Subject: Drink--Water absorbed

Michael Williamson (pita@whale.simmons.edu)
Tue, 22 Oct 1996 18:36:57 -0400 (EDT)

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---------- Forwarded message ----------
Date: 18 Oct 96 14:12 EST
From: CLAPHAM.PHIL@SIMNH.SI.EDU
To: "CAW1@CALLER.INFI.NET"@SIVM.SI.EDU,
    "G.ask [Private Mail Group]"@SIMNH.SI.EDU
Subject: Copy of: (NO SUBJECT)

Original message: "(NO SUBJECT)"
From: <<caw1@caller.infi.net>>

My six year old has developed an keen interest in whales and has asked me 
a question I have no certain answer for.

How does a whale drink or absorb water when it lives in the ocean?

My own guess is that they absorb water through their intestines, but if 
there is a specific organ to do this function which book will have the 
best illistration for him?

Thank you.
C. Wheeler

Hi:

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.

I can't think of a good illustration for your son, I'm afraid.  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