Modeling the Effects of Future Outflow on the Abiotic Habitat of an Imperiled Estuarine Fish
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Future development and climate change pose potentially serious threats to estuarine fish populations around the world. We examined how habitat suitability for delta smelt (Hypomesus transpacificus), a state and federally protected species, might be affected by changes in outflow in the San Francisco Estuary due to future development and climate change. Forty years of sampling data collected during fall from 1967 to 2008 were examined to define abiotic habitat suitability for delta smelt as a function of salinity and water transparency, and to describe long-term trends in habitat conditions. The annual habitat index we developed, which incorporated both quantity and quality of habitat, decreased by 78% over the study period. Future habitat index values under seven different development and climate change scenarios, representing a range of drier and wetter possibilities, were predicted using a model which related estuarine outflow to the habitat index. The results suggested that each of the scenarios would generally lead to further declines in delta smelt habitat across all water year types. Recovery targets for delta smelt will be difficult to attain if the modeled habitat conditions are realized.
KeywordsDelta smelt Native fish Annual species Sacramento-San Joaquin Delta San Francisco Estuary Climate change Abiotic habitat Future development Generalized additive model
This study was conducted with data collected by the Interagency Ecological Program, a consortium of state and federal agencies studying the San Francisco Estuary. We thank R. Baxter, R. Breuer, M. Chotkowski, B. Herbold, P. Hrodey, A. Mueller-Solger, and K. Souza for providing support. Comments by L. Brown improved an early draft of the manuscript. The views and opinions expressed in this paper are those of the authors and do not necessarily reflect the official policy or position of their respective agencies.
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