Earth Notes: Colorado Pike Minnows

Sep 26, 2012

The muddy San Juan River was once home to giant specimens of America’s largest minnow—a fish that could grow as long as a man is tall, and to a weight of a hundred pounds.

Colorado Pike Minnow
Credit U.S. Bureau of Reclamation.

In recent years, though, Colorado pikeminnows there weigh between four and nine pounds and are less than a foot long.

Why the change? Dams, water diversions, power plants, habitat destruction, and nonnative fish have made it hard for the pikeminnow to flourish in the San Juan, which flows into Utah and Arizona before entering Lake Powell.

But efforts by The Nature Conservancy, Navajo Nation, private companies, and government agencies along six key stretches of the San Juan are improving conditions for the pikeminnow.

Invasive tamarisk and Russian olive are being removed from the river’s banks. Secondary river channels, once clogged with vegetation or allowed to dry up, are being improved to provide nursery and spawning areas. Nonnative fish are more carefully controlled.

Some of the money spent on the project comes from government and utility dollars set aside specifically to restore ecological damage caused by dam operations and water diversions. Scientists and government officials are working with technicians to balance competing needs.

The upstream Navajo Dam, for example, now releases some stored water to better mimic natural flows. That benefits recreational users of the San Juan as well as its native plants and wildlife—including the fish that may once again regain some of its old stature as a giant of Southwest rivers.