Posted Thursday, 21 April 2011 01:00
LAKEWOOD, Colo. — Upper Colorado River Endangered Fish Recovery Program (Recovery Program) researchers are optimistic that Mother Nature will provide flows in several Upper Colorado rivers this spring that will help reduce populations of certain species of nonnative fishes as they work to recover the endangered humpback chub, bonytail, razorback sucker and Colorado pikeminnow.
Weather models show significantly higher than normal percentages of snowpack in the Green and Yampa river subbasins. "If this remains true during spring snowmelt, Yampa River runoff is projected at 157 percent of average, which is in the top five wettest years on record and comparable to 1984," said Bureau of Reclamation Hydraulic Engineer Heather Hermansen. "The Duchesne River runoff is projected at 200 percent of average, a record high for the last 30 years."
Because the Yampa and Duchesne rivers flow into the Green River below Flaming Gorge Dam in northeast Utah, the Green River is also expected to experience higher than normal flows.
"While high flows are known to benefit the endangered fishes, we are aware and certainly concerned about the effects of flooding on private property," said Recovery Program Director Tom Chart. The Bureau of Reclamation, a partner in the Recovery Program, controls releases from Flaming Gorge Dam.
"This year the Recovery Program has asked that Reclamation hold Flaming Gorge releases until the Yampa River flows are in decline," Chart said. "While this is intended to benefit young razorback suckers, it should result in runoff flows near Jensen, Utah, that are smaller but longer in duration."
Reclamation's operations at Flaming Gorge Dam almost always provide a measure of flood control except in the wettest years when the priority shifts to dam safety.
High spring flows are important to the life cycle of endangered fish. Rushing water clears the riverbed and exposes small rocks and gravel that the fish seek to spawn and lay their eggs and creates space between the rocks for aquatic insects that the endangered fish eat. High flows also fill shallow floodplain habitats with warm, still water that allows young fish to grow to a size where they are more likely to survive when they reenter swift current of the river's mainstem.
The same high flows that benefit endangered and other native fishes may have the opposite effect on some nonnative fish species such as smallmouth bass by delaying their spawning. High flows are good news to Recovery Program researchers who have been working since 1999 to reduce the threat to endangered fishes posed by nonnative fishes in Upper Colorado River Basin rivers.
"Data shows that nonnative smallmouth bass populations respond to low flows and quickly multiply during times of drought," said Recovery Program Nonnative Fish Coordinator Pat Martinez. "Those same conditions had the opposite effect on endangered fish whose spawning decreased during that time. Prolonged years of drought since 2002 resulted in river habitat that favored the rise in numbers of nonnative fish in the Green and Yampa rivers which is designated critical habitat for the endangered fishes."
Sampling in the Green River and other areas suggests that higher stream flow, coupled with increased water turbidity and lower water temperatures, often results in abandonment of spawning nests by the guarding male smallmouth bass, after which developing eggs and just-hatched young are susceptible to predation and other mortality factors. Also, late-hatching, weak-swimming, young smallmouth bass may be swept away from nests or quiet near-shore habitat, resulting in high mortality.
"The Recovery Program analyzes data each year to determine the most effective approach to controlling nonnative fish," Martinez said. "This year, high flows may contribute to the efforts of our crews by reducing the numbers of young smallmouth bass in the system."
As in the past, Recovery Program researchers will focus nonnative fish management efforts primarily on removal of smallmouth bass and northern pike, two nonnative fish species identified as posing the greatest threat to the endangered fishes.
"We are also concerned about walleye and burbot," Martinez said. Walleye numbers may be increasing in the Green River, and a single burbot was captured in 2010. These large-bodied species also have the capacity to eat native and endangered fish and compete with them for food and space in the river."
Nonnative fish management work will occur from April through October in more than 500 miles of the Upper Basin, including the Colorado, Gunnison, Duchesne, Green and Yampa rivers in the states of Utah and Colorado. Biologists from the Utah Division of Wildlife Resources, the Ute Indian Tribe Fish and Wildlife Department, the Colorado Division of Wildlife, the Larval Fish Laboratory at Colorado State University and the U.S. Fish and Wildlife Service will conduct the work.
Nonnative fish management is one of many recovery actions that enables use and development of water from the Upper Basin to proceed in compliance with the Endangered Species Act (ESA). Since 1988, recovery actions implemented by the Recovery Program have provided ESA compliance for 1,846 water projects depleting more than 2.8 million acre-feet of water in the Upper Basin.
For more information, visit Colorado River Recovery or call the Recovery Program at 303-969-7322, ext. 227.
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