Echolocation in cetaceans

Echolocation is a system of active perception used by many cetaceans to find their way, hunt and interact in an aquatic environment where light is often absent. The mechanism rests on the emission of sound waves and the analysis of their echoes after reflection off surrounding objects.

The biological principle of echolocation

In odontocetes (toothed whales), echolocation rests on the emission of ultrasonic clicks produced in the nasal passages. These sounds are concentrated and directed by a fatty structure called the melon. The echoes are then picked up by the lower jaw, which transmits them through the skull bones to the inner ear.

• Emitting organ: phonic lips in the nasal passage
• Focusing organ: melon filled with specialised lipids
• Receiving organ: lower jaw and inner auditory system

Frequencies and precision

Echolocation clicks vary between species, with frequencies ranging from 10 to 150 kHz. Dolphins use highly directional signals, able to detect prey a few centimetres across at distances of several tens of metres. Some odontocetes such as the common bottlenose dolphin (Tursiops truncatus) reach a spatial resolution finer than 1 cm.

Functional roles

Echolocation serves several functions in cetaceans:

• Navigation in turbid or deep water
• Detection and selection of prey, even when buried in sediment
• Avoidance of obstacles (rocks, conspecifics, fishing nets)
• Social communication in some species, although secondary

Differences between species

Toothed whales are the only cetaceans with a developed echolocation system. Mysticetes (baleen whales) do not emit clicks to locate themselves, but produce low-frequency vocalisations to communicate over long distances.

Morphological adaptations

The anatomical adaptations associated with echolocation include:

• An asymmetrical skull (in particular in odontocetes)
• Lipid tissues specialised in acoustic reception
• A highly developed brain in the auditory areas

Threats and disturbance

Human activities disturb echolocation by introducing anthropogenic noise into the marine environment:

• Military sonar, which can disorient cetaceans
• Shipping traffic saturating the acoustic space
• Seismic surveys altering the behaviour of prey and of cetaceans

Key points

Echolocation is a three-dimensional acoustic perception system of extreme precision, which allows some cetaceans to find their way, hunt and interact in the darkness of the oceans. This highly specialised biological sense is now threatened by the rise in underwater noise.