Responses of humpback whales to sonar sounds

Abstract

Controlled sound playback experiments were used to assess effects of a low‐frequency sonar system on humpback whales, Megaptera novaeangliae, in Hawaiian waters. Focal pods were presented with sounds of a 3.3‐kHz sonar pulse, a sonar frequency sweep from 3.1 to 3.6 kHz, or a control (blank) tape. Behavior, movement, and underwater vocalizations were monitored and compared with baseline periods. While the two types of sonar signals differed in their effects on the whales, both elicited avoidance behaviors. Humpbacks responded to the pulse by increasing their distance from the sound source. The strength of this effect varied directly with time. Responses to the frequency sweep primarily consisted of increased swimming speeds and track linearity. The latter was a direct function of increasing sound intensity. Overall, the sounds did not strongly or consistently affect the whales’ dive cycles or vocalizations. Observed avoidance reactions may have resulted from possible resemblance between the sonar signals and natural sounds in humpbacks’ environment that are associated with biological threats or warnings.