The ocean, home to some of the planet’s largest creatures, often seems silent to human ears. However, whales produce sounds essential for communication, navigation, and finding food across immense distances. Our inability to hear these vocalizations directly without specialized equipment stems from the unique physics of sound in water, the specific characteristics of whale sounds, and the limitations of human hearing.
Sound’s Behavior in Water
Sound behaves differently in water compared to air, which significantly impacts how we perceive underwater noises. Sound waves travel much faster and further through water than through air. In air, sound moves at approximately 340 meters per second, but in water, it speeds up to around 1500 meters per second. This increased speed is due to water’s higher density and lower compressibility.
Water also acts as a more efficient medium for sound propagation, meaning sound energy attenuates less rapidly over distance than it does in air. While sound does attenuate in water, it can still travel thousands of miles with minimal loss of signal. This allows whales to communicate across vast ocean basins, but sounds may be too faint or distorted for human ears by the time they reach the surface.
Whale Sounds and Human Hearing Limits
Whales produce diverse vocalizations, many of which fall outside the typical range of human hearing. The human auditory system generally detects sounds with frequencies between 20 Hertz (Hz) and 20,000 Hz (20 kilohertz, kHz). Sounds below 20 Hz are infrasound, and those above 20 kHz are ultrasound; both are inaudible to humans.
Large baleen whales, such as blue whales and fin whales, primarily vocalize in the infrasonic range. Blue whale calls, for instance, typically range from 8 Hz to 25 Hz and can reach up to 189 underwater decibels. Fin whale vocalizations, often called “20-Hz pulses,” range from 16 Hz to 40 Hz and can be as loud as 220 decibels. These low-frequency sounds are too low for human ears to perceive.
Toothed whales, like dolphins and sperm whales, often use higher-frequency sounds. Dolphins produce whistles from 0.2 kHz to 24 kHz for social communication. They also generate clicks for echolocation, ranging from 0.2 kHz up to 150 kHz, well into the ultrasonic range. While some clicks may contain components within the human hearing spectrum, their primary function and most intense frequencies are beyond our auditory capabilities.
How We Listen to Whales
Since most whale sounds are inaudible or too faint for direct human perception, scientists rely on specialized technology to detect and study them. The primary tool for this purpose is the hydrophone, an underwater microphone. Hydrophones convert the pressure changes caused by sound waves in water into electrical signals.
These devices often contain piezoelectric materials that generate an electrical charge when subjected to mechanical pressure. When a sound wave interacts with the hydrophone’s sensing element, these materials vibrate and produce a corresponding electrical signal. This electrical signal can then be amplified, recorded, and processed using specialized software. Scientists use this data to create visual representations of sounds, such as spectrograms, which display sound frequency over time, making it possible to analyze vocalizations that are inaudible to the human ear.
Environmental Challenges to Hearing Whales
Beyond the inherent differences in sound physics and hearing ranges, environmental factors can impede our ability to hear whales, even with technology. Natural oceanographic features like temperature layers, known as thermoclines, and variations in pressure and salinity can bend or refract sound waves. These conditions can sometimes create “sound channels” where sounds can travel thousands of miles with minimal energy loss, but they can also redirect sounds away from detection points.
Human-made noise pollution significantly interferes with the detection and study of whale vocalizations. Sounds from shipping, naval sonar, and seismic surveys introduce considerable background noise into the marine environment. This anthropogenic noise can mask whale calls, making them harder to distinguish and analyze. Such interference impacts scientific research and the whales’ own ability to communicate and navigate their underwater world effectively.