Seals, belonging to the group of marine mammals called pinnipeds, are highly social animals that rely on an extensive array of vocalizations for survival and communication. Sound is a primary sense for these animals, especially in the dark or murky ocean environment where vision is limited. These semi-aquatic creatures must adapt their sound production to function efficiently in both air and water, two mediums with vastly different acoustic properties. This reliance on sound has led to a diverse and complex repertoire of calls used throughout their life cycle.
The Range of Seal Vocalizations
The specific sounds produced by seals vary significantly between the two main groups: true seals (Phocidae) and eared seals (Otariidae), which include sea lions and fur seals. True seals, such as harbor seals and elephant seals, are generally quieter on land, often vocalizing with soft grunts, growls, and hisses for close-range social signaling. Underwater, however, these species produce a complex range of sounds, including the elaborate and individually distinctive calls of the Weddell seal. Eared seals, in contrast, are notably noisier in air, with species like California sea lions known for their repetitive, loud barks used in crowded breeding colonies to maintain territories or assert dominance.
Communication: Why Seals Make Noise
Vocalizations serve several functions for seals, mostly revolving around reproduction and social structure. One primary use is mother-pup recognition, particularly in colonial species where a mother must quickly relocate her young upon returning from foraging. Mothers and pups use individually specific vocalizations, often described as an attraction call, to reliably distinguish each other from the crowded rookery. Male seals use loud and elaborate calls during the breeding season to attract females and establish dominance over rivals, sometimes producing highly ritualized underwater sounds. Warning calls and aggressive vocalizations, such as growls and roaring, are also used for territorial defense to warn off competitors or predators.
Sound Production: How Seals Vocalize
Seals, like all mammals, generate sound using a pneumatic, or air-driven, mechanism involving the larynx and vocal folds. Air from the lungs is pushed across the vocal folds, causing them to vibrate and create the initial sound waves. This sound is then shaped and filtered by the supralaryngeal vocal tract, which includes the throat, mouth, and nasal cavities. Producing sound underwater presents a unique challenge, as the larynx must be sealed to protect the respiratory tract from water. Some species adapt by using specialized air sacs or modified nasal passages to circulate air internally for sound generation, while others push air past the vocal structures, resulting in visible air bubbles.
Airborne vs. Underwater Acoustics
The way sound travels differs dramatically between air and water, forcing seals to adapt their vocal strategies to the medium. Sound travels approximately four times faster in water than in air because water is denser, allowing sound waves to propagate more efficiently. Consequently, underwater vocalizations, especially those of lower frequencies, can travel much farther and more reliably than their airborne counterparts. When communicating on land or ice floes, seals use airborne sounds like barks or grunts, which are effective for short-range social signaling. This ability to adjust calls demonstrates the high degree of vocal plasticity necessary for their dual existence.