Endangered and Threatened Wildlife and Plants; Listing Gila Chub as Endangered With Critical Habitat, 66664-66721 [05-21498]

Agencies

• Fish and Wildlife Service
• DEPARTMENT OF THE INTERIOR

[Federal Register Volume 70, Number 211 (Wednesday, November 2, 2005)]
[Rules and Regulations]
[Pages 66664-66721]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-21498]



[[Page 66663]]

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Part IV





Department of the Interior





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Fish and Wildlife Service



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50 CFR Part 17



Endangered and Threatened Wildlife and Plants; Listing Gila Chub as 
Endangered With Critical Habitat; Final Rule

Federal Register / Vol. 70, No. 211 / Wednesday, November 2, 2005 / 
Rules and Regulations

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

RIN 1018-AG16


Endangered and Threatened Wildlife and Plants; Listing Gila Chub 
as Endangered With Critical Habitat

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), list the 
Gila chub (Gila intermedia) as endangered with critical habitat under 
the Endangered Species Act of 1973, as amended (Act). Gila chub were 
historically found throughout the Gila River basin in southern Arizona, 
southwestern New Mexico, and northeastern Sonora, Mexico. The Gila chub 
has been reduced in numbers and distribution in the majority of its 
historical range (Minckley 1973; Weedman et al. 1996). Where it is 
still present, populations are often small, fragmented, and at risk 
from known and potential threats and from random events such as 
drought, flood events, and wildfire. The primary threats to Gila chub 
include predation by and competition with nonnative organisms, 
including fish in the family Centrarchidae (Micropterus spp., Lepomis 
spp.), other fish species, bullfrogs (Rana catesbeiana), and crayfish 
(Orconectes virilis), and habitat degradation from surface water 
diversions and ground water withdrawals. Secondary threats include 
habitat alteration, destruction, and fragmentation resulting from 
numerous factors that are discussed in this final rule. The current 
status of the Gila chub is much degraded from historical levels. The 
species exists as a few, small isolated, populations. The small size of 
these populations, and their degree of fragmentation and isolation, 
cause them to be highly susceptible to threats. We believe that due to 
the current reduced status of the Gila chub and the severity of 
threats, including nonnative species predation and habitat destruction, 
the Gila chub is likely to become extinct throughout all or a 
significant portion of its range. This final rule will implement the 
Federal protection and recovery provisions of the Act for this species. 
We are also designating approximately 160.3 river miles (mi) (258.1 
kilometers (km)) of critical habitat located in Grant County, New 
Mexico, and Yavapai, Gila, Greenlee, Graham, Cochise, Santa Cruz, Pima, 
and Pinal Counties in Arizona.

DATES: This final rule is effective December 2, 2005.

ADDRESSES: Supporting documentation for this rulemaking is available 
for public inspection, by appointment, during normal business hours at 
the U.S. Fish and Wildlife Service, Arizona Ecological Services Field 
Office, 2321 West Royal Palm Road, Suite 103, Phoenix, AZ 85021-4951. 
The final rule, economic analysis, environmental assessment, and more 
detailed color maps of critical habitat are also available online at 
https://www.fws.gov/arizonaes/. GIS files of the critical habitat maps 
are also available online at https://criticalhabitat.fws.gov/.

FOR FURTHER INFORMATION CONTACT: Steven L. Spangle, Field Supervisor, 
Arizona Ecological Services Field Office (telephone, 602-242-0210; 
facsimile, 602-242-2513).

SUPPLEMENTARY INFORMATION: This final rule lists the Gila chub as 
endangered and designates critical habitat.

Designation of Critical Habitat Provides Little Additional Protection 
to Species

    In 30 years of implementing the Act, the Service has found that the 
designation of statutory critical habitat provides little additional 
protection to most listed species, while consuming significant amounts 
of available conservation resources. The Service's present system for 
designating critical habitat has evolved since its original statutory 
prescription into a process that provides little real conservation 
benefit, is driven by litigation and the courts rather than biology, 
limits our ability to fully evaluate the science involved, consumes 
enormous agency resources, and imposes huge social and economic costs. 
The Service believes that additional agency discretion would allow our 
focus to return to those actions that provide the greatest benefit to 
the species most in need of protection.

Role of Critical Habitat in Actual Practice of Administering and 
Implementing the Act

    While attention to and protection of habitat is paramount to 
successful conservation actions, we have consistently found that, in 
most circumstances, the designation of critical habitat is of little 
additional value for most listed species, yet it consumes large amounts 
of conservation resources. Sidle (1987) stated, ``Because the Act can 
protect species with and without critical habitat designation, critical 
habitat designation may be redundant to the other consultation 
requirements of section 7.'' Currently, only 470 species or 38 percent 
of the 1,253 listed species in the United States under the jurisdiction 
of the Service have designated critical habitat.
    We address the habitat needs of all 1,253 listed species through 
conservation mechanisms such as listing, section 7 consultations, the 
section 4 recovery planning process, the section 9 protective 
prohibitions of unauthorized take, section 6 funding to the States, and 
the section 10 incidental take permit process. The Service believes 
that it is these measures that may make the difference between 
extinction and survival for many species.
    We note, however, that two courts found our definition of adverse 
modification to be invalid (March 15, 2001, decision of the United 
States Court Appeals for the Fifth Circuit, Sierra Club v. U.S. Fish 
and Wildlife Service, et al., F.3d 434 and the August 6, 2004, Ninth 
Circuit judicial opinion, Gifford Pinchot Task Force, et al. v. United 
States Fish and Wildlife Service). On December 9, 2004, the Director 
issued guidance to be used in making section 7 adverse modification 
determinations.

Procedural and Resource Difficulties in Designating Critical Habitat

    We have been inundated with lawsuits for our failure to designate 
critical habitat, and we face a growing number of lawsuits challenging 
critical habitat determinations once they are made. These lawsuits have 
subjected the Service to an ever-increasing series of court orders and 
court-approved settlement agreements, compliance with which now 
consumes nearly the entire listing program budget. This leaves the 
Service with little ability to prioritize its activities to direct 
scarce listing resources to the listing program actions with the most 
biologically urgent species conservation needs.
    The consequence of the critical habitat litigation activity is that 
limited listing funds are used to defend active lawsuits, to respond to 
Notices of Intent (NOIs) to sue relative to critical habitat, and to 
comply with the growing number of adverse court orders. As a result, 
listing petition responses, the Service's own proposals to list 
critically imperiled species, and final listing determinations on 
existing proposals are all significantly delayed.
    The accelerated schedules of court-ordered designations have left 
the Service with almost no ability to provide for adequate public 
participation or to ensure a defect-free rulemaking process before 
making decisions on listing and critical habitat

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proposals due to the risks associated with noncompliance with 
judicially imposed deadlines. This in turn fosters a second round of 
litigation in which those who fear adverse impacts from critical 
habitat designations challenge those designations. The cycle of 
litigation appears endless, is very expensive, and in the final 
analysis provides little additional protection to listed species.
    The costs resulting from the designation include legal costs, the 
cost of preparation and publication of the designation, the analysis of 
the economic effects and the cost of requesting and responding to 
public comment, and in some cases the costs of compliance with the 
National Environmental Policy Act (NEPA). None of these costs result in 
any benefit to the species that is not already afforded by the 
protections of the Act enumerated earlier, and they directly reduce the 
funds available for direct and tangible conservation actions.

Background

    It is our intent to discuss only those topics directly relevant to 
this final listing and critical habitat rule. For more information on 
biology of the Gila chub, refer to the August 9, 2002, proposed rule 
(67 FR 51948). However, some of the information presented in the 
proposed rule is discussed below in this final rule, where appropriate, 
such as the summary of factors affecting the species.
    Description and taxonomy. The Gila chub is a member of the minnow 
family Cyprinidae. The Gila chub is small-finned, deep-bodied, chubby 
(chunky), and darkly colored. Adult males average about 150 millimeters 
(mm) (6 inches (in)) in total length; females can exceed 200 mm (8 in). 
Scales are coarse, thick, and broadly overlapped, and radiate out from 
the base (Minckley 1973; Weedman et al. 1996).
    Baird and Girard (1854:28) published a description of the Gila 
chub, as Gila gibbosa, based on the type specimen collected in 1851 
from the Santa Cruz River. For nomenclature reasons, the name was 
changed by Girard to Tigoma intermedia in 1856, working with specimens 
from the San Pedro River. Despite that and other name changes, the Gila 
chub has been recognized as a distinct species since the 1850s, with 
the exception of a short period in the mid-1900s when it was placed as 
a subspecies of Gila robusta (Miller 1945). For the past 30 years, Gila 
intermedia has been recognized as a full monotypic species, separate 
from the polytypic species Gila robusta, both currently accepted as 
valid species (Nelson et al. 2004). Minckley and DeMarais (2000) 
described a new species within the Gila River Basin, Gila nigra. It is 
similar to Gila intermedia in that it is another headwater-type chub, 
whereas Gila robusta is more often found in the mainstems of the major 
rivers within the Gila River Basin. Gila intermedia is the only species 
being addressed in this rule.
    Distribution and Habitat. Historically, Gila chub have been 
recorded in approximately 43 rivers, streams, and spring-fed 
tributaries throughout the Gila River basin in southwestern New Mexico, 
central and southeastern Arizona, and northern Sonora, Mexico (Miller 
and Lowe 1967; Minckley 1973; Rinne 1976; DeMarais 1986; Bestgen and 
Propst 1989). Several populations may have originally had basin-wide 
distributions (e.g., Babocomari River and Santa Cruz River).
    Gila chub commonly inhabit pools in smaller streams, springs, and 
cienegas (a desert wetland), and can survive in small artificial 
impoundments, such as man made ponds (Miller 1946; Minckley 1973; Rinne 
1975). Gila chub are highly secretive, preferring quiet, deeper waters, 
especially pools, or remaining near cover including terrestrial 
vegetation, boulders, and fallen logs (Minckley 1973).
    Riparian and aquatic communities across the southwest have been 
degraded or destroyed by human activities (Hastings 1959; Hastings and 
Turner 1965; Henderickson and Minckley 1984; Tellman et al. 1997). 
Humans have affected southwestern riparian systems over a period of 
several thousand years. Before the 1800s, indigenous people and 
missionaries used southern Arizona cienegas and riparian areas mostly 
for subsistence enterprises, including woodcutting, agriculture 
(including livestock grazing), and food and fiber harvesting.
    Historically, beaver also used riparian areas in the Gila River 
basin almost anywhere perennial water and appropriate vegetation could 
be found. The activities of beaver are believed to have helped promote 
Gila chub habitat by inhibiting erosion and downcutting of stream 
channels (Parker et al. 1985), and increasing ponded water behind their 
dams. Beaver were extirpated (i.e. lost from a particular area) from a 
majority of their range by the late 1800s and are still not abundant or 
have not recolonized areas where they have been extirpated and were 
historically common (Hoffmeister 1986). For example, beaver were 
extirpated from the Santa Cruz and San Pedro Rivers in Arizona. Loss of 
this large mammal and the dams they constructed may have contributed to 
rendering reaches of some streams and rivers unsuitable as habitat for 
the Gila chub.
    There was a significant human population increase in southern 
Arizona and northern Sonora, Mexico, in the early to mid 1800s (Tellman 
et al. 1997). New immigrants substantially increased subsistence and 
commercial livestock production and agriculture. By the late 1800s, 
many southern Arizona watersheds were in poor condition primarily due 
to uncontrolled livestock grazing, mining, hay harvesting, timber 
harvesting, and other management practices, such as fire suppression 
(Bahre 1991; Humphrey 1985; Martin 1975). The watershed degradation 
caused by these management practices led to widespread erosion and 
channel entrenchment when above-average rainfall and flooding occurred 
in the late 1800s (Bryan 1925; Martin 1975; Hastings and Turner 1980; 
Dobyns 1981; Hendrickson and Minckley 1984; Sheridan 1986; Bahre 1991; 
Webb and Betancourt 1992). These events led to long-term stream, 
cienega, and riparian habitat degradation throughout southern Arizona 
and northern Mexico. Physical evidence of cienega and other riparian 
area alterations can be found in the black organic soils of the 
drainage cut banks in places like the San Rafael Valley (Hendrickson 
and Minckley 1984), and San Pedro River (Hereford 1993). Although these 
changes took place nearly a century ago, these ecosystems have not 
fully recovered, and in some areas may never recover.
    We estimate, based on collection records, historical habitat data, 
the 1996 Arizona Game and Fish Department (AGFD) Gila chub status 
review (Weedman et al. 1996), and information in our files documenting 
currently occupied habitat (see Table 1), that the Gila chub has been 
eliminated from approximately 85 to 90 percent of its formerly occupied 
habitat. Of 47 known populations (see Table 1), 29 are considered 
occupied (i.e., Gila chub have been documented within the last 5 
years); 4 of these are newly established populations. All 29 
populations are considered small, isolated, and subject to some form of 
threat; nonnative species are present in 27 of the populations (Table 
1). Weedman (1996) categorized the status of the Gila chub populations 
into one of four categories: (1) Stable-secure-Gila chubs are common, 
data over the last 5 to 10 years show a stable reproducing population, 
no nonnative predatory or competitive species are present, no current 
or future land use threats were identified; (2) Stable-threatened-Gila 
chub are common to uncommon, potential

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threats by nonnatives exist, some habitat-altering land and water uses 
were identified, or lack of recruitment (i.e., reproduction and 
survival of young) was detected within the population; (3) Unstable-
threatened--Gila chub are rare, have limited distribution, predatory or 
competitive nonnatives are present, or the habitat is modified or 
threatened; (4) Extirpated (i.e., liminated)-Gila chub are no longer 
found within a particular river system. These four categories are 
reflected in the following discussion of the current status of Gila 
chub populations beginning with the next paragraph, and are summarized 
for each of the currently known occupied populations and critical 
habitat areas in Table 1; threat information is also summarized for 
each population in Table 1. Of the 29 currently occupied populations, 
we estimate that 10 can be considered stable-threatened and 19 are 
considered unstable-threatened; none are considered stable-secure.

Table 1.--Gila Chub Locations (Major Drainages in Parentheses) Including Status Classification [Based on Weedman
  et al.1996; S=stable, U=unstable, T=threatened, E=Extirpated (See Distribution and Habitat Section)], Threats
(From Service Files), Last Year of Documented Occupancy, and Source of Occupancy Information. No Information Was
                           Available for Current Status and Threats on the Blue River
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                                                                                  Last year
       Gila Chub Locations         Status  classification         Threats         occupancy         Source
                                                                                  confirmed
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                                             Critical Habitat Areas
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Area 1: Upper Gila River
    Turkey Creek, NM (Gila        UT                        Fire, grazing,              2005  P.C. Marsh, ASU in
     River).                                                 nonnative species.                litt. 2005.
    Eagle/East Eagle Creek (Gila  UT                        Fire, grazing,              2005  Marsh 2005.
     River).                                                 nonnative speices.
    Harden Cienega Creek (San     ST                        Fire, grazing,              2005  McKell 2005.
     Francisco River).                                       nonnative species.
    Dix Creek (San Francisco      ST                        Fire, grazing.....          2005  McKell 2005.
     River).
Area 2: Middle Gila River Area
    Mineral Creek/Devil's Canyon  UT                        Fire, grazing,              2000  Weedman et al.
     (Gila River).                                           nonnative species.                2000.
Area 3: Babocomari River
    O'Donnell Creek (Babocomari   UT                        Fire, grazing,              2004  Dean Foster, AGFD,
     River).                                                 nonnative species.                in litt. 2005.
    Turkey Creek (Babocomari      E                         Fire, grazing,              1991  Weedman et al.
     River).                                                 nonnative species.                1996.
Area 4: Lower San Pedro River
    Bass Canyon (San Pedro        ST                        Fire..............          2003  Bob Rogers, The
     River).                                                                                   Nature
                                                                                               Conservancy
                                                                                               (TNC), in litt.
                                                                                               2005.
    Hot Springs Canyon (San       ST                        Fire..............          2004  Bob Rogers, TNC,
     Pedro River).                                                                             in litt. 2005.
    Redfield Canyon (San Pedro    ST                        Fire, grazing,              2001  Bob Rogers, TNC,
     River).                                                 nonnative species.                in litt. 2005.
Area 5: Lower Santa Cruz
    Cienega Creek (lower, Santa   UT                        Fire, nonnative             2005  Doug Duncan, in
     Cruz River).                                            species, water                    litt.
                                                             use.
    Cienega Creek (upper, Santa   ST                        Fire, nonnative             2005  Dean Foster, AGFD,
     Cruz River).                                            species.                          in litt. 2005.
    Mattie Canyon (Santa Cruz     UT                        Fire, grazing,              2005  Jeff Simms, BLM,
     River).                                                 nonnative species.                in litt. 2005.
    Empire Gulch (Santa Cruz      UT                        Fire, grazing,....          2001  (67 FR 51948).
     River).
    Sabino Canyon (Santa Cruz     UT                        Fire, nonnative             2005  Service files.
     River).                                                 species.
Area 6: Verde River
    Walker Creek (Verde River)..  ST                        Fire, grazing,              2005  Service files.
                                                             nonnative species.
    Red Tank Draw (Verder River)  UT                        Fire, grazing,              2005  Service data.
                                                             nonnative species.
    Spring Creek (Verde River)..  ST                        Fire, grazing,              2005  Service files.
                                                             nonnative
                                                             species,
                                                             residential
                                                             development,
                                                             water use.
    Williamson Valley Wash        UT                        Nonnative species           2003  Bill Leibfried, in
     (Verde River).                                          residential                       litt. 2005.
                                                             development,
                                                             water use.
Area 7: Agua Fria
    Little Sycamore Creek (Agua   ST                        Fire, grazing,              2003  A .Silas, FS,
     Fria River).                                            nonnative species.                pers. comm. 2005.
    Sycamore Creek (Agua Fria     UT                        Fire, grazing,              2005  Hedwall et al.
     River).                                                 nonnative species.                2005.
    Indian Creek (Agua Fria       UT                        Fire, grazing,              2005  J. Voeltz, AGFD in
     River).                                                 nonnative species.                litt. 2005.
    Silver Creek (Agua Fria       UT                        Fire, grazing,              2005  D. Weedman, AGFD
     River).                                                 nonnative species.                in litt. 2005.
    Larry Creek (Agua Fria        ST                        Fire, grazing.....          2003  Service files.
     River).

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    Lousy Canyon (Agua Fria       ST                        Fire, grazing.....          2005  Service files.
     River).
---------------------------------
                                     Locations Not in Critical Habitat Areas
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Bonita Creek (Gila River).......  ST                        Fire, grazing,              2005  Heidi Blasius,
                                                             recreatoin,                       BLM, pers. com.
                                                             roads, water use,                 2005.
                                                             nonnative species.
Blue River (Gila River).........  No information            No information....          2000  Weedman et al.
                                                                                               (1996) Minckley
                                                                                               and DeMarais
                                                                                               (2000).
Romero Canyon (Santa Cruz River)  UT Introduced             Fire, nonnative             2005  AGFD 2005a.
                                                             species.
Bear Canyon (Santa Cruz River)..  UT Introduced             Fire, nonnative             2005  AGFD 2005a.
                                                             species.
Sheehy Spring (Santa Cruz River)  UT                        Fire, nonnative             2005  D. Foster, AGFD,
                                                             species.                          in litt. 2005.
Babocomari River at T4 Spring     UT                        Fire, nonnative             2005  D. Foster, AGFD,
 (San Pedro River).                                          psecies.                          in litt. 2005.
Double R Canyon (San Pedro        UT                        Fire..............          2003  Bob Rogers, TNC,
 River).                                                                                       in litt. 2005.
Wildcat Canyon (San Pedro River)  UT                        Fire..............          2003  Bob Rogers, TNC,
                                                                                               in litt. 2005.
Post Canyon (Babocomari River)..  E                         Fire, grazing,              1989  Weedman et al.
                                                             nonnative species.                1996.
Arroyo La Cieneguita, Mexico      E                         Fire, grazing,              1990  Varela-Romero et
 (San Pedro River).                                          nonnative species.                al. 1992.
Los Fresnos River, Mexico (San    E                         Fire, grazing,              1990  Varela-Romero et
 Pedro River).                                               nonnaative                        al. 1992.
                                                             species.
---------------------------------
                              Localities Where the Gila chub is Believed Extirpated
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Aqua Fria River.................  ........................  ..................          1966  Weedman et al.
                                                                                               1996.
Big Chino Wash (Verde River)....  ........................  ..................          1950  Weedman et al.
                                                                                               1996.
Birmingham Pond (Santa Cruz       ........................  ..................          1943  Weedman et al.
 River).                                                                                       1996.
Cave Creek/Seven Springs Wash     ........................  ..................          1978  Weedman et al.
 (Salt River).                                                                                 1996.
Fish Creek (Salt River).........  ........................  ..................          1965  Weedman et al.
                                                                                               1996.
Monkey Spring (Santa Cruz River)  ........................  ..................          1968  Weedman et al.
                                                                                               1996.
Queen Creek (Gila River)........  ........................  ..................          1938  Weedman et al.
                                                                                               1996.
Arnett Creek (Gila River).......  ........................  ..................          1945  Weedman et al.
                                                                                               1996.
San Pedro.......................  ........................  ..................          1912  Weedman et al.
                                                                                               1996.
San Simon River.................  ........................  ..................          1939  Weedman et al.
                                                                                               1996.
Santa Cruz River................  ........................  ..................          1977  Weedman et al.
                                                                                               1996.
Haunted Canyon (Salt River).....  ........................  ..................          1959  University of
                                                                                               Michigan Museum
                                                                                               of Zoology [UMMZ]
                                                                                               collection record
                                                                                               176179.
----------------------------------------------------------------------------------------------------------------

    In New Mexico, Gila chub likely inhabited numerous tributaries of 
the Gila River basin historically. These include Apache Creek, Catron 
County; Duck Creek, Grant County; San Francisco River, Catron County; 
San Simon Cienega, Hidalgo County; and Turkey Creek, Grant County 
(Rinne 1969, 1976; Hubbard et al. 1979; Bestgen and Propst 1989; 
Sublette et al. 1990; Propst 1999). All of these populations are now 
extirpated (Bestgen and Propst 1989), with the exception of Turkey 
Creek (Propst 1999; P. C. Marsh, Arizona State University [ASU] in 
litt. 2005). We consider Turkey Creek unstable-threatened because the 
population was recently decimated by wildfire, and nonnative species 
are present (B. Thompson, New Mexico Game and Fish Department [NMGF], 
in litt. 2005).
    In Arizona, Gila chub are known to have occupied portions of the 
Salt, Verde, Santa Cruz, San Pedro, San Carlos, San Simon, San 
Francisco, and Agua Fria drainages in addition to smaller tributaries 
of the mainstem Gila River. Small remnant populations remain in most of 
these drainages with the exception of the Salt and San Simon Rivers, 
where all known populations have been extirpated (Weedman et al. 1996; 
Propst 1999).
    In the Verde River basin, Walker and Spring creeks, located in 
Yavapai County, chub populations are considered stable-threatened 
populations; the population in Williamson Valley Wash, also in Yavapai 
County, is considered unstable-threatened. The Santa Cruz River has 
five tributaries with extant populations of Gila chub, which include 
Bear, Romero, and Sabino canyons (Pima County) that were established 
this year (these are considered unstable-threatened); Sheehy Spring 
(Santa Cruz

[[Page 66668]]

County) has an unstable-threatened population (Arizona Game and Fish 
Department [AGFD] 2005a); and Cienega Creek (Pima and Santa Cruz 
Counties) has a stable-threatened population of Gila chub. The San 
Pedro River Basin has four extant, stable-threatened populations: Bass, 
Hot Springs, and Redfield canyons (Graham and Pima Counties), and 
O'Donnell Canyon (Santa Cruz County; B. Rogers, The Nature Conservancy 
(TNC), in litt. 2005; D. Foster, AGFD in litt. 2005). There is an 
unstable-threatened population of Gila chub at T4 Spring in the 
Babocomari River (Santa Cruz and Cochise Counties; D. Duncan, U.S. Fish 
and Wildlife Service in litt. 2003). The San Carlos River and the Blue 
River are tributaries to the Gila River (Gila and Graham Counties) on 
San Carlos Apache tribal lands. We are aware that Gila chub are extant 
on the Reservation, but we do not have information to document the 
status of Gila chub in those drainages.
    The San Francisco River has two tributaries with extant 
populations, Dix Creek in Greenlee County, Arizona, and Harden Cienega 
in Greenlee County, Arizona, and Grant County, New Mexico. Based on 
surveys in June 2005, these populations appear to be doing well and can 
be characterized as stable-threatened (McKell 2005). The Agua Fria 
River has two tributaries with stable-threatened populations, Silver 
and Sycamore creeks (Yavapai County), as well as two unstable-
threatened populations in Little Sycamore Creek and Indian Creek 
(Yavapai County) (Weedman et al. 1996; A. Silas, U.S. Forest Service 
[FS], pers. comm. 2005). In addition, there are two introduced 
populations in the Agua Fria River, Larry Creek and Lousy Canyon 
(Yavapai County); both appear to be stable-threatened based on recent 
surveys. Populations of all of the Aqua Fria populations may have been 
affected by wildfires that occurred in summer 2005 (Knowles et al. 
2005). Two tributaries of the Gila River in Arizona have extant 
populations of Gila chub: Eagle Creek (Graham and Greenlee Counties) 
has an unstable-threatened population, and Bonita Creek (Graham County) 
has a stable-threatened population (Weedman et al. 1996; Marsh 2005; H. 
Blasius, Bureau of Land Management (BLM), in litt. 2005).
    In Mexico, Gila chub historically occupied significant portions of 
the Santa Cruz and San Pedro river basins. The current known 
distribution of Gila chub in Mexico has been reduced to two small 
spring areas, Cienega los Fresnos and Cienega la Cienegita, adjacent to 
the Arroyo los Fresnos (tributary of the San Pedro River), within 1.2 
mi (2 km) of the Arizona-Mexico border (Varela-Romero et al. 1992). No 
Gila chub remain in the Mexican portion of the Santa Cruz River basin 
(Weedman et al. 1996).
    Establishment of new populations of Gila chub has been attempted in 
six sites in Arizona; five sites remain extant. Lousy Canyon and Larry 
Creek (Yavapai County) are tributaries to the Agua Fria River that were 
stocked with 200 Gila chub from Silver Creek on July 6, 1995. Recent 
surveys indicate that these populations are doing well, with good 
recruitment. Gardner Canyon (Cochise County) was stocked with 150 Gila 
chub from Turkey Creek (Santa Cruz County) in July 1988. Follow up 
surveys in May 1995 did not detect Gila chub in Gardner Canyon; 2005 
surveys also did not detect the species (AGFD 2005a). In May 2005, Gila 
chub that were salvaged from Sabino Canyon during the Aspen fire in 
2003 were returned to Sabino Canyon and introduced into two other 
streams in the Santa Catalina Mountains: approximately 350 Gila chub 
were stocked into Sabino Canyon, 120 into Romero Canyon, and 85 into 
Bear Canyon (all in Pima County; AGFD 2005a). The status information 
presented above is summarized in Table 1.

Previous Federal Actions

    For more information on previous Federal actions concerning the 
Gila chub, refer to the proposed rule to list the Gila chub as 
endangered with critical habitat published in the Federal Register on 
August 9, 2002 (67 FR 51948). On May 18, 2004, the Center for 
Biological Diversity filed a complaint against the Department of the 
Interior because the Service had not published a final rule for the 
Gila chub in a timely manner. On August 3, 2004, the United States 
District Court of Arizona ordered that we, via a stipulated settlement 
agreement, submit for publication to the Federal Register, a final rule 
by October 21, 2005 (Center for Biological Diversity v. Norton, No. CV 
04-2061 TUC CRP). On August 31, 2005 (70 FR 51732), we published a 
notice to reopen the public comment period on the August 9, 2002, 
proposed rule for 30 days and announce the availability of the draft 
economic analysis, draft environmental assessment, and hearing dates 
for the proposed listing and critical habitat designation for the Gila 
chub.

Summary of Comments and Recommendations

    We requested written comments from the public on the proposed 
listing and designation of critical habitat for the Gila chub on August 
9, 2002 (67 FR 51948), and in our notice to reopen the comment period 
(August 31, 2005; 70 FR 51732). We also contacted appropriate Federal, 
State, and local agencies; scientific organizations; and other 
interested parties and invited them to comment on the proposed rule. We 
also requested information pertaining to any actions that affect the 
Gila chub, its current status, distribution, and threats, and the 
status of nonnative fishes in the historical range of Gila chub. We 
requested this information in order to make a final listing 
determination based on the best available scientific and commercial 
data. We published newspaper notices inviting public comment and 
announcing the public hearings in the following newspapers in Arizona 
and New Mexico: Albuquerque Tribune, Albuquerque Journal, the Arizona 
Republic, Daily Courier (Prescott), Santa Fe New Mexican, Silver City 
Daily Press, Sierra Vista Herald, Tucson Citizen, Arizona Daily Star 
(Tucson), the Bulletin (Sonoita), Eastern Arizona Courier (Safford), 
the Verde Independent, Camp Verde Bugle, and the Copper Country News 
(Globe). On September 13, 14, and 15, 2005, we held public hearings in 
Silver City, New Mexico; Safford, Arizona; and Camp Verde, Arizona, 
respectively, to solicit comments on the proposed rule.
    During the first comment period that opened on August 9, 2002, and 
closed on October 9, 2002, we received 97 pieces of correspondence (e-
mails, letters, and faxes). Of these, we received 5 comments from 
Federal agencies, 1 from a State representative, and 91 from 
organizations or individuals. Thirty-one of the comments were requests 
for public hearings of which 26 concerned Willow Creek. During the 
second comment period that opened on August 31, 2005, and closed on 
September 30, 2005, we received 29 comments. Of these latter comments, 
6 were from peer reviewers, 1 from another nation, 2 from Federal 
agencies, 3 from State agencies, and 17 from organizations or 
individuals.
    Of the written comments received during the first comment period, 
40 supported, 17 were opposed, and 44 included comments or information 
but did not express support for or opposition to the proposed listing 
and critical habitat designation. Of the written comments received 
during the second comment period, 18 supported, 0 were opposed, and 10 
included comments or information but did not express support for or 
opposition to the proposed listing and critical habitat designation. We 
received a number of comments concerning Willow Creek in

[[Page 66669]]

Catron County, New Mexico. Willow Creek is neither occupied nor 
historical habitat for Gila chub and was not part of the proposed 
critical habitat determination. In addition, there are no plans to 
establish a population of Gila chub in Willow Creek. Therefore, these 
comments will not be addressed further. All substantive information 
written and verbal, provided during the public comment periods, either 
has been incorporated directly into this final determination or is 
addressed below. We also wish to recognize that the Mexican Federal 
Government commented on the proposed rule; the Director de Conservacion 
de la Vida Silvestre, Secretario de Medio Ambiente y Recursos 
Naturales, did not provide specific comment, but generally supported 
the listing. Similar comments are grouped together by issue.

Peer Review

    In accordance with our policy published on July 1, 1994 (59 FR 
34270), we solicited expert opinions from eight knowledgeable 
individuals with scientific expertise that included familiarity with 
the species, the geographic region in which the species occurs, and 
conservation biology principles, and that represented Federal agencies, 
State agencies, university researchers, and private consultants. We 
received responses from six of the peer reviewers; two of these were 
from State biologists via the Arizona and New Mexico Game and Fish 
Departments and were not specifically identified as peer review, and 
are addressed below as ``State Comments.'' Five of the six peer 
reviewers, including both State wildlife agencies, concurred with our 
methods and conclusions, supported our determination that the species 
is endangered, and provided additional information, clarifications, and 
suggestions to improve the final critical habitat rule. A sixth peer 
reviewer suggested that we may have overestimated the extinction threat 
to Gila chub, and recommended that we consider listing the species as 
threatened. Peer reviewer comments are addressed in the following 
summary and incorporated into the final rule as appropriate.

Peer Reviewer Comments

    (1) Comment: Limiting critical habitat to only those areas that are 
occupied will not achieve the purposes of the Act and satisfy the 
definition of critical habitat, particularly when the proposed rule 
states that stabilization of the Gila chub at its present population 
level and distribution will not achieve conservation. Critical habitat 
should be expanded to include unoccupied areas that provide 
connectivity between populations to allow gene flow and repopulation of 
formerly occupied suitable habitat.
    Our Response: Section 3(5)(A) of the Act defines critical habitat 
as the specific areas within the geographical area occupied by the 
species on which are found those physical and biological features (I) 
essential to the conservation of the species and (II) which may require 
special management considerations or protection. In our critical 
habitat designation, we use the provisions outlined in section 3(5)(A) 
of the Act to evaluate those specific areas that contain the features 
that are essential to the conservation of the species and that may 
require special management considerations or protections. Critical 
habitat designation for the Gila chub includes many areas of known 
occupancy that have features that are essential to the conservation of 
the species, as well as one unoccupied area that we consider essential 
to the conservation of the Gila chub because of its connection with or 
proximity to known occupied areas. This is discussed in further detail 
in the ``Justification for Including Unoccupied Areas'' section below. 
We believe we have considered and applied to this designation the best 
available scientific information regarding the Gila chub. Thus, while 
not all areas important for potential Gila chub recovery were proposed 
as critical habitat, we believe this designation defines those areas 
that are essential. We also acknowledge that critical habitat can 
contribute to the overall recovery strategy for a listed species, but 
does not, by itself, achieve recovery. We encourage Federal and State 
agencies, Tribal governments, municipalities, private groups, and 
landowners to work with us as we develop a recovery plan for the Gila 
chub and to continue to work towards establishing additional 
populations and aid in the recovery of the species. As discussed in 
this rule, even if an area is not designated as critical habitat, it 
does not mean that area is not important for Gila chub recovery.
    (2) Comment: Listing the Gila chub may not be supported because the 
Service's assertion that the Gila chub has lost 85-90 percent of its 
habitat is based on the assumptions that the Gila chub was distributed 
throughout contiguous river reaches containing suitable habitat, that 
status information indicates that 60 percent of the currently known 
populations are stable or secure, and that data necessary to determine 
status (i.e. quantitative abundance estimates and accurate historical 
records) for Gila chub are lacking. The Service should consider that 
the species may better meet the definition of threatened.
    Our Response: We disagree and refer to the ``Background'' section 
above for detailed information on our estimate of habitat loss. We also 
note that in some cases, entire rivers that were habitat for Gila chub 
have largely disappeared or been so degraded they no longer support the 
species (e.g., the Santa Cruz and San Pedro Rivers; Weedman et al. 
1996; Tellman et al. 1997). The Gila chub has been eliminated from 12 
streams (see Table 1). Sabino Creek would have been lost due to 
wildfire had it not been salvaged by Service, AGFD, and the FS in 2003, 
and three additional populations were salvaged this year in response to 
wildfires; the status of these populations post-fire has not yet been 
ascertained. Only two populations are free from nonnative species, and 
all populations are small and isolated and thus at risk (Fagan et al. 
2002). The past decline, current threats, and status of Gila chub are 
well documented and reflected in this final rule.
    (3) Comment: Conservation actions since the proposed rule was 
published have been insufficient to improve the status of the species 
to the point it is no longer endangered or threatened, indicating that 
existing regulatory protections, including concerted efforts by the 
States to conserve the Gila chub, are not sufficient to prevent its 
extinction.
    Our Response: We agree that the status of the Gila chub has not 
improved since the publication of the proposed rule, despite efforts to 
conserve the species. However, we value the cooperative conservation 
partnerships that have been formed between Federal and State agencies, 
municipalities, and the public to work to improve the status of the 
Gila chub, and we recognize that the decline of the species occurred 
over a number of years and that it would be difficult to address all 
threats facing the species in the short amount of time since the 
proposed listing. We will continue to pursue such partnerships and 
conservation projects involving the Gila chub following this final rule 
and as we develop a recovery plan. In ``Inadequacy of Existing 
Regulatory Mechanisms'' (Factor D) below, we discuss existing 
regulatory mechanisms as they relate to the protection being afforded 
to the Gila chub.
    (4) Comment: Listing the Gila chub will alienate stakeholders that 
otherwise would have been amenable to conserving the species because 
the Act is so restrictive. Conservation agreements between the various

[[Page 66670]]

stakeholders would be a more effective method to conserve the Gila 
chub.
    Our Response: As discussed above, we agree that cooperative 
conservation utilizing partnerships between Federal and State agencies, 
municipalities, and the public is a good approach to conservation, and 
we have pursued such partnerships on numerous projects involving the 
Gila chub and will continue these partnerships after this final rule to 
list the chub as endangered is effective. However, we are required to 
list a species as endangered if we determine that the species is likely 
to become extinct throughout all or a significant portion of its range. 
After evaluating the current status of the species and threats to 
extant populations in the five factor analysis below, we have 
determined that the Gila chub is endangered.
    (5) Comment: The Service needs to provide a more explicit 
explanation of the primary constituent elements (PCEs) that exist in 
each segment of critical habitat.
    Our Response: All of the areas that we have designated as critical 
habitat have one or more of the PCEs. We have provided in our area 
descriptions (below), those primary constituent elements that are 
present in each of the critical habitat areas.
    (6) Comment: The confusing taxonomic history of the Gila chub has 
led to errors in the Service's estimation of its current and former 
range. The Service has thus likely overstated the species' historic 
range, inflated the degree to which the species has declined, and thus 
exaggerated its need for listing.
    Our Response: Gila intermedia is part of the Gila robusta species 
complex that includes six other taxa: G.cypha, G. elegans, G. nigra, G. 
robusta, G. r. jordani, and Gila seminuda (Gerber et al. 2001); all of 
these species have experienced declines and face similar threats. The 
evolution of the species in the complex is novel in some respects, and 
research on the complex has led to insight about the various ways in 
which speciation occurs (Gerber et al. 2001; Minckley and DeMarais 
2000). However, we have found that the taxonomy of the Gila chub has 
come to be well understood (Minckley and DeMarais 2000), and that Gila 
chub as a species is valid and qualifies as a taxon that may be listed 
under the Act (50 CFR 424.02(k)). As Minckley and DeMarais (2000) 
illustrate, the three forms of Gila represent distinct species that 
have consistently and repeatedly been identified in the same streams; 
based on this work, we are confident of our evaluation of the status of 
the species, its formerly occupied range, and its current distribution. 
Our consideration of Gila chub with regard to its status and 
consideration for listing has evolved as more information has become 
available regarding its biology, status, and threats, which is 
reflected in this final rule. We note that the status of the Gila chub 
has appreciably declined over the last 25 years, and we have 
information to document new threats facing the species, such as 
frequent catastrophic fires, also noted by both AGFD and NMGF in their 
comments on the proposed rule (B. Broschied, AGFD, in litt. 2005; B. 
Thompson, NMGF, in litt. 2005).
    (7) Comment: Since the Gila chub resembles closely related taxa 
(i.e., the roundtail and headwater chubs), its listing will cause 
substantial enforcement problems for enforcing ``take.'' This could 
potentially cause significant economic impact to stakeholders, 
especially if the Service lists these other forms under similarity of 
appearance as defined in Section 4(e) of the Act. This problem is 
confounded because these forms also apparently interbreed.
    Our Response: Although the Gila, roundtail, and headwater chubs are 
closely related and appear similar, we find no need for listing the 
latter two under similarity of appearance for several reasons. The 
primary reason is that these species occur in geographically separate 
places. As Minckley and DeMarais (2001) stated, ``persistent parapatry 
[geographic separation] of morphologically distinguishable robusta, 
intermedia, and nigra [roundtail, Gila, and headwater chubs], has been 
documented, confirmed, and reconfirmed by collections since the 1920s * 
* * In no instance was any two of the three caught at the same 
locality.'' Because roundtail chub is considered a sport fish in 
Arizona, we have considered unintended harvest of Gila chub as a 
potential threat to the species under our five factor analysis below. 
We do not believe this represents a significant threat to Gila chub 
because AGFD prohibits the collection of Gila chub without a permit, 
and allows possession of only 1 roundtail chub over 13 inches in total 
length (AGFD 2005c). Gila chub do not achieve this size, thus the 
existing AGFD regulations adequately protect Gila chub from this 
threat. Although the headwater chub is thought to be of hybrid origin 
from hybridization of related chubs in geologically recent times 
(Minckley and DeMarais 2001), we know of no evidence that the current 
three forms hybridize in nature.
    (8) Comment: Listing the Gila chub may not be the most effective 
method for removing threats; the States have primary authority over 
regulating all non-listed aquatic organisms, including nonnative 
species, a primary threat to the Gila chub.
    Our Response: We realize that there are existing authorities which 
could and often do provide protection for the Gila chub, and the States 
have been and will continue to be a key partner in the conservation of 
the Gila chub. However, we have determined that the protection afforded 
by existing regulatory mechanisms is insufficient to preclude the 
listing of the Gila chub (see Inadequacy of Existing Regulatory 
Mechanisms (Factor D) below).

General Comments Issue 1: Biological Concerns

    (9) Comment: The lateral extent of critical habitat should be 
expanded to include the 100-year floodplain or entire watersheds.
    Our Response: Critical habitat includes the stream channels within 
the identified stream reaches defined by upstream and downstream 
boundaries, as well as areas within these reaches potentially inundated 
during high flow events. Critical habitat also includes the area of 
bankfull width plus 300-feet on either side of the banks. The bankfull 
width is the width of the stream or river at bankfull discharge, i.e., 
the flow at which water begins to leave the channel and move into the 
floodplain (Rosgen 1996). Bankfull discharge, while a function of the 
size of the stream, is a fairly consistent feature related to the 
formation, maintenance, and dimensions of the stream channel (Rosgen 
1996). This 300-foot width defines the lateral extent of those areas 
that contain the features that are essential to the species' 
conservation.
    We determined the 300-foot lateral extent for several reasons. 
First, the implementing regulations of the Act require that critical 
habitat be defined by reference points and lines as found on standard 
topographic maps of the area (50 CFR 424.12). Although we considered 
using the 100-year floodplain, as defined by the Federal Emergency 
Management Agency (FEMA), we found that it was not included on standard 
topographic maps, and the information was not readily available from 
FEMA or from the U.S. Army Corps of Engineers for the areas designating 
critical habitat. We suspect this is related to the remoteness of 
various stream reaches. Therefore, we selected the 300-foot lateral 
extent, rather than some other delineation, for three biological 
reasons: (1) The

[[Page 66671]]

biological integrity and natural dynamics of the river system are 
maintained within this area (i.e., the floodplain and its riparian 
vegetation provide space for natural flooding patterns and latitude for 
necessary natural channel adjustments to maintain appropriate channel 
morphology and geometry, store water for slow release to maintain base 
flows, provide protected side channels and other protected areas, and 
allow the river to meander within its main channel in response to large 
flow events); (2) conservation of the adjacent riparian area also helps 
provide essential nutrient recharge and protection from sediment and 
pollutants; and (3) vegetated lateral zones are widely recognized as 
providing a variety of aquatic habitat functions and values (e.g., 
aquatic habitat for fish and other aquatic organisms, moderation of 
water temperature changes, and detritus for aquatic food webs) and help 
improve or maintain local water quality (see U.S. Army Corps of 
Engineers' final notice concerning Issuance and Modification of 
Nationwide Permits, March 9, 2000, 65 FR 12818-12899). Please see the 
section entitled ``Critical Habitat'' below for more information.
    (10) Comment: Using a 300-foot distance from bankfull width as a 
lateral extent of critical habitat captures areas in some segments that 
are outside the floodplain, and thus should not be considered essential 
to Gila chub.
    Our Response: In the proposed rule, critical habitat segments were 
proposed to include ``the stream channels within the identified stream 
reaches and areas within these reaches potentially inundated during 
high flow events.'' Our intent is to capture areas that correspond to 
the 100-year floodplain. We determined that the 300 foot distance from 
the bankfull width was the best method to define this area. As 
described elsewhere in this rule, we find that all the critical habitat 
areas contain sufficient PCEs to provide for one or more of the life 
history functions of the Gila chub. We have also refined the 
designation, based upon comments received, to define more precisely the 
boundaries of the critical habitat designation.
    (11) Comment: Critical habitat should be expanded to include 
additional occupied habitat in Indian Creek, Little Sycamore Creek, 
Sycamore Creek, and Bonita Creek; critical habitat in Spring Creek 
should be contracted to exclude unsuitable habitat at both ends.
    Our Response: We have slightly adjusted a number of the critical 
habitat stream segments, both to correct errors and to better capture 
areas of occupied habitat that contain the features that are essential 
to the conservation of the species. Also, Bonita Creek, Blue River, and 
portions of Spring and Cienega creeks have been excluded from the 
designation pursuant to 4(b)(2) of the Act.
    (12) Comment: Birds or other native predators may be a threat, as 
opposed to anthropogenic (man made) causes.
    Our Response: Although a number of piscivorous birds occur 
throughout the range of the Gila chub, such as the great blue heron 
(Ardea herodias) and belted kingfisher (Ceryle alcyon), we found no 
information to support bird predation as a significant threat to Gila 
chub. Bird predation can, however, be a significant concern at fish 
hatcheries (U.S.D.A. Animal Plant Health Inspection Service 1997), 
where fish are concentrated in ponds or raceways, and thus may be a 
consideration in recovery actions for Gila chub that require use of 
such facilities.
    (13) Comment: Gila chub is a member of a species assemblage in the 
genus Gila along with six other species, all of which warrant listing 
as endangered under the Act.
    Our Response: We are aware that Gila intermedia is part of a 
species complex. We also note that for taxonomically complex groups 
that warrant conservation, species-based approaches may be inadequate, 
and new approaches that conserve evolutionary processes that generate 
taxonomic biodiversity may be a preferable conservation strategy (Ennos 
et al. 2005). However, all of the fishes of the Gila robusta species 
complex are currently listed as endangered under the Act, with the 
exception of G. nigra and G. robusta (U.S. Fish and Wildlife Service 
2005a). With regard to these two unlisted species, we published a 
positive 90-day finding on a petition to list a distinct population 
segment of G. robusta in the lower Colorado River basin, and to list G. 
nigra throughout its range, on July 12, 2005 (70 FR 39981). G. robusta 
is also part of a multistate conservation agreement that addresses 
conservation of the species throughout its range (Utah Department of 
Natural Resources 2004).
    (14) Comment: The threats to Gila chub are largely unsubstantiated; 
much of the literature is overly general in nature and is not site- or 
species-specific, and thus the listing of Gila chub is not warranted.
    Our Response: The threats to Gila chub are well documented (see 
``Summary of Factors Affecting the Species'' section below). The 
current status of the species is that it has been eliminated from 
approximately 85 to 90 percent of its formerly occupied habitat as a 
direct result of these threats (Weedman et al. 1996), and it currently 
exists as a collection of very small, isolated, and highly fragmented 
populations (Weedman et al. 1996; Service files presented in Table 1). 
In some cases, such as Sheehy Spring, a population exists in a habitat 
not much larger than a common backyard swimming pool. Because of this, 
the species is much more susceptible to threats such as predation and 
competition from nonnative species (Dudley and Matter 2000), habitat 
destruction from various land use practices (Weedman et al. 1996), 
stochastic events such as wildfire (Knowles et al. 2005), and an 
increased risk of extinction due the high degree of fragmentation of 
the remaining populations (Fagan et al. 2000). Although some of our 
citations are not specific to these species or the geographic area, the 
citations offer evidence that certain threats exist because similar 
examples have been documented elsewhere, and based on biological 
principles and effects observed in other fishes, we can draw reasonable 
conclusions about what we would expect to happen to this species were 
it not listed.
    (15) Comment: The critical habitat designation is overly broad 
because it includes areas that are unoccupied and that have not been 
shown to be essential to the conservation of the species. Eagle, 
Turkey, Post, and Little Sycamore creeks are not occupied and so should 
not be included in critical habitat without a justification that these 
areas are essential to the conservation of the species. Critical 
habitat areas are not recovery areas, and critical habitat does not, in 
itself, lead to recovery of a species.
    Our Response: Gila chub were documented in Eagle Creek in 2005 
(Marsh 2005), and in Little Sycamore Creek in 2005 (A. Silas, FS, pers. 
comm. 2005). In this final rule, all of the critical habitat areas have 
been documented as occupied by Gila chub within the last 5 years, with 
the exception of one: Turkey Creek (AZ). Gila chub were last detected 
in Turkey Creek in 1991. This tributary is connected to O'Donnell 
Creek, which was documented as occupied in 2004 (D. Foster, AGFD, in 
litt. 2005), and while we believe this stream can be recolonized 
naturally by Gila chub in high water years, we are also working with 
the AGFD to reestablish Gila chub in this stream. Turkey Creek contains 
sufficient PCEs to provide for one or more of the life history 
functions of the Gila chub. We provide further information on our 
determination that this area is essential to the conservation

[[Page 66672]]

of the species, pursuant to the definition in section 3(5)(A)(ii) of 
the Act, in the ``Justification for Including Unoccupied Areas'' 
section below. We are not including Post Canyon in the final 
designation (see the ``Summary of Changes'' section below).
    (16) Comment: The term ``banks'' needs to be defined in the 
description of critical habitat.
    Our Response: As mentioned in response to comment 9 and 10 above, 
and discussed in the ``Critical Habitat'' discussion below, we defined 
``bank'' to mean the line at which the stream is at ``bankfull'' 
discharge, as defined by Rosgen (1996), i.e., the flow at which water 
begins to leave the channel and move into the floodplain. While a 
function of the size of the stream, bankfull width is a consistent 
feature related to the formation, maintenance, and dimensions of the 
stream channel. Bankfull discharge is a quantifiable measure that is 
essential to classifying streams, to reducing variability in diagnosing 
stream impairment, and to determining management objectives for a given 
stream reach (Rosgen 1996).
    (17) Comment: The Central Arizona Project (CAP) canal does not 
result in the transfer of nonnative species into the Gila River Basin.
    Our Response: There is a large body of research to support the 
contention that the CAP is a potential vector for nonnative aquatic 
species (U.S. Fish and Wildlife Service 2001a). Additionally, one 
nonnative species has been documented to have entered the Gila River 
Basin through the canal: striped bass (Morone saxatalis); another, pacu 
(Piaractus brachypomus) has invaded the Gila River Basin, potentially 
through the CAP; and numerous nonnative species appear to have 
increased their range within the Gila River Basin via the canal (U.S. 
Fish and Wildlife Service 1999a, 1999b, 2001a, 2001b).
    We completed a section 7 consultation with the Bureau of 
Reclamation (Reclamation) on the effects of the CAP, and the resulting 
biological opinion addressed the transfer of nonnative species into the 
Gila River drainage (U.S. Fish and Wildlife Service 2001b). Recognizing 
the potential of the CAP to transfer nonnative species into the Gila 
River Basin and threaten listed native fish populations, Reclamation 
proposed to build a number of fish barriers to protect native fish 
populations in the Gila River Basin as a conservation measure. Building 
a concrete barrier on the lower segments of tributary streams is 
thought to prevent nonnative fish species from moving upstream, which 
protects the native fish populations above the barrier while allowing 
downstream passage of native fish. Future planned barriers include one 
on Bonita Creek, which is occupied by the Gila chub.
    (18) Comment: The rule does not make clear what specific 
conservation actions would be necessary in proposed reaches of critical 
habitat to improve them to desired conditions for Gila chub.
    Our Response: All of the stream reaches included in the c