Using Hydroacoustics to Monitor Tidal Behavior and Movement of Fish

The Calaveras River is a Delta-area tributary to the San Joaquin River, and home to over 20 fish species, many of which are threatened or endangeredincluding fall-run Chinook salmon (Oncorhynchus tshawytscha) and federally threatened steelhead (Oncorhynchus mykiss). Unfortunately, most studies focus on the San Joaquin or Sacramento River leaving relatively few studies involving smaller tributaries like the Calaveras which are just as significant indicators of the health and diversity of the Delta. The lower reaches of the Calaveras experience mixed semidiurnal tides; it is currently unknown how these influence fish populations. And wWith rising interest in restoring the portion of the Calaveras that runs through the University of the Pacific, it is important to know when and what kinds of fish are present. In hopes of seeing order to detect differences in fish flux up and down stream at differentas related to tidal cycles stage, we examined the tidal related behavior of fish using a Dual-frequency Identification Sonar (DIDSON). This high quality frequency multibeam sonar produces video quality images with enough resolution to differentiate behaviors and even possibly identify species. The sonar was deployed at varying tidal stages and water flows just west of the footbridge on the University of the Pacific campus in Stockton, CA. Each fish that was captured on screen would have its length measured, swim direction recorded, and behavior tallied. So far we have deployed during both flood and ebb cycles as well as during days of high flow. More data still needs to be collected to make definite conclusions, but pPreliminary results show a clear change of behavior between ebb and flood cycles. Continued study throughout the year and added seining for species verification should reveal clearer data and conclusions on behavior and species presentfish community composition and individual behaviors