Sampling Uncharted Waters: Examining Longfin Smelt Rearing Habitat in Fringe Marshes of the Low Salinity Zone of the Upper San Francisco Estuary

Despite a rich monitoring history for aquatic organisms in the San Francisco Estuary, very little is known about how invertebrates and fish use tidal marshes in the low salinity zone region of estuary.  Our study investigated the abundance and distribution of larval fish communities in fringe marshes and shallow waters of Suisun Bay (between Antioch and Benicia) that have been overlooked by the long-term monitoring programs.  Ichthyoplankton were sampled every two weeks between February and June in 2013 and 2014 using a 505 µm mesh net towed from the stern of a small boat.  Zooplankton and water quality (salinity, turbidity, DO, PH, Chl a) were sampled concurrently to determine what factors affected abundance and distribution of ichthyoplankton.  Longfin Smelt were widely distributed in shallow waters and tidal marshes of the low salinity zone, and in some surveys, densities were similar or higher than densities observed in the channel stations of the California Department of Fish and Wildlife Smelt Larval Survey.  Information from our study could be used to guide future restoration in the area, design additional monitoring stations for the larval fish surveys, and understand the role of food generated within marshes to support secondary production in adjacent open waters.