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.

The California Endangered Species Act (CESA) is one of the most impor- tant legal tools available to the Fish and Game Commission and Department of Fish and Wildlife to protect the State’s wildlife resources. The listing process, together with the prohibitions in section 2080 of the Fish and Game Code, are the law’s regulatory teeth. At the same time, because any interested person can petition to list a species, the listing process invites citizen participation in the regulatory scheme. Listing decisions can be the difference between persistence and extinction of a species. They can also cause severe economic disruption and, for this reason, should in our view be made with […]
In a recent Comment in these pages, five researchers affiliated with the University of California, Davis critiqued a biological opinion issued by the U.S. Fish and Wildlife Service (FWS) under §7(a)(2) of the Endangered Species Act (ESA) that analyzes the effects of ongoing operations of the Central Valley Project (CVP) and State Water Project (SWP) on the Delta smelt. The subject is consequential because the Delta smelt’s historical habitat has been transformed and severely degraded since the California Gold Rush, leading to a significant decline in the size of its population; and because the CVP and SWP are far and away the two largest water supply projects in California, delivering […]
The habitat for any species results from a complex interplay of the environmental conditions that meet the resource needs of each of its life stages. In this paper, available data on water clarity, temperature, salinity, prey, and water body type are used to specify ranges of suitable conditions for delta smelt through its life cycle. The authors develop “affinity curves” that portray the adequacy of environmental conditions for each life stage. The curves are fundamentally important in guiding conservation management decisions for delta smelt. They depict, for example, when salinity is too low or too high for delta smelt to develop and how much food is sufficient to keep them feeding […]
The tiny crustaceans referred to as copepods comprise the prey, the main food source, for delta smelt. The lack of copepods in certain areas of the Delta and at certain times in much of the Delta is a primary factor limiting the abundance of delta smelt. It has been assumed that increased flows though the Delta should bring food into areas occupied by delta smelt; however the supply of food to the fish is determined by multiple factors, such as the number of copepods already in an area, availability of certain nutrients, water temperature and clarity, and copepod residence time, that is, how long copepods may stay in suitable ambient […]
The extent of the low-salinity zone has long been used as a measure of the health of the aquatic ecosystem in the upper San Francisco Estuary. Consistent with that concept, the US Fish and Wildlife Service in analyzing and responding to the impacts of ongoing water export operations on delta smelt has imposed conservation actions that assume that the low-salinity zone can serve as a “surrogate indicator” for the fish’s habitat. When freshwater is exported in autumns in years with greater freshwater input into the estuary, habitat for delta smelt is assumed to be reduced in extent and quality. But available scientific information countermands that finding. Notably large expanses of […]
Peer review, more accurately described as independent scientific review, is an essential contributor to the federal wildlife agencies’ ability to meet the “best available science” standard required for determinations under the federal Endangered Species Act. Despite the high risk of extinction experienced by a number of native fishes in the upper San Francisco Estuary and the attending social and economic costs of implementing the Act’s prohibitions, neither federal nor state resource agencies employ independent outside expert review as frequently as would be prudent. Moreover, such reviews when engaged often fail to meet acceptable standards. We describe nine essential attributes of a rigorous independent scientific review that necessarily should be met […]
The study took a spatiotemporal modeling approach in an effort to account for sampling and observation variation by employing both stochastic and deterministic elements. Smelt density was spatially and temporally autocorrelated, strongly tracking prey availability, while constrained by hydrological factors, salinity, turbidity, and velocity. Specifically, juvenile smelt preferred slightly saline, turbid, and slow‐moving water with ample copepod prey. Poor swimming capabilities reduced the capacity of juvenile delts smelt to mix throughout the estuary and disperse from areas with habitat of lesser quality to locate areas that offer better habitat conditions. Through-Delta outflow appeared to influence the spatial distribution of covariates and juvenile smelt, with delta smelt densities tending to peak […]
Identifying the environmental factors that are responsible for the decline in numbers of delta smelt is prerequisite to identifying management actions that can contribute to reversing the trend and recovering the species. A number of empirical models that consider multiple environmental factors and employ innovative multivariate-statistical approaches have attempted to identify the causes of the decline, but they have produced inconsistent and even contradictory results. That explanatory ambiguity has been unhelpful to resource managers responsible for protecting the delta smelt and its habitat in the degraded upper San Francisco Estuary, and has resulted in the implementation of ineffective and often costly management actions. In this paper we approach the problem […]
Processing...
Thank you! Your subscription has been confirmed. You'll hear from us soon.
Subscribe to DeltaCurrents
ErrorHere