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CURRENT ANNOUNCEMENTS AND NEWS RELEASES
SOURCE: Federal Register, December 22, 1999
NOTE: ON MARCH 20, THE FISH AND WILDLIFE SERVICE ANNOUNCED THAT THE COMMENT PERIOD HAS BEEN REOPENED AND WILL EXTEND THROUGH APRIL 19.
DEPARTMENT OF THE INTERIOR - Fish and Wildlife Service
Endangered and Threatened Wildlife and Plants:
Proposed Endangered Status for the Southern California Distinct Vertebrate
Population Segment of the Mountain Yellow-Legged Frog
ACTION: Proposed rule.
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SUMMARY: We, the Fish and Wildlife Service (Service), propose to list the
southern California distinct vertebrate population segment (DPS) of mountain yellow-legged
frog (Rana muscosa) as endangered, pursuant to the Endangered Species Act of 1973, as
amended (Act). In southern California, this DPS has been reduced to only a few
isolated remnants in the San Gabriel, San Jacinto, and San Bernardino Mountains. Hypothesized
causes of the decline include predation from introduced trout or possibly some other
widespread environmental effects such as airborne contaminants. These effects have
probably acted in combination to produce the decline. The chronology of the decline is not
well documented, but it appears that a precipitous decline occurred over the last three or
four decades. The decline went largely unnoticed and was not studied. In addition to
predation from trout and other widespread factors, the few remaining frogs are now
threatened by recreational suction dredging for gold and human activities at campgrounds
and day use areas. The remnant populations are so small that they are now at risk from
random genetic, demographic, and environmental effects as well. This proposed rule
constitutes the 12-month finding on a petition to list the southern California population
of mountain yellow-legged frog as threatened or endangered. This proposed rule, if made
final, would implement the Federal protection and recovery provisions afforded by the Act
for this DPS. We welcome data and comment from the public on this proposal.
DATES: You must submit any comments by February 22, 2000 and public
hearing requests by February 7, 2000. (SEE REVISED DATE AT
TOP OF PAGE)
ADDRESSES: You may send comments and materials concerning this proposal
to the Field Supervisor, U.S. Fish and Wildlife Service, Carlsbad Fish and Wildlife
Office, 2730 Loker Avenue West, Carlsbad, California 92008. You may inspect comments and
materials received, by appointment, during normal business hours at the above address.
FOR FURTHER INFORMATION CONTACT: Ken Berg at the above address
(telephone 760/431-9440).
SUPPLEMENTARY INFORMATION:
Background
The mountain yellow-legged frog is a true frog in the family Ranidae. Mountain
yellow-legged frogs were originally described by Camp in 1917 (as cited by Zweifel 1955)
as a subspecies of Rana boylii. Zweifel (1955) demonstrated that frogs from the high
Sierra and the mountains of southern California were somewhat similar to each other yet
were distinct from the rest of the R. boylii (=boylei) group. Since that time, most
authors have followed Zweifel, treating the mountain yellow-legged frog as a full species,
Rana muscosa.Mountain yellow-legged frogs are moderately sized, about 40 to 80 millimeters
(mm) (1.5 to 3 inches (in)) from snout to urostyle (the pointed bone at the base of the
backbone) (Jennings and Hayes 1994; Zweifel 1955). The pattern is variable, ranging from
discrete dark spots that can be few and large, to smaller and more numerous spots with a
mixture of sizes and shapes, to irregular lichen-like patches or a poorly defined network
(Zweifel 1955). The body color is also variable, usually a mix of brown and yellow, but
often with gray, red, or green-brown. Some individuals may be dark brown with little
pattern (Jennings and Hayes 1994). The back half of the upper lip is pale. Folds are
present on each side of the back, but usually they are not prominent (Stebbins 1985). The
throat is white or yellow, sometimes with mottling of dark pigment (Zweifel 1955). The
belly and undersurface of the high limbs are yellow, which ranges in hue from pale lemon
yellow to an intense sun yellow. The iris is gold with a horizontal, black counter shading
stripe (Jennings and Hayes 1994). In the Sierra Nevada Mountains of California, the
mountain yellow-
legged frog ranges from southern Plumas County to southern Tulare County (Jennings and
Hayes 1994), at elevations mostly above 1,820 meters (m) (6,000 feet (ft)). The frogs of
the Sierra Nevada are isolated from the frogs of the mountains of southern California by
the Tehachapi Mountains and a distance of about 225 kilometers (km) (140 miles (mi)). The
southern California frogs now occupy portions of the San Gabriel, San Bernardino, and San
Jacinto Mountains. Zweifel (1955) noted the presence of an isolated southern population on
Mt. Palomar in northern San Diego County, but this population appears to be extinct
(Jennings and Hayes 1994). In southern California, the elevation range reported by
Stebbins (1985) is 182 m (600 ft) to 2,273 m (7,500 ft). Representative localities,
including some that are no longer occupied, which demonstrate the wide elevation range
that mountain yellow-legged frogs inhabited in southern California, include Eaton Canyon,
Los Angeles County (370 m (1,220 ft)) and Bluff Lake, San Bernardino County (2,290 m
(7,560 ft)). The southern California locations now occupied by mountain yellow-legged
frogs range from City Creek, in the San Bernardino Mountains (760 m (2,500 ft)), to Dark
Canyon in the San Jacinto Mountains (1,820 m (6,000 ft)).
Southern California mountain yellow-legged frogs are diurnal, highly aquatic frogs,
occupying rocky and shaded streams with cool waters originating from springs and snowmelt.
In these areas, juveniles and adults feed on small, streamside arthropods (Jennings and
Hayes 1994). They do not occur in the smallest creeks. The coldest winter months are spent
in hibernation, probably under water or in crevices in the bank. Mountain yellow-legged
frogs emerge from overwintering sites in early spring, and breeding soon follows. Eggs are
deposited in shallow water where the egg mass is attached to vegetation or the substrate.
In the Sierra Nevada, larvae select warm microhabitats (Bradford 1984 cited in Jennings
and Hayes 1994), and the time to develop from fertilization to metamorphosis reportedly
varies from 1 to 2.5 years (Jennings and Hayes 1994).
Prior to the late 1960s, mountain yellow-legged frogs were abundant in many southern
California streams (G. Stewart, in litt. 1995), but they now appear to be absent from most
places in which they previously occurred. Jennings and Hayes (1994) believe that mountain
yellow-legged frogs are now absent from more than 99 percent of their previous range in
southern California. This decline is part of a well-known larger pattern of declines among
native ranid frogs in the western United States (Hayes and Jennings 1986; Drost and
Fellers 1996). Some of the western ranid frog species experiencing noticeable declines are
the California red-legged frog (Rana aurora draytonii) (61 FR 25813), the spotted frog (R.
pretiosa and R. luteventris), the Cascades frog (R. cascadae), and the Chiricahua leopard
frog (R. chiricauhensis) (62 FR 49398). Nowhere have the declines been any more pronounced
than in southern California, where, besides declines in mountain yellow-legged frogs, the
California red-legged frog has been reduced to a few small remnants (61 FR 25813), and the
foothill yellow-legged frog (R. boylii) may be extinct (Jennings and Hayes 1994.)
The mechanisms causing the declines of western frogs are not well understood and are
certain to vary somewhat among species, but the two most common and well-supported
hypotheses for widespread declines of western ranid frogs are: (1) Past habitat
destruction related to unregulated activities such as logging and mining and more recent
habitat conversions for water development, irrigated agriculture, and commercial
development (Hayes and Jennings 1986; 61 FR 25813); and (2) alien predators and
competitors (Bradford 1989; Knapp 1996; Kupferberg 1997). Natural populations may be
killed off directly by these factors operating alone or in combination, or these factors
so severely disrupt the normal population dynamics that when local extinctions occur,
regardless of the cause, natural recolonization is impossible. Other environmental factors
that could have adverse effects over a wide geographic range include pesticides, certain
pathogens, and ultraviolet-B (beyond the visible spectrum) radiation, but their role, if
any, in amphibian declines is not well understood (Reaser 1996). These factors, acting
singly or in combination, may be contributing to widespread, systematic declines of
western ranid frogs. Determining their effects, however, is not an easy task (Reaser 1996;
Wake 1998), and the Department of the Interior (USDOI) currently supports an initiative to
fund research on the causes of amphibian declines (see examples in USDOI 1998).
Some of the same factors that are hypothesized to have caused declines of other western
ranid frogs are likely to be responsible for the reduction of the mountain yellow-legged
frog in southern California. Because the declines have been so precipitous, and have
spared only a small number of frogs in a few localities, the factors, and their
interactions, that caused the decline may never be fully understood. We believe that these
factors are still operating, and unless reversed, a high probability exists that this frog
may be extinct in southern California within a few decades. In the case of the mountain
yellow-legged frog, the only factor listed above that we believe can be ruled out as a
likely cause of decline is habitat destruction related to activities such as logging,
mining, irrigated agriculture, and commercial development. The range of the mountain
yellow-legged frog in southern California is mainly on public land administered by the
U.S. Forest Service (FS). Most of the rugged canyons and surrounding mountainous terrain
have been altered little and look much the same today as they did when earlier naturalists
such as Lawrence Klauber collected mountain yellow-legged frogs there in the early decades
of the 1900s.
Current Range and Status
In southern California, mountain yellow-legged frogs can still be found in four small
streams in the San Gabriel Mountains, the upper reaches of the San Jacinto River system in
the San Jacinto Mountains, and at a single locality on City Creek, a tributary of the
Santa Ana River, in the San Bernardino Mountains (Jennings and Hayes 1994; M. D. Wilcox in
litt., 1998). These areas along with the numbers of frogs most recently observed in each
area are described below.
San Gabriel Mountains: Surveys conducted from 1993 to 1997 revealed small isolated
populations in the upper reaches of Prairie Creek/Vincent Gulch, Devil's Canyon, and Alder
Creek/East Fork, on the East Fork of the San Gabriel River, and Little Rock Creek on the
Mojave River (Jennings and Hayes 1994 and references therein; Jennings 1995; Jennings
1998). The surveys involved one to three field biologists and were conducted over 1-5 days
per site. Over the course of these field studies, 15 adults or fewer were observed at any
1 site, and, after the 1995 season, Jennings (1995) concluded that the actual population
at each of the sites was only 10-20 adults.
San Jacinto Mountains: Small populations of mountain yellow-legged frogs also occur in
four tributaries in the upper reaches of the North Fork, San Jacinto River on Mount San
Jacinto: Dark Canyon, Hall Canyon, Fuller Mill Creek, and the main North Fork, San Jacinto
River (Jennings and Hayes 1994; Jennings 1995; Jennings 1998). The number of frogs
occupying these sites is not known, but fewer than 10 adult frogs per site per year have
been observed in surveys from 1995 to the present.
San Bernardino Mountains: A few tadpoles and 26 recently transformed juveniles, but no
adults, were rediscovered on a roughly 1-mile reach of the East Fork, City Creek during
the summer of 1998 (M. D. Wilcox in litt., 1998). Previous to this finding, mountain
yellow-legged frogs had not been observed in the San Bernardino Mountains since the 1970s
(Jennings and Hayes 1994), even though surveys were conducted during the summer and fall
of 1997 and 1998 (Holland 1997; Tierra Madre 1999).When frogs were encountered during
field surveys accomplished between 1988 and 1995, only a few individuals were observed.
Jennings and Hayes (1994) and Jennings (1995) suggested that the entire population of
mountain yellow-legged frogs in the San Gabriel and San Jacinto Mountains (8 more or less
isolated sites) was probably fewer than 100 adult frogs. Their rough estimate is based on
a compilation of the results of visual surveys generally conducted on a single day, not on
formal population abundance estimation techniques. While the precise number of adult frogs
may be greater than 100, we concur with Jennings and Hayes (1994) that, in the San Gabriel
and San Jacinto Mountains, the available data indicate that this once widespread species
is now found in only a small number of relatively isolated populations. We do not know the
population size of adult frogs at the recently rediscovered site on the east fork of City
Creek in the San Bernardino Mountains, but because no adults and only a few juveniles and
tadpoles were encountered, the adult population is probably small. Thus, we conclude that
each of the three mountain ranges (San Gabriel, San Jacinto, San Bernardino) contains a
small number of small, relatively isolated populations.
Distinct Vertebrate Population Segment
We analyzed the mountain yellow-legged frog according to the joint Service and National
Marine Fisheries Service Policy Regarding the Recognition of Distinct Vertebrate
Populations, published in the Federal Register on February 7, 1996 (61 FR 4722). We
consider three elements in determining whether a vertebrate population segment could be
treated as threatened or endangered under the Act: discreteness, significance, and
conservation status in relation to the standards for listing. Discreteness refers to the
isolation of a population from other members of the species and is based on two criteria:
(1) Marked separation from other populations of the same taxon resulting from physical,
physiological, ecological, or behavioral factors, including genetic discontinuity, or (2)
populations delimited by international boundaries. We determine significance either by the
importance or contribution, or both, of a discrete population to the species throughout
its range. Our policy lists four examples of factors that may be used to determine
significance: (1) Persistence of the discrete population segment in an ecological setting
unusual or unique for the taxon; (2) evidence that loss of the discrete population segment
would result in a significant gap in the range of the taxon; (3) evidence that the
discrete population segment represents the only surviving natural occurrence of the taxon
that may be more abundant elsewhere as an introduced population outside its historic
range; and (4) evidence that the discrete population segment differs markedly from other
populations of the taxon in its genetic characteristics. If we determine that a population
segment is discrete and significant, we evaluate it for endangered or threatened status
based on the Act's standards.
Discreteness: The range of the mountain yellow-legged frog is divided by
a natural geographic barrier, the Tehachapi Mountains, which isolate Sierran frogs from
those in the mountains of southern California. The distance of the separation is about 225
km (140 mi), but the separation may not have been this great in the recent past because a
frog collected in 1952 on Breckenridge Mountain in Kern County was identified by Jennings
and Hayes (1994) as a mountain yellow-legged frog. The geographic separation of the
Sierran and southern California frogs was recognized in the earliest description of the
species by Camp (1917, cited in Zweifel 1955), who treated frogs from the two localities
as separate subspecies within the R. boylii group. He designated the Sierran frogs R. b.
sierrae and the southern California frogs R. b. muscosa, based on geography and subtle
morphological differences. Zweifel (1955) reevaluated the morphological evidence and found
it insufficient to warrant Camp's recognition of two subspecies, the chief difference
between the two being hind-limb length.
More recently, Ziesmer (1997) analyzed the calls of Sierran (Alpine and Mariposa Counties)
and southern California (San Jacinto Mountains and Riverside County) mountain
yellow-legged frogs. He found that the calls of Sierran frogs differed from southern
California frogs in pulse rate, harmonic structure, and dominant frequency. Based on a
limited sample, Ziesmer concluded that the results supported the hypothesis that mountain
yellow-legged frogs from the Sierra Nevada and southern California are separate species.
Allozyme (a form of an enzyme produced by a gene) variation throughout the range of the
mountain yellow-legged frog has been examined, but the results are open to interpretation
(Jennings and Hayes 1994 and references therein). In the work most applicable to the
question of the distinctiveness of the Sierran and southern California frogs, David Green
(pers. comm., 1998) analyzed allozyme variation in central Sierran mountain yellow-legged
frogs (four individuals, Tuolumne County) and southern California mountain yellow-legged
frogs (two individuals, Riverside County). He found fixed differences at 6 of 28 loci
(sites on a chromosome occupied by specific genes). These limited, unpublished data
suggest that Sierran and southern California mountain yellow-legged frogs are different at
a level that could support the recognition of full species. However, because of the small
number of individuals per sample and the limited number of samples, we view these results
cautiously. It is possible that existing variation at those six loci may not have been
detected with such a small number of individuals sampled. To better understand whether a
genetic discontinuity significant enough to warrant full species rank exists between
Sierran frogs and those from the mountains of southern California, samples of frogs from
the southern Sierra Nevada, especially the Greenhorn Mountains, would be of particular
interest. Although Green's limited allozyme analysis may not be sufficient to support
recognizing the Sierran and southern California populations as separate species, it does
support the conclusion of significant geographic separation. This conclusion is also
supported by earlier observations of morphological differences (Zweifel 1955, and
references therein) and differences in vocalizations (Ziesmer 1997). Considered together,
the evidence supports an interpretation of isolation between the two populations of frogs
over a very long period. We find that the southern California frogs meet the criterion of
``marked separation from other populations of the same taxon'' and qualify as discrete
according to the Policy Regarding the Recognition of Distinct Vertebrate Populations (61
FR 4722).
Significance: One of the most striking differences between Sierran and
southern California mountain yellow-legged frogs is the habitats they occupy. Zweifel
(1955) observed that the frogs in southern California are typically found in steep
gradient streams in the chaparral belt, even though they may range up into small meadow
streams at higher elevations. In contrast, Sierran frogs are most abundant in high
elevation lakes and slow-moving portions of streams. Bradford's (1989) southern Sierra
Nevada study site, for example, was in Sequoia and Kings Canyon National Parks at high
elevations (between 2,910-3,430 m (9,600-11,319 ft)). The rugged canyons of the arid
mountain ranges of southern California bear little resemblance to the alpine lakes of the
Sierra Nevada. On the basis of habitat alone, one might easily conclude that these are two
very different frogs.
The mountain yellow-legged frogs of southern California comprise the southern portion of
the species' range. The extinction of this southern group would be significant because it
would substantially reduce the overall range as it is currently understood, and what is
now a gap in the distribution, the Tehachapi Mountains, would become the southern limit of
the species' range.
In addition, evidence exists that the mountain yellow-legged frog is not simply a single
specieswith a disjunct distribution (cited in Zweifel 1955; Stebbins 1985). As discussed
above, vocal and genetic differences exist between Sierran and southern California
mountain yellow-legged frogs. Although the data are limited and some important variation
may have been missed, they are consistent with the earlier interpretation by Camp (1917
cited in Zweifel 1955) and numerous other authors prior to Zweifel (e.g., Stebbins 1954)
who treated the two forms as taxonomically distinct. If the differences in vocalization
described by Ziesmer (1997) and the allozyme variation described by Green (per. comm.,
1998) accurately characterize differences between the two forms, then the Sierran and
southern California frogs are quite different and have been isolated for a very long time.
Our conclusion that Sierran and southern California frogs are very different from each
other, and may even merit recognition as separate subspecies or possibly even species, is
based on the cumulative weight of the available evidence. We find that the mountain
yellow-legged frogs inhabiting the mountains of southern California meet the significance
criteria under our Policy Regarding the Recognition of Distinct Vertebrate Populations (61
FR 4722) on the basis of the geographical, ecological, vocal, and genetic discontinuities
described above.
In the remainder of this proposed rule, we evaluate the southern California mountain
yellow-legged frog for endangered status based on the Act's standards. For clarity, we
refer to all mountain yellow-legged frogs south of the Tehachapi Mountains as the southern
California DPS. We use the word ``population'' to describe all of the frogs living in a
particular place.
Previous Federal Action
On July 13, 1995, we received a petition dated July 10, 1995, from D.C. ``Jasper'' Carlton
(of the Biodiversity Legal Foundation), Bonnie M. Dombrowski, and Michael C. Long to list
as threatened or endangered the southern California populations of the mountain
yellow-legged frog (Rana muscosa) pursuant to the Act. Accompanying the petition was
supporting information related to the taxonomy, ecology, and the past and present
distribution of the species. We reviewed the petition, supporting documentation, and other
information cited in this proposed rule to determine if substantial information was
available to indicate that the requested action may be warranted. On July 8, 1997, we
published a 90-day finding for the petition to list the southern California populations of
the mountain yellow-legged frog (62 FR 36481). We found the southern California population
to be a DPS and furthermore found the petition presented substantial information
indicating the listing of the species (DPS) may be warranted. Once we made the finding
that the petition presented substantial information, we commenced a status review pursuant
to section 4(b)(3)(A) of the Act. However, consistent with the applicable Listing Priority
Guidances (62 FR 55268; 63 FR 25502), our Carlsbad Field Office completed work on higher
priority listing actions before completing this 12-month finding and proposed rule to list
this DPS of the mountain yellow-legged frog.The processing of this proposed rule conforms
with our Listing Priority Guidance published in the Federal Register 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. The processing of critical habitat
determinations (prudency and determinability decisions) and proposed or final designations
of critical habitat will be funded separately from other section 4 listing actions and
will no longer be subject to prioritization under the Listing Priority Guidance. The
processing of this proposed rule is a Priority 3 action.
Summary of Factors Affecting the Species
Section 4 of the Endangered Species Act (16 U.S.C. 1531 et seq.) and the regulations (50
CFR part 424) that 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 southern California DPS of mountain
yellow-legged frogs are as follows:
A. The Present or Threatened Destruction, Modification, or Curtailment
of its Habitat or Range.
All nine known populations of southern California Rana muscosa occur on lands owned and
managed by the FS and are clustered within three drainages, one in the San Gabriel
Mountains, one in the San Bernardino Mountains, and another on Mount San Jacinto. As such,
the habitats in which they live are protected against wholesale conversions to other uses.
However, with so few populations remaining, and with each of those numbering only a few
individuals, localized habitat alterations, which would not be appreciable if the DPS were
more wide-ranging and abundant, threaten the DPS. Local habitat changes caused by
recreational suction dredging for gold and human use around campgrounds, picnic grounds,
and heavily used trails may harm the habitat and contribute to local extinctions wherever
these activities intersect with mountain yellow-legged frogs. Jennings (1995) observed
suction dredging within the Wilderness Area where mountain yellow-legged frogs occur on
the East Fork, San Gabriel River. He reported observing large quantities of trash and
toxic materials being dumped into the stream bed. If this practice is continued, it could
have harmful effects on the population inhabiting the East Fork, San Gabriel River. The
consequences for populations on other San Gabriel River tributaries is difficult to
predict, but any losses would further isolate the remaining populations and probably
reduce the time to extinction for the DPS. Other than the East Fork, San Gabriel River
site, we do not know if recreational gold mining occurs or at what level on or near sites
occupied by frogs. Extensive suction dredging activity at or near a breeding site could
have the harmful effect of killing eggs or larvae or changing the hydrology, rendering it
unsuitable for breeding. Some of the habitat effects of suction dredging on streams are
described by Harvey (1986), who found dredging altered substrates and changed the habitat
for fish and invertebrates.Fairly heavy camping and day use coincides with frog habitat
along the East Fork, San Gabriel River (dispersed camping), Prairie Fork Creek
(campground, recently burned and presently closed by the FS), Little Rock Creek (trail,
rock climbing), Dark Canyon (campground), and Fuller Mill Creek (picnic ground). In areas
occupied by frogs, human presence in and along streams can disrupt the lives of eggs,
larvae, and adult frogs and change the entire character of the stream and its bank and
associated vegetation in ways that make whole sections of stream less suitable for frogs.
Only nine very small populations remain, and at least four of these are in areas that
receive reasonably heavy human camping or day use. The loss of even small numbers of frogs
from any of these populations due to human camping or day use, either alone or in
combination with other factors, will increase the probability of local extinction. Any
local extinctions will further isolate the remaining populations and probably reduce the
time to extinction for the DPS.
B. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes
Numerous museum specimens from many localities (Jennings and Hayes 1994) attest to the
fact that, for decades, mountain yellow-legged frogs from the southern DPS have been
collected for scientific purposes. These collections probably did not have an appreciable
effect. Now that the DPS has declined precipitously, populations are so few in number, and
the size of each population is so small, very little or no scientific collecting of the
southern DPS occurs. Collecting, scientific or amateur, if it did occur, could seriously
increase the probability of extinction of any of the remaining populations. Any local
extinctions will further isolate the remaining populations and probably reduce the time to
extinction for the DPS.
C. Disease or Predation
Predation by introduced trout, including rainbow trout (Oncorhynchus mykiss), is one of
the best documented causes of the decline of Sierran mountain yellow-legged frogs. Careful
study of the distributions of introduced trout and mountain yellow-legged frogs for
several years has shown conclusively that introduced trout have had negative impacts on
mountain yellow-legged frogs over much of the Sierra Nevada (Bradford 1989; Knapp 1996).
Bradford (1989) and Bradford et al. (1993) concluded that introduced trout eliminate many
populations of mountain yellow-legged frogs and the presence of trout in intervening
streams sufficiently isolates other frog populations so that recolonization after
stochastic (random, naturally occurring) local extinctions is essentially impossible. This
mechanism is sufficient to explain the elimination of Sierran mountain yellow-legged frogs
from the majority of sites they once inhabited, and, alone or in combination with other
factors, introduced trout have almost certainly contributed to the widespread and
systematic decline of the southern DPS as well.
Virtually all streams in the mountains of southern California contain populations of
introduced rainbow trout, and trout are routinely planted in Dark Canyon, Fuller Mill
Creek in the San Jacinto Mountains, and City Creek in the San Bernardino Mountains. Most
of the other streams still occupied by mountain yellow-legged frogs have histories of
trout introductions and probably contain naturally reproducing, sustainable populations
at, or very near, the sites occupied by the frogs. Wherever the two species co-occur,
trout are likely to eliminate mountain yellow-legged frogs or keep populations low and
limit dispersal. The widespread occurrence of introduced trout in the mountains of
southern California may make it very difficult to reverse the decline to extinction of the
DPS.
Another introduced predator that could have effects on the DPS similar to those of the
trout, yet on a more limited scale, is the bullfrog, Rana catesbeiana. Bullfrogs have been
listed among the threats to other western frogs (61 FR 25813; Kiesecker and Blaustein
1998) and toads (59 FR 64859). Bullfrogs are now widespread in southern California and
occur in many drainages formerly and currently occupied by mountain yellow-legged frogs.
The negative effects of bullfrogs on mountain yellow-legged frogs in the mountains of
southern California are probably less widespread than those of introduced trout because
there is less overlap in their occurrence. Any habitat alterations that are favorable to
bullfrogs, however, will cause them to become abundant locally. In areas where mountain
yellow-legged frogs occur, this increase could lead to local extinctions and increased
isolation of the remaining populations, which would probably reduce the time to extinction
for the entire DPS.
Bradford (1991) documented the loss of a Sierran population of Rana muscosa due to the
combined effect of ``red-leg'' disease (caused by the bacterium Aeromonas hydrophila) and
predation by Brewer's blackbirds, Euphagus cyanocephalus. Another pathogen that is
generating concern among those who study amphibian declines is the chytrid fungus.
Chytrids may be seriously affecting amphibians in many places around the world, and they
have recently been discovered on larval mountain yellow-legged frogs in the Sierra Nevada
(Gary Fellers, pers. comm. 1999). Because of the small and isolated nature of the
remaining populations, disease could be serious. Any local extinctions caused by disease
would further isolate the remaining populations and probably reduce the time to extinction
for the entire DPS.
D. The Inadequacy of Existing Regulatory Mechanisms
Existing regulatory mechanisms have not stopped the decline of mountain yellow-legged
frogs in southern California. Existing regulatory mechanisms that could provide some
protection for the mountain yellow-legged frog include: (1) Consideration under the
California Environmental Quality Act (CEQA); (2) consideration under section 404 of the
Clean Water Act (CWA); and (3) co-occurrence with other species protected by the
Endangered Species Act of 1973.
The State of California considers mountain yellow-legged frogs a species of special
concern, but it is not a threatened or endangered species and receives no protection under
the California Endangered Species Act. California Sport Fishing Regulations include the
mountain yellow-legged frog as a protected species that may not be taken or possessed at
any time except under special permit from the California Department of Fish and Game. This
prohibition may help prevent threats from collecting, but this threat is not a significant
cause of the decline, and the DPS is expected to continue declining toward extinction even
in the absence of collecting.
The CEQA requires a full public disclosure of the potential environmental impact of
proposedprojects. The public agency with primary authority or jurisdiction over the
project is designated as the lead agency and is responsible for conducting a review of the
project and consulting with other agencies concerned with resources affected by the
project. Section 15065 of the CEQA guidelines require a finding of significance if a
project has the potential to ``reduce the number or restrict the range of a rare or
endangered plant or animal.'' Species that are eligible for listing as rare, threatened,
or endangered but are not so listed are given the same protection as those species that
are officially listed with the State. Once significant impacts are identified, the lead
agency has the option to require mitigation for effects through changes in the project or
to decide that overriding considerations make mitigation infeasible. In the latter case,
projects may be approved that cause significant environmental damage, such as destruction
of endangered species. Protection of listed species through CEQA is, therefore, at the
discretion of the lead agency involved. The CEQA provides that, when overriding social and
economic considerations can be demonstrated, project proposals may go forward, even in
cases where the continued existence of the species may be threatened, or where adverse
impacts are not mitigated to the point of insignificance.
Besides the Act, the primary Federal law that potentially affords some protection for the
mountain yellow-legged frog is section 404 of the CWA. The CWA may provide some general
protections for species, however, this DPS has declined precipitously under this Federal
law.The arroyo toad (Bufo microscaphus californicus), a federally listed endangered
species, is present in the San Gabriel Mountains, but there is no benefit to the mountain
yellow-legged frog because the two species occupy different areas in the San Gabriel
Mountains and the arroyo toads are not known to occur elsewhere in the limited range of
the mountain yellow-legged frog.
The Angeles and San Bernardino National Forests manage all known locations of mountain
yellow-legged frogs in southern California. However, the FS does not include Rana muscosa
on its list of sensitive species, although the Angeles and San Bernardino National Forests
manage the frog as if it were sensitive (M. Rogers, in litt., 1997). Nevertheless, the FS
does not have a management plan for the mountain yellow-legged frog or an adaptive
management strategy that addresses the specific conservation and recovery needs of the
species. As noted in the discussion of factors A through C above, the presence of
introduced trout on FS lands is a serious threat, and, now that the DPS has been reduced
to small isolated remnants, some other legal recreational activities occurring on FS lands
may threaten the remaining frogs. The perilous status of the mountain yellow-legged frog
reflects the overall failure or inability of existing CEQA, National Environmental Policy
Act, and other Federal, State, and local ordinances and statutes to protect and provide
for the conservation of this DPS.
E. Other Natural or Manmade Factors Affecting its Continued Existence
Because the remaining populations of the DPS are small, isolated remnants, they are
vulnerable to random natural events that could quickly eliminate them. It is a widely
recognized principle that, in general, small populations are more vulnerable to extinction
than large ones (Pimm 1991; Noss and Cooperrider 1994). Noss and Cooperrider (1994)
identified four major factors that predispose small populations to extinction: (1)
Environmental variation and natural catastrophes like unusually harsh weather, fires, or
other unpredictable environmental phenomena; (2) chance variation in age and sex ratios or
other population parameters (demographic stochastisity); (3) genetic deterioration
resulting in inbreeding depression and genetic drift (random changes in gene frequencies);
and (4) disruption of metapopulation dynamics (i.e., some species are distributed as
systems of local populations linked by occasional dispersal, which wards off demographic
or genetic deterioration).
It is likely that some or a combination of these factors contribute to an increased
probability of extinction of the remaining populations and the entire DPS. For example,
Stewart (in litt., 1995) and Jennings (in litt., 1995) believe that flooding and fires
could easily eliminate entire populations of mountain yellow-legged frogs, and Stewart (in
litt., 1995) believes flooding during the winter of 1969 was the major factor in the loss
of mountain yellow-legged frogs from Evey Canyon in the San Gabriel Mountains. An
illustration of possible demographic effects is seen in the results of a limited survey by
Jennings (1995), who found skewed sex ratios in the San Gabriel Mountains populations. If
the results accurately reflect the real sex ratios in these populations, the effective
population sizes are much lower than the census populations. When effective population
size is small, the negative consequences can be demographic (e.g., not enough individuals
of a given sex) or genetic (e.g., inbreeding depression), and can predispose these
populations to a higher risk of extinction. The population genetics and metapopulation
dynamics of the southern mountain yellow-legged frog have not been investigated, but we
believe that the connectivity of populations within the DPS is substantially reduced
compared to the recent past.
Because the southern DPS consists of small, isolated populations, it is particularly
vulnerable to some or all of the effects of chance listed above. Given the low probability
of improving the status of the DPS under the status quo, the probability of small
population size playing a role in the extinction of one or more local populations within
the next few years is high. Any local extinctions will further isolate the remaining
populations and probably reduce the time to extinction for the entire DPS.
In summary, in southern California the mountain yellow-legged frog DPS is threatened by
predation from introduced trout and possibly by other factors (e.g., airborne
contaminants, pathogens) that are difficult to pinpoint and are currently the subject of
national and worldwide investigations. Other local factors (recreational dredging,
camping, day use), that would not cause appreciable harm if the DPS had not been reduced
to small remnants, now represent serious actual or potential local threats. Compounding
the effects of the large-scale (trout) and local (recreation) threats, the DPS has been
reduced to very small isolated or semi-isolated populations that random events are now
likely to contribute to local extinctions, which will reduce the time to extinction of the
entire DPS. Even though we may never fully understand all the causes of decline, the
available information suggests a high probability that this frog may be extinct in
southern California within a few decades. We have carefully assessed the best scientific
and commercial information available regarding the past, present, and future threats
facing the DPS in determining to propose listing. Based on this evaluation, we propose to
list the southern California DPS of mountain yellow-legged frog as endangered. We
considered but did not select other alternatives to this action because not listing this
DPS as endangered, or listing it as threatened, would not provide adequate protection and
would not be in keeping with the purpose of the Act or the definitions therein. This DPS
consists of 9 small, relatively isolatedpopulations from which a combined total of fewer
than 100 adults have been observed in recent surveys. Although all of the factors that
have caused it to decline to this low level may never be known, the DPS is in immediate
danger of extinction.
Critical Habitat
Critical habitat is defined in section 3 of the Act as: (i) the specific areas within the
geographical area occupied by a species, at the time it is listed in accordance with the
provisions of section 4 of the Act, on which are found those physical or biological
features (I) essential to the conservation of the species and (II) that may require
special management considerations or protection, and (ii) specific areas outside the
geographical area occupied by a species at the time it is listed, upon a determination by
the Secretary that such areas are essential for the conservation of the species (16 U.S.C.
1532(5)). ``Conservation'' means the use of all methods and procedures needed to bring an
endangered or threatened species to the point at which protection under the Act is no
longer necessary.
Due to the small number of populations, the mountain yellow-legged frog is vulnerable to
unrestricted collection, vandalism, or other disturbance. We are concerned that these
threats might be exacerbated by the publication of critical habitat maps and further
dissemination of locational information. However, we have examined the evidence available
for the mountain yellow-legged frog and have not found significant specific evidence of
taking, vandalism, collection, or trade of this species or any similarly situated species.
Consequently, consistent with applicable regulations (50 CFR 424.12(a)(1)(i)) and recent
case law, we do not expect that the identification of critical habitat will increase the
degree of threat to this species of taking or other human activity.
In the absence of a finding that critical habitat would increase threats to a species, if
there are any benefits to critical habitat designation, then a prudent finding is
warranted. In the case of this species, there may be some benefits to designation of
critical habitat. The primary regulatory effect of critical habitat is the section 7
requirement that Federal agencies refrain from taking any action that destroys or
adversely modifies critical habitat. While a critical habitat designation for habitat
currently occupied by this species would not be likely to change the section 7
consultation outcome because an action that destroys or adversely modifies such critical
habitat would also be likely to result in jeopardy to the species, there may be instances
where section 7 consultation would be triggered only if critical habitat is designated.
Examples could include unoccupied habitat or occupied habitat that may become unoccupied
in the future. There may also be some educational or informational benefits to designating
critical habitat. Therefore, we find that critical habitat is prudent for this DPS of the
mountain yellow-legged frog.
The Final Listing Priority Guidance for FY 2000 (64 FR 57114) states, ``The processing of
critical habitat determinations (prudency and determinability decisions) and proposed or
final designations of critical habitat will be funded separately from other section 4
listing actions and will no longer be subject to prioritization under the Listing Priority
Guidance. Critical habitat determinations, which were previously included in final listing
rules published in the Federal Register, may now be processed separately, in which case
stand-alone critical habitat determinations will be published as notices in the Federal
Register. We will undertake critical habitat determinations and designations during FY
2000 as allowed by our funding allocation for that year.'' As explained in detail in the
Listing Priority Guidance, our listing budget is currently insufficient to allow us to
immediately complete all of the listing actions required by the Act. Deferral of the
critical habitat designation for this DPS of the mountain yellow-legged frog will allow us
to concentrate our limited resources on higher priority critical habitat and other listing
actions, while allowing us to put in place protections needed for the conservation of the
mountain yellow-legged frog without further delay.We plan to employ a priority system for
deciding which outstanding critical habitat designations should be addressed first. We
will focus our efforts on those designations that will provide the most conservation
benefit, taking into consideration the efficacy of critical habitat designation in
addressing the threats to the species, and the magnitude and immediacy of those threats.
We will develop a proposal to designate critical habitat for this DPS of the mountain
yellow-legged frog as soon as feasible, considering our workload priorities.
Available Conservation Measures
Conservation measures provided to species listed as endangered or threatened under the Act
include requirements for Federal protection, prohibitions against certain practices, and
recovery actions. The Act provides for possible land acquisition/exchange and cooperation
with the States. The protection required of Federal agencies and the prohibitions against
certain activities involving listed species are discussed, in part, below. Listing of the
southern California DPS as endangered will provide for the development of a recovery plan.
Such a plan will bring together both State and Federal efforts for the mountain
yellow-legged frog's conservation. The plan will establish a framework for cooperation and
coordination among agencies in conservation efforts. The plan will set recovery priorities
and estimate costs of various tasks necessary to accomplish them. It will also describe
site-specific management actions necessary to achieve conservation and survival of the
southern California DPS of the mountain yellow-legged frog.
Section 7(a) of the Act, as amended, requires Federal agencies to evaluate their actions
with respect to any species that is proposed or listed as endangered or threatened and
with respect to its critical habitat, if any is being designated. Regulations implementing
this interagency cooperation provision of the Act are codified at 50 CFR part 402. Section
7(a)(4) requires Federal agencies to confer informally with the Service on any action that
is likely to jeopardize the continued existence of a proposed species or result in
destruction or adverse modification of its proposed critical habitat. If a species is
listed subsequently, Section 7(a)(2) requires Federal agencies to ensure that activities
they authorize, fund, or carry out are not likely to jeopardize the continued existence of
such a species or to destroy or adversely modify its critical habitat. If a Federal action
may affect a listed species or its critical habitat, the responsible Federal agency must
enter into formal consultation with the Service. Federal agencies expected to have
involvement with section 7 regarding the southern California DPS of mountain yellow-legged
frog include the U.S. Forest Service through its management activities and the U.S. Army
Corps of Engineers through its permit authority under section 404 of the Clean Water Act.
These agencies either administer lands containing the DPS or authorize, fund, or otherwise
conduct activities that may affect the DPS.
The Act and implementing regulations found at 50 CFR 17.21 set forth a series of general
prohibitions and exceptions that apply to all endangered wildlife. These prohibitions, in
part, make it illegal for any person subject to the jurisdiction of the United States to
take (including harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, collect, or
attempt any such conduct), import or export, transport in interstate or foreign commerce
in the course of commercial activity, or sell or offer for sale in interstate or foreign
commerce any listed species. It is also illegal to possess, sell, deliver, carry,
transport, or ship any such wildlife that has been taken illegally. Certain exceptions
apply to agents of the Service and State conservation agencies.
It is the policy of the Service published in the Federal Register on July 1, 1994 (59 FR
34272), to identify to the maximum extent practical at the time a species is listed those
activities that would or would not constitute a violation of section 9 of the Act. The
intent of this policy is to increase public awareness of the effect of a listing on
proposed and ongoing activities within a species' range. If the DPS is eventually listed,
we believe the following actions would not be likely to result in a violation of section
9:Possession, delivery, or movement, including interstate transport and import into or
export from the United States, involving no commercial activity, of dead specimens of this
taxa that were collected prior to the date of publication in the Federal Register of the
final regulation adding this taxa to the list of endangered species.Activities that the
Service believes could potentially harm the southern California DPS of mountain
yellow-legged frog and result in a violation of section 9 of the Act include, but are not
limited to:
(1) Take of southern California mountain yellow-legged frogs without a permit, which
includes harassing, harming, pursuing, hunting, shooting, wounding, killing, trapping,
capturing, or collecting, or attempting any of these actions;
(2) Possessing, selling, delivering, carrying, transporting, or shipping illegally taken
mountain yellow-legged frogs;
(3) Interstate and foreign commerce (commerce across State and international boundaries)
and import/export (as discussed earlier in this section);
(4) Introduction of nonnative species that compete or hybridize with, or prey on, mountain
yellow-legged frogs; and
(5) Destruction or alteration of mountain yellow-legged frog habitat by dredging,
channelization, diversion, in-stream vehicle operation or rock removal, or other
activities that result in the destruction or significant degradation of cover, channel
stability, substrate composition, temperature, and habitat used by the species for
foraging, cover, migration, and breeding; and
(6) Discharges or dumping of toxic chemicals, silt, or other pollutants into waters
supporting mountain yellow-legged frogs by mining, or other developmental or land
management activities that result in destruction or significant degradation of cover,
channel stability, substrate composition, temperature, and habitat used by the species for
foraging, cover, migration, and breeding.
Questions regarding whether specific activities may constitute a violation of section 9
should be directed to the Field Supervisor of our Carlsbad Fish and Wildlife Office (see
ADDRESSES section). Requests for copies of the regulations and inquiries regarding them
may be addressed to the U.S. Fish and Wildlife Service, Ecological Services, Endangered
Species Permits, 911 Northeast 11th Avenue, Portland, Oregon 97232-4181 (503/231-6241; FAX
503/231-6243).Permits may be issued to carry out otherwise prohibited activities involving
endangered wildlife species under certain circumstances. Regulations governing these
permits are at 50 CFR 17.22 and 17.23. Such permits are available for scientific purposes,
to enhance the propagation or survival of the species, for incidental take in connection
with otherwise lawful activities, and/or for economic hardship.
Public Comments Solicited
The Service intends that any final action resulting from this proposal will be as accurate
and as effective as possible. Therefore, comments or suggestions from the public, other
concerned governmental agencies, the scientific community, industry, or any other
interested party concerning this proposed rule are hereby solicited. Comments particularly
are sought concerning:
(1) Biological, commercial trade, or other relevant data concerning any threat (or lack
thereof) to this species;
(2) The distribution of resident rainbow trout in the mountains of southern California
prior to the stocking programs of the California Department of Fish and Game;
(3) The location of any additional occurrences of this species and the reasons why any
habitat should or should not be determined to be critical habitat as provided by section 4
of the Act;
(4) Additional information concerning the range, distribution, and population size of this
species; and
(5) Current or planned activities in the subject area and their possible impacts on the
southern California population of mountain yellow-legged frogs.
Final promulgation of the regulation(s) on this species will take into consideration the
comments and any additional information received by the Service. Such communications may
lead to a final regulation that differs from this proposal.
The Endangered Species Act provides for one or more public hearings on this proposal, if
requested. Requests must be received within 45 days of the date of publication of the
proposal in the Federal Register. Such requests must be made in writing and addressed to
Supervisor, U.S. Fish and Wildlife Service, Carlsbad Fish and Wildlife Office (see
ADDRESSES section).
(Source: Federal Register, December 22, 1999, slightly edited)
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