A better understanding of the needs of native fish on the Lower Dolores River below McPhee Dam is key to their survival, two fish biologists say.
Jim White and David Graf of Colorado Parks and Wildlife briefed board members of the Dolores Water Conservancy District and Montezuma Valley Irrigation District recently on current surveys for the flannelmouth sucker, bluehead sucker and roundtail chub.
Both districts depend on McPhee Reservoir to store water and deliver it for customers and shareholders. But below the dam, fish populations struggle in low-water conditions.
As part of an ongoing collaborative process to accommodate all users of the river, the native fish are getting some attention with an aim toward establishing where they are and what can be done to help them.
White, an aquatic biologist, and Graf, a water specialist, gave an update about their activities monitoring fish populations.
The first 11 miles downriver from McPhee Dam is managed for the cold-water trout fishery. The spillway is monitored for bass and unwanted sucker species that may have slipped through from the reservoir. Bass can outcompete trout for food and habitat.
From Bradfield Bridge to the Dove Creek pump station, the Lower Dolores flows for 19 miles through the Ponderosa Gorge, a pristine wilderness canyon accessible only by boat.
During lower flows, the river below Bradfield Bridge can warm to the point it is not favorable to trout, but it may become more acceptable for native fish.
Below the Dove Creek pump station, the summer season can leave only deep pools on the river.
Antenna arrays that track fish movements are set up at two locations on the Lower Dolores – one just downstream from the Dove Creek pump station and the other near James Ranch. Fish handled in surveys are tagged by injecting a small glass tube with a copper wire inside into their abdomen. Stretched across the river are antennae lines that ping off the imbedded tag when the fish swims underneath. The information is relayed to a satellite and downloaded by biologists.
Biologists are learning what the native fish need. Roundtail chubs are more particular about what habitat they want to be in. They are more site-specific and prefer complex pools with cover like logs and bank overhangs.
“They are not aimless swimmers; they will swim four miles downstream, and return to the exact same spot,” White said. “We don’t know as much for the flannel and bluehead suckers.”
The board wondered if cost-shares could be arranged to install additional antennae arrays to better estimate the native fish population. The units cost around $90,000.
An additional array at Bedrock would give biologists a clearer picture of how native fish handle a high salinity gradient in that area. Does the salty water act as a fish barrier, forcing native fish to back up into the San Miguel River?
Native fish have become a focus as of late. Working to preserve a healthy habitat and population helps avoid species being listed under the Endangered Species Act, which prompts federal intervention and tougher conservation regulations.
“We want to avoid the (Gunnison) sage-grouse situation and get in a better position to make progress on sustaining native populations,” said Mike Preston, Dolores Water Conservancy general manager.
The U.S. Fish and Wildlife Service is recommending that the sage grouse be listed as endangered around Dove Creek because of rapidly declining populations there.
More study is also needed to determine ideal conditions for native fish larvae. Knowing where they go would help to adjust flow management to improve their chances.
