Scientific observations of fishes in tidal wetlands of the upper Sacramento San Joaquin Delta using imaging sonar devices, derived from 2018 field data

Major tidal wetland habitat restoration efforts are planned to benefit Delta Smelt and other imperiled species in the Sacramento-San-Joaquin Delta. However, successful implementation of habitat restoration is constrained by a paucity of information on the services and functions tidal wetlands provide for fishes. This knowledge gap is largely due to the difficulties of collecting ecological data in these challenging environments. For example, the dynamic nature of tidally influenced habitats requires high frequency sampling in order to accurately characterize environmental conditions and how fishes responses to them. 
We accomplished this by monitoring fish movements into and out of two tidal wetland habitats and examining the environmental drivers underlying our observations. The California Water Science Center hydrodynamic group collected water quality and flow information and this data was processed and stored in Aquarius.The California Water Science Center, Aquatic Ecology group collected observational footage of fishes at a commensurate frequency using imaging sonar devices. Imaging sonars are underwater devices that use sound waves to collect information regarding fish movement and behavior. Specific measurements provided by this technique include estimates of fish size, position, and speed of movement. This data was used to compare fish movements and behavior at the entrance points of two disparate tidal wetland habitats in the northern Sacramento-San Joaquin Delta. 
We selected two adjacent, hydrodynamically-connected-but-geomorphically-distinct wetland study sites: Little Holland Tract and Liberty Island Conservation Bank (sometimes referred to as Wildlands). Little Holland Tract is a former agricultural tract that flooded due to levee failure in 1983. This site contains a large open water area with a broad expanse of intertidal mud flats and relatively small stands of tules along its periphery. In contrast, Liberty Island Conservation Bank is an engineered tidal wetland restoration project constructed in 2010 exhibiting shallow, dendritic tidal channels and tidal marsh plain. 
Our use of acoustic cameras in this study facilitated direct observations of fishes in these habitats commensurate with the rapid rate of environmental (tidal) change. Preliminary results revealed that fish densities are substantially higher than what had been inferred previously from traditional sampling approaches. Overall, we found that drivers of fish movement into and out of each habitat varied broadly as a function of the permanency of available wetted habitat area. Ultimately, this information will be used to optimize the design of tidal wetland restoration to achieve functional habitat for native fishes. This data release contains information about the fishes observed during this study.

Tags: aquatic-biology, california, ecology, oceans, sacramento-san-joaquin-delta, state-of-california, unites-states-of-america, usgs-5df027d9e4b02caea0f4f4c5, wetland-ecosystems
Organization: Department of the Interior