65FR37343 Endangered and Threatened Wildlife and Plants; Proposal to List the Chiricahua Leopard Frog as Threatened With a Special Rule, Part 1/2
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[Federal Register: June 14, 2000 (Volume 65, Number 115)]
[Proposed Rules]
[Page 37343-37357]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr14jn00-37]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
RIN 1018-AF41
Endangered and Threatened Wildlife and Plants; Proposal to List
the Chiricahua Leopard Frog as Threatened With a Special Rule
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Proposed rule.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose
threatened status pursuant to the Endangered Species Act of 1973, as
amended (Act), for the Chiricahua leopard frog (Rana chiricahuensis).
The Chiricahua leopard frog is now absent from many historical
localities and numerous mountain ranges, valleys, and drainages within
its former range. In areas where it is still present, populations are
often few, small, and widely scattered. Known threats include habitat
alteration, destruction, and fragmentation, predation by nonnative
organisms, and disease. Habitat loss results from water diversions,
dredging, livestock grazing, mining, degraded water quality, and
groundwater pumping. Problems associated with small population numbers
and size also threaten the species. Evidence suggests that adverse
effects from water-borne contaminants may also threaten this species.
This proposed rule, if made final, would implement Federal protection
to this species and provide funding for development and implementation
of recovery actions.
DATES: We must receive comments from all interested parties by
September 12, 2000. We must receive public hearing requests by July 31,
2000.
ADDRESSES: Send comments and materials to the Field Supervisor, Arizona
Ecological Services Field Office, U.S. Fish and Wildlife Service, 2321
West Royal Palm Road, Suite 103, Phoenix, Arizona 85021-4951. Comments
and information received will be available for public inspection, by
appointment, during normal business hours at the above address.
FOR FURTHER INFORMATION CONTACT: Jim Rorabaugh, Herpetologist, at the
above address (telephone 602/640-2720; facsimile 602/640-2730).
SUPPLEMENTARY INFORMATION:
Background
Leopard frogs (Rana pipiens complex), long considered to consist of
a few highly variable species, are now recognized as a diverse
assemblage of more than two dozen species (Hillis et al. 1983), with
many species described in the last 20 years. Mecham (1968) recognized
two distinct variations of ``Rana pipiens'' in the White Mountains of
Arizona. One of these, referred to as the ``southern form,'' was
depicted as a stocky frog with raised folds down both sides of the back
(dorsolateral folds) that were interrupted and deflected medially
towards the rear. The other form matched previous descriptions of Rana
pipiens. Based on morphology, mating calls, and genetic analyses
(electrophoretic comparisons of blood protein samples), Platz and Platz
(1973) demonstrated that at least three distinct forms of leopard frogs
occurred in Arizona, including the southern form. This southern form
was subsequently described as the Chiricahua leopard frog (Rana
chiricahuensis) (Platz and Mecham 1979).
[[Page 37344]]
This new species was distinguished from other members of the Rana
pipiens complex by a combination of characters, including a distinctive
pattern on the rear of the thigh consisting of small, raised, cream-
colored spots or tubercles on a dark background, dorsolateral folds
that were interrupted and deflected medially, stocky body proportions,
relatively rough skin on the back and sides, and often green coloration
on the head and back (Platz and Mecham 1979). The species also has a
distinctive call consisting of a relatively long snore of 1 to 2
seconds in duration (Davidson 1996, Platz and Mecham 1979). Snout-vent
lengths of adults range from approximately 54 to 139 millimeters (mm)
(2.1 to 5.4 inches (in)) (Stebbins 1985, Platz and Mecham 1979). The
Ramsey Canyon leopard frog (Rana subaquavocalis) is similar in
appearance to the Chiricahua leopard frog, but it often grows to a
larger size and has a distinct call that is typically given under water
(Platz 1993).
Recent articles in the scientific literature report the extirpation
and extinction of amphibians in many parts of the world (Berger et al.
1998, Lips 1998, Laurence et al. 1996, Vial and Saylor 1993, Pechmann
et al. 1991, Blaustein and Wake 1990). Frogs in the family Ranidae,
which includes the Chiricahua leopard frog, are particularly affected
(Sredl et al. 1997, Sredl 1993, Bradford 1991, Clarkson and Rorabaugh
1989, Hayes and Jennings 1986, Corn and Fogleman 1984). Although these
population declines are thought to result in many cases from habitat
loss, predation by introduced predators, or other factors, populations
are sometimes extirpated from seemingly pristine habitats or from areas
where no obvious cause of decline can be identified (Meyer and Mikesic
1998, Sredl 1993, Drost and Fellers 1993, Corn and Fogleman 1984, Hines
et al. 1981). Although natural long-term fluctuations in the size of
populations and the number of populations within a species are often
not well studied, increased extirpation rates and in some cases
apparent extinction, coupled with recent declining trends in the status
of many amphibian species is alarming and may represent a very recent
and rapid global decline of an entire class of vertebrates (Blaustein
et al. 1994, Wake 1991).
Observers have speculated that these declines may have resulted
from one or more factors, including habitat disturbance, predation by
introduced predators such as nonnative fish and amphibians, disease,
drought, pesticides, acid rain, heavy metals, increased ultraviolet
radiation due to atmospheric ozone depletion, over-collection, natural
events such as severe storms or floods, global warming or other
climatic events, and as a result of the dynamics of small populations
and groups of small populations or metapopulations (Berger et al. 1998,
Lips 1998, Lind et al. 1996, Rosen et al. 1996, 1994; Hale et al. 1995,
Blaustein et al. 1994, Sredl and Howland 1994, Pounds and Crump 1994,
Sredl 1993, Bradford 1991, Wyman 1990, Clarkson and Rorabaugh 1989,
Corn and Fogleman 1984, Baxter and Meyer 1982, Dimmitt 1979).
The Chiricahua leopard frog is an inhabitant of cienegas (mid-
elevation wetland communities often surrounded by arid environments),
pools, livestock tanks, lakes, reservoirs, streams, and rivers at
elevations of 1,000 to 2,710 meters (m) (3,281 to 8,890 feet (ft)) in
central and southeastern Arizona; west-central and southwestern New
Mexico; and in Mexico, northern Sonora and the Sierra Madre Occidental
of Chihuahua (Sredl et al. 1997, Degenhardt et al. 1996, McCranie and
Wilson 1987, Platz and Mecham 1979). The taxonomic status of frogs in
southern Chihuahua and possibly Durango is in question. The species has
been reported from southern Chihuahua and Durango (Hillis et al. 1983,
Platz and Mecham 1984, 1979); however, Webb and Baker (1984) concluded
that frogs from southern Chihuahua were not Chiricahua leopard frogs,
as expected. The range of the species is divided into two parts,
including--(1) a southern group of populations (the majority of the
species' range) located in mountains and valleys south of the Gila
River in southeastern Arizona, extreme southwestern New Mexico, and
Mexico; and (2) northern montane populations in west central New Mexico
and along the Mogollon Rim in central and eastern Arizona (Platz and
Mecham 1979). There are historical records in Pima, Santa Cruz,
Cochise, Graham, Apache, Greenlee, Gila, Coconino, Navajo, and Yavapai
counties, Arizona; and Catron, Grant, Hidalgo, Luna, Soccoro, and
Sierra counties, New Mexico (Sredl et al. 1997, Degenhardt et al.
1996). Historical records for the Chiricahua leopard frog also exist
from several sites in northern and central Chihuahua, northern Sonora,
and possibly southern Chihuahua and Durango (Platz and Mecham 1984,
1979; Webb and Baker 1984; Hillis et al. 1983).
Male Chiricahua leopard frogs exhibit variable development of
vestigial (small, nonfunctional) oviducts. Vestigial oviducts are
absent in most specimens from the northern populations but are
generally present in specimens from southern populations (Platz and
Mecham 1979). This and other characteristics that differ regionally
throughout the range of the species suggest genetic differentiation.
This differentiation is being investigated and may result in a
description of the northern populations as a separate species from the
southern populations (James Platz, Creighton University, pers. comm.
1994). If the species is split into two distinct taxa, fewer
populations would exist within each taxon.
Chiricahua leopard frogs were either collected or observed at 212
localities in Arizona (B. Kuvlesky, Buenos Aires National Wildlife
Refuge, pers. comm. 1997; Terry Myers, Apache-Sitgreaves National
Forest, pers. comm. 1997; Sredl et al. 1997; Rosen et al. 1996; Snyder
et al. 1996; C. Schwalbe, University of Arizona, pers. comm. 1995; R.
Zweifel, Portal, Arizona, pers. comm. 1995; Hale 1992; Clarkson and
Rorabaugh 1989; Fish and Wildlife Service files, Phoenix, Arizona). In
New Mexico, the species was either collected or observed at 170
localities (Jennings 1995; Randy Jennings, Western New Mexico
University, pers. comm. 1999; Charles Painter, New Mexico Game and Fish
Department, pers. comm. 1999). Eleven historical localities were listed
by Platz and Mecham (1979) in Mexico, mostly from the eastern base and
foothills of the Sierra Madre Occidental in Chihuahua and Durango, and
one site in northern Sonora, Mexico. Hillis et al. (1983) list another
locality from Durango. However, the presence of Chiricahua leopard
frogs in the Sierra Madre Occidental of southern Chihuahua was
questioned by Webb and Baker (1984). Frogs at a locality on the Sonora-
Chihuahua border have been tentatively identified as Chiricahua leopard
frogs (Holycross 1998). Some museums still have many southwestern
leopard frogs catalogued as Rana pipiens. Once these specimens have
been reexamined, additional historical localities for Rana
chiricahuensis may result. Also, frogs observed at some localities,
which may have been Rana chiricahuensis, were not positively
identified.
Many collections of Chiricahua leopard frogs were made before 1980
(Jennings 1995; Platz and Mecham 1979; Frost and Bagnara 1977; Mecham
1968). Recent surveys to document the status and distribution of the
species were conducted primarily from the mid-1980's to the present
(Sredl et al. 1997, 1995, 1994, 1993; Rosen et al. 1996; Fernandez and
Bagnara 1995; Jennings 1995; Rorabaugh et al. 1995; Rosen 1995; Zweifel
1995; Sredl and Howland 1994, 1992; Hale 1992; Scott 1992;
[[Page 37345]]
Wood 1991; Clarkson and Rorabaugh 1989; Rosen and Schwalbe 1988). These
surveys were summarized by Jennings (1995) for New Mexico and Sredl et
al. (1997) for Arizona. In 1995, Jennings reported Chiricahua leopard
frogs at 11 sites in New Mexico. An additional 16 populations have been
found since 1995 (R. Jennings, pers. comm. 1999, C. Painter, pers.
comm. 1999), for a total of 27. Twenty-two of these occur north of
Interstate 10 (northern populations), and five are in the southwestern
corner of the state (southern populations). Sredl et al. (1997)
reported that during 1990-1997 Chiricahua leopard frogs were found at
61 sites in southeastern Arizona (southern populations) and 15 sites in
central and east-central Arizona (northern populations). As a means to
make the Arizona and New Mexico status information more comparable, the
number of sites at which Chiricahua leopard frogs were observed from
1995 to the present in Arizona were tallied. Based on available data,
particularly Sredl et al. (1997) and Rosen et al. (1996), Chiricahua
leopard frogs were observed at 52 sites in Arizona from 1995 to the
present, including 9 northern localities and 43 southern localities.
Recent surveys of potential habitats in Arizona are more complete
than surveys done in New Mexico. Sredl et al. (1997) conducted 656
surveys for ranid frogs (frogs in the family Ranidae) within the range
of the Chiricahua leopard frog in southeastern Arizona. Rosen et al.
(1996, 1994), Hale (1992), Wood (1991), Clarkson and Rorabaugh (1989),
and others have also surveyed wetlands in southeastern Arizona
extensively. It is unlikely that many additional new populations will
be found there. A greater potential exists for locating frogs at
additional localities in Arizona's northern region. Sredl et al. (1997)
conducted 871 surveys for ranid frogs in the range of the northern
localities, but report that only 25 of 46 historical Chiricahua leopard
frog localities were surveyed during 1990-1997. Unsurveyed historical
localities are primarily located on the San Carlos and Fort Apache
Reservations, in areas that have generally not been accessible to State
and Federal biologists. Additional populations of Chiricahua leopard
frogs of which we are currently unaware may occur on these tribal
lands.
Of the historical localities in New Mexico, 80 of 170 were not
revisited since frogs were last collected or observed. Twenty-four of
these unvisited sites have imprecise locality information that
precludes locating or revisiting them. Many others are on private lands
to which the owners have denied access to biologists (the privately
owned Gray and Ladder ranches are notable exceptions). As in Arizona,
potential habitat within the range of the southern populations has been
surveyed more extensively than that of the northern populations. From
1990-1991, Scott (1992) conducted extensive surveys of the Gray Ranch,
which contains much of the Chiricahua leopard frog habitat in
southwestern New Mexico. Observations from numerous other
herpetologists were included within his reports, and cowboys and ranch
hands were interviewed to locate potential habitats. Jennings (1995)
surveyed other potential habitats in southwestern New Mexico outside of
the Gray Ranch in the Peloncillo Mountains. Other herpetologists
working in that area, including Charles Painter (pers. comm. 1998) and
Andy Holycross, Arizona State University (pers. comm. 1997), also
worked extensively in this area. Probably few if any unknown
populations of Chiricahua leopard frogs occur in southwestern New
Mexico.
Surveys in the northern portion of the species' range in New Mexico
have been less complete. Jennings (1995) believed that the wilderness
areas of the Gila National Forest have the greatest potential for
supporting additional extant populations and for securing an intact
metapopulation that would have a good chance of long-term persistence.
In Mexico systematic or intensive surveys for Chiricahua leopard
frogs were not conducted. However, it is expected that the species
almost certainly occurs or occurred at more than the 12 (or 13)
reported localities in Chihuahua, Sonora, and Durango (Platz and Mecham
1979, Hillis et al. 1983, and Holycross 1998). However, the identity of
leopard frogs in southern Chihuahua (and perhaps Durango) is in some
question (Webb and Baker 1984). Only one locality has been documented
in Sonora, yet populations occur or occurred in the mountain ranges and
valleys adjacent to the Sonora border in Arizona. Other localities
probably occur or occurred in Sonora.
The Chiricahua leopard frog is reported absent from a majority of
historical localities. In Arizona, Clarkson and Rorabaugh (1989) found
the species at only 2 of 36 sites that supported Chiricahua leopard
frogs in the 1960s and 1970s. In New Mexico, Jennings (1995) found
Chiricahua leopard frogs at 6 of 33 sites supporting the species during
the previous 11 years. Sredl and Howland (1994) reported finding
Chiricahua leopard frogs at only 12 of 87 historical sites. In 1994,
during surveys of 175 wetland sites in southeastern Arizona, Rosen et
al. (1994) reported the Chiricahua leopard frog was extant at 19
historical and new sites, but was not found at 32 historical
localities. Throughout Arizona, Sredl et al. (1997) found the species
present at 21 of 109 historical localities.
Determining whether a species is declining based on its presence or
absence at historical sites is difficult. Where frogs are observed at a
particular site, they are considered extant. However, a failure to find
frogs does not necessarily indicate the species is absent. Corn (1994)
notes that leopard frogs may be difficult to detect, museum records do
not always represent breeding localities, collections have occurred
from marginal habitat, and museum and literature records often
represent surveys over long periods of time, which ignores natural
processes of geographical extinction and recolonization. The natural
processes of extinction and recolonization may be particularly
important for the Chiricahua leopard frog because its habitats are
often small and very dynamic. Because the Chiricahua leopard frog and
other southwestern leopard frogs exhibit a life history that
predisposes them to high rates of extirpation and recolonization (Sredl
and Howland 1994), its absence from at least some historical sites is
expected.
The failure of experienced observers to find frogs indicates that
frogs are probably absent, particularly in relatively simple aquatic
systems such as most stock tanks and stream segments. Howland et al.
(1997) evaluated visual encounter surveys at five leopard frog
localities. At sites with known populations that were not dry, frogs
were detected in 93 of 100 surveys conducted during the day from April
through October. During a drought in 1994, Rosen et al. (1996, 1994)
surveyed all known localities of the Chiricahua leopard frog in
southeastern Arizona and other accessible waters, and discussed
locations of waters and faunal occurrence with landowners. By focusing
on aquatic sites that did not go dry, and through careful and often
multiple surveys at each site, the authors were able to define
distribution at a time when aquatic faunal patterns were clear. The
authors believed that nearly all potential habitat was surveyed, and,
if frogs were present, they would be detectable at most sites.
Although survey data strongly suggest that the species is absent at
a high percentage of historical sites (absent from 76 and 82 percent of
historical sites in New Mexico and Arizona, respectively) (Sredl et al.
1997, Jennings
[[Page 37346]]
1995), additional analyses are warranted to determine whether
extirpations represent natural fluctuations or long-term declines
caused by human impacts (Blaustein et al. 1994, Pechman et al. 1991).
Numerous studies indicate that declines and extirpations of
Chiricahua leopard frogs are at least in part caused by predation and
possibly competition by nonnative organisms, including fish in the
family Centrarchidae (Micropterus spp., Lepomis spp.), bullfrogs (Rana
catesbeiana), tiger salamanders (Ambystoma tigrinum mavortium),
crayfish (Oronectes virilis and possibly others), and several other
species of fish (Fernandez and Rosen 1998, Rosen et al. 1996, 1994;
Snyder et al. 1996; Fernandez and Bagnara 1995; Sredl and Howland 1994;
Clarkson and Rorabaugh 1989). For instance, in the Chiricahua region of
southeastern Arizona, Rosen et al. (1996) found that almost all
perennial waters investigated that lacked introduced predatory
vertebrates supported Chiricahua leopard frogs. All waters except three
that supported introduced vertebrate predators lacked Chiricahua
leopard frogs. The authors noted an alarming expansion of nonnative
predatory vertebrates over the last 2 decades. In the Chiricahua
region, Chiricahua leopard frogs were primarily limited to habitats
subject to drying or near drying, such as stock tanks, which
discourages the establishment of nonnative predatory fish and
bullfrogs. These habitats are highly dynamic and may be marginal
habitats for leopard frogs (Rosen et al. 1994).
Additional evidence that the observed absence of Chiricahua leopard
frogs from historical sites is not the result of a natural phenomenon
emerges from the analyses of regional occurrence. If the extirpation of
the Chiricahua leopard frog were a natural artifact of metapopulation
dynamics or other population-level processes, then an observer would
not expect to find the species absent from large portions of its range.
Rather, Chiricahua leopard frogs might be absent from some historical
sites, but would still be found at other new or historical sites in the
region. In New Mexico, Jennings (1995) reported extant Chiricahua
leopard frog populations in each of the six major drainages where the
species was found historically (Tularosa/San Francisco, Mimbres,
Alamosa/Seco/Rio Grande, Gila, Playas, and Yaqui). However, all six are
characterized by few, mostly small, isolated populations. Populations
in the Playas drainage are limited to two livestock tanks. The species
was not found on the mainstem, Middle Fork, and East Fork of the Gila
River, where the species occurred historically at many localities.
In Arizona, the species is still extant in all major drainages of
historical occurrence (Little Colorado, Salt, Verde, Gila, San Pedro,
Santa Cruz, Yaqui/Bavispe, and Magdalena river drainages), but was not
found recently in some major tributaries and/or from river mainstems.
For instance, the species was not reported from 1995 to the present
from the following drainages or river mainstems where it historically
occurred: White River, East Clear Creek, West Clear Creek, Silver
Creek, Tonto Creek, Verde River mainstem, San Francisco River, San
Carlos River, upper San Pedro River mainstem, Santa Cruz River
mainstem, Aravaipa Creek, Babocomari River mainstem, and Sonoita Creek.
In southeastern Arizona, no recent records (1995 to the present) exist
for the following mountain ranges or valleys: Pinaleno Mountains,
Peloncillo Mountains, Sulphur Springs Valley, Huachuca Mountains, and
Canelo Hills. In many of these regions, Chiricahua leopard frogs were
not found for a decade or more despite repeated surveys.
These apparent regional extirpations provide further evidence that
the species is disappearing from its range. Once extirpated from a
region, natural recolonization of suitable habitats is unlikely to
occur in the near future. Where the species is still extant, sometimes
several small populations are found in close proximity suggesting
metapopulations are important for preventing regional extirpation
(Sredl et al. 1997).
Disruption of metapopulation dynamics is likely an important factor
in regional loss of populations (Sredl et al. 1997, Sredl and Howland
1994). Chiricahua leopard frog populations are often small, and
habitats are dynamic, resulting in a relatively low probability of
long-term population persistence. However, if populations are
relatively close together and numerous, extirpated sites can be
recolonized.
Human disturbances can result in increased rates of extinction and
decreased rates of recolonization. If the extinction rate for a given
population exceeds the colonization rate, that population will go
extinct (Hanski 1991). Various human impacts (see Summary of Factors
Affecting the Species) can result in increased extinction rates and/or
increased isolation of populations within a metapopulation with
resulting decreased colonization rates. In addition, big rivers, lakes,
and reservoirs that once probably supported large populations of
Chiricahua leopard frogs, and were likely stable source populations for
dispersal to smaller sites, are almost all inhabited by nonnative
predators and are unsuitable as habitat for this species (Sredl et al.
1997, Sredl and Howland 1994). The currently extant smaller populations
almost certainly exhibit greater extinction rates than these larger
populations did historically.
Rosen et al. (1996) hypothesized that ``the ongoing restriction of
Chiricahua leopard frogs to shallow, marginal habitat types means that
eventually the species will be wiped out by a drought (see Fellers and
Drost 1993, Corn and Fogelman 1984) that it would readily have
weathered in refugia now pre-empted by nonnative species. Our
hypothesis clearly predicts that this species will go extinct in
southern Arizona, and probably elsewhere, unless appropriate action is
taken.'' In New Mexico, Painter (1996) reported similar findings:
``Rana chiricahuensis is rapidly disappearing from southwest New Mexico
(Jennings 1995, pers. obs.). Unless these unexplainable trends are
quickly reversed, I expect the species to be extirpated from 90-100
percent of its former range in New Mexico within the next decade * *
*''.
Previous Federal Action
Based on status information indicating the species was recently
extirpated from historical localities (Clarkson and Rorabaugh 1989),
the Chiricahua leopard frog was added to the list of category 2
candidate species with the publication of a comprehensive Notice of
Review on November 21, 1991 (56 FR 58804). We also included the species
as a category 2 candidate in the November 15, 1994, Notice of Review
(59 FR 58982). Category 2 candidates were those taxa for which we had
some evidence of vulnerability and threats, but for which we lacked
sufficient data to support a listing proposal.
Beginning with our February 28, 1996, candidate notice of review
(61 FR 7596), we discontinued the designation of multiple categories of
candidates, and only those taxa meeting the definition for former
category 1 candidates are now considered candidates for listing
purposes. Category 1 candidates were taxa for which we had on file
sufficient information on biological vulnerability and threats to
support proposals to list them as endangered or threatened, but for
which preparation of listing proposals was precluded by higher priority
listing actions. In the February 28, 1996, notice, we identified the
Chiricahua leopard frog as a candidate species.
[[Page 37347]]
On June 10, 1998, we received a petition dated June 4, 1998, from
the Southwest Center for Biological Diversity to list the Chiricahua
leopard frog as endangered and to designate critical habitat for the
species. In a letter dated July 7, 1998, we informed the petitioner
that, pursuant to the Service's July 1996 Petition Management Guidance,
we consider candidate species to be under petition and covered by a
``warranted but precluded'' finding under section 4(b)(3)(B)(iii) of
the Act. Because listing of candidates is, by definition, already
warranted, petitions on candidates are redundant. Accordingly, we do
not prepare 90-day findings for petitioned candidate species. We
address the resolution of the conservation status of the Chiricahua
leopard frog and other candidates through the Listing Priority
Guidance.
The processing of this proposed rule conforms with the Fiscal Year
2000 Listing Priority Guidance, published on October 22, 1999 (64 FR
57114). The guidance clarifies the order in which we will process
rulemakings. Highest priority is processing emergency listing rules for
any species determined to face a significant and imminent risk to its
well-being (Priority 1). Second priority (Priority 2) is processing
final determinations on proposed additions to the lists of endangered
and threatened wildlife and plants. Third priority is processing new
proposals to add species to the lists. The processing of administrative
petition findings (petitions filed under section 4 of the Act) is the
fourth priority. This proposed rule is a Priority 3 action and is being
completed in accordance with the current Listing Priority Guidance.
Peer Review
In accordance with the policy promulgated July 1, 1994 (59 FR
34270), we will solicit the expert opinions of at least three
appropriate and independent specialists regarding this proposed rule.
The purpose of such review is to ensure listing decisions are based on
scientifically sound data, assumptions, and analyses, including input
of appropriate experts and specialists. Peer reviewers will be mailed
copies of this proposed rule to list the Chiricahua leopard frog as a
threatened species immediately following publication in the Federal
Register. We solicit peer reviewers to comment during the public
comment period upon the specific assumptions and conclusions regarding
this proposed listing. In the preparation of the final rule, we
consider all comments received.
Summary of Factors Affecting the Species
Section 4 of the Act and regulations (50 CFR part 424) promulgated
to implement the listing provisions of the Act set forth the procedures
for adding species to the Federal lists. A species may be determined to
be an endangered or threatened species due to one or more of the five
factors described in Section 4(a)(1). These factors and their
application to the Chiricahua leopard frog (Rana chiricahuensis Platz
and Mecham) are as follows:
A. The present or threatened destruction, modification, or
curtailment of its habitat or range. Riparian (in or associated with
wetted areas) and wetland communities throughout the range of the
Chiricahua leopard frog are much altered and/or reduced in size
compared to early-to mid-19th century conditions (Arizona Department of
Water Resources 1994; Brown 1985; Hendrickson and Minckley 1984;
Minckley and Brown 1982). Dams, diversions, groundwater pumping,
introduction of nonnative organisms, woodcutting, mining, urban and
agricultural development, road construction, overgrazing, and altered
fire regimes all contributed to reduced quality and quantity of
riparian and wetland habitat (Belsky and Blumenthal 1997; Wang et al.
1997; DeBano and Neary 1996; Bahre 1995; Brown 1985; Hadley and
Sheridan 1995; Ohmart 1995; Stebbins and Cohen 1995; Hendrickson and
Minckley 1984; Arizona State University 1979; Gifford and Hawkins
1978).
Many of these changes began before ranid frogs were widely
collected or studied in Arizona and New Mexico. The Chiricahua leopard
frog may have been much more widely distributed in pre-settlement times
than is indicated by historical collections. Extant localities are
generally located in stream and river drainage headwaters, springs, and
stock tanks. However, historical records exist for the Verde, San
Pedro, Santa Cruz, Mimbres, and Gila Rivers, and the species is extant
in the mainstem of the San Francisco River in New Mexico and on the
Blue River in Arizona. These findings suggest that it may have occurred
in other major drainages, such as the mainstems of the Salt, White,
Black, and Little Colorado Rivers. Habitat degradation, diversions,
loss or alteration of stream flows, groundwater pumping, introduction
of nonnative organisms, and other changes are often most apparent on
these larger drainages (Sredl et al. 1997, State of Arizona 1990).
Although the cumulative effect of such changes to its habitat is
unknown, the extirpation of the Chiricahua leopard frog may have
occurred in some major drainages prior to its occurrence being
documented. These large drainages connect many of the extant and
historical populations and may have served as important corridors for
exchange of genetic material and as a source of frogs for
recolonization if extirpations occurred within populations (Sredl et
al. 1997, Rosen et al. 1996).
Beavers (Castor canadensis) likely promoted the creation of
Chiricahua leopard frog habitat. The activities of beavers tend to
inhibit erosion and downcutting of stream channels (Parker et al.
1985), and ponded water behind beaver dams is favored habitat for ranid
frogs. However, beavers were extirpated from some areas by the late
1800s and are still not abundant or are extirpated from other areas
where they were once common (Hoffmeister 1986). For example, in Arizona
beavers are extirpated from the Santa Cruz River and, before recent
reintroductions, were extirpated from the San Pedro River. Loss of this
large mammal and the dams it constructed likely resulted in loss of
backwater and pool habitat favored by the Chiricahua leopard frog.
These changes occurred before leopard frogs were widely collected;
thus, hypotheses concerning correlations between extirpations of beaver
and Chiricahua leopard frogs cannot be tested by comparing historical
versus extant frog populations. Where beavers occur within the range of
the Chiricahua leopard frog today, beaver ponds are often inhabited by
nonnative predators, such as introduced fish and bullfrogs, that prey
upon and likely preclude colonization by Chiricahua leopard frogs.
Because nonnative species often thrive in beaver ponds, the presence of
beavers could actually hinder recovery of the Chiricahua leopard frog
in some systems.
Stock tanks, constructed as water sources for livestock, are very
important habitats for the Chiricahua leopard frog throughout its
range. In some areas, stock tanks replaced natural springs and cienegas
and provide the only suitable habitat available to the Chiricahua
leopard frog. For instance, the only known localities of the Chiricahua
leopard frog in the San Rafael and San Bernardino Valleys, Fossil Creek
drainage, and in the Patagonia Mountains of Arizona are stock tanks.
Sixty-one percent of extant Chiricahua leopard frog localities in
Arizona are stock tanks, versus only 35 percent of extirpated
localities (Sredl and Saylor
[[Page 37348]]
1998), suggesting Arizona populations of this species have fared better
in stock tanks than in natural habitats. However, this generalization
may not be true for New Mexico, where in recent years many stock tank
populations were extirpated. Sredl and Saylor (1998) also found that
stock tanks are occupied less frequently by nonnative predators (with
the exception of bullfrogs) than natural sites. Therefore, a high
probability exists that the Chiricahua leopard frog would be extirpated
from many more areas if ranchers had not built and maintained stock
tanks for livestock production.
Although stock tanks provide refugia for frog populations and are
very important for this species, only small populations are supported
by such tanks, and these habitats are very dynamic. Tanks often dry out
during drought, and flooding may destroy downstream impoundments or
cause siltation, either of which may result in loss of aquatic habitat
and extirpation of frog populations. Periodic maintenance to remove
silt from tanks may also cause a temporary loss of habitat. Populations
of nonnative introduced predaceous fish and bullfrogs, although less
prevalent than in natural habitats, sometimes become established in
stock tanks and are implicated in the decline of the Chiricahua leopard
frog (Rosen et al. 1996, 1994). Stock tanks may facilitate spread of
nonnative organisms by providing aquatic habitats in arid landscapes
that otherwise may have served as barriers to the spread of such
organisms. In New Mexico, stock tank populations in some areas were
eliminated by disease (Declining Amphibian Populations Task Force
1993).
Grazing by domestic livestock occurs throughout the range of the
Chiricahua leopard frog. The effects of livestock grazing on leopard
frog populations are not well studied. As discussed, construction of
tanks for livestock has created important leopard frog habitat, and in
some cases has replaced destroyed or altered natural wetland habitats.
A large and healthy population of Chiricahua leopard frogs coexists
with cattle and horses on the Tularosa River, New Mexico (Randy
Jennings, Western New Mexico University, pers. comm. 1995).
Maintenance of viable populations of Chiricahua leopard frogs is
thought to be compatible with well-managed livestock grazing. However,
adverse effects to the species and its habitat may occur under certain
circumstances. These effects to habitats include deterioration of
watersheds, erosion and/or siltation of stream courses, elimination of
undercut banks that provide cover for frogs, and loss of wetland and
riparian vegetation and backwater pools (Belsky et al. 1999, Ohmart
1995; Hendrickson and Minckley 1984; Arizona State University 1979).
Eggs and tadpoles of the Chiricahua leopard frog are probably trampled
by cattle on the perimeter of stock tanks and in pools along streams.
Cattle can also contribute to degraded water quality at stock tanks,
including elevated hydrogen sulfide concentrations, which are toxic to
frogs (Sredl et al. 1997).
Many large impoundments or lakes were created within the range of
the Chiricahua leopard frog for water storage, recreation, and as a
source of hydroelectric power. Historical records exist for the species
from Luna Lake, Nelson Reservoir, Hawley Lake, and Rainbow Lake north
of the Gila River in Arizona; and Lake Roberts, Patterson Lake, and Ben
Lilly Lake in New Mexico, but surveys at these sites since 1985 located
no frogs (Jennings 1995, Arizona Game and Fish Department (AGFD) 1997).
Currently, large impoundments invariably support populations of
nonnative fish and/or bullfrogs. Predation and possibly competition
with leopard frogs by these introduced predators likely contributed to
the disappearance of the Chiricahua leopard frog from reservoir
habitats.
Construction and operation of reservoirs also alter downstream
flows and can result in dramatic changes in stream hydrology, rates of
erosion and sedimentation, riparian vegetation, and other components of
riparian ecosystems (Johnson 1978). The effects of these changes on
Chiricahua leopard frog populations are unknown. However, downstream
effects of such impoundments are implicated in the decline of other
anurans (frogs and toads), including the endangered arroyo toad (Bufo
californicus) (Service 1993) and the foothill yellow-legged frog (Rana
boylii) (Lind et al. 1996).
On the Trinity River in California, the extent of riparian
vegetation increased with an accompanying decrease in sandbar habitat,
of which the latter was breeding habitat of the yellow-legged frog.
Unseasonably high flows from dam releases also resulted in loss of
entire cohorts or age groups of larval frogs (Lind et al. 1996).
Similar effects may occur in Chiricahua leopard frog habitat. Water
temperatures are often colder below dams than in similar unaltered
systems (Lind et al. 1996), which may retard development of frog eggs
and larvae (Stebbins and Cohen 1995). Lack of scouring flood flows
below dams may also create relatively stable pool habitat with
established vegetation that favors establishment of bullfrogs (Lind et
al. 1996). Dispersal of nonnative fish from impoundments to either
downstream or upstream reaches may have resulted in further adverse
effects to frog populations.
Only a few extant or historical Chiricahua leopard frog localities
are thought to be directly affected by current mining operations.
Active mining occurs in California Gulch, Pajarito Mountains, Arizona,
but is limited to a short reach of the drainage. The recently proposed
Gentry Iron Mine may be located within 1.6 km (1.0 mi) of two
Chiricahua leopard frog populations on the Tonto National Forest,
Arizona. The resulting effects of the proposed mining activities on
these populations are uncertain at this time, but may include changes
in water quality and flow rates. Populations of Chiricahua leopard frog
northeast of Hurley, Grant County, New Mexico, may also be affected by
mining. Evidence of mining can be found at or near many other
localities, but few mines are currently active and most do not directly
affect the wetland and riparian habitats occupied by the species.
Although mining activities were more widespread historically and may
have constituted a greater threat in the past, the mining of sand and
gravel, iron, gold, copper, or other materials remains a potential
threat to the habitat of the Chiricahua leopard frog. In addition, as
noted in Factor C of this section, mining also has indirect adverse
effects to this species.
Fire frequency and intensity in the mountain ranges of southeastern
Arizona and southwestern New Mexico are much altered from historic
conditions. Before 1900, surface fires generally occurred at least once
per decade in montane forests with a pine component. Beginning about
1870-1900, these frequent ground fires ceased to occur due to intensive
livestock grazing that removed fine fuels, followed by effective fire
suppression in the mid to late 20th century (Swetnam and Baisan 1996).
Absence of ground fires allowed a buildup of woody fuels that
precipitated infrequent but intense crown fires (Danzer et al. 1997,
Swetnam and Baisan 1996). Absence of vegetation and forest litter
following intense crown fires exposes soils to surface and rill erosion
during storms, often causing high peak flows, sedimentation, and
erosion in downstream drainages (DeBano and Neary 1996). Following the
1994 Rattlesnake fire in the Chiricahua Mountains, Arizona, a debris
flow filled in Rucker Lake, a historic Chiricahua leopard frog
locality. Leopard frogs
[[Page 37349]]
(either Chiricahua or Ramsey Canyon leopard frogs) apparently
disappeared from Miller Canyon in the Huachuca Mountains, Arizona,
after a 1977 crown fire in the upper canyon and subsequent erosion and
scouring of the canyon during storm events (Tom Beatty, Miller Canyon,
pers. comm. 2000). Leopard frogs were historically known from many
localities in the Huachuca Mountains; however, natural pool and pond
habitat is largely absent now, and the only breeding leopard frog
populations occur in man-made tanks and ponds. Bowers and McLaughlin
(1994) list six riparian plant species they believed might have been
eliminated from the Huachuca Mountains as a result of floods and debris
flow following destructive fires.
Other activities have also affected the habitat of the Chiricahua
leopard frog. For instance, in an attempt to increase flow, explosives
were used at Birch Springs in the Animas Mountains to open up the
spring. The explosion resulted in destruction of aquatic habitat, flows
were reduced rather than increased, and Chiricahua leopard frogs
subsequently disappeared (N. Scott, pers. comm. 1994).
B. Overutilization for commercial, recreational, scientific, or
educational purposes. The collection of Chiricahua leopard frogs in
Arizona is prohibited by Arizona Game and Fish Commission Order 41,
except where such collection is authorized by special permit.
Collection of Chiricahua leopard frogs is also prohibited in Mexico.
The collection of Chiricahua leopard frogs is not prohibited in the
State of New Mexico.
Over-collection for commercial purposes is known to be a
contributing factor in the decline of other ranid frogs (Jennings and
Hayes 1985, Corn and Fogelman 1984). Although collection is not
documented as a cause of population decline or loss in the Chiricahua
leopard frog, the collection of large adult frogs for food, scientific,
or other purposes, particularly after a winter die-off or other event
that severely reduces the adult population, can hasten the extirpation
of small populations. The listing of the Chiricahua leopard frog and
its recognition as a rare species is reasonably expected to increase
its value to collectors. In 1995, many large adult Ramsey Canyon
leopard frogs (closely related to the Chiricahua leopard frog) were
illegally collected from a site in the Huachuca Mountains, Arizona,
following publicity about the rare status of the frog.
C. Disease or predation. Predation by introduced, nonnative
bullfrogs and fish was implicated as a contributing factor in the
decline of ranid frogs in western North America (Bradford et al. 1993,
Hayes and Jennings 1986, Moyle 1973), and may be the most important
factor identified so far in the current decline of the Chiricahua
leopard frog (Rosen et al. 1994, 1996). In southeastern Arizona, Rosen
et al. (1994, 1996) documented 13 nonnative predaceous vertebrate
species in aquatic habitats in the range of the Chiricahua leopard
frog, including bullfrog, tiger salamander, and 11 fish species
including bass, trout, and catfish, among others.
Rosen et al. (1994, 1996) found that Chiricahua leopard frogs were
replaced by bullfrogs and centrarchid fish. Sixteen of 19 localities
where Chiricahua leopard frogs occurred lacked nonnative vertebrates.
All historical frog localities that lacked Chiricahua leopard frogs
supported nonnative vertebrates. At the three sites where Chiricahua
leopard frogs occurred with nonnatives (one site with green sunfish,
Lepomis cyanellus, and two with tiger salamanders), either the frog or
the nonnative vertebrate was rare. In two of the three cases, frogs may
have derived from other nearby localities (Rosen et al. 1996), and thus
may have represented immigrants rather than a viable population.
In the San Rafael Valley, Arizona, Chiricahua leopard frogs were
found only at sites that lacked nonnative fish and bullfrogs (Snyder et
al. 1996). In the White Mountains of Arizona, disappearance of
Chiricahua leopard frogs from most historical localities correlated
with the appearance of tiger salamanders and nonnative crayfish
(Fernandez and Bagnara 1995). Crayfish were found to prey upon
Chiricahua leopard frog larvae, metamorphs, and adults. Crayfish
recently spread to the breeding pond of one of the last and possibly
the most robust populations of Chiricahua leopard frogs in the White
Mountains, Arizona (M. Sredl, pers. comm. 1999, Fernandez and Rosen
1998).
Sredl and Howland (1994) noted that Chiricahua leopard frogs were
nearly always absent from sites supporting bullfrogs and nonnative
predatory fish; however, Rosen et al. (1996) suggested further study
was needed to evaluate the effects of mosquitofish, trout, and catfish
on frog presence. Rosen et al. (1996) suspected that catfish would
almost always exclude Chiricahua leopard frogs, and that trout may
exclude leopard frogs.
In contrast to nonnative aquatic vertebrates, numerous species of
native fish, the Sonoran mud turtle (Kinosternon sonoriense), other
species of native ranid frogs, and native garter snakes (Rosen et al.
1996, Platz and Mecham 1979) commonly coexist with the Chiricahua
leopard frog. Tiger salamanders are native to the following portions of
the Chiricahua leopard frog's range: San Rafael Valley in southeastern
Arizona (Ambystoma tigrinum stebbinsi), the northern portion of the
species' range (Ambystoma tigrinum nebulosum), and the mountains of
Sonora, Chihuahua, and Durango (Ambystoma rosaceum). Native fishes,
such as trout (Oncorhynchus), chub (Gila), and topminnow
(Poeciliopsis), also occur within the range of the Chiricahua leopard
frog.
The Rio Grande leopard frog (Rana berlandieri) is a recent
introduction to southwestern Arizona, (Platz et al. 1990). Although the
species does not presently occur within the range of the Chiricahua
leopard frog, the Rio Grandes leopard frog is rapidly expanding its
distribution and currently occurs as far east as the Phoenix area
(Rorabaugh et al. in prep.). If it continues to spread eastward, the
ranges of the Rio Grande and Chiricahua leopard frogs may overlap in
the future. This large, introduced leopard frog might prey on small
Chiricahua leopard frogs (Platz et al. 1990), and tadpoles of the two
species may compete.
In June 1994, a die-off of Chiricahua leopard frogs occurred at a
stock tank in the Chiricahua Mountains, Arizona, that reduced the frog
population from 60-80 adults to fewer than 10 (Sredl et al. 1997).
Analysis of dead and moribund frogs and water from the tank indicated
that disease was unlikely to be the cause of the die-off, however,
levels of hydrogen sulfide were high enough to be toxic to wildlife.
The authors suspected that high detritus loads (including cattle
feces), low water levels, high water temperature, and low
concentrations of dissolved oxygen created a suitable environment for
sulphur-producing bacteria that produced toxic levels of hydrogen
sulfide. Chiricahua leopard frogs were not found at this site in 1998.
The disease Postmetamorphic Death Syndrome (PDS) was implicated in
the extirpation of Chiricahua leopard frog populations in Grant County,
New Mexico, as well as in other frog and toad species (Declining
Amphibian Populations Task Force 1993). All stock tank populations of
the Chiricahua leopard frog in the vicinity of Gillette and Cooney
tanks in Grant County disappeared within a 3-year period, apparently as
a result of PDS (Declining Amphibian Populations Task Force 1993). The
syndrome is characterized by death of all or most recently
metamorphosed frogs in a short period
[[Page 37350]]
of time. Dead or moribund frogs are often found during or immediately
following winter dormancy or unusually cold periods. The syndrome
appears to spread among adjacent populations causing regional loss of
populations or metapopulations. Evidence suggests that PDS may also be
present in the Santa Rita and Pajarito mountains, Arizona. Although
winter die-offs are not documented, Steve Hale (Tucson, AZ, pers. comm.
1994) observed very few Chiricahua leopard frogs in the spring,
suggesting that frogs are dying during the winter months. The apparent
post-metamorphic death of the Tarahumara frog was documented in
southern Arizona and northern Sonora (Hale et al. 1995, Hale and
Jarchow 1988), and numbers of Ramsey Canyon leopard frogs declined in
the Huachuca Mountains, Arizona, during the winters of 1997-1998 and
1998-1999.
Arsenic poisoning may be a contributing factor in PDS (Hale and
Jarchow 1988). Elevated arsenic levels may have contributed to the
extirpation of the Tarahumara frog at a site in northern Sonora (Hale
and Jarchow 1988). Arsenic often occurs at high levels near sulfitic
mine tailings and may be leached by rainfall containing elevated levels
of sulfate (Hale and Jarchow 1988). Rainfall near Elgin in southeastern
Arizona contained high levels of sulfate, probably due to emissions
from copper smelters in Cananea and Nacozari, Sonora, and Douglas,
Arizona (Blanchard and Stromberg 1987). The smelters at Cananea and
Douglas are no longer in operation.
The size of the Chiricahua leopard frog population in Sycamore
Canyon in the Pajarito Mountains of Arizona appears to vary greatly
from year to year. This annual variation in population size may be
attributable, in part, to cadmium toxicity (Hale and Jarchow 1988). A
likely source of cadmium in Chiricahua leopard frog habitat is
emissions from copper smelters at Cananea and Nacozari, Sonora (Hale
and Jarchow 1988, Blanchard and Stromberg 1987). Elevated levels of
cadmium also occur in and near tailings of copper, lead, and zinc mines
(Peterson and Alloway 1979). Cadmium may be mobilized and deposited
into stream courses through rainfall.
From 1980 to 1985, Chiricahua leopard frogs were abundant in
Sycamore Canyon only at Hank and Yank Tank and in the creek immediately
downstream of it. In May 1982 the ratio of zinc to cadmium in this
reach was 5 to 30 times that of downstream reaches where frogs were
absent or very rare (Hale and Jarchow 1988). Cumulative leaching and
deposition in drainages likely results in elevated concentrations of
cadmium in downstream reaches. Thus, stream headwaters and springs,
such as Hank and Yank Tank, may be important refugia for frogs during
times when toxic conditions exist in downstream reaches. Decreased zinc
to cadmium ratios may have also contributed to the extirpation of the
Tarahumara frog from one site in southern Arizona and three sites in
northern Sonora (Hale and Jarchow 1988).
Other contaminants or pathogens may also be contributing to the
decline of the Chiricahua leopard frog. Lips (1998) documented reduced
abundance and skewed sex ratios of two anuran species, and dead and
dying individuals of six other amphibian species in Puntarenas
Province, Costa Rica. She attributed these changes to biotic pathogens
or chemicals, or the combined effects of environmental contamination
and climate change. Toxic agrochemicals may have been transported via
winds and the atmosphere over long distances to the remote sites
studied in Costa Rica. Her observations are also consistent with a
pathogen outbreak, and recent evidence suggests a chytridiomycete skin
fungi may be responsible for the declines (Longcore et al. 1999, Berger
et al. 1998). Lips (1998) noted that declines in her study area are
similar to those reported for Monteverde, Costa Rica, the Atlantic
coast of Brazil, and Australia. Amphibian decline in these areas has
spread wave-like across the landscape, suggestive of pathogen
dispersal. Chytrid fungi have recently been shown to be associated with
amphibian declines in Panama and Queensland, Australia (Berger et al.
1998); the authors hypothesize that it is the proximate cause of
amphibian decline in these areas. Chytrid fungi have also been found in
captive arroyo toads, Bufo californicus, in California, cricket frogs,
Acris crepitans, in Illinois, American toads, Bufo americanus, in
Maryland, and in Arizona, lowland leopard frogs, Rana yavapaiensis, Rio
Grande leopard frogs, Ramsey Canyon leopard frogs, and four populations
of Chiricahua leopard frogs (M. Sredl, pers. Comm., 2000; Milius 1998).
The role of the fungi in the population dynamics of the Chiricahua
leopard frog and these other North American species is as yet
undefined; however, it may well prove to be an important contributing
factor in observed population decline. Rapid death of recently
metamorphosed frogs, typical of post-metamorphic death syndrome, is
also characteristic of chytrid infections. Thus, chytrids may have
played a role in extirpation of stock tank populations of Chiricahua
leopard frog in New Mexico (Declining Amphibian Populations Task Force
1993), as well as overwinter die-offs in the mountains of southern
Arizona.
D. The inadequacy of existing regulatory mechanisms. A variety of
existing international conventions and law and Federal and State
regulations provide limited protection to the Chiricahua leopard frog
and its habitat. State regulations prohibit collection or hunting of
Chiricahua leopard frogs in Arizona, except under special permit.
Collection is not prohibited in New Mexico, and although collecting has
not been documented as a cause of population loss, the typically small,
geographically isolated populations of this species are extremely
vulnerable to collection pressure. Regulations have not been adequate
to stem habitat loss and degradation or to address factors such as
introduction of nonnative predators.
In Mexico, the collection of threatened species is prohibited. The
habitats of the Chiricahua leopard frog and other threatened species
are protected from some activities in Mexico. The species is not
protected by the Convention on International Trade in Endangered
Species of Wild Fauna and Flora, which regulates international trade.
The Lacey Act (16 U.S.C. 3371 et seq.), as amended in 1982,
provides some protection for the Chiricahua leopard frog. This
legislation prohibits the import, export, sale, receipt, acquisition,
purchase, and engagement in interstate or foreign commerce of any
species taken, possessed, or sold in violation of any law, treaty, or
regulation of the United States, any Tribal law, or any law or
regulation of any State.
The Federal Land Policy Management Act of 1976 (43 U.S.C. 1701 et
seq.) and the National Forest Management Act of 1976 (16 U.S.C. 1600 et
seq.) direct Federal agencies to prepare programmatic-level management
plans to guide long-term resource management decisions. In addition,
the Forest Service is required to ``maintain viable populations of
existing native and desired nonnative species'' in their planning areas
(36 CFR 219.19). These regulations have resulted in the preparation of
a variety of land management plans by the Forest Service and the Bureau
of Land Management that address management and resource protection of
areas that support, or in the past supported, populations of Chiricahua
leopard frogs.