Evaluation of a Floating Fish Guidance Structure at a Hydrodynamically Complex River Junction in the Sacramento-San Joaquin River Delta, California, USA

Survival of imperiled out migrating juvenile salmonids in the Sacramento-San Joaquin River Delta, California, USA depends on migration route.  Survival of fish that enter the interior and southern delta can be as low as half that of fish in the main stem Sacramento River.  Reducing entrainment into these high-mortality routes that branch off the Sacramento River is one approach to increasing fish survival.  We used spatially explicit acoustic telemetry to evaluate the effect of an experimental floating fish guidance structure (FFGS) on entrainment to Georgiana Slough.  The FFGS was deployed just upstream of the Georgiana Slough divergence and designed to guide fish to the Sacramento River.  At intermediate flows (250-350 m³s^-1) entrainment into Georgiana Slough was eight percentage points lower when in the on position (13.5%) versus the off position (21.2%).  At higher flows (351-597 m³s^-1), entrainment was higher when the FFGS was in the on position (11.7% off; 17.3% on), and at lower flows (-123-249 m³s^-1) the entrainment was negligible (35.1% off; 36.6% on).  We found that discharge, cross-stream position, time of day, and the location of the streakline contributed to the fate of fish as they transited the junction.