Recently, the Interagency Ecological Program (IEP) — an interagency consortium charged “to provide and integrate relevant and timely ecological information for management of the Bay-Delta” — released a report presenting data and studies regarding a major conservation action for delta smelt, referred to as the Fall X2 Action. The Fall X2 Action purports to benefit the delta smelt during the autumn by increasing outflow through the Sacramento-San Joaquin Delta during that period in years where there is above normal precipitation in the preceding winter and spring.  Increasing outflow through the Delta moves the position of the tidally influenced low-salinity zone westward. The federal and state wildlife agencies contend that this action increases the extent and quality of habitat for delta smelt. As the report explains, a record wet year occurred in 2017, providing the study authors with an opportunity to evaluate the hypothesis that increasing outflow would contribute to the conservation of delta smelt. Nearly four years later the report entitled Synthesis of data and studies relating to Delta Smelt biology in the San Francisco Estuary finally hit the streets. 

The bottom-line finding of the report is that data that were collected and studies undertaken did not identify any evidence that increasing outflow through the Delta in 2017 contributed to the conservation of delta smelt.  This finding is particularly notable because the cost of implementing the Fall X2 Action in just 2017 alone exceeded $100 million. Rather than the end of the story, the release of the report might be viewed as the beginning. That is the case because with the appearance of the 265-page report, the IEP released a two-page summary.  In the summary, the IEP describes the “main finding” of the report — “High fall outflow is necessary, but not sufficient to provide favorable conditions for Delta Smelt.” The statement is remarkable because nowhere in the report does the IEP conclude that high through-Delta outflow is “necessary” to provide favorable conditions for delta smelt. More to the point, none of the data gathered in 2017 and studies conducted in reliance on those data — which were the focus of the report — provide evidence that high outflow is “necessary” to provide favorable conditions for delta smelt. To the contrary, statements in the report contradict the summary’s “main finding.” The two-page summary amounts to misrepresentation of the report’s scientific findings. This is one of several recurring errors in agency analyses of agency actions and conservation measures described in the article I co-authored, The Route to Best Science in Implementation of the Endangered Species Act’s Consultation Mandate: The Benefits of Structured Effects Analysis.  As we explain in the article, these recurring errors in the interpretation of data and analytical results can lead to misinformed policy decisions and misdirected resource management plans.


The IEP report (pages 40-51) presents conceptual ecological models depicting the life history of delta smelt. The report authors use the models to help predict the responses of delta smelt to the Fall X2 Action. One model highlighted by the authors predicts that the low-salinity zone in the western Delta “represents the optimal region for Delta Smelt production” in the autumn (at page 44).  Relying on the suite of conceptual models, the IEP report authors predicted greater growth and survival of delta smelt in the autumn of 2017 when the Fall X2 Action was implemented than in other years. But the data did not support the predictions. The report authors state (at page 158, emphasis added) that “[t]he prediction in this report that Delta Smelt would grow better in 2017…was not supported.”  Similarly, the predictions of higher abundance and survival of delta smelt in 2017 when the Fall X2 Action was implemented were not supported (pages 214-15). Further, the authors searched for a relationship between outflow through the Delta in the autumn and delta smelt survival using trawl data from surveys going back to 1969, concluding that there was “no significant relationship.” They reached the same conclusion when assessing a nearer-term data set from the period from 2002 to 2017 (both on page 215).


Contrary to the “main finding” presented in the two-page summary, the IEP report itself includes no analyses that support the notion that high outflow in the autumn is “necessary” to provide favorable conditions for delta smelt. Instead, the report relies on prior analyses by others to support the proposition that delta smelt are most often found in the low-salinity zone in the autumn (report page 22, citing Moyle et al. 1992) and that increased outflow in the autumn could improve delta smelt habitat (page 22, citing Feyrer et al. 2007, Feyrer et al. 2011, Bever et al. 2016 – these and the other short-form citations here can be found in the IEP report). Those prior analyses used the IEP’s own data drawn from fish surveys that do not cover the entire geographic range of delta smelt, do not include all of the habitat strata that are occupied by the fish, and do not sample the full complement environmental factors that are likely to affect the fish’s distribution and abundance. 


Moyle and his colleagues, without reference to any supporting data, state that “[d]elta smelt are most abundant in low-salinity water associated with the mixing zone in the estuary.” Fresh information in the IEP report and earlier studies cited in it (page 161 citing Sommer and Meija 2013, Bush 2017, Hobbs et al. 2019) present a different picture of delta smelt distribution. Likewise, Feyrer and coauthors erred in their investigations by limiting the environmental correlates of delta smelt occupancy to just three physical variables (temperature, turbidity, and salinity), ignoring other physical variables that appear in the agency’s own conceptual models linking delta smelt population responses to physical environmental attributes, and disregarding biotic variables including predators, competitors, and prey species. 


It is improper to rely on those earlier analyses to make the conclusory claim that outflow through the Delta in the autumn plays any role at all in the population dynamics of delta smelt or determines the extent or quality of delta smelt habitat. Absent among the scientific journal articles cited in either the IEP report or the summary is an analysis of the premise that delta smelt perform better when higher outflow pushes the low-salinity zone in the Delta bayward to the west. In The low-salinity zone in the San Francisco Estuary as a proxy for delta smelt habitat: A case study in the misuse of surrogates in conservation planning I demonstrate that the foundational assumption for the Fall X2 Action, that the position of the low-salinity zone defines the extent and quality of delta smelt habitat in the upper San Francisco Estuary, is unfounded.  Drawing on a substantial literature on use of surrogates in conservation biology, we can observe both that the regulatory agencies have failed to validate the existence of a surrogate relationship between position of the low-salinity zone and the extent and quality of delta smelt habitat, and that available data suggest the regulatory agencies erred when they assumed that such a relationship exists.


More to the immediate point, in the IEP report as compared to the two-page summary, the authors are more circumspect in presenting their findings, noting (on page 237, emphasis added) that “while high outflow might be a critical component of Delta Smelt habitat in the estuary, an increase in freshwater flows alone is not sufficient to address the habitat needs of this endangered species.” The distinction between the finding summary that high outflow “is necessary” and the actual conclusion drawn by the authors that high outflow might be a critical component of Delta Smelt habitat is far too significant to be left uncorrected. If the IEP hopes to retain credibility as a group of scientists interested in pursuing greater knowledge of how the Delta ecosystem functions and how its constituent species can be conserved, as opposed to advocating for a pre-ordained policy agenda, then they should withdraw their two-page summary and amend the full report to make explicit the data basis for the assertion that high outflow through the Delta in the autumn of wet years is necessary to sustain delta smelt.

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