Here's a fact. Cod eat capelin. It's a pretty known fact. That's the main predator of capelin, whether it's on the east coast of North America, especially in the northeast coast, or if it's off the coast of Norway in the Atlantic. cod eat capelin. But just imagine how much. Because today we're going to be talking about one of the biggest predation events ever witnessed. It was back in 2014, so almost 10 years ago, where 10 million capelin were eaten by 2 million cod.
Imagine witnessing that. Imagine seeing that for the first time and really thinking about how does this happen on a regular. How does this happen where it sustains the population? Well, I'm going to tell you how, and I'm going to tell you that the entire population of Capelin in that ball during that event was 23 million. So just under 50% were eaten. But does this happen often somewhere else? And what's going to happen with climate change? How's this going to be affected? And is
this a problem for Capelin in the future? We're going to be talking about that all in today's episode of the How to Protect the Ocean podcast. Let's start the show. Hey everybody, welcome back to another exciting episode of the How to Protect the Ocean podcast. I'm your host Andrew Luen, and this is the podcast where you find out what's happening with the ocean, how you can speak up for the ocean, and what you can do to live for
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And it wasn't by a whale. It wasn't by a shark. It was by cod. It was by Atlantic cod eating their main prey diet, capelin. And in this study that was just published recently, oceanographers from MIT and Norway published a study after observing a staggeringly large predation event. In 2014, in the Barents Sea off the coast of Norway, over
10 million fish were eaten in just a few hours. sort of spawning event so essentially what happens is the capelin come in and they start swimming on their own they're just chilling they're swimming on their own and after a while they start to dive deep and they dive deep and as they dive deep they get closer and closer together and then more get closer and closer together until they form probably the largest bait ball you've ever seen. Now
capelin are used for a number of different things. They are used for fish bait, they're used for as fertilizer, they're used as food as a food source for select communities and so they're You know, they're used quite a bit, but they do tend to have these bait balls, and a lot of times you'll see it. They're very, like, anchovy-like fish, so they're very small. They're probably about this big. They're Arctic fish. They're normally in the North Atlantic or here in the Barents Sea, and
they like the cold water. They like to dive deep. They like to be in a bait ball. Why do they go in this bait ball? It's to protect themselves. So, the fish in the middle will be protected from predators from the outside, and the fish on the outside are a bit altruistic, meaning
that they're probably going to get eaten. There's a good chance they're probably going to get affected, damaged, you know, hurt in some sort of way, or just eaten in general, because they're on the outside of this massive bait ball. Now, when I say massive, I'm talking about 10 kilometers long. That's how big, that's how much, like 23 million fish in one area, 10 kilometers long. That's how many there were. And 10 million of those were eaten by approximately
2 million codfish. Now you're probably wondering, how do you count? all of those, Andrew, like that doesn't make sense. You don't just have someone, you're just counting all the fish. No, this was done by a specific instrument that's called the Ocean Acoustic Waveguide Remote Sensing System, so the O-A-W-R-S. I don't know if it's called ORS or what have you. Scientists, we love our acronyms, right?
But it was recorded a decade ago during an exploratory trip where a team of scientists used this sonic imaging technique known as the acoustic waveguide remote sensing system. This acoustic ray attached to the bottom of the vessel where it sends sound waves in all directions. Those waves are bounced off anything and everything in their
path. So if there's fish in the way or there's anything, it bounces off. Now, like another set of acoustic receivers picks up the reflected sounds, giving the viewer an idea of what's happening for miles around. So it's on a screen. It's almost like how they do seismic surveys. When they send an acoustic sound to the bottom of the ocean, it bounces up. And depending on how it hits and how it reflects back, you get to see these pockets of sort of like hydrocarbon pockets, right, where you
want to see oil and gas. In this case, you're seeing fish. Now, how do we tell between different species of fish? Well, it just so happens that cod have swim bladders. The swim bladders allow them to float in the water column, so they're not always sinking like a lot of these sharks, but you have these swim bladders. Cod have bigger swim bladders than the
capelin. So when a cod has a low resonance, like a big bend bell, whereas capelin have tiny swim bladders, so the resonance tends to be high-pitched notes like piano. you get the difference in the pitches as they come back and the computer is able to decipher between those pitches. And if you just do a
little bit of programming, these are MIT people here. I'm not sure what background the people in Norway have, but the MIT people have this coding experience and they're able to decipher between and show how big these bait balls are, how big the population of each of these different species are. So that was kind of cool. So the MIT paper goes on, and I'll link to the article in the show notes, but the MIT paper goes on to explain that the data was collected during the very
heat of Capeland's spawning season. So as the array pinged off, Often in the early morning hours, they were seen to be moving mostly as individuals along the coast of Norway. As the day progressed, however, they swam deeper, perhaps in an effort to avoid the light of the rising sun, so they're not seen. But I think, and this is a quote from, I
don't know who. But one of the people, it says, the team observed that as the capelin descended, they began shifting from individual to group behavior, individually forming a huge shoal of about 23 million fish that moved in a coordinated wave spanning over 10 kilometers long. That is huge. I would love to see sort of like a bait ball that much, or that much of a shoal of fish, because that's just cool. A shoal of fish is essentially a school of fish, but just in the large
area and very compact. And soon the master shoal began swimming as one, a behavior seen in other fish and some flocks of birds. So just imagine a flock of birds, as they switch directions, they all switch directions. And the cod in the area responded, forming a shoal of their own of over 2 million strong. The cod began systematically attacking. Macris, who was one of the scientists on the study, he says it's the first time seeing predatory prey interaction on a huge scale, and it's
a coherent battle of survival. So this is happening over a monster scale, and we're watching a wave of capelin zoom in, like a wave around a sports stadium, and they kind of gather together to form a defense. It's also happening with predators coming together to coherently attack. This is unprecedented. We've never really had the chance to observe such a large-scale predatory event like this. We've seen bait balls before, never in the 10 millions that
we've seen. So this is great to be able to have this data in now. What we worry about in the long run is how these bait balls are going to be affected by climate change. We know fish spawning, we know currents changing, climate change, it all gets affected with climate change, right? So heating of the oceans, switching of currents and wind patterns in the ocean and in the atmosphere can really change how things are done and how
things work and function within the ocean. you know it's the small fish when their larvae they get taken by the currents to another place and that that pattern is dependent on by predators and prey itself to run their regular life cycle as those change during climate change or throughout climate change this will change the pattern and may affect, whether short-term or long-term, whether it's gonna be capelin success in reproduction or the cod success in predating these
fish, this prey, right, these capelins. So it could be a problem when we see these massive bait balls. As the team said, the study team said, it's like, once we get the last bait ball and we know it's the last population and we know it's gonna be a mass feeding and predation population event, Once they're gone, they're gone. If they don't recover fast enough to take on 10 million, or however many get eaten at that one time, that bait
ball, that population will not recover in time. It is dependent on numbers. It's a numbers game. So if those numbers aren't successful in having 10 million more offspring, or more of that, or less, if it's less, then we know that the cod population is gonna go down. So that's, you know, these and other predators that depend on capelin as well. It's all going
to be affected. It's all in a food web and it's all negatively responding or positively responding depending on how much reproduction we see on a daily, on a annual basis, semi-annual basis, you know, every couple of years. This is the problem with climate change. This is the problem with any kind of environmental disturbance that we see, is will we have more capelin to be able to witness these massive feeding events?
I don't know. I haven't read the full study yet. I don't know if there have been other events after that, that it shows a pattern of these massive 10 million, this 10 million feeding event, but That's pretty cool. That's pretty cool to see it and be able to recover after that. So hopefully we'll see more recovery. I know in certain places like off the coast of Canada, capelin are in a critical point as well as cod is
just over a critical point, but like slightly. And you know, there's been an increase in fishing for cod, Atlantic cod off the Atlantic coast of Canada. And so there's an opening of that. That could be dangerous as well. So these, these fish populations are not, You know, they're not unlimited. There is a limit to each one. They can go down in population depending on what happens. Climate change is rearing its ugly head faster and faster than we've ever seen. So
we don't know how this is going to affect this fish population. I'll try and get more information and maybe try and get an interview. to talk about the capelin-cod-predation-prey relationship on that side of the Atlantic and be able to bring that back to you. But I thought it was an interesting story. I wanted to bring it to you because I think it's something that we should share together. And I'd love to hear your thoughts on it. Have
you ever heard of this before? Have you ever seen any more studies? Who's working on this? I would love to hear. And what you think of the content of the topic of this $10 million strong bait ball. 23 million bait ball, but 10 million being consumed in less than a few hours. I think that's amazing. I want to hear your thoughts. You can hit me up on a comment on Spotify, on YouTube, or you can hit me up on Instagram at howtoprotecttheocean. Just
send me a DM that's at how to protect the ocean. I would love to hear your thoughts on the podcast, the thoughts on this episode, and just your thoughts in general relating to ocean conservation and science. Feel free to contact me, ask me any kind of questions, I'd be more than happy to answer it either here or to you directly. I want to thank you so much for joining me on this episode of the How to Protect the Ocean podcast. Have