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 episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
Lauren bolg bomb 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 some prehistoric monstrosity. It's actually the

(00:25):
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 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 even bigger. It's not like they have to

(00:47):
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. Their analysis determined that aquatic mammals actually

(01:09):
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 because they're warm blooded mammals, they have

(01:33):
to be large enough to keep from losing too much
body heat to the surrounding water. Thermoregulation than it keeps
whales from being the size of, say dogs. Study co
author Jonathan Payne, a professor of geological sciences at Stanford's
School of Earth, Energy and Environmental Sciences, explained in a
press statement, when you're very small, you lose heat back

(01:53):
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 that the metabolism of whales only

(02:15):
gets faster as they get bigger, and so they can
only get so large. Another study co author, Craig McLaine
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 they can be. So it boils down

(02:37):
to how much 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 bailean
instead of teeth and strain their food a little shrimp
like creatures called krill instead of chewing it. Krill are
only a few centimeters long, but they really add up.

(02:58):
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
was written by Kristen hall Geisler and produced by Tyler
Clang for iHeart Media and How Stuff Works. For more

(03:20):
on this and lots of other huge topics, visit our
home planet, How stuff Works dot com,