Interagency Ecological Program San Francisco Estuary Smelt Larva Survey 2009 – 2025

The Interagency Ecological Program's Smelt Larva Survey was initiated by the California Department of Fish and Wildlife (CDFW) in 2009 to monitor the distribution and abundance of newly hatched Longfin Smelt (Spirinchus thaleichthys) in the San Francisco Estuary. Surveys are conducted bi-weekly, and sampling begins in December and continues through mid-March. The SLS samples at fixed stations, from San Pablo Bay through Suisun Bay and into the Sacramento-San Joaquin River Delta. Napa River stations were added in 2014 and the San Pablo Bay expansion stations were added in December 2022. Each sampling week currently consists of 59 stations. At each station, one 10-minute stepped oblique (bottom to top) tow is conducted following a prescribed tow schedule. The net is a conical 500 µm mesh lashed to a D-shaped frame mounted on skis. Larval fish samples are preserved in the field in 10% formalin and brought back to the CDFW Stockton Lab for identification and enumeration under a microscope. Several types of data are collected at each station in addition to the larval fish sample, including the volume of water sampled by the net, surface water temperature, surface and bottom specific conductance (EC normalized at 25˚C), Secchi disk depth, tow duration, tidal condition, and surface water turbidity.