Effects of Ultrasonic Frequencies on Schooling Behavior of American Shad (Alosa sapidissima)

Abstract

The behavioral responses of the American shad (Alosa sapidissima) to ultrasonic frequencies are of interest to the scientific community and the natural resource agencies that manage diadromous fish stocks. American shad have been reported to respond with changes in schooling behavior to different frequencies of sound. Their two regions of auditory sensitivity are from 200-800Hz and 25-150 kHz. These are relatively high frequencies for hearing in most fishes. Frequencies within this range are also used in fish population assessments. Researchers and resource managers have used 120 kHz and 200 kHz echo-sounders to visualize the number, position, and timing of fish in aquatic and marine environments. Changes in behavior, e.g. avoidance, due to these acoustic beams could bias counts used in fisheries management. In spring 2010, schooling A. sapidissima were subjected to different frequencies and power levels of acoustics while their behavior was recorded using a Dual Frequency Identification Sonar (DIDSON), operating at 1.8MHz, outside the hearing range of American shad. The number of fish within a school decreased when exposed to 120 kHz. The median number of fish per school during the control periods before and after treatment, was 23(13.5-61.5) and 36(21-64), respectively, and 9(6.25-15.25) during treatment period 5. The time schools were present in the DIDSON image was also affected by this treatment. The average time schools were present during time period 5 was 9.83s ± 1.02s, and after treatment rose to 24.6s ± 5.16s. No fish were detected while a treatment of 120 kHz was present during treatment period 8. These data are preliminary but indicate an affect of 120 kHz on American shad behavior.