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

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 (

Villosa iris

) glochidia have been demonstrated to be more sensitive to mercury than juvenile mussels, with the median lethal concentration value of 14 parts per billion (ppb) for glochidia, compared to 114 ppb for the juvenile life stages (Valenti 2005, p. 1242). The chronic toxicity tests conducted determined that juveniles exposed to mercury greater than or equal to 8 ppb exhibited reduced growth. Acute mercury toxicity was determined to be the cause of extirpation of a diverse mussel community for a 112 km (70 mi) portion of the North Fork Holston River in Virginia (Brown

et al.

2005, pp. 1455-1457). Mercury has been documented throughout the Guadalupe and San Antonio Rivers, with particularly high concentrations in fish in the upper reaches of both rivers (Lee and Schultz 1994, p. 8). As with copper, we do not have information on the concentration of mercury that Texas fatmucket is being exposed to in these streams, but the higher than expected levels in fish indicate high mercury levels in the area, which may be adversely affecting Texas fatmucket.

Pesticides are another source of contaminants in streams. Elevated concentrations of pesticides frequently occur in streams due to pesticide runoff, overspray application to row crops, and lack of adequate riparian buffers. The timing of agricultural pesticide applications in the spring often coincides with the reproductive and early life stages of mussels, which may increase the vulnerability of mussels to pesticides (Bringolf

et al.

2007a, p. 2094). Little is known regarding the effect of currently used pesticides to freshwater mussels even though some pesticides, such as glyphosate (active ingredient in Roundup®), are used globally. Recent studies tested the toxicity of glyphosate, its formulations, and a surfactant (MON 0810) used in several glyphosate formulations, to early life stages of the fatmucket (

Lampsilis siliquoidea

) (Bringolf

et al.

2007a, p. 2094), a freshwater mussel closely related to the Texas fatmucket. Studies conducted with fatmucket juveniles and glochidia determined that the surfactant was the most toxic of the compounds tested and that fatmucket glochidia were the most sensitive organisms tested to date (Bringolf

et al.

2007a, p. 2094). Roundup®, technical grade glyphosate isopropylamine salt, and isopropylamine were also acutely toxic to juveniles and glochidia (Bringolf

et al.

2007a, p. 2097). These commonly applied pesticides may be adversely affecting Texas fatmucket populations.

The effects of other widely used pesticides, including atrazine, chlorpyrifos, and permethrin, on glochidia and juvenile life stages have also recently been studied (Bringolf

et al.

2007b, p. 2101). Environmentally relevant concentrations (concentrations that may be found in streams) of permethrin and chlorpyrifos were found to be toxic to glochidia and juvenile fatmucket (Bringolf

et al.

2007b, pp. 2104-2106). Commonly applied pesticides are a threat to mussels as a result of their widespread use. All of these pesticides are commonly used on agricultural lands throughout the range of the Texas fatmucket, which may be adversely affecting the species.

A potential, but undocumented, threat to freshwater mussels, including Texas fatmucket, are compounds referred to as “emerging contaminants” that are being detected in aquatic ecosystems at an increasing rate. These include pharmaceuticals, hormones, and other organic contaminants that have been detected downstream from urban areas and livestock production (Kolpin

et al.

2002, p. 1202) and have been shown to affect fish behavior (TCEQ 2010b, p. 3). In samples of the Trinity River, for example, compounds such as antidepressants, antihistamines, blood pressure lowering medication, anti-seizure medication, and antimicrobial compounds were all detected during a 2006 study (TCEQ 2010b, pp. 27-28). A

large potential source of these emerging contaminants is wastewater being discharged through both permitted (National Pollutant Discharge Elimination System (NPDES)) and non-permitted sites within the Colorado and Guadalupe River systems. Although streams within the range of Texas fatmucket have not been tested for these emerging contaminants, permitted discharge sites are ubiquitous in watersheds with Texas fatmucket populations, providing many opportunities for contaminants to impact the species.

A study in the Blanco River found that mussels may be adversely affected by sewage effluent (Horne and McIntosh 1979, p. 132). Ammonia levels below the outfall were three times higher than the levels above the outfall and were higher than recently determined toxicity values of ammonia for mussels (Augsperger

et al.

2003, p. 2572). The river was nutrient-enriched for miles downstream, and mussels were less abundant below the outfall than above (Horne and McIntosh 1979, pp. 124-125, 132). Texas fatmucket have not been found alive in the Blanco River since 1978.

Texas Commission on Environmental Quality (TCEQ) data for 2010 indicated that 26 of the 98 assessed water bodies within the Texas fatmucket's historical and current range did not meet surface water quality standards and were classified as impaired water bodies under the Clean Water Act (Texas Clean Rivers Program 2010a, p. 5; 2010b, p. 13), including Elm Creek, due to high ammonia. These water bodies were impaired with dissolved solids, nitrates, bacteria, low dissolved oxygen, aluminum, sulfates, selenium, chloride, and low pH associated with agricultural, urban, municipal, and industrial runoff. Of these, nitrates and low dissolved oxygen pose the greatest threat to Texas fatmucket, as discussed above. Chemical contaminants, such as oil, ammonia, copper, mercury, nutrients, pesticides, and other compounds, are currently a threat to the Texas fatmucket. The species is vulnerable to acute contamination from spills, which have been documented in four of the seven remaining populations, as well as chronic contaminant exposure, which is occurring rangewide.

Summary of Factor A

The reduction in numbers and range of the Texas fatmucket is primarily the result of the long-lasting effects of habitat alterations such as the effects of impoundments, sedimentation, dewatering, sand and gravel mining, and chemical contaminants. Impoundments occur throughout the range of the species and have far-reaching effects both up- and downstream. Both the Colorado and Guadalupe River systems have experienced a large amount of sedimentation from agriculture, mining, urban development, and widespread

Juniperus ashei

removal. Sand and gravel mining affects Texas fatmucket habitat by increasing sedimentation and channel instability downstream and causing headcutting upstream. Finally, chemical contaminants have been documented throughout the range of the species and are significant concern to Texas fatmucket. Based upon our review of the best commercial and scientific data available, we conclude that the present or threatened destruction, modification, or curtailment of its habitat or range is an immediate threat of high magnitude to the Texas fatmucket.

Factor B. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes.

The Texas fatmucket is not a commercially valuable species and has never been harvested in Texas as a commercial mussel species (Howells 2010c, p. 11), although in the Llano River shells were found that were apparently collected by anglers for use as bait (Howells 1996, p. 22; 2010c, p. 11). Additionally, the Elm Creek population is suspected to have declined in part due to the publication of detailed location information, which may have inspired collectors to visit the site (Howells 2009, pp. 5-6). Scientific collecting is not likely to be a significant threat to the status of the species, although disturbing gravid females can result in glochidial loss and subsequent reproductive failure. Additionally, handling has been shown to reduce shell growth in other mussel species, including several other species of

Lampsilis

(Haag and Commens-Carson 2008, pp. 505-506). Repeated handling by researchers may adversely affect Texas fatmucket individuals, but these activities are occurring rarely and are not likely to be a threat to populations. Handling for scientific purposes contributes to the long-term conservation of the species.

We do not have any evidence of risks to the Texas fatmucket from overutilization for commercial, recreational, scientific, or educational purposes, and we have no reason to believe this factor will become a threat to the species in the future. Based upon the best scientific and commercial information available, we conclude that overutilization for commercial, recreational, scientific, or educational purposes does not pose a significant threat to the Texas fatmucket.

Factor C. Disease and Predation.

Disease

Little is known about disease in freshwater mussels. However, disease is believed to be a contributing factor in documented mussel die-offs in other parts of the United States (Neves 1987, pp. 11-12). Diseases have not been documented or observed during any studies of Texas fatmucket.

Predation

Raccoons have preyed on individual Texas fatmuckets stranded by low waters or deposited in shallow water or on bars following flooding or low water periods (Howells 2010c, p. 12). Predation of Texas fatmucket by raccoons may be occurring occasionally but there is no indication it is a significant threat to the status of the species.

Some species of fish feed on mussels, such as common carp (

Cyprinus carpio),

freshwater drum, and redear sunfish (

Lepomis microlophus

), all of which are common throughout the range of Texas fatmucket (Hubbs

et al.

2008, pp. 19, 45, 53). Common species of flatworms are voracious predators of newly metamorphosed juvenile mussels of many species (Zimmerman

et al.

2003, p. 30), including other species in the genus

Lampsilis

(Delp 2002, pp. 12-13). Predation is a normal aspect of the population dynamics of a healthy mussel population; however, predation may amplify declines in small populations.

Summary of Factor C

Disease in freshwater mussels is poorly known, and we do not have any information indicating it is a threat to the Texas fatmucket. Additionally, while predation is likely occurring within Texas fatmucket populations, it is a natural ecological interaction and we have no information indicating the extent of such predation is large enough to be a threat to populations of Texas fatmucket. Based upon the best scientific and commercial information available, we conclude that disease or predation is not a threat to the Texas fatmucket.

Factor D. The Inadequacy of Existing Regulatory Mechanisms.

The Act requires us to examine the adequacy of existing regulatory mechanisms with respect to threats that may place the Texas fatmucket in danger of extinction or increase its likelihood of becoming so in the future. Existing regulatory mechanisms that could affect threats to the Texas

fatmucket include State and Federal laws such as the Texas Threatened and Endangered Species regulations, Texas freshwater mussel sanctuaries, State and Federal sand and gravel mining regulations, and regulation of point and non-point source pollution.

Texas Threatened and Endangered Species Regulations

On January 8, 2010, the Texas Parks and Wildlife Commission placed 15 species of freshwater mussels, including the Texas fatmucket, on the State threatened list (Texas Register 2010, pp. 6-10). Section 68.002 of the Texas Parks and Wildlife (TPW) Code and Section 65.171 of the Texas Administrative Code (TAC) prohibit the direct take of a threatened species, except under issuance of a scientific collecting permit. “Take” is defined in Section 1.101(5) of the TPW Code as collect, hook, hunt, net, shoot, or snare, by any means or device, and includes an attempt to take or to pursue in order to take. While this law protects individuals from take, it is difficult to enforce and does not provide any protection for Texas fatmucket habitat. Moreover, our assessment finds that the species is not threatened by take (see Factor B above). There are no State provisions under the Texas Threatened and Endangered Species Regulations for reducing or eliminating the threats (see Factor A above) that may adversely affect Texas fatmucket or its habitat. In addition, these State regulations do not call for development of a recovery plan that will restore and protect existing habitat for the species. For these reasons, we find that existing Texas regulatory mechanisms for State-listed threatened species are currently inadequate to protect Texas fatmucket and its habitat or to prevent further decline of the species.

Freshwater Mussel Sanctuaries

The TPWD has designated specific areas of streams and reservoirs as no-harvest mussel sanctuaries (31 TAC, part 2, chapter 57, subpart B, Rule 57.157). The locations of the designated mussel sanctuaries were selected because they support populations of rare and endemic mussel species or are important for maintaining, repopulating, or allowing recovery of mussels in watersheds where they have been depleted. As a result of the designation of mussel sanctuaries, four of the Texas fatmucket populations are protected from harvesting disturbance of other species (Howells 2010f, p. 12). Unfortunately, mussel sanctuaries only restrict the harvest of mussels and do not address other activities that may affect mussels or their habitats. Therefore, these designations provide no regulatory mechanisms to protect Texas fatmucket from habitat alteration.

State Sand and Gravel Mining Regulations

TPWD has been responsible for regulating the “disturbance of taking” streambed materials since 1911 (Meador and Layher 1998, p. 11) and has issued several permits for ongoing activities within the Texas fatmucket range (for more information on the effects of sand and gravel mining on Texas fatmucket, please refer to “Sand and Gravel Mining” under Factor A in

Five-Factor Evaluation for Texas Fatmucket

). In addition to authorized activities, there are ongoing unauthorized sand and gravel mining activities within the range of Texas fatmucket. For example, the LCRA, which monitors water quality permit applications submitted through other agencies (LCRA 2011b, p. 1), found unpermitted sand removal from the Llano River in Llano County during a site visit in 2010 (Lehman 2010, p. 1). This site is located upstream from a known population of the Texas fatmucket and other rare mussels (Howells 1994, p. 6), and the sand removal may have increased turbidity and sedimentation downstream within Texas fatmucket habitat. Sand and gravel mining may be one of the least regulated of all mining activities (Meador and Layher 1998, p. 10).

Clean Water Act

The U.S. Army Corps of Engineers (USACE) retains oversight authority and requires a permit for gravel and sand mining activities that deposit fill into streams under section 404 of the Clean Water Act (33 U.S.C. 1251

et seq.

). Additionally, a permit is required under section 10 of the Rivers and Harbors Act (33 U.S.C. 401

et seq.

) for navigable waterways. However, many mining operations do not fall under these two categories. For example, nationwide permits are issued by the USACE for types of projects that are presumed to have minimal environmental impacts. However, projects permitted by nationwide permits, such as small mining operations, may have cumulative effects on aquatic species like the Texas fatmucket through increased sedimentation and channel instability.

Point source discharges of potential contaminants within the range of the Texas fatmucket have been reduced since the inception of the Clean Water Act, but this reduction may not provide adequate protection for filter-feeding organisms that can be affected by extremely low levels of contaminants (see “Chemical Contaminants” under Factor A in the

Five-Factor Evaluation for Texas Fatmucket

section). The EPA's established water quality criteria may not be protective of mussels. Current water quality standards applied by EPA were established to be protective of aquatic life; however, freshwater mussels were not used to develop these standards (EPA 2005, p. 5), and current research reveals mussels to be more sensitive to many aquatic pollutants than the tested organisms (Augsperger

et al.

2007, p. 2025). For example, Augspurger

et al.

(2003, p. 2572) and Sharpe (2005, p. 28) suggested that the criteria for ammonia may not be sufficient to prevent impacts to mussels under current and future climate conditions. In addition, chronic copper concentrations lethal to juvenile freshwater mussels have been shown to be less than the EPA's 1996 chronic water quality criterion for copper (Wang

et al.

2007b, pp. 2052-2055), and, as stated above (see “Chemical Contaminants” under Factor A in

Five-Factor Evaluation for Texas Fatmucket

), high copper concentrations have been documented in the lower Guadalupe and San Antonio Rivers (Lee and Schultz 1994, p. 8). Based on this information, the existing EPA water quality criteria may not be sufficient to prevent negative effects to the Texas fatmucket.

Nonpoint source pollution such as sedimentation and chemical contaminantation is considered a significant threat to Texas fatmucket habitat; however, the Clean Water Act does not adequately protect Texas fatmucket habitat from nonpoint source pollution, because most activities that cause nonpoint source pollution are not regulated under the Clean Water Act.

Summary of Factor D

Despite some State and Federal laws protecting the species and water quality, the Texas fatmucket continues to decline due to the effects of habitat destruction, poor water quality, contaminants, and other factors. The regulatory measures described above are not sufficient to significantly reduce or remove the threats to the Texas fatmucket. Based upon our review of the best commercial and scientific data available, we conclude that the lack of existing regulatory mechanisms is an immediate threat of moderate magnitude to the Texas fatmucket.

Factor E. Other Natural or Manmade Factors Affecting Its Continued Existence.

Other natural and manmade factors that threaten the Texas fatmucket

include climate change, population fragmentation and isolation, and nonnative species.

Climate Change

It is widely accepted that changes in climate are occurring worldwide (International Panel on Climate Change (IPCC) 2007, p. 30). Understanding the effects of climate change on the Texas fatmucket is important because the disjunct nature of the remaining Texas fatmucket populations, coupled with the limited ability of mussels to migrate, makes it unlikely that the Texas fatmucket can adjust its range in response to changes in climate (Strayer 2008, p. 30). For example, changes in temperature and precipitation can increase the likelihood of flooding or increase drought duration and intensity, resulting in direct effects to freshwater mussels like the Texas fatmucket (Hastie

et al.

2003, pp. 40-43; Golloday

et al.

2004, p. 503). Because the range of the Texas fatmucket has been reduced to isolated locations with low population numbers in small rivers and streams, the Texas fatmucket is vulnerable to climatic changes that could decrease the availability of water or produce more frequent scouring flood events. Indirect effects of climate change may include declines in host fish populations, habitat reduction, and changes in human activity in response to climate change (Hastie

et al.

2003, pp. 43-44).

For the next two decades, a warming of about 0.2 °C (0.4 °F) per decade is projected across the United States (IPCC 2007, p. 12), and hot extremes, heat waves, and heavy precipitation and flooding are expected to increase in frequency (IPCC 2007, p. 18). As with many areas of North America, central Texas is projected to experience an overall warming trend in the range of 2.5 to 3.3 °C (4.5 to 6 °F) over the next 50 to 200 years (Mace and Wade 2008, p. 656). Even under lower greenhouse gas emission scenarios, recent projections forecast a 2.8 °C (5 °F) increase in temperature and a 10 percent decline in precipitation in central Texas by 2080-2099 (Karl

et al.

2009, pp. 123-124). Based on our current understanding of climate change, air temperatures are expected to rise and precipitation patterns are expected to change in areas occupied by the Texas fatmucket. Karl

et al.

(2009, p. 12) also suggests that climate change impacts on water resources in the southern Great Plains (including central Texas) are expected as rising temperatures and decreasing precipitation exacerbate an area already plagued by low rainfall, high temperatures, and unsustainable water use practices.

One preliminary study forecasting the possible hydrological impacts of climate change on the annual runoff and its seasonality in the upper Colorado River watershed was conducted by CH2M HILL (2008). In this initial evaluation, four modeling scenarios (chosen to represent a range of possible future climatic conditions) were each run under a 2050 and 2080 time scenario, producing annual surface water runoff estimates at multiple sites with stream gages in the Colorado River basin. For the 2050 scenarios, the results from all four climate change scenarios predicted significant decreases in annual runoff totals compared to historic averages (CH2M HILL 2008, pp. 7-30—7-32). For the 2080 scenarios, one model predicted increases in annual runoff; the other three 2080 scenarios predicted decreases in annual runoff (CH2M HILL 2008, pp. 7-30—7-33). The modeling efforts from this study focus on annual averages and cannot necessarily account for the seasonal variations in flooding events or long periods of drought. However, the study demonstrates the potential effects of climate change on surface water availability, which is forecasted to result in an overall decline in stream flows in the region where the Texas fatmucket occurs.

In summary, climate change could affect the Texas fatmucket through the combined effects of global and regional climate change, along with the increased probability of long-term drought. Climate change exacerbates threats such as habitat degradation from prolonged periods of drought, increased water temperature, and the increased allocation of water for municipal, agricultural, and industrial use. As such, climate change, in and of itself, may affect the Texas fatmucket, but the magnitude and imminence (when the effects occur) of the effects remain uncertain. Based upon our review of the best commercial and scientific data available, we conclude that the effects of climate change in the future will likely exacerbate the current and ongoing threats of habitat loss and degradation caused by other factors, as discussed above.

Population Fragmentation and Isolation

All of the remaining populations of the Texas fatmucket are small and geographically isolated and thus are susceptible to genetic drift (change of gene frequencies in a population over time), inbreeding depression, and random or chance changes to the environment, such as toxic chemical spills (Watters and Dunn 1995, pp. 257-258) or dewatering. Inbreeding depression can result in death, decreased fertility, smaller body size, loss of vigor, reduced fitness, and various chromosomal abnormalities (Smith 1974, pp. 350). Despite any evolutionary adaptations for rarity, habitat loss and degradation increase a species' vulnerability to extinction (Noss and Cooperrider 1994, pp. 58-62). Numerous authors (including Noss and Cooperrider 1994, pp. 58-62; Thomas 1994, p. 373) have indicated that the probability of extinction increases with decreasing habitat availability. Although changes in the environment may cause populations to fluctuate naturally, small and low-density populations are more likely to fluctuate below a minimum viable population (the minimum or threshold number of individuals needed in a population to persist in a viable state for a given interval) (Gilpin and Soule 1986, pp. 25-33; Shaffer 1981, p. 131; Shaffer and Samson 1985, pp. 148-150).

The Texas fatmucket was widespread throughout much of the Colorado and Guadalupe River systems when few natural barriers existed to prevent migration (via host species) among suitable habitats. Construction of dams, however, likely destroyed many Texas fatmucket populations through drastic habitat changes and isolated the remnant populations from each other. For fertilization, Texas fatmucket females need an upstream male to release sperm; populations with few individuals reduce the likelihood that females will be exposed to sperm while siphoning. Therefore, recruitment failure is a potential problem for many small populations rangewide, a potential condition exacerbated by its reduced range and increasingly isolated populations. If downward population trends continue, further significant declines in total Texas fatmucket population size and consequent reduction in long-term survivability may soon become apparent.

The small, isolated nature of the Texas fatmucket's remaining populations also increases the species' vulnerability to stochastic (random) natural events. When species are limited to small, isolated habitats, as the Texas fatmucket is, they are more likely to become extinct due to a local event that negatively effects the population (McKinney 1997, p. 497; Minckley and Unmack 2000, pp. 52-53; Shepard 1993, pp. 354-357). While the populations' small, isolated nature does not represent an independent threat to the species, it does substantially increase the risk of extirpation from the effects of all other threats, including those addressed in

this analysis, and those that could occur in the future from unknown sources.

Based upon our review of the best commercial and scientific data available, we conclude that fragmentation and isolation of small remaining populations of the Texas fatmucket exacerbate ongoing threats to the species throughout all of its range and are expected to continue.

Nonnative Species

Various nonnative species of aquatic organisms are firmly established within the range of the Texas fatmucket and pose a threat to the species. Golden algae (

Prymnesium parvum

) is a microscopic algae considered to be one of the most harmful algal species to fish and other gill-breathing organisms (Lutz-Carrillo

et al.

2010, p. 24). Golden algae was first discovered in Texas in 1985 and is presumed to have been introduced from western Europe (Lutz-Carrillo

et al.

2010, p. 30). Since its introduction, golden algae has been found in Texas rivers and lakes, including two lakes in central Texas (Baylor University 2009, p. 1). Under certain environmental conditions, this algae can produce toxins that can cause massive fish and mussel kills (Barkoh and Fries 2010, p. 1; Lutz-Carrillo

et al.

2010, p. 24). Evidence shows that golden algae probably caused fish kills in Texas as early as the 1960s, but the first documented fish kill due to golden algae in inland waters of Texas occurred in 1985 on the Pecos River in the Rio Grande basin (TPWD 2002, p. 1). The range of golden algae has increased to include portions of the Brazos and Colorado River basins, among others, and it has been responsible for killing more than 8 million fish in the Brazos River since 1981 and more than 2 million fish in the Colorado River since 1989 (TPWD 2010a, p. 1). Although actual mussel kills in Texas due to golden algae have not been recorded in the past, the toxin can kill mussels. Therefore, the elimination of host fish and the poisonous nature of the toxin to mussels make future golden algae blooms a threat to the Texas fatmucket.

An additional nonnative species, the zebra mussel (

Dreissena polymorpha

), poses a potential threat to the Texas fatmucket. This invasive species has been responsible for the extirpation of freshwater mussels in other regions of the United States, including the Higgin's eye (

Lampsilis higginsii

) in Wisconsin and Iowa (Service 2006, pp. 9-10). Zebra mussels attach in large numbers to the shells of live native mussels and are implicated in the loss of entire native mussel beds (Ricciardi

et al.

1998, p. 615). This fouling impedes locomotion (both laterally and vertically), interferes with normal valve movements, deforms valve margins, and essentially suffocates and starves the native mussels by depleting the surrounding water of oxygen and food (Strayer 1999, pp. 77-80). Heavy infestations of zebra mussels on native mussels may overly stress the animals by reducing their energy reserves. Zebra mussels may also filter the sperm and possibly glochidia of native mussels from the water column, thus reducing reproductive potential. Habitat for native mussels may also be degraded by large deposits of zebra mussel pseudofeces (undigested waste material passed out of the incurrent siphon) (Vaughan 1997, p. 11).

Zebra mussels are not currently found within the range of the Texas fatmucket. However, a live adult zebra mussel was first documented in Lake Texoma on the Red River (on the north Texas border with Oklahoma) in 2009 (TPWD 2009a, p. 1). Since that time, additional zebra mussels have been reported from Lake Texoma, where they are now believed to be well established (TPWD 2009c, p. 1). Zebra mussels are likely to spread to many other Texas reservoirs through accidental human transport (Schneider

et al.

1998, p. 789). Although zebra mussels tend to proliferate in reservoirs or large pools, released zebra mussel larvae, called veligers, float downstream and attach to any hard surface available, rendering downstream Texas fatmucket populations extremely vulnerable to attachment and fouling. Because zebra mussels are so easily introduced to new locations, the potential for zebra mussels to continue to expand in Texas and invade the range of the Texas fatmucket is high. If this occurs, the Texas fatmucket is vulnerable to zebra mussel attachment and subsequent deprivation of oxygen, food, and mobility.

A molluscivore (mollusk eater), the black carp (

Mylopharyngodon piceus

) is a potential threat to the Texas fatmucket. The species has been commonly used by aquaculturists to control snails or for research in fish production in several States, including Texas (72 FR 59019, October 18, 2007). Black carp can reach more than 1.3 m (4 ft) in length and 150 pounds (68 kilograms (kg)) (Nico and Williams 1996, p. 6). Foraging rates for a 4-year-old fish average 3 to 4 pounds (1.4 to1.8 kg) a day, indicating that a single individual could consume 10 tons (9,072 kg) of native mollusks over its lifetime (Mississippi Interstate Cooperative Resource Association (MICRA) 2005, p. 1). Black carp can escape from aquaculture facilities. For example, in 1994 30 black carp escaped from an aquaculture facility in Missouri during a flood. Other escapes into the wild by non-sterile carp are likely to occur. Because of the high risk to freshwater mussels and other native mollusks, the Service recently listed black carp as an injurious species under the Lacey Act (72 FR 59019, October 18, 2007), which prevents importations and interstate transfer of this harmful species, but does not prevent its release into the wild once it is in the State. If the black carp were to escape within the range of the Texas fatmucket, it would likely negatively affect native mussels, including the Texas fatmucket.

Based upon our review of the best commercial and scientific data available, we conclude that golden algae is an ongoing threat to the Texas fatmucket, and other nonnative species, such as zebra mussels and black carp, are a potential future threat to the Texas fatmucket that is likely to increase as these exotic species expand their occupancy within the range of the Texas fatmucket.

Summary of Factor E

The effects of climate change, while difficult to quantify at this time, are likely to exacerbate the current and ongoing threat of habitat loss caused by other factors, and the small sizes and fragmented nature of the remaining populations render them more vulnerable to extirpation. In addition, nonnative species, such as golden algae, currently threaten the Texas fatmucket, and the potential introduction of zebra mussels and black carp are potential future threats. Based upon our review of the best commercial and scientific data available, we conclude that other natural or manmade factors are immediate threats of moderate magnitude to the Texas fatmucket.

Finding for Texas Fatmucket

As required by the Act, we considered the five factors in assessing whether Texas fatmucket is threatened or endangered throughout all of its range. We examined the best scientific and commercial information available regarding the past, present, and future threats faced by the Texas fatmucket. We reviewed the petition, information available in our files, and other available published and unpublished information, and we consulted with recognized Texas fatmucket experts and other Federal and State agencies.

This status review identified threats to the Texas fatmucket attributable to Factors A, D, and E. The primary threat to the species is from habitat destruction and modification (Factor A) from

impoundments, which scour riverbeds, thereby removing mussel habitat, decrease water quality, modify stream flows, and prevent fish host migration and distribution of freshwater mussels, as well as sedimentation, dewatering, sand and gravel mining, and chemical contaminants. Additionally, most of these threats may be exacerbated by the current and projected effects of climate change (discussed in Factor E). Threats to the Texas fatmucket and its habitat are not being adequately addressed through existing regulatory mechanisms (Factor D). Because of the limited distribution of this endemic species and its lack of mobility, these threats are likely to result in the extinction of the Texas fatmucket in the foreseeable future.

On the basis of the best scientific and commercial information available, we find that the petitioned action to list the Texas fatmucket under the Act is warranted. We will make a determination on the status of the species as threatened or endangered when we complete a proposed listing determination. When we complete a proposed listing determination, we will examine whether the species may be endangered or threatened throughout all of its range or whether the species may be endangered or threatened in a significant portion of its range. However, as explained in more detail below, an immediate proposal of a regulation implementing this action is precluded by higher priority listing actions, and progress is being made to add or remove other qualified species from the Lists of Endangered and Threatened Wildlife and Plants.

We reviewed the available information to determine if the existing and foreseeable threats render the Texas fatmucket at risk of extinction now such that issuing an emergency regulation temporarily listing the species under section 4(b)(7) of the Act is warranted. We determined that issuing an emergency regulation temporarily listing the species is not warranted for the Texas fatmucket at this time, because we have not identified a threat or activity that poses a significant risk, such that losses to the species during the normal listing process would endanger the continued existence of the entire species. However, if at any time we determine that issuing an emergency regulation temporarily listing Texas fatmucket is warranted, we will initiate this action at that time.

Listing Priority Number for Texas Fatmucket

The Service adopted guidelines on September 21, 1983 (48 FR 43098), to establish a rational system for utilizing available resources for the highest priority species when adding species to the Lists of Endangered and Threatened Wildlife and Plants or reclassifying species listed as threatened to endangered status. These guidelines, titled “Endangered and Threatened Species Listing and Recovery Priority Guidelines,” address the immediacy and magnitude of threats, and the level of taxonomic distinctiveness by assigning priority in descending order to monotypic genera (genus with one species), full species, and subspecies (or equivalently, distinct population segments of vertebrates).

As a result of our analysis of the best available scientific and commercial information, we have assigned the Texas fatmucket a Listing Priority Number (LPN) of 2, based on our finding that the species faces threats that are of high magnitude and are imminent. These threats include habitat loss and degradation from impoundments, sedimentation, sand and gravel mining, and chemical contaminants; other natural or manmade factors such as climate change, small, isolated populations, and nonnative species; and the fact that the threats to the species are not being adequately addressed by existing regulatory mechanisms. Our rationale for assigning the Texas fatmucket an LPN of 2 is outlined below.

Under the Service's guidelines, the magnitude of threat is the first criterion we look at when establishing a listing priority. The guidance indicates that species with the highest magnitude of threat are those species facing the greatest threats to their continued existence. These species receive the highest listing priority. We consider the threats that the Texas fatmucket faces to be high in magnitude. Habitat loss and degradation from impoundments, sedimentation, sand and gravel mining, and chemical contaminants are widespread throughout the range of the Texas fatmucket and profoundly affect its survival and recruitment. Remaining populations are small, isolated, and highly vulnerable to stochastic events.

Under our LPN guidelines, the second criterion we consider in assigning a listing priority is the immediacy of threats. This criterion is intended to ensure that the species facing actual, identifiable threats are given priority over those for which threats are only potential or that are intrinsically vulnerable but are not known to be presently facing such threats. We consider the threats to the Texas fatmucket as described under Factors A, D, and E in the

Five-Factor Evaluation for Texas Fatmucket

section to be imminent because these threats have affected the species in the past, are ongoing, and will continue in the foreseeable future. Habitat loss and destruction have already occurred and will continue as the human population continues to grow in central Texas. Texas fatmucket populations may already be below the minimum viable population requirement, which would cause a reduction in the number of populations and an increase in the species

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