Observations of Fish Behavior Recorded by a DIDSON Sonar Concurrent with Blasting Events During Renovation of the Lyle Falls Fish Ladder
A Dual-Frequency Identification Sonar (DIDSON) sonar was deployed to record fish behavior within the trap of the Lyle Falls Fish Ladder during periods when rock blasting events occurred – events associated with renovation/construction activities. The DIDSON was operated intermittently over the period from April 16 to May 6, 2010. During operation, it was programmed to record sequential 1-hour files. Records from the construction contractor indicated that 11 blasting events occurred during times when DIDSON files were recorded. “Echograms” were processed from the original DIDSON video files which contained these 11 events. The precise moment of each blast was noted in the associated echogram and DIDSON file, and fish behavior for the 5 minutes preceding and following each event was qualitatively assessed. During the period of recordings, there was a near constant presence of small fish, most likely hatchery released coho smolts, which schooled in a position 1-3 m in front of the sonar, oriented into the direction of water flow. In 7 of the 11 files, there was a sudden scattering of these fish concurrent with the explosion. In 2 cases the scattering was barely noticeable, and in 2 instances no disturbance of the fish was apparent. In the 9 cases where a disturbance in behavior occurred, the fish generally re-established their position in front of the sonar within 10-20 seconds. While the explosions associated with the rock blasting events were indeed of an alarming nature to the fish in the Lyle Falls trap, the perturbation to their behavior was short-lived.
Galbreath, P. F., S. Keep, J. Zendt and C. R. Frederiksen. 2010. Observations of Fish Behavior Recorded by a DIDSON Sonar Concurrent with Blasting Events During Renovation of the Lyle Falls Fish Ladder. Columbia River Inter-Tribal Fish Commission Technical Report 10-02, Portland, Oregon.