Sharks, rays, skates
Sharks
Rays
Skates
Class Chondrichthyes
• Members of the Chondrichthyes all lack true bone and
have a skeleton made of cartilage (the flexible material
you can feel in your nose and ears). Only their teeth, and
sometimes their vertebrae, are calcified.
• They also have jaws, paired fins, and paired nostrils.
• Cartilaginous fish also have thick, fleshy fins, unlike bony
fish. The tail of cartilaginous fish is also distinctive: the
tail is divided into two lobes. The vertebrae extend into
the upper lobe, which is elongated past the lower half.
Such a tail is called heterocercal.
More Characteristics
• They have five to seven gill slits on each side of the
body. Sharks and rays reproduce by passing sperm from
the male to the female, the male using modified fins
called claspers. Some species produce large egg cases
while others produce live young.
• There are about 600 species. Most are marine, some
live in mid-water, while many live on or near to the sea
bed.
• Sharks must swim constantly or they will sink to the
bottom of the ocean. Unlike fish, which have a gas-filled
swim bladder that keeps them afloat in the water, sharks
rely upon a huge, oily liver to provide some buoyancy.
Senses
• Sharks have acute senses, befitting their carnivorous
lifestyle.
• Sharp vision (no color).
• Olfactory nostrils used only for smelling.
• can detect electric fields set up by other animals.
• Lateral line system, a row of microscopic organs
spanning the length of the animals that are sensitive to
water pressure.
• Sharks have auditory organs.
Digestive System
• Digestive system with a j-shaped stomach;
intestine short but surface area increased
by a spiral valve.
Locomotion
• Sharks are known for their speed and
maneuverability in the water. Most species can
swim at speeds of 30 to 50 kilometer per hour.
The speed of the Mako when attacking has been
recorded at more than 90 kilometer per hour!
• With a few exceptions, sharks have torpedoshaped bodies, an efficient, streamlined design
for fast-swimming predators.
Respiratory System
• Sharks and rays have "plate-gills". Typically,
sharks pull water in through their mouths and
spiracles (small holes on top of the head in
some species) as they swim, and pass it through
five to seven gill slits on each side of the head.
As water passes over the gills, oxygen is
extracted. Most sharks, but not all (the nurse
shark is one exception), must swim all the time
to keep water flowing over their gills and oxygen
moving through their circulatory system.
Circulatory System
• Sharks have a two-chambered heart, with an atrium
(also called the auricle) and a ventricle. The heart is an
S-shaped tube that is located in the head region of the
shark.
• The blood is pumped by the heart through the afferent
branchial arteries (ventral aorta) to capillaries in the gills
(where the blood is oxygenated). The blood then flows
through efferent branchial arteries (paired dorsal aorta),
then through the tissues of the body, and then back to
heart in veins.
Shark Attacks
Attacks continued
• Contrary to popular belief, only a few
species of sharks are potentially
dangerous to humans, and most attacks
are due to the shark confusing a human
for a seal or another animal; this is typical
in case of an attack against a surfer. While
sharks cause a few dozen human deaths
yearly, in the same time millions of sharks
are killed by fishing.
Attacks
• Most shark attacks occur on the inshore side of
a sandbar or between sandbars because fish
congregate there and because sharks can
become trapped at low tide. Sharp drop-offs also
attract lots of fish and, therefore, sharks.
• The most common type of attack is the so-called
"hit and run" assault. The shark bites and then
quickly releases the person and disappears.
These attacks usually involve injuries to the leg
below the knee and are not usually fatal.
Humans are usually considered too bony to be a
good meal for a shark.
• Considering that tens of thousands of
people come in close contact with sharks
each year while swimming, surfing, or
boating, numbers of shark attacks are
negligible. In 2004, there were 61
confirmed "unprovoked" shark attacks in
the world, resulting in 7 deaths
Number of Attacks
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Region Confirmed Attacks/Deaths
United States 761,390
Hawaii 100,150
Australia
294,134
Africa 264,690
Asia 116,550
Europe 38,180
South America
96,220
Antilles and the Bahamas 59,190
Bermuda
4,000
Mexico and Central America 58,310
Pacific Islands, Oceania
114,470
New Zealand 45,900
Other 20,600
World 1969,464
2008 Attacks
• For 2008, the Global Shark Attack File
records 69 unprovoked attacks of which
five were fatal.
Realistic Facts
• The fact is, you're more likely to get hit by pieces
of an airplane falling out of the sky while on your
way to the mailbox, then you are getting bit by a
shark. If you don't have a mailbox, then here's
another one; you are more likely to get struck by
lightening or drown in the bath tub, then you are
getting attacked by a shark.
• Out of 350 species of sharks, there are only a
handful that have actually been know to attack
people. They include the Great White, Maco,
Tiger, Bull, Dusky Brown, Lemon, and Nurse
Sharks.