Study: Ruedi changes could further improve trout habitat | PostIndependent.com
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Study: Ruedi changes could further improve trout habitat

BASALT – A new study confirms what a lot of avid anglers know: Ruedi Reservoir has helped transform the Fryingpan River into a world-class trout stream.

But the impacts of the dam at Ruedi on the Fryingpan downstream haven’t been all positive for fish, the study found. And it recommends some things to consider for further improving trout habitat.

While confirming that trout habitat and populations have improved since construction of the reservoir in the mid-1960s, the research also concluded that it’s seriously hindering spawning of rainbow trout, which have fallen off in proportion to brown trout over the years on the Fryingpan. And it also calls for boosting minimum winter flows to benefit trout.



Miller Ecological Consulting, Inc., conducted the two-year study for the Roaring Fork Conservancy. The conservancy calls it the most comprehensive look to date at the ecological processes occurring on both the lower Fryingpan and the Roaring Fork rivers below Ruedi.

Kristine Crandall, research and writing specialist for the nonprofit conservancy, said the study’s goal was to get baseline information regarding Ruedi and its effects on the river, possibly in order to help guide policy regarding the reservoir’s management.



Ruedi “is already being kind of pushed and pulled in several ways now,” she said.

The study highlights the impacts releases of water from Ruedi to benefit endangered species on the Colorado River may be having on brown trout, and suggests that the Colorado Water Conservation Board’s current instream flow requirements for the Fryingpan are outdated and should be re-evaluated.

Crandall said one interesting finding regarded Ruedi’s impact on rainbow trout spawning. Monitoring below the reservoir found that water temperatures are warmer than normal in the winter and cooler in the summer. Researchers concluded that extremely low water temperatures during the spring incubation period for rainbow trout eggs are probably sharply reducing their rate of survival.

The Fryingpan’s trout population was dominated by rainbows in the late 1970s and in the 1980s, but is dominated by browns today. Researchers say the cold water temperatures probably combined with a dropoff in stocking programs and the arrival of whirling disease to impact rainbow populations.

At the same time, by creating warmer river temperatures in the fall, when brown trout spawn, Ruedi may be improving survivability of brown trout eggs, researchers say.

Overall trout populations in the Fryingpan below Ruedi are high. Total numbers and fish sizes have increased dramatically in the last 25 years, the study found. One reason is that macroinvertebrates, upon which trout feed, are extraordinarily high in density below Ruedi due to the stable environment and nutrient-rich water provided by the reservoir. Densities may be four to 20 times higher than before dam was built.

Special fishing regulations also have helped trout populations. So have the warmer winter waters produced by Ruedi, and winter flows higher than before the dam was built.

However, because those winter flows are warmer, they ironically are more susceptible to formation of “anchor ice,” which harms macroinvertebrates and trout eggs. Before Ruedi, the colder Fryingpan was more likely to freeze over on the surface, insulating the river and resulting in less anchor ice.

Maintaining winter flows near 100 cubic feet per second would minimize anchor ice formation, researchers said. Currently, the CWCB minimum flow allocation is around 40 cfs.

Researchers also recommended minimizing rapid flow fluctuations. And they raised concerns about elevations in fall releases of water from Ruedi since 1989 on behalf of endangered fish. While they can’t be sure of the impacts, they fear that an elevated fall discharge, followed by a rapid decrease in flows, could impact brown trout spawning.

As a result, they recommend that when elevated fall releases occur, the flows be reduced before the spawning begins, to stabilize water levels for the trout.

Crandall said some members of the public have been concerned about issues addressed in the study. By helping to provide an understanding of Ruedi’s impacts on the Fryingpan, the study could assist the Roaring Fork Conservancy in eventually making recommendations on mitigating those impacts, she said.

The study is part of the “Ruedi Futures Study,” an effort initiated by the conservancy, Ruedi Water and Power Authority, and Colorado River Water Conservation District to more fully understand the status of recreation activities and the aquatic environment in relation to Ruedi Reservoir’s operations.

The Fryingpan Valley Economic Study, an evaluation of the impact of Ruedi Reservoir and Fryingpan River recreation activities on the local and regional economy, was completed in 2002 by the conservancy.

To view or download the final fishery study report (including an executive summary), you can go to the conservancy’s Web site (www.roaringfork.org). Also available on the Web site is a literature review of biological investigations that have taken place on the Fryingpan River since 1943, as well as the economic study’s final report.

For additional information, please contact Kristine Crandall or Ann Burns at the Roaring Fork Conservancy, 927-1290.

Contact Dennis Webb: 945-8515, ext. 516

dwebb@postindependent.com


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