One area of particular interest is located approximately 12 miles south of Steamboat Springs in Northwest Colorado. It is comprised of approximately seven river miles situated between Stagecoach Reservoir on the upstream end, and Lake Catamount (a private lake) on the downstream end. This reach is unique in that it is, and historically has been, virtually a pure rainbow trout fishery.

In 2000, fly and lure, catch and release regulations were implemented on the upper .6 miles of the river just below Stagecoach Reservoir due to a significant increase in angler use. This protection resulted in a robust rainbow trout population from 2000 – 2002, when WD began afflicting this population (figure 1). Whirling disease invaded the Yampa River Drainage in the late 1990’s. Studies in 2002 revealed high levels of whirling disease infectivity within this section of the Yampa River between the two reservoirs. By the fall of 2006, annual inventory work revealed low numbers of larger trout and multiple missing age classes. These sampling efforts also revealed a collapse in the adult population to less than 1000 rainbow trout (>6”) per mile, down from a previous high of more than 6000 per mile in 2001.

Figure 1

Following  the  collapse of this rainbow trout fishery, we began stocking WD resistant rainbow trout in 2006. This Hofer strain has demonstrated strong resistance to the parasite (Myxobolus cerebralis), causative agent of whirling disease. These fish originated from the Kamloops rainbow trout in the Columbia River system in North America. In the late 1800’s these fish were transported to Germany to be grown as food fish in local hatcheries. Because whirling disease is endemic in Germany, these fish were reared in whirling disease-positive waters. Over time this rainbow trout strain developed a resistance to the WD parasite. The WD resistant  strain was brought to Colorado in 2003. 

Because of traits associated with long-term domestication and the goal of reestablishing a wild rainbow trout population, we are using a hybrid of this WD resistant strain and the Harrison Lake rainbow trout from Montana. The Harrison Lake strain has exhibited a higher level of resistance than other strains in Colorado and will migrate between lake and river systems. Given the connectivity of the Yampa River with Lake Catamount, having a mobile component of this population with the ability to use the Lake Catamount resources for better growth and increased fecundity (number of eggs produced), should significantly benefit the fishery.

The management objectives for this fishery are as follows:

• Rehabilitate a heavily used rainbow trout fishery severely depleted by whirling disease.
• Produce a naturally reproducing rainbow trout population using WD resistant genetics to combat WD infectivity.
• Perpetuate a rare pure rainbow trout fishery
• Create a wild spawn operation to help meet statewide needs. A wild spawn take will provide our state hatchery section with a variety of WD resistant rainbow trout that have been subjected to natural selection pressure (environmental conditions will filter out weaker, less resistant individuals).

This unique system, between two reservoirs affords the state a very rare opportunity from a statewide research and management perspective. Following WD most of the riverine systems statewide are now comprised of the more resistant brown trout and there are very few virtually pure rainbow trout fisheries remaining in Colorado. To have a highly infected system, absent brown trout predation and competition, in which we can research the potential of establishing a naturally reproducing rainbow trout population in the face of WD is a great opportunity. Monitoring will continue in 2010 to see if a reduction in whirling disease infectivity levels has been realized following four years of stocking WD resistant trout in the system.