Oncorhynchus gilae (Miller, 1950)

Rounded Global Status Rank: 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.

Current Listing Status Summary

Status: Threatened
Date Listed: 03/11/1967
Lead Region:   Southwest Region (Region 2) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: T

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

Global Short Term Trend: Relatively stable (=10% change)

Comments: Trend over the past 10 years or three generations has been relatively stable. Three generations span probably about 12 years

Global Long Term Trend: Decline of 50-70%

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.

Degree of Threat: A : Very threatened throughout its range communities directly exploited or their composition and structure irreversibly threatened by man-made forces, including exotic species

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).