DeltaCurrents, the Center’s blog, offers science-based observations and opinion on pressing contemporary issues in resource management and conservation planning in the Sacramento-San Joaquin Delta and adjacent upper San Francisco Estuary.

The State of California has committed to a policy of protecting wild runs of its Chinook salmon. It’s reflected in both State law, in the Delta Reform Act, and in State policy, including the State Board’s Bay-Delta Water Quality Control Plan and Delta Stewardship Council’s Delta Plan. The State implements salmon policy by imposing considerable restrictions on the agencies that supply water to residents, businesses, and farmers across much of California at a cost that runs into the hundreds of millions of dollars annually. Yet this year returns of wild spring-run Chinook salmon from the ocean were vanishingly small. State officials report that fewer than 25 returning adults were recorded in two of the three […]
The directive from Congress that the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS) must base their decisions on the “best scientific and commercial data available” under section 7 of the federal Endangered Species Act (ESA) has inarguably contributed to the conservation of imperiled species. The California condor, the gray wolf, and the bald eagle are all examples of this. Unfortunately, the federal wildlife agencies predictably drift from value-neutral assessment of the status of species and the effects of human activity on those species to assumptions in line with the precautionary principle, when confronted with substantive uncertainties regarding the ecologies of listed species and the environments […]
The Northern California Guides and Sportsmen’s Association (NCGASA) has filed a petition for regulatory change with the California Fish and Game Commission that would alter sport fishing such that only striped bass within a 10-inch size range could be legally harvested. Stripers less than 20 inches would be protected from harvest, as would stripers larger than 30 inches. The existing regulations allow anglers to keep any fish 18 inches or greater in length. The stated purpose of the proposed change to a “slot limit” is to contribute to the conservation of striped bass — to grow the population in the San Francisco Estuary and its tributary rivers and to boost […]
Just about every one of us was introduced to the scientific method in a middle-school science class. We were told that science happens when hypotheses about how things work are evaluated using observations and data. Facts we were told emerge when hypotheses stand up or don’t stand up to that test. And that we learned is how science is done  Of course, for the very most of us that straightforward explanation had no ready adolescent application, and the lesson like so many others was lost in the white noise of stuff that mattered at the time. Now, even for the teenagers who were later to become scientists, that early in-one-ear-and-out-the-other […]
If conservation scientists agree on one big thing, it’s that the destruction and fragmentation and degradation of habitats are the dominant threats to the persistence of most imperiled species.  Congress recognized that fact a half century ago in the purpose statement to the Endangered Species Act (ESA) – that is, “to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved.” In that light it is curious that the principal focus of the ESA is on species rather than their habitats. Concurrent with a determination to list a species as endangered or threatened under the ESA, Congress instructs the Fish and Wildlife Service […]
This past week a number of federal, state, and local agencies took a significant first step toward negotiation of Voluntary Agreements (VAs) that could be the basis for implementing updated water quality objectives for California’s Bay-Delta. This is a notable milestone but much work remains. The participating agencies must agree upon the details of the VAs, and ultimately, the State Water Resources Control Board must consider whether to adopt the VAs as the means to implement the Bay-Delta Water Quality Control Plan. The memorandum of understanding (MOU) signed by the VA parties, and the term sheet attached to the MOU, explain the intent of those parties to present VAs to […]
American shad are the Chinook salmon of herring. Like Chinook salmon, adult American shad spend several years in the ocean before returning to rivers for spawning — they’re anadromous. Also, like salmon, anglers love shad because they’re fun to catch and good to eat. Well, okay, shad are not as good to eat as ocean caught salmon, but they are delicious when prepared well.  American shad are native to the east coast of North American. They were introduced to the Sacramento River after repeated releases of shad fry — transported via the then newly completed transcontinental railroad — between 1871 and 1880. Shad quickly became abundant in the Sacramento River […]
For the past three decades, the federal and California governments and diverse stakeholders have looked to scientists to explain the causes of the long-term population declines in fish species native to California’s Bay-Delta in an effort to chart a course to conserve those species. Water agencies across the State have invested billions of dollars in data collection and scientific research with the hope of finding clear answers to vexing problems stemming from more than a century of large-scale environmental change to the Pacific Coast’s most expansive estuary. Armed with a sense of urgency, regulatory agencies have felt the compulsion to act. “Clean narratives” sometimes supplied by scientists, but more often […]
Adaptive resource management is widely acknowledged as the de rigueur approach to the management of natural resources. It is a form of structured decision-making that facilitates use of the best available scientific information by resource managers, and it draws approval from the involvement of stakeholders in its design and implementation. So, when the Delta Reform Act of 2009 identified adaptive management as the format and approach to resource management, the State of California showed a commitment to ensuring that the best professional standards of resource-management practice would be used to address the damaged ecosystems and imperiled species in the Sacramento-San Joaquin Delta and adjacent San Francisco Bay.  The Act is anchored by […]
Even that fraction of the public that is the least interested in California’s environmental health likely has heard of the delta smelt — the imperiled fish of the upper San Francisco Estuary. The diminutive fish that’s launched way more than its share of controversy. The fish that appears to be inching closer to extinction by the month.  To be sure, the delta smelt’s numbers are in decline. And the apparent causes are many. The most abundant fishes in the Delta are non-native species that both compete with and prey upon the delta smelt. Contaminants known and unknown poison its waters. Summer-time water temperatures, increasing in real time with climate change, […]
Recently, at the direction of the Biden White House, the U.S. Fish and Wildlife Service and National Marine Fisheries Service proposed to rescind a Trump-era rule that defines the term “habitat” for the purpose of informing the designation of “critical habitat” by those two agencies under the federal Endangered Species Act (ESA). While the federal wildlife agencies offer certain rationales for the proposed rescission, there is no question that the primary motivation is to provide discretion to federal wildlife agency regions, offices, and line staff to make ad hoc determinations regarding the meaning of the term “habitat.” This shift away from an explicit definition of habitat that provides for transparency and consistency […]
California is at the southern boundary of the distributions of cold-water dependent fish species like salmon and steelhead. In many California rivers, flows and water temperatures challenge the performance and survival of salmonids even in years with average levels of precipitation. Drought and warmer summer air temperatures associated with climate change further exacerbate those stresses.  At and above the Sierra Nevada foothills, Central Valley rivers are heavily regulated.  The dams there provide a variety of benefits for humans — water supply, flood control, hydropower, and recreation — but have some predictable and well-understood adverse impacts on salmonid populations. Dams block upstream passage of adult salmonids, preventing those anadromous fishes from reaching […]
On his first day in office, January 20, 2021, President Biden issued an Executive Order on Protecting Public Health and the Environment and Restoring Science to Tackle the Climate Crisis.  In that Order, the President stated that “the Federal Government must be guided by the best science and be protected by processes that ensure the integrity of Federal decision-making.”  He went on to direct all federal agencies to address federal actions during the prior four years that conflict with that objective.  In an accompanying list of agency actions for review, the President identified precisely two biological opinions that his Administration would review to determine if they were “guided by the best science” and adopted […]
Recently, the Interagency Ecological Program (IEP) — an interagency consortium charged “to provide and integrate relevant and timely ecological information for management of the Bay-Delta” — released a report presenting data and studies regarding a major conservation action for delta smelt, referred to as the Fall X2 Action. The Fall X2 Action purports to benefit the delta smelt during the autumn by increasing outflow through the Sacramento-San Joaquin Delta during that period in years where there is above normal precipitation in the preceding winter and spring.  Increasing outflow through the Delta moves the position of the tidally influenced low-salinity zone westward. The federal and state wildlife agencies contend that this action […]
In the 1981 blockbuster film “Raiders of the Lost Ark”, the nefarious French archaeologist Belloq holds up a cheap pocket watch and explains to Indiana Jones “It’s worthless. Ten dollars from a vendor in the street.  But I take it, I bury it in the sand for a thousand years, it becomes priceless…” Here in the Delta, fisheries monitoring data are treated a lot like Belloq’s watch. An ancient, sandy watch isn’t valued for keeping precise time. Just the same, long-term fisheries monitoring data aren’t necessarily valued because they provide information effective for monitoring and managing Delta fishes. Consider one of the simplest fisheries monitoring tools; the seine, a length of net […]
Monitoring serves two essential purposes when it comes to fish and wildlife conservation. First, it informs our understanding of the status and trend of populations that we want to conserve and recover. Second, it informs the design and implementation of conservation measures to benefit those populations and allows resource managers to assess the effectiveness of such measures.  Absent monitoring, we are guided by intuition, surmise, or plain faith in determining whether we should intervene to protect a species and how we should go about doing so. While delta smelt have been protected under the California and federal Endangered Species Acts for almost three decades and federal and state regulatory agencies have […]
Recently, Courthouse News Service reported on a case pending in the United States Court of Appeals for the Ninth Circuit involving dredging of portions of the San Francisco Estuary and impacts from those activities on fishes protected under state and federal Endangered Species Acts. The U.S. Army Corps of Engineers, faced with the never-ending challenge of keeping shipping corridors open to large vessels in the San Francisco Bay, the Delta, and lower Sacramento and the San Joaquin rivers, have an ongoing consultation with the National Marine Fisheries Service and U.S. Fish and Wildlife Service intended to minimize dredging impacts on longfin smelt, delta smelt, steelhead, and several Chinook salmon runs. The Corps […]
Delta smelt have nearly ceased to appear in “pelagic” fish surveys carried out in their narrow geographic range in the upper San Francisco Estuary. As trawl-generated index values for delta smelt have declined over the past quarter century – understand there is no reliable estimate of the size of the delta smelt population — the chorus of voices advocating for captive rearing and releases of the species has grown louder. When in 2019 the Bureau of Reclamation proposed to include development of a conservation hatchery as a component of its ongoing operation of the federal Central Valley Project, it was building on work to culture delta smelt that was initiated […]
Increasing Central Valley salmon populations in a highly regulated river system is a complex undertaking. Restoring habitats and ecosystem processes, augmenting fish passage, screening diversions, hatchery reform, and improved harvest management are integral components of successful conservation efforts. But restoring a semblance of a natural flow regime — sometimes termed “functional flows” — is often the focus of efforts to improve the status of salmon in Pacific Coast rivers. While it might seem straightforward to reestablish a natural hydrograph in efforts to encourage the ecological and biophysical processes to sustain salmon life stages — well, it’s not. Between obligations related to dam operations (flood control, water storage) and environmental requirements […]
It’s not lost on those concerned with the environmental health of the Sacramento-San Joaquin Delta and adjacent upper San Francisco Estuary that efforts to reverse declines of its imperiled fishes are failing. All the region’s fishes that are protected under the federal Endangered Species Act appear to have suffered reductions, some dramatic reductions, in abundance over the past two decades. The failure to respond to a native fishery in crisis falls in substantive part on the collective shoulders of the well-funded scientific community. From long-term surveys incapable of accurately monitoring the status and trends in numbers of those imperiled fishes to laboratory studies that can’t possibly mimic in-situ estuary conditions, […]
Conceptual models help us to understand the world around us without becoming overwhelmed with its complexity. Societal use of conceptual models is pervasive. Corporate organizational charts offer means to understand and express relationships within the business entity. Road maps represent transportation systems and the built environment. Depictions of food webs give insights into ecosystem structure, function, and composition. Conceptual ecological models are a specialized subset of conceptual models generally intended to describe the environmental factors that affect an ecological community, a species, or a population.  Conceptual ecological models are useful in a variety of contexts ranging from development of research proposals and monitoring schemes, to regulatory decision-making applied in the development […]
Policy makers and scientists often attribute the poor progress being made toward resolving fish conservation and water allocation issues — despite billions of dollars of invested over the past half century — to the physical and ecological complexities of the Sacramento-San Joaquin Delta. The challenge of meeting the goals established in California’s Delta Reform Act, ensuring statewide water-supply reliability and restoring a vibrant and healthy Delta ecosystem, has been referred to as a “wicked” problem, one that may be not fully resolvable. It is doubtless the case that a century-and-a-half of human impacts have altered the system in many ways that are, as a practical matter, irreversible. But a recent article in […]
Conservation science has offered one widely appreciated truism above all others. Habitat loss and fragmentation is the primary cause of imperilment and extinction for very many species. This is certainly the case for the delta smelt, which has seen its habitat diminished and transformed by human activities dating back to California’s gold rush era. Congress recognized the importance of habitat when it enacted the federal Endangered Species Act nearly five decades ago, declaring as its purpose — “to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved” — in other words, to protect and restore the habitats that support imperiled species. The […]
Oncorhynchus mykiss is perhaps the most popular freshwater sport fish in the United States. The geographic distribution of native Oncorhynchus mykiss within the lower 48 states is limited to a handful of states along and adjacent to the west coast — California, Oregon, Washington, and Idaho, although it extends south to Baja California and north to British Columbia and Alaska.  It is artificially propagated by federal and state fish and game agencies and in private aquaculture for game fishing purposes in hundreds of hatcheries and is now established in all of the 48 lower states, at least 45 countries, and every continent except Antarctica. Fly-fishing enthusiasts who live east of the Rockies might be surprised to […]
Off the coast of California and southern Oregon, Chinook salmon are subjected to a uniquely intense commercial and recreational fishery. The fishery relies upon the availability of abundant, hatchery-produced Central Valley fall-run Chinook. However, as currently managed, the fishery provides minimal protection for natural-origin (wild) fall-run Chinook and for winter-run and spring-run Chinook that are listed under the federal Endangered Species Act (ESA), especially fish maturing at age-4 or older. Variation in age-at-maturity is essential for the viability of all runs of Chinook salmon because it buffers populations from short-term environmental changes in freshwater habitats and from catastrophic events. The age-structure of Central Valley Chinook salmon populations is severely truncated. […]
Spring-run Chinook salmon have long played second fiddle to winter-run Chinook salmon when it comes to conservation planning for the Central Valley salmonids protected under the California and federal Endangered Species Acts. But earlier this year, the California Department of Fish and Wildlife issued an Incidental Take Permit (ITP) that promises increased attention for spring-run Chinook. The ITP calls for the aggressive development of a spring-run Juvenile Production Estimate (JPE). The purpose of the JPE is to better track the abundance of juvenile spring-run Chinook and, ostensibly, to provide a basis for setting the number of juvenile spring-run Chinook that the State Water Project is allowed to entrain at the […]
In recent years, the Department of Fish and Wildlife (Department) has taken steps to strengthen its science capacity in response to the enactment of AB 2402 by the Legislature and Governor in 2012. Among other things, AB 2402 required the Department and the Fish and Game Commission (Commission) to develop a strategic plan and authorized the Department to establish a Science Institute to inform the work of the Department and the Commission. To strengthen its science capacity, the Department developed a Scientific Integrity Policy in 2017. That Policy states “work that has a substantial scientific or management impact or large expenditure of funds or is especially controversial in nature should […]
Late last year the State Water Contractors hosted a first-ever Longfin Smelt Science Symposium on in Sacramento. The meeting featured and was attended by all researchers with first-hand and on-the-water experiences with the species in a forum that addressed both its ecology and genetics. Information emerged that has direct and immediate application in the conservation of the fish. The longfin smelt was listed as threatened by the State of California in 2009. The then Department of Fish and Game in its status review of the species, noted spare survey data and anecdotal records of the species across its coastal range from Alaska to just south of San Francisco Bay. The […]
After suing the federal government, in Spring 2020 the State of California sought an emergency injunction in federal district court requiring the U.S. Bureau of Reclamation to curtail water exports to central and southern California to protect steelhead migrating down the San Joaquin River and through the Sacramento-San Joaquin Delta on their way to the Pacific Ocean. The State argued that, if the Bureau failed to impose the San Joaquin River inflow to export ratio (referred to as the I:E ratio) in May 2020, it would undermine the overall prospects for recovery of the steelhead.
 In litigation in the same federal court less than a decade ago, the State argued […]


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