Publications

Publications

The Center supports research on issues of immediate importance to resource managers and policymakers who are challenged to manage the San Francisco Estuary’s natural resources. Obligated to provide a reliable supply of water to agriculture and urban users while protecting and recovering threatened and endangered species and restoring their degraded habitats, responsible state and federal resources agencies face misinformation and critical uncertainties about how at-risk fishes and their habitats are affected by environmental stressors. The Center recognizes Congress’ directive that determinations and decision under the federal Endangered Species Act should be informed by the best available scientific information. The Center’s investigative agenda is intended to provide that scientific information and offer procedural guidance to engage it in structured decision-making and adaptive resource management.

Sometimes, the result of the same people talking to the same people in the same institutions leads to commonly held conclusions that are not supported by available data and analyses. Such was the case with disinformation on dispersion of delta smelt prior to their spawning each year.  Numerous presentations at numerous conferences, as well as conceptual diagram repeated in agency documents, depicted delta smelt adults migrating eastward migration taking them from the center of their range into the central and south delta where the population would be vulnerable to entrainment at state and federal water-export facilities. That description of inter-seasonal movements of delta smelt stands in contrast to findings drawn from previous […]
Winter-run Chinook salmon complete their life cycle across a diversity of habitat types (or habitat strata), which complicates attempts to understand how specific environmental stressors impact the population as a whole. In this study we constructed a life-cycle model for Sacramento River winter-run Chinook to evaluate potential management actions and project operations on their population dynamics. The model incorporates multiple life-history stages, including spawning, egg incubation, fry rearing, smolt migration/Delta passage, and ocean rearing.  The investigation describes model functions and presents a sensitivity analysis to estimate fish-environmental factor relationships with strong effects on the winter-run Chinook population. Evaluation of potential management actions was demonstrated by perturbing flow, export volumes, and […]
Previous studies indicate that both river flows and predation by non-native predatory fishes, such as largemouth bass, striped bass, and sunfish, can influence survival of out-migrating juvenile salmon in the Delta. This study was the first of its kind in the Delta to manipulate experimentally both predators and flows to assess responses in juvenile salmon survival and migration rate.  Chinook salmon with acoustic tags were released in study reaches before and after predator removal using electrofishing. Salmon survival improved significantly after the first predator removal, but survival rates returned to pre-removal levels one week later. Opening of the Delta Cross Channel (DCC) gates caused hydrodynamic conditions in the study area to […]
The delta smelt, endemic to the Sacramento-San Joaquin Delta and adjacent upper San Francisco Estuary, has experienced record low abundances since 2004. We address three questions in this investigation: What is the relative importance of environmental factors with direct effects on abundance? Do factors that may have indirect effects provide an explanation of abundance changes? Are effects of environmental factors better accounted for individually or as criteria defining the volume of water with suitable abiotic attributes? Strong evidence was found of density-dependent population regulation. The density of prey was the most important environmental factor explaining variation in delta smelt abundance from 1972 to 2006 and over the recent period of […]
The first step to understanding the ecological needs of a threatened or endangered species is to identify its geographic range and its temporal distribution within that range. Nearly two decades after the delta smelt was listed as threatened under the federal Endangered Species Act that foundational information had not been synthesized and displayed on maps. In this paper we map the distribution of the fish by life stage, providing coverages that enable resources managers to focus conservation activities, including targeted restoration efforts, where and near where delta smelt are most frequently found. Delta smelt are endemic to and narrowly distributed in the upper San Francisco Estuary wherein a single population […]
The U.S. Fish and Wildlife Service and National Marine Fisheries Service are obliged to consult with federal agencies when the actions of those agencies may affect species listed and threatened or endangered under the Endangered Species Act and determine whether such actions are likely to jeopardize the continued existence of the species or result in the destruction or adverse modification of their critical habitats.  The heart of the consultation process is effects analysis, that is, the analysis of the effects of a proposed action on listed species and their designated critical habitats. We propose a structured framework for conducting effects analysis that includes three essential steps—the collection of reliable scientific […]
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