RIFLE — On a recent morning at the Rifle Falls Fish Hatchery in western Garfield County, a tanker truck sidled up to a shallow concrete canal full of rainbow trout.
As a mechanical scooping arm on the back of the truck extended toward the water, workers dressed in fishing waders pushed a large screen toward the bottom of the canal, corralling the fish for capture.
After scooping, the driver hoisted a bucketful of about 200 pounds of 4-inch-long fish above the water and dumped it into a 550-gallon tank on the truck bed. An aerator and oxygen diffuser in the tank were switched on, and the fish swiveled toward them, in the direction that felt like upstream.
That day, technicians at the Rifle hatchery would move some 100,000 fish to Dillon Reservoir in the central Rockies. It was only a fraction of the 5 million fish that the fishery will place in lakes, rivers and streams around the state this year, along with nearly 1 million fish measuring at least 10 inches long.
Beneath the bucolic natural veneer of fishing in Colorado waters is a highly engineered management program, orchestrated by Colorado Parks and Wildlife (CPW). It’s calibrated to make sure that when a fisherman casts on a given stretch of water, there’s a fish somewhere nearby.
Coloradoans love to fish, and fish in many areas see extreme human pressure throughout the spring, summer and fall. Fish also contend every year with drought, high temperatures, acidic water and a range of other environmental challenges.
Although plenty of naturally sustaining fish populations exist, there are other areas where fishing would be practically impossible if not for human stocking.
“There are some waters where the fishing demand is so high that it’s almost impossible to satisfy that demand,” said Sherman Hebein, CPW’s senior aquatic biologist for the northwest region.
“You have to limit it,” he said. “You can stock as many as 1,000 fish per surface acre, but you have to ask: is it the same clientele coming again and again, or do you have different people coming to enjoy the fish?”
The need to stock Colorado’s lakes, rivers and streams originated after settlers in the 1800s depleted the fish population. Today, it’s a tool to accommodate the state’s recreation industry.
Colorado’s fish stocking infrastructure is substantial: Statewide, there are 11 hatcheries charged with spawning fish, 15 involved with hatching and rearing, and 18 that release stocked fish into the wild.
In the Roaring Fork Valley alone there are three hatcheries charged with spawning, raising and stocking fish in waters from Independence Pass to Utah, and from the Wyoming border down to the lower Gunnison River Basin.
Sept. 1 is a day of celebration at the Crystal River Fish Hatchery south of Carbondale — it’s the birthday that hatchery technicians have assigned to every one of the hundreds of thousands of fish raised there.
Technicians at the hatchery raise Snake River Cutthroat Trout, Bel Air Rainbow Trout and Hofer Harrison Rainbow Trout. Knowing the rough age of the fish is critical, so that they are moved from incubators to troughs to outdoor concrete canals — called raceways — at the proper times.
On a recent day, technician Jake Eichler was hunched over a screen covered with bright orange fish eggs in a squat cinderblock building at the hatchery. He examined the eggs for a small black dot, a sign of fertility.
The fertile eggs would be placed in holding trays or buckets and immersed in fresh, circulating water. Ultimately, about 95 percent of them will hatch into fish. Eggs in the wild, by comparison, have a 1 to 3 percent survival rate.
At the age of 6 months, the survivors will move outdoors, into the shadow of Mount Sopris. At the age of 2, they’ll be separated by gender, and around that time, spawning will begin.
“We are a brood unit and we focus on egg production,” said Robert Streater, the hatchery manager. “Our whole purpose is to produce and distribute anywhere from 6 to 10 million trout eggs annually.”
To do that, technicians conduct a massive spawning operation each fall, manually mixing female eggs with the sperm from male fish — called milt — to fertilize them.
Most of the eggs are distributed to hatcheries across Colorado and the West, sometimes sent via Federal Express in little more than a wet paper towel.
The rest are hatched in Carbondale to maintain the hatchery’s breeding population. Despite their domestication, once they enter the raceways the fish always orient themselves “upstream” toward the place where water is flowing in.
Ask any angler to describe their perfect fishing day and you’ll likely get a range of responses. Some will mention the value of fishing with family, some the poetry of an isolated mountain lake and some the pleasure of a 12-pack of the finest lager.
But if you ask Hebein, the CPW biologist, he’ll tell you precisely: the perfect fishing day is catching one fish per hour, 2.5 fish per trip.
That rather odd standard (who wants to catch half of a fish?) is used by CPW as a benchmark of ideal stocking levels in rivers, lakes and streams across the state.
In the Aspen area, the task of getting it right falls largely on the shoulders of Kendall Bakich, a field biologist who spends her days roaming the waters of the Roaring Fork, Frying Pan, Colorado and Eagle rivers, sampling fish populations and interviewing fishermen about their catch.
Bakich starts by gauging the health of fish in a given stream. To attract fish, she uses a technique called electro-fishing that sends a mild electrical current into the water through a hand-held wand.
“It just causes the fish to roll over, and actually, they will orient to the electrode,” she said. “It’s uncomfortable for them, but they recover right away.”
Bakich tags the fish, either by punching a small hole in its tail or attaching an identifying tag. She measures and records weight and length before letting the specimen go.
“You can never get every fish, so it isn’t exact, but we get a pretty good idea of the population over time,” she said.
To supplement that fieldwork, Bakich talks to as many fishermen as she can about what they’re catching, and how long they’re staying out each day. Sometimes she’ll simply call them up, since anyone purchasing a fishing license must list their phone number.
So-called “creel surveys,” she said, are an unbiased way of figuring out how much fishing pressure there is.
Yet prescribing stocking levels is only one aspect of Bakich’s job. When high temperatures, overly acidic waters, or other factors stress fish in a stream, it falls on CPW biologists like her to recommend voluntary or mandatory fishing restrictions and closures.
“Above 65 degrees, we get concerned, above 70 we ask people to stop fishing,” said Hebein. “At those temperatures you can stress a fish out, and it will swim away and experience something called delayed mortality. We don’t really want to see how far we can push a fish.”
Each year, the majority of state-sponsored stocking is over by the Fourth of July, since that’s typically when water temperatures begin to rise and fishing pressure spikes.
“As the summer goes on, we have to be careful about where we stock,” said Hebein. “Fish that are already in the river can acclimate to changes in acidity and temperature, but if you were to drop a hatchery fish into warmer water in August, it would have a hard time adapting.”
The rules are different for cooler, high elevation areas like mountain lakes, where CPW technicians will sometimes stock spring spawning species like cutthroat trout well into August or September.
“Sometimes we’ll bring fish in on a horse, just put them in some big plastic bags and pack [the bags] out,” said Bakich.
Such low-tech approaches are complimented by aerial stocking, where fish are dumped from prop planes flying low across the surface of high mountain lakes.
The state maintains a fleet of four stocking planes, and stocks between 200 and 300 high mountain lakes each year. Each plane is equipped with hoppers that can hold 10 fish species at a time.
Large fish are unsuited for aerial stocking. If the fish are about one-and-a-half inches long, though, most of them will survive the impact of hitting the water, according to Rifle Falls Fish Hatchery Assistant Superintendent Mark Jimerson.
Jimerson has accompanied pilots on many aerial stocking trips, and he said they often involve some tricky flying.
“They try to drop them 20 feet over the lake,” he said. “They will drop the plane, then pull up just over the lake, then pull out of it and clear the trees. Those guys are good pilots and they’re just a little bit crazy.”
For a fishing guide, it might seem like fish stocking has some obvious benefits. After all, a stocked river increases the chances that a client — even an unskilled one — will experience the thrill of catching a fish.
Yet some fly fishing guides in the Roaring Fork Valley have a less than friendly view of the practice, claiming that stocking can “dumb” down the fish population in local rivers by stripping fish of their wild instincts.
No strong opponents contacted by the Aspen Daily News of stocking would go on the record for this story.
Still, it’s easy to see how stocking might be bad public relations for the guiding industry. It makes paying guests wonder whether the fish they’re catching are actually wild, and lends an engineered feel to a pursuit that some guides try to pass off as entirely natural.
But Dave Johnson, owner of the Crystal Fly Shop in Carbondale, said stocking is a necessary part of keeping some local stretches of river healthy.
“Certain areas definitely depend on stocking, and even a gold-medal river can benefit hugely from stocking in places where there’s intense pressure,” he said.
Johnson noted that because rainbow trout tend to spawn just before spring runoff, high water can sometimes wash away entire nests. When that happens, stocking is essential to maintain the population.
Opinions differ widely on whether stocked fish can ever fully develop their wild instincts, or how quickly that happens.
The difference between a stocked fish and a wild fish, said Crystal River Hatchery veteran technician Rodney Bland, is “about five minutes.”
Johnson said adaptation takes a bit longer, but it happens nonetheless.
“I think stocked fish develop wild instincts within no longer than a week of being in the river,” he said. “Areas where fish get stocked tend to be very accessible areas, where the stocking truck can pull up, and those areas see high pressure. Those fish are educated very quickly. Besides, this valley gets such massive fishing pressure that we need stocking, pure and simple.”