Fish 'sing' to communicate

How fish sing in a bid to communicate with one another...

Will - What you're hearing right now are fish - singing fish. Okay. Perhaps singing is somewhat inaccurate, but you can't deny there's something remarkable about the sound being made. These noises in question were recorded as part of a series of papers released by the International Quiet Ocean Experiment. A group of scientists hoping to survey and ID fish based on their acoustics all over the ocean. The IQOE has an offshoot organization called the Global Library of Underwater Biological Sounds or GLUBS, yes. And member Miles Parsons took me through how fish make these sounds and what they tell us about the fish in question.

Miles - These sounds are produced for many species by particular muscles that are used to contract around a swim bladder. A swim bladder is a little gassiest body that they normally use for buoyancy, but several species of fish have developed the ability to use that swim bladder to produce sound. So these muscles contract around it, they change the shape of the swim bladder, and as that's pulsating, it creates noise. So if you can imagine that you have a healthier fish, a bigger fish, they have longer, stronger muscles that can contract around that swim bladder and that takes ever so slightly longer to do it. So they actually create a deeper sound because of that. And you'll actually find that in some species, the females that might be trying to meet a mate are attracted to the deepest sounding voice. So the size of the fish and the sounds it produces essentially are related and the sound gives information about the fish producing the sound.

Will - So these noises can create a handy sound profile when trying to ID fish in murky or dark water. Much easier than having a look. But the fish aren't making the noises for us, so what are they trying to say?

Miles - There's quite a few reasons why fishes produce sound. The main one is realistically spawning, or reproduction. They also make sounds in terms of territorial defense. There's also distress or alarm signals that they give off. And some species we think, actually communicate to each other to talk about feeding. So you get what you have called an evening chorus, which is a lot of fish coming together. Now, whether or not the sound they produce is a byproduct of feeding or it's actually fish calling on mass to tell others where the food is at. We're not quite sure, but there's a number of different reasons for why they produce sound.

Will - So now we know how they do it and what they're trying to communicate. Do these noises change as the environment does? What causes a fish to change its tune?

Miles - It's all really related to the behaviour that's associated with the sound. So if we use spawning as an example, in Australia we have in this one River we've got a big fish called the mulloway. And this makes a loud croaking sound. If you listen through the hull of a boat, it sounds like someone farting. Now that sound is produced with spawning and they are trying to time their spawning for the maximum chances of success for their eggs. So it happens mostly after sunset. It happens when temperatures are high enough in the water for the fish to be able to spawn successfully, and it happens after high tide when the tide will take the eggs out from the river out to sea. So realistically, lots of these spawning, or whatever communication purposes they're using for sound, can be related to long-term environmental effects. So you'll get daily patterns, you'll get tidal patterns, you can get lunar patterns and you'll get seasonal patterns.

Will - But the factors behind changing a fish's noise are not limited to naturally occurring events. Humans are never far from the subject of altering a natural habitat.

Miles - Yes. So the most typical one there is vessel noise. And you'll have some species of fish that have been shown to stop calling when there's a vessel nearby. But one of the main problems really would be the communication space that they have if they're being exposed to noise. So if you think about it from the fish's point of view, you have a male trying to attract a female. The female can hear it a long distance away if it's nice and quiet, so you've got a good chance of them meeting up and having a successful mate. But if there's boats around, then those chances are much lower, mainly because they're using sound as their main method of meeting.

Will - But sound and the marine environment isn't a complete match made in hell. There are still many good things that we can use marine acoustics for when it comes to protecting fish as well.

Miles - One of the uses that you've got is fisheries management. You can actually locate these fish by the timing of their calling and the sounds that they're making. So that means that you can work out when and where their best chances of spawning are. And you can use that to identify what we call essential fish habitat. And in some cases you could have a space and timing based closure of a fishery so you can identify the periods where you don't want to have someone targeting them. And you can use that to help manage the fishery.