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February 9, 2024

Physics to Fish: Understanding the Factors that Create and Sustain Native Fish Habitat in the San Francisco Estuary

This research project was led by the USGS California Water Science Center's Larry Brown, research biologist. The research and monitoring described in this report comprises the period 2015–19 and focuses on management issues related to native fish species of concern.


The Bureau of Reclamation (Reclamation) operates the Central Valley Project (CVP), one of the nation’s largest water projects. Reclamation has an ongoing need to improve the scientific basis for adaptive management of the CVP and, by extension, joint operations with California’s State Water Project. The U.S. Geological Survey (USGS) works cooperatively with the Bureau of Reclamation to provide scientific support for the management of Reclamation’s CVP project.

The approach for this cooperative project is based on the “physics to fish” concept, the idea that high-quality habitat is generated and sustained by the interaction between physical processes and the landscape. These interactions create a template for chemical and biological processes that can change across a variety of spatial and temporal scales. Following this concept, this project (hereafter referred to as “the physics to fish project”) included monitoring and studies of water flows, sediments, water quality, and invertebrate and fish dynamics across a range of spatial and temporal scales and in regions relevant to resource managers tasked with managing water supplies and ecosystem health in the San Francisco Estuary.

What's it all about?

Peter Pearsall, science communication specialist for the USGS Pacific Coastal and Marine Science Center, offers insight on the recent Physics to Fish publication. He is a naturalist, writer, photographer & videographer, and public-relations professional with almost a decade of experience working with federal governmental agencies on issues of land use, conservation, and science.

In a new report, U.S. Geological Survey scientists working in collaboration with the Bureau of Reclamation (BOR) have laid the foundation for a comprehensive understanding of how habitat restoration can significantly benefit native fish populations in California's Central Valley. The study focuses on the Central Valley Project (CVP), one of the largest water projects in the nation.

The Central Valley Project is a complex network of dams, reservoirs, canals, hydroelectric powerplants and other facilities that extends 400 miles across central California. It reduces flood risk for the Central Valley and supplies water to major urban centers in the Greater Sacramento and San Francisco Bay area.

The Central Valley Project has an ongoing need for scientific improvements in adaptive management. The cooperative project between BOR and USGS aims to provide the necessary scientific information to evaluate the effectiveness of current and future adaptive management actions. The overarching goal is to enhance the scientific basis for more flexible CVP operations that ensure water-supply reliability, while also protecting native fish species such as the federally endangered Delta smelt, endemic to the San Francisco Estuary.

At the core of this cooperative project is the "physics to fish" concept, emphasizing the crucial role of habitat in the interaction between physical processes and the landscape. These interactions create a foundation for chemical and biological processes that vary across spatial and temporal scales. The approach involves documenting habitat conditions, essential processes, and their interactions to objectively assess the likely effects of future management actions, such as habitat restoration.

The report outlines ideas related to habitat restoration and channel modifications that could enhance conditions for native fishes with minimal or no additional water cost beyond what is already allocated for other management actions. 

For this project, researchers from the USGS Pacific Coastal and Marine Science Center led an investigation of sediment dynamics in two flooded agricultural tracts slated for habitat restoration. They sought to determine the potential for these tracts to export turbidity, which could potentially improve habitat in adjacent waters for the Delta smelt, a species that prefers more turbid waters.

This “physics to fish” framework addresses fish conservation at regional and landscape scales. By bridging the gap between physical processes and the habitat needs of native fishes, this cooperative effort sets the stage for a more informed and effective approach to habitat restoration, offering hope for the preservation and enhancement of California's native fish populations.


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