Subject: abstract - hypothermia and diving(fwd)

Mike Williamson (pita@www1.wheelock.edu)
Sun, 12 Oct 1997 15:57:20 -0400 (EDT) 

---------- Forwarded message ----------
Date: Thu, 9 Oct 1997 10:37:30 -0400
From: Dagmar Fertl <Dagmar_Fertl@mms.gov>
Reply-To: Marine Mammals Research and Conservation Discussion
     <MARMAM@UVVM.UVIC.CA>
To: MARMAM@UVVM.UVIC.CA
Subject: abstract - hypothermia

     The following is an abstract of an article that appeared this summer
     in _Nature_ that is about penguins primarily, but talks about diving
     ability also in marine mammals, and thus might be of interest to some
     of you.

     Handrich, Y., R.M. Bevan, J.-B. Charrassin, P.J. Butler, K Putz, A.J.
     Woakes, J. Lage, and Y.Le. Maho.  1997.  Hypothermia in foraging king
     penguins.  Nature 388: 64-67.


     The ability to dive for long periods increases with body size, but
     relative to the best human divers, marine birds and mammals of similar
     or even smaller sizes are outstanding performers.  Most trained human
     divers can reach a little over 100 m in a single-breath dive lasting
     for 4 min, but king and emperor penguins (weighing about 12 and 30 kg,
     respectively) can dive to depths of 304 and 534 m for as long as 7.5
     and 15.8 min, respectively.  On the basis of their assumed metabolic
     rates, up to half of the dive durations were believed to exceed the
     aerobic dive limit, which is the time of submergence before all the
     oxygen stored in the body has been used up.  But in penguins and many
     diving mammals, the short surface intervals between dives are not
     consistent with the recovery times associated with a switch to
     anaerobic metabolism.  We show here that the abdominal temperature of
     king penguins may fall to as low as 11 degrees Celsius during
     sustained deep diving.  As these temperatures may be 10 to 20 degrees
     Celsius below stomach temperature, cold ingested food cannot be the
     only cause of abdominal cooling.  Thus, the slower metabolism of
     cooler tissues resulting from physiological adjustments associated
     with diving _per se_, could at least partially explain why penguins
     and possibly marine mammals can dive for such long durations.