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The Mountain-Prairie Region


U.S. Fish and Wildlife Service
134 Union Boulevard
Lakewood, Colorado 80228


July 8, 2005

CONTACT:     Debbie Felker,  303-969-7322, x227  


 Lakewood, Colo.—Mother Nature helped provide the perfect flow conditions this year to enable biologists to conduct four important research studies in the Green River in northeast Utah to gain information needed to help recover the razorback sucker. The Green River system is considered vital to recovery of the razorback sucker and three other endangered fish species – the humpback chub, bonytail and Colorado pikeminnow. Designed in cooperation with the Upper Colorado River Endangered Fish Recovery Program (Recovery Program), the studies had been postponed for several years due to the drought.  

Three of the studies focused on learning how drifting razorback sucker larvae are transported by water currents out of the fast-flowing river into the calmer waters of floodplain wetlands that serve as nursery habitat.  The fourth study focused on measuring the amount of sediment deposited onto a razorback spawning site.  

Successful completion of these studies depended on high spring flows that provide the habitat conditions that razorback suckers need to spawn and connect the river to floodplain nursery areas.  

“This spring, the U.S. Bureau of Reclamation helped us keep a close eye on weather and river flow forecasts to determine if this would be the year we could conduct these studies,” said Recovery Program Director Bob Muth.  “When we realized that snowpack and warm spring temperatures would likely result in the high flows we needed, our partner agencies quickly rallied to launch the studies.  We knew we would have a narrow window of opportunity to get out on the river and conduct our work.” 

The Bureau of Reclamation assisted the research by releasing some additional water from Flaming Gorge Dam for two days before and after the peak flow.  This helped support the necessary flow conditions.  For several days in May, more than 20 researchers and volunteers worked around the clock to simultaneously conduct the various studies. 

The Utah Division of Wildlife Resources and Colorado State University took the lead to evaluate larval transport and habitat use.  At each targeted flow, they released 3 million biodegradable, color-coded beads that simulated drifting larvae and between 100,000 and 400,000 marked razorback sucker larvae at razorback sucker spawning areas near Jensen, Utah.  They later captured the larvae and beads in drift nets as they entered selected floodplain habitats, some as far as 54 miles downstream from the spawning areas. 

At the same time, staff from Tetra Tech, an engineering firm hired by the Recovery Program, obtained on-the-ground measurements of inflows to habitats to determine if modifications to both manmade and natural levees would help drifting razorback sucker larvae gain access to nursery habitats.  

While all of this work took place on the river, aerial photos were taken during rising flows to help biologists understand how much floodplain is covered with water at various flows. 

“Razorback suckers spawn during rising spring flows,” said Recovery Program Habitat Coordinator Pat Nelson.  “After several days the eggs hatch, larvae emerge from the spawning gravel, and then begin drifting down river.  If larvae remain in the river they do not survive.  If they can reach suitable floodplain nursery habitats, however, survival has been documented.  One of the remaining pieces of the razorback sucker life history puzzle is to determine how to get drifting larvae from the river and into suitable floodplain nursery habitats.”

The U.S. Geological Survey also took advantage of the high flows to conduct a fourth study to determine the amount of sediment deposited on a razorback spawning site and to give biologists a better understanding of flows needed to clean the spawning gravel prior to razorback reproduction.  

“Completion of these research studies clearly demonstrates the cooperation and commitment of Recovery Program partners,” Bob Muth said.  “The information we gain will greatly contribute to our understanding of how habitat helps contribute to recovery of the razorback sucker.  We will use the data to help plan and implement future actions that will help us achieve self-sustaining populations.” 

Data and samples collected during the studies are being processed and analyzed. Study results are anticipated by year’s end. 

The Recovery Program is a voluntary, cooperative program whose purpose is to recover the endangered fishes while water development proceeds in accordance with federal and state laws and interstate compacts. For more information, 303-969-7322, ext. 227, or



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