Devices that emit sounds of such high intensity that they cause pain or alarm in certain underwater species. The minimum sound level is approximately 200 dB re 1 _Pa @ 1m. References for AHDs primarily dealt with aquaculture operations. These devices may exclude some animals from important habitat (Olesiuk et al., 2002), and pose a risk of impairing an animal’s hearing. These drawbacks render this approach potentially harmful and dangerous.