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Re: Anaerobic Stamina (Was Re: [Terramegathermy in the Time of the Titans (long...)])



From: <archosaur@usa.net>
Sent: Tuesday, April 24, 2001 11:01 AM


> The tests were performed on 7 _C.porosus_ rangin from 0.43-7.0 kg. The
> "excercise" was accomplished by prodding the animal's tails and legs by
hand.
> The result was many repeated, explosive, bursts of energy which continued
for
> 1-2 minutes and then gradually died off until exhaustion was reached at 5
> minutes.

It's important to note that the paper describes these "explosive bursts of
energy" as "bouts". In other words, they are not continuous. Crocodiles
characteristically struggle violently for several seconds, then pause for a
short period that lasts longer than the struggling bout, then struggle
again. Larger animals over 1.5 metres pause for greater periods (often
minutes) between each stuggling bout of perhaps 10 seconds. Even a
struggling bout is not a continuous period of thrashing, but punctuated with
brief pauses of 2 to 3 seconds in which the animal glowers at you menacingly
and does its best to look po'd.


> Animals <1.0 kg struggled for 5 minutes till exhaustion
> Animals  that were between 10-100kg took 10-20 minutes and animals that
were
> >100kg took 30 minutes or more before exhaustion was reached.

In the context of what I say above, this is a bit misleading. Crocs over 100
kg cannot struggle continuously for 30 minutes - that's impossible. The
paper means that they are capable of explosive movements of gradually
shorter duration for up to 30 minutes if being continually stimulated, but
there are pauses between these movements, often several minutes apart.
Essentially, bigger crocodilians have greater anaerobic capacity, but they
also have less anaerobic scope. Baldwin et al 1995 point out a negative
allometric scaling with anaerobic scope in crocodilians, and suggest that
changes in predator-prey interactions and social interactions (ie. short,
sharp bursts of toothy death) mean reduced dependence upon frequent bursts
of anaerobic muscle mass with increasing body mass. If _Deinosuchus_
physiology was analogous, and it might not have been, then this implies that
it was capable of very intense, very short-lived explosive episodes that
could be repeated for a longer period of time.


> Indeed even after all that most of the animals had already shown partial
> recovery 2 hrs later. The only acception was one individual who was still
> highly acidic 4 hours into the recovery period. This croc was exceptional
> though, since it excercised to the greatest amount of exhaustion and wound
up
> with a blood PH of 6.87 immediately after excercise (which later fell to
6.42,
> the lowest blood PH for any known animal).

Very large crocs over 5 metres in length are known to take 24 to 30 hours to
recover from exhaustive exercise. From Seymour et al (1997) (see my previous
email with the citation):

"Recovery from exercise was slow. In general, the first compensatory
response to the acidosis was hyperventilation to reduce the Pco2 and allow
more bicarbonate ions to combine with excess hydrogen ions, thus raising the
pH. This was accompanied by a longer term metabolic compensation as lactic
acid was removed from the blood and either oxidised or recoverted into
glycogen. Large field animals required more than 4 h to recover. In fact one
large animal took about 30 h to recover from a profound acidosis. Two hours
after exercise its blood pH decreased to about 6.4. At 4 and 14 h, it was
still markedly acidotic despite deep breathing that reduced blood Pco2 to
low levels.

Further, they said: "This extremely acidotic crocodile was completely
unresponsive during the first hours of recovery. We have seen other animals
in a similar condition after capture. If they are left on the river bank,
they will not voluntarily enter the water for sometimes over a day. In this
condition, they are very weak but can swim slowly away if forced into the
water. Perhaps these crocodiles are reluctant to enter the water because
they are liable to drown if further harassed."

So be careful - blood acidosis has very serious implications for crocodiles
if it goes beyond a certain point. Recovery time can be extensive for larger
animals. There's a well-known case of a big 5 metre crocodile called
Sweetheart in northern Australia that died from blood acidosis after
extensive struggling during capture. It's pH clearly fell below 6.4. Capture
of very large crocodiles is often assisted with non-depolarising
immobilisation drugs to prevent anaerobic muscle contraction from lowering
the pH to dangerous levels.

Adam Britton