Endangered Grand Canyon Fish Making Comeback

April 27, 2009

Release from: Brandon Loomis
Salt Lake Tribune

Endangered humpback chubs in the Grand Canyon have increased their numbers by half since 2001, federal biologists report.

The fish's rebound apparently results from a combination of deliberate trout removals, experimental floods and drought-related warming of flows out of Lake Powell.

Biologists who catch, tag and later recapture the fish to help estimate the population have noted a continuing upward trend in the adult population since 2001, said U.S. Geological Survey biologist Matthew Anderson. This year they estimated a population of about 7,650 in the Colorado River through the canyon -- a 50 percent increase since 2001.

"It's a pleasant surprise," he said.

It remains unclear what positive effect a variety of flow experiments may have had, Anderson said, though it appears clear that they did not hurt the fish. Dam managers unleashed floods from Glen Canyon Dam last year, in 2004 and 1996 in attempts to replicate historic natural floods that build sandbars along the Colorado. Those bars trap backwater eddies that biologists believe favor survival of young chubs.

Those releases, favored by national park managers, are controversial because they cost electric ratepayers who rely on the dam's hydropower.

One key to the chub population increase may be the drought that the interior West experienced earlier this decade. As Lake Powell's surface sank closer to the dam's water intakes, warmer water made it through the dam.

Chubs need warmer water for breeding, and the dam's releases of cold water are cited as one reason for the species' previous decline.

By 2005, the water released from Glen Canyon reached as high as 61 degrees Fahrenheit, Anderson said. That's about the minimum warmth needed for chub breeding, though the water warms further as it flows downstream.

The highest averages from 1992 to 2006, by contrast, were just 50 degrees.

Fish managers also systematically removed 19,000 trout and other non-native predators from below the dam between 2003 and 2006, Anderson said.

The chub's rebound does not necessarily mean it's headed for removal from federal protection. The fish's status above Lake Powell on the Colorado, Green and Yampa rivers remains in question, said Tom Czapla, research coordinator for the U.S. Fish and Wildlife Service's Colorado River endangered fish recovery program.

Besides, he said, fish numbers are only part of the equation. Threats from predators and cold water may yet return to the Grand Canyon.