as young individuals or 
gravid females (females with mature larvae within the gills) 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

[[Page 5723]]

2014, p. 19). Between 2008 and 2014, researchers collected 11 
individuals from upstream in the Devils River (Burlakova and Karatayev 
2014, p. 16; Karatayev et al. 2015, p. 4). More intensive surveys 
conducted in 2014, 2015, and 2017, including 20 sites, have yielded 
more than 150 individuals in approximately 29 mi (47 km) of the river--
all from The Nature Conservancy's Dolan Falls Preserve and 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; Diaz 2017, p. 1). 
Because of the increased number of individuals collected since 2014, it 
is likely that the Devils River population is more numerous than 
previously thought, although we do not expect that this 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 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. The 
species is found in low density (approximately 40 individuals per km) 
in this region of the Rio Grande (Burlakova and Karatayev 2014, p. 16). 
Subsequent surveys 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 (Randklev et al. 2015, entire). For 
purposes of this analysis, we believe the species is present in the 
entire section between these collections, approximately 62 mi (100 km). 
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). 
We expect Texas hornshell to occur between the known occupied sections 
where we have documented presence of the species, near the confluence 
with San Francisco Creek (Howells 2001a, p. 6), but limited access has 
prevented recent surveys for the species. Young individuals and gravid 
females have been found throughout the Lower Canyons reach, indicating 
recruitment is occurring (Randklev et al. 2015, p. 8). Scientific 
modeling reveals that Texas hornshell are found in areas near spring 
inflows in rocky habitats in the Lower Canyons reach (Randklev et al. 
2017, pp. 5-6).
    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 was 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). Within this reach, Texas hornshell are 
found in rocky habitats in areas with appropriate water quality 
(Randklev et al. 2017, pp. 5-6). No live Texas hornshell have been 
found downstream of the city of Laredo in recent years.
    Mexico: The species historically occurred in the Rio Salado basin, 
which is a tributary to the Rio Grande in Mexico. Rio Salado and 
several tributaries were surveyed in the early 2000s, with several 
recently dead shells collected in 2001 and 2002 in a tributary to Rio 
Salado, the Rio Sabinas (Strenth et al. 2004, p. 225). The surveyed 
portions of riverbed were reported to be dry with no evidence of recent 
water flow, so it is unlikely these shells represent an abundant Texas 
hornshell population.
    In the mainstem Rio Salado, several old shells and one recently 
dead shell were collected at two sites in 2002 (Strenth et al. 2004, p. 
227). As with the Rio Sabinas, the river exhibited no flow; at one 
site, household waste was reported. These rivers, and many others in 
this region of Mexico, have been noted as losing flow and becoming dry 
or intermittent since the mid-1990s (Contreras-B. and Lozano-V. 1994, 
p. 381).
    In 2017, eight sites in four rivers in the Rio Salado basin were 
surveyed for Texas hornshell. No live individuals were found at any 
site, and three long dead shells were found at one site in the Rio 
Nadadores (Hein et al. 2017, p. 3), further indicating that the species 
may be extirpated from the Rio Salado basin.
    Separately, Texas hornshell were thought to occur in approximately 
15 rivers that flow into the Gulf of Mexico and are not tributaries to 
the Rio Grande. Recent genetic analysis of museum samples indicates 
that individuals that had previously been identified as Texas hornshell 
in these Mexican Gulf Coastal streams belong to a different, 
undescribed species (Inoue 2017, p. 1). Therefore, we conclude that the 
Texas hornshell was never native to Gulf Coastal rivers outside of the 
Rio Grande basin, and it is endemic to the Rio Grande basin in the 
United States and Mexico.

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 excess fine sediment accumulation. They need water 
quality parameters to be within a suitable range (Randklev et al. 2017, 
p. 5) (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 and bacteria 
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 timeframes 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

[[Page 5724]]

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 hydrologically 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 and 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 
single 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 successfully recruiting young individuals into the 
reproducing population. Population size and abundance reflects previous 
influences on the population and habitat, while reproduction and 
recruitment indicate 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 inches (in)) are very hard 
to detect. Therefore, reproduction is verified by repeatedly capturing 
small-sized individuals near the low end of the detectable size range 
(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 taxonomic 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 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). 
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 for 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

    Section 4 of the Act (16 U.S.C. 1533) and its implementing 
regulations (50 CFR part 424) set forth the procedures for determining 
whether a species is an ``endangered species'' or a ``threatened 
species.'' The Act defines an endangered species as a species that is 
``in danger of extinction throughout all or a significant portion of 
its range,'' and a threatened species as a species that is ``likely to 
become an endangered species within the foreseeable future throughout 
all or a significant portion of its range.'' The Act directs us to 
determine whether any species is an endangered species or a threatened 
species because of one or more of the following factors affecting its 
continued existence: (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 completed a comprehensive assessment of the biological status of 
the Texas hornshell and prepared a report, which provides a thorough 
account of the species' overall viability. We define viability as the 
ability of the Texas hornshell to sustain populations in natural river 
systems over time. 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. Please refer to Chapter 4 of the 
SSA report for a more detailed discussion of the factors affecting the 
Texas hornshell.

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 final 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

[[Page 5725]]

collection and disease, are not discussed here. The primary risk 
factors affecting the status of the Texas hornshell are: (1) Increased 
fine sediment (Factor A), (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 the effects of climate change (Factor E). We also 
factored into our analysis the degree to which existing regulatory 
mechanisms either ameliorate or exacerbate these risk factors (Factor 
D). We also 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 inhabiting 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, and 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 
concurrent 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 deposition may continue to occur sporadically. 
Fine sediments are also accumulating at the Rio Grande-Laredo 
population. Low water levels in 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 the effects of climate change (Nohara et 
al. 2006, p. 1087; Bren School of Environmental Management 2014, p. 91; 
Miyazono et al. 2015, p. A-3).
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, 
nutrients, heavy metals, pesticides, herbicides, and a wide variety of 
newly emerging contaminants to the aquatic environment. Ammonia is of 
particular concern below wastewater 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; Randklev et al. 2017, p. 5).
    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 change the timing of spawning 
and glochidial release. 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 accumulate on irrigated lands 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, and Pecos Rivers), a single spill 
could eliminate the entire population.
    In August of 2017, 18,000 barrels of wastewater from oil and gas 
production and 11 barrels of oil were spilled from a ruptured pipeline 
into the Delaware River, upstream of the Texas hornshell reintroduction 
site (Eaton 2017, p. 1), demonstrating a risk of contaminant spills in 
this area. A boom was deployed to collect some of the oil, but 
wastewater mixes with river water and cannot be collected (Onsurez 
2017, p. 1). An Administrative Order was issued by the Environmental 
Protection Agency (EPA) on October 16, 2017 (EPA 2017), directing that 
a pollution prevention plan be created to prevent such spills in the 
future, but no other regulatory action was taken. Safety concerns due 
to poor water quality from the spill have prevented surveys to 
determine if the reintroduced individuals survived the event.
    Any reduction in surface flow from drought, instream diversion, or 
groundwater extraction results in concentrated contaminant and salinity 
levels, increased water temperatures in

[[Page 5726]]

streams, and exacerbated effects to Texas hornshell individuals and 
populations.
    Poor water quality currently affects most Texas hornshell 
populations 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 only a short time (days or weeks, 
depending on the time of year), 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 also detrimental to Texas hornshell 
populations. 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, 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). These changes are 
exacerbated by increased groundwater pumping resulting from increased 
water demand in response to changes in water availability. The rivers 
inhabited by Texas hornshell have some resiliency to drought because 
they are spring-fed (Black and Devils Rivers) or 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), the 
contribution of the Rio Conchos has fallen to as low as 40 percent 
(Carter et 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 flows. 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 to 
desiccation 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 m\3\)) 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, Texas hornshell 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 (Toll et al. 
2017, pp. 46-47). 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 
and death.
Barriers to Fish Movement
    Two of the Texas hornshell's primary host fish species (river 
carpsucker and red shiner) are 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 as described below.
    Texas hornshell were likely historically distributed throughout the 
Rio Grande, Pecos River, Devils River, and Black River basins in Texas, 
New Mexico, and Mexico 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

[[Page 5727]]

juveniles would excyst from host fish in new locations. The loss of 
historical range has resulted in remaining populations that 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 by 
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. No opportunity for 
natural interaction currently exists 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 all 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 (Lang 2001, 
p. 26; Robertson 2016, p. 1). As drought and low flow conditions are 
projected to occur more often and for longer periods due to the effects 
of climate change, the Devils River in particular is 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 projected to be one of 
the areas most affected by 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 and ammonia. 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 increased water temperature and flow 
loss (Wuebbles et 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, declines 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 as a result of the effects of climate change.
Conservation Actions and Regulatory Mechanisms
    About 7 percent of known occupied habitat for the Texas hornshell 
is in New Mexico, and the Service collaborated with water users, oil 
and gas developers, landowners, and other partners to develop candidate 
conservation agreements (CCAs) and candidate conservation agreements 
with assurances (CCAAs) for the species on State, Federal, and private 
lands (Regulations pertaining to these types of agreements are at 50 
CFR 17.22 and 17.32.). These agreements provide voluntary conservation 
that will, if executed properly, reduce threats to the species while 
improving physical habitat and water quality. The key conservation 
measures in the agreements are 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. These 
agreements were approved by the Service in October 2017. Enrollment in 
the agreements is available until this rule becomes effective. Because 
enrollment under these agreements is just beginning, the conservation 
measures have not yet become effective at reducing or eliminating 
threats to the species. As discussed elsewhere in this decision, we do 
not expect these agreements to modify the overall conservation status 
of the species because of the relatively small amount of habitat 
subject to these agreements; however, they will provide good 
conservation benefits to the hornshell populations within the covered 
area.
    In 2013, the New Mexico Department of Game and Fish (NMDGF) began 
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, as well as the effect of the produced water and oil spill in 
2017 on these individuals. Mussel reintroductions take many years to 
show success, because

[[Page 5728]]

the size of the juvenile mussel prevents detecting natural 
reintroduction for at least 3 years or more. As a positive sign, NMDGF 
biologists captured two gray redhorse from the Delaware River that 
appeared to be infested with Texas hornshell glochidia (NMDGF 2017, p. 
1). We expect the reintroduction effort to continue over the next 
several years, but we are not considering the population to have been 
successfully reestablished until progeny from the reintroduced adults 
have been found in the river.
    In Texas, The Nature Conservancy and Texas Parks and Wildlife 
Department manage lands under their purview in the Devils River 
watershed for native fish, wildlife, and plant 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.
Summary of Risks to Texas Hornshell
    Our analysis of the past, current, and future influences on what 
the Texas hornshell needs for long-term viability revealed that five 
influences pose the largest risk to future viability of the species. 
These risks are primarily related to habitat changes: The accumulation 
of fine sediments, the loss of flowing water, and impairment of water 
quality; these are all exacerbated by the effects of climate change. 
Additionally, predation and barriers to fish movement exacerbate the 
effects of these risks. We did not assess overutilization for 
scientific and commercial purposes or disease in detail, because these 
risks do not appear to be occurring at a level that affects Texas 
hornshell populations. The accumulation of fine sediments, the loss of 
flowing water, impairment of water quality, predation, and barriers to 
fish movement, as well as conservation and management efforts, are 
acting individually and cumulatively to affect the current and future 
viability of the Texas hornshell.

Current Condition

    Overall, five known populations of Texas hornshell remain, 
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 length (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 impacts 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.
    The CCA/CCAA being implemented for the Black River will help reduce 
the likelihood of a spill and help maintain water flows, but extended 
droughts are nevertheless likely, resulting in low water flows. 
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 to moderate resiliency.
    Pecos River: The Pecos River population is extremely small and 
exhibits no evidence of reproduction. The age, poor condition, and 
small number of live individuals found among the very high number of 
dead shells indicates a population in severe decline; this situation 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 impacts 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 the Rio 
Conchos will continue to be an 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

[[Page 5729]]

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 population has 
moderate resiliency.
    Mexico: The Rio Salado basin has not yielded any evidence of an 
existing population despite several surveys since 2000. Texas hornshell 
is presumed to be extirpated from this basin. There are no other 
historical locations of Texas hornshell in Mexico.

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. The additional future 
scenarios project conditions that are worse for the Texas hornshell 
than the current condition or status quo projection. 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 of Species Status, below), we are not 
presenting the results of the other future scenarios in this final 
rule. 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 2018) for the full analysis of 
future scenarios.

Summary of Changes From the Proposed Rule

    We made no changes from the proposed rule to the text of the rule 
itself. Since the publication of the August 10, 2016, proposed rule to 
list the Texas hornshell as endangered (81 FR 52796), we have made the 
following substantive changes in our supporting materials:
    (1) Genetic analysis of individuals from the Rio Panuco basin in 
Mexico (representing the Mexican Gulf Coastal streams) indicates that 
they are not Texas hornshell; instead, they are a different, as yet 
undescribed species. The Rio Panuco basin contained the majority of 
historical records of Texas hornshell in the Mexican Gulf Coastal area. 
In light of this information, it is unlikely Texas hornshell occurred 
in the remainder of the Mexican Gulf Coastal streams. We have 
incorporated this information into the historical, current, and future 
conditions of the species in our SSA analysis and report.
    (2) The Office of the Texas Comptroller of Public Accounts provided 
additional survey information regarding the Delaware River, which we 
have incorporated into our SSA report.

Summary of Comments and Recommendations

    In the proposed rule published on August 10, 2016 (81 FR 52796), we 
requested that all interested parties submit written comments on the 
proposal by October 11, 2016. We also contacted appropriate Federal and 
State agencies, scientific experts and organizations, and other 
interested parties and invited them to comment on the proposal. 
Newspaper notices inviting general public comment were published in the 
San Antonio Express News and the Carlsbad Current-Argus. We received 
requests for public hearings, and we held two public hearings: in 
Laredo, Texas, on June 13, 2017, and in Carlsbad, New Mexico, on June 
15, 2017. The comment period was reopened for 30 days on May 30, 2017 
(82 FR 24654), until June 29, 2017, and for another 30 days on August 
10, 2017 (82 FR 37397), until September 11, 2017.
    During the first comment period, we received 24 comment letters 
directly addressing the proposal. During the second comment period and 
at the public hearings, we received 16 comment letters and statements 
directly addressing the proposal. During the third comment period, we 
received 697 comment letters--including 685 form letters--directly 
addressing the proposal. All substantive information provided during 
the comment periods has either been incorporated directly into this 
final determination, into the SSA report, or addressed below. We 
received several comments that clarified various topics within the SSA 
report or this rule, and we incorporated them as appropriate. Comments 
received were grouped into 10 general issues specifically relating to 
the proposed listing status for the Texas hornshell and are addressed 
in the following summary and incorporated into the final rule as 
appropriate.

Peer Reviewer Comments

    In accordance with our peer review policy published on July 1, 1994 
(59 FR 34270), we solicited expert opinion from five knowledgeable 
individuals with scientific expertise that included familiarity with 
Texas hornshell and its habitat, biological needs, and threats. During 
development of the SSA report, we reached out to five peer reviewers 
and received responses from four; all comments were incorporated into 
the SSA report prior to the proposed rule. During the comment period 
for the proposed rule, we reached out to an additional five peer 
reviewers, and we received responses from three. We reviewed all 
comments received from the peer reviewers for substantive issues and 
new information regarding the listing of the Texas hornshell. The 
reviewers were generally supportive of our approach and made 
suggestions and comments that strengthened our analysis. Peer reviewer 
comments are addressed in the following summary and incorporated into 
the SSA report and this final rule as appropriate.
    (1) Comment: One peer reviewer, NMDGF, the New Mexico State Lands 
Office (NMSLO), and five commenters stated that we should not presume 
the species has been extirpated from all locations in Mexico, given the 
lack of surveys particularly from the Gulf Coastal region.
    Our Response: We recently learned that the populations in the Gulf 
Coastal region in Mexico previously identified as Texas hornshell are a 
different species, and we have updated our analysis accordingly. The 
remaining historical Texas hornshell populations in Mexico are in the 
Rio Salado basin in Nuevo Leon. This population was originally reported 
in 1891 (Mussel Project 2015). When this area was revisited in 2004 
(Strenth et al. 2004, p. 227), household waste was found throughout the 
river and no live individuals were found. This basin was visited again 
in 2017, with surveys at eight sites in four rivers, and no live 
individuals were found (Hein et al. 2017, p. 3). Therefore, we have no 
evidence that any populations of Texas hornshell persist in Mexico. We 
have updated the SSA report to reflect the new genetic information and 
survey findings.
    (2) Comment: One peer reviewer suggested we incorporate the effects 
of population fragmentation and isolation on the species.
    Our Response: We discussed population isolation in our analysis of 
barriers to fish movement. Because the host fish may no longer move 
between populations of Texas hornshell, there is no immigration of 
individuals to increase genetic diversity and recolonize after 
stochastic events. The effect of this isolation is incorporated

[[Page 5730]]

into our analysis of the current and future condition of populations.

Comments From States

    (3) Comment: We received one comment from the Texas Commission on 
Environmental Quality (TCEQ) clarifying the surface water rights and 
treaty obligations in the rivers inhabited by Texas hornshell.
    Our Response: In the SSA report, we have clarified water management 
responsibilities of inland rivers occupied by Texas hornshell, as well 
as obligations under the 1944 Treaty between the United States and 
Mexico, which governs water management in the mainstem Rio Grande.
    (4) Comment: We received comments from NMDGF, NMSLO, and one 
commenter expressing concern that listing may affect relationships with 
landowners along the Black River and that we have not adequately 
considered the conservation being implemented in the Black and Delaware 
River watersheds. In particular, NMSLO suggested that the Policy for 
Evaluation of Conservation Efforts when Making Listing Decisions (PECE) 
(68 FR 15100, March 28, 2003) requires ``the Service to evaluate the 
conservation efforts of state and foreign governments or federal 
agencies, among others.''
    Our Response: We share the commenters' desire to maintain 
relationships with landowners along the Black River. NMDGF has spent 
considerable time and effort developing relationships with the private 
landowners on the Black River in order to access the river, survey for 
Texas hornshell, and implement conservation measures for the species. 
In the Black and Delaware River watersheds, the Service, NMDGF, NMSLO, 
Bureau of Land Management (BLM), and private landowners have developed 
CCAs/CCAAs for Texas hornshell, which will provide voluntary 
conservation that will reduce threats to the species while improving 
physical habitat and water quality. A notice of availability on the 
permit application packages, including the draft CCA, draft CCAAs, and 
draft environmental assessment was published in the Federal Register on 
July 7, 2017, and was available for public comment for 30 days (82 FR 
31625, July 7, 2017). The final agreements were signed by the Service, 
BLM, the New Mexico Land Commissioner, and the Center of Excellence on 
October 19, 2017. For private landowners who choose to enroll in these 
agreements, the agreements support the conservation of Texas hornshell 
while providing the landowner with a permit for incidental take of the 
species during the course of otherwise lawful activities. It is our 
intent that these agreements will help maintain landowner relationships 
in the Black and Delaware River watersheds.
    We have addressed all relevant conservation efforts, as required by 
the Act, in this decision. Consistent with the PECE we find that the 
potential reduction in threats resulting from the CCAs/CCAAs in the 
Black and Delaware River watersheds limited to these watersheds and is 
not widespread enough to preclude listing the Texas hornshell as an 
endangered species. The PECE does not set standards for how much 
conservation is needed to make listing unnecessary. The PECE explains 
that we evaluate the significance of plans that address only a portion 
of a species' range in the context of the species' overall status. 
While a formalized conservation effort may be effective in reducing or 
removing threats in a portion of the species' range, that effort may or 
may not be sufficient to remove the need to list the species as 
threatened or endangered. Although the CCAs/CCAAs are expected to 
improve the status of the Texas hornshell in the Black and Delaware 
Rivers, four populations of Texas hornshell will not be affected by the 
agreements. Therefore, the agreements, even if fully implemented and 
effective, will not improve the status of Texas hornshell such that it 
does not meet the Act's definition of a threatened or endangered 
species. Because of the limited scope of the agreements, it was 
unnecessary to conduct a PECE analysis.
    (5) Comment: TCEQ and four commenters stated that our population 
survey information is limited and that we need to delay a final 
determination until more surveys are conducted and more data are 
collected.
    Our Response: The Act requires the Service to publish a final rule 
within 1 year from the date we propose to list a species. This 1-year 
timeframe can be extended only if there is substantial disagreement 
regarding the sufficiency or accuracy of the available data relevant to 
the determination or revision concerned, but only for 6 months and only 
for purposes of soliciting additional data. In such a case, under 
section 4(b)(6)(B)(i) of the Act, the Secretary may extend the 1-year 
period to make a final determination by up to 6 months for the purposes 
of soliciting additional data. In light of this comment, due to 
disagreements about the species' status in the Gulf Coastal region of 
Mexico, we extended the final determination by 6 months (82 FR 37397, 
August 10, 2017).
    In accordance with section 4 of the Act, we are required to 
determine whether a species warrants listing on the basis of the best 
scientific and commercial data available. Further, our Policy on 
Information Standards under the 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 (www.fws.gov/informationquality/), 
provide criteria and guidance, and establish procedures 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 determining whether a 
species warrants listing as an endangered or threatened species.
    Science is a cumulative process, and the body of knowledge is ever-
growing. In light of this fact, the Service will always take new 
research into consideration. If plausible new research supports 
amendment or revision of this rule in the future, the Service will 
modify the rule consistent with the Act and our established work 
priorities at that time.
    (6) Comment: We received two comments from NMDGF regarding our 
analysis of the current and future influences on Texas hornshell 
viability. They cautioned us not to presume all sedimentation is 
detrimental to Texas hornshell; some sedimentation is part of the 
natural state of the watershed. Additionally, they did not agree that 
predation is a significant risk to the species, stating that low water 
levels would cause mortality before predation levels increase.
    Our Response: Texas hornshell require seams of fine sediment under 
boulders and bedrock and in streambanks in order to anchor themselves 
into place. However, too much sedimentation, which can cause 
smothering, is a significant risk to the species rangewide. Chapter 4.1 
and Appendix B of the SSA report contain more discussion of the risks 
of sedimentation.
    In most of the streams occupied by Texas hornshell, we agree that 
low water levels would affect populations before predation is a 
significant factor. This scenario is because the species occupies 
crevices in streambanks and under boulders, which provide protection 
from predators. However, in the Devils River, Texas hornshell are found 
in gravel and cobble substrate in

[[Page 5731]]

riffles. These habitats become easily accessible to terrestrial 
predators, such as raccoons (Procyon lotor), when water levels drop, 
and significant levels of predation on Texas hornshell have been 
observed during times of low water levels. We have clarified in the SSA 
report and above in this preamble that this situation is primarily a 
concern for the population in the Devils River.

Public Comments

    (7) Comment: Three commenters stated that existing laws and 
policies related to oil and gas production and surface water rights, 
such as the Clean Water Act, Oil Pollution Act, Resource Conservation 
and Recovery Act, and Pollution Prevention Act, will provide sufficient 
protection to Texas hornshell populations. According to the commenters, 
these laws and subsequent regulations provide many protections for 
freshwater systems including spill prevention measures, stormwater 
measures, and hazardous waste management, among others, which prevent 
the Texas hornshell in the Black River from being affected by oil and 
gas exploration. Further, the commenters state that groundwater use in 
Texas is governed by the Texas Groundwater Act, and ground and surface 
water rights in New Mexico are permitted by the Office of the State 
Engineer, and that these laws and policies provide at least as much 
protection as listing under the Act.
    Our Response: While the laws and regulations related to water 
quality have reduced the risk of contamination of the Black River in 
New Mexico from oil and gas production, the risk from the high volume 
of truck traffic crossing the river at low-water access points remains 
high. In particular, one highly used crossing occurs at the upper end 
of the range of Texas hornshell in the Black River; a spill of water 
that has been collected as a byproduct of oil and gas production at 
this location could eliminate the entire population. For example, an 
overturned truck at a road crossing on the Clinch River in Virginia in 
1998 resulted in the extirpation of three endangered species of mussels 
for 6 miles downstream (Jones et al. 2001, p. 28). While not from a 
road crossing, a spill of 18,000 barrels of produced water and 11 
barrels of oil from a ruptured pipeline occurred on the Delaware River, 
which is adjacent to the Black River, in August 2017, demonstrating the 
high risk of a spill in this area. Produced water mixes with river 
water and cannot be absorbed by boom lines, and so once a spill has 
happened, there is little clean up that can occur. In this case, the 
only regulatory response was the issuance of an Administrative Order by 
EPA (EPA 2017) directing the development of a pollution prevention 
plan.
    Regarding water law, while extraction of water is regulated by the 
States of New Mexico and Texas, instream flow is affected by many 
factors, including local precipitation, high-altitude groundwater 
recharge, surface water-groundwater interactions, local groundwater 
table elevation, evapotranspiration, and anthropogenic water use. The 
Black River is expected to lose streamflow due to increased air 
temperature and reduced precipitation alone (Bren School of 
Environmental Management 2014, p. 91). Appropriate water management can 
help ensure sufficient streamflow, but if the amount of water entering 
the system decreases and anthropogenic water use remains at the same 
rate, streamflow levels will decrease. Therefore, although existing 
water law may mitigate water flow reductions, it is not sufficient to 
protect Texas hornshell from the effects of reduced streamflow.
    (8) Comment: One commenter requested we provide data on water flow, 
water quality, the risk of spills, and on the Pecos River population of 
Texas hornshell.
    Our Response: This information is provided in the SSA report in the 
following locations: Water flow (Chapter 4.3 and Appendix B); water 
quality and spill risk (Chapter 4.2 and Appendix B); and Pecos River 
population data (Chapter 3.2.2). References cited are available at 
www.regulations.gov in Docket No. FWS-R2-ES-2016-0077.
    (9) Comment: Two commenters stated that climate change does not 
exacerbate the risk factors in our analysis, and that our analysis is 
based on opinion rather than fact.
    Our Response: We recognize that there are scientific differences of 
opinion on many aspects of climate change, including the role of 
natural variability in climate and the uncertainties involved with 
climate change projections and how local ecosystems may respond. We 
relied on synthesis documents (e.g., IPCC 2013) that present the 
consensus view of a very large number of experts on climate change from 
around the world. Additionally, we relied on downscaled climate change 
projections (e.g., Nohara 2006, CH2MHILL 2008, Mace and Wade 2008, Bren 
School of Environmental Management 2014) that forecast what is expected 
to occur to landscapes in New Mexico and Texas. We have found that 
these reports, as well as the scientific papers used in those reports 
or resulting from those reports, represent the best available 
scientific information we can use to inform our decision and have 
relied upon them and provided citations within our analysis. Climate 
change impacts are expected to result in lower stream flows, poorer 
water quality, increased accumulation of fine sediments, and, in the 
Devils River, increased predation.
    (10) Comment: Two commenters expressed that the risks to the Black 
River from low flows and contamination are high.
    Our Response: The Texas hornshell population in the Black River is 
at risk of reduction or extirpation from low flows or contamination. 
The CCA/CCAA for the Black and Delaware Rivers with water users, oil 
and gas developers, landowners, and other partners will be critical to 
reduce threats to the species in this area while improving physical 
habitat and water quality.

Determination of Species Status

    Section 4 of the Act (16 U.S.C. 1533) and its implementing 
regulations (50 CFR part 424) set forth the procedures for determining 
whether a species meets the definition of ``endangered species'' or 
``threatened species.'' The Act defines an ``endangered species'' as a 
species that is ``in danger of extinction throughout all or a 
significant portion of its range,'' and a ``threatened species'' as a 
species that is ``likely to become an endangered species within the 
foreseeable future throughout all or a significant portion of its 
range.'' The Act requires that we determine whether a species meets the 
definition of ``endangered species'' or ``threatened species'' because 
of any of the following factors: (A) The present or threatened 
destruction, modification, or curtailment of its habitat or range; (B) 
overutilization for commercial, recreational, scientific, or 
educational purposes; (C) disease or predation; (D) the inadequacy of 
existing regulatory mechanisms; or (E) other natural or manmade factors 
affecting its continued existence.

Texas Hornshell Determination of Status Throughout All of Its Range

    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 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 (Factor E). Predation (Factor C) is also 
affecting those populations

[[Page 5732]]

already experiencing low stream flow, and barriers to host fish 
movement (Factor E) prevent gene flow and recolonization after 
stochastic events. The regulatory mechanisms we considered include the 
Clean Water Act, Oil Pollution Act, Texas Endangered Species Act, and 
New Mexico Wildlife Conservation Act (Factor D) and were not enough to 
remove these influences on the viability of Texas hornshell.
    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. 
The resulting remnant populations occupy shorter reaches compared to 
likely 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. The effects of climate 
change--increased temperature and decreased stream flow--exacerbate 
these impacts. Because of these threats acting in combination, the 
remaining Texas hornshell populations currently face moderate to high 
levels of risk of extirpation. For the populations occupying the 
smaller reaches (such as the Black River, Devils River, and Pecos River 
populations), a single stochastic event such as a 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 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 (Wuebbles et 
al. 2013, p. 16; Bren School of Environmental Management 2014, p. 91; 
Kinniburgh et al. 2015, p. 88; Miyazono et al. 2015, appendix A; Toll 
et al. 2017, pp. 46-47). 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 known remaining isolated populations in the United 
States, 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. 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.
    Thus, after assessing the best available information, we conclude 
that the Texas hornshell is in danger of extinction throughout all of 
its range. 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 
current range has been significantly reduced from the historical range 
of the species, and the remaining habitat and populations face a 
multitude of threats 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 list 
the Texas hornshell as an endangered species 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), 
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.
    Because we found that the species is an endangered species because 
of its status throughout all of its range, we do not need to conduct an 
analysis of it status in any portions of its range. This is consistent 
with the Act because the species is currently in danger of extinction 
throughout all of its range due to high-magnitude threats across its 
range, or threats that are so high in particular areas that they 
severely affect the species across its range. Therefore, the species is 
in danger of extinction throughout every portion of its range, and an 
analysis of whether the species is in danger of extinction or likely to 
become so throughout any significant portion of its range would be 
redundant and unnecessary. 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 37577).

Texas Hornshell Determination of Status

    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
to the Texas hornshell. Because the species is in danger of extinction 
throughout all of its range, the species meets the definition of an 
endangered species.

Available Conservation Measures

    Conservation measures provided to species listed as endangered or 
threatened species under the Act include recognition, recovery actions,

[[Page 5733]]

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 requires that recovery actions be carried out for all 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 requires 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 identifies site-
specific management actions that set a trigger for review of the five 
factors that control whether a species remains endangered or may be 
downlisted (reclassified from endangered to threatened) or delisted 
(removed from the Lists of Endangered and Threatened Wildlife and 
Plants), and methods for monitoring recovery progress. Recovery plans 
also establish a framework for agencies to coordinate their recovery 
efforts and provide estimates of the cost of implementing recovery 
tasks. Recovery teams (composed of species experts, Federal and State 
agencies, nongovernmental organizations, and stakeholders) are often 
established to develop recovery plans. When completed, the recovery 
outline, draft recovery plan, and the final recovery plan will be 
available on our website (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 habitat 
restoration (e.g., restoration of native vegetation), research, captive 
propagation and reintroduction, and outreach and education. The 
recovery of many listed species cannot be accomplished solely on 
Federal lands because their range may occur primarily or solely on non-
Federal lands. To achieve recovery of these species requires 
cooperative conservation efforts on private, State, and Tribal lands.
    Following publication of this final listing rule, 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 New Mexico 
and Texas will 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.
    Please let us know if you are interested in participating in 
recovery efforts for the Texas hornshell. 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 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)(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 any endangered or threatened species or destroy 
or adversely modify its critical habitat. If a Federal action may 
affect a listed species or its critical habitat, the responsible 
Federal agency must enter into consultation with the Service.
    Federal agency actions within the species' habitat that may require 
conference or consultation or both as described in the preceding 
paragraph include management and any other landscape-altering 
activities on Federal lands administered by the National Park Service 
(Big Bend National Park and Rio Grande Wild and Scenic River); issuance 
of section 404 Clean Water Act permits by the 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 final listing 
on proposed and ongoing activities within the range of a listed 
species. Based on the best available information, the following actions 
are unlikely to result in a violation of section 9, if these activities 
are carried out in accordance with existing regulations and permit

[[Page 5734]]

requirements; this list is not comprehensive:
    (1) Normal agricultural and silvicultural practices, including 
herbicide and pesticide use, which are carried out in accordance with 
any existing regulations, permit and label requirements, and best 
management practices; and
    (2) Normal residential landscape activities.
    Based on the best available information, the following activities 
may potentially result in a violation of section 9 of the Act; 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, 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 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: (i) Information sufficient to perform 
required analyses of the impacts of the designation is lacking, or (ii) 
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. We are completing the 
required analyses of the impacts related to possible exclusions to the 
designation of critical habitat and anticipate publishing a proposed 
critical habitat rule in the near future.

[[Page 5735]]

Therefore, we conclude that critical habitat is not determinable for 
the Texas hornshell at this time.

Required Determinations

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).

Government-to-Government Relationship With Tribes

    In accordance with the President's memorandum of April 29, 1994 
(Government-to-Government Relations with Native American Tribal 
Governments; 59 FR 22951), Executive Order 13175 (Consultation and 
Coordination With Indian Tribal Governments), and the Department of the 
Interior's manual at 512 DM 2, we readily acknowledge our 
responsibility to communicate meaningfully with recognized Federal 
Tribes on a government-to-government basis. In accordance with 
Secretarial Order 3206 of June 5, 1997 (American Indian Tribal Rights, 
Federal-Tribal Trust Responsibilities, and the Endangered Species Act), 
we readily acknowledge our responsibilities to work directly with 
tribes in developing programs for healthy ecosystems, to acknowledge 
that tribal lands are not subject to the same controls as Federal 
public lands, to remain sensitive to Indian culture, and to make 
information available to tribes.
    The Kickapoo Indian Reservation of Texas owns 1.3 km (0.8 mi) 
adjacent to the Rio Grande, downstream of Eagle Pass, Texas. We sent 
notification letters to the tribe on August 10, 2016, and June 1, 2017, 
inviting their review and comment on the proposed rule. We did not 
receive a response. We also sent notification letters on August 10, 
2016, to the following tribes with interests in the Black and Delaware 
River watersheds: Comanche, Hopi, Isleta, Mescalero Apache, Oklahoma 
Apache, Tesuque, and Ysleta del Sur tribes, and we did not receive a 
response.

References Cited

    A complete list of references cited is available in Appendix A of 
the SSA report (U.S. Fish and Wildlife Service. 2018. Species status 
assessment report for the Texas hornshell (Popenaias popeii), Version 
1.2. Albuquerque, NM), available online at https://www.regulations.gov 
under Docket Number FWS-R2-ES-2016-0077.

Authors

    The primary authors of this final 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.

Regulation Promulgation

    Accordingly, we amend part 17, subchapter B of chapter I, title 50 
of the Code of Federal Regulations, as follows:

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 to read as follows:


Sec.  17.11  Endangered and threatened wildlife.

* * * * *
    (h) * * *

----------------------------------------------------------------------------------------------------------------
                                                                                          Listing citations and
          Common name              Scientific name      Where listed         Status          applicable rules
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                                      CLAMS
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Hornshell, Texas...............  Popenaias popeii..  Wherever found....               E  83 FR [insert Federal
                                                                                          Register page where
                                                                                          the document begins],
                                                                                          2/9/2018.
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------

* * * * *

    Dated: December 19, 2017.
James W. Kurth,
Deputy Director, U.S. Fish and Wildlife Service, Exercising the 
Authority of the Director for the U.S. Fish and Wildlife Service.
[FR Doc. 2018-02672 Filed 2-8-18; 8:45 am]
 BILLING CODE 4333-15-P