Oncorhynchus gilae - (Miller, 1950)
Gila or Apache Trout
Taxonomic Status: Accepted
Related ITIS Name(s): Oncorhynchus gilae (Miller, 1950) (TSN 161985)
Unique Identifier: ELEMENT_GLOBAL.2.105167
Element Code: AFCHA02100
Informal Taxonomy: Animals, Vertebrates - Fishes - Bony Fishes - Salmon and Trouts
Kingdom Phylum Class Order Family Genus
Animalia Craniata Actinopterygii Salmoniformes Salmonidae Oncorhynchus
Genus Size: C - Small genus (6-20 species)
Check this box to expand all report sections:
Concept Reference
Concept Reference: Behnke, R. J. 1992. Native trout of western North America. American Fisheries Society Monograph 6. xx + 275 pp.
Concept Reference Code: B92BEH01NAUS
Name Used in Concept Reference: Oncorhynchus gilae
Taxonomic Comments: Subspecies gilae: Hybridizes with rainbow trout (e.g., in Gila National Forest in Black Canyon, Langstroth, Lipsey, upper Mogollon, White, and Sycamore Canyon creeks; see Sublette et al. 1990). Chitty, Sycamore, Lipsey, and W. F. Mogollon creek populations are rainbow trout, apparently with introgressed gilae genes (Loudenslager et al. 1986).

Subspecies apache: Hybridizes with O. mykiss. Populations in Ft. Apache Indian Reservation are more genetically pure than those in Apache-Sitgreaves National Forest (Rinne and Minckley 1985). Paddy Creek population apparently comprises apache-mykiss hybrids (Loudenslager et al. 1986). Allozyme and mtDNA data may yield different conclusions regarding gene exchange between Apache trout and rainbow trout; exteme care must be exercised when considering elimination of any population that is presumed to be genetically contaminated based on allozyme data alone (Dowling and Childs 1992).

MtDNA data indicate that the nominal species O. apache and O. gilae are very similar to each other, and more similar to rainbow trout (O. mykiss) than to cutthroat trout (O. CLARKI) (Dowling and Childs 1992). Data from karyotyping, electrophoresis, and mtDNA comparisons indicate a close genetic relationship between Gila and Apache trout, much closer than among the four major subspecies of cutthroat trout (Behnke 1992). For this reason, Behnke (1992) recognized the Gila and Apache trouts as two subspecies of a single species, O. gilae. He stated that further taxonomic revisions, based on quantitative genetic data and the lack of reproductive isolation, might classify Gila and Apache trout as subspecies of rainbow trout. Behnke (2002) retained gilae and apache as subspecies of O. gilae, noting that recognition of O. gilae is a compromise between taxonomic splitting (treating gilae and apache as different species) and lumping (including gilae and apache as subspecies of O. mykiss). The latest AFS checklist (Nelson et al. 2004) also regarded apache as a subspecies of O. gilae.

MtDNA data indicate the presence of a diagnosable Gila trout (narrow sense) lineage in four relictual populations from the Gila River and San Francisco River drainages, New Mexico; results suported recognition of a O. gilae/apache ESU (evolutionarily significant unit); also, mtDNA data indicated that the population in the Gila River drainage should be treated as a separate management unit relative to the San Francisco drainage (Riddle et al. 1998).

Formerly included in the genus Salmo (see Smith and Stearley 1989, Robins et al. 1991).
Conservation Status

NatureServe Status

Global Status: G3
Global Status Last Reviewed: 01Aug2012
Global Status Last Changed: 15Mar1996
Ranking Methodology Used: Ranked by inspection
Rounded Global Status: G3 - Vulnerable
Reasons: Small range in New Mexico and Arizona; negatively impacted by habitat isolation and fragmentation, non-native species, wildfire, and climate change; significant management has occurred; may be conspecific with rainbow trout.
Nation: United States
National Status: N3 (05Dec1996)

U.S. & Canada State/Province Status
United States Arizona (S1), New Mexico (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LT: Listed threatened (18Jul2006)
Comments on USESA: USFWS reclassified the federally endangered Gila trout (Oncorhynchus gilae) to threatened status. They also finalized a special rule under section 4(d) of the Act that would apply to Gila trout found in New Mexico and Arizona. This special rule will enable the New Mexico Department of Game and Fish (NMDGF) and the Arizona Game and Fish Department (AGFD) to promulgate special regulations in collaboration with the Service, allowing recreational fishing of Gila trout (Federal Register, 18 July 2006).
IUCN Red List Category: EN - Endangered
American Fisheries Society Status: Endangered, Threatened

NatureServe Global Conservation Status Factors

Range Extent: 5000-20,000 square km (about 2000-8000 square miles)
Range Extent Comments: Range of subspecies gilae: Upper Gila and San Francisco River drainages (USFWS 2009), New Mexico and Arizona, at elevations of 1,660-2,810 meters (Propst and Stefferud 1997).

Range of subspecies apache: Historically occurred in Arizona in the upper Salt River division of the Gila River basin (Black and White rivers), in the headwaters of Little Colorado River drainage, and in the Blue River (specimen from KP Creek) in the San Francisco River drainage; these streams all are close to each other in the White Mountains (Behnke 1992). Introduced in several streams and lakes in Arizona. Mainly in small headwater streams at elevations above 1,800 meters in the White Mountains (Behnke 1992).

A now extinct trout population in the upper tributaries of the Verde River in Arizona exhibited characteristics of both Gila and Apache trouts (Behnke 2002).

Area of Occupancy: 101-500 1-km2 grid cells
Area of Occupancy Comments: Area of occupancy is less than 2,000 square kilometers. Subspecies apache: now occurs in approximately 199 km of stream within historical range (USFWS 2009). Subspecies gilae: the four original pure population lineages are currently protected and replicated in 109 km of stream (USFWS 2006).

Number of Occurrences: 21 - 80
Number of Occurrences Comments: This species is represented by a moderate number of occurrences (subpopulations) and locations (as defined by IUCN). Subspecies gilae: currently, 12 viable populations of Gila trout exist in the absence of non-native salmonids (USFWS 2006). Subspecies apache: 28 populations now exist within historical range (USFWS 2009).

Population Size: 10,000 - 1,000,000 individuals
Population Size Comments: Total adult population size is unknown but certainly exceeds 10,00 and may exceed 100,000.

Overall Threat Impact Comments: Subspecies gilae: Declined mainly due to hybridization and competitive/predatory interactions with introduced trout species (rainbow, cutthroat, brown) and to habitat degradation through overgrazing, fires, lumbering, and mining (Sublette et al. 1990). Natural catastrophes such as drought, fires, and flooding can decimate populations (Propst et al. 1992, Brown et al. 2001). During the 1800s and 1900s, habitat degradation and loss through livestock grazing and timber harvest practices, overfishing, and the introduction of non-native trout reduced Gila trout to a few isolated populations. Current threats to Gila trout are habitat isolation and fragmentation, non-native species, wildfire, and climate change (USFWS 2009).

The short length of the occupied stream fragments and resulting small population sizes is also of concern; stream length is important to ensure adequate complexity and suitable habitat for life history requirements (see USFWS 2009). Restoration of Gila trout populations has not been successful in Raspberry, Dude, or Sheep Corral Creeks, most likely because of poor quality and/or limited habitat; failure of the Dude Creek restoration was likely a consequence of continued post-wildfire disturbances to the stream (USFWS 2009). Stocking and naturalization of nonnative trout and ensuing hybridization, predation, and competition are major causes for the imperiled status of the Gila trout (USFWS 2009).

Wildfires capable of eliminating or decimating fish populations are relatively recent phenomena resulting from the cumulative effects of historical or ongoing grazing practices (removes fine fuels needed to carry low-intensity, natural ground fire), fire suppression, and climate change. The absence of ground fires allowed a buildup of woody fuels that promotes infrequent, yet intense, crown fires. Since the mid-1990s, wildfire has occurred within or near all drainages containing Gila trout populations. High-severity wildfires, and subsequent floods and ash/debris flows have caused the extirpation of six populations of Gila trout since 1989. Widespread and intense wildfires remain a threat to Gila, especially in light of the projected effects of climate change. An emergency evacuation plan is in place, and has been used to help offset the immediate loss of populations from wildfire and subsequent channel degradation. Source: USFWS (2009, which see for supporting documentation).

Climate change is predicted to have four major effects on the cold-water stream habitat: 1) increased water temperature; 2) decreased stream flow; 3) a change in the hydrograph; and 4) an increased occurrence of extreme events (fire, drought, and floods) (USFWS 2009). It is anticipated that any of these outcomes, alone or in combination would reduce that amount of suitable habitat available to Gila trout. Kennedy et al. (2008) predicted a 20 percent decrease in summer precipitation and a 2° C increase in average summertime air temperature by mid-century in watersheds occupied by Gila trout. Because of the warmer air temperatures and corresponding increase in water temperature, a 70 percent loss of suitable habitat in existing Gila trout streams was predicted (Kennedy et al. 2008).

Subspecies apache: Suffered 95 percent reduction in range due to hybridization with rainbow trout and competition with brook and brown trouts (Lee et al. 1980). Much more vulnerable to angling exploitation than is the brown trout when the two live together in the same stream (see Behnke 1992). Release of hatchery-produced fishes into waters in which pure wild populations exist probably would be detrimental. Small populations of Apache trout have persisted throughout history in several small headwater streams where they are isolated from non-native trout, but those populations may be subject extirpation from stochastic events such as drought, fire, and periodic flooding (USFWS 2009).

Short-term Trend: Relatively Stable (<=10% change)
Short-term Trend Comments: Trend over the past 10 years or three generations has been relatively stable. Three generations span probably about 12 years

Long-term Trend: Decline of 50-70%
Long-term Trend Comments: Subspecies apache: The estimated historic distribution of 965-1,320 kilometers of stream habitat (USFWS 2009) was reduced to about 50 km before restoration efforts began (Behnke 1992). Occupied habitat has increased greatly through intensive management in recent decades.

Other NatureServe Conservation Status Information

Inventory Needs: Determine current population numbers.

Protection Needs: Protect existing EOs from habitat degradation and hybridization with other trout.

Global Range: (5000-20,000 square km (about 2000-8000 square miles)) Range of subspecies gilae: Upper Gila and San Francisco River drainages (USFWS 2009), New Mexico and Arizona, at elevations of 1,660-2,810 meters (Propst and Stefferud 1997).

Range of subspecies apache: Historically occurred in Arizona in the upper Salt River division of the Gila River basin (Black and White rivers), in the headwaters of Little Colorado River drainage, and in the Blue River (specimen from KP Creek) in the San Francisco River drainage; these streams all are close to each other in the White Mountains (Behnke 1992). Introduced in several streams and lakes in Arizona. Mainly in small headwater streams at elevations above 1,800 meters in the White Mountains (Behnke 1992).

A now extinct trout population in the upper tributaries of the Verde River in Arizona exhibited characteristics of both Gila and Apache trouts (Behnke 2002).

U.S. States and Canadian Provinces
Color legend for Distribution Map
Endemism: endemic to a single nation

U.S. & Canada State/Province Distribution
United States AZ, NM

Range Map
No map available.

U.S. Distribution by County Help
State County Name (FIPS Code)
AZ Apache (04001), Coconino (04005), Graham (04009), Greenlee (04011)
NM Catron (35003), Grant (35017), Hidalgo (35023), Sierra (35051)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
13 Mimbres (13030202)+
15 Lower Colorado-Marble Canyon (15010001)+, Little Colorado headwaters (15020001)+, Upper Little Colorado (15020002)+, Upper Gila (15040001)+, Upper Gila-Mangas (15040002)+, San Francisco (15040004)+, Upper Gila-San Carlos Reservoir (15040005)*, Willcox Playa (15050201)+, Black (15060101)+, White (15060102)+, Upper Verde (15060202)*, Lower Verde (15060203)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
U.S. Distribution by Watershed (based on multiple information sources) Help
Ecology & Life History
Basic Description: A trout.
General Description: Subspecies apache: Grows much larger (to at least 2 kg) in lakes than in native small stream habitat (rarely exceeds 300 mm) (Behnke 1992).
Reproduction Comments: Subspecies GILAE: Spawns apparently in spring and summer in New Mexico (March-June when water temperature is 8 C or greater). Egg production is considered low (usually a few hundred or fewer). Fry emerge in 45-60 days at 20-25 TL (Lee et al. 1980), or in 8-10 weeks at 15-20 mm TL (Sublette et al. 1990). Females sexually mature at 3-5 years, depending on conditions; males mature usually 1-2 years sooner than do females in the same stream (Sublette et al. 1990). Maximum lifespan is 5-9 years in different streams.

Subspecies APACHE: Reaches maturity in three years. Spawning occurs March-mid June, when water temperature about 8 C. Egg production is variable, (70-4000+ per female), usually listed as 200-600. Hatches at 30 days, young emerge at 20-25 mm SL in 60 days (Lee et al. 1980).

See Stearley (1992) for a discussion of the historical ecology and life history evolution of Pacific salmons and trouts (ONCORHYNCHUS).

Ecology Comments: See Turner (1989) for information on seasonal and annual population changes in subspecies GILAE in headwater streams in New Mexico. Populations of subspecies APACHE become depleted during severe winters.
Habitat Type: Freshwater
Non-Migrant: Y
Locally Migrant: Y
Long Distance Migrant: N
Mobility and Migration Comments: Subspecies apache: Migrates between spawning and nonspawning areas.
Riverine Habitat(s): CREEK, High gradient, MEDIUM RIVER, Moderate gradient, Pool, Riffle
Lacustrine Habitat(s): Deep water, Shallow water
Special Habitat Factors: Benthic
Habitat Comments: Subspecies gilae: Habitat includes clear, cold mountain streams in arid regions; streams largely intermittent (not flowing in summer and fall) (Behnke 1979); clear runs in mountain streams that typically are narrow and shallow; trout may be confined to pools during prolonged drought (Sublette et al. 1990). Usually these fishes congregate in deeper pools and in shallow water only where there is protective debris or plant beds (Matthews and Moseley 1990).

Subspecies apache: Habitat is presently restricted to clear, cool, high-elevation mountain streams that flow through cienegas (marshes) and coniferous forests, upstream from natural barriers. This subspecies also has been introduced into several streams and lakes.

Spawning occurs in flowing water in saucer-like depression excavated by female. Eggs are covered with gravel after fertilization takes place (Minckley 1973).

Adult Food Habits: Invertivore
Immature Food Habits: Invertivore
Food Comments: Subspecies GILAE: Feeds opportunistically on insects and insect larvae (e.g.: Trichoptera, Ephemeroptera, Diptera, Coleoptera, simuliid larvae, terrestrial organisms). Subspecies APACHE: Feeds on aquatic and terrestrial insects (e.g., Ephemeroptera, Trichoptera, and Diptera).
Phenology Comments: Subspecies GILAE: Peak feeding period is 0900-1300 h (Sublette et al. 1990).
Length: 26 centimeters
Economic Attributes
Economic Comments: Regulations have been proposed that would allow sport fishing of subspecies gilae in New Mexico (USFWS 1987); this is not expected to interfere with recovery.
Management Summary Not yet assessed
Population/Occurrence Delineation
Group Name: Nonanadromous Salmonids

Use Class: Not applicable
Subtype(s): Spawning Area
Minimum Criteria for an Occurrence: Occurrences are based on evidence of historical presence, or current and likely recurring presence, at a given location. Such evidence minimally includes collection or reliable observation and documentation of one or more individuals (including eggs and larvae) in appropriate habitat.
Mapping Guidance: Conceptually, the occurrence includes the entire area used by the population, including spawning, rearing, migration, and wintering areas. Occupied locations that are separated by a gap of 10 km or more of any aquatic habitat that is not known to be occupied represent different occurrences. However, it is important to evaluate migrations and seasonal changes in habitat (see separation justification) to ensure that spawning areas and nonspawning areas for a single population are not artificially segregated as different occurrences simply because there have been no collections/observations in an intervening area that may exceed the separation distance.
Separation Barriers: Dam lacking a suitable fishway; high waterfall; upland habitat.
Alternate Separation Procedure: Separation distance is 10 stream-km for both suitable and unsuitable habitat. However, if it is known that the same population occupies sites separated by more than 10 km (e.g., this may be common for migratory populations), those sites should be included within the same occurrence. In lakes, occurrences include all suitable habitat that is presumed to be occupied (based on expert judgment), even if documented collection/observation points are more than 10 km apart. Separate sub-occurrences or source features may usefully document locations of critical spawning areas within a lake.

Separation Justification: Separation distance is arbitrary; little is known about juvenile dispersal (e.g., how far fishes may move between between their embryonic developmental habitat and eventual spawning site). "Restricted movement is the norm in populations of stream salmonids during nonmigratory periods," but there is considerable variation in movements within and among species (Rodriguez 2002).

Migrations can be extensive. For example, in the Kennebecasis River, New Brunswick, brook trout moved upstream 65-100 km in spring after ice loss; summer movements were minimal; movements to spawning areas in fall were less than 10 km, then the fish moved back downstream to wintering areas in the lower to middle reaches of the river (Curry et al. 2002).

Because of the difficulty in defining suitable versus unsuitable habitat, especially with respect to dispersal, and to simplify the delineation of occurrences, a single separation distance is used regardless of habitat quality.

Date: 11Mar2003
Author: Hammerson, G.
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
NatureServe Conservation Status Factors Edition Date: 01Aug2012
NatureServe Conservation Status Factors Author: Hammerson, G.
Element Ecology & Life History Edition Date: 01Aug2012
Element Ecology & Life History Author(s): Hammerson, G.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

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References for Watershed Distribution Map
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