The rainbow time machine
Back to the future with Colorado Rainbow Trout
If this story was a movie, the kind you hear about but never actually see, it might go something like this: Curious young boy meets crazy old professor who invents and attaches a time machine to a fancy car.
Together they travel where no man has gone before: Back To The Future. Not without travails, their time travel gives a glimpse of what we commoners can expect to encounter in the coming years.
Eric Gardunio, Colorado Parks and Wildlife aquatic biologist, like the professor, is looking to the future. I, somewhat like the young boy, except for the young part and the boy part, am just along for the ride.
Our destination? Not a year but a place: the Gunnison River to be exact.
Travel back in time with me for a moment. It is the 1980s and the early 1990s, when fishing in the Black Canyon of the Gunnison from the East Portal downstream to the North Fork confluence commonly yielded rod-bending rainbows, “forearm fish” I called them because they stretched past the bend in your forearm.
These were fat, colorful, spirited fish, having evolved in the fast, cold waters of a steeply dropping canyon fit for their style.
Biologists say they officially are a Colorado River rainbow. Yes, but unscientific fisherman like me will say they have developed their own flair, calling them a Gunnison River strain.
Then before you can say 2000 and welcome in the new century, the fish are gone, the numbers dropping away faster than the steep drop of the precipitous canyon they live in, victims of an imported parasite, whirling disease.
Whirling disease is one of those invasive species that is here to stay. The goal is not to eradicate it, but rather to minimize its effects and manage around it. Gardunio and his partners with Parks and Wildlife have for two decades been working on that.
One solution has been to stock a strain of rainbows from Europe, the Hofer rainbow, that has for a long time been exposed to and developed resistance to whirling disease.
Colorado River rainbows and Hofer rainbows were hybrid with the result known as HXC, Hofer Cross Colorado.
Since 2000, hundreds of thousands of HXC fry have been stocked in the Gunnison from the East Portal to below the North Fork confluence. And the experiment has worked to some degree, not only in the Gunnison, but other rivers across the state.
The Hofer cross is fast-growing and whirling-disease resistant, but having been domesticated in hatcheries in Europe, its genetics don’t seem to be conducive to survival in the wild.
But the professor has other ideas. Some years ago, rainbows that seemed to be not HXC fish started showing up in Parks and Wildlife fishery surveys in the Gunnison.
This means they might be pre-whirling disease Gunnison variety rainbows. Biologists monitoring this say it appears a small but significant percentage of the rainbows in the East Portal area are Gunnison rainbows.
Two years ago, DNA testing was conducted on these rainbows by taking a tissue sample from a fin. Preliminary results show no Hofer DNA.
The theory is that just enough of the original Gunnison strain survived to reproduce. Could it be we have indeed traveled back to the future?
Gardunio’s goal is to move away from stocking HXC fish and build on stocking Colorado River rainbows taken from the Gunnison fish themselves.
Each spring, Parks and Wildlife takes spawn from Gunnison rainbows, raises the fish in a hatchery until the fish reach one to two inches and restocks them into the Gunnison, not only in the East Portal area, but in the Gunnison Gorge as well.
Last year, about 88,000 Gunnison-spawned rainbow fry were stocked.
Long term, the goal is to discontinue stocking as populations become self-sustaining.
Prior to whirling disease, the Gunnison River in the Black Canyon was self-sustaining, a wild-trout fishery balanced with rainbow and brown trout.
But now, the browns dominate in numbers and size.
Gardunio said he expects the stocking of rainbows to continue until rainbow numbers and individual fish size reach a tipping point that allows the rainbows to reproduce and flourish without stocking.
That could happen when rainbows are 30 to 50 percent of the population.
With a movie, the writers get to script the ending as they see fit. For the Gunnison, we can only hope that ending will include wild Gunnison rainbows, adapted to whirling disease, again growing to forearm size.
On behalf of the future of the granddaughters of this not-so-young boy, who is just along for the ride, I trust the professor is right.
Joel Evans is a freelance outdoors writer in Montrose. On his days off, he usually can be found prowling the depths of the Black Canyon, fishing rod in hand.