|Scientific Name:||Gila intermedia|
|Species Authority:||(Girard, 1856)|
Tigoma intermedia Girard, 1856
|Red List Category & Criteria:||Endangered B2ab(ii,iii,iv,v) ver 3.1|
|Reviewer/s:||Smith, K. & Darwall, W.R.T.|
|Facilitator/s:||Hammerson, G.A. & Ormes, M.|
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.
|Range Description:||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).
|Range Map:||Click here to open the map viewer and explore range.|
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).
|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.
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).
|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.|
|Citation:||NatureServe 2013. Gila intermedia. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 10 December 2013.|
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