Whales navigate a world where light penetrates only so far. Sound serves as their primary sense for interacting with surroundings. Whale vocalizations are complex signals used for various purposes, connecting individuals across vast distances. These sounds are fundamental to their survival and social structures.
How Far Whale Sounds Travel
Whale sounds can travel extraordinary distances underwater. Sound moves approximately four times faster in water than in air, at about 1,500 meters per second. The distance a whale’s sound travels depends significantly on the type of whale and the frequency of the sound produced. Low-frequency sounds, particularly those made by baleen whales like blue whales and fin whales, can propagate for thousands of kilometers.
For instance, the low-frequency calls of a fin whale can travel 250 kilometers near the surface, and over 6,000 kilometers within the deep sound channel. Some researchers suggest certain low-frequency whale sounds could travel more than 16,000 kilometers in specific ocean layers. Toothed whales, such as killer whales and dolphins, typically produce higher-frequency clicks and whistles. These sounds are primarily used for echolocation over shorter ranges, with killer whale calls traveling between 10 to 16 kilometers for long-range communication and 5 to 9 kilometers for short-range interactions.
Factors Influencing Sound Propagation
The ocean is an efficient medium for sound transmission because water molecules are more tightly packed than air molecules, allowing sound waves to propagate effectively. Several environmental conditions and sound properties influence how far whale sounds travel. Temperature, salinity, and pressure are the primary oceanographic variables affecting the speed and propagation of sound underwater. Sound generally travels faster in warmer, denser water with higher salinity, and with increasing pressure.
As sound waves move through the ocean, their speed changes with depth. Temperature typically decreases with depth, causing sound speed to decrease, while pressure consistently increases with depth, which tends to increase sound speed. This dynamic creates the SOFAR (Sound Fixing And Ranging) channel, or deep sound channel, where sound waves are refracted and channeled, allowing them to travel vast distances with minimal energy loss. Whales exploit this natural acoustic waveguide to communicate across entire ocean basins. Lower frequency sounds, for example, travel farther with less scattering and distortion, making them ideal for long-distance communication.
The Purpose of Long-Distance Communication
Whales rely on sound for essential behaviors in the marine environment. Long-distance vocalizations serve multiple purposes, including navigation, foraging, and maintaining social cohesion. Whales use sound to find prey, locate other individuals, and navigate by listening to echoes off distant features like the seafloor or coastlines.
Mating calls, particularly the complex songs of male humpback whales, are a key use of long-distance communication. These intricate songs attract mates during breeding seasons. Vocalizations also facilitate social interactions, maintaining bonds within pods and conveying information like distress or playfulness. Different whale populations can develop distinct vocal “dialects” to identify group members.
Human Noise and Whale Communication
Human-generated noise in the ocean poses a challenge to whale communication. Sources of this anthropogenic noise include shipping traffic, sonar, and seismic surveys, which have increased background noise levels. This noise can mask whale sounds, making it difficult for them to hear each other, navigate, or find food.
Shipping noise overlaps with the low-frequency vocalizations of baleen whales, which are important for their long-distance communication. This overlap can reduce their communication range, disrupting behaviors like foraging. Seismic surveys produce low-frequency sounds that can also interfere with baleen whale acoustic signals. Whales respond to such noise by altering their vocalizations, changing migration paths, or avoiding noisy areas, impacting their survival and reproductive success.