Climate change and hydrologic alteration by dams are reshaping river systems worldwide, threatening freshwater biodiversity, ecosystem function, and the sustainability of critical ecosystem services. Environmental flows – allocating water specifically to sustain ecosystems – offer an opportunity to integrate ecosystem needs into water management. However, flow recommendations may need to be continually reassessed as climate change shifts the environmental context under which recommendations were originally developed.
STREAM, the Simulation Toolkit for River Ecosystem Adaptive Management, is a decision support platform that simulates how changing streamflow and temperature influence the productivity (i.e., net change in population size over time) of Yellowstone cutthroat trout in the upper Snake River watershed, Wyoming. Built for fisheries and water managers and conservation professionals, STREAM integrates long-term environmental and biological data to support adaptive, climate-resilient management strategies.
What the Model Represents
STREAM is based on a hierarchical Bayesian Ricker stock-recruitment model fit to long-term redd count data (gravel nests built by spawning trout) collected from 13 populations of trout spawning in groundwater-fed tributaries to the Snake River, Wyoming. The model describes how observed redd densities (i.e., recruits) change over time in response to spawning densities four years previously, the average age at maturity (i.e., spawners), and environmental variables representing streamflow and temperature regimes during the juvenile period. The hierarchical structure of the model allows the strength of density dependence and effects of environmental variables to vary among populations. Productivity, i.e., population growth in response to environmental drivers, is calculated as the natural logarithm of the number of recruits divided by the number of spawners. Because groundwater-fed streams are located (sometimes far) downstream of Jackson Lake Dam, the effects of water management are mediated by climate-driven changes in streamflow from unregulated tributaries and temperature.
What Data Does the Model Use?
Redd count data
- Redds are gravel nests built by spawning trout to incubate eggs.
- Redd count data were collected annually by the Wyoming Game and Fish Department from trout populations spawning in 13 groundwater-fed tributaries to the Snake River. Redd densities represent the number of redds per kilometer of stream surveyed.
- Redd counts are strongly correlated with juvenile densities and serve as a reliable index of spawning effort and juvenile recruitment.
- Field observations indicate that most juvenile trout emigrate to the Snake River shortly after emergence from redds, where fish are directly exposed to variation in climate and water management at Jackson Lake Dam. Emigrants from the 13 groundwater-fed streams considered here account for up to 75% of the mainstem Snake River population of cutthroat trout.
Streamflow data
- Daily streamflow is monitored by the USGS at two key locations: the Snake River at Moran (gage A, immediately below Jackson Lake Dam) and the Snake River below Flat Creek (gage B).
- Managed flow variables: we summarized regulated flow regimes (daily streamflow from gage A) to represent important water management periods (e.g., peak spring flows, summer irrigation flows, autumn ramp down).
- Nutratural flow variables: we isolated streamflow contributions from all unregulated tributaries (e.g., Buffalo Fork, Gros Ventre River, Fish Creek) by subtracting daily mean discharge at gage A from that at gage B. We summarized “natural” flow regimes as the timing and magnitude of peak spring flows.
Temperature data
- Because Snake River water temperature data are largely unavailable, we used daily mean air temperature data from NOAA’s Moose, WY station to represent thermal conditions in the Snake River.
- We summarized air temperature data as seasonal means (e.g., winter, summer).
How to Use STREAM
- Model Controls (sliders): Adjust values for flow and temperature variables (e.g., timing of ramp down, timing of peak spring flows, mean winter temperature) to see how each affects productivity, recruitment, and/or carrying capacity.
- Stock-Recruitment Curve: Displays expected recruits per spawner under the selected values of environmental variables. The dashed 1:1 line shows the line of replacement (i.e., equilibrium); where the stock-recruitment curve crosses the line of replacement is the carrying capacity for that population (K).
- Carrying Capacity Distribution: Shows the estimated K (maximum recruits per kilometer) and uncertainty across posterior samples.
- Future Projections Tab: Explore how modeled recruitment may change under projected climate scenarios.
- Scenarios Tab: Compare recruitment distributions under management or climate scenarios for different stream sites.
Disclaimer
This tool is intended for exploratory analysis and visualization. Results represent modeled estimates, not observed redd counts, and should be interpreted in the context of data sources, assumptions, and uncertainty. The model simplifies complex ecological processes but provides valuable insight into how environmental variability can shape trout productivity in groundwater-fed tributaries to the Snake River, Wyoming.
These data are preliminary or provisional and are subject to revision. They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data.
This software is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The software has not received final approval by the U.S. Geological Survey (USGS). No warranty, expressed or implied, is made by the USGS or the U.S. Government as to the functionality of the software and related material nor shall the fact of release constitute any such warranty. The software is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the software.