Rainbow trout history in Gunnison River a survivor tale
BY PAT OGLESBY
Colorado River cutthroat trout were found throughout the Gunnison River Basin until the late 1800s when early settlers discovered the area.
Populations of cutthroats were reduced as the early miners used them for food, mining activities polluted the waters and nonnative trout were introduced.
Railroads reaching into the Gunnison Basin in 1882 brought with them special cars to stock brook, brown and rainbow trout, finny enticements for angling-hungry tourists.
Cutthroat trout, unable to compete against the nonnatives, drastically declined.
Instead, the Gunnison River was changed into a world-class rainbow trout fishery attracting anglers from around the world.
National Geographic magazine once called the Gunnison River, “The best trout fishery in the country.”
With the completion of the Gunnison Tunnel in 1909, most of the Gunnison River was diverted through the tunnel to irrigate the arid Uncompahgre Valley.
That diversion left low flows in the river downstream toward the confluence of the North Fork of the Gunnison. Trout could no longer survive in the higher water temperatures resulting from the lower water.
The river changed again with the construction of the Aspinall Unit dams in the early 1970s.
Water released from Blue Mesa, Morrow Point and Crystal dams cooled the river, and, in the Black Canyon downstream of the East Portal, an excellent rainbow fishery was created.
The rainbow trout stocked more than 100 years ago again flourished.
The number and size of the fish increased and the river gained Gold Medal Water status, which is given to waters with more than 60 pounds of fish per acre and at least 12 fish, 14 inches or longer, per acre.
The Gunnison also was given Wild Trout Status, meaning trout populations are naturally reproducing.
For the next 20 years, the river attracted anglers from around the world eager to catch what were referred to as Gunnison River rainbows.
This all changed in 1993 when whirling disease was discovered in the river.
Whirling disease is caused by a parasite that attacks the skeletal structure of young fish.
The resulting deformity changes a trout’s swimming behavior and leaves it vulnerable to predators.
The parasite affects all trout but rainbows seem to be the most vulnerable.
Although the adult rainbows continued to spawn for the next six to seven years, all young trout that hatched soon died from the parasite.
With no recruitment of young rainbows from 1994 to 2007, when the last of the adult rainbows were gone, the Gunnison River rainbow population crashed.
With the rainbows virtually gone, the brown trout population flourished.
Dan Kowalski, aquatics biologist for the Colorado Division of Wildlife in Montrose, and other biologists within the DOW, discovered a strain of rainbow trout from Germany, known as the Hofer strain, that had resistance to whirling disease.
Ironically, this strain probably originated with fish spawned in the Gunnison River 100 years ago.
They were shipped to Germany and used in aquaculture where whirling disease was present, and eventually these Hofers, named for the facility in which they were raised, developed a natural resistance to whirling disease.
The DOW crossed these domesticated rainbows with wild, river-born rainbows and began stocking them in the Gunnison River.
Thousands of young fish were stocked in the 2-mile Ute Park section and lower down in the 4-mile section between the Smith Fork and the confluence of the North Fork.
Speaking recently to the Grand Valley Anglers Chapter of Trout Unlimited, Kowalski reported rainbow trout again are reproducing naturally in the river and there are surviving juvenile trout.
It has taken years to get the wild-fish genetics back into rainbow trout so they can survive and reproduce in the wild.
Pat Oglesby of Grand Junction is a member of the Grand Valley Anglers Chapter of Trout Unlimited and Federation of Fly Fishers and is a Federation of Fly Fishers-certified casting instructor.