# Endangered and Threatened Wildlife and Plants; Endangered Status for Six West Texas Aquatic Invertebrate Species and Designation of Critical Habitat

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2012-19829

## Record

- **Collection:** Federal Register
- **Document type:** Proposed Rule
- **Published:** August 16, 2012
- **Citation:** 77 FR 49602

## Text

DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[Docket No. FWS-R2-ES-2012-0029; 4500030113]
RIN 1018-AX70
Endangered and Threatened Wildlife and Plants; Endangered Status for Six West Texas Aquatic Invertebrate Species and Designation of Critical Habitat

AGENCY:

Fish and Wildlife Service, Interior.

ACTION:

Proposed rule.

SUMMARY:

We, the U.S. Fish and Wildlife Service, propose to list as endangered and propose critical habitat for six west Texas aquatic invertebrate species under the Endangered Species Act. These actions are being taken as the result of a court-approved settlement agreement. These are proposed regulations, and if finalized the effect of these regulations will be to conserve the species and protect their habitat under the Endangered Species Act.

DATES:

We will accept comments received or postmarked on or before October 15, 2012. We must receive requests for public hearings, in writing, at the address shown in
FOR FURTHER INFORMATION CONTACT
by October 1, 2012.

ADDRESSES:

You may submit comments by one of the following methods:

(1)
Electronically:
Go to the Federal eRulemaking Portal:
http://www.regulations.gov
and search for FWS-R2-ES-2012-0029, which is the docket number for this rulemaking.

(2)
By hard copy:
Submit by U.S. mail or hand-delivery to: Public Comments Processing, Attn: FWS-R2-ES-2012-0029; Division of Policy and Directives Management; U.S. Fish and Wildlife Service; 4401 N. Fairfax Drive, MS 2042-PDM; Arlington, VA 22203.

We request that you send comments only by the methods described above. We will post all comments on
http://www.regulations.gov.
This generally means that we will post any personal information you provide us (see the Public Comments section below for more information).

The coordinates, or plot points, or both from which the critical habitat maps are generated are included in the administrative record for this rulemaking and are available at (
http://www.fws.gov/southwest/es/AustinTexas/
),
http://www.regulations.gov
at Docket No. FWS-R2-ES-2012-0029, and at the Austin Ecological Services Field Office (see
FOR FURTHER INFORMATION CONTACT
). Any additional tools or supporting information that we may develop for this rulemaking will also be available at the Fish and Wildlife Service Web site and Field Office set out above, and may also be included in the preamble and/or at
http://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT:

Adam Zerrenner, Field Supervisor, U.S. Fish and Wildlife Service, Austin Ecological Services Field Office, 10711 Burnet Road, Suite 200, Austin, TX 78758; by telephone 512-490-0057; or by facsimile 512-490-0974. Persons who use a telecommunications device for the deaf (TDD) may call the Federal Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION:

Executive Summary

This document consists of proposed rules to list six west Texas aquatic invertebrate species as endangered and propose critical habitat designations for the six species. The six west Texas aquatic invertebrate species are: Phantom Cave snail
(Pyrgulopsis texana),
Phantom springsnail
(Tryonia cheatumi),
diminutive amphipod
(Gammarus hyalleloides),
Diamond Y Spring snail
(Pseudotryonia adamantina),
Gonzales springsnail
(Tryonia circumstriata),
and Pecos amphipod
(Gammarus pecos).
The current range for the first three species is limited to spring outflows in the San Solomon Springs system near Balmorhea in Reeves and Jeff Davis Counties, Texas. The current range of the latter three species is restricted to spring outflow areas within the Diamond Y Spring system north of Fort Stockton in Pecos County, Texas.

Why we need to publish a rule.
Under the Endangered Species Act, a species may warrant protection through listing if it is endangered or threatened throughout all or a significant portion of its range. In this proposal we are explaining why these six species warrant protection under the Endangered Species Act. Five of the six species of aquatic invertebrates are currently identified as candidates for listing based on threats to their habitat. The table below summarizes the status of each species:

Species
Present range
Status of species

Phantom Cave snail
San Solomon Spring system (four springs)
common in a very restricted range.

Phantom Lake springsnail
San Solomon Spring system (four springs)
very rare in a very restricted range.

diminutive amphipod
San Solomon Spring system (four springs)
common in a very restricted range.

Diamond Y Spring snail
Diamond Y Spring system (two springs)
very rare in a very restricted range.

Gonzales springsnail
Diamond Y Spring system (two springs)
very rare in a very restricted range.

Pecos amphipod
Diamond Y Spring system (two springs)
common in a very restricted range

These rules propose that all six of these species should be listed as endangered.
We are proposing a listing status of endangered for these six species of aquatic invertebrates from west Texas.

The Endangered Species Act provides the basis for our action.
Under the Endangered Species Act, we can determine that a species is endangered or threatened based on any of 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. We are proposing that all six species are endangered by the combined effects of:

• Habitat loss and degradation of aquatic resources, particularly the current and ongoing decline in spring flows that support the habitat of all the species, and the potential for future water contamination at the Diamond Y Spring system.

• Inadequate existing regulatory mechanisms that allow significant threats such as groundwater withdrawal.

• Other natural or manmade factors, including the presence of nonnative snails and the small, reduced ranges of the species.

These rules also propose designation of critical habitat for each of the six species.
Under the Endangered Species Act, we designate specific areas as

critical habitat to foster conservation of listed species. Future actions funded, permitted, or otherwise carried out by Federal agencies will be reviewed to ensure they do not adversely modify critical habitat. Critical habitat does not affect private actions on private lands. We are proposing the following areas in Texas as critical habitat for Phantom Cave snail, Phantom springsnail, and diminutive amphipod:

Critical habitat unit
Land ownership by type
Size of unit in hectares (acres)

San Solomon Spring, Reeves County
State—Texas Parks and Wildlife Department
1.8 (4.4)

Giffin Spring, Reeves County
Private
0.7 (1.7)

East Sandia Spring, Reeves County
Private—The Nature Conservancy
1.2 (3.0)

Phantom Lake Spring, Jeff Davis County
Federal—Bureau of Reclamation
0.02 (0.05)

Total

3.7 (9.2)

Note:
Area sizes may not sum due to rounding.

We are proposing the following areas as critical habitat for Diamond Y Spring snail, Gonzales springsnail, and Pecos amphipod:

Critical habitat unit
Land ownership by type
Size of unit in hectares (acres)

Diamond Y Spring System, Pecos County
Private—The Nature Conservancy
178.6 (441.4)

Total

178.6 (441.4)

We are preparing an economic analysis.
We are preparing an economic analysis of the proposed designations of critical habitat to allow for consideration of the economic impacts of the proposed designations of critical habitat. We will publish an announcement and seek public comments on the draft economic analysis when it is completed.

We will request peer review of the methods used in our proposal.
We are seeking comments from independent specialists with scientific expertise in these species or related fields. We have invited these peer reviewers to comment on the scientific information and methods that we used in making this proposal. Because we will consider all comments and information received during the comment period, our final determinations may differ from this proposal.

We are seeking public comment on these proposed rules.
Anyone is welcome to comment on our proposal or provide additional information on the proposal that we can use in making a final determination on the status of these species. Please submit your comments and materials concerning these proposed rules by one of the methods listed in the
ADDRESSES
section. Within 1 year following the publication of this proposal, we will publish in the
Federal Register
a final determination to list one or more of these species as threatened or endangered, or withdraw the proposals if new information is provided that supports that decision.

Public Comments

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

(1) Biological, commercial trade, or other relevant data concerning any threats (or lack thereof) to this species and regulations that may be addressing those threats.

(2) Additional information concerning the historical and current status, range, distribution, and population size of this species, including the locations of any additional populations of this species.

(3) Any information on the biological or ecological requirements of the species, and ongoing conservation measures for the species and its habitat.

(4) Current or planned activities in the areas occupied by the species and possible impacts of these activities on this species.

(5) The reasons why we should or should not designate habitat as “critical habitat” under section 4 of the Act (16 U.S.C. 1531
et seq.
) including whether there are threats to the species from human activity, the degree of which can be expected to increase due to the designation, and whether that increase in threat outweighs the benefit of designation such that the designation of critical habitat may not be prudent.

(6) Specific information on:

(a) The amount and distribution of habitat for the six west Texas aquatic invertebrates;

(b) What areas, that were occupied at the time of listing (or are currently occupied) and that contain features essential to the conservation of the species, should be included in the designation and why;

(c) Special management considerations or protection that may be needed in critical habitat areas we are proposing, including managing for the potential effects of climate change; and

(d) What areas not occupied at the time of listing are essential for the conservation of the species and why.

(7) Land use designations and current or planned activities in the subject areas and their possible impacts on proposed critical habitat.

(8) Information on the projected and reasonably likely impacts of climate change on the six west Texas aquatic invertebrates and proposed critical habitat.

(9) Any probable economic, national security, or other relevant impacts of designating any area that may be included in the final designation; in particular, any impacts on small entities or families, and the benefits of including or excluding areas that exhibit these impacts.

(10) Whether any specific areas we are proposing for critical habitat designation should be considered for exclusion under section 4(b)(2) of the Act, and whether the benefits of

potentially excluding any specific area outweigh the benefits of including that area under section 4(b)(2) of the Act.

(11) Whether the benefits of exclusion outweigh the benefits of including the area proposed as critical habitat around San Solomon Spring at Balmorhea State Park based on the existing habitat conservation plan or other relevant factors.

(12) Whether we could improve or modify our approach to designating critical habitat in any way to provide for greater public participation and understanding, or to better accommodate public concerns and comments.

Please note that submissions merely stating support for or opposition to the action under consideration without providing supporting information, although noted, will not be considered in making a determination, as section 4(b)(1)(A) of the Act directs that determinations as to whether any species is a threatened or endangered species must be made “solely on the basis of the best scientific and commercial data available.”

You may submit your comments and materials concerning these proposed rules by one of the methods listed in the
ADDRESSES
section. We request that you send comments only by the methods described in the
ADDRESSES
section.

If you submit information via
http://www.regulations.gov,
your entire submission—including any personal identifying information—will be posted on the Web site. If your submission is made via a hardcopy that includes personal identifying information, you may request at the top of your document that we withhold this information from public review. However, we cannot guarantee that we will be able to do so. We will post all hardcopy submissions on
http://www.regulations.gov.
Please include sufficient information with your comments to allow us to verify any scientific or commercial information you include.

Comments and materials we receive, as well as supporting documentation we used in preparing these proposed rules, will be available for public inspection on
http://www.regulations.gov,
or by appointment, during normal business hours, at the U.S. Fish and Wildlife Service, Austin Ecological Services Field Office (see
FOR FURTHER INFORMATION CONTACT
).

Previous Federal Actions

We first proposed the Phantom Cave snail and Phantom springsnail as endangered species on April 28, 1976 (41 FR 17742). At that time, the Phantom Cave snail
(Pyrgulopsis texana)
was referred to as the Reeves County snail
(Cochliopa texana),
and the Phantom springsnail was referred to as the Cheatum's snail. The proposal was withdrawn on March 6, 1979 (44 FR 12382), following 1978 amendments to the Act that made additional requirements necessary for designating critical habitat. Both species were added as candidates for listing in the May 22, 1984, Notice of Review of Invertebrate Wildlife for Listing as Endangered or Threatened Species (49 FR 21664). At that time they were categorized as Category 2 Candidates, which meant that we had information that proposed listing is possibly appropriate, but conclusive data on biological vulnerability and threats was not available to support a proposed rule at the time. They remained so designated in our subsequent annual Candidate Notices of Review (54 FR 554, January 6, 1989; 56 FR 58804, November 21, 1991; and 59 FR 58982, November 15, 1994). In the February 28, 1996, Notice (61 FR 7596), we discontinued the designation of Category 2 species as candidates, which removed these two species from the candidate list.

Both species were then added back to the candidate list on October 30, 2001 (66 FR 54808). Species on the candidate list are those fish, wildlife, and plants for which we have on file sufficient information on biological vulnerability and threats to support preparation of a listing proposal, but for which development of a listing regulation is precluded by other higher priority listing activities. Since 2001, the listing priority number for both species has been a 2, reflecting species with threats that are both imminent and high in magnitude in accordance with our priority guidance published on September 21, 1983 (48 FR 43098). These two snails remained candidates in subsequent Candidate Notices of Review (67 FR 40657, June 13, 2002; 69 FR 24876, May 4, 2004). Both species were also petitioned for listing on May 11, 2004, and were found to be warranted for listing but precluded by higher priority activities in subsequent Candidate Notice of Reviews (70 FR 24870, May 11, 2005; 71 FR 53756, September 12, 2006; 72 FR 69034, December 6, 2007; 73 FR 75176, December 10, 2008; 74 FR 57804, November 9, 2009; and 75 FR 69222, November 10, 2010). The October 26, 2011, Candidate Notice of Review (76 FR 66370) stated that we were working on proposed listing rules for these species.

We identified the Diamond Y Spring snail and Gonzales springsnail as candidates for listing in the January 6, 1989, Endangered or Threatened Wildlife and Plants, Annual Notice of Review (54 FR 554). These snails were designated as Category 1 candidates, indicating we had substantial information to support listing, but a proposed rule was precluded by other listing activities. These two species were included in all of our subsequent annual Candidate Notices of Review even after discontinuing the candidate categories (56 FR 58804, November 21, 1991, and 59 FR 58982, November 15, 1994). From 1996 to 1999 these two species had a listing priority number of 5, reflecting species with high magnitude but nonimminent threats (61 FR 7596, February 28, 1996; 62 FR 49398, September 19, 1997; and 64 FR 57534, October 25, 1999). In 2001 we elevated the listing priority number from 5 to 2 because of a new, imminent threat associated with the introduction of nonnative snails into the species' habitat. A listing priority of 2 indicates both high magnitude and imminent threats. Both species have maintained a listing priority of 2 since then (66 FR 54808, October 30, 2001; 67 FR 40657, June 13, 2002; and 69 FR 24876, May 4, 2004). These two species were also petitioned for listing on May 11, 2004, and were found to be warranted for listing but precluded by higher priority activities in subsequent Candidate Notice of Reviews (70 FR 24870, May 11, 2005; 71 FR 53756, September 12, 2006; 72 FR 69034, December 6, 2007; 73 FR 75176, December 10, 2008; 74 FR 57804, November 9, 2009; and 75 FR 69222, November 10, 2010). The October 26, 2011, Candidate Notice of Review (76 FR 66370) stated that we were working on proposed listing rules for these species.

We identified the diminutive amphipod and Pecos amphipod as Category 2 candidate species for listing in the May 22, 1984, Notice of Review of Invertebrate Wildlife for Listing as Endangered or Threatened Species (49 FR 21664). They remained so designated in our subsequent annual Candidate Notices of Review (54 FR 554, January 6, 1989; 56 FR 58804, November 21, 1991; and 59 FR 58982, November 15, 1994). In the February 28, 1996, Notice (61 FR 7596), we discontinued the designation of Category 2 species as candidates, which removed these two species from the candidate list. The diminutive amphipod was added back to the candidate list on May 11, 2005 (70 FR 24870), and has remained a candidate with a listing priority number of 2 (reflecting both high-magnitude and imminent threats) since that time (71 FR 53756, September 12, 2006; 72 FR

69034, December 6, 2007; 73 FR 75176, December 10, 2008; 74 FR 57804, November 9, 2009; and 75 FR 69222, November 10, 2010). The October 26, 2011, Candidate Notice of Review (76 FR 66370) stated that we were working on a proposed listing rule for the diminutive amphipod.

The Pecos amphipod was not included in recent candidate notices along with the other species in this proposal because of taxonomic uncertainties, which have since been resolved. In the past it was unclear whether this species range was limited to Diamond Y Spring. Recent genetic research has confirmed that the species is endemic to Diamond Y Spring (see full discussion below under
Taxonomy, Distribution, and Abundance of Amphipods,
Pecos Amphipod). The Pecos amphipod was included in the June 25, 2007, petition by WildEarth Guardians to the Service seeking the listing of 475 species in the southwestern United States. On January 6, 2009, we published a partial 90-day finding of the petition for listing 475 species which included a finding that the petition did not present substantial scientific or commercial information indicating that the listing of the Pecos amphipod may be warranted (74 FR 419). During our current review of the other species endemic to the Diamond Y Spring system, we reviewed the status of the Pecos amphipod. Based on the results of that review, we are proposing to list it as endangered.

Background

We intend to discuss below only those topics directly relevant to the consideration of the listing of the six west Texas aquatic invertebrates as endangered and proposed critical habitat designations. We have organized this
Background
section into three parts. The first part is a general description of the two primary spring systems where the six species occur. The second part is a general description of the life history and biology of the four snail species, followed by specific biological information on each of the four snail species. The third part is a general description of the life history and biology of the two amphipod species, followed by specific biological information on each of the two amphipod species.

Description of Chihuahuan Desert Springs Inhabited by Invertebrate Species

The six west Texas aquatic invertebrate species (Phantom Cave snail, Phantom springsnail, diminutive amphipod, Diamond Y Spring snail, Gonzales springsnail, and Pecos amphipod) occur within a relatively small area of the Chihuahuan Desert of the Pecos River drainage basin of west Texas. The habitats of these species are now isolated spring systems in expansive carbonate (limestone) deposit. The region includes a complex of aquifers (underground water systems) where the action of water on soluble rocks (like limestone and dolomite) has formed abundant “karst” features such as sinkholes, caverns, springs, and underground streams. These hydrogeological formations provide unique settings where a diverse assemblage of flora and fauna has evolved at the points where the aquifers discharge waters to the surface through spring openings. The isolated limestone and gypsum springs, seeps, and wetlands located in this part of west Texas provide the only known habitats for several endemic species of fish, plants, mollusks, and crustaceans, including the six endemic aquatic invertebrate species addressed in these proposed rules.

In the Chihuahuan Desert, spring-adapted aquatic species are distributed in isolated, geographically separate populations. They likely evolved into distinct species from parent species that once enjoyed a wider distribution during wetter, cooler climates of the Pleistocene epoch (about 10,000 to 2.5 million years before present). As ancient lakes and streams dried during dry periods (since the Late Pleistocene, within about the last 100,000 years), aquatic species in this region became patchily distributed across the landscape as geographically isolated populations exhibiting a high degree of endemism (species found only in a particular region, area, or spring). Such speciation through divergence has been reported for these species (Gervasio
et al.
2004, p. 521; Brown
et al.
2008, pp. 486-487; Seidel
et al.
2009, p. 2304).

San Solomon Spring System

In these proposed rules we reference the San Solomon Spring system to include four different existing spring outflows: San Solomon Spring, Giffin Spring, Phantom Lake Spring, and East Sandia Spring. The springs in this area are also commonly referred to by some authors as Toyah Basin springs or Balmorhea area springs. All of the springs historically drained into Toyah Creek, an intermittent tributary of the Pecos River that is now dry except following large rainfall events. All four springs are located in proximity to one another; it is about 13 kilometers (km) (8 miles (mi)) between the farthest two (East Sandia Spring to Phantom Lake Spring). Brune (1981, pp. 258-259, 382-386) provides a brief overview of each of these springs and documents their declining flows during the early and middle twentieth century.

The San Solomon Spring system is located in the Chihuahuan Desert of west Texas at the foothills of the Davis Mountains near Balmorhea, Texas. Phantom Lake Spring is in Jeff Davis County (on the county boundary with Reeves County), while the other major springs in this system are in Reeves County. In addition to being an important habitat for rare aquatic fauna, area springs have served for centuries as an important source of irrigation water for local farming communities. They are all located near the small town of Balmorhea (current population of less than 500 people) in west Texas. The area is very rural with no nearby metropolitan centers. Land ownership in the region is mainly private, except as described below around the spring openings, and land use is predominantly dry-land ranching with some irrigated farmland.

The base flows from all of these springs are thought to ultimately originate from a regional groundwater flow system. Studies show that groundwater moves through geologic faults from the Salt Basin northwest of the Apache and Delaware Mountains, located 130 km (80 mi) or more to the west of the springs (Sharp 2001, pp. 42-45; Angle 2001, p. 247; Sharp
et al.
2003, pp. 8-9; Chowdhury
et al.
2004, pp. 341-342; Texas Water Development Board 2005, p. 106). The originating groundwater and spring outflow are moderately to highly mineralized and appear to be of ancient origin, with the water being estimated at 10,000 to 18,000 years old (Chowdhury
et al.
2004, p. 340; Texas Water Development Board 2005, p. 89). The Salt Basin Bolson aquifer is part of the larger West Texas Bolsons and is made up of connected sub-basins underlying Wild Horse, Michigan, Lobo, and Ryan Flats, in the middle and southern Salt Basin Valley in Texas (Angle, 2001, p. 242). (The term bolson is of Spanish origin and refers to a flat-floored desert valley that drains to a playa or flat.) These aquifers, which support the base flows (flows not influenced by seasonal rainfall events) of the San Solomon Spring system, receive little to no modern recharge from precipitation (Scanlon
et al.
2001, p. 28; Beach
et al.
2004, pp. 6-9, 8-9). Studies of the regional flow system indicate groundwater may move from south to north through the Salt Basin from Ryan to Lobo to Wild Horse Flats before being discharged through the Capitan

Formation, into the Lower Cretaceous rocks (older than Pleistocene) via large geologic faults then exiting to the surface at the springs (LaFave and Sharp 1987, pp. 7-12; Angle 2001, p. 247; Sharp 2001, p. 42-45; Chowdhury
et al.
2004, pp. 341-342; Beach
et al.
2004, Figure 4.1.13, p. 4-19, 4-53). Chemical analysis and hydrogeological studies support this hypothesis, and the water elevations throughout these parts of the Salt Basin Bolson aquifer are higher in elevation than the discharge points at the springs (Chowdhury
et al.
2004, p. 342).

In contrast to the base flows, the springs also respond with periodic short-term increases in flow rates following local, seasonal rainstorms producing runoff events through recharge areas from the Davis Mountains located to the southwest of the springs (White
et al.
1941, pp. 112-119; LaFave and Sharp 1987, pp. 11-12; Chowdhury
et al.
2004, p. 341). These freshwater recharge events provide very temporary increases in spring flows, sometimes resulting in flow spikes many times larger than the regular base flows. The increased flows are short-lived until the local stormwater recharge is drained away and spring flows return to base flows supported by the distant aquifers. Historically, many of the springs in this spring system were likely periodically interconnected following storm events with water flowing throughout the Toyah Creek watershed. In recent times, however, manmade structures altered the patterns of spring outflows and stormwater runoff, largely isolating the springs from one another except through irrigation canals.

San Solomon Spring is by far the largest single spring in the Toyah Basin (Brune 1981, p. 384). The artesian spring issues from the lower Cretaceous limestone at an elevation of about 1,008 meters (m) (3,306 feet (ft)). Brune (1981, p. 385) reported spring flows in the range of 1.3 to 0.8 cubic meters per second (cms) (46 to 28 cubic feet per second (cfs)) between 1900 and 1978 indicating an apparent declining trend. Texas Water Development Board (2005, p. 84) studies reported an average flow rate of about 0.85 cms (30 cfs) from data between 1965 to 2001 with a calculated slope showing a slight decline in discharge.

San Solomon Spring now provides the water for the large, unchlorinated, flow-through swimming pool at Balmorhea State Park and most of the irrigation water for downstream agricultural irrigation by the Reeves County Water Improvement District No. 1 (District). The swimming pool is concrete on the sides and natural substrates on the bottom and was originally constructed in 1936. Balmorhea State Park is owned and managed by Texas Parks and Wildlife Department and encompasses about 19 hectares (ha) (46 acres (ac)) located about 6 km (4 mi) west of Balmorhea in the historic community of Toyahvale. The Park provides recreational opportunities of camping, wildlife viewing, and swimming and scuba diving in the pool. The District holds the water rights for the spring which is channeled through an extensive system of concrete-lined irrigation channels, and much of the water is stored in nearby Lake Balmorhea and delivered through canals for flood irrigation on farms down gradient (Simonds 1996, p. 2).

Balmorhea State Park's primary wildlife resource focus is on conservation of the endemic aquatic species that live in the outflow of San Solomon Spring (Texas Parks and Wildlife Department 1999, p. 1). Texas Parks and Wildlife Department maintains two constructed ciénegas that are flow-through, earth-lined pools in the park to simulate more natural aquatic habitat conditions for the conservation of the rare species, including the Phantom Cave snail, Phantom springsnail, and diminutive amphipods. (Ciénega is a Spanish term that describes a spring outflow that is a permanently wet and marshy area.) San Solomon Spring is also inhabited by two federally listed fishes, Comanche Springs pupfish
(Cyprinodon elegans)
and Pecos gambusia
(Gambusia nobilis).
No nonnative fishes are known to occur in San Solomon Spring, but two nonnative aquatic snails, red-rim melania
(Melanoides tuberculata)
and quilted melania
(Tarebia granifera),
do occur in the spring outflows and are a cause for concern for the native aquatic invertebrate species.

Giffin Spring is on private property less than 1.6 km (1.0 mi) west of Balmorhea State Park, across State Highway 17. The spring originates from an elevation similar to San Solomon Spring. Brune (1981, p. 385) reported flow from Giffin Spring ranging from 0.07 to 0.17 cms (2.3 to 5.9 cfs) between 1919 and 1978, with a gradually declining trend. During calendar year 2011, Giffin Spring flow rates were recorded between 0.10 and 0.17 cms (3.4 and 5.9 cfs) (U.S. Geological Survey 2012, p. 1). Giffin Spring water flows are captured in irrigation earthen channels for agricultural use. Giffin Spring is also inhabited by the federally listed Comanche springs pupfish and Pecos gambusia, and the only nonnative aquatic species of concern there is the red-rim melania.

Phantom Lake Spring is at the base of the Davis Mountains about 6 km (4 mi) west of Balmorhea State Park at an elevation of 1,080 m (3,543 ft). The outflow originates from a large crevice on the side of a limestone outcrop cliff. The 7-ha (17-ac) site around the spring and cave opening is owned by the U.S. Bureau of Reclamation. Prior to 1940 the recorded flow of this spring was regularly exceeding 0.5 cms (18 cfs). Outflows after the 1940s were immediately captured in concrete-lined irrigation canals and provided water for local crops before connecting to the District's canal system in Balmorhea State Park. Flows declined steadily over the next 70 years until ceasing completely in about the year 2000 (Brune 1981, pp. 258-259; Allan 2000, p. 51; Hubbs 2001, p. 306). The aquatic habitat at the spring pool has been maintained by a pumping system since then. Phantom Lake Spring is also inhabited by the two federally listed fishes, Comanche Springs pupfish and Pecos gambusia, and the only nonnative aquatic species of concern there is the red-rim melania.

East Sandia Spring is the smallest spring in the system located in Reeves County in the community of Brogado approximately 3 km (2 mi) northeast of the town of Balmorhea and 7.7 km (4.8 mi) northeast of Balmorhea State Park. The spring is within a 97-ha (240-ac) preserve owned and managed by The Nature Conservancy—a private nonprofit conservation organization (Karges 2003, pp. 145-146). In contrast to the other springs in the San Solomon Spring system that are derived directly from a deep underground regional flow system, East Sandia Spring discharges from alluvial sand and gravel from a shallow groundwater source at an elevation of 977 m (3,224 ft) (Brune 1981, p. 385; Schuster 1997, p. 92). Water chemistry at East Sandia Spring indicates it is not directly hydrologically connected with the other springs in the San Solomon Spring system in the nearby area (Schuster 1997, pp. 92-93). Historically there was an additional, smaller nearby spring outlet called West Sandia Spring. Brune (1981, pp. 385-386) reported the combined flow of East and West Sandia Springs as declining, with measurements ranging from 0.09 to 0.02 cms (3.2 to 0.7 cfs) between 1932 and 1976. In 1976 outflow from East Sandia was 0.01 cms (0.5 cfs) of the total 0.02 cms (0.7 cfs) of the two springs. In 1995 and 1996 Schuster (1997, p. 94) reported flows from both springs ranging from 0.12 to 0.01 cms (4.07 cfs to 0.45 cfs),

with an average of 0.05 cms (1.6 cfs). The outflow waters from the spring discharge to an irrigation canal within a few hundred meters from its source. East Sandia Spring is also inhabited by two federally listed fishes, Comanche Springs pupfish and Pecos gambusia, as well as the federally endangered Pecos assiminea
(Assiminea pecos)
snail and the federally threatened Pecos sunflower
(Helianthus paradoxus).
No nonnative aquatic species of concern are known from East Sandia Spring.

Historically there were other area springs along Toyah Creek that were part of the San Solomon Spring system. Saragosa and Toyah Springs occurred in the town of Balmorhea along Toyah Creek. Brune (1981, p. 386) reported historic base flows of about 0.2 cms (6 cfs) in the 1920s and 1940s, declining to about 0.06 cms (2 cfs) in the 1950s and 1960s, and no flow was recorded in 1978. Brune (1981, p. 385) reported that the flow from West Sandia Spring was about 0.01 cms (0.2 cfs) in 1976, after combined flows from East and West Sandia Springs had exceeded 0.07 cms (2.5 cfs) between the 1930s and early 1960s. The Texas Water Development Board (2005, p. 12) reported West Sandia and Saragosa Springs did not discharge sufficient flow for measurement. Karges (2003, p. 145) indicated West Sandia has only intermittent flow and harbors no aquatic fauna. It is unconfirmed whether the six aquatic invertebrates discussed in this document occurred in these now dry spring sites, but given their current distribution in springs located upstream and downstream of these historic springs, we assume that they probably did. However, because these springs have been dry for many decades, they no longer provide habitat for the aquatic invertebrates.

Diamond Y Spring System

The Diamond Y Spring system is within a tributary drainage flowing northeast to the Pecos River. Diamond Y Spring (previously called Willbank Spring) is located about 80 km (50 mi) due east of San Solomon Spring and about 12 km (8 mi) north of the City of Fort Stockton in Pecos County. The Diamond Y Spring system is composed of disjunct upper and lower watercourses, separated by about 1 km (0.6 mi) of dry stream channel.

The upper watercourse is about 1.5 km (0.9 mi) long and starts with the Diamond Y Spring head pool, which drains into a small spring outflow channel. The channel enters a broad valley and braids into numerous wetland areas and is augmented by numerous small seeps. The Diamond Y Spring outflow converges with the Leon Creek drainage and flows through a marsh-meadow, where it is then referred to as Diamond Y Draw. All of the small springs and seeps and their outflow comprise the upper watercourse. These lateral water features, often not mapped, are spread across the flat, seasonally wetted area along Diamond Y Draw. Therefore, unlike other spring systems that have a relatively small footprint, aquatic habitat covers a relatively large area along the Diamond Y draw.

The lower watercourse of Diamond Y Draw has a smaller head pool spring, referred to as Euphrasia Spring, with a small outflow stream as well as several isolated pools and associated seeps and wetland areas. The total length of the lower watercourse is about 1 km (0.6 mi) and has extended below the bridge at State Highway 18 during wetter seasons in the past. The upper watercourse is only hydrologically connected to the lower watercourse by surface flows during rare large rainstorm runoff events. The lower watercourse also contains small springs and seeps laterally separated from the main spring outflow channels.

Virtually all of the Diamond Y Spring area (both upper and lower watercourses and the area in between) occurs on the Diamond Y Spring Preserve, which is owned and managed by The Nature Conservancy. The Diamond Y Spring Preserve is 1,603 ha (3,962 ac) of contiguous land around Diamond Y Draw. The surrounding watershed and the land area over the contributing aquifers are all privately owned and managed as ranch land and have been developed for oil and gas extraction. In addition, a natural gas processing plant is located within 0.8 km (0.5 mi) upslope of the headpool in the upper watercourse of Diamond Y Spring. Diamond Y Spring is also inhabited by two federally listed fishes, Leon Springs pupfish
(Cyprinodon bovinus)
and Pecos gambusia, as well as the federally endangered Pecos assiminea snail and the federally threatened Pecos sunflower. The only nonnative species of concern at Diamond Y Spring is the red-rim melania, which is only known to occur in the upper watercourse.

Studies by Boghici (1997, p.
v
) indicate that the spring flow at Diamond Y Spring originates chiefly from the Rustler aquifer waters underlying the Delaware Basin to the northwest of the spring outlets (Boghici and Van Broekhoven 2001, p. 219). The Rustler aquifer underlies an area of approximately 1,200 sq km (480 sq mi) encompassing most of Reeves County and parts of Culberson, Pecos, Loving, and Ward Counties (Boghici and Van Broekhoven 2001, p. 219). Much of the water contains high total dissolved solids (Boghici and Van Broekhoven 2001, p. 219) making it difficult for agricultural or municipal use; therefore, the aquifer has experienced only limited pumping in the past (Mace 2001, pp. 7-9).

Other springs in the area may have once provided habitat for the aquatic species but limited information is generally available on historic distribution of the invertebrates. Leon Springs, a large spring that historically occurred about 14 km (9 miles) upstream along Leon Creek, historically discharged about 0.7 cms (25 cfs) in 1920, 0.5 cms (18 cfs) in the 1930s, 0.4 cms (14 cfs) in the 1940s, and no discharge from 1958 to 1971 (Brune 1981, p. 359). Nearby groundwater pumping to irrigate farm lands began in 1946, which lowered the contributing aquifer by 40 m (130 feet) by the 1970s and resulted in the loss of the spring. The only circumstantial evidence that any of the three invertebrates that occur in nearby Diamond Y Spring may have occurred in Leon Springs is that the spring is within the same drainage and an endemic fish, Leon Springs pupfish, once occurred in both Diamond Y and Leon Springs.

Comanche Springs is another large historic spring located in the City of Fort Stockton. Prior to the 1950s, this spring discharged more than 1.2 cms (42 cfs) (Brune 1981, p. 358) and provided habitat for rare species of fishes and invertebrates. As a result of groundwater pumping for agriculture, the spring ceased flowing by 1962 (Brune 1981, p. 358), eliminating all aquatic-dependent plants and animals (Scudday 1977, pp. 515-518; Scudday 2003, pp. 135-136). Although we do not have data confirming that Comanche Springs was inhabited by all of the Diamond Y Spring species, there is evidence that at least the two snails (Diamond Y Spring snail and Gonzales springsnail) occurred there at some time in the past (see
Taxonomy, Distribution, Abundance, and Habitat of Snails,
below).

Life History and Biology of Snails

The background information presented in this section applies to all four species of snails in these proposed rules: Phantom Cave snail, Phantom springsnail, Diamond Y Spring snail, and Gonzales springsnail. All four of these snails are in the family Hydrobiidae and are strictly aquatic with respiration occurring through an internal gill. These hydrobiid snails (snails in the family Hydrobiidae)

typically reproduce several times during the spring to fall breeding season (Brown 1991, p. 292) and are sexually dimorphic (males and females are shaped differently), with females being characteristically larger and longer-lived than males. Snails in the
Pyrgulopsis
genus (Phantom Cave snail) reproduce through laying a single small egg capsule deposited on a hard surface (Hershler 1998, p. 14). The other three snail species are ovoviviparous, meaning the larval stage is completed in the egg capsule, and upon hatching, the snails emerge into their adult form (Brusca and Brusca 1990, p. 759; Hershler and Sada 2002, p. 256). The lifespan of most aquatic snails is thought to be 9 to 15 months (Taylor 1985, p. 16; Pennak 1989, p. 552).

All of these snails are presumably fine-particle feeders on detritus (organic material from decomposing organisms) and periphyton (mixture of algae and other microbes attached to submerged surfaces) associated with the substrates (mud, rocks, and vegetation) (Allan 1995, p. 83; Hershler and Sada 2002, p. 256; Lysne
et al.
2007, p. 649). Dundee and Dundee (1969, p. 207) found diatoms (a group of single-celled algae) to be the primary component in the digestive tract, indicating they are a primary food source.

These hydrobiid snails from west Texas occur in mainly flowing water habitats such as small springs, seeps, marshes, spring pools, and their outflows. Proximity to spring vents, where water emerges from the ground, plays a key role in the life history of springsnails. Many springsnail species exhibit decreased abundance farther away from spring vents, presumably due to their need for stable water chemistry (Hershler 1994, p. 68; Hershler 1998, p. 11; Hershler and Sada 2002, p. 256; Martinez and Thome 2006, p. 14). Several habitat parameters of springs, such as temperature, substrate type, dissolved carbon dioxide, dissolved oxygen, conductivity, and water depth have been shown to influence the distribution and abundance of other related species of springsnails (O'Brien and Blinn 1999, pp. 231-232; Mladenka and Minshall 2001, pp. 209-211; Malcom
et al.
2005, p. 75; Martinez and Thome 2006, pp. 12-15; Lysne
et al.
2007, p. 650). Dissolved salts such as calcium carbonate may also be important factors because they are essential for shell formation (Pennak 1989, p. 552). Hydrobiid snails as a group are considered sensitive to water quality changes, and each species is usually found within relatively narrow habitat parameters (Sada 2008, p. 59).

Native fishes have been shown to prey upon these snails (Winemiller and Anderson 1997, pp. 209-210; Brown
et al.
2008, p. 489), but it is unknown to what degree predatory pressure may play a role in controlling population abundances or influencing habitat use. There are currently no nonnative fishes in the springs where the species occur, so there is no unnatural predation pressure from fish suspected.

Because of their small size and dependence on water, significant dispersal (in other words, movement between spring systems) does not likely occur, although on rare occasions aquatic snails have been transported by becoming attached to the feathers and feet of migratory birds (Roscoe 1955, p. 66; Dundee
et al.
1967, pp. 89-90). In general, the species have little capacity to move beyond their isolated aquatic environments.

Taxonomy, Distribution, Abundance, and Habitat of Snails

Phantom Cave Snail
(Pyrgulopsis texana
Pilsbry 1935)

The Phantom Cave snail was first described by Pilsbry (1935, pp. 91-92). It is a very small snail, measuring only 0.98 to 1.27 millimeters (mm) (0.04 to 0.05 inches (in)) long (Dundee and Dundee 1969, p. 207). Until 2010, the species was placed in the genus
Cochliopa
(Dundee and Dundee 1969, p. 209; Taylor 1987, p. 40). Hershler
et al.
(2010, pp. 247-250) reviewed the systematics of the species and transferred Phantom Cave snail to the genus
Pyrgulopsis
after morphological and mitochondrial DNA analysis. Hershler
et al.
(2010, p. 251) also noted some minimal differences in shell size (individuals were smaller at East Sandia Spring) and mitochondrial DNA sequence variation among populations of Phantom Cave snails in different springs. The low level of variation (small differences) among the populations did not support recognizing different conservation units for the species. Hershler
et al.
(2010, p. 251) expected this small difference among the populations because of their proximity (separated by 6 to 13 km (4 to 8 mi)) and the past connectedness of the aquatic habitats by Toyah Creek that would have allowed mixing of the populations before human alterations and declining flows. Based on these published studies we conclude that Phantom Cave snail is a listable entity under the Act.

The Phantom Cave snail only occurs in the four remaining desert spring outflow channels associated with the San Solomon Spring system (San Solomon, Phantom, Giffin, and East Sandia springs). Hershler
et al.
(2010, p. 250) did not include Giffin Spring in this species distribution, but unpublished data from Lang (2011, p. 5) confirms that the species is also found in Giffin Spring outflows as well as the other three springs in the San Solomon Spring system. The geographic extent of the historic range for the Phantom Cave snail was likely not larger than the present range, but the species may have occurred in additional small springs contained within the current range of the San Solomon Spring system, such as Saragosa and Toyah Springs. It likely also had a larger distribution within Phantom Lake Spring and San Solomon Spring before the habitat there was modified and reduced in conversion of spring outflow channels into irrigation ditches.

Within its current, limited range, Phantom Cave snails can exist in very high densities. Dundee and Dundee (1969, pp. 207) described the abundance of the Phantom Cave snails at Phantom Lake Spring in 1968 as persisting “in such tremendous numbers that the bottom and sides of the canal appear black from the cover of snails.” Today the snails are limited to the small pool at the mouth of Phantom Cave and cannot be found in the irrigation canal downstream. At San Solomon Spring, Taylor (1987, p. 41) reported the Phantom Cave snail was abundant and generally distributed in the canals from 1965 to 1981. Density data and simple population size estimates based on underwater observations indicate there may be over 3.8 million individuals of this species at San Solomon Spring (Bradstreet 2011, p. 55). Lang (2011) also reported very high densities (not total population estimates) of Phantom Cave snails (with ± standard deviations): San Solomon Spring from 2009 sampling in the main canal, 71,740 per sq m (6,672 per sq ft; ±47,229 per sq m, ±4,393 per sq ft); Giffin Spring at road crossing in 2001, 4,518 per sq m (420 per sq ft; ±4,157 per sq m, ±387 per sq ft); East Sandia Spring in 2009, 41,215 per sq m (3,832 per sq ft; ±30,587 per sq m, ±2,845 per sq ft); and Phantom Lake Spring in 2009, 1,378 per sq m (128 per sq ft; ±626 per sq m, ±58 per sq ft). From these data, it is evident that when conditions are favorable Phantom Cave snails can reach tremendous population sizes in very small areas.

Phantom Cave snails are found concentrated near the spring source (Hershler
et al.
2010, p. 250) and can occur as far as a few hundred meters downstream of a large spring outlet like San Solomon Spring. Despite its common name, it has not been found

within Phantom Cave proper, but only within the outflow of Phantom Lake Spring. Bradstreet (2011, p. 55) found the highest abundances of Phantom Cave snails at San Solomon Spring outflows in the high-velocity areas in the irrigation canals and the lowest abundances in the San Solomon Ciénega. The species was not collected from the newest constructed ciénega in 2010. Habitat of the species is found on both soft and firm substrates on the margins of spring outflows (Taylor 1987, p. 41). They are also commonly found attached to plants, particularly in dense stands of submerged vegetation
(Chara
sp.). Field and laboratory experiments have suggested Phantom Cave snails prefer substrates harder and larger in size (Bradstreet 2011, p. 91).

Phantom Springsnail
(Tryonia cheatumi
Pilsbry 1935)

The Phantom springsnail was first described by Pilsbry (1935, p. 91) as
Potamopyrgus cheatumi.
The species was later included in the genus
Lyrodes
and eventually placed in the genus
Tryonia
(Taylor 1987, pp. 38-39). It is a small snail measuring only 2.9 to 3.6 mm (0.11 to 0.14 in) long (Taylor 1987, p. 39). Systematic studies of
Tryonia
snails in the Family Hydrobiidae using mitochondrial DNA sequences and morphological characters confirms the species is a “true
Tryonia,”
in other words, it is appropriately classified in the genus
Tryonia
(Hershler
et al.
1999, p. 383; Hershler 2001, p. 6; Hershler
et al.
2011, pp. 5-6). Based on these published studies, we conclude that Phantom springsnail is a listable entity under the Act.

The Phantom springsnail only occurs in the four remaining desert spring outflow channels associated with the San Solomon Spring system (San Solomon, Phantom, Giffin, and East Sandia springs) (Taylor 1987, p. 40; Allan 2011, p. 1; Lang 2011, entire). The historic range for the Phantom springsnail was likely not larger than present, but the species may have occurred in other springs within the San Solomon Spring system, such as Saragosa and Toyah Springs. It likely also had a wider distribution within Phantom Lake Spring and San Solomon Spring before the habitat there was modified and reduced.

Within its current, limited range, Phantom springsnails can have moderate densities of abundance, but have never been recorded as high as the Phantom Cave snail. In the 1980s, Taylor (1987, p. 40) described Phantom springsnails as abundant in the outflow ditch several hundred meters downstream of Phantom Lake Spring. The snails are now limited to low densities in the small pool at the mouth of Phantom Cave and cannot be found in the irrigation canal downstream as it does not have water (Allan 2009, p. 1). Density data and simple population size estimates based on underwater observations indicate there may be over 460,000 individuals of this species at San Solomon Spring (Bradstreet 2011, p. 55). Lang (2011) reports the following densities (not population estimates) of Phantom springsnails (with ± standard deviations): San Solomon Spring from 2009 sampling in the main canal, 11,681 per sq m (1,086 per sq ft; ±11,925 per sq m, ±1,109 per sq ft); Giffin Spring at road crossing in 2001, 3,857 per sq m (358 per sq ft; ±6,110 per sq m, ±568 per sq ft); East Sandia Spring in 2009, 65,845 per sq m (6,123 per sq ft; ±60,962 per sq m, ±5,669 per sq ft); and Phantom Lake Spring in 2009, 31,462 per sq m (2,926 per sq ft; ±20,251 per sq m, ±1,883 per sq ft). Phantom springsnails can reach high population sizes in very small areas with favorable conditions.

Phantom springsnails are usually found concentrated near the spring source but once occurred as far as a few hundred meters downstream when Phantom Lake Spring was a large flowing spring (Dundee and Dundee 1969, p. 207; Taylor 1987, p. 40). The species is most abundant in the swimming pool at Balmorhea State Park, but has not been found in either of the constructed ciénegas at the Park in 2010 and 2011 (Allan 2011, p. 3; Bradstreet 2011, pp. 55). The species is found on both soft and firm substrates on the margins of spring outflows (Taylor 1987, p. 41), and they are also commonly found attached to plants, particularly in dense stands of submerged vegetation (
Chara
sp.).

Diamond Y Spring Snail
(Pseudotryonia adamantina
Taylor 1987)

The Diamond Y Spring snail was first described by Taylor (1987, p. 41) as
Tryonia adamantina.
It is a small snail measuring only 2.9 to 3.6 mm (0.11 to 0.14 in) long (Taylor 1987, p. 41). Systematic studies (Hershler
et al.
1999, p. 377; Hershler 2001, pp. 7, 16) of these snails have been conducted using mitochondrial DNA sequences and morphological characters. These analyses resulted in the Diamond Y Spring snail being reclassified into the new genus
Pseudotryonia
(Hershler 2001, p. 16). Based on these published studies, we conclude that Diamond Y Spring snail is a listable entity under the Act.

Taylor (1985, p. 1; 1987, p. 38) was the earliest to document the distribution and abundance of aquatic snails in the Diamond Y Spring system, referencing surveys from 1968 to 1984. In 1968, the Diamond Y Spring snail was considered abundant in the outflow of Diamond Y Spring in the upper watercourse for about 1.6 km (1 mi) downstream of the spring head pool, but by 1984 the species was present in only areas along stream margins (near the banks) (Taylor 1985, p. 1). Average density estimates in 1984 at 12 of 14 sampled sites in the upper watercourse ranged from 500 to 93,700 individuals per sq m (50 to 8,700 per sq ft), with very low densities in the upstream areas near the headspring (Taylor 1985, p. 25). However, the Diamond Y Spring snail was largely absent from the headspring and main spring flow channel where it had been abundant in 1968 surveys (Taylor 1985, p. 13). Instead it was most common in small numbers along the outflow stream margins and lateral springs (Taylor 1985, pp. 13-15). Over time, the distribution of the Diamond Y Spring snail in the upper watercourse has continued to recede so that it is no longer found in the outflow channel at all but may be restricted to small lateral spring seeps disconnected from the main spring flow channel (Landye 2000, p. 1; Echelle
et al.
2001, pp. 24-25). Surveys by Lang (2011, pp. 7-8) in 2001 and 2003 found only 2 and 7 individuals, respectively, in the outflow channel of Diamond Y Spring. Additional surveys in 2009 and 2010 (Ladd 2010, p. 18; Lang 2011, p. 12) did not find Diamond Y Spring snails in the upper watercourse. However, neither researcher surveyed extensively in the lateral spring seeps downstream from the main spring outflow.

The Diamond Y Spring snail was not previously reported from the lower watercourse until first detected there in 2001 at the outflow of Euphrasia Spring (Lang 2011, p. 6). It was confirmed there again in 2009 (Lang 2011, p. 13) and currently occurs within at least the first 50 m (160 feet) in the outflow channel of Euphrasia Spring (Ladd 2010, p. 18). Ladd (2010, p. 37) roughly estimated the total number of Diamond Y Spring snails in the lower watercourse to be about 35,000 individuals with the highest density reported as 2,500 individuals per sq m (230 per sq ft). Lang (2011, p. 13) estimated densities of Diamond Y Spring snails in 2009 at 16,695 per sq m (1,552 per sq ft; ±18,212 per sq m, ±1,694 per sq ft) in Euphrasia Spring outflow, which suggests a much larger population than that estimated by Ladd (2010, p. 37).

In summary, the Diamond Y Spring snail was historically common in the upper watercourse and absent from the lower watercourse. Currently it is very

rare in the upper watercourse and limited to small side seeps (and may be extirpated), and it occurs in the lower watercourse in the outflow of Euphrasia Spring. The historic distribution of this species may have been larger than the present distribution. Other area springs nearby such as Leon and Comanche Springs may have harbored the species. There is one collection of very old, dead shells of the species that was made from Comanche Springs in 1998 (Worthington 1998, unpublished data) whose identification was recently confirmed as Diamond Y Spring snail (Hershler 2011, pers. comm.). However, because these springs have been dry for more than four decades and shells can remain intact for thousands of years, it is impossible to know how old the shells might be. Therefore, we are unable to confirm if the recent historic distribution included Comanche Springs.

Habitat of the species is primarily soft substrates on the margins of small springs, seeps, and marshes in shallow flowing water associated with emergent bulrush
(Scirpus americanus)
and saltgrass
(Distichlis spicata)
(Taylor 1987, p. 38; Echelle
et al.
2001, p. 5).

Gonzales Springsnail
(Tryonia circumstriata
Leonard and Ho 1960)

The Gonzales springsnail was first described as a late Pleistocene fossil record,
Calipyrgula circumstriata,
from the Pecos River near Independence Creek in Terrell County, Texas (Leonard and Ho 1960, p. 126). The snail from Diamond Y Spring area was first described as
Tryonia stocktonensis
by Taylor (1987, p. 37). It is a small snail, measuring only 3.0 to 3.7 mm (0.11 to 0.14 in) long. Systematic studies later changed the name to
Tryonia circumstriata,
integrating it with the fossilized snails from the Pecos River (Hershler 2001, p. 7), and confirming the species as a “true
Tryonia,
” in other words, it is appropriately classified in the genus
Tryonia
(Hershler
et al.
2011, pp. 5-6). Based on these published studies, we conclude that Gonzales springsnail is a listable entity under the Act.

Taylor (1985, pp. 18-19; 1987, p. 38) found Gonzales springsnail only in the first 27 m (90 ft) of the outflow from Euphrasia Spring. The species has been consistently found in this short stretch of spring outflow channel since then (Echelle
et al.
2001, p. 20; Lang 2011, pp. 6, 13). Ladd (2010, pp. 23-24) reported that Gonzales springsnails no longer occurred in the lower watercourse and had been replaced by Diamond Y Spring snails. However, reevaluation of voucher specimens collected by Lang (2011, p. 13) concurrently in 2009 with those by Ladd (2010, p. 14) confirmed the species is still present in the Euphrasia Spring outflow channel of the lower watercourse.

Gonzales springsnail was first reported in the upper watercourse in 1991 during collections from one site in the Diamond Y Spring outflow and one small side seep near the spring head (Fullington and Goodloe 1991, p. 3). The species has since been collected from this area (Lang 2011, pp. 7-9), and Echelle
et al.
(2001, p. 20) found it to be the most abundant snail for the first 430-m (1,400-ft) downstream from the spring head. Ladd (2010, p. 18) also found Gonzales springsnail in the outflow of Diamond Y Spring, but only from 125 to 422 m (410 to 1,384 ft) downstream of the spring head (Ladd 2011, pers. comm.). The Gonzales springsnail appears to have replaced the Diamond Y Spring snail in some of the habitat in the upper watercourse (Brown 2008, p. 489) since 1991.

Taylor (1985, p. 19) calculated densities for Gonzales springsnails in the outflow of Euphrasia Spring in the range of 50,480 to 85,360 individuals per sq m (4,690 to 7,930 individuals per sq ft) and estimated the population size in that 27-m (90-ft) stretch to be at least 162,000 individuals and estimated the total population of over one million individuals as a reasonable estimate. Lang (2011, p. 13) estimated the density of Gonzales springsnails in the Euphrasia Spring outflow to be 3,086 individuals per sq m (287 per sq ft; ±5,061 per sq m, ±471per sq ft). Ladd (2010, p. 37) estimated the population of Gonzales springsnails in the upper watercourse to be only about 11,000 individuals.

As with the Diamond Y Spring snail, the historic distribution of the Gonzales springsnail may have been larger than the present distribution. Other area springs nearby such as Leon and Comanche Springs may have harbored the species. There is one collection of dead shells of the species that was made from Comanche Springs in 1998 (Worthington 1998, unpublished data) whose identification was recently confirmed as Gonzales springsnail (Hershler 2011, pers. comm.). However, because these springs have been dry for more than four decades and shells can remain intact for thousands of years, it is impossible to know how old the shells might be. Therefore, we are unable to confirm if the recent historic distribution included Comanche Springs.

Habitat of the species is primarily soft substrates on the margins of small springs, seeps, and marshes in shallow flowing water associated with emergent bulrush and saltgrass (Taylor 1987, p. 38; Echelle
et al.
2001, p. 5).

Life History, Biology, and Habitat of Amphipods

The background information presented here applies to both species of amphipods in these proposed rules: diminutive amphipod and Pecos amphipod. These amphipods, in the family Gammaridae, are small freshwater inland crustaceans sometimes referred to as freshwater shrimp. Gammarids commonly inhabit shallow, cool, well-oxygenated waters of streams, ponds, ditches, sloughs, and springs (Smith 2001, p. 574). These bottom-dwelling amphipods feed on algae, submergent vegetation, and decaying organic matter (Smith 2001, p. 572). Amphipod eggs are held within a marsupium (brood pouch) within the female's exoskeleton (Smith 2001, p. 573). Most amphipods complete their life cycle in 1 year and breed from February to October, depending on water temperature (Smith 2001, p. 572). Amphipods form breeding pairs that remain attached for 1 to 7 days at or near the substrate while continuing to feed and swim (Bousfield 1989, p. 1721). They can produce from 15 to 50 offspring, forming a “brood.” Most amphipods produce one brood, but some species produce a series of broods during the breeding season (Smith 2001, p. 573).

These two species, diminutive amphipod and Pecos amphipod, are part of a related group of amphipods, referred to as the
Gammarus pecos
species complex, that are restricted to desert spring systems from the Pecos River Basin in southeast New Mexico and west Texas (Cole 1985, p. 93; Lang
et al.
2003, p. 47; Gervasio
et al.
2004, p. 521). Similar to the snails, it is thought that these freshwater amphipods are derived from a widespread ancestral marine amphipod that was isolated inland during the recession of the Late Cretaceous sea, about 66 million years ago (Holsinger 1967, pp. 125-133; Lang
et al.
2003, p. 47). They likely evolved into distinct species during recent dry periods (since the Late Pleistocene, about 100,000 years ago) through allopatric speciation (that is, speciation by geographic separation) following separation and isolation in the remnant aquatic habitats associated with springs (Gervasio
et al.
2004, p. 528).

Amphipods in the
Gammarus pecos
species complex only occur in desert spring outflow channels on substrates, often within interstitial spaces on and

underneath rocks and within gravels (Lang
et al.
2003, p. 49) and are most commonly found in microhabitats with flowing water. They are also commonly found in dense stands of submerged vegetation (Cole 1976, p. 80). Because of their affinity for constant water temperatures, they are most common in the immediate spring outflow channels, usually only a few hundred meters downstream of spring outlets.

Amphipods play important roles in the processing of nutrients in aquatic ecosystems and are also considered sensitive to changes in aquatic habitat conditions (for example, stream velocities, light intensity, zooplankton availability, and the presence of heavy metals) and are often considered ecological indicators of ecosystem health and integrity (Covich and Thorpe 1991, pp. 672-673, 679; Lang
et al.
2003, p. 48). Water chemistry parameters, such as salinity, pH, and temperature, are also key components to amphipod habitats (Covich and Thorpe 1991, pp. 672-673).

Taxonomy, Distribution, and Abundance of Amphipods

Diminutive Amphipod
(Gammarus hyalleloides
Cole 1976)

W.L. Minckley first collected the diminutive amphipod from Phantom Lake Spring in the San Solomon Spring system in 1967, and the species was first formally described by Cole (1976, pp. 80-85). The name comes from the species being considered the smallest of the known North American freshwater
Gammarus
amphipods. Adults generally range in length from 5 to 8 mm (0.20 to 0.24 in).

There has been some disparity in the literature regarding the taxonomic boundaries for the amphipods from the San Solomon Spring system. In Cole's (1985, pp. 101-102) description of the
Gammarus pecos
species complex of amphipods based solely on morphological measurements, he considered the diminutive amphipod to be endemic only to Phantom Lake Spring, and amphipods from San Solomon and Diamond Y Springs were both considered to be the Pecos amphipod
(G. pecos).
This study did not include samples of amphipods from East Sandia or Giffin Springs. However, allozyme electrophoresis data on genetic variation strongly support that the populations from the San Solomon Spring system form a distinct group from the Pecos amphipod at Diamond Y Spring (Gervasio
et al.
2004, pp. 523-530). Based on these data, we consider the Pecos amphipod to be limited to the Diamond Y Spring system.

The results of these genetic studies also suggested that the three
Gammarus
amphipod populations from San Solomon, Giffin, and East Sandia Springs are a taxonomically unresolved group differentiated from the diminutive amphipod at Phantom Lake Spring (Gervasio
et al.
2004, pp. 523-530). Further genetic analysis using mitochondrial DNA (mtDNA) by Seidel
et al.
(2009, p. 2309) also indicates that the diminutive amphipod may be limited to Phantom Lake Spring and the
Gammarus
species at the other three springs should be considered a new and undescribed species. However, the extent of genetic divergence measured between these populations is not definitive. For example, the 19-base pair divergence between the population at Phantom Lake Spring and the other San Solomon Spring system populations (Seidel
et al.
2009, Figure 3, p. 2307) represents about 1.7 percent mtDNA sequence divergence (of the 1,100 base pairs of the mitochondrial DNA sequenced (using the cytochrome c oxidase I (COI) gene). This is a relatively low level of divergence to support species separation, as a recent review of a multitude of different animals (20,731 vertebrates and invertebrates) suggested that the mean mtDNA distances (using the COI gene) between subspecies is 3.78 percent (±0.16) divergence and between species is 11.06 percent (±0.53) divergence (Kartavtsev 2011, pp. 57-58).

Recent evaluations of species boundaries of amphipods from China suggest mtDNA genetic distances of at least 4 percent were appropriate to support species differentiation, and the species they described all exceeded 15 percent divergence (Hou and Li 2010, p. 220). In addition, no species descriptions using morphological or ecological analysis have been completed for these populations, which would be important information in any taxonomic revision (Hou and Li 2010, p. 216). Therefore, the data available does not currently support taxonomically separating the amphipod population at Phantom Lake Spring from the populations at San Solomon, Giffin, and East Sandia Springs into different listable entities under the Act. So, for the purposes of these proposed rules, based on the best available scientific information, we are including all four populations of
Gammarus
amphipods from the San Solomon Spring system as part of the
Gammarus hyalleloides
species (diminutive amphipod), and we consider diminutive amphipod a listable entity under the Act. We recognize that the taxonomy of these populations could change as additional information is collected and further analyses are published.

The diminutive amphipod only occurs in the four springs from the San Solomon Spring system (Gervasio
et al.
2004, pp. 520-522). There is no available information that the species' historic distribution was larger than the present distribution, but other area springs (such as Saragosa, Toyah, and West Sandia Springs) may have contained the species. However, because these springs have been dry for many decades, if the species historically occurred there, they are now extirpated. There is no opportunity to determine the full extent of the historic distribution of these amphipods because of the lack of historic surveys and collections.

Within its limited range, diminutive amphipod can be very abundant. For example, in May 2001, Lang
et al.
(2003, p. 51) estimated mean densities at San Solomon, Giffin, and East Sandia Springs of 6,833 amphipods per sq m (635 per sq ft; standard deviation ±5,416 per sq m, ±504 per sq ft); 1,167 amphipods per sq m (108 per sq ft; ±730 per sq m, ±68 per sq ft), and 4,625 amphipods per sq m (430 per sq ft; ±804 per sq m, ±75 per sq ft), respectively. In 2009 Lang (2011, p. 11) reported the density at Phantom Lake Spring as 165 amphipods per sq m (15 per sq ft; ±165 per sq m, ±15 per sq ft).

Pecos Amphipod
(Gammarus pecos
Cole and Bousfield 1970)

The Pecos amphipod was first collected in 1964 from Diamond Y Spring and was described by Cole and Bousfield (1970, p. 89). Cole (1985, p. 101) analyzed morphological characteristics of the
Gammarus pecos
species complex and suggested the
Gammarus
amphipod from San Solomon Spring should also be included as Pecos amphipod. However, updated genetic analyses based on allozymes (Gervasio
et al.
2004, p. 526) and mitochondrial DNA (Seidel
et al.
2009, p. 2309) have shown that Pecos amphipods are limited in distribution to the Diamond Y Spring system. In addition, Gervasio
et al.
(2004, pp. 523, 526) evaluated amphipods from three different locations within the Diamond Y Spring system and found no significant differences in genetic variation, indicating they all represented a single species. Based on these published studies, we conclude that Pecos amphipod is a listable entity under the Act.

The Pecos amphipod is generally found in all the flowing water habitats associated with the outflows of springs and seeps in the Diamond Y Spring

system (Echelle
et al.
2001, p. 20; Lang
et al.
2003, p. 51; Allan 2011, p. 2; Lang 2011, entire). There is no available information to determine if the species' historic distribution was larger than the present distribution. Other area springs, such as Comanche and Leon Springs, may have contained the same or similar species of amphipod, but because these springs have been dry for many decades (Brune 1981, pp. 256-263, 382-386), there is no opportunity to determine the potential historic occurrence of amphipods. Pecos amphipods are often locally abundant, with reported mean densities ranging from 2,208 individuals per sq m (205 per sq ft; ±1,585 per sq m, ±147 per sq ft) to 8,042 individuals per sq m (748 per sq ft; ±7,229 per sq m, ±672 per sq ft) (Lang
et al.
2003, p. 51).

Summary of Factors Affecting the Species

Section 4 of the Act (16 U.S.C. 1533), and its implementing regulations at 50 CFR part 424, set forth the procedures for adding species to the Federal Lists of Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of the Act, the Service determines whether a species is endangered or threatened because of any of the following five factors: (A) The present or threatened destruction, modification, or curtailment of its habitat or range; (B) overutilization for commercial, recreational, scientific, or educational purposes; (C) disease or predation; (D) the inadequacy of existing regulatory mechanisms; and (E) other natural or manmade factors affecting its continued existence. Listing actions may be warranted based on any of the above threat factors, singly or in combination. Each of these factors is discussed below.

Based on the similarity in geographic ranges and threats to habitats, we have divided this analysis into two sections, one covering the three species from the San Solomon Spring system and then a second analysis covering the three species from the Diamond Y Spring system. After each analysis we provide proposed determinations for each species.

San Solomon Spring Species—Phantom Cave Snail, Phantom Springsnail, and Diminutive Amphipod

The following analysis applies to the three species that occur in the San Solomon Spring system in Reeves and Jeff Davis Counties, Texas: Phantom Cave snail, Phantom Lake springsnail, and diminutive amphipod.

A. The Present or Threatened Destruction, Modification, or Curtailment of Their Habitat or Range (San Solomon Spring Species)

The three species in the San Solomon Spring system are threatened by the past and future destruction of their habitat and reduction in their range. The discussion below evaluates the stressors of: (1) Spring flow declines; (2) water quality changes and contamination; and (3) modification of spring channels.

Spring Flow Declines

The primary threat to the continued existence of the San Solomon Spring species is the degradation and potential future loss of aquatic habitat (flowing water from the spring outlets) due to the decline of groundwater levels in the aquifers that support spring surface flows. Habitat for these species is exclusively aquatic and completely dependent on spring flows emerging to the surface from underground aquifer sources. Spring flows throughout the San Solomon Spring system have and continue to decline in flow rate, and as spring flows decline, available aquatic habitat is reduced and altered. If one spring ceases to flow continually, all habitats for the Phantom Cave snail, Phantom Lake springsnail, and diminutive amphipod are lost, and the populations will be extirpated. If all of the springs lose consistent surface flows, all natural habitats for these aquatic invertebrates will be gone, and the species will become extinct.

The springs do not have to cease flowing completely to have an adverse effect on invertebrate populations. The small size of the spring outflows at Phantom, Giffin, and East Sandia Springs makes them particularly susceptible to changes in water chemistry, increased water temperatures during the summer and freezing in the winter. Because these springs are small, any reductions in the flow rates from the springs can reduce the quantity and quality of available habitat for the species, which decreases the number of individuals available and increases the risk of extinction. Water temperatures and chemical factors in springs, such as dissolved oxygen and pH, do not typically fluctuate to a large degree (Hubbs 2001, p. 324), and invertebrates are narrowly adapted to spring conditions and are sensitive to changes in water quality (Hershler 1998, p. 11; Sada 2008, p. 69). Spring flow declines can lead to the degradation and loss of aquatic invertebrate habitat and present a substantial threat to these species.

The precise reason for the declining spring flows remains uncertain, but it is presumed to be related to a combination of groundwater pumping, mainly for agricultural irrigation, and a lack of natural recharge to the supporting aquifers due to limited rainfall and geologic circumstances that prevent recharge. In addition, future changes in the regional climate are expected to exacerbate declining flows. The San Solomon Spring system historically may have had a combined discharged of about 2.8 cms (100 cfs) or 89 million cubic meters per year (cmy) (72,000 acre-feet per year (afy)) (Beach
et al.
2004, p. 4-53), while today the total discharge is roughly one-third that amount. Some smaller springs, such as Saragosa, Toyah, and West Sandia Springs have already ceased flowing and likely resulted in the extirpation of local populations of these species (assuming they were present there historically). The most dramatic recent decline in flow rates have been observed at Phantom Lake Spring, which is the highest elevation spring in the system and, not unexpectedly, was the first large spring to cease flowing.

Phantom Lake Spring was a historically large desert ciénega with a pond of water more than several acres in size (Hubbs 2001, p. 307). The spring outflow is at about 1,080 m (3,543 ft) in elevation and previously provided habitat for the endemic native aquatic fauna. The outflow from Phantom Lake Spring was originally isolated from the other surface springs in the system, as the spring discharge quickly recharged back underground (Brune 1981, p. 258). Human modifications to the spring outflow captured and channeled the spring water into a canal system for use by local landowners and irrigation by the local water users (Simonds 1996, p. 3). The outflow canal joins the main San Solomon canal within Balmorhea State Park. Despite the significant habitat alterations, the native aquatic fauna (including these three invertebrates) have persisted, though in much reduced numbers of total individuals, in the small pool of water at the mouth of the spring.

Flows from Phantom Lake Spring have been steadily declining since measurements were first taken in the 1930s (Brune 1981, p. 259). Discharge data have been recorded from the spring at least six to eight times per year since the 1940s by the U.S. Geological Survey, and the record shows a steady decline of base flows from greater than 0.3 cms (10 cfs) in the 1940s to 0 cms (0 cfs) in 1999 (Service 2009b, p. 23). The data also show that the spring can have short-term flow peaks resulting from local rainfall events in the Davis Mountains (Sharp
et al.
1999, p. 4;

Chowdhury
et al.
2004, p. 341). These flow peaks are from fast recharge of the local aquifer system and discharge through the springs. The flow peaks do not come from direct surface water runoff because the outflow spring is within an extremely small surface drainage basin that is not connected to surface drainage basins from the Davis Mountains upslope. However, after each flow increase, the base flow has returned to the same declining trend within a few months.

Exploration of Phantom Cave by cave divers has led to additional information about the nature of the spring and its supporting aquifer. Over 2,440 m (8,000 ft) of the underwater cave have been mapped. Beyond the entrance, the cave is a substantial conduit that transports a large volume of water, in the 0.6 to 0.7 cms (20 to 25 cfs) range, generally from the northwest to the southeast (Tucker 2009, p. 8), consistent with regional flow pattern hypothesis (Chowdhury
et al.
2004, p. 319). The amount of water measured is in the range of the rate of flow at San Solomon Spring and, along with water chemistry data (Chowdhury
et al.
2004, p. 340), confirms that the groundwater flowing by Phantom Lake Spring likely discharges at San Solomon Spring. Tucker (2009, p. 8) recorded a 1-m (3-ft) decline in the water surface elevation within the cave between 1996 and 2009 indicating a decline in the amount of groundwater flowing through Phantom Cave.

Phantom Lake Spring ceased flowing in about 1999 (Allan 2000, p. 51; Service 2009b, p. 23). All that remained of the spring outflow habitat was a small pool of water with about 37 sq m (400 sq ft) of wetted surface area. Hubbs (2001, pp. 323-324) documented changes in water quality (increased temperature, decreased dissolved oxygen, and decreased coefficient of variation for pH, turbidity, ammonia, and salinity) and fish community structure at Phantom Lake Spring following cessation of natural flows. In May 2001, the U.S. Bureau of Reclamation, in cooperation with the Service, installed an emergency pump system to bring water from within the cave to the springhead in order to prevent complete drying of the pool and loss of the federally listed endangered fishes and candidate invertebrates that occur there. Habitat for the San Solomon Spring system invertebrates continues to be maintained at Phantom Lake Spring, and in 2011 the small pool was enlarged, nearly doubling the amount of aquatic habitat available for the species (Service 2012, entire).

The three San Solomon Spring species have maintained minimal populations at Phantom Lake Spring despite the habitat being drastically modified from its original state and being maintained by a pump system since 2000. However, because the habitat is sustained with a pump system, the risk of extirpation of these populations continues to be extremely high from the potential for a pump failure or some unforeseen event. For example, the pump system failed several times during 2008, resulting in stagnant pools and near drying conditions, placing severe stress on the invertebrate populations (Allan 2008, pp. 1-2). Substantial efforts were implemented in 2011 to improve the reliability of the pump system and the quality of the habitat (Service 2012, pp. 5-9). However, because the habitat is completely maintained by artificial means, the potential loss of the invertebrate population will continue to be an imminent threat of high magnitude to the populations at Phantom Lake Spring.

Although long-term data for San Solomon Spring flows are limited, they appear to have declined somewhat over the history of record, though not as severely as Phantom Lake Spring (Schuster 1997, pp. 86-90; Sharp
et al.
1999, p. 4). Some recent declines in overall flow have likely occurred due to drought conditions and declining aquifer levels (Sharp
et al.
2003, p. 7). San Solomon Spring discharges are usually in the 0.6 to 0.8 cms (25 to 30 cfs) range (Ashworth
et al.
1997, p. 3; Schuster 1997, p. 86) and are consistent with the theory that the water bypassing Phantom Lake Spring discharges at San Solomon Spring.

In Giffin Spring, Brune (1981, pp. 384-385) documented a gradual decline in flow between the 1930s and 1970s, but the discharge has remained relatively constant since that time, with outflow of about 0.08 to 0.1 cms (3 to 4 cfs) (Ashworth
et al.
1997, p. 3; U.S. Geological Survey 2012, p. 2). Although the flow rates from Giffin Spring appear to be steady in recent years, its small size makes the threat of spring flow loss imminent and of high magnitude because even a small decline in flow rate may have substantial impacts on the habitat provided by the spring flow. Also, it would only take a small decline in spring flow rates to result in desiccation of the spring.

Brune (1981, p. 385) noted that flows from Sandia Springs (combining East and West Sandia Springs) were declining up until 1976. East Sandia may be very susceptible to over pumping of the local aquifer in the nearby area that supports the small spring. Measured discharges in 1995 and 1996 ranged from 0.013 to 0.12 cms (0.45 to 4.07 cfs) (Schuster 1997, p. 94). Like the former springs of West Sandia and Saragosa, which also originated in shallow aquifers and previously ceased flowing (Ashworth
et al.
1997, p. 3), East Sandia Spring's very small volume of water makes it particularly at risk of failure from any local changes in groundwater conditions.

The exact causes for the decline in flow from the San Solomon Spring system are unknown. Some of the possible reasons, which are likely acting together, include groundwater pumping of the Salt Basin Bolson aquifer areas west of the springs, long-term climatic changes, or changes in the geologic structure that permits regional interbasin flow of groundwater (Sharp
et al.
1999, p. 4; Sharp
et al.
2003, p. 7). Studies indicate that the base flows originate from ancient waters to the west (Chadhury
et al.
2004, p. 340) and that many of the aquifers in west Texas receive little to no recharge from precipitation (Scanlon
et al.
2001, p. 28) and are influenced by regional groundwater flow patterns (Sharp 2001, p. 41).

Ashworth
et al.
(1997, entire) provided a brief study to examine the cause of declining spring flows in the San Solomon Spring system. They concluded that declines in spring flows in the 1990s were more likely the result of diminished recharge due to the extended dry period rather than from groundwater pumpage (Ashworth
et al.
1997, p. 5). Although possibly a factor, drought is unlikely the only reason for the declines because the drought of record in the 1950s had no measurable effect on the overall flow trend at Phantom Lake Spring (Allan 2000, p. 51; Sharp 2001, p. 49) and because the contributing aquifer receives virtually no recharge from most precipitation events (Beach
et al.
2004, pp. 6-9, 8-9). Also, Ashworth
et al.
(1997, entire) did not consider the effects of the regional flow system in relation to the declining spring flows. Further, an assessment of the springs near Balmorhea by Sharp (2001, p. 49) concluded that irrigation pumpage since 1945 has caused many springs in the area to cease flowing, lowering water-table elevations and creating a cone of depression in the area (that is, a lowering of the groundwater elevation around pumping areas).

The Texas Water Development Board (2005, entire) completed a comprehensive study to ascertain the potential causes of spring flow declines in the San Solomon Spring system, including a detailed analysis of historic regional groundwater pumping trends. The study was unable to quantify direct

correlations between changes in groundwater pumping in the surrounding counties and spring flow decline over time at Phantom Lake Spring (Texas Water Development Board 2005, p. 93). However, they suggested that because of the large distance between the source groundwater and the springs and the long travel time for the water to reach the spring outlets, any impacts of pumping are likely to be reflected much later in time (Texas Water Development Board 2005, p. 92). The authors did conclude that groundwater pumping will impact groundwater levels and spring flow rates if it is occurring anywhere along the flow path system (Texas Water Development Board 2005, p. 92).

Groundwater pumping for irrigated agriculture has had a measurable effect on groundwater levels in the areas that likely support the spring flows at the San Solomon Spring system. For example, between the 1950s and 2000 the Salt Basin Bolson aquifer in Lobo Flat fell in surface elevation in the range of 15 to 30 m (50 to near 100 ft), and in Wild Horse Flat from 6 to 30 m (20 to 50 ft) (Angle 2001, p. 248; Beach
et al.
2004, p. 4-9). Beach
et al.
(2004, p. 4-10) found significant pumping, especially in the Wild Horse Flat area, locally influences flow patterns in the aquifer system. The relationship of regional flow exists because Wild Horse Flat is located in the lowest part of the hydraulically connected Salt Basin Bolson aquifer, and next highest is Lobo, followed by Ryan Flat, which is at the highest elevations (Beach
et al.
2004, p. 9-32). This means that water withdrawn from any southern part of the basin (Ryan and Lobo Flats) may affect the volume of water discharging out of Wild Horse Flat toward the springs. Because these bolson aquifers have little to no direct recharge from precipitation (Beach
et al.
2004, pp. 6-9, 8-9), these groundwater declines can be expected to permanently reduce the amount of water available for discharge in the springs in the San Solomon Spring system. This is evidenced by the marked decline of groundwater flow out of the Wild Horse Flat toward the southeast (the direction of the springs) (Beach
et al.
2004, p. 9-27). Based on this information, it appears reasonable that past and future groundwater withdrawals in the Salt Basin Bolson aquifers are likely one of the causes of decreased spring flows in the San Solomon Spring system.

Groundwater pumping withdrawals in Culberson, Jeff Davis, and Presidio Counties in the Salt Basin Bolson aquifer are expected to continue in the future mainly to support irrigated agriculture (Region F Water Planning Group 2010, pp. 2-16-2-19) and will result in continued lowering of the groundwater levels in the Salt Basin Bolson aquifer. The latest plans from Groundwater Management Area 4 (the planning group covering the relevant portion of the Salt Basin Bolson aquifer) expect over 69 million cubic m (56,000 af) of groundwater pumping per year for the next 50 years, resulting in an average drawdown of 22 to 24 m (72 to 78 feet) in the West Texas Bolsons (Salt Basin) aquifer by 2060 (Adams 2010, p. 2; Oliver 2010, p. 7). There have been no studies evaluating the effects of this level of anticipated drawdown on spring flows. The aquifer in the Wild Horse Flat area (the likely spring source) can range from 60 to 300 m (200 to 1,000 ft) thick. So although it is impossible to determine precisely, we anticipate the planned level of groundwater drawdown will likely result in continued future declines in spring flow rates in the San Solomon Spring system.

Another reason that spring flows may be declining is from an increase in the frequency and duration of local and regional drought associated with climatic changes. The term “climate” refers to the mean and variability of different types of weather conditions over time, with 30 years being a typical period for such measurements, although shorter or longer periods also may be used (IPCC 2007a, p. 78). The term “climate change” thus refers to a change in the mean or variability of one or more measures of climate (e.g., temperature or precipitation) that persists for an extended period, typically decades or longer, whether the change is due to natural variability, human activity, or both (IPCC 2007a, p. 78).

Although the bulk of spring flows appear to originate from ancient water sources with limited recent recharge, any decreases in regional precipitation patterns due to prolonged drought will further stress groundwater availability and increase the risk of diminishment or drying of the springs. Drought affects both surface and groundwater resources and can lead to diminished water quality (Woodhouse and Overpeck 1998, p. 2693) in addition to reducing groundwater quantities. Lack of rainfall may also indirectly affect aquifer levels by resulting in an increase in groundwater pumping to offset water shortages from low precipitation (Mace and Wade 2008, p. 665).

Recent drought conditions may be indicative of more common future conditions. The current, multiyear drought in the western United States, including the Southwest, is the most severe drought recorded since 1900 (Overpeck and Udall 2010, p. 1642). In 2011, Texas experienced the worst annual drought since recordkeeping began in 1895 (NOAA 2012, p. 4), and only one other year since 1550 (the year 1789) was as dry as 2011 based on tree-ring climate reconstruction (NOAA 2011, pp. 20-22). In addition, numerous climate change models predict an overall decrease in annual precipitation in the southwestern United States and northern Mexico.

Future global climate change may result in increased magnitude of droughts and further contribute to impacts on the aquatic habitat from reduction of spring flows. There is high confidence that many semi-arid areas like the western United States will suffer a decrease in water resources due to ongoing climate change (IPCC 2007b, p. 7; Karl
et al.
2009, pp. 129-131), as a result of less annual mean precipitation. Milly
et al.
(2005, p. 347) also project a 10 to 30 percent decrease in precipitation in mid-latitude western North America by the year 2050 based on an ensemble of 12 climate models. Even under lower greenhouse gas emission scenarios, recent projections forecast a 10 percent decline in precipitation in western Texas by 2080 to 2099 (Karl
et al.
2009, pp. 129-130). Assessments of climate change in west Texas suggest that the area is likely to become warmer and at least slightly drier (Texas Water Development Board 2008, pp. 22-25).

The potential effects of future climate change could reduce overall water availability in this region of western Texas and compound the stressors associated with declining flows from the San Solomon Spring system. As a result of the effects of increased drought, spring flows could decline indirectly as a result of increased pumping of groundwater to accommodate human needs for additional water supplies (Mace and Wade 2008, p. 664; Texas Water Development Board 2012c, p. 231).

In conclusion, the Phantom Cave snail, Phantom springsnail, and diminutive amphipod all face significant threats from the current and future loss of habitat associated with declining spring flows. Some springs in the San Solomon Spring system have already gone dry, and aquatic habitat at Phantom Lake Spring has not yet been lost only because of the maintenance of a pumping system. While the sources of the stress of declining spring flows are not known for certain, the best available scientific information indicates that it is the result of a combination of factors including past and current groundwater

pumping, the complex hydrogeologic conditions that produce these springs (ancient waters from a regional flow system), and climatic changes (decreased precipitation and recharge). The threat of habitat loss from declining spring flows affects all four of the remaining populations, as all are at risk of future loss from declining spring flows. All indications are that the source of this threat will persist into the future and will result in continued degradation of the species' habitats, putting the Phantom Cave snail, Phantom springsnail, and diminutive amphipod at a high risk of extinction.

Water Quality Changes and Contamination

Another potential factor that could impact habitat of the San Solomon Spring species is the potential degradation of water quality from point and nonpoint pollutant sources. This can occur either directly into surface water or indirectly through contamination of groundwater that discharges into spring run habitats used by the species. The primary threat for contamination in these springs comes from herbicide and pesticide use in nearby agricultural areas. There are no oil and gas operations in the area around the San Solomon Spring system.

These aquatic invertebrates are sensitive to water contamination. Hydrobiid snails as a group are considered sensitive to water quality changes, and each species is usually found within relatively narrow habitat parameters (Sada 2008, p. 59). Amphipods generally do not tolerate habitat desiccation (drying), standing water, sedimentation, or other adverse environmental conditions; they are considered very sensitive to habitat degradation (Covich and Thorpe 1991, pp. 676-677).

The exposure of the spring habitats to pollutants is limited because most of the nearby agricultural activity mainly occurs in downstream areas where herbicide or pesticide use would not likely come into contact with the species or their habitat in upstream spring outlets. To ensure these pollutants do not affect these spring outflow habitats, their use has been limited in an informal protected area in the outflows of San Solomon and Giffin Springs (Service 2004, pp. 20-21). This area was developed in cooperation with the U.S. Environmental Protection Agency and the Texas Department of Agriculture. While there are more agriculture activities far upstream in the aquifer source area, there is no information indicating concerns about contaminants from those sources.

In addition, Texas Parks and Wildlife Department completed a Habitat Conservation Plan and received an incidental take permit (Service 2009a, entire) in 2009 under section 10(a)(1)(B) (U.S.C. 1539(a)(1)(B)) of the Act for management activities at Balmorhea State Park (Texas Parks and Wildlife Department 1999, entire). The three aquatic invertebrate candidate species from the San Solomon Spring system were all included as covered species in the permit (Service 2009a, pp. 20-22). This permit authorizes “take” of the invertebrates (which were candidates at the time of issuance) in the State Park for ongoing management activities while minimizing impacts to the aquatic species. The activities included in the Habitat Conservation Plan are a part of Texas Parks and Wildlife Department's operation and maintenance of the State Park, including the drawdowns associated with cleaning the swimming pool and vegetation management within the refuge canal and ciénega. The Habitat Conservation Plan also calls for restrictions and guidelines for chemical use in and near aquatic habitats to avoid and minimize impacts to the three aquatic invertebrate species (Service 2009a, pp. 9, 29-32).

Because the use of potential pollutants is very limited within the range of the San Solomon Spring species, at this time we do not find that the Phantom Cave snail, Phantom springsnail, and diminutive amphipod are at a heightened risk of extinction from water quality changes or contamination.

Modification of Spring Channels

The natural ciénega habitats of the San Solomon Spring system have been heavily altered over time primarily to accommodate agricultural irrigation. Most significant was the draining of wetland areas and the modification of spring outlets to develop the water resources for human use. San Solomon and Phantom Lake Springs have been altered the most severely through capture and diversion of the spring outlets into concrete irrigation canals. Giffin Spring appears to have been dredged in the past, and the outflow is now immediately captured in high-banked, earthen-lined canals. The outflow of East Sandia Spring does not appear to have been altered in an appreciable way, but it may have been minimally channelized to connect the spring flow to the irrigation canals.

The Reeves County Water Improvement District No. 1 maintains an extensive system of about 100 km (60 mi) of irrigation canals that now provide only minimal aquatic habitat for the invertebrate species near the spring sources. Most of the canals are concrete-lined with high water velocities and little natural substrate available. Many of the canals are also regularly dewatered as part of the normal water management operations. Before the canals were constructed, the suitable habitat areas around the spring openings, particularly at San Solomon Spring, were much larger in size. The conversion of the natural aquatic mosaic of habitats into linear irrigation canals represents a past impact resulting in significant habitat loss and an increase in the overall risk of extinction by lowering the amount of habitat available to the species and, therefore, lowering the overall number of individuals in the populations affected. These reductions in population size result in an increase in the risk of extirpation of local populations and, ultimately, the extinction of the species as a whole. Because the physical conditions of the spring channels have changed dramatically in the past, the species are now at a greater risk of extinction because of the alterations to the ecosystem and the overall lower number of individuals likely making up the populations.

A number of efforts have been undertaken at Balmorhea State Park to conserve and maintain aquatic habitats at some of the spring sites to conserve habitat for the native aquatic species. First, a refuge canal encircling the historic motel was built in 1974 to create habitat for the endangered fishes, Comanche Springs pupfish and Pecos gambusia (Garrett 2003, p. 153). Although the canal was concrete-lined, it had slower moderate water velocities, and natural substrates covered the wide concrete bottom and provided usable habitat for the aquatic invertebrates. Second, the 1-ha (2.5-ac) San Solomon Ciénega was built in 1996 to create an additional flow-through pond of water for habitat of the native aquatic species (Garrett 2003, pp. 153-154). Finally, during 2009 and 2010, a portion of the deteriorating 1974 refuge canal was removed and relocated away from the motel. The wetted area was expanded to create a new, larger ciénega habitat. This was intended to provide additional natural habitat for the federally listed endangered fishes and candidate invertebrates (Service 2009c, p. 3; Lockwood 2010, p. 3). All of these efforts have been generally successful in providing additional habitat areas for the aquatic invertebrates, although neither the snails nor amphipods have been shown to use the newest ciénega pond to date (Allan 2011, p. 3).

At Phantom Lake Spring, a pupfish refuge canal was built in 1993 (Young
et al.
1993, pp. 1-3) to increase the available aquatic habitat that had been destroyed by the irrigation canal. Winemiller and Anderson (1997, pp. 204-213) showed that the refuge canal was used by endangered fish species when water was available. Stomach analysis of the endangered pupfish from Phantom Lake Spring showed that the Phantom Cave snail and diminutive amphipod were a part of the fish's diet (Winemiller and Anderson 1997, pp. 209-210), indicating that the invertebrates also used the refuge canal. The refuge canal was constructed for a design flow down to about 0.01 cms (0.5 cfs), which at the time of construction was the lowest flow ever recorded out of Phantom Lake Spring. The subsequent loss of spring flow eliminated the usefulness of the refuge canal because the canal went dry beginning in about 2000.

All the water for the remaining spring head pool at Phantom Lake Spring is being provided by a pump system to bring water from about 23 m (75 ft) within the cave out to the surface. The small outflow pool was enlarged in 2011 (U.S. Bureau of Reclamation 2011, p. 1; Service 2012, entire) to encompass about 75 sq m (800 sq ft) of wetted area. In 2011, the pool was relatively stable and all three of the San Solomon Spring invertebrates were present (Allan 2011, p. 3; Service 2012, p. 9).

In summary, the modifications to the natural spring channels at San Solomon, Phantom Lake, and Giffin Springs represent activities that occurred in the past and resulted in a deterioration of the available habitat for the Phantom Cave snail, Phantom springsnail, and diminutive amphipod. Actions by conservation agencies over the past few decades have mitigated the impacts of those actions by restoring some natural functions to the outflow channels. While additional impacts from modifications are not likely to occur in the future because of land ownership by conservation entities at three of the four spring sites, the past modifications have contributed to the endangerment of these species by reducing the overall quantity of available habitat and, therefore, reducing the number of individuals of each species that can inhabit the spring outflows. The lower the overall number of individuals of each species and the lower the amount of available habitat, the greater the risk of extinction. Therefore, the modification of spring channels contributes to increased risk of extinction in the future as a consequence of the negative impacts of the past actions.

Other Conservation Efforts

All four of these springs in the San Solomon Spring system are inhabited by two fishes federally listed as endangered—Comanche Springs pupfish (Service 1981, pp. 1-2) and Pecos gambusia (Service 1983, p. 4). Critical habitat has not been designated for either species. In addition, East Sandia Spring is also inhabited by the federally threatened Pecos sunflower (Service 2005, p. 4) and the federally endangered Pecos assiminea snail (Service 2010, p. 5). Both the Pecos sunflower and the Pecos assiminea snail also have critical habitat designated at East Sandia Spring (73 FR 17762, April 1, 2008; 76 FR 33036, June 7, 2011, respectively).

The Phantom Cave snail, Phantom springsnail, and diminutive amphipod have been afforded some protection indirectly in the past due to the presence of these other listed species in the same locations. Management and protection of the spring habitats by Texas Parks and Wildlife Department at San Solomon Spring, U.S. Bureau of Reclamation at Phantom Lake Spring, and The Nature Conservancy at East Sandia Spring have benefited the aquatic invertebrates. However, the primary threat from the loss of habitat due to declining spring flows related to groundwater changes have not been abated by the Federal listing of the fish or other species. Therefore, the conservation efforts provided by the concomitant occurrence of species already listed under the Act have not prevented the past and ongoing habitat loss, nor is it expected to prevent future habitat loss.

Summary of Factor A

Based on our evaluation of the best available information, we conclude that the present and future destruction and modification of the habitat of the Phantom Cave snail, Phantom springsnail, and diminutive amphipod is a significant threat. Some of these impacts occurred in the past from the loss of natural spring flows at several springs likely within the historic range. The impacts are occurring now and are likely to continue in the future throughout the current range as groundwater levels decline and increase the possibility of the loss of additional springs. As additional springs are lost, the number of populations will decline and further increase the risk of extinction of these species. The sources of this threat are not confirmed but are presumed to include a combination of factors associated with groundwater pumping, hydrogeologic structure of the supporting groundwater, and climatic changes. The risk of extinction is also heightened by the past alteration of spring channels reducing the available habitat and the number of individuals in each population.

B. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes (San Solomon Spring Species)

There are very few people who are interested in or study springsnails and amphipods, and those who do are sensitive to their rarity and endemism. Consequently, collection for scientific or educational purposes is very limited. There are no known commercial or recreational uses of these invertebrates. For these reasons we conclude that overutilization for commercial, recreational, scientific, or educational purposes is currently not a threat to the Phantom Lake snail, Phantom springsnail, and diminutive amphipod, and we have no indication that these factors will affect these species in the future.

C. Disease or Predation (San Solomon Spring Species)

The San Solomon Spring species are not known to be affected by any disease. These invertebrates are likely natural prey species for fishes and crayfishes that occur in their habitats. Native snails and amphipods have been found as small proportions of the diets of native fishes at San Solomon and Phantom Lake Springs (Winemiller and Anderson 1997, p. 201; Hargrave 2010, p. 10), and crayfish are a known predator of snails (Hershler 1998, p. 14). Bradstreet (2011, p. 98) assumed that snails at San Solomon Spring were prey for both fishes and crayfishes and suspected that the native snails may be more susceptible than the nonnative snails because of their small body size and thinner shells. In addition, Ladd and Rogowski (2012, p. 289) suggested that the nonnative red-rim melania
(Melanoides tuberculata)
may prey upon native snail eggs of a different species. However, our knowledge of such predation is very limited, and the extent to which the predation might affect native springsnails is unknown. For more discussion about red-rim melania see “Factor E. Other Natural or Manmade Factors Affecting Its Continued Existence.” We are not aware of any other information indicating that the San Solomon Spring species are affected by disease or predation factors. For these reasons we conclude that disease or predation are not significant threats to the Phantom Lake snail,

Phantom springsnail, and diminutive amphipod, and we have no indication that these factors will affect these species more severely in the future.

D. The Inadequacy of Existing Regulatory Mechanisms (San Solomon Spring Species)

Under this factor, we examine whether existing regulatory mechanisms are inadequate to address the threats to the species discussed under Factors A and E. Section 4(b)(1)(A) of the Endangered Species Act requires the Service to take into account “those efforts, if any, being made by any State or foreign nation, or any political subdivision of a State or foreign nation, to protect such species * * *.” We interpret this language to require the Service to consider relevant Federal, State, and Tribal laws or regulations that may minimize any of the threats we describe in threat analyses under the other four factors, or otherwise enhance conservation of the species. An example would be the terms and conditions attached to a grazing permit that describe how a permittee will manage livestock on a BLM allotment. They are nondiscretionary and enforceable, and are considered a regulatory mechanism under this analysis. Other examples include State governmental actions enforced under a State statute or constitution, or Federal action under statute.

Having evaluated the significance of the threat as mitigated by any such conservation efforts, we analyze under Factor D the extent to which existing regulatory mechanisms are inadequate to address the specific threats to the species. Regulatory mechanisms, if they exist, may reduce or eliminate the impacts from one or more identified threats. In this section, we review existing State and Federal regulatory mechanisms to determine whether they effectively reduce or remove threats to the three San Solomon Spring species.

Texas laws provide no specific protection for these invertebrate species, as they are not listed as threatened or endangered by the Texas Parks and Wildlife Department. However, even if they were listed by the State, those regulations (Title 31 Part 2 of Texas Administrative Code) would only prohibit the taking, possession, transportation, or sale of any animal species without the issuance of a permit. The State makes no provision for the protection of the habitat of listed species, which is the main threat to these aquatic invertebrates.

Some protection for the habitat of this species is provided with the land ownership of the springs by Federal (Phantom Lake Spring owned by the U.S. Bureau of Reclamation) and State (San Solomon Spring owned by Texas Parks and Wildlife Department) agencies, and by The Nature Conservancy (East Sandia Spring). However, this land ownership only protects the spring outflow channels and provides no protection for maintaining groundwater levels to ensure continuous spring flows.

In the following discussion, we evaluate the existing local regulations related to groundwater management within areas that might provide indirect benefits to the species' habitats through management of groundwater levels.

Local Groundwater Regulations

One regulatory mechanism that could provide some protection to the spring flows for these species comes from local groundwater conservation districts. Groundwater in Texas is generally governed by the rule of capture unless there is a groundwater district in place. The rule of capture allows a landowner to produce as much groundwater as he or she chooses, as long as the water is not wasted (Mace 2001, p. 11). However, local groundwater conservation districts have been established throughout much of Texas and are now the preferred method for groundwater management in the State (Texas Water Development Board 2012, pp. 23-258). Groundwater districts “may regulate the location and production of wells, with certain voluntary and mandatory exemptions” (Texas Water Development Board 2012, p. 27).

There are currently four local groundwater districts in the area west of the springs (Texas Water Development Board 2011, p. 1) that could possibly manage groundwater to protect spring flows in the San Solomon Spring system. The Culberson County Groundwater Conservation District covers the southwestern portion of Culberson County and was confirmed (established by the Texas legislature and approved by local voters) in 1998. The Jeff Davis County Underground Water Conservation District covers all of Jeff Davis County and was confirmed in 1993. The Presidio County Underground Water Conservation District covers all of Presidio County and was confirmed in 1999. The Hudspeth County Underground Water District No. 1 covers the northwest portion of Hudspeth County and was confirmed in 1957. This area of Hudspeth County manages the Bone Spring-Victoria Peak aquifer (Hudspeth County Underground Water District No. 1 2007, p. 1), which is not known to contribute water to the regional flow that supplies the San Solomon Spring system (Ashworth 2001, pp. 143-144). Therefore, we will not further consider that groundwater district.

In 2010 the Groundwater Management Area 4 established “desired future conditions” for the aquifers occurring within the five-county area of west Texas (Adams 2010, entire; Texas Water Development Board 2012a, entire). These projected conditions are important because they guide the plans for water use of groundwater within groundwater conservation districts in order to attain the desired future condition of each aquifer they manage (Texas Water Development Board 2012c, p. 23). In the following discussion we review the plans and desired future conditions for the groundwater conservation districts in Culberson, Jeff Davis, and Presidio Counties relative to the potential regulation of groundwater for maintaining spring flows and abating future declines in the San Solomon Spring system.

The Culberson County Groundwater Conservation District seeks to implement water management strategies to “prevent the extreme decline of water levels for the benefit of all water right owners, the economy, our citizens, and the environment of the territory inside the district” (Culberson County Groundwater Conservation District 2007, p. 1). The missions of Jeff Davis County Underground Water District and Presidio County Underground Water Conservation District are to “strive to develop, promote, and implement water conservation and management strategies to protect water resources for the benefit of the citizens, economy, and environment of the District” (Jeff Davis County Underground Water Conservation District 2008, p. 1; Presidio County Underground Water Conservation District 2009, p. 1). However, all three management plans specifically exclude addressing natural resources issues as a goal because, “The District has no documented occurrences of endangered or threatened species dependent upon groundwater resources” (Culberson County Groundwater Conservation District 2007, p. 10; Jeff Davis County Underground Water Conservation District 2008, p. 19; Presidio County Underground Water Conservation District 2009, p. 14). This lack of acknowledgement of the relationship of the groundwater resources under the Districts' management to the conservation of the spring flow habitat at the San Solomon Spring system prevents any direct benefits of their management plans for the three aquatic invertebrates.

We also considered the desired future condition of the relevant aquifer that supports San Solomon Spring system flows. The Culberson County Groundwater Conservation District manages the groundwater where the bulk of groundwater pumping occurs in the Salt Basin Bolson aquifer (part of the West Texas Bolson, the source of the water for the San Solomon Spring system) (Oliver 2010, p. 7). The desired future condition for aquifers within the Culberson County Groundwater Conservation District area includes a 24-m (78-ft) drawdown for the West Texas Bolsons (Salt Basin Bolson aquifer in Wild Horse Flat) to accommodate an average annual groundwater pumping of 46 million cm (38,000 af) (Adams 2010, p. 2; Oliver 2010, p. 7). The desired future condition for the West Texas Bolsons for Jeff Davis County Underground Water Conservation District includes a 72-ft (22-m) drawdown over the next 50 years to accommodate an average annual groundwater pumping of 10 million cm (8,075 af) (Adams 2010, p. 2; Oliver 2010, p. 7). The desired future condition for the West Texas Bolsons for Presidio County Underground Water District also includes a 72-ft (22-m) drawdown over the next 50 years to accommodate an average annual groundwater pumping of 12 million cm (9,793 af) (Adams 2010, p. 2; Oliver 2010, p. 7). These drawdowns are based on analysis using groundwater availability models developed for the Texas Water Development Board (Beach
et al.
2004, p. 10-6-10-8; Oliver 2010, entire). We expect that these groundwater districts will use their district rules to regulate water withdrawals in such a way as to implement these desired future conditions.

The Salt Basin Bolson aquifer in the Wild Horse Flat area (the likely spring source) can range from 60 to 300 m (200 to 1,000 ft) thick. So although it is impossible to determine precisely, we anticipate the planned level of groundwater drawdown will likely result in continued future declines in spring flow rates in the San Solomon Spring system. Therefore, we expect that continued drawdown of the aquifers as identified in the desired future conditions will contribute to ongoing and future spring flow declines. Based on these desired future conditions from the groundwater conservation districts, we conclude that the regulatory mechanisms available to the groundwater districts directing future groundwater withdrawal rates from the aquifers that support spring flows in the San Solomon Spring system are inadequate to protect against ongoing and future modification of habitat for the Phantom Cave snail, Phantom springsnail, and diminutive amphipod.

Summary of Factor D

Although there are some regulatory mechanisms in place, such as the existence of groundwater conservation districts, we find that the mechanisms are not serving to alleviate or limit the salient threats to the Phantom Cave snail, Phantom springsnail, or diminutive amphipod. We, therefore, conclude that these existing regulatory mechanisms are inadequate to sufficiently reduce the identified threats to the Phantom Cave snail, Phantom springsnail, and diminutive amphipod now and in the future.

E. Other Natural or Manmade Factors Affecting Their Continued Existence (San Solomon Spring Species)

We considered three other factors that may be affecting the continued existence of the San Solomon Spring species: nonnative snails, other nonnative species, and the small, reduced ranges of the three San Solomon Spring species.

Nonnative Snails

Another factor that may be impacting the San Solomon Spring species is the presence of two nonnative snails that occur in a portion of their range. The red-rim melania and quilted melania both occur at San Solomon Spring, and the red-rim melania also occurs at Phantom Lake and Giffin Springs (Allan 2011, p. 1; Bradstreet 2011, pp. 4-5; Lang 2011, pp. 4-5, 11). Both species are native to Africa and Asia and have been imported into the United States as aquarium species. They are now established in various locations across the southern and western portions of the United States (Bradstreet 2011, pp. 4-5; U.S. Geological Survey 2009, p. 2; Benson 2012, p.

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2012-19829. Public record. Not legal advice.