Date of this Version
A self-sustaining rainbow trout population has developed in the North Platte River drainage. This population inhabits McConaughy Reservoir and reproduces successfully in tributary streams of the North Platte River located approximately 11.3 to 145 km above the reservoir. Fall and spring spawning populations migrate from the reservoir.
Scale analysis indicated 92% of the juveniles had spent 1 yr and 8% had spent 2 yr in the stream before the spring migration to the reservoir as 175-250 mm smolts. In the 1965-1969 spawning populations 1.3 life history categories were present. The spawning runs were composed of 76% maiden spawners, 22% second-year spawners and 2% third-year spawners. The sex ratio of the spawning runs ranged between 2.0-2.2 females per male.
The rainbow trout population is subjected to a variety of conditions in tributary streams of the North Platte during summer including flooding, irrigation return water and high water temperatures. However, spawning rainbow trout utilize these groundwater streams from November through April. In addition the coldwater habitat in the reservoir is restricted throughout the summer, especially during August.
The established rainbow trout population survived better in this environment than hatchery rainbow trout.