Water Year 2024 and 2025 Winter-run Chinook Salmon Annual Loss Independent Peer Review
Background
The California Department of Water Resources (DWR) and the U.S. Bureau of Reclamation (Reclamation) operate, maintain, and manage the State Water Project (SWP) and the Central Valley Project (CVP) facilities, respectively. Both projects are water storage and delivery systems, comprising reservoirs, aqueducts, power plants, and pumping plants. Their main purpose is to store water and release it for flood control, hydropower generation, water supply diversion, and environmental and fishery beneficial uses.
Sacramento River Winter-run Chinook Salmon (Oncorhynchus tshawytscha) is listed as an endangered species under both the California and federal Endangered Species Acts. Historically, Winter-run Chinook Salmon spawned in the upper reaches of Sacramento River tributaries, but are now limited to downstream of Shasta Dam. Juvenile Winter-run Chinook Salmon emigrate downstream through the Sacramento River starting in July, reaching the Delta from October through April. Populations are supplemented by juvenile salmon released from hatcheries.
Juvenile Winter-run Chinook Salmon face many threats during their migration, including entrainment in the large pumping facilities of the SWP and CVP in the Delta. Entrainment refers to fish being carried by the flow of water into water project facilities. In 2024, the National Oceanic and Atmospheric Administration (NOAA)’s National Marine Fisheries Service issued a Programmatic Biological Opinion for the Long-Term Operation of the CVP and SWP that included an incidental take statement for winter-run Chinook salmon. The California Department of Fish and Wildlife (CDFW) issued an Incidental Take Permit to DWR in 2024, which lists the maximum number (as a proportion of the estimated population) of natural and hatchery-raised juvenile salmon that can be entrained by water projects to stay within permit requirements, referred to as the annual loss threshold. Both documents include a commitment to convene an independent peer review if salvage loss (meaning deaths at water operations facilities) exceeds defined thresholds. These thresholds were exceeded in Water Years 2024 and 2025.
This independent scientific peer review intends to review the actions and decisions contributing to the loss trajectory that led to an exceedance of the annual loss threshold, and make recommendations on modifications to SWP and CVP operations, or additional actions to be conducted to stay within the threshold in subsequent years including the use of indicators from in-season monitoring (e.g., existing/new monitoring data) and tools (e.g. modeling tools).
Panel Letter Review
The Delta Science Program coordinates scientific peer reviews in accordance with its mission to provide the best possible unbiased scientific information to inform water and environmental decision-making in the Delta (Water Code Section 85280(b)(4)). As requested by Reclamation and DWR, the review will include a Panel Letter developed by the entire panel, which will address the Review Questions in the Charge based on the panel's collective expertise.
View Reclamation and DWR’s request letter to Delta Lead Scientist, Dr. Lisamarie Windham-Myers.
View Dr. Windham-Myers's response in PDF format.
Panel Letter Review Materials
Review Documents
- Weekly Assessment of CVP and SWP Delta Operations on ESA-listed Species
- Final State Water Project Incidental Take Permit Risk Assessments for Winter-run and Spring-run Chinook Salmon
- Long-Term Operation - Biological Assessment. Appendix AB, Chapter 3 - Proposed Action
- 2019 Biological Opinions, Consultation on the Coordinated Long-Term Operation of the Central Valley Project and State Water Project. Chapter 4: Proposed Action. 4.10.5 Delta, 4-54; 4.10.5.1 Seasonal Operations, 4-55; 4.10.5.10 OMR Management, 4-66 to 4-80
- Biological Opinion for the Reinitiation of Consultation on the Long-Term Operation of the Central Valley Project and State Water Project (2019) - Section 8.6.9.2.1 Sacramento River Winter-run Chinook salmon exposure pages 486-489; Section 8.6.9.2.2 Juvenile Salvage Estimates using the Salvage-Density Model 489-497; Sections 8.6.9.2.9 - 8.6.9.2.24 pages 519-549
- Endangered Species Act Section 7(a)(2) Programmatic Biological Opinion for the Reinitiation of Consultation on the Long-Term Operation of the Central Valley Project and State Water Project (2024) - Section 7.5.1.6 Old and Middle River Flow Management pages 586-614
- Please contact reviewadvice@deltacouncil.ca.gov
- Effects Analysis, State Water Project Effects on Winter-run and Spring-run Chinook Salmon (March 2020) - Section 8.14, pages 119-145
- Please contact reviewadvice@deltacouncil.ca.gov
- Effects Analysis, State Water Project Effects on Winter-run and Spring-run Chinook Salmon, Attachment 6 (November 2024) - pages 217-227
- Winter-run Chinook Salmon Machine Learning Model
- Using Monitoring Data as an Early Warning Indicator of Salvage
- Winter-run Chinook Salmon Machine Learning Model Old and Middle River Scenarios
- Please contact reviewadvice@deltacouncil.ca.gov
- Winter-run Chinook Salmon Juvenile Production Estimates, Appendix F
- Water Operations Management Team Notes
- Incidental Take Permit: Long-term Operations of the State Water Project in the Sacramento-San Joaquin Delta (2020) - pages 66-75; 87-89
- Please contact reviewadvice@deltacouncil.ca.gov
- Incidental Take Permit: Long-term Operations of the State Water Project in the Sacramento-San Joaquin Delta (2024) - pages 62-66; 73-75
Supplemental Material
- Salmon Monitoring Team notes
- Water Year 2024 Seasonal Report for Old and Middle River Flow Management
- Appendix H. Winter-Run Chinook Salmon Cohort Report (Brood Year 2023)
- Water Year 2025 Seasonal Report for Old and Middle River Flow Management
- Appendix A. Water Year 2025 Old and Middle River Entrainment Seasonal Report Data
- Appendix C. Winter-Run Chinook Salmon Cohort Report (Brood Year 2024)
- Appendix D. Genetic Analysis
- Please contact reviewadvice@deltacouncil.ca.gov
- Effects of Water Project Operations on Juvenile Salmonid Migration and Survival in the South Delta Report, Volume 1 (2017). Section 3.13 Migration and Survival as a Function of Old and Middle River Flows pages 72-73; Section 3.18 Discussion and Summary of Key Findings pages 80-95
- Enhanced Acoustic Tagging, Analysis, and Real-Time Monitoring of Wild and Hatchery Salmonids in the Sacramento San Joaquin Rivers and Delta 2021-2024 Final Report
- 2024 Salmon Scoping Team Report
- Please contact reviewadvice@deltacouncil.ca.gov
- Brood Year 2024 Juvenile Production Estimate Letter (January 17, 2025)
- Brood Year 2023 Juvenile Production Estimate Letter (January 12, 2024)
Charge to the Independent Review Panel
The Charge to the independent review Panel provides the direction, context, and timeline for the review. The Charge includes orientation and focus for the review effort, support materials to be considered, and specific questions for the panel to address during the review process.
Final Panel Report
- Expected February 2026.
- View the Transmittal Letter from Delta Lead Scientist, Dr. Lisamarie Windham-Myers. Expected January 2026.
Review Panel Members
Nancy Monsen (Panel Chair)
Nancy E. Monsen, Ph.D.
Dr. Monsen’s research has focused on multi-dimensional hydrodynamic modeling of the Sacramento-San Joaquin Delta and Suisun Bay for the last twenty-five years. Her Ph.D. research was based on the TRIM3D hydrodynamic model, and more recently, she worked on Stanford’s SUNTANS hydrodynamic model. She also has consulting experience with the DELFT3d hydrodynamic model. Nancy Monsen joined Stanford University in August 2011, having worked previously with Philip Williams & Associates, Ltd. (now ESA PWA) and the U.S. Geological Survey (USGS). Funding for her Stanford research ended in August 2014, but she continued as a visiting scholar at Stanford until August 2015, writing papers and assisting Ph.D. candidates and Post-Doctoral researchers in the Environmental Fluid Mechanics Laboratory. She has been on several science review panels including the Independent Review of the Draft Bay Delta Conservation Plan Effects Analysis (2014), the State of the Science Workshop on Fish Predation on Central Valley Salmonids in the Bay-Delta Watershed (2013), and the Independent Review Expert Science Panel of the Collaborative Adaptive Management Team (CAMT) Proposed Investigations on Understanding Population Effects and Factors that Affect Entrainment of Delta Smelt at the State Water Project and Central Valley Project (2014), and the Calculation of Net Delta Outflow (NDO) Review (2016). At the beginning of 2017, Dr. Monsen was the lead author on the CA WaterFix Aquatic Science Peer Reviews Phase 2a and Phase 2b. She served on the annual independent science review panels for the Long-term Operations of the Central Valley Project and State Water Project biological Opinions (LOBO) in 2014, 2015, and 2017. She served on the NMFS 2019 Independent Review of the Coordinated Long-Term Operation of the Central Valley Project and State Water Project. Most recently, she served on the 2024 Review of the Long-Term Operations for the Central Valley Project and State Water Project Fish and Aquatic Effects Analysis. Dr. Monsen earned her doctorate in Civil and Environmental Engineering at Stanford University.
Anna Sturrock (Lead Author)
University of Essex
Dr. Anna Sturrock is an Associate Professor at the University of Essex in the United Kingdom. Her research focuses on fish ecology and migration, using natural and applied tags to generate empirical data to inform management and conservation. She received her bachelor’s degree in zoology from the University of Edinburgh, her master’s degree in marine science from the University of Otago (New Zealand) as a Leverhulme Trust Study Abroad Fellow, and her Ph.D. in ocean and earth science from the University of Southampton and the Centre for the Environmental Fisheries and Aquaculture Science as an FSBI fellow. Her postdoctoral research focused on Pacific salmon migration, growth, and resilience in the California Central Valley, while she was a senior researcher (2012-20) and Delta Science Fellow (2014-16) at the University of California, Santa Cruz, Berkeley, and then Davis. She led a series of projects with NOAA Fisheries, USFWS, and CDFW, and was part of an expert team investigating alternative approaches to storing water for the environment for the Public Policy Institute of California from 2020 to 2022. Her work has been highlighted in the Guardian, BBC News, The Conversation, and High Country News. She was a founding member of a European COST Action focused on unifying concepts and approaches to marine connectivity for improved ecosystem and resource management for the seas, her working group bringing together >150 scientists from >30 countries (SEA-UNICORN; 2020-24), and was awarded a prestigious 7-year UK Research and Innovation Future Leaders Fellowship in 2022.
Richard W. Zabel
Zabel Ecoscience LLC
Dr. Zabel’s research has focused on the population dynamics, bioenergetics, and behavior of fish, especially in relation to climate change and human impact. Key areas of his work include: Population viability modeling: Using demographic models to assess the viability of fish populations and the effects of factors like density dependence and anthropogenic impacts, and then using the models to forecast alternative future scenarios; Climate impacts: Studying how climate variability and change affect fish populations; Migrational behavior: Modeling dispersal patterns and life history traits in fish, including examining how environmental conditions affect the migration of salmon populations; Hydropower impacts: Assessing the effects of hydropower development on fish through the development of decision-support tools. Rich earned a B.S. and M.S. from the University of Michigan and a Ph.D. in Quantitative Ecology and Resource Management from the University of Washington.