DeltaCurrents

DeltaCurrents

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.

Captive breeding of delta smelt: Worthy experiment or well-intended folly?

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 […]
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Spring flow pulses in drought years can help salmon. So, what’s stopping us?

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 […]
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Resource managers should consider the law of “limiting factors” if they have any hope of saving the imperiled delta smelt

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, […]
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The role of conceptual ecological models in implementing the federal Endangered Species Act

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 […]
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In pursuit of the Delta’s co-equal goals, facts matter

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 […]
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Whither habitat for the imperiled delta smelt?

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 […]
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Regulations falling behind science: the artificial distinction between rainbow trout and steelhead

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 […]
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Ocean harvest of Central Valley Chinook salmon: a threat to viability of California’s wild salmon?

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. […]
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A regulatory Catch-22 inhibits recovery of Central Valley spring-run Chinook salmon

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 […]
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California’s Department of Fish and Wildlife must do more to conform to best practices for Independent Science Review

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 […]
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A new understanding of the status of longfin smelt and its conservation needs

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 […]
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A cynical display of concern for imperiled steelhead in the Central Valley

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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