Sound, Air and Light Barrier Keeps Chinook Out of Old River

Preliminary results from a U.S. Bureau of Reclamation-led project show that a sound, air and light barrier was successful in keeping juvenile Chinook salmon in the San Joaquin River and out of Old River on their way to the ocean. Salmon migrating through Old River have a lower survival rate than salmon using the main stem San Joaquin River route.

In the past, a solid rock barrier was installed at the junction of the Old and San Joaquin rivers near Lathrop during the spring salmon migration period to keep the smolts out of Old River and away from the State and Federal water project diversion pumps. The rock barrier can no longer be installed in this location, however, because of adverse hydrodynamic impacts on delta smelt, as outlined in the U.S. Fish and Wildlife Service Biological Opinion (BO) on delta smelt issued in December 2008.

In response to the BO, Vernalis Adaptive Management Program (VAMP) team members suggested testing a non-physical barrier as an alternative to the rock barrier.

A Bio-Acoustic Fish Fence (BAFF) (proprietary design by Fish Guidance Systems, Southampton, UK) is an alternative to a solid barrier that deters fish, but lets water flow freely and also allows for boat passage. The BAFF that was installed this year in the San Joaquin River just upstream of the head of Old River at the junction with the San Joaquin River was made up of sound, an air bubble curtain and strobe lights. This strobe-lit curtain of bubbles and low-frequency sound generators creates an underwater sheet of light and sound that deters the juvenile salmon from entering Old River where they might be entrained into the Central Valley Project and State Water Project intakes.

“Research in the United Kingdom suggested that this sound frequency variation and the sound level could deter Atlantic salmon. So, there was reason to believe it could work for west coast salmonids (Chinook, Coho, and steelhead),” said U.S. Department of Interior/Bureau of Reclamation fishery biologist Mark Bowen who coauthored the Technical Memorandum on the project. “That is why we decided to test this particular non-physical barrier (NPB). In addition to a proprietary sound stimulus, there is a second important unique component to this NPB-the bubble pipe is under the sound projector. The bubble layer constrains the sound and concentrates the barrier in a small area. Finally, the strobe lights are reflected off the bubbles,” Bowen said. The barrier looks more solid to a human observer when the strobes are on than when they are off. This suggests a similar phenomenon may occur to fish approaching the barrier.

Monitoring of the barrier was conducted by Reclamation with the cooperation of the VAMP team who used acoustic telemetry to assess survival rate for several routes through the Sacramento-San Joaquin River Delta.


“This project is important because the BAFF deters Chinook smolts from entering Old River. And . . . it continues to allow movement of sturgeon through the area.”

--Mark Bowen, U.S. Bureau of Reclamation


“This project is important because the BAFF deters Chinook smolts from entering Old River,” Bowen said. “And, because the BAFF is elevated 45 centimeters above the substrate, it continues to allow movement of sturgeon through the area.” Unfortunately, although the BAFF was very successful at keeping fish out of Old River, many of those fish were still eaten by predators.

Using both acoustic telemetry and a Dual-frequency Identification Sonar (DIDSON) camera, behavior of predators at the BAFF site were also studied. The DIDSON showed striped bass swimming in looping and patrolling patterns throughout the BAFF area. Uniquely identifiable tags were inserted in the smolts so they could be tracked acoustically. Often however, a striped bass would eat the tagged smolt. When such a predation event occurred, the acoustic 2-D traces would shift from a smolt-like linear downstream trace to the DIDSON-observed looping and patrolling striped bass behavior. So, salmon were deterred by the BAFF, but their fate often was predation. “A great number of tags exhibited this behavior: deterred then eaten and never proceeding down the San Joaquin or Old Rivers,” Bowen said in the memorandum.

Although an unintended outcome of the project showed a heavy predation rate on the young salmon that were effectively deterred by the barrier, it’s possible those predation rates won’t occur every year. “This year, 2009, was a dry year,” Bowen said. “Discharge in the San Joaquin River was low. So, prey may have been forced into a smaller volume of water with predators, leading to an increased encounter rate between prey and predator, resulting in increased predation rates compared to average or wet years.”

Bowen said that “it may be necessary to manage exotic predators in the Delta if we wish to increase the number of Chinook smolts that reach the ocean.” It is not known whether or not predation was a problem when the rock barrier was installed, since no measurements of predation were made during those years.

These non-physical barrier results are preliminary and many more studies still need to be done before definite conclusions can be reached.