BrainStuff Classics: Why Are Whales Big (But Not Bigger)?

Whales are some of the largest creatures on Earth -- but why? And why aren't they bigger? Learn a whale of a tale about ocean mammals in this classic episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:01):
Welcome to brain Stuff, a production of iHeartRadio. Hey brain Stuff.
I'm Lauren Vogelebomb, and this is a classic episode from
the Vault. Today's classic has to do with whales. They
are seemingly impossibly bigger than any of their cousins that
live on land for a few good reasons. But given those,

(00:23):
why aren't they even bigger? Hey brain stuff? Lauren Voglebomb. Here.
If you've ever been whale watching, visited a large aquarium,
or even seen the skeleton of a whale in a
museum of natural history, you know the majestic massiveness of
these aquatic mammals. The largest mammal to have ever lived
on Earth in the history of the planet is not

(00:44):
some prehistoric monstrosity. It's actually the blue whale, and is
alive right now swimming around in our oceans. Whales range
in size from the massive blue whales, which can grow
to more than ninety feet that's twenty seven meters in length,
to the relatively tiny pigmy sperm whales, which measure a
measly ten feet or three meters in length. But with
all that ocean to swim around in, why aren't whales

(01:07):
even bigger? It's not like they have to support their
big bodies on legs and walk around. For that matter, though,
why aren't they smaller? Both answers have to do with
food and heat. At least that's what researchers at Stanford
University found when they compiled the body mass data for
nearly four thousand living whales and three thousand fossilized species.

(01:28):
Their analysis determined that aquatic mammals actually face more size
constraints than their counterparts on land. The study authors determined
that there are two main factors why whales are big
but not bigger, heat loss and metabolism. Oceans can be
pretty cold places to live, and whales, while very intelligent,
don't really have the aquatic equivalent to thermal underwear. So

(01:52):
because they're warm blooded mammals, they have to be large
enough to keep from losing too much body heat to
the surrounding water thermoregulation. Then it keeps whales from being
the size of, say dogs. Study co author Jonathan Payne,
a professor of geological sciences at Stanford School of Earth,
Energy and Environmental Sciences, explained in a pressed statement, when

(02:13):
you're very small, you lose heat back into the water
so fast there's no way to eat enough food to
keep up. And speaking of eating, whales have to do
it a lot. Like all mammals, they convert that food
into energy for swimming, growing, and doing other whale like things.
That's the metabolic system at work. But the researchers suggest

(02:34):
that the metabolism of whales only gets faster as they
get bigger, and so they can only get so large.
Another study co author, Craig McLain of the Louisiana University's
Marine Consortium, explained it this way. Basically, animals are machines
that require energy to operate. This need for energy places
hard limits on what animals can do and how big

(02:56):
they can be. So it boils down to how much
which whales can eat versus their metabolic rate that keeps
whales from getting infinitely large. But how do those massive
blue whales get so massive? They have bay lean instead
of teeth and strain their food a little shrimp like
creatures called krill instead of chewing it. Krill are only

(03:17):
a few centimeters long, but they really add up. Every
day a blue whale eats about eight thousand pounds. That's
over three thousand, six hundred kilos of krill so blue
whales are not only the largest whales in the ocean,
they're also the most efficient eaters of all. Today's episode

(03:40):
is based on the article why are Whales so Big?
On HowStuffWorks dot com written by Kristin Halgeisler. Brainstuff is
production of iHeartRadio in partnership with how stuffworks dot Com
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