Endangered and Threatened Wildlife and Plants; Removal of the Concho Water Snake From the Federal List of Endangered and Threatened Wildlife and Removal of Designated Critical Habitat, 66780-66804 [2011-27375]
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telecommunications device for the deaf
(TDD), call the Federal Information
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SUPPLEMENTARY INFORMATION:
DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[FWS–R2–ES–2008–0080; 92220–1113–
0000–C6]
RIN 1018—AU97
Endangered and Threatened Wildlife
and Plants; Removal of the Concho
Water Snake From the Federal List of
Endangered and Threatened Wildlife
and Removal of Designated Critical
Habitat
Fish and Wildlife Service,
Interior.
ACTION: Final rule.
AGENCY:
The best available scientific
and commercial data indicate that the
Concho water snake (Nerodia
paucimaculata), a reptile endemic to
central Texas, is recovered. Therefore,
under the authority of the Endangered
Species Act of 1973, as amended (Act),
we, the U.S. Fish and Wildlife Service
(Service) remove (delist) the Concho
water snake from the Federal List of
Endangered and Threatened Wildlife,
and accordingly, also remove its
federally designated critical habitat.
This determination is based on a
thorough review of all available
information, including new information,
which indicates that the threats to this
species have been eliminated or reduced
to the point that the species has
recovered and no longer meets the
definition of threatened or endangered
under the Act. We are also providing
notice that the final post-delisting
monitoring for the Concho water snake
has been completed.
DATES: This final rule becomes effective
on November 28, 2011.
ADDRESSES: The proposed rule, all
comments received, the post-delisting
monitoring plan, and this final rule are
all available on the Internet at https://
www.regulations.gov and https://
www.fws.gov/southwest/es/
AustinTexas/. Supporting
documentation we used in preparing
this final rule will be available for
public inspection, by appointment,
during normal business hours, at the
U.S. Fish and Wildlife Service, Austin
Ecological Services Field Office, 10711
Burnet Road, Suite 200, Austin, TX
78758; telephone 512–490–0057;
facsimile 512–490–0974.
FOR FURTHER INFORMATION CONTACT:
Adam Zerrenner, Field Supervisor, U.S.
Fish and Wildlife Service, Austin
Ecological Services Field Office (see
ADDRESSES). If you use a
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SUMMARY:
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Background
It is our intent to discuss in this final
rule only those topics directly relevant
to the removal of the Concho water
snake from the Federal list of threatened
species under the Endangered Species
Act of 1973, as amended (Act; 16 U.S.C.
1531 et seq.). The Concho water snake
is endemic to the Colorado and Concho
Rivers in central Texas (Tennant 1984,
p. 344; Scott et al. 1989, p. 373). It
occurs on the Colorado River from E.V.
Spence Reservoir to Colorado Bend
State Park, including Ballinger
Municipal Lake and O.H. Ivie Reservoir,
and on the Concho River from the City
of San Angelo, Texas, to its confluence
with the Colorado River at O.H. Ivie
Reservoir. At the time the species was
listed as threatened in 1986 (51 FR
31412), there were considered to be two
subspecies of Nerodia harteri, the
Concho water snake (N.h.
paucimaculata) and the Brazos water
snake (N.h. harteri). Densmore et al.
(1992, p. 66) determined the Concho
water snake was a distinct species, and
in 1996 we changed our reference to the
species to recognize the scientific name
N. paucimaculata (50 CFR 17.11). Some
authors use the common name of
Concho watersnake, based on Crother
(2000, p. 67). However, this has not
been universally adopted, so we
continue to use Concho water snake in
this rule. For more background
information on the Concho water snake,
refer to the proposed delisting rule
published in the Federal Register on
July 8, 2008 (73 FR 38956), the final
listing rule published in the Federal
Register on September 3, 1986 (51 FR
31412), Campbell (2003, pp. 1–4), the
2004 revised biological opinion (BO) on
water operations on the Concho and
Colorado Rivers (Service 2004, pp. 1–
76), and the 1993 Concho Water Snake
Recovery Plan available online at https://
ecos.fws.gov/docs/recovery_plan/
930927b.pdf. We note that research
conducted since the recovery plan was
completed in 1993 has provided new
information on the species.
Previous Federal Actions
In June 1998, we received a petition
from the Colorado River Municipal
Water District (District) to delist the
Concho water snake because our
original data (regarding snake
distribution and abundance and threats)
for listing the snake were in error. On
August 2, 1999, we published a 90-day
petition finding (1999 petition finding)
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that the petitioner did not present
substantial information indicating that
delisting the species may be warranted
(64 FR 41903). The petition did not
contain any information addressing the
threats to the species nor did it include
a discussion of the three recovery
criteria. As a result of the negative 90day finding, we did not conduct a full
status review at that time. However, in
the process of revising the biological
opinion under section 7 of the Act for
the operations of the upper Colorado
River dams in 2004 (Service 2004a), the
Service determined there was sufficient
new information available to warrant a
status review of the species. This final
rule constitutes the conclusion of a full
status review of the Concho water snake
and analyzes all of the outstanding
concerns from the 1999 petition finding.
On July 8, 2008, we published a
proposed rule to remove the Concho
water snake from the list of threatened
species (73 FR 38956). A draft of the
post-delisting monitoring plan was
made available for public review and
comment on September 23, 2009 (74 FR
48595).
Additional background information
regarding other previous Federal actions
for the Concho water snake can be
obtained by consulting the species’
regulatory profile found at: https://
ecos.fws.gov/speciesProfile/
SpeciesReport.do?spcode=C04E.
Recovery
Section 4(f) of the Act directs us to
develop and implement recovery plans
for listed species unless the Director
determines that such a plan will not
benefit the conservation of the species.
The Service completed the Concho
Water Snake Recovery Plan in 1993
(Service 1993). The Concho Water
Snake Recovery Plan outlines recovery
criteria to assist in determining when
the snake has recovered to the point that
the protections afforded by the Act are
no longer needed (Service 1993, p. 33).
These criteria are: (1) Adequate instream
flows are assured even when the species
is delisted. (2) Viable populations are
present in each of the three major
reaches (the Colorado River above
Freese Dam (forms O.H. Ivie Reservoir),
Colorado River below Freese Dam, and
the Concho River). Here, population is
defined as all Concho water snakes in a
given area, in this case, each major river
reach. (3) Movement of an adequate
number of Concho water snakes is
assured to counteract the adverse
impacts of population fragmentation.
These movements should occur as long
as Freese Dam is in place or until such
time that the Service determines that
Concho water snake populations in the
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three reaches are viable and ‘‘artificial
movement’’ among them is not needed.
We used the recovery plan to provide
guidance to the Service, State of Texas,
and other partners on methods to
minimize and reduce the threats to the
Concho water snake and to provide
criteria that could be used to help
determine when the threats to the
Concho water snake had been reduced
so that it could be removed from the
Federal List of Endangered and
Threatened Wildlife.
Provisions in recovery plans are
recommendations that are not binding
and can be superseded by more current
scientific information. There are many
paths to accomplishing recovery of a
species in all or a significant portion of
its range. The main goal is to remove the
threats to a species, which sometimes
may occur without meeting all recovery
criteria contained in a recovery plan.
For example, one or more criteria may
have been exceeded while other criteria
may not have been accomplished. In
that instance, the Service may judge
that, overall, the threats have been
reduced sufficiently, and the species is
robust enough, to reclassify the species
from endangered to threatened or
perhaps to delist the species. In other
cases, recovery opportunities may be
recognized that were not known at the
time the recovery plan was finalized.
Achievement of these opportunities may
result in progress toward recovery in
lieu of methods identified in the
recovery plan. Likewise, we may learn
information about the species that was
not known at the time the recovery plan
was finalized. The new information may
change the extent that criteria need to be
met for recognizing recovery of the
species. Overall, recovery of a species is
a dynamic process requiring adaptive
management. Judging the degree of
recovery of a species is also an adaptive
management process that may, or may
not, fully follow the guidance provided
in a recovery plan.
A review of the best scientific and
commercial data currently available (see
Summary of Factors Affecting the
Species section below) indicates that all
three criteria in the Concho water snake
recovery plan (adequate instream flows
even after delisting, viable populations
in each of the three major river reaches,
and movement of snakes to assure
adequate genetic mixing) have been met.
Further, recovery of the Concho water
snake has been a dynamic process,
which has been fostered by the
significant amount of new data collected
on the biology and ecology of the
species by numerous species experts.
Since the time of listing and preparation
of the recovery plan, biologists have
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discovered that the snakes are able to
persist and reproduce along the
shorelines of reservoirs and that the
snakes have managed to persist in all
three population segments, surviving
many years of drought. Including this
new information, the analysis below
considers the best available data in
determining that the Concho water
snake no longer meets the definition of
a threatened or endangered species.
Summary of Comments and
Recommendations
In our proposed rule (71 FR 38956),
we requested comments from the public
on the proposed removal of the Concho
water snake from the list of threatened
species during a 60-day comment period
that ended on September 8, 2008. We
also contacted Federal agencies, State
agencies, local officials, and
congressional representatives to invite
comment on the proposed rule.
During the public comment period,
we received no requests for a public
hearing and none was held. Overall we
received 23 written comments from the
public. Twenty of these were similar
letters that supported removal of the
species from the protected list and
stated that our decision to delist the
Concho water snake was based on
sound science. Two of these letters of
support came from the Texas
Department of Transportation (TxDOT)
and Texas Parks and Wildlife
Department (TPWD). Six of these letters
were from city officials, ten were from
river authorities or water districts,
including the Colorado River Municipal
Water District (District), and two were
from private businesses. We also
received one nonsubstantive comment
and two substantive critical comments
from professional biologists (one
specifically expressed opposition to the
proposal). Our responses are provided
below to a summary of each substantive
comment received.
Peer Review
In accordance with our policy
published on July 1, 1994 (59 FR
34270), we solicited independent expert
opinions from knowledgeable
individuals with scientific expertise that
included ecology of water snakes,
conservation biology principles, and
river hydrology. Out of seven
individuals that agreed to provide peer
review, we received six peer review
comments. One peer reviewer stated
support for the proposal. Three peer
reviewers were noncommittal on their
support, but provided many substantive
comments and questions. Two peer
reviewers stated opposition to the
proposal and provided substantive
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criticism. Our responses are provided
below to a summary of each substantive
comment received from the peer
reviewers.
Comments From Peer Reviewers
(1) Comment: It is premature to delist
the Concho water snake because
essential data are lacking. For example,
no data are presented on population
structure, demographics, trends, or
genetics.
Our Response: The Act requires us to
consider the best available information
when making decisions on what species
should be protected. Population
demographic estimates have been
reported for the Concho water snake
(Whiting et al. 2008, pp. 441–442).
While more quantitative analysis of
population structure, trends, and
genetics would be informative and
useful to us in formulating this rule, we
believe the data used in this final rule
support our decision because it is
derived from many years of monitoring
collections (Thornton 1996, pp. 26–50,
Forstner et al. 2006, p. 18) and
consistent with the opinion of most
experts on the Concho water snake.
Reference the following sections below
for descriptions of the best available
information related to population
structure, demographics, and genetics:
A. The Present or Threatened
Destruction, Modification, or
Curtailment of Its Habitat or Range,
Habitat Modification from
Fragmentation; and Application of the
Recovery Plan’s Criteria, Population
Viability. We find that the best available
information supports the decision that
the Concho water snake has recovered
and no longer qualify as threatened.
Past studies of the Concho water
snake were intended to monitor the
populations over time using markrecapture techniques (that is, inserting a
tag in captured snakes so that
individuals can be identified when they
are recaptured). Although these studies
by the District (summarized in District
1998) resulted in a large number of
snakes collected over 10 years (9,069
unique snakes), the study did not
quantify the amount of effort expended
during each survey, so that reliable
population estimates or trends over time
could not be calculated. Whiting et al.
(2008) utilized these data to attempt to
model population trends. However, the
results proved too unreliable to
effectively model population trends
because the dispersal rates of snakes out
of the study areas were not quantified.
This resulted in a potential overestimate
of the death rate of snakes that were not
recaptured, when they could have, in
fact, simply moved out of the study area
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(Whiting et al. 2008, p. 443). The
original study was not designed to
accommodate a population viability
analysis and attempts to do so provided
results with an unacceptable degree of
uncertainty and with imprecise
conclusions. As a result, the best
available information on snake
populations supports that the snakes
have persisted over a long time period
throughout the majority of their historic
range and have continued to persist
following habitat alterations from
reservoir inundation and drought.
(2) Comment: The Concho water
snake occupies an extremely small area
of Texas, and one small mistake could
easily cause the extinction in a
significant portion (i.e., all) of its range.
It is better to err on the side of caution
than face the consequences of early
protection removal.
Our Response: The current range of
the snake is estimated to total about 280
miles (mi) (451 kilometers (km)) of river
and about 40 mi (64 km) of reservoir
shoreline. The best available
information, including the reports of
species experts (in particular Dr. James
Dixon and Dr. Michael Forstner), does
not indicate that the species is
vulnerable to extinction. The recent
studies available to us report that the
species is capable of withstanding
significant environmental perturbations
(Dixon 2004, pp. 10–11; Forstner et al.
2006, pp. 16–18; Whiting et al. 2008, p.
343). Under our post-delisting
monitoring plan, we will be monitoring
the status of the species and can
emergency list it if necessary (see the
Post-Delisting Monitoring Plan section
below).
(3) Comment: My strong conclusion is
that viable populations of the Concho
water snake have not been
demonstrated. Documentation of
persistence and reproduction is not
adequate to determine population
viability.
Our Response: Please see our
response below to Comment (28). We
have updated the discussion of viable
population in the final rule to be more
consistent with the description used in
the recovery plan for the species (see
Application of the Recovery Plan’s
Criteria section below).
(4) Comment: Survey results from
Dixon (2004) and Forstner et al. (2006)
failed to find snakes at some sample
sites, indicating possible local
extinctions and suggesting that recovery
criterion 2 for viable populations has
not been met and site occupancy may
have decreased by 23 to 27 percent.
Our Response: Dixon made only one
sampling visit to 13 sites and found
Concho water snakes at all but 3 sites
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(Dixon 2004, pp. 4–5). Forstner et al.
(2006, pp. 6–7, 12) surveyed several
sites up to three times in 2005. They
found snakes at all sites except for three
sites on the Concho River, which were
only sampled one time following a
rainstorm event making detection
difficult (Forstner et al. 2006, p. 12). In
contrast, earlier studies (District 1998, p.
13) resulted in consistent captures of
snakes at nearly all sites surveyed,
however, those sites were sampled three
times or more annually. Both Dixon
(2004, pp. 9, 14–15) and Forstner et al.
(2006, p. 13) explain that there are a
variety of field conditions that influence
the ability to capture snakes at a given
time and location. Variability of
sampling success is common in field
investigations, and both of these reports
consisted of sampling efforts too small
to interpret negative capture data as
local extinctions or a decline in site
occupancy.
(5) Comment: I agree with the
proposed rule to delist the Concho
water snake, although I don’t know if I
believe that the Concho water snake has
‘‘recovered’’ as much as it continues to
persist despite marked modifications to
its habitat along the Colorado and
Concho rivers. The snake is more of a
habitat generalist than originally
thought, and successful reproduction
takes place under lower stream flows
than previously indicated. The 2008
Memorandum of Understanding (MOU)
between the Service and the Colorado
Municipal Water District ensures
adequate stream flows, although it may
be strained by drought conditions.
Twenty years of field studies
demonstrate continued reproductive
success in both the Concho and
Colorado Rivers, including reservoirs.
Dixon (2004) reports finding that dense
vegetation and beavers failed to impede
reproduction at the Freese Dam site, and
he found the Elm Creek site, devoid of
water for three years, still contained a
reproducing population.
Our Response: We agree that the best
available information supports the
decision to remove the Concho water
snake from the list of threatened species
under the Act. We recognize that our
understanding of the snake’s ecology
has benefitted from new information
that has been collected since the listing
and since the recovery plan was
completed. The removal of the snake
from the list of threatened species is due
both to recovery actions, such as the
2008 MOU with the District, and new
biological information on the species’
ability to persist in habitats such as
reservoirs and no change (or slight
increase) in the species’ known range
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(about 80 river miles more than known
at the time of listing).
(6) Comment: The proposed rule uses
an inappropriate timeframe for analysis
of factors that could affect the species in
the future. Factors that are not
considered threats on a 20-year
timeframe may threaten the species on
a more meaningful timeframe of 50–100
years, which is consistent with the
recovery plan.
Our Response: We agree the 20-year
foreseeable future was not a sufficiently
long timeframe for our analysis. We
have updated the rule to evaluate the
threats to the species considering longer
timeframes, as available information
allows. In considering the foreseeable
future in the threats analysis, we
generally regarded 50 to 100 years as a
time frame where some reasonable
predictions could be made. This range
of time originated from the analysis of
forecasting for water management,
which is looking ahead to expected
conditions in the year 2060 (TWDB
2007, p. 2), and consideration of climate
change models, which typically forecast
50 to 100 years into the future
(Bernstein et al. 2007, pp. 8–9; Jackson
2008, p. 8; Mace and Wade 2008, p.
656).
(7) Comment: Lake populations are
not as robust as the river populations
(low densities via low recruitment), and
their mere presence is not an indicator
of population health. Lake populations
appear to be isolated sinks and there
may not be riverine recruitment from
these populations. Due to the relatively
recent appearance of the lakes, the data
are only isolated snapshots and more
monitoring is necessary before we know
the true effects of river modification on
Concho water snake populations.
Our Response: Recruitment is the
successful influx of new members into
a population by reproduction or
immigration (Lincoln et al. 1998, p.
257). Sinks are populations or breeding
groups that do not produce enough
offspring to maintain themselves
without immigrants from other
populations. Please see our responses to
Comments (1) and (28) for related
information. Dixon (2004, p. 14) states
that both reservoirs (Ivie and Spence)
provide prime habitat for Concho water
snakes along the rocky shorelines.
Whiting et al. (1997, p. 331) found over
300 individual snakes in Lake Spence
20 years after the reservoir was filled.
Also, analysis by Whiting et al. (2008,
pp. 439, 443) found no evidence of a
difference in survival among the five
subpopulations (including three riverine
reaches and two reservoirs). This
suggests there may be no difference in
survival rates between reservoir and
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riverine snake populations, although the
authors recognize that the data from
reservoirs were not sufficient for reliable
estimates of snake survival and
population growth (Whiting et al. 2008,
p. 443).
Successful use of the reservoirs by
Concho water snakes is one factor we
considered in this decision and
provides some added assurance that the
snakes are not likely to become
endangered in the foreseeable future. It
is not unexpected that populations of
the snakes in the artificial habitat of the
reservoirs may not be as robust by some
measures compared with populations in
the natural riverine habitat. However,
we have no information that indicates
the snakes in reservoirs are population
sinks. We know that the snakes have
been shown to persist and reproduce in
Spence Reservoir for at least 35 years
after construction (1969 to 2005) and in
Ivie Reservoir for at least over 15 years
after construction (1989 to 2005)
(Forstner et al. 2006, p. 12). The Service
finds that this is a sufficient amount of
time to determine that snakes are likely
to continue to persist in reservoirs in the
foreseeable future.
(8) Comment: Evidence of successful
reproduction from Forstner et al. (2006)
is based on flawed analysis of masslength relationships for female snakes.
This relationship is curvilinear
(represented by a curved, rather than
straight, line) and, therefore, the data
should have been log transformed or fit
using a power function rather than a
simple linear analysis. Based on this, at
most only one of the four females found
by Forstner et al. (2006) appears to have
low mass suggesting a post-partum state
that indicates reproduction. Also, since
evidence of reproduction was found at
only a single site below Freese Dam
(Ivie Reservoir) by Forstner et al. (2006),
it is premature to conclude that a viable
population exists in this reach.
Our Response: We agree that the use
of a curvilinear function analysis would
have been more statistically robust in
the Forstner et al. (2006, p. 11) report to
evaluate reproductive status of females.
However, this analysis was not intended
to make a strong statistical argument,
but simply to substantiate the field
observations of females appearing to be
post-partum. These adult female snakes
had lower body tone in the rear third of
the body indicating (in the authors’
experience with this taxon and with
snakes in general) that recent offspring
had been released. Although access to
the river reach downstream of Freese
Dam (Ivie Reservoir) was limited due to
private property, Forstner et al. (2006, p.
18) conclude that, even with limited
samples, snakes were found at the two
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sites available in this reach
documenting that the species was
persisting and reproducing in this reach.
This information serves to confirm the
results of the earlier 10 years of
monitoring studies that found large
numbers of snakes in this reach, and
throughout the species’ current range.
(9) Comment: The simple
interpretation of lambda (l, a
calculation of the finite rate of
population increase) from Whiting et al.
(2008) using the preferred stage-based
model (l = 0.67 to 0.78) is that the
species is declining 22 to 33 percent per
generation. This, in addition to low
survivorship of neonates, is strong
evidence that Concho water snake
populations are not viable.
Our Response: Whiting et al. (2008, p.
443) explains that the modeling results
of the finite rate of increase from the
mark-recapture study were biased low
due to the effect of dispersal of snakes
out of the study areas, and this is what
produced the low estimate of l. Since
dispersal rates were not measured in the
study, the analysis resulted in a large
standard error and imprecise
conclusions with high uncertainty.
Whiting et al. (2008, p. 443) go on to
conclude that the Concho water snakes
have evolved through stochastic
environmental fluctuation (such as
droughts, floods, and fires) and occur in
high densities in riverine habitats, with
low extinction risk. This finding is
consistent with the conclusion by
Forstner et al. (2006, p. 19) that the
populations of the snake appear to be
viable. Whiting et al. (2008, p. 442)
suggested that low survivorship values
(for both juveniles and adults—rates for
neonates were not calculated) compared
to other similar snakes are being offset
by increased reproductive effort with
higher clutch sizes (number of young
produced) in Concho water snakes than
other similar snakes (Greene et al. 1999,
pp. 706–707). Also see our response to
(1) Comment above.
(10) Comment: The documented
persistence of Concho water snakes
during long-term droughts, coupled
with the 2008 MOU, which will
maintain minimum flow releases,
provide a reasonable amount of
confidence that the recovery criterion
for maintaining adequate flows has been
met. Loss of flows no longer poses a
significant threat to the Concho water
snake.
Our Response: We agree. The
minimum flow releases provided by the
2008 MOU, other reservoir releases for
water delivery and water quality
management, and natural inputs to the
rivers from springs and tributary
streams, combined with the snakes’
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ability to withstand stochastic events
like droughts, make this threat no longer
of sufficient magnitude to warrant the
species’ listing as threatened.
(11) Comment: The 2008 MOU states
that the District can further reduce or
even terminate flows during times of
extremely low inflow. Given the fairly
well documented climate change that is
now occurring, which may influence the
lengths of drought in the region (and
hence the amount of inflow), coupled
with the thought that these animals
rarely live longer than 5 years, I
question whether it is reasonable to
leave the MOU so loosely written.
Perhaps the Service might choose to be
notified after some length of time has
passed with no flow occurring so that an
assessment can be made as to its effects
on the snake populations?
Our Response: The 2008 MOU
between the Service and the District
does provide the District the ability to
forego the minimum flow releases in the
event of ‘‘extended hydrological drought
and to provide water for health and
human safety needs.’’ The drought
measure is based on reservoir elevation
(1,843.5 feet (ft) (561.9 meters (m))
above mean sea level at Spence
Reservoir, and 1,504.5 ft (458.5 m) at
Ivie Reservoir). These elevations
represent the stage when the reservoirs
are at about 12 percent of reservoir
capacity. These criteria for foregoing
minimum flow releases are consistent
with the operations included in the
2004 Biological Opinion (Service 2004a,
pp. 11–12). Since Spence Reservoir was
initially filled in 1971, the water level
elevation has only been below this mark
during 2002 to 2004, at the end of a
prolonged drought extending from 1992
to 2003 (District 2005, pp. 39–43). This
reach of the Colorado River below
Spence Reservoir makes up about 36
percent of all estimated available habitat
within the current range of the Concho
water snake (Service 2004a, p. 72). Ivie
Reservoir has not been below this mark
since it initially filled in 1991.
Discharge in the river is well-monitored
with gauges maintained by the U.S.
Geological Survey (USGS), and flow
data (historical and real time) are
available on-line. Reservoir stage data
are also available on-line on the
District’s webpage. Therefore, these data
can be easily accessed making a
notification process unnecessary. Under
our post-delisting monitoring plan, we
will be using existing stream gauges to
monitor instream flows throughout the
range of the snake. This information
will be used in combination with
biological monitoring data to assess the
status of the species in the future (see
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the Post-Delisting Monitoring Plan
section below).
We have revised our discussion of the
effects of drought on the Concho water
snake and included in the discussion a
consideration of future climate change
(see section A. The Present or
Threatened Destruction, Modification,
or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced
Instream Flows, below). Also, see our
response to Comment 12 below.
(12) Comment: Drought continues to
be a threat because, despite the species’
persistence through historic droughts, it
now occurs in combination with other
stressors, such as reduced availability of
riffles, vegetation encroachment, and
changing prey base that may
compromise survival and population
recovery following a drought.
Our Response: We have substantially
increased our analysis in this final rule
of the potential effects of declining
flows due to drought, as well as other
threats (see Summary of Factors
Affecting the Species). We found none
of these potential threats, either acting
alone or in combination, have resulted
in negative responses by the snake
sufficient to justify the species’
continued listing as threatened.
Forecasting the impacts from future
climatic events, such as drought, is
difficult to quantify because of the large
amount of uncertainty associated with
climate modeling, particularly related to
precipitation forecasting. However, we
revised our discussion of threats related
to drought and climate change in this
final rule (see section A. The Present or
Threatened Destruction, Modification,
or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced
Instream Flows below).
We do not foresee future habitat
conditions deteriorating to a point
where the species is likely to become
endangered. Forstner et al. (2006, pp.
15–17) and Whiting et al. (2008, p. 343)
explain that the snake is well adapted
to extreme drought conditions. This is
demonstrated in the Concho River
where the snake continues to persist
despite extremely low flow conditions
(Dixon 2004, pp. 8–9, Forstner et al.
2006, p. 8). The snake has been shown
to be more abundant and widespread
than originally thought and capable of
surviving in reservoirs (District 1998,
pp. 18–29). Reservoir operations have
provided continual stream flows that
have sustained the habitat for the
species, even during the prolonged
drought extending from 1992 to 2003
(District 2005, pp. 39–43), and we
expect minimum reservoir releases to
continue. In addition, the snake is
equipped to handle stochastic
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environmental fluctuations, such as low
stream flow conditions resulting from
drought, and has demonstrated the
ability to persist in these less-thanfavorable habitat conditions (Forstner et
al. 2006, p. 17; Whiting et al. 2008, p.
443). Also, the threat of vegetation
encroachment is no longer considered a
significant threat because the snake has
shown the ability to maintain
populations in river reaches with
substantial vegetation encroachment
(Dixon 2004, p. 9). Additionally, habitat
restoration efforts such as the removal of
salt cedar and other brushy species and
the creation of artificial instream riffle
structures are aimed at improving
habitat for the Concho water snake to
increase their likelihood of survival
during droughts and other stressors. We
expect some salt cedar control efforts to
continue into the foreseeable future.
(13) Comment: The importance of
groundwater-surface water interactions
to maintain adequate flows is stressed in
the proposed rule. However, there does
not appear to be a clear understanding
of where groundwater pumpage for
consumptive use has influenced base
flows. Existing groundwater-surface
water interaction models, and even
simple gain and loss studies, could
provide critical information regarding
where the influence of groundwater
pumping may influence critical flows
and available habitat.
Our Response: We agree this could be
important information to consider. We
assume there is some influence of local
and regional groundwater withdrawals
on the availability of water for instream
flows. However, we are not aware that
such information is currently available
or that to quantify this relationship
within the range of the Concho water
snake is possible at this time.
(14) Comment: Has the occurrence
and status of riffle habitat been
quantified using GIS or remote imagery
in the reaches where the species is
known to occur?
Our Response: We are not aware of
the availability of this type of
information, and the publicly available
imagery is not of sufficient resolution to
reliably quantify snake habitat in the
river. The Service did estimate the
quantity and quality of snake habitat by
reach in the 2004 Biological Opinion
(Service 2004a, Appendix B, pp. 70–72),
and we consider it to still be reasonably
accurate and the best information
available . The information has been
added to this final rule (see A. The
Present or Threatened Destruction,
Modification, or Curtailment of Its
Habitat or Range, Habitat Quality and
Quantity section below). The river
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reaches in question remain largely
undeveloped.
(15) Comment: The suggestion that
pool habitats, created by the backwater
behind low-head dams, provide refuges
for snakes during drought is
unsubstantiated. These habitats may
represent population sinks, where
mortality exceeds recruitment.
Our Response: The suggestion that
pools behind low-head dams act as
refuge habitats comes from the expert
opinion of Dr. James Dixon (Dixon 2004,
p. 16). Dr. Dixon is considered a reliable
source, as he has studied this species
since 1991 (see Werler and Dixon 2000,
pp. 209–216).
(16) Comment: The proposed rule
indicates that ‘an excellent first step’ in
reversing vegetation encroachment has
been accomplished (73 FR 38962).
While laudable, a ‘first step’ should not
be construed as success in eliminating
vegetation encroachment as a threat.
Our Response: Recent efforts by the
District to control salt cedar are
conservation actions that we expect will
benefit the Concho water snake through
maintaining native riparian vegetation
and possibly providing additional
instream flows. These actions do not
completely eliminate vegetation
encroachment. However, vegetation
encroachment, such as has occurred on
the Concho River, is not considered a
significant threat since the snake has
shown the ability to maintain
populations in river reaches with
substantial vegetation encroachment
(Dixon 2004, p. 9). We have revised the
discussion of vegetation encroachment
within this final rule (see A. The Present
or Threatened Destruction,
Modification, or Curtailment of Its
Habitat or Range, Habitat Modification
from Reduced Channel Maintenance
Flows section below).
(17) Comment: It seems reasonable to
assume that there is likely movement
between snake populations with the
discovery that the snakes are living in
the reservoirs, and, therefore, likely
little threat from population
fragmentation. Have there been studies
of possible gene flow between the
populations?
Our Response: We agree that
fragmentation has been reduced with
the new information on the persistence
of the snake in reservoirs. We presume
that over time, this allows snakes from
the upper Colorado River reach (below
Spence Reservoir) to interact with
snakes from the Concho River reach by
moving through Ivie Reservoir. Previous
studies conducted on gene flow
suggested that populations of snakes
above and below Freese Dam should be
more than large enough to maintain
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existing genetic variation based on
mitochondrial DNA analysis (Sites and
Densmore 1991, p. 10). We presume that
is still the case. Densmore (1991, pp.
10–11) went on to say that periodic
transfer of snakes should probably be
implemented to mimic gene flow. More
recent analysis has been initiated using
modern molecular techniques to
evaluate possible gene flow between
populations, but data or results from
these studies by Dr. Michael Forstner
(2008) have not yet been reported.
Forstner (2008, p. 14) does suggest that
there is no evidence that Freese Dam
(Ivie Reservoir) is a barrier to gene flow
for either water snake in the Colorado
River. However, the report notes that it
may have been too short a time to detect
such a change (Forstner 2008, pp. 14–
15), and we do not know whether there
are adequate sample sizes from this
study to reliably describe gene flow
levels between populations or river
reaches; however, the 2008 MOU calls
for the movement of snakes to provide
some gene flow between river reaches.
(18) Comment: Have any mark and
recapture studies been done to
demonstrate the movement of snakes
between fragmented habitat, e.g., from
reservoir to below reservoir and to
quantify dispersal of individuals within
reservoirs?
Our Response: Some mark-recapture
and radio telemetry studies have
documented movements in Concho
water snakes (Werler and Dixon 2000, p.
212). Although most snakes showed
strong site fidelity, some snakes moved
as far as 12 mi (19 km). No studies have
documented long-range movements
between populations or around a large
dam. However, the 2008 MOU calls for
periodic movement of snakes around
the large dams. In addition, the 2008
MOU was amended in 2011 to also
include the movement of five snakes
from above both dams to below both
dams. The 2008 MOU calls for the
movement of five snakes from below
Spence and Freese dams to above these
dams every 3 years. This amount of
transfer of snakes should be more than
sufficient to maintain gene flow, as
studies have shown that as few as one
individual exchanged with each
generation may be sufficient to maintain
adequate gene flow between animal
populations (Mills and Allendorf 1996,
p. 1,557). Also see the discussion below
under Habitat Modification from
Fragmentation.
(19) Comment: What is the evidence
that fish populations are viable and that
cyprinids (minnows) and their habitat
(e.g., riffles) are of sufficient quality and
quantity in all three reaches? Is the
opinion of one or more scientists
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adequate, or is there sufficient data on
the status or trends of fishes in the three
reaches to support the assumption that
the fish prey base for the Concho water
snake is sufficient? Are there data, such
as the Texas Commission on
Environmental Quality’s (TCEQ) Clean
Rivers Program data on fishes, which
could be analyzed to determine if there
are any trends in fish populations worth
noting? How are the fish populations
that the snakes depend on for food going
to fare in situations like prolonged
drought?
Our Response: We have revised the
discussion of forage fish availability
under the section A. The Present or
Threatened Destruction, Modification,
or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced
Instream Flows below to better explain
why we do not find that lack of forage
fish is a significant threat to the snake.
We are not aware of additional fish data
that could inform our decision on the
Concho water snake. However, a review
of the 10 years of fish surveys by the
District from 1987 to 1996 showed that
the snakes were opportunistic predators
on a variety of fish species (Service
2004a, Appendix A, pp. 68–69). The
most abundant fish available and in the
snakes’ diet are fish species that are
adapted to harsh stream conditions
(intermittent flow and poor water
quality), such as red shiners (Cyprinella
lutrensis) (Burkhead and Huge 2002, p.
1) and fathead minnows (Pimephales
vigilax) (Sublette et al. 1990, pp. 162–
166). Together these two fishes made up
two-thirds of the diet of the Concho
water snakes. We expect populations of
these fish species to persist in harsh
environments with intermittent water
available (Burkhead and Huge 2002, p.
1; Sublette et al. 1990, pp. 162–166). We
also expect them to quickly recolonize
stream reaches from reservoirs or other
refuge habitats after dewatered
conditions due to drought have ended.
This is based on observations of the
snakes being found at sites where they
were absent due to lack of water and
being found again when the water
returns. This occurred in 2004 at
Ballinger Lake and Elm Creek (Dixon
2004, pp. 4, 11–12; Forstner et al. 2006,
p. 15).
(20) Comment: Were nutrient
concentrations in water actually
evaluated in relation to algal
productivity? Is the fish assemblage
changing in species composition or
relative abundance in response to
changing nutrient conditions?
Our Response: The reference to
nutrient concentrations and algal
productivity was related to past
concerns as a possible threat to the
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Concho water snake during the 1986
listing. We are not aware of data
connecting increases in nutrient
concentrations to algal productivity or
changes in fish species composition or
relative abundance within the range of
the Concho water snake. There has been
no subsequent indication that these
threats are actually occurring or are
affecting fish communities or snake
populations.
(21) Comment: References in reports
indicate decreased cooperation by
private landowners, indicating
stakeholder buy-in is inadequate, raising
the possibility that harassment and
persecution of snakes now and
following delisting is a threat.
Our Response: We have no
information that intentional harassment
and persecution by landowners or
recreationists are likely to affect the
species on a rangewide or local
population level. The reference
(Forstner et al. 2006, p. 18) did not
indicate decreased cooperation by
private landowners, but that new
landowners were not easily contacted
due to changing ownership. We have
revised the discussion to further explain
this threat under Factor B.
Overutilization for Commercial,
Recreational, Scientific, or Educational
Purposes.
Comments From State Agencies
(22) Comment: The TPWD accepted
the District’s 1998 arguments to delist
the Concho water snake and did so on
November 16, 2000. TPWD believes the
continuing conservation efforts of the
District and other interested parties will
ensure the snake’s place as a member of
the native fauna of Texas for the
foreseeable future.
Our Response: We agree with the
comment by the TPWD that the Concho
water snake no longer qualifies as a
threatened species.
(23) Comment: Removing the Concho
water snake from protection under the
Act will reduce the costs and time
associated with section 7 consultations
with the U.S. Fish and Wildlife Service.
As a result, TxDOT may now delay the
letting of some projects until after the
final delisting occurs.
Our Response: We understand that
removing the species from the Federal
list of threatened species will benefit
some planned actions by eliminating the
requirement for section 7 consultations
for actions with a Federal nexus that
may affect the Concho water snake.
Comments From the Public
(24) Comment: A comment from the
District explained that they conducted
field studies on the Concho water snake
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from 1987 to 1996 that demonstrated the
snake population was much more stable
than previously thought. Later field
studies in 2003 to 2007 determined the
snake was in a recovered state.
Additionally, the District agreed to
provide stream flow discharge from two
of its Colorado River reservoirs (E.V.
Spence and O.H. Ivie Reservoirs), which
further supports the long-term existence
of the snake.
Our Response: The Service recognizes
the many years of field studies that the
District conducted, and the benefits of
the District’s partnership with the
Service in signing the 2008 MOU to
provide reservoir releases for the
Concho water snake. The recovery of the
Concho water snake and its removal
from the list of threatened species are
largely due to the efforts of the District
to provide reservoir releases to maintain
snake habitats over the past 20 years
and into the future, and to collect new
information documenting the biology,
distribution, and abundance of the
snake.
(25) Comment: The proposed delisting
fails to make a convincing case that
recovery of the Concho water snake is
sufficient to justify its removal from
threatened species protections. The
proposal’s arguments are vague,
circular, repetitive, and sometimes
contradictory. There is little supporting
data or science provided. The delisting
is premature and unsupported.
Our Response: We disagree with the
commenter’s conclusions. We have
updated and clarified the text in this
final rule in response to this and other
comments received to better explain our
analysis and conclusions. Specifically,
we revised the discussion and analysis
under section A. The Present or
Threatened Destruction, Modification,
or Curtailment of Its Habitat or Range.
The Service believes the removal of the
snake is warranted based on the best
available scientific information.
(26) Comment: The proposed rule
fails to adequately address availability
of, and threats to, the important riffle
habitats of the Concho water snake. For
example, reservoir habitats used by the
snake must be equal to or greater than
the amount of riverine riffle habitats lost
due to effects of the reservoir
construction at O.H. Ivie Reservoir. The
range extension for the snake does not
include information on the amount and
quality of habitat and its use by snakes.
There is no estimate provided of past or
future loss of riffle habitat, or an
assessment of the long-term success of
the artificial riffles, to support that riffle
habitat loss is not still a threat to the
Concho water snake.
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Our Response: We recognize that
there has been, and will continue to be,
changes in the characteristics of the
riverine habitat within the range of the
Concho water snake as a result of past
and ongoing human activities. While
there have not been any recent studies
to quantify these changes, the best
available data indicate that any possible
loss of riffle habitat is not resulting in
impacts that would likely cause the
snake to become endangered. The best
example is observed in the Concho
River where the long-term substantial
decline in minimum stream flows and
the loss of flushing flood flows have
reduced natural riffle habitats available
(Dixon 2004, pp. 8–9). However, Concho
water snakes continue to persist in
relatively high numbers in this reach.
For example, 20 of the 45 Concho water
snakes observed or captured by Forstner
et al. (2006, p. 8) were from the Concho
River. In addition, the snake’s use of
other habitats, including reservoir
shorelines, lessens the overall effect of
decreased riffle habitat availability. We
have revised our discussion in this final
rule and provided a quantified estimate
of habitat availability by reach
throughout the range of the species (see
section A. The Present or Threatened
Destruction, Modification, or
Curtailment of Its Habitat or Range,
Habitat Quality and Quantity below).
(27) Comment: The proposed rule
fails to address the size and health of
reservoir populations. Whiting et al.
(2008) notes that the species occurs in
relatively low densities in reservoirs,
and they believe the snake may be more
vulnerable to extinction in reservoirs. It
appears unlikely that the use of
reservoir habitats by Concho water
snakes provides sufficient improvement
in species status to support removal of
threatened protection.
Our Response: The ability of Concho
water snakes to survive and reproduce
in reservoirs is one factor among many
we considered in determining that the
species is no longer threatened. There is
some evidence that snake populations
in the reservoirs are not as robust as
those in their native riverine habitats.
We would expect this given that the
snake habitat in reservoirs is likely of a
somewhat lower quality and in less
abundance compared to natural riverine
habitats. This is because the reservoirs
may have less shallow flowing water
over rocky substrates that support small
fish that are the prey base for the snake.
However, Whiting et al. (2008, p. 443)
concluded that data are not sufficient
for truly reliable estimates of snake
survival and population growth in
either of the two main reservoirs.
Although the authors aimed to compare
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populations in reservoirs with those in
rivers, data did not allow that analysis
due to the inability to sufficiently
quantify immigration rates (Whiting et
al. 2008, p. 443). The statement by
Whiting et al. (2008, p. 443) that Concho
water snakes may be more vulnerable to
local extinction in lakes was in the
context that the extinction risk in
natural river habitats is relatively low
due to the snake’s occurrence in high
densities and their ability to grow fast
and mature early. The ability of the
species to utilize reservoirs is a positive
discovery and supports the conclusion
that the impacts of the reservoirs were
not as great as initially predicted. Also,
see our response to (1) Comment above.
(28) Comment: The proposed rule
indicated that confirming that a species
has persisted over time and continues to
demonstrate reproductive success is
sufficient to assume that populations are
viable. Persistence and reproduction are
not adequate to demonstrate population
viability. The statement that the
populations are ‘‘seemingly viable’’ is a
tentative conclusion that is scientifically
and legally unsupportable.
Our Response: Our explanation of
population viability may have
oversimplified the explanation by
Forstner et al. (2006, p. 20) describing
the status of Concho water snake
populations. We understand that
documenting persistence and
reproduction is not adequate to
precisely determine viability in most
quantitative ecological contexts. In
response to this comment, we have
updated our explanation to describe that
there are not adequate data for
quantitative modeling for population
viability analysis of this species (see
Application of the Recovery Plan’s
Criteria section below). We have revised
this discussion in the final rule to
instead refer to the definition of viable
population given in the recovery plan.
The recovery plan defines viable
population as one that is self-sustaining,
can persist for the long-term (typically
hundreds of years), and can maintain its
vigor and its potential for evolutionary
adaptation (Service 1993, p. 33). We
have also included a more detailed
summary of the results of the 10 years
of snake monitoring, which concluded
in 1996. These extensive data, in
conjunction with updated limited
survey data in 2004 and 2005, are the
basis for determining that populations
of Concho water snake are viable. In
addition, it is important to recognize the
standard under the Act is to determine
if the species is likely to become
endangered in the foreseeable future.
Given the best available information,
weighing the status of the species and
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the current and future threats, we have
concluded that the snake is no longer
likely to become endangered in the
foreseeable future throughout all or a
significant portion of its range.
(29) Comment: The discussion in the
proposed rule regarding effects of
drought is poorly articulated and
circular. The stated belief that the
Concho water snake and its fish prey
base can and will survive any level and
duration of drought is unsupported by
data or analysis in the proposal.
Our Response: We did not intend to
imply that snakes can survive any level
of drought, but we believe they can
survive the expected drought conditions
in the foreseeable future, based on
historical records and considerations
over the last thousand years based on
tree-ring analysis (summarized in
Forstner et al. 2006, p. 16). We are
relying on the expert opinion and field
experience of long-term herpetologists,
explained in Forstner et al. (2006, pp.
15–17) and Whiting et al. (2008, p. 443)
that the Concho water snake has
evolved in a drought-prone,
hydrologically dynamic system and has
demonstrated the ability to withstand
stochastic environmental fluctuations.
This characteristic of the snake to
endure periods of drought and resulting
poor habitat conditions was
documented for the Concho River reach
and at Lake Ballinger on Elm Creek, a
Colorado River tributary (Dixon 2004,
pp. 9, 11–12; Forstner et al. 2006, p. 17;
Whiting et al. 2008, p. 443). Due to
water management and climate change,
future droughts could be more severe
than the historical record over the last
100 years. However, we cannot foresee
that these conditions are likely to be so
severe as to result in the extinction or
endangerment of the snake. To make
this explanation clearer, we have
rewritten the discussion in this final
rule (see section A. The Present or
Threatened Destruction, Modification,
or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced
Instream Flows below).
(30) Comment: The success in
abatement of threats over the 22 years
since the Concho water snake was listed
appears to be overstated in the proposed
rule. Long-term success of artificial riffle
construction to increase riverine habitat
is not yet determinable. The 15 or so
years since artificial riffle installation
are not long-term in a hydrologic sense.
It is my understanding the artificial
riffles have not been assessed for several
years.
Our Response: The artificial riffles
constructed in 1989 produced
immediate results as snakes were found
there by 1991 (District 1998, pp. 13, 15).
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The six riffles were monitored from
their creation in 1991 through 1996, and
snakes were consistently found at five of
the six sites (Thornton 1996, pp. 44–49).
The success of the snakes in the
reservoirs and in the artificial riffles
resulted in less attention being given to
the need to mitigate further for the
habitat loss from reservoir construction.
We are not aware of any recent
monitoring efforts focused on the
artificial riffles, but we have no reason
to believe the snakes are not continuing
to persist there.
(31) Comment: Other than species
persistence, data and studies upon
which the 2004 reduction of minimum
instream flows was based are not
discussed. There are also no studies
documenting the results of the
reductions in the required flow.
Our Response: A full explanation and
analysis of effects of the 2004 reduction
in required flows is documented in the
Service’s biological opinion provided to
the U.S. Army Corps of Engineers as a
conclusion to the formal section 7
interagency consultation for the change
in reservoir operations (Service 2004a,
pp. 1–76). The analysis included
updated biological information that the
snakes use more diverse riverine
habitats (such as pools, in addition to
riffles) and were found in the reservoirs
and tributaries (Dixon 2004, pp. 9, 16;
Service 2004, pp. 53–54). As a result of
that consultation, we gave our biological
opinion that the reduced reservoir
releases described in the proposed
agency action were not likely to
jeopardize the continued existence of
the Concho water snake and were not
likely to destroy or adversely modify
designated critical habitat. These same
flow rates were used in the 2008 MOU.
In making the delisting proposal and
now the final rule, we relied heavily on
the results of monitoring by Forstner et
al. (2006, p. 1–22) in concluding that the
reduced flow rates are sufficient for the
snake.
(32) Comment: The 2004 Biological
Opinion substantially changed the 1986
requirement for high discharge channel
maintenance flows below O.H. Ivie
Reservoir. That change is not discussed
in the proposed rule, and would be of
particular importance in understanding
the basis for the habitat loss
downstream of reservoirs.
Our Response: We have added
information to the final rule explaining
the changes in requirements for channel
maintenance flows (see section A. The
Present or Threatened Destruction,
Modification, or Curtailment of Its
Habitat or Range, Habitat Modification
from Reduced Channel Maintenance
Flows below). The 2004 Biological
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Opinion and the 2008 MOU both
recognize the benefits of periodic high
discharges from either reservoir releases
or flood runoff events to function in
river channel maintenance to maintain
suitable rock substrates and abate
vegetation invasion of riffle habitat. Our
analysis concludes that some flushing
flows are likely to naturally occur,
slowing the degradation of aquatic
habitats. In addition, the snakes appear
capable of sustaining populations in
areas where instream habitats have been
altered due, in part, to reducing flushing
flows. In some areas, such as on the
Concho River, the dominant substrate is
solid bedrock and not as subject to
invasion of vegetation. Cracks and
breaks in the bedrock provide foraging
habitat similar to riffles. Therefore, we
did not find that the threats of reduced
flushing flows are significant.
(33) Comment: Although the proposed
rule says that the District has
implemented every activity requested
by the Service in previous biological
opinions, the District’s compliance was
largely due to removal of requirements
that they objected to prior to finalizing
the opinion and removal of others by
later amendments. The statement that
the District has an excellent track record
of carrying out conservation actions
should be supported by information.
Our Response: The 1986 Biological
Opinion was amended many times up
until the major revision in 2004 due to
changing conditions based on new
information being collected (Service
2004a, pp. 1–3). A discussion of the
District’s compliance efforts under the
previous biological opinions is
documented in the 2004 revised
biological opinion (Service 2004a, pp.
42–47). We have also added information
throughout this final rule to document
important areas where the District has
fulfilled its requirements.
(34) Comment: There is no evidence
provided that the instream flow
requirements from the 2004 Biological
Opinion and 2008 MOU are sufficient to
ensure long-term species survival.
Our Response: We believe the flows
provided in the 2008 MOU are sufficient
to ensure long-term species survival.
This is based on the information
demonstrating that the species can
survive under substantially lower flows
compared to what was previously
thought. These conclusions are based on
the observations and reports of species
experts (Dixon 2004, p. 16; Forstner et
al. 2006, pp. 19–21; Whiting et al. 2008,
p. 443). We have also revised the
discussion of the threats from reduced
instream flows in this final rule to
include additional information and
discussion on hydrology, climate
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change, and the potential response by
the snake (see section A. The Present or
Threatened Destruction, Modification,
or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced
Instream Flows below).
(35) Comment: The 2008 MOU was
entered in good faith, but it is not
legally enforceable. There is no
consequence to the District for a lapse
in conservation actions. The MOU is not
an adequate substitute for legal
protection under the Act.
Our Response: We do not consider the
2008 MOU (including the 2011
amendment) as a substitute for the legal
protections under the Act. It does
document the commitment that the
District will continue to cooperate in
maintaining instream flows downstream
of the two Colorado River reservoirs.
These flows are in addition to other
reservoir releases for water delivery and
water quality management, and natural
inputs to the rivers from springs and
tributary streams. Given the District’s
track record of compliance and
completing conservation actions, we
have no reason to doubt that the District
will continue to carry out the actions
agreed to in the 2008 MOU (including
the 2011 amendment). In addition,
Section 5.2 of the MOU notes the
Service’s ability to list the snake again
under protection of the Act. This
provision includes use of emergency
listing procedures if warranted.
(36) Comment: Initiation of salt cedar
control does nothing to guarantee threat
abatement to Concho water snake
habitat. Salt cedar control has a long
history of variable and generally quite
limited success. It will be many years
before it can be determined if the
recently initiated project will provide
any benefit to the snake.
Our Response: Salt cedar control is
one conservation action that can
provide benefits to the Concho water
snake through restoration of native
riparian vegetation to provide natural
stream-side habitat conditions and
potential water savings for instream
flow increases. We agree with the
comment that it will take time to
document the actual benefits to the
snake.
(37) Comment: The proposal
acknowledges that delisting recovery
criteria from the recovery plan have not
been met, but claims additional
information has rendered those criteria
partially invalid. This undermines the
recovery planning process and is
offensive to the many stakeholders who
participate in recovery plan
development. If the recovery plan is outof-date or otherwise invalid, the Service
should convene the recovery team and
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amend or rewrite the plan with
appropriate public and stakeholder
review. This will yield a firmer basis
and greater support than the current
process for delisting.
Our Response: The Service believes
that the Concho water snake has
recovered and generally met the criteria
from the 1993 recovery plan. Although
meeting the recovery criteria is not
necessarily required for delisting, we
have discussed the criteria below in this
final rule section Application of the
Recovery Plan’s Criteria. The Service
does not believe it is necessary to revise
the recovery plan for the Concho water
snake. We have found the current
information is sufficient to support that
the species no longer qualifies as a
threatened species. Therefore,
additional time and resources would not
be well spent to revise the recovery
plan. Also we have sought the input of
the public, stakeholders, and experts,
including former recovery team
members, during the comment period
for the proposal to remove the snake
from the threatened list.
(38) Comment: While District water
rights may ensure water deliveries to
downstream users, they do not ensure
that deliveries will occur through the
natural streambed where Concho water
snake exists. Such rights can be fulfilled
through other means, like canals, water
trades, storage, etc., that result in
dewatered stream channels.
Our Response: The primary water
releases for downstream water users that
provide benefits to the snake occur from
the required minimum flow releases
from Ivie Reservoir for the Lower
Colorado River Authority (LCRA). These
releases are required by the District’s
State water right permit for Ivie
Reservoir. The deliveries are made using
the natural channel. Other deliveries
made for water quality improvement
occur between Spence and Ivie
Reservoirs and also use the natural
channel. We have no reason to believe
that these water deliveries would not
use the natural stream channel in the
future. The District already uses a
sophisticated system of pipelines to
deliver most of their water to its
customers, the majority of whom are
cities upstream of the two reservoirs
(District 2005, pp. 2–5). Therefore, we
do not foresee the District using any
other methods than the natural channel
to deliver water downstream.
(39) Comment: The Service statement
that the snakes may not need to be
transferred between populations to
prevent genetic isolation illustrates the
prematurity of this proposed rule. A
delisting decision should be based on
something more reliable than that the
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species ‘‘may not need’’ this
conservation action.
Our Response: We have clarified this
language in this final rule (see
Application of the Recovery Plan’s
Criteria section below). Section 4.1 of
the 2008 MOU, as amended in 2011,
states that, ‘‘In the springtime once
every 3 years, the District, in
coordination with the Service, should
move five male snakes (each) from
below Spence and below Freese [Ivie
Reservoir] dams to above these dams,
and move 5 different male snakes from
above both dams to below both dams.
Moving snakes will be dependent upon
availability of funding for the District.’’
This requirement was included in the
2004 Biological Opinion (Service 2004a,
p. 61). Should funding be unavailable in
any particular snake-moving year, every
effort will be made to move snakes in
the succeeding year. Previously,
movement of snakes was suggested with
the Concho River population as well
(Service 1986, p. 24). However, because
the snakes exist in Ivie Reservoir they
have access from the Colorado River to
the Concho River so transferring snakes
to the Concho River was determined not
necessary.
(40) Comment: The reference to the
uncertainties in the results from
Whiting et al. (2008) should be clarified
that the uncertainties resulted from the
data being insufficient to estimate
survival and trend reliably due
primarily to insufficient sampling at any
single study site, along with a host of
variables, especially environmental
variability within a site and among sites,
and also because dispersal rates were
not measured among sites. Therefore,
study results have not been robust
enough to allow either population or
trend estimates with satisfactory
precision.
Our Response: We have updated the
text in the final rule to be consistent
with this comment (see Application of
the Recovery Plan’s Criteria section
below).
(41) Comment: A reliable trend
estimate for the Concho water snake
over a span of years seems to be lacking
for the species, and there are no reasons
given for why this was so. A trend
analysis would be better to ascertain if
the species should be delisted.
Our Response: We agree that a reliable
trend analysis over time would be
useful in confirming the status of the
species. Despite many years of
monitoring surveys over time, no
reliable trend analysis has been
completed due to variations in study
efforts and methods and to
environmental conditions (District 1998,
p. 18; Service 2004a, p. 23; Forstner et
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al. 2006, p. 12–13; Whiting et al. 2008,
p. 343). However, the best available
information on the population status of
the snake from the large numbers of
snakes captured during the 10 years of
monitoring (District 1998, p. 21) and
confirmed in 2005 (Forstner et al. 2005,
pp. 19–20) demonstrates that its status
is sufficiently good to warrant removal
from the list of threatened species. For
more discussion on this issue, see
Application of the Recovery Plan’s
Criteria, Viable Populatins section of
this rule.
Summary of Factors Affecting the
Species
Section 4 of the Act and its
implementing regulations (50 CFR part
424) set forth the procedures for listing,
reclassifying, or removing species from
listed status. ‘‘Species’’ is defined by the
Act as including any species or
subspecies of fish or wildlife or plants,
and any distinct vertebrate population
segment of fish or wildlife that
interbreeds when mature (16 U.S.C.
1532(16)). Once the ‘‘species’’ is
determined, we then evaluate whether
that species may be endangered or
threatened because of one or more of the
five factors described in section 4(a)(1)
of the Act. We must consider these same
five factors in delisting a species. We
may delist a species according to 50
CFR 424.11(d) if the best available
scientific and commercial data indicate
that the species is neither endangered
nor threatened for one of the following
reasons: (1) The species is extinct; (2)
the species has recovered and is no
longer endangered or threatened (as is
the case with the Concho water snake);
and/or (3) the original scientific data
used at the time the species was
classified were in error.
A recovered species is one that no
longer meets the Act’s definition of
threatened or endangered. The analysis
for a delisting due to recovery must be
based on the five factors outlined in
section 4(a)(1) of the Act. This analysis
must include an evaluation of threats
that existed at the time of listing, those
that currently exist, and those that could
potentially affect the species once the
protections of the Act are removed.
The Act defines ‘‘endangered species’’
as any species which is in danger of
extinction throughout all or a significant
portion of its range, and ‘‘threatened
species’’ as any species that is likely to
become an endangered species within
the foreseeable future throughout all or
a significant portion of its range. The
word ‘‘range’’ in the phrase ‘‘significant
portion of its range’’ refers to the range
in which the species currently exists.
For the purposes of this analysis, we
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will evaluate whether the currently
listed species, the Concho water snake,
should be considered threatened or
endangered throughout all of its range.
Then we will consider whether there are
any significant portions of the Concho
water snake’s range in which it is in
danger of extinction or likely to become
endangered within the foreseeable
future (see Significant Portion of the
Range Analysis section below). For the
purposes of this finding, the
‘‘foreseeable future’’ is the period of
time over which events or effects
reasonably can be anticipated, or trends
reasonably extrapolated, such that
reliable predictions can be made
concerning the status of the species. We
considered this temporal component in
the analysis in each substantive
discussion under the five factors below
and provide a discussion of the
foreseeable future in the Conclusion of
the Five-Factor Analysis section below.
Section 4(a)(1) of the Act requires that
we determine whether a species is
endangered or threatened based on one
or more of the five following factors: (A)
The present or threatened destruction,
modification, or curtailment of its
habitat or range; (B) overutilization for
commercial, recreational, scientific, or
educational purposes; (C) disease or
predation; (D) the inadequacy of
existing regulatory mechanisms; and (E)
other natural or manmade factors
affecting its continued existence. Our
evaluation of these five factors is
presented below. Following this threats
analysis, we evaluate whether the
Concho water snake is threatened or
endangered within any significant
portion of its range.
A. The Present or Threatened
Destruction, Modification, or
Curtailment of Its Habitat or Range
Habitat Description
Concho water snakes are known to
occur in rivers, streams, and along the
shoreline of reservoirs. These snakes are
air-breathing; however, they feed almost
exclusively on fish and are, therefore,
found only near water sources capable
of supporting at least a minimal fish
population. Unlike many other species
of Nerodia, Concho water snakes do not
seem to move far from water (Werler
and Dixon 2000, p. 208). During
Greene’s (1993, p. 96) visual and radio
telemetry surveys, all snakes occurred
within 33 ft (10 m) of water.
Stream and river habitat used by the
Concho water snake is primarily
associated with riffles (Greene 1993, p.
96; Werler and Dixon 2000, p. 210;
Forstner et al. 2006, p. 13) where the
water is usually shallow and the current
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is of greater velocity than in the
connecting pools. Riffles begin when an
upper pool overflows at a small change
in gradient and forms rapids. The
stream flows over rock rubble or solid
to terraced bedrock substrate through a
chute channel that is usually narrower
than the streambed. The riffle can
extend to over 300 feet (100 m) in some
locations and ends when the rapids
enter the next downstream pool. Riffles
are believed to be the favored habitat for
foraging, with young snakes using
shallow parts of riffles and adult snakes
using deeper parts of riffles (Williams
1969, p. 8; Scott et al. 1989, pp. 380–
381; Greene 1993, pp. 13, 96; Werler
and Dixon 2000, p. 215; Forstner et al.
2006, p. 13). Juvenile snakes are closely
associated with gravel shallows or riffles
(Scott and Fitzgerald 1985, p. 35; Rose
1989, pp. 121–122; Scott et al. 1989, p.
379). This habitat is likely the best for
juvenile snakes to successfully prey on
small fish because the rocky shallows
concentrate prey and are inaccessible to
large predatory fish. The exposed rocky
shoals act as thermal sinks, which
maintain heat and may help keep the
juvenile snakes warm and maintain a
high growth rate (Scott et al. 1989, pp.
380–381).
Observations on the Concho and
Colorado Rivers also indicated Concho
water snakes were found in the shallow
pools between riffles (Williams 1969, p.
8; Dixon 2004, p. 16). Dixon et al. (1989,
p. 16) demonstrated that adult snakes
used a variety of cover sites for resting,
including exposed bedrock, thick
herbaceous vegetation, debris piles, and
crayfish burrows. Adult and maturing
Concho water snakes use a wider range
of habitats than do juveniles including
pools with deeper, slower water
(Williams 1969, p. 8; Scott et al. 1989,
pp. 379–381; Werler and Dixon 2000, p.
211).
Range
Historically the Concho water snake
was known to occur in spotty
distribution in central Texas on the
Colorado River below E.V. Spence
Reservoir (constructed in 1969) near the
City of Robert Lee, Texas, downstream
to the F.M. 45 highway bridge crossing
and then not again until further
downstream near the City of Bend,
Texas (Tinkle and Conant 1961, pp. 42–
43; Williams 1969, p. 3). On the Concho
River and its tributaries, Concho water
snakes were historically known from
Spring Creek, Dove Creek, and the
South Concho River, all upstream of the
Twin Buttes and O.C. Fisher Reservoirs
near San Angelo, Texas, and in the
Concho River downstream from San
Angelo to the confluence with the
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Colorado River (Marr 1944, pp. 486–
487; Tinkle and Conant 1961, pp. 42–
43). Prior to the Federal listing of the
Concho water snake in 1986, it had been
extirpated from Concho River tributaries
upstream of the City of San Angelo
(Flury and Maxwell 1981, p. 31), and
surveys had not located snakes in lakes
or reservoirs (Scott and Fitzgerald 1985,
pp. 17, 34). At the time of listing, the
range of the snake had been affected by
O.C. Fisher, Twin Buttes, and Spence
Reservoirs and one tributary creek
reservoir, Ballinger Municipal Lake (on
Elm Creek). A fifth reservoir, O.H. Ivie
Reservoir (formerly known as Stacy),
was planned for construction at the
confluence of the Concho and Colorado
Rivers and was expected to reduce the
snake’s range by more than 50 percent
(Scott and Fitzgerald 1985, pp. 31, 35).
At the time of listing in 1986 the
range was described as approximately
199 mi (320 km) (51 FR 31412). By
1993, Scott et al. (1989, pp. 382, 384),
Thornton (1992, pp. 3–16), and Whiting
(1993, pp. 8, 28, 117–118, 121) had
found additional locations of the snake
upstream and downstream and
determined the Concho water snake’s
distribution to be approximately 233 mi
(375 km) of river (Service 1993, p. 9).
While the Concho water snake has been
extirpated from some reaches of its
historical distribution, mainly upstream
of San Angelo (Flury and Maxwell 1981,
p. 31), since the time of listing it has
been confirmed farther downstream
from Ivie Reservoir and farther upstream
from Spence Reservoir (District 1998,
pp. 10, 22, 26, Dixon et al. 1988, p. 12;
1990, pp. 50, 62–65; 1991, pp. 60–67;
1992, pp. 84, 87, 96–97; Scott et al.
1989, p. 384). Analysis for the 2004
revision to the 1986 Biological Opinion
(BO; Service 2004a, p. 32) summarized
the current known distribution of the
Concho water snake as being the
Colorado River from the confluence of
Beals Creek (upstream of Spence
Reservoir), depending on reservoir
stage, to downstream of Ivie Reservoir
(constructed in 1989) to Colorado Bend
State Park, and on the Concho River
downstream of the City of San Angelo
to the confluence with the Colorado
River. This is a total of about 280 mi
(451 km) of river and about 40 mi (64
km) of reservoir shoreline.
The information on the current range
of the snake is based largely on the
monitoring studies performed by the
District between 1987 and 1996 (District
1998, p.10). In addition to monitoring 3
times a year at 15 riverine sites, the
District also conducted searches
throughout the upper Colorado River
and Concho River basins. Additional
surveys taught researches that late
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summer and early fall were the times
when the snake was most active and
that snakes can often be captured in
minnow traps when they are not found
with searches (District 1998, pp. 16, 18).
The results confirmed a larger
distribution than was thought at the
time of listing. For example, the snake
was believed to be extirpated from the
area downstream of Spence Reservoir in
the Colorado River, but was found to
occur there with more intensive sample
efforts (District 1998, p. 22). The snake
overall was found throughout its
historic range, with the only exception
being the small tributary streams
upstream of San Angelo, where only a
few snakes had been collected in the
past.
To confirm the distribution of the
species, Concho water snake surveys
were conducted across the species’
range in 2004 and 2005 (Dixon 2004;
Forstner et al. 2006). One goal of
Forstner et al. (2006, pp. 4–5) was to
evaluate whether viable Concho water
snake populations existed in all reaches
of the Colorado and Concho Rivers. To
do this, snake localities were surveyed
‘‘for evidence of reproduction (one
measure of sustainability).’’ In all, 14
sites were sampled, and 45 Concho
water snakes were collected from 11 of
those sites (Forstner et al. 2006, pp. 9–
12). Sample efforts were limited to the
extent necessary to document the
presence of the species and evidence of
reproduction in each reach, based on
the capture of either neonate snakes or
post-partum females. The collection
efforts were brief, and more effort would
have likely increased the total number
of snakes collected (Forstner et al. 2006,
p. 11).
Persistence and reproduction were
documented in the Concho River and
upstream of Ivie Reservoir in the
Colorado River, as well as in both
Spence and Ivie Reservoirs (Forstner et
al. 2006, pp. 12, 18). However, access
downstream of Ivie Reservoir was
limited by inability to contact private
property owners, preventing a thorough
assessment downstream of that
impoundment (Dixon 2004, p. 2;
Forstner et al. 2006, p. 18). Despite
limited access downstream of Ivie
Reservoir, four snakes were captured
during the surveys at two sites and at
least one female exhibited signs of
recently giving birth. Forstner et al.
(2006, p. 18) described these results as
technically sufficient to demonstrate
persistence and reproduction
downstream of Ivie Reservoir 15 years
after its construction. These authors
conclude that, ‘‘Even in the face of
landscape scale or ecosystem wide
stresses by severely reduced
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precipitation, increased human uses of
instream flows, introduced species, and
ever increasing human densities, the
Concho water snake remains in the
majority of the sites visited and
continues to reproduce at those
locations’’ (Forstner et al. 2006, p. 18).
Forstner et al. (2006, p. 20) state that
‘‘self sustain[ing], seemingly viable
populations in the Concho and Colorado
rivers at the end of a decade of
monitoring’’ occur in the three reaches
of the snake’s range. We find that the
range of the species has not declined
since it was listed in 1986 and has been
found to be larger, about 80 more rivermi (129 river-km), than at the time of
listing. Therefore, because of its
continued persistence throughout its
range, the species is not threatened with
endangerment due to range reduction.
Population Trends
Following listing of the Concho water
snake in 1986, a 10-year monitoring
study began throughout the snake’s
range, including several reservoirs and
tributaries (District 1998, pp. 10, 22, 26).
The study included mark-recapture
techniques by inserting a unique tag in
each captured snake of sufficient size so
that individuals could be identified
when they were recaptured. Over the 10
years of study, 9,069 unique Concho
water snakes were captured (District
1998, p. 21). Of this total, 1,535 (17
percent) were captured in reservoirs,
1,517 (17 percent) were captured in the
Concho River reach, 5,586 (62 percent)
were captured in the Colorado River
reach, and another 415 (5 percent) were
captured in tributary streams. All of the
more than 20 study sites monitored had
multiple captures of snakes every year,
with a variety of age classes (Thornton
1996, pp. 26–50). Sampling effort at
each survey site was not quantified, and
was highly variable. Therefore, an
increase or decrease in numbers of
snakes at a site or cluster of sites in a
river reach over the 10 years of the
survey does not necessarily indicate an
actual increase or decrease in snakes
because the effort made to find them
varied from survey to survey. The high
variation in sample efforts and
environmental conditions prevented a
thorough analysis of population trends
over time or calculation of total
population estimates (District 1998, p.
18).
Forstner et al. (2006, pp. 6–8, 18, 20)
updated the past information by
conducting brief field surveys in 2004
and 2005 to verify that snakes continued
to be present and were reproducing in
each river reach and reservoir where it
had been documented in previous
studies. This study, which incorporated
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the results by Dixon (2004), confirmed
reproducing populations of Concho
water snakes in each river reach and in
both Ivie and Spence Reservoirs
(Forstner et al. 2006, p. 12). Based on
the snakes’ persistence and
reproduction throughout its range over
the past 20 years, Forstner et al. (2006,
pp. 18, 20) concluded that viable
populations of Concho water snakes
could be presumed to exist in all three
reaches of the species’ range.
Only two sample locations (below
Freese Dam and at River Bend Ranch,
about 25 miles (40 km) downstream of
the dam) were available for access by
the updated study in the reach of the
Colorado River downstream of Freese
Dam (Ivie Reservoir) (Dixon 2004, pp. 8,
14). This was due to the difficulties in
establishing contact with private
landowners in this area. However,
Dixon did collect three snakes from
these two sites in 2004, and one was a
juvenile female (Dixon 2004, pp. 16–17).
In 2005, Forstner et al. (2006, pp. 12, 18)
collected one post-partum female below
Freese Dam indicating the snake had
given birth to young and confirming
reproduction. Although only four
snakes were captured in limited
sampling efforts in 2004 and 2005 in
this reach, data from the District’s
earlier monitoring showed large
numbers of snakes in this reach (District
1998, pp. 34–38, 50). We have no reason
to conclude that the snake population
downstream of Freese Dam is of
additional concern.
The 10 years of Concho water snake
monitoring data (1987 to 1996) was
reanalyzed in an attempt to evaluate
population trends and quantify longterm viability (Whiting et al. 2008, pp.
438–439). The results, however, were
inconclusive because the data were
insufficient to reliably estimate survival
and emigration. This was due primarily
to insufficient sampling at any single
study site to quantify dispersal rates,
along with a host of other variables,
especially different environmental
conditions within a site and among sites
(Whiting et al. 2008, p. 443). This
resulted in the survival rates from the
capture-recapture study being biased
low and producing low estimates of
annual survival with large standard
errors (Whiting et al. 2008, p. 443). The
study stated that snakes continued to
persist even in drought-prone areas,
some with almost total water loss, with
hydrologically dynamic systems
(Whiting et al. 2008, pp. 442–443).
In conclusion, although recent data on
population trends are sparse, data
showing a stable range, long-term
persistence, and continuing breeding
success indicate that populations have
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persisted and remain distributed
throughout the species’ range over time
and do not indicate population
concerns.
Habitat Quality and Quantity
At the time of listing, we believed the
Concho water snakes did not exist in
reservoir habitats. In fact, at the time of
listing, the imminent construction of
Ivie Reservoir was considered a primary
threat because of the assumed habitat
loss that would occur due to the
reservoir. However, the magnitude of
this threat did not materialize because
subsequent research confirmed that
Concho water snakes inhabit shallow
water with minimal wave action and
rocks along reservoir shorelines (Scott et
al. 1989, pp. 379–380; Whiting 1993, p.
112). Juvenile Concho water snakes are
generally found in low-gradient, looserock shoals adjacent to silt-free cobble.
However, Concho water snakes have
also been observed on steep shorelines
(Whiting 1993, p. 112) and around the
foundations of boat houses (Scott et al.
1989, p. 379).
We quantified the amount and quality
of potential Concho water snake habitat
and compared it by river reach and
reservoir (Service 2004a, Appendix B,
pp. 70–72). These data were habitat
quality estimates provided by District
biologist and species expert, Mr. Okla
Thornton, and were digitized and
summarized by the Service using a
Geographic Information System. We
categorized the habitat quality as high,
medium, or low, and calculated the
quantity of habitat based on linear
meters of river bank or shoreline and
summed the results by river reach and
reservoir. The results were presented by
five segments: (1) The Concho River
segment (San Angelo to the inflow of
Ivie Reservoir); (2) the Spence Reservoir
segment (shoreline of the lake); (3) the
upper Colorado River segment (outflow
of Spence Reservoir downstream to the
inflow of Ivie Reservoir) segment; (4) the
Ivie Reservoir (shoreline of the lake);
and (5) the lower Colorado River
segment (outflow of Ivie Reservoir
downstream to Colorado Bend State
Park).
In total, the analysis showed over 112
mi (180 km) of snake habitat is generally
available along the rivers and in the
reservoirs within the species’ range. The
results indicated that 82 percent of
overall available habitat is found in the
three river reaches and 18 percent of
available snake habitat is in the two
reservoirs. The largest percent of ‘‘high
quality’’ habitat (total of 59 mi (96 km))
was found in the upper and lower
Colorado River segments (42 percent
and 27 percent, respectively) (Service
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2004a, p. 71). The two reservoirs
combined contain 15 percent of
available ‘‘high quality’’ habitats and the
Concho River segment contained 16
percent (Service 2004a, p. 71). These
data demonstrate that Concho water
snake habitat is distributed throughout
its range in both the riverine and
reservoir segments.
Habitat Destruction From Reservoir
Inundation
At the time we listed the Concho
water snake in 1986, we believed the
construction of Ivie Reservoir would
result in the loss of Concho water snake
habitat upstream of the dam by
inundating the natural riverine rocky
and riffle habitats. The site of the
proposed reservoir on the Colorado
River was believed to support the
highest concentration of Concho water
snakes (Flurry and Maxwell 1981, pp.
36, 48; 51 FR 31419). Outside of this
area, the snake had been found only in
isolated occurrences, which indicated
an already disjunct, fragmented
distribution. The snake had not been
found in reservoirs or in the silted-in
riverine habitat below Spence Reservoir
(Scott and Fitzgerald 1985, pp. 13, 28).
It also had not been found in perennial
tributaries except Elm Creek near
Ballinger (Scott and Fitzgerald 1985, pp.
15, 34). Thus, in 1986 we believed the
inundation by Ivie Reservoir would
result in a substantial loss of habitat (as
much as 50 percent) for the Concho
water snake by eliminating them from a
substantial portion of their range.
As a result of a 1986 formal
consultation conducted under section 7
of the Act with the U.S. Army Corps of
Engineers on construction of Freese
Dam to form Ivie Reservoir (1986 BO),
the District agreed to implement a
number of conservation measures under
required reasonable and prudent
alternatives to avoid jeopardizing the
snake. These measures included, but
were not limited to: Long-term
monitoring of the snakes, completing
life-history studies, maintaining specific
flow regimes from Spence and Ivie
Reservoirs, creating six artificial riffles
below Spence Reservoir, and
transplanting snakes between
populations above and below Ivie
Reservoir (Service 1986, pp. 12–24). Ivie
Reservoir was constructed in 1989 and
the District carried out the required
measures over the following 10 years
(District 1998, p. 29; Service 2004a, pp.
42–47).
As part of their long-term monitoring
plan, District field biologists conducted
extensive searches for the Concho water
snake beginning in 1987. According to
Dixon et al. (1988, p. 12; 1990, pp. 50,
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62–65; 1991, pp. 60–67; 1992, pp. 84,
87, 96–97), snakes were documented
within and above Spence Reservoir,
downstream of Spence Reservoir in the
artificial riffles, at Ballinger Municipal
Lake, the old Ballinger Lake, and the
connecting channel between the two
Ballinger lakes. The snake was also
documented in multiple locations on
Elm Creek and two of its tributaries,
Bluff Creek and Coyote Creek (Scott and
Fitzgerald 1985, pp.14–15, 30; and Scott
et al. 1989, p. 384). Snakes were
regularly found in Spence, Ivie, and
Lake Ballinger Reservoirs, a habitat type
they were not known to occupy at the
time of listing. Concho water snakes
have continued to be found in
reservoirs. Dixon’s (2004, pp. 3–4)
surveys in 2004 confirmed that snakes
persist in Spence and Ivie Reservoirs. In
2004, Ballinger Lake had only a small
pool of water remaining, and no snakes
were found there at that time. However,
after rains in 2005, Forstner et al. (2006,
p. 12) confirmed snakes were again
present and reproducing within Lake
Ballinger. These observations confirm
that Concho water snakes have adapted
to using reservoirs as habitat.
Studies have found that rocky
shorelines were the single most
important component of snake habitat
in reservoirs, and that changes in water
surface elevation of Spence Reservoir
will affect the availability of that
shoreline habitat (Whiting 1993, p. 13;
Whiting et al. 1997, pp. 333–334).
Although Forstner et al. (2006, p. 17)
refer to the lakes overall as ‘‘very poor
Concho water snake habitat,’’ while
Dixon (2004, p. 14) calls them ‘‘prime
habitat,’’ both reports conclude that
there are rocky outcrops and boulder
slopes in limited areas within the
reservoirs that are occupied by the
snake. The snakes have remained in
Spence Reservoir for nearly 40 years
following its construction and for at
least 15 years following construction of
Ivie Reservoir. Because Concho water
snakes are now known to be
reproducing and persisting over time in
reservoirs and their current distribution
is larger than reported historically and
at the time of listing, habitat loss from
reservoir inundation is no longer
believed to be a threat to the long-term
survival of the species.
Habitat Modification From Reduced
Instream Flows
a. Hydrology and Historic Instream
Flows.
Even prior to the Concho water snake
listing in 1986, a primary concern for
the conservation of the species has been
the potential impacts of habitat
modification that occurs with
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reductions in instream river flow rates
throughout its range (Scott and
Fitzgerald 1985, p. 33). The source of
these concerns originates from the
storage and use of water for human
consumption (primarily the damming
and diversion of surface water for
municipal uses) and the compounding
effects of drought (natural rainfall levels
below average). In the following
discussions we analyze the sources,
potential mechanisms, and possible
effects arising from the threats related to
the reduction of instream flows.
Beginning in eastern New Mexico, the
upper Colorado River watershed,
including the Concho River drainage, is
semi-arid with average annual rainfall
ranging from 15 to 35 inches (in) (38 to
89 centimeters (cm)) (TWDB 2007, p.
132). The area has a warm and windy
climate that produces average annual
gross lake surface evaporation of 65 to
80 in (165 to 203 cm) (TWDB 2007, p.
133). The water that produces river
flows where the Concho water snake
occurs originates exclusively from
rainfall precipitation. This occurs
through either direct surface runoff or
natural groundwater storage of rainfall
and then later discharge to surface flows
through spring flows or seepage out of
stream banks. The Colorado River
generally increases in flow rate
downstream, depending on rainfall,
aquifer conditions, and water releases
from reservoirs.
Since the early 1900s the upper
Colorado River watershed (including the
Concho River) has been modified to
accommodate human water demands,
primarily for agricultural irrigation
(about 80 percent of all water used),
municipal, and industrial uses. The
construction of numerous reservoirs for
surface water storage significantly
affects the hydrology in every part of the
river system and all of the snake’s range.
Most of the surface water storage in
reservoirs is for municipal use, while
groundwater pumping serves most
agricultural irrigation needs. To assess
the changes in stream flow conditions
over time that have already occurred,
we reviewed the flow data derived from
stream flow gauges within the snake’s
range.
The USGS operates many stream
gauges that monitor stream flow
conditions within the range of the
Concho water snake. Asquith and
Heitmuller (2008, pp. 1–10) analyzed
streamflow data in Texas using
statistical tools to evaluate trends over
time in low-flow discharge rates. A
review of seven mainstem stream gauges
within the range of the Concho water
snake found statistically significant
declining trends in mean streamflow
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over the period of record at six of these
seven stream gauges. They also found
significant declining trends in harmonic
mean streamflow for the period of
record at four of the seven gauges
(Asquith and Heitmuller 2008, pp. 810–
813, 846–853). The period of record
encompassed by analysis of these
gauges ranged from 39 to 100 years of
data, ending in water year 2007. The
‘‘harmonic mean streamflow’’ is a
statistic derived from daily mean
streamflow and is commonly used as a
design streamflow for contaminant load
allocations by Texas Commission on
Environmental Quality (TCEQ) to
address the effects of dilution to protect
human health and other aquatic life
forms. It is a useful statistic for
evaluation of low-flow conditions to
explain hydrologic changes resulting
from streamflow regulation, climate
change, or land-use practices (Asquith
and Heitmuller 2008, p. 2). Other
abbreviated analyses of stream flows
have also indicated substantial
historical declines (Service 2004a, pp.
35–38; Forstner et al. 2006, pp. 13–16).
Although annual precipitation in this
region varies substantially from year to
year (TWDB 2007, p. 135), an
assessment of statewide annual average
trends of precipitation and temperature
across Texas suggested no significant
changes over more than the last 100
years (TWDB 2007, pp. 299–300). This
suggests that human-induced changes in
land and water uses over the past 50 to
100 years have resulted in lesser overall
flows in the rivers of the upper Colorado
River watershed.
Asquith and Heitmuller (2008, p. 8)
also analyzed the percent of days where
the stream gauges recorded zero flow in
the river. These data are important as
they would be indicative of extreme
environmental conditions that could
cause stress to the snake or its fish prey
base. For the period of record at these
gauges, the results ranged from 0.1
percent of days with zero flow at the
stream gauge near San Angelo on the
Concho River to 9.3 percent at the
stream gauge measuring outflow from
Spence Reservoir. The outflow of
Spence Reservoir had many no-flow
days in the period of time prior to the
listing of the snake when the District
routinely did not release water from the
reservoir. Over the 10 years from 1998
to 2007, the percent of zero-flow days
ranged from none at two gauges on the
Colorado River to 25.8 percent at the
gauge on the Concho River at Paint Rock
(Asquith and Heitmuller 2008, pp. 810–
813, 846–853). These data demonstrate
that there have been considerable
periods of time in recent history where
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there has been no flow in the river
where the snakes occur. Asquith et al.
(2007b, pp. 469–473, 493–494) also
summarized the percentage of zerostream-flow days by month at USGS
gauges and found the highest proportion
of zero-stream-flow days at the seven
gauges on the Colorado River within the
snake’s range occur during the months
of July and August. For example, the
stream gauge near Ballinger (located on
the Colorado River between Spence and
Ivie Reservoirs) had 5.1 percent of zero
mean daily flow for all days from 1908
through 2003. Of the zero-flow days,
over 15 percent occurred in each of the
months of July and August, which was
more than any other months (Asquith et
al. 2007b, pp. 473). This may be a
critical period in the life history of the
snake because it is generally this time of
year when female snakes give birth to
young snakes (Werler and Dixon 2000,
p. 216).
b. Future Instream Flows
To consider the expected water
availability conditions in the foreseeable
future within the upper Colorado River
watershed, we reviewed the 2007 Texas
State Water Plan. This planning
document was developed from
information provided by local regional
water planning groups and it was
approved by the Texas Water
Development Board. It represents the
best available information to use in
forecasting the likely future water
availability and use in Texas in the year
2060 (TWDB 2007, pp. 1–10). The range
of the Concho water snake occurs in the
Texas Water Planning Region F.
Although this Region is somewhat larger
than the upper Colorado River
watershed, it is a reasonable area for us
to consider for future water conditions
in the range of the Concho water snake.
The Region encompasses the entire
upper Colorado River watershed and
projections for the larger area would not
be expected to differ greatly from the
portion within the upper Colorado River
watershed that comprises Concho
watersnake habitat.
The projections from this water plan
indicate that the overall human water
use in Region F is expected to increase
only slightly in the next 50 years. The
human population is predicted to grow
about 17 percent in the next 50 years,
from 620,000 people in 2010 to 724,000
in 2060 (TWDB 2007, p. 43). Over the
same time, the total water use in the
region is expected to increase by only
about 2 percent, from 807,453 acre-feet
used in 2010 to 825,581 acre-feet in
2060 (TWDB 2007, p. 43). Agricultural
irrigation demands are expected to
decrease by 5 percent and make up
551,774 acre-feet in 2060, while
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municipal water demands are projected
to increase 11 percent over the same
period, to 135,597 acre-feet in 2060
(TWDB 2007, p. 44). Based on these
projections, we do not foresee the threat
of losses of instream flow substantially
increasing beyond their current level in
the next 50 years. However, the
forecasting of future water conditions
within this area has high uncertainty,
largely due to the unpredictable climatic
conditions (TWDB 2007, p. 297–299).
The region is particularly susceptible to
extreme drought, where precipitation is
below average for extended periods of
time (10 years or more), as the region
experienced during the late 1990s and
early 2000s (TWDB 2006, 1–60, 1–67).
Droughts will certainly continue to
occur and produce additional
challenges to the water system of the
upper Colorado River watershed.
An additional source of uncertainty
for future instream flows is the potential
effects of global climate change on water
availability in this region. According to
the Intergovernmental Panel on Climate
Change, ‘‘Warming of the climate
system is unequivocal, as is now
evident from observations of increases
in global average air and ocean
temperatures, widespread melting of
snow and ice, and rising global average
sea level’’ (IPCC 2007, p. 1). Average
Northern Hemisphere temperatures
during the second half of the 20th
century were very likely higher than
during any other 50-year period in the
last 500 years and likely the highest in
at least the past 1300 years (IPCC 2007,
p. 1). It is very likely that over the past
50 years cold days, cold nights and
frosts have become less frequent over
most land areas, and hot days and hot
nights have become more frequent (IPCC
2007, p. 1). Data suggest that heat waves
are occurring more often over most land
areas, and the frequency of heavy
precipitation events has increased over
most areas (IPCC 2007, p. 1).
The IPCC (2007, p. 6) predicts that
changes in the global climate system
during the 21st century are very likely
to be larger than those observed during
the 20th century. For the next two
decades a warming of about 0.2 °C (0.4
°F) per decade is projected (IPCC 2007,
p. 6). Afterwards, temperature
projections increasingly depend on
specific emission scenarios (IPCC 2007,
p. 6). Various emissions scenarios
suggest that, by the end of the 21st
century, average global temperatures are
expected to increase 0.6 °C to 4.0 °C (1.1
°F to 7.2 °F) with the greatest warming
expected over land (IPCC 2007, p. 6–8).
Localized projections suggest the
Southwest may experience the greatest
temperature increase of any area in the
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lower 48 States (IPCC 2007, p. 8), with
warming in southwestern States greatest
in the summer. The IPCC also predicts
hot extremes, heat waves, and heavy
precipitation will increase in frequency,
resulting in high intensity and
variability of precipitation that increases
flooding events and long periods of
drought (IPCC 2007, p. 8). Modeling
efforts evaluating climate change in this
region of Texas have only recently been
initiated (CH2M HILL 2008; Jackson
2008; Mace and Wade 2008; TWDB
2008). As with many areas of North
America, this area (central and western
Texas) is projected to experience an
overall warming trend in the range of
2.5–3.9 °C (4.5–6 °F) over the next 50 to
200 years (IPCC 2007, p. 9; CH2M HILL
2008, p. 6–3; Mace and Wade 2008, p.
656). The IPCC (2007, p. 8) states there
is high confidence that semi-arid areas,
like the western United States, will
suffer a decrease in water resources by
mid-century due to climate change.
Although more local precipitation
models vary substantially, with some
even predicting increased annual
precipitation, a consensus is emerging
that evaporation rates in central and
western Texas are likely to increase
significantly (Jackson 2008, p. 21; CH2M
HILL 2008, p. 7–30, 7–31). Many models
are also predicting that seasonal
variability in flow rates is likely to
increase with more precipitation
occurring in the wet seasons and more
extended dry periods (CH2M HILL
2008, p. 7–30; Jackson 2008, p. 19; Mace
and Wade 2008, p. 656).
An evaluation of the hydrological
impacts of climate change on the annual
runoff and its seasonality in the upper
Colorado River watershed was
conducted by CH2M HILL (2008). Four
modeling scenarios (chosen to represent
a range of possible future climatic
conditions) were each run under a 2050
and 2080 time scenario producing
annual runoff estimates at 6 sites in this
watershed. For the 2050 scenarios, the
results from all 4 scenarios predicted
declines in annual runoff at all 6 gauges
ranging from 11 to 44 percent. Annual
runoff at the stream gauge on the
Colorado River at Ballinger, for
example, was predicted to decline by 19
to 38 percent (CH2M HILL 2008, pp. A–
1–A–4). For the 2080 scenarios, one
model predicted increases in annual
runoff ranging from 41 to 90 percent.
The other three 2080 scenarios
predicted declines in annual runoff
ranging from 9 to 65 percent at 6 gauges.
Annual runoff at the stream gauge at
Ballinger was predicted to decline by 25
to 40 percent (CH2M HILL 2008, pp. A–
1–A–4). However, the modeling efforts
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from this study focus on annual
averages and do not account for the
flooding events or long periods of
drought. It is these specific extreme
events that are important for
maintaining habitat for the snake, and
they cannot be reliably based on historic
patterns upon which this study was
predicated.
In addition, all climate change
modeling has inherently large
uncertainties due to the incorporation of
many variables that are difficult, if not
impossible, to accurately predict (CH2M
HILL 2008, p. ES–1; Jackson 2008, p.
20). As an example, the Texas State
Water Plan considered future global
climate change to be a challenge for
water availability forecasting in 2060.
However, the uncertainties associated
with climate change were very large in
comparison with other uncertainties,
such as those associated with
population growth and water demand.
As a result, the State did not believe that
climate change concerns warranted
specific planning measures at the time
(TWDB 2007, p. 299). However,
expected future warming from climate
change could significantly increase
potential evaporation rates in the region,
in combination with expected reduced
precipitation and extended droughts in
western Texas.
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c. Maintenance of Instream Flows
Efforts to minimize the potential
impacts of reduced instream flows by
securing minimum flow releases from
the Colorado River reservoirs began
with the 1986 BO. It included measures
for the District to maintain certain flow
conditions downstream of both Spence
and Ivie Reservoirs (Service 1986, pp.
14–19) for the benefit of the snake and
its habitat. These two reaches represent
an estimated 57 percent of all snake
habitat available and 69 percent of
available high-quality habitat (Service
2004a, p. 70). These minimum reservoir
releases were maintained by the District
until 2004 (Service 2004a, pp. 43, 45)
when the Service revised the 1986 BO
and reduced the required flow rates
from both reservoirs (Service 2004a, pp.
11–13). The analysis in the 2004 BO
included updated biological information
that the snakes use more diverse
riverine habitats (such as pools, in
addition to riffles) and were found in
the reservoirs and tributaries (Dixon
2004, pp. 9, 16; Service 2004a, pp. 53–
54). As a result of that consultation we
gave our biological opinion that the
reduced reservoir releases described in
the proposed agency action were not
likely to jeopardize the continued
existence of the Concho water snake and
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were not likely to destroy or adversely
modify designated critical habitat.
The Service determined that lower
minimum flow rates were sufficient to
maintain the habitat and populations of
the Concho water snake (Service 2004a,
pp. 53–54). The District will, to the
extent there is inflow into Spence
Reservoir, maintain a minimum flow in
the Colorado River downstream of not
less than 4.0 cubic feet per second (cfs)
(0.11 cubic meters per second (cms))
during April through September and 1.5
cfs (0.04 cms) during October through
March. To the extent there is inflow into
Ivie Reservoir, the District will maintain
a minimum flow in the Colorado River
downstream of Ivie Reservoir of not less
than 8.0 cfs (0.23 cms) during the
months of April through September and
2.5 cfs (0.07 cms) during the months of
October through March (Service 2004,
pp. 11–12). The expectation for the
District to implement the 2008 MOU
and the expected extent of low-flow
conditions are addressed in detail in
discussions below.
When the Concho water snake is
delisted, the minimum flow
requirements required by the 2004 BO
will no longer apply. However, the
purpose of the 2008 MOU is for the
District to provide assurance that
minimum reservoir releases will
continue in perpetuity, consistent with
the 2004 Biological Opinion (BO,
Service 2004a, pp. 11–12). The releases
are the same as those required in the
2004 BO, and the District has agreed to
maintain these flows, to the extent there
is inflow, when the Concho water snake
is removed from the Federal list of
threatened species. The 2008 MOU
acknowledges the Service’s ability to
add the Concho water snake back to the
list of protected wildlife, even under
emergency listing provisions, if future
conditions warrant.
We have confidence that the District
will implement the MOU in good faith
after the Concho water snake is removed
from the threatened list. The District has
implemented every activity requested
by the Service in previous biological
opinions beginning in 1986 (Service
2004a, p. 42–47). The minimum flows
required in the 2004 BO have been
implemented by the District, and those
flow requirements were duplicated in
the 2008 MOU. The District has an
excellent track record of carrying out
conservation actions to benefit the
Concho water snake (Freese and Nichols
2006, pp. 6.1–6.13). In addition, the
post-delisting monitoring plan for the
Concho water snake includes
monitoring of instream flows to monitor
stream conditions and verify that flows
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called for in the 2008 MOU are being
realized.
The District has maintained flows
from both Spence and Ivie Reservoirs.
This is demonstrated by measures of the
daily median flow at two gauges
downstream of the reservoirs. Daily
median flows (i.e., the number where
half the recorded flows are higher and
half are lower within a given day of
records) provide a better assessment for
this purpose than the daily mean flow,
which would be skewed higher due to
very short-term high-flow flood events.
Daily median flows (calculated for each
calendar day from the mean daily
discharges for the time period
referenced) in the reach of the Colorado
River below Spence Reservoir (as
measured at the USGS gauge near
Ballinger since Spence Reservoir was
constructed, 1969–2007) exceeded 4.0
cfs (0.11 cms) in the summer (April
through September) all but 12 days out
of a total of 183 days. During the winter
(October through March), daily median
flows always exceeded 1.5 cfs (0.04
cms). Daily median flows in the reach
of the Colorado River below Ivie
Reservoir (as measured at the USGS
gauge at Winchell since Ivie Reservoir
was constructed, 1990–2007) exceeded
8.0 cfs (0.23 cms) in the summer (April
through September) all but 15 days out
of a total of 183 days. During the winter
(October through March), daily median
flows always exceeded 2.5 cfs (0.07
cms). Based on these past actions, we
believe that the District will continue to
maintain instream flows in the
foreseeable future.
The 2008 MOU allows the District to
reduce or discontinue minimum flow
releases below either reservoir based on
inflow or when water storage in that
reservoir falls below about 12 percent of
capacity. Since Spence Reservoir was
initially filled in 1971, the water level
elevation has only been below this mark
during the period from 2002 to 2004, at
the end of a prolonged drought from
1992 to 2003 (District 2005, pp. 39–43).
Ivie Reservoir has not been below this
mark since it initially filled in 1991
(District 2008, pp. 1–2). Based on the
historic record and the foreseeable
future of about 50 years, we would
expect these conditions to occur
infrequently. Using data from Spence
Reservoir where this storage level has
occurred, it has happened less than 10
percent of the time since 1971 (3 years
out of 37 years of operation).
We also anticipate that small amounts
of water and minimal stream flows will
still be present at most times of the year
in the gaining reaches of the Colorado
River and below Spence and Ivie
Reservoirs due to dam leakage and
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seepage, contributing inflow from creeks
and sub drainages, and discharges from
springs where shallow groundwater
interfaces with the stream (Dixon 2004,
p. 9). The gaining nature of the river
reach downstream of Spence Reservoir
is particularly evident as both the
annual mean flow and harmonic mean
streamflow increased between the
stream gauge measuring outflow of the
reservoir and the gauge at Ballinger,
some 50 mi (80 km) downstream
(Asquith and Heitmuller 2008, pp. 810–
813). This gaining stream trend is
greatly controlled by ambient weather
conditions. For example, during periods
of long-term drought (more than 10
years), the tributaries and springs will
cease flowing or have significantly
lower flow. However, during average
rainfall periods, these sources of water
help to restore and maintain more stable
instream flows in the main rivers
(Service 2004a, p. 50). Additionally,
even when releases from dams have
ceased, normal seepage from a dam
occurs and provides for the formation of
pools (large and small) that can provide
habitat for the Concho water snake and
the fish it preys upon for varying
periods of time. When dam releases are
resumed, the pools (located upstream of
low-head dams and up and downstream
from spring areas) that may have served
as refuge habitat are reconnected by
flowing water (Dixon 2004, p. 16).
Texas water law requirements also
result in maintenance of some instream
flow. Texas observes traditional
appropriative water rights, which is also
known as the ‘‘first in time, first in
right’’ rule (see Texas Water Code
§ 11.027). The State’s water policy
requires the TCEQ to set, to the extent
practicable, minimum instream flows to
protect the State’s water quality when
issuing water rights permits (see Texas
Water Code § 11.0235(c)). Furthermore,
Texas water law prohibits the owner of
stored water from interfering with water
rights holders downstream or releasing
water that will degrade the water
flowing through the stream or stored
downstream (Texas Water Code
§ 297.93). The District’s 1985 water
rights permit associated with Ivie
Reservoir (TCEQ 1985, Permit #3676, p.
4) requires the District to maintain
minimum flows below Ivie Reservoir of
8 cfs (0.23 cms) from April through
September and 2.5 cfs (0.07 cms) from
October through March (consistent with
flows called for in the 2008 MOU).
Flows are often also provided
downstream of both Spence and Ivie
Reservoirs to ensure water quality and
provide for downstream water rights.
Releases from Spence Reservoir are
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periodically made to improve the
quality of water entering Ivie Reservoir.
Spence Reservoir is known to be high in
dissolved solids and chlorides (District
2005, pp. 24–27), so if flows into Spence
Reservoir are low, water quality in the
reservoir can become degraded unless
high volumes of water are released.
Therefore, long-term low-flow releases
or no releases from Spence and Ivie
Reservoirs are rare unless an emergency
situation occurs.
d. Response of Species to Reduced
Instream Flows
We considered the potential impacts
on the Concho water snake of reduction
of instream flows from water
management actions. We also
considered the effects of short-term
large-magnitude instream flow declines
resulting from droughts that are
expected to occur in some frequency
over the next 50 years in the foreseeable
future. In summary, we found that the
best available information from
numerous ecological studies by snake
experts supports the conclusion that the
species is well adapted to endure the
occasional conditions of extreme low
flows or periodic cessation of flows.
There are no specific studies that have
evaluated the effects of declining
instream flows on the snake’s habitat or
populations. However, we can assume
that the linear extent of dewatered
riverine habitats during extended
drought periods could be quite large and
the length of time without flows could
extend for several months or more
(Service 2004a, p. 51). These habitat
modifications could impact the snake by
decreasing reproductive success during
the summer months, reducing the
snake’s fish prey base, or reducing overwinter survival during their hibernation
period.
Recent monitoring studies have
provided observations that suggest
Concho water snakes have the ability to
survive extreme low-flow periods. For
example, Elm Creek had experienced a
number of extended no-flow periods
over several years prior to 2004 and
then flooded in August 2004. A review
of the flow data from the USGS stream
gauge on Elm Creek near Ballinger
found 44 percent of all days between
January 2000 and July 2004 recorded no
discharge. In September 2004, Dixon
(2004, p. 11) noted Concho water snakes
inhabited the site. Dixon (2004, p. 12)
surmised that snakes either moved from
the mouth of Elm Creek at the Colorado
River (a distance of 4.6 mi (7.4 km)), or
existed in deep pools somewhere within
a returnable distance to the site.
Another example of snake persistence
during dry times was the drying of
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Ballinger Lake in 2004 and confirmation
of reproductive snakes in the lake in
2005 following rains (Dixon 2004, p. 4;
Forstner et al. 2006, p. 15; Whiting et al.
2008, p. 443).
The best demonstration of the Concho
water snake’s endurance of low-flow
conditions is found in the Concho River.
Two large dams on the Concho River
just upstream of the City of San Angelo
capture essentially the entire upper
Concho River watershed. There have
never been minimum flows purposely
provided for the snake in the Concho
River. This has resulted in extreme low
flows in the downstream reaches. We
presume the low flows are maintained
from small gains from groundwater
discharge or return flows (Dixon 2004,
pp. 8–9). Since 1916, the annual mean
streamflow at the flow gauge at Paint
Rock on the Concho River has declined
from 136 cfs (3.85 cms) for the 92-year
period of record down to 24.8 cfs (0.7
cms) for the recent 10 years from 1998
through 2007. The harmonic mean
streamflow at this gauge has declined
from 1.0 cfs (0.03 cms) for the period of
record to 0.3 cfs (0.01 cms) for the
recent 10 years (Asquith and Heitmuller
2008, pp. 849–850). Over the same time
periods the gauge has recorded zero
flow for 8 percent of the days for the
period of record and 25 percent of the
days from the recent 10 years (Asquith
and Heitmuller 2008, pp. 849–850).
These flow data represent extreme lowflow conditions resulting from longterm human water use and recent shortterm drought and have been
accompanied by degradation of habitat
by silting in of the stream and
encroachment of vegetation (Dixon
2004, pp. 8–9). Despite this apparent
long-term habitat modification, the
snake continues to persist in this reach,
and Forstner et al. (2006, p. 8) found the
highest numbers of Concho water
snakes (20 of all 45 snakes captured or
observed during their brief surveys) in
this reach of the Concho River.
The mechanism for persistence in
these conditions of long periods of
drought, according to Dixon (2004, p. 9),
is the ability of the snakes to use pools
of water that form upstream of low-head
dams (small private dams, a few feet
tall, that create pools upstream and
riffle-like areas downstream). Within
both the Concho and Colorado Rivers,
these pools can extend two-thirds of a
mile (1 km) or more up river (depending
on dam height). The riffles and pools
that lie upstream of these low-head
dams may not completely dry up
because of small springs and creeks
nearby. These pools act as refuges for
juvenile and adult Concho water snakes
when measurable flow ceases (Dixon
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2004, p. 9). Concho water snakes have
been located in pools behind low-head
dams along the Colorado River, and
Dixon (2004, p. 9) states that it is
reasonable to expect the small pools
behind low-head dams on the Concho
River to act in the same way. Also, even
during drought, water continues to flow
over bedrock in some areas, and snakes
have been observed foraging for fish in
the diminished flow. The extent of solid
bedrock in some of the riffle systems
tends to maintain the nature of the riffle
and does not allow vegetation to root
and collect debris and silt (Dixon 2004,
p. 9).
Another way the snakes may endure
drying conditions is to use deep
burrows for over-winter hibernacula
(shelters for hibernating snakes). Greene
(1993, pp. 89, 94) found Concho water
snake hibernacula within 19.7 ft (6 m)
of water with a mean depth of 1.7 ft
(0.52 m). Hibernacula types included
crayfish burrows, rock ledges, debris
piles, and cracks in concrete of low
water crossings for adults and loose
embankments of rock and soil for
juveniles. Dixon (2006, p. 2) stated that
during droughts the snakes were
possibly in the crayfish burrows, since
they may retain moisture longer.
Lack of forage fishes available for prey
by the snakes is another reason that
drought and resulting decreasing flows
could impact Concho water snakes. Fish
are the principal food of the Concho
water snake (Williams 1969, pp. 9–10;
Dixon et al. 1988, p. 16; 1989, p. 8;
1990, p. 36; 1992, p. 6; Thornton 1990,
p. 14; Greene et al. 1994, p. 167). At the
time of listing, we believed that
declining flows, inundation, pollution,
and other habitat threats would have
adverse impacts on riffle-dwelling fish
(51 FR 31419). However, the snakes are
not species-specific and have been
shown to take advantage of whatever
small-bodied species is most abundant.
A review of the 10 years of fish surveys
by the District from 1987 to 1996
showed that the snakes were
opportunistic predators on a variety of
fish species (Thorton 1992, pp. 16–34;
Service 2004a, pp. 68–69). The most
abundant fish available and in the snake
diet are fish species that are adapted to
harsh stream conditions (intermittent
flow and poor water quality), such as
red shiners (Burkhead and Huge 2002,
p. 1) and fathead minnows (Sublette et
al. 1990, pp. 162–166). Together these
two fishes made up two-thirds of the
diet of the Concho water snakes.
Because of their ability to withstand
harsh stream conditions, we expect
these fish species to persist in the
harshest environments, and they can
recolonize stream reaches after
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dewatered conditions end. In addition,
information indicates the snake is able
to survive in captivity for up to 12
months with a reduced food supply
(Dixon 2006, p. 2). This suggests that the
snakes can endure a short-term absence
of food resources when forage fish are
scarce. The periodic loss of stream flows
due to drought will impact fish
availability in the river, but the snakes
are adaptable to prey upon whatever
fish species survives the low flows or
survive without food for short periods.
e. Summary of Habitat Modification
From Reduced Instream Flows
In conclusion, we expect extreme
low-flow and drying river conditions to
occur only rarely within most of the
range of the snake. However, when
extreme drought (10 years or more of
below-average annual precipitation)
does occur, the snake is adapted to
withstand harsh conditions. Species
experts are confident that the Concho
water snake has evolved and adapted for
thousands of years through many
documented extreme droughts (Forstner
et al. 2006, pp. 17–19). Forstner et al.
(2006, pp. 16, 20) indicate that, despite
the inevitable impacts and future
stressors on this taxon by anthropogenic
and natural cycles, the snake has
persisted in an environment for the past
several millennia that has seen
‘‘frighteningly intense periods of
drought.’’ The Concho water snake has
survived historically under extreme
drought and low-flow conditions
(Forstner et al. 2006, p. 22). Climate
change could alter the overall water
availability and seasonality of flows in
the range of the snake, but the
uncertainties associated with forecasting
the effects of climate change and where
they will occur are so great, relative to
the threats of population growth and
water demand, that the State did not
believe that it warranted planning
efforts. Because of the high uncertainty
on the effects of climate change, we
cannot reliably predict if river
conditions in the foreseeable future will
be significantly worse than historical
conditions. Thus, we find that the threat
of habitat modification from the
reduction of instream flows caused by
reservoir operations and drought is not
likely to endanger the Concho water
snake in the foreseeable future.
Habitat Modification From Reduced
Channel Maintenance Flows
At the time of listing, we were
concerned that the construction of Ivie
Reservoir would prevent floodwater
scouring by large flows that serve to
maintain natural river conditions.
Channel scouring occurs when flood
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waters transport silt and fine materials
downstream and displace encroaching
vegetation from the river channel. In
other words, large flood events serve to
physically displace vegetation growing
in the silt and sand along the banks
within the stream channel. These
channel maintenance flows are
important to remove the fine substrates
and vegetation and maintain the riffles,
gravel bars, and rocky stream bank
habitats often used by the snakes as
foraging habitat. Without such flooding,
riffle habitat is modified as the rocky
streambed becomes covered with silt
and vegetation becomes established and
armors the stream bank. Riffle habitat
creates sites for reproduction and
habitat for small fish that young snakes
prey upon. Although in some reaches,
such as some sites on the Concho River,
the dominant substrate is solid bedrock,
and the cracks and breaks in the rock
serve the same purpose as riffles as a
place for snakes to feed (Dixon 2004, p.
9).
Asquith et al. (2007a, pp. 469–473,
491–494) analyzed trends over time for
the annual maximum streamflow and
found statistically significant declining
trends in flow during the period of
record at six of the seven gauges on the
Concho and Colorado Rivers within the
range of the Concho water snake. Also,
review of the hydrograph of the daily
stream flow data for the period of record
at these seven stream gauges shows a
decline in the frequency and duration of
high-flow events (Asquith and
Heitmuller 2008, pp. 810–813, 846–
853).
However, some high flows continue to
occur naturally even during recent
drought periods. For example, over the
10 years from 1999 to 2008 the USGS
stream gauge on the Colorado River near
Ballinger, downstream of Spence
Reservoir, recorded streamflow events
of over 1,000 cfs (28 cms) in 6 of the 10
years and had a peak flow of over 9,500
cfs (270 cms) in June of 2000 (USGS
2008). For the same time period at the
gauge at Winchell, downstream of Ivie
Reservoir, 9 years had flow events
exceeding 1,000 cfs (28 cms) with a
peak flow of 16,500 cfs (470 cms) in July
2002 (USGS 2008). The gauge at Paint
Rock, on the Concho River, also had
streamflow events exceeding 1,000 cfs
(28 cms) for 9 of the 10 years with a
peak flow of over 5,000 cfs (140 cms) in
November 2004 (USGS 2008). In
addition, the 2008 MOU with the
District calls for periodic high rates of
discharges to manage water quality in
the reservoirs. These releases could be
coupled with flood runoff events and
may function as channel maintenance
flows. We have no reliable means to
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reasonably forecast the frequency and
occurrence of future high flows in the
river. However, some global climate
change models are indicating a possible
future trend of more precipitation
occurring during wet seasons (Mace and
Wade 2008, p. 656), although there is
substantial uncertainty with future
predictions. If this occurs over the next
50 years, it could increase the number
and magnitude of high discharge events
that would serve as channel
maintenance flows in the range of the
Concho water snake.
One consequence of reduced flushing
flows is the increase in abundance of
salt cedar (Tamarisk sp.), a nonnative
species of tree that was introduced to
the United States in the 1800s from
southern Europe or the eastern
Mediterranean region (DiTomaso 1998,
p. 326). In the watersheds of Spence and
Ivie Reservoirs, these plants are
abundant and have been reported to
have affected water quality and quantity
because they consume large volumes of
water and then transport salts from the
water to the surfaces of their leaves.
When the leaves are dropped in the fall,
the salt is concentrated at the soil
surface (DiTomaso 1998, p. 334; Freese
and Nichols 2006, p. 5.5). The lack of
flushing flows in the rivers allows these
invasive plants to become established in
the fine substrates along the banks and
eventually reduce the amount of gravel
and rocky stream substrates.
In an effort to increase water yield
and reduce salt concentrations in
Spence and Ivie Reservoirs, the District,
in cooperation with the Texas
Cooperative Extension Service, the
Texas Department of Agriculture, the
U.S. Department of AgricultureAgricultural Research Service, and the
Texas State Soil and Water Conservation
Board (TSSWCB), has initiated a salt
cedar control project in the Upper
Colorado River Basin. The program
includes spraying an herbicide to
eradicate mass concentrations of salt
cedar and then using a leaf beetle for
biological control of new plant growth
(Freese and Nichols 2006, p. 6.4).
According to Freese and Nichols (2006,
pp. 6.5–6.6), this project ‘‘is an excellent
first step in the recovery of the Upper
Colorado River Basin back to many of its
[pre-infestation] functions, including
native riparian habitat for wildlife and
improved habitat for fish and other
aquatic organisms,’’ and is ‘‘one of the
most crucial options for improving
water quality and quantity.’’ We have no
information that the herbicide to be
used (Arsenal) poses a direct poisoning
threat to the Concho water snake and a
previous section 7 consultation found
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only beneficial effects to the species
(Service 2004b, p. 39).
Additionally, control programs for
invasive brush species, such as juniper
(Juniperus sp.) and mesquite (Prosopis
sp.), are also being implemented in the
Concho and Upper Colorado River
Basins to increase water quantity
(TSSWCB 2004, pp. 2–3; Freese and
Nichols 2006, p. 6.6). The TSSWCB is
focusing above O.C. Fisher and Twin
Buttes Reservoirs upstream of San
Angelo on the Concho River and over
175,000 acres (70,820 hectares) of
invasive brush have been treated in
these watersheds (TSSWCB 2004, pp. 2–
3). The removal and control of salt cedar
and other invasive brush from the
riparian reaches of the Colorado and
Concho Rivers helps augment existing
stream discharge and also reduces
buildup of dissolved solids (salts) in the
soils of the riparian zone (Service 2004a,
p. 56). Additionally, this removal
encourages reformation of riffle areas,
increases stream flow, and reduces
sediment deposition, which improves
instream habitat for the Concho water
snake and other aquatic species (Freese
and Nichols 2006, p. 6.6).
While both Dixon (2004, pp. 8–9) and
Forstner et al. (2006, pp. 12, 15)
document degradation of riffles from
siltation, there are still numerous riffles
throughout the range continuing to
support Concho water snakes (Dixon
2004, pp. 5–8). In their recent survey of
the Concho water snake and its habitat,
Forstner et al. (2006, pp. 14, 16) found
that the lack of flushing flows has
allowed silt to settle and cover many of
the riffles at historically occupied sites
and that several sites have changed from
riffles to slow-flowing sandy sections of
river. Sand and silt fill in graveled
cobble substrate and provide areas for
growth of salt cedar and other
vegetation, which further eliminates the
rocky-bottomed riffle areas required by
Concho water snakes (51 FR 31419;
Scott and Fitzgerald 1985, p. 13;
Forstner et al. 2006, p. 15). These
changes are particularly evident at sites
on the Concho River (Dixon 2004, p. 9).
However, despite some riffle habitat loss
and the presence of other system
stressors, Forstner et al. (2006, p. 18)
noted that the Concho water snake
persisted and continued to reproduce at
the majority of the sites they visited. In
fact, the Concho River, where
degradation has been most evident,
contained the largest number of Concho
water snakes captured by Forstner et al.
(2006, p. 8).
Dixon (2004, p. 9) indicated that
changes in the Concho River where the
lack of flushing flow has allowed the
accumulation of vegetation and debris
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likely caused the adult and juvenile
snakes to retreat to refuge habitats in
nearby pools and to areas where water
flows over bedrock. Although some
changes have occurred in the riverine
habitat as a result of the loss of channel
maintenance flows over time, the snakes
appear to be adaptable to using other
habitats and maintaining populations
despite these changes. Therefore, we
find that the threats associated with
habitat modification from the reduction
of frequency and magnitude of highdischarge channel-maintenance flows
are not likely to endanger the Concho
water snake in the foreseeable future.
Habitat Modification From
Fragmentation
At the time of listing, we believed
construction of Ivie Reservoir (Freese
Dam) would likely segment Concho
water snakes into three separate
populations and thereby reduce genetic
exchange (Scott and Fitzgerald 1985, p.
34). Prior to the snake’s listing in 1986,
no researchers had documented Concho
water snakes traveling over land to
circumvent the barriers caused by large
dams, and snakes had not been located
in reservoirs. Due to this separation, a
reasonable and prudent measure in the
1986 BO was to transfer snakes annually
between the river reaches separated by
the dam. In 1995, four male snakes were
moved from below Ivie Reservoir to
river habitats above the Reservoir
(District 199, p. 1). In 2006, five adult
male snakes and one adult female snake
were captured below Ivie Reservoir and
released in the Concho River upstream
of Ivie Reservoir (District 2006, pp. 1–
2). Also in 2006, three male snakes and
one female snake were transferred from
the Concho River to Spence Reservoir
(District 2006, pp. 3–4).
Because we now know Ivie Reservoir,
which receives flow from both the
Concho and Colorado Rivers, is
occupied by the snake, we believe it is
reasonable to surmise that snakes are
capable of genetic interchange between
the Concho and Colorado Rivers via the
reservoir’s shoreline. The District (1998,
p. 14) summarized Concho water snake
habitat within Ivie Reservoir and found
that although the habitat is not linearly
consistent, it does occur throughout the
reservoir. Concho water snakes have
been documented in mark-recapture
studies to move up to 12 mi (19 km)
(Werler and Dixon 2000, p. 212). Based
on the occupancy of reservoirs by the
snakes and the ability to move large
distances, we have a high level of
confidence that gene flow occurs
between these river reaches.
In 2005 surveys, Forstner et al. 2006
(pp. 10–13, 18) found that Concho water
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snakes were reproducing in the Concho
and Colorado Rivers above Ivie
Reservoir and in the Colorado River
below it; they concluded that the
populations in those three river reaches
were self sustaining and seemingly
viable (Forstner et al. 2006, pp. 16–18,
20). The 2008 MOU, as amended in
2011 and described above, Article 4.1
also provides that, in the springtime at
3-year intervals, the District, in
coordination with the Service, should
move five male snakes from below
Spence and Freese dams to above these
dams and move five different male
snakes from above to below both dams.
Moving snakes will be dependent upon
availability of funding for the District. If
the District is unable to carry out the
snake movements, the Service will work
with TPWD or other partners to ensure
it occurs. We believe this movement
will benefit the snake by enhancing
genetic exchange between the three
river reaches. The periodic movement of
five snakes is believed to be sufficient
to mimic natural gene flow (Sites and
Densmore 1991, pp. 10–11) and reduce
potential effects of genetic isolation
among separated populations. This level
of exchange exceeds the rule-of-thumb
minimum of one individual exchanged
with each generation (Mills and
Allendorf 1996, p. 1,557). Should
funding be unavailable in any particular
snake-moving year, every effort will be
made to move snakes in the succeeding
year.
Based on the available information,
we do not believe the species is likely
to become endangered in the foreseeable
future due to genetic isolation or habitat
fragmentation.
Habitat Modification From Pollution
and Water Quality Degradation
At the time of listing, we believed
buildup of algae in riffle areas reduced
oxygen and nutrients available to
populations of fish, the Concho water
snake’s primary food (51 FR 31419). We
were also concerned that the inflow of
nutrients into the Concho River in the
San Angelo area, along with reduced
dilution capability associated with
lower flows, created large
concentrations of algae in portions of
the river (51 FR 31419). A summary of
the 1987–1996 fish surveys in the
Colorado and Concho rivers, included
in the Service’s 2004 BO (Service 2004a,
Appendix A, pp. 68–69), suggested that
fish populations have persisted despite
the presence of algae. Also, no impacts
to snakes have been observed or
documented as a result of water quality
conditions during the ongoing drought
(Service 2004a, p. 52). We have no
further indication that algae buildup has
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occurred or has impacted the snake or
its prey base. Therefore, we no longer
consider algal growth and nutrient
enrichment to be significant threats to
the snake’s survival.
The Texas State Legislature
implemented the Texas Clean Rivers
program in 1991. The District has
actively participated in the program
since that time and monitors surface
water quality in the upper Colorado
River basin, which includes the
distribution of the Concho water snake
above Freese Dam (District 2005, p. 28).
The LCRA has the responsibility for
water quality monitoring below Freese
Dam. Both of these entities have
participated in the Clean Rivers Program
since 1991 and have provided a
proactive response for ensuring a high
level of surface water quality in the
Colorado River and its main stem
reservoirs (LCRA et al. 2007, pp. 3–4).
These programs (including routine
chemical and biological monitoring,
environmental education, oil field clean
up, superfund site cleanup, and well
plugging) are ongoing and designed to
ensure water quality integrity for all
aquatic resources, including the Concho
water snake and fish, its primary food
source, in the upper basin (LCRA et al.
2007, pp. 13–15, 22, 28, 33–34). As
water quality problems (biological or
chemical) are detected, swift responses
by the District and LCRA to affect
corrective actions through State of Texas
regulatory agencies (TCEQ and the
Texas Railroad Commission) are
completed (Service 2004a, pp. 52–53).
Additional water quality protections
for Concho water snakes in riverine and
reservoir habitats will continue
indirectly under the Clean Water Act
(CWA). According to the U.S.
Environmental Protection Agency (2006,
p. 1), the CWA establishes basic
structures for regulating discharges of
pollutants into United States waters,
protecting water quality for species
dependent on rivers and streams for
their survival. Discharges are controlled
through permits issued by TCEQ; within
the range of the Concho water snake,
these permits are mainly to small towns.
With human population growth in the
region forecasted at relatively small
rates (estimated 17 percent increase)
over the next 50 years (TWDB 2007, p.
43), we do not predict any significant
increase in this threat in the foreseeable
future.
Based on the lack of information
documenting effects of pollution or
water quality degradation on snake
populations and the ongoing efforts of
water agencies to monitor and maintain
healthy water quality, we find that the
pollution and water quality degradation
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is not a significant threat to the Concho
water snake.
Summary of Factor A Threats
The Concho water snake was listed in
1986 largely due to threats to its habitat
from the potential for habitat
modification resulting from the
construction and operation of reservoirs
within its range. Since the listing, the
snake has been shown to be more
abundant and widespread than
originally thought and capable of
surviving in reservoirs (District 1998,
pp. 18–29). Reservoir operations have
provided continual stream flows that
have sustained the habitat for the
species, even during an extreme
drought, and we expect minimum
reservoir releases to continue into the
foreseeable future. In addition, the
snake has been shown to be equipped to
handle stochastic environmental
fluctuations, such as low stream-flow
conditions, and has demonstrated the
ability to persist even when habitat
conditions appear to be less than
favorable (from reservoir inundation,
low river flows, or silting in of riffles)
(Forstner et al. 2006, pp. 13–18; Whiting
et al. 2008, p. 443). Additionally, habitat
restoration efforts such as the removal of
salt cedar and other brushy species and
the creation of artificial instream riffle
structures are aimed at improving
habitat for the Concho water snake and
other aquatic species. Other potential
threats to snake habitat from reduced
flushing flows, fragmentation, and
pollution and water quality degradation
have not been found to occur at the
level anticipated when the species was
listed in 1986, and no impacts to the
Concho water snakes have been
documented.
Therefore, we believe that
destruction, modification, or
curtailment of the Concho water snake
habitat or range due to habitat loss,
altered instream flows and floodwater
scouring, drought, vegetation
encroachment, fragmentation, and
pollution no longer threaten the Concho
water snake with becoming endangered
in the foreseeable future of about 50
years.
B. Overutilization for Commercial,
Recreational, Scientific, or Educational
Purposes
At the time of listing, Concho water
snakes were known to sometimes be
captured or killed by recreationists (51
FR 31420). The effect of this activity on
Concho water snake populations was
and still is believed to be minimal.
However, instances of Concho and
Brazos (a closely related species
occurring in an adjacent drainage) water
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snakes being killed have been reported
in both populated and unpopulated
areas (Werler and Dixon 2000, p. 215).
For example, Brazos water snakes have
been crushed under stones at the water’s
edge by people walking on the banks
and snakes have been shot by small
caliber firearms. Concho water snakes
may be confused with poisonous
species of snakes. Fishermen have
commented on their success in
removing the ‘‘water moccasins’’ from
the river (Forstner et al. 2006, pp. 18–
19). At one of the historically most
productive localities for Brazos water
snakes, Forstner et al. (2006, p. 18)
found no snakes in two years of
searching. They noted dozens to
hundreds of campers at the site each
year. According to Dixon (2004, p. 2),
there is not as much recreation
occurring on the Concho and Colorado
rivers, where the Concho water snake
occurs, as there is on the Brazos River.
The vast majority of the range of the
Concho water snake occurs in remote,
rural locations with very limited human
access or use of the river. This fact
suggests there is limited opportunity for
direct mortality by humans. Even in
areas with high recreational use, such as
Paint Rock Park (a city park on the
Concho River) the snake was still
collected there in relatively large
numbers in 2005 (Forstner et al. 2006,
p. 8). We are unaware of any plans to
increase recreational opportunities on
the Colorado and Concho Rivers.
Therefore, we believe that impacts from
recreationists will continue to be
minimal in the foreseeable future in the
areas occupied by Concho water snakes.
While some limited killing of snakes
is likely still occurring, there is no
indication that any possible mortalities
are affecting the species population
levels, either rangewide or locally.
Werler and Dixon (2000, p. 215) stated
that malicious destruction of Concho
water snakes ‘‘probably does not
constitute a major cause of mortality.’’
We also have no reason to believe that
this threat is likely to increase in the
future.
Therefore, we find that mortality from
this factor is not likely to cause the
species to become threatened or
endangered in the foreseeable future.
C. Disease or Predation
At the time of listing, no problems of
disease or predation on Concho water
snakes were known to exist (51 FR
31420). While currently no disease
problems are known, predators on
Concho water snakes have been
identified. As is true for most snakes,
predation by other wildlife is
considered a major natural source of
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mortality for Concho water snakes
(Werler and Dixon 2000, p. 215).
Predators documented to prey on
Concho water snakes include
kingsnakes (Lampropeltis getula),
coachwhip snakes (Masticophis
flagellum), racers (Coluber constrictor),
raccoons (Procyon lotor), and great blue
herons (Ardea herodias) (Williams 1969,
p. 15; Dixon et al. 1988, p. 18; Greene
1993, p. 102). Raptors such as hawks
(Buteo spp.) and falcons (Falco spp.) are
also known to prey upon snakes
(Steenhof and Kochert 1988, p. 42).
Predatory fish include bass (Micropterus
salmoides) and channel catfish
(Ictaclurus punctatus) (McGrew 1963,
pp. 178–179; Jordan and Arrington
2001, p. 158). However, all of these
predators are native to this region,
Concho water snakes evolved tolerating
predation by these species, and we have
no information indicating that the
natural levels of predation are likely to
increase.
Therefore, we find that impacts from
predation by other wildlife are not
likely to cause the Concho water snake
to become threatened or endangered in
the foreseeable future.
D. The Inadequacy of Existing
Regulatory Mechanisms
The Concho water snake was listed as
endangered by the State of Texas in
1984. In 2000, it was removed from the
State’s list of threatened species (TPWD
2000, p.3) because TPWD no longer
considered it likely to become
endangered based on the information
provided by the District (District 1998);
therefore, it will not protect Concho
water snakes if we delist the species.
However, the lack of protection of the
Concho water snake by the State is not
considered a threat because TPWD
regulations only prohibit the taking,
possession, transportation, or sale of
designated animal species without the
issuance of a permit. There is no
protection by State law for the habitat of
state-listed species. Since the Concho
water snake is not threatened due to
taking, possession, or sale of
individuals, the lack of State protections
does not affect the status of the species.
The Texas Clean Rivers program, the
Clean Water Act, and other Texas water
law requirements, all discussed earlier
under Factor A, provide some benefits
to protect the habitat of the Concho
water snake. These programs, in
conjunction, with natural stream
inflows and minimum flows from dam
operations, indirectly conserve riverine
habitats for the species.
As a result, inadequacy of existing
regulatory mechanisms does not
constitute a threat to the Concho water
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snake such that it is likely to become
endangered in the foreseeable future.
E. Other Natural or Manmade Factors
Affecting Its Continued Existence
We are unaware of any other natural
or manmade factors affecting the
continued existence of the Concho
water snake at this time.
Conclusion of the Five-Factor Analysis
Foreseeable Future
In considering the foreseeable future
in the threats analysis for the Concho
water snake, we generally regarded
about 50 years as a timeframe where
some reasonable predictions could be
made. This range of time originated
from the analysis of forecasting for
water management, which is looking
ahead to expected conditions in the year
2060 (TWDB 2007, p. 2), and
consideration of climate change models,
which typically forecast 50 to 100 years
into the future; however, there was too
much uncertainty with the 100-year
timeframe to serve as a reasonable
foreseeable future (Jackson 2008, p. 8;
Mace and Wade 2008, p. 656). Since
habitat modification from changing
stream flows as a result of water
availability and management is the
primary threat of concern, this
timeframe is appropriate for our
analysis. This is also a reasonable
timeframe for analysis considering the
biology of the Concho water snake. The
snakes become sexually mature at 2 or
3 years old and reproduce annually
(Werner and Dixon 2000, p. 216), with
a likely lifespan rarely exceeding 5 years
(Mueller 1999, p. iii; Greene et al. 1999,
p. 707). A 50-year timeframe would
encompass about 10 lifespans and
multiple generations for the species.
Considering multiple generations is
important for any possible changes over
time in rates of reproductive success
and recruitment (growth to adulthood).
This timeframe also captures the future
stochastic hydrologic conditions
(particularly droughts of 10 years or
more and floods) and the expected
responses by a short-lived, fast-growing
species such as the Concho water snake.
Application of the Recovery Plan’s
Criteria
The recovery plan provides important
guidance on the direction and strategy
for recovery, and indicates when a
rulemaking process may be initiated; the
determination to remove a species from
the Federal List of Endangered and
Threatened Wildlife is ultimately based
on an analysis of whether a species is
no longer endangered or threatened. The
following discussion provides a brief
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review of the recovery criteria and goals
as they relate to evaluating the status of
the species.
Recovery Criterion 1: Adequate Instream
Flows
The 1993 Recovery Plan called for
assurance of adequate instream flows to
maintain both the quantity and quality
of Concho water snake habitat so that
occupied habitat would continue to
support viable populations of the
species (Service 1993, p. 33). At the
time the recovery plan was completed,
adequate instream flow rates were based
on the constituent elements identified
in the 1989 critical habitat designation
(54 FR 27382) and the reasonable and
prudent alternatives identified in the
1986 BO for the construction of Ivie
Reservoir. However, as the following
new information became available, our
understanding of the instream flow
requirements necessary to support
viable population of the Concho water
snake has changed substantially. The
topics summarized here are discussed at
length above in section A. The Present
or Threatened Destruction,
Modification, or Curtailment of Its
Habitat or Range, Habitat Modification
from Reduced Instream Flows.
First, lower flow rates have supported
reproductive snake populations despite
extended droughts. The revised lower
flow rates were found adequate to
support riverine habitat for the snake
(Service 2004a, pp. 50–52). This was
based on new information from
numerous studies funded by the District
in the 1990s that greatly added to our
knowledge of the biology of the snake
and its habitat (District 1998, pp. 18–
29). Additional monitoring of the snake
indicated that the population was
sustained by the lower flows required in
the 2004 BO (Forstner et al. 2006, pp.
13–18). While riverine habitat is
important for the conservation of the
snake, the need to maintain continuous
flows at levels previously required were
determined to no longer be necessary to
provide adequate habitat for snakes. The
flows described in the Recovery Plan
and the specific flows included in the
1989 critical habitat designation were
based on the best scientific information
at that time. However, subsequent
information provided by species experts
Forstner, Dixon, and Thornton indicates
that the snake will survive, reproduce,
and maintain population viability with
less stream flow.
Second, information on the snake’s
habitat indicates they are more of a
generalist (Dixon 2004, pp. 8–9)
occurring in reservoirs and pools in
rivers and do not depend on the
previously accepted narrow habitat
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requirements restricted to riffles in
rivers (Dixon 2004, 14–16). In addition
to riverine habitat, the snake is known
to use areas above and below low-head
dams, pools created by the dams, manmade lakes, naturally occurring pools in
the river, and tributaries, as Concho
water snake has been found in Elm
Creek and two of its tributaries.
Third, adequate flow to maintain the
snake’s habitat and the snake
population is provided by a variety of
sources in addition to the minimum
flows agreed to in the 2004 BO (Service
2004a, p. 11–12), and subsequently
agreed to in the 2008 MOU. We expect
minimal stream flows will be present at
most times of the year in the gaining
reaches of the Colorado River from
contributing inflow from creeks and
subdrainages, and discharges from
springs where shallow groundwater
interfaces with the stream (Dixon 2004,
p. 9). Low flows are also present below
Spence and Ivie Reservoirs due to dam
leakage and seepage even when no
releases are being made (Dixon 2004, p.
9). In addition, Texas water law
requirements also result in maintenance
of some instream flow, particularly in
the river reach below Ivie Reservoir
where the District’s water right permit
requires minimum flows of 8 cfs (0.23
cms) from April through September and
2.5 cfs (0.07 cms) from October through
March. Finally, dam releases from
Spence Reservoir are periodically made
to improve the quality of water (by
diluting the salt content) entering Ivie
Reservoir. All of these sources help
maintain instream flows that provided
habitat to the Concho water snake.
Recovery Criterion 2: Viable
Populations
The Recovery Plan (Service 1993,
p.33) also called for maintaining viable
populations of the snake in each of the
three major reaches. The Recovery Plan
defines viable population as one that is
self-sustaining, can persist for the longterm (typically hundreds of years), and
can maintain its vigor and its potential
for evolutionary adaptation (Service
1993, p. 33).
As previously described (see A. The
Present or Threatened Destruction,
Modification, or Curtailment of Its
Habitat or Range, Range and Population
Trends), monitoring studies from 1987
through 1996 confirmed a larger and
more consistent distribution of the
Concho water snake throughout its
range, including several reservoirs and
tributaries (District 1998, pp. 10, 22, 26).
In addition, over the 10 years of study,
9,069 Concho water snakes were
captured (excluding recaptures) (District
1998, p. 21). Of this total, 1,535 (17
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percent) were captured in reservoirs,
1,517 (17 percent) were captured in the
Concho River reach, 5,586 (62 percent)
were captured in the Colorado River
reach, and another 415 (5 percent) were
captured in tributary streams. Although
the results varied by year and location,
each of the more than 20 sites
monitored throughout the study had
multiple captures of snakes, usually
with a variety of age classes (Thornton
1996, pp. 26–50).
Unfortunately, the high variation in
sample efforts and environmental
conditions prevented a thorough
analysis of population trends over time
or calculation of total population
estimates (District 1998, p. 18). In other
words, in order to measure the changes
in abundance over time the study would
have had to include a quantification of
the amount of effort expended during
each survey. Such data would have
allowed a standardization of results over
time to evaluate potential trends in
population abundance of the snake. The
researchers decided there was too much
variation in the environmental
conditions and resulting catch rates to
produce such estimates and did not
report the amount of effort expended
during the surveys, making a trend
analysis inappropriate.
Forstner et al. (2006, pp. 6–8, 18, 20)
reviewed the past population data
collected on the snake (District 1998, p.
18–26), as well as conducted field
surveys in 2004 and 2005 to document
that snakes continued to be present and
were reproducing in each river reach
and reservoir where they occurred in
previous studies. The study, which
incorporated the results by Dixon
(2004), confirmed reproducing
populations of Concho water snakes in
each river reach and in both Ivie and
Spence Reservoirs (Forstner et al. 2006,
p. 12). Based on the snakes’ persistence
and continued reproduction throughout
its range over the past 20 years, Forstner
et al. (2006, pp. 18, 20) concluded that
viable populations of Concho water
snakes could be presumed to exist in all
three reaches of the species’ range.
There was some concern by peer
reviewers of the proposed rule regarding
the population of the snake in the reach
of the Colorado River downstream of
Freese Dam (Ivie Reservoir) where only
two sample locations (below Freese
Dam and at River Bend Ranch, about 25
miles (40 km) downstream of the dam)
(Dixon 2004, pp. 8, 14) were sampled
due to the difficulties in establishing
contact with private landowners in this
reach. Dixon collected three snakes from
these two sites in 2004, and one was a
juvenile female (Dixon 2004, pp. 16–17).
In 2005, Forstner et al. (2006, pp. 12, 18)
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reports collection of one post-partum
female below Freese Dam indicating the
snake had given birth to young,
confirming reproduction. Although only
four snakes were captured in limited
sampling efforts in 2004 and 2005 in
this reach, data from the District’s
earlier monitoring showed healthy
populations in this reach (District 1998,
pp. 34–38, 50). We have no reason to
conclude that the snake population
downstream of Freese Dam is of
additional concern.
A reanalysis of Concho water snake
monitoring data collected from 1987 to
1996 attempted to evaluate the
population dynamics of the species and
quantitatively assess the long-term
viability (Whiting et al. 2008, pp. 438–
439). The results, however, were
inconclusive because the data were
insufficient to reliably estimate survival
and emigration. This was due primarily
to insufficient sampling at any single
study site, along with a host of
variables, especially different
environmental conditions within a site
and among sites, and also because
dispersal rates were not measured
among sites (Whiting et al. 2008, p.
443). This situation resulted in the
survival rates from the capturerecapture study being biased low and
producing low estimates of annual
survival with large standard errors
(Whiting et al. 2008, p. 443). However,
Whiting also stated that snakes
continued to persist even in droughtprone areas, some with almost total
water loss, with hydrologically dynamic
systems (Whiting et al. 2008, pp. 442–
443). Although we lack recent data on
population size and viability, we have
used data on current range, long-term
persistence, and verification of recent
breeding success as indicators that the
current populations meet the definition
of a viable population.
Recovery Criterion 3: Movement of
Snakes
The Recovery Plan also provided for
the movement of Concho water snakes
(Service 1993, p. 33) to counteract
adverse impacts of population
fragmentation and prescribed the
movement of four snakes (two of each
sex) every 5 years in a specific pattern
above and below Ivie Reservoir and
between the Concho River reach and the
Colorado River reach downstream of
Spence Reservoir. The 2004 BO
discussed population fragmentation
(Service 2004a, p. 52) and found that the
specific requirement for snake
movements would best be served by
moving five male snakes from
downstream to upstream of both the
dams at Spence and Ivie Reservoirs once
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every 3 years. The 2008 MOU, as
amended in 2010, now calls for the
same movements of snakes and also
includes movement of snakes from
above to below both dams by the
District even after the species is
delisted. Since snakes are now known to
occur in Ivie Reservoir, there is no
longer a need to move snakes between
the Concho River reach and the
Colorado River reach downstream of
Spence Reservoir, as those reaches are
naturally connected. We added the
requirement to move snakes above
Spence Reservoir so that the population
in Spence Reservoir can maintain
genetic mixing with the riverine snakes
downstream. We determined that
moving only male snakes was sufficient
to accomplish the objective of genetic
exchange because a male will fertilize
multiple females, providing
opportunities for maintaining genetic
diversity. We increased the frequency of
snake transfers from 5 years called for
in the recovery plan to an interval of 3
years to decrease the likelihood of
population fragmentation. The Service
believes that these movements are more
than sufficient to maintain genetic
heterogeneity between the separated
populations (Service 2004a, p. 52)
because research has shown that as few
as one individual exchanged with each
generation is sufficient to maintain
adequate gene flow between animal
populations (Mills and Allendorf 1996,
p. 1,557). Also see the discussion above
under Habitat Modification From
Fragmentation.
Conclusion
As required by the Act, we considered
all potential threats under the 5 factors
to assess whether the Concho water
snake is threatened or endangered
throughout its range. We found that the
best available information indicates that
the Concho water snake is no longer
threatened with becoming endangered
throughout all of its range due to
recovery accomplishments and new
information on the ecology of the
species. Concho water snakes can
survive lower flows than previously
thought necessary for their survival.
Natural inflows and downstream senior
water rights, in concert with assurances
from the 2008 MOU, will maintain
adequate instream flows and reduce the
impacts of uncontrollable extreme
drought periods. Populations of
reproducing Concho water snakes are
persisting in all 3 reaches of the species’
range. The snake is capable of living and
reproducing in reservoirs and persisting
during droughts and in apparently
degraded habitats. Considering these
findings, evaluated in the five-factor
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analysis above, and that the three
Recovery Plan Criteria have either been
met outright, determined here to no
longer be appropriate, or conditions are
insured to meet the intent of each of the
criteria, we have determined that none
of the existing or potential threats,
either alone or in combination with
others, are likely to cause the Concho
water snake to become in danger of
extinction throughout all of its range
within the foreseeable future of about 50
years.
Significant Portion of the Range
Analysis
Having determined that the Concho
water snake is not endangered or
threatened throughout all its range, we
must next consider whether there are
any significant portions of the range
where the Concho water snake is in
danger of extinction or is likely to
become endangered in the foreseeable
future.
The Act defines ‘‘endangered species’’
as any species which is ‘‘in danger of
extinction throughout all or a significant
portion of its range,’’ and ‘‘threatened
species’’ as any species which is ‘‘likely
to become an endangered species within
the foreseeable future throughout all or
a significant portion of its range.’’ The
definition of ‘‘species’’ is also relevant
to this discussion. The Act defines the
term ‘‘species’’ as follows: ‘‘The term
‘species’ includes any subspecies of fish
or wildlife or plants, and any distinct
population segment [DPS] of any
species of vertebrate fish or wildlife
which interbreeds when mature.’’ The
phrase ‘‘significant portion of its range’’
(SPR) is not defined by the statute, and
we have never addressed in our
regulations: (1) The consequences of a
determination that a species is either
endangered or likely to become so
throughout a significant portion of its
range, but not throughout all of its
range; or (2) what qualifies a portion of
a range as ‘‘significant.’’
Two recent district court decisions
have addressed whether the SPR
language allows the Service to list or
protect less than all members of a
defined ‘‘species’’: Defenders of Wildlife
v. Salazar, 729 F. Supp. 2d 1207 (D.
Mont. 2010), concerning the Service’s
delisting of the Northern Rocky
Mountain gray wolf (74 FR 15123, Apr.
12, 2009); and WildEarth Guardians v.
Salazar, 2010 U.S. Dist. LEXIS 105253
(D. Ariz. Sept. 30, 2010), concerning the
Service’s 2008 finding on a petition to
list the Gunnison’s prairie dog (73 FR
6660, Feb. 5, 2008). The Service had
asserted in both of these determinations
that it had authority, in effect, to protect
only some members of a ‘‘species,’’ as
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defined by the Act (i.e., species,
subspecies, or DPS), under the Act. Both
courts ruled that the determinations
were arbitrary and capricious on the
grounds that this approach violated the
plain and unambiguous language of the
Act. The courts concluded that reading
the SPR language to allow protecting
only a portion of a species’ range is
inconsistent with the Act’s definition of
‘‘species.’’ The courts concluded that,
once a determination is made that a
species (i.e., species, subspecies, or
DPS) meets the definition of
‘‘endangered species’’ or ‘‘threatened
species,’’ it must be placed on the list
in its entirety and the Act’s protections
applied consistently to all members of
that species (subject to modification of
protections through special rules under
sections 4(d) and 10(j) of the Act).
Consistent with that interpretation,
and for the purposes of this finding, we
interpret the phrase ‘‘significant portion
of its range’’ in the Act’s definitions of
‘‘endangered species’’ and ‘‘threatened
species’’ to provide an independent
basis for listing; thus there are two
situations (or factual bases) under which
a species would qualify for listing: a
species may be endangered or
threatened throughout all of its range; or
a species may be endangered or
threatened in only a significant portion
of its range. If a species is in danger of
extinction throughout an SPR, it, the
species, is an ‘‘endangered species.’’
The same analysis applies to
‘‘threatened species.’’ Therefore, the
consequence of finding that a species is
endangered or threatened in only a
significant portion of its range is that the
entire species shall be listed as
endangered or threatened, respectively,
and the Act’s protections shall be
applied across the species’ entire range.
We conclude, for the purposes of this
finding, that interpreting the SPR phrase
as providing an independent basis for
listing is the best interpretation of the
Act because it is consistent with the
purposes and the plain meaning of the
key definitions of the Act; it does not
conflict with established past agency
practice (i.e., prior to the 2007
Solicitor’s Opinion), as no consistent,
long-term agency practice has been
established; and it is consistent with the
judicial opinions that have most closely
examined this issue. Having concluded
that the phrase ‘‘significant portion of
its range’’ provides an independent
basis for listing and protecting the entire
species, we next turn to the meaning of
‘‘significant’’ to determine the threshold
for when such an independent basis for
listing exists.
Although there are potentially many
ways to determine whether a portion of
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a species’ range is ‘‘significant,’’ we
conclude, for the purposes of this
finding, that the significance of the
portion of the range should be
determined based on its biological
contribution to the conservation of the
species. For this reason, we describe the
threshold for ‘‘significant’’ in terms of
an increase in the risk of extinction for
the species. We conclude that a
biologically based definition of
‘‘significant’’ best conforms to the
purposes of the Act, is consistent with
judicial interpretations, and best
ensures species’ conservation. Thus, for
the purposes of this finding, a portion
of the range of a species is ‘‘significant’’
if its contribution to the viability of the
species is so important that, without
that portion, the species would be in
danger of extinction.
We evaluate biological significance
based on the principles of conservation
biology using the concepts of
redundancy, resiliency, and
representation. Resiliency describes the
characteristics of a species that allow it
to recover from periodic disturbance.
Redundancy (having multiple
populations distributed across the
landscape) may be needed to provide a
margin of safety for the species to
withstand catastrophic events.
Representation (the range of variation
found in a species) ensures that the
species’ adaptive capabilities are
conserved. Redundancy, resiliency, and
representation are not independent of
each other, and some characteristic of a
species or area may contribute to all
three. For example, distribution across a
wide variety of habitats is an indicator
of representation, but it may also
indicate a broad geographic distribution
contributing to redundancy (decreasing
the chance that any one event affects the
entire species), and the likelihood that
some habitat types are less susceptible
to certain threats, contributing to
resiliency (the ability of the species to
recover from disturbance). None of these
concepts is intended to be mutually
exclusive, and a portion of a species’
range may be determined to be
‘‘significant’’ due to its contributions
under any one of these concepts.
For the purposes of this finding, we
determine if a portion’s biological
contribution is so important that the
portion qualifies as ‘‘significant’’ by
asking whether, without that portion,
the representation, redundancy, or
resiliency of the species would be so
impaired that the species would have an
increased vulnerability to threats to the
point that the overall species would be
in danger of extinction (i.e., would be
‘‘endangered’’). Conversely, we would
not consider the portion of the range at
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issue to be ‘‘significant’’ if there is
sufficient resiliency, redundancy, and
representation elsewhere in the species’
range that the species would not be in
danger of extinction throughout its
range if the population in that portion
of the range in question became
extirpated (extinct locally).
We recognize that this definition of
‘‘significant’’ establishes a threshold
that is relatively high. On the one hand,
given that the consequences of finding
a species to be endangered or threatened
in an SPR would be listing the species
throughout its entire range, it is
important to use a threshold for
‘‘significant’’ that is robust. It would not
be meaningful or appropriate to
establish a very low threshold whereby
a portion of the range can be considered
‘‘significant’’ even if only a negligible
increase in extinction risk would result
from its loss. Because nearly any portion
of a species’ range can be said to
contribute some increment to a species’
viability, use of such a low threshold
would require us to impose restrictions
and expend conservation resources
disproportionately to conservation
benefit: listing would be rangewide,
even if only a portion of the range of
minor conservation importance to the
species is imperiled. On the other hand,
it would be inappropriate to establish a
threshold for ‘‘significant’’ that is too
high. This would be the case if the
standard were, for example, that a
portion of the range can be considered
‘‘significant’’ only if threats in that
portion result in the entire species’
being currently endangered or
threatened. Such a high bar would not
give the SPR phrase independent
meaning, as the Ninth Circuit held in
Defenders of Wildlife v. Norton, 258
F.3d 1136 (9th Cir. 2001).
The definition of ‘‘significant’’ used in
this finding carefully balances these
concerns. By setting a relatively high
threshold, we minimize the degree to
which restrictions will be imposed or
resources expended that do not
contribute substantially to species
conservation. But we have not set the
threshold so high that the phrase ‘‘in a
significant portion of its range’’ loses
independent meaning. Specifically, we
have not set the threshold as high as it
was under the interpretation presented
by the Service in the Defenders
litigation. Under that interpretation, the
portion of the range would have to be
so important that current imperilment
there would mean that the species
would be currently imperiled
everywhere. Under the definition of
‘‘significant’’ used in this finding, the
portion of the range need not rise to
such an exceptionally high level of
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biological significance. (We recognize
that if the species is imperiled in a
portion that rises to that level of
biological significance, then we should
conclude that the species is in fact
imperiled throughout all of its range,
and that we would not need to rely on
the SPR language for such a listing).
Rather, under this interpretation we ask
whether the species would be
endangered everywhere without that
portion, i.e., if that portion were
completely extirpated. In other words,
the portion of the range need not be so
important that even being in danger of
extinction in that portion would be
sufficient to cause the remainder of the
range to be endangered; rather, the
complete extirpation (in a hypothetical
future) of the species in that portion
would be required to cause the
remainder of the range to be
endangered.
The range of a species can
theoretically be divided into portions in
an infinite number of ways. However,
there is no purpose to analyzing
portions of the range that have no
reasonable potential to be significant
and threatened or endangered. To
identify only those portions that warrant
further consideration, we determine
whether there is substantial information
indicating that: (1) The portions may be
‘‘significant,’’ and (2) the species may be
in danger of extinction there or likely to
become so within the foreseeable future.
Depending on the biology of the species,
its range, and the threats it faces, it
might be more efficient for us to address
the significance question first or the
status question first. Thus, if we
determine that a portion of the range is
not ‘‘significant,’’ we do not need to
determine whether the species is
endangered or threatened there; if we
determine that the species is not
endangered or threatened in a portion of
its range, we do not need to determine
if that portion is ‘‘significant.’’ In
practice, a key part of the portion status
analysis is whether the threats are
geographically concentrated in some
way. If the threats to the species are
essentially uniform throughout its
range, no portion is likely to warrant
further consideration. Moreover, if any
concentration of threats applies only to
portions of the species’ range that
clearly would not meet the biologically
based definition of ‘‘significant’’, such
portions will not warrant further
consideration.
Based on our review of the best
available information concerning the
distribution of the species and the
potential threats, we have determined
that the Concho water snake does not
warrant further consideration to
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determine if there is a significant
portion of the range that is threatened or
endangered. Through the five-factor
analysis we found no areas where one
or more threats are geographically
concentrated. The range of the snake
can readily be divided into three
portions, based on the presence of large
dams: (1) The Concho River segment
(San Angelo to the inflow of Ivie
Reservoir); (2) the upper Colorado River
segment (Spence Reservoir and the
Colorado River outflow downstream to
Ivie Reservoir); and (3) the lower
Colorado River segment (outflow of Ivie
Reservoir downstream to Colorado Bend
State Park). Generally, all of the
potential threats to the species that were
evaluated in the Summary of Factors
Affecting the Species section above
occur at similarly low levels in each of
the three segments. However, there are
some differences in flow regimes that
were described in the Habitat
Modification from Reduced Instream
Flows section above and are considered
here.
The Concho River segment has
undergone the most dramatic flow
reduction due to upstream dams and
water diversion for human use. The
result has been extended periods of very
low discharges throughout much of the
reach (Asquith and Heitmuller 2008, pp.
849–850). Despite the habitat
alterations, the snake continues to
persist in this reach and Forstner et al.
(2006, p. 8) found the highest numbers
of Concho water snakes (20 of all 45
snakes captured or observed during
their brief surveys in 2004 and 2005) in
this reach of the Concho River. Dixon
(2004, p. 9) explains that the snakes
endure these conditions by using lowflow areas over bedrock substrate for
foraging and also using the pools that
form behind low-head dams as habitat.
Therefore, we find that the potential
threats from low flows, or any other
threats, in this portion of its range do
not warrant continued listing of the
snake.
Both the upper and lower Colorado
River segments have also undergone
hydrologic changes and decreases in
stream flows from reservoir construction
and operation (Asquith et al. 2008, pp.
810–813; 850–853). However, river
flows have been maintained due to
natural drainage inflows and minimum
reservoir releases (Service 2004, pp. 35–
38). Water has been released from
Spence Reservoir for the benefit of the
Concho water snake under the
requirements of biological opinions and
as part of the 2008 MOU. In addition,
releases from Ivie Reservoir are required
to fulfill requirements for downstream
users, consistent with the flows called
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66803
for in the 2008 MOU, which will
continue to be implemented even if the
snake is delisted. As evaluated under
Summary of Factors Affecting the
Species section above, we find that
these flow reductions, or any other
threats, in either of these segments are
not threatening the species. Because the
low level of threats to the species is
essentially uniform throughout its
range, no portion warrants further
consideration to determine if they are
significant.
Therefore, we find the Concho water
snake is no longer threatened with
becoming endangered throughout all or
a significant portion of its range within
the foreseeable future. We believe the
Concho water snake no longer requires
the protection of the Act, and, therefore,
we are removing it from the Federal List
of Endangered and Threatened Wildlife.
Effects of the Rule
This final rule revises 50 CFR 17.11(h)
to remove the Concho water snake from
the Federal List of Endangered and
Threatened Wildlife. Promulgation of
this final rule will affect protection
afforded the Concho water snake under
the Act. Taking, interstate commerce,
import, and export of Concho water
snakes are no longer prohibited under
the Act. Federal agencies are no longer
required to consult with us under
section 7 of the Act to ensure that any
action they authorize, fund, or carry out
is not likely to jeopardize the species’
continued existence. This final rule also
revises 50 CFR 17.95(c) to remove the
critical habitat designation.
Post-Delisting Monitoring Plan
Section 4(g)(1) of the Act requires us,
in cooperation with the States, to
implement a monitoring program for not
less than 5 years for all species that have
been recovered and delisted (50 CFR
17.11, 17.12). The purpose of this postdelisting monitoring (PDM) is to verify
that the species remains secure from
risk of extinction after it has been
removed from the protections of the Act.
The PDM is designed to detect the
failure of any delisted species to sustain
itself without the protective measures
provided by the Act. If, at any time
during the monitoring period, data
indicate that protective status under the
Act should be reinstated, we can initiate
listing procedures, including, if
appropriate, emergency listing under
section 4(b)(7) of the Act. Section 4(g) of
the Act explicitly requires cooperation
with the States in development and
implementation of PDM programs, but
we remain responsible for compliance
with section 4(g) and, therefore, must
remain actively engaged in all phases of
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PDM. We also seek active participation
of other entities that are expected to
assume responsibilities for the species’
conservation, post-delisting.
The Service has developed a PDM
plan in cooperation with the District
and TPWD. We published a notice of
availability of the draft plan in the
Federal Register on September 23, 2009,
(74 FR 48595) to solicit public
comments and peer review on the plan.
No public comments on the PDM plan
were received. Comments from six peer
reviewers were considered and
incorporated into the final PDM plan as
appropriate. The final PDM plan and
any future revisions will be posted on
our Endangered Species Program’s
national web page (https://
endangered.fws.gov) and on the Austin
Ecological Services Field Office web
page (https://www.fws.gov/southwest/es/
AustinTexas/).
PDM for Concho water snakes will
consist of two monitoring components:
biological (to monitor the status of the
snake) and hydrological (to monitor
instream flow conditions). Over a 14year period, surveys to measure the
presence, reproduction, and abundance
of snakes will be conducted annually in
the fall for 13 consecutive years at 9
core biological sample sites across the
snake’s range. In addition, more intense
biological surveys will be conducted
during the spring and fall of 3 years
spread over the monitoring period at 18
sample sites. Evaluation of stream
conditions will consist of analysis of
hydrologic data collected at eight
existing stream gauges from across the
snake’s range, which will verify that
flows called for in the 2008 MOU are
being realized. Quantitative and
qualitative monitoring triggers for
additional conservation actions are
based on documented changes to the
snake’s range-wide distribution;
observed presence and abundance at
sample sites; and successful
reproduction. Triggers are also
established based on instream flow
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conditions within the snake’s habitat. If
monitoring results in concern regarding
the snake’s status or increasing threats,
possible responses may include an
extended or intensified monitoring
effort, additional research (such as
modeling metapopulation dynamics or
assessing the status of the fish prey
base), enhancement of riverine or
shoreline habitats, or an increased effort
to improve habitat connectivity by
additional translocation of snakes
between reaches. If future information
collected from the PDM, or any other
reliable source, indicates an increased
likelihood that the species may become
endangered with extinction, the Service
will initiate a status review of the
Concho water snake and determine if
relisting the species is warranted.
Paperwork Reduction Act
This rule does not contain any new
collections of information that require
approval by OMB under the Paperwork
Reduction Act (44 U.S.C. 3501 et seq.).
This rule will not impose recordkeeping
or reporting requirements on State or
local governments, individuals,
businesses, or organizations. An agency
may not conduct or sponsor, and a
person is not required to respond to, a
collection of information unless it
displays a currently valid OMB control
number.
National Environmental Policy Act
We have determined that an
Environmental Assessment or an
Environmental Impact Statement, as
defined under the authority of the
National Environmental Policy Act of
1969, need not be prepared in
connection with regulations adopted
pursuant to section 4 of the Act. We
published a notice outlining our reasons
for this determination in the Federal
Register on October 25, 1983 (48 FR
49244).
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References Cited
A complete list of all references cited
herein is available upon request from
the U.S. Fish and Wildlife Service,
Austin Ecological Services Field Office
(see FOR FURTHER INFORMATION CONTACT
above).
Authors
The primary authors of this document
are staff located at the Austin Ecological
Services Field Office (see FOR FURTHER
INFORMATION CONTACT above).
List of Subjects in 50 CFR Part 17
Endangered and threatened species,
Exports, Imports, Reporting and
recordkeeping requirements, and
Transportation.
Regulation Promulgation
Accordingly, we amend part 17,
subchapter B of chapter I, title 50 of the
Code of Federal Regulations as set forth
below:
PART 17—[AMENDED]
1. The authority citation for part 17
continues to read as follows:
■
Authority: 16 U.S.C. 1361–1407; 16 U.S.C.
1531–1544; 16 U.S.C. 4201–4245; Pub. L. 99–
625, 100 Stat. 3500; unless otherwise noted.
§ 17.11
[Amended]
2. Amend § 17.11(h) by removing the
entry ‘‘Snake, Concho water’’ under
‘‘REPTILES’’ from the List of
Endangered and Threatened Wildlife.
■
§ 17.95
[Amended]
3. Amend § 17. 95(c) by removing the
critical habitat entry for ‘‘Concho Water
Snake (Nerodia harteri
paucimaculata).’’
■
Dated: October 7, 2011.
Gregory E. Siekaniec,
Acting Director, U.S. Fish and Wildlife
Service.
[FR Doc. 2011–27375 Filed 10–26–11; 8:45 am]
BILLING CODE 4310–55–P
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[Federal Register Volume 76, Number 208 (Thursday, October 27, 2011)]
[Rules and Regulations]
[Pages 66780-66804]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2011-27375]
[[Page 66779]]
Vol. 76
Thursday,
No. 208
October 27, 2011
Part II
Department of Interior
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Fish and Wildlife Service
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50 CFR Part 17
Endangered and Threatened Wildlife and Plants; Removal of the Concho
Water Snake From the Federal List of Endangered and Threatened Wildlife
and Removal of Designated Critical Habitat; Final Rule
Federal Register / Vol. 76 , No. 208 / Thursday, October 27, 2011 /
Rules and Regulations
[[Page 66780]]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[FWS-R2-ES-2008-0080; 92220-1113-0000-C6]
RIN 1018--AU97
Endangered and Threatened Wildlife and Plants; Removal of the
Concho Water Snake From the Federal List of Endangered and Threatened
Wildlife and Removal of Designated Critical Habitat
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Final rule.
-----------------------------------------------------------------------
SUMMARY: The best available scientific and commercial data indicate
that the Concho water snake (Nerodia paucimaculata), a reptile endemic
to central Texas, is recovered. Therefore, under the authority of the
Endangered Species Act of 1973, as amended (Act), we, the U.S. Fish and
Wildlife Service (Service) remove (delist) the Concho water snake from
the Federal List of Endangered and Threatened Wildlife, and
accordingly, also remove its federally designated critical habitat.
This determination is based on a thorough review of all available
information, including new information, which indicates that the
threats to this species have been eliminated or reduced to the point
that the species has recovered and no longer meets the definition of
threatened or endangered under the Act. We are also providing notice
that the final post-delisting monitoring for the Concho water snake has
been completed.
DATES: This final rule becomes effective on November 28, 2011.
ADDRESSES: The proposed rule, all comments received, the post-delisting
monitoring plan, and this final rule are all available on the Internet
at https://www.regulations.gov and https://www.fws.gov/southwest/es/AustinTexas/. Supporting documentation we used in preparing this final
rule will be available for public inspection, by appointment, during
normal business hours, at the U.S. Fish and Wildlife Service, Austin
Ecological Services Field Office, 10711 Burnet Road, Suite 200, Austin,
TX 78758; telephone 512-490-0057; facsimile 512-490-0974.
FOR FURTHER INFORMATION CONTACT: Adam Zerrenner, Field Supervisor, U.S.
Fish and Wildlife Service, Austin Ecological Services Field Office (see
ADDRESSES). If you use a telecommunications device for the deaf (TDD),
call the Federal Information Relay Service (FIRS) at 800/877-8339.
SUPPLEMENTARY INFORMATION:
Background
It is our intent to discuss in this final rule only those topics
directly relevant to the removal of the Concho water snake from the
Federal list of threatened species under the Endangered Species Act of
1973, as amended (Act; 16 U.S.C. 1531 et seq.). The Concho water snake
is endemic to the Colorado and Concho Rivers in central Texas (Tennant
1984, p. 344; Scott et al. 1989, p. 373). It occurs on the Colorado
River from E.V. Spence Reservoir to Colorado Bend State Park, including
Ballinger Municipal Lake and O.H. Ivie Reservoir, and on the Concho
River from the City of San Angelo, Texas, to its confluence with the
Colorado River at O.H. Ivie Reservoir. At the time the species was
listed as threatened in 1986 (51 FR 31412), there were considered to be
two subspecies of Nerodia harteri, the Concho water snake (N.h.
paucimaculata) and the Brazos water snake (N.h. harteri). Densmore et
al. (1992, p. 66) determined the Concho water snake was a distinct
species, and in 1996 we changed our reference to the species to
recognize the scientific name N. paucimaculata (50 CFR 17.11). Some
authors use the common name of Concho watersnake, based on Crother
(2000, p. 67). However, this has not been universally adopted, so we
continue to use Concho water snake in this rule. For more background
information on the Concho water snake, refer to the proposed delisting
rule published in the Federal Register on July 8, 2008 (73 FR 38956),
the final listing rule published in the Federal Register on September
3, 1986 (51 FR 31412), Campbell (2003, pp. 1-4), the 2004 revised
biological opinion (BO) on water operations on the Concho and Colorado
Rivers (Service 2004, pp. 1-76), and the 1993 Concho Water Snake
Recovery Plan available online at https://ecos.fws.gov/docs/recovery_plan/930927b.pdf. We note that research conducted since the recovery
plan was completed in 1993 has provided new information on the species.
Previous Federal Actions
In June 1998, we received a petition from the Colorado River
Municipal Water District (District) to delist the Concho water snake
because our original data (regarding snake distribution and abundance
and threats) for listing the snake were in error. On August 2, 1999, we
published a 90-day petition finding (1999 petition finding) that the
petitioner did not present substantial information indicating that
delisting the species may be warranted (64 FR 41903). The petition did
not contain any information addressing the threats to the species nor
did it include a discussion of the three recovery criteria. As a result
of the negative 90-day finding, we did not conduct a full status review
at that time. However, in the process of revising the biological
opinion under section 7 of the Act for the operations of the upper
Colorado River dams in 2004 (Service 2004a), the Service determined
there was sufficient new information available to warrant a status
review of the species. This final rule constitutes the conclusion of a
full status review of the Concho water snake and analyzes all of the
outstanding concerns from the 1999 petition finding.
On July 8, 2008, we published a proposed rule to remove the Concho
water snake from the list of threatened species (73 FR 38956). A draft
of the post-delisting monitoring plan was made available for public
review and comment on September 23, 2009 (74 FR 48595).
Additional background information regarding other previous Federal
actions for the Concho water snake can be obtained by consulting the
species' regulatory profile found at: https://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=C04E.
Recovery
Section 4(f) of the Act directs us to develop and implement
recovery plans for listed species unless the Director determines that
such a plan will not benefit the conservation of the species. The
Service completed the Concho Water Snake Recovery Plan in 1993 (Service
1993). The Concho Water Snake Recovery Plan outlines recovery criteria
to assist in determining when the snake has recovered to the point that
the protections afforded by the Act are no longer needed (Service 1993,
p. 33). These criteria are: (1) Adequate instream flows are assured
even when the species is delisted. (2) Viable populations are present
in each of the three major reaches (the Colorado River above Freese Dam
(forms O.H. Ivie Reservoir), Colorado River below Freese Dam, and the
Concho River). Here, population is defined as all Concho water snakes
in a given area, in this case, each major river reach. (3) Movement of
an adequate number of Concho water snakes is assured to counteract the
adverse impacts of population fragmentation. These movements should
occur as long as Freese Dam is in place or until such time that the
Service determines that Concho water snake populations in the
[[Page 66781]]
three reaches are viable and ``artificial movement'' among them is not
needed.
We used the recovery plan to provide guidance to the Service, State
of Texas, and other partners on methods to minimize and reduce the
threats to the Concho water snake and to provide criteria that could be
used to help determine when the threats to the Concho water snake had
been reduced so that it could be removed from the Federal List of
Endangered and Threatened Wildlife.
Provisions in recovery plans are recommendations that are not
binding and can be superseded by more current scientific information.
There are many paths to accomplishing recovery of a species in all or a
significant portion of its range. The main goal is to remove the
threats to a species, which sometimes may occur without meeting all
recovery criteria contained in a recovery plan. For example, one or
more criteria may have been exceeded while other criteria may not have
been accomplished. In that instance, the Service may judge that,
overall, the threats have been reduced sufficiently, and the species is
robust enough, to reclassify the species from endangered to threatened
or perhaps to delist the species. In other cases, recovery
opportunities may be recognized that were not known at the time the
recovery plan was finalized. Achievement of these opportunities may
result in progress toward recovery in lieu of methods identified in the
recovery plan. Likewise, we may learn information about the species
that was not known at the time the recovery plan was finalized. The new
information may change the extent that criteria need to be met for
recognizing recovery of the species. Overall, recovery of a species is
a dynamic process requiring adaptive management. Judging the degree of
recovery of a species is also an adaptive management process that may,
or may not, fully follow the guidance provided in a recovery plan.
A review of the best scientific and commercial data currently
available (see Summary of Factors Affecting the Species section below)
indicates that all three criteria in the Concho water snake recovery
plan (adequate instream flows even after delisting, viable populations
in each of the three major river reaches, and movement of snakes to
assure adequate genetic mixing) have been met. Further, recovery of the
Concho water snake has been a dynamic process, which has been fostered
by the significant amount of new data collected on the biology and
ecology of the species by numerous species experts. Since the time of
listing and preparation of the recovery plan, biologists have
discovered that the snakes are able to persist and reproduce along the
shorelines of reservoirs and that the snakes have managed to persist in
all three population segments, surviving many years of drought.
Including this new information, the analysis below considers the best
available data in determining that the Concho water snake no longer
meets the definition of a threatened or endangered species.
Summary of Comments and Recommendations
In our proposed rule (71 FR 38956), we requested comments from the
public on the proposed removal of the Concho water snake from the list
of threatened species during a 60-day comment period that ended on
September 8, 2008. We also contacted Federal agencies, State agencies,
local officials, and congressional representatives to invite comment on
the proposed rule.
During the public comment period, we received no requests for a
public hearing and none was held. Overall we received 23 written
comments from the public. Twenty of these were similar letters that
supported removal of the species from the protected list and stated
that our decision to delist the Concho water snake was based on sound
science. Two of these letters of support came from the Texas Department
of Transportation (TxDOT) and Texas Parks and Wildlife Department
(TPWD). Six of these letters were from city officials, ten were from
river authorities or water districts, including the Colorado River
Municipal Water District (District), and two were from private
businesses. We also received one nonsubstantive comment and two
substantive critical comments from professional biologists (one
specifically expressed opposition to the proposal). Our responses are
provided below to a summary of each substantive comment received.
Peer Review
In accordance with our policy published on July 1, 1994 (59 FR
34270), we solicited independent expert opinions from knowledgeable
individuals with scientific expertise that included ecology of water
snakes, conservation biology principles, and river hydrology. Out of
seven individuals that agreed to provide peer review, we received six
peer review comments. One peer reviewer stated support for the
proposal. Three peer reviewers were noncommittal on their support, but
provided many substantive comments and questions. Two peer reviewers
stated opposition to the proposal and provided substantive criticism.
Our responses are provided below to a summary of each substantive
comment received from the peer reviewers.
Comments From Peer Reviewers
(1) Comment: It is premature to delist the Concho water snake
because essential data are lacking. For example, no data are presented
on population structure, demographics, trends, or genetics.
Our Response: The Act requires us to consider the best available
information when making decisions on what species should be protected.
Population demographic estimates have been reported for the Concho
water snake (Whiting et al. 2008, pp. 441-442). While more quantitative
analysis of population structure, trends, and genetics would be
informative and useful to us in formulating this rule, we believe the
data used in this final rule support our decision because it is derived
from many years of monitoring collections (Thornton 1996, pp. 26-50,
Forstner et al. 2006, p. 18) and consistent with the opinion of most
experts on the Concho water snake. Reference the following sections
below for descriptions of the best available information related to
population structure, demographics, and genetics: A. The Present or
Threatened Destruction, Modification, or Curtailment of Its Habitat or
Range, Habitat Modification from Fragmentation; and Application of the
Recovery Plan's Criteria, Population Viability. We find that the best
available information supports the decision that the Concho water snake
has recovered and no longer qualify as threatened.
Past studies of the Concho water snake were intended to monitor the
populations over time using mark-recapture techniques (that is,
inserting a tag in captured snakes so that individuals can be
identified when they are recaptured). Although these studies by the
District (summarized in District 1998) resulted in a large number of
snakes collected over 10 years (9,069 unique snakes), the study did not
quantify the amount of effort expended during each survey, so that
reliable population estimates or trends over time could not be
calculated. Whiting et al. (2008) utilized these data to attempt to
model population trends. However, the results proved too unreliable to
effectively model population trends because the dispersal rates of
snakes out of the study areas were not quantified. This resulted in a
potential overestimate of the death rate of snakes that were not
recaptured, when they could have, in fact, simply moved out of the
study area
[[Page 66782]]
(Whiting et al. 2008, p. 443). The original study was not designed to
accommodate a population viability analysis and attempts to do so
provided results with an unacceptable degree of uncertainty and with
imprecise conclusions. As a result, the best available information on
snake populations supports that the snakes have persisted over a long
time period throughout the majority of their historic range and have
continued to persist following habitat alterations from reservoir
inundation and drought.
(2) Comment: The Concho water snake occupies an extremely small
area of Texas, and one small mistake could easily cause the extinction
in a significant portion (i.e., all) of its range. It is better to err
on the side of caution than face the consequences of early protection
removal.
Our Response: The current range of the snake is estimated to total
about 280 miles (mi) (451 kilometers (km)) of river and about 40 mi (64
km) of reservoir shoreline. The best available information, including
the reports of species experts (in particular Dr. James Dixon and Dr.
Michael Forstner), does not indicate that the species is vulnerable to
extinction. The recent studies available to us report that the species
is capable of withstanding significant environmental perturbations
(Dixon 2004, pp. 10-11; Forstner et al. 2006, pp. 16-18; Whiting et al.
2008, p. 343). Under our post-delisting monitoring plan, we will be
monitoring the status of the species and can emergency list it if
necessary (see the Post-Delisting Monitoring Plan section below).
(3) Comment: My strong conclusion is that viable populations of the
Concho water snake have not been demonstrated. Documentation of
persistence and reproduction is not adequate to determine population
viability.
Our Response: Please see our response below to Comment (28). We
have updated the discussion of viable population in the final rule to
be more consistent with the description used in the recovery plan for
the species (see Application of the Recovery Plan's Criteria section
below).
(4) Comment: Survey results from Dixon (2004) and Forstner et al.
(2006) failed to find snakes at some sample sites, indicating possible
local extinctions and suggesting that recovery criterion 2 for viable
populations has not been met and site occupancy may have decreased by
23 to 27 percent.
Our Response: Dixon made only one sampling visit to 13 sites and
found Concho water snakes at all but 3 sites (Dixon 2004, pp. 4-5).
Forstner et al. (2006, pp. 6-7, 12) surveyed several sites up to three
times in 2005. They found snakes at all sites except for three sites on
the Concho River, which were only sampled one time following a
rainstorm event making detection difficult (Forstner et al. 2006, p.
12). In contrast, earlier studies (District 1998, p. 13) resulted in
consistent captures of snakes at nearly all sites surveyed, however,
those sites were sampled three times or more annually. Both Dixon
(2004, pp. 9, 14-15) and Forstner et al. (2006, p. 13) explain that
there are a variety of field conditions that influence the ability to
capture snakes at a given time and location. Variability of sampling
success is common in field investigations, and both of these reports
consisted of sampling efforts too small to interpret negative capture
data as local extinctions or a decline in site occupancy.
(5) Comment: I agree with the proposed rule to delist the Concho
water snake, although I don't know if I believe that the Concho water
snake has ``recovered'' as much as it continues to persist despite
marked modifications to its habitat along the Colorado and Concho
rivers. The snake is more of a habitat generalist than originally
thought, and successful reproduction takes place under lower stream
flows than previously indicated. The 2008 Memorandum of Understanding
(MOU) between the Service and the Colorado Municipal Water District
ensures adequate stream flows, although it may be strained by drought
conditions. Twenty years of field studies demonstrate continued
reproductive success in both the Concho and Colorado Rivers, including
reservoirs. Dixon (2004) reports finding that dense vegetation and
beavers failed to impede reproduction at the Freese Dam site, and he
found the Elm Creek site, devoid of water for three years, still
contained a reproducing population.
Our Response: We agree that the best available information supports
the decision to remove the Concho water snake from the list of
threatened species under the Act. We recognize that our understanding
of the snake's ecology has benefitted from new information that has
been collected since the listing and since the recovery plan was
completed. The removal of the snake from the list of threatened species
is due both to recovery actions, such as the 2008 MOU with the
District, and new biological information on the species' ability to
persist in habitats such as reservoirs and no change (or slight
increase) in the species' known range (about 80 river miles more than
known at the time of listing).
(6) Comment: The proposed rule uses an inappropriate timeframe for
analysis of factors that could affect the species in the future.
Factors that are not considered threats on a 20-year timeframe may
threaten the species on a more meaningful timeframe of 50-100 years,
which is consistent with the recovery plan.
Our Response: We agree the 20-year foreseeable future was not a
sufficiently long timeframe for our analysis. We have updated the rule
to evaluate the threats to the species considering longer timeframes,
as available information allows. In considering the foreseeable future
in the threats analysis, we generally regarded 50 to 100 years as a
time frame where some reasonable predictions could be made. This range
of time originated from the analysis of forecasting for water
management, which is looking ahead to expected conditions in the year
2060 (TWDB 2007, p. 2), and consideration of climate change models,
which typically forecast 50 to 100 years into the future (Bernstein et
al. 2007, pp. 8-9; Jackson 2008, p. 8; Mace and Wade 2008, p. 656).
(7) Comment: Lake populations are not as robust as the river
populations (low densities via low recruitment), and their mere
presence is not an indicator of population health. Lake populations
appear to be isolated sinks and there may not be riverine recruitment
from these populations. Due to the relatively recent appearance of the
lakes, the data are only isolated snapshots and more monitoring is
necessary before we know the true effects of river modification on
Concho water snake populations.
Our Response: Recruitment is the successful influx of new members
into a population by reproduction or immigration (Lincoln et al. 1998,
p. 257). Sinks are populations or breeding groups that do not produce
enough offspring to maintain themselves without immigrants from other
populations. Please see our responses to Comments (1) and (28) for
related information. Dixon (2004, p. 14) states that both reservoirs
(Ivie and Spence) provide prime habitat for Concho water snakes along
the rocky shorelines. Whiting et al. (1997, p. 331) found over 300
individual snakes in Lake Spence 20 years after the reservoir was
filled. Also, analysis by Whiting et al. (2008, pp. 439, 443) found no
evidence of a difference in survival among the five subpopulations
(including three riverine reaches and two reservoirs). This suggests
there may be no difference in survival rates between reservoir and
[[Page 66783]]
riverine snake populations, although the authors recognize that the
data from reservoirs were not sufficient for reliable estimates of
snake survival and population growth (Whiting et al. 2008, p. 443).
Successful use of the reservoirs by Concho water snakes is one
factor we considered in this decision and provides some added assurance
that the snakes are not likely to become endangered in the foreseeable
future. It is not unexpected that populations of the snakes in the
artificial habitat of the reservoirs may not be as robust by some
measures compared with populations in the natural riverine habitat.
However, we have no information that indicates the snakes in reservoirs
are population sinks. We know that the snakes have been shown to
persist and reproduce in Spence Reservoir for at least 35 years after
construction (1969 to 2005) and in Ivie Reservoir for at least over 15
years after construction (1989 to 2005) (Forstner et al. 2006, p. 12).
The Service finds that this is a sufficient amount of time to determine
that snakes are likely to continue to persist in reservoirs in the
foreseeable future.
(8) Comment: Evidence of successful reproduction from Forstner et
al. (2006) is based on flawed analysis of mass-length relationships for
female snakes. This relationship is curvilinear (represented by a
curved, rather than straight, line) and, therefore, the data should
have been log transformed or fit using a power function rather than a
simple linear analysis. Based on this, at most only one of the four
females found by Forstner et al. (2006) appears to have low mass
suggesting a post-partum state that indicates reproduction. Also, since
evidence of reproduction was found at only a single site below Freese
Dam (Ivie Reservoir) by Forstner et al. (2006), it is premature to
conclude that a viable population exists in this reach.
Our Response: We agree that the use of a curvilinear function
analysis would have been more statistically robust in the Forstner et
al. (2006, p. 11) report to evaluate reproductive status of females.
However, this analysis was not intended to make a strong statistical
argument, but simply to substantiate the field observations of females
appearing to be post-partum. These adult female snakes had lower body
tone in the rear third of the body indicating (in the authors'
experience with this taxon and with snakes in general) that recent
offspring had been released. Although access to the river reach
downstream of Freese Dam (Ivie Reservoir) was limited due to private
property, Forstner et al. (2006, p. 18) conclude that, even with
limited samples, snakes were found at the two sites available in this
reach documenting that the species was persisting and reproducing in
this reach. This information serves to confirm the results of the
earlier 10 years of monitoring studies that found large numbers of
snakes in this reach, and throughout the species' current range.
(9) Comment: The simple interpretation of lambda ([lambda], a
calculation of the finite rate of population increase) from Whiting et
al. (2008) using the preferred stage-based model ([lambda] = 0.67 to
0.78) is that the species is declining 22 to 33 percent per generation.
This, in addition to low survivorship of neonates, is strong evidence
that Concho water snake populations are not viable.
Our Response: Whiting et al. (2008, p. 443) explains that the
modeling results of the finite rate of increase from the mark-recapture
study were biased low due to the effect of dispersal of snakes out of
the study areas, and this is what produced the low estimate of
[lambda]. Since dispersal rates were not measured in the study, the
analysis resulted in a large standard error and imprecise conclusions
with high uncertainty. Whiting et al. (2008, p. 443) go on to conclude
that the Concho water snakes have evolved through stochastic
environmental fluctuation (such as droughts, floods, and fires) and
occur in high densities in riverine habitats, with low extinction risk.
This finding is consistent with the conclusion by Forstner et al.
(2006, p. 19) that the populations of the snake appear to be viable.
Whiting et al. (2008, p. 442) suggested that low survivorship values
(for both juveniles and adults--rates for neonates were not calculated)
compared to other similar snakes are being offset by increased
reproductive effort with higher clutch sizes (number of young produced)
in Concho water snakes than other similar snakes (Greene et al. 1999,
pp. 706-707). Also see our response to (1) Comment above.
(10) Comment: The documented persistence of Concho water snakes
during long-term droughts, coupled with the 2008 MOU, which will
maintain minimum flow releases, provide a reasonable amount of
confidence that the recovery criterion for maintaining adequate flows
has been met. Loss of flows no longer poses a significant threat to the
Concho water snake.
Our Response: We agree. The minimum flow releases provided by the
2008 MOU, other reservoir releases for water delivery and water quality
management, and natural inputs to the rivers from springs and tributary
streams, combined with the snakes' ability to withstand stochastic
events like droughts, make this threat no longer of sufficient
magnitude to warrant the species' listing as threatened.
(11) Comment: The 2008 MOU states that the District can further
reduce or even terminate flows during times of extremely low inflow.
Given the fairly well documented climate change that is now occurring,
which may influence the lengths of drought in the region (and hence the
amount of inflow), coupled with the thought that these animals rarely
live longer than 5 years, I question whether it is reasonable to leave
the MOU so loosely written. Perhaps the Service might choose to be
notified after some length of time has passed with no flow occurring so
that an assessment can be made as to its effects on the snake
populations?
Our Response: The 2008 MOU between the Service and the District
does provide the District the ability to forego the minimum flow
releases in the event of ``extended hydrological drought and to provide
water for health and human safety needs.'' The drought measure is based
on reservoir elevation (1,843.5 feet (ft) (561.9 meters (m)) above mean
sea level at Spence Reservoir, and 1,504.5 ft (458.5 m) at Ivie
Reservoir). These elevations represent the stage when the reservoirs
are at about 12 percent of reservoir capacity. These criteria for
foregoing minimum flow releases are consistent with the operations
included in the 2004 Biological Opinion (Service 2004a, pp. 11-12).
Since Spence Reservoir was initially filled in 1971, the water level
elevation has only been below this mark during 2002 to 2004, at the end
of a prolonged drought extending from 1992 to 2003 (District 2005, pp.
39-43). This reach of the Colorado River below Spence Reservoir makes
up about 36 percent of all estimated available habitat within the
current range of the Concho water snake (Service 2004a, p. 72). Ivie
Reservoir has not been below this mark since it initially filled in
1991. Discharge in the river is well-monitored with gauges maintained
by the U.S. Geological Survey (USGS), and flow data (historical and
real time) are available on-line. Reservoir stage data are also
available on-line on the District's webpage. Therefore, these data can
be easily accessed making a notification process unnecessary. Under our
post-delisting monitoring plan, we will be using existing stream gauges
to monitor instream flows throughout the range of the snake. This
information will be used in combination with biological monitoring data
to assess the status of the species in the future (see
[[Page 66784]]
the Post-Delisting Monitoring Plan section below).
We have revised our discussion of the effects of drought on the
Concho water snake and included in the discussion a consideration of
future climate change (see section A. The Present or Threatened
Destruction, Modification, or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced Instream Flows, below). Also, see our
response to Comment 12 below.
(12) Comment: Drought continues to be a threat because, despite the
species' persistence through historic droughts, it now occurs in
combination with other stressors, such as reduced availability of
riffles, vegetation encroachment, and changing prey base that may
compromise survival and population recovery following a drought.
Our Response: We have substantially increased our analysis in this
final rule of the potential effects of declining flows due to drought,
as well as other threats (see Summary of Factors Affecting the
Species). We found none of these potential threats, either acting alone
or in combination, have resulted in negative responses by the snake
sufficient to justify the species' continued listing as threatened.
Forecasting the impacts from future climatic events, such as drought,
is difficult to quantify because of the large amount of uncertainty
associated with climate modeling, particularly related to precipitation
forecasting. However, we revised our discussion of threats related to
drought and climate change in this final rule (see section A. The
Present or Threatened Destruction, Modification, or Curtailment of Its
Habitat or Range, Habitat Modification from Reduced Instream Flows
below).
We do not foresee future habitat conditions deteriorating to a
point where the species is likely to become endangered. Forstner et al.
(2006, pp. 15-17) and Whiting et al. (2008, p. 343) explain that the
snake is well adapted to extreme drought conditions. This is
demonstrated in the Concho River where the snake continues to persist
despite extremely low flow conditions (Dixon 2004, pp. 8-9, Forstner et
al. 2006, p. 8). The snake has been shown to be more abundant and
widespread than originally thought and capable of surviving in
reservoirs (District 1998, pp. 18-29). Reservoir operations have
provided continual stream flows that have sustained the habitat for the
species, even during the prolonged drought extending from 1992 to 2003
(District 2005, pp. 39-43), and we expect minimum reservoir releases to
continue. In addition, the snake is equipped to handle stochastic
environmental fluctuations, such as low stream flow conditions
resulting from drought, and has demonstrated the ability to persist in
these less-than-favorable habitat conditions (Forstner et al. 2006, p.
17; Whiting et al. 2008, p. 443). Also, the threat of vegetation
encroachment is no longer considered a significant threat because the
snake has shown the ability to maintain populations in river reaches
with substantial vegetation encroachment (Dixon 2004, p. 9).
Additionally, habitat restoration efforts such as the removal of salt
cedar and other brushy species and the creation of artificial instream
riffle structures are aimed at improving habitat for the Concho water
snake to increase their likelihood of survival during droughts and
other stressors. We expect some salt cedar control efforts to continue
into the foreseeable future.
(13) Comment: The importance of groundwater-surface water
interactions to maintain adequate flows is stressed in the proposed
rule. However, there does not appear to be a clear understanding of
where groundwater pumpage for consumptive use has influenced base
flows. Existing groundwater-surface water interaction models, and even
simple gain and loss studies, could provide critical information
regarding where the influence of groundwater pumping may influence
critical flows and available habitat.
Our Response: We agree this could be important information to
consider. We assume there is some influence of local and regional
groundwater withdrawals on the availability of water for instream
flows. However, we are not aware that such information is currently
available or that to quantify this relationship within the range of the
Concho water snake is possible at this time.
(14) Comment: Has the occurrence and status of riffle habitat been
quantified using GIS or remote imagery in the reaches where the species
is known to occur?
Our Response: We are not aware of the availability of this type of
information, and the publicly available imagery is not of sufficient
resolution to reliably quantify snake habitat in the river. The Service
did estimate the quantity and quality of snake habitat by reach in the
2004 Biological Opinion (Service 2004a, Appendix B, pp. 70-72), and we
consider it to still be reasonably accurate and the best information
available . The information has been added to this final rule (see A.
The Present or Threatened Destruction, Modification, or Curtailment of
Its Habitat or Range, Habitat Quality and Quantity section below). The
river reaches in question remain largely undeveloped.
(15) Comment: The suggestion that pool habitats, created by the
backwater behind low-head dams, provide refuges for snakes during
drought is unsubstantiated. These habitats may represent population
sinks, where mortality exceeds recruitment.
Our Response: The suggestion that pools behind low-head dams act as
refuge habitats comes from the expert opinion of Dr. James Dixon (Dixon
2004, p. 16). Dr. Dixon is considered a reliable source, as he has
studied this species since 1991 (see Werler and Dixon 2000, pp. 209-
216).
(16) Comment: The proposed rule indicates that `an excellent first
step' in reversing vegetation encroachment has been accomplished (73 FR
38962). While laudable, a `first step' should not be construed as
success in eliminating vegetation encroachment as a threat.
Our Response: Recent efforts by the District to control salt cedar
are conservation actions that we expect will benefit the Concho water
snake through maintaining native riparian vegetation and possibly
providing additional instream flows. These actions do not completely
eliminate vegetation encroachment. However, vegetation encroachment,
such as has occurred on the Concho River, is not considered a
significant threat since the snake has shown the ability to maintain
populations in river reaches with substantial vegetation encroachment
(Dixon 2004, p. 9). We have revised the discussion of vegetation
encroachment within this final rule (see A. The Present or Threatened
Destruction, Modification, or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced Channel Maintenance Flows section
below).
(17) Comment: It seems reasonable to assume that there is likely
movement between snake populations with the discovery that the snakes
are living in the reservoirs, and, therefore, likely little threat from
population fragmentation. Have there been studies of possible gene flow
between the populations?
Our Response: We agree that fragmentation has been reduced with the
new information on the persistence of the snake in reservoirs. We
presume that over time, this allows snakes from the upper Colorado
River reach (below Spence Reservoir) to interact with snakes from the
Concho River reach by moving through Ivie Reservoir. Previous studies
conducted on gene flow suggested that populations of snakes above and
below Freese Dam should be more than large enough to maintain
[[Page 66785]]
existing genetic variation based on mitochondrial DNA analysis (Sites
and Densmore 1991, p. 10). We presume that is still the case. Densmore
(1991, pp. 10-11) went on to say that periodic transfer of snakes
should probably be implemented to mimic gene flow. More recent analysis
has been initiated using modern molecular techniques to evaluate
possible gene flow between populations, but data or results from these
studies by Dr. Michael Forstner (2008) have not yet been reported.
Forstner (2008, p. 14) does suggest that there is no evidence that
Freese Dam (Ivie Reservoir) is a barrier to gene flow for either water
snake in the Colorado River. However, the report notes that it may have
been too short a time to detect such a change (Forstner 2008, pp. 14-
15), and we do not know whether there are adequate sample sizes from
this study to reliably describe gene flow levels between populations or
river reaches; however, the 2008 MOU calls for the movement of snakes
to provide some gene flow between river reaches.
(18) Comment: Have any mark and recapture studies been done to
demonstrate the movement of snakes between fragmented habitat, e.g.,
from reservoir to below reservoir and to quantify dispersal of
individuals within reservoirs?
Our Response: Some mark-recapture and radio telemetry studies have
documented movements in Concho water snakes (Werler and Dixon 2000, p.
212). Although most snakes showed strong site fidelity, some snakes
moved as far as 12 mi (19 km). No studies have documented long-range
movements between populations or around a large dam. However, the 2008
MOU calls for periodic movement of snakes around the large dams. In
addition, the 2008 MOU was amended in 2011 to also include the movement
of five snakes from above both dams to below both dams. The 2008 MOU
calls for the movement of five snakes from below Spence and Freese dams
to above these dams every 3 years. This amount of transfer of snakes
should be more than sufficient to maintain gene flow, as studies have
shown that as few as one individual exchanged with each generation may
be sufficient to maintain adequate gene flow between animal populations
(Mills and Allendorf 1996, p. 1,557). Also see the discussion below
under Habitat Modification from Fragmentation.
(19) Comment: What is the evidence that fish populations are viable
and that cyprinids (minnows) and their habitat (e.g., riffles) are of
sufficient quality and quantity in all three reaches? Is the opinion of
one or more scientists adequate, or is there sufficient data on the
status or trends of fishes in the three reaches to support the
assumption that the fish prey base for the Concho water snake is
sufficient? Are there data, such as the Texas Commission on
Environmental Quality's (TCEQ) Clean Rivers Program data on fishes,
which could be analyzed to determine if there are any trends in fish
populations worth noting? How are the fish populations that the snakes
depend on for food going to fare in situations like prolonged drought?
Our Response: We have revised the discussion of forage fish
availability under the section A. The Present or Threatened
Destruction, Modification, or Curtailment of Its Habitat or Range,
Habitat Modification from Reduced Instream Flows below to better
explain why we do not find that lack of forage fish is a significant
threat to the snake. We are not aware of additional fish data that
could inform our decision on the Concho water snake. However, a review
of the 10 years of fish surveys by the District from 1987 to 1996
showed that the snakes were opportunistic predators on a variety of
fish species (Service 2004a, Appendix A, pp. 68-69). The most abundant
fish available and in the snakes' diet are fish species that are
adapted to harsh stream conditions (intermittent flow and poor water
quality), such as red shiners (Cyprinella lutrensis) (Burkhead and Huge
2002, p. 1) and fathead minnows (Pimephales vigilax) (Sublette et al.
1990, pp. 162-166). Together these two fishes made up two-thirds of the
diet of the Concho water snakes. We expect populations of these fish
species to persist in harsh environments with intermittent water
available (Burkhead and Huge 2002, p. 1; Sublette et al. 1990, pp. 162-
166). We also expect them to quickly recolonize stream reaches from
reservoirs or other refuge habitats after dewatered conditions due to
drought have ended. This is based on observations of the snakes being
found at sites where they were absent due to lack of water and being
found again when the water returns. This occurred in 2004 at Ballinger
Lake and Elm Creek (Dixon 2004, pp. 4, 11-12; Forstner et al. 2006, p.
15).
(20) Comment: Were nutrient concentrations in water actually
evaluated in relation to algal productivity? Is the fish assemblage
changing in species composition or relative abundance in response to
changing nutrient conditions?
Our Response: The reference to nutrient concentrations and algal
productivity was related to past concerns as a possible threat to the
Concho water snake during the 1986 listing. We are not aware of data
connecting increases in nutrient concentrations to algal productivity
or changes in fish species composition or relative abundance within the
range of the Concho water snake. There has been no subsequent
indication that these threats are actually occurring or are affecting
fish communities or snake populations.
(21) Comment: References in reports indicate decreased cooperation
by private landowners, indicating stakeholder buy-in is inadequate,
raising the possibility that harassment and persecution of snakes now
and following delisting is a threat.
Our Response: We have no information that intentional harassment
and persecution by landowners or recreationists are likely to affect
the species on a rangewide or local population level. The reference
(Forstner et al. 2006, p. 18) did not indicate decreased cooperation by
private landowners, but that new landowners were not easily contacted
due to changing ownership. We have revised the discussion to further
explain this threat under Factor B. Overutilization for Commercial,
Recreational, Scientific, or Educational Purposes.
Comments From State Agencies
(22) Comment: The TPWD accepted the District's 1998 arguments to
delist the Concho water snake and did so on November 16, 2000. TPWD
believes the continuing conservation efforts of the District and other
interested parties will ensure the snake's place as a member of the
native fauna of Texas for the foreseeable future.
Our Response: We agree with the comment by the TPWD that the Concho
water snake no longer qualifies as a threatened species.
(23) Comment: Removing the Concho water snake from protection under
the Act will reduce the costs and time associated with section 7
consultations with the U.S. Fish and Wildlife Service. As a result,
TxDOT may now delay the letting of some projects until after the final
delisting occurs.
Our Response: We understand that removing the species from the
Federal list of threatened species will benefit some planned actions by
eliminating the requirement for section 7 consultations for actions
with a Federal nexus that may affect the Concho water snake.
Comments From the Public
(24) Comment: A comment from the District explained that they
conducted field studies on the Concho water snake
[[Page 66786]]
from 1987 to 1996 that demonstrated the snake population was much more
stable than previously thought. Later field studies in 2003 to 2007
determined the snake was in a recovered state. Additionally, the
District agreed to provide stream flow discharge from two of its
Colorado River reservoirs (E.V. Spence and O.H. Ivie Reservoirs), which
further supports the long-term existence of the snake.
Our Response: The Service recognizes the many years of field
studies that the District conducted, and the benefits of the District's
partnership with the Service in signing the 2008 MOU to provide
reservoir releases for the Concho water snake. The recovery of the
Concho water snake and its removal from the list of threatened species
are largely due to the efforts of the District to provide reservoir
releases to maintain snake habitats over the past 20 years and into the
future, and to collect new information documenting the biology,
distribution, and abundance of the snake.
(25) Comment: The proposed delisting fails to make a convincing
case that recovery of the Concho water snake is sufficient to justify
its removal from threatened species protections. The proposal's
arguments are vague, circular, repetitive, and sometimes contradictory.
There is little supporting data or science provided. The delisting is
premature and unsupported.
Our Response: We disagree with the commenter's conclusions. We have
updated and clarified the text in this final rule in response to this
and other comments received to better explain our analysis and
conclusions. Specifically, we revised the discussion and analysis under
section A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range. The Service believes the removal
of the snake is warranted based on the best available scientific
information.
(26) Comment: The proposed rule fails to adequately address
availability of, and threats to, the important riffle habitats of the
Concho water snake. For example, reservoir habitats used by the snake
must be equal to or greater than the amount of riverine riffle habitats
lost due to effects of the reservoir construction at O.H. Ivie
Reservoir. The range extension for the snake does not include
information on the amount and quality of habitat and its use by snakes.
There is no estimate provided of past or future loss of riffle habitat,
or an assessment of the long-term success of the artificial riffles, to
support that riffle habitat loss is not still a threat to the Concho
water snake.
Our Response: We recognize that there has been, and will continue
to be, changes in the characteristics of the riverine habitat within
the range of the Concho water snake as a result of past and ongoing
human activities. While there have not been any recent studies to
quantify these changes, the best available data indicate that any
possible loss of riffle habitat is not resulting in impacts that would
likely cause the snake to become endangered. The best example is
observed in the Concho River where the long-term substantial decline in
minimum stream flows and the loss of flushing flood flows have reduced
natural riffle habitats available (Dixon 2004, pp. 8-9). However,
Concho water snakes continue to persist in relatively high numbers in
this reach. For example, 20 of the 45 Concho water snakes observed or
captured by Forstner et al. (2006, p. 8) were from the Concho River. In
addition, the snake's use of other habitats, including reservoir
shorelines, lessens the overall effect of decreased riffle habitat
availability. We have revised our discussion in this final rule and
provided a quantified estimate of habitat availability by reach
throughout the range of the species (see section A. The Present or
Threatened Destruction, Modification, or Curtailment of Its Habitat or
Range, Habitat Quality and Quantity below).
(27) Comment: The proposed rule fails to address the size and
health of reservoir populations. Whiting et al. (2008) notes that the
species occurs in relatively low densities in reservoirs, and they
believe the snake may be more vulnerable to extinction in reservoirs.
It appears unlikely that the use of reservoir habitats by Concho water
snakes provides sufficient improvement in species status to support
removal of threatened protection.
Our Response: The ability of Concho water snakes to survive and
reproduce in reservoirs is one factor among many we considered in
determining that the species is no longer threatened. There is some
evidence that snake populations in the reservoirs are not as robust as
those in their native riverine habitats. We would expect this given
that the snake habitat in reservoirs is likely of a somewhat lower
quality and in less abundance compared to natural riverine habitats.
This is because the reservoirs may have less shallow flowing water over
rocky substrates that support small fish that are the prey base for the
snake. However, Whiting et al. (2008, p. 443) concluded that data are
not sufficient for truly reliable estimates of snake survival and
population growth in either of the two main reservoirs. Although the
authors aimed to compare populations in reservoirs with those in
rivers, data did not allow that analysis due to the inability to
sufficiently quantify immigration rates (Whiting et al. 2008, p. 443).
The statement by Whiting et al. (2008, p. 443) that Concho water snakes
may be more vulnerable to local extinction in lakes was in the context
that the extinction risk in natural river habitats is relatively low
due to the snake's occurrence in high densities and their ability to
grow fast and mature early. The ability of the species to utilize
reservoirs is a positive discovery and supports the conclusion that the
impacts of the reservoirs were not as great as initially predicted.
Also, see our response to (1) Comment above.
(28) Comment: The proposed rule indicated that confirming that a
species has persisted over time and continues to demonstrate
reproductive success is sufficient to assume that populations are
viable. Persistence and reproduction are not adequate to demonstrate
population viability. The statement that the populations are
``seemingly viable'' is a tentative conclusion that is scientifically
and legally unsupportable.
Our Response: Our explanation of population viability may have
oversimplified the explanation by Forstner et al. (2006, p. 20)
describing the status of Concho water snake populations. We understand
that documenting persistence and reproduction is not adequate to
precisely determine viability in most quantitative ecological contexts.
In response to this comment, we have updated our explanation to
describe that there are not adequate data for quantitative modeling for
population viability analysis of this species (see Application of the
Recovery Plan's Criteria section below). We have revised this
discussion in the final rule to instead refer to the definition of
viable population given in the recovery plan. The recovery plan defines
viable population as one that is self-sustaining, can persist for the
long-term (typically hundreds of years), and can maintain its vigor and
its potential for evolutionary adaptation (Service 1993, p. 33). We
have also included a more detailed summary of the results of the 10
years of snake monitoring, which concluded in 1996. These extensive
data, in conjunction with updated limited survey data in 2004 and 2005,
are the basis for determining that populations of Concho water snake
are viable. In addition, it is important to recognize the standard
under the Act is to determine if the species is likely to become
endangered in the foreseeable future. Given the best available
information, weighing the status of the species and
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the current and future threats, we have concluded that the snake is no
longer likely to become endangered in the foreseeable future throughout
all or a significant portion of its range.
(29) Comment: The discussion in the proposed rule regarding effects
of drought is poorly articulated and circular. The stated belief that
the Concho water snake and its fish prey base can and will survive any
level and duration of drought is unsupported by data or analysis in the
proposal.
Our Response: We did not intend to imply that snakes can survive
any level of drought, but we believe they can survive the expected
drought conditions in the foreseeable future, based on historical
records and considerations over the last thousand years based on tree-
ring analysis (summarized in Forstner et al. 2006, p. 16). We are
relying on the expert opinion and field experience of long-term
herpetologists, explained in Forstner et al. (2006, pp. 15-17) and
Whiting et al. (2008, p. 443) that the Concho water snake has evolved
in a drought-prone, hydrologically dynamic system and has demonstrated
the ability to withstand stochastic environmental fluctuations. This
characteristic of the snake to endure periods of drought and resulting
poor habitat conditions was documented for the Concho River reach and
at Lake Ballinger on Elm Creek, a Colorado River tributary (Dixon 2004,
pp. 9, 11-12; Forstner et al. 2006, p. 17; Whiting et al. 2008, p.
443). Due to water management and climate change, future droughts could
be more severe than the historical record over the last 100 years.
However, we cannot foresee that these conditions are likely to be so
severe as to result in the extinction or endangerment of the snake. To
make this explanation clearer, we have rewritten the discussion in this
final rule (see section A. The Present or Threatened Destruction,
Modification, or Curtailment of Its Habitat or Range, Habitat
Modification from Reduced Instream Flows below).
(30) Comment: The success in abatement of threats over the 22 years
since the Concho water snake was listed appears to be overstated in the
proposed rule. Long-term success of artificial riffle construction to
increase riverine habitat is not yet determinable. The 15 or so years
since artificial riffle installation are not long-term in a hydrologic
sense. It is my understanding the artificial riffles have not been
assessed for several years.
Our Response: The artificial riffles constructed in 1989 produced
immediate results as snakes were found there by 1991 (District 1998,
pp. 13, 15). The six riffles were monitored from their creation in 1991
through 1996, and snakes were consistently found at five of the six
sites (Thornton 1996, pp. 44-49). The success of the snakes in the
reservoirs and in the artificial riffles resulted in less attention
being given to the need to mitigate further for the habitat loss from
reservoir construction. We are not aware of any recent monitoring
efforts focused on the artificial riffles, but we have no reason to
believe the snakes are not continuing to persist there.
(31) Comment: Other than species persistence, data and studies upon
which the 2004 reduction of minimum instream flows was based are not
discussed. There are also no studies documenting the results of the
reductions in the required flow.
Our Response: A full explanation and analysis of effects of the
2004 reduction in required flows is documented in the Service's
biological opinion provided to the U.S. Army Corps of Engineers as a
conclusion to the formal section 7 interagency consultation for the
change in reservoir operations (Service 2004a, pp. 1-76). The analysis
included updated biological information that the snakes use more
diverse riverine habitats (such as pools, in addition to riffles) and
were found in the reservoirs and tributaries (Dixon 2004, pp. 9, 16;
Service 2004, pp. 53-54). As a result of that consultation, we gave our
biological opinion that the reduced reservoir releases described in the
proposed agency action were not likely to jeopardize the continued
existence of the Concho water snake and were not likely to destroy or
adversely modify designated critical habitat. These same flow rates
were used in the 2008 MOU. In making the delisting proposal and now the
final rule, we relied heavily on the results of monitoring by Forstner
et al. (2006, p. 1-22) in concluding that the reduced flow rates are
sufficient for the snake.
(32) Comment: The 2004 Biological Opinion substantially changed the
1986 requirement for high discharge channel maintenance flows below
O.H. Ivie Reservoir. That change is not discussed in the proposed rule,
and would be of particular importance in understanding the basis for
the habitat loss downstream of reservoirs.
Our Response: We have added information to the final rule
explaining the changes in requirements for channel maintenance flows
(see section A. The Present or Threatened Destruction, Modification, or
Curtailment of Its Habitat or Range, Habitat Modification from Reduced
Channel Maintenance Flows below). The 2004 Biological Opinion and the
2008 MOU both recognize the benefits of periodic high discharges from
either reservoir releases or flood runoff events to function in river
channel maintenance to maintain suitable rock substrates and abate
vegetation invasion of riffle habitat. Our analysis concludes that some
flushing flows are likely to naturally occur, slowing the degradation
of aquatic habitats. In addition, the snakes appear capable of
sustaining populations in areas where instream habitats have been
altered due, in part, to reducing flushing flows. In some areas, such
as on the Concho River, the dominant substrate is solid bedrock and not
as subject to invasion of vegetation. Cracks and breaks in the bedrock
provide foraging habitat similar to riffles. Therefore, we did not find
that the threats of reduced flushing flows are significant.
(33) Comment: Although the proposed rule says that the District has
implemented every activity requested by the Service in previous
biological opinions, the District's compliance was largely due to
removal of requirements that they objected to prior to finalizing the
opinion and removal of others by later amendments. The statement that
the District has an excellent track record of carrying out conservation
actions should be supported by information.
Our Response: The 1986 Biological Opinion was amended many times up
until the major revision in 2004 due to changing conditions based on
new information being collected (Service 2004a, pp. 1-3). A discussion
of the District's compliance efforts under the previous biological
opinions is documented in the 2004 revised biological opinion (Service
2004a, pp. 42-47). We have also added information throughout this final
rule to document important areas where the District has fulfilled its
requirements.
(34) Comment: There is no evidence provided that the instream flow
requirements from the 2004 Biological Opinion and 2008 MOU are
sufficient to ensure long-term species survival.
Our Response: We believe the flows provided in the 2008 MOU are
sufficient to ensure long-term species survival. This is based on the
information demonstrating that the species can survive under
substantially lower flows compared to what was previously thought.
These conclusions are based on the observations and reports of species
experts (Dixon 2004, p. 16; Forstner et al. 2006, pp. 19-21; Whiting et
al. 2008, p. 443). We have also revised the discussion of the threats
from reduced instream flows in this final rule to include additional
information and discussion on hydrology, climate
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change, and the potential response by the snake (see section A. The
Present or Threatened Destruction, Modification, or Curtailment of Its
Habitat or Range, Habitat Modification from Reduced Instream Flows
below).
(35) Comment: The 2008 MOU was entered in good faith, but it is not
legally enforceable. There is no consequence to the District for a
lapse in conservation actions. The MOU is not an adequate substitute
for legal protection under the Act.
Our Response: We do not consider the 2008 MOU (including the 2011
amendment) as a substitute for the legal protections under the Act. It
does document the commitment that the District will continue to
cooperate in maintaining instream flows downstream of the two Colorado
River reservoirs. These flows are in addition to other reservoir
releases for water delivery and water quality management, and natural
inputs to the rivers from springs and tributary streams. Given the
District's track record of compliance and completing conservation
actions, we have no reason to doubt that the District will continue to
carry out the actions agreed to in the 2008 MOU (including the 2011
amendment). In addition, Section 5.2 of the MOU notes the Service's
ability to list the snake again under protection of the Act. This
provision includes use of emergency listing procedures if warranted.
(36) Comment: Initiation of salt cedar control does nothing to
guarantee threat abatement to Concho water snake habitat. Salt cedar
control has a long history of variable and generally quite limited
success. It will be many years before it can be determined if the
recently initiated project will provide any benefit to the snake.
Our Response: Salt cedar control is one conservation action that
can provide benefits to the Concho water snake through restoration of
native riparian vegetation to provide natural stream-side habitat
conditions and potential water savings for instream flow increases. We
agree with the comment that it will take time to document the actual
benefits to the snake.
(37) Comment: The proposal acknowledges that delisting recovery
criteria from the recovery plan have not been met, but claims
additional information has rendered those criteria partially invalid.
This undermines the recovery planning process and is offensive to the
many stakeholders who participate in recovery plan development. If the
recovery plan is out-of-date or otherwise invalid, the Service should
convene the recovery team and amend or rewrite the plan with
appropriate public and stakeholder review. This will yield a firmer
basis and greater support than the current process for delisting.
Our Response: The Service believes that the Concho water snake has
recovered and generally met the criteria from the 1993 recovery plan.
Although meeting the recovery criteria is not necessarily required for
delisting, we have discussed the criteria below in this final rule
section Application of the Recovery Plan's Criteria. The S