Whales are among the most powerful acoustic producers on Earth, generating sounds that can travel across entire ocean basins. Sound is a fundamental sense for these marine mammals, serving as their primary tool for navigating the dark, vast underwater world. The ability of whales to communicate across immense distances is a biological necessity, directly linked to the sheer volume of their vocalizations. These sounds, which range from complex songs to high-intensity clicks, establish the ocean as an acoustically rich environment.
Understanding Decibels Underwater
A comparison of whale vocalizations to familiar sounds on land often leads to confusion because the decibel (dB) scale is not directly interchangeable between air and water. Decibels are a logarithmic unit that expresses the ratio of a measured sound pressure level to a fixed reference pressure. For sounds measured in air, the standard reference pressure is 20 microPascals (µPa), roughly the threshold of human hearing. In the ocean, the standard reference pressure is one µPa, a pressure twenty times lower than the air standard. This difference means any sound will be numerically measured as 26 dB higher in water than in air. Therefore, the extremely high decibel numbers reported for whales are not directly comparable to sounds measured on land. Water is denser than air, causing sound to travel approximately four times faster and with less energy loss over distance.
The Most Powerful Acoustic Producers
The loudest animals in the world live in the ocean, and their sounds are measured at extraordinary source levels. The Blue Whale produces low-frequency moans, pulses, and rumbles that can reach up to 188 dB (re 1 µPa at 1 m). These long calls are typically around 20 Hertz, at the low end of human hearing, and are powerful enough to be detected thousands of kilometers away. The Fin Whale produces loud, low-frequency down-swept pulses, often called 20-Hz notes, with source levels estimated between 186 and 190 dB. These short, repetitive calls are infrasonic and are thought to be related to reproductive displays by males. In contrast, the Sperm Whale, a toothed whale, holds the record for the loudest sound ever recorded, emitting intense, broadband clicks that can reach between 230 and 236 dB for echolocation.
Essential Functions of Whale Vocalizations
The immense loudness of whale vocalizations is a necessary adaptation for survival in the deep ocean, where light is rapidly absorbed. Sound allows baleen whales to communicate over vast distances. Low-frequency sounds, like the moans of a Blue Whale, propagate with minimal energy loss, enabling individuals to maintain contact across hundreds or even thousands of miles. This long-distance communication is crucial for coordinating migration, locating foraging grounds, and finding mates. Toothed whales, such as the Sperm Whale, rely on powerful clicks for echolocation, which acts as a highly accurate biological sonar. By emitting these high-intensity clicks and listening to the returning echoes, the whale can determine the distance, size, and density of objects, allowing them to hunt prey in the deep sea. Male Humpback Whales produce elaborate, loud songs during the breeding season to attract females and establish dominance.
The Phenomenon of Acoustic Masking
The reliance of whales on powerful acoustics makes them vulnerable to interference from human-generated noise, a phenomenon known as acoustic masking. Masking occurs when background noise raises the overall ambient sound level in the ocean, effectively drowning out the whale’s own sounds or their ability to hear others. Low-frequency noise from commercial shipping is a major source of this interference, as the frequency range of ship propellers significantly overlaps with the calls of baleen whales like the Fin and Blue Whale. This noise reduces the effective range over which a whale can communicate, shrinking its acoustic habitat or “communication space.” Whales must then expend more energy by calling louder, altering their call frequency, or losing contact with other members of their species.