While the numbers for brown trout weren't as outstanding, they still took a significant leap between Holter Dam and Cascade recently, with an estimated 850 per mile that were longer than 10 inches. The average is 384 brown trout per river mile in that stretch.
Chris Strainer, owner of CrossCurrents fly shops in Helena and Craig, said those numbers are translating into "fish on."
"Everyone who has been fishing has noticed that catch rates are up and visibly, you can see more fish out there," Strainer said. "It makes the guides look pretty good, even though those big numbers don't always mean it's easier to catch fish. There are times when you can catch a couple with very little effort, but if it's smoky, hot and windy, it's hard to catch fish in those conditions."
Eric Roberts, another FWP biologist, said there are strong brown and rainbow numbers upriver from Craig and below Canyon Ferry and Hauser dams.
All three men attribute the bump in trout numbers to recent high water years. Grisak noted that 2010 and 2011 had springtime flows of more than 18,000 cubic feet per second (cfs) downstream of Holter Dam and when that happens, a lot of fish are flushed over the dams.
"We found when flows are over 18,000 cfs, we generally have record numbers of rainbow trout," Grisak said. "A similar situation occurred in 1996, '97 and '98."
Roberts added that the high-water years also flush out sediments from the cobbles in the river and their tributaries, which helps enhance trout habitat and leads to healthier fish.
"That flushing opens up a lot of spawning habitat and cleans out the gravels that get buried with sedimentation," Roberts said. "Cleaning the gravels also invigorates the invertebrates — the bugs — and then there's sort of a cascading effect through your food chain. That leads to bigger fish, more robust fish and more reproduction."
FWP stocks a few varieties of trout in Canyon Ferry Reservoir, and Strainer said about 40 percent of the rainbows below the dam were hatchery fish in 2011. That percentage is falling as the wild fish population grows.
"You can tell the difference between hatchery and wild trout because the hatchery fish have fins that are warn off or bit off," Strainer said. "Wild fish have good looking full fins."
While brown trout larger than 10 inches long in the Pelican Point section of the Missouri north of Craig were estimated at 545 per mile, compared to the long-term average of 384, Roberts said he's not seeing as many large brown trout as they have in the past upstream in Hauser.
"The big old trophy-size browns have aged out," Roberts said. "But we're seeing good recruitment with the younger fish."
He reminds anglers that browns are strictly catch and release regardless of the size, since their numbers are still below historical levels.
Roberts said that he's seeing a lot of activity on the river in recent months. Fish tend to congregate in the winter, so if ice anglers find the right hole they're getting a lot of bites. Rainbows also are spawning, with the extra activity making them more prone to biting on hooks.
"Right below Canyon Ferry Dam — which technically is still Hauser Reservoir — the fishing is good in the springtime with rainbows coming up from Hauser," Roberts said. "But the rainbow bite on all three of the big reservoirs already is cranking up, including on Holter near the Gates of the Mountains."
The increased number of fish in the river brought plenty of anglers. In 2011, the Missouri River from Holter Dam to Cascade had an estimated 105,989 angler days. It was the number two fishery in the state, after the Bighorn River, and translates into nearly $14.5 million in revenue.
Strainer said he's noticed an uptick in business, and while this is a good time to fish, he cautions people to stay away from the "redds," which are clean piles of small stones that the fish have created to lay eggs.
"The worst thing you can do is walk on those spawning redds," Strainer said. "One person can destroy thousands of eggs by walking on them."