“And what did you say the name
of this shark is?”-Mayor Vaughn
“It's a Carcharodon carcharias. It's a Great White!”-HooperThe Great White Shark |
When
they do attack, sharks make quite a scene!
Of all the exaggerations in Jaws, the depiction of what a shark attack
looks like straddles the line of truth. Sharks
do most of their hunting in areas where their prey enter or exit the water,
where there is a greater chance of ambush.
This usually means they are close to shore; in fact, most attacks happen
25-450 meters from land (not 10 feet, as Hooper states in the movie). Attacks begin either underwater, resulting in
a huge pool of blood in the vicinity, or with an explosive splash as the shark
hits its target. This can be
accomplished with the shark remaining underwater. After this, the rest of the attack can
usually be observed from the surface of the water. Great white sharks do swim back and forth at
high speeds carrying dying prey, like the first traumatic (yet slightly
overdone) attack seen in the movie.
However, contrary to the movie, the prey cannot usually be seen from the
surface because they are held in the jaws of the animal as it swims.
Great white sharks are mainly solitary creatures. They will approach each other when mating and
after a kill, but in the case of the latter are often warned away by a violent
tail slap against the water. If this
does not work, they will fight. When no prey
is present in the water, they are for the most part ambivalent towards one
another. They also do most of their
hunting during the day, indicated by observational studies and the fact that
the retina of a great white has a high density of cones and a reduced number of
rods. Cones and rods are photoreceptors
that allow us to see light. Cones are
used for daytime, color vision, and rods pick up shades of grey, black, and
white and are often very concentrated in organisms that are active at night.
Attack patterns of the great white shark |
There is little evidence of territoriality in sharks, at
least in the sense of them being protective over their own area and keeping
other great whites out. They do exhibit
Hooper’s version of territoriality (see quote below), moving with food
availability that corresponds to water temperature and breeding seasons of the
prey (juveniles are easier to catch).
“It's called "territoriality". It's just a theory that I happen to... agree with.”-Hooper
“Well, this is not a boat accident! And it wasn't any propeller; and it wasn't any coral reef; and it wasn't Jack the Ripper! It was a shark.”- Hooper
Great white sharks
kill their prey but exsanguination, or extreme blood loss. When and if the prey surfaces after being
attacked, it is no longer bleeding as most of the blood is lost underwater.
“What we are dealing with here is a perfect engine, an eating machine. It's really a miracle of evolution. All this machine does is swim and eat and make little sharks, and that's all.” –Hooper
As juveniles, great white sharks
mainly feed on fish. As they grow older,
they hunt bigger prey like seals and sea lions.
Besides learning this from looking at stomach contents of recently
captured animals, we can also see this in their migratory patterns. On the coast of California, great whites
given birth off the coast of Southern California in the Spring, and then move
north to the seal and sea lion breeding grounds of Ano Nuevo and the Farallon
Islands, near San Francisco. This prey
preference based on age can also be studied by looking at the teeth of great
whites. Juveniles have narrow, sharply
pointed teeth without serrated edges that are better for grasping fish. Adults have broader and serrated teeth that
can more easily bite through thick skin.
Humans are not preferred prey for sharks. In the case of most attacks, the victim (often
with a surfboard) is mistaken for a seal or sea lion and released once the
shark realizes its mistake. People are
too bony with not enough fat to be a good meal for a great white, a fact that
is only comforting from dry land.
“probably not the shark that
killed the little boy…which I wanted to prove today, by cutting the shark open.”-Hooper
As it turns out, the metabolism of
great white sharks is very similar to that of birds and mammals. There are several indicators of metabolic
speed that were used to compare these different groups. The hemoglobin (molecule that carries oxygen) count
and hematocrit (proportion of red blood cells) can be measured as a
determination of the oxygen carrying capacity of blood. A higher metabolic rate means higher oxygen
consumption, and that the blood needs to be able to carry more oxygen. Also, the heart weight to body weight ratio and
the size and output volume of the ventricles of the heart of great white sharks
is very close to that of humans. This indicates that the work the heart must do
to pump blood through the body is similar.
This high metabolic rate allows sharks to be very active and catch fast
swimming prey, as well as enables them to live in many different water
temperatures.
It takes about 24 hours or possibly
more for humans to digest a meal. It is
believed that this would be the same for sharks, however because of their
different diet, it usually takes them much longer than this for them to digest
a meal. One seal can feed a shark for up
to six weeks. This is because the fat
content of seals, the usual prey organism for great whites on the West Coast,
is extremely high. Seals and sea lions
have a lot of blubber to keep them warm in the cold waters around us. Blubber is extremely rich in fat, which
contains a lot of energy for the shark to consume. It also means that it is very slow to digest. However, because great white sharks have a
high metabolism they are able to digest fat faster than other species of
sharks; this is beneficial because the faster a shark can digest food, the less
energy it needs to expend and more energy can be put away for storage.
Would Hooper and Brody have found
the body of Alex Kintner had they caught the correct shark? Probably, if they
were there fast enough. But they would
have had to rely on bones at that point; the low fat content of a young boy
means that he would have been digested rapidly!
Great white sharks are endothermic, which means that they
produce their own heat (due to their metabolism) to maintain body
temperature. Along with the digestive
speed that we just discussed, this allows great white sharks to live in cold
water and still be able to move fast enough to catch rapidly moving prey. They have a body temperature that can be kept
higher than the 55 degrees Fahrenheit off the California coast. In particular, their brains, eyes, stomachs,
and swimming muscles are much warmer than the water, even compared to the rest
of their body. How does this
happen? The same mechanism can be seen
in animals that walk on ice or snow, like polar bears. It is due to the presence of vascular counter
current exchangers, which allow organisms to retain some heat rather than
losing more to the environment. In
sharks, this happens when blood passes through the gills, picking up oxygen but
losing heat.
Counter current exchangers are sets
of parallel arteries and veins, or other vessels that transport blood in
opposite directions. Warm blood from the
body of the shark travels through the blood vessels of the animal. As it passes through the thin tissue of the gills,
it becomes extremely cold because it is closer to the external environment. Luckily, vessels carrying blood the opposite
direction run very close to these warm vessels and are already cold due to
having passed through the gills first.
Because of the proximity of these sets of arteries and veins, the warm
blood transfers heat to the cold blood through the vessel walls, so by the time
it actually gets to the gills, there is not as much heat to lose and more of it
is retained by the animal, saving a lot of energy and preventing tissue damage
caused by cold! In great white sharks,
this allows them to swim faster, see better, and keep digesting!
“Smile, you son of a [you know…].”-Brody
References
Estrada, J.A., A.N. Rice, L.J. Natanson, and G.B. Skomal.
2006. Use of isotopic analysis of vertebrae in reconstructing ontogenetic
feeding ecology in white sharks. Ecology
87(4):829-834
Image References
http://oceanlink.island.net/biodiversity/shark/shark.html
http://www.arkive.org/great-white-shark/carcharodon-carcharias/image-G2550.html
Klimley, A..P. 1994. The predatory behavior of the white shark. American Scientist 82(2):122-133.
http://www.huffingtonpost.com/2012/10/31/scott-stevens-eureka-shark-attack-surfer-california-humboldt-video_n_2049345.html
http://tolweb.org/treehouses/?treehouse_id=4847
http://www.releasedonkey.com/dvd/jaws-dvd-release-date-1533/still-3176771584
Hello , you say in your comments that the body of the boy alex kintner would have been digested rapidly by the shark , what about the red swim trunks he was wearing, what will happen to them. thanks
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