Sperm whales communicate through click sequences called 'codas,' a unique communication method among cetaceans. At the University of Toulon, Pascale Giraudet, a lecturer at the UFR Sciences et techniques and researcher at the LIS laboratory, is conducting in-depth research on this underwater language.
With her team, consisting of three students, a member of Longitude 181, and two doctoral students, she analyzes these clicks to identify specimens, reconstruct their dialogues, and recognize whales by their voices. These clicks are used for echolocation, to hunt in total darkness at great depths, and for communication, distinguishing them from whale songs or dolphin whistles by their particular temporal dynamics.
The key to this work lies in measuring the inter-click interval (ICI) and inter-pulse interval (IPI). The IPI allows for determining the animal's head size, and thus identifying it individually. By cross-referencing these measurements with visual identification data of individuals provided by the association Longitude 181, the team attributes each click to its emitter.
Research has revealed dialogues between sperm whales, such as between the females Vanessa and Delphine, where their click sequences intermingle and influence each other. Each sperm whale appears to have an 'acoustic personality' and a signature coda, culturally transmitted within clans, thus creating different 'dialects' depending on the groups.
Although a complete 'sperm whale-French dictionary' is impossible, researchers can link codas to circumstances and behaviors, such as a specific sequence accompanying physical contact between two females. The University of Toulon team is the only one in the world capable of identifying who says what, when, and in response to which behavior.
The methods employed include signal processing to extract the IPI in noisy environments, and artificial intelligence to separate intertwined codas using clustering and unsupervised learning. The university's SMIOT platform and LIS laboratory cover the entire chain, from data acquisition to interpretation.
The challenges for the next ten years include protecting sperm whales, which are highly sensitive to human disturbances like boat collisions and anthropogenic noise. Knowing their locations and social times would allow for better protection, particularly in the Pelagos sanctuary. Scientific curiosity also remains, viewing sperm whales as a 'Rosetta Stone' for animal communication.
