Courtesy of Renata Sousa-Lima

Figure 1. A humpback whale (Megaptera novaeangliae) exposes its tail or fluke, a common occurrence while singing, in Abrolhos Marine National Park. Scientists use the unique black-and-white markings of the underside of the fluke to identify individuals. Brazilian Navy facilities are visible on Santa Bárbara Island in the background.

MALE HUMPBACK WHALES (MEGAPTERA NOVAE ANGLIAE) (fig. 1, above) produce “songs”—long, patterned sequences of sounds—that are presumed to function as a reproductive display on the breeding grounds (Payne and McVay 1971; Winn and Winn 1978; Tyack 1981). (Click to hear humpback whale singing.) Many preferred breeding areas are conservation hot spots protected by marine parks, and the whale-watching industry has flourished in those sites (Hoyt 2001). Noise generated from whale-watching boat traffic can mask important aspects of whale communication. This raises concerns about the potential influence of noise on reproductive success and population growth. Gray whales may temporarily or permanently abandon critical areas because of excessive exposure to boat noise (Bryant et al. 1984). Therefore, managers in parks created to protect and conserve whales are often faced with the task of managing noise-generating tourism activities, especially in breeding areas.

“Noise generated from whale-watching boat traffic can mask important aspects of whale communication. This raises concerns about the potential influence of noise on reproductive success and population growth.”

Because whales are acoustic specialists (Richardson et al. 1995), investigations can rely on listening to understand their social system. Recent advances in passive acoustic technology allow researchers to follow the movements of whales by locating and tracking vocalizing individuals. By continuously sampling and simultaneously following multiple whales, investigators can describe the movements of cohorts of individuals. By comparing whale tracks with the tracks and acoustic characteristics of human activities, investigators can measure whale responses to human-caused disturbance, such as an approaching vessel.

In this study, we used passive acoustic technology to evaluate the effects of boat traffic on the spatial-acoustic behavior of vocally active male humpback whales in the Abrolhos Marine National Park, Brazil (fig. 2); this park is situated in the main humpback whale breeding grounds in the southwestern Atlantic Ocean (Engel 1996). Our specific objectives were (1) to determine the types of singer responses to an approaching boat, and (2) to identify the “distance of disturbance”—the distances to which avoidance (i.e., movement away from boat) and behavioral disruption (i.e., cessation of singing) are observed.