Lower Dolores study details native fish needs
Two suckers and a chub focus of restoration effort
A conceptual plan for aiding native fish on the Lower Dolores River was approved by the Dolores Water Conservancy District in June.
The District has been negotiating with Colorado Parks and Wildlife, the BLM, Forest Service, and conservation groups on ways to improve native fish habitat below McPhee Dam.
The result is the Lower Dolores River Implementation, Monitoring, and Evaluation Plan, focusing on three native fish: the flannelmouth sucker, bluehead sucker, and roundtail chub.
"The plan provides a more coordinated approach for improving native fish habitat, with a focus on additional monitoring," said Amber Clark, with the San Juan Citizen's Alliance.
After McPhee Dam was built, small spills, as well as nonspill years from 2001-2004, began reducing the quality and amount of habitat required to meet the needs of native fish. Spring releases from the dam are later in the season, which has reduced the chance for spawning and survival of native fish.
"Protecting the native fish species locally is important because the healthier they are, the less likely they will be seen by the (U.S. Fish and Wildlife) agency as requiring protective status under the Endangered Species Act," said Ken Curtis, an engineer with the Dolores Water Conservancy District. "Working to help these species keeps control of our river at a local level."
The implementation plan presents known and preferred habitat conditions and lifecycles of native fish within six separate stretches of the river below McPhee dam, four of which are a focus of conservation: Dove Creek Pump Station to Pyramid (Reach 3), Pyramid to Big Gypsum Valley (Reach 4), Slickrock Canyon (Reach 5), and Bedrock to San Miguel confluence (Reach 6) Reach 3 (nine miles)
Roundtail Chub are most abundant in Reach 3 and have a relatively stable population there. Mature roundtail are smaller than in other Western Slope rivers, indicating they are adapting to low flows. Fish counts at the Dove Creek area counted 140 roundtail chub, the highest in 13 years.
Bluehead and flannelmouth suckers are present, but in low abundance. In 2013, eight bluehead and one flannelmouth were counted. Habitat is good for bluehead, a more cold tolerant fish.
Reach 4 (38 miles)
Disappointment enters the Dolores in this stretch, flushing sediment into the main channel.
All three native species are found in this stretch as well as problematic non-natives including the black bullhead and smallmouth bass, a voracious predator.
Studies show that populations shift toward non-native species during prolonged low-flow periods. In 2004, native species made up less than 50 percent of the fish caught. After a prolonged spill in 2005, 84 percent of the fish sampled were flannelmouth sucker or roundtail chubs. Because of silt buildup from Disappointment Creek, improving flows here would especially help native fish beat out non-natives.
In August 2013, flooding showed that Reach 4 below Disappointment caused unnatural silting, causing a significant fish kill.
A lack of water limits critical dilution effects, and there is an unnatural buildup of silt because of infrequent flushing flows. "During a flash flood event on Disappointment, the surge of debris-filled water flows into the Dolores River, but there is no water to help dilute the surge of silt-laden water," said Jim White, a CPW fish biologist.
Monitoring native species at Big Gypsum will remain a priority as it appears that the population may be sensitive to low flow.
Flows are a big factor. In 2005, when there was a managed spill, biologists found 150 flannelmouth per hectare at the Big Gypsum site. While in 2004 when there was no spill, flannelmouth were counted at five fish per hectare.
In April 2013, a PIT-tag array was installed across the river just above the Disappointment Creek confluence. Fish are implanted with grain-size microchips and can be detected when they move. Only a few fish have been tagged in the lower Dolores, but more implants are planned. Data shows native fish move up and down the river. The cost of the PIT-tag array is about $75,000.
Slickrock Canyon (32 miles)
All three native fish species are found,but in low abundance. This canyon is difficult to survey, and can usually be floated if there is a spill from McPhee reservoir. The last survey was in 2007, but more are needed to determine if the stretch has rearing habitats for native fish. A relatively large number of small native fish was found near the mouth of Coyote Wash, suggesting tributaries play an important role for young fish.
Bedrock to the San Miguel River confluence (12 miles)
There are a lot of unknowns. It is highly affected by natural salt loading through the Paradox Valley. The salinity is a barrier for fish between the Dolores River below the San Miguel and Slickrock Canyon. A salinity injection well is operated by the Bureau of Reclamation here to mitigate the problem. Researchers want to ascertain the levels of salinity. A second PIT-tag array is considered near Bedrock to help figure out how fish move .
Mimicking a natural hydrograph for native fish is one goal of the implementation plan.
McPhee stores most of the Dolores River spring runoff, and exports much of the storage to the Montezuma Valley of the San Juan River Basin. The result is a lack of spring flushing flows in the Lower Dolores to move sediment and create natural habitat.
When inflow into the reservoir exceeds capacity, the spill benefits boaters and the downstream fishery. However, a prolonged drought has limited spill years. The reservoir holds a fishery pool of 29,824 acre-feet allocated downstream throughout the year by CPW. Spill water doesn't count against the fishery pool, but it is subject to shortages in dry years.
The report suggests ways to optimize the fish pool and spills for the benefit of native fish.
Thermal regime management sends water downstream earlier, in March and April rather than in May, to keep water cooler and delay the fish spawn until after the whitewater season.
Biologists have documented that when spill water is released in May, the low flows on the lower Dolores have heated up, cueing fish to spawn early.
"The fry and eggs are washed away in the whitewater, a hit on survival," White said.
A model indicates that flow volumes of 125-200 cfs on May 1 may be necessary to keep water below 15C at the Dove Creek Pumps. More water downstream may keep water cool enough to delay spawning. A gauge at James Ranch will monitor conditions.
Flushing flows range from 400-800 cfs are important to prepare spawning areas and improve oxygenated flow around eggs.
Habitat flows ranging from 2,000 cfs to 3,400 cfs are necessary for resetting channel geometry, scouring pools, creating channels for fish nurseries. The Bureau of Reclamation urges increasing the fish pool to 36,500 acre-feet a year. A fund of $400,000 is earmarked for buying additional water, but none has been acquired using these funds.
"There has always been a desire for more water for the downstream fishery," says Curtis, of DWCD. "Before there is a blanket grab for additional water, there needs to be a specific focus on how it will help, and those questions are being pursued."
The goal of the Implementation Plan is to maintain, protect, and enhance the native fish populations in the Dolores River.
The area is susceptible to being overrun by small mouth bass and affords opportunity for their suppression by removing caught fish.
Managed spills scour the river bottom, and move sediment in ways that benefit native fish and their young.
Blueheads are rarely detected in this stretch.
Biologists see the problem as two-fold:
The Snaggletooth Rapid is in this stretch, making fish sampling a challenge, but regular fish monitoring is encouraged in the report.