Responses of humpback whales to playback of natural and artificial sounds in Hawaii

Humpback whales were exposed to the playback of humpback song, social sounds, Alaskan feeding call, artificially synthesized sounds, and blank tape control with a source level of 162 dB re: 1 μPA. Whales were observed and tracked from shore. A 20‐min baseline observation preceded the 20‐min sound presentation. The J‐11 transducer was deployed at 7‐m depth in water from 20 to 200‐m deep. Acoustic velocity profiles conducted nearby indicated a uniform acoustic velocity field. The strongest reaction observed was the rapid approach response where whales changed course and approached the boat. The percentage of such responses varied with sound condition. Rapid approach responses were observed from whales up to a 1.5‐km distance. Received levels can be approximated from the range between transducer and whale. The minimum received level that produced a strong reaction was probably between 100–115 dB, for 20 and 15 log R transmission loss models. These estimates could be improved as some playback experiments were recorded by a second vessel.