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LatestPhoto
A blue whale.
Photo: Chris Johnson

March 15, 2002
Why are blue whales so big and so loud?
  Real Audio
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Log Transcript

This is Roger Payne speaking to you from the Odyssey

We are moving South down the coast of Australia into ever colder waters as we head for the sperm whales once caught by the whaling station in Albany, Western Australia. This is also our first entrance into the Southern Ocean.

I ended my last log by asking what it is that has driven baleen whales like the giant blue and fin whales to be so large. That is to say: why do baleen whales look like baleen whales? What are the forces that designed them to be so big, to carry tons of blubber on their bodies, and to emit the loudest, lowest sounds made by any animal on earth?

I believe that it was (and still is) their main prey-the tiny shrimp called krill. Because, I believe, that it was only by being very large that these whales could gain access to the greatest food blooms, the most abundant, concentrated, renewable animal protein source on earth-the annual summer mating swarms of krill in the Antarctic and Arctic oceans.

It is only when krill are concentrated into their huge mating swarms that whales gain access them. At other times of year, the krill are too spread out to be worth any whale's effort to collect them. Of course, from the krill's standpoint, spreading out is therefore a great means of starving out predators (to say nothing of avoiding competition with other krill for food). Spreading out can also save Krill from letting populations of their other predators get too large-species like seals, sealions, fish, penguins, and several kinds of flying seabirds. Such predators cannot feed exclusively, or even principally on krill the way whales can, because they cannot starve as long as a whale, and their populations are therefore limited by the need to find other prey besides krill to eat during the majority of the year when the krill are too spread out to bother with. But this predator avoidance strategy of krill doesn't work on the largest baleen whales because they are masters of fasting (it has been calculated that they can starve for over a year-a longer period than any other non-hibernating mammal). Thus whales can wait patiently for eight months or more until the krill start their mating swarms again and the whales can once again feast abundantly.

I theorize that if you are a mammal and want to be able to find and feed on krill you have to be able to fast for months at a time while you wait for the krill swarms to reappear; you also have to be a strong swimmer (meaning you need to keep your muscles warm); and, you have to have a fully functioning brain, so as to find your prey and pursue it with enough skill to catch it. The main trouble is that these last two requirements force you to be warm blooded, and that requirement doesn't fit very well with being able to fast for months at a time, since to do that you will need to keep your metabolism going. And that requires more food than you can store. An animal with cold muscles swims more slowly, and its cold brain limits its behavior. While its brain is cool it is probably functionally blind and scarcely able to hear. Before it can perceive very well, or flee, or attack, or retreat, or stand and fight, it must warm up its brain enough to process information faster. The owner of a warm brain and warm muscles can at all times see and hear and swim and manoeuvre fast enough to pursue prey or run away at a moment's notice-and do so at any hour of the day or night.

The fastest fish-tuna, billfish, and sharks) aren't entirely cold blooded they maintain a warm body core temperature and keep their brain and muscles working well enough to swim and maneuver faster than their cold-blooded prey. After long dives into deep, cold water such predators have to return to warmer surface waters; some species even sun-bathe at the surface for minutes or hours at a time, getting ready for their next descent to where their prey lies, awaiting its slower-witted, slower-moving, colder-blooded fate.

The requirement of being warm blooded would seem to make it impossible for a mammal to reach and harvest krill in polar seas-since those krill are living in an impregnable fortress: ice water, at the ends of the earth, where staying warm while immersed is simply not feasible for a warm-blooded mammal.

Or is it?

Simply by being large an animal like a whale can take advantage of a simple but little-appreciated fact: the fact that the larger an animal's body, the smaller is its surface area in relation to the volume of that body. The reason this is important is that the volume of any animal's body is its furnace-the place where its metabolism generates heat, while the surfaces of its trunk, head, and limbs are its radiators, the things through which heat is lost. Tiny mammals, like mice, have relatively huge surfaces for their small volumes; which means that they have small furnaces and large radiators and therefore have to produce lots of heat to keep from cooling down. But large animals have relatively small surfaces for their large volumes-they have a large furnace and small radiators. That means that their problem is not losing heat but keeping from overheating-particularly when they exercise.

LatestPhoto
A blue whale feeding.
Photo: Doc Watson

Contrary to popular belief, blubber is not principally for keeping warm but for fuel storage. Since the problem big whales have is not staying warm but avoiding overheating, the blubber is not evenly spread over their bodies; it is concentrated in particular zones-just as the fuel on this boat isn't found in all spaces but in specific fuel tanks placed in a few areas of the hull. It is Blubber that fuels whales throughout their long fasts-fasts that can probably last up to a year or more.

Thus, simply by being big, baleen whales end up with a high body temperature even in ice water where krill live without needing to have a high metabolism that would use up all their blubber and cause them to starve to death or need to hibernate before their prey started to reconvene in its enormous swarms.

Once whales had adapted to the point where they were able to bide their time awaiting the reappearance of krill concentrations, the krill had to evolve countermeasures. One such countermeasure is that mating swarms of krill convene in unpredictable places-sometimes swarming hundreds of miles away from where there were major swarms last year. I believe that the whales' response to this is to spread out over vast areas and when one of them encounters a large krill concentration to announce that find for the benefit of its relatives and herd mates. Evolution will only select for such an altruistic act if it is reciprocated by the beneficiary and thereby turns into reciprocal altruism (you know; you help me, and I return the favor). It makes sense to announce the find of a huge krill swarm that you cannot possibly eat by yourself (some are too large for the largest whales, or even thousands of the largest whales to eat alone). By sharing such information, you can expect to get help in later years (when you yourself, may be starving-the exchange of favors is called reciprocal altruism.

Blue and fin whales make the loudest sounds known for any animal species. Their low-frequency calls carry for hundreds, even thousands of miles underwater at useful intensities. Although it has not been demonstrated that whales use such sounds to share information on food finds I find it hard to see how evolution could overlook such a function since the sounds carry so far in the seas, and are emitted at a frequency that travels particularly well through icy seas-a place where they feed but do not, apparently, breed.

I believe that blue and fin whales probably cooperate in widely scattered societies that are held together by calls carrying hundreds of miles. I further believe that these societies exist for the purpose not just of their members finding one another but also for sharing information on food finds, and that they are probably maintained by reciprocal altruism. If this turns out to be so, then the entire social structure of blue whales' lives may simply be a consequence of the strategies they must employ in order to find krill.

Therefore, in summary: the great size of their bodies, their blubber fuel supply, their loud voices, and the very fabric of blue and fin whale social structure may have been shaped by the predator-avoidance mechanisms of their principle prey-krill. In other words it is krill that forced baleen whales to look like baleen whales.

This is Roger Payne wishing you a good dinner-and that you don't have to wait 8 months to get it.

Log by Roger Payne

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