Low flows increase predation by non-native game fish; recovery effort could see temporary setback
By Bob Berwyn
SUMMIT COUNTY — With 2012 shaping up to be at least a near-record drought year in the high country, some of the Colorado River’s endangered native fish could be facing a battle for survival, especially in key tributaries like the Yampa, in northwestern Colorado.
As flows are reduced to a trickle, the Colorado pikeminnow, razorback sucker, and especiallly the humpback chub and bonytail chub, will face serious threats from competing non-native species.
But they’ll get a little help from Upper Colorado River Endangered Fish Recovery Program biologists, who will be doing their best to remove remove smallmouth bass, northern pike, and in some areas, white sucker, walleye and burbot.
Overall, recovery program leaders say they’ll manage the little bit water they do have based on experience from the drought in the early 2000s.
“We’ve been there before,” said program director Tom Chart, explaining that low flows will likely result in a temporary setback for recovery efforts, especially in tributaries like the Yampa River.
There are places we saw on Yampa in 2002 where there was virtually no surface flow,” Chart said. “It was just a connected series of pools on the river. Native fish seem to have a propensity to vacate those places … but some of them don’t, and that’s the real concern.”
Those conditions favor non-native fish, especially smallmouth bass, which in 2002 all but wiped out the Colorado River natives that were left in the system, Chart explained.
Smallmouth bass were introduced and managed as a popular sport fish and remain a desirable species in certain settings. But so-called bucket biologists complicated the native recovery equation with homegrown (and illegal) transplants of bass, Chart said.
“Biologists have identified prime smallmouth bass spawning habitat. They can predict the height of spawning activity, and have adapted … removal efforts,” said Patrick Martinez, the non-native fish coordinator for the recovery program. “This year we really need to draw on those past experiences to keep smallmouth bass and other nonnative species in check.”
The native fish recovery program is focused on four species: Colorado pikeminnow, razorback sucker, humpback chub and bonytail chub. All evolved in the Colorado River Basin over milennia to be able to survive epic droughts and floods and to hunt for food in powerful flows. Learn more about the fish at this website.
As dams and diversions became ubiquitous during the 20th century, their habitat all but disappeared and numbers dwindled until the far-reaching collaborative recovery effort was launched in 1988.
“The endangered fish are hearty, long-lived species that evolved over thousands of years and have survived periods of both extreme high flows as well as drought,” Chart said. Last year, the fish experienced some of the highest flows in recent history. We hope the favorable river conditions we saw last year carry the endangered fish populations through what is shaping up as an extreme drought year.”
But that adaptation is based on a natural ebb and flow, especially with spawning linked to the rhythm of high and low flows during different seasons. That cycle has been deeply disrupted by water storage and diversions. As a result, the recovery program managers work with water users and providers to try and recreate at least a shadow of that natural hydrograph, providing when they can at the times when it’s needed most.
Chart said the endangered fish did take a noticeable hit during the drought of the early 2000s, but bounced back nicely in subsequent years, when near-normal snowfall bolstered flows.
Overall, the recovery program has made progress, especially with the Colorado pikeminnow and the razorback sucker. The two chub species have been hit harder by the non-native fish, Chart said, adding that program is still on-track to meet its current goal of getting the fish off the endangered species list by 2023.
The program managers will use lessons from previous droughts, with information on fish spawning patterns, movements, and habitat preferences during periods of low river flows enabling biologists to focus their time and efforts to best assist in the recovery.
This year, like every year since the Recovery Program began in 1988, those efforts will occur throughout nearly 900 miles of the Colorado, Gunnison, Green, White and Yampa rivers in Colorado and Utah.
The recovery effort involves biologists from Colorado and Utah, the U.S. Fish and Wildlife Service and Colorado State University’s Larval Fish Laboratory. Recovery activity includes managing flows; stocking of hatchery-raised razorback sucker and bonytail; obtaining Colorado pikeminnow and humpback chub population estimates; and controlling nonnative species that prey on native fish.
To cope with drought conditions, the Recovery Program will use water leases, contracts and other agreements established during its 24-year history to maintain adequate river flows that endangered fish need to spawn and grow. All flows are provided in accordance with state water law, individual water rights and interstate compacts.
Chart said there are “pools of un-contracted water” in some reservoirs that are available to help boost flows in years like this, including Green Mountain and Ruedi. Water potentially is also available from Wolford Mountain and Williams Fork reservoirs under certain circumstances, he said.
Even with those pools, the recovery program likely won’t meet many of its target flows, for example on the Colorado just upstream of its confluence with the Gunnision, where the target flow for part of the summer is 810 cubic feet per second.
“When we get into years like this, the U.S. Fish and wildlife Service adjusts those targets. It becomes a triage situation,” Chart said.
Since the non-native fish can pose the biggest threat during low-flow years, major efforts will be made to control them. Depending on the river reach, biologists will remove nonnative smallmouth bass and northern pike. In some instances, white sucker, walleye and burbot will also be removed. All of these nonnative fish species pose a significant threat to endangered fish because they compete for food and space in the river and may eat the eggs, young, or even adults of endangered fish.