Bridging the recruitment gap: ten years of managing flows & habitats to improve recruitment of wild Razorback Sucker, Xyrauchen texanus

Authors: M. Jones, Kevin Bestgen, David Speas, Matthew Breen, Christian Smith, Robert Schelly, Michael Partlow

Year: 2022

Abstract

The Upper Colorado River Endangered Fish Recovery Program manages river flows and wetland habitats in the Green and upper Colorado rivers to increase recruitment of wild-spawned Razorback Sucker. Since 2012, experimental spring peak releases from Flaming Gorge Dam are timed to coincide with the presence of drifting river-produced Razorback Sucker larvae that are subsequently entrained into warm, food-rich floodplain wetlands. These experiments are based on previous data on the timing of larval drift, dam release operations, and habitat availability and fish use, which led to the development of the “Larval Trigger Study Plan.” Initially, biologists inundated a single wetland, Stewart Lake, which was managed as a native fish nursery habitat. In the last 10 years, the Program has constructed four additional managed wetlands and re-operated a fifth to improve Razorback Sucker growth and recruitment. These sites share common features designed to facilitate juvenile survival including: 1) a water control structure that regulates filling and draining of the habitat; 2) screens to reduce wetland colonization by adult nonnative fishes during filling; and 3) a mechanism to add water during hot summer months to improve water quality. After wetlands are filled with cold river water during spring flows, entrained Razorback Sucker larvae grow relatively quickly through the summer season. At the end of summer, or when water quality cannot be maintained, wetlands are drained, juvenile fish are collected for enumeration and tagging, and native fishes are released back to the river. The resulting wetland operations have increased our knowledge of the species’ life history while producing over 5,000 wild, juvenile Razorback Sucker. In addition, forty-eight presumptive wild Bonytail, Gila elegans, have been produced in two of these managed wetlands. In 2020, wetland-reared Razorback Sucker larvae were first observed as age-6 adults at known spawning locations. Additional wild Razorback Sucker are needed to maintain riverine populations, therefore wetland managers continue to refine their operations, address challenges, and improve facilities in the face of increased conservation challenges from drought, climate change, and invasive species.