Behavior and Fine Scale Habitat Usage Patterns of Juvenile Green Sturgeon in the Sacramento-San Joaquin Delta

The habitat usage and movement patterns of juvenile green sturgeon in the Sacramento-San Joaquin Delta has received little attention.  We reared, tagged and tracked six individual juvenile green sturgeon over the course of three years. Temperature- and depth-sensing tags were used for tracking.   Tracks were conducted for a period of up to five days while continuously recording GPS coordinates, depths, and water temperatures at the sturgeon’s location.  We used first-passage times, defined as the amount of time spent in a given area, as a metric of fine-scale habitat usage.  High values of first passage times at recorded positions may reflect high quality habitat or environmental characteristics.  All but one fish stayed in the main-stem San Joaquin River.  Movements of individual sturgeon occurred both day and night and apparently, independent of tidal action (e.g., movements were made both against and with current direction during most tidal phases). Based on the frequencies of depths utilized, green sturgeon typically used the slope or shoulder of navigational channels when not on the shallower shoals (depths < 7 m).  However, several individuals were tracked near the center of deepwater navigation channels at depths > 12 m.  The use of navigational channels may pose additional risk to juvenile green sturgeon as there may be potential for dredge entrainment.