Early Life History of Fishes in the San Francisco Estuary and Watershed

Vertical Distribution of Larval Delta Smelt and Striped Bass near the Confluence of the Sacramento and San Joaquin Rivers

Andrew K. Rockriver

doi: https://doi.org/10.47886/9781888569599.ch7

Abstract.—The goal of this study was to determine if the vertical distribution of larval delta smelt Hypomesus transpacificus and striped bass Morone saxatilis was affected by tidal stage and diel period. Delta smelt and striped bass have similar early life histories in that their larvae drift downstream from freshwater spawning habitats to brackish water rearing habitats. Little is known on whether the larvae undergo a vertical migration as they move downstream. Conical plankton nets were used to collect larval fishes from the surface, middle, and bottom sections of the main channels of the Sacramento and San Joaquin rivers. Samples were collected over six paired day–night cruises. Approximately 45,000 fish were collected; 82% were striped bass and 2% were delta smelt. More delta smelt were caught at night than during the day, and more at middle depth than surface or bottom. Very few striped bass were found at surface during day; most were caught at middle depth. Both species were fairly dispersed throughout the water column at night. Although striped bass larvae appear to undergo a small surface to middepth migration, this study indicates that larval delta smelt and striped bass do not undergo a mass diel or tidal vertical migration as they drift down the Sacramento and San Joaquin rivers.