When an Arctic cod grunts, these people listen

Arctic cod are a key food source for most polar predators. Researchers are becoming fluent in cod grunts so they can use sound to help keep the species going.

A new podcast – sorry, Codcast – from the University of Victoria takes people through the science behind the noises Arctic cod make.

Underwater, sight and smell are much harder for many species to meaningfully use. That makes sound vitally important.

Shaye Ogurek is part of the cod team, having first worked on the bioacoustics of another fish, the midshipman.

Ogurek spoke with Cabin Radio about the project.

“Arctic cod are up to 80 percent of the fish populations in the Arctic. They’re a small species. They’re considered a forage fish, they feed quite literally everything in the Arctic some way or another. They’re so, so important,” Ogurek said.

“We’re hearing from different Arctic communities that cod aren’t spawning in the places that people are used to seeing them spawning. They’re not there any more, their populations are reducing.

“It’s important, as this is happening, to really understand the magnitude of what’s happening so we can predict the impacts and then potentially help conserve in any way that we can.”

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This interview was recorded on April 16, 2025. The transcript has been edited for clarity and length.

Ollie Williams: Why do we care about the grunt of the Arctic cod?

Shaye Ogurek: Sound is really important underwater for lots of fish species. They use sound for communication. It really makes sense: sound travels so well underwater, which is a very murky environment. It’s really hard, visually. You can’t really use chemical cues or smells or anything like that, because the currents will take them away.

Sound is a really reliable way for organisms to communicate. We’re finding that, similar to whales, fish are using sounds to communicate for reproduction, for courting, for mating, for parental care. The ability for fish to send and receive sound signals is important, ultimately, for their population stability.

If we think about the broader ocean, climate change, this is connected to noise pollution – the noise humans are making underwater with boats and shipping, but also seismic surveys for oil and gas, renewable energy projects, dredging. Any activity we’re doing on the water is making a lot of noise. That’s concerning in terms of drowning out the sounds fish make and preventing them from using that mode of communication for reproduction and stuff.

If we want to think about the Arctic cod, with climate change, the ice sheets are melting. We’re going to see the opening of the Northwest Passage for shipping in the near future. That’s going to be a potential major disturbance in that otherwise pristine ecosystem that these fish haven’t had to contend with before.

We’re hoping we can understand how and why they’re using the sound now, so we can potentially earmark important areas where we don’t allow shipping or have regulations for noise underwater similar to what we do for regulations for noise on land. You can’t do construction in the middle of the night in a residential site, for example.

Finally, the fact fish use sound is a key way we can track their populations. These fish live in the Arctic under the ice. We don’t know a lot about their population size, their movements, where they spawn. We know very little about this really important fish species in the Arctic.

We can put a recording device called a hydrophone in the water and leave it there. It records the surrounding sound for an extended period of time, up to a year, and then you to change the battery. We can look at those sounds and say, “OK, Arctic cod were spawning here. They weren’t here from January to February, but they were here some other months,” for example. That’s really important information.

Are we at the point where we’re beginning to draw conclusions, or are we essentially establishing our baseline fish sounds at this point so we can draw conclusions later?

We have established the baseline, what the Arctic cod grunt looks like. I’ve gone through quite a few hours of sounds.

We are working with tank data right now – all the data we have, the Arctic cod are in tanks in a facility in Oregon and we’re recording them in there so we can get nice, clear calls. We know it’s Arctic cod. There’s minimal wild background noise.

We’ve gone through a year’s worth of data and we’re definitely starting to see some patterns in the seasonality of their calling. They call way more during spawning season, which is January to March. We’re seeing a lot more calls in males versus females. We haven’t looked too much into the calling rate of females yet, so that’s something we’re excited to look into. And it’s starting to look like there might be a difference in the frequency of their calls in and out of spawning season, but that’s really preliminary right now.

So eventually, then, the plan would be to go get the sound of Arctic cod in the wild – in an Arctic environment – and be able to match that up to the sounds you had in the tank to get a sense of what the cod in the wild are doing.

Yeah, exactly.

Can you replicate the grunt of an Arctic cod? Is it a pleasant sigh? Is it more of a staccato expression of dissatisfaction?

I can replicate it, I’ve heard it so many times. It really is like a grunt.

Honestly, the way we analyze it is through visual software. I can see the calls on what we call a spectrogram, and then I can also listen to them. Lots of times when I’m super familiar with the data, I don’t even have to listen. I can just look. So it’s definitely one of those things that you can throw on a podcast and do. You can watch a movie and do it.

Surely the next stage of the research is to play different music to the cod?

And see how they respond!

Can we play them some Metallica to suggest, “Look, there’s an inbound cruise ship,” for example? If the cod learn to associate Nothing Else Matters with a cruise ship arriving, maybe we can signal to the cod in advance to clear the area?

What’s so funny is that is kind-of another part of our research project. We are looking at the hearing of cod as well.

We did some experiments on them to see the acoustic range that they could hear. You put electrodes on the auditory nerves, and then you play them sounds of different frequencies at different volumes. The computer can tell if they’re hearing the sound or not.

I believe there is an accompanying podcast that people can go check out.

Yes, it’s called the Codcast. It’s on all podcast platforms. It’s a total of four episodes, so one will drop every week.

And on that podcast, we can hear from the cod?

Absolutely, yes. They play the grunt multiple times along with many other very cool fish sounds, which you probably didn’t know about. So you should definitely check that out.

As much as we have a bit of fun here, this is something we’ve got to get right, hey, scientifically? In terms of understanding what we’re going to do to our northern fish populations if that ocean opens up any more than it already is?

Arctic cod are up to 80 percent of the fish populations in the Arctic. They’re a small species. They’re considered a forage fish, they feed quite literally everything in the Arctic some way or another. They’re so, so important.

We’re hearing from different Arctic communities that cod aren’t spawning in the places that people are used to seeing them spawning. They’re not there any more, their populations are reducing. It’s been predicted with climate change that this would happen – it makes sense, because the water is getting slightly warmer. They’re a really cold-adapted species, they need sea ice, things like that.

It’s important, as this is happening, to really understand the magnitude of what’s happening so we can predict the impacts and then potentially help conserve in any way that we can. It is all coming down to climate change and our use of fossil fuels and oil and gas for energy as a world. That is ultimately the most important thing we need to focus on and need to rectify as a society.