Gila Trout

Oncorhynchus gilae gilae

Native Trout Fly Fishing

A Gila Trout from a small stream in the Gila Wilderness Area of New Mexico.

Introduction

The Gila trout were once found throughout much of the higher reaches of the Gila and Verde River basins of Arizona and New Mexico, but have suffered major declines in the past century. It is thought that the Verde population may have represented an intermediate between the Gila and Apache trout, however this population has long since been exasperated a little is known about it (Behnke 2002). While it was once thought that Gila trout were more closely aligned with cutthroat, recent research indicates that they are more closely associated with rainbow trout and likely represent a relic lineage that migrated up the Colorado River during a period when the climate was cooler.

Life History Information

Gila trout historically occurred as both fluvial and stream resident populations. However due to their rapid disappearance across their native range, little is known about the fluvial life history form that likely occurred in the Gila and Verde River systems. A few stream resident populations are still found across the native range of the Gila trout and it is from these populations that we have gained our knowledge of the habits of these fish. Gila trout like other western trout are spring spawning fish and have the ability to spawn more than once. Spawn timing is largely controlled by flows and temperature and generally occurs when the stream temperature reaches 45 degrees Fahrenheit in early April in lower elevations and continues through June in the higher elevations (Rinne 1980). According to Behnke (2003) Gila trout typically spawn for the first time at around age three and at a size of 5 to 9 inches, with females of nine inches long producing around 300 eggs. Although it is temperature dependent, fry generally emerge from the gravel about 8 to 10 weeks after they were spawned and inhabit riffles (Rinne 1980). As Gila trout grow they seek out the better habitat provided by pools, undercut banks and log jams. While Gila trout require cold clean water to survive, Lee and Rinne (1980) have showen that they are able to survive temperatures up to 80 degrees for limited periods of time and will continue to feed until temperatures exceed 73 degrees. Generally speaking stream resident Gila trout are homebodies and tend to remain within about a 350 foot stretch of stream habitat (Rinne 1982). Gila trout are thought to be generalists in their feeding behavior and their diet is primarily made up of aquatic and terrestrial insects. While the availability of food plays a large role in population sizes, Gila trout density tends to be greater in higher elevation reaches of streams (Propst and Stefferud 1997).

Status

The Gila trout have long been one of the rarest trout in North America and since the arrival of Euro-Americans they have dangled on the edge of extinction. The decline of the Gila trout has stemmed from a number of sources, but the introduction of non-native trout as played the largest role in their demise. As with other trout that have been isolated for a long time, the Gilas are not well suited to cope with competition. This has been especially problematic with brook and brown trout, which have the advantage of being fall spawners. This means that their young emerge months before the offspring of the native Gila trout allowing them to gain size secure the best territories, forcing the juvenile Gilas into only marginal habitat. Also once brown trout reach a substantial size, they become piscivorous and feed heavily on the smaller Gila trout. As if competition wasn't enough, Gila trout like cutthroat are still closely enough related to rainbow trout to hybridize with them. This hybridization leads genetic dilution and after many years of stocking rainbows, only slight Gila traits may remain in a given populations.

While non-natives have caused the majority of the Gila trout's problems, several other factors have also played a role. If there is a second place to be awarded for the near annilation of the Gila trout, it would have to be poor land management practices. The environment in the Gila River watershed is very unstable, poor practices in regards to livestock grazing, logging and farming have only made this worst. All three of the practices result in increases in stream temperatures and sediment loads, leading poor survival for eggs and stress or even death in adults. The increased sediment loads experienced during spring run off, also end up giving the fall spawning brook and brown trout another advantage over the spring spawning Gilas, since they experience more favorable spawning conditions.

The decline of the Gila trout has not gone unnoticed and when the Endangered Species Act was passed in 1973, the Gila trout were among the first animals to be listed as endangered. Since their listing in 1973, the restoration of the Gila trout has been an uphill battle. In 1989 just when things were starting to look up for the Gila trout and they proposed to be downlisted to threated, the unstable environment of the Gila watershed threw a curveball in things and set restoration efforts back by 15 years. The first issue was a severe drought in the region resulting in low flows and high stream temperatures, severely reducing population sizes across the Gila's range. Some streams were hit harder than others, and McKnight Creek was among the hardest hit, losing approximately 90% of its population (Propst et al. 1992). However it was Main Diamond Creek, which had hosted the strongest remaining Gila trout population that got hit the hardest. The disastrous chain of events for the stream's Gila trout started when a forest fire swept up the valley greatly reducing the population size. Shortly after the fire a flood swept down the basin eliminating the stream's remaining Gila trout. Luckily the New Mexico Fish and Game Department had the foresight to remove around 500 Gilas from the stream just after the fire and transplant them into the beguiled McKnight Creek, preserving some of the Main Diamond lineage. When the dust settled from the 1989 events, the remaining populations of Gila trout had been reduced by 80% to 90% of their former abundance (Propst et al. 1992). Since these set backs, the Gila trout restoration project has slowly but surely continued to make progress and in 2006 the Gila trout had recovered enough that they were finally downlisted to threatened status (USFWS 2006). Since then some limited catch and release opportunities for Gila trout have been opened in New Mexico and Arizona is also starting to reestablish populations across the state.

Description

It is thought that the Gila and Apache trout both diverged from a common ancestor and as such the two trout share a number of similarities. One of the major differences between the two fish is the spotting pattern. While Apache trout tend to have moderate sized spots, Gila trout have much smaller spots, that are profusely distributed across the body primarily above the lateral line. The coloration of the Gila trout is a bronze to olive-brown on the back and transitions to a golden-yellow color along the sides. Gilas often exhibit a reddish or pink band along the lateral and the same color on the gill plates. This trait is most pronounces in spawning males, although it may be present on females as well. Like the Apache trout, Gilas have deeper and more compact bodies than other western trout and also tend to have longer fins. In fact the Gila trout are known to have the longest adipose fin of any western North American trout. The dorsal, pelvic and anal fins on the Gila trout are all tipped with white, as is common among many rainbow trout populations. Also like the Apache trout, some Gilas may display "bandit" like horizontal bars across their irises.

Stream Resident Form

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Native Trout Fly Fishing
Native Trout Fly Fishing
Native Trout Fly Fishing
Native Trout Fly Fishing
Native Trout Fly Fishing
Native Trout Fly Fishing
Native Trout Fly Fishing

 

Native Range

Native Trout Fly Fishing

A map of the original native range of the Gila trout. Data Source: Behnke (2002) and Propst et al. (1992).