The sounds of the sea.

Updated: Aug 30, 2022

Is it just me, or does the sound of waves crashing onto the shore something that makes you feel relaxed? The sounds of waves is the sound we humans are most familiar with when we talk about the sounds of the sea. We most think of the sea and ocean as a quiet place, but when you dive underneath the surface there is a complete cacophony of sounds coming from various natural sources. In this blog I want to dive into the natural sounds of the ocean and how marine life use sounds and how these animals make sounds.

Most sounds heard come from waves, wind, rainfall, earthquakes and ice, these sounds are described as ambient sounds. Other sources of ambient sounds are anthropogenic noise, such as; shipping, drilling and so on. But I am not going to talk about human noise and the effect they have on marine life. A lot of the sounds also comes from the animals themselves. The sounds of marine animals are described as vocalizations.

The longest recorded humback song lasted 22hours!

Marine mammals

The most well-known marine animals who vocalize are whales and dolphins. And the make a variety of different sounds. Whales can sing and produce social calls. Only certain baleen whales are able to sing, blue, fin, minke, bowhead and humpback whales. Its is still being debated how whales vocalize, as they don’t have vocal chords. But what is a song? A song is a series of vocalizations in a (predictable) pattern which can last for 30minutes or even hours. Only males can song and most song activity happens during breeding season. It is therefore thought that males sing to attract mates. There are Both males and females use social calls which can be a wide range of vocalizations, from cries, whistles, pulse trains, wops, grunts and grumbles. Most of the calls and songs can be heard from a great distance. This is because sounds travel much faster underwater than through the sky. Sounds underwater can travel 1500meters per second, where sound waves in sky travel 340 meters per second. The loudest whales are sperm whales and blue whales. Sperm whales are the loudest animals their clicks can reach 230decibels (dB), initially it was thought that the blue whale was the loudest animal with calls that reached 188dB. These decibel numbers are already louder than a jet engine! And in the Netherlands the maximum dB that is allowed during concerts is 103dB and even then you need ear plugs to be really safe. Besides being loud whales can also be very quiet, a couple of researches encountered whale whispers, this happens between a mother calf pair and they do this to avoid detection.

Dolphins use whistles and clicks to communicate with each other, but also to find food. They do this through echolocation. Echolocation is produced by a complex system of air sacs and specialized soft tissues that vibrate as air moves through the nasal sacs. The sound produced in the nasal sacs is channelled through the fats of the melon. Dolphins can modify the shape of the melon to produce a narrow or broad beam of sound.

What is interesting with cetaceans, at least with orca, sperm whale and humpback whale, is that they have different dialects between pods and geographical locations. And researches can actually recognize the vocalizations from these different pods and specimens from different geographical location.

Other marine mammals are very similar to humans when it comes to producing sounds. Just like us sounds are produced by vibration of the vocal chords in the larynx as air passes from the lungs through the larynx, into the throat, and out through the mouth.

Crustaceans and invertebrates

Beside the sperm whale and the blue whale another very loud creature is the snapping shrimp. Only this sound doesn’t come from the inside of the body but from the closure of its large claw. When the claw closes a bubble is formed that cavitates, this produces a loud plopping sound that can reach 200 dB. This cavitating bubble is so powerful that is can actually stun or even kill its prey, but they also use it to ward of predators. Also lobsters use sound as a defence mechanism

These sounds aren’t only used for defence, cleaning shrimp actually use sound as a way to advertise. Cleaner shrimp feed on parasites which can be found on the skin of fishes. The cleaner shrimps clap their claws when a fish approaches, this clapping basically tells the fishes, ‘’ hello there, are you in need of a cleaning service? I am available right now!’’

Fishes

Fishes also produce vocalizations, this mostly happens to attract mates, warn for danger and scaring competitors and predators. But they also use vocalizations to maintain the social hierarchy. Fishes have a swim bladder in their abdomen. The swim bladder is a gas-filled sac with which they control their buoyancy. If fishes want to swim higher in the water they fill the swim bladder with more gas, when they want to swim lower gas is removed from the swim bladder. There are fishes that also use their swim bladder to produce sounds. These fishes have a sonic muscle which is attached to the swim bladder, this muscle contracts and relaxes in sequence, this causes the swim bladder to vibrate and produce vocalizations. Most of these vocalizations can be described as thumps, purrs, knocks and pulses this all depends on the fish species.

Acoustic marine research

Most marine animals use vocalizations to communicate, protect and attract mates. Most of these vocalizations are very species specific. Which is amazing for researches, as this gives a passive way to research these fishes, crustaceans and cetaceans. This can be done with a technique called passive acoustic monitoring (PAM). This technique only uses a hydrophone (under water microphone) to record the underwater sounds. It is even possible to place a hydrophone underwater for months at a time.

During my project internship and my thesis project I have used data sets that come from long term PAM recordings. During these projects I mostly used the data to look at the occurrence of minke whales in Scotland and humpback whales in the Dutch Caribbean. But the data sets from PAM recordings can also be used for distribution data, the daily pattern of the vocalization (diurnal pattern), the mapping of human made noise (anthropogenic noise) and to investigate vocalization patterns. Honestly I loved doing these researches, just going through the data, looking at spectrograms and listening at the vocalizations. I didn’t only hear the whales but I would also hear the vocalizations of fishes and crustaceans.

https://dosits.org/galleries/audio-gallery/ This website of discovery of sounds in the sea has vocalization examples of many different marine species. If you want to listen to the sounds of marine animals just go through the dosits website. I do recommend listening to these vocalizations with headphones.

Below I will add some links to my favourite sounds.