Most people would have heard about the “songs” of various whale species. Humpbacks are well known for their songs, which evolve over time. Whales and dolphins use sound to communicate, attract mates, warn of danger and for echolocation (a sort of biosonar that for example dolphins use to navigate their environment).
Whale song is made up of a mixture of sounds. For some species the sounds have been described as sounding like moans, snores, chirps and cries. Blue and fin whale songs are so low in frequency that parts of them are inaudible to humans. Humpback whales produce the most complex song of the lot. It consists of repeated phrases arranged in themes in a hierarchical structure, and often lasts 35 minutes, but can last longer.
Passive Acoustic Monitoring (PAM) research is undertaken by placing an underwater microphone (called a hydrophone) in the water and recording the sounds. Hydrophone can be integrated into a data logging system than can be deployed into the water and remain in place for very long periods. Processing of the resulting data can be used to detect sounds of whales and other species, as well as boats and ships. Monitoring whales in this way provides information about sounds whales make when the whale is underwater, at the surface of the water (e.g., breaching) and at night. Other methods of monitoring rely on visual sightings.
In 2021 GMR deployed an acoustic data logger in Geographe Bay during the whale migration season. During this season GMR drone pilots also recorded over 1000 minutes of video from drones. This allows us to identify an event on the video, and easily locate the corresponding audio recordings. One example is a case where a video showed a southern right whale mother and calf being circled by a shark. The mother was heard “talking” to the calf, and then there was silence. Was the mother telling the calf to keep quiet? We will probably never know, but eventually this type of evidence will lead to a more complete understanding of whale behaviour.