Fish surveys last year indicate rainbow and brown trout numbers are up in the Missouri River between Holter Dam and the town of Cascade.
State fisheries crews last fall estimated 7,312 rainbow trout greater than 10 inches long per mile near the town of Craig on the Missouri. The long-term average for that section is 3,036.
Fish, Wildlife and Parks fisheries biologist Grant Grisak attributes the larger number of fish to the high water years of 2010 and 2011. Both years had flows in the springtime of over 18,000 cubic feet per second downstream of Holter Dam.
“We found when flows are over 18,000 cfs,” Grisak says, “we generally have record numbers of rainbow trout. A similar situation occurred in 1996, ‘97 and ’98.”
Besides more water in the Missouri River main stem, the increased flows, Grisak says, “flushes fish out of the tributaries. That increases survival with more space, more food and less chance of whirling disease infecting young rainbows.”
Brown trout numbers near Craig were also up. Brown trout greater than 10 inches long were estimated at 850 per mile. That compares with the long-term average of 570 per mile.
In the Pelican Point section, just upstream from the town of Cascade, rainbows were estimated at 2,182 per mile, which is higher than the long-term average of 1,506.
Brown trout larger than 10 inches long in the Pelican Point section were estimated at 545 per mile. The long-term average is 384.
The increased number of fish in the river brought plenty of anglers. In 2011, the Missouri River from Holter Dam to the town of Cascade had an estimated 105,989 angler days. That makes it the number two fishery in the state, after the Bighorn River, and translates into nearly $14.5 million in revenue to the state.
Brown trout populations are sampled in the spring and rainbow populations are sampled in the fall.
(Report by Bruce Auchly, Montana Fish, Wildlife and Parks – Region 4)