JUST
THE
FACTS, PLEASE
. . .
Let's face it, any animal that grows to be nearly 20 feet long
and weighing 5000 lbs. with teeth as sharp as my mom's best steak
knife would be pretty frightening almost any way you look at it.
However, as regular viewers of the Discovery Channel can well attest
to, the shark of fact is not really the shark of fiction . . . but
it's pretty darn close!
While what follows is
certainly not a complete picture of the great white shark (hereafter
known as the GW to save typing!), it represents a collection of
answers to questions commonly asked about the shark.
TALES
OF THE PASTA
SHARK
Let's start from the top.
In the beginning, Carolus Linnaeus (1707 - 1778), the author of the
taxonomic system for naming all living things, grouped all sharks
together in the genus Squalus giving the GW its original
designation as Squalus carcharias. It was Sir Andrew
Smith who suggested the genus Carcharodon in 1838 but it took
40 years of customary scientific bickering to settle on the now
familar Carcharodon carcharias. This comes from the
Greek words carcharos, meaning "ragged," and odon
for "tooth." For the record, among the "losing"
species names were lamia, atwoodi & rondeletti. Thankfully,
the latter didn't stick or my favorite animal would probably be known
as the 'pasta shark' today! Just imagine what 'Jaws' would have been
like: "This was no boating accident . . . it was a pasta shark!"
Scientific names are useful as the
GW is known by many different names the world over. Here's a quick breakdown
of some of them and the country of origin.
|
Germany |
Weisshai |
| France |
grand requin blanc |
| Italy |
grande squalo bianco |
| Spain |
tiburon blanco |
| Australia |
white pointer, white
death |
| Russia |
seldevaja akula |
| Japan |
hohojirozame |
However, the scientific name is
always the same.
IT
WAS HOW
BIG??
The size of the GW is of great
interest to not only the general public but also to marine biologists. It is
not known how large the GW gets but a top size of approximately 7 meters
(approx. 21 feet) is the most often quoted figure. How long is this? Picture a
couple of Hondas parked in a row and then picture a shark as long as the two
cars with a mouth about 3-4 feet wide and you've got a pretty good idea. The
average GW is not nearly as large being only about 10-15 feet in length.
However, this is still longer than my Outback . . . which is big enough for me!
A SKELETON
MADE
OF NOSES
AND EARLOBES
Like all sharks, the GW's
skeleton is composed of cartilage. This stiff flexible material is found
in the ridge of your nose and also in your earlobes. While not are hard
as bone, cartilage is still quite rigid. Because
cartilage does not leave fossil remains like bone, we do not have any
fossils of ancient sharks - just their teeth!
WHO
ORDERED
THE
SEAL?
The GW is an apex
predator meaning that it is at the top of the food chain with
no natural predators. The Great White is the only Apex predator today that has not been kept or tamed by man and it should remain that way! This means that they have their pick of the buffet
table when it comes to selecting their prey. It seems that they are not
picky, choosing fish, squids, other sharks, dolphins, &
whales. Their favorite prey, however, are pinnipeds, a fancy name for
seals & sea lions. They feed on carcasses as well, especially large
whales.
OLD
JAWS
LIVED
A LONG
HEALTHY
LIFE
No one knows accurately how
long the lifespan of the GW is and the sharks themselves aren't making
it any easier for us to find out. The GW population is quite isolated
from one fish to the next. In addition, the sharks are highly migratory,
moving from one spot to the next over a vast area. This makes it
impossible for scientists to pick one fish and follow it for a long
period of time to gather the data necessary to answer this
question.
Scientists have been
observing GW's off the coast of the Farallon Islands near San Francisco
for several years, identifying individual animals by scars and
coloration markings. One such animal, nicknamed 'Stumpy' because the top
portion of her caudal (tail) fin has been bitten off, has
or had been observed returning to the islands each fall to feed on seals
for several years. In addition, examining growth patterns of
sharks caught off the California coast revealed that they were approx.
14-15 years old. This indicates a lifespan of 20 or so years is
not unrealistic.
WHAT
BIG
AMPULLAE
OF LORENZINI
YOU
HAVE,
GRANDMA
. . .
The better to sense your
electrical field, my dear little Red Riding Hood! The GW is equipped
with two of the most powerful sensing mechanisms in Nature, a highly
developed sense of "smell" and the ability to sense the
electrical fields radiating from living creatures.
|
|
As anyone familiar with
the 'Jaws' movie posters can tell you, GW's have a pair of
nostrils near the tip of their snout. Since "breathing"
takes place in the gills, the nostrils of a shark are used solely
for olfactory purposes - to sniff out their prey.
Each nostril is divided by a small skin flap that separates the
water the shark is swimming through into two flows, one incoming
and one outgoing. This flow passes through an area that contains a
large number of small sensory organs known as lamellae. These
lamellae are shaped like tiny flower petals and are in turn
covered with millions of olfactory cells. These cells are in turn
directly connected to the center of the brain responsible for
detecting odors, turning the shark into a swimming nose. |
| The second system is the
more specialized of the two and warrants a closer look due to its
unusual nature. Notice in this picture the large number of tiny
black dots marking the snout of the GW. These pore-like markings
are the ampullae of Lorenzini, the secret weapon in
the GW's arsenal of predation. Each is a minute capsule
filled with a gel-like substance excreted by the shark, sensitive
to electrical discharges as small as .005 microvolts. Dr. John
McCosker and Richard Ellis point out in their book 'The Great
White Shark' that these ampullae collectively give the GW the
ability to sense the electrical field distributed by a copper wire
1000 miles long hooked up to a D-sized battery! This amazing
sensitivity is due to both the large number of ampullae present
and also the fact that like the lamellae, each ampulla utilizes a
large number of sensory cells to "pick up" the signal.
These sensory cells lie inside alveoli, small sacs
within each ampulla which are in turn connected directly to the
brain of the shark - no muss, no fuss . . . just a straight signal
to Eating Central that prey lies dead ahead, if you'll excuse the
pun.
So what good does a built-in
electrical field detection system do the GW? Plenty, it turns out.
Every creature in the briny blue generates a small electrical
field from where their skin meets the water. The mucous
membranes that coat the mouth and gills of fish also create steady
current fields which are affected by their breathing patterns.
Furthermore, a wounded animal bleeds, producing yet another set of
electrical information. By honing in on this information, the GW
can detect and distinguish between prey items who are swimming
along peacefully, who are moving quickly about in a panic, and
better yet, who might be bleeding and incapacitated - making them
a hassle-free lunch.
|
|
In summary, these two sensory
packages, the nasal lamellae and the ampullae of Lorenzini, have evolved over
millions of years into detection systems for the very things that make prey
more attractive to our friend the GW - blood, indicating animals that are
injured and thus easier to catch and movement, telling the GW both where their
prey is and what state it might be in when the shark catches it.
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