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 11, Issue 1, 2013
Various schemes are often suggested to reverse the subsidence of lands below sea level in California’s Sacramento—San Joaquin Delta, an area protected by levees (dikes) that have significant probabilities of failure. Elementary modeling is used to estimate the probability distribution of land elevations at time of failure for 36 of these subsided islands, assuming a reasonable potential subsidence reversal rate. Given estimated annual probabilities of levee failure, elevation gains at this rate are not expected to exceed 1 to 2 m before flooding, which would be insufficient to restore most subsided islands to mean sea level (msl). However, under some circumstances 1- to 2-m gains are significant. A framework is introduced for evaluating islands as promising candidates for subsidence reversal based on elevation goals other than msl, as demonstrated though a hypothetical aquatic habitatexample. Here, we recommend relevant subsidence reversal strategies by comparing an elevation goal with each island’s anticipated flooded depth, and we prioritize islands for investment based on trade-offs between anticipated outcome and lost agricultural revenues. This approach might help integrate subsidence reversal activities into long-term Delta planning under a range of flooding, land use, and habitat management scenarios.
Ecosystem-scale Selenium Model for the San Francisco Bay-Delta Regional Ecosystem Restoration Implementation Plan
Environmental restoration, regulatory protections, and competing interests for water are changing the balance of selenium (Se) discharges to the San Francisco Bay–Delta Estuary (Bay–Delta). The model for Se described here as part of the Delta Regional Ecosystem Restoration Implementation Plan (DRERIP) draws both from the current state of knowledge of the Bay–Delta and of environmental Se science. It is an ecosystem-scale methodology that is a conceptual and quantitative tool to (1) evaluate implications of Se contamination; (2) better understand protection for fish and aquatic-dependent wildlife; and (3) help evaluate future restoration actions. The model builds from five basic principles that determine ecological risks from Se in aquatic environments: (1) dissolved Se transformation to particulate material Se, which is partly driven by the chemical species of dissolved Se, sets dynamics at the base of the food web; (2) diet drives bioavailability of Se to animals; (3) bioaccumulation differs widely among invertebrates, but not necessarily among fish; (4) ecological risks differ among food webs and predator species; and (5) risk for each predator is driven by a combination of exposures via their specific food web and the species’ inherent sensitivity to Se toxicity. Spatially and temporally matched data sets across media (i.e., water, suspended particulate material, prey, and predator) are needed for initiating modeling and for providing ecologically consistent predictions. The methodology, applied site-specifically to the Bay–Delta, includes use of (1) salinity-specific partitioning factors based on empirical estuary data to quantify the effects of dissolved speciation and phase transformation; (2) species-specific dietary biodynamics to quantify foodweb bioaccumulation; and (3) habitat use and life-cycle data for Bay–Delta predator species to illustrate exposure. Model outcomes show that the north Bay–Delta functions as an efficient biomagnifier of Se in benthic food webs, with the greatest risks to predaceous benthivores occurring under low flow conditions. Improving the characterization of ecological risks from Se in the Bay–Delta will require modernization of the Se database and continuing integration of biogeochemical, ecological, and hydrological dynamics into the model.
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Migration Patterns of Juvenile Winter-run-sized Chinook Salmon (Oncorhynchus tshawytscha) through the Sacramento–San Joaquin Delta
The decline of Sacramento River winter-run Chinook salmon (Oncorhynchus tshawytscha) remains one of the major water management issues in the Sacramento River. Few field studies have been published on winter-run, leaving gaps in our knowledge about their life history. This is especially true in the Sacramento–San Joaquin Delta, which provides essential rearing and migratory habitats for winter-run, and serves as the center of water operations for California. Using long-term monitoring data that identified winter-run-sized fish (“winter-run”) using length-at-date criteria, we examined patterns of juvenile migration in terms of geographic distribution, timing, numbers, and residence times. We analyzed the role of flow, turbidity, temperature, and adult escapement on the downstream movement (“migration”) of winter-run. Winter-run passed Knights Landing (rkm 144 or 51 rkm upstream of the Delta) between October and April, with substantial variation in peak time of entry that was strongly associated with the first high flows of the migration season. Specifically, the first day of flows of at least 400 m3 s-1 at Wilkins Slough (rkm 190) coincided with the first day that at least 5% of the annual total catch was observed at Knights Landing. While the period during which winter-run left the Delta spanned several months based on Chipps Island (rkm 29) catch data, the median catch typically occurred over a narrow window in March. Differences in timing of cumulative catch at Knights Landing and Chipps Island indicate that apparent residence time in the Delta ranges from 41 to 117 days, with longer apparent residence times for juveniles arriving earlier at Knights Landing. We discuss the potential importance of the Yolo Bypass floodplain as an alternative rearing and migratory corridor, contingent on the timing, duration, and magnitude of floodplain inundation. These results carry implications for habitat restoration and management of Sacramento River flows.
- 1 supplemental PDF