As organizations and agencies scramble to preserve the Central Valley’s dwindling Chinook salmon runs, a group of scientists believes they may be overlooking a key factor in the decades-long decline of the fish: disease.

As organizations and agencies scramble to preserve the Central Valley’s dwindling Chinook salmon runs, a group of scientists believes they may be overlooking a key factor in the decades-long decline of the fish: disease.

In a paper published in September’s issue of San Francisco Estuary and Watershed Science, a research team proposes that diseases—caused by viruses, bacteria and other microbes—could be suppressing juvenile salmon survival in a river system that once hosted millions of adult spawners each year. According to tracking studies, nearly all juvenile Chinook born from natural spawning die before they reach the Golden Gate Bridge; habitat enhancement efforts have failed to mitigate this mortality rate. Short-term studies of Central Valley salmon...
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Current estimates of young salmon lost to the south Delta pumps are based on a smattering of studies from the 1970s and should be updated, according to a new analysis.

“They don’t represent current operations,” says Ukiah-based consultant Andrew Jahn, lead author of the analysis reported in the September 2020 issue of San Francisco Estuary and Watershed Science. Current operations at the State Water Project (SWP) and the Central Valley Project (CVP) can reverse flows in the Old and Middle rivers, diverting salmon on their way to the ocean towards the projects. Existing salmon loss estimates also fail to account for a likely Old River hotspot for predators, drawn to the...
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Fish passage structures can be improved for the benefit of multiple species, if they are designed to account for differences in behavior, physical ability and size, according to a new literature review.

Historically, most fish passages have been designed to help native salmon return to their upstream habitat and spawning grounds, with little consideration for other migrating species such as sturgeon and lampreys. “There is an assumption that if you just build a fish passage structure, fish will go thorough it, but that is not always the case,” says Department of Water Resources fisheries biologist Zoltan Matica, who conducted the review. “The challenge is to understand that this isn’t only a physical...
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Spawning and rearing habitat for important forage-fish species in San Francisco Bay apparently shifts geographically by many miles depending on how much freshwater is flowing into the Estuary.

In a recent study, a team of scientists found that in a dry year, Pacific herring and longfin smelt larvae occurred farther up the Estuary than in a wet year, when spawning and recruitment was pushed seaward. The results suggest that the fish have broader geographic ranges than previously believed, a finding that could inform efforts to manage and protect their habitat. Biologists have long assumed that longfin smelt, a protected species in steep decline for decades, spawn strictly in...
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Heavy Lifting for Fish

Ted Frink recalls watching Jacques Cousteau’s television specials when he was growing up in coastal Orange County. “I envisioned myself as Cousteau,” says Frink, a fisheries biologist with the California Department of Water Resources (DWR) now approaching retirement. “My folks encouraged my interest in science. I knew I could be a biologist.” That early inspiration sparked a long and varied career, culminating in his work as chief of DWR’s Special Restoration Initiatives Branch and his role in mitigating obstacles to...
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Trolling for Salmon by Kayak

Whales scare us much more than sharks. They erupt from the ocean with a rush of displaced water and a poof of air. A collision could be disastrous. “Whale – go-go-go!” I shout. We pedal double-time to dodge the humpback, behind us and approaching from the left. A moment later it surfaces again, with another poof, now off to our right, moving away. We relax and slow back to our standard trolling speed of about 2.5 miles per hour, and...
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Yet another non-native aquatic species may have made itself at home in the Delta.

As described by US Fish and Wildlife Service fish biologist Brian Mahardja and his co-authors in San Francisco Estuary & Watershed Science, the newcomer is an inch-long, minnow-like fish called the bluefin killifish (Lucania goodei), indigenous to Florida and adjacent southeastern states. It was first detected in the Delta Cross Channel during a beach seine survey in October 2017, and subsequently found in Beaver and Hog sloughs and at Decker, Sherman, and Brannan islands. With surveys curtailed by the coronavirus...
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By looking solely at the results of a single annual fish-counting survey, Californians may be seeing an incomplete reflection of Bay-Delta fish population trends.

A team of scientists analyzed 14 survey programs carried out by state and federal agencies, as well as UC Davis, and concluded that employing such a diverse variety of long-term surveys is essential for accurately tracking and assessing the overall health of San Francisco Estuary’s ecosystem and its resident fishes. The research is described in the June issue of San Francisco Estuary and Watershed Science. Lead author Dylan Stompe, of UC Davis, explains that the research arose from concerns that...
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A unique adaptive behavioral trait that may once have helped winter-run Chinook salmon thrive in the Sacramento River system could now be working against the fish as they face extinction.

The trait – which cues fish when to spawn based on water temperature – isn’t syncing up with current conditions in the Sacramento River below Shasta Dam. A paper published in the June issue of San Francisco Estuary and Watershed Science, reports that cooler springtime river temperatures seem to prompt earlier winter-run spawning while warmer temperatures push back the peak spawning period by a week or two. Under historic conditions, when winter-run Chinook spawned in high-elevation streams now inaccessible to...
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Great whales, the largest creatures in the sea, can help mitigate climate change by locking up carbon in their massive bodies and boosting phytoplankton with their waste products.

A preliminary study by researchers with the International Monetary Fund’s Institute for Capacity Development, the University of Notre Dame, and Duke University found that each great whale sequesters an average of 33 tons of CO2 over its lifetime, taking that carbon out of the atmosphere for centuries: when a whale dies and sinks to the sea floor, it takes that carbon with it, says Joe Roman, conservation biologist and author of Whale. (Compare that to a tree, which sequesters about...
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More than half the water diverted from Central Valley rivers is used to irrigate cattle-feed crops, implicating beef and dairy as top drivers of recent fish declines.

Recent findings, published in Nature Sustainability in March, strengthen the environmental arguments for going vegan while rewriting the familiar narrative that almonds and other high-value tree crops are the top hogs of Central Valley water resources. The study’s authors, led by Brian Richter of Virginia-based Sustainable Waters, focused on the arid West and found that irrigated crops like alfalfa and hay, more than any others, are drying out rivers. The reduced flows are pushing dozens of fish species toward extinction....
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Sacramento pikeminnow and introduced striped bass in the middle Sacramento River eat a surprisingly similar diet, says a new study in San Francisco Estuary and Watershed Science.

Both species have been implicated in the decline of vulnerable native species in the river, particularly juvenile Chinook salmon, says lead author Dylan Stompe, a PhD student and researcher at the University of California at Davis. For eight months in 2017, Stompe and fellow researchers with the California State University at Chico and the California Department of Fish and Wildlife surveyed a 35 kilometer reach of the river outside Chico for the two predatory fish. They baited hooks with with...
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Should the striped bass be a suspect in the decline of the Delta smelt?

Writing in the March issue of San Francisco Estuary and Watershed Science, US Fish and Wildlife Service biologists Matt Nobriga and Will Smith suggest that the smelt’s baseline might have shifted long before anyone was paying attention, and striped bass predation may have constrained its numbers before recent water diversions and food web changes added their effects. The smelt’s historic abundance is unknown; systematic surveys didn’t begin until 1959. But it’s thought to have evolved its boom-and-bust life history in...
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Beaver dams may offer wildfire protection to western watersheds, in addition to providing better-known benefits such as groundwater recharge, wetland and habitat creation, and riparian restoration.

A new study by California State University Channel Islands professor Emily Fairfax analyzed satellite-derived vegetation indices of riparian areas and beaver dams mapped via Google Earth. At the same time, Fairfax analyzed data for large (over 30,000 acre) wildfires that had occurred between 2000 and 2018 in California, Wyoming, Colorado, Idaho, and Oregon, and compared the fate of beaver-dammed areas to areas without dams. Fairfax found that riparian corridors within 100 meters of beaver ponds were buffered from wildfires. “In...
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A new project should dramatically improve conditions for endangered steelhead trout in the lower reaches of Alameda Creek.

The project is part of a long-term effort to restore steelhead to Alameda Creek. Last year, for the first time in decades, the San Francisco Public Utilities Commission began releasing water from a newly retrofitted dam, effectively reviving an important tributary stream. Also in 2019, the Alameda County Flood Control District began construction of a key fish ladder at the BART line crossing that will allow adult steelhead to access the river’s headwaters. The new fish passage enhancement plan focuses...
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A resurgence of dinoflagellates, which can cause harmful algal blooms, may be in the cards for some bays along the U.S. West Coast.

A resurgence of dinoflagellates, which can cause harmful algal blooms, may be in the cards for some bays along the U.S. West Coast. Scientists at UC Santa Cruz have been monitoring phytoplankton weekly at the town’s Municipal Wharf since 2002. In 2018, Alexis Fischer, then a postdoctoral fellow at UC Santa Cruz, augmented these observations with an Imaging FlowCytobot (IFCB) that photographed wharf phytoplankton hourly. She also developed a machine learning classification algorithm to automate identification of the organisms. In...
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New archaeological evidence from the South Bay strengthens the case that Chinook salmon spawned naturally in the Guadalupe River.

Albion Environmental, a Santa Cruz research consulting firm, and researchers from Santa Clara University analyzed thousands of fish bones excavated from a 19th century indigenous village on Mission Creek, a historical Guadalupe River tributary long since buried under modern urban development. In an abstract of their research, which has not yet been published, the authors describe using DNA sequencing on 55 confirmed salmonid bones. They identified 52 as belonging to steelhead trout and three as Chinook salmon. Whether Chinook occurred...
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A grassroots effort to move migrating newts across a Marin County road has drawn to a close, but organizers hope it leads to a more permanent solution.

For roughly half a mile, the two-lane road in a hilly rural area west of Petaluma travels alongside a large, natural body of water called Laguna Lake. On the other side is an oak woodland: the perfect place for California and rough-skinned newts, which spend the dry season in moist terrestrial habitat under leaf litter and wood debris or inside animal burrows. After seeing a number of native newts flattened along the road on rainy winter evenings, a small group...
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Urchinomics

By Alastair Bland As purple urchins have multiplied, kelp forests, already stressed by unusually warm water, have collapsed. Norwegian company Urchinomics proposes to capture the overpopulated urchins, fatten them up in circulating seawater tanks, and sell them to restaurants—hopefully in volumes sufficient to dent the urchin armies and allow a kelp comeback. Greater Farallones National Marine Sanctuary press liaison MaryJane Schramm says combatting the urchin takeover “goes directly to our mandate to maintain or restore ecosystem balance.” Citizen science, she...
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Kinky Fish Spines Linked to Selenium

By Joe Eaton Scientists with the U.S. Geological Survey and the National Oceanic and Atmospheric Administration are using new tools to track selenium, with the Sacramento splittail, a California-endemic fish, as an indicator species. Robin Stewart, lead author of a new paper on splittail and selenium, is one of the region’s most seasoned current experts on bioaccumulation of metals in estuarine species. In some sampled splittail, selenium levels exceeded the proposed EPA protective criteria for fish ovaries. Liver levels, not...
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