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Cutthroat Confusion

Brief by Central Staff

Wildlife – October 2007 – Colorado Central Magazine

While the Colorado Division of Wildlife was stocking 264 high-mountain lakes with cutthroat trout fingerlings in August and September, genetic researchers at the University of Colorado announced that the cutthroats appear to be the wrong variety.

The cutthroat has been Colorado’s official state fish since 1994, and it is the only trout that is native to the state. It gets its name from a red stripe extending back from its lower jaw.

The species comes in several varieties, based on geography. The greenback, originally native to the upper Arkansas and South Platte basins, is the official state variety, and the one the DOW has been trying to spread. It was believed to have gone extinct in 1937, but small remnant populations were discovered in the 1950s.

Other varieties are the Colorado River cutthroat, native to the Western Slope; the Rio Grande cutthroat, native to the San Luis Valley; and the yellowfin cutthroat, which once grew as large as 10 pounds and dwelt in Twin Lakes, but is now extinct.

The greenback cutthroat was declared an endangered species in 1973. Private, state, and federal organizations began an effort to save the greenback cutthroat, using sperm and eggs from nine relic populations to start new generations in hatcheries. Then the fish were released into the greenback’s historic range.

But the genetic researchers discovered that five of the nine relic populations were actually Colorado River cutthroats, not greenbacks. “This was a very surprising result,” said Jennifer Metcalf, who led the study. “It’s not at all what we expected.”

Metcalf said that her team was perplexed by their original findings, based on DNA analysis, and started looking at historical stocking records, as well as journals and diaries kept by people who ran fish hatcheries a century ago. They discovered that stocking was widespread even back then, and that some Colorado River cutthroats were likely moved across the Divide to greenback territory on the Eastern Slope.

Does it make much difference? Bruce Rosenlund of the U.S. Fish and Wildlife Service observed that “Our feeling for a long time has been that they were very, very closely related and indistinguishable, in fact, in their morphology.”

In other words, they’re the same species and look the same. Presumably, if they reproduce naturally in their native habitats, distinctions will re-appear over time.