Salmon River Fly Fishing Articles

Westslope Cutthroat Trout Thrive in the Middle Fork

Status

Idaho’s state fish, the westslope cutthroat trout, is native to the Middle Fork of the Salmon River. One of the Corps of Discovery leaders, William Clark, of the Lewis and Clark Expedition, not only discovered the westslope cutthroat trout, but named it in 1804. Hence the name Oncorhynchus clarki lewisi.

It has been estimated that westslope cutthroat trout populations are strong in only 22% of their original range. Although the strength and number of westslope cutthroat trout stocks in large rivers and lakes and their principal tributaries has declined from historic levels, the US Fish and Wildlife Service found that viable, self-sustaining westslope cutthroat trout stocks remain in the Middle Fork and its tributaries.

Life History

Westslope cutthroat reach maturity at about age three and tend to spawn at four or five. As with other trout species, westslope cutthroat can spawn more than once in a lifetime, however the rigors of mating behavior can lead to high rates of mortality especially in males. Spawning occurs between March and July depending on stream temperatures and flows.

As winter approaches and stream temperatures drop, westslope cutthroat begin to seek out deep, slow moving pools to spend the winter. As temperatures drop, a trout’s metabolism slows down. As a result of their decreased metabolism the trout do not need to eat as much, and they lack the energy needed to swim in strong currents. Deep pools with abundant cover, such as large boulders and logs, are important over winter habitat.

Westslope cutthroat trout in the Middle Fork Salmon drainage tend to exhibit two major life history types: migratory and resident. Adult migratory fish may travel up to 150 km (93 miles) from wintering areas in the Middle Fork Salmon River to small headwater streams where they spawn. In some areas after spawning the adults will spend the entire summer in or near the spawning tributaries, and in other areas the adults return to the Middle Fork Salmon River soon after spawning in the spring. Resident westslope cutthroat trout populations spend their entire lives in small headwater streams and tend to be smaller than migratory cutthroat because of the limited food and space available in small, cold, headwater streams.

Whether a population of westslope cutthroat trout is migratory or not probably depends on the environment they live in. Migration requires the expenditure of a great deal of energy and may expose fish to a number of hazards, such as predators. An advantage of migration is that it allows fish to grow much larger and produce more eggs by feeding on the abundant prey in large rivers and lakes. More eggs mean more fish.

Behavior

Westslope cutthroat trout tend to feed mostly on aquatic insects, terrestrial insects that fall into the water, and other small organisms. Westslope cutthroat trout rarely feed on other fish, which is common behavior for other types of cutthroat trout. By feeding primarily on invertebrates, westslope cutthroat trout may avoid competition for food with fish eating species, such as bull trout, and squawfish. Westslope cutthroat trout may avoid competition with other fish species by using different habitat. As many anglers know, a fly cast into faster, turbulent water is more likely to draw a strike from a rainbow trout, steelhead smolt or whitefish. However, casts into deep, slow moving, boulder strewn, glides, along the river bank and the tails of slower moving pools will often draw out westslope cutthroat.

Vulnerability to Human Impacts

Of the numerous impacts humans can have on the westslope cutthroat’s environment an increase in the rate of fine sediment delivery may be the most common and have the most far-reaching effects. Abnormal increases in fine sediment in streams can fill in the hiding spaces for fish between rocks, smother fish eggs, and reduce the number of aquatic insects that provide food for fish. Improper road drainage, poor grazing, logging, and mining practices, and catastrophic fires are the main problems. However of the above only catastrophic fires are a concern on the Middle Fork and its tributaries, as they all flow within the 2.4 million acre Frank Church River of No Return Wilderness, where no road building, cattle grazing, logging etc, are not allowed. The Middle Fork Salmon drainage is located within a geologic region known as the Idaho Batholith Granitics. The granitic soils of the region are highly erodible, hence the fear of catastrophic fires.

Westslope cutthroat trout are highly vulnerable to angling pressure and as a result special fishing regulations have been implemented to protect populations in many systems, like the Middle Fork Salmon River. On the bright side, the blue ribbon fishery on the Middle Fork Salmon River provides testament to the responsiveness of westslope cutthroat trout populations to catch and release regulations that were enacted in the early 70’s. The westslope cutthroat trout is alive and well in the Middle Fork.