The Biggest Mouthful: How Blue Whales Eat and Why Krill Matters

0:00 I want you to picture a blue whale, 30 meters long, 200 meters down, closing in on a swarm of krill so thick it looks like a huge cloud. The whale beats its tail, picks up a bunch of speed, and opens its mouth. In about the time it takes you to read a text message, it swallows a volume of water bigger than its own body. And the move only pays off when the krill is thick. And here's the kicker. The lunge move that these massive whales do only works when the krill is thick, like that cloud is thick of full of krill. And the krill is something we're catching more often every year as humans. And that's gonna be the focus of this episode. And the next four episodes, we're gonna be focusing on the biology of the biggest whales and what that biology tells us about protecting them.

0:47 And we talked yesterday with Ashley Blawas, who is a postdoc talking about whales and lunge feeding and the heart rates and everything. We're gonna dive deep into that in this series for the next four episodes because I think it's important this week to talk about the physiology of these large mammals because it's fun to know. And it has a little bit of, connection with us as humans. So I think it's interesting to look at that. And most of us, grew up with the idea that whales were, quote-unquote saved, back in the 1980s when commercial whaling was paused. And then you hear about ship strikes and entanglements and climate change, and you start to wonder if the comeback is real or are we gonna go on a downward trend? So this episode starts with the most basic question about a giant whale: How does it eat enough to have its large body stay alive?

1:30 And once you see that answer, you see exactly where the pressure points are and exactly where the good news is. I've spent 15 years talking to people who study whales, and the thing that always gets me is how much of a whale's life comes down to one single meal done right. So to understand the threat, you first need to picture the meal. Blue whales, fin whales, and humpbacks belong to a group called rorquals. So the word comes from the Old Norse term of translated as furrow whale because of the long grooves running down their throats and bellies. Those grooves are the secret. The skin and blubber on the rorquals underside is pleated like an accordion, and it runs about half or 60% of the whale's body length.

2:12 When the whale opens its mouth at speed, water rushes in and those pleats stretch out like a balloon filling with water. And a blue whale can take in a volume of water bigger than its own body in a single gulp. Then it closes its mouth, pushes all that water out through the baleen, the fringe plates, the hanging from its upper jaw, and the water leaves, the krill stays, and the whale swallows. A scientist who modeled the energy of a blue whale lunge found that one gulp cost the whale somewhere between about 3,000 and 8,000 kilojoules of energy. In a thin patch of krill, the whale gets about six times what it spent. In a thick, dense swarm cloud, it gets back more than 200 times what it spent.

2:52 So the same whale, same lunge, the only thing that changes how tightly the food was packed in those clouds. Now giant whale doesn't survive on oceans average, it survives on finding the densest swarms and hitting them hard. They gotta eat most of that swarm. A blue whale in the Eastern North Pacific can eat about 16 tons of krill a day when it's feeding. So if the whole strategy depends on dense swarms of krill, what's the problem? We're gonna talk about it right now. Antarctic krill are small shrimp-like animals about half the length of your finger. They gather in swarms so dense that they can tint the water, and they feed penguins, seals, fish, seabirds, and the biggest whales on earth. They also feed an industry. So the fishing vessels in the Southern Ocean catch krill for omega-3 supplements for feed on salmon farms and for pet food.

3:38 The international body that manages the fishery is the Commission for the Conservation of Antarctic Marine Living Resources, or the CCAMLR. It's a lot to say. And it set a precautionary ceiling back in 1991. It's called the trigger level, so 620,000 of tons a year. That's as much as they can catch. And for more than three decades, the fisheries never reached it. But in 2005 it did. The fleet hit 620,000 tons by early August, and the season closed months ahead of the schedule for the first time ever. This total isn't only a concern. A rule that spread the catch out across areas lapsed the year before. So in waters in the Antarctic Peninsula, the catches went past 355,000 tons, more than double the old limit for that area.

4:22 These are the same waters where humpbacks and other whales come to feed. Phil Trathan, a longtime Antarctic ecosystem scientist, pointed out that the commission does not have any mechanism in place to monitor baleen whales even though whales likely eat more krill in that area than anything else. Now a fishing fleet goes where krill is densest, and so does a lunge feeder. They are hunting in the same exact swarms. Now, the industry says the closure shows the system is working as designed. They have a quota, they met that quota, they shut it down. And both things can be true. The limit held and the limit was set before anyone knew how much whales could eat. I wanna talk about something that scientists figured out that changes the thinking about all this. In the 20th century, industrial whaling killed somewhere between two and three million whales with most of the krill eaters gone.

5:07 So people expected the Southern Ocean to fill up with krill, but it didn't. Krill numbers seemed to fall instead. In 2021, a team of scientists put tags on 321 whales and measured how much they actually eat. They found baleen whales eat about three times more than older estimates. And when whales eat, they also poop near the surface, where it could act as fertilizers for the ocean. Whale poop is rich in iron, and iron is the nutrient that limits plankton growth in much of the Southern Ocean. So before whaling, the team estimated Southern Ocean whales recycled about 12,000 tons of iron a year. Today, it's around 1,200 tons, about one tenth of that amount. More plankton means more krill. More krill means more food for whales.

5:48 The whales were helping grow the very swarms that they actually ate. Nicholas Pyenson, a Smithsonian scientist on this study, put it this way: "If we restore whale populations to pre-whaling levels, we'll restore the huge amount of lost function to the ocean. Whales play a more important role than we actually think. They help farm their own food. That's the strongest reason to protect swarms they feed on. Now here's an example. South Georgia is a remote island in the South Atlantic, east of the Falkland Islands. In the early 1900s, its waters were full of blue whales, these massive, massive animals. So whaling stations of course, were built on its shores. Between 1904 and 1971, whalers killed 42,698 blue whales off South Georgia.

6:29 Most of them died before the mid-1930s. By the end, the blue whales were gone. From 1998 to 2018, survey after survey recorded exactly one blue whale sighting in those waters. Scientists began to treat South Georgia as the textbook case of a population hunted past the point of return. The lead author of a later study, Susanna Calderon, described it as an iconic example of a population that was locally exploited beyond recovery. Then, in February 2020, a research team went back. In three weeks of surveys, they recorded 58 blue whale sightings. Their underwater microphones picked up blue whale calls again and again. And then they compared photos of 41 blue whales seen around South Georgia over the previous decade with a catalog of 517 known Antarctic blue whales.

7:15 None of them matched. These were new whales finding their way back to feeding grounds their species had used for thousands of years. Now, the return took about 50 years after the last whaling station closed. And it's because whales are slow to recover, and they do recover when they have food and space. But you gotta remember, these are large animals. They don't just reproduce like fish, where, they put out, like, millions of eggs, and then, those get fertilized, they get a higher fecundity, so higher reproduction rate. These whales will, give birth to calves. Those calves have to reach sexual maturity, which takes a long time. They will reproduce. And it takes a long time for these whales to recover because of their slow life history. Antarctic blue whale populations are still a small fraction of what they once were.

7:56 And the krill fishery is legal and is regulated. The question is now is whether the rules keep up with what we know about how much whales eat. And this is not just the fact of these fishers are taking away the krill cause of the whales. It's the fact of, hey, we know these whales actually will produce more krill. When we now know that these whales will produce the food that will help the krill survive, and that will help grow the krill. We keep taking the krill, and we don't allow the whales to recover, then that whole loop, that feedback loop just gets destroyed, And the fact is, like, we don't just have a lack of blue whales happening here. We have other things that are happening. Krill face warming seas, shrinking sea ice which young krill rely on, and the whales can't afford to share the shrinking pantry.

8:41 So the fact is, is your call to action for this episode is skip the krill oil. If you take an omega-3 supplement, choose one that's made from algae. Fish get their omega-3s from eating algae in the first place, so algal-based supplements go straight to the source. If you start to think about how you can get and how you can save the planet, is get away from those types of omega-3 fatty acids and go towards the algae-based ones. It's just the same. You won't even taste the difference, and you'll still get your omega-3 fatty acids. Now every capsule of krill oil starts as a krill swarm. That swarm is, same dense patch a blue whale needs to make its lunge pay off. Most of the krill catch goes to farm fish feed, which is harder for one person to change, but the supplement aisle is the piece you control directly, you can do that even today.

9:29 Next time you buy that supplement, Go towards that algae-based instead of animal-based. So you think about it, in South Georgia we had one sighting in 20 years, then we had 58 in three weeks. These blue whales will recover if we give them time and we get them to have their food. Them having their food equals more krill in the long run, blue whales, lunging into krill swarms in the same waters where their species was nearly erased. This is what is important. They almost got hunted to extinction. The recovery takes a little bit longer. Krill swarms are going down 'cause we are trying to catch them more. We have a quota, but the thing is, is now that the blue whales have been gone, it has been harder to reproduce those krill. They have no food provided for the phytoplankton, which the phytoplankton is food for the krill.

10:11 So the biggest animal that ever lived only needs two things to come back. They need room to swim and a swarm worth opening its mouth for. That's really what it comes down to. Now that's the episode for today. Tomorrow we're gonna follow that whale down a dive and listen to its heartbeat, it does something that no human heart could survive. We're gonna talk about that on next episode. But until then, if you have a question about this episode and you're listening to it on Spotify, hit me in the comments. I would love to hear about that. I check those all the time. As soon as I get a comment, I get an alert, so I'd love to chat back. And of course, if you're listening to this on your favorite podcast app that doesn't allow comments, which is too bad 'cause I really like that feedback area, you can hit me up on my socials. The links are in the show notes. I wanna thank you for watching this episode of the How to Protect the Ocean podcast.

10:52 I'm your host, Andrew Lewin. Have a great day. We'll talk to you tomorrow, and happy conservation.