From The Grand Junction Daily Sentinel (Gary Harmon) via The Aspen Times:
the endangered Colorado pikeminnow faces a new threat, a predator that eagerly scarfs down young pikeminnow, taking a jagged bite out of the species’ overall numbers.
Unfamiliar predation on the pikeminnow comes from a species of fish that’s native to the flatwaters of Canada and the northern tier of the United States. Walleye is a prized food fish, but its voracious appetite for pikeminnow is proving to be a setback to expectations that the pikeminnow could be removed from the endangered species list.
“Walleye have gone gangbusters in Lake Powell,” said Tom Chart, a fisheries biologist who heads the Upper Colorado River Endangered Species Recovery Program for the U.S. Fish and Wildlife Service.
It’s likely that walleye found their way up the Colorado from Lake Powell, Chart said. It’s also possible that the hungry newcomers could have swum down from Rifle Gap and Elkhead reservoirs in Colorado and from two reservoirs in Utah, Red Fleet and Starvation, both near Vernal, said Henry Maddux, director of Utah’s species recovery programs.
On a barely encouraging note, “We haven’t seen walleye reproduce in the rivers,” Chart said. “Yet.”
Walleye nonetheless have taken up residence in waters where they don’t belong, feasting on the young pikeminnow that hatched in the critical 15-mile reach of the Colorado River through the Grand Valley and washed downriver into the slower waters where for eons they have grown to become the apex predators on the river.