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Open Access Publications from the University of California


SFEWS provides credible scientific information on California's complex water issues, linking new science to policy with great effect. SFEWS retains a regional focus on the San Francisco Bay and the Sacramento–San Joaquin Delta, also known as the Bay–Delta watershed. At the heart of open access from the California Digital Library, SFEWS's scholarly output ranks #1 for the UC Davis Institute  of the Environment and ranks #3 campus wide.

Volume 18, Issue 4, 2020

Issue cover
Cover Caption:Sunset on the Sacramento River. Courtesy of Pikist / public domain license.


Signs of Optimism Beyond 2020

The year 2020 is one we are unlikely to forget. At a time when a global pandemic and an economic collapse drove changing technologies and social and economic inequalities, extreme weather events across the country reminded us, especially here in California, that the effects of a warming earth are undeniable. A tumultuous presidency ended, leaving behind a science establishment uncertain about what lies ahead. Such disruptions add to the concern about the disappearance of journals from the Internet, and so it is only natural that readers might be interested in the status of SFEWS. Even as formidable challenges lie ahead, Editor-in-Chief, Sam Luoma, provides an editorial describing the stability and resilience of SFEWS as one sign of optimism to carry into 2021.


Getting Our Heads Above Water: Integrating Bird Conservation in Planning, Science, and Restoration for a More Resilient Sacramento–San Joaquin Delta

The Sacramento–San Joaquin Delta is an important region for bird conservation in California, particularly as part of a large, productive estuary on the Pacific Flyway. The Delta currently provides habitat to an abundant, diverse community of birds, but it is likely only a small fraction of what the Delta’s bird community once was. Meeting the goal of restoring a healthy Delta ecosystem is legislatively required to include providing habitat for birds among the conservation goals and strategies in the Delta Plan, yet birds and their habitat needs are often not addressed in science syntheses, conservation planning, and large-scale restoration initiatives in the Delta. In this essay, we provide an avian perspective on the Delta, synthesizing recent scientific work to describe factors that contribute to the Delta’s current importance for birds, and the conservation needs of the diverse array of bird species that call the Delta home. We also evaluate the potential for the Delta to become even more important for birds in the future, incorporating climate change effects, species range shifts, and changes to the composition and configuration of the Delta’s landscape. Finally, recognizing the uncertainties about the Delta’s future landscape and the complexity of this social-ecological system, we provide recommendations—aimed at a higher- level policy and planning audience—for integrating bird conservation with other goals in the Delta. To improve ecosystem integrity, conserve biodiversity, and provide benefits to local communities of people, we urge a focus on creating a more resilient Delta and employing a diversified portfolio of conservation strategies, both old and new.

Research Article

Using Life-Cycle Models to Identify Monitoring Gaps for Central Valley Spring-Run Chinook Salmon

Life cycle models (LCMs) provide a quantitative framework that allows evaluation of how management actions targeting specific life stages can have population-level impacts on a species. The LCM building process is also a powerful tool that can be used to identify data gaps existing in the knowledge of the target species, and that might strongly influence overall population dynamics. LCMs are particularly useful for species such as salmon that are highly migratory and use multiple aquatic ecosystems throughout their life. Furthermore, they are lacking for threatened Central Valley spring-run Chinook (Oncorhynchus tshawytscha; CVSC). Here, we developed a CVSC LCM to describe the dynamics of Mill, Deer and Butte Creek CVSC populations. We used model construction, calibration and a global sensitivity analysis to highlight important data gaps in the monitoring of those populations. In particular, we found strong model sensitivity and high uncertainty in various egg, juvenile and adult ocean life stages’ biological processes. We concluded that the current CVSC monitoring network is insufficient to support using a LCM to inform how future management actions (e.g., hydrology and habitat restoration) influence CVSC dynamics. We propose a series of monitoring recommendations, such as the development of an enhanced juvenile tracking monitoring program and the implementation of juvenile trapping efficiency methodology combined with genetic identification tools, to help fill highlighted data gaps. These additional data collection efforts will provide critical quantitative information about the status of this imperiled species at key life stages (e.g., CVSC juvenile abundance estimates), and create a more comprehensive monitoring framework fundamental for working on the recovery of the entire stock. Furthermore, additional data collection will strengthen the LCM parameterization and calibration process, and ultimately improve the model’s predictive performance.

  • 2 supplemental PDFs

Estuarine Habitat Use by White Sturgeon (Acipenser transmontanus)

White Sturgeon (Acipenser transmontanus), a species of concern in the San Francisco Estuary, is in relatively low abundance due to a variety of factors.  The purpose of our study was to identify the estuarine habitat used by White Sturgeon to aid in the conservation and management of the species locally and across its range. We seasonally sampled sub-adult and adult White Sturgeon in the central estuary using setlines across a habitat gradient representative of three primary structural elements: shallow wetland channels (mean sample depth = 2 m), shallow open-water shoal (mean sample depth = 2 m), and deep open-water channel (mean sample depth = 7 m). We found that the shallow open-water shoal and deep open-water channel habitats were consistently occupied by White Sturgeon in spring, summer, and fall across highly variable water quality conditions, whereas the shallow wetland channel habitat was essentially unoccupied. We conclude that sub-adult and adult White Sturgeon inhabit estuaries in at least spring, summer, and fall and that small, shallow wetland channels are relatively unoccupied.