Plan to Aid River’s Native Species

Some brown and rainbow trout will be removed from the Grand Canyon beginning in January to protect the native fish on which they have been preying.

Officials will use two approaches to thin the populations of nonnative fish by as many as 30,000 over two years.

They will vary the water levels in the Colorado River below Glen Canyon Dam, which should disrupt spawning and keep some young fish from surviving to adulthood. But most of the fish will be captured and killed.

The removals are part of a two-year experiment aimed at restoring some of the natural conditions along the Colorado, which has grown cooler, clearer, and less hospitable for native species since Glen Canyon Dam was built more than 30 years ago.

Scientists believe the trout that moved into the river after the dam’s completion have contributed to the decline of the humpback chub and other native fish.

Drought forced a 1-year delay of the experiment’s centerpiece, an artificial flood designed to mimic the river’s seasonal flows. Theoretically, the floods will move sediment from the mouths of the Colorado’s tributaries and deposit the material along beaches downstream.

A 1996 attempt to replicate a flood produced only short-term results, and many scientists now believe the temporary high flows need to occur on a regular basis.

“We need to figure out a way to do this year in and year out,” said Nikolai Ramsey, a program officer for the Grand Canyon Trust and a member of the U.S. Bureau of Reclamation group that devised the experiment.

But bureau spokesman Barry Wirth said the 1996 flood experiment taught scientists the importance of the sediment. Without it, the floods would fail to deposit enough material to build up the beaches and habitat.

The bureau is under order to develop new management techniques for the Colorado below Glen Canyon Dam, which trapped sediment and lowered the water temperature. The new conditions allowed nonnative species like the trout to thrive but threatened native species.