Gila Trout

Oncorhnynchus gilae

Description

The Gila trout, Oncorhnychus gilae, grows 10-14 in (25-34 cm) in length and is readily identified by its iridescent golden sides, which grade to a dark copper on the gill covers. Irregular spotting is prominent on the back and sides. Dorsal, pelvic, and anal fins have white to yellowish tips. During spawning season, the normally white belly may be streaked with yellow or orange.

Behavior

Spawning occurs in April and May when midday water temperatures reach 46-54°F (8-12°C). Gila trout are opportunistic predators, feeding on insects and aquatic invertebrates.

Habitat

The Gila trout inhabits clear, cool headwater streams with moderate current and sufficient depth and cover to provide refuge during severe droughts. Gila trout usually congregate in deeper pools and in shallow water only where there is protective debris or plant beds.

Distribution

The Gila trout is native to the Mogollon Plateau of New Mexico and Arizona. It was once common in the Gila and San Francisco Rivers and tributary streams, in southwestern New Mexico, and in the Verde and Agua Fria drainages in Arizona. By the 1960s, it was eliminated from the Verde and Agua Fria drainages.

When the Recovery Plan was completed in 1978, native populations of the Gila trout were confined to five streams in New Mexico—Diamond, South Diamond, McKenna, Spruce, and Upper Iron Creeks. In addition, two other streams in Mexico and Arizona harbored introduced populations— McKnight and Sheep Corral Creeks. The 1992 population numbers were for fewer than 10,000 individuals; many were stunted because of crowding or insufficient food sources. Fortunately, healthy breeding populations survived on protected land in the Gila Wilderness Area, providing a strong base for reintroduction efforts.

Threats

The Gila trout declined in its native waters because of degraded water quality, heavy fishing, and hybridization with non-native trout, which were introduced as game fish into the watersheds. Dam building, water pumping, stream channeling, road building, and logging have radically altered the water system within the Gila trout's range.

Conservation and Recovery

Recovery efforts have focused on removing non-native trouts from selected sections of higher quality streams, erecting barriers to prevent their return, and then restocking the waters with populations of the Gila trout. This strategy essentially creates refuges within the streams, where the Gila trout is the preferred and dominant trout species. The U.S. Fish and Wildlife Service (FWS), the Forest Service, New Mexico Department of Game and Fish, and New Mexico State University have collaborated on recovery.

By the end of 1987, biologists had restored seven populations in designated wilderness areas—six within the Gila National Forest in New Mexico, and one in Prescott National Forest in Arizona. Restoration has been so successful that the FWS has proposed to "downlist" the Gila trout from Endangered to Threatened, although by the time the 1993 Recovery Plan revision was released, that action had not yet taken place. The revision estimated that downlisting could be possible by 2000 if continuous progress was made.

The recovery team has attracted the support of local residents and sport fishermen by emphasizing the Gila trout's potential as a game fish. Because many of the habitat streams are at or near their carrying capacity, sport fishing is not expected to interfere with the recovery of the Gila trout. If unforeseen problems developed, the sport season could be terminated.

Recovery efforts have had varying levels of success. In the late 1980s, for instance, FWS biologists implemented a captive propagation program by transferring 36 adult fish and 1,800 eggs to Mescalero National Fish Hatchery in New Mexico. Captive-raised fingerlings will be used to build a brood stock and restock new streams. Future efforts will concentrate on rehabilitating and restocking larger streams to expand the Gila trout's range.

Other recovery efforts have included replication of the five relictual populations, completion of several biological and ecological studies, initiation of development of hatchery techniques, and the development of a population monitoring protocol. Survey efforts are continuing in an attempt to locate new populations, and studies are being conducted to establish the degree of genetic divergence among the five indigenous populations and related fish. Public information efforts about the plight of the Gila trout and the need for its recovery have included brochures, a slide series and videotape, and publication of public education articles.

The goal of the Gila Trout Recovery Plan is to improve the status of the fish to the point where survival of all indigenous lineages is secured and maintained. To accomplish this goal, a large array of factors was considered, including the species' historical distribution, its habitat requirements and preferences, and available management alternatives.

The 1993 revised plan outlined two possible strategies for recovery; the first involves the preservation of the Gila trout as a relictual species in a few small, isolated headwater streams without expanding distribution within the historic range to any appreciable degree. The second, preferred strategy, is to accelerate expansion of current distribution of Gila trout within its historic range into larger, more stable, resilient habitats. Adoption of this strategy would greatly reduce the likelihood of local extinction caused by natural, stochastic events and human-induced disturbances.

Contact

U.S. Fish and Wildlife Service
Division of Endangered Species
P.O. Box 1306
Albuquerque, New Mexico 87103
http://southwest.fws.gov/

References

Behnke, R. J., and M. Zarn. 1976. Biology and Management of Threatened and Endangered Western Trouts. U.S.D.A. Forest Service General Technical Report RM-23 Rocky Mountain Forest and Range Experiment Station, Fort Collins.

Minckley, W. L. 1973. Fishes of Arizona. Arizona Game and Fish Department, Phoenix.

U.S. Fish and Wildlife Service. 1979. "Gila Trout Recovery Plan." U.S. Fish and Wildlife Service, Albuquerque.