Response of Harbor Porpoises to Pingers and Acoustic Harassment Devices

Pingers and acoustic harassment devices (AHDs) are used by industries (e.g., fisheries, aquaculture, and offshore wind development) all over the world to mitigate harmful impacts on marine mammals such as the harbor porpoise (Phocoena phocoena). This review compares different devices and their effects specifically on harbor porpoises and gives recommendations with regard to which device to use for the desired outcome. Pingers mainly emit acoustic signals at sound pressure levels between 115 and 155 dB re 1 μPa (rms) @ 1 m at frequency ranges between 2.7 and 160 kHz, whereas AHDs mainly emit signals at sound pressure levels between 172 and 194 dB re 1 μPa (rms) @ 1 m at frequency ranges between 1 and 150 kHz. Therefore, harbor porpoises generally show a smaller avoidance radius around pingers than around AHDs. Selecting an appropriate device should not only depend on the cost and user-friendly installation, but primarily on the desired range of the acoustic signals, keeping the size of the area to be exposed to sound and the duration as small as possible (e.g., pingers for a minimum deterrence distance of 100–300 m and APDs for a minimum deterrence distance of 500–750 m). Factors including habituation and effects on species other than the target species need to be considered in choosing mitigation devices and monitored on a regular basis. When selecting an appropriate device in a targeted manner, pingers and AHDs are a good tool to deter harbor porpoises from an area where they may suffer harm, such as hearing damage or entanglement in fishing nets.