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ANSWER TO BRILLIANT QUESTION:
Dear Greg,
How
did you know we wanted to talk about whales?
The Sperm Whale - Multiple
Record Holder
(see the World
Records box in the left column)
Whales are beautiful, mysterious, and some of them
are really really big. One of the biggest is the sperm whale. I don't know if
you can measure "mysteriousness" but if you could, the sperm whale would
be one of the top contenders.
They spend most of their time in a world that is
more hostile and difficult for humans (and tortoises) to survive in than outer
space. Even on the surface they usually hang out in deep water far from shore.
All of which means they are darn hard to watch and scientists have more questions
than answers about them. Nevertheless, they have managed to get some idea of approximately
how deep some whales can dive. It seems likely from what we know, that of all
the cetaceans, those that go the deepest are the mighty sperm whales.
Mind-Boggling Depths
How deep do they go? And what's so hard about it?
They go deep. Exactly how deep is not certain. But
it's really deep (keep reading, we do have some numbers for you).
Mind-boggling is the best word to describe how deep
they dive. If no one had ever heard of Sperm Whales (or some of the other deep
diving mammals) and you asked any sensible scientist or engineer to design an
air breathing animal to dive several thousand feet into the ocean, they would
tell you to forget it. Can't be done. "Impossible!" they'd shout.
Well, as often happens, no one told the sperm whale
not to go there. So they go, over and over again, every day. How they do it is
wondrous. Let's explore this amazing feat.
(You're still waiting to learn how deep they go? Be patient.)
Diving with a Sperm
Whale
The very idea terrifies me, but let's go on a dive
with a sperm whale.
We start at the surface. Our sperm whale is getting
ready to go hunting. Her hunting grounds are where the squid and other tasty sea
creatures are bountiful - a world where the sun don't shine. Straight
down. Way down. Into total cold crushing blackness.
If our whale has just come up from a dive she first
spends 10 minutes or more clearing her lungs, blowing a breath in and out every
12 seconds. She's getting rid of old carbon dioxide from the last dive and loading
up with fresh oxygen. She's got to store up a lot of oxygen because she will be
holding her breath for the next 45 to 60 minutes. Most of the excess oxygen
for the next dive will be stored in the huge powerful swimming muscles.
Finally our whale is ready to dive. She takes two
more huge gulps of air, points her head down, raises her flukes (tail fins) out
of the water and dives straight down. Now she starts swimming straight for the
bottom. She is swimming steadily (or gliding - new research indicates that many
cetaceans, and other diving marine mammals, glide more than swim when they are
going down) at 3 1/2 miles per hour (5.6 km/hr). This is a fast walking pace for
humans. It is probably the most efficient speed for the whale. It is important
to be efficient now. Swimming too fast would waste oxygen. Too slow would waste
time.
Down and down at 1 and 1/2 meters per second. It
takes over a minute to go as deep as a football field. After 3 long minutes we
are 270 meters (885 feet) below the surface and still a long way to go. It is
getting cold and dark. There is some light down here but not much. I'm wanting
to go back to the surface. There is almost 3 football fields of water above us.
If my calculations are correct the pressure here is 355 pounds per square inch,
or 24 atmospheres. There are over 51,000 pounds pressing on every square foot of
the whale's body.
This is already past the limit that a human diver
breathing air can survive. If his rib cage hasn't collapsed from the pressure,
it soon will. Why doesn't the sperm whale's rib cage collapse? It does. But the
sperm whale's rib cage is designed to fold up and collapse. Also the lungs have
collapsed and the air in the whale's body is squished to one forth of the volume
it was on the surface. The whale's lungs will collapse completely before very
long.
After 3 minutes of not breathing most humans have
passed out and, if they don't start breathing soon, are heading for another existence.
But our sperm whale is just starting.
She continues her journey downward, still going
straight down. Now it is pitch black. No light, except possibly the bioluminescent
glow of some of the deep sea creatures down here. How does she know which way
is up? Echolocation? Or perhaps an unerring sense of gravity we don't have? Humans
(and tortoises) would be hopelessly disorientated and confused.
After five and a half minutes the whale reaches
five hundred meters (1640 feet). Humans can live and work down here but it takes
days of compression to get there and days of decompression to get back. It also
requires a mixture of special gasses. The sperm whale does it over and over again
several times a day. The pressure is now over 700 psi (48 atmospheres).
After eleven minutes of steady swimming straight down,
mostly in complete utter blackness, our whale reaches her happy hunting grounds.
Now she is about 1000 meters (3280 feet or 3/5 of a mile) below the surface. Eleven
football field lengths of water is above us. The pressure is 1421 pounds per square
inch (almost 100 atmospheres). 200,000 pounds (100 tons) of water press on every
square foot of the whale. All the time, day and night, winter and summer, the
water temperature is 2 degrees celsius (36 degrees Farenheit).
This is the typical hunting depth for a sperm whale.
Somewhere between 500 and 1000 meters. For the next 20 to 40 minutes our whale
will stay down here in the dark and cold, hunting and eating. There are many unanswered
mysteries about what goes on down here, but alas, we must save them for another
article.
At this depth the air in the whale's body is one
percent of its original volume, and it is 100 times more dense.
Finally a Maximum
Depth - Sort Of, Maybe
Is this as deep as they can go? Hec no.
No one knows how deep they can go. We found a lot
of different maximum depths listed at different web sites (be careful when you
are surfing for "fast facts" - not everyone is as careful as we are
- and even we make mistakes - at least check several sources - and books and libraries
are still an important part of learning). The most reputable source told us that
submarine sonar readings have documented sperm whales at 2500 meters (8200 feet
or 27.3 football fields or 1.6 miles below the surface)! There were even deeper
depths claimed at a couple of web sites, but we are inclined to be suspicious
of those.
So our answer to how deep a sperm whale can dive is about
2500 meters - maybe. But no one really knows. Who knows what a sperm whale
could do if it was really trying?
Back to the Surface
After spending 20 or 30 minutes catching and somehow
swallowing a lot of fish and squid, our whale, still holding her breath, heads
back for the surface. She could probably stay significantly longer, but the longer
she stays down, the longer she will have to recover on the surface.
She swims back up at about the same speed she came
down, so it takes another 11 minutes or so. The deeper the dive, the longer it
would take to get there and back. It would take over 27 minutes to reach 2500
meters (where the pressure is over 3500 psi).
Is this another factor that limits how deep a sperm
whale can practically dive? There must be a point of diminishing returns. The
longer it takes to get to the tasty hunting grounds, the less time is available
for hunting. A typical dive lasts 60 minutes. No one knows how long a sperm whale
can hold its breath but estimates range from 90 minutes to 2 hours.
What must it feel like to rise toward the
surface. She can feel her body getting lighter, feel the pressure change from
100 atmospheres to 1 atmosphere, see the light coming (does it hurt her eyes),
feel the air in her nasal passages and lungs expand to 100 times the volume it
was at depth, and then, finally after an hour, she bursts to the surface and blows
out all that old air, rich in carbon dioxide, followed by a huge gasp of fresh
oxygen rich sea air. Is it a great relief? Or does she hardly notice? Just another
day at the office.
If a human spends much time diving at high pressure
the tissues in his body become saturated with gas kept compressed and dense by
the high pressure. If the diver comes to the surface too fast, the gas forms bubbles
in the body which can cause serious harm and even death. This unpleasant condition
is known as "the bends". To prevent this, human divers have
to decompress very slowly after a deep dive. The decompression process after a
deep dive can take days. Sperm whales go down to much deeper depths and back up
several times a day. Some of the mechanisms that they use to avoid this problem
are understood, some are not. (One big factor in the whale's favor is that they
are holding their breath while human divers are breathing compressed air. Record
holding deep diving humans, holding their breath and being pulled down quickly
by weighted "sleds", have shown they can go deeper than scientists had
previously thought possible. But that is a good subject for another page.)
There are many adaptations that we know sperm whales
have made to allow them to dive to such remarkable depths. There are probably
many other adaptations scientists have not even guessed yet.
More Dr G on Whales:
Whale Bones
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Dr. Galapagos in his fabulous Single-Tortoise Copter
