Scientific Investigations Report 2014–5041
AbstractIn fall 2011, a large-scale investigation (fall low-salinity habitat investigation) was implemented by the Bureau of Reclamation in cooperation with the Interagency Ecological Program to explore hypotheses about the ecological role of low-salinity habitat in the San Francisco Estuary—specifically, hypotheses about the importance of fall low-salinity habitat to the biology of delta smelt Hypomesus transpacificus, a species endemic to the San Francisco Estuary and listed as threatened or endangered under federal and state endangered species legislation. The Interagency Ecological Program is a consortium of 10 agencies that work together to develop a better understanding of the ecology of the Estuary and the effects of the State Water Project and Federal Central Valley Project operations on the physical, chemical, and biological conditions of the San Francisco Estuary. The fall low-salinity habitat investigation constitutes one of the actions stipulated in the Reasonable and Prudent Alternative issued with the 2008 Biological Opinion of the U.S. Fish and Wildlife Service, which called for adaptive management of fall Sacramento-San Joaquin Delta outflow following “wet” and “above normal” water years to alleviate jeopardy to delta smelt and adverse modification of delta smelt critical habitat. The basic hypothesis of the adaptive management of fall low-salinity habitat is that greater outflows move the low-salinity zone (salinity 1–6), an important component of delta smelt habitat, westward and that moving the low-salinity zone westward of its position in the fall of recent years will benefit delta smelt, although the specific mechanisms providing such benefit are uncertain. An adaptive management plan was prepared to guide implementation of the adaptive management of fall low-salinity habitat and to reduce uncertainty. This report has three major objectives:
The basic approach of this report is to evaluate predictions derived from the hypotheses included in the conceptual model developed within the adaptive management plan. All available data from studies and monitoring conducted in fall 2011 and similar data from fall 2006, which was the most recent wet year preceding 2011, were considered. Data from 2005 and 2010 were also considered, to include the conditions antecedent to those years. Many of the predictions either could not be evaluated with the data available, or the needed data were not collected. Most of the predictions that could be addressed involved either the abiotic habitat components (that is, the physical environment) or delta smelt responses. In general, the fall low-salinity habitat investigation has been largely inconclusive as of the writing of this report. This is not to be unexpected in the first year of what is intended to be a multi-year adaptive-management effort. This report can be viewed as the first chapter of a “living document” that is to be continually updated as part of the adaptive management cycle. The results of this report, especially predictions with insufficient data for evaluation, indicate a number of science-based approaches to improve the fall low-salinity habitat investigations:
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Brown, L.R., Baxter, R., Castillo, G., Conrad, L., Culberson, S., Erickson, G., Feyrer, F., Fong, S., Gehrts, K., Grimaldo, L., Herbold, B., Kirsch, J., Mueller-Solger, A., Slater, S., Souza, K., and Van Nieuwenhuyse, E., 2014, Synthesis of studies in the fall low-salinity zone of the San Francisco Estuary, September–December 2011: U.S. Geological Survey Scientific Investigations Report 2014–5041, 136 p., http://dx.doi.org/10.3133/sir20145041.
ISSN 2328-0328 (online)
Abstract
Introduction
Purpose and Scope
Background
Methodology
Evaluation of Predictions
Discussion
References Cited
Appendixes
Appendix 1. Dayflow
Appendix 2. Surface Area and Maps of the Low-Salinity Zone
Appendix 3. Delta Smelt Habitat Index
Appendix 4. Fall Midwater-Trawl Survey
Appendix 5. U.S. Geological Survey Sediment Monitoring and Analysis
Appendix 6. Environmental Monitoring Program
Appendix 7. U.S. Geological Survey Water-Quality Monitoring
Appendix 8. California Department of Fish and Wildlife Fish Sampling