USGS and Grand Canyon National Park Service researchers investigated the increased dispersal of brown trout (Salmo trutta) into the Colorado River tailwater below Glen Canyon Dam.
Restricting access to Bright Angel Creek and releasing experimental fall-timed floods increases brown trout immigration into Glen Canyon Dam’s tailwater
The Colorado River ecosystem has been altered by flow regulation from Glen Canyon Dam and non-native species introductions. To recover sandbar beaches, experimental high flows (HFEs) have been implemented periodically since 1996. To benefit native fishes, non-native species suppression has been implemented in different portions of the Colorado River system since 2003.
Brown trout are a highly predatory non-native species that were introduced in the 1920s into Bright Angel Creek, a Colorado River tributary, and until recently, were rare immediately below Glen Canyon Dam. Brown trout movements from the Colorado River into Bright Angel Creek have been partially blocked by a weir as part of a suppression program, yet their population has increased in the Lees Ferry reach downstream of the dam. Brown trout pose a predation risk to federally-listed threatened humpback chub populations, so understanding the mechanisms by which they are increasing and dispersing is vital for ecosystem management.
Using a multi-state model to analyze long-term mark-recapture data, researchers assessed whether brown trout movement was affected by the operation of the weir (restricting access to spawning habitat), experimental releases of fall-timed high flows (Fall HFEs), or simply increased during the fall, spawning season. Results of the study suggest that the weir blocked brown trout homing into tributary spawning habitat, and that Fall high-flow experiments increased upstream movement leading to expansion of the brown trout population into the tailwater below the dam.
Read the paper here:
Healy, B.D., Yackulic, C.B., and Schelly, R.C., 2022, Impeding access to tributary spawning habitat and releasing experimental fall-timed floods increases brown trout immigration into a dam's tailwater: Canadian Journal of Fisheries and Aquatic Sciences, online, https://doi.org/10.1139/cjfas-2022-0231.
Yackulic, C.B., Yard, M., Korman, J., Rogowski, D., Healy, B.D., Schelly, R.C., Omana-Smith, E., and Nelson, C., 2022, Brown trout movement data in Glen and Grand Canyons, Arizona, USA: U.S. Geological Survey data release, https://doi.org/10.5066/P96NII4B.