The Belly of the Beast
Blue whales, the biggest animal that has ever lived on earth, feed exclusively on one of the smallest: krill. Cold, deep ocean waters
are home to superabundant populations of these small shrimplike creatures. Individual krill are approximately 2 cm long, but swarms of
these tiny crustaceans can take up hundreds of square kilometers of ocean.
Blue whales dive as deep as 300 m in search of krill swarms, and when they find them, they open their great jaws, allowing their
pleated throats to fill up like sails. A blue whale's throat extends from its chin to its navel, and is made of a stretchy tissue that
can expand to four times its original width. Incredibly, they can fill their throats with a volume of water greater than the volume of
their entire body, according to Jeremy Goldbogen, a PhD student at UBC who studies whale feeding. Once its mouth is full of water and
krill, a blue whale will force the water out through the sieve-like baleen that it has in place of teeth, pushing the water out and
leaving tens or hundreds of kilograms of krill behind in its mouth.
A mature blue whale can eat as much as 4-6 tonnes of krill per day, and must feed for upwards of four hours a day. At approximately
25 m long, these giants are 1250 times larger than their food (krill are ~2 cm long). If we humans ate food so much smaller than we are,
we would eat nothing larger than a grain of sand, ~ 1mm across. No wonder blue whales must eat 40 million krill per day.
