Spatiotemporal occurrence of green sturgeon at dredging and placement sites in the San Francisco estuary

Abstract

We used acoustic telemetry to determine the spatial and temporal overlap between adult Green Sturgeon movements and areas affected by dredging within the San Francisco Estuary. Autonomous receivers were deployed for 3 years within the lower Estuary at priority locations to assess the potential for adverse effects on Green Sturgeon. Green Sturgeon were present at the designated placement sites during all months of the year but more were detected during two time periods (February–March and June–September). Of the 134 tagged fish detected in the estuary, 109 (81%) were detected at one or more dredged or dredged material placement sites. The median duration of residence at dredged material placement sites was 72.5 min near the Carquinez Strait, 141.1 min in San Pablo Bay, and 37.1 min near Alcatraz Island in San Francisco Bay. The median duration of residence at the dredged San Pablo Channel was 77.5 min. Nine fish were detected with depth sensing transmitters. The majority of detections (95.2%) from these fish were at depths greater than five meters. Combined with information regarding the specific impacts of dredging on Green Sturgeon (e.g., suspended sediments, toxicity, entrainment, and behavior changes), these spatiotemporal data could be used to make recommendations for reassessing best management practices.