New water agreements and release patterns are a good thing for the region’s trout populations, according to Colorado Parks and Wildlife biologists.
On the Little Cimarron River, a new split season in-stream flow agreement is pioneering a new way to support river habitat while maintaining agricultural water use.
In the Gunnison Gorge, biologists have been pleasantly surprised to see higher peak flows resulting in greater recruitment of fry (juvenile trout).
SUPPORTING FISH AND FARMS
On April 23, the Colorado Water Conservation Board and the Colorado Water Trust finalized a new type of water agreement that restores stream flows to the Little Cimarron River while maintaining early summer irrigation via the McKinley Ditch.
A CWCB press release explained, “Under the agreement, up to five cubic feet per second of water that was historically diverted by the McKinley Ditch out of the Little Cimarron River (a tributary to the Cimarron River and Gunnison River in Gunnison and Montrose counties) will continue to be diverted and applied to the historically irrigated ranch until mid-summer. At that time, the water will be left in the river for instream flow use by the CWCB on a reach of the Little Cimarron River that historically saw low to no flows due to water rights diversions, as well as on the Cimarron River.”
Linda Bassi of the CWCB’s Stream and Lake Protection Section explained the agreement allows the “re-watering” of a reach of the Little Cimarron.
Portions of the Cimarron rivers have historically dried up in late summer due to legal water diversions.
The agreement would restore connectivity between the rivers year-round, providing significant benefits to the health of the river and the trout populations it supports.
Bassi said the arrangement allows the timing of irrigation diversions or instream flow use to be determined based on current water conditions on a yearly basis.
Amy Beatie of CWT explained her organization, a Colorado-based non-profit, acquired the water rights and is working in partnership with CWCB, the only entity in Colorado capable of holding an “in-stream” water right.
CWT was formed to work with CWCB’s water acquisition program, which compensates water right holders for transferring existing water rights back into rivers. CWT also provides technical expertise and capacity for this type of agreement.
“The idea is to maintain agricultural productivity and to be used for flow restoration purposes in the Little Cimarron and Cimarron rivers,” Beatie explained.
Beatie said the agreement is now making its way through water court.
Describing the agreement as a “new approach” Bassi said, “It is something we are hoping we can repeat.”
CPW Southwest Senior Aquatic Biologist John Alves said the main biological benefit of the project is the protection of stream habitat, including pools and riffles, throughout the summer.
Additionally, Alves explained the restoration of “river connectivity” allows trout to travel to colder water as smaller streams warm up and reach chronic or lethal water temperatures.
“It might be part of their life history to spawn in either reach,” he added.
The Cimarron rivers contain brook and rainbow trout
HIGH FLOWS HELP FISH GROW
Last year, anglers and biologists alike were concerned how higher peak flows in the Gunnison Gorge tailwaters would affect the popular trout fishing destination.
Releases from three dams on the Gunnison River control the river’s flow — Blue Mesa Dam, Morrow Point Dam and Crystal Dam, comprising the Wayne N. Aspinall Unit — and are dictated by a 2012 Environmental Impact Statement.
This 2012 EIS stated Aspinall Unit operations would meet endangered fish species needs downstream as well as needs for flood control, hydropower creation and irrigation needs.
As a result, flows last summer approached 10,000 cfs in the Gunnison Gorge.
But CPW research on the river last summer and fall found more bugs to eat and more fry in the river after the higher flows, according to CPW aquatic biologist Eric Gardunio.
Gardunio said CPW recorded a three percent increase in brown trout fry and a four percent increase in rainbow trout fry versus the previous year.
CPW estimates fry numbers each year in September by floating the river on a raft and sampling via an electoshocking method.
Gardunio said they are expecting a decline in the number of brown trout and perhaps rainbow trout too.
Looking through historical data, Gardunio said fry numbers were also high in 2011 after high peak flows.
Gardunion said this year CPW also recorded a decline in the amount of 1 year old fish, in the six to 10 inch range; and 2 year old fish, in the 12 to 14 inch range.
These yough fish prey heavily on fry.
The high flows also create space between rocks for fry to hide by clearing out sediment.
“I think it’s great for our rainbows,” Gardunio said.
Rainbow trout are a highly desired sport fish and their populations in the river were depleted by whirling disease, a lethal parasite that entered Colorado in the 1980s.
Gardunio said the CPW is seeing rainbow trout reproducing in the river and creating offspring that are whirling disease resistant. However, those offspring have not yet been detected in adult trout populations.
He said the Gunnison Gorge has the ability to overpopulate trout and higher flows may mean bigger trout.
“From what I saw last year, I think (the higher flows) are good for the fishery,” Gardunio said.
According to the Bureau of Reclamation’s Current Status webpage updated on April 29, the Aspinall Unit record of decision would call for a one day peak flow of 2,660 cfs and one day of 6,660 cfs if water inflow forecasts remain constant through May 1.
Ouray County Plaindealer