San Francisco Estuary and Watershed Science

There is a large and complex literature that addresses the question of optimally employing science in environmental policy. That literature mostly focuses on the challenges of efficient and effective interactions: it is probably fair to say it is long on identifying problems and short on answers. As a complement to the existing literature as well as the BDCP and the DSC's science plan, we invited nine experts each to write a 2,000-word essay to address the statement that science will guide policies concerning water supply reliability and ecosystem restoration in the Bay-Delta.

Large-scale ecosystem restoration projects seldom undergo comprehensive evaluation to determine project effectiveness. Consequently, there are missed opportunities for learning and strategy refinement. Before our study, monitoring information from California’s middle Sacramento River had not been synthesized, despite restoration having been ongoing since 1989. Our assessment was based on the development and application of 36 quantitative ecological indicators. These indicators were used to characterize the status of terrestrial and floodplain resources (e.g., flora and fauna), channel dynamics (e.g., planform, geomorphology), and the flow regime. Indicators were also associated with specific goal statements of the CALFED Ecosystem Restoration Program. A collective weight of evidence approach was used to assess restoration success. Our synthesis demonstrates good progress in the restoration of riparian habitats, birds and other wildlife, but not in restoration of streamflows and geomorphic processes. For example, from 1999 to 2007, there was a > 600% increase in forest patch core size, and a 43% increase in the area of the river bordered by natural habitat > 500 m wide. Species richness of landbirds and beetles increased at restoration sites, as did detections of bats. However, degraded post-Shasta Dam streamflow conditions continued. Relative to pre-dam conditions, the average number of years that pass between flows that are sufficient to mobilize the bed, and those that are of sufficient magnitude to inundate the floodplain, increased by over 100%. Trends in geomorphic processes were strongly negative, with increases in the amount of bank hardened with riprap, and decreases in the area of floodplain reworked. Overall the channel simplified, becoming less sinuous with reduced overall channel length. Our progress assessment presents a compelling case for what needs to be done to further advance the ecological restoration of the river. The most important actions to be taken relate to promoting river meander and floodplain connectivity, and restoring components of the natural flow regime.

Differing and confounding understandings of the seasonal movements of the delta smelt (Hypomesus transpacificus) in the San Francisco Estuary persist nearly 2 decades after its listing as threatened under the federal and state endangered species acts. The U.S. Fish and Wildlife Service and the U.S. Bureau of Reclamation have characterized the delta smelt as a species that migrates extensive distances from Suisun Bay and the Sacramento and San Joaquin rivers confluence in the fall and winter, eastward and upstream to the central and east Sacramento–San Joaquin Delta to spawn, with the next generation returning to downstream rearing areas in the following spring (OCAP Technical Support Team unpublished; USBR 2012). This description of inter-seasonal movements of delta smelt stands in contrast to findings drawn from previous studies, which describe movements by pre-spawner delta smelt from open waters in bays and channels to proximate marshlands and freshwater inlets (e.g., Moyle et al. 1992; Bennett 2005). In an effort to resolve this disagreement over the movements of delta smelt, we use publicly available data on its distribution drawn from trawl surveys to generate maps from which we infer seasonal patterns of dispersal. In the fall, before spawning, delta smelt are most abundant in Suisun Bay, the Sacramento and San Joaquin rivers confluence, the lower Sacramento River, and the Cache Slough complex. By March and April, the period of peak detection of spawning adults, relative densities in Suisun Bay and the rivers’ confluence have diminished in favor of higher concentrations of delta smelt in Montezuma Slough and the Cache Slough complex. A relatively small percentage of fish are observed in areas of the Sacramento River above Cache Slough. We conclude that inter-seasonal dispersal of delta smelt is more circumscribed than has been previously reported. This conclusion has real-world implications for efforts to conserve delta smelt. Our findings support a conservation strategy for delta smelt that focuses on habitat restoration and management efforts for tidal marsh and other wetlands in north Delta shoreline areas directly adjacent to open waters that have been documented to support higher concentrations of the fish.