How Whales Got Whale-Sized
We live in a time of giants. Whales are both the largest living animals, and, in the case of 110-foot-long blue whales, the largest animals that have ever been alive on the planet.
But whales haven’t always been gigantic. Until about 3 million years ago, the fossil record shows that the average whale length was only about 20 feet long. They were big, but not big. The rise—and growth—of the lineages that gave rise to humpbacks, fin whales, and other behemoths happened, in evolutionary time, overnight.
So, why are whales big—and why are whales so big now?
Biologists speculate this change occurred because of food. After all, 3 million years ago, the oceans also gave rise to an abundance of the kind of prey that big baleen whales are perfectly suited to feast on.
But what about toothed whales, which must dive to find high-calorie prey like seals and squid? Is their size—which is generally smaller than baleen whales, except in the case of sperm whales—equally determined by their food?
Now, researchers who parsed data from feeding events of a dozen different whale species think they have the mathematical confirmation. Writing in Science this week, they say baleen whales, who become more energy-efficient as they grow, benefit from bigness because it lets them migrate to food sources that appear and disappear at different points around the globe.
Meanwhile, they say, deep-diving toothed whales are limited by the availability of large prey. The largest toothed whales, sperm whales, which could thrive on a diet of giant squid, are operating at borderline energy efficiency because it’s easier for them to hunt less nourishing but more abundant medium-sized squid.
Study co-author Jeremy Goldbogen, a marine biologist for Stanford University’s Hopkins Marine Station, explains the delicate balance of energy and size for giant mammals, and why bigness is such a compelling biological question.
Jeremy Goldbogen is an assistant professor of Biology at Stanford University Hopkins Marine Station in Pacific Grove, California.
IRA FLATOW: This is Science Friday. I’m Ira Flatos– Flatow, I got my own name wrong. Why are whales so big? I mean, ever wonder about that? It is a serious science question, though. Why would an animal need to be a particular size, and is being big worth the cost in food and energy? I mean, your 100 foot long, 100,000 pound average blue whale needs to keep a lot of cells fed, hydrated, oxygenated, and warm. Plus, you have to move all of that mass around the ocean. So being big take takes work.
And yet, we live in an age of marine giants. You have your blue whale down to the minke, all bigger than the largest living land animal. Why are these whales so big? And OK, if they’re this big, why aren’t they bigger? Well, dozens of scientists have been working for almost 10 years and they’ve been doing the math on one possible explanation. And it has to do with food sources. And in new research published in Science this week, they suggest that for baleen whales, getting big was the best way to take advantage of the ocean’s massive clumps of tiny Krill. Meanwhile, tooth whales, who dive and hunt individual animals, have a finer balance between calories in, calories out, which could explain why they are generally smaller.
Here with more on the biology of big is Dr. Jeremy Goldbogen, assistant professor of biology at Stanford University’s Hopkins Marine Lab. He joins us from the studios of KAZU in Monterey, California. Welcome to Science Friday.
JEREMY GOLDBOGEN: Hi, Ira. Happy to be here.
IRA FLATOW: Nice to have you. So can you answer for me what makes, why is an animal so big, a scientific question and not just a philosophical one?
JEREMY GOLDBOGEN: Yeah, physiologists have long been fascinated by large baleen whales, principally because they’re so big, and as a comparative physiologist who’s interested in how animals function, how they work, how they interact with their environment, blue whales really create a sense of wonder trying to understand how life operates at the upper house dream of body mass. What is the pace of life and what is it like to be so big?
IRA FLATOW: Was there a time in whale history where they were not this big and over time they’ve evolved into bigger creatures?
JEREMY GOLDBOGEN: Yeah that’s– and I tell my students about this a lot, is that we’re living in a time of giants. So if you look at the fossil record, you really don’t see anything that’s larger than today’s baleen whales. And what’s really interesting is they got big very recently, only in the last about 5 million years. And so they went from about maximum size of about 10 meters in length up to the ocean giants that we see today for humpback whales, fin whales, and blue whales. And that’s at least a doubling in length, but remember that doubling in length really results in a tremendous amount of weight gain.
And especially for something like a humpback whale, that’s very girthy per unit length. That’s a lot of body mass that these animals have evolved very recently.
IRA FLATOW: And even the smaller whales have nothing to sneeze at, right. The minke whales are pretty big.
JEREMY GOLDBOGEN: Oh, Yeah, certainly. It’s definitely elephant sized if not a little bit bigger.
IRA FLATOW: All right, let’s talk about how they got big, why they’re big, can they get bigger? Let’s begin with the theory that food and the cost of acquiring. It might be the answer to how whales got so big. You’ve been investigating that theory for years, right?
JEREMY GOLDBOGEN: Yeah that’s another thing that’s so fascinating is that these animals are so big you can’t have them in the lab. A lot of them occur in these offshore environments. So they really eluded our ability to measure just about anything. So there’s a lot of gaps in our knowledge. We just don’t understand basic aspects of their biology. But they’re a field that has now really come on the scene as a field, we now refer to as biologging.
So we basically have these small computers that we attach to whales using suction cups. So they’re non-invasive, they give us a really rich picture of what these whales are doing underwater. We know when and where they feed. We know how often they feed. We now have cameras in these tags. So it’s like watching whale TV, it’s really fascinating.
So I like to call these daily diaries. And so it’s sort of a digital form of Natural History and it’s really an amazing tool, not only to share with the public, but also allows us to test a lot of age old questions like why are whales big and why they aren’t bigger.
IRA FLATOW: Well, I want to get to that in a minute. But I want to talk about something you have talked about, and that is the huge difference between the whales that have teeth and the filter feeders like the blue whales. Give us an idea of how much energy– why did they feed on different things and how does that allow them to survive?
JEREMY GOLDBOGEN: Yeah, so that the two great clades of whales, toothed whales, which in our study we had tagged data from very small Harbor porpoise, which you could pretty much hold in your arms, up to sperm whales of course, which are the largest tooth whales. And they feed on single prey. So one prey item at a time using echolocation. And that contrasts with baleen whales, of course, which have no teeth. They use a filter inside the mouth. Using these baleen plates and fringes on the inside of those plates that act as a filter to filter volumes of water that have very small prey like Krill suspended in that water column.
And so what’s interesting is that– and this was really unexpected– is that if you look at the stomach contents for these different tooth whale species, what you find is that the size of the prey item that you can reconstruct using these small bits of anatomy that are left over after digestion. So a lot of these deep diving tooth whales feed on squid. And you get these beaks that are left inside the stomachs. And so depending on the beak, the anatomy of it and the size of that beak, you can actually reconstruct the size of the prey item.
And so we use that data in order to reconstruct these energy budgets for different whale species across scale. So what’s fascinating, and I’m sure everyone’s probably heard of sperm whales feeding on giant squid, but it turns out, if you look at the data, the giant squid are very rare in the stomachs of these animals. And much more frequently, tooth whales, especially the large tooth whales, are feeding on say small or medium sized squid. But they’re feeding on them much more frequently.
So for example, these large tooth whales, in particular, beaked whales and sperm whales, they’ve evolved these incredible diving capacities. So several of these species can dive for more than an hour. They can dive as deep as a kilometer deep into the ocean. And that allows them to find really reliable hot spots of these medium sized squid. And they can feed up to 40 or 50 times per dive. And so that’s their solution to supporting their large body size.
But there is a problem with that. If you’re limited by feeding on one single squid at a time, your ability to support larger and larger body sizes becomes really constrained. And that’s what we found. We found that because there is a lack of large squid, the energetic efficiency– and by that I mean, the energy in that they get from all the food that they eat during a dive, divided by the energy out, which is all the exercise and the resting metabolism– that starts to decrease when you get to the size of a sperm whale. And we think it’s because there’s this constraint that’s imposed because there just aren’t enough large, giant squid to go around.
IRA FLATOW: And that’s why they’re really giant whales then don’t feed that way? They go to be the filter feeders?
JEREMY GOLDBOGEN: Yeah, absolutely. So if you’re a filter feeder, large body size then becomes a tremendous advantage. And the large filter feeders are fascinating because they have the specialized anatomy that allows them to be, basically, feeding machines. They have this enormous feeding pouch that’s highly extensible. And the feeding pouch is roughly half the size of the animal. And it inflates with water and food as they take a single gulp of water.
For something like the blue whale, which could easily be 100 metric tons in body mass, they are practically doubling the size of their body because they’re engulfing a volume of water and Krill that’s larger than their own body.
IRA FLATOW: Wow.
JEREMY GOLDBOGEN: So because of that, because of that specialized mechanism to filter feed in this tremendous, what we call engulfment capacity, they can get a tremendous amount of food per feeding event. And because smaller animals like Krill are much more abundant than, say, very large, giant squid, the limitation really doesn’t appear to be there, at least in terms of these very productive summer months where baleen whales can be found in feeding very intensely all day long.
IRA FLATOW: So you’re saying that the whales relatively, I mean, three million years, grew to such enormous sizes. And you say there’s really no limit to the size that the baleen whales can grow to. Could we expect them to get bigger over time?
JEREMY GOLDBOGEN: Oh, yeah. That’s the next question that I I’m really fascinated by is, are we looking at a snapshot in time where large baleen whales are in the process of evolving even greater body sizes? Because it’s only been a few million years. So it’s pretty amazing that they’ve evolved that body size so quickly. And I think that’s another reason why it’s important to study these animals get this basic data so we can ensure that we can conserve these animals and make sure our kids and their grandkids can see and enjoy these amazing animals.
IRA FLATOW: Speaking of which, conserving the future, is climate change and the crisis in the climate affecting the oceans? Is that possibly going to affect the future of the baleen whales and all the whales?
JEREMY GOLDBOGEN: I think that’s a good question. I don’t think there’s great data to say one way or another, whether we’re going to have winners and losers among the great whales. I’m hopeful because I’ve seen that a lot of these species have very flexible foraging strategies, like humpback whales seem to be doing very well. They can feed on a lot of different prey. It appears that they can switch between Krill feeding and fish feeding, for example.
But it also might be a hard time to be a large whale in an urban ocean ecosystem. There are cargo ships that go pretty fast, they’re very loud. Maybe they can mask the calls between individual whales. Maybe whales might get hit by ships, maybe they get entangled in fishing gear. So there are some threats that I think we need to make sure we can measure their impacts. But I’m pretty hopeful that a lot of these species will do pretty well in the future.
IRA FLATOW: You know, everything you talked about is how fascinating these big creatures are, these big whales. And one of the most fascinating parts I found about one of the papers that you recently published was that the heart rate of the blue whales is really, really slow. How slow is–
JEREMY GOLDBOGEN: Yeah, well what was amazing about that paper and we were just amazed that this worked at all, so basically we had a very similar tag. So a suction cup attached tags, so there’s four suction cups that hold this little computer to the whale’s body. And in two of those suction cups, we had surface electrodes similar to what you might have in the doctor’s office. And just from those two electrodes alone, and when we got the tag in just the right place on the left side of a blue whale’s body, just behind the left flipper, we were able to detect and measure heart rate.
And what was really fascinating is when those blue whales were diving to depth, this is about a 10 to 15 minute dive, diving to about 100 to 200 meters in depth, and then feeding, what was really fascinating is that they drop their heart rate down to about two beats per minute. So that’s an incredibly low.
IRA FLATOW: Two beats per minute, not per second?
JEREMY GOLDBOGEN: Yeah, absolutely. What was more fascinating is when they take this big gulp of water, it’s a very expensive behavior. I mean, if you just think about the physics of that– accelerating the high speed, going up to about 5 meters per second, lowering their jaws at high speed, there’s a lot of drag involved. They decelerate as they’re inflating this pouch. So there’s a lot of energy that’s required.
And even though when they took that gulp of water, they did raise the heart rate from that low bottom of two beats per minute a little bit, so they doubled it up to about four to five beats per minute, but it’s still stayed very low. But what’s even more fascinating than that is what happened at the sea surface. So when they go back up to the sea surface they take a series of breaths. So they’re reloading their oxygen stores. The heart rate then goes all the way up to about 35, 36, 37 beats per minute. So that’s a pretty big range if you just think about the range.
But also when we looked at the duration of the heartbeat itself, it was almost two seconds in duration. So it appears that the heart rate is at maximum.
IRA FLATOW: Let me just drop in and say I’m Ira Flatow. This is Science Friday from WNYC Studios.
JEREMY GOLDBOGEN: And that’s a maximum heart rate during routine forging behavior. And this is something blue whales do all day long, they do these deep dives. They go back up to the surface. As soon as they’re done taking about 10 breaths, they go back down, they keep feeding. So that begs the question, are these animals at some type of physiological extreme? Are they at the biggest they can be? How can you make a circulatory system and a heart that can meet these types of energetic demands?
IRA FLATOW: And I would also say, knowing from work we’ve talked about with whales on land– I mean with the elephants on land, we know there’s a size on land where you as you grow exponentially, right? And you can’t get rid of your heat well enough. So there’s a limit. Is there a limit in the ocean? I would think the water dissipates the heat so well, you can get much bigger.
JEREMY GOLDBOGEN: Yeah, my guess is that the heat constraints may not be as much of a problem compared to terrestrial animals because well, large, large whales still have blubber. So it appears they still need to have that blubber in order to retain heat. But also what’s really fascinating is that a lot of marine mammals are well known to have thermal windows. So they can basically dedicate some blood flow to an extremity like a flipper or a fluke and they can basically dump heat that way. Or they can constrict flow to that surface as well if they don’t want to dump that heat.
So I think they have some specialized mechanisms that allow them to thermoregulate, whether they need to dump heat or whether they need to keep that heat in. So my guess is there are ways around some of those constraints. But indeed, as you get bigger, your surface area relative to your volume certainly is an interesting question.
IRA FLATOW: I’ve got about less than a minute. I want to know what one main question you still haven’t answered is.
JEREMY GOLDBOGEN: Oh, how do whales find food, I think is the– maybe it’s a $10 million question at this point. It’s really fascinating. And so, for example, blue whales will migrate across the ocean and somehow find these really dense patches of Krill. Is it a memory based process? Can they– perhaps can they smell where the food is? Dimethyl sulfide has been implicated and being associated with a lot of these Krill resources. Maybe they just it’s trial and error, who knows. So I think that’s the next big question.
IRA FLATOW: Thank you very much. Fascinating stuff about the whales. Dr. Jeremy Goldbogen is Assistant Professor of biology at Stanford University’s Hopkins Marine Lab. He joins us from the studios of KAZU in Monterey, California.