All kinds of seals communicate vocally by making noise with their throat and air. The range, pitch, and variety of these noises, however, are all vast. Arctic seals can groan, chug, or growl in the course of their communication. Weddell seals send out long, low whistles underwater at very high decibel levels, and harbor seals make quiet calls. The variation of these methods shows the highly specified development of each species of seal in response to its environment. Each style of communication suits a particular need.
Male seals are the most vocal because they use their calls to defend their territories. The sounds are amplified underwater and can be heard by other seals over large distances. Arctic seals make long-range calls underwater designed to attract females. Up north under the polar ice, these calls can be heard 30 kilometers away. Above-ground snorts, whistles, and growls are responses to threats from other seals.
Seals that live in polar areas with heavy ice can make loud, long-range calls because their predators cannot get through the ice. Bearded seals in the Arctic make a long whistle underwater that can last for 70 seconds. Harbor seals and others that live in the open oceans would attract killer whales with these loud calls. Instead of being loud, male harbor seals will choose a spot where females will pass by and put on a display of poses and low guttural noise. This is the safer way to attract a mate in open waters.
Dr. Jack Terhune studies seal communication at the University of New Brunswick and has measured the amplitude of seal calls. His research has shown that harp seals, often living in groups of up to 150, can alter the pitch of their calls so that each seal can be heard. Off the coast of Newfoundland there are between 5.5 and 6.5 million harp seals in regular migration up and down the eastern seaboard. One seal's call could be heard by 10,000 other seals at a range of two to four kilometers away, so the changes of pitch and frequency are important to avoid overlap.
Seals can also communicate through movements. Harbor seals slap the water with their bodies or flippers to show aggression. Posing or similar aggressive displays are common in courtship as well. Elephant seals are famous for the beach battles, in which males fight for control of a rookery or breeding colony. The strongest fighter can breed with the females on the beach. Full-grown males rise up to their full height to launch their attacks while making guttural throat noises to intimidate the opponent. The physical pose and raised position of the males nose is a call to fight.
Pups, or baby seals, also call out more often than adults. Harbor seal pups make a sheep-like noise that their mothers can distinguish individually. This kind of communication shows the strength of the initial bond between the baby seal and its mother, who only gives birth to one pup at a time.