Effectiveness of Strobe Lights and an Infrasound Device for Eliciting Avoidance by Juvenile Salmon

Our primary objectives were to videotape and characterize vertical responses of juvenile salmon to strobe light and infrasound in controlled tests in a net pen that was 4-m long and 1.5-m in diameter. Experiments were conducted near the Hiram M. Chittenden Locks, Seattle, in spring and summer, 1997, for the U.S. Army Engineer District, Portland. Four underwater video cameras mounted on the perimeter of the vertically oriented net pen were used to record responses of schools of juvenile salmon during test and control treatments. When strobe lights were tested within 1 m of the pen, the frequency of avoidance by hatchery-reared juvenile coho Oncorhynchus kisutch and chinook O. tshawytscha salmon was 80-100%. Fish usually moved toward the top of the pen in response to strobe light directed either horizontally or 45 degree upward into the bottom section of the pen. In contrast, fish did not respond to strobe light directed straight up through the bottom of the pen. A particle-motion generator consisting of a high-volume pump and rotary valve produced 10-35 Hz infrasounds that failed to elicit avoidance from hatchery yearling coho and sub-yearling coho and chinook salmon