New research indicates that survival of juvenile Chinook salmon in the Sacramento River system can be significantly boosted by achieving key thresholds for river flow.

New research indicates that survival of juvenile Chinook salmon in the Sacramento River system can be significantly boosted by achieving key thresholds for river flow.

The findings, published in the journal Ecosphere, add important context to the general scientific understanding that more water in the river improves fish survival. Previous studies, the authors explain in their paper, have demonstrated that more juvenile salmon migrating toward the sea complete their journey when the Sacramento River system contains more water. Just how much water has been the source of much controversy among user groups. “These studies have not explored the potential nonlinearities between flow and survival, giving...
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Electrofishing is a powerful but underutilized tool for monitoring Delta fish, particularly species favoring “structured” habitats that are difficult to sample using more common methods like trawls and seines.

By analyzing fish catch data from past surveys, researchers Ryan McKenzie, of the US Fish and Wildlife Service, and Brian Mahardja, of the US Bureau of Reclamation, determined that electrofishing resulted in better detection rates for many native and non-native species than net-based surveys. Although electrofishing is currently restricted to freshwater areas of the Estuary and is more selective of larger fish and those with swim bladders, McKenzie and Mahardja recommend that resource managers employ the technique more widely to...
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The robust monitoring programs established to track now-rare Delta smelt could benefit other native fishes, too.

Decades ago, resource managers first learned of declining Delta smelt numbers not through surveys targeting the once-abundant native fish, but rather as a byproduct of long-term monitoring programs for non-native striped bass. Now, the authors of a new study published in the March 2021 issue of San Francisco Estuary and Watershed Science advocate for the use of bycatch data from the recently established Enhanced Delta Smelt Monitoring (EDSM) program to better understand juvenile Chinook salmon distribution. “The scope of [this...
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New insights into Delta smelt swimming behavior could help locate the increasingly elusive fish and prevent losses at the pumps.

Scientists know that smelt use tidal ebbs and flows to migrate landward to spawn, but the degree to which external cues influence behavior remains unclear. In a new study published in the March 2021 issue of San Francisco Estuary and Watershed Science, researchers used computer modeling to predict smelt distribution based on hypothesized swimming behaviors. Six increasingly complex behaviors were tested. For example, the “passive” category assumes that smelt do not swim at all, simply drifting with currents and tides....
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Water turbidity in the Sacramento-San Joaquin Delta can be used as a reliable indicator of smelt entrainment rates in the fish screens of the export pumps at the southern edge of the Estuary.

In a new study published in the March 2021 issue of San Francisco Estuary and Watershed Science, researchers Lenny Grimaldo, William Smith, and Matthew Nobriga used advanced statistical approaches to understand what factors best predict Delta smelt entrainment at the pumps. The paper builds upon research that Grimaldo conducted in the 2000s, which provided the basis for regulations established in the 2008 Delta smelt Biological Opinion. “This study reinforces previous work that adult Delta smelt salvage is largely explained by...
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sunset delta climate map

MEGA-PEARLS Part 4-Climate, Bay-Delta Science Conference, April 2021

A Stream of Science Takeaways. ESTUARY News sent reporters to the biennial Bay-Delta Science Conference in September. This special edition of Pearls shares more than 20 takeaways.
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Science-in-Short ~ Podcast

Drift, Drop or Floc? Tailing Sediment as it Moves Through Marsh Margins This June two USGS scientists will be trying to get as close as they can to the edge of the South Bay’s Whale’s Tail Marsh to lay out their tools: tiles, filter paper, current profilers, and other sediment accretion measuring instruments. Estuary Reporter Ariel Rubissow Okamoto interviews reseachers Jessie Lacy and Karen Thorne about what they’re looking for at the marsh edge, and how it may help us...
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pesticide resistance delta map

MEGA-PEARLS Part 3-HABs & More, Bay-Delta Science Conference, April 2021

A Stream of Science Takeaways. ESTUARY News sent reporters to the biennial Bay-Delta Science Conference in September. This special edition of Pearls shares more than 20 takeaways.
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photo of salmon injection USFWS

MEGA-PEARLS Part 2-Fish-Birds, Bay-Delta Science Conference, April 2021

A Stream of Science Takeaways. ESTUARY News sent reporters to the biennial Bay-Delta Science Conference in September. This special edition of Pearls shares more than 20 takeaways.
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Above: Lewis holding white sturgeon in Delta. Photo: Jim Ervin

MEGA-PEARLS-Part 1-Diversity, April 2021

A Stream of Science Takeaways. ESTUARY News sent reporters to the biennial Bay-Delta Science Conference in September. This special edition of Pearls shares more than 20 takeaways.
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Dutch Slough Laboratory

For a hawk’s-eye view of one of the Estuary’s most ambitious restoration efforts, visit the Dutch Slough Tidal Marsh Habitat Restoration Project’s YouTube channel. Drone-shot footage shows what the Department of Water Resources has been doing on 1,200 acres of former wetland, converted to pasture and subsided up to 15 feet, in the West Delta between Big Break and Jersey Island. After moving millions of cubic yards of soil to elevate the marsh plain, a team of engineers, scientists, and...
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Scientists Nail Climate Links to Extreme Events

While a supermajority of Americans finally believe we are warming the world, a 2020 Yale Climate Opinion survey shows that most people still aren’t very worried about it. “Climate change is abstract to them,” says UCLA climate scientist Daniel Swain. “They don’t connect it to their personal lives.” But Californians do. Reeling from a decade of record-shattering drought, heat waves, and wildfires, people in the Golden State overwhelmingly tell Public Policy Institute of California pollsters that the effects of global...
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Sub-Standard Snow

At a glance, the recent winter storms and inches of snow in the Sierra seem like a reassuring sign: more snow means more snow melt, which means more water moving through our freshwater systems during dry summer months. But it turns out that there are different types of snow with differing levels of moisture locked up inside — and the latest Sierra snowfall appears to be holding less water than usual. This means the Bay’s streams and estuaries could have...
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Sediment Paparazzi

As the Estuary faces drowning marshes due to rising seas, people want to see action – acres saved, walls built, marsh mice whisked to safety after crawling to the tip of the tallest gumplant. In terms of action, “sediment monitoring” doesn’t come immediately to mind. Monitoring is something you do after all the action is over, isn’t it? And as for “sediment,” well what’s all the fuss over some dirt and mud? In fact, there is quite a fuss. The...
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North America’s largest and most ancient freshwater fish species, white sturgeon, hang out in some kinds of Estuary waterways more than others, scientists find.

 Researchers with the U.S. Geological Survey found that adult and sub-adult white sturgeon occupy deep open-water channels and shallow open-water shoals in equal measure, but don’t use shallow wetland channels. As a group, white sturgeon are characterized as amphidromous, meaning they regularly migrate between freshwater and the sea, in both directions, but not for the purpose of breeding. According to the study, which appears in the December 2020 issue of San Francisco Estuary and Watershed Science, adults in the local...
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Filling significant recently identified gaps in monitoring spring-run Chinook is critical to protecting these threatened Central Valley salmon.

“There’s no way we can manage them for recovery if we don’t understand the biological processes that govern their dynamics through time and space,” says UC Santa Cruz/NOAA salmon expert Flora Cordoleani, lead author of a study reported in the December 2020 issue of San Francisco Estuary and Watershed Science. Cordoleani and colleagues identified the monitoring gaps while building a model of the spring-run Chinook life cycle. The model accounts for three self-sustaining populations of these at-risk fish, assessing survival...
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Science in Short ~ Podcast

David Ayers: How Fish Interact with Wetlands Topography  In this podcast, Estuary News reporter Alastair Bland and UC Davis PhD student and fish researcher David Ayers discuss the Sacramento-San Joaquin Delta, its fish, its marshlands, its flows, and its future. Ayers explains the focus of his research, which seeks to reveal how underwater topography in the wetlands fringing the estuary affects interactions between predators and small fish. While restoration projects often focus on adding more water to this ecosystem and...
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A Fragile Fleet

The naming of boats and ships is a serious matter. Each larger vessel’s name starts with a code that tells what it carries, what propels it, or what purpose it serves. If it were your hobby to keep tabs on traffic on San Francisco Bay, you’d see a lot of big UCCs (container ships) and TCHs and TCRs (tankers). You’d see ferries emblazoned with MV, standing for “motor vessel.” Before COVID-19, you would have spotted the occasional SS, standing for...
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A team of scientists is close to chasing down every last thing that happens to nitrogen in wastewater as it passes through the soils and plants of a horizontal levee.

Not only is 97% of the nitrogen removed, but also trace pharmaceuticals. “You just have to focus on where the water is going,” says environmental engineer Aidan Cecchetti, referring to the UC Berkeley-Stanford-ReNUWIt team’s experimentation with three components of flow through the levee system—under the surface, over the surface, or into the air (through evapotranspiration). “In the wastewater pumped to the subsurface, you see full removal of every contaminant except phosphorous.” What’s most astonishing is how much of the work...
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Surface water diversions in California’s Central Valley can be estimated based on readily available climate data, say researchers—a boon to efforts to track groundwater use.

Valley groundwater pumping is calculated as the total water demand minus surface water deliveries. However, today’s water model relies on individually reported diversions across the entire valley, and compiling all these data is a slow process; by the time the numbers are crunched, assessments of groundwater use are already outdated. “It can take years,” says Jordan Goodrich of University of Waikato in New Zealand. “It’s one of the biggest problems we face in tracking the Central Valley water budget.” Overdrafting...
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