Missouri River trout surveys indicate rainbow numbers remain above the long-term average and brown trout numbers are near average between Holter Dam and the town of Cascade, said a state fisheries biologist.
State fisheries crews last fall estimated 4,073 rainbow trout greater than 10 inches long per mile near the town of Craig on the Missouri. Not only is that above the long-term average of 3,307 rainbows per mile, but continues a trend of above average numbers for the fifth consecutive year.
The population was bigger in size and slightly lower in abundance than the past several years, said Fish, Wildlife and Parks fisheries biologist Jason Mullen, which is typical as the current population reaches its maximum size.
“This year,” Mullen said, “the most abundant length group of rainbows in the Craig section was 18 inches, with 43 percent of the population being 18 inches long or longer.”
Brown trout in the Craig section at 10 inches long and greater were estimated at 433 per mile. The long-term average is 572.
Downstream in the Cascade section, near the town of Cascade, the estimate for rainbow trout 10 inches long and greater was 1,862 per mile. The long-term average is 1,600 per mile. While estimates include only fish 10 inches and greater, crews also handle fish less than 10 inches, and rainbow trout of this size were much more abundant in 2015 than the last several years in this section.
Brown trout in the Cascade section 10 inches long and greater were estimated at 476 per mile. The long term average is 397.
Brown trout populations are sampled in the spring and rainbow populations are sampled in the fall to avoid handling fish during their spawning seasons.