Subject: Do whales drink from the ocean?

Tokitae (
Thu, 8 Jan 1998 21:41:47 -0500 (EST)

At 09:27 PM 1/8/98 -0500, you wrote:
>Do Whales drink the water from the sea and oceans?  My 8th grade daughter
>asked this question to me tonight.  I ask her where this question came from,
>she replied that her science teacher asked the question of them.  I thought
>that we could find it on the web, but we could not.  I found the site ASK
>the scientist so we are asking? please reply ASAP
>Curtis and Clare McMillan

Dear Curtis and Clare,

I'll answer that excellent question by borrowing previous answers by Martine
Berube and Phil Clapham, which can be found in the ASK archives (click on
the button with the big question mark).

Answer: Whales require fresh water just like other mammals.  Because they
live in
the ocean, they have to obtain their water in ways that are different from
most mammals that live on land.  Scientists speculate that mammals that
live in the ocean obtain their water from the food they eat.  Their bodies
appear to be adapted to
absorb salt-free water from the fish, krill, and other organisms they eat.  Some
species might even have mechanisms to take in ocean water and take out the
salt so that their bodies can use the salt-free water for metabolic
purposes.  Scientists are still studying this aspect of whale physiology.

Martine Berube

Good question!  The ability to deal with salt water - and, conversely,
to obtain sufficient fresh water - must have been one of the largest
evolutionary challenges facing whales and dolphins when they were
evolving from their land ancestors around 50 million years ago.

The basic answer is twofold.  First, fresh water is obtained largely
from the whale's food (depending on the species of whale, this is
either fish, krill or small planktonic critters like copepods); this
occurs when the food is metabolized.  The way in which they deal with
intake of salt water is essentially by having highly specialized
kidneys; these are much more efficient than ours at extracting and
eliminating salt.

This is dealt with in detail (technical, but very readably so) in a book
called "Whales" by E.J. Slijper (Cornell University Press), but it's
not easy to find these days.  I'm not aware of any more current books
which illustrate cetacean kidneys and the water issue.

Hope this helps!

Phil Clapham

Howard Garrett
Lolita Project