Common Predator, Rare Prey: Exploring Juvenile Striped Bass Predation on Delta Smelt in California's San Francisco Estuary

Abstract

There is growing concern that predation by juvenile (ages 1–3) Striped Bass Morone saxatilis may negatively affect the population dynamics of Delta Smelt Hypomesus transpacificus, an imperiled species listed as threatened under the U.S. Endangered Species Act and endangered under the state of California's Endangered Species Act. We explored the potential predator–prey interaction between juvenile Striped Bass and Delta Smelt in California's San Francisco Estuary. Specifically, we addressed two study questions. (1) Is juvenile Striped Bass abundance correlated with Delta Smelt survival? (2) What is the estimated peak monthly consumption of Delta Smelt by juvenile Striped Bass during summer? We addressed the first study question using regression techniques and the second with functional responses to estimate per capita Striped Bass consumption of Delta Smelt using Delta Smelt biomass densities estimated from trawl surveys as input to the functional responses. We found no evidence for a correlation between juvenile Striped Bass abundance and Delta Smelt survival. Based upon available data, we estimated that consumption of Delta Smelt may range from a level not discernibly different from 0 g·Striped Bass⁻¹·month up to about 11 g·Striped Bass⁻¹·month⁻¹. These are the first estimates of potential Striped Bass consumption of Delta Smelt.

Received June 14, 2012; accepted June 18, 2013

ACKNOWLEDGMENTS

This study emerged from work done by the authors for the Bay–Delta Conservation Plan. The viewpoints expressed are those of the authors and do not necessarily reflect the opinions of the U.S. Department of the Interior, the U.S. Fish and Wildlife Service, the U.S. Bureau of Reclamation, or the California Department of Water Resources. We thank K. Newman for statistical advice. The manuscript was greatly improved by the helpful comments of several anonymous reviewers.