SFEWS: Volume 19, Issue 2
Welcome to the June issue of San Francisco Estuary and Watershed Science. At midyear in 2021, research surrounding the San Francisco Estuary looks forward. Here, six articles in four categories offer advances in science using new technologies and a re-examination of past efforts.
Photo: CA Dept. of Water Resources, public domain.
In Honor of Dr. Larry R. Brown
Herbold et al. remember Dr. Larry R. Brown, who died suddenly in February of 2021. This note captures how important his scientific work was in the San Francisco Estuary and why he will be intensely missed by many of his colleagues.
Photo: Canva stock image
Preparing Scientists, Policymakers, and Managers for a Fast-Forward Future
To accelerate forward-looking science, policy, and management in the Delta, Norgaard et al. propose that the State of California create a Delta Science Visioning Process to fully and openly assess the challenges of more rapid change to science, policy, and management and offer appropriate solutions, including legislation.
Photo: CA Dept. of Water Resources, public domain
Ecological Effects of Climate-Driven Salinity Variation in the San Francisco Estuary: Can We Anticipate and Manage the Coming Changes?
Ghalambor et al. review and summarize the presentations and discussions that arose during the symposium “Ecological and Physiological Impacts of Salinization of Aquatic Systems from Human Activities,” which brought together an interdisciplinary group of scientists, managers, and policy-makers to answer the central question: can we use existing knowledge and future projections to predict and manage anticipated ecological impacts?
Photo: Canva stock image
Effects of Tidally Varying River Flow on Entrainment of Juvenile Salmon into Sutter and Steamboat Slough
Previous studies suggest that fish generally “go with the flow”—however, complex tidal hydrodynamics at sub-daily time-scales may be decoupled from net flow. To further examine entrainment of acoustically tagged juvenile Chinook Salmon into Sutter and Steamboat sloughs, Romine et al. modeled routing of acoustic tagged juvenile salmon as a function of tidally varying hydrodynamic data. Results indicate that discharge, the proportion of flow that entered the slough, and the rate of change of flow were good predictors of the probability of an individual fish being entrained.
Photo: John Burau
Examining Retention-at-Length of Pelagic Fishes Caught in the Fall Midwater Trawl Survey
A study was conducted in 2014-2015 to investigate and quantify the efficiency of the Fall Midwater Trawl for catching the endangered fish species Delta Smelt (Hypomesus transpacificus). Mitchell and Baxter revisit the same gear efficiency study and further utilize the data set by fitting selectivity curves for three additional pelagic fish species: Threadfin Shad (Dorosoma petenense), American Shad (Alosa sapidissima), and Mississippi Silverside (Menidia beryllina), and by applying more statistically sensitive approaches.
Photo: Lara Mitchell
Use of the SmeltCam as an Efficient Fish Sampling Alternative Within the San Francisco Estuary
Resource managers often rely on long-term monitoring surveys to detect trends in biological data. However, no survey gear is 100% efficient, and many sources of bias can both detect or miss biological trends. Huntsman et al. evaulate the SmeltCam, an imaging apparatus developed as a sampling alternative to long-term trawling gear surveys within the San Francisco Estuary, with the potential to reduce handling stress on sensitive species like the Delta Smelt (Hypomesus transpacificus).
Photo: Ken Newman
Volume 13, Issue 3, 2015
Abstracts are not presented with Editorials. --SFEWS Editors
Aquatic trophic interactions in the upper San Francisco Estuary are synthesized here as a conceptual food web model, using over 35 years of scientific research, and highlighting key uncertainties for restoration. The food web was created as part of the Delta Regional Ecosystem Restoration Implementation Program to evaluate the benefits of restoration actions. Historic changes to the hydrology and geomorphology of the region have decreased ecosystem resiliency. More recently, pressures from water export, alien species introductions, and nutrient loading have disrupted the food web and increased the vulnerability of pelagic and juvenile fishes. One of the key features of the contemporary food web is a decoupling of pelagic and the detrital pathways. Low production and high mortality of phytoplankton since the 1980s have led to declines of pelagic organisms, including zooplankton, mysids, and planktivorous fish. In contrast, detrital pathways support abundant epibenthic invertebrates, such as amphipods and crayfish, which have become a dominant food source for adult demersal and piscivorous fish. Fishes that are obligate to the pelagic web will likely continue to decline, although fishes able to use the detrital pathway may be more robust. Fishes with pelagic larvae may be vulnerable to recruitment failures if they are unable to obtain planktonic food during the critical period of their ontological development. Options for increasing pelagic production at large scales are limited, but may include management of clams, nutrient ratios, and off-channel habitat subsidies. Restorations at small to intermediate scales may produce pelagic food, but volumetric constraints will limit the extent of subsidies. Creating spatial opportunities where pelagic and detrital food webs can re-integrate may offer some opportunities for local recruitment, and species able to use localized detritally-based webs will benefit strongly from such activities.
The Aquatic Trophic Ecology of Suisun Marsh, San Francisco Estuary, California, During Autumn in a Wet Year
Using stable isotopes of carbon (δ13C) and nitrogen (δ15N) and mixing models, we investigated the trophic levels and carbon sources of invertebrates and fishes of a large tidal marsh in the San Francisco Estuary. Our goal was to better understand an estuarine food web comprised of native and alien species. We found the following: (1) the food web was based largely on carbon from phytoplankton and emergent-aquatic and terrestrial vegetation, but carbon from submerged aquatic vegetation and phytobenthos was also used; (2) alien species increased the complexity of the food web by altering carbon-flow pathways and by occupying trophic positions different from native species; and (3) most consumers were dietary generalists.
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Freshwater is a scarce and precious resource in California; its overall value is being made clear by the current severe drought. The Sacramento–San Joaquin Delta is a critical node in a complex water supply system that extends throughout much of the western U.S. wherein demand is exceeding supply. The Delta also underpins a major component of the U.S. economy, helps feed a substantial part of the country, is a unique and valuable ecological resource, and is a place with a rich cultural heritage. Sustaining the Delta is a problem that manifests itself in many dimensions including the physical structure of the Delta, the conflicting demands for water, changing water quality, rapidly evolving ecological character, and high institutional complexity. The problems of the California Delta are increasingly complex, sometimes chaotic, and always contentious. There is general agreement that current management will sustain neither the Delta ecosystem nor high-quality water exports, as required under the Delta Reform Act, so there is a renewed urgency to address all dimensions of the problem aggressively. Sustainable management of the Delta ecosystem and California’s highly variable water supply, in the face of global climate change, will require bold political decisions that include adjustments to the infrastructure but give equal emphasis to chronic overuse and misuse of water, promote enhanced efficiency of water use, and facilitate new initiatives for ecosystem recovery. This new approach will need to be underpinned by collaborative science that supports ongoing evaluation and re-adjustment of actions. Problems like the Delta are formally “wicked" problems that cannot be “solved” in the traditional sense, but they can be managed with appropriate knowledge and flexible institutions. Where possible, it is advisable to approach major actions incrementally, with an eye toward avoiding catastrophic unexpected outcomes. Collaborative analyses of risks and benefits that consider all dimensions of the problem are essential. Difficult as the problems are, California has the tools and the intellectual resources to manage the Delta problem and achieve the twin goals of a reliable water supply and an ecologically diverse Delta ecosystem.