Scientists hope bug experiment fattens Colorado River fish

FELICIA FONSECA
Arizona, US | May 2

Any great fishing hole depends on the health and well-being of its bugs.

In a key stretch of the Colorado River below a dam on the ArizonaUtah border, anglers have been pulling out long, skinny trout that don’t give up much of a fight with a hook in their mouths.

Turns out, they don’t have enough to eat, scientists say.

Researchers with the U.S. Geological Survey are hoping a monthslong experiment to release low, steady flows of water from Glen Canyon Dam will give the eggs that bugs lay just below the water’s surface a better chance at survival. It starts this weekend.

“For whatever reason, downstream of Glen Canyon Dam really lacks diversity,” said Scott VanderKooi, who oversees the U.S. Geological Survey’s Grand Canyon Monitoring and Research Center in Flagstaff.

Scientists are anticipating a 26 percent increase in black flies and midges by next summer, and the eventual return of bigger bugs seen in other stretches of the Colorado River that largely have disappeared from a prized fishery known as Lees Ferry. When insects thrive, so do fish, bats, birds and other predators, scientists say.

Insects attach their eggs to hard surfaces like rocks, wood or cattails near the river’s shore. Fluctuations in the water for hydropower create artificial tides that can expose the eggs and dry them out.