Author: Cal Water

Monitoring is usually among the first actions taken to help inform recovery planning for declining species, but these data are rarely used formally to inform conservation decision making. For example, Central Valley Chinook salmon were once abundant, but anthropogenic activities have led to widespread habitat loss and degradation resulting in significant population declines. Monitoring data suggest survival through the southern Sacramento-San Joaquin River Delta, in particular, may be a limiting factor for juvenile Chinook salmon outmigrating from the San Joaquin River and its tributaries. However, survival and routing monitoring data have not been formally used to inform water management in a decision analytic framework. Here, we illustrate how estimates derived […]
A Fall X2 Action, intended to benefit delta smelt by increasing outflow through the Sacramento-San Joaquin Delta in years with greater precipitation in the watershed that feeds the Delta, wetter years, was included in the USFWS 2008 Biological Opinion as a “reasonable and prudent alternative.” The management action requires increases in outflow through the Delta during September and October of wet and above-normal years. A similar flow-enhancing management action, but with differing outflow targets, was included in the operations analyzed in the 2019 Biological Opinion. Those Fall X2 Actions have been controversial since first being implemented because of their uncertain conceptual foundations, their large water costs, and the difficulty in […]
Correctly identifying the environmental factors that limit population growth and recovery of imperiled species is an essential element of any targeted conservation program. Abundance index values for delta smelt (Hypomesus transpacificus), an imperiled fish in the upper San Francisco Estuary, have exhibited substantial inter-annual variation and the population is now at historically low numbers. Drawing from conceptual ecological models, we developed and applied a new multivariate analytical technique that incorporates a fundamental characteristic of limiting environmental factors– recognition that certain factors influence abundance in certain seasons or years, but they may have no influence on the species’ performance at other times. We observe that delta smelt occasionally experience years 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 use of surrogates in conservation planning is commonplace in California and elsewhere.  A substantial body of empirical literature has demonstrated the limited effectiveness of surrogates as management tools unless it is first established that the target species and surrogate will respond similarly to a given set of environmental conditions.  We explain that, while the National Marine Fisheries Service historically used hatchery Chinook salmon survival data as a surrogate for wild Chinook salmon, steelhead, and green sturgeon survival, it erred by doing so without first validating that the surrogate responds in the same manner to environmental conditions as the target species.  The consequence of use of surrogates absent validation is […]


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