AUTHORS: McKensie Vaske, Iowa State University; Ryan Hupfeld, Iowa DNR; Gene Jones, Iowa DNR; Rebecca Krogman, Iowa DNR; Daniel Paulson, Iowa State University; Michael Weber, Iowa State University; Michael Moore, U.S. Geological Survey
ABSTRACT: Environmental flows in large rivers are crucial for maintaining ecosystem health, supporting biodiversity, and ensuring the sustainability of water resources for human, wildlife, and fish populations. Low and rapidly fluctuating river levels due to drought and dam operations downstream of impoundments may adversely affect the reproduction of native fishes by disrupting migratory cues and the transport of larvae to downstream nursery habitats. The United States Army Corps of Engineers and The Nature Conservancy developed the Sustainable Rivers Program (SRP) to implement science-based management of 45 river ecosystems across the nation. At the Des Moines River SRP site in Iowa, partners hypothesized that implementing experimental spring flow pulses at Red Rock Dam could promote native fish reproduction, including Shovelnose Sturgeon (Scaphirhynchus platorynchus) in low-flow years. However, it remains unclear whether these actions have been effective. Therefore, from 2021-2023 we conducted larval drift sampling to examine relationships between flow pulses, water temperatures, and reproductive timing of Shovelnose Sturgeon, a long-lived periodic spawning species found throughout the Mississippi River basin. We sampled four sites from April through June spanning ~84 river kilometers in ~15-20°C water temperatures 1-2 times each week. We collected 4 eggs/larvae in 2021, 17 in 2022, and 20 in 2023. There was a positive relationship with discharge and the number of Shovelnose Sturgeon eggs/larvae collected during 2021-2023. We conducted larval drift sampling again in 2024 in additional rivers to compare flow-reproduction relationships between the regulated Des Moines and Iowa rivers with the less-regulated Cedar River. These data may allow dam managers to adjust the timing and magnitude of flow pulses to benefit native fish reproduction without also promoting the reproduction of later spawning invasive carps.
