Creatures of the sea hold many mysteries, not least of all fish. Far from being silent entities of the ocean, some species of fish have been recorded singing, and their songs can help researchers to understand more about their biodiversity and ecosystems.
Associate Professor Robert McCauley and Research Fellow Dr Miles Parsons from the Centre of Marine Science and Technology, led a research team that recorded the sounds of fish in the coastal waters off Port Hedland, Western Australia for 18 months.
From the recordings, the researchers identified seven unique fish choruses that occur predominately during spring and late autumn, and have been able to attribute some of these to particular species.
Fish can be solo singers, repeating the same sound over and over, or they can overlap their singing to form a chorus. Though these calls are not quite as melodic as, say, that of birds, they are certainly diverse, from the horn-like parps of the Black Jewfish (Protonibea diacanthus), to the bee-like buzz of the Terapontidae, to the quiet, staccato beat of the Batfish (Platax orbicularis).
“I’ve been listening to fish squawks, burble and pop for nearly 30 years now, and they still amaze me with their variety,” says head researcher, Associate Professor Robert McCauley. “Though not beautiful, some are fun – Terapontidae calls are great for kids – all are interesting … We still have only a crude idea of what is going on in the undersea acoustic environment.”
McCauley and his research team were able to observe that the fish choruses occurred most at sunrise or sunset, and sometimes both. These diurnal patterns can assist the researchers to better determine fishes’ feeding and breeding habits, as well as social behaviour.
Fish that hide during the day, for example, are most active just before dusk when they start foraging for food, and this is when they produce noise. They also feed again just before dawn before they go into hiding for the day, which will result in another noise burst.
“Many other fish spawn at night,” explains McCauley on how fish also use sound for breeding purposes. “Fish release eggs and sperm into the water separately, with males and females needing to be centimetres apart for this to be successful. Many fish use calling in spawning to attract mates.
“Schooling fish generally mate by rapidly shooting up in the water column as a pair and releasing eggs and sperm at the highest point of swimming up – they use a certain sound type to mediate this act.”
All species of fish can make sounds, but only some can sing. This evolutionary talent occurs in the ‘swim bladder’, a large bubble of gas inside most fish that is used to control their buoyancy. Singing fish can control the muscles of their swim bladder, driving it to create sound.
“Bubbles are highly efficient generators of sound in the ocean,” says McCauley. “The swim bladder is very efficient at transferring any vibratory motion as driven by the attached muscles into backward and forward motion of the surrounding water, or sound.
“Singing offers considerable advantages as it means the fish can communicate at night, when predators can’t see them, and they can communicate over long distances to bring animals together for spawning events.”
The song of a good soloist fish can typically be heard up to one kilometre away; a chorus can be heard up to tens of kilometres, displaying a pitch from 50 Hz to >4 kHz. A pitch of 4 kHz is equivalent to that of a baby’s scream; if you were in the centre of a fish chorus, the noise would be deafening.
McCauley has been studying the singing fish since the 1980s. As a marine biologist, McCauley travelled frequently on yachts, and would hear sounds through the hull that he found most perplexing.
“On learning that they were fish calls, I was fascinated,” he says. “Then on making recordings and seeing firsthand how important the sound must be to the fish, based on how much calling they made, I set about trying to find out more and use these sounds to study the fish.”
So how does one actually listen to these musical creatures?
“We place a hydrophone (underwater microphone) in the water, connect to the appropriate electronics, like a pre-amplifier and digitising system, and either listen directly or record it as samples,” says McCauley.
The team’s most recent study used recordings captured by two sea-noise loggers located 21.5km apart in eight and 18m of water off the coast of Port Hedland. The results of the study have been published in the journal Bioacoustics, and can potentially be used to examine the effects of noise pollution and climate change on marine biodiversity.
“People don’t realise that fish have complex social lives, like most other animals,” says McCauley. “They are more than the slimy things we eat.”
McCauley hopes to seek more funding to capture larger fish choruses that occur locally offshore, such as in the Perth Canyon, and to use camera and sonar systems to observe fish choruses at night.
A fish chorus recorded by Professor Robert McCauley.