# 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

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URL: https://www.frixlaw.com/law-library/documents/fr%3A2011-25471

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** October 6, 2011
- **Citation:** 76 FR 62166

## Text

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.

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
http://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
http://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
http://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.

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.

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

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

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

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

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).

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

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 collected (Howells 2006, pp. 63-64; Burlakova and Karatayev 2010a, p. 10). No live individuals have been found in over a decade despite repeated sampling efforts, and it is likely the Texas pimpleback has been extirpated from this stream.

The Concho River in Concho County supports the largest Texas pimpleback population. Thirteen and 28 individuals were collected in 1993 and 1994, respectively (Howells 1995, pp. 24-25; 2006, p. 61). However, low water and high temperatures in 1997 killed large numbers of many freshwater mussel species in the area up and downstream of Paint Rock, and 63 recently dead Texas pimpleback were found (Howells 1998, pp. 14-15). A severe drought in 1999 resulted in this area of the Concho River being reduced to a series of small pools. Few live Texas pimpleback were collected during this drought, in addition to many recently dead individuals (Howells 2000a, p. 23). No evidence of the species was found in 2004 (Howells 2005, p. 9), but eight live individuals were found in 2005 (Howells 2006, p. 60), evidence that the species had survived the extreme dewatering of the river. In 2008, 61 live Texas pimpleback were collected in this same area, and the population was estimated to contain approximately 4,000 individuals (Burlakova and Karatayev 2010a, p. 10; 2010b, p. 1). However, the average length of individuals collected at this site was over 90 mm (3.5 in), indicating that reproduction is limited in this population. Further, although no mussel surveys occurred in 2009 and 2010, the

river was reported to be extremely low during this time (Howells 2010e, p. 6); the result of this additional dewatering on the population is unknown.

The San Saba River historically contained Texas pimpleback (Randklev
et al.
2010c, p. 2), but no live individuals had been collected in over a decade until recently when shells were collected in 1992 and 1995 (Howells 1994, p. 7; 1996, p. 21), and five live individuals were collected in 1997 (Howells 1998, p. 16). However, subsequent surveys were conducted in 2000, 2004, and 2005, with only shell material being found in 2000 (Howells 2001, pp. 28-29), and no evidence of Texas pimpleback was found in 2004 and 2005 (Howells 2005, pp. 8-9; 2006, pp. 64-65). A single shell was collected in 2008 (Burlakova and Karatayev 2010b, p. 1). However, in 2011, 39 live individuals were found at two sites in San Saba County (Burlakova and Karatayev 2011, p. 3). The individuals found were of various sizes and ages, indicating a reproducing population (Burlakova and Karatayev 2011, p. 4). Further surveys at this site confirm a large population in the area, with 140 individuals, including many juveniles, found here (Randklev 2011b, p. 1).

The Texas pimpleback also historically occurred in the North Concho, Pedernales, and Llano Rivers, as well as Onion Creek (Howells 2010e, p.5; Randklev
et al.
2010c, p. 4; OSUM 2011d, p. 1); all are tributaries within the Colorado River system. In the North Concho River, all freshwater mussels are presumed extirpated from historically occupied areas (Howells 1995, pp. 22-23). The Pedernales River historically harbored a Texas pimpleback population (OSUM 2011d, p. 1), but only old shells have been collected in this river in recent years (Howells 1994, p. 5). Since 1993, no evidence of Texas pimpleback has been found (Howells 1995, pp. 27-28; 1999, p. 16), and the species is presumed to be extirpated. Additionally, repeated surveys in the Llano River in Kimble and Mason Counties consistently failed to collect live Texas pimpleback, with shells found only in Llano County in 1997 (Howells 1996, pp. 21-22; 1998, p. 17; 2005, p. 8). The Texas pimpleback is likely extirpated from all of these streams.

Guadalupe River System

In the Guadalupe River system, the Texas pimpleback has been extirpated from nearly the entire reach of the mainstem Guadalupe, San Antonio, and Blanco Rivers. Very small populations remain only in the lower Guadalupe and San Marcos Rivers, represented by one or two individuals in each.

In the mainstem Guadalupe River, the Texas pimpleback was historically known throughout the length of the river, from as long ago as 1905 (Randklev
et al.
2010c, p. 1; OSUM 2011d, p. 1). Numerous surveys between 1992 and 2005 have not yielded any evidence of the species anywhere but in Victoria County (Howells 1994, pp. 7-9; 1995, pp. 30-32; 1996, pp. 25-27; 1997a, pp. 37-40; 1999, pp. 18-19; 2002a, p. 8; 2003, pp. 15, 17; 2006, pp. 71-72; Johnson 2009, p. 1), where two live individuals were collected in 2009. A small population may remain in the lower Guadalupe River.

In the San Marcos River near the confluence with the Blanco River in Hays County, repeated surveys between 1992 and 2000 yielded no evidence of Texas pimpleback (Howells 1994, pp. 9-10; 1995, pp. 33-34; 1996, p. 27; 1997a, p. 40; 2000a, p. 28; 2001, pp. 32-33). However, in 2003 two shells were collected (Howells 2004, p. 16), and in 2004, a single live individual was found (Howells 2005, p. 10). The Texas pimpleback likely persists in this river in very low numbers.

The Texas pimpleback appears to be extirpated from the San Antonio River, with only shell fragments found near the City of San Antonio in Bexar County in 1993 (Howells 1995, p. 35). No evidence of the species was found downstream in Karnes County in 1996 (Howells 1997a, pp. 41-42).

The Texas pimpleback was once described as abundant in the Blanco River just upstream of its confluence with the San Marcos River in Hays County (Horne and Mcintosh 1979, p. 126), but repeated surveys of this area between 1992 and 1995 yielded no recent evidence of the species (Howells 1994, p. 9; 1995, pp. 32-33; 1996, p. 27), with only a subfossil shell collected in 1993 (Howells 1995, p. 33). No shell material or live individuals were found in additional surveys in 2011 (Johnson 2011, p. 1).

Summary

The Texas pimpleback has been eliminated from long reaches of former habitat in hundreds of miles of the Colorado and Guadalupe River systems. Only two populations appear large enough to be stable, but evidence of recruitment in the Concho River population is limited. The San Saba River population may be the only remaining recruiting population of Texas pimpleback. Two additional populations are represented by one or two individuals; all populations are highly disjunct.

Species Information for Texas Fawnsfoot

Species Description

The Texas fawnsfoot is a small, relatively thin-shelled freshwater mussel that can reach 60 mm (2.4 in) in length but is usually much smaller (Howells 2010d, p. 2). The shell is long and oval, generally free of external sculpturing, with external coloration that varies from yellowish- or orangish-tan, brown, reddish-brown, to smoky-green with a pattern of broken rays or irregular blotches (Howells 2010d, p. 2). The nacre is bluish-white or white and iridescent posteriorly (Howells 2010d, p. 2).

Taxonomy

The Texas fawnsfoot was first described as
Unio macrodon
by Lea in 1859 and was subsequently placed in the genus
Margaron
by Lea in 1870

and then moved to
Plagiola
by Simpson (1900, p. 605). Ultimately the species was placed in the genus
Truncilla
by Strecker (1931, pp. 63, 65). The Texas fawnsfoot 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 Texas fawnsfoot. However, other species in the genus
Truncilla
parasitize freshwater drum (
Aplodinotus grunniens
) (OSUM 2011f, p. 1), and it is likely the Texas fawnsfoot does as well. Freshwater drum are ubiquitous throughout the range of Texas fawnsfoot (Hubbs
et al.
2008, p. 53).

Habitat

Since Texas fawnsfoot were not found alive for many years, very little information is available about its habitat preferences. In the past only Texas fawnsfoot shells and recently dead individuals were occasionally found along rivers following drought-related dewatering or bank deposition after high floods. These shells and recently dead individuals indicated that the Texas fawnsfoot occurs in flowing water, as it was never found in ponds, lakes, or reservoirs, suggesting that it is intolerant of deep, low-velocity waters created by artificial impoundments (Howells 2010d, p. 3). The recently discovered live population in the Brazos River indicates that the species occurs in rivers with soft, sandy sediment with moderate water flow (Randklev and

Lundeen 2010, p. 1; Randklev
et al.
2010a, p. 298; Johnson 2011, p. 1).

Distribution and Abundance

Historical Distribution

The Texas fawnsfoot is endemic to the Brazos and Colorado Rivers of central Texas (Howells
et al.
1996, p. 143; Randklev
et al.
2010a, p. 297). From the 1960s to the 1990s, malacologists working in central Texas found few individuals and few new population locations (Howells 2010d, p. 6). Historical records suggest the Texas fawnsfoot inhabited much of the Colorado River, from Wharton County upstream as far as the North Fork Concho River in Sterling County, as well as throughout the Concho, San Saba, and Llano Rivers and Onion Creek within the Colorado River basin (Howells 2010d, p. 4; Randklev
et al.
2010b, p. 24). In the Brazos River, the species occurred from Fort Bend County upstream to the lower reaches of the Clear Fork Brazos River in Shackelford County, as well as in the Leon River, Little River, San Gabriel River, Deer Creek, and Yegua Creek (Howells 2010d, pp. 4-5; Randklev
et al.
2010b, p. 24). Species reports from the Trinity River and other east Texas locations are of misidentified fawnsfoot (
Truncilla donaciformis
) (Howells 2010d, p. 4).

Current Distribution

Relatively few Texas fawnsfoot have been documented since this species was first described in 1859, and very few live individuals have been found in recent decades (Randklev
et al.
2010a, p. 297). All of these animals were flood deposited on gravel bars and near death just prior to collection (Randklev
et al.
2010a, p. 297), preventing information from being gathered about population size, preferred habitat, and other parameters. A live population of Texas fawnsfoot was not discovered until 2008 in the Brazos River near its confluence with the Navasota River (Randklev
et al.
2010a, p. 297). A second live population was found in 2009 in the Colorado River (Johnson 2009, p. 1). These two locations contain the only confirmed populations of the species to date. Evidence of other remnant populations has also been found in the Clear Fork Brazos River, San Saba River, and Deer Creek.

Colorado River System

The Texas fawnsfoot has been eliminated from almost all of the Colorado River system. Live individuals were found in the lower mainstem Colorado River in 2009, and the only other evidence of current occurrence of Texas fawnsfoot in the Colorado River basin is in the San Saba River, where a population persists.

In the mainstem Colorado River, the Texas fawnsfoot historically occurred from Wharton County upstream into the headwaters (Randklev
et al.
2010c, p. 4; OSUM 2011e, p. 1). Surveys throughout the upper Colorado River between 1993 and 2009 yielded no evidence of Texas fawnsfoot (Howells 1994, pp. 20-21, 29; 1996, pp. 20-21, 23; 1997a, pp. 27, 31, 34-35; 1998, p. 10; 2000a, p. 27; 2002a, p. 6; 2004, p. 7; Burlakova and Karatayev 2010a, p. 16), except for one recently dead individual found in 1999 in San Saba County when the entire river was dewatered and all mussels were eliminated from the area (Howells 2000a, pp. 25-26; 2009, p. 17). The lack of evidence of the species since that time indicates that the population may have been lost. In the lower Colorado River in Colorado County, several old shells of Texas fawnsfoot were found at several sites in 1996 (Howells 1997a, p. 35), and, subsequently in 2009, two live individuals were discovered (Johnson 2011, p. 1). The population was later estimated to be approximately 2,800 individuals, with individuals ranging in size from 21 to 38 mm (0.8-1.5 in) (Burlakova and Karatayev 2010a, p. 17), indicating that reproduction and recruitment is occurring.

Texas fawnsfoot were not known to occur in the San Saba River until a single live individual was collected in 2011 (Burlakova and Karatayev 2011, p. 6). Additional surveys yielded 16 Texas fawnsfoot of various ages collected at the site (Randklev 2011b, p. 1), indicating a persistent, recruiting population.

Texas fawnsfoot is presumed extirpated from the remainder of the Colorado River basin. Although historical records exist in the North Concho, Concho, and Llano Rivers and in Onion Creek (Randklev
et al.
2010c, p. 4), numerous surveys of these streams indicate the extirpation of the species (Howells 1994, pp. 5-6; 1995, pp. 22-25, 28-29; 1996, pp. 21-22; 1998, pp. 14-17; 1999, pp. 15-16; 2000a, pp. 23, 25; 2001, p. 27; 2005, p. 9; Burlakova and Karatayev 2011, p. 6).

Brazos River System

In the Brazos River system, the Texas fawnsfoot persists in the mainstem Brazos River, Clear Fork Brazos River, Navasota River, and possibly in Deer Creek. The species has been extirpated from the Leon River, Little River, San Gabriel River, and Yegua Creek.

In the mainstem Brazos River, the Texas fawnsfoot historically occurred throughout the length of the river, from Palo Pinto County downstream to Fort Bend County (Randklev
et al.
2010c, pp. 2-4; Burlakova and Karatayev 2010b, p. 1; OSUM 2011e, p. 1). While the species appears to have retained its range through the length of the Brazos River, occurrences are represented by very few live or recently dead individuals. In the upper Brazos River in Palo Pinto and Parker Counties, two live individuals were found at each of two sites in 1996, as well as numerous shells (Howells 1997a, pp. 16, 17). A survey in 2000 yielded no evidence of Texas fawnsfoot in this area (Howells 2001, p. 19). Nearby, in Somervell County, four recently dead individuals were found in the mainstem Brazos River in 1996 (Howells 1997a, pp. 18-19. In 2007, only one old shell was found in the same area (Burlakova and Karatayev 2010b, p. 1).

Surveys in Milam and Falls Counties have not yielded any evidence of Texas fawnsfoot, indicating the species has been extirpated from this section of the Brazos River (Howells 1995, p. 17; 1999, pp. 12-13).

In the middle Brazos River, Texas fawnsfoot persists in low numbers in the vicinity of Brazos County. One live individual was found in 1994 (Howells 1996, pp. 17-18), representing the first live collection of the species anywhere since the 1970s. In 1999, numerous recently dead Texas fawnsfoot of mixed sizes and ages were found at several sites in Burleson and Brazos Counties (Howells 2000a, pp. 21-22), indicating a recruiting population existed in the area. The species has been documented here in repeated surveys in 2000, 2003, and 2006 (Howells 2001, p. 22; Karatayev and Burlakova 2008, p. 7; Howells 2009, p. 17), indicating that the species continues to persist in the area.

The first account of a living population of Texas fawnsfoot (animals living
in situ
rather than deposited on or near the banks by floods) occurred in 2008 in the lower Brazos River near its confluence with the Navasota River (Randklev
et al.
2010a, p. 297). Ten live individuals were collected, and all were small, indicating successful reproduction and recent recruitment. An additional Texas fawnsfoot was found in this area in 2011 (Randklev 2011a, p. 1).

The farthest downstream collection of Texas fawnsfoot in the Brazos River in recent years was in Austin and Waller Counties, when one live individual was found in 2006 (Karatayev and Burlakova 2008, p. 39). It is likely the species occurs sporadically through the section of the Brazos River between Brazos and Austin Counties.

Texas fawnsfoot was first discovered in the Navasota River in 2011, when three individuals were found in Washington and Grimes Counties (Randklev 2011a, p. 1). Previous surveys had not yielded evidence of the species in this river (Howells 2001, p. 23).

In Deer Creek, a tributary to the Brazos River in Falls County, a recently dead Texas fawnsfoot was collected in 2006 (Burlakova and Karatayev 2010b, p.1), despite previous surveys that yielded no evidence of the species (Howells 1999, p. 12).

Additionally, a Texas fawnsfoot population persists in the Clear Fork Brazos River. Recently dead Texas fawnsfoot have been collected in several locations along the length of the river, in Shackelford, Stephens, and Young Counties (Randklev
et al.
2010c, p. 4; Randklev 2011, pers. comm.). Several other tributaries to the Brazos River that historically contained Texas fawnsfoot appear to no longer support the species after numerous surveys reveal no living or dead individuals, including the Leon River (Howells 1994, pp. 18-20; 1997a, pp. 19-20), the Little River (Howells 1997a, pp. 22-23), the San Gabriel River (Howells 1997a, p. 23), and Yegua Creek (Howells 1997a, pp. 24, 25-26; 1999, p. 14; 2001, p. 22; 2004, p. 6).

Summary

The Texas fawnsfoot has declined rangewide and is now known from only five populations. The species has been extirpated from nearly all of the Colorado River basin and from much of the Brazos River basin. Of the populations that remain, only the Colorado, San Saba, and Brazos River populations are likely to be stable and recruiting; the remaining populations are disjunct and restricted to short stream reaches.

Five-Factor Evaluation and Findings

Texas fatmucket, golden orb, smooth pimpleback, Texas pimpleback, and Texas fawnsfoot all occur in central Texas across four major river basins (Brazos, Colorado, Guadalupe, and Nueces-Frio River basins). These species depend on similar physical and biological features and on the successful functioning of riverine ecosystems to survive. Many of the species face the same or very similar threats. For each species, we identified and evaluated all the factors that may be threatening the species. However, to avoid redundancy of information when the analysis of the threats is the same between species, we referenced the reader to the initial description of the common threats. For example, the degradation of habitat and habitat loss due to dams and impoundments is a common threat to all five species, so a full description of the threat was provided for the Texas fatmucket, and for the remaining species the initial description was referenced with species-specific information provided, as available.

Five-Factor Evaluation for Texas Fatmucket

Information pertaining to the Texas fatmucket in relation to the five factors provided in section 4(a)(1) of the Act is discussed below.

Factor A. The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or Range.

The decline of mussels in Texas and across the United States is primarily the result of habitat loss and degradation (Neves 1991, pp. 252, 265; Howells
et al.
1996, pp. 21-22). Chief among the causes of mussel decline in Texas are the effects of impoundments, sedimentation, dewatering, sand and gravel mining, and chemical contaminants (Neck 1982a, pp. 33-35; Howells
et al.
1996, pp. 21-22; Winemiller
et al.
pp. 17-18). These threats are discussed below.

Impoundments

A major factor in the decline of freshwater mussels across the United States has been the large-scale impoundment of rivers (Vaughn and Taylor 1999, p. 913).

Dams are the source of numerous threats to freshwater mussels: They block upstream and downstream movement of species by blocking host fish movement; they eliminate or reduce river flow within impounded areas, thereby trapping silts and causing sediment deposition; and dams change downstream water flow timing and temperature, decrease habitat heterogeneity, and affect normal flood patterns (Layzer
et al.
1993, pp. 68-69; Neves
et al.
1997, pp. 63-64; Watters 2000, pp. 261-264; Watters 1996, p. 80). Within reservoirs (the impounded waters behind dams), the decline of freshwater mussels has been attributed to sedimentation, decreased dissolved oxygen, and alteration of resident fish populations (Neves
et al.
1997, pp. 63-64; Pringle
et al.
2000, pp. 810-815; Watters 2000, pp. 261-264). Dams significantly alter downstream water quality and stream habitats (Allan and Flecker 1993, p. 36; Collier
et al.
1996, pp. 1, 7) resulting in negative effects to tailwater (the area downstream of a dam) mussel populations (Layzer
et al.
1993, p. 69; Neves
et al.
1997, p. 63; Watters 2000, pp. 265-266). Below dams, mussel declines are associated with changes and fluctuation in flow regime, scouring and erosion of stream channels, reduced dissolved oxygen levels and water temperatures, and changes in resident fish assemblages (Williams
et al.
1992, p. 7; Layzer
et al.
1993, p. 69; Neves
et al.
1997, pp. 63-64; Pringle
et al.
2000, pp. 810-815; Watters 2000, pp. 265-266). Numerous dams have been constructed throughout the Colorado, Guadalupe, Brazos, and Nueces-Frio River systems within the range of all five mussels addressed in this finding (Stanley
et al.
1990, p. 61).

Population losses due to the effects of dams and impoundments have likely contributed more to the loss of diversity and abundance of freshwater mussels across Texas, including the Texas fatmucket, than any other factor. Stream habitat throughout nearly all of the range of Texas fatmucket has been affected by numerous impoundments, leaving generally short, isolated patches of remnant habitat between dams. Impoundments have resulted in profound changes to the nature of the rivers, primarily replacing free-flowing river systems with a series of large reservoirs.

There are no natural lakes within the range of the Texas fatmucket, nor has it ever been found in reservoirs. Surveys of the reservoirs on the Guadalupe and Colorado Rivers have been ongoing since at least 1992, and no evidence of live or dead Texas fatmucket has been found in any reservoir (Howells 1994, pp. 1-20; 1995, pp. 1-50; 1996, pp. 1-45; 1997a, pp. 1-58; 1998, pp. 1-30; 1999, pp. 1-34; 2000a, pp. 1-56; 2001, pp. 1-50; 2002a, pp. 1-28; 2003, pp. 1-42; 2004, pp. 1-48; 2005, pp. 1-23; 2006, pp. 1-106; Karatayev and Burlakova 2008, pp. 1-47; Burlakova and Karatayev 2010a, pp. 1-30; 2011, pp. 1-8), further indicating this species is not tolerant of impoundments.

Impoundments occur throughout the range of the Texas fatmucket. The majority of the Nueces-Frio, Guadalupe, San Antonio, Colorado, and Brazos Rivers, as well as many tributaries, are now impounded. There are 31 major reservoirs within the Colorado River basin, with another reservoir (Goldthwaite Reservoir) being considered on the Colorado River in Mills and San Saba Counties; this reservoir was the number one recommendation in the water plan for the region (Texas Water Development Board (TWDB) 2011, p. 4-85). There are 29 reservoirs throughout the Guadalupe River basin and 34 reservoirs throughout the San Antonio River basin, each with a storage capacity of 3000 acre-feet or more, and many smaller reservoirs (Exelon 2010, p. 2.3-4). The majority of the large dams were

constructed for power generation, flood control, and water supply, primarily by the Lower Colorado River and Guadalupe-Blanco River Authorities, beginning in the early twentieth century (Guadalupe-Blanco River Authority 2011, p. 1; Lower Colorado River Authority (LCRA) 2011a, p. 1). These, and numerous smaller dams, occur throughout the Colorado and Guadalupe River basins and have resulted in ongoing destruction and modification of Texas fatmucket habitat and the curtailment of its range.

Dams threaten freshwater mussels in several ways. First, they can prevent the movement of freshwater mussel host fish. The overall distribution of mussels is a function of the dispersal of their hosts (Watters 1996, p. 83). For example, Watters (1996, p. 80) found that the distributions of the fragile papershell (
Leptodea fragilis
)

and pink heelsplitter (
Potamilus alatus
)

in five midwestern rivers were determined by the presence of low-head dams. These dams were non-navigable (without locks), lacked fish ladders, and varied in height from 1 to 17.7 m (3 ft to 58 ft), and the host fish could not disperse through them. Although the distribution of mussels may depend on many ecological factors, the evidence presented in Watters (1996, pp. 79-85) illustrates that dams as small as 1 m (3 ft) high can limit the distribution of mussels. There are many dams that occur throughout the range of the Texas fatmucket that lack fish ladders and may be a barrier to the movement of fish hosts and, therefore, the distribution of mussels. Because the Texas fatmucket populations are all separated by dams of various sizes that are not passable by fish, the mussel is unable to disperse from its current occupied range through host fish migration.

Dams also alter aquatic habitat within the resulting impoundments. It is well documented that many mussel species that are adapted to flowing water stream environments do poorly in the altered aquatic conditions found within impoundments (Williams
et al.
1992, p. 7; Vaughn and Taylor 1999, p. 913). Once a dam is constructed, the original river channel upstream remains intact but under much deeper water with much lower velocities. As water velocity decreases, water loses its ability to carry sediment; sediment falls to the substrate, eventually smothering mussels that cannot adapt to soft substrates (Watters 2000, p. 263). Over time, the original mussel species composition of the stream channel may be eliminated or changed in favor of silt-tolerant species (Watters 2000, p. 264). The mussel community may be altered from one with many different species to a community dominated by one to several very common species (Neck 1982b, p. 174). Texas fatmucket does not occur in reservoirs, indicating it is not tolerant of lentic conditions, and it is now extirpated from impounded areas where it occurred prior to inundation. The inundation of stream habitat by impoundments is a likely cause of the reduction in the distribution of the Texas fatmucket. The presence of the impoundments has caused the permanent loss of Texas fatmucket habitat throughout its range.

The loss of seven freshwater mussel species native to Texas, including Texas fatmucket and golden orb, due to impoundment construction was documented on the Medina River (Neck 1989, p. 323). The Medina River was impounded in 1913 by construction of Medina Dam, and now only three different species of mussels, all of which are tolerant of lentic habitats, occur in the impounded area. The bottom of Medina Lake now consists of moderate and steep limestone slopes and excessive silt deposits, whereas before it was most likely made up of a combination of silt, sand, and gravel substrates. Most mussels native to the Medina River were unable to adapt to the change in flowing water and substrate conditions (Neck 1989, p. 323), including the Texas fatmucket, which is no longer found in the river.

Mussels downstream of impoundments are often affected through changes in fish host availability, water quality (particularly lower water temperatures), habitat structure, and stream channel scouring (Vaughn and Taylor 1999, p. 916). The release of cold water from the hypolimnion (deeper and colder layer of water in reservoirs) can decrease the occurrence of fish species adapted to warm water and increase the occurrence of fish species adapted to colder water (Edwards 1978, pp. 73-75). This changes the species composition of suitable host fish and may prevent mussels from completing an essential part of their reproductive cycle. This has been demonstrated by the extirpation of mussel species from several rivers on the eastern seaboard of the United States, which has been linked to the disappearance of appropriate host fish; the reintroduction of the host fish to rivers has enabled mussel species to recolonize areas (Kat and Davis 1984, p. 174). In addition, because mussel reproduction is temperature dependent (Watters and O'Dee 1999, pp. 455-456), it is likely that individual mussels living in cold waters downstream of dam releases may reproduce less frequently, if at all (Layzer
et al.
1993, p. 69). Low water temperatures can also significantly delay or prevent metamorphosis (Watters and O'Dee 1999, pp. 454-455) and glochidial release, which is often triggered by water temperature (Watters and O'Dee 2000, p. 136).

Similar changes in water temperatures downstream of dams may be responsible for the loss of some Texas fatmucket populations. For example, Canyon Reservoir on the Guadalupe River in Comal County is a deep impoundment built in 1964 that has hypolimnetic water releases. Temperature monitoring stations throughout the Guadalupe River basin show that maximum temperatures above Canyon Reservoir averaged 29.6 degrees Celsius (°C) (85.3 degrees Fahrenheit (°F)); the maximum stream temperatures below the reservoir averaged only 19.7 °C (67.5 °F) (Edwards 1978, p. 72). After impoundment, dissolved oxygen and water temperature dropped, with an accompanying drop in mussel numbers and species diversity (Young
et al.
1976, p. 216). According to historical museum records analyzed by Randklev
et al.
(2010b, pp. 1-32), the Texas fatmucket once occurred in this area of the Guadalupe River prior to the construction of Canyon Reservoir. The Guadalupe River and Canyon Lake in Comal and Kendall Counties were surveyed in 2009, and no live or recently dead Texas fatmucket were found (Burlakova and Karatayev 2010a, pp. 12-13). We reasonably conclude that the loss of the Texas fatmucket from this area was caused by the changes to the aquatic habitat of the Guadalupe River from the effects of Canyon Reservoir. Many of the dams throughout the range of Texas fatmucket have hypolimnetic water releases, including Canyon Reservoir on the Guadalupe River (Magnelia 2001, p. 1), and Inks Lake, Lake LBJ (Schnoor and Fruh 1979, p. 506), and Lake Travis (Texas Natural Resource Conservation Commission 2001, p. 4) on the Colorado River, among others. We anticipate that changes in water temperatures from water released by these and other reservoirs also alter mussel habitats in streams, causing the elimination of mussel populations downstream.

In addition to the temperature of water released from dams, highly fluctuating, turbulent tailwaters devoid of sediment will scour the riverbed downstream of dams, rendering the area without mussel habitat (Layzer
et al.
1993, p. 69). Depending on the use of the dam, water levels may fluctuate on a regular interval (for hydroelectric purposes) or at random (for flood

control) (Watters 2000, p. 265). On the Colorado River, Inks Lake, Lake Marble Falls, Lake Buchanan, Lake Austin, Lake Travis, and Lady Bird Lake are each used for one or both of these purposes. Mortality of another rare mussel species in Texas, the Texas heelsplitter (
Potamilus amphichaenus
) was attributed to scheduled dewatering of the Neches River below B.A. Steinhagen Reservoir in east Texas (Neck and Howells 1994, p. 15).

Fluctuating water levels below dams also result in dramatic changes in water velocity. Downstream of Lake Livingston on the Trinity River in east Texas, for example, high-volume water discharges and abrupt stoppages of flow resulted in a river bed composed of large rocks and shifting sand (Neck and Howells 1994, p. 14); these kinds of habitat changes would be inhospitable to Texas fatmucket below the dams within its range. In some rivers this unstable zone may be extensive. For example, on the Brazos River downstream of Possum Kingdom Reservoir in Texas exhibited unstable substrate for 150 km (240 mi) below the dam (Yeager 1993, p. 68).

In one study of the downstream effects of dams, Vaughn and Taylor (1999, p. 915) found a strong, gradual, linear increase in mussel species richness and abundance at sites on the Little River in Oklahoma downstream from Pine Creek Reservoir. Their research revealed that mussel species richness and total abundance did not begin to rebound until 20 km (12 mi) downstream of the impoundment and did not peak until 53 km (33 mi) downstream. They noted the most obvious difference since reservoir construction has been the alteration of the flow and temperature regimes, which gradually return to pre-impoundment levels with downstream distance from the dam. These alterations appear to have produced an extinction gradient of mussels that is most severe near the dam (Vaughn and Taylor 1999, p. 915). We expect similar effects on the Texas fatmucket and other Texas mussels downstream of dams.

In one area on the Guadalupe River in Kerr County, a Texas fatmucket population once existed directly below a small dam (Howells 1997a, p. 36), indicating the effects of the dam construction and closure were not immediately lethal. However, the population has been presumed extirpated since 1998 (Howells 2006, p. 71), and it is likely that fluctuating downstream flows from the dam contributed to the loss of this population.

Dam construction also fragments the range of Texas fatmucket, leaving remaining habitats and populations isolated by the structures as well as by extensive areas of deep uninhabitable, impounded waters. These isolated populations are unable to naturally recolonize suitable habitat that may be impacted by temporary but devastating events, such as severe drought, floods, or pollution. Dams impound river habitats throughout almost the entire range of the species, and these impoundments have left short and isolated patches of remnant habitat, typically between impounded reaches.

In summary, the widespread construction of dams has affected the Texas fatmucket throughout its range by significantly altering stream habitat both upstream and downstream of the dams by changing fish assemblages, water depths and velocities, water temperature, dissolved oxygen, substrate, and stream channels. The effects of dams are ongoing and continue to negatively impact the Texas fatmucket rangewide. Because of this loss of habitat and its effects on the populations, we find that the effects of impoundments are a threat to the Texas fatmucket.

Sedimentation

Siltation and general sediment runoff is a pervasive problem in streams and has been implicated in the decline of stream mussel populations (Ellis 1936, pp. 39-40; Vannote and Minshall 1982, p. 4105; Dennis 1984, p. ii; Brim Box and Mossa 1999, p. 99; Fraley and Ahlstedt 2000, pp. 193-194). Specific biological effects on mussels from excessive sediment include reduced feeding and respiratory efficiency from clogged gills (Ellis 1936, p. 40), disrupted metabolic processes, reduced growth rates, increased substrate instability, limited burrowing activity (Marking and Bills 1979, pp. 208-209; Vannote and Minshall 1982, p. 4106), physical smothering, and disrupted host fish attractant mechanisms (Hartfield and Hartfield 1996, p. 373). The primary effects of excess sediment on mussels are sublethal, with detrimental effects not immediately apparent (Brim Box and Mossa 1999, p. 101).

The physical effects of sediment on mussel habitats are multifold and include changes in suspended material load; changes in streambed sediment composition from increased sediment production and runoff in the watershed; changes in the form, position, and stability of stream channels; changes in water depth or the width-to-depth ratio, which affects light penetration and flow regime; actively aggrading (filling) or degrading (scouring) channels; and changes in channel position that may leave mussels stranded (Brim Box and Mossa 1999, pp. 109-112).

Increased sedimentation and siltation may explain, in part, why Texas fatmucket appear to be experiencing recruitment failure in some streams. Interstitial spaces (small openings between rocks and gravels) in the substrate provide essential habitat for juvenile mussels. 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. Juvenile freshwater mussels, including Texas fatmucket juveniles, burrow into interstitial substrates, making it particularly susceptible to degradation of this habitat.

Even in 1959, both the Colorado and Guadalupe Rivers were noted as having high sedimentation rates from agricultural activities (Soil Conservation Service 1959, pp. 56, 59). Approximately 40 percent of U.S. river miles do not meet Clean Water Act standards due to excessive sediment loads (Environmental Protection Agency (EPA) 2000, p. 1), with agricultural activities being the primary source of sediment in streams (Waters 1995, p. 170). In general, sedimentation, resulting from unrestricted access by livestock, has been shown to be a significant threat to many streams and their mussel populations (Fraley and Ahlstedt 2000, p. 193). A primary land use throughout the range of the Texas fatmucket is grazing by cattle, sheep, and goats (Hersh 2007, p. 11). Soil compaction, which reduces vegetative growth, from intensive grazing may reduce infiltration rates and increase runoff and erosion, and trampling of riparian vegetation increases the probability of erosion (Armour
et al.
1994, p.10; Brim Box and Mossa 1999, p. 103).

Another cause of increased sediments in streams is widespread brush removal, such as that of the native plant,
Juniperus ashei
(Ashe juniper), throughout central Texas.
Juniperus ashei
removal can cause a marked increase in sediment runoff into streams (Greer 2005, p. 76). The Texas State Soil and Water Conservation Board has a funding program specifically for
Juniperus ashei
removal in Blanco, Gillespie, Kerr, Kendall, and Travis Counties (Gillespie County Soil and Water Conservation District 2011, p. 1), which includes the watersheds of three known Texas fatmucket populations in Live Oak Creek, Threadgill Creek, and the upper Guadalupe River. In one example, Howells (2010f, p. 6) noted

increased sediment deposition after widespread
Juniperus ashei
removal upstream of the Texas fatmucket population in Live Oak Creek.

Sedimentation may become an increasing threat to the Texas fatmucket in the Colorado and Guadalupe River basins as the Austin and San Antonio metro areas continue to expand. Activities associated with urbanization, such as road construction and increased impervious surfaces (surfaces that do not allow infiltration of rain water), can be detrimental to stream habitats (Couch and Hamilton 2002, p. 1). Runoff from increased impervious surfaces increases sediment loads in streams and destabilizes stream channels (Pappas
et al.
2008, p. 151). Impervious surfaces also result in channel instability by accelerating stormwater runoff, which increases bank erosion and bed scouring, thereby further increasing downstream sedimentation (Brim Box and Mossa 1999, p. 103). While erosion and sedimentation associated with road construction may be temporary, the existence of road crossings is shown to have ongoing impacts to mussel habitat. For example, in the Guadalupe River, road crossings were found to cause a long-term increase in sedimentation both upstream and downstream, as channel constriction reduced flow upstream, causing sediment deposition, and runoff from the road increased sedimentation downstream (Keen-Zebert and Curran 2009, p. 301). Urban development activities may also affect streams and their mussel fauna where adequate streamside buffers are not maintained and erosion from adjacent land is allowed to enter streams (Brainwood
et al.
2006, p. 511).

Large projects that reduce vegetative cover within the watersheds supporting Texas fatmucket populations can also increase sedimentation flowing into streams. For example, the Lower Colorado River Authority Transmission Services Corporation (LCRA TSC) is proposing to construct two new 345-kilovolt (kV) electric transmission line facilities between Tom Green (in the Colorado River basin near San Angelo) and Kendall Counties (in the Guadalupe River basin north of San Antonio) to provide electrical power to accommodate increased human populations (Clary 2010, p. 1). All of the proposed project routes occur within the range of the Texas fatmucket. Two proposed segments would cross through Live Oak Creek, one through the San Saba River, and one through the upper Guadalupe River; all of these streams contain populations of the Texas fatmucket. The proposed project could negatively affect Texas fatmucket habitat if construction or maintenance of the transmission line requires removal of vegetation within the riparian zone and that removal results in an increase in sediment runoff into Live Oak Creek and the Guadalupe and San Saba Rivers (Clary 2010, pp. 7, 9, 15). Similar infrastructure development activities to accommodate Texas population growth are expected to be undertaken across the species' range and will likely lead to additional sources of sediment in the streams inhabited by the Texas fatmucket.

Streams occupied by Texas fatmucket are subject to increasing levels of sedimentation from agricultural activities, instream sand and gravel mining, vegetation removal, and urbanization. All of these activities are ongoing throughout the range of the Texas fatmucket and are unlikely to decrease, resulting in significant threats to the Texas fatmucket.

Dewatering

River dewatering can occur in several ways: Anthropogenic activities such as surface water diversions and groundwater pumping, and natural events, such as drought. Surface water diversions and groundwater pumping can lower water tables, reducing river flows and reservoir levels. When water levels in streams and reservoirs are lowered dramatically, it can result in mussels being stranded and dying in previously wetted areas. This is a particular concern within and below reservoirs where water levels are managed for purposes that result in water levels in the reservoir or downstream to rise or fall in very short periods of time, such as when hydropower facilities release water during peak energy demand periods. Rivers can also be dewatered to expedite construction activities, which happened in the upper Guadalupe River in Kerr County in 1998 for bridge construction; numerous Texas fatmuckets were exposed and desiccated (dried out and died) (Howells 1999, pp. 18-19).

Drought can also severely affect Texas fatmucket populations. For example, near-record dry conditions in 2008, followed by a pattern of below-normal rainfall during the winter and spring of 2009, led to one of the worst droughts in recorded history for most of central Texas, including the range of the Texas fatmucket (Nielsen-Gammon and McRoberts 2009, p. 2). This drought's severity was exacerbated by abnormally high air temperatures, a likely effect of climate change, which has increased average air temperatures in Texas by at least 1 °C (1.8 °F) (Nielsen-Gammon and McRoberts 2009, p. 22). The reservoirs within the Colorado River basin were extremely low during this time due to the drought (Clean Water Action 2011, p. 1), as were river levels. Minimal to no flow was recorded at numerous sites within the basin (U.S. Geological Survey (USGS) 2011a, p. 1). Four of the five current sites of the Texas fatmucket may have had very low flows during the 2009 drought, including populations in the San Saba, Llano, Pedernales, and Guadalupe Rivers (Howells 2010c, pp. 9-10). As low flows persist, mussels face oxygen deprivation, increased water temperature, and, ultimately, stranding (Golladay
et al.
2004, p. 501). Only the Llano River has been surveyed since 2009, and the species persists in that river (Burlakova and Karatayev 2011, p. 1). Central Texas is currently experiencing another extreme drought, with rainfall between October 2010 and July 2011 being the lowest on record during those months (LCRA 2011c, p. 1), and the effects of this drought are being observed but are not yet fully known. As of the date of publication of this finding, the Llano River has nearly stopped flowing (Mashhood 2011, p. 1); this has undoubtedly affected Texas fatmucket populations in this river.

We do not know the extent of the impacts of stream dewatering on the Texas fatmucket; however, because this species' populations are so small and isolated, the loss of numerous individuals at a site can have dramatic consequences to the population. Hydropower facilities, construction, surface water diversions, groundwater pumping, and drought are occurring throughout the range of the Texas fatmucket; therefore, the effects of dewatering are ongoing and unlikely to decrease in the future, resulting in significant threats to the Texas fatmucket.

Sand and Gravel Mining

Sand and gravel mining (removing bed materials from streams) has been implicated in the destruction of mussel populations across the United States (Hartfield 1993, pp. 136-138). Sand and gravel mining causes stream instability by increasing erosion and turbidity (a measure of water clarity) and causing subsequent sediment deposition downstream (Meador and Layher 1998, pp. 8-9). These changes to the stream can result in large-scale changes to aquatic fauna, by altering habitat and affecting spawning of fish, mussels, and other aquatic species (Kanehl and Lyons 1992, pp. 4-11).

Sedimentation and increased turbidity can accrue from instream mining activities. In the Brazos River, a gravel dredging operation was

documented as depositing sediment as far as 1.6 km (1 mi) downstream (Forshage and Carter 1973, p. 697). Accelerated streambank erosion and downcutting of streambeds are common effects of instream sand and gravel mining, as is the mobilization of fine sediments during sand and gravel extraction (Roell 1999, p. 7).

Mining activities may threaten some local Texas fatmucket populations. Currently, one mining operation is permitted near the population in Onion Creek (TPWD 2008c, p. 1), and another in the Llano River watershed in Kimble County (TPWD 2008a, p. 1). The permits allow for repeated removal of sand and gravel at various instream locations. Two additional mining operations occur in historical habitat for the species—the mainstem Colorado River (U.S. Army Corps of Engineers (USACE) 2010, p. 2) and Johnson Creek (TPWD 2007a, p. 1).

In areas where repeated mining occurs, an upstream progression of channel degradation and erosion (called headcutting) can occur (Meador and Layher 1998, p. 8). Headcutting may move miles upstream in a zipper-like fashion as the upper boundary of the modified area collapses. Headcutting can be found within the majority of rivers and streams in Texas, including within the Texas fatmucket's current and historical range (Kennon
et al.
1967, p. 22). Headcuts induced by sand and gravel mining can cause dramatic changes in streambank and channel shape that may affect instream flow, water chemistry and temperature, bank stability, and siltation (Meador and Layher 1998, p. 8), all of which are harmful to freshwater mussels. Mussels are particularly vulnerable to channel degradation and sedimentation processes associated with headcutting due to their immobility (Pringle 1997, p. 429).

In addition to headcutting, mines that are located near stream channels are subject to the gravel pit being captured by the stream during flood events or due to gradual channel migration (Simmang and Curran 2006, p. 1). For example, two gravel mines along the Colorado River downstream of Austin were inundated; one by stream channel migration in 1984, one by stream capture in 1991 (Simmang and Curran 2006, p. 1). Once captured by the mainstem river, gravel mines contribute large amounts of suspended sediment to the river, causing additional turbidity and sedimentation and further degrading mussel habitat.

Two Texas fatmucket populations in the mainstem Colorado River and Johnson Creek may be currently affected by sand and gravel mining. These activities occur over a long period of time, destabilizing habitat and altering substrates and banks both upstream and downstream. Altered habitat will cause a decrease in the likelihood of recolonization by mussels after the activity has been completed. Therefore, the effects of sand and gravel mining are an ongoing threat to the Texas fatmucket.

Chemical Contaminants

Chemical contaminants are ubiquitous throughout the environment and are a major reason for the decline of freshwater mussel species nationwide (Richter
et. al.
1997, p. 1081; Strayer
et al.
2004, p. 436; Wang
et al.
2007a, p. 2029). Chemicals enter the environment through both point and nonpoint discharges, including spills, industrial sources, municipal effluents, and agriculture runoff. These sources contribute organic compounds, heavy metals, pesticides, herbicides, and a wide variety of newly emerging contaminants to the aquatic environment. As a result, water quality can be degraded to the extent that mussel populations are adversely affected.

Chemical and oil spills can be especially devastating to mussels because they may result in exposure of a relatively immobile species to elevated concentrations that far exceed toxic levels. Acute and chronic exposure to oil spills in freshwater systems is largely understudied; therefore, little information is available on effects of oil spills on freshwater ecosystems (Harrel 1985, p. 223; Bhattacharyya
et al.
2002, p. 205). Oil is retained much longer in marshes and other low-energy environments, such as slow-moving streams and rivers, than on wave-swept coasts (Bhattacharyya
et al.
2002, p. 205). Oils have been found in sediments at low energy sites as much as 5 years after the occurrence of spills, and they may be released into the water column long after the initial spill. Oil may have various chronic effects on water-column and benthic (bottom-dwelling) species. These effects include sensory disruption, behavioral and developmental abnormalities, and reduced fertility (Bhattacharyya
et al.
2002, p. 205). Oil spilled on the water surface may also limit oxygen exchange, coat the gills of aquatic organisms, and cause pathological lesions on respiratory surfaces, thereby affecting respiration in aquatic organisms. Effects of oil on freshwater mussels may result from oil settling on the sediment surfaces and accumulating in the sediment. This can prevent invertebrate colonization (Bhattacharyya
et al.
2002, p. 205). Complete recovery of benthic communities may be a matter of years, with communities in the meantime consisting solely of pollutant-tolerant organisms (Bhattacharyya
et al.
2002, p. 205). Oil spills can occur from on-site accidents (tank, pipeline spills) or from tanker truck accidents within watersheds occupied by Texas fatmucket. For example, 450 gallons of oil were spilled into Lake Bastrop, a reservoir on a tributary to the Colorado River, in February 2011 (Cihock 2011, p. 1).

Exposure of mussels to persistent low concentrations of contaminants likely to be found in aquatic environments can also adversely affect mussels and their populations. Such concentrations may not be immediately lethal, but over time can result in mortality, reduced filtration efficiency, reduced growth, decreased reproduction, changes in enzyme activity, and behavioral changes to all mussel life stages (Naimo 1995, pp. 351-352; Baun
et al.
2008, p. 392). Frequently, procedures that evaluate the “safe” concentration of an environmental contaminant (for example, national water quality criteria) do not have data for freshwater mussel species or do not consider data that are available for freshwater mussels (March
et al.
2007, pp. 2066-2067, 2073).

One chemical that is particularly toxic to early life stages of mussels is ammonia. Sources of ammonia include agricultural activities (animal feedlots and nitrogenous fertilizers), municipal wastewater treatment plants, and industrial waste (Augspurger
et al.
2007, p. 2026), as well as precipitation and natural processes (decomposition of organic nitrogen) (Goudreau
et al.
1993, p. 212; Hickey and Martin 1999, p. 44; Augspurger
et al.
2003, p. 2569; Newton 2003, p. 2543). Therefore, ammonia is considered a limiting factor for survival and recovery of some mussel species due to its ubiquity in aquatic environments, high level of toxicity, and because the highest concentrations typically occur in mussel microhabitats (Augspurger
et al.
2003, p. 2574). In addition, studies have shown that ammonia concentrations increase with increasing temperature and low-flow conditions (Cherry
et al.
2005, p. 378; Cooper
et al.
2005, p. 381), which may be exacerbated during low-flow events in streams. Within the range of Texas fatmucket, high ammonia levels are common, either chronically, such as in Elm Creek, which is listed as impaired due to high ammonia concentrations (Texas Commission on Environmental Quality (TCEQ) 2010a, p. 294), or due to spills. A wastewater leak in August 2010 spilled approximately 380,000

liters (L) (100,000 gallons (gal)) of sewage into Elm Creek (Bramlette and Cosel 2010, p. 1); ammonia is present in high concentrations in sewage, among other pollutants. Additionally, a sewage spill in 2008 in Onion Creek discharged nearly 380,000 L (100,000 gal), and another sewage spill occurred in April 2011 in Quinlan Creek, a tributary to the Guadalupe River near the Kerr County population (MacCormack 2011, p. 1). High ammonia levels from chronic sources as well as from spills may be affecting Texas fatmucket populations.

In addition to ammonia, agricultural sources of chemical contaminants include two broad categories that have the potential to adversely affect mussel species: Nutrients and pesticides. High amounts of nutrients, such as nitrogen and phosphorus, in streams can stimulate excessive plant growth (algae and periphyton, among others), which in turn can reduce dissolved oxygen levels when dead plant material decomposes. Nutrient over-enrichment in streams is primarily a result of runoff of fertlizer and animal manure from livestock farms, feedlots, and heavily fertilized row crops (Peterjohn and Correll 1984, p. 1471). Over-enriched conditions are exacerbated by low-flow stream conditions, such as those experienced during typical summer season flows. Bauer (1988, p. 244) found that excessive nitrogen concentrations can be detrimental to the adult freshwater pearl mussel (
Margaritifera margaritifera
), as was evident by the positive linear relationship between mortality and nitrate concentrations. Also, a study of mussel life span and size (Bauer 1992, p. 425) showed a negative correlation between growth rate and high nutrient concentrations, and longevity was reduced as the concentration of nitrates increased. Juvenile mussels in interstitial habitats are particularly affected by depleted dissolved oxygen levels resulting from nutrient over-enrichment (Sparks and Strayer 1998, p. 133). The Texas fatmucket occurs within the Concho River watershed, which has been documented as having particularly high nitrates for nearly 20 years, likely due to intensive agriculture in the area (Texas Clean Rivers Program 2008, p. 2), which may be affecting the Texas fatmucket population.

Mussels are also affected by metals (Keller and Zam 1991, p. 543) such as cadmium, chromium, copper, mercury, and zinc, which can negatively affect biological processes such as growth, filtration efficiency, enzyme activity, valve closure, and behavior (Keller and Zam 1991, p. 543; Naimo 1995, pp. 351-355; Jacobson
et al.
1997, p. 2390; Valenti
et al.
2005, p. 1244). Metals occur in industrial and wastewater effluents and are often a result of atmospheric deposition from industrial processes and incinerators. Studies have shown that copper can have toxic effects on glochidia and juvenile freshwater mussels (Wang
et al.
2007a, pp. 2036-2047; Wang
et al.
2007b, pp. 2048-2056). In the range of Texas fatmucket, high copper concentrations have been recorded in fish in the lower Guadalupe River and San Antonio River (Lee and Schultz 1994, p. 8). While these high levels of copper in fish are not directly informative of the level of copper within the habitat of the Texas fatmucket, these observations demonstrate that copper levels are likely high in the lower Guadalupe and San Antonio Rivers. Because we know that copper contamination in water can lead to death of mussels, we conclude that the copper may be adversely affecting Texas fatmucket.

Mercury is another heavy metal that has the potential to negatively affect mussel populations, and it is widely distributed in the environment. Mercury has been detected throughout aquatic environments as a product of municipal and industrial waste and atmospheric deposition from coal burning plants. Rainbow mussel (
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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2011-25471. Public record. Not legal advice.