Wild trout thriving and multiplying in Boise River
Wily redband rainbows are prospering in the middle of Idaho’s biggest city.
BOISE, Idaho — Idahoans have a lot to be proud of in the Boise River, especially anglers.
It flows through the middle of Idaho’s largest metropolitan area and within sight of the state Capitol and Bronco Stadium.
The Greenbelt and its walkers, joggers and bikers parallel the river while Canada geese honk from the river and nearby ponds, and bald eagles keep a watchful eye from above.
What’s below the surface is no less impressive. Trout, and lots of them, feed in riffles and hide beneath brushy shoreline. They’re not just any trout — they’re wild, naturally reproducing redband rainbow trout.
If you’ve ever tried to catch those trout, it can be humbling.
There are lots of them, possibly more than you realize, and some that are much bigger than you’d expect.
Every three years, crews from the Idaho Department of Fish and Game take their scary (to the fish) aluminum canoe and go “electrofishing.” The canoe has a generator with long wands that shoot electrical currents into the river.
The stunned fish wash downstream, and Fish and Game biologists and technicians scoop them up and measure, weigh and record what they find, then compare it with past surveys from the river.
Crews were out in fall checking different sections of the river.
The news has been good. The river’s trout population has seen explosive growth since the early 1990s, after minimum winter flows were established, according to Art Butts, regionally fish biologist for Fish and Game.
“It’s remarkable how this river has recovered,” he said.
Trout numbers have stabilized since then, and they’re down slightly from the 2010 survey, but the fish are also larger on average.
There’s a healthy mix of young and old trout, and there seems to be plenty of natural reproduction.
The hatchery rainbow trout that are stocked monthly in the river typically stick to the areas near where they are planted, and they’re either caught or die within a few weeks, Butts said.
Angler surveys have shown anywhere from 25 to 65 percent of the stocked trout are caught, depending on where they’re released and the time of year.
Hatchery trout are also the bulk of the harvest, Butts said. Creel surveys done in 2008 showed wild trout comprised less than 5 percent of the angler harvest.
Also, only about 2 percent of the trout the crews captured were remnant hatchery rainbows. Those fish are sterile, so they can’t spawn with wild trout.
Speaking of spawning, despite finding abundant young trout, Butts said they can’t pinpoint where the fish are spawning, even though the numbers of small trout in the population make it obvious they are.
He said if they can identify spawning habitat, Fish and Game may be able to increase the trout population more.
“We need to start looking a little more at how the river functions,” he said.
Butts thinks the river can support even more trout if spawning areas can be identified and habitat improved.
“I think it’s a pretty neat stream, and I think it’s only going to get better,” he said.
The Boise River is an interesting stream that differs from its upstream tributaries, the North, South and Middle forks.
The best trout habitat is from Lucky Peak Dam down to about Star, then water conditions downstream tend to favor warmer-water fish.
In the stretch between the dam and Star, there are numerous diversions but few natural tributaries, and tons of development.
The river flows are regulated by the dam, and the flow cycles differ from its free-flowing tributaries.
Those streams rise when snowmelt comes out of the mountains, then flows decline throughout late spring and summer.
The Boise River rises with the snowmelt in the spring but stays at a higher, regulated flow as cool water is released from the depths of the reservoir all summer.
That time of year is when many anglers prefer to fish, but higher flows make it a challenging river because it tends to fill bank-to-bank with swift current.
Trout are also wary because there is no shortage of predators ranging from mink to ospreys to larger trout.
Crews captured a 26-inch brown trout during their fall surveys, and it probably didn’t get that big eating insects.
Despite that monster, brown trout haven’t been faring as well, Butts said, despite recent stockings of fingerlings that all but disappear.
He said browns are harder to raise in hatcheries and transport than rainbows, and they’re not seeing good natural reproduction from browns in the river.
They’re also finding the average size of the trout tends to decrease as you move downstream, and the area around Eagle Island seems to be rearing habitat for smaller trout, as well as brown trout.
The river also seems to lack the prolific insect hatches of other dam-controlled rivers, such as the South Fork upstream and the nearby Owyhee River in Eastern Oregon.
“It (Boise River) seems to be more of a nymph fishery year-round, even in summer when most people prefer dry fly fishing,” Butts said.
That’s not to say the Boise is ignored by anglers. It gets thousands of hours of fishing, and people catch a lot of trout there. It’s just not easy, and that’s part of its charm, and also what makes the whole thing remarkable.
A river runs through Idaho’s most populated and densely developed area, it teems with wild trout, but they can confound even expert anglers.