The effect of fish bodies on the source level and beam pattern of acoustic transmitters in juvenile Chinook salmon.

The effect of the fish body on the source level and beam pattern of an acoustic fish tag signal was investigated through laboratory experiments and an analytical method. In laboratory experiments, the source level and beam pattern were measured in both a tag-only group and a tag-in-fish group. In the analytical method, both forward and backward scattering were calculated by assuming the acoustic tag was a point source and the swimbladder was an air-filled prolate spheroid. The mean source level of five tested tags decreased by ∼4 dB after implantation in fish bodies, which is important for designing fish migration studies using acoustic telemetry.