The Colorado River cutthroat, nearly driven to extinction by ravenous early-day miners and generations that followed, is regaining a foothold in its ancestral home.
The recovery, started in 2002, is being helped along through April at the state Division of Wildlife’s fish hatchery in Durango, where pure-strain Colorado River cutthroat eggs are being fertilized by hand. The resulting hatchlings are raised for release in lakes, rivers and reservoirs.
From fertilized egg to fry, the survival rate of hatchery-spawned cutthroat trout is 50 percent, Toby Mourning, manager of the hatchery, said last week. “In the wild, only 2 to 3 percent of eggs become a fish,” he said.
Colorado River cutthroat, one of three subspecies that became isolated during glacial times in what is now Colorado, need all the help they can get.
In 1990, biologists from across the state, fearing that the Colorado River cutthroat would be listed as threatened or endangered, began to look for genetically pure examples of the species in remote areas of the San Juan Basin.
They concentrated on streams that had an insurmountable barrier at the lower end and no lake at the top of the drainage. Otherwise, those streams would have gone the way of waterways and lakes stocked with nonnative species after the Colorado cutthroat all but disappeared.
In 2002, 2003 and 2004, Division of Wildlife biologists collected enough eggs and milt of genetically pure cutthroat to create populations at the hatchery.
The brood stock – there are two strains, Weminuche and Navajo – is not artificially spawned until the fish are 3 years old.
This spring, about 500 cutthroat from the classes of 2007 and 2008 will be spawned, producing 350,000 eggs. Of these eggs, 60,000 will be sent to the Rifle Falls hatchery near Rifle and 40,000 to the Pitkin hatchery about 20 miles east of Gunnison.
About 2,500 will be kept at the hatchery for brood stock, to be spawned in 2013 when they’re 3 years old.
Others will be stocked in local lakes and streams when they’re 1 to 3 inches long.
“We return to our source streams every three years for wild spawn,” Mourning said.
Manual fertilization of eggs is a methodical, 45-second-or-less process for each cutthroat, which are cordoned, according to sex, into separate sections of a hatchery raceway.
Outfitted in chest-high waders, thigh-deep in 50-degree water, Mourning, Riley Morris and Ray Archuleta took their positions in a raceway one afternoon last week.
Mourning and Morris faced each other across a low concrete wall. Mourning scooped a few females into a tub of water containing a short-lived anesthetic. Morris did the same with male cutthroat.
Mourning then squeezed the eggs of two females into a bowl and passed it to Morris who squeezed the milky-colored milt of two males onto the orange eggs.
“It may look like we’re putting a lot of pressure on the fish,” Mourning told an observer. “But it’s really gentle pressure because they’re ready to spawn.”
Morris passed the bowl to Archuleta, who bathed the mixture in water to activate the milt and wash out extraneous material, including feces.
The clean eggs go into a bucket of water.
The motions of the trio are precise and almost nonstop because the milt begins to lose potency after 45 seconds. The eggs remain viable for several minutes.
The fertilized eggs are placed in hatchery trays to begin a life cycle. They spend 21 days in incubators, at which time they develop eyes. Defective eggs are removed, and the others are returned to the incubators. Two weeks later, they hatch.
Cutthroat that hatched a year ago are still indoors, but they will be moved to outdoor raceways this spring.