Acoustic deterrent devices (ADD) use sound in an effort to repel marine mammals from fisheries activities.
The idea behind these devices is that they keep marine mammals away by introducing a local acoustic
annoyance. Pingers are used in some fisheries to reduce the bycatch of marine mammals. These are
typically low-power ADDs with source levels of 130 – 150 dB re 1µPa @ 1 m. Acoustic harassment
devices (AHD) are used to reduce depredation by marine mammals on caught or cultured fish. These are
high-powered devices with source levels of 185 – 195 dB re 1µPa @ 1 m. Both pingers and AHDs have
frequencies in the 5 – 160 kHz band, and generate pulses lasting from 2 – 2000 msec. To reduce
habituation, a single device may transmit a variety of waveforms and have pseudo-random time intervals
between transmissions