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 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 […]
Defenders of Wildlife personnel analyzed data gathered from the U.S. Fish and Wildlife Service and National Marines Fisheries Service from 2008 to 2015 regarding their consultations under section 7 of the Endangered Species Act (ESA). The authors reported that approximately 80 percent of formal consultations are completed within the time limit mandated by the ESA. They also reported that the number of instances where consultation led to a determination that a proposed action is likely to jeopardize one or more listed species or result in the destruction or adverse modification of designated critical habitat is extremely small. Based on those observations, the authors conclude that consultation does not hinder economic […]
Congress displayed great prescience when it directed the US Fish and Wildlife Service and National Marine Fisheries Service to use “the best available scientific and commercial data” to inform its determinations under the federal Endangered Species Act. But those agencies’ stubbornly default to surmise and assertion in many regulatory and decisions that rightfully should be informed by scientific information. We describe the role of the best science directive in the implementation of the Act and best practices that should be employed to realize Congress’s intent. We identify the types of data, analyses, and modeling efforts that can serve as best science in support of agency findings and policy documents. Finally, […]
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