Predation on Fishes in the Sacramento–San Joaquin Delta: Current Knowledge and Future Directions

University of California, Davis (UC Davis) | July 1st, 2016

The Delta is a diverse, highly modified aquatic system. This paper reviews relevant predator–prey theory, describes data on predator–prey relationships of Delta fishe

The Delta is a diverse, highly modified aquatic system. This paper reviews relevant predator–prey theory, describes data on predator–prey relationships of Delta fishes, ranks predator consumption rates, and presents hypotheses for the effects of predation on native and invasive species. Thiry-two different predator categories and 41 different prey categories are identified. The analysis yielded few generalizations regarding predator–prey interactions for Delta fishes. The only evidence for predator specialization occurred in Prickly Sculpin which, when it consumed fishes, ate mostly native species. Data for reptilian, avian, and mammalian predators were sparse; however, these predators may be significant fish predators in altered habitats or when hatchery salmonids are released. The database for predators and their fish prey was not strong, and long-term dietary studies combined with prey availability and behavioral and experimental studies are needed. The behavioral effects of contaminants on prey species also warrant further examination. Although it has been suggested that a reduction in the Striped Bass population be implemented to reduce predation mortality of Chinook Salmon, the large number of salmon predators in the Delta make it unlikely that this effort will significantly affect salmon mortality.

Predicting Sediment Bulk Density for San Francisco Estuary

University of California, Davis (UC Davis) | December 19th, 2025

Sediment bulk density (ρ-dry) and particle size are two important parameters for predicting sediment bed erosion. ρ-dry, however, is difficult to measure accurately. Th

Sediment bulk density (ρ-dry) and particle size are two important parameters for predicting sediment bed erosion. ρ-dry, however, is difficult to measure accurately. The units of ρdry have not been consistently reported in the literature, leading to confusion, particularly in the calculation of sediment budgets that typically require integrating mass-based and volumetric components. Relationships between ρdry and sediment composition have been developed for multiple regions and differ between systems. Developing a system-specific predictive model for ρdry can help fill data gaps and improve sediment budgets, model accuracy, and estimates of quantities of sediment needed for restoration. In this study, we investigate whether ρdry in San Francisco Estuary can be predicted from organic carbon content or percent of fines, which are more easily or frequently measured than ρdry. We compiled sediment properties from samples collected over the past decade throughout the intertidal and subtidal regions of San Francisco Bay and the Sacramento–San Joaquin Delta to examine this relationship. Sample composition ranged from 2.18 to 99.97% fines (particles < 0.0625 mm), ρ-dry ranged from 0.22 to 1.60 g cm-3, and organic carbon ranged from 0.06 to 7.98%. Regression analysis indicates that the percent of fines explains 93% of the variation of ρ-dry (p-value < 0.05, N = 81). The coefficient of determination decreased by ~1% when organic carbon was incorporated in the regression analysis. Comparison of this predictive ρ-dry model to four published models based on samples from other regions supports previous findings that the relationship between ρdry and grain size may vary by system. We also examined additional factors that may affect sediment erodibility, such as hydrographic and oceanographic conditions. Classification of sample sites as intertidal vs. subtidal or wavy vs. non-wavy each significantly explained the residuals from the ρdry model, and both intertidal and wavy conditions were associated with higher ρ-dry values.

Predicting Streamflow Elasticity Based on Percolation Theory and Ecological Optimality

American Geophysical Union (AGU) | July 20th, 2023

Preface to the Environmental Assessment for 2019 Ocean Salmon Fisheries Management Measures

National Marine Fisheries Service (NMFS) | April 1st, 2019

Preseason Report I Stock Abundance Analysis and Environmental Assessment Part 1 for 2019 Ocean Salmon Fishery Regulations (PRE I)

Pacific Fishery Management Council | March 1st, 2019

Preseason Report II Proposed Alternatives and Environmental Assessment Part 2 for 2019 Ocean Salmon Fishery Regulations (PRE II)

Pacific Fishery Management Council | March 21st, 2019

Preseason Report III Council Adopted Management Measures and Environmental Assessment Part 3 for 2019 Ocean Salmon Fishery Regulations (PRE III)

Pacific Fishery Management Council | April 30th, 2019

Primary Production in the Delta: Then and Now

University of California, Davis (UC Davis) | October 3rd, 2016

To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function

To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function. Primary production is a crucial ecosystem process, which directly limits the quality and quantity of food available for secondary consumers such as invertebrates and fish. The Delta has a low rate of primary production, but it is unclear whether this was always the case. Recent analyses from the Historical Ecology Team and Delta Landscapes Project provide quantitative comparisons of the areal extent of 14 habitat types in the modern Delta versus the historical Delta (pre-1850). Here we describe an approach for using these metrics of land use change to: (1) produce the first quantitative estimates of how Delta primary production and the relative contributions from five different producer groups have been altered by large-scale drainage and conversion to agriculture; (2) convert these production estimates into a common currency so the contributions of each producer group reflect their food quality and efficiency of transfer to consumers; and (3) use simple models to discover how tidal exchange between marshes and open water influences primary production and its consumption. Application of this approach could inform Delta management in two ways. First, it would provide a quantitative estimate of how large-scale conversion to agriculture has altered the Delta's capacity to produce food for native biota. Second, it would provide restoration practitioners with a new approach—based on ecosystem function—to evaluate the success of restoration projects and gauge the trajectory of ecological recovery in the Delta region.

Primary Production in the Sacramento-San Joaquin Delta: A Science Strategy to Quantify Change and Identify Future Potential

San Francisco Estuary Institute (SFEI) | May 20th, 2019

Today’s Sacramento-San Joaquin Delta is an unusually low-productivity estuary. The constraints on primary production and the relative importance of different production

Today’s Sacramento-San Joaquin Delta is an unusually low-productivity estuary. The constraints on primary production and the relative importance of different production sources to the food web are major ecological uncertainties in the Delta system. Understanding how the extensive historical changes in the Delta landscape have altered primary production has the potential to inform restoration planning and management across the region.  The Delta Landscapes Project (SFEI-ASC 2014) has recently produced information that allows us, for the first time, to answer questions about historical primary production and carrying capacity from quantified changes in the areal extent and spatial configuration of habitat types in the Delta since the mid-19th century. Our focus is on estimating primary production because the potential capacity of ecosystems to support fish, bird and other wildlife populations is set by primary production – the supply of food required to produce animal biomass. 

Principles and Requirements for Federal Investments in Water Resources

Council on Environmental Quality (CEQ) | March 22nd, 2013

Chapter I – Principles for Federal Investments in Water Resources 1. Purpose and Scope 2. The Federal Objective 3. Guiding Principles A. Healthy and Resilient Ecosy

Chapter I – Principles for Federal Investments in Water Resources 1. Purpose and Scope 2. The Federal Objective 3. Guiding Principles A. Healthy and Resilient Ecosystems B. Sustainable Economic Development C. Floodplains D. Public Safety E. Environmental Justice F. Watershed Approach Chapter II – Requirements 1. General Requirements A. Evaluation Framework B. Best Available Science and Commensurate Level of Detail C. Collaboration D. Risk & Uncertainty i. Climate Change ii. Future Land Use iii. Adaptive Management E. Water Use F. Nonstructural Approaches G. International Concerns H. Design of Alternatives I. Transparency in Decision Making J. Plan Selection 2. Interagency Guidelines 3. Effective Date 4. Approval