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Colorado river dams decimate native fish

July 10, 2008 |  2:26 pm

Colo_river_small We may love our trout, smallmouth bass and green sunfish -- but these game fish are aliens in the Colorado and many other western rivers. Thanks to widespread damming, these "introduced species" are decimating the more fragile natives such as the Colorado's razorback sucker, humpback and roundtail chub, bonytail chub and pikeminnow.

The natives are more susceptible because their larvae are usually less developed when they hatch, and are less able to escape from predators, than those of the sturdier game fish, according to Alice Gibb, a Northern Arizona University scientist whose research was funded by the National Science Foundation. Before dams were built, native fish larvae could hide in sediment and turbulent water.  Now the large, still artificial lakes along the 1,450-mile-long river leave the native larvae "at a grave disadvantage," said Gibb, who presented her findings today at the Society for Experimental Biology's annual meeting in Marseille, France.

"We suggest to management agencies that, in addition to removing introduced predators of native fishes from key river reaches, efforts must be undertaken to re-create the high-flow, sediment-rich, warm waters that gave the Colorado its name," Gibbs reported. "Dam removal may be critical for rehabilitating fish populations across the U.S., and almost certainly in other, less-studied areas of the world."

So where's that Monkey Wrench Gang when it's needed?

--Margot Roosevelt

Photo: Confluence of the Little Colorado and Colorado rivers in the Grand Canyon. Credit: David Ward, Arizona Game and Fish