Bioacoustics, the science that studies the sounds produced by living organisms, is revolutionizing the way we monitor marine biodiversity. This emerging field of research uses sophisticated recording and analysis tools to capture and interpret underwater sounds, providing valuable information about the presence and behavior of marine species.

This is why One Ocean Foundation, during its research activities in the Mediterranean Sea — such as the Canyon of Caprera project and the M.A.R.E. project — uses bioacoustics to monitor local wildlife. This year, particularly during the 10 weeks of navigation in the western Mediterranean Sea for the M.A.R.E. project, the Foundation's team of marine biologists identified various cetaceans species, including Striped dolphins  (Stenella coeruleoalba) and Tursiops, sperm whales (Physeter macrocephalus), and Risso's dolphins (Grampus griseus) using this methodology.

The language of cetaceans

The sea is a rich soundscape: from the vocalizations of marine mammals, like whales and dolphins, to the noises generated by ecosystems, such as the crackling of coral reefs. Cetaceans, in particular, use sounds to communicate, hunt, and navigate, exploiting the ability of sound waves to travel better and farther underwater than light.

The sperm whale, for example, produces high-frequency sounds called "clicks" to hunt. These sounds, easily recognizable from recordings, have a steady rhythm that increases in speed when the sperm whale finds its favorite prey, the squid. This behavior, known as echolocation, involves producing sound waves that bounce off objects and return to the animal, allowing it to create a mental map of the surrounding environment and locate prey. Once the meal is finished, the sperm whale stops hunting and thus stops producing sounds, heading to the surface to breathe, a moment when the animal can be spotted.

How bioacoustics works

Bioacoustics uses hydrophones — underwater microphones capable of capturing a wide range of sound frequencies — to register sounds under the sea. Once collected, acoustic data are analyzed using advanced software that can identify the species present, analyze their behaviors, and monitor changes over time. This non-invasive approach allows for detailed information to be obtained without disturbing the natural habitats of the studied species.

Monitoring noise pollution

Often, however, the recordings contain boat noise. This, along with sounds produced by oil and gas exploration and other human activities, represents one of the main threats to marine mammals, and in particular for the cetaceans. The frequencies of these sounds interfere with the normal behavior of these animals, causing disorientation, collisions with boats, strandings and sometimes hearing damage.

A sad example is the recent stranding of Cuvier's beaked whales (Ziphius cavirostris) that occurred in the spring of 2024 on the coasts of Elba Island and Corsica, most likely caused by high-frequency sounds produced at sea due to anthropogenic activities.

Future prospects

The use of bioacoustics represents a promising frontier in monitoring marine biodiversity. Firstly, it allows for continuous and long-term monitoring, covering vast ocean areas that are difficult to survey using traditional methods. Additionally, it enables the detection of elusive species that might escape visual monitoring activities.

Despite the challenges, with advancing technologies and growing international collaboration, bioacoustics has the potential to become an increasingly powerful tool for protecting marine biodiversity. Pilot projects in various parts of the world are already demonstrating the effectiveness of this approach, paving the way for a future where the sound of the sea will be a fundamental resource for science and conservation.