Acoustic ecology of humpback whales in Brazilian waters investigated with basic and sophisticated passive acoustic technologies over 17 years

Whales are difficult to study. These large marine mammals cannot be maintained in captivity so they have to be studied in nature, and observing their underwater behavior becomes a challenge. The extensive distribution, large size, and aquatic life style of these leviathans constrain efforts to observe and understand the scale of what is being studied. Researchers have dealt with this challenge with wit, determination and creativity. Large whales are known for using long distance acoustic communication to coordinate social interactions such as mate attraction and group feeding, as well as a means for orientation and navigation. Therefore, sound is relied on to help “see” beyond the surface. Marine mammalogists were the first to modify existing technology from ocean bottom sensors to develop novel ways to listen underwater, taking advantage of the fact that these animals rely mostly on sound to survive and reproduce. In effect, biologists eavesdrop on the underwater lives of marine mammals by listening. Researchers listen to humpback whales using different passive acoustic technologies that span a variety of spatial and temporal scales. In this paper, studies conducted in Brazilian waters are reviewed, primarily in the Abrolhos Bank region, where basic and advanced technologies have been used to understand the acoustic ecology of this large marine mammal species. Male humpback whale culture, their social dynamics revealed by spatial and temporal vocal activity patterns, and their interaction with the encroaching noise generated by humans, are reviewed.