Abiotic and Biotic Effects on Delta Smelt Abundance and Distribution

Protecting and managing special status fish species requires an understanding of their ecology and habitat. Delta smelt (Hypomesus transpacificus) is an annual fish species endemic solely to the euryhaline portion of the San Francisco Estuary, California. It is listed as a threatened species by the U.S. Fish and Wildlife Service and as an endangered species by the State of California. Understanding the ecology of delta smelt is critical to the management of California's water supply. Delta smelt has undergone a substantial long-term decline in abundance since the 1960s leading to its listing while water exported from the Bay-Delta supplies approximately 25 million people in California and a multi-billion dollar agricultural industry in California's Central Valley. Managing water operations while protecting delta smelt habitat is a key management goal in the estuary.

The goal of this study is determine the relative importance of abiotic versus biotic (food supply) habitat features as drivers of delta smelt abundance and distribution. Specific objectives include determining the density and distribution of delta smelt in the lower Sacramento River near Decker Island upstream into the Sacramento Deepwater Shipping Channel, and if water quality factors or food supply are meaningful drivers. A key aspect of this study is the application of the SmeltCam to sample delta smelt non-destructively.

Planning and coordination will begin immediately. Field work sampling delta smelt will take place in the late fall, including collection of ancillary water quality and biological information. The resulting data will be analyzed using various statistical techniques during the remainder of the 2015 fiscal year. At least one draft journal article will be prepared in fiscal year 2015.

This study will provide much needed information on the ecology of an endangered fish species. It will provide new information on the habitats occupied by delta smelt. Understanding the relative importance of salinity, turbidity and food supply as drivers of delta smelt abundance and distribution will provide scientists and managers with information to better contextualize the habitat requirements for delta smelt. This information will be especially important in evaluating the flow requirements in the U.S. Fish and Wildlife Service biological opinion and it will also inform habitat restoration efforts for the Bay Delta Conservation Plan. This proposal supports several elements of the USGS strategic plan and will contribute to multiple missions of the USGS: 1) describe and understand the Earth; 2) manage water and biological resources; and 3) enhance and protect our quality of life. The project will contribute to the Program thrust to strategically position the USGS as the provider of choice for assessments of real and anticipated changes in the environment and resources. More specifically, the project will showcase the unique capabilities of the USGS to further our understanding of environmental change.