Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List Texas Fatmucket, Golden Orb, Smooth Pimpleback, Texas Pimpleback, and Texas Fawnsfoot as Threatened or Endangered, 62166-62212 [2011-25471]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 76, Number 194 (Thursday, October 6, 2011)]
[Proposed Rules]
[Pages 62166-62212]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-25471]



[[Page 62165]]

Vol. 76

Thursday,

No. 194

October 6, 2011

Part II





Department of the Interior





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Fish and Wildlife Service





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50 CFR Part 17





Endangered and Threatened Wildlife and Plants; 12-Month Finding on a 
Petition To List Texas Fatmucket, Golden Orb, Smooth Pimpleback, Texas 
Pimpleback, and Texas Fawnsfoot as Threatened or Endangered; Proposed 
Rule

Federal Register / Vol. 76 , No. 194 / Thursday, October 6, 2011 / 
Proposed Rules

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[FWS-R2-ES-2011-0079; MO 92210-0-0008 B2]


Endangered and Threatened Wildlife and Plants; 12-Month Finding 
on a Petition To List Texas Fatmucket, Golden Orb, Smooth Pimpleback, 
Texas Pimpleback, and Texas Fawnsfoot as Threatened or Endangered

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Notice of 12-month petition finding.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a 
12-month finding on a petition to list five mussel species in Texas as 
threatened or endangered and to designate critical habitat under the 
Endangered Species Act of 1973, as amended (Act). The five species are 
Texas fatmucket (Lampsilis bracteata), golden orb (Quadrula aurea), 
smooth pimpleback (Q. houstonensis), Texas pimpleback (Q. petrina), and 
Texas fawnsfoot (Truncilla macrodon). After review of all available 
scientific and commercial information, we find that listing these five 
mussel species is warranted. Currently, however, listing of these 
species is precluded by higher priority actions to amend the Federal 
Lists of Endangered and Threatened Wildlife and Plants. Upon 
publication of this 12-month petition finding, we will add these five 
species to our candidate species list. We will develop a proposed rule 
to list these species as our priorities allow. We will make any 
determination on critical habitat during development of the proposed 
listing rule. In any interim period, we will address the status of the 
candidate taxa through our annual Candidate Notice of Review.

DATES: The finding announced in this document was made on October 6, 
2011.

ADDRESSES: This finding is available on the Internet at https://www.regulations.gov at Docket Number FWS-R2-ES-2011-0079. Supporting 
documentation we used in preparing this finding is available for public 
inspection, by appointment, during normal business hours at the U.S. 
Fish and Wildlife Service, 1505 Ferguson Lane, Austin, TX 78754. Please 
submit any new information, materials, comments, or questions 
concerning this finding to the above address.

FOR FURTHER INFORMATION CONTACT: Gary Mowad, Texas State Administrator, 
U.S. Fish and Wildlife Service (see ADDRESSES); by telephone at 512-
927-3557; or by facsimile at 512-927-3592. If you use a 
telecommunications device for the deaf (TDD), please call the Federal 
Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION:

Background

    Section 4(b)(3)(B) of the Act (16 U.S.C. 1531 et seq.) requires 
that, for any petition to revise the Federal Lists of Endangered and 
Threatened Wildlife and Plants that contains substantial scientific or 
commercial information that listing the species may be warranted, we 
make a finding within 12 months of the date of receipt of the petition. 
In this finding, we will determine that the petitioned action is: (1) 
Not warranted, (2) warranted, or (3) warranted, but the immediate 
proposal of a regulation implementing the petitioned action is 
precluded by other pending proposals to determine whether species are 
threatened or endangered, and expeditious progress is being made to add 
or remove qualified species from the Federal Lists of Endangered and 
Threatened Wildlife and Plants. Section 4(b)(3)(C) of the Act requires 
that we treat a petition for which the requested action is found to be 
warranted but precluded as though resubmitted on the date of such 
finding, that is, requiring a subsequent finding to be made within 12 
months. We must publish these 12-month findings in the Federal 
Register.

Previous Federal Actions

    This 12-month petition finding covers five species of mussels that 
are grouped together because of their overlapping or proximate ranges 
within the river basins of central Texas. The petitions for listing 
these five species were parts of two multi-species petitions, dated 
June 18, 2007, and October 9, 2008. The other species from those 
petitions, including other Texas mussels, will be considered in 
separate petition findings.
    On June 25, 2007, we received a formal petition dated June 18, 
2007, from Forest Guardians (now WildEarth Guardians), requesting that 
we: (1) Consider all full species in our Southwest Region ranked as G1 
or G1G2 by the organization NatureServe, except those that are 
currently listed, proposed for listing, or candidates for listing; and 
(2) List each species as either threatened or endangered with critical 
habitat. The petitioned group of species included four Texas mussels, 
two of which are included in this finding: the Texas fatmucket and 
golden orb. Two additional mussels from eastern Texas, the Texas 
heelsplitter (Potamilus amphichaenus) and Salina mucket (P. 
metnecktayi), were also included in this petition. The petition 
incorporated all analyses, references, and documentation provided by 
NatureServe in its online database at https://www.natureserve.org/ into 
the petition. Included in NatureServe was supporting information 
regarding the species' taxonomy and ecology, historical and current 
distribution, present status, and actual and potential causes of 
decline. We sent a letter dated July 11, 2007, to Forest Guardians 
acknowledging receipt of the petition and stating that the petition was 
under review by staff in our Southwest Regional Office.
    On October 15, 2008, we received a petition dated October 9, 2008, 
from WildEarth Guardians, requesting that the Service list as 
threatened or endangered and designate critical habitat for six species 
of freshwater mussels, including the smooth pimpleback, Texas 
pimpleback, and Texas fawnsfoot. Two additional mussels from the Rio 
Grande basin, the false spike (Quincuncina mitchelli) and Mexican 
fawnsfoot (Truncilla congata), were also included in this petition. In 
addition to other information, the petition incorporated all analyses, 
references, and documentation provided by NatureServe in its online 
database at https://www.natureserve.org/. In a November 26, 2008, letter 
to the petitioner, we acknowledged receipt of the second petition and 
stated that the petition for the six mussel species was under review by 
staff in our Southwest (Region 2) and Southeast (Region 4) Regional 
Offices. The southern hickorynut (Obovaria jacksoniana) was also 
included in this 2008 petition, and on March 23, 2010 (75 FR 13717), we 
found that the petition did not present substantial information 
supporting that that species may be endanagered or threatened.
    On December 15, 2009, we published our 90-day finding that the 
petitions presented substantial scientific information indicating that 
listing nine Texas mussels may be warranted (74 FR 66260). As a result 
of the finding, we initiated a status review for all nine species. This 
notice constitutes the 12-month finding on the June 18, 2007, petition 
to list the Texas fatmucket and golden orb and the October 9, 2008, 
petition to list the smooth pimpleback, Texas pimpleback, and Texas 
fawnsfoot as threatened or endangered. Our petition findings for the 
remaining Texas mussel species will be published at a later time.

[[Page 62167]]

Summary of Procedures for Determining the Listing Status of Species

Review of Status Based on Five Factors
    Section 4 of the Act (16 U.S.C. 1533) and implementing regulations 
(50 CFR part 424) set forth procedures for adding species to, removing 
species from, or reclassifying species on the Federal Lists of 
Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of 
the Act, a species may be determined to be endangered or threatened 
based on any of the following five factors:
    (A) The present or threatened destruction, modification, or 
curtailment of its habitat or range;
    (B) Overutilization for commercial, recreational, scientific, or 
educational purposes;
    (C) Disease or predation;
    (D) The inadequacy of existing regulatory mechanisms; or
    (E) Other natural or manmade factors affecting its continued 
existence.
    In making these findings, we discuss below information pertaining 
to each species in relation to the five factors provided in section 
4(a)(1) of the Act. In considering what factors might constitute 
threats to a species, we must look beyond the exposure of the species 
to a particular factor to evaluate whether the species may respond to 
the factor in a way that causes actual impacts to the species. If there 
is exposure to a factor and the species responds negatively, the factor 
may be a threat, and during the status review, we attempt to determine 
how significant a threat it is. The threat is significant if it drives 
or contributes to the risk of extinction of the species such that the 
species warrants listing as endangered or threatened as those terms are 
defined by the Act. However, the identification of factors that could 
impact a species negatively may not be sufficient to compel a finding 
that the species warrants listing. The information must include 
evidence sufficient to suggest that the potential threat has the 
capacity (i.e., it should be of sufficient magnitude and extent) to 
affect the species' status such that it meets the definition of 
endangered or threatened under the Act.
Evaluation of the Status of Each of the Five Mussel Species
    In this finding, we first provide a description of general mussel 
biology. Then, for each of the five species, we describe the species, 
its life history, and habitat; evaluate listing factors for that 
species; and present our finding that the petitioned action is 
warranted or not for that species. We follow these descriptions, 
evaluations, and findings with a discussion of the priority and 
progress of our listing actions.

General Mussel Biology

    All five species are freshwater mussels in the family Unionidae and 
occur only in Texas, in portions of the Colorado, Guadalupe, Nueces-
Frio, and Brazos River systems (Howells et al. 1996, p. 1). Adult 
freshwater mussels are suspension feeders, drawing in food and oxygen 
through their incurrent siphon (tube that draws water into the shell). 
They may also feed on organic particles in sediment using the large, 
muscular foot (an organ used to anchor the mussel in the substrate or 
for locomotion) (Raikow and Hamilton 2001, p. 520). Adults feed on 
algae, bacteria, detritus (dead organic material), microscopic animals, 
and dissolved organic matter (Fuller 1974, pp. 221-222; Silverman et 
al. 1997, p. 1862; Nichols and Garling 2000, pp. 874-876; Christian et 
al. 2004, p. 109). For their first several months, as they inhabit 
interstitial spaces (small spaces between sediment particles) within 
the substrate, juvenile mussels feed using cilia (fine hairs) on the 
foot to capture suspended as well as depositional material, such as 
algae and detritus (Yeager et al. 1994, pp. 253-259). Mussels tend to 
grow relatively rapidly for the first few years, and then slow 
appreciably at sexual maturity, when energy presumably is being 
diverted from growth to reproductive activities (Baird 2000, pp. 66-
67).
    As a group, mussels are extremely long lived, living from two to 
several decades (Rogers et al. 2001, p. 592), and possibly up to 200 
years in extreme instances (Bauer 1992, p. 427). Most mussel species, 
including the five in this finding, have distinct forms of males and 
females. During reproduction, males release clouds of sperm into the 
water column, which females draw in through their siphons. 
Fertilization takes place internally, and the resulting eggs develop 
into specialized larvae (called glochidia) within the female gills. The 
females release matured glochidia individually, in small groups, or 
embedded in larger mucus structures called conglutinates.
    The glochidia of freshwater mussels are obligate parasites (cannot 
live independently of their hosts) on the gills 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. 299). Glochidia encyst (enclose in a cyst-
like structure) on the host's tissue and develop into juvenile mussels 
weeks or months after attachment (Arey 1932, pp. 214-215). Mussels 
experience their primary opportunity for dispersal and movement within 
the stream as glochidia attached to a 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 released 
from the host fish.

Species Information for Texas Fatmucket

Species Description

    The Texas fatmucket is a large, elongated mussel that reaches a 
maximum length of 100 millimeters (mm) (3.94 inches (in)) (Howells 
2010c, p. 2). The shell is oval to elliptical or somewhat rhomboidal 
and tan to greenish-yellow with numerous irregular, wavy, and broad and 
narrow dark brown rays, with broad rays widening noticeably as they 
approach the ventral (underside) margin. The nacre (inside of the 
shell) is white with occasional yellow or salmon coloration and 
iridescent posteriorly (Howells 2010c, p. 2). Females have mantle flaps 
(extensions of the tissue that covers the visceral mass) that often 
resemble minnows, including eye spots, lateral line, and fins (Howells 
2010c, p. 2).

Taxonomy

    The Texas fatmucket was first described in 1855 by Gould as Unio 
bracteatus and later moved to the genus Lampsilis by Simpson (1900, p. 
543). Some forms found in headwater streams were historically split 
into a different species, L. elongatus, but they have since been 
determined to be ecophenotypes (individuals whose shape is determined 
by their environment) of L. bracteata (Howells 2010c, p. 5). The Texas 
fatmucket is recognized by the Committee on Scientific and Vernacular 
Names of Mollusks of the Council of Systematic Malacologists, American 
Malacological Union (Turgeon et al. 1998, p. 34), and we recognize it 
as a valid species.

[[Page 62168]]

Biology and Life History

    Although there is no specific information on age and size of 
maturity of the Texas fatmucket, it is likely similar to a related 
species, the Louisiana fatmucket (L. hydiana), which reaches sexual 
maturity around 36 mm (1.4 in) (Howells 2000b, pp. 35-48; Howells 
2010c, p. 3). Texas fatmucket females have been found gravid (with 
glochidia in the gill pouch) from July through October, although 
brooding may continue throughout much of the year (Howells 2010c, p. 
3). Texas fatmucket females display a mantle lure to attract host fish, 
releasing glochidia when the lure is bitten or struck by the fish. 
Bluegill (Lepomis macrochirus) and green sunfish (L. cyanellus) have 
been successful hosts in laboratory studies (Howells 1997b, p. 257). 
Hosts such as these sunfishes are common, widely distributed species in 
Texas that occur in an array of habitat types (Hubbs et al. 2008, p. 
45) and would not generally be expected to be a limiting factor in 
Texas fatmucket reproduction and distribution (Howells 2010c, p. 3).

Habitat

    The Texas fatmucket occurs in moderately sized rivers in mud, sand, 
or gravel, or mixtures of these substrates (Howells 2010c, p. 4) and 
sometimes in narrow crevices between bedrock slabs (Howells 1995, p. 
21). Live individuals have been found in relatively shallow water, 
rarely more than 1.5 meters (m) (4.9 feet (ft)) deep, and usually less. 
Remaining populations typically occur at sites where one or both banks 
are relatively low, allowing floodwaters to spread out over land and 
thereby reducing damage from scouring (Howells 2010c, p. 4). The 
species does not occur in ponds, lakes, or reservoirs, suggesting that 
it is intolerant of deep, low-velocity water created by artificial 
impoundments.

Distribution and Abundance

Historical Distribution
    The Texas fatmucket historically had populations in at least 18 
rivers in the upper Colorado, Guadalupe, and San Antonio River systems 
in the Texas Hill Country and east-central Edwards Plateau region of 
central Texas. In the Colorado River, it ranged from Travis County 
upstream approximately 320 kilometers (km) (200 miles (mi)) to Runnels 
County in the Colorado River. It was also found in many tributaries, 
including the Pedernales, Llano, San Saba, and Concho Rivers, and Jim 
Ned, Elm, and Onion Creeks (Howells et al. 1996, p. 61).
    In the Guadalupe-San Antonio River basin, the Texas fatmucket 
occupied approximately 240 km (150 mi) of the Guadalupe River, from 
Gonzales County upstream to Kerr County, including the North Guadalupe 
River, Johnson Creek, and the Blanco River. In the San Antonio River, 
it ranged from its confluence with the Medina River in Bexar County 
upstream to the City of San Antonio, as well as in the Medina River and 
Cibolo Creek (Howells et al. 1996, p. 61; Howells 2010c, p. 6). 
Strecker (1931, pp. 66-68) reported Texas fatmucket from a lake in 
Victoria County in the lower Guadalupe River drainage (Howells 2010c, 
p. 6), but this is probably a misidentified Louisiana fatmucket, which 
occurs in lakes or impoundments. A Salado Creek record from Bell County 
(Strecker 1931, pp. 62-63) is also probably a misidentified Louisiana 
fatmucket, since the Texas fatmucket is not known to occur in the 
Brazos River basin or its western tributaries (Howells et al. 1996, p. 
61; Howells 2010c, p. 6).
Current Distribution
    Based on historical and current data, the Texas fatmucket has 
declined significantly rangewide and is now known from only nine 
streams in the Colorado and Guadalupe River systems in very limited 
numbers. All existing populations are represented by only one or two 
individuals and are likely not stable or recruiting (juvenile mussels 
joining the adult population). In the streams where the species is 
extant (surviving), populations are highly fragmented and restricted to 
short reaches with few exceptions. The Texas fatmucket has been 
considered a species of special concern by some malacologists for 
several decades (Athearn 1970, p. 28).
Colorado River System
    The Texas fatmucket was historically known to occur throughout the 
Colorado River and numerous tributaries (Randklev et al. 2010c, p. 4). 
However, in the mainstem Colorado River, the Texas fatmucket has not 
been found, live or dead, in several decades despite numerous surveys 
(Howells 1994, p. 4; 1995, pp. 20-21, 25, 29; 1996, pp. 20, 23; 1997a, 
pp. 27, 31, 34-35; 1998, p. 10; 1999, p. 18; 2000a, pp. 25-27; 2002a, 
pp. 6-7; 2004, pp. 7, 10-11; 2005, p. 6; Johnson 2009, p. 1; Burlakova 
and Karatayev 2010a, p. 12), and thus is considered extirpated 
(eliminated from) from the Colorado River mainstem. Within this system, 
the species is only known from sparse populations in Colorado River 
tributaries, including the South Concho River, Spring Creek, Llano 
River (including Threadgill Creek), Pedernales River (including Live 
Oak Creek), Onion Creek, Jim Ned Creek, Elm Creek, and the San Saba 
River.
    Evidence of persisting Texas fatmucket populations has been found 
in Spring Creek, a tributary to the Middle Concho River, which flows 
into the Concho River, a large tributary of the Colorado River. 
Historically, Spring Creek harbored Texas fatmucket in Irion and Tom 
Green Counties (Randklev et al. 2010c, p. 1). In 1993, discovery of 
shell material prompted additional surveys, and in 1997, one live 
individual was found in Irion County (Howells 1998, p. 13). Farther 
downstream, in Tom Green County, two live individuals were recorded in 
1997, upstream of Twin Buttes Reservoir (Howells 1998, pp. 13-14), but 
no evidence of this population was found in 2008 (Burlakova and 
Karatayev 2010a, p. 12). Spring Creek was reported to have dried in 
1999 and 2000, which may have eliminated the population there (Howells 
et al. 2003, p. 5).
    In the Llano River, there are three areas that are currently known 
to contain Texas fatmucket populations. The species occurred throughout 
the length of the river historically (Ohio State University Museum 
(OSUM) 2011a, p. 1). A single shell was collected in Llano County in 
1992 (Howells 1994, p. 6), and eight live individuals were found in 
2011 (Burlakova and Karatayev 2011, p. 1). Individuals were small in 
size, indicating a potentially reproducing population. The species also 
persists in Mason County, where two shell fragments of recently dead 
Texas fatmucket were found in 1995 (Howells 1996, p. 22), and two live 
individuals were collected at the same site in 2009 (Burlakova and 
Karatayev 2010a, pp. 12-13). The species also appears to persist in 
Kimble County, where one live Texas fatmucket was recorded in 2009 
(Burlakova and Karatayev 2010a, pp. 12-13).
    In 2004, four live Texas fatmucket were recorded from Threadgill 
Creek, a tributary to the Llano River in Gillespie and Mason Counties 
(Howells 2005, pp. 6-7). This population is on private land, which 
limits survey access, but Howells (2009, p. 5) indicates it likely 
persists due to favorable land management.
    Live Oak Creek, a tributary to the Pedernales River in Gillespie 
County, also contains a sparse Texas fatmucket population. In 2002, 11 
shells were discovered, and in 2003, one live individual was recorded, 
confirming the species persisted in low numbers (Howells 2003, p. 10; 
Howells 2004, pp. 8-9). Since that time, surveys have been

[[Page 62169]]

conducted in Live Oak Creek on a fairly regular basis. The stream was 
visited in two different occasions in 2004, with only shell material 
found (Howells 2005, pp. 7-8), and again in 2005, when two live 
individuals were recorded (Burlakova and Karatayev 2010a, p. 12). The 
stream was surveyed in 2007 and 2008, but no evidence of the species 
was found (Howells 2009, p. 5). This population is presumed to be small 
but persisting.
    Original records of speckled pocketbook (Lampsilis streckeri) from 
Onion Creek in Travis County in 1931 are now believed to have been 
misidentified; instead they represent records of Texas fatmucket 
(Howells 2010c, p. 6; Randklev et al. 2010c, p. 4). The stream was 
surveyed in 1993, and no live freshwater mussels were found (Howells 
1995, p. 28). However, in 2010, several live Texas fatmucket were found 
during a survey near Highway 71 (Groce 2011, pers. comm.), indicating 
the species persists there.
    Elm Creek, a tributary to the Colorado River, has been known to 
harbor a Texas fatmucket population since 1993, when 10 live 
individuals were recorded (Howells 1995, p. 21). Since that time, the 
population has declined, with two individuals found in 1995 (Howells 
1996, pp. 19-20), and no live individuals found in 2001 or 2005 
(Howells 2002a, p. 5; 2006, p. 63). In 2008, additional sites 
downstream of the known population were surveyed and one live 
individual was recorded after 15 person-hours of searching (Burlakova 
and Karatayev 2010a, p. 12), indicating that the species continues to 
persist in Elm Creek, although in very low numbers.
    Texas fatmucket also persist in the San Saba River, where the 
species has been known to occur historically (Randklev et al. 2010c, p. 
2; OSUM 2011a, p. 1). The river was surveyed in 1997, and three live 
individuals were found (Howells 1998, p. 16). In 2000 and 2004, no 
Texas fatmucket were found in this stretch of river (Howells 2001, p. 
29; Howells 2005, pp. 8-9). One live individual was found in 2005 
(Howells 2006, p. 64), and, in 2008, only one shell of a recently dead 
individual was found (Burlakova and Karatayev 2010a, p. 12). In 2005, 
the number of mussels of all species collected was about 40 percent of 
the 1997 numbers (Howells 2006, p. 64), indicating an overall decline 
in the freshwater mussel fauna. Aquatic macrophyte (aquatic plants 
larger than algae) abundance has increased in this river, confounding 
survey efforts and degrading mussel habitat (Howells 2006, p, 64).
    Texas fatmucket have not been found alive in the Pedernales River 
since 1978 (Howells 1999, p. 16). In 1992, a thorough search of the 
habitat yielded no live Texas fatmuckets, with only very old dead shell 
material collected in the banks above the normal high water line 
(Howells 1994, p. 4). Because the species was documented from Blanco 
County by museum records (OSUM 2011a, p. 1), additional sections of the 
river were also surveyed in 1992, with no evidence of Texas fatmucket 
found, although in 1993, very old Texas fatmucket shell fragments were 
discovered in Pedernales Falls State Park (Howells 1995, p. 28). Mussel 
habitat in this area is poor, and it is unlikely the species persists 
there. Subsequent searches of the river in 1998 yielded only dead shell 
material (Howells 1999, p. 16).
    The Texas fatmucket is considered extirpated from the South Concho 
River and Jim Ned Creek. In the South Concho River, old Texas fatmucket 
shell fragments were found in gravel bars in Tom Green County in 1997, 
but there has been no additional evidence of the species (Howells 1998, 
p. 12). Additionally, three live individuals were recorded from Jim Ned 
Creek in Brown County in 1979 (Randklev et al. 2010c, p. 3), but the 
species has not been found in this stream since then (Howells 1997a, 
pp. 29-30).
Guadalupe River System
    While the Texas fatmucket was never widely distributed in the 
Guadalupe River system, the only remaining populations are in the 
mainstem Guadalupe River and possibly the North Fork Guadalupe River. 
It is presumed extirpated from the entire San Antonio River system, as 
well as the Blanco River and Johnson Creek.
    In the mainstem Guadalupe River, Texas fatmucket historically 
occurred in Kerr County (OSUM 2011a, p. 1). In 1992 and 1995, surveys 
yielded no evidence of the species (Howells 1994, pp. 7-8; Howells 
1996, p. 25), although shell fragments collected in 1993 in Guadalupe 
County may have been Texas fatmucket but were too weathered for an 
accurate determination (Howells 1995, p. 31). In 1996, two live 
individuals were recorded in Kerr County directly below a dam (Howells 
1997a, p. 36), and in 1997, three shells were found at the same site 
following a flood (Howells 1998, p. 18). No Texas fatmucket or other 
freshwater mussels have been found at that site since, and it is 
unlikely that Texas fatmucket persist there (Howells 2006, p. 71). 
However, 20 recently dead individuals were discovered approximately 1 
km (0.6 mi) downstream in Louise Hayes Park during a drawdown (Howells 
1999, pp. 18-19), and 6 live individuals were found at the same 
location in 2005 (Howells 2006, pp. 71-72). Surveys in 2007 and 2008 
yielded no live or recently dead individuals (Burlakova and Karatayev 
2010a, p. 12). It is likely that the species persists in the vicinity. 
There has been no other evidence of Texas fatmucket in the mainstem 
Guadalupe River in recent years.
    In 1999, two recently dead Texas fatmucket were found in North Fork 
Guadalupe River (Howells 2000a, p. 27). This river was surveyed again 
in 2000 and 2003 at several sites, and no Texas fatmucket were found 
(Howells 2001, p. 31; Howells 2004, pp. 13-14).
    Johnson Creek was a historical location for Texas fatmucket, but no 
live freshwater mussels of any species have been found in this stream 
for decades (Howells 1996, p. 25; Howells 1998, p. 18; Howells 2002a, 
p. 8). Additionally, the Blanco River has been surveyed extensively 
since 1992, and no evidence of Texas fatmucket has been collected, nor 
is suitable habitat present (Howells 1994, p. 9; Howells 1995, pp. 32-
33; Howells 1996, p. 28; Johnson 2011, p. 1). The last collection of 
Texas fatmucket from the Blanco River occurred in the 1970s or 1980s 
(Howells 2005, p. 10).
    Texas fatmucket have also been extirpated from the entire San 
Antonio River system. The mainstem San Antonio River was surveyed in 
1993 and 1996, and no live or dead Texas fatmucket were found (Howells 
1995, p. 35; 1997a, pp. 41-42). It was known from the Medina River, a 
tributary to the San Antonio River, historically (Randklev et al. 
2010c, p. 3), but no mussels of any species have been found in this 
river in recent years (May 2011, pers. comm.). Additionally, although 
Texas fatmucket were collected from Cibolo Creek historically (OSUM 
2011a, p. 1) and shell material, likely from Texas fatmucket, was found 
in 1993 (Howells 1995, p. 36), no live freshwater mussels have been 
found in Cibolo Creek since (Howells 1997a, pp. 40-41).
Summary
    Based on historical and current data, the Texas fatmucket has 
declined significantly rangewide and has been extirpated from most of 
the Guadalupe River system and hundreds of miles of the Colorado River, 
as well as from numerous tributaries. Extant populations are 
represented by only a few individuals, and they are highly disjunct and 
restricted to short reaches. Two of the populations considered extant 
in recent years may now be

[[Page 62170]]

extirpated, and the remaining seven populations are extremely small and 
likely not stable. No evidence of recent recruitment has been found in 
any of the populations, with the possible exception of the Llano River.

Species Information for Golden Orb

Species Description

    The golden orb is small, usually less than 82 mm (3.2 in), with an 
oval to nearly round, smooth, and unsculptured shell, except for 
concentric growth rings (Howells 2002b, p. 6). External shell 
coloration varies from yellow-brown, gold, or orangish-brown to dark 
brown or black, and some individuals may show faint greenish rays. 
Internally, the nacre is white to bluish-white (Howells 2002b, p. 6).

Taxonomy

    The golden orb was originally described as Unio aureas by Lea in 
1859 and later moved to the genus Quadrula in 1900 (Simpson 1900, p. 
783). Graf and Cummings (2007, p. 18) have proposed moving it to the 
genus Amphinaias, but other freshwater mussel taxonomists recommend 
waiting for additional work to be completed on members of Quadrula 
before splitting the genus (Bogan 2011, pers. comm.). Because the 
golden orb can exhibit an elongated shell structure in headwater 
riffles, old records of Unio bolli in the Colorado River (Dall 1882, p. 
956) are very likely elongated forms of golden orb (Howells 2010a, p. 
5). The golden orb is recognized by the Committee on Scientific and 
Vernacular Names of Mollusks of the Council of Systematic 
Malacologists, American Malacological Union (Turgeon et al. 1998, p 
36), and we recognize it as a valid species.

Biology and Life History

    There is no specific information on age, size of maturity, or host 
fish use for golden orb. Other species in the genus Quadrula 
successfully parasitize catfish, and it is likely golden orb do as well 
(Howells 2010a, p. 3). Gravid females have been found from May through 
August (Howells 2000b, p. 38). Mussels in the genus Quadrula are short-
term brooders, which are species that hold fertilized eggs and 
glochidia for a short period, usually 3 to 6 weeks, before releasing 
glochidia (Gorden and Layzer 1989, p. 6; Garner et al. 1999, p. 277).

Habitat

    The golden orb has been found almost exclusively in flowing waters 
in moderately sized rivers (Howells 2010a, p. 3). It has been found in 
only one reservoir in the lower Nueces River (Lake Corpus Christi), 
where wave action may simulate flowing water conditions (Howells 2010a, 
p. 3). This species is found in substrates of firm mud, sand, and 
gravel, and it does not appear to tolerate more unstable substrates 
such as loose sand or silt (Howells 2002b, p. 6).

Distribution and Abundance

Historical Distribution
    The golden orb is endemic (native) to nearly the entire lengths of 
the Guadalupe, San Antonio, and Nueces-Frio River basins in central 
Texas (Howells 2010a, p. 5), including the Guadalupe, Medina, San 
Antonio, Frio, and Nueces Rivers and Cibolo Creek. It was originally 
reported from four sites in the Brazos River system (Strecker 1931, p. 
63), but these are almost certainly misidentified smooth pimpleback 
(Howells 2002b, p. 5) based on numerous mussel surveys throughout the 
Brazos River system since the 1970s that failed to find any golden orb. 
The species has not been found in studies of archaeological specimens 
from the Brazos River (Howells 2010a, p. 5), further indicating golden 
orb did not historically occur in the Brazos River system.
    The golden orb has also been reported from the upper Colorado River 
drainage (Howells et al. 1996, pp. 108-109; Randklev et al. 2010c, p. 
4), but these appear to have been misidentified Texas pimpleback 
(Howells 2010a, p. 5). Since no other golden orb have been reported 
from the Colorado River system, we do not believe it occurred in that 
basin.
Current Distribution
    Based on historical and current data, the golden orb has declined 
significantly rangewide and is now known from only four streams in 
disjunct locations. Despite mussel surveys across the historical range, 
since 1995 golden orb has only been found in Lake Corpus Christi and 
the Guadalupe, lower San Marcos, and lower San Antonio Rivers. The 
species has been extirpated from the entire Nueces-Frio River basin, 
except at the extreme downstream end of the Nueces River, where a 
population persists in Lake Corpus Christi. Aside from the upper 
Guadalupe River, all existing populations occur in the lower portion of 
occupied basins in a small geographical area; only about 130 km (80 mi) 
separate the farthest two populations. Only four populations appear to 
be relatively stable and recruiting, while the remaining five 
populations are represented by only a few individuals.
Guadalupe River System
    In the Guadalupe River system, the golden orb historically ranged 
throughout the length of the Guadalupe, San Antonio, and San Marcos 
Rivers. Currently in this basin, the species only persists in the 
uppermost Guadalupe River and lower San Marcos, San Antonio, and 
Guadalupe Rivers. The lower portion of this basin (within approximately 
120 km (75 mi) of the Gulf of Mexico) harbors all four of the large, 
presumably reproducing populations of golden orb.
    Historically known from the mainstem Guadalupe River (Howells 
2002a, p. 8), the golden orb was not seen in the upper Guadalupe River 
in Kerr County again, despite repeated surveys (Howells 1994, pp. 7-8; 
1996, p. 30; 1997a, p. 36), until 1997, when three shells were 
discovered (Howells 1998, p. 18). No live freshwater mussels of any 
species have been found in this area, just downstream of a dam, since 
1997 (Howells 1999, p. 18; Howells 2006, p. 71), and it is unlikely 
golden orb persists there. However, upstream of this area, above the 
dam and impounded reach, a single recently dead individual was found in 
1998 during an extended drawdown of the river to construct a footbridge 
in a local park (Howells 1999, pp. 18-19). In 2005, two live 
individuals were also found at this site (Howells 2006, pp. 71-72), 
showing that the species had survived the drawdown and persists at the 
site.
    Golden orb also occurs farther downstream in the mainstem Guadalupe 
River, near Lake Gonzales in Gonzales County. Upstream of the 
reservoir, subfossil shells (very old shells that are brittle, 
crumbling, and with extensive erosion) were found in 1993 (Howells 
1995, p. 31), but the species has not been found there since. However, 
below the reservoir, one recently dead individual was collected in 1995 
(Howells 1996, pp. 26-27), and in 1996, 25 live golden orb were 
recorded at two sites in this area (Howells 1997a, pp. 37-38). Later, 
in 2006, three live golden orb were also found in this area (Howells 
2006, pp. 85-86). A small population apparently continues to persist 
below Lake Gonzales.
    A large golden orb population occurs farther downstream in the 
mainstem Guadalupe River, below Lake Wood, also in Gonzales County. 
Although none were found during a survey in 1995 (Howells 1996, p. 27), 
36 live golden orb were found at two sites below Lake Wood in 1996 
(Howells 1997a, pp. 38-40). Density estimates were calculated based on 
the quantitative information collected from these surveys, but they

[[Page 62171]]

were not considered statistically valid (Howells 1997a, p. 40) and so 
are not reported here. Only one live golden orb was found at this site 
in 2002 (Howells 2003, p. 11), but a relatively large population 
continues to persist; a total of around 100 live golden orb were found 
at three sites within 2 km (1.2 mi) of the Lake Wood Dam in 2006 
(Howells 1996, pp. 87-91). Also, in 2008, 33 golden orb were recorded 
alive downstream of Lake Wood (Burlakova and Karatayev 2010a, p. 14). 
This portion of the Guadalupe River supports a relatively large 
population of golden orb, and it also contains one of the most abundant 
freshwater mussel communities in Texas (Burlakova and Karatayev 2010a, 
p. 14).
    In 2009, a large population of golden orb was discovered farther 
downstream in the mainstem Guadalupe River in Victoria County, when 
over 100 individuals were found (Johnson 2009, p. 1). Multiple size 
classes were observed, including juveniles, indicating this population 
is reproducing and recruiting new individuals into the population. A 
large number of shells was collected upstream of this site in 1994 
(Burlakova and Karatayev 2010c, p.1), but no golden orb were seen alive 
until 2009.
    The San Marcos River, a tributary to the Guadalupe River, also 
supports a large golden orb population near its confluence with the 
tailwaters (outflow) of Lake Wood Dam. Although much of the San Marcos 
River has been extensively surveyed, with very few freshwater mussels 
present of any species (Howells 1995, pp. 33-34; 1997a, p. 40; 2004, 
pp. 15-16, 18; 2005, p. 10), one old golden orb shell was found near 
the town of Staples (Howells 1998, p. 19), and a single live individual 
was found near the town of Luling (Howells 1999, p. 28). Downstream 
from these locations, a large population persists in the vicinity of 
Palmetto State Park in Gonzales County. In 1995, a recently dead 
individual was discovered downstream of the park, indicating the recent 
presence of the species (Howells 1996, p. 28), and, based on surveys 
from 2000-2006, a relatively large population was confirmed to be in 
the area (Howells 2001, pp. 32-33; 2006, pp. 72-73; 2006, p. 91; 
Burlakova and Karatayev 2010a, pp. 14-15).
    Historically, golden orb were numerous in the San Antonio River in 
Karnes County (OSUM 2011b, p. 1), but only a single subfossil shell was 
found at each of two sites in Karnes County in 1996 (Howells 1997a, pp. 
41-42). No live animals have been found there since, although abundant 
shell material remains present (Karatayev and Burlakova 2008, p. 40).
    The lower portion of the San Antonio River supports the largest 
known golden orb population. In 2007, 37 live golden orb were recorded 
near Goliad in Goliad County, both within and downstream of Goliad 
State Park (Howells 2009, p. 11). The following year, 285 live golden 
orb were found within the park and downstream surrounded by private 
lands (Burlakova and Karatayev 2010a, p. 15). This site represents the 
largest known population of golden orb.
    In 2009, a single live golden orb was discovered in the lower San 
Antonio River south-southwest of Victoria in Victoria County (Johnson 
2009, p. 1); this site has not been surveyed since. We presume golden 
orb may persist in this stretch of river.
    The golden orb appears to have been extirpated from the Medina 
River. The species historically occurred in Medina and Bexar Counties 
(Randklev et al. 2010b, p. 4; OSUM 2011b, p. 1), but no live or dead 
mussels of any species have been found in this river in recent years 
(May 2011, pers. comm.).
    Cibolo Creek, a tributary to the San Antonio River, was extensively 
surveyed in the 1990s, with only old golden orb shells collected in 
Wilson County (Howells 1995, pp. 35-37; 1997a, pp. 40-41). In 2006 and 
2007, Burlakova and Karatayev (2010b, p. 1) surveyed this same general 
area and found only shell material. It is unlikely golden orb remain in 
Cibolo Creek.
Nueces-Frio River System
    Information is limited on the occurrence of golden orb in the 
Nueces River. Other than a population that occurs in a reservoir on the 
lower Nueces River (Lake Corpus Christi), the species appears to be 
extirpated from the remainder of the basin.
    Historically, the golden orb occurred in the Nueces River in Live 
Oak County (OSUM 2011b, p. 1). It was last seen alive in the Nueces 
River in 1993, when unreported numbers were found in the same area 
(Burlakova and Karatayev 2010c, p. 1). A shell was collected in the 
same general area in 1995 (Burlakova and Karatayev 2010c, p. 1), but 
additional surveys in 1996 and 1997 found no evidence of the species 
(Howells 1997a, pp. 43-44; 1998, p. 20). We presume the species no 
longer occurs in the upper portions of the Nueces River.
    An anomalous (odd) population of golden orb has persisted in Lake 
Corpus Christi Reservoir in the lower Nueces River. While the species 
does not typically inhabit lentic (ponded) water, wave action is 
presumed to simulate flowing water conditions and has supported a 
golden orb population since at least the 1970s (OSUM 2011b, p. 1). A 
few live individuals of golden orb have been found within the reservoir 
consistently since 1994 (Howells 1995, p. 39; 1996, pp. 30-31; 
Burlakova and Karatayev 2010c, p. 1). Numbers of golden orb collected 
increased in 1996, when 86 live golden orb were found at three 
different locations within the reservoir (Howells 1996, pp. 30-31). 
However, a drawdown of the lake in 1996 resulted in large numbers of 
golden orb stranded and killed (Howells 2010a, p. 9), and in 1998 no 
live individuals were found (Howells 1999, p. 19). Again in 2005, no 
live individuals were found during surveys, but in 2006, a total of 
nine were collected at three different sites within the reservoir 
(Howells 2006, pp. 73-76, 91-93). A small golden orb population likely 
persists in the reservoir.
    Very little information is available on the distribution of golden 
orb in the Frio River. Shells were last seen in McMullen County in 1994 
(Burlakova and Karatayev 2010c, p. 1), but no evidence of the species 
has been found in this river since (Howells 1995, pp. 37-38; 1996, p. 
29; 2002a, pp. 9-10; 2004, pp. 19-20).
Summary
    Based on historical and current data, the golden orb has declined 
rangewide and is now known from only nine populations in four rivers 
and has been eliminated from nearly the entire Nueces-Frio River 
system. Four of these populations appear to be stable and reproducing; 
the remaining five populations are small and isolated and show no 
evidence of recruitment. Only the populations in the middle Guadalupe 
River and lower San Marcos River are likely connected; the remaining 
extant populations are highly fragmented and restricted to short 
reaches.

Species Information for Smooth Pimpleback

Species Description

    The smooth pimpleback is a nearly round, thick-shelled freshwater 
mussel that generally reaches at least 60 mm (2.6 in) in length 
(Howells 2010b, p. 4). It is moderately thick, solid, and inflated. 
Externally, the smooth pimpleback, like its name suggests, is 
relatively smooth with minute sculpturing; it may or may not have a few 
small pustules (raised bumps) (Howells 2010b, p. 2). The external 
coloration of the shell ranges from tan

[[Page 62172]]

to light brown, dark brown, and black with no rays (Howells 2010b, p. 
4).

Taxonomy

    The smooth pimpleback was originally described by Lea in 1859 as 
Unio houstonensis. It was later placed in the genus Margaron and 
ultimately moved to Quadrula by Simpson (1900, p. 782). Graf and 
Cummings (2007, p. 18) have proposed moving it to the genus Amphinaias, 
but other freshwater mussel taxonomists recommend waiting for 
additional work to be completed on members of Quadrula before splitting 
the genus (Bogan 2011, pers. comm.). The smooth pimpleback is 
recognized by the Committee on Scientific and Vernacular Names of 
Mollusks of the Council of Systematic Malacologists, American 
Malacological Union (Turgeon et al. 1998, p 37), and we recognize it as 
a valid species.

Biology and Life History

    There is no specific information on age, size of maturity, or host 
fish use for smooth pimpleback. Numerous individuals were examined for 
gravidity between June and November, with no evidence of eggs or 
glochidia (Howells 2000b, p. 38). Other species in the genus Quadrula 
successfully parasitize catfish, and it is likely smooth pimpleback 
does as well (Howells 2010b, p. 2); additionally, mussels in the genus 
Quadrula are typically short-term brooders (Gorden and Layzer 1989, p. 
6; Garner et al. 1999, p. 277), and we expect the same of the smooth 
pimpleback.

Habitat

    The smooth pimpleback has been found in mud, sand, and fine gravel 
in medium-to-large rivers and some reservoirs (Howells 2010b, p. 3). 
Unlike most other Quadrula species in central Texas, smooth pimpleback 
do occur in some reservoirs (Howells 2002b, p. 8; 2010b, p. 3).

Distribution and Abundance

Historical Distribution
    The smooth pimpleback is native to the central and lower Brazos and 
Colorado Rivers and their tributaries in central Texas (Howells 2010b, 
p. 4). The smooth pimpleback has also been reported from the Trinity 
River and other drainages in Texas, as well as from areas outside of 
Texas, including southern Arkansas and the Verdigris River in Kansas. 
These reports are likely misidentifications of other pimpleback species 
that can sometimes closely resemble smooth pimpleback (Howells 2010b, 
pp. 4-5). The smooth pimpleback was historically uncommon where it 
occurred; from the 1960s through the 1990s, experts failed to find 
large populations persisting throughout its range (Howells 2009, p. 
12).
    In the Colorado River, historical reports indicate that the smooth 
pimpleback occurred from San Saba County downstream to Wharton County, 
as well as in the Llano River and Onion and Skull Creeks. Within the 
Brazos River basin, the species historically occurred throughout the 
length of the mainstem of the Brazos River (Howells 2009, p. 12), as 
well as in the Clear Fork Brazos, Leon, Navasota, Little Brazos, San 
Gabriel, Lampasas, and Little Rivers and Yegua Creek (Howells 2010b, 
pp. 4-6; Randklev et al. 2010b, p. 20).
Current Distribution
    The smooth pimpleback has been nearly extirpated from the Colorado 
River basin, and a few small populations persist in the Brazos River 
basin. Recent surveys suggest a greater abundance and distribution of 
the smooth pimpleback in the central Brazos River drainage than was 
indicated by collections from the past 40 years, with five populations 
represented by more than a few individuals.
Colorado River System
    The smooth pimpleback historically occurred throughout the mainstem 
Colorado River as well as several tributaries, but it is currently 
restricted to one mainstem reservoir, two sites on the mainstem 
Colorado River, and the San Saba River. Populations in all of the other 
historically occupied tributaries and two reservoirs appear to have 
been extirpated.
    In the mainstem Colorado River, smooth pimpleback were historically 
known from much of the length of the river (Howells 1996, p. 21; 1997a, 
pp. 34-35; Randklev et al. 2010c, p. 4; OSUM 2011c, p. 1). Numerous 
surveys in many locations on the Colorado River occurred between 1993 
and 2009, and no evidence of smooth pimpleback was found (Howells 1995, 
p. 29; 1996, p. 23; 1997a, pp. 27, 31; 2002a, p. 6; 2004, p. 7, 11; 
2005, p. 6; Burlakova and Karatayev 2010a, pp. 15-16), except for in 
Colorado County in 1999, when three live smooth pimpleback were found 
(Howells 2000a, p. 27). During two surveys in 2009, live smooth 
pimpleback were found in the same general area as in 1999 (Burlakova 
and Karatayev 2010a, p. 16; Johnson 2009, p. 1). Farther downstream, in 
Wharton County, live smooth pimpleback were found at two sites in 2009 
(Burlakova and Karatayev 2010a, p. 16), despite having been surveyed in 
1995 and none found (Howells 1996, p. 23).
    Inks Lake is a small mainstem reservoir on the Colorado River in 
Burnet County. Several live smooth pimpleback were found in 1992 
(Howells 1994, p. 4); however, since that time only shell material has 
been found during four separate surveys between 1996 and 2005 (Howells 
1997a, pp. 32-33; 1999, p. 16; 2005, p. 8; 2006, p. 67). Frequent 
drawdowns in this lake appear to have affected all species of 
freshwater mussels, as there has been a sharp decline in the overall 
mussel community (Howells 1999, p. 16).
    One live smooth pimpleback was found in Lake Lyndon B. Johnson, a 
large mainstem reservoir on the Colorado River, in 2001, but no live 
individuals have been found since (Howells 2002a, pp. 6-7; 2006, pp. 
68-69). Farther downstream, in Lake Marble Falls, 13 live smooth 
pimpleback were found in 1995 during a drawdown of lake levels (Howells 
1996, p. 22), but subsequent surveys in 1996 failed to find any 
additional living animals (Howells 1997a, p. 33). The small recent 
survey effort is not sufficient to conclude that the smooth pimpleback 
no longer occur in these lakes, and small populations may still persist 
there.
    Smooth pimpleback were recently found in the San Saba River in San 
Saba County, when 29 individuals were found at two locations (Burlakova 
and Karatayev 2011, p. 5). Various size and age classes were 
represented, indicating a reproducing, recruiting population (Burlakova 
and Karatayev 2011, p. 5). Even more recently, 206 smooth pimpleback, 
including adults and juveniles, were recorded in this same area in 
riffle and pool habitat (Randklev 2011b, p. 1).
    No smooth pimpleback populations remain in any of the Colorado 
River tributaries in which the species was historically known to occur, 
including the full length of the Llano River (Howells 1996, pp. 21-22; 
1998, p. 17; 2000a, p. 25; 2005, p. 8; Randklev et al. 2010c, p. 4; 
OSUM 2011c, p. 1). A single subfossil shell, likely a smooth 
pimpleback, was found in the Llano River in Kimble County in 1995 
(Howells 1996, pp. 21-22), but no other evidence of the species has 
been found in the Llano River in recent years. Additionally, although 
Onion and Skull Creeks were historically occupied by smooth pimpleback 
(Randklev et al. 2010c, p. 4), the species has not been found recently 
in either stream (Howells 1995, pp. 28-29).

[[Page 62173]]

Brazos River System
    The smooth pimpleback historically occurred in the Brazos River 
system from Palo Pinto County downstream to Austin and Waller Counties, 
as well as in numerous tributaries. The species has been extirpated 
from the upstream half of the mainstem Brazos River and from at least 
three tributaries. Substantial populations persist in the Leon River, 
Navasota River, and Yegua Creek, and small populations remain in the 
lower Brazos and Little Brazos Rivers.
    In the mainstem Brazos River, surveys in Palo Pinto, Somervell, and 
Bosque Counties between 1996 and 2000 indicate that the smooth 
pimpleback has been extirpated from the upstream portion of the river 
(Howells 1997a, pp. 16, 18-19; 1999, pp. 11-12; 2001, p. 19). Despite 
surveys in 1996 and 1998 in which no individuals were found (Howells 
1997a, p. 21; 1999, p. 12), a single live smooth pimpleback was found 
in McLennan County in the middle Brazos River in 2005 (Howells 2010b, 
p. 5), and two live individuals were recorded in Falls County in 2006 
(Karatayev and Burlakova 2008, pp. 6-10).
    Although not extirpated from the middle Brazos River, the smooth 
pimpleback occurs only in low numbers. In Milam and Robertson Counties, 
no smooth pimpleback were found in 1998 (Howells 1999, p. 13), but 
eight live individuals were found in 2006 (Burlakova and Karatayev 
2010b, p. 1). More recently, in 2008, 13 live smooth pimpleback were 
found at the same site (Randklev et al. 2009, p. 18). Additionally, 
downstream in Burleson and Brazos Counties, which were historically 
occupied by the smooth pimpleback (OSUM 2011c, p. 1), a small 
population persists. In 1995, one live and one recently dead individual 
were collected within Brazos County (Howells 1996, pp. 17-18). Although 
none were found here in 1999 (Howells 2000a, pp. 21-22), in 2006 a 
single live smooth pimpleback was collected at this site (Karatayev and 
Burlakova 2008, pp. 6-10). Additionally, further downstream in Grimes 
and Waller Counties, a single live individual was found in 2006 
(Burlakova and Karatayev 2010b, p. 1) and again in 2008 (Randklev et 
al. 2009, p. 18). Smooth pimpleback are more numerous in the lower 
mainstem Brazos River, in Austin and Waller Counties, where 38 live 
individuals were found in 2006 (Karatayev and Burlakova 2008, pp. 6-
10).
    Tributaries to the Brazos River also contain smooth pimpleback 
populations. The Leon River, in the Little River drainage of the 
Brazos, historically contained smooth pimpleback throughout its length 
in Hamilton, Coryell, and Bell Counties (Howells 1994, p. 19, 1997a, p. 
20; Randklev et al. 2010c, p. 4; OSUM 2011c, p. 1). Currently, a smooth 
pimpleback population persists in Hamilton County, where numerous live 
individuals were found in 2006 and 2011 (Howells 2006, pp. 82-83; 
Randklev 2011a, p. 1), as well as several locations in Coryell County, 
where numerous individuals were also recently found (Randklev 2011a, p. 
1).
    Only subfossil smooth pimpleback shells have been found in the 
Lampasas River in Bell County in 1996 (Howells 1997a, pp. 20, 23). 
Subsequent surveys of the river in both Bell and Lampasas Counties 
yielded no evidence of smooth pimpleback (Howells 1999, p.14; 2001, p. 
20), and the species has likely been extirpated from the Lampasas 
River.
    The Little River in Milam County is also a historical location for 
the smooth pimpleback (Randklev et al. 2010c, p. 4). Old shells were 
found at this site in 1996 (Howells 1997a, p. 22), and a single live 
individual was found here in 2006 (Karatayev and Burlakova 2008, p. 6). 
Farther downstream, at the confluence with the Brazos River, none have 
been found (Howells 1996, p. 17).
    A single old smooth pimpleback shell has been found in the San 
Gabriel River in Milam County (Howells 1997a, p. 23), and it is likely 
the species has been extirpated from this Brazos River tributary as 
well.
    In the Little Brazos River, the smooth pimpleback appears to 
persist in low numbers. Although none were found in Robertson County in 
1993 and there had appeared to be a die off of numerous freshwater 
mussel species (Howells 1995, p. 18), one live smooth pimpleback was 
found during a 2006 survey (Karatayev and Burlakova 2008, p. 6). 
Farther downstream in Brazos County, recently dead individuals were 
discovered in 2001 (Howells 2002a, pp. 4-5). The species occurred in 
this area historically (Randklev et al. 2010c, p. 4), and reports of 
mussels in the Little Brazos River from the 1950s described the 
freshwater mussel community as numerous, including smooth pimpleback 
(Gentner and Hopkins 1966, pp. 458-459), but no live individuals have 
been collected in this area in recent years (Howells 1996, p. 18; 1999, 
p. 14).
    The smooth pimpleback has been extirpated from the Clear Fork 
Brazos River. Although this species was originally documented from this 
river in Shackelford County in 1893 (Randklev et al. 2010c, p. 4), none 
have been found in this stream since (Howells 1999, p. 19).
    In the Navasota River, smooth pimpleback historically occurred in 
Leon, Brazos, Grimes, and Washington Counties (Randklev et al. 2010c, 
p. 4; OSUM 2011c, p. 1). Currently, the species persists in each of 
those counties, with a large population occurring in the lower river. 
In Leon County three recently dead smooth pimpleback shells were found 
in 2000 (Howells 2001, p. 23), indicating that a few individuals may 
persist in the area. However, one of the largest known populations 
occurs farther downstream near the confluence of the Navasota and 
Brazos Rivers. Nine live individuals were found in this area in 2006 
(Karatayev and Burlakova 2008, pp. 6-10), and in 2008 a total of 117 
live smooth pimpleback were recorded at 3 different locations within 
Washington and Grimes Counties (Randklev et al. 2009, pp. 6, 18). A 
large population continues to persist in the Navasota River, with a 
total of 314 smooth pimpleback recorded at two sites in 2011 (Randklev 
2011a, p. 1).
    In Yegua Creek, no smooth pimpleback were found during several 
surveys between 1996 and 2003 (Howells 1997a, pp. 24-26; 2001, p. 22; 
2004, p. 6), although subfossil shells were found in Washington County 
in 1996. However, in 2006, a live individual was discovered (Karatayev 
and Burlakova 2008, pp. 6-10), which prompted further surveys in 2008. 
Numerous smooth pimpleback were found during subsequent surveys at four 
different locations within Washington and Burleson Counties (Randklev 
et al. 2009, pp. 16-18; Randklev 2011a, p. 1), indicating the presence 
of a potentially large population in this stream.
Summary
    Based on historical and current data, the smooth pimpleback has 
declined rangewide and is now known from only nine locations. The 
species has been eliminated from nearly the entire Colorado River and 
all but one of its tributaries, as well as from the upper Brazos River 
and several tributaries. The San Saba River, lower Brazos River, 
Navasota River, Leon River, and Yegua Creek populations appear to be 
stable and reproducing, but the remaining populations are small, 
isolated, and represented by only a few individuals.

Species Information for Texas Pimpleback

Species Description

    The Texas pimpleback is a large pimpleback species with a 
moderately

[[Page 62174]]

inflated shell that generally reaches 60-90 mm (2.4-3.5 in) (Howells 
2002b, pp. 3-4). With the exception of growth lines, the shell of the 
Texas pimpleback is generally smooth and moderately thick (Howells 
2002b, p. 4). Externally, coloration ranges from yellowish-tan to dark 
brown with some individuals mottled or with dark green rays. 
Internally, the nacre is white and iridescent posteriorly (Howells 
2002b, p. 4).

Taxonomy

    The Texas pimpleback was originally described as Unio petrinus by 
Gould in 1855. It was placed in the genus Margaron by Lea in 1870 and 
ultimately moved to Quadrula by Simpson in 1900 (Simpson 1900, p. 783). 
Graf and Cummings (2007, p. 18) have proposed moving it to the genus 
Amphinaias, but other freshwater mussel taxonomists recommend waiting 
for additional work to be completed on members of Quadrula before 
splitting the genus (Bogan 2011, pers. comm.). The Texas pimpleback is 
recognized by the Committee on Scientific and Vernacular Names of 
Mollusks of the Council of Systematic Malacologists, American 
Malacological Union (Turgeon et al. 1998, p. 37), and we recognize it 
as a valid species.

Biology and Life History

    There is very little specific information on age, size of maturity, 
or host fish use for Texas pimpleback. Gravid females have been found 
from June through August, and the smallest documented gravid female was 
45 mm (1.8 in) long (Howells 2000b, p. 38). Glochidia are hookless and 
elliptical in shape (Howells et al. 1996, p. 120). To date, no host 
fish have been confirmed for the Texas pimpleback; however, glochidia 
have been reported attached to and encysted on flathead catfish 
(Pylodictis olivaris), yellow bullhead (Ameiurus natalis), and bluegill 
in laboratory settings, although none transformed to the juvenile stage 
(Howells 2010e, p. 3). This is consistent with other species in the 
genus Quadrula, which also parasitize catfish species.

Habitat

    The Texas pimpleback typically occurs in moderately sized rivers, 
usually in mud, sand, gravel, and cobble, and occasionally in gravel-
filled cracks in bedrock slab bottoms (Horne and McIntosh 1979, p. 122; 
Howells 2002b, p. 4). The species has not been found in water depths 
over 2 m (6.6 ft). Texas pimpleback have not been found in reservoirs, 
which indicates that this species is intolerant of deep, low-velocity 
waters created by artificial impoundments (Howells 2002b, p. 4). In 
fact, Texas pimpleback appear to tolerate faster water more than many 
other mussel species (Horne and McIntosh 1979, p. 123).

Distribution and Abundance

Historical Distribution
    The Texas pimpleback is endemic to the Colorado and Guadalupe-San 
Antonio River basins of central Texas (Howells 2002b, p. 3). In the 
Colorado River basin, Texas pimpleback occurred throughout nearly the 
entire mainstem, as well as numerous tributaries, including the Concho, 
North Concho, San Saba, Llano, and Pedernales Rivers, and Elm and Onion 
Creeks (Howells 2010e, p. 5; Randklev et al. 2010c, p. 4; OSUM 2011d, 
p. 1). Within the Guadalupe-San Antonio River basin, it occurred 
throughout most of the length of the Guadalupe River, as well as in the 
San Antonio, San Marcos, Blanco, and Medina Rivers (Horne and McIntosh 
1979, p. 122; Howells 2010e, p. 5; OSUM 2011d, p. 1).
Current Distribution
    The Texas pimpleback has declined significantly rangewide, and only 
four streams--the San Saba River, Concho River, Guadalupe River, and 
San Marcos River--are known to harbor persisting Texas pimpleback 
populations. These populations are disjunct, small, and isolated. The 
species has been extirpated from the remainder of its historical range.
Colorado River System
    In the Colorado River system, Texas pimpleback once occurred 
throughout the mainstem and in many major tributaries. Currently, the 
species has been extirpated from the Pedernales, North Concho, and 
Llano Rivers, as well as Onion Creek. It has also likely been 
extirpated from the mainstem Colorado River and Elm Creek. The Concho 
River contains the most abundant population of Texas pimpleback and one 
of only two populations of the species likely to be remaining in the 
Colorado River system, but most individuals are old and there has been 
very little evidence of recruitment.
    In the mainstem Colorado River, Texas pimpleback historically 
occurred from Runnels County downstream to Colorado County (Howells 
2010e, p. 5; Randklev et al. 2010c, pp. 3-4; OSUM 2011d, p. 1). 
However, surveys in numerous locations along the river yielded no 
evidence of the species anywhere except in Runnels and San Saba 
Counties (Howells 1995, pp. 20, 29; 1997a, pp. 27, 31, 35; 2000a, p. 
27; 2002a, p. 7). In Runnels County, Texas pimpleback shells were found 
in 1993 (Howells 1995, p. 20), but several subsequent surveys between 
1996 and 2008 detected no further evidence of the species (Howells 
1997a, p. 27; 1998, p. 10; 2002a, p. 7; 2004, p. 7; Burlakova and 
Karatayev 2010a, p. 10). In San Saba County, a single shell was 
collected in 1989 (Howells 2002b, p. 6), and three recently dead 
individuals were found in 1999 (Howells 2000a, pp. 25-26). An 
additional shell was collected in 2001 (Howells 2002a, p. 6). No live 
individuals have been collected from this reach of the Colorado River.
    In Runnels County, Elm Creek once supported a Texas pimpleback 
population. Small numbers of Texas pimpleback were found in 1993 and 
1995 (Howells 1995, p. 21; 1996, p. 20), but none were found in 1997, 
2001, or 2003 (Howells 1998, p. 11; 2002a, p. 5; 2004, p. 7). In 2005 
and 2008, only dead individuals were col