The ocean is far from silent, filled with sounds from its largest inhabitants: whales. These marine giants depend on sound as their primary sense for navigating their underwater world. Unlike light, which quickly dissipates in water, sound travels efficiently, making it an indispensable tool for survival. Whale vocalizations highlight the unique adaptations these animals have developed to thrive where visibility is limited.
The Remarkable Range of Whale Sounds
Whale sounds can traverse extraordinary distances beneath the ocean’s surface. Low-frequency calls from large whale species can travel for hundreds, even thousands, of miles. Blue whales produce sounds detectable up to 1,600 kilometers (994 miles) away. Fin whale calls reach 6,000 kilometers (3,728 miles) in deeper waters, and humpback whale songs extend over 6,400 kilometers (3,977 miles). These ranges underscore the magnitude of their acoustic communication networks across vast oceanic expanses.
Oceanic Factors Influencing Sound Travel
The physical properties of seawater directly influence how far whale sounds travel. Several factors dictate sound propagation underwater, including temperature, salinity, and pressure. Sound travels faster in warmer, higher salinity water and under increased pressure.
As depth increases, pressure also increases, speeding up sound propagation. However, temperature generally decreases with depth, which can slow sound down. The interplay of these variables creates distinct layers in the ocean where sound behaves differently.
A significant phenomenon facilitating long-distance sound travel is the SOFAR (Sound Fixing and Ranging) channel. This horizontal layer exists at depths where sound speed is at its minimum, typically several hundred meters deep. In this channel, sound waves refract back towards the channel’s axis, effectively trapping and guiding them over vast distances with minimal energy loss. Whales, particularly those producing low-frequency sounds, utilize this natural waveguide to maximize their vocalizations’ reach, spanning entire ocean basins. Lower frequencies generally travel farther underwater than higher frequencies, as they are absorbed less rapidly.
Why Whales Rely on Far-Reaching Sounds
In the underwater environment, sound is the primary sense for whales to interact with their surroundings. They depend on it for communication, navigation, and foraging. Whales use various vocalizations, such as clicks, whistles, and pulsed calls, each serving a specific purpose.
For communication, whales produce diverse sounds for social interaction, maintaining contact within their pods, and for mating calls. Male humpback whales, for example, sing complex songs during breeding season to attract mates. Sound is also essential for navigation, allowing whales to create a “sound map” of their environment. Toothed whales, such as sperm whales, use echolocation by emitting clicks and interpreting echoes to detect objects, locate prey, and navigate. Some species use coordinated vocalizations during group hunting to improve foraging efficiency.
Underwater Noise and Whale Communication
The increasing presence of human-generated noise in the ocean poses a challenge to whale communication and survival. Sources of this noise include commercial shipping traffic, naval sonar operations, and seismic surveys for oil and gas exploration. Over the last 50 years, underwater background noise levels have doubled each decade, largely due to the global merchant fleet’s growth.
This pervasive noise can mask whale vocalizations, reducing the distance they can hear each other. It disrupts their ability to communicate, navigate, find food, and avoid predators. Exposure to intense or prolonged noise can lead to behavioral changes, such as altered migration paths, disrupted feeding patterns, and changes in social behavior. Loud noises from military sonar have been linked to mass strandings and fatalities among certain whale species, particularly beaked whales, due to disorientation or physical injury. These impacts can affect whale health, fertility, and population sustainability.