The Influence of Zooplankton Availability on Delta Smelt Condition and Foraging Across Habitat Contexts

Publisher not available | December 19th, 2025

Strategies for endangered species conservation may have different outcomes depending on the habitat context in which they are implemented. Understanding these context-dep

Strategies for endangered species conservation may have different outcomes depending on the habitat context in which they are implemented. Understanding these context-dependent effects can help optimize and target management efforts. In this analysis, we investigate how environmental and food-web conditions interactively affect condition and foraging of Delta Smelt (Hypomesus transpacificus), an endangered fish endemic to the San Francisco Estuary (the estuary). Food limitation, in terms of pelagic zooplankton availability, is considered a main factor that contributes to the decline in Delta Smelt abundance. Our overarching objective was to examine whether the effect of zooplankton on Delta Smelt depended on habitat context. Specifically, we hypothesized that zooplankton would less positively effect Delta Smelt condition—as measured by hepatosomatic index (HSI)—and foraging success in areas with nearby tidal wetlands, because these adjacent habitats may provide access to prey items from the epibenthos and fringing vegetation. In contrast, in regions with limited proximity to wetlands, we hypothesized that Delta Smelt would rely more on pelagic prey, which would manifest as a more positive effect of zooplankton on body condition and foraging success for Delta Smelt. Using models that accounted for habitat in multiple ways, we found little evidence that zooplankton and habitat interactively influenced Delta Smelt condition or gut fullness. Rather, the influence of zooplankton on HSI and gut fullness was generally positive across habitat contexts. Given the well-documented food limitation in the estuary, promoting the availability of pelagic zooplankton is a rational, albeit complex, management aim. Furthermore, our results suggest that efforts to increase zooplankton would broadly benefit Delta Smelt across a wide range of habitat contexts.

The Klamath River’s dams are being removed. Inside the effort to restore a scarred watershed

Los Angeles Times | March 24th, 2024

HORNBROOK, Calif. — Near the California-Oregon border, reservoirs that once submerged valleys have been drained, revealing a stark landscape that had been underwater fo

HORNBROOK, Calif. — Near the California-Oregon border, reservoirs that once submerged valleys have been drained, revealing a stark landscape that had been underwater for generations. A thick layer of muddy sediment covers the sloping ground, where workers have been scattering seeds and leaving meandering trails of footprints. In the cracked mud, seeds are sprouting and tiny green shoots are appearing. With water passing freely through tunnels in three dams, the Klamath River has returned to its ancient channel and is flowing unhindered for the first time in more than a century through miles of waterlogged lands.

The National Significance of California’s Ocean Economy

National Oceanic and Atmospheric Administration (NOAA) | December 17th, 2015

The purpose of this report is to present empirical evidence that illustrates the inland significance of California’s marine transportation and ocean tourism sec

The purpose of this report is to present empirical evidence that illustrates the inland significance of California’s marine transportation and ocean tourism sectors. This report begins with a discussion of California’s economy and then takes a closer look at six economic sectors that depend on ocean resources. Finally, we take an even closer look at two of these sectors—marine transportation and coastal tourism and recreation—and the way these ocean-based activities support local economies across the country.

The NOAA NCEI marine microplastics database

Nature Portfolio (Springer Nature) | October 20th, 2023

Microplastics (<5 mm) pollution is a growing problem affecting coastal communities, marine ecosystems, aquatic life, and human health. The widespread occurrence of m

Microplastics (<5 mm) pollution is a growing problem affecting coastal communities, marine ecosystems, aquatic life, and human health. The widespread occurrence of marine microplastics, and the need to curb its threats, require expansive, and continuous monitoring. While microplastic research has increased in recent years and generated significant volumes of data, there is a lack of a robust, open access, and long-term aggregation of this data. The National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (NCEI) now provides a global open access to marine microplastics data on an easily discoverable and accessible GIS web map and data portal. The objective of this data portal is to develop a repository where microplastics data are aggregated, archived, and served in a user friendly, consistent, and reliable manner. This work contributes to NCEI’s efforts towards data standardization, integration, harmonization, and interoperability among national and international collaborators for monitoring global marine microplastics. This paper describes the NOAA NCEI global marine microplastics database, its creation, quality control procedures, and future directions.

The Pacific Decadal Oscillation modulated marine heatwaves in the Northeast Pacific during past decades

Nature Portfolio (Springer Nature) | June 19th, 2023

The Pulse of the Bay: The 25th Anniversary of the RMP

San Francisco Estuary Institute (SFEI) | July 1st, 2017

San Francisco Bay is the defining feature of our region and a world-class ecosystem. The Bay Area is also known world-wide as a cradle of innovation, excellence, and succ

San Francisco Bay is the defining feature of our region and a world-class ecosystem. The Bay Area is also known world-wide as a cradle of innovation, excellence, and success, especially in the technology sector. Less well known is the fact that over the past 25 years the Bay Area has been a world leader in water quality monitoring, supporting a pioneering program for the Bay that demonstrates how regional collaboration can provide the science needed to protect and improve water quality in a treasured ecosystem. The Regional Monitoring Program for Water Quality in San Francisco Bay (RMP) was established in 1993 and, with sustained local funding and continuous improvement, is going stronger than ever a quarter century later.

The Rebirth of California Fish & Game Code Section 5937: Water for Fish

University of California, Davis (UC Davis) | July 1st, 2012

Swarms of living creatures will live wherever the river flows. There will be large numbers of fish, because this water flows there and makes the salt water fresh; so wh

Swarms of living creatures will live wherever the river flows. There will be large numbers of fish, because this water flows there and makes the salt water fresh; so where the river flows everything will live. Fishermen will stand along the shore; from En Gedi to En Eglaim there will be places for spreading nets. In an average year, California receives inflows and imports of water totaling around 200 million acre-feet,2 enough water to cover the entire state twenty-three inches deep. But California is a state of spatial and temporal water extremes. Spatially, precipitation varies wildly: Death Valley in the Southeast averages less than three inches per year, yet the northwestern corner of the state averages over 140 inches per year. More than 70% of California’s stream flow originates north of Sacramento, but more than 80% of the water is used south of Sacramento. Temporally, precipitation varies both seasonally and annually. California’s wet season typically runs from October or November to April or May, with little or no precipitation during the growing season, from May to September.7 Annual rainfalls of 40% or more below average and 36% or more above average each typically occur once every six to seven years.  To balance these extremes, over 1,300 dams store water across the state, supplying water for urban, industrial, and agricultural uses. While these uses sustain a tremendous part of California’s economy, they also come at high, often unappreciated costs. Fish also need water, so dams that alter water flows for human benefits may also have marked negative impacts on fish.

The San Francisco Bay-Delta Agreement: Principles for Agreement on Bay-Delta Standards Between the State of California and the Federal Government

California State Water Resources Control Board (SWRCB) | December 15th, 1994

The Status of Rainbow Trout (Oncorhynchus mykiss) in the Stanislaus River Summary report of 2015 snorkel surveys

Delta Stewardship Council (Delta Council) | August 1st, 2016

The Use of Smolt Survival Estimates to Quantify the Effects of Habitat Changes on Salmonid Stocks in the Sacramento-San Joaquin Rivers, California

Canada Department of Fisheries and Oceans (DFO) | July 1st, 1989