27900 Federal Register / Vol. 73, No. 94 / Wednesday, May 14, 2008 / Proposed Rules 

DEPARTMENT OF THE INTERIOR 

Fish and Wildlife Service 

50 CFR Part 17 

[FWS–R2–ES–2008–0056; 1111 FY07 MO– 

B2] 

Endangered and Threatened Wildlife 

and Plants; Status Review for Rio 

Grande Cutthroat Trout 

AGENCY: Fish and Wildlife Service, 

Interior. 

ACTION: Notice of candidate status 

review. 

SUMMARY: We, the U.S. Fish and 

Wildlife Service (Service), announce the 

results of the status review for the Rio 

Grande cutthroat trout (Oncorhynchus 

clarki virginalis) under the Endangered 

Species Act of 1973 (Act), as amended. 

After a thorough review of all available 

scientific and commercial information, 

we find that listing the Rio Grande 

cutthroat trout is warranted but 

precluded by higher priority actions. 

Upon publication of this status review, 

we will add the Rio Grande cutthroat 

trout to our list of candidate species 

with a listing priority number of 9, 

because the threats affecting it have a 

moderate magnitude and are imminent. 

We will develop a proposed rule to list 

the subspecies as our priorities allow. 

We ask the public to continue to submit 

to us any new information that becomes 

available concerning the status of or 

threats to the subspecies. This 

information will help us to monitor and 

encourage the ongoing conservation of 

this subspecies. 

DATES: The finding announced in this 

document was made on May 14, 2008. 

ADDRESSES: This finding is available on 

the Internet at http:// 

www.regulations.gov. Supporting 

documentation we used in preparing 

this finding is available for public 

inspection, by appointment, during 

normal business hours at the U.S. Fish 

and Wildlife Service, New Mexico 

Ecological Services Field Office, 2105 

Osuna Road, NE., Albuquerque, New 

Mexico 87113; telephone (505) 346– 

2525; facsimile (505) 248–6788. Please 

submit any new information, materials, 

comments, or questions concerning this 

finding to the above address or via 

electronic mail (e-mail) at 

r2fwe_al@fws.gov. 

FOR FURTHER INFORMATION CONTACT: 

Wally ‘‘J’’ Murphy, Field Supervisor, 

U.S. Fish and Wildlife Service, 2105 

Osuna Road, NE., Albuquerque, New 

Mexico 87113. (505) 346–2525 ext 106. 

If you use a telecommunications device 

for the deaf (TDD), call the Federal 

Information Relay Service (FIRS) at 

800–877–8339. 

SUPPLEMENTARY INFORMATION: 

Background 

Section 4(b)(3)(B) of the Act (16 

U.S.C. 1531 et seq.) requires that, for 

any petition containing substantial 

scientific and commercial information 

that listing may be warranted, we make 

a finding within 12 months of the date 

of receipt of the petition on whether the 

petitioned action is: (a) Not warranted, 

(b) warranted, or (c) warranted, but that 

immediate proposal of a regulation 

implementing the petitioned action is 

precluded by other pending proposals to 

determine whether species are 

threatened or endangered, and 

expeditious progress is being made to 

add or remove qualified species from 

the Lists of Endangered and Threatened 

Wildlife and Plants. Section 4(b)(3)(C) of 

the Act requires that we treat a petition 

for which the requested action is found 

to be warranted but precluded as though 

resubmitted on the date of such finding, 

that is, requiring a subsequent finding to 

be made within 12 months. We must 

publish these 12-month findings in the 

Federal Register. 

Previous Federal Actions 

On February 25, 1998, we received a 

petition from Kieran Suckling, of the 

Southwest Center for Biological 

Diversity requesting that the Service add 

the Rio Grande cutthroat trout 

(Oncorhynchus clarki virginalis) to the 

list of threatened and endangered 

species. The petition addressed the 

range-wide distribution of the Rio 

Grande cutthroat trout that includes 

populations in Colorado and New 

Mexico. We subsequently published a 

notice of a 90-day finding in the Federal 

Register (63 FR 49062) on September 

14, 1998. In the 90-day finding we 

concluded that the petition did not 

present substantial information 

indicating that listing of the Rio Grande 

cutthroat trout may be warranted. 

On June 9, 1999, a complaint was 

filed by the Southwest Center for 

Biological Diversity alleging that the 

September 14, 1998, 90-day petition 

finding violated the Administrative 

Procedure Act. While the litigation was 

pending, we received information 

(particularly related to the presence of 

whirling disease in hatchery fish in the 

wild) that led us to believe that further 

review of the status of the subspecies 

was warranted. On November 8, 2001, a 

settlement agreement executed by both 

parties (the Service and the Southwest 

Center for Biological Diversity) was filed 

with the court. The settlement 

stipulated that the Service would 

initiate a status review for the Rio 

Grande cutthroat trout, make a 

determination on or before June 4, 2002, 

and shortly thereafter, publish our 

determination in the Federal Register. 

On June 11, 2002, we published our 

determination that listing of Rio Grande 

cutthroat trout was not warranted (67 

FR 39936). 

Subsequently, on February 25, 2003, 

the Center for Biological Diversity, along 

with several other organizations, sued 

the Service for failing to list Rio Grande 

cutthroat trout. On June 7, 2005, the 

New Mexico Federal District Court 

(Court) ruled that our finding was not 

arbitrary and capricious, but also 

required that we explain in more detail 

our analysis of ‘‘significant portion of 

the range’’. The Court ordered the 

Service to provide a supplemental 

briefing discussing in more detail our 

analysis of significant portion of the 

range. We submitted this briefing on 

July 20, 2005. On December 19, 2005, 

the Court ruled in favor of the Service 

and upheld our interpretation of 

significant portion of the range and 

determined that our evaluation of Rio 

Grande cutthroat trout’s status under the 

listing criteria was not arbitrary and 

capricious. Plaintiffs appealed this 

decision. 

The appeal was pending with the 

Tenth Circuit Court of Appeals, when 

other courts issued opinions for other 

species that required the Service to 

reexamine our position on significant 

portion of the range. On March 16, 2007, 

a formal opinion was issued by the 

Solicitor of the Department of the 

Interior, ‘‘The Meaning of In Danger of 

Extinction Throughout All or a 

Significant Portion of Its Range’’ (U.S. 

DOI 2007). Because of this new formal 

opinion and because of our knowledge 

of changes in status of some populations 

that we had defined as ‘‘secure’’ in our 

2002 review, in consultation with the 

court and the plaintiffs, the Service 

agreed to initiate a new status review. 

We subsequently published a notice 

seeking new information concerning the 

status of Rio Grande cutthroat trout on 

May 22, 2007 (72 FR 28664). 

In response to our 2007 requests for 

information regarding Rio Grande 

cutthroat trout (72 FR 28664, 72 FR 

46030 (August 16, 2007)), we received 

comments and information from 

Colorado Division of Wildlife (CDOW), 

New Mexico Department of Game and 

Fish (NMDGF), U.S. Bureau of Land 

Management (BLM), U.S. Forest Service 

(USFS), private citizens and 

organizations, and the Rio Grande 

Cutthroat Trout Conservation Team. The 

Rio Grande Cutthroat Trout 


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Conservation Team is composed of 

biologists from CDOW, NMDGF, BLM, 

USFS, National Park Service, the 

Jicarilla Apache Nation and the Service. 

The Rio Grande Cutthroat Trout 

Conservation Team recently completed 

a range-wide status report (Alves et al. 

2007) concerning the Rio Grande 

cutthroat trout. The status report and 

the comprehensive database (referred to 

as ‘‘2007 database’’ in this finding) that 

is the basis for the report, along with 

other supplemental submissions from 

the agencies listed above, provide the 

best scientific and commercial 

information available on Rio Grande 

cutthroat trout. The report summarizes 

information provided by 15 fisheries 

professionals from Colorado and New 

Mexico having specific knowledge of 

Rio Grande cutthroat trout (Alves et al. 

2007, p. 58). In making this finding, we 

considered all scientific and commercial 

information that we received or 

acquired since our previous status 

review. We relied primarily on 

published and peer-reviewed 

documentation for our conclusions. 

Biology and Distribution 

The Rio Grande cutthroat trout, one of 

14 subspecies of cutthroat trout, is 

native to the Rio Grande, Pecos, and the 

Canadian river basins in New Mexico 

and Colorado (Behnke 2002, p. 219). Rio 

Grande cutthroat trout has the 

distinction of being the first North 

American trout recorded by Europeans 

(Behnke 2002, p. 139). In 1541, 

Francisco de Coronado’s expedition 

discovered Rio Grande cutthroat trout in 

the upper Pecos River (Behnke 2002, p. 

139). The first specimens that were 

collected for scientific purposes came 

from Ute Creek in Costilla County, 

Colorado, in 1853. Rio Grande cutthroat 

trout was originally described in 1856 

(Behnke 2002, p. 210). Cutthroat trout 

subspecies are distinguished by the red 

to orange slashes in the throat folds 

beneath the lower jaw. 

The historical distribution of Rio 

Grande cutthroat trout is not known 

with certainty. In general, it is assumed 

that Rio Grande cutthroat trout occupied 

all streams capable of supporting trout 

in the Rio Grande, Pecos, and Canadian 

basins (Alves et al. 2007, p. 9). The 

Pecos River is a tributary of the Rio 

Grande, so a historic connection 

between the two basins likely existed. 

Although no early museum specimens 

document its occurrence in the 

headwaters of the Canadian River, it is 

almost certainly native there as well 

(Behnke 2002, p. 208). The Canadian 

River, tributary to the Mississippi River, 

has no connection with the Rio Grande. 

It is possible that through headwater 

capture (a tributary from one watershed 

joins with a tributary from another) 

there may have been natural migration 

of fish between the Pecos and Canadian 

headwater streams. There is evidence 

that Rio Grande cutthroat trout may 

have occurred in Texas (Garrett and 

Matlock 1991, p. 405; Behnke 1967, pp. 

5, 6) and Mexico (Behnke 1967, p. 4). 

Currently, the southernmost distribution 

of Rio Grande cutthroat trout occurs in 

Animas Creek, Sierra County, New 

Mexico, and Indian Creek on the 

Mescalero Apache Indian Reservation in 

Otero County, New Mexico. Distribution 

in the southern portion of the range is 

currently limited and no conservation 

populations (see discussion of 

conservation populations below) exist 

south of Santa Fe, New Mexico. 

In the range-wide status report, 

historically occupied habitat was based 

on habitat believed to be inhabited by 

Rio Grande cutthroat trout when early 

European explorers entered the 

Southern Rocky Mountain Region of 

Colorado and New Mexico (circa 1800) 

(Alves et al. 2007, p. 9). In general, 

streams currently capable of supporting 

trout (elevations of 1,829 meters (m) 

(6,000 feet (ft)) and above; 1,671 m 

(5,500 ft) and above on north-facing 

slopes) were assumed to have been 

historically occupied if they were not 

above a barrier to fish movement (e.g., 

an impassable waterfall). Streams which 

cannot currently support trout were 

assumed not to have been historically 

occupied unless they were known to 

have been degraded by such things as 

water withdrawals, channel alterations, 

human-caused barriers, or chemical 

contamination. Based on these criteria, 

10,622 kilometers (km) (6,660 miles 

(mi)) of stream habitat were identified as 

having the potential of being historically 

occupied by Rio Grande cutthroat trout 

(Alves et al. 2007, p. 9). The estimated 

amount of historical range in each State 

is about 5,196 km (3,229 mi) in 

Colorado (48 percent), and 5,521 km 

(3,431 mi) (52 percent) in New Mexico 

(Alves et al. 2007, p. 9). 

To facilitate management and 

conservation efforts, the Rio Grande 

cutthroat trout range is divided into 

Geographic Management Units (GMUs) 

based on watersheds (Alves et al. 2007, 

p. 2). The GMUs are, from north to 

south, Rio Grande headwaters, Lower 

Rio Grande, Canadian, Pecos, and 

Caballo. Historical occupancy by GMU 

is 5,277 km (3,279 mi) (49 percent) in 

Rio Grande Headwaters, 3,396 km 

(2,110 mi) (32 percent) in Lower Rio 

Grande, 1,027 km (638 mi) (10 percent) 

in the Canadian, 1,003 km (623 mi) (9 

percent) in Pecos, and 16 km (10 mi) 

(0.2 percent) in Caballo (Alves et al. 

2007, p. 9). 

In our prior status review (67 FR 

39936; June 11, 2002), we focused our 

analysis primarily on ‘‘core’’

populations, which we defined using 

conservative criteria for genetic 

integrity, population stability, and 

security from invasion by nonnative 

salmonids (trout and salmon). The 

genetic criterion for these core 

populations was that the populations 

have less than one percent 

representation of genetic markers from 

another subspecies of cutthroat trout or 

from rainbow trout (Oncorhynchus 

mykiss), as determined by genetic 

testing. Rio Grande cutthroat trout are 

able to interbreed, or hybridize, with 

other subspecies of cutthroat trout and 

rainbow trout. This hybridization may 

result in genes of one species or 

subspecies being incorporated into the 

other species or subspecies. The 

incorporation of genes from one species 

into another is referred to by the 

technical term ‘‘introgression’’ (Mayr 

1970) and a species that has received 

such genes is referred to as 

‘‘introgressed.’’ To simplify discussion 

in this review, we will also use these 

terms when describing when genetic 

markers of another subspecies are found 

in Rio Grande cutthroat trout, although 

we recognize that these terms, as strictly 

defined, refer to species. 

Our previous status review concluded 

that the core populations, as then 

defined by conservative criteria, were 

sufficiently abundant, distributed, and 

secure to conclude that listing of the Rio 

Grande cutthroat trout was not 

warranted. As described later in this 

review, the status of several of the 

original core populations has 

subsequently declined and we believe 

those populations alone are not 

sufficient to conserve the Rio Grande 

cutthroat trout. 

For the current review, the genetic 

criterion for core populations is that 

they be less than one percent 

introgressed, which is the same genetic 

criterion for core populations followed 

in the previous review. Although 

population stability and security from 

invasion are not used to define core 

populations, as they were in the 

previous review, those factors are still 

addressed as attributes affecting the 

status of core and other populations. 

Core populations in the current review 

correspond to the core populations 

described in the multi-state position 

paper for cutthroat management (Utah 

Division of Wildlife Resources (UDWR) 

2000, pp. 3, 4). In addition to these core 

populations, we focused our review on 

‘‘conservation populations’’ as defined 


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by the position paper (UDWR 2000): 

populations less than 10 percent 

introgressed, as measured by genetic 

markers, and that retain the ecological, 

behavioral, and phenotypic 

characteristics of Rio Grande cutthroat 

trout. In addition, we have included as 

conservation populations those 

populations which have not been 

genetically tested, but that retain the 

ecological, behavioral, and phenotypic 

characteristics of Rio Grande cutthroat 

trout and are not suspected to be 

introgressed or co-occurring with 

hybridizing species. 

The above criteria for core and 

conservation populations have been 

applied in Service status reviews of 

other subspecies of cutthroat trout 

published since 2002 (71 FR 8818; 72 

FR 32589). The status review (68 FR 

46989; August 7, 2003) for the westslope 

cutthroat trout (Oncorhynchus clarki 

lewisi) included populations with up to 

20 percent introgression, based on 

several studies of genetic markers and 

morphological traits of introgressed 

populations that indicate that 

populations with up to 20 percent of 

their nuclear genes derived from 

rainbow trout were morphologically 

indistinguishable from nonintrogressed 

westslope cutthroat trout populations. 

Comparable studies, where genetic and 

morphological characters in the same 

population are studied, have not been 

performed on Rio Grande cutthroat 

trout; therefore, we have no justification 

for departing from the general criterion 

of less than 10 percent introgression 

proposed in the position paper on 

cutthroat trout genetics (UDWR 2000). 

In the remainder of this review, we 

collectively refer to both core and 

conservation populations, as defined 

above, as conservation populations. 

Inclusion of conservation populations 

with up to 10 percent introgression in 

the present review does not mean we 

are any less concerned about the effects 

of introgression on Rio Grande cutthroat 

trout. Our evaluation of introgression as 

a threat to the Rio Grande cutthroat 

trout will be described along with other 

applicable threats later in this review. 

Alves et al. (2007, p. 26) report that 

120 conservation populations of Rio 

Grande cutthroat trout currently occupy 

about 1110 km (690 mi) of habitat, or 

10.4 percent of the historical range of 

the subspecies. The 120 conservation 

populations include 12 populations that 

have not been tested for introgression 

and are suspected to be hybridized and 

one population that to date has tested as 

nonintrogressed but in which rainbow 

trout, a hybridizing species, co-occurs 

(Alves et al. 2007, p. 34; 2007 data base). 

An additional two streams (Placer Creek 

and Comanche Creek) included in the 

120 are undergoing restoration and are 

currently unoccupied by Rio Grande 

cutthroat trout. Although we fully 

expect these two streams will become 

conservation populations within the 

next five years, they are not occupied by 

viable populations currently. Although 

we included in our analysis untested 

populations that are suspected to be 

nonintrogressed as conservation 

populations, we do not feel it is 

appropriate to include untested 

populations that are suspected to be 

introgressed or that co-occur with 

hybridizing species. Alves et al. (2007) 

provided all summary statistics (e.g., 

percent populations with nonnative 

trout, percent historical habitat 

occupied, number of populations in 

each state) for 120 conservation 

populations. Although the inclusion of 

these populations in Alves et al. (2007) 

inflates the number of conservation 

populations and miles of stream 

occupied by Rio Grande cutthroat trout, 

their inclusion does not make a material 

difference in the outcome of our finding. 

Therefore, we have decided to present 

all summary statistics as presented in 

Alves et al. (2007) rather than 

recalculate the summary statistics to 

reflect the 105 populations we would 

classify as conservation populations. 

Rio Grande cutthroat trout 

conservation populations currently 

occupy about 473 km (294 mi) in 

Colorado (9.1 percent of Colorado 

historical habitat) and 637 km (396 mi) 

in New Mexico (11.6 percent of 

historical habitat) (Alves et al. 2007, p. 

26). The Lower Rio Grande GMU 

contains the largest amount of occupied 

habitat (489 km (304.1 mi)), followed by 

the Rio Grande Headwaters GMU (452 

km (281.4 mi)), Canadian GMU (109 km 

(67.5 mi)), and Pecos GMU (60 km (37.3 

mi)) (Alves et al. 2007, p. 26). The 

Caballo GMU contains a hybridized 

population of cutthroat trout that was 

not included as a conservation 

population. Rio Grande cutthroat trout 

occupy habitat in 14 of 19 watersheds 

that supported historical habitat. They 

are believed to be extirpated from the 

following watersheds: Arroyo Del 

Macho, Caballo, Upper Canadian, Rio 

Hondo, and Rio Penasco (Alves et al. 

2007, p. 11). If Rio Grande cutthroat 

trout once occurred in Texas and 

Mexico, there is no evidence that they 

occur there now. 

Life History 

As is true of other subspecies of 

cutthroat trout, Rio Grande cutthroat 

trout is found in clear cold streams. 

Unlike some subspecies of cutthroat 

trout, such as the Bonneville 

(Oncorhynchus clarki utah) and 

Yellowstone (Oncorhynchus clarki 

bouvieri), Rio Grande cutthroat trout did 

not originally inhabit large lake systems. 

However, they have been introduced 

into coldwater lakes and reservoirs. 

They spawn as high water flows from 

snowmelt recede. In New Mexico, this 

typically occurs from the middle of May 

to the middle of June (NMDGF 2002, p. 

17). Spawning is believed to be tied to 

day length, water temperature, and 

runoff (Sublette et al. 1990, p. 54; 

Behnke 2002, p. 141). 

It is unknown if Rio Grande cutthroat 

trout spawn every year or if some 

portion of the population spawns every 

other year as has been recorded for 

westslope cutthroat trout (McIntyre and 

Rieman 1995, p. 1). Likewise, while it 

is assumed that females mature at age 3, 

they may not spawn until age 4 or 5 as 

seen in westslope cutthroat trout 

(McIntyre and Rieman 1995, p. 3). Sex 

ratio also is unknown with certainty, 

but based on field data, a ratio skewed 

towards more females might be 

expected (Pritchard and Cowley 2006, p. 

27). Although Yellowstone (Gresswell 

1995, p. 36), Bonneville (Shrank and 

Rahel 2004, p. 1532), and westslope 

(Bjornn and Mallet 1964, p. 73; 

McIntyre and Rieman 1995, p. 3) 

cutthroat trout subspecies are known to 

have a migratory life history phase, it is 

not known if Rio Grande cutthroat trout 

once had a migratory form when there 

was connectivity among watersheds. 

Most cutthroat trout are opportunistic 

feeders, eating both aquatic 

invertebrates and terrestrial insects that 

fall into the water (Sublette et al. 1990, 

p. 54). Rio Grande cutthroat trout 

evolved with Rio Grande chub (Gila 

pandora), longnose dace (Rhinichthys 

cataractae) (all basins); Rio Grande 

sucker (Catastomus plebius) (Rio 

Grande Basin); white sucker (C. 

commersoni) and creek chub (Semotilus 

atromaculatus) (Pecos and Canadian 

Basins); and the southern redbelly dace 

(Phoxinus erythrogaster) (Canadian 

River Basin) (Rinne 1995, p. 24). Many 

of these fish have either been extirpated 

from streams with Rio Grande cutthroat 

trout or are greatly reduced in number 

(Sublette et al. 1990, p. 162; Calamusso 

and Rinne 1999, pp. 233–236). It is not 

known if they once were an important 

component of Rio Grande cutthroat 

trout diet. Other subspecies of cutthroat 

trout become more piscivorous (fish 

eating) as they mature (Moyle 1976, p. 

139; Sublette et al. 1990, p. 54) and 

cutthroat trout living in lakes will prey 

heavily on other species of fish (Echo 

1954, p. 244). It is possible that native 

cyprinids (i.e., chubs, minnows, and 

dace) and suckers may have once been 


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important prey items for Rio Grande 

cutthroat trout. Growth of cutthroat 

trout varies with water temperature and 

availability of food. Most populations of 

Rio Grande cutthroat trout are found in 

high elevation streams. Under these 

conditions growth may be relatively 

slow and time to maturity may take 

longer than is seen in subspecies that 

inhabit lower elevation (warmer) 

streams. 

Typical of trout, Rio Grande cutthroat 

trout require several types of habitat for 

survival: spawning habitat, nursery or 

rearing habitat, adult habitat, and 

refugial habitat. Spawning habitat 

consists of clean gravel (little or no fine 

sediment present) that ranges between 6 

to 40 millimeters (mm) (0.24–1.6 inches 

(in)) (NMDGF 2002, p. 17). Nursery 

habitat is usually at the stream margins 

where water velocity is low and water 

temperature is slightly warmer. Harig 

and Fausch (2002, pp. 542, 543) found 

that water temperature may play a 

critical role in the life history of the 

young-of-year cutthroat. Streams with 

mean daily temperature in July of less 

than 7.8 °C (46 °F) may not have 

successful recruitment (survival of 

individuals to sexual maturity and 

joining the reproductive population) or 

reproduction in most years. Adult 

habitat consists of pools with cover and 

riffles for food production and foraging. 

Refugial habitat in the form of large 

deep pools is also necessary for 

survival. The primary form of refugial 

habitat is deep pools that do not freeze 

in the winter and do not dry in the 

summer or during periods of drought. 

Lack of large pools may be a limiting 

factor in headwater streams (Harig and 

Fausch 2002, p. 543). Refugial habitat 

may also be a downstream reach of 

stream or a connected adjacent stream 

that has maintained suitable habitat in 

spite of adverse conditions. 

A technical review of Rio Grande 

cutthroat trout was recently completed 

(Pritchard and Cowley 2006) which 

covers the biology of the subspecies in 

greater detail and the reader is referred 

to that document for additional 

background information on the 

subspecies. 

Summary of Factors Affecting the 

Subspecies 

Section 4 of the Act and regulations 

(50 CFR 424) promulgated to implement 

the listing provisions of the Act set forth 

the procedures for adding species to the 

Federal list of endangered or threatened 

species. A species may be determined to 

be threatened or endangered due to one 

or more of the five factors described in 

section 4(a)(1) of the Act. The following 

analysis examines the listing factors and 

their application to Rio Grande 

cutthroat trout. 

A. The Present or Threatened 

Destruction, Modification, or 

Curtailment of Its Habitat or Range 

Population Isolation and Fragmentation 

The historic range of Rio Grande 

cutthroat trout has been greatly reduced 

over the last 150 years. Populations 

have been lost because of water 

diversions, stream drying, dams, habitat 

degradation, changes in hydrology, 

hybridization with rainbow trout, or 

competition with brown (Salmo trutta) 

and brook trout (Salvelinus fontinalis) 

(Pritchard and Cowley 2006, pp. 16, 34–

37; 67 FR 39939). Quantifying the exact 

magnitude of loss in either number of 

fish or habitat is difficult because there 

are no baseline data. Alves et al. (2007, 

p. 26) estimate that conservation 

populations occupy about 10 percent of 

historically inhabited stream miles. 

Also, the current distribution of 

occupied miles on the landscape differs 

from the historical distribution. The 

range has contracted northward, Rio 

Grande cutthroat trout are now 

restricted primarily to headwater 

streams, and the large connected 

networks that once linked hundreds of 

stream miles together no longer exist. 

The change in distribution is discussed 

briefly followed by a discussion of 

fragmentation which has modified and 

curtailed habitat. 

Historically, 43 percent of Rio Grande 

cutthroat trout populations occupied 

streams 2,438 m (8,000 ft) or less in 

elevation (Alves et al. 2007, p. 18). 

Currently, only about 1.6 percent of the 

populations are in streams less than 

2,438 m (8,000 ft) (Alves et al. 2007, p. 

18). Conservation populations, as 

defined above, are now concentrated in 

elevations from 2,743–3048 m (9,000–

10,000 ft) (Alves et al. 2007, p. 18). 

High-elevation streams (above 2,743 m 

(9,000 ft)) are subject to extreme and 

fluctuating environmental conditions 

including forest fires, freezing, and 

dewatering (Novinger and Rahel 2003, 

p. 779). In addition, headwater 

mountain streams often lack critical 

resources such as deep pools (Harig and 

Fausch 2002, p. 546) and provide 

insufficient refuge from catastrophic 

disturbance (Pritchard and Cowley 

2006, p. 17). Because high-elevation 

headwater streams are narrow and small 

compared to the larger downstream 

reaches that Rio Grande cutthroat trout 

once occupied, the absolute loss of 

habitat in both quantity and quality is 

greater than stream miles might 

indicate. 

Historically, many watersheds 

supporting Rio Grande cutthroat trout 

contained streams that were connected. 

For example, in Colorado, the 

Trinchera, Conejos, Culebra, Costilla, 

and Alamosa rivers would all have been 

connected through the upper Rio 

Grande, forming a vast network of 

streams (Alves et al. 2007, p. 10). As a 

consequence of habitat loss, each of 

these watersheds is now isolated from 

the other and Rio Grande cutthroat trout 

are restricted to fragments of streams 

(Alves et al. 2007, pp. 12, 29). Of the 

120 conservation populations, 112 

(representing 80 percent of occupied 

miles) are in isolated stream fragments 

(Alves et al. 2007, p. 29). No 

populations are considered to have 

strong connectivity (i.e., ≥ 5 connected 

streams with open migration corridors) 

(Alves et al. 2007, pp. 29, 77). One 

population has a moderate degree of 

connectivity (4 to 5 connected streams); 

however, this watershed (Comanche 

Creek) is currently under restoration 

and has very few fish present. Seven 

populations have very little connectivity 

(2–3 connected streams, infrequent 

straying of adults may occur) (Alves et 

al. 2007, pp. 29, 77). Because Rio 

Grande cutthroat trout habitat is 

severely fragmented and because the 

effects of fragmentation are considered 

one of the primary threats to Rio Grande 

cutthroat trout populations, the 

consequences of fragmentation are 

discussed in detail below. 

Habitat fragmentation reduces the 

total area of habitat available, reduces 

habitat complexity, and prevents gene 

flow (Saunders et al. 1991, p. 25; 

Rieman and McIntyre 1995, p. 293; 

Burkey 1995, pp. 527, 528; Dunham et 

al. 1997, pp. 1126, 1127; Frankham et 

al. 2002, p. 310; Noss et al. 2006, p. 

219). Fragmentation accelerates 

extinction, especially when movement 

of fish among fragments is not possible, 

as is the case with Rio Grande cutthroat 

trout (Burkey 1995, p. 540; Frankham et 

al. 2002, p. 314). Isolated populations 

are vulnerable to extinction through 

demographic stochasticity (random 

changes in the population structure, 

e.g., uneven male/female ratios); 

environmental stochasticity (random 

changes in the fishes’ surroundings) and 

catastrophes (e.g., fires, stream drying, 

freezing); loss of genetic heterozygosity 

(genetic diversity) and rare alleles 

(inherited forms of a genetic trait); and 

human disturbance (Shaffer 1987, p. 71; 

Rieman et al. 1993, pp. 9–15; Burkey 

1995, pp. 527, 528; Dunham et al. 1997, 

p. 1130; Frankham et al. 2002, pp. 310–

324). Completely isolated fragments are 

the most severe form of fragmentation 


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because the isolation prevents fish from 

mating with other fish carrying different 

genes, thereby preventing new genes 

from entering the isolated population 

(Frankham et al. 2002, p. 314). Of 120 

Rio Grande cutthroat trout conservation 

populations, 112 (93 percent, 80 percent 

of occupied miles) exist as isolated 

segments or have very little connectivity 

(Alves et al. 2007, p. 29). 

Apart from the isolation (lack of gene 

flow) that fragmentation causes, the 

short length of the fragments and small 

population size that they support are 

also of concern for Rio Grande cutthroat 

trout. Seventy-one percent of Rio 

Grande cutthroat trout conservation 

populations occupy stream segments of 

8.1 km (5 mi) or less (median 6.2 km 

(4.2 mi)) (Alves et al. 2007, p. 26). 

Several researchers have found that 

population viability of cutthroat trout is 

correlated with stream length 

(Hilderbrand and Kershner 2000, p. 515; 

Young et al. 2005, p. 2405; Cowley 

2007, DOI: 10.1002/aqc.845). Stream 

length is important because trout need 

a variety of habitats to complete their 

life cycle (i.e., spawning habitat, rearing 

habitat, adult habitat, refugial habitat) 

(Rieman and McIntyre 1995, p. 293; 

Horan et al. 2000, p. 1251; Harig and 

Fausch 2002, p. 546; Young et al. 2005, 

p. 2406). The shorter the stream, the 

more likely it is that one or more of the 

Rio Grande cutthroat trout’s required 

habitats is either missing, or inadequate 

for completion of the species life cycle 

(Hilderbrand and Kershner 2000, p. 

513). This is particularly true in highelevation streams which are narrower 

and shallower than larger, lower 

elevation, streams. The longer a stream 

is, the more complexity it encompasses 

and the higher the probability that no 

particular habitat type limits the 

population. 

Hilderbrand and Kershner (2000, p. 

515) estimated 8.3 km (5.1 mi) were 

required to maintain a population of 

2,500 cutthroat trout when fish 

abundance was high (0.3 fish/m (0.09 

fish/ft)). Adding a 10 percent loss rate, 

to account for emigration and mortality, 

increased the length up to 9.3 km (5.8 

mi) in order to maintain 2,500 fish. For 

abundances of 0.2 fish/m (0.06 fish/ft) 

and 0.1 fish/m (0.03 fish/ft), the 

corresponding length increased to 12.5 

km (7.8 mi) and 25 km (15.5 mi), 

respectively (assuming no losses) 

(Hilderbrand and Kershner 2000, p. 15). 

Young et al. (2005, p. 2405) found that 

to maintain a population of 2,500 

cutthroat trout, 8.8 km (5.5 mi) of stream 

were needed. Cowley (2007 DOI: 

10.1002/aqc.845) determined that in 

stream widths of approximately 2 m (6.6 

ft) (average width of most Rio Grande 

cutthroat trout streams), a stream length 

of 11 km (6.8 mi) would be needed to 

support a population of 2,750 fish. 

Because the majority (71 percent) of Rio 

Grande cutthroat trout conservation 

populations occur in short stream 

fragments of 8.1 km (5 mi) or less, these 

studies indicate that stream 

fragmentation (resulting in short stream 

lengths) pose a threat to Rio Grande 

cutthroat trout conservation 

populations. 

Longer streams support larger 

populations (Harig and Fausch 2002, p. 

546; Young et al. 2005, p. 2405). 

Population size is a major determinant 

of species persistence (Reed et al. 2003, 

p. 23). Population persistence decreases 

as population size decreases (Rieman 

and McIntyre 1993, p. 15). Long-term 

persistence of a population depends on 

having a sufficient number of 

individuals to avoid inbreeding 

depression, which decreases population 

viability, and to maintain genetic 

variation (Franklin 1980, pp. 135–148; 

Frankham et al. 2002, pp. 190–192; 

Reed 2005, pp. 563, 564). Genetic 

variability within a population is 

necessary for adaptability (Reed 2005, p. 

564; Cowley 2007 DOI: 10.1002/ 

aqc.845). Genetic variation will be lost 

through time in isolated populations 

and the loss occurs more quickly in 

small populations than in large 

populations (Rieman and Allendorf 

2001, p. 761). When a population is 

greatly reduced in size (bottlenecked), 

genetic diversity is decreased 

(Frankham et al. 2002, p. 183) 

In our previous status review (67 FR 

39938), we concluded that a population 

size of 2,500 fish would ensure longterm persistence of Rio Grande cutthroat 

trout, i.e., would reduce the risks 

associated with small population size 

alone. Since that time other peerreviewed literature has been published 

that allows us to further evaluate this 

number. Reed et al. (2003, p. 30), in a 

review of 102 vertebrate species, 

estimate that sufficient habitat should 

be present to allow for approximately 

7,000 breeding age adults in order to 

ensure long-term species persistence. 

Cowley (2007 DOI: 10.1002/aqc.845) 

found that a population size of 2,500 

Rio Grande cutthroat trout failed to meet 

the desired long-term effective 

population size (number of adults 

actually contributing offspring to the 

population) of at least 500. A minimum 

population size of 2,750 was sufficient 

if there was infrequent loss of year 

classes (all the individuals of a 

population of fishes born or hatched in 

the same year). He found that a larger 

population size was required as survival 

rate of young fish (one year or less) 

decreased. He concluded that managing 

for Rio Grande cutthroat trout 

population sizes in the range of 8,000 to 

16,000 would be more likely to ensure 

population viability when there are low 

to intermediate survival rates of young 

fish. While any population number we 

might use to assess the status of the 

subspecies is unlikely to satisfy all 

interested parties, we believe 2,500 

continues to be a reasonable standard by 

which to evaluate the populations. 

While the range of acceptable standards 

may range from 2,500 to 16,000, there is 

relative certainty that populations below 

2,500 are likely at risk and may not be 

contributing to long-term persistence of 

the subspecies. 

In 2007, fifteen of the 120 

conservation populations had 2,500–

7,000 Rio Grande cutthroat trout. The 

120 conservation populations occur in 

161 individual streams. Several 

conservation populations occupy 

multiple individual stream segments 

that are connected, thus the numbers of 

occupied streams segments is larger 

than the total number of conservation 

populations. Of those 161 individual 

streams, a minimum of 53 contain 

populations of under 500 reproducing 

adult fish. Because population estimates 

are unavailable for 38 streams, and most 

of the 38 are short segments (2007 

database), the total number of 

populations with fewer than 500 

reproducing adult fish is much likely 

greater than 53. Of the 99 conservation 

populations with quantitative estimates, 

19 have an abundance of 0–0.03 fish/m 

(0–50 fish/mi) and 31 have an 

abundance of 0.03–0.09 fish/m (50–150 

fish/mi). These low abundances indicate 

that on average, Rio Grande cutthroat 

trout need longer, rather than shorter, 

stream segments to ensure their longterm persistence because longer streams 

support larger numbers of fish 

(Hilderbrand and Kershner 2000, p. 

515). 

In 2002, we identified 13 Rio Grande 

cutthroat trout populations as secure (67 

FR 39940). All 13 had populations over 

2,500, contained no nonnative trout, 

and were protected from invasion by 

nonnative fish by a barrier. By 2007, 5 

of these populations had fewer than 

1,000 fish and 3 others had fewer than 

2,000. One of the populations 

(approximately 13,000 fish in 2002) is 

thought to have been extirpated by low 

water effects (the stream either dried or 

froze). Brown trout were discovered 

above the barrier on one of the streams. 

The status of only 5 populations 

remained unchanged between 2002 and 

2007. 

A ‘‘general health assessment’’ was 

used by Alves et al. (2007, pp. 41–43) 


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to look at the health of individual 

populations. Sixty-eight populations 

(798 km (496 mi)) were judged to have 

a moderately high degree of health, 50 

(264 km (164 mi)) moderately low, and 

1 (3.2 km (2 mi)) ranked as having low 

health (Alves et al. 2007, p. 42). Four 

factors were considered in the 

assessment: isolation, temporal 

variability (a measure of variability in 

the physical environment which 

correlates with stream length), 

population size, and population 

production (a composite score based on 

habitat condition, presence of 

nonnatives, and disease) (Alves et al. 

2007, pp. 82, 83, 89). These factors were 

weighted in the following order: 

isolation (0.5), stream length (0.7), 

population size (1.2), and population 

production (1.6). The first 3 factors have 

a range of 1 to 4, while the last, 

population production, has a range of 2 

to 8 (Alves et al. 2007, p. 89), effectively 

doubling its importance beyond the 

greater weighting (1.6) assigned to it. 

Rationale for the weighting scheme is 

not provided. Many scoring systems 

could be devised to determine 

population health and it is unclear why 

isolation and stream length, two factors 

that have been discussed extensively in 

conservation biology and cutthroat trout 

conservation literature (e.g., Saunders et 

al. 1991, pp. 18–26; Dunham et al. 1997, 

p. 1130; Hilderbrand and Kershner 

2000, p. 513; Frankham et al. 2002, 

Chapter 13; Young et al. 2005, p. 2405; 

Noss et al. 2006, Chapter 7) were 

assigned the lowest weights. This rating 

system is heavily biased towards 

production and does not provide a 

balanced assessment of population 

health. However, even with this 

unbalanced health assessment, only one 

stream ranked as having high health, 

Comanche Creek. A major restoration of 

Comanche Creek began in 2007, and 

while we fully expect it to be restocked 

with nonintrogressed Rio Grande 

cutthroat trout in the future, it has no 

Rio Grande cutthroat trout currently. 

It has been argued that small, isolated 

populations have persisted for decades 

(Patten and Sloane 2007, p. 3). However, 

Rio Grande cutthroat trout populations 

have only been monitored and 

intensively managed during the last 50 

years or less, and habitat conditions and 

stressors are very different from historic 

conditions. Consequently, long-term 

persistence cannot be appropriately 

assessed. In addition, as Hilderbrand 

and Kershner state (2000, p. 517), 

although some isolated populations may 

have persisted for centuries, these 

populations are probably exceptions. To 

assume all isolated populations will 

behave similarly may lead to 

insufficient protection (Hilderbrand and 

Kershner 2000, p. 517). 

Based on the arguments presented 

above, we determined that stream 

length, population size, and absence of 

nonnative trout are the most important 

criteria by which to evaluate long-term 

population persistence. We have 

evaluated the status of Rio Grande 

cutthroat trout conservation populations 

primarily on stream length (9.6 km (6 

mi) or greater), population size (more 

than 2,500 fish), and presence or 

absence of nonnative fish (Tables 1 and 

2). All streams with a length of over 9.6 

km (6 mi) were initially evaluated. 

Stream miles in Tables 1 and 2 include 

all miles in the conservation population 

when more than one stream is 

connected. Habitat condition and 

presence of a barrier are also presented 

in Tables 1 and 2 because these factors 

are also considered important in 

evaluating the status of the populations. 

Eight streams (4 in Colorado, 3 in New 

Mexico, one shared) currently have over 

2,500 fish, are 9.6 km (6 mi) or longer, 

and have no nonnative fish present 

(Table 1). In addition, the main stem of 

these streams is greater than 1.5 m (5 ft) 

(although tributaries to the main stem 

may be less than this width) and all 

have abundances of 151 fish per mile or 

greater. Five of the streams, Cross, 

Medano, San Francisco, Canones, and El 

Rito creeks, were identified as secure in 

2002. Although these eight streams meet 

the criteria, some have characteristics 

that are less than optimal (Table 1). For 

instance, habitat quality in Cross and 

Canones creeks is judged as ‘‘Fair.’’ In 

Canones Creek, the percentage of pools 

(9 percent) is low and it was found to 

be at risk by Santa Fe National Forest 

temperature standards (Ferrell 2006) 

(discussed in more detail in the 

‘‘Climate Change’’ section below). 

TABLE 1.—RIO GRANDE CONSERVATION POPULATIONS WITH UNALTERED (< 1%) GENETIC STATUS OCCURRING IN

STREAM LENGTHS GREATER THAN 9.6 KM (6 MI), WITH GREATER THAN 2,500 FISH, AND NO NONNATIVE TROUT PRESENT

Population 

size 

Length in km 

(mi) Habitat condition Ownership State Barrier 

San Francisco Creek ... 3,820 23.5 (14.6) Excellent ..................... USFS, Private ............ CO Water diversion. 

Torcido Creek .............. 6,042 16.7 (10.4) Good ........................... Private ........................ CO Drying. 

Medano Creek ............. 5,795 33.6 (20.9) Excellent ..................... NPS, USFS ................ CO None. 

Cross Creek ................. 3,675 12.9 (8.0) Fair ............................. BLM, USFS, Private ... CO None. 

Costilla Creek .............. 5,200 21.1 (13.1) Excellent ..................... Private ........................ NM, CO Temporary/Manmade. 

Alamitos Creek ............ 3,080 11.4 (7.1) Good ........................... USFS .......................... NM Partial/Water diversion. 

El Rito Creek ............... 4,401 10.3 (6.4) Good ........................... USFS .......................... NM Temporary/Manmade.

Canones Creek ............ 3,683 9.7 (6.0) Fair ............................. USFS .......................... NM Waterfall. 

Table 2 shows all the other Rio 

Grande cutthroat trout conservation 

populations in stream lengths greater 

than 9.6 km (6 mi). Six of the 

populations have more than 2,500 Rio 

Grande cutthroat trout, but all of these 

have nonnative brook trout present as 

well. In addition, 4 of these have habitat 

quality judged as fair and one is in a 

stream with a width less than 1.5 m (5 

ft) wide, which puts it at risk for drying 

(as discussed below). Abundance (fish 

per mile) is provided in Table 2 because 

some of these have less than 150 fish 

per mile, and, as mentioned above, for 

populations with 0–50 or 50–150 fish 

per mile, a longer stream length would 

be needed to ensure long-term 

persistence. It should also be noted that 

Sangre de Cristo Creek has tested 

positive for whirling disease. For all of 

these reasons, although the Rio Grande 

cutthroat conservation populations 

presented in Table 2 occur in stream 

lengths greater than 9.6 km (6 mi), all 

appear at risk for one or more reasons. 

Two additional streams (Osier and 

Cascade) have strong populations 3,239 

and 2,372, respectively, with no 

nonnative trout present. However, 

stream length for Osier Creek is only 5.9 

km (3.7 mi) and for Cascade it is 4.7 km 

(2.9 mi). While these populations do 

currently contribute to the status of the 

subspecies range-wide, they are 

considered too short to ensure long-term 


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persistence as their shorter length makes 

them more vulnerable to extirpation 

from ash flow or other localized 

disturbance. 

TABLE 2.—RIO GRANDE CONSERVATION POPULATIONS IN STREAM LENGTHS GREATER THAN 9.6 KM (6 MI), SORTED BY

POPULATION SIZE. NONNATIVE SPECIES MAY BE PRESENT OR ABSENT. BRK = BROOK TROUT, BRN = BROWN

TROUT, WS = WHITE SUCKER

Stream name Population 

size 

Abundance 

(fish per 

mile) 

Length in km 

(mi) 

Nonnatives 

present 

Habitat 

condition 

Width in 

feet State Barrier 

Jacks Creek ................. 4,849 ........ > 400 ........ 18.5 (11.5) BRK .......... Fair ........... < 5 ............ CO Drying. 

Cabresto Creek ........... 4,570 ........ > 400 ........ 13.7 (8.5) BRK .......... Fair ........... 5 to 10 ...... NM Diversion. 

Sangre de Cristo Creek 3,793 ........ 151 to 400 36.2 (22.5) BRK .......... Fair ........... 5 to 10 ...... CO Partial/Diversion. 

South Carnero Creek .. 3,748 ........ 151 to 400 22.9 (14.2) BRK, BRN, 

WS.

Fair ........... 10 to 15 .... CO None. 

West Indian Creek ....... 3,345 ........ 151 to 400 17.1 (10.6) BRK .......... Excellent .. 5 to 10 ...... CO Manmade dam. 

Trinchera Creek ........... 2,941 ........ 151 to 400 14.5 (9.0) BRK .......... Excellent .. 10 to 15 .... CO None. 

Polvadera Creek .......... 2,045 ........ 151 to 400 12.1 (7.5) None ......... Poor ......... < 5 ............ NM Waterfall. 

Jacks Creek ................. 1,504 ........ 151 to 400 11.3 (7.0) None ......... Good ........ 5 to 10 ...... NM Temporary/Manmade. 

Jim Creek .................... 1,283 ........ 151 to 400 10.0 (6.2) BRK .......... Poor ......... 5 to 10 ...... CO None. 

Ute Creek .................... 1,260 ........ 50 to 150 .. 13.8 (8.6) None ......... Good ........ 5 to 10 ...... NM None. 

Rio de Truchas ............ 692 ........... 50 to 150 .. 10.5 (6.5) None ......... Fair ........... 5 to 10 ...... NM Diversion. 

Little Vermejo Creek .... 680 ........... 50 to 150 .. 11.9 (7.4) BRK .......... Excellent .. 5 to 10 ...... NM Temporary/Manmade. 

Vallejos Creek ............. 678 ........... 50 to 150 .. 11.7 (7.3) BRN .......... Good ........ 10 to 15 .... CO None. 

Cave Creek ................. 411 ........... 50 to 150 .. 10.1 (6.3) BRK, BRN, 

WS.

Fair ........... 5 to 10 ...... CO None. 

East Pass Creek ......... 369 ........... 50 to 150 .. 11.1 (6.9) None ......... Fair ........... < 5 ............ CO Drying. 

Middle Carnero Creek 344 ........... < 50 .......... 11.3 (7.0) WS ............ Fair ........... < 5 ............ CO Manmade dam. 

Ricardo Creek ............. 271 ........... 50 to 150 .. 14.5 (9.0) BRK .......... Good ........ 5 to 10 ...... CO Temporary/Manmade. 

Torsido Creek .............. 250 ........... 50 to 150 .. 10.3 (6.4) BRK .......... Poor ......... < 5 ............ CO None. 

Wagon Creek .............. 246 ........... 151 to 500 20.9 (13.0) BRK .......... Good ........ 5 to 10 ...... CO Partial/Diversion. 

McCrystal Creek .......... 236 ........... < 50 .......... 15.1 (9.4) None ......... Good ........ 5 to 10 ...... NM Temporary. 

South Ponil Creek ....... 202 ........... < 50 .......... 15.3 (9.5) None ......... Good ........ 5 to 10 ...... NM Temporary/Manmade. 

Rio de Oso .................. 194 ........... < 50 .......... 12.4 (7.7) None ......... Fair ........... < 5 ............ NM None. 

Capulin Creek .............. 186 ........... < 50 .......... 11.9 (7.4) None ......... Excellent .. 5 to 10 ...... NM Drying. 

North Fork Carnero 

Creek.

97 ............. < 50 .......... 13.0 (8.1) WS ............ Fair ........... < 5 ............ CO Manmade dam. 

Cat Creek .................... Unknown .. Unknown .. 15.1 (9.4) None ......... Fair ........... < 5 ............ CO Drying. 

Habitat fragmentation is a threat that 

can be partially alleviated by 

management activities. Three major 

watershed-scale projects have been 

initiated on both private and USFS 

lands and are in various phases of 

implementation. A joint project between 

Vermejo Park Ranch and the states of 

Colorado and New Mexico to restore the 

Costilla Creek watershed began in 2002 

(Patten et al. 2007, pp 95–102). The 

restoration removed brook trout, brown 

trout, and introgressed cutthroat trout 

and reintroduced Rio Grande cutthroat 

trout into Costilla Creek, 2 tributaries, 

and 3 small lakes, totaling 22 km (13.6 

miles) of stream and 9.5 ha (23.5 ac) of 

lake (project is discussed further in the 

‘‘Fisheries Management’’ section below). 

As part of the larger Costilla Project, 34 

km (21.1 mi) of Comanche Creek and 

selected tributaries were chemically 

treated with piscicides (chemicals that 

kill fish) in 2007. Most likely a second 

treatment will be required and will be 

completed in 2008 before Rio Grande 

cutthroat trout are stocked back into the 

watershed. A draft Candidate 

Conservation Agreement with 

Assurances with private landowners has 

been drafted so that the Costilla Creek 

project can be extended downstream. 

Successful implementation of this 

project would lead to the restoration of 

approximately 241 km (150 mi) and 25 

lakes (Patten and Sloane 2007, p. 7). The 

Placer watershed in Colorado also 

underwent chemical treatment in 2007. 

This watershed has the potential for 

approximately 80.5 km (50 mi) of 

connected stream. If successful, the 

Costilla and Placer watersheds would 

represent substantial gains in the goal of 

creating connected stream systems for 

Rio Grande cutthroat trout. 

While watershed restoration can 

reconnect streams and is the best 

method for addressing fragmentation, 

major restoration projects face many 

challenges including: negative public 

sentiment towards using piscicides in 

streams which slows or stops projects 

(Patten et al. 2007, p. 102), incomplete 

treatment which leaves nonnatives 

present, sabatoge of the treatment area 

(unauthorized introduction of nonnative 

trout) (Japhet et al. 2007, p. 17), 

subsequent barrier failure which allows 

nonnatives to reinvade a system (Japhet 

et al. 2007, p. 15), and inadvertent 

mistakes. While many stream segments 

have been restored and the Costilla and 

Placer watershed projects are in 

progress, no major watershed 

restorations have been completed. 

The Service has evaluated the data 

presented by Alves et al. (2007) and 

supplemental information requested 

related to the database. Based on our 

knowledge of Rio Grande cutthroat trout 

populations that we previously 

classified as secure in 2002, and all of 

the information available to us we 

conclude: 

(1) The majority of Rio Grande 

cutthroat trout populations (93 percent) 

are in isolated fragments less than 8 km 

(5 mi) long (71 percent); 

(2) Populations are concentrated in 

high elevation (2,438 to 3,048 m (8,000 

to 10,000 ft)) headwater streams that 

provide marginal habitat, especially in 

regards to the number and depth of 

pools critical for trout survival in times 

of environmental extremes; 

(3) The drought in the early 2000s had 

resulted in adverse effects on several 

populations (discussed in more detail in 

the ‘‘Climate Change’’ section below); 

(4) Eight of 13 populations we had 

identified as secure in 2002 would no 


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longer meet the criteria we used at that 

time (67 FR 39937); and 

(5) Only eight populations currently 

meet our revised criteria for long-term 

persistence. 

Although additional populations may 

have greater than 2,500 fish or are in 

streams longer than 9.6 km (6 mi), there 

are additional significant threats to 

those populations that put their longterm persistence in question. For these 

reasons, we find that Rio Grande 

cutthroat trout is threatened by 

fragmentation, isolation, and loss of 

habitat throughout its range. While 

watershed restoration may alleviate this 

threat in the future, insufficient progress 

has been made to alleviate the threat of 

fragmentation range-wide at this time. 

Habitat Condition 

Many Rio Grande cutthroat trout 

conservation populations currently 

occupy lands administered by Federal 

agencies. Of the total 1,110 km (690 mi) 

of occupied habitat, 698 km (434 mi) (63 

percent) are under Federal jurisdiction, 

with the majority (59 percent) occurring 

within National Forests (Alves et al. 

2007). Rio Grande cutthroat trout 

occupy 6.1 km (3.8 mi) of land 

administered by the BLM, 30.5 km (19 

mi) managed by the National Park 

Service, and 397 km (247 mi) that are 

owned privately. 

Land uses associated with each 

conservation population were identified 

in Alves et al. (2007, p. 49, Table 33), 

but the impact of the activities was not 

evaluated in relation to individual 

populations or the conservation of the 

subspecies. Non-angling recreation (e.g., 

camping, hiking, ATV use, etc.) occurs 

in 90 percent of the conservation 

populations, and angling occurs in 84 

percent of the conservation populations. 

Livestock grazing occurs within the 

zone of influence (area around the 

stream in which activities influence 

stream habitat) of 87 percent of the 

conservation populations, roads in 58 

percent, timber harvest in 19 percent, 

dewatering in 17 percent, and mining in 

3 percent. Only 3 populations (3 

percent) were judged as having no land 

use activities within a zone that would 

influence the stream habitat. Many 

populations have more than one land 

use occurring in the area. 

An evaluation of habitat quality was 

conducted for currently occupied 

habitat (Alves et al. 2007, p. 20). The 

evaluation considered both natural 

habitat features and human 

disturbances, including land use 

practices. A stream ranked excellent if 

it had ample pool habitat, low sediment 

levels, optimal temperatures, and 

quality riparian habitat. Good habitat 

quality had some attributes that are less 

than ideal, and fair habitat has a greater 

number of attributes that are less than 

ideal. Poor habitat quality is found 

where most habitat attributes reflect 

inferior conditions. Approximately 224 

km (139 mi) (20.2 percent of occupied 

habitat) received an excellent habitat 

rating. Good habitat conditions were 

found in 426 km (265 mi) of habitat 

(38.4 percent of occupied habitat), and 

fair habitat conditions were found in 

335 km (208 mi) of habitat (30.1 percent 

of occupied habitat). Poor conditions 

were found in 35 km (22 mi) (3.2 

percent of occupied habitat), and habitat 

conditions in 90 km (56 mi) (8.1 

percent) were unknown (Alves 2007, p. 

2). The majority of occupied habitat 

(58.6 percent) is considered in good or 

excellent condition (Alves et al. 2007, p. 

20). 

The Service also reviewed 19 detailed 

stream survey reports which were 

conducted by the Santa Fe and Carson 

national forests in the period 2001–

2006. Although these surveys represent 

only about one quarter of the 

conservation populations in New 

Mexico (19 of 84 populations), both 

large (i.e., Pecos River, Rio de las Vacas, 

Comanche Creek) and small (i.e., Yerba, 

Manzanita creeks) streams are 

represented. Therefore, these surveys 

provide additional insight into the 

habitat condition on USFS lands. Of the 

19 streams surveyed, the most 

consistent problem is lack of pool 

habitat. Of the 19 streams, 18 had less 

than the 30 percent pool habitat (range 

1–21 percent) needed to be considered 

properly functioning trout streams. For 

eight of these streams, a target value of 

30 percent pool habitat was not 

considered appropriate because they 

were 1st or 2nd order streams (i.e., 

headwater streams) which often have 

few pools naturally because they occur 

on high gradient slopes. But for four of 

these eight streams, the pool habitat 

ranged from 1–3 percent and the reports 

noted that even for headwater streams 

this was an insufficient number of 

pools. 

In most streams (16 of 19) the average 

residual pool volume, which represents 

initial pool depth if the stream were to 

dry, met the USFS standard of 0.3 m (1 

ft) or greater. However, the deepest 

average residual pool volume was only 

0.67 m (2.2 ft) and the mean depth of 

pools for all 19 streams was 0.39 m (1.3 

ft), indicating that the majority of pools 

are relatively shallow. 

Pools are recognized as important 

overwintering habitat and also are 

holding areas for trout when streams 

dry. Not only are the number of pools 

consistently fewer than desirable, but 

they are also relatively shallow, and 

thus provide limited refugial habitat in 

times of stream freezing or drying. Lack 

of deep pools could affect year-class 

survival. As noted by Cowley (2007 

DOI: 10.1002/acq.845) loss of a year 

class of fish would suggest that longer 

stream length is needed to provide 

adequate habitat for long-term 

population persistence. However, as 

mentioned above, the sample size (19 

streams) is relatively small and it is not 

known if the results accurately 

represent Rio Grande cutthroat trout 

streams range-wide. 

Livestock grazing occurs in the 

vicinity of 87 percent of the Rio Grande 

cutthroat trout populations (Alves 2007, 

p. 49). We recognize that improper 

grazing does cause adverse impacts (e.g., 

loss of cover, increased sedimentation, 

loss of riparian vegetation) to some 

individual populations of Rio Grande 

cutthroat trout, especially during 

drought conditions when the cattle tend 

to concentrate in riparian areas. While 

a few of the USFS stream surveys noted 

that impacts by cattle (or elk) were 

causing localized problems, grazing was 

not cited as causing damage throughout 

the length of any stream. Specific 

information on grazing impacts to Rio 

Grande cutthroat trout habitat on a 

range-wide basis is not available. We 

have no information that leads us to 

conclude that improper grazing is a 

significant threat to Rio Grande 

cutthroat trout range-wide. 

Timber harvest and associated road 

building has also led to the deterioration 

of Rio Grande cutthroat trout habitat. 

However, timber harvest in the National 

Forests has declined appreciably in the 

last 20 years. As an example, on the two 

forests in New Mexico that have 

conservation populations, the Santa Fe 

National Forest and Carson National 

Forest, there has been a total of 3.2 ha 

(8 ac) clear cut since 1995 (Fink 2008 

pp. 2, 3). The average amount of timber 

cut per year from 1984 to 1994 in these 

forests was 27.6 and 19 million board 

feet (MBF), respectively. From 1995 to 

2005, the average amount cut per year 

was 3.5 and 0.09 MBF, respectively 

(Fink 2008, pp. 2, 3). While the effects 

of past logging practices may still be 

evident on the landscape in some 

locations, we conclude that timber 

harvest is not currently a threat to Rio 

Grande cutthroat trout populations. 

Roads and off-road vehicles can have 

negative impacts on stream habitat 

primarily through increased 

sedimentation which degrades 

spawning habitat. Non-angling 

recreation (which includes hiking and 

camping as well as off-road vehicle use) 

is present near 90 percent of the 


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conservation populations. On November 

9, 2005, the USFS published revised 

rules regarding travel management on 

their lands (70 FR 68264). One of the 

primary purposes of the rule is to 

protect natural resources. The final rule 

requires the designation of roads, trails, 

and areas that are open to motor vehicle 

use by class of vehicle and, if 

appropriate, time of year. Use of motor 

vehicles off designated routes will be 

prohibited (70 FR 68264). The Service 

has begun consultation on the Travel 

Management Plans proposed by 

National Forests in USFS Region 3 

(Arizona and New Mexico) and 

protecting aquatic resources is an 

important component of these plans. 

While roads have been identified as an 

area of concern for some streams (e.g., 

Tio Grande, Rio Grande del Rancho, 

Martinez 2001, 2002), we conclude that 

roads are not a threat to Rio Grande 

cutthroat trout populations range-wide. 

Management agencies are actively 

working towards improving habitat 

conditions for Rio Grande cutthroat 

trout. In addition to the travel 

management rule on USFS lands, 

several projects have been completed 

recently to address habitat degradation 

caused by roads. For example, grant 

money was obtained and used to 

inventory and identify 97 road 

improvement projects to reduce 

sediment input into Comanche Creek 

(Martinez 2006, p. 5). Six culverts were 

installed or realigned and ten sediment 

traps and energy dissipaters were 

installed below culvert spillways. 

Culverts that drained directly into 

Comanche Creek were removed. 

Abandoned logging roads were 

stabilized and unneeded roads were recontoured to natural slope and revegetated (USFS 2006, pp.18–19). In 

2006, on the Santa Fe National Forest, 

over 1,829 m (6,000 ft) of buck and pole 

fence was constructed to improve traffic 

control and enforce an off-road vehicle 

closure around Rio Cebolla. 

Approximately 17.7 km (11 mi) of 

stream and riparian habitat was 

protected by this project (USFS 2006, 

p. 12). On the Rio Grande National 

Forest, road-stream crossing inventories 

and assessments were conducted for all 

streams with conservation populations 

to determine if the culverts were 

barriers to fish (USFS 2006, p. 4). Most 

of the 120 conservation populations (90 

percent) have one or more restoration, 

conservation, or management activities 

either completed or currently being 

implemented (Alves et al. 2007, p. 60). 

Range-wide habitat quality is still 

difficult to accurately assess. Although 

an insufficient amount of pool habitat 

exists on the majority of streams 

sampled by the USFS in New Mexico, 

we cannot draw the same conclusion 

range-wide at this time because of lack 

of data. Alves et al. (2007 database) did 

not identify a lack of pools as a 

systematic problem. While land 

management practices have clearly 

improved and have less direct impact 

on Rio Grande cutthroat trout streams, 

some streams are still recovering from 

past land management practices. 

Therefore we conclude that there is 

insufficient information to indicate that 

habitat quality currently is a significant 

threat to Rio Grande cutthroat trout 

rangewide. 

Nonnative Species 

The introduction of nonnative trout is 

widely recognized as one of the leading 

causes of range reduction in cutthroat 

trout subspecies (Griffith 1988, pp. 134, 

137; Lassuy 1995, p. 394; Henderson et 

al. 2000, pp. 584, 585; Dunham et al. 

2002, p. 374; Peterson et al. 2004, 

p. 769). Dunham et al. (2004) provide an 

overview of the impact of nonnatives on 

headwater systems in North America. 

Since the late 1800s, fishery managers 

introduced nonnative salmonids (trout 

and salmon species) into lake and 

stream habitats of Rio Grande cutthroat 

trout. Nonnative rainbow, brook, brown 

trout and Yellowstone cutthroat trout 

have been introduced extensively 

throughout the range of Rio Grande 

cutthroat trout, and they compete (brook 

and brown trout) and hybridize 

(rainbow and other cutthroat 

subspecies) with Rio Grande cutthroat 

trout. Forty-six of 120 conservation 

populations (38 percent) have nonnative 

trout present (2007 database). When Rio 

Grande cutthroat trout occur in the same 

stream as nonnative trout, Rio Grande 

cutthroat trout typically occupy the 

colder, headwater reaches and the 

nonnative trout occupy areas 

downstream (Griffith 1988, p. 135; 

Dunham et al. 1999, p. 885). 

Competition from nonnative trout, 

especially brook trout, is recognized as 

a threat to Rio Grande cutthroat trout 

(Behnke 2002, p. 147; Peterson et al. 

2004, pp. 768, 769). When brook trout 

invade streams occupied by cutthroat 

trout, the native cutthroat trout decline 

or are displaced (Griffith 1988, p. 136; 

Harig et al. 2000, pp. 994, 998, 999; 

Dunham et al. 2002, p. 378; Peterson et 

al. 2004, p. 769; Young and GuentherGloss 2004, p. 193; Fausch et al. 2006, 

p. 6). Brook trout are the most common 

nonnative trout sympatric (co-occurring) 

with Rio Grande cutthroat trout 

populations in Colorado (2007 

database). Brook trout reduce 

recruitment of cutthroat trout and 

reduce inter-annual survival of 

juveniles, leading to a reduction in 

population size (Peterson et al. 2004, p. 

769). Experiments where brook trout 

were removed from cutthroat trout 

populations showed an increase in the 

survival of juvenile cutthroat trout 

(Peterson et al. 2004, p. 767). Paroz 

(2005, p. 22) found that mean density 

and relative weight of Rio Grande 

cutthroat trout were lower in 

populations sympatric with brook trout. 

Several Rio Grande cutthroat trout 

conservation populations have been 

identified as at risk and declining 

because of brook trout (Alves et al. 2002, 

pp. 1–4). 

In New Mexico, brown trout is the 

most common nonnative trout present 

in Rio Grande cutthroat trout 

conservation populations (summarized 

from 2007 database). Not only are brown 

trout piscivores (feed on other fish), but 

they have also been shown to compete 

with Rio Grande cutthroat trout for 

resources such as food and space. 

Research has shown that Rio Grande 

cutthroat trout confined with brown 

trout grew significantly less, while the 

brown trout grew significantly more, 

than control fish (Shemai et al. 2007, 

pp. 315, 320, 321). A similar result was 

seen in experiments conducted with 

Bonneville cutthroat trout and brown 

trout (McHugh and Budy 2005, p. 2788). 

These results indicate that brown trout 

represent a threat to Rio Grande 

cutthroat trout from competition as well 

as predation (Paroz 2005, p. 34). 

The primary threat to Rio Grande 

cutthroat trout from rainbow trout and 

other cutthroat trout subspecies is 

through hybridization and introgression 

(Rhymer and Simberloff 1996, pp. 83, 

97). The genetic distinctiveness of Rio 

Grande cutthroat trout can be lost 

through hybridization (Allendorf et al. 

2004, p. 1205). Of the 120 conservation 

populations, 95 (79 percent) range-wide 

have been tested and are less than 1 

percent introgressed (Alves et al. 2007, 

p. 31). These nonintrogressed 

populations occupy 870 km (541 mi), or 

78 percent, of the 1110 km (690 mi) 

occupied by conservation populations 

(Alves et al. 2007, p. 31). Another 161 

km (100 mi) are occupied by 

populations that are 90–99 percent 

genetically pure, and 104 km (65 mi) are 

occupied by populations that have not 

been tested but are connected to 

nonintrogressed populations and have 

no record of stocking (Alves et al. 2007, 

p. 34). 

To minimize the contact of nonnative 

trout with Rio Grande cutthroat trout, 

barriers have been constructed where 

natural barriers didn’t already exist in 

order to prevent nonnatives from 

invading. Alves et al. (2007, pp. 35, 36) 


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rated the genetic risk to the 120 

conservation populations. A 

combination of barrier condition or 

presence and distance to hybridizing 

species, determined if a population was 

at moderate or low risk (Alves et al. 

2007, p. 80). Populations protected by a 

complete barrier fell into the no risk 

category. They determined that 80 had 

no risk of genetic mixing with nonnative 

trout, 32 were at moderate risk, and 4 

were at low risk. As mentioned earlier, 

four populations that Alves et al. (2007, 

pp. 35, 36) consider conservation 

populations are sympatric with a 

hybridizing species, and, therefore, we 

consider them at high risk. 

Since 2002, NMDGF and CDOW 

visited approximately 40 and 50 Rio 

Grande cutthroat trout conservation 

populations, respectively, to assess 

barrier presence and condition. Seven 

new barriers have been installed since 

2002, and maintenance was done on at 

least eight (Japhet et al. 2007, pp. 24, 25; 

Patten et al. 2007, pp. 6, 11, 12, 16, 17, 

53). Both agencies have also 

mechanically and chemically removed 

nonnative trout from Rio Grande 

cutthroat trout streams. NMDGF 

removed nonnatives from 11 streams, 

and CDOW removed them from two 

(Patten and Sloane 2007, p. 5; Japhet et 

al. 2007, p. 26). 

Since 2002, CDOW and NMDGF have 

also proactively pursued genetic testing 

of Rio Grande cutthroat trout 

populations using the best technologies 

available. In many instances, the results 

confirmed previous assessments of 

genetic purity, while in other cases 

populations were either upgraded or 

downgraded (Japhet et al. 2007, pp. 46–

47; Patten et al. 2007, pp. 43–45). 

Diagnostic markers for Yellowstone 

cutthroat trout were also identified, 

which has led to more refined testing 

and more confidence in the 

categorization of the populations. The 

most recent results were used in the 

2007 database. Results of the testing can 

be found in peer-reviewed literature 

(e.g., Pritchard et al. 2007a, Pritchard et 

al. 2007b) and in reports to the States 

(e.g., Pritchard and Cowley 2005). 

Approximately 38 percent of Rio 

Grande cutthroat trout conservation 

populations co-occur with nonnative 

trout (2007 database). Competition, 

predation, and hybridization with 

nonnative trout are considered an 

important source of stress that can 

depress Rio Grande cutthroat trout 

population numbers or, under the right 

circumstances, displace them (Fausch et 

al. 2006, pp. 9, 10). Although resource 

agencies remove nonnative trout 

through electrofishing when they cooccur with cutthroat trout subspecies, 

seldom if ever is complete removal 

possible (Patten et al. 2007, p. 104). 

Peterson et al. (2004, p. 769) show that 

over 90 percent of the brook trout 

population must be removed each year 

for 3 consecutive years to allow a large 

cohort of Colorado River cutthroat trout 

to survive from age 0 to age 2. This level 

of effort has not been documented for 

stream segments occupied by Rio 

Grande cutthroat trout populations (e.g., 

Japhet et al. 2007, p. 26). 

The Service concludes that nonnative 

fish are a threat to Rio Grande cutthroat 

trout range-wide based on the following 

facts: 

(1) Approximately 38 percent of the 

conservation populations have 

nonnative trout present; 

(2) Nonnative fish are a documented 

threat to Rio Grande cutthroat trout 

populations; 

(3) Mechanical removal cannot 

remove all of the nonnative fish; 

(4) The level of effort required to 

reduce brook trout populations to levels 

sufficient for survival of young Rio 

Grande cutthroat trout is not currently 

being conducted; and, 

(5) The number of streams that need 

regular treatment exceeds the capability 

of resource managers at their current 

staffing levels. 

Drought 

The relatively short-term drought of 

the early 2000s negatively impacted or 

extirpated 14 Rio Grande cutthroat trout 

populations in Colorado and New 

Mexico (Japhet et al. 2007, pp. 42–44; 

Patten et al. 2007, pp. 14–40). A 

fifteenth population is thought to have 

been extirpated in 2006 by complete 

freezing caused by low flow in the 

winter (Ferrell 2006, p. 11). The number 

of streams impacted may have been 

greater, because managers only survey a 

fraction of the 120 conservation 

populations in any given year. 

We assume that small streams (1.5 m 

(5 ft) wide or less) are more susceptible 

to drying, increased water temperatures, 

and freezing than larger ones and that 

stream width is an indicator of risk. 

Decreased stream flow reduces the 

amount of habitat available for aquatic 

species, and water quality (e.g., 

temperature, dissolved oxygen) may 

become unacceptable in declining flow. 

Approximately 27 conservation 

populations are in streams that are 1.5 

m (5 ft) or less in width throughout their 

entire length (2007 database). An 

additional 29 stream segments that are 

tributaries to the conservation 

populations are also less than 1.5 m (5 

feet) in width (2007 database). Although 

not all small streams have equal risk, 

small headwater streams, especially 

those with an inadequate number of 

deep pools, are most likely to lose 

suitable habitat. Even if streams do not 

dry (or freeze) completely, stream length 

can be truncated during drought and 

many fish can perish, greatly reducing 

the population number (bottleneck) and 

reducing genetic diversity (Frankham et 

al. 2002, p. 183). 

Because of the documented 

extirpation and population reductions 

of Rio Grande cutthroat trout caused by 

drought, the possibility of more 

widespread drought accompanying 

climate change, and the lack of a rangewide plan to address drought, we 

conclude that drought is a threat to Rio 

Grande cutthroat trout throughout its 

range (discussed in ‘‘Climate Change’’

section below). 

Fire 

Wildfires are a natural disturbance in 

forested watersheds. However, since the 

mid-1980s, wildfire frequency in 

western forests has nearly quadrupled 

compared to the average frequency 

during the period 1970–1986. The total 

area burned is more than six and a half 

times the previous level (Westerling et 

al. 2006, p. 941). In addition, the 

average length of the fire season during 

1987–2003 was 78 days longer 

compared to that during 1970–1986 and 

the average time between fire discovery 

and control was 29.6 days longer 

(Westerling et al. 2006, p. 941). 

Westerling et al. (2006, p. 942) found 

that wildfire sensitivity was related to 

snowmelt timing with 56 percent of 

fires and 72 percent of burned area 

occurring in early snowmelt years. Early 

spring snowmelt is strongly associated 

with spring temperature (Stewart et al. 

2004, p. 218; Westerling et al. 2006, p. 

942). Westerling et al. (2006, p. 942) 

conclude that there are robust statistical 

associations between wildfire and 

climate in western forests and that 

increased fire activity over recent 

decades reflects responses to climate 

change (discussed further in the 

‘‘Climate Change’’ section below). 

In the Southwest, the fire season is 

followed by the monsoon season (July to 

August). Consequently, denuded 

watersheds are susceptible to heavy 

precipitation leading to severe floods 

and ash flows. Although fish may 

survive the fire, ash and debris flows 

that occur after a fire can eliminate 

populations of fish from a stream (Rinne 

1996, p. 654; Brown et al. 2001, p. 142; 

USFS 2006, p. 32; Patten et al. 2007, p. 

33), and the fire suppression activities 

(e.g., fire retardant, water removal, road 

construction) may also impact stream 

ecosystems (Buhl and Hamilton 2000, 

pp. 410–416; Backer et al. 2004, pp. 942, 


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943). Wildfires within the range of Rio 

Grande cutthroat trout have impacted or 

eliminated fish populations (Japhet et 

al. 2007, p. 20; Ferrell 2006, p. 32; 

Patten et al. 2007, pp. 33, 36), and the 

effects of large fires are recognized as a 

threat to greenback cutthroat 

(Oncorhynchus clarki stomias) 

populations in Colorado (Young and 

Guenther-Gloss 2004, p. 194). Imperiled 

fish populations can be rescued if ash 

flows are imminent, but a rescue and 

evacuation plan should be in place (e.g., 

Brooks 2004, pp. 1–15). 

Dunham et al. (2007, p. 342) found 

significantly elevated stream 

temperatures for at least a decade after 

a stand-replacing wildfire because of the 

lack of stream shading. In addition, the 

authors suggest that longer term (over 20 

years) increases in stream temperatures 

are likely in systems where debris flows 

or severe floods completely eliminate 

streamside vegetation and reorganize 

the channel. Rainbow trout were found 

to be resilient and recolonized the 

burned streams within 1 year of 

extirpation in spite of elevated water 

temperatures (Dunham et al. 2007, p. 

343). Dunham et al. (2003a, pp. 188, 

189) suggest that fire poses a greater 

threat to fish populations when habitat 

is fragmented. Moyle and Light (1996, p. 

157) argue that habitat degradation 

favors nonnative fishes and that species 

with narrow habitat requirements are 

expected to be more sensitive to habitat 

alteration caused by fire than generalist 

species such as rainbow trout (Dunham 

et al. 2003a, p. 189). 

Fire risk can be reduced through fuels 

reduction and prescribed burns. The 

National Forests in New Mexico have 

active programs to improve forest 

health. As an example, 28,314 ha 

(69,965 ac) have undergone fuelreduction treatment, thereby improving 

watershed conditions associated with 

100 km (62 miles) of stream, and an 

additional 58,912 ha (145,575 ac) are 

planned for treatment to improve 

conditions associated with an additional 

128 km (79.5 mi) of stream (Ferrel 2002, 

p. 12). Such techniques have been found 

to reduce fire severity even under 

extreme weather conditions in lowelevation ponderosa pine forests 

(Schoennagel et al. 2004, p. 669). 

However, for mid-elevation, mixedseverity fire regimes, fuel-reduction 

treatments had virtually no effect on the 

2002 Hayman Fire (Colorado), and 

extreme climate can override the 

influence of stand structure and fuels on 

fire behavior (Schoennagel et al. 2004, 

pp. 672, 673). Climate variation, not fuel 

levels, is seen as the dominant influence 

on fire frequency and severity in 

subalpine forests (Schoennagel et al. 

2004, p. 666). 

Wildfires that eliminate nonnative 

fish provide the opportunity to reclaim 

streams for Rio Grande cutthroat trout. 

The 1996 Dome Fire in the Jemez 

Mountains (Santa Fe National Forest) 

extirpated the fish residing in Capulin 

Canyon. In 2006, after 10 years of 

habitat recovery, 100 Rio Grande 

cutthroat trout from Canones Creek were 

stocked into Rio Capulin adding 11.2 

km (7.0 mi) of occupied habitat in New 

Mexico (Patten et al. 2007, p. 94). In 

addition, ash flows after the 2004 

Peppin Fire in the Capitan Wilderness 

(Lincoln National Forest) apparently 

eliminated all fish from Pine Lodge 

Creek and Copeland Creek (Patten et al. 

2007, pp. 255–258), and there are plans 

to restore Rio Grande cutthroat trout 

into these streams. Restoration of Pine 

Lodge Creek would add approximately 

4 km (2.5 mi) of habitat in the Pecos 

Headwaters GMU (Patten et al. 2007, p. 

255). 

Although we recognize that Rio 

Grande cutthroat trout evolved in a 

landscape that included fire, wildfire 

intensities and size are likely changing 

because of increased fuel loads and 

possibly climate change (see ‘‘Climate 

Change’’ section below). Wildfire today 

is much more of a threat than it was 

historically to Rio Grande cutthroat 

trout because of existing habitat loss, 

fragmentation, and climate change. 

These multiple stressors may 

overwhelm the subspecies’ resilience to 

disturbance such as fire (Rieman et al. 

2005, pp. 2, 3). Although fire may also 

provide opportunity for repatriation of 

Rio Grande cutthroat trout by 

eliminating nonnative fish, total 

elimination of nonnative fish from fireaffected streams is not guaranteed, and 

it may take many years for the habitat 

to become suitable. For these reasons, 

we conclude that wildfire is a 

significant threat to Rio Grande 

cutthroat trout throughout its range. 

Summary of Factor A 

In summary, Rio Grande cutthroat 

trout populations have been and 

continue to be impacted by habitat 

fragmentation and isolation, nonnative 

species interactions, drought, and fire. 

Rio Grande cutthroat trout conservation 

populations occupy a fraction of their 

historical habitat, they are confined 

primarily to small high-elevation 

streams with marginal habitat, they are 

highly fragmented, and the stream 

segments they occupy are short in 

length. All of these factors work to 

reduce gene flow between populations 

and reduce the ability of populations to 

recover from catastrophic events thus 

threatening their long-term persistence. 

Detailed habitat surveys, although not 

available range-wide, are uniformly 

consistent in documenting a lack of 

pools in streams occupied by Rio 

Grande cutthroat trout. Deep pools are 

considered a critically important 

element of Rio Grande cutthroat trout 

habitat. As discussed above, in order to 

ensure some level of population 

stability and contribute to the long-term 

persistence of the subspecies, 

populations should consist of more than 

2,500 fish, occupy 9.6 km (6 mi) of 

stream or more, and have no nonnative 

trout present. Currently, only eight Rio 

Grande cutthroat trout populations meet 

these criteria. Nonnative trout co-occur 

with 38 percent of Rio Grande cutthroat 

trout conservation populations. Because 

of the documented negative impacts of 

nonnative trout on cutthroat trout 

discussed above, nonnatives are an 

ongoing threat to the security of Rio 

Grande cutthroat trout. Additionally, 

although drought and fire have 

impacted a limited number of 

populations since the last status review, 

negative impacts from these two factors 

may increase in response to climate 

change (as discussed in the ‘‘Climate 

Change’’ section below). Based on the 

best scientific and commercial 

information available to us, we 

conclude that the present or threatened 

destruction, modification, or 

curtailment of its habitat or range is a 

threat to the continued existence of Rio 

Grande cutthroat trout. 

B. Overutilization for Commercial, 

Recreational, Scientific, or Educational 

Purposes 

No commercial harvest occurs for Rio 

Grande cutthroat trout. Recreational 

angling occurs on approximately 84 

percent of the populations (Alves et al. 

2007, p. 49). Fishing regulations in New 

Mexico and Colorado appropriately 

manage recreational angling. For 

example, many of the streams with Rio 

Grande cutthroat trout are ‘‘catch and 

release.’’ Those that are not have a 2 

(New Mexico) or 4 (Colorado) fish limit. 

Many of the streams with pure 

populations of Rio Grande cutthroat 

trout are remote and angling pressure is 

light. For these reasons, angling is not 

considered a threat to Rio Grande 

cutthroat trout. 

Scientific collection of Rio Grande 

cutthroat trout for scientific or 

educational purposes is controlled by a 

strict permitting process that prevents 

excessive sampling. In addition, 

advancements in molecular technology 

have resulted in the need for only a 

small clipping from a fin to provide 

sufficient material to perform molecular 


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analysis of genetic purity. To test for 

whirling disease (see ‘‘Disease’’ section 

below for further discussion), usually 60 

fish are collected and sacrificed. 

However, to minimize the collection of 

Rio Grande cutthroat trout during 

whirling disease testing, nonnative trout 

are collected preferentially over Rio 

Grande cutthroat trout, or sample sites 

are selected below a barrier that protects 

a population of Rio Grande cutthroat 

trout from nonnative trout. In some 

situations fewer than 60 Rio Grande 

cutthroat trout will be collected and 

sacrificed for testing. For these reasons, 

overutilization for scientific purposes is 

not considered a threat to Rio Grande 

cutthroat trout. 

Summary of Factor B 

Because no commercial harvest 

occurs for Rio Grande cutthroat trout, 

fishing regulations in New Mexico and 

Colorado minimize the impact of 

recreational angling, and scientific 

collection of Rio Grande cutthroat trout 

for scientific or educational purposes is 

controlled by a strict permitting process 

that prevents excessive sampling, we 

conclude that the best scientific and 

commercial information available to us 

indicates that Rio Grande cutthroat trout 

is not threatened by overutilization for 

commercial, recreational, scientific, or 

educational purposes. 

C. Disease or Predation 

Disease 

Whirling disease is of great concern to 

fishery managers in western States. 

Whirling disease is caused by the 

nonnative myxosporean parasite, 

Myxobolus cerebralis. This parasite was 

introduced to the United States from 

Europe in the 1950s and requires two 

separate hosts, a salmonid fish and an 

aquatic worm (Tubifex tubifex) to 

complete its life cycle. Spores of the 

parasite are released from infected fish 

when they die. The spores are ingested 

by T. tubifix where they undergo 

transformation in the gut to produce 

actinosporean triactionomyxons 

(TAMs). Trout are infected either by 

eating the worms (and TAMs) or 

through contact with water in which 

TAMs are present. 

The myxosporean parasite became 

widely distributed in Colorado in the 

early 1990s through the stocking of 

millions of catchable size trout from 

infected hatcheries (Nehring 2007, p. 1). 

Up to 2001, it was estimated that 

whirling disease infection had 

negatively impacted recruitment of wild 

rainbow and brook trout fry (small 

recently emerged fish) in 560–600 km 

(350–400 mi) of stream in Colorado 

(Nehring 2007, p. 2). In 2006, the 

number of sites that tested positive for 

whirling disease was considerably 

higher than in any of the previous field 

seasons (Nehring 2007, p. 11). Whirling 

disease is also present in several streams 

in New Mexico (67 FR 39943, Patten 

and Sloane 2007, p. 11). Laboratory 

(DuBey et al. 2007, pp. 1411, 1412) and 

field (Thompson 1999, pp. 323–325) 

experiments have shown that Rio 

Grande cutthroat trout is very 

susceptible to whirling disease. 

Among the four lineages (I, III, V, and 

VI) of T. tubifix known to occur in 

Colorado, New Mexico, and other states, 

lineage III is the only one susceptible to 

infection by M. cerebralis (DuBey and 

Caldwell 2004, p. 183; Nehring 2007, p. 

11). Because T. tubifix is typically found 

in degraded habitat with higher levels of 

sediment and warmer temperatures, it 

had been hypothesized that Rio Grande 

cutthroat trout were provided some 

level of protection because they occur in 

high-elevation cold-water streams (67 

FR 39943). Extensive sampling of 

tubificid worms in Colorado does not 

support this hypothesis. Nehring (2007) 

collected tubificid worm samples from 

over 100 sites in Colorado, including 

streams occupied by Rio Grande 

cutthroat trout. He stratified his results 

by 305 m (1,000 ft) elevation groups 

from 1829 m (6,000 ft) to 3657 m 

(12,000 ft) (e.g. 1829–2134 m (6,000–

7000 ft), 2134–2438 m (7001–8,000 ft), 

etc.). Lineage III worms had the greatest 

abundance, outnumbering all of the 

other lineages combined, at all 

elevations. The number of sites with 

lineage III worms was approximately the 

same at all elevations from the 1829–

2134 m (6,000–7,000 ft) band up to the 

3048–3353 m (10,000–11,000 ft) band 

(Nehring 2007, p. 10) indicating that the 

high-elevation cold-water streams do 

not provide protection from lineage III 

worms. 

One hundred and five conservation 

populations (88 percent) are judged to 

have very limited risk from whirling 

disease or other potential diseases 

because the pathogens are not known to 

exist in the watershed or a barrier blocks 

upstream fish movement (Alves et al. 

2007, p. 38). Six populations are at 

minimal risk because they are greater 

than 10 km (6.2 mi) from the pathogen 

or they are protected by a barrier, but 

the barrier may be at risk of failure 

(Alves et al. 2007, p. 38). Eight 

populations were identified as being at 

moderate risk because whirling disease 

had been identified within 10 km of 

occupied habitat (Alves et al. 2007, p. 

38). In 2006, it was discovered that 

whirling disease had infected brook 

trout and Rio Grande cutthroat trout in 

Placer Creek, Colorado, a conservation 

population, and in 2007 it was 

chemically treated to remove infected 

fish and nonnative brook trout. 

In 2002, the Pecos, Cebolla, San Juan, 

Cimarron, Red, and Canones rivers in 

New Mexico were listed as being 

infected with whirling disease (67 FR 

39943). By 2007, more than 80 streams 

and lakes had been tested for the disease 

(Patten and Sloane 2007, pp. 10–13). 

North Bonito Creek, Brazos River, and 

Los Pinos River were added to the list 

of streams testing positive for whirling 

disease. Canones and Jacks creeks, 

which had tested positive in 2000, 

tested negative in 2005, and 2003, 

respectively (Patten and Sloane 2007, 

pp. 10–13). Of the streams listed, Rio 

Cebolla, Pecos River and Cimarron River 

are occupied by Rio Grande cutthroat 

trout upstream above barriers. 

NMDGF policies and regulations 

prohibit the stocking of any whirling 

disease positive fish in the State of New 

Mexico (Patten and Sloane 2007, p. 10). 

All private facilities must maintain a 

pathogen-free certification. The Seven 

Springs Hatchery, which is used for Rio 

Grande cutthroat trout broodstock, has 

tested negative on all occasions since it 

was refurbished (Patten and Sloane 

2007, p. 10). In Colorado stocking of 

whirling disease positive fish in 

protected habitats, which include native 

cutthroat trout waters, is prohibited 

(Japhet et al. 2007, p. 12). Colorado and 

New Mexico have web sites, brochures, 

and information in their fishing 

regulations regarding whirling disease 

and what anglers can do to prevent its 

spread. In addition, both States have 

regulations regarding the stocking of 

fish by private landowners that are 

designed to eliminate the importation of 

whirling disease positive fish. It states 

clearly in the fishing regulations that it 

is illegal to stock fish in public waters 

without prior permission from a State 

agency. 

Whirling disease remains a concern 

for Rio Grande cutthroat trout 

populations. One Rio Grande cutthroat 

trout conservation population was 

infected in Colorado, and restoration 

efforts were immediately implemented 

to address the issue. Although 

widespread increases in M. cerebralis 

have not been seen, additional infected 

sites have been documented. Because of 

the limited level of infection currently, 

whirling disease is not seen as a 

significant threat to populations rangewide. However, climate change and 

warmer stream temperature may 

facilitate the spread of whirling disease 

in the future (discussed in the ‘‘Disease’’

section in Factor E below). 


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Predation 

Brown trout are piscivores and are the 

most likely predator on Rio Grande 

cutthroat trout. Additionally, brown 

trout have been found to have a 

significant negative impact on the 

condition of coexisting Rio Grande 

cutthroat trout through harassment (e.g., 

chasing) (Shemai 2004, pp. 315–323; 

McHugh and Budy 2005, p. 2788). It is 

probable that larger brown trout prey on 

young Rio Grande cutthroat trout and, 

unchecked, brown trout can depress 

population levels. Warmer water 

temperatures in the future may give 

brown trout a greater competitive 

advantage over Rio Grande cutthroat 

trout (discussed in the ‘‘Climate 

Change’’ section below). However, we 

have insufficient information at this 

time to conclude that predation by 

brown trout is currently a significant 

threat to Rio Grande cutthroat trout. 

Summary of Factor C 

One population of Rio Grande 

cutthroat trout has been infected with 

whirling disease since our 2002 status 

review and eight conservation 

populations are considered to be at 

moderate risk of infection. Although 

whirling disease is currently limited in 

distribution and effect, it has the 

potential to become a more widespread 

problem due to warmer waters that 

could result from climate change 

(discussed in the ‘‘Climate Change’’

section below). We have insufficient 

information to conclude that predation 

is a significant threat at this time. 

Therefore, we conclude that the best 

scientific and commercial information 

available to us indicates that, although 

the status of Rio Grande cutthroat trout 

has not yet been affected by disease, Rio 

Grande cutthroat trout is likely to be 

threatened by disease in the foreseeable 

future. 

D. The Inadequacy of Existing 

Regulatory Mechanisms 

The NMDGF and the CDOW have 

authority and responsibility for the 

management of Rio Grande cutthroat 

trout. Rio Grande cutthroat trout is 

designated as a species of special 

concern by the State of Colorado and of 

special management concern by the 

State of New Mexcio. The agencies’

capabilities include the regulation of 

fishing, law enforcement, research, and 

conservation and educational activities 

relating to Rio Grande cutthroat trout. 

Policies regarding the stocking of 

nonnative fish (no nonnatives are 

stocked in Rio Grande cutthroat trout 

populations), minimization of exposure 

to whirling disease and other diseases, 

and broodstock management are in 

place in both States. In 2004, the 

‘‘Conservation Plan for Rio Grande 

Cutthroat trout in Colorado’’ was 

approved by the Director of CDOW. The 

goal of the plan is to assure the longterm persistence of Rio Grande cutthroat 

trout throughout its historic range by 

preserving genetic integrity, reducing 

population fragmentation, and 

providing suitable habitat to support 

self-sustaining populations (Japhet et al. 

2007, p. ii). New Mexico (2002) has an 

approved management plan currently 

being implemented that will ‘‘facilitate 

long range cooperative, interagency 

conservation of Rio Grande cutthroat 

trout.’’

Rio Grande cutthroat trout 

populations have been lost because of 

stream drying (Japhet et al. 2007 pp. 42–

44), and other trout populations in the 

Southwest have been extirpated as the 

result of ash flows following fire (Brown 

et al. 2001 p. 142). Imperiled fish 

populations can be rescued from 

streams (Brooks 2004, pp. 1–15; Japhet 

et al. 2007, p. 20). In the face of 

widespread drought or fire (discussed in 

the ‘‘Climate Change’’ section below) it 

is expected that many streams would be 

affected at one time, as seen in the 2002 

drought (Japhet et al. 2007, pp. 42–44; 

Patten et al. 2007, pp. 14–40). An 

emergency rescue and evacuation plan 

is not in place for Rio Grande cutthroat 

trout, nor do we anticipate that this 

strategy would be effective in 

eliminating the threat of stream drying 

or post-fire ash flows in the face of 

widespread drought. 

In 2003, a range-wide conservation 

agreement was signed by CDOW, 

NMDGF, USFS, the Service, BLM, NPS, 

and Jicarilla Apache Nation. The 

purpose of the agreement is to facilitate 

cooperation and coordination among 

State, Federal, and tribal agencies in the 

conservation of Rio Grande cutthroat 

trout. The Conservation Team has met 

several times and the ‘‘Range-wide 

Status of Rio Grande Cutthroat Trout 

(Oncorhynchus clarki virginalis): 2007’’

is a product of the team’s cooperative 

effort. 

Regulatory Mechanisms Involving Land 

Management 

Numerous State and Federal laws and 

regulations help to minimize adverse 

effects of land management activities on 

Rio Grande cutthroat trout. Federal laws 

that protect Rio Grande cutthroat trout 

and their habitats include the Clean 

Water Act (33 U.S.C. 1251 et seq.), 

Federal Land Policy and Management 

Act (43 U.S.C. 1701 et seq.), National 

Forest Management Act (16 U.S.C. 1600 

et seq.), Wild and Scenic Rivers Act (16 

U.S.C. 1271 et seq.), Wilderness Act (16 

U.S.C. 1131 et seq.), and the National 

Environmental Policy Act (42 U.S.C. 

4321 et seq.). Approximately 59 percent 

of Rio Grande cutthroat trout habitat 

occurs on lands managed by Federal 

agencies. The majority of those lands are 

managed by the USFS. Rio Grande 

cutthroat trout occur over a large 

geographic area within the Rio Grande, 

Santa Fe, and Carson National Forests in 

Colorado and New Mexico. Rio Grande 

cutthroat trout is designated as a 

sensitive species on all USFS lands. 

The Regional Forester’s Sensitive 

Species List policy is applied to projects 

implemented under the 1982 National 

Forest Management Act Planning Rule. 

However, in 2005, USFS implemented a 

new planning rule (70 FR 1023, January 

5, 2005), which directs land 

management plans to be more strategic 

and less prescriptive. Under the new 

rule, land management plans identify 

ecosystem-level desired conditions and 

provide management objectives and 

guidelines to move toward the desired 

conditions. The land management plans 

also will provide species-specific 

direction for special status species when 

the broader ecosystem-level desired 

conditions do not provide for their 

needs. However, the United States 

District Court in Citizens for Better 

Forestry et al. v. U.S. Department of 

Agriculture (N.D. Calif.) enjoined the 

Forest Service from implementation and 

utilization of the National Forest land 

management planning rule published on 

January 5, 2005 (70 FR 1023). Currently, 

the U.S. Department of Agriculture 

Office of General Counsel is reviewing 

this matter and will provide legal advice 

to USFS on how to proceed with forest 

planning. Therefore, efforts specific to 

forest planning are postponed until 

further direction is available (USFS 

2008). 

Threats to depletion of stream flow 

can be reduced by the U.S. Forest 

Service utilizing its authorities, if any, 

to further secure additional instream 

flows in Colorado. Rio Grande cutthroat 

trout conservation populations are 

protected by State instream flow water 

rights or USFS Reserve water rights 

along 620 km (385 mi) in 63 stream 

segments (approximately 70 percent of 

occupied habitat) within the Rio Grande 

basin in Colorado. Most of the 

remaining Rio Grande cutthroat trout 

conservation populations that are not 

associated with instream flow water 

rights are found on private property 

within the boundaries of the old 

Spanish Land Grants where natural 

resource stewardship is practiced. 

Regulatory controls of water quality in 

Colorado are implemented by the 


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Colorado Water Quality Control 

Division and Commission. Water quality 

standards are in place to protect the 

maintenance of aquatic life in coldwater 

environments, and special resource 

restrictions are also available to provide 

further site-specific protection to water 

quality (Japhet et al. 2007, p. 18). 

Summary of Factor D 

The NMDGFG, CDOW and USFS are 

actively managing Rio Grande cutthroat 

trout and its habitat. They also have 

authority for and are undertaking 

fisheries management, research, 

educational and law enforcement 

activities designed to improve the 

conservation status of the species. There 

is a range-wide conservation agreement 

that also involves the Service and other 

parties. Existing regulations, authorities, 

and policies address current threats to 

the species that are subject to regulatory 

control. However, climate change will 

have potential impact throughout the 

range of this species. At this time it is 

difficult to state how these effects will 

be addressed through existing regulatory 

mechanisms. 

E. Other Natural or Manmade Factors 

Affecting Its Continued Existence 

Climate Change 

In this section, we discuss the aspects 

of climate change that will most likely 

affect the habitat of Rio Grande 

cutthroat trout. We begin by presenting 

the evidence that indicates that climate 

change is occurring globally. We then 

discuss literature related to climate 

change that has been published for the 

Southwest and southern Rocky 

Mountains that documents changes 

either that have already occurred or that 

researchers predict will occur. Finally, 

we present data that have been collected 

for streams occupied by Rio Grande 

cutthroat trout that indicate that the 

effects of climate change could 

exacerbate the threats discussed above. 

The Intergovernmental Panel on 

Climate Change (IPCC) is a scientific 

body set up by the World 

Meteorological Organization and the 

United Nations Environment Program in 

1988. It was established because 

policymakers needed an objective 

source of information about the causes 

of climate change, its potential 

environmental and socio-economic 

consequences, and the adaptation and 

mitigation options to respond to it. The 

Service considers the IPCC an impartial 

and legitimate source of information on 

climate change. In 2007, the IPCC 

published its Fourth Assessment Report, 

which is considered the most 

comprehensive compendium of 

information on actual and projected 

global climate change currently 

available. 

Although the extent of warming likely 

to occur is not known with certainty at 

this time, the IPCC (2007a, p. 5) has 

concluded that warming of the climate 

is unequivocal and continued 

greenhouse gas emissions at or above 

current rates would cause further 

warming (IPCC 2007a, p. 13). The IPCC 

also projects that there will very likely 

be an increase in the frequency of hot 

extremes, heat waves, and heavy 

precipitation (IPCC 2007a, p. 15). 

Warming in the Southwest is expected 

to be greatest in the summer (IPCC 

2007b, p. 887). Annual mean 

precipitation is likely to decrease in the 

Southwest and the length of snow 

season and snow depth are very likely 

to decrease (IPCC 2007b, p. 887). Most 

models project a widespread decrease in 

snow depth in the Rocky Mountains and 

earlier snowmelt (IPCC 2007b, p. 891). 

In consultation with leading scientists 

from the Southwest, the New Mexico 

Office of the State Engineer prepared a 

report for the Governor (State of New 

Mexico 2006) which made the following 

observations about the impact of climate 

change in New Mexico: 

(1) Warming trends in the American 

Southwest exceed global averages by 

about percent (p. 5); 

(2) Models suggest that even moderate 

increases in precipitation would not 

offset the negative impacts to the water 

supply caused by increased temperature 

(p. 5); 

(3) Temperature increases in the 

Southwest are predicted to continue to 

be greater than the global average (p. 5); 

(4) There will be a delay in the arrival 

of snow and acceleration of spring snow 

melt, leading to a rapid and earlier 

seasonal runoff (p. 6); and 

(5) The intensity, frequency, and 

duration of drought may increase (p. 7). 

By the late 21st century, one simulation 

predicts no sustained snowpack south 

of Santa Fe or in the Sangre de Cristo 

Mountains (State of New Mexico 2006, 

p. 13). Snow pack would remain in far 

northern New Mexico and southern 

Colorado but would be greatly reduced 

in mass, with a decrease in water mass 

between one-third and one-half (State of 

New Mexico 2006, p. 14). 

Consistent with the outlook presented 

for New Mexico, Hoerling (2007, p. 35) 

states that, relative to 1990–2005, 

simulations indicate that a 25 percent 

decline in stream flow will occur from 

2006–2030 and a 45 percent decline will 

occur from 2035–2060 in the Southwest. 

Seager et al. (2007, p. 1181) show that 

there is a broad consensus among 

climate models that the Southwest will 

get drier in the 21st century and that the 

transition to a more arid climate is 

already under way. Only one of 19 

models has a trend toward a wetter 

climate in the Southwest (Seager et al. 

2007, p. 1181). Stewart et al. (2004, 

p. 1152) show that timing of spring 

streamflow in the western United States 

during the last five decades has shifted 

so that the major peak now arrives 1 to 

4 weeks earlier, resulting in less flow in 

the spring and summer. They conclude 

that almost everywhere in North 

America, a 10 to 50 percent decrease in 

spring-summer streamflow fractions 

will accentuate the seasonal summer 

dry period with important consequences 

for warm-season water supplies, 

ecosystems, and wildfire risks (Stewart 

et al. 2004, p. 1154). An increase in 

average mean air temperature of just 

over 1 °C (2.5 °F) in Arizona and just 

under 1 °C (1.8 °F) in New Mexico since 

1976 has already been documented 

(Lenart 2007, p. 4). Udall (2007, p. 7) 

found that multiple independent data 

sets confirm widespread warming in the 

West. Long-term studies (25 plus years) 

of Mexican jays (Aphelocoma 

ultramarina) in Arizona and of yellowbellied marmots (Marmota flaviventris) 

in the Rocky Mountains indicate 

changes in the timing of important life 

history events (e.g., breeding, emergence 

from hibernation) for both species 

related to warmer temperatures 

(Parmesan and Galbraith 2004, pp. 18, 

19). 

As we will discuss below, climate 

change is predicted to have four major 

effects on the cold water habitat 

occupied by Rio Grande cutthroat trout: 

(1) Increased water temperature; (2) 

decreased stream flow; (3) a change in 

the hydrograph (a graphical 

representation of the distribution of 

water discharge or runoff over a period 

of time); and (4) an increased 

occurrence of extreme events (fire, 

drought, and floods). 

Increased Water Temperature 

Water temperature influences the 

survival of salmonids in all stages of 

their life cycle. Alterations in the 

temperature regime from natural 

background conditions negatively affect 

population viability, when considered 

at the scale of the watershed or 

individual stream (McCullough 1999, 

p. 160). Salmonids are classified as 

coldwater fish with thermal preferences 

centered around 15 °C (59 °F) (Shuter 

and Meisner 1992, p. 8). High 

temperatures suppress appetite and 

growth, can influence behavioral 

interactions with other fish (Shrank et 

al. 2003, p. 100), or can be lethal 


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(McCullough 1999, 

p. 156). Salmonids inhabiting warm 

stream segments have higher 

probabilities of dying from stress 

(McCullough 1999, p. 156). 

Eaton and Scheller (1996, p. 1111) 

state that the maximum temperature 

tolerance for cutthroat trout is 23.3 °C 

(74 °F), but Dunham et al. (2003b, p. 

1042) state that Lahontan cutthroat trout 

(Oncorhynchus clarki henshawi) show 

signs of stress (decreased growth and 

appetite and increased mortality) when 

water temperature exceeds 22 °C 

(71.6 °F) for even a short time (less than 

1 day). For Bonneville cutthroat trout, 

the 7-day upper incipient lethal 

temperature (temperature lethal to 50 

percent of the fish) was 24.2 °C (75.6 °F) 

under constant thermal conditions 

(Johnstone and Rahel 2003, p. 96). 

However, when the temperature was 

cycled daily between 16–26 °C (60.8–

78.8 °F) for 7 days, similar to what the 

trout would experience in high 

mountain streams, all trout survived 

(Johnstone and Rahel 2003, p. 97). 

Dickerson and Vineyard (1999, pp. 519, 

520) found a similar result (cycling 

between 20 and 26 °C (68 and 78.8 °F)) 

for Lahontan cutthroat trout. Although 

trout may survive cyclic exposures to 

high temperatures, growth is slowed or 

stopped due to the high metabolic costs 

and reduced food intake (Dickerson and 

Vineyard 1999, p. 519; Johnstone and 

Rahel 2003, p. 98). 

Although temperature preferences of 

Rio Grande cutthroat trout have not 

been researched specifically, their 

optimum growth temperature (appetite 

is high and maintenance requirements 

low) is most likely in the range of 13–

15 °C (55.4–59 °F), similar to other 

cutthroat trout (Meeuwig et al. 2004, p. 

213; Bear et al. 2007, p. 1118) and their 

upper incipient lethal limit is most 

likely near 23–24 °C (73.4–75.2 °F), as 

has been found for other subspecies of 

cutthroat trout (Wagner et al. 2001, 

p. 434; Johnstone and Rahel 2003, p. 

97). Upper incipient lethal limit 

(temperature at which 50 percent of the 

fish can survive for 7 days) for rainbow 

trout ranges from 24–26 °C (75.2–

78.8 °F), for brown trout 23–26 °C (73.4–

78.8 °F), and for brook trout 24–25 °C 

(75.2–77 °F) (McCullough 1999, pp. 47, 

48), which means these nonnative trout 

are better able to tolerate higher water 

temperatures than cutthroat trout. 

The IPCC states that of all ecosystems, 

freshwater ecosystems will have the 

highest proportion of species threatened 

with extinction due to climate change 

(Kundzewicz et al. 2007, p. 192). 

Species with narrow temperature 

tolerances will likely experience the 

greatest effects from climate change, and 

it is anticipated that populations located 

at the margins of species’ hydrologic 

and geographic distributions will be 

affected first (Meisner 1990a, p. 282). 

Climate change has already had or is 

predicted to have negative 

consequences on coldwater fisheries 

globally (Nakano et al. 1996, p. 711; 

Hari et al. 2006, p. 24), across North 

America (Meisner 1990a, pp. 287, 290; 

Regier and Meisner 1990, p. 11; 

Carpenter et al. 1992, p. 124; Eaton and 

Scheller 1996, p. 1111; O’Neal 2002, 

p. 3; Poff et al. 2002, p. iv; Chu et al. 

2005, p. 303; Preston 2006, pp. 106, 107, 

110, 111, 115; Reiman et al. 2007, pp. 

1553, 1558), and in the Southwest and 

Rocky Mountains specifically (Keleher 

and Rahel 1996, p. 1; Rahel et al. 1996, 

pp. 1116, 1122; O’Neal 2002, pp. 43, 44; 

Preston 2006, pp. 101, 102, 113) through 

increases in ground and surface water 

temperature. 

The magnitude of habitat loss due to 

increased water temperature depends on 

the climate change model used, the 

model used to predict the air 

temperature/water temperature 

relationship, and the timeframe. Keleher 

and Rahel (1996, p. 4) found that the 

distribution of salmonids in Wyoming 

streams was limited to areas where 

mean July air temperature did not 

exceed 22 °C (71.6 °F). They projected 

that for temperature increases of 1, 2, 3, 

4, or 5 °C, there would be a 

corresponding loss of area suitable for 

salmonids of 16.2, 29.1, 38.5, 53.3, and 

68.0 percent, respectively (Keleher and 

Rahel 1996, p. 4). Rahel et al. (1996) 

used three approaches to examine 

potential salmonid habitat loss due to 

warming in the North Platte river 

drainage of the Rocky Mountains. They 

found that there was a loss of 9 to 76 

percent of coldwater habitat based on 

air temperature increases of 1 to 5 °C 

(Rahel et al. 1996, p. 1120). Other 

studies have predicted losses of 18–92 

percent of suitable natal bull trout 

(Salvelinus confluentus) habitat 

(Rieman et al. 2007, p. 1558), and 

Preston (2006, p. 92), in a re-analysis of 

other studies, found a 20, 35, and 50 

percent loss of coldwater habitat from 

the Rocky Mountains in 2025, 2050, and 

2100, respectively. 

In these studies, habitat loss occurs in 

the lower elevation stream reaches (or 

lower latitude streams) due to increased 

temperatures. As a result, salmonid 

populations will be restricted to 

increasingly higher elevations or to 

more northern latitudes (Meisner et al. 

1988, p. 6; Regier and Meisner 1990, p. 

11; Keleher and Rahel 1996, p. 2; 

Nakano et al. 1996, pp. 716, 717; Rahel 

et al. 1996, p. 1122; Poff et al. 2002, p. 

7; Rieman et al. 2007, p. 1558). 

Consequently, coldwater species 

occupying the southern distributions of 

their range are seen as more susceptible 

to extirpation as a consequence of global 

climate change (Poff et al. 2002, p. 8; 

Rieman et al. 2007, pp. 1552, 1553). Rio 

Grande cutthroat trout are the 

southernmost subspecies of cutthroat 

trout (Behnke 2002, p. 143). 

Rio Grande cutthroat trout primarily 

occupy high-elevation headwater 

tributaries. Dispersal to new habitats is 

unlikely because they currently occupy 

the uppermost available habitat. 

Warming of lower elevation stream 

segments may limit restoration 

opportunities in the future and provide 

a competitive advantage to brown, 

rainbow, and brook trout in locations 

where these nonnatives occur with Rio 

Grande cutthroat trout (De Staso and 

Rahel 1994, pp. 293, 294; Dunham et al. 

2002, p. 380; Paroz 2005, p. vi; Bear et 

al. 2007, p. 1118; Shemai et al. 2007, p. 

322). 

The Santa Fe and Carson National 

Forests have monitored stream 

temperature data using thermographs 

(instruments that record temperature at 

designated intervals, e.g., once every 4 

hours) (Eddy 2005, Martinez 2007). 

From 2001–2003, 47 thermograph 

stations were used to monitor 21 

streams on the Santa Fe National Forest, 

representing 385 km (239 mi) of stream 

(Eddy 2005, p. 5). Seven of the 21 

streams are currently occupied by Rio 

Grande cutthroat trout conservation 

populations; all 21 are believed to be 

historical habitat. Temperature data 

collected were compared with New 

Mexico Environment Department 

(NMED) standards for high quality 

coldwater fisheries and with Santa Fe 

National Forest standards, which are 

slightly more stringent than NMED but 

are more in line with standards for 

coldwater fisheries in the western States 

(Table 3) (Eddy 2005, p. 4). ‘‘Properly 

functioning’’ indicates that the water 

temperature of the stream is within the 

optimal range for feeding, physiology, 

and behavior for coldwater fish. ‘‘At 

risk’’ indicates that the water 

temperature is slightly warmer than 

optimal, and ‘‘not properly functioning’’

indicates that the water temperature is 

too warm to support a healthy coldwater 

fishery. 


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TABLE 3.—SANTA FE NATIONAL FOREST AND NMED 

[Water quality temperature standards for high quality coldwater fisheries] 

Water temperature standards Properly functioning At risk Not properly 

functioning 

Santa Fe National Forest 7-Day Average Maximum .............................. ≤64 °F (≤17.8 °C) ....... 64 to 70 °F .................

(17.8–21.1 °C) ...........

>70 °F (>21.1 °C). 

NMED 3-Day Average Maximum ............................................................ <68 °F (<20 °C) .......... 68 to <73.4 °F ............

(20 to <23 °C) ............

≥73.4 °F (23 °C). 

Using the Santa Fe National Forest 

standards, stream segments represented 

by 12 thermograph stations were 

properly functioning (67.3 km (41.8 

mi)), stream segments represented by 20 

stations were at risk (162.1 km (100.7 

mi)), and stream segments represented 

by 15 stations were not properly 

functioning (154.7 km (96.1 mi)) (Eddy 

2005, p. 5). Using NMED standards, 

stream segments represented by 23 

stations (172.7 km (107.3 mi)) were 

properly functioning, stream segments 

represented by 12 stations (82.2 km 

(51.1 mi)) were at risk, and stream 

segments represented by 12 stations 

(129.1 km (80.2 mi)) were not properly 

functioning (Eddy 2005, p. 5). Only nine 

streams were properly functioning for 

their entire length, using both standards. 

Of these, only one is occupied by a Rio 

Grande cutthroat trout conservation 

population (Cave Creek) (Eddy 2005, p. 

5). The Pecos River and Rio de las Vacas 

are properly functioning in occupied 

Rio Grande cutthroat trout habitat but 

have at risk (Pecos River) or not 

properly functioning sections (Rio de las 

Vacas) below occupied habitat (Eddy 

2005, pp. 34, 35, 92). Canones, 

Polvadera, and Rio Cebolla were the 

other streams monitored that have 

conservation populations of Rio Grande 

cutthroat trout. These streams were 

identified as at risk or not properly 

functioning (Rio Cebolla) in occupied 

habitat (Eddy 2005, pp. 9, 19, 26). 

Monitoring on the Carson National 

Forest indicated that Comanche Creek 

had several periods in which 

temperature standards were exceeded 

(Martinez 2007, pp. 3–22). Eight sites on 

Comanche Creek were monitored in 

1998, 1999, and 2004. Temperatures 

were highest in 1998 and 1999, years of 

lower runoff. Temperatures in 1998 

were very high, with 5 of the 8 sites 

recording temperatures from 26.6–

29.5 °C (80–85 °F) (Martinez 2007, pp. 

3–22). At the remaining three sites, 

temperatures reached 26.4 °C (79.5 °F). 

Thermographs went in on June 23 each 

year, and in 1998, maximum 

temperatures ranged from 22.9–24 °C 

(73.2–76 °F) at all eight sites on the first 

day the recorders were deployed, 

indicating that there were probably 

several days of warm temperatures that 

occurred before monitoring began 

(Martinez 2007, pp. 3–22). In total, of 14 

streams occupied by Rio Grande 

cutthroat trout and monitored by 

thermographs on the Santa Fe and 

Carson National Forests, 8 streams were 

either at risk or not properly functioning 

because of high water temperature 

(NMED 2007, pp. 15–331; Eddy 2005, 

pp. 8–116; Martinez 2007, pp. 3–22). An 

additional conservation population in 

Colorado was also identified at risk from 

high water temperatures by Pritchard 

and Cowley (2006, p. 39). Because only 

a fraction of the streams occupied by 

Rio Grande cutthroat trout have been 

monitored, there are likely more that are 

at risk. 

The thermograph data collected on 

the Santa Fe and Carson National 

Forests indicate that stream 

temperatures in several streams are 

already at risk or are considered ‘‘not 

properly functioning’’ for trout. Because 

air temperature and consequently water 

temperature are expected to increase 

with climate change, we would 

anticipate that more streams that are 

currently not properly functioning will 

become unsuitable for Rio Grande 

cutthroat trout, those currently at risk 

will enter the not properly functioning 

category, and more streams will fall into 

the at risk category for temperature. As 

a consequence, suitable habitat will 

decrease and fragmentation will 

increase. 

In contrast to the potential negative 

impacts of water temperature increase 

on Rio Grande cutthroat trout, there 

could also be a potential benefit. Cold 

summer water temperatures (mean July 

temperature of less than 7.8 °C (46 °F)) 

have been found as a limiting factor to 

recruitment of cutthroat trout in highelevation streams (Harig and Fausch 

2002, p. 545; Coleman and Fausch 2007, 

pp. 1238–1240). Coleman and Fausch 

(2007, p. 1240) found that cold summer 

water temperatures in Colorado streams 

likely limited recruitment of cutthroat 

trout because of reduced survival of age0 fish (fish less than 1 year old). Harig 

and Fausch (2002, p. 538) recorded 

summer water temperatures in 5 streams 

in New Mexico and 11 streams in 

Colorado from 1996 to 1999 (Harig and 

Fausch 2002, p. 540). None of the 

streams in New Mexico had July water 

temperatures below 7.8 °C (46 °F) 

(lowest July average was in the Pecos 

River, 9.2 °C (48.6 °F)). Three of four 

streams in Colorado that no longer had 

translocated fish present had summer 

averages below 7.8 °C (46 °F) (Harig and 

Fausch 2002, pp. 538, 539). The 

remaining 8 streams in Colorado had 

summer averages ≥8.3 °C (46.9 °F), 

indicating that cold summer water 

temperatures were most likely not 

limiting for these Rio Grande cutthroat 

trout populations (Harig and Fausch 

2002, pp. 538, 539). Two of the four 

streams (Little Medano and Unknown 

Creek), which no longer had 

transplanted fish at the time of Harig 

and Fausch’s research (1996–1998), 

dried in 2002 (Alves et al. 2007, pp. 43, 

44), raising the possibility that 

insufficient refugial habitat may have 

been limiting, not low summer water 

temperatures. 

Cold summer water temperatures 

have been identified as limiting in one 

stream: Deep Canyon, Colorado 

(Pritchard and Cowley 2006, p. 42). 

However, Alves et al. (2007 database) 

indicate that Deep Canyon has 

temperatures from 8 to 16 °C (46.4 to 

60.8 °F) during spawning and 

incubation periods. Of the 14 Rio 

Grande cutthroat trout streams 

monitored with thermographs on the 

Santa Fe and Carson National Forests, 

two (Pecos and Mora rivers) were found 

to have July temperatures less than 

7.8 °C (46 °F) (data summarized from 

Eddy 2005, Martinez 2007). The result 

for the Pecos River contrasts with the 

data Harig and Fausch (2002, p. 540) 

collected (9.2 °C (48.6 °F)) and likely 

reflects a difference in thermograph 

placement or year (e.g., temperature 

variability, amount of runoff). 

In summary, we find that data 

collected thus far indicate that warm 

water temperatures have already 

reached the likely limits of suitability in 

some Rio Grande cutthroat trout streams 

and several others are at risk. Water 

temperatures are expected to increase in 

the future, affecting more streams and 

making lower elevation reaches either 


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marginal or unsuitable. This is 

particularly true for populations that are 

located in New Mexico and are at the 

southernmost extent of the range but 

could also be true for smaller streams in 

Colorado. Although cold water 

temperatures are limiting to some highelevation salmonid populations, cold 

water limitation has not been 

convincingly demonstrated for any Rio 

Grande cutthroat trout population. 

Therefore, we view the negative impact 

of stream warming to outweigh any 

benefit that may occur from increased 

water temperature. 

The studies cited above that forecast 

coldwater habitat loss, calculate the loss 

of habitat based on increases in 

temperature alone, assuming 

temperatures will rise above the thermal 

tolerance limits of coldwater species, 

thereby limiting the amount of suitable 

habitat available. The ancillary effects of 

increased temperature, such as 

increased habitat fragmentation (Rahel 

et al. 1996, pp. 1121, 1122; Rieman et 

al. 2007, pp. 1553, 1560, 1562), changes 

in invertebrate prey base (both species 

composition and availability) (Ries and 

Perry 1995, p. 204; O’Neal 2002, p. 4; 

IPCC 2002, p. 17; Harper and Peckarsky 

2006, p. 618; Bradshaw and Holazpel 

2008, p. 157), effects on spawning (Jager 

et al. 1999, p. 236), increased 

competitive interactions with nonnative 

trout (Meisner 1990b, p. 1068; De Staso 

and Rahel 1994, pp. 289, 294; O’Neal 

2002, p. 33; Chu et al. 2005, p. 307; 

Sloat et al. 2005, p. 235), additional 

invasive species (IPCC 2002, p. 32), 

increased susceptibility to disease (Hari 

et al. 2006, p. 24), and effects on water 

quality (e.g., dissolved oxygen, 

nutrients, pH) (Meisner et al. 1988, p. 7), 

are not considered in calculating the 

potential habitat loss. 

Of these factors, increased 

fragmentation, increased effects from 

nonnative fish, and increased disease 

risk are considered of particular 

importance to Rio Grande cutthroat 

trout and are discussed in more detail. 

Fragmentation. Climate change is 

predicted to increase fragmentation of 

coldwater fish habitat (Nakano et al. 

1996, p. 719; Rahel et al. 1996, p. 1122; 

Rieman et al. 2007, p. 1553). Currently, 

112 of 120 (93 percent) conservation 

populations of Rio Grande cutthroat 

trout exist as fragments, with no wellconnected populations (Alves et al. 

2007, p. 29). Only one population has a 

moderate degree of connectivity 

(Comanche Creek) (2007 database). As 

noted above, Comanche Creek currently 

has very high water temperatures 

(Martinez 2007, pp. 3–22), and several 

of the small tributaries of upper 

Comanche Creek dried in 2006 (Patten 

et al. 2007, p. 76). Consequently, the 

one moderately well-connected 

population may already be at risk. 

Seven Rio Grande cutthroat trout 

conservation populations are considered 

weakly networked (occupied habitat 

consists of 2–3 connected streams, 

possible infrequent straying of adults 

may occur) (Alves et al. 2007, p. 77). Of 

these seven, six have connecting stream 

segments less than 5 feet in width (2007 

database), and are therefore considered 

at risk from drying. Consequently, 

fragmentation of these weakly 

networked systems appears reasonably 

likely in the foreseeable future. 

Nonnative Fish Interactions. Water 

temperature is a determining factor in 

the distribution of salmonids (Rahel and 

Hubert 1991, p. 326; Schrank et al. 

2003, p. 100; Sloat et al. 2005, p. 225). 

Additionally, temperature regime is a 

key determinant of the outcome of 

competitive interactions in a fish 

community (MuCullough 1999, p. 156). 

Fish living within their optimum 

temperature range have improved 

performance relative to other species 

not within their optimum range 

(MuCullough 1999, p. 156). There is 

evidence that the reason cutthroat trout 

occupy headwater streams and rainbow, 

brook, and brown trout occupy 

downstream reaches is because of the 

influence of temperature on competitive 

abilities (Dunham et al. 2002, p. 380). 

DeStaso and Rahel (1994, pp. 293, 294) 

looked at competition between Colorado 

River cutthroat trout (Oncorhynchus 

clarki pleuriticus) and brook trout. They 

found that at warmer water 

temperatures (20 °C (68 °F)) brook trout 

was dominant, as evidenced by a higher 

level of interspecific aggression, more 

time spent at the optimal feeding 

position, and greater food consumption 

(DeStaso and Rahel 1994, pp. 293, 294). 

Brook trout also tolerated higher 

temperatures (DeStaso and Rahel 1994, 

p. 294). 

As mentioned earlier, when brook 

trout co-occur with cutthroat trout, 

species interactions act to suppress 

cutthroat trout populations (Dunham et 

al. 2002, p. 378; Young and GuentherGloss 2004, p. 193; Peterson et al. 2004, 

pp. 765–769). Because brook trout 

tolerate higher temperatures, warmer 

stream temperatures would provide a 

competitive advantage to brook trout 

over Rio Grande cutthroat trout, 

exacerbating the problems that already 

exist for Rio Grande cutthroat trout 

populations. 

In New Mexico, brown trout is the 

most common nonnative trout present 

in Rio Grande cutthroat trout 

conservation populations (summarized 

from 2007 database). Jager et al. (1999, 

p. 232) modeled the effects of an 

increase of 2 °C air temperature on 

brown trout distribution in the Sierra 

Nevada, California. They found that 

brown trout numbers would increase in 

upstream cooler reaches, and decrease 

downstream through starvation of 

juvenile and adult fish (Jager et al. 1999, 

p. 235). This is consistent with 

observations in Switzerland. In 

Switzerland in 1987, after a long period 

of essentially stable river water 

temperatures, water temperatures took 

an abrupt and significant increase to a 

higher mean level, which was attributed 

to a corresponding increase in air 

temperature (Hari et al. 2006, pp. 10, 

21). Suitable habitat for brown trout, a 

trout species native to the area, moved 

upstream, and downstream portions 

became unsuitable (Hari et al. 2006, pp. 

10, 21). 

McHugh and Budy (2005, p. 2791) 

hypothesized that cold incubation 

temperatures might explain why brown 

trout did not form self-sustaining 

populations at high elevations in Logan 

River, Utah, where upstream water 

temperatures were not too cold for adult 

brown trout. Because brown trout have 

a higher optimal growth temperature 

(between 13–18 °C) than cutthroat trout 

(12–13 °C), and because cold incubation 

temperatures may currently be limiting 

brown trout range expansion upstream, 

it is anticipated that warmer water 

temperatures will make additional 

upstream habitat suitable for brown 

trout, reducing the area where Rio 

Grande cutthroat trout are now 

dominant. 

When cutthroat trout co-occur with 

rainbow trout, cutthroat trout typically 

occupy the upper colder reaches and 

rainbow trout occupy the lower, warmer 

stream reaches (Sloat et al. 2005, p. 235; 

Robinson 2007, p. 80). As identified by 

Alves et al. (2007, p. 35), rainbow trout 

occupy the same stream reaches as four 

conservation populations of Rio Grande 

cutthroat trout. Rainbow trout have a 

higher thermal tolerance than do 

cutthroat trout (Bear et al. 2007, pp. 

1115, 1116). Because rainbow trout are 

able to tolerate higher temperatures than 

Rio Grande cutthroat trout, we expect 

that warming stream temperatures will 

give rainbow trout a competitive 

advantage over Rio Grande cutthroat 

trout. Monitoring and maintenance of 

barriers will continue to be essential, to 

prevent hybridization and competition. 

White sucker is native to the middle 

elevations of the Pecos and Canadian 

river drainages in New Mexico, but it 

has been introduced widely throughout 

the State and is sympatric with at least 

two populations of Rio Grande cutthroat 

trout (Sublette et al. 1990, p. 199; 2007 


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database). White sucker has a preferred 

water temperature of 22.4–27.1 °C (72.3–

80.8 °F) (Sublette et al. 1990, p. 198). 

Sublette et al. (1990, p.199) note that 

white sucker is highly fecund (able to 

reproduce) and often dominates a body 

of water. Comanche Creek (elevation 

approximately 2900 m (9500 ft)) has an 

abundant white sucker population, most 

likely due to the warm water 

temperatures discussed above. In 2007, 

over 20,000 white sucker were removed 

from Comanche Creek during a Rio 

Grande cutthroat trout restoration 

project (Patten 2007). Before the 

restoration, fish biomass was dominated 

by white sucker, and an inverse 

relationship was found between Rio 

Grande cutthroat trout density and 

white sucker density (Patten et al. 2007, 

pp. 17, 18). Because both white sucker 

and Rio Grande cutthroat trout feed on 

aquatic insects, there is the potential for 

high numbers of white sucker to 

negatively impact food availability for 

Rio Grande cutthroat trout. We would 

anticipate the warmer stream 

temperatures would lead to more stream 

habitat becoming suitable for white 

sucker with potential negative impacts 

on Rio Grande cutthroat trout 

populations. 

Disease. As mentioned earlier (see the 

‘‘Disease and Predation’’ section in 

Factor C above) it had been thought that 

Rio Grande cutthroat trout were 

provided some level of protection 

against whirling disease because 

tubificid worms are most abundant in 

warm, degraded habitats and Rio 

Grande cutthroat trout occur in highelevation, coldwater streams (67 FR 

39943). However, Nehring (2007, p. 10) 

found equal abundance of lineage III 

tubificid worms in elevations from 

1,829 m (6,000 ft) to 3,657 m (12,000 ft). 

Thus, it is clear that elevation does not 

provide protection from exposure to the 

disease. 

El-Matubouli et al. (1999) found that 

temperatures from 10–15 °C (50–59 °F) 

were optimum for development and 

maturation of the parasite inside the 

tubificid worm. Blazer et al. (2003, p. 

24) found that the greatest production of 

TAMs occurred at temperatures from 

13–17 °C (55.4–62.6 °F). Although the 

effect of temperature on survival of the 

tubificid worms was not statistically 

detectable, DuBey et al. (2005, p. 341) 

found that survival was consistently 

higher at 17 °C (62.6 °F) than at 5 °C 

(41 °F). Schisler et al. (2000, p. 862) 

found that multiple stressors on 

rainbow trout, especially the 

combination of M. cerebralis infection 

and temperature, increased mortality 

drastically. At 12.5 °C (54.5 °F) mean 

mortality of rainbow trout exposed to M. 

cerebralis was 41.7 percent. Mean 

mortality of rainbow trout exposed to M. 

cerebralis and held at a temperature of 

17 °C (62.6 °F) was 60 percent (Schisler 

2000, p. 861). Water temperature often 

exceeds 17 °C (62.6 °F) in July and 

August in Rio Grande cutthroat trout 

streams that have been monitored (Eddy 

2005, Martinez 2007). 

Thompson et al. (1999, p. 318) found 

that as water temperature increased 

from May to July, rainbow and cutthroat 

trout infected with M. cerebralis 

suffered high rates of mortality even 

though they had survived well in the 

winter. In a field study of the effects of 

water temperature, discharge, substrate 

size, nutrient concentration, primary 

productivity, and relative abundance of 

T. tubifix, de la Hoz Franco and Budy 

(2004, p. 1183) found that prevalence of 

M. cerebralis in trout increased with 

water temperature. Across sites where 

cutthroat trout were present, the lowest 

prevalence of infection occurred in the 

headwaters where average daily water 

temperature was 9.2 °C (48.6 °F), 

whereas the highest levels of infection 

occurred at a low elevation site where 

the temperature was the highest (>12 °C 

(53.6 °F)) (de la Hoz Franco and Budy 

2004, p. 1186). 

While water temperature in some 

streams may warm to the point (>20 °C 

(68 °F)) of inhibiting the production of 

TAMs (Blazer et al. 2003, p. 24), it is 

anticipated that the overall increases in 

water temperature will be favorable for 

T. tubifix and TAM production. From 

these studies we conclude that elevation 

does not provide protection to Rio 

Grande cutthroat trout populations and 

that increasing water temperature would 

increase the production of TAMs and 

the survival of tubificid worms (up to 

about 20 °C (68 °F)), and increased water 

temperature would increase mortality of 

infected Rio Grande cutthroat trout. 

In summary, stream warming will 

most likely decrease the amount of 

suitable habitat available for Rio Grande 

cutthroat trout. Warmer stream 

temperatures may in the foreseeable 

future make currently occupied reaches 

of stream more stressful or unsuitable. 

Suitable habitat is likely to be reduced, 

primarily at the downstream end of 

stream reaches and in small tributaries, 

leading to increased fragmentation, 

shorter occupied segments, and 

increased risk of extirpation. Warmer 

water temperatures will allow nonnative 

fishes to expand their range and give 

them a competitive advantage over Rio 

Grande cutthroat trout. Stress from 

warm water temperatures increases 

susceptibility to and mortality from 

disease. Although whirling disease 

positive sites are currently still limited 

within the range of Rio Grande cutthroat 

trout, managers will need to continue to 

monitor the disease closely. Increased 

water temperatures would increase the 

threat posed by whirling disease. 

Decreased Stream Flow 

Current models suggest a decrease in 

precipitation in the Southwest (Seager 

et al. 2007, p. 1181; Kundzewicz et al. 

2007, p. 183), which would lead to 

reduced stream flows and a reduced 

amount of habitat for Rio Grande 

cutthroat trout. Stream flow is also 

predicted to decrease in the Southwest 

even if precipitation were to increase 

moderately (Nash and Gleick 1993, p. 

ix; State of New Mexico 2005, p. 6; 

Hoerling 2007, p. 35). Winter and spring 

warming causes an increased fraction of 

precipitation to fall as rain, resulting in 

a reduced snow pack, an earlier 

snowmelt, and decreased summer 

runoff (Christensen et al. 2004, p. 4; 

Stewart et al. 2005, p. 1137; Regonda et 

al. 2005, p. 373). Earlier snowmelt and 

warmer air temperatures lead to a longer 

dry season, which affects stream flow. 

Warmer air temperatures lead to 

increased evaporation, increased evapotranspiration, and decreased soil 

moisture. These three factors would 

lead to decreased stream flow even if 

precipitation increased moderately. 

The effect of decreased stream flow is 

that streams become smaller, thereby 

reducing the amount of habitat available 

for aquatic species (Lake 2000, p. 577). 

A smaller stream is affected more by air 

temperature than a larger one, 

exacerbating the effects of warm (and 

cold) air temperature (Smith and Lavis 

1975, p. 229). Small headwater streams, 

such as those occupied by Rio Grande 

cutthroat trout, and intermittent streams 

may dry completely. Seventy-one 

percent of Rio Grande cutthroat trout 

streams are less than 8 km (5 mi) in 

length (Alves et al. 2007, p. 26). Because 

stream length is one indicator of 

population viability (Harig et al. 2000, 

p. 997; Hilderbrand and Kershner 2000, 

p. 515; Young et al. 2005, p. 2405; 

Cowley 2007 10.1002/aqc.845), further 

shortening of Rio Grande cutthroat trout 

streams due to drying is expected to 

have a negative impact on populations. 

In fact, fourteen Rio Grande cutthroat 

trout streams with conservation 

populations became intermittent, and 

had populations negatively impacted or 

lost because of the 2002 drought (Japhet 

et al. 2007, pp. 42–44; Patten et al. 2007, 

pp. 14, 31, 32, 34, 39, 76). The number 

of streams impacted was most likely 

higher, because managers only survey a 

fraction of the 120 conservation 

populations in any given year. 

Approximately 27 conservation 


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populations are in streams that are 1.5 

m (5 ft) or less in width throughout their 

entire length (2007 database). An 

additional 29 stream segments that are 

tributaries to the conservation 

populations are also less than 1.5 m (5 

ft) in width (2007 database), which 

indicates that fragmentation of existing 

connected populations could increase. 

We recognize that not all streams less 

than 1.5 m (5 ft) wide have an equal 

probability of drying. Some are likely 

spring fed or are narrow and deep, thus 

decreasing the likelihood of drying. 

However, because of the high number of 

Rio Grande cutthroat trout streams less 

than 8 km (5 mi) in length (71 percent 

of conservation populations) and less 

than 1.5 m (5 ft) wide, the risk of drying 

is considered high. 

Insight into the effects that climate 

change may have on headwater streams 

is provided by research done at the 

Experimental Lakes Area in 

northwestern Ontario (Schindler et al. 

1996). The experimental area was set up 

in 1968, and precipitation, evaporation, 

air temperature, wind velocity, and 

other meteorological and hydrological 

parameters were monitored 

continuously throughout the 1970 to 

1990 study period (Schindler et al. 

1996, p. 1005). During this period, the 

area experienced gradual air 

temperature warming (1.6 °C (2.9 °F)) 

and decreased precipitation (as 

measured by a decline of over 50 

percent in annual runoff) (Schindler et 

al. 1996, p. 1004). Whether these 

changes can be attributed to climate 

change or local variation is unknown, 

but they are consistent with changes 

that are predicted under global climate 

change scenarios. In the early 1970s, 

two streams in the area were perennial 

and one stream was dry for less than 10 

days per year. By the late 1980s all three 

streams were dry for 120–160 days 

during the summer (Schindler et al. 

1996, p. 1006). Because northern 

latitude ecosystems mimic higher 

elevation systems in southern latitudes, 

the effects seen on these streams likely 

represent what may happen at highelevation streams in New Mexico and 

Colorado, within the range of Rio 

Grande cutthroat trout. 

In summary, stream drying has 

already had a negative impact on several 

Rio Grande cutthroat trout populations; 

71 percent of Rio Grande cutthroat trout 

conservation populations are in stream 

fragments 8 km (5 mi) or less in length, 

and many of the populations are in 

streams less than 1.5 m (5 ft) wide. 

Further, the increased risk of stream 

drying as a result of climate change, 

leading to shorter stream segments and 

increased fragmentation, is seen as high. 

A rangewide emergency rescue and 

evacuation plan does not exist for Rio 

Grande cutthroat trout and would likely 

not be effective. If widespread drought 

were to occur, affecting many streams at 

the same time, it is unclear if sufficient 

facilities or donor streams exist to 

accept the rescued fish, or if the effort 

would take place according to a 

carefully conceived, well-organized 

plan. 

Change in Hydrograph 

Changes in air temperature and 

precipitation will likely lead to changes 

in the magnitude, frequency, timing, 

and duration of runoff (Poff et al. 2002, 

p. 4). Stewart et al. (2004, p. 1152) show 

that spring streamflow during the last 

five decades has shifted so that the 

major peak now arrives 1 to 4 weeks 

earlier, resulting in declining fractions 

of flow in the spring and summer. The 

life history of salmonids is closely tied 

to the flow regime, runoff in particular 

(Fausch et al. 2001, p. 1440). A change 

in timing or magnitude of floods can 

scour the streambed, destroy eggs, or 

displace recently emerged fry 

downstream (Erman et al. 1988, p. 2199; 

Montgomery et al. 1999, p. 378; Fausch 

et al. 2001, p. 1440). The environmental 

cues for spawning of Rio Grande 

cutthroat trout are not known with 

certainty, but they are most likely tied 

to increasing water temperature, 

increasing day length, and possibly 

flow, as it has been noted that they 

spawn when runoff from snowmelt has 

peaked and is beginning to decrease 

(Behnke 2002, p. 141; Pritchard and 

Cowley 2006, p. 25). Consequently, a 

change in the timing of runoff from 

spring to winter could disrupt spawning 

cues because peak flow would occur 

when the days are still short in length 

and water temperatures cold. 

Increased winter temperatures cause 

more precipitation to fall as rain instead 

of snow (Regonda et al. 2005, p. 373). 

Snow covering small streams provides 

valuable insulation that protects aquatic 

life (Needham and Jones 1959, p. 470; 

Gard 1963, p. 197). Gard (1963, p. 196) 

measured temperatures above, within, 

and below the snow at Sagehen Creek, 

California, a small Sierra Nevada 

mountain stream. He found that 

although there was a 35.4 °C (63.8 °F) 

diurnal air temperature variation, 

within the snow the temperature 

variation was only 1.3 °C (2.3 °F) and the 

water temperature in the stream below 

varied by only 0.3 °C (0.55 °F). Stream 

freezing, which is more likely absent 

insulating snow cover, has been 

suggested as the cause of the extirpation 

of one Rio Grande cutthroat trout 

population (Ferrell 2006, p. 11). Anchor 

ice (ice frozen on the stream bed) and 

frazil ice (ice crystal suspended in the 

water) can also have negative impacts 

on trout (Needham and Jones 1959, p. 

465). High-elevation streams are rarely 

visited in winter; consequently, it is 

difficult to document the extent to 

which freezing may impact populations. 

However, the combination of reduced 

stream flow and reduced snow pack 

could lead to an increased probability of 

stream freezing in small headwater Rio 

Grande cutthroat trout streams. 

Earlier snowmelt, which leads to less 

flow in the spring and summer, could 

either benefit Rio Grande cutthroat trout 

or be detrimental. The benefit could 

come because the young-of-year would 

have a longer growing season before 

winter. However, as discussed above, a 

longer season of lower flows would lead 

to increased stream temperatures and 

increased probability of intermittency 

and drying. 

In summary, it is difficult to project 

how changes in the hydrograph as a 

result of climate change will affect Rio 

Grande cutthroat trout populations. If 

growing season is increased, water 

temperatures remain suitable, and the 

stream does not dry, a beneficial effect 

could occur. If spawning cues are 

disrupted or egg and fry success is 

reduced because of winter floods or 

unseasonal extreme floods, a negative 

impact would occur. In addition, stream 

freezing may reduce suitable overwinter habitat or reduce population size 

in susceptible streams. 

Extreme Events 

An increase in extreme events such as 

drought, fires, and floods is predicted to 

occur because of climate change (IPCC 

2007a, p. 15). It is anticipated that an 

increase in extreme events will most 

likely affect populations living at the 

edge of their physiological tolerances. 

The predicted increases in extreme 

temperature and precipitation events 

may lead to dramatic changes in the 

distribution of species or to their 

extirpation or extinction (Parmesan and 

Matthews 2006, p. 344). 

Drought. The relatively short-term 

drought of the early 2000s had a 

negative impact on or extirpated 14 Rio 

Grande cutthroat trout populations in 

Colorado and New Mexico (Japhet et al. 

2007, pp. 42–44; Patten et al. 2007, pp. 

14–40). A fifteenth population is 

thought to have been extirpated in 2006 

by complete freezing caused by low 

flow in the winter (Ferrell 2006, p. 11). 

As discussed above, in the ‘‘Decreased 

Stream Flow’’ section, it is anticipated 

that a prolonged, intense drought would 

affect many Rio Grande cutthroat trout 

populations, in particular those less 


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than 1.5 m (5 ft) wide and less than 8 

km (5 mi) long because of their small 

size. 

Most Rio Grande cutthroat trout 

populations are currently protected 

from downstream populations of 

nonnative trout by barriers. Downstream 

reaches are larger streams that 

historically could have provided refugia 

for populations threatened by stream 

drying. If Rio Grande cutthroat trout 

disperse downstream now, they are lost 

from their conservation population once 

they pass over the barrier because they 

will not be able to pass back over the 

barrier moving the upstream direction. 

In the future, downstream water 

temperatures may be too warm to be 

suitable for Rio Grande cutthroat trout. 

In addition to stream drying, there is a 

clear association between severe 

droughts and large fires in the 

Southwest (Swetnam and Baisan 1994, 

pp. 11, 24, 28), as discussed below. 

Fire. Since the mid-1980s, wildfire 

frequency in western forests has nearly 

quadrupled compared to the average of 

the period 1970–1986. The total area 

burned is more than six and a half times 

the previous level (Westerling et al. 

2006, p. 941). In addition, the average 

length of the fire season during 1987–

2003 was 78 days longer compared to 

1970–1986 and the average time 

between fire discovery and control 

increased from 7.5 days to 37.1 days for 

the same timeframes (Westerling et al. 

2006, p. 941). McKenzie et al. (2004, p. 

893) suggest, based on models, that the 

length of the fire season will likely 

increase further and that fires in the 

western United States will be more 

frequent and more severe. In particular, 

they found that fire in New Mexico 

appears to be acutely sensitive to 

summer climate and temperature 

changes and may respond dramatically 

to climate warming. 

Changes in relative humidity, 

especially drying over the western 

United States, are also projected to 

increase the number of days of high fire 

danger (Brown et al. 2004, p. 365). Highelevation, subalpine forests in the Rocky 

Mountains typically experience 

infrequent (i.e., one to many centuries), 

high severity crown fires (Schoennagel 

et al. 2004, p. 664). These fires usually 

occur in association with extremely dry 

regional climate patterns (Swetnam and 

Baisan 1994, p. 28; Schoennagel et al. 

2004, p. 664). Short drying periods do 

not create the conditions appropriate for 

fire in these typically cool, humid 

forests. Schoennagel et al. (2004, p. 665, 

666) conclude that recent increases in 

the area burned in subalpine forests are 

not attributable to fire suppression but 

that variation in climate exerts the 

largest influence on the size, timing, and 

severity of the fires. In contrast, lowelevation, ponderosa pine forests in the 

Rocky Mountains were historically 

characterized by frequent, low-severity 

fires (Schoennagel et al. 2004, p. 669). 

Fire suppression has significantly 

increased ladder fuels (fuels that allow 

fire to climb from the forest floor to the 

tops of trees) and tree densities leading 

to unprecedented high-severity fires in 

these ecosystems (Schoennagel et al. 

2004, p. 669). Rio Grande cutthroat trout 

streams occur in both forest types. 

As discussed in the ‘‘Fire’’ section in 

Factor A above, because of the observed 

and predicted increase in fire season 

length; the predicted increase in 

frequency and severity of fires; the 

observation that fuel treatment is only 

effective in low-elevation, ponderosa 

pine forests; the expectation of an 

increase in the frequency of hot 

extremes, heat waves, and heavy 

precipitation (IPCC 2007a, p. 15); and 

the fact that most Rio Grande cutthroat 

trout streams occur within a forested 

landscape, we conclude that wildfire 

associated with climate change will 

exacerbate habitat loss to Rio Grande 

cutthroat trout populations across their 

range. 

Floods. The life history of salmonids 

is tied to the timing of floods (Fausch et 

al. 2001, p. 1440). A change in timing 

or magnitude of floods can scour the 

streambed, destroy eggs, or displace 

recently emerged fry downstream 

(Erman et al. 1988, p. 2199; 

Montgomery et al. 1999, p. 378; Fausch 

et al. 2001, p. 1440). Floods that occur 

after intense wildfires that have 

denuded the watershed are also a threat. 

As described above, in the ‘‘Fire’’

section under Factor A, several streams 

in the Southwest have had populations 

of trout extirpated as a result of ash 

flows which occurred after fire (Rinne 

1996, p. 654; Brown et al. 2001, p. 142; 

Patten et al. 2007, p. 33). Consequently, 

an increase in rain or snow events, 

intense precipitation that is 

unseasonable, or precipitation that 

occurs after fire could extirpate affected 

Rio Grande cutthroat trout populations. 

In summary, extreme events, 

especially widespread fire and drought, 

will likely affect Rio Grande cutthroat 

trout populations in the foreseeable 

future through population extirpation, 

extreme population reduction, or habitat 

reduction. Several Rio Grande cutthroat 

trout populations have already been 

impacted by drought. Fire has thus far 

primarily affected nonnative trout 

streams within the range of Rio Grande 

cutthroat trout, but there is no safeguard 

for Rio Grande cutthroat trout streams. 

The impact of a change in the timing of 

runoff may be significant but is more 

difficult to predict. 

Climate Change Summary 

The extent to which climate change 

will affect Rio Grande cutthroat trout is 

not known with certainty at this time. 

Preliminary projections point to a 

possible rangewide negative impact 

through increased water temperatures, 

decreased stream flow, a change in 

hydrograph, and an increased 

occurrence of extreme events, which 

will all tend to exacerbate the threats to 

the Rio Grande cutthroat trout and its 

habitat discussed under Factors A and 

C above. Although the extent that the 

global climate will change in the future 

is not known, even a minimal increase 

in temperature will lead to increased 

habitat unsuitability and will exacerbate 

most other known threats to the 

subspecies. 

Fisheries Management 

Future management of Rio Grande 

cutthroat trout will depend in part on 

the use of hatchery-reared fish. 

Although hatcheries can produce many 

fish in a short period of time, the use of 

hatchery fish is not without risks 

(Busack and Currens 1995, pp. 73–78). 

Two recent papers have explored the 

risks of captive propagation used to 

supplement species that are declining in 

the wild (Araki et al. 2007, Frankham 

2007). Araki et al. (2007, p. 102) found 

that there was approximately a 40 

percent decline in reproductive 

capabilities per captive-reared 

generation when steelhead trout 

(Oncorhynchus mykiss) were moved to 

natural environments. Frankham (2007, 

p. 2) notes that characteristics selected 

for under captive breeding conditions 

are overwhelmingly disadvantageous in 

the natural environment. Minimizing 

the number of generations in captivity 

or making the captive environment 

similar to the wild environment are 

effective means for minimizing genetic 

adaptation to captivity (Frankham 2007, 

pp. 4, 5). 

The history of brood stock 

management in New Mexico has been 

marked by many challenges (Cowley 

and Pritchard 2003, pp. 12, 13). The 

most recent challenges came from 

whirling disease infection at Seven 

Springs Hatchery and the discovery that 

the brood stock was introgressed with 

Yellowstone cutthroat trout (Patten et 

al. 2007, p. 42). The hatchery was 

refurbished to eliminate M. cerebralis 

and the brood stock program was 

restarted in 2005 (Patten et al. 2007, p. 

42). A recently revised brood stock 

management plan was completed for 


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New Mexico (Cowley and Pritchard 

2003). 

Although the intent of fisheries 

management is positive, fisheries 

management may result in 

unanticipated outcomes. For example, 

Costilla Creek restoration efforts were 

unfortunately marred by the 

introduction of rainbow trout into the 

recently reclaimed stream (Patten et al. 

2007, p. 101, Appendices VIII-X). The 

rainbow trout came from Seven Springs 

Hatchery, even though this hatchery is 

designated as a Rio Grande cutthroat 

trout facility (NMDGF 2002, p. 28; 

Pattten et al. 2007, p. 379). It is unclear 

why Seven Springs Hatchery was 

holding rainbow trout. Through a 

coordinated effort, managers believe 

they captured most, if not all, of the 

rainbow trout that were stocked into 

Costilla Creek along with Rio Grande 

cutthroat trout (Patten et al. 2007, pp. 

18, 102). While electrofishing to recover 

the rainbow trout, two brook trout were 

also caught, indicating that the lower 

barrier was compromised, not all the 

fish were killed during treatment, or 

that an angler had released the fish 

above the barrier. In addition, because 

the stocked Rio Grande cutthroat trout 

came from Seven Springs Hatchery 

before the introgression with 

Yellowstone cutthroat trout was 

discovered, the Rio Grande cutthroat 

trout that were stocked were slightly 

introgressed (Patten et al. 2007, p. 102). 

For these reasons, relying on hatcheryreared Rio Grande cutthroat trout does 

not provide certainty that repatriation 

will be successful. 

Fisheries managers have worked very 

hard in the last several years to monitor 

populations, check and maintain 

barriers, test the genetic purity of 

populations, test streams for whirling 

disease, fund research, and reintroduce 

populations into appropriate streams 

(Patten et al. 2007, pp. 4–19; Japhet et 

al. 2007, pp. 22–27). New populations 

have been established in Costilla, South 

Ponil, Leandro, and Capulin creeks in 

New Mexico and in Big Springs, East 

Costilla, and West Costilla creeks in 

Colorado. Populations were restarted in 

Cat Creek and Little Medano Creek, 

Colorado, after being lost to the drought 

(Japhet et al. 2007, pp. 42–44). In 

addition, major restoration projections 

have gone through environmental 

review and are in progress on Placer 

Creek, Comanche Creek, and Costilla 

Creek. Completion of these projects will 

contribute to the long-term persistence 

of Rio Grande cutthroat trout. The 

USFS, BLM, and NPS have been active 

partners in project implementation and 

have completed many miles of detailed 

stream surveys, which adds greatly to 

our knowledge of habitat condition. 

New Mexico Tribes and Pueblos have 

recently taken initiatives to restore Rio 

Grande cutthroat trout on their 

homelands. The Mescalero Apache 

Tribe began inventorying their streams 

to determine presence, and has 

reopened the Mescalero Tribal Fish 

Hatchery. The Tribe hopes to establish 

a Rio Grande cutthroat trout brood stock 

and raise Rio Grande cutthroat trout to 

support native fish restoration projects 

on Tribal lands. Santa Clara Pueblo 

received a Tribal Wildlife grant for 

nearly $200,000 for Rio Grande 

cutthroat trout restoration. The Pueblo 

is in the initial phases of project 

planning for restoring the Santa Clara 

Creek watershed. Nambe Pueblo has 

also expressed an interest in Rio Grande 

cutthroat trout restoration and is 

working in collaboration with USFS, the 

Service, Southwest Tribal Fisheries 

Commission (SWTFC), and NMDGF to 

formulate a restoration plan to restore 

Rio Grande cutthroat trout in the Nambe 

River watershed. The Jicarilla Apache 

Nation has also been involved in Rio 

Grande cutthroat trout restoration and 

plans to expand their restoration efforts 

to additional creeks on the reservation 

in the near future. The SWTFC, an 

organization composed of southwestern 

Native American tribes, has developed a 

Memorandum of Understanding with 

NMDGF to acquire Rio Grande cutthroat 

trout eggs for juvenile and adult 

production in support of tribal 

restoration Rio Grande cutthroat trout 

projects. Currently, the Memorandum is 

still awaiting approval by both 

participants. If successful, these actions 

would provide further conservation for 

Rio Grande cutthroat trout. 

The Santa Fe National Forest, led by 

their fisheries biologist, has been very 

proactive about public education. They 

estimate that up until 2006 their 

‘‘Respect the Rio’’ program directly 

reached over 9,300 people (Ferrell 2006, 

p. 16). They developed the Rio Grande 

Cutthroat Trout Life Cycle Game, which 

has traveled to classrooms, Earth Day 

events, and Kids’ Fishing Day 

celebrations (Ferrell 2006, p. 15). The 

game has also been translated into 

Spanish to reach students who speak 

English as a second language. It is 

estimated that over 1,000 children and 

adults have played the game. 

In New Mexico, a Rio Grande 

cutthroat trout Working Group meets 

monthly to discuss Rio Grande cutthroat 

trout conservation, projects, and 

volunteer opportunities, and to 

coordinate and communicate efforts 

among the participants. Regular 

members are NMDGF, the Service, Trout 

Unlimited, New Mexico Trout, and the 

USFS. The members are committed to 

Rio Grande cutthroat trout conservation. 

One obstacle to fisheries managers in 

New Mexico has been the difficult 

process of approval for chemical 

treatment of streams. In August 2004, 

the New Mexico Game Commission 

voted to prohibit the use of piscicides in 

New Mexico (Patten et al. 2007, p. 102). 

This decision effectively terminated a 

project on Animas Creek, Gila National 

Forest, and has made stream restoration 

project approval difficult. Another 

obstacle to successful stream renovation 

is the stocking of nonnative trout by 

anglers into streams that have been 

treated to remove them (Japhet et al. 

2007, p. 17). Although education and 

regulation may help, there is no known 

way to stop this illegal activity. 

Summary of Factor E 

Fisheries management is integral to 

the conservation of Rio Grande cutthroat 

trout. Although there are some risks 

associated with fisheries management, 

we conclude that the benefits outweigh 

the risks. We also conclude that the best 

scientific and commercial information 

available to us indicates that the threats 

facing Rio Grande cutthroat trout will be 

exacerbated by climate change. 

Continued management actions to 

connect fragmented populations are 

essential. However, at this time, it is not 

clear that management actions can 

outpace some of the projected effects of 

climate change. 

Finding 

We have carefully assessed the best 

scientific and commercial information 

available regarding the past, present, 

and future threats faced by Rio Grande 

cutthroat trout. We have reviewed 

information supplied to us by State and 

Federal agencies, peer-reviewed 

literature, comments from private 

citizens, and other unpublished 

documents. The information 

summarized in this status review 

includes substantial information that 

was not available at the time of our 2002 

finding (67 FR 39936). On the basis of 

this review, we find that listing of Rio 

Grande cutthroat trout as threatened or 

endangered is warranted, due to a 

combination of population 

fragmentation, isolation, small 

population size, nonnative trout, 

drought, and fire. We anticipate these 

threats will be compounded by the 

projected effects of climate change. 

However, listing of the Rio Grande 

cutthroat trout is precluded at this time 

by pending proposals for other species 

with higher listing priorities and 

actions. 


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In the context of the Act, the term 

‘‘threatened species’’ means any species 

(or subspecies or, for vertebrates, 

distinct population segments) that is 

likely to become an endangered species 

within the foreseeable future throughout 

all or a significant portion of its range. 

The term ‘‘endangered species’’ means 

any species that is in danger of 

extinction throughout all or a significant 

portion of its range. The Act does not 

indicate threshold levels of historic 

population size at which, as the 

population of a species declines, listing 

as either ‘‘threatened’’ or ‘‘endangered’’

becomes warranted. Instead, the 

principal considerations in the 

determination of whether or not a 

species warrants listing as a threatened 

or an endangered species under the Act 

are the threats that now confront the 

species and the probability that the 

species will persist into ‘‘the foreseeable 

future.’’ The Act does not define the 

term ‘‘foreseeable future.’’ However, we 

consider the ‘‘foreseeable future’’ to be 

20 to 30 years, which equates to 

approximately 4 to 10 Rio Grande 

cutthroat trout generations, depending 

on the productivity of the environment. 

We find that this is both reasonable and 

appropriate for the present status review 

because it is long enough to take into 

account multi-generational dynamics of 

life-history and ecological adaptation, 

yet short enough to incorporate social 

and political change that affects species 

management. 

Evidence shows that populations of 

Rio Grande cutthroat trout have been 

greatly reduced over the last 200 years. 

The range of Rio Grande cutthroat trout 

has contracted northward and 

populations are primarily restricted to 

high-elevation headwater streams. We 

attribute the decline in the distribution 

of Rio Grande cutthroat trout to habitat 

degradation and the introduction of 

nonnative sport fish into Rio Grande 

cutthroat trout habitat that began in the 

late 1800s. The wide distribution of 

rainbow trout and nonnative cutthroat 

trout have compromised Rio Grande 

cutthroat trout populations through 

competition, hybridization, and 

predation. These introduced fish have 

expanded and colonized new habitat 

and formed naturally reproducing 

populations that occupy the former, and 

in some cases current, range of Rio 

Grande cutthroat trout. 

We find that populations we 

considered secure in 2002 suffered 

severe to moderate population declines. 

We considered 13 populations secure in 

2002, and now we find that only 8 

populations (5 identified in 2002, 3 new 

populations) would meet our definition 

of long-term persistence (over 2,500 

fish, 9.6 km (6 mi) of occupied habitat, 

no nonnatives present). Although 97 

additional conservation populations 

exist, they all are affected by one or 

more threats (e.g., small population size, 

short stream length, poor habitat 

quality, nonnative trout) that we 

consider significant enough to threaten 

their long-term survival. The 

overarching threat that magnifies the 

problems for each individual population 

is fragmentation. Over 90 percent of Rio 

Grande cutthroat trout populations exist 

in stream fragments. Consequently, 

recolonization of streams cannot occur 

after a natural disaster occurs and 

populations are much more susceptible 

to extirpation. 

Because of the increases in air 

temperature that have already been 

documented in the Southwest, and 

other changes that have been 

documented in hydrology, fire patterns, 

and the life history of animals in the 

region, there is evidence that the effects 

of climate change are already occurring 

in the range of Rio Grande cutthroat 

trout. Every aspect of climate change we 

examined will likely have a negative 

effect on Rio Grande cutthroat trout. Rio 

Grande cutthroat trout populations are 

currently surviving with multiple 

stressors. Adding the effects of climate 

change on these populations may 

exacerbate the existing threats and 

stressors on the species. 

There is documented commitment of 

agency personnel, tribes, and private 

landowners to continue conservation 

efforts for Rio Grande cutthroat trout. 

This is evidenced by the lists of 

accomplishments the States and 

agencies have provided to us. Both State 

and Federal agencies have been actively 

involved in Rio Grande cutthroat trout 

management. Several habitat restoration 

projects are in progress and several 

others are planned. It is too early to 

determine the level of success of current 

large watershed projects as they have 

not been fully completed and evaluated. 

Listing Priority Number 

In accordance with guidance we 

published on September 21, 1983, we 

assign a Listing Priority Number (LPN) 

to each candidate species (48 FR 43098). 

Such a priority ranking guidance system 

is required under section 4(h)(3) of the 

Act (16 U.S.C. 1533(h)(3)). Using this 

guidance, we assign each candidate an 

LPN of 1 to 12, depending on the 

magnitude of threats (high vs. moderate 

to low); immediacy of threats (imminent 

or non-imminent); and taxonomic status 

of the species, in order of priority 

(monotypic genus (i.e., a species that is 

the sole member of a genus), species, 

subspecies, distinct population segment, 

or significant portion of the range). The 

lower the listing priority number, the 

higher the listing priority (that is, a 

species with an LPN of 1 would have 

the highest listing priority). 

Many of the threats to this subspecies 

could result in complete loss of a given 

population at any time (e.g., fire, 

disease, nonnative introgression). 

However, because there are many 

known conservation populations and 

because many populations are being 

actively managed, the threats to this 

subspecies as a whole are considered 

moderate. 

An increase in average mean air 

temperature of just over 1 °C (2.5 °F) in 

Arizona and just under 1 °C (1.8 °F) in 

New Mexico since 1976 (Parmesan and 

Galbraith 2004, pp. 18, 19; State of New 

Mexico 2006, p. 5; Lenart 2007, p. 4) 

suggest that climate change is already 

occurring in the Southwest. Coldwater 

species like Rio Grande cutthroat trout 

are expected to be among the most 

sensitive species to climate change. 

Water temperatures in some Rio Grande 

cutthroat trout streams are already 

elevated beyond recommended 

temperatures for coldwater trout. At 

least 14 Rio Grande cutthroat trout 

streams either dried up or had 

populations negatively affected by the 

2002 drought. Rio Grande cutthroat 

trout populations already face multiple 

stresses such as nonnative trout, 

fragmented habitat, and limited habitat. 

The additional effects of climate change 

are expected to cause population 

extirpations and population bottlenecks. 

Consequently, threats to this species are 

considered imminent. Therefore, based 

on the moderate magnitude and 

immediacy of threats, we have given 

this subspecies an LPN of 9. 

Preclusion and Expeditious Progress 

Preclusion is a function of the listing 

priority of a species in relation to the 

resources that are available and 

competing demands for those resources. 

Thus, in any given fiscal year (FY), 

multiple factors dictate whether it will 

be possible to undertake work on a 

proposed listing regulation or whether 

promulgation of such a proposal is 

warranted but precluded by higher 

priority listing actions. 

The resources available for listing 

actions are determined through the 

annual Congressional appropriations 

process. The appropriation for the 

Listing Program is available to support 

work involving the following listing 

actions: proposed and final listing rules; 

90-day and 12-month findings on 

petitions to add species to the Lists of 

Endangered and Threatened Wildlife 

and Plants (Lists) or to change the status 


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of a species from threatened to 

endangered; annual determinations on 

prior ‘‘warranted but precluded’’

petition findings as required under 

section 4(b)(3)(C)(i) of the Act; proposed 

and final rules designating critical 

habitat; and litigation-related, 

administrative, and program 

management functions (including 

preparing and allocating budgets, 

responding to Congressional and public 

inquiries, and conducting public 

outreach regarding listing and critical 

habitat). The work involved in 

preparing various listing documents can 

be extensive and may include, but is not 

limited to: gathering and assessing the 

best scientific and commercial data 

available and conducting analyses used 

as the basis for our decisions; writing 

and publishing documents; and 

obtaining, reviewing, and evaluating 

public comments and peer review 

comments on proposed rules and 

incorporating relevant information into 

final rules. The number of listing 

actions that we can undertake in a given 

year also is influenced by the 

complexity of those listing actions; that 

is, more complex actions generally are 

more costly. For example, during the 

past several years, the cost (excluding 

publication costs) for preparing a 12- 

month finding, without a proposed rule, 

has ranged from approximately $11,000 

for one species with a restricted range 

and involving a relatively 

uncomplicated analysis to $305,000 for 

another species that is wide-ranging and 

involving a complex analysis. 

We cannot spend more than is 

appropriated for the Listing Program 

without violating the Anti-Deficiency 

Act (see 31 U.S.C. 1341(a)(1)(A)). In 

addition, in FY 1998 and for each fiscal 

year since then, Congress has placed a 

statutory cap on funds which may be 

expended for the Listing Program, equal 

to the amount expressly appropriated 

for that purpose in that fiscal year. This 

cap was designed to prevent funds 

appropriated for other functions under 

the Act (for example, recovery funds for 

removing species from the Lists), or for 

other Service programs, from being used 

for Listing Program actions (see House 

Report 105–163, 105th Congress, 1st 

Session, July 1, 1997). 

Recognizing that designation of 

critical habitat for species already listed 

would consume most of the overall 

Listing Program appropriation, Congress 

also put a critical habitat subcap in 

place in FY 2002 and has retained it 

each subsequent year to ensure that 

some funds are available for other work 

in the Listing Program: ‘‘The critical 

habitat designation subcap will ensure 

that some funding is available to 

address other listing activities’’ (House 

Report No. 107–103, 107th Congress, 1st 

Session, June 19, 2001). In FY 2002 and 

each year until FY 2006, the Service has 

had to use virtually the entire critical 

habitat subcap to address courtmandated designations of critical 

habitat, and consequently none of the 

critical habitat subcap funds have been 

available for other listing activities. In 

FY 2007, we were able to use some of 

the critical habitat subcap funds to fund 

proposed listing determinations for 

high-priority candidate species; we 

expect to also be able to do this in FY 

2008. 

Thus, through the listing cap, the 

critical habitat subcap, and the amount 

of funds needed to address courtmandated critical habitat designations, 

Congress and the courts have in effect 

determined the amount of money 

available for other listing activities. 

Therefore, the funds in the listing cap, 

other than those needed to address 

court-mandated critical habitat for 

already listed species, set the limits on 

our determinations of preclusion and 

expeditious progress. 

Congress also recognized that the 

availability of resources was the key 

element in deciding whether, when 

making a 12-month petition finding, we 

would prepare and issue a listing 

proposal or make a ‘‘warranted but 

precluded’’ finding for a given species. 

The Conference Report accompanying 

Public Law 97–304, which established 

the current statutory deadlines and the 

warranted-but-precluded finding, states 

(in a discussion on 90-day petition 

findings that by its own terms also 

covers 12-month findings) that the 

deadlines were ‘‘not intended to allow 

the Secretary to delay commencing the 

rulemaking process for any reason other 

than that the existence of pending or 

imminent proposals to list species 

subject to a greater degree of threat 

would make allocation of resources to 

such a petition [that is, for a lowerranking species] unwise.’’

In FY 2008, expeditious progress is 

that amount of work that can be 

achieved with $8,206,940, which is the 

amount of money that Congress 

appropriated for the Listing Program at 

this time (that is, the portion of the 

Listing Program funding not related to 

critical habitat designations for species 

that are already listed). Our process is 

to make our determinations of 

preclusion on a nationwide basis to 

ensure that the species most in need of 

listing will be addressed first and also 

because we allocate our listing budget 

on a nationwide basis. The $8,206,940 

for listing activities (that is, the portion 

of the Listing Program funding not 

related to critical habitat designations 

for species that already are listed) will 

be used to fund work in the following 

categories: Compliance with court 

orders and court-approved settlement 

agreements requiring that petition 

findings or listing determinations be 

completed by a specific date; section 4 

(of the Act) listing actions with absolute 

statutory deadlines; essential litigationrelated, administrative, and program 

management functions; and highpriority listing actions. The allocations 

for each specific listing action are 

identified in the Service’s FY 2008 Draft 

Allocation Table (part of our 

administrative record). We are working 

on completing our allocation at this 

time. More funds are available in FY 

2008 than in previous years to work on 

listing actions that are not the subject of 

court orders or court-approved 

settlement agreements. 

We currently have more than 120 

species with an LPN of 2. Therefore, we 

further rank the candidate species with 

an LPN of 2 by using the following 

extinction-risk type criteria: 

International Union for the 

Conservation of Nature and Natural 

Resources (IUCN) Red list status/rank, 

Heritage rank (provided by 

NatureServe), Heritage threat rank 

(provided by NatureServe), and species 

currently with fewer than 50 

individuals, or 4 or fewer populations. 

Those species with the highest IUCN 

rank (critically endangered), the highest 

Heritage rank (G1), the highest Heritage 

threat rank (substantial, imminent 

threats), and currently with fewer than 

50 individuals, or fewer than 4 

populations, comprise a list of 

approximately 40 candidate species 

(‘‘Top 40’’). These 40 candidate species 

have the highest priority to receive 

funding to work on a proposed listing 

determination. To be more efficient in 

our listing process, as we work on 

proposed rules for these species in the 

next several years, we are preparing 

multi-species proposals when 

appropriate, and these may include 

species with lower priority if they 

overlap geographically or have the same 

threats as a species with an LPN of 2. 

In addition, available staff resources are 

also a factor in determining highpriority species provided with funding. 

Finally, proposed rules for 

reclassification of threatened species to 

endangered are lower priority, since the 

listing of the species already affords the 

protection of the Act and implementing 

regulations. We assigned the Rio Grande 

cutthroat trout an LPN of 9, based on 

our finding that the subspecies faces 


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Federal Register / Vol. 73, No. 94 / Wednesday, May 14, 2008 / Proposed Rules 27923 

threats of moderate magnitude that are 

imminent. 

As explained above, a determination 

that listing is warranted but precluded 

must also demonstrate that expeditious 

progress is being made to add or remove 

qualified species to and from the Lists 

of Endangered and Threatened Wildlife 

and Plants. (We note that we do not 

discuss specific actions taken on 

progress towards removing species from 

the Lists because that work is conducted 

using appropriations for our Recovery 

program, a separately budgeted 

component of the Endangered Species 

Program. As explained above in our 

description of the statutory cap on 

Listing Program funds, the Recovery 

Program funds and actions supported by 

them cannot be considered in 

determining expeditious progress made 

in the Listing Program.) As with our 

‘‘precluded’’ finding, expeditious 

progress in adding qualified species to 

the Lists is a function of the resources 

available and the competing demands 

for those funds. Our expeditious 

progress in FY 2007 in the Listing 

Program, up to the date of making this 

finding for the Rio Grande cutthroat 

trout, included preparing and 

publishing the following 

determinations: 

FY 2007 COMPLETED LISTING ACTIONS

Publication date Title Actions FR pages 

10/11/2006 ................. Withdrawal of the Proposed Rule to List the Cow Head Tui 

Chub (Gila biocolor vaccaceps) as Endangered.

Final withdrawal, Threats 

eliminated.

71 FR 59700–59711. 

10/11/2006 ................. Revised 12-Month Finding for the Beaver Cave Beetle 

(Pseudanophthalmus major).

Notice of 12-month petition 

finding, Not warranted.

71 FR 59711–59714. 

11/14/2006 ................. 12-Month Finding on a Petition to List the Island Marble Butterfly (Euchloe ausonides insulanus) as Threatened or Endangered.Notice of 12-month petition 

finding, Not warranted.

71 FR 66292–66298. 

11/14/2006 ................. 90-Day Finding for a Petition to List the Kennebec River Population of Anadromous Atlantic Salmon as Part of the Endangered Gulf Of Maine Distinct Population Segment.Notice of 90-day petition finding, Substantial.71 FR 66298–66301. 

11/21/2006 ................. 90-Day Finding on a Petition To List the Columbian SharpTailed Grouse as Threatened or Endangered.Notice of 90-day petition finding, Not substantial.71 FR 67318–67325. 

12/5/2006 ................... 90-Day Finding on a Petition To List the Tricolored Blackbird 

as Threatened or Endangered.

Notice of 90-day petition finding, Not substantial.71 FR 70483–70492. 

12/6/2006 ................... 12-Month Finding on a Petition To List the Cerulean Warbler 

(Dendroica cerulea) as Threatened with Critical Habitat.

Notice of 12-month petition 

finding, Not warranted.

71 FR 70717–70733. 

12/6/2006 ................... 90-Day Finding on a Petition To List the Upper Tidal Potomac 

River Population of the Northern Water Snake (Nerodia 

sipedon) as an Endangered Distinct Population Segment.

Notice of 90-day Petition Finding, Not substantial.71 FR 70715–70717. 

12/14/2006 ................. 90-Day Finding on a Petition to Remove the Uinta Basin 

Hookless Cactus From the List of Endangered and Threatened Plants; 90-Day Finding on a Petition To List the 

Pariette Cactus as Threatened or Endangered.

Notice of 5-year Review, Initiation.

Notice of 90-day petition finding, Not substantial.

Notice of 90-day petition finding, Substantial.

71 FR 75215–75220. 

12/19/2006 ................. Withdrawal of Proposed Rule to List Penstemon grahamii 

(Graham’s beardtongue) as Threatened With Critical Habitat.

Notice of withdrawal, More 

abundant than believed, or 

diminished threats.

71 FR 76023–76035. 

12/19/2006 ................. 90-Day Finding on Petitions to List the Mono Basin Area Population of the Greater Sage-Grouse as Threatened or Endangered.Notice of 90-day petition finding, Not substantial.71 FR 76057–76079. 

1/9/2007 ..................... 12-Month Petition Finding and Proposed Rule To List the 

Polar Bear (Ursus maritimus) as Threatened Throughout Its 

Range; Proposed Rule.

Notice of 12-month petition 

finding, Warranted.

Proposed Listing, Threatened

72 FR 1063–1099. 

1/10/2007 ................... Endangered and Threatened Wildlife and Plants; Clarification 

of Significant Portion of the Range for the Contiguous 

United States Distinct Population Segment of the Canada 

Lynx.

Clarification of findings ............ 72 FR 1186–1189. 

1/12/2007 ................... Withdrawal of Proposed Rule To List Lepidium papilliferum 

(Slickspot Peppergrass).

Notice of withdrawal, More 

abundant than believed, or 

diminished threats.

72 FR 1621–1644. 

2/2/2007 ..................... 12-Month Finding on a Petition To List the American Eel as 

Threatened or Endangered.

Notice of 12-month petition 

finding, Not warranted.

72 FR 4967–4997. 

2/13/2007 ................... 90-Day Finding on a Petition To List the Jollyville Plateau 

Salamander as Endangered.

Notice of 90-day petition finding, Substantial.72 FR 6699–6703. 

2/13/2007 ................... 90-Day Finding on a Petition To List the San Felipe 

Gambusia as Threatened or Endangered.

Notice of 90-day petition finding, Not substantial.72 FR 6703–6707. 

2/14/2007 ................... 90-Day Finding on A Petition to List Astragalus debequaeus 

(DeBeque milkvetch) as Threatened or Endangered.

Notice 90-day petition finding, 

Not substantial.

72 FR 6998–7005. 

2/21/2007 ................... 90-Day Finding on a Petition To Reclassify the Utah Prairie 

Dog From Threatened to Endangered and Initiation of a 5- 

Year Review.

Notice of 5-year Review, Initiation.

Notice of 90-day petition finding, Not substantial.

72 FR 7843–7852. 

3/8/2007 ..................... 90-Day Finding on a Petition To List the Monongahela River 

Basin Population of the Longnose Sucker as Endangered.

Notice of 90-day petition finding, Not substantial.72 FR 10477–10480. 

3/29/2007 ................... 90-Day Finding on a Petition To List the Siskiyou Mountains 

Salamander and Scott Bar Salamander as Threatened or 

Endangered.

Notice 90-day petition finding, 

Substantial.

72 FR 14750–14759. 


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27924 Federal Register / Vol. 73, No. 94 / Wednesday, May 14, 2008 / Proposed Rules 

FY 2007 COMPLETED LISTING ACTIONS—Continued 

Publication date Title Actions FR pages 

4/24/2007 ................... Revised 12-Month Finding for Upper Missouri River Distinct 

Population Segment of Fluvial Arctic Grayling.

Notice of 12-month petition 

finding, Not warranted.

72 FR 20305–20314. 

5/2/2007 ..................... 12-Month Finding on a Petition to List the Sand Mountain 

Blue Butterfly (Euphilotes pallescens ssp. arenamontana) 

as Threatened or Endangered with Critical Habitat.

Notice of 12-month petition 

finding, Not warranted.

72 FR 24253–24263. 

5/22/2007 ................... Status of the Rio Grande Cutthroat Trout ................................ Notice of Review ..................... 72 FR 28664–28665. 

5/30/2007 ................... 90-Day Finding on a Petition To List the Mt. Charleston Blue 

Butterfly as Threatened or Endangered.

Notice of 90-day petition finding, Substantial.72 FR 29933–29941. 

6/5/2007 ..................... 12-Month Finding on a Petition To List the Wolverine as 

Threatened or Endangered.

Notice of Review ..................... 72 FR 31048–31049. 

6/6/2007 ..................... 90-Day Finding on a Petition To List the Yellow-Billed Loon 

as Threatened or Endangered.

Notice 90-day Petition Finding, 

Substantial.

72 FR 31256–31264. 

6/13/2007 ................... 12-Month Finding for a Petition To List the Colorado River 

Cutthroat Trout as Threatened or Endangered.

Notice 12-month petition finding, Not warranted.72 FR 32589–32605. 

6/25/2007 ................... 12-Month Finding on a Petition To List the Sierra Nevada 

Distinct Population Segment of the Mountain YellowLegged Frog (Rana muscosa).

Notice amended 12-month petition finding, Warranted but 

precluded.

72 FR 34657–34661. 

7/5/2007 ..................... 12-Month Finding on a Petition To List the Casey’s June Beetle (Dinacoma caseyi) as Endangered With Critical Habitat.Notice 12-month petition finding, Warranted but precluded.72 FR 36635–36646. 

8/15/2007 ................... 90-Day Finding on a Petition To List the Yellowstone National 

Park Bison Herd as Endangered.

Notice 90-day Petition Finding, 

Not substantial.

72 FR 45717–45722. 

08/16/2007 ................. 90-Day Finding on a Petition To List Astragalus anserinus 

(Goose Creek milk-vetch) as Threatened or Endangered.

Notice 90-day Petition Finding, 

Substantial.

72 FR 46023–46030. 

8/28/2007 ................... 12-Month Finding on a Petition To List the Gunnison’s Prairie 

Dog as Threatened or Endangered.

Notice of Review ..................... 72 FR 49245–49246. 

9/11/2007 ................... 90-Day Finding on a Petition To List Kenk’s Amphipod, Virginia Well Amphipod, and the Copepod Acanthocyclops 

columbiensis as Endangered.

Notice 90-day Petition Finding, 

Not substantial.

72 FR 51766–51770. 

9/18/2007 ................... 12-month Finding on a Petition To List Sclerocactus 

brevispinus (Pariette cactus) as an Endangered or Threatened Species; Taxonomic Change From Sclerocactus 

glaucus to Sclerocactus brevispinus, S. glaucus, and S. 

wetlandicus.

Notice 12-month petition finding for uplisting, Warranted 

but precluded.

72 FR 53211–53222. 

In FY 2007, we provided funds to 

work on proposed listing 

determinations for the following highpriority species: 3 southeastern aquatic 

species (Georgia pigtoe, interrupted 

rocksnail, and rough hornsnail), 2 Oahu 

plants (Doryopteris takeuchii, Melicope 

hiiakae), 31 Kauai species (Kauai 

creeper, Drosophila attigua, Astelia 

waialealae, Canavalia napaliensis, 

Chamaesyce eleanoriae, Chamaesyce 

remyi var. kauaiensis, Chamaesyce 

remyi var. remyi, Charpentiera 

densiflora, Cyanea eleeleensis, Cyanea 

kuhihewa, Cyrtandra oenobarba, 

Dubautia imbricata ssp. imbricata, 

Dubautia plantaginea ssp. magnifolia, 

Dubautia waialealae, Geranium 

kauaiense, Keysseria erici, Keysseria 

helenae, Labordia helleri, Labordia 

pumila, Lysimachia daphnoides, 

Melicope degeneri, Melicope paniculata, 

Melicope puberula, Myrsine mezii, 

Pittosporum napaliense, Platydesma 

rostrata, Pritchardia hardyi, Psychotria 

grandiflora, Psychotria hobdyi, 

Schiedea attenuata, Stenogyne kealiae), 

4 Hawaiian damselflies (Megalagrion 

nesiotes, Megalagrion leptodemas, 

Megalagrion oceanicum, Megalagrion 

pacificum), and one Hawaiian plant 

(Phyllostegia hispida (no common 

name)). In FY 2008, we are continuing 

to work on these listing proposals (we 

are now including an additional 17 

species in the Kauai species proposed 

listing determination package). In 

addition, we are continuing to work on 

several other determinations listed 

below, which we funded in FY 2007 

and are scheduled to complete in FY 

2008. 

ACTIONS FUNDED IN FY 2007 THAT HAVE YET TO BE COMPLETED

Species Action 

Actions Subject to Court Order/Settlement Agreement: 

Western sage grouse ........................................................................ 90-day petition finding (remand). 

Actions with Statutory Deadlines: 

Polar bear .......................................................................................... Final listing determination. 

Ozark chinquapin .............................................................................. 90-day petition finding. 

Tucson shovel-nosed snake ............................................................. 90-day petition finding. 

Gopher tortoise—Florida population ................................................. 90-day petition finding. 

Sacramento valley tiger beetle .......................................................... 90-day petition finding. 

Eagle lake trout ................................................................................. 90-day petition finding. 

Smooth billed ani ............................................................................... 90-day petition finding. 

Mojave ground squirrel ...................................................................... 90-day petition finding. 

Gopher Tortoise—eastern population ............................................... 90-day petition finding. 

Bay Springs salamander ................................................................... 90-day petition finding. 

Tehachapi slender salamander ......................................................... 90-day petition finding. 


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ACTIONS FUNDED IN FY 2007 THAT HAVE YET TO BE COMPLETED—Continued 

Species Action 

Evening primrose .............................................................................. 90-day petition finding. 

Northern leopard frog ........................................................................ 90-day petition finding. 

Cactus ferruginous pygmy owl .......................................................... 90-day petition finding. 

Our expeditious progress so far in FY 

2008 in the Listing Program, includes 

preparing and publishing the following: 

FY 2008 COMPLETED LISTING ACTIONS

Publication date Title Actions FR pages 

10/09/2007 ................. 90-Day Finding on a Petition To List the Black-Footed Albatross (Phoebastria nigripes) as Threatened or Endangered.Notice of 90-day Petition Finding, Substantial.72 FR 57278–57283. 

10/09/2007 ................. 90-Day Finding on a Petition To List the Giant Palouse Earthworm as Threatened or Endangered.Notice of 90-day Petition Finding, Not Substantial.72 FR 57273–57276. 

10/23/2007 ................. 90-Day Finding on a Petition To List the Mountain Whitefish 

(Prosopium williamsoni) in the Big Lost River, ID, as 

Threatened or Endangered.

Notice of 90-day Petition Finding, Not Substantial.72 FR 59983–59989. 

10/23/2007 ................. 90-Day Finding on a Petition To List the Summer-Run 

Kokanee Population in Issaquah Creek, WA, as Threatened or Endangered.

Notice of 90-day Petition Finding, Not substantial.72 FR 59979–59983. 

11/08/2007 ................. Response to Court on Significant Portion of the Range, and 

Evaluation of Distinct Population Segments, for the Queen 

Charlotte Goshawk.

Response to Court .................. 72 FR 63123–63140. 

12/13/2007 ................. 12-Month Finding on a Petition To List the Jollyville Plateau 

Salamander (Eurycea tonkawae) as Endangered With Critical Habitat.

Notice of 12-month Petition 

Finding, Warranted but Precluded.

72 FR 71039–71054. 

1/08/2008 ................... 90-Day Finding on a Petition To List the Pygmy Rabbit 

(Brachylagus idahoensis) as Threatened or Endangered.

Notice of 90-day Petition Finding, Substantial.73 FR 1312–1313. 

1/10/2008 ................... 90-Day Finding on Petition To List the Amargosa River Population of the Mojave Fringe-Toed Lizard (Uma scoparia) as 

Threatened or Endangered With Critical Habitat.

Notice of 90-day Petition Finding, Substantial.73 FR 1855–1861. 

1/24/2008 ................... 12-Month Finding on a Petition To List the Siskiyou Mountains Salamander (Plethodon stormi) and Scott Bar Salamander (Plethodon asupak) as Threatened or Endangered.Notice of 12-month Petition 

Finding, Not Warranted.

73 FR 4379–4418. 

2/05/2008 ................... 12-Month Finding on a Petition To List the Gunnison’s Prairie 

Dog as Threatened or Endangered.

Notice of 12-month Petition 

Finding, Warranted.

73 FR 6660–6684. 

2/07/2008 ................... 12-Month Finding on a Petition To List the Bonneville Cutthroat Trout (Oncorhynchus clarki utah) as Threatened or 

Endangered.

Notice of Review ..................... 73 FR 7236–7237. 

2/19/2008 ................... Listing Phyllostegia hispida (No Common Name) as Endangered Throughout Its Range.Proposed Listing, Endangered 73 FR 9078–9085. 

2/26/2008 ................... Initiation of Status Review for the Greater Sage-Grouse 

(Centrocercus urophasianus) as Threatened or Endangered.

Notice of Review ..................... 73 FR 10218–10219. 

3/11/2008 ................... 12-Month Finding on a Petition To List the North American 

Wolverine as Endangered or Threatened.

Notice of 12-month Petition 

Finding, Not Warranted.

73 FR 12929–12941. 

3/20/2008 ................... 90-Day Finding on a Petition To List the U.S. Population of 

Coaster Brook Trout (Salvelinus fontinalis) as Endangered.

Notice of 90-day Petition Finding, Substantial.73 FR 14950–14955. 

Our expeditious progress also 

includes work on listing actions, which 

we are funding in FY 2008. These 

actions are listed below. We are 

conducting work on those actions in the 

top section of the table under a deadline 

set by a court. Actions in the middle 

section of the table are being conducted 

to meet statutory timelines, that is, 

timelines required under the Act. 

Actions in the bottom section of the 

table are high priority listing actions, 

which include at least one or more 

species with an LPN of 2, available staff 

resources, and, when appropriate, 

species with a lower priority if they 

overlap geographically or have the same 

threats as the species with the high 

priority. 

ACTIONS FUNDED IN FY 2008 THAT HAVE YET TO BE COMPLETED

Species Action 

Actions Subject to Court Order/Settlement Agreement: 

Bonneville cutthroat trout .................................................................. 12-month petition finding (remand).

Mexican garter snake ........................................................................ 12-month petition finding (remand).

Actions with Statutory Deadlines: 

Polar bear .......................................................................................... Final listing determination. 


jlentini on PROD1PC65 with PROPOSALS2
27926 Federal Register / Vol. 73, No. 94 / Wednesday, May 14, 2008 / Proposed Rules 

ACTIONS FUNDED IN FY 2008 THAT HAVE YET TO BE COMPLETED—Continued 

Species Action 

Phyllostegia hispida ........................................................................... Final listing. 

Yellow-billed loon .............................................................................. 12-month petition finding. 

Black-footed albatross ....................................................................... 12-month petition finding. 

Mount Charleston blue butterfly ........................................................ 12-month petition finding. 

Goose Creek milk-vetch .................................................................... 12-month petition finding. 

Mojave fringe-toed lizard ................................................................... 12-month petition finding. 

White-tailed prairie dog ..................................................................... 12-month petition finding. 

Pygmy rabbit (rangewide) ................................................................. 12-month petition finding. 

Delta smelt (uplisting) ........................................................................ 90-day petition finding. 

Mono Basin sage grouse (vol. remand) ............................................ 90-day petition finding. 

Ashy storm petrel .............................................................................. 90-day petition finding. 

Longfin smelt—San Fran. Bay population ........................................ 90-day petition finding. 

Black-tailed prairie dog ...................................................................... 90-day petition finding. 

Lynx (include New Mexico in listing) ................................................. 90-day petition finding. 

Wyoming pocket gopher ................................................................... 90-day petition finding. 

Llanero coqui ..................................................................................... 90-day petition finding. 

Least chub ......................................................................................... 90-day petition finding. 

American pika .................................................................................... 90-day petition finding. 

Dusky tree vole ................................................................................. 90-day petition finding. 

Sacramento Mts. checkerspot butterfly ............................................. 90-day petition finding. 

Kokanee—Lake Sammamish population .......................................... 90-day petition finding. 

206 species ....................................................................................... 90-day petition finding. 

475 Southwestern species ................................................................ 90-day petition finding. 

High Priority Listing Actions: 

48 Kauai species 1 ............................................................................. Proposed listing. 

21 Kauai species ............................................................................... Proposed listing. 

11 packages of high-priority candidate species ................................ Proposed listing. 

Flatwoods salamander (taxonomic revision) ..................................... Proposed listing. 

1Funds used for this listing action were also provided in FY 2007. 

We have endeavored to make our 

listing actions as efficient and timely as 

possible, given the requirements of the 

relevant law and regulations, and 

constraints relating to workload and 

personnel. We are continually 

considering ways to streamline 

processes or achieve economies of scale, 

such as by batching related actions 

together. Given our limited budget for 

implementing section 4 of the Act, these 

actions described above collectively 

constitute expeditious progress. 

We will list the Rio Grande cutthroat 

trout as threatened or endangered when 

funding is available for discretionary 

listing actions. We intend any listing 

action for the Rio Grande cutthroat trout 

to be as accurate as possible. Therefore, 

we will continue to accept additional 

information and comments on the status 

of and threats to this subspecies from all 

concerned governmental agencies, the 

scientific community, industry, or any 

other interested party concerning this 

finding. If an emergency situation 

develops with this subspecies that 

warrants an emergency listing, we will 

act immediately to provide additional 

protection. 

References Cited 

A complete list of all references cited 

in this document is available from the 

New Mexico Ecological Services Field 

Office (see ADDRESSES section). 

Author 

The primary author of this notice is 

the staff of the Albuquerque Ecological 

Services Field Office, 2105 Osuna Road 

NE., Albuquerque, NM 87113. 

Authority: The authority for this action is 

the Endangered Species Act of 1973, as 

amended (16 U.S.C. 1531 et seq.). 

Dated: April 30, 2008. 

Kenneth Stansell, 

Director, Fish and Wildlife Service. 

[FR Doc. E8–10182 Filed 5–13–08; 8:45 am] 

BILLING CODE 4310–55–P 


jlentini on PROD1PC65 with PROPOSALS2