Final: The Anatomy of our Favorite Friendly Man Hunter

This discussion topic submitted by Virginia J. Simpson (simpsovj@miamioh.edu) at 10:15 am on 8/4/99. Additions were last made on Wednesday, May 7, 2014.

The Anatomy of our Favorite Friendly Man Hunter--The Shark


A reef shark cruises the wall on San Salvador, Bahamas

For all of you children of the eighties I'm sure you can sympathize with me when I mention how my irrational fear of sharks originated. It was a dark and stormy night (okay, so it wasn't so dark and it wasn't so stormy but it was night) when a group of ten eight-year-olds got together for a slumber party. We ate our pizza, did our hair and nails, then sat down to watch an adult movie...JAWS. Although, none of us will admit it to this day, that night and that movie with lots of red-colored water changed our opinions of going into the ocean blue dramatically. We weren't the only ones either, the scuba industry and ocean tourism took a major hit after JAWS came out and a lot of scuba businesses went under the cold jaws of a creeped-out society. But that is a different story for a different day.

So as I prepared myself for going to the Bahamas with Hays I rationalized that if I were going to get eaten by something that I was most likely to meet, maybe I should know a little more about how the fish works. (Which, incidentally was extremely useful for my peace of mind during an encounter I would later have with one other lonely snorkeler at the barrier reef just outside of the Bahamian Field Station, San Salvador, with a very large reef shark.)

Perhaps I should first start with the fact that there are only 50-70 shark attacks worldwide per year according to the Shark Attack File and of those, very few are fatal and of the fatalities most of them occur in Australia. Although it is not known exactly why some sharks attack, in general it is guessed that sharks confuse humans for one of its normal meals or are provoked. There are roughly 350 different species of this non-bony fish and they range from gentle filter feeders to the great hunter often villianized in media, the great white. The characteristics of a "typical" shark are never absolute but there are some generalization or commonalties in traits among this fascinating group and that is what I will try to explain. It should also be noted that the shark is an extremely difficult creature to study for several reasons. One, most cannot survive in captivity and two, they are very fast and elusive in their home turf. However, enough with this dry prelude and onto the shark.

Order of the Outline
Cartilage
Form
Swim
Skin
Teeth
Jaws
Eyes
Detection of Prey
Spiral Valve
Reproduction
Courtship/Mating
Development/Birth

Cartilage
-connective tissue that is strong enough to give support
-composed of singular, paired or clustered cells called chondroates
suspended in protein matrix
-may become calcified (especially the jaw bone dependent on of good source)
-less dense, more elastic than bone
-provides buoyancy and flexibility

Form
-streamlined
-most have a compact, fusiformed body, 2 dorsal fins, a pair of pectoral
and pelvic fins, a protruding snout with nostrils near tip, and a crescent
shaped mouth underneath
-generally have 5 gill slits (some up to 6 or 7)
-spiracle, an opening posterior to the eyes
-passes water over gills
-for bottom-feeders the spiracle helps keep the gills
and mouth from clogging with mud.

Swim
-efficiently
-caudal tale creates the power
-all are heterocercal caudal
-the vertebrae column extends into the upper lobe of the fin
-allows for sudden changes in direction
-left/right, up/down, rolling
-no air bladder to help with floating
-cartilage is less dense than water
-live can take up 90% of body cavity and 25% of weight
-oil is lighter than water
-overall, a shark is denser than water and must continually move to
remain afloat

Skin
-pet a shark from head to tail and it is smooth
-pet a shark form tail to head and it is a rough, sand-paper-like texture
-most sharks are completely covered by small, sharp, tack-like placoid
scales that are modifications of teeth called dermal deticles
-hard outer layer of enamel
-core of dentine, nerve cells and blood vessels
-coat is continually replaced throughout life
-causes no drag

Teeth
-variety dependent on individual
-large/small, blunt/sharp, saw-like or knife-life
-useful with identifying a species of shark and
even the genera and family
-endlessly replaceable
-in multiple rows
-only on jaw
-only embedded in gum
-usually front one or two rows are upright and
functional, others are replacement teeth in waiting
that are gradually erected and pushed forward
-increase in size over life
-direct relationship between the largest tooth and shark size
-used sometimes with fossil record
-some estimate that a shark may lose 30,000 teeth in a life
-ex. a lemon shark will replace a row of teeth in 7.8-8.2 days
-same shapes and their uses:
-awl shaped, impaling a fish
-saw shaped, rip off chunks of flesh
-low and blunt, crush molluscs
-small, no visible use in feeding

Jaws
-loosely connected to braincase and short in relative size to length of head
-enables a shark to widen the gape and extend the jaw
-bite in any position
-cannot chew
-varying levels of calcification are indications of feeding preferences

Eyes
-similar to other vertebrates
-lens are nearly spherical and constant in shape
-questionable if sharks can focus their eyes
-in human terms they are moderately far-sighted
-can maintain a constant visual field and near panoramic vision
-pupils
-multiple shapes (slits, ovals, vertical, horizontal)
-quick to move from constriction to dilation
-some can move within 1 minute (faster than humans)
-tapetum lucidum
-gives the shark excellent night vision
-behind the retina
-two parts
1. series of silvery reflection plates with crystals of
pigment, guanine
2. mobile cells, melanoblasts with pigment, menalin
-can block the reflection of light or let it in
-possibly can see in color

Detection of Prey
-senses
-sound, most used, travels faster in water than air
-even at distances greater than a mile, a shark is
attracted to irregular, low frequencies and vibrations
-no external ear, the internal ear is connect to outside by
a tube, located on each side of head
-sight, important for distances within 15 meters
-sensitive to light, movement and contrast
-smell, can detect one part blood to one million parts sea water
-follow the trail where there is more blood in water
-taste, used more in accepting or rejecting a prey
-lateral-line system
-extends on both sides from head to the length of body
-series of fluid-filled sensory canals sensitive to
vibrations, pressure changes, waves and movement in water
-(some) bioelectrical system, the ampulae of Lorenzini
-scattered dots over the front of the head
-used for detection of prey and location of self in the world
*every animal produces electricity so without sight or
smell a shark can locate and catch prey. (wow!) so, have you ever seen a great white attack a cage instead of the meat in one of those sensationalist documentaries?...the cage's electrical field had a stronger force than
the meat.

Spiral Valve
-sharks have non-coiled intestines, would cause food to pass through quickly
-slow down food passage through an enlarged portion of intestines with an
area similar to a thread wrapped around to increase the absorptive surface
-also creates white blood cells

Reproduction
-internal fertilization
-male reproductive organ
-external, clasper, a fin near the caudal end that serves as a way
to attach to the female's colaoca, sometimes through spikes/hooks, a
facilitate the passage of sperm
-internal, elongated testis and lots of plumbing
-female reproductive organs
-paired ovaries and oviducts
-usually only the right ovary is functional and the other one
shrinks in size

Courtship/Mating
-severe and violent
-males nip, bite, and harass females
-seldom inflict fatal wounds
-sometimes the female fights back and kills the male
-seldom has been observed in both the wild or captivity
-generally though, males bite on pectoral fin of female, immobilized her
and wraps his tail around to insert the clasper to the colaoca

Development/Birth
-sharks produce few eggs, all are retained by the female
-lay eggs (oviparous)
-live birth (viviparous)
-unattached eggs kept inside (oviviparous)
-intrauterine cannibalism (ovaphagy)
-brothers and sisters eat one another
-both unfertilized eggs and unborn embryos

And that folks is a little bit of interesting information on the shark. If you are planning on going down to the Bahamas you don't really need to worry about not making it home because of a shark bite. The top three that may attack a human are the great white, the bull and the tiger. Although the tiger and bull may be found near the Bahamas it isn't likely that you will be lucky enough to come across one. Besides, if your group is anything like ours you will tend to scare away any shark you may see--at least hammerheads.

BIBLIOGRAPHY
Bohensky, Fred. PHOTO MANUAL AND DISECTION GUIDE TO THE SHARK. (WAYNE, N.J.:
AVERY) 1981

Couseau, J. Y. and Cousteau, P. THE SHARK: SPLENDID SAVAGE OF THE SEAS (Garden
City, N.Y.: Doubleday) 1970

Dingurkus, Guido. THE SHARKWATCHER'S GUIDE (New York: Messner) 1985

Moss, Stanford A. SHARKS: INTRODUCTION FOR THE AMATEUR NATURALIST. (Englewood
Cliffs, N. J.: Prentice-Hall) 1994

For Further Info on this Topic, Check out this WWW Site: http://www.discovery.com/area/nature/sharks/sharks.html.
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