| Abstract |
On May 10, 2023, the AFS Western Division held a half‐day symposium focused on nonperennial streams. Attended by approximately 100–150 persons and given the increasing importance of temporary streams and rivers, we felt it would be useful to provide some of the highlights for the entire Fisheries readership.
Leanne Roulson introduced the session with background on what makes nonperennial streams a focus for fisheries conservation and how the diverse projects covered share a common nexus with Clean Water Act objectives. Niall Clancy presented a basin‐scale approach to identify climate refugia that account for streamflow intermittency in addition to temperature, invasive species, and barriers. He presented a case study for Longnose Dace Rhinichthys cataractae in a central Montana basin by mapping the extent of wetted streams in a drought year by using nationally available, high‐resolution imagery, because of inaccuracies in landscape‐level streamflow models. By accounting for intermittency, the extent of predicted climate refugia was reduced by 20% compared to accounting for temperature alone. Accounting for stream intermittency is critical to determining how climate change will affect native fishes.
To adapt to future challenges, we need to estimate how well current hydrologic models represent low‐ and no‐flow in nonperennial rivers and streams and where uncertainties lie in the physical representations of hydrologic processes. Adam Price compared a suite of process‐based hydrologic models to better understand low‐ and no‐flow variability and process uncertainties. Preliminary results indicated that process‐based models displayed varying degrees of accuracy at representing non‐perennial systems versus field observations. More representative models of nonperennial systems are essential for understanding the dominant hydrologic drivers of low‐ and no‐flow and predicting associated ecological, biogeochemical, and societal impacts to better manage and conserve these systems.
Cienna Hanson assessed the vulnerability and resilience of fish assemblages in four tributaries of the Colorado River basin, Texas, to drought‐induced intermittent flows. Intermittent sites had lower fish‐species richness (mean = 9.6 species; SD = 2.6) than perennial sites (mean = 13.6 species, SD = 1.2).
Zachary Hooley‐Underwood reported that over 10,000 fish—primarily native catostomids—spawn in an intermittent tributary to the Gunnison River, Colorado, during seasonal runoff, and that native suckers migrate farther upstream to spawn than invasive nonnatives. Migratory differences between the two sustain genetically pure recruitment in some tributaries. Unimpeded access to nonpermanent waters has reduced hybridization rates in portions of the Colorado River basin, and focused management and conservation of these nonpermanent waters going forward may improve abundances of those vulnerable native species.
Skylar Rousseau found that hydrologic conditions in some intermittent tributaries to the Logan River, Utah, provided suitable spawning habitat for native Bonneville Cutthroat trout Oncorhynchus clarkii utah. However, there was substantial variation in the suitable spawn window among tributaries, owing to differential climate and landscape attributes driving flow permanence and temperature. The results of his research can inform the targeted management of temporary aquatic habitat by identifying how and when intermittent streams contribute to native salmonid population productivity.
Chris Walser investigated the impact of low summer flows on the feeding ecology of Redband Trout O. mykiss gairdnerii in an intermittent Idaho stream at three study sites during lotic and lentic conditions. Trout reduced their foraging frequency by four times as study sites transitioned from lotic to lentic environments. During lotic conditions, trout primarily foraged in the pelagic zone; terrestrial macroinvertebrates (Orthoptera sp. and Coleoptera sp.) and aquatic macroinvertebrates (Ephemeroptera sp.) were common prey. Trout rarely fed at the surface during lentic conditions, shifting their foraging towards benthic and pelagic prey (Chironomidae and Ephemeroptera). This suggests that prolonged low flows (as predicted by climate change models) could reduce trout persistence in intermittent streams of the western United States.
Although the Supreme Court of the United States chose not to use science in its decision on Sackett vs. the Environmental Protection Agency (2022), that decision removes federal protections for the waters and biota discussed above. Instead, those protections now must reside with state legislatures and agencies, which vary markedly in their safeguards (McElfish 2022). We urge readers to work with their AFS Chapters and nongovernment organizations to maximize protections for nonpermanent waters in their states. |
, Niall G. Clancy 
