The oceans are a veritable cacophony of noise. The dark abyss echoes with everything from soft mating calls to paralyzing, lethal snaps. Some animals sing solos; others team up and form huge choirs to sing serenades. Some animals echolocate at the highest decibel level of the animal kingdom, while others emit sounds that generate pressure waves and make the water churn.
Being heard is vital for all of them, and they do everything they can to make their voices count, because although the sounds of the ocean are varied, their main purposes are the same ones served by noise on land: power and sex.
Marine biologists need only immerse their listening gear a few inches into the water to hear the sounds of the sea. And what they hear puts the calls, cries, buzzes and snorts of landlubbing creatures to shame. Among vertebrates, neither birds nor mammals have developed as many different methods of producing sound as fish, which boast a record number of ways of generating and detecting sounds.
The drum fish is just one of many fish that use their swim bladder as an instrument: Contracting special muscles around the organ quickly and continuously causes it to produce short, rapid drumming sounds that are used to attract mates. Males also use the noises to discourage rivals.
And the drum fish is not the only fish that has developed special powers to produce characteristic sounds. Some fish make noise by nodding with special muscles connected to their skulls, whereas others crack their vertebrae, vibrate their pectoral fins or move other parts of their bodies.
There is also a profusion of noisy fish whose ability to produce sound is still a mystery to biologists. The sounds are as different from one another as the fish themselves, varying from simple clicking noises to serenades of grunts, clucks, growls, hums and even screams.
Fish sounds are rarely melodious, but they’re an efficient way to send a message. Many sounds can be produced from a hiding place where the fish is protected from predators, and in muddy water where sight cues are a poor option, sound may be the only way to communicate. Small males sometimes listen carefully before entering into fights over territories or females, since sound can often reveal the size of the competitor, allowing an overmatched male to forgo a fight before it ever gets started.
Usually, male fish take their territories very seriously, defending them fiercely against any competitor. Among some species, dominant males with their own territories can use sound to distinguish known neighbors from new males trying to muscle in, which allows them to chase away rival newcomers.
While males use sound to discourage competitors, females use it to size up potential mates. Female fish seem to have the ability to gauge a male’s qualities, namely his prospects for fertilizing her eggs, based on the sound he produces. And the connection between sound and quality is clear. Large male cod with lots of muscle mass around their swim bladders are noisier, making them particularly attractive to females.
Summer nights hum with sound
Some fish even sing, producing music that ranges from love-seeking solos to big choral numbers where the sounds of countless fish vocalizing fill the night air in some areas.
As night falls on Florida’s coastline during the summer, a number of species, such as weakfish, begin a nightly concert worthy of a rock festival. For up to nine consecutive hours, the serenading fish produce a sound level between 103 and 124 decibels (dB), and nothing can stop the party — not even a hurricane. In fact, American biologists have observed that the passage of a Category 4 hurricane only made the fish sing longer and pump up the volume even higher.
Biologists don’t understand the reasons for the fishes’ nightly summertime cacophony, but one theory holds that the males’ hormone levels are higher while the females are spawning, sending them into a mating frenzy.
And just as fish produce sounds in many different ways, they also have different ways to detect sound. Some have developed air-filled cavities connected to the internal ear, while the ears of others are connected to the swim bladder: In goldfish and catfish, small bones connect the internal ear to the swim bladder, functioning much like the eardrum does in a mammal.
Cetacean acoustical channels
Sound travels more easily through water than light does, so it is not only important to fish living in lakes, streams and coastal waters, but also for the giants of the deep ocean: whales. Although most lack functional external ears, whales have excellent hearing and, unlike humans, can precisely determine the direction that sound is traveling in water.
This ability is vital for whales. A blind whale has little problem finding food, but a deaf whale is often soon a dead whale. Biologists think that whales replaced their land-based method of hearing by one customized to submarine sounds roughly 50 million years ago. With their new marine-adapted “ears,” whales developed myriad sounds for communicating and also for creating acoustic images of the dark abyss — essential for echolocating prey. The return frequency of the whales’ clicking sounds reveals the size of the prey, while the return volume reveals how far away it is.
Although the oceans are full of clicks, whistles and love songs, whales have a clever way of tuning out irrelevant noise: Different species operate on different acoustical levels, so they can discern which messages are from their own species versus other species that just happen to be nearby. Large baleen whales, such as blue whales and right whales, generally make noise at frequencies below 5,000 hertz, while dolphins, porpoises and beaked whales typically use higher frequencies, up to 150,000 hertz.
For thousands of years, marine animals have used sounds in many ways and for many purposes — mating, marking territory, isolating prey — but scientists are only now beginning to understand the many languages of the ocean. And we’ve got a lot to learn.
Male leopard seals are summertime soloists
During Antarctica’s short summers, male leopard seals sing almost around the clock, sending out songs that are so personalized that biologists using old military listening gear can identify individual animals. In fact, this is how scientists learned that young males are forced to huddle together in the poorest hunting grounds when older males chase them out of their prey-rich territories.
Snaps signal sex
To a female downfish, a booming snap is the sound of desire. Males produce mating calls by violently snapping their jaws, using a special tendon in the mouth that moves very quickly to create the loudest possible sound. This attracts females that are listening for the loudest, and thus sexiest, males.
Spawning a love frenzy
When female perciform fish spawn, the males go berserk in a love frenzy. They race through the water, producing cascades of clicking sounds with their mouths, hoping that their loud antics will inspire one or more females to spawn her eggs, which the males then will be allowed to fertilize.