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Overview

Distribution

National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (20,000-200,000 square km (about 8000-80,000 square miles)) Historically, this species occurred in springs and small streams in the upper Gila River basin in southern Arizona, southwestern New Mexico, and northeastern Sonora, Mexico (Miller and Lowe 1964, Minckley 1973, USFWS 2002, Page and Burr 2011). The vast majority of the range is in Arizona.

In Arizona, Gila chubs are known to have occupied portions of the Salt, Verde, Santa Cruz, San Pedro, San Carlos, San Simon, San Francisco, and Agua Fria drainages and 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.

An observation of a Gila chub in Turkey Creek in the upper Gila River Basin in New Mexico was made in 2001 (Telles, pers. comm., 2001, cited by USFWS 2002).

The current known distribution 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 2 km (1.2 mi) of the Arizona-Mexico border (Varela-Romero et al. 1992). No Gila chubs remain in the Mexican portion of the Santa Cruz River basin (Weedman et al. 1996).

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North America: Found in the US and Mexico.
  • Robins, C.R., R.M. Bailey, C.E. Bond, J.R. Brooker, E.A. Lachner, R.N. Lea and W.B. Scott 1991 Common and scientific names of fishes from the United States and Canada. Am. Fish. Soc. Spec. Pub. (20):183 p. (Ref. 3814)
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Historic Range:
U.S.A. (AZ, NM), Mexico

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Southwestern U.S.A. and northern Mexico.
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Physical Description

Diagnostic Description

The Gila chub is most similar morphologically to the roundtail chub. The latter usually is lighter colored, less robust, and with scales that are relatively smaller, thinner, and only slightly embedded; basal radii on scales are absent to weakly developed; the number of dorsal, anal and pelvic fin rays in roundtail chubs usually is nine; there are usually 81 or more scales in the lateral line and 43 to 49 total vertebrae; the length of the head divided by the depth of the caudal peduncle is typically 3.3 to 4.3, rarely greater than 4.0.

The Yaqui chub, GILA PURPUREA, and the Sonora chub, GILA DITAENIA, have radii strongly developed on all fields of scales, the mouth is horizontal to oblique, and a basicaudal spot is present albeit possibly discrete or diffuse.

GILA ELEGANS is distinctive as adults and may be distinguished from the Gila chub using characteristics described by Douglas et al. (1989). GILA ELEGANS has been extirpated from areas where the Gila chub occurs and, unless reintroductions of these species occur, these three species will not be taken in the same collections.

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Type Information

Syntype for Gila intermedia
Catalog Number: USNM 344867
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Preparation: Photograph
Collector(s): J. Clark
Year Collected: 1851
Locality: R. Santa Cruz, Arizona, United States, North America
  • Syntype: Baird, S. F. & Girard, C. F. 1854. Proceedings of the Academy of Natural Sciences of Philadelphia. 7: 28.
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Syntype for Gila intermedia
Catalog Number: USNM 223
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Preparation: Dry Osteological Specimen; Photograph
Collector(s): J. Clark
Year Collected: 1851
Locality: R. Santa Cruz, Arizona, United States, North America
  • Syntype: Baird, S. F. & Girard, C. F. 1854. Proceedings of the Academy of Natural Sciences of Philadelphia. 7: 28.
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Syntype for Gila intermedia
Catalog Number: USNM 232
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Fishes
Preparation: Dry Osteological Specimen
Collector(s): J. Clark
Year Collected: 1851
Locality: Rio San Pedro, of the Gila, Arizona, United States, North America
  • Syntype: Girard, C. F. 1857. Proceedings of the Academy of Natural Sciences of Philadelphia. 8: 206.
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Ecology

Habitat

Habitat Type: Freshwater

Comments: Gila chubs commonly inhabit pools in creeks and small rivers, springs, and cienegas, and they can survive in small artificial impoundments (Miller 1946, Minckley 1973, Rinne 1975, Page and Burr 2011). They are highly secretive, preferring quiet, deeper waters, especially pools, or remaining near cover including terrestrial vegetation, boulders, and fallen logs (Minckley 1973, Rinne and Minckley 1991). Minckley (1973) suggested that spawning may occur over beds of aquatic plants.

Specific habitat associations are known to vary ontogenetically and likely vary seasonally and geographically. Young in Monkey Spring, Arizona (from which the species is now extirpated), 25-75 mm total length (TL), were found in swifter areas than were adults, which utilized undercut banks and heavily vegetated margins of the spring run (Minckley 1969). Griffith and Tiersch (1989) collected Gila chubs from both riffles and pools in Redfield Canyon, Arizona.

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Habitat and Ecology

Habitat and Ecology
Gila Chubs commonly inhabit pools in creeks and small rivers, springs, and cienegas, and they can survive in small artificial impoundments (Miller 1946, Minckley 1973, Rinne 1975, Page and Burr 2011). They are highly secretive, preferring quiet, deeper waters, especially pools, or remaining near cover including terrestrial vegetation, boulders, and fallen logs (Minckley 1973, Rinne and Minckley 1991). Minckley (1973) suggested that spawning may occur over beds of aquatic plants.

Specific habitat associations are known to vary ontogenetically and probably vary seasonally and geographically. Young in Monkey Spring, Arizona (from which the species is now extirpated), 25-75 mm total length (TL), were found in swifter areas than were adults, which utilized undercut banks and heavily vegetated margins of the spring run (Minckley 1969). Griffith and Tiersch (1989) collected Gila Chubs from both riffles and pools in Redfield Canyon, Arizona.

Systems
  • Freshwater
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Environment

benthopelagic; freshwater
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Migration

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Feeds mainly on aquatic and terrestrial insects and filamentous and diatomaceous algae (Minckley 1973, Griffith and Tiersch 1989). Of 27 specimens examined for stomach contents in Redfield Canyon, four contained remains of fishes; three contained RHINICHTHYS OSCULUS (Griffith and Tiersch 1989). Gila chubs were observed chasing Gila topminnows in Monkey Spring (Minckley 1969). No information is available on dietary differences between size or age classes. Larger individuals feed during evening and early morning hours, whereas young chubs feed during all daylight hours (Minckley 1973, Griffith and Tiersch 1989).

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

Comments: Historically, 47 populations were recorded in approximately 43 rivers, streams, and spring-fed tributaries (Miller and Lowe 1967, Rinne and Minckley 1970, Minckley 1973, Rinne 1976, DeMarais 1986, Bestgen and Propst 1989, Weedman 1996, USFWS 2005). Of the 47 known populations, 29 are regarded as extant (USFWS 2005).

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Global Abundance

Unknown

Comments: Population size is unknown but not very large.

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General Ecology

The Gila chub is associated with a native fish fauna that includes loach minnow (TIAROGA COBITIS), spikedace (MEDA FULGIDA), speckled dace (RHINICHTHYS OSCULUS), longfin dace (AGOSIA CHRYSOGASTER), Sonora sucker (CATOSTOMUS INSIGNIS) and desert sucker (PANTOSTEUS CLARKI). Historically it also was associated with the woundfin (PLAGOPTERUS ARGENTISSIMUS), bonytail (GILA ELEGANS), squawfish (PTYCHOCHEILUS LUCIUS), razorback sucker (XYRAUCHEN TEXANUS), and Gila topminnow (POECILIOPSIS OCCIDENTALIS), all of which are now extirpated from the Gila River basin. Gila chub and roundtail chub are sometimes found in the same stream systems, separated by only tens of meters; however, the two species have never been collected together at the same site (DeMarais 1990; Minckley 1985, 1990).

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Life History and Behavior

Cyclicity

Comments: Young are active throughout the day; larger individuals tend to be most active in evening and early morning.

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Reproduction

In Monkey Spring, a relatively-constant spring-fed pond, reproduction may have last throughout late winter, spring, and summer, and perhaps into autumn (Minckley 1969, 1985). In other areas it occurs mostly in late spring and summer (Minckley 1973). Most Gila chub probably mature in their second or third year of life (Griffith and Tiersch 1989).

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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N2 - Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G2 - Imperiled

Reasons: Extirpated or much reduced in numbers and distribution in majority of historical range in the upper Gila River basin in Arizona, New Mexico, and adjacent Sonora, Mexico; has been detrimentally affected by habitat degradation and interactions with exotic fishes.

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.

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IUCN Red List Assessment


Red List Category
EN
Endangered

Red List Criteria
B2ab(ii,iii,iv,v)

Version
3.1

Year Assessed
2013

Assessor/s
NatureServe

Reviewer/s
Smith, K. & Darwall, W.R.T.

Contributor/s

Justification
This species is listed as Endangered because its area of occupancy is less than 500 sq km; distribution is severely fragmented; and distribution, abundance, and habitat quality/quantity are subject to ongoing declines.

History
  • 1994
    Rare
    (Groombridge 1994)
  • 1990
    Rare
    (IUCN 1990)
  • 1988
    Vulnerable
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Vulnerable
    (IUCN Conservation Monitoring Centre 1986)
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Current Listing Status Summary

Status: Endangered
Date Listed: 11/02/2005
Lead Region:   Southwest Region (Region 2) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: E

For most current information and documents related to the conservation status and management of Gila intermedia , see its USFWS Species Profile

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Global Short Term Trend: Relatively stable to decline of 30%

Comments: Trend over the past 10 years or three generations is uncertain but probably slowly declining. Range reductions have been severe in past years (Minckley 1973), and with continuing land and water development in Arizona, additional populations are expected to be reduced or extirpated. Of the 29 extant populations, 10 can be considered stable-threatened and 19 are considered unstable-threatened; none are considered stable-secure (USFWS 2005).

Global Long Term Trend: Decline of 70-90%

Comments: Extirpated or much reduced in numbers and distribution in majority of historical range (Minckley 1973, Weedman et al. 1996, USFWS 2002). This species has been eliminated from approximately 85 to 90 percent of the formerly occupied habitat, and much of the loss is unrecoverable (USFWS 2002, 2005).

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Population

Population
Historically, 47 populations were recorded in approximately 43 rivers, streams, and spring-fed tributaries (Miller and Lowe 1967, Rinne and Minckley 1970, Minckley 1973, Rinne 1976, DeMarais 1986, Bestgen and Propst 1989, Weedman 1996, USFWS 2005). Of the 47 known populations, 29 are regarded as extant (USFWS 2005).

Population size is unknown but not very large.

It is extirpated or much reduced in numbers and distribution in the majority of its historical range (Minckley 1973, Weedman et al. 1996, USFWS 2002). This species has been eliminated from approximately 85 to 90 percent of the formerly occupied habitat, and much of the loss is unrecoverable (USFWS 2002, 2005).

The trend over the past 10 years or three generations is uncertain but probably slowly declining. Range reductions have been severe in past years (Minckley 1973), and with continuing land and water development in Arizona, additional populations are expected to be reduced or extirpated. Of the 29 extant populations, 10 can be considered stable-threatened and 19 are considered unstable-threatened; none are considered stable-secure (USFWS 2005).

Population Trend
Decreasing
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Threats

Endangered (EN) (B2ab(ii,iii,iv,v))
  • IUCN 2006 2006 IUCN red list of threatened species. www.iucnredlist.org. Downloaded July 2006.
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Comments: Where still present, populations are often small, scattered, and at risk from known and potential threats and from random events. Threats 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 alteration, destruction, and fragmentation resulting from water diversions, dredging, recreation, roads, livestock grazing, changes in the natural flow pattern, extirpation of beavers and loss of habitats they generated, mining, degraded water quality (including contaminants from mining activities and excessive sedimentation), and groundwater pumping (see USFWS 2002 and 2005 for further details; see also Hubbs 1954, Miller 1961, Minckley and Deacon 1968, and Meffe 1985).

Chubs in and adjacent to the San Carlos Reservation have been recorded with various skin lesions, likely due to water contaminants (Weedman et al. 1996). Watershed changes and the introduction of non-native fishes have occurred concurrently and it would be difficult to separate out one factor as a primary cause for the decline; most likely, multiple factors are involved. Destruction of cienegas and associated habitats undoubtedly has had an adverse impact (Hastings 1959, Hendrickson and Minckley 1984). A population in Monkey Spring was decimated from predation by largemouth bass following the introduction of this gamefish (Minckley 1973). Increasing green sunfish abundance in the San Carlos River was correlated with the decline or disappearance of Gila chub (Minckley 1985, Propst et al. 1985). Unfortunately, dietary data documenting predation by exotic fishes on the Gila chub are lacking. In addition to predatory and competitive impacts, exotic fishes also may spread exotic parasites. Of the 24 populations extant in the mid-1990s, at least 14 were subject to grazing at the site or upstream, at least 10 contained exotic fishes, 6 had limited habitat, and 6 had water diversions or impoundments; many were subject to multiple impacts from these or other factors (Weedman et al. 1996).

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Major Threats
Where still present, populations are often small, scattered, and at risk from known and potential threats and from random events. Threats 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 alteration, destruction, and fragmentation resulting from water diversions, dredging, recreation, roads, livestock grazing, changes in the natural flow pattern, extirpation of beavers and loss of habitats they generated, mining, degraded water quality (including contaminants from mining activities and excessive sedimentation), and groundwater pumping (see USFWS 2002 and 2005 for further details; see also Hubbs 1954, Miller 1961, Minckley and Deacon 1968, and Meffe 1985).

Chubs in and adjacent to the San Carlos Reservation have been recorded with various skin lesions, probably due to water contaminants (Weedman et al. 1996). Watershed changes and the introduction of non-native fishes have occurred concurrently and it would be difficult to separate out one factor as a primary cause for the decline; most probably, multiple factors are involved. Destruction of cienegas and associated habitats has undoubtedly had an adverse impact (Hastings 1959, Hendrickson and Minckley 1984). A population in Monkey Spring was decimated from predation by Largemouth Bass following the introduction of this gamefish (Minckley 1973). Increasing Green Sunfish abundance in the San Carlos River was correlated with the decline or disappearance of Gila Chub (Minckley 1985, Propst et al. 1985). Unfortunately, dietary data documenting predation by exotic fishes on the Gila Chub are lacking. In addition to predatory and competitive impacts, exotic fishes also may spread exotic parasites. Of the 24 populations extant in the mid-1990s, at least 14 were subject to grazing at the site or upstream, at least 10 contained exotic fishes, 6 had limited habitat, and 6 had water diversions or impoundments; many were subject to multiple impacts from these or other factors (Weedman et al. 1996).
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Management

Restoration Potential: Lack of knowledge of the biology of Gila chub clearly is a deterrent to its recovery. Recovery potential is good only if critical habitat is vigorously protected. Remaining populations continue to be threatened by habitat modification and interactions with non-native fishes. Reestablishment in former range is problematic until the causes of the decline are corrected.

Preserve Selection and Design Considerations: Habitat in the form of headwater cienegas or spring-fed streams are critical for the continued existence of the Gila chub. Gila chub also does well in spring-fed ponds if non-native fish are excluded (Minckley 1969).

Management Requirements: Existing populations not infected by non-native fishes should be protected through the establishment of fish barriers if such is judged not to be detrimental to the Gila chub. Necessary habitat and landscape improvements (including removal of non-native fishes) need to be determined and implemented. Stream flows and temperatures should not be modified by activities such as damming or diversion that substantially alter natural regimes. State or other fish management agencies and private entities should discontinue stockings of non-native, warmwater sport, forage, or bait fishes into streams occupied by Gila chub; this protection should extend downstream at least to the first absolute barrier to upstream fish movement.

Proper management and maintenance of riparian zones are essential to native fish populations. Changes in the riparian zone can affect leaf fall and energy flow, stream flow, natural cover, temperature, and deposition of eroded materials (Baltz and Moyle 1984). Of five riparian systems studied in Arizona, only Aravaipa Creek, where cattle have been excluded since 1973, showed successful reproduction and dominance of the broadleaf riparian community (Rucks 1984). Cattle browsing is a major factor in the replacement of a broadleaf riparian community by a riparian scrub community (Rucks 1984). A change from a broadleaf to scrub riparian community can change energy flow, tree-fall cover and amount of shade, and temperature profiles of a stream.

Fire would be a preferred method of watershed management when necessary. However, the choice of fire as a management tool must take into account the fuel levels present. A crown fire ("hot fire") can lead to increased runoff and result in the filling of riffle or other spawning areas. The effects of a crown fire and subsequent runoff were reversed in three years in the upper Carmel River, California (Hecht 1984). If watershed management is necessary, controlled burns, frequent enough to prevent build-up of high fuel levels, set during nonspawning periods or periods of decreased spawning activity (winter), should be employed.

Populations should be reintroduced into selected streams within the historic range. Potential dispersal routes should be closed to preclude reinvasion of non-native fishes. Barrier design should not significantly alter stream flow and the potential impact on natural upstream and downstream movements of native fishes should be assessed. Habitat improvement should be implemented, which may include removal of non-native fishes by piscicide. Reintroduced stocks should have a genetic affinity with those formerly occupying target streams. Stockings should be done according to guidelines set up by the American Fisheries Society (Williams et al. 1988), consultants familiar with GILA taxonomy, and the U.S. Fish and Wildlife Service. Reintroduced populations should be monitored for success or failure. Populations that are rapidly declining should be secured in a hatchery facility such as the Dexter National Fish Hatchery, Dexter, New Mexico. Techniques for spawning and rearing GILA sp. are available (Hamman 1981, 1982, 1982, Muth et al. 1985).

Management Research Needs: Knowledge of all aspects of Gila chub life history is incomplete. The genus GILA is one of the most fascinating and important fish groups known to taxonomists. Detailed observation and experimentation on the effects of non-native fishes on all life stages of the chubs are needed. The following specific topics are among those that need to be addressed: (1) habitat used and required by all life stages, (2) range of natural variation in absolute and relative abundances of Gila chub and community members, (3) dietary preferences of larvae, juveniles, and adult, (4) nature and significance of direct and indirect interactions with non-native fishes, (5) effects of physical habitat modification on life cycle completion, (6) movement patterns of adults and larvae, (7) impacts of water diversion, irrigation, and barriers, and (8) taxonomic relationships.

Biological Research Needs: The impact of flooding on nutrient cycling, substrate renewal, and availability of cover, with respect to native fishes, needs to be examined.

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Needs: Protect existing populations. Acquire available lands and associated water rights needed to protect populations/habitat. Detrimental water- and land-use practices should be discouraged by providing information to all users, especially private landowners. Ensure perennial flows with natural or simulated variation in flow regime. Curtail transport and introduction of non-native fishes.

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Conservation Actions

Conservation Actions
Existing Gila Chub populations need to be identified and carefully monitored. Protection would be enhanced by the elimination of detrimental water and land use practices and the removal of non-native fishes. Degraded habitats should be reclaimed and enhanced, and chubs should be reintroduced where chances for success are judged to be good. Research is needed to identify specific threats.
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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: Existing Gila chub populations need to be identified and carefully monitored. Protection would be enhanced by the elimination of detrimental water and land use practices and the removal of non-native fishes. Degraded habitats should be reclaimed and enhanced, and chubs should be reintroduced where chances for success are judged good. Research is needed to identify specific threats.

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Wikipedia

Gila intermedia

The Gila chub (Gila intermedia) is a species of ray-finned fish in the Cyprinidae family. It is found in Mexico and the United States. The Gila chub is closely related to Gila robusta robusta and Gila robusta grahami (roundtail chub species).[1] This species is commonly found in association with the Gila topminnow, the desert and Sonora sucker, and the longfin and speckled dace.

Contents

Description[edit]

The Gila chub has a large, chunky body, with large, thick scales. The body is dark overall, and sometimes is lighter on the belly. In larger females, a soft, fat, and broad hump sometimes develops on the nape of the neck. Mature, breeding males have a red or orange color on the lower cheek, back parts of the lips, and on parts of the fin. This coloration can also be found on the male’s caudal peduncle (tail side). [2] Males usually grow to be only about 15 cm (5.9 in), while females can reach to 25 cm (9.8 in)—a significant difference. [3]

Range[edit]

The Gila chub has been found in streams of the Gila River drainage in Arizona, and in the Santa Cruz River system in Sonora, Mexico; however, recently, the Gila chub species has not been documented in the San Pedro drainage in Sonora, Mexico.

The Gila chub has also been recently discovered in these specific drainages in Arizona: Santa Cruz River, Middle Gila River, San Pedro River, Agua Fria River, and the Verde River. These fish have also been extirpated from the Monkey Spring of the Santa Cruz River, and Fish and Cave Creeks of the Salt River.

Habitat[edit]

Gila chub of the Gila River basin usually occupies the smaller headwater streams, springs or marshes. Their choice of diverse habitats varies, depending on the season or age of the fish. Juveniles are found in riffles (a patch of waves), pools, and banks. However, in larger streams, these fish are found in parts of heavy vegetation, for cover and foraging. Gila chubs are also considered to be highly “secretive” when it comes to habitats; since fish of this species are constantly looking for deeper waters near cover and shade.

Diet[edit]

Gila chubs are omnivores, and their diet mainly includes aquatic (and terrestrial) insects. These fish are also known to consume other fish at large sizes, which include eating speckled dace (Rhinichthys osculus) and other small cyprinid fish. Juveniles feed throughout the day while the adults are out during the early morning and late night; juveniles usually consume insects and algae.

Reproduction[edit]

Gila chub have a unique breeding season, which occurs from late spring to summer (some populations can go as far as late winter if the water temperature stays constant). The breeding period is long because Gila chub mature in their second or third year, and are more active at this age. Reproduction occurs in heavily vegetated areas. [2] Actively breeding fish have distinct intense coloration—parts of the body become fire-red (ventro-lateral surfaces) and the eyes transform to a yellow-orange. [2]

Conservation[edit]

Little is known about the population of Gila chub in Mexico, but the populations that reside in Arizona are expected to decrease because of these ongoing threats: aquifer pumping, stream diversion, habitat alterations by non-native crayfishes, and mainly, predation/competition with nonnative fishes. Currently, the Gila chub are sharing the waters with green sunfish (Lepomis cyanellus) in many areas; however, introducing any other kind of exotic fish to the Gila chub must be managed and observed (it is crucial to their survival). In fact, the Gila chub has been extirpated on many occasions because of exotic fish such as the largemouth bass (Micropterus salmoides).

According to the Arizona Fish and Game Department, the Bureau of Land Management Phoenix District is proposing translocations of the Gila chub from Silver Creek to an adjacent stream in the Agua Fria headwaters. Here, the Arizona Game and Fish Department can complete their status review of warranting the Gila chub under the Endangered Species Act.

References[edit]

  1. ^ Rinne, J.N. 1969. Cyprinid fishes of the genus Gila from the lower Colorado River basin. Masters thesis, Arizona State University, Tempe.
  2. ^ a b c Minckley, W.L. 1973. Fishes of Arizona. Arizona Game and Fish Department, Phoenix. pp. 104-106.
  3. ^ Rinne, J.N. and W.L. Minckley. 1991. Native fishes of arid lands: a dwindling resource of the desert southwest. U.S. Department of Agriculture, Forest Service, General Technical Report RM-206. Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado. pp. 24-25.

Source[edit]

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Names and Taxonomy

Taxonomy

Comments: Previously considered a subspecies of G. ROBUSTA. Rinne (1976) and DeMarais (1986) provided convincing evidence that the Gila chub is a distinct species; most authors now recognize G. INTERMEDIA as a species (Douglas et al. 1989, Sublette et al. 1990, Robins et al. 1991). Specific status for GILA INTERMEDIA was supported by DeMarais (1986) for the following primary reasons: (1) morphological differences (if not for phenotypic intermediates between these two types, of unknown origin, their separate-species status would be unquestioned) and (2) contiguous populations of G. ROBUSTA and G. INTERMEDIA have maintained and continue to perpetuate their independence over evolutionary and recent time.

Minckley and DeMarais (2000) proposed that "GILA NIGRA," an assemblage that possibly arose through more than one hybridization event between GILA ROBUSTA and GILA INTERMEDIA, be recognized as a distinct species.

However, Gerber et al. (2001) cited several studies of allozymic and mtDNA characters that failed to identify any diagnostic characters among G. INTERMEDIA, G. NIGRA, and G. ROBUSTA ROBUSTA; they referred to these taxa as "G. ROBUSTA."

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