Concerns have arisen that use of AHDs in aquaculture facilities leads to unintended displacement of marine
mammals in the cases of killer whales (Morton and Symonds 2002) and harbor porpoises (Olesiuk et al.
2002) in the vicinity of salmon farms off British Columbia. Likewise, there are concerns that widespread
use of AHDs may lead to the exclusion of porpoises from important feeding habitat (Johnston 2002).
AHDs have sufficiently high source levels that they could result in hearing damage to marine mammals
exposed at close range.