If you happen to have one of those moth-gnawed mounts of an ancient cutthroat trout your great-grandfather caught from a tributary of the South Platte River during a wagon train stop, you may hold the key to the mystery of Colorado’s official state trout.
Don’t laugh. This is serious stuff, perhaps the linchpin to the continued restoration of the greenback trout, once the nation’s greatest endangered fish species recovery story but now turned upside down.
The saga of the greenback, believed extinct until the discovery of a remnant population in the 1950s, took a dramatic twist last week with the revelation that key colonies used for recovery carried the genes of a close cousin, the Colorado River cutthroat.
A University of Colorado research team headed by Jessica Metcalf, a recent doctoral graduate, disclosed in an online scientific journal that five of nine relic greenback populations carry genetic traces of the Colorado River subspecies.
Word of the research had circulated widely among the local community of biologists in recent months and had been discussed on this page earlier this year. But the formal details of the report produced a sort of bombshell effect, casting doubt upon a joint recovery effort of the U.S. Fish and Wildlife Service and Colorado Division of Wildlife to get the trout removed from the federal threatened species list.
This program previously counted 20 viable greenback populations in the South Platte and Arkansas river basins. Based on the report’s DNA evidence, some of these can no longer be considered genetically pure. During the discovery of remnant populations in the 1950s, the greenback subspecies was identified using conventional methods of taxonomy. The more recent delineations were made with more precise nuclear DNA technology.
Metcalf believes late 19th century stocking by miners or railroad workers brought the Colorado River natives across the Continental Divide. But a contrary theory, espoused by noted Colorado State University professor emeritus Robert J. Behnke, holds that greenbacks originated from a trans-Continental Divide migration during the most recent ice age, hence the genetic connection.
Metcalf rejects this premise, citing finely tuned elements of DNA research that indicate the separation occurred in relatively recent years. She further identifies genetic fingerprints linking the South Platte fish to a Colorado River cutthroat strain found in the San Juan River basin – far from any point of presumed transmountain migration.
But this lingering suspicion has given rise to further DOW-sponsored study, which is where that ancient taxidermy comes into play. If DNA analysis of greenback trout captured before any presumed transplants shows no evidence of Colorado River genes, then Metcalf’s finding rings true. If the opposite is true, then Behnke’s hypothesis comes into play.
The earlier reference to finding research subjects on someone’s mantelpiece was intended in jest. Actually, Metcalf already has her stuffed trout, mostly from specimens collected on an 1889 scientific expedition and from other gatherings taken in the 1850s.
All have been preserved in museums, which provided tissue samples for the tests.
“It’s very tedious work, since the DNA has been degraded,” said Metcalf, who expects to have the results in about a year.
Although many have characterized the CU study in dark terms as a setback to greenback recovery, Metcalf believes it actually contains good news.
“It’s a new piece of science to be implemented into management strategy,” she said. “It proves there are distinctly different subspecies: the Colorado River and the greenback.”
The revelation suggests a new direction for the recovery team, one that Bruce Rosenlund, project leader with the U.S. Fish and Wildlife Service, says will continue to follow a moving target.
“We’ll go back and redo our broodstocks and use the best available science for initiating new projects,” Rosenlund said. “Taxonomy is an evolving field. We get better information all the time. This is subject to change on the next bit of information that comes in. It’s the evolution of science.”
This initial finding also has given rise to follow-up research to determine whether similar mining-era transplants crossing The Divide in the opposite direction carried greenbacks to the Western Slope.
That, of course, might require an entirely different set of those old moth-eaten mounts.
