Non-physical barrier design and environmental conditions alter routing and survival of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento-San Joaquin River Delta

Pacific salmon face substantial challenges when migrating through anthropogenically modified river systems, such as the Sacramento-San Joaquin River Delta (the Delta). Non-physical behavioral barriers, such as the bioacoustic fish fence (BAFF), are one potential solution for guiding fish away from hazards without obstructing water flow. However, the effectiveness of these technologies depends on abiotic and biotic conditions. In the Delta, a BAFF was deployed at Georgiana Slough in 2011, 2012, and 2024 to deter juvenile Chinook salmon (Oncorhynchus tshawytscha) from migrating into the interior Delta, a region associated with lower survival than the mainstem Sacramento River. We leveraged nine years of acoustic telemetry data to evaluate BAFF performance across flow conditions and two BAFF designs (2011/2012 vs. 2024), and to assess the BAFF's contribution to improving through-Delta survival. The BAFF reduced routing into Georgiana Slough from 26.5% without a barrier to 8.9% in 2011/2012 and 15.9% in 2024. In general, routing into Georgiana Slough increased with the proportion of flow entering the channel during periods without a BAFF and during the 2024 deployment but remained constant during the 2011/2012 deployment. Additionally, BAFF effectiveness declined with increasing input flow. Ultimately, reduced routing into Georgiana Slough during the 2024 BAFF deployment resulted in an increase in estimated through-Delta survival between 0.2 and 1.6 percentage points depending on release group. Our results provide valuable insights into the role of non-physical barriers in complex river systems and inform future management strategies for protecting migrating juvenile Chinook salmon in the Sacramento-San Joaquin River Delta.