In spring 2022, the Bureau of Reclamation determined that 500,000 acre-feet of water needed to be released from Flaming Gorge Reservoir to keep water in Lake Powell above the minimum power plant level. The releases allowed biologists with the Upper Colorado River Endangered Fish Recovery Program to implement three experiments all affecting recruitment of fish species. Recruitment is the biological term for growing from baby (or larval) fish into adults. Biologists want to increase recruitment for native, endangered species, and stop recruitment for nonnative, invasive predator species.
The first experiment starts with sampling for larval razorback sucker in the Green River. Once larvae are found in the river, the flows are increased to push those larvae into warm-food rich floodplain wetlands. The larvae then grow all summer long to be released in the fall as juveniles. In 2022, 4 wetlands produced over 4,200 fish, a record for the Program. The Program released about 4,600 fish in the last 9 years combined.
The second experiment targets smallmouth bass, a toothy predator introduced into the Green River for sportfishing. Unlike largemouth bass, smallmouth bass are very successful at reproducing in the river, creating many, many hungry mouths that have big impacts on native species. They are successful in the river because male bass provide protection for their babies by setting up nests and guarding them. Again, the experiment starts with finding the larval fish. Once they are present, the Bureau of Reclamation turns up the flows again, this time to push those baby bass away from their protective fathers, making survival less likely in the river.
The third experiment provides long, continuous backwaters to support baby Colorado pikeminnow, another endangered species whose population has been quickly declining in recent years. After the spring peaks, designed for razorback sucker, scour and move sand around the river bottom, large backwater environments are formed. The backwaters work just like the wetlands, protecting young fish from large predators while providing warmer, food rich environments.
Because of the declining Colorado pikeminnow population, crews of biologists are out collecting young fish to bring into the hatcheries, just in case stocking is needed in the future. During one such trip, crews found both wild razorback sucker and Colorado pikeminnow – a sign that at least two of the three experiments worked as intended. Data is still forthcoming on the third. “This is the first time in I’ve picked up a razorback sucker and a Colorado pikeminnow in the same seine haul and I’ve been working this river for more than 25 years”, said Bruce Haines, a retired U.S. Fish and Wildlife Service employee who now does volunteer work with the Upper Colorado River Endangered Fish Recovery Program.
“These successes would not be possible without the diligent work of years of biologists in the Recovery Program and the full and willing cooperation of the Bureau of Reclamation”, said Julie Stahli, director of the Recovery Program, “Collaboration and many conversations turned what could have been a dire year for endangered fish into a true bright spot in endangered fish recovery.”
