Whitehorse Basin Cutthroat

Oncorhynchus clarki ssp.

Native Trout Fly Fishing

A cutthroat from a small stream in the Whitehorse Basin of southeastern Oregon.

Introduction

The Whitehorse basin cutthroat is a minor subspecies that is closest related to the Lahontan cutthroat. This trout is native to two small streams, Willow and Whitehorse Creeks, which flow from the Trout Creek Mountains in the southern Oregon desert and as such are also known as the Willow-Whitehorse cutthroat. During the cooler climate of the last ice age these fish inhabited Coyote Lake, which once filled much of the basin. However when the lake receded about 10,000 years ago due the shift to a dryer climate, these trout became isolated in Willow and Whitehorse Creeks. Today these streams flow through a rugged and arid region where water daily water temperatures can reach the 80's (Fahrenheit) and flows are often very unstable.

Life History Information

Being isolated in two small streams that both dry up in the desert before reaching any larger bodies of water, the Whitehorse basin cutthroat are found only in a stream resident form. However no formal life history studies have been conducted in the basin and ODFW (2005) suggested that they may be a migratory component to the population. Like other varieties of trout living in an arid environment, these trout have adapted an incredible ability to survive under extreme conditions and even reach some respectable size. It has been shown that these fish are at least able to withstand short periods of time at temperatures between 80 and 85 degrees Fahrenheit (Smith 1984; Dunham 1999). However adult fish seem to favor the habitat in beaver ponds and at the outflows of these ponds during these high temperatures and as overwintering habitat (Talabere 2002). Under these conditions cutthroat of the Whitehorse basin are known to attain an average size of around 6" to 10", with a general maximum at around 14" long (Behnke 2002). However size is greatly correlated to elevation and the productivity of the stream reach and Jones et al. (1998) showed that age one and older fish were significantly larger in lower elevation reaches. These fish are generalists and their diet consists primarily of both aquatic and terrestrial insects. It is thought that these fish reach sexual maturity at age two and have a maximum age of between four and five years old. Spawning takes place during the spring once flows begin to subside and the eggs develop quickly after being spawned. However extreme conditions of the basin may limit the survival of juvenile fish and juvenile recruitment tends to be best during wet years.

Status

Due to its very restricted range and the extreme conditions of the area that it inhabits, this cutthroat is very susceptible to extinction. Luckily today the populations of cutthroat in the Whitehorse basin are more stable than in the past and since no non-native trout have been introduced into the basin their chances of their continued survival seem good. However this was not always the case and at one time habitat degradation had seriously threatened the viability of the Whitehorse basin cutthroat. The main cause of this habitat degradation was from poor grazing practices, which caused a wide variety of problems for the streams and trout. These problems generally start with the loss of riparian vegetation, which in turn leads to in an increase in water temperature and the de-stabilization of stream banks. The second issue of de-stabilized stream banks is only made worse as livestock continue to visit the stream and cave the banks in, greatly increasing the sediment load of the stream. These high sediment loads can cause trout eggs to suffocate, greatly reducing survivability and the welling being of the population. In the 1960's these factors combined with a fire that was initially set to improve cattle grazing to began to take their toll on the cutthroat and the populations showed drastic declines (Trotter 2008). It took a long time for things to start improving for these fish and when the population hit a low of 8,000 fish in 1989, it was time for action. Since then several recovery efforts have been put into place and things have gotten a bit better for the cutthroat in these two drainages. The most successful of these included fenced areas to keep the cattle out of the riparian zones of the stream and setting up an ecologically friendly grazing rotation cycle. Things have gotten better for the Whitehorse basin cutthroat and in 1994 the population reach a high of around 40,000 fish (Jones et al. 1998). However a 2005 study showed another drop in the population size as several years of drought dropped the numbers down to their lowest levels since 1989, with only 14,000 fish estimated to be found in the basin (Gunkel and Jacobs 2005). While numbers of these fish continue to fluctuate, both the Willow and Whitehorse Creek populations have been deemed to be stable enough to permit catch and release fishing and with a couple of wet years it is hoped that the population will rebound once again.

Description

The coloration of the Whitehorse basin cutthroat is very similar to that of the Humboldt cutthroat. Typically these fish are a brownish-olive color on their backs, which transitions to dull brassy or yellowish color along their sides. Some fish may be rather silvery, especially during the early summer and they often display a rosy coloration along their lateral line. Parr marks are often retained into adulthood and are typically a purplish color. These fish are typically more sparesly spotted than their Lahontan cutthroat cousins and have relatively large spots distributed primarily above the lateral line.

Stream Resident Form

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Native Range

Native Trout Fly Fishing

A map of the original native range of the Whitehorse Basin Cutthroat trout. Data Source: Behnke (2002) and Trotter (2008).