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 10, Issue 1, 2012
Embryonic and larval development of Sacramento splittail (Pogonichthys macrolepidotus) was characterized from zygote to metamorphosis in laboratory conditions. Fertilized eggs were obtained from induced and natural tank spawning of adults caught in the Yolo Bypass of the Sacramento River. Splittail produced transparent adhesive eggs with a moderate perivitelline space. Duration of embryonic development from fertilization to hatching was 100 h at 18 ± 0.5 °C. Newly hatched larvae were 5.2 to 6.0 mm total length with no mouth opening. Yolk-sac larvae were demersal and absorbed the yolk within 10 days post-hatch. Exogenous feeding started at 6 days post-hatch, concomitant with swim bladder inflation and swim-up movement. Fin differentiation began at approximately 10 d post-hatch (ca. 8.3 to 8.85 mm total length) and was completed at 50 d post-hatch (ca. 19.6 to 20.85 mm total length) when larval finfold was fully resorbed and the adult complement of fin rays was present in all fins, but scales were still lacking.
We examined the spatial and temporal distributions of fishes at a reference and three restored marshes between April 1998 and July 1999 in the Sacramento–San Joaquin Delta, California, to determine the factors that influence fish assemblages in space and time. Shallow-water fishes were sampled using beach seines with and without block-net enclosures in open-water shoals and submerged aquatic vegetation (SAV). Purse seining was used to sample fishes in deep water, including offshore, tidal slough, and marsh-edge habitats. Overall, fish assemblages in reference and restored marshes were dominated by introduced species. One-way analysis of similarity (ANOSIM) did not reveal study site differences in fish assemblages in either data set. However, nonmetric multi-dimensional scaling (NMS) and ANOSIM tests of the shallow-water collections revealed differences in fish assemblages using habitats with and without SAV. Introduced fishes, including predatory centrarchid fishes, were abundant in SAV. NMS and ANOSIM tests of the deep-water collections revealed differences in fish assemblages between offshore and nearshore (marsh-edge and tidal slough) habitats. Notably, native fishes were abundant in tidal sloughs. Temporal analyses revealed a suite of species more common in winter and spring, versus another group of introduced species that were more common in summer and fall. Our study findings indicate that newly restored habitats in the Sacramento–San Joaquin Delta will be invaded by introduced fishes. To promote native fish habitat, restoration planning should focus on areas and regions of the Delta where tidal marshes can be restored with little intervention, and where invasive SAV is less likely to colonize.
Individual-level and Population-level Historical Prey Demand of San Francisco Estuary Striped Bass Using a Bioenergetics Model
Striped bass are both a major predator of native fishes and support a recreational fishery in the San Francisco Estuary (the estuary). Quantifying their demands on their prey is important for understanding long-term trends of fish in the estuary. In this study, we: (i) applied a bioenergetics model of sub-adult (age 1 and age 2) and adult (age 3+) striped bass (Morone saxatilis) to quantify long-term consumption patterns from 1969 through 2004 in the estuary; (ii) developed a method to estimate the abundances of sub-adult striped bass; (iii) evaluated how consumption varied by age and gender; and (iv) identified factors that affect the resulting consumption estimates. On a ‘per capita’ basis, modeled individual prey fish consumption increased after 1990, and individual total and prey fish consumption by age-2 striped bass increased after 1994. Conversely, individual total and prey fish consumption by adult striped bass decreased over the period analyzed. This decline in individual consumption over the study period was related to a decline in mean length at age of adults. As expected, long-term trends in population consumption (total and prey fish) by all ages of striped bass (ages 1 through 6) closely followed their respective population- abundance trends. Population total consumption and prey fish-specific consumption by sub-adult striped bass was found to be similar to the population consumption by adult striped bass, largely because of the high abundance of sub-adults. Unlike adult striped bass that may emigrate and forage in the Pacific Ocean, the majority of sub-adult striped bass reside within the estuary; hence, consumption by the relatively abundant sub-adult population may have significant effects upon their estuarine prey species.
Contemporaneous Subsidence and Levee Overtopping Potential, Sacramento-San Joaquin Delta, California
The levee system in California’s Sacramento-San Joaquin Delta helps protect freshwater quality in a critical estuarine ecosystem that hosts substantial agricultural infrastructure and a large human population. We use space-based synthetic aperture radar interferometry (InSAR) to provide synoptic vertical land motion measurements of the Delta and levee system from 1995 to 2000. We find that Delta ground motion reflects seasonal hydrologic signals superimposed on average subsidence trends of 3-20 mm/yr. Because the measurements are insensitive to subsidence associated with peat thickness variations over Delta-island length scales, it is most likely that InSAR rates reflect underlying Quaternary sedimentary column compaction. We combine InSAR rates with sea-level rise scenarios to quantify 21st century levee overtopping potential. If left unmitigated, it is likely that 50 to 100 years from now much of the levee system will subside below design thresholds.
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