For hungry trout, few meals compare to the giant salmonfly, a finger-size slug of protein that packs more meat in one gulp than a handful of lesser bugs.
“Think T-bone steaks on the river,” said Woodland Park fly fishing guide Robert Younghanz.
But on the Arkansas River, Pteronarcys californica has been missing from the menu for upward of a century, the casualty of a toxic past.
One state aquatic biologist hypothesizes they suffered a localized extinction, or extirpation, during an era when Leadville mine waste flowed unchecked into the Arkansas. That was before new water treatment measures initiated a turnaround that began in the early 1990s and eventually spawned one of the state’s most popular fisheries, reported The Gazette.
Now an effort to re-establish the bug, also known as the giant stonefly, seeks to add a fresh chapter to the unfolding success story. It has anglers sitting up and taking notice, even as it puts the river’s vaunted recovery to the test.
In 2012, Colorado Parks and Wildlife launched a three-year effort that scooped up an estimated 135,000 giant salmonfly nymphs from the Colorado River near Kremmling and deposited them at eight test sites near Salida.
After mounting what the agency calls the largest insect transplantation on record, a problem emerged at a critical juncture.
In 2015, a year after the last of the salmonfly deliveries to the Arkansas, state wildlife workers went back to the test areas to gauge their progress, searching the riverbank in 100-foot swaths, from the water’s edge to the willows.
After 58 man hours, they found no evidence that transplanted salmonflies had crawled out of the river to shed their exoskeletons and sprout wings, the culminating change in their roughly three-year life cycle.
Further searches this spring and summer turned up no adults and little more than a “handful” of exoskeletal chucks, said Greg Policky, the state aquatic biologist who devised the experiment.
The hunt to figure out why has Policky, a more than two-decade veteran of the agency’s Salida office, mulling troubling questions about a river he’s spent much of his career rehabilitating.
Of all the rivers in Colorado, the Arkansas holds special allure for anglers.
They come to enjoy a 102-mile stretch of Gold Medal water, the state’s designation for its highest-quality fisheries, recognizing those with a standing fish stock of 60 pounds per acre and at least 12 trout per acre larger than 14 inches.
By those standards, the Arkansas has the most prime fishing in Colorado.
When the river won its designation in 2014, it boosted the state’s total mileage of Gold Medal streams by a third, to 322 miles.
It wasn’t always so.
After mining came to Leadville in 1859, heavy metals began filtering into the Arkansas and ravaged its ecosystem, killing all fish around Leadville. Further downstream, near Salida, trout for decades lived for no more than two to three years — long enough to spawn, but too brief to acquire significant size.
“The Arkansas was a dead river,” said Jean Van Pelt of the Southeastern Colorado Water Conservancy District.
The river’s fate began to change in 1992, when two treatment facilities were constructed near Leadville to remove heavy metals like cadmium and zinc, generated on mine runoff, before they reached the river.
The effect was nearly immediate.
“It turned things around,” Policky said. “By 1994, we had a self-sustaining population of brown trout here.”
Better water quality cleared the way for two decades of piecemeal improvements, including efforts to restore the Arkansas to a natural state in areas where it had been straightened or otherwise modified, a common occurrence in the developing West.
Downstream near Salida, the effect of the river’s rehabilitation was profound, fattening up trout and extending their life expectancy to up to a decade.
In theory, it should have created trophy conditions for the giant salmonfly, too.
On rivers where Pteronarcys californica thrive, the anglers are as happy as the fish.
The bugs grow up to 2½ to 3 inches long, and their annual hatches in May and June induce feeding frenzies in streams across the Rocky Mountain West.
On the Frying Pan River, trout pick salmonflies off rocks jutting from the water until their bellies grow distended.
“You land them and they’re puking stoneflies out,” said Dave Way of the Western Anglers fly shop and guide service in Grand Junction.
A recent hatch in the Black Canyon of the Gunnison created a spectacle on par with the towering cliffs, said Bill Edrington, founder of Royal Gorge Anglers in Cañon City.
“It looked like thousands of hummingbirds in the sky, catching thermals and rising,” he said.
Unlike commercial rafting, an industry in which every customer is accounted for, fishing is harder to track. But it appears to be on the uptick, and a big part of the draw is the Gold Medal designation, said Bob Hamel, owner of Arkansas River Tours.
“It’s a marketing tool as well as a fact of the condition of the river,” Hamel said. “Obviously, people want to fish Gold Medal water. They want to go to Blue Ribbon rivers in Montana. It’s a draw. The good thing for us is it’s pretty much the whole river you can access, so it’s pretty spread out.”
Aside from their incredible size, the giant salmonfly is also known for its sensitivity to pollution.
Where mayflies and caddisflies tolerate some level of heavy metals, for example, conditions must be right for giant salmonflies, which prefer pristine, fast-moving, highly oxygenated streams with large cobble bottoms.
Reintroducing the giant salmonfly was meant as another effort to reverse decades-old missteps on the Arkansas.
During all three years the bugs were stocked, they hatched in mid-May, fueling hopes it would be a matter of time before they took off like “gangbusters,” he said.
Back-to-back years without hatches suggest the process will be slower than expected; it could also indicate the experiment has been a failure.
Policky urges patience.
Any number of factors could explain the bugs’ apparent absence, Policky said, including competition from other bugs, or the large amount of sediment that washes into the river from the overgrown forests cloaking the Collegiate Peaks.
But he acknowledges the problem could also be environmental. For that reason, the search to explain the bugs’ failure to take wing is centered on water quality data measured by sensors by the river’s headwaters near Leadville.
So far, the data show no evidence of heavy metals in the water, but the monitoring isn’t continuous, raising the possibility that some level of contamination could be finding its way back in.
Standing at the river bank, he mulled the possibilities.
“Did heavy metals rear their ugly head again? Did we have a release that we don’t know about? This is the canary in the coal mine.”
An army of fishing guides is keeping an eye out to see if the bug has gained a toehold somewhere out of sight.
Strictly speaking, the brown and rainbow trout in the Arkansas don’t need another insect; the river’s transformation spawned a “veritable buffet line” of options, Edrington said.