Download Sharks part 1

Sharks part 1
Sharks
Characteristics &
Physiology
Characteristics & Facts
• Largest shark in the world is the Whale Shark
• Average length- 15 meters
–
–
–
–
Average weight- 10 tons
Typically found in tropical waters
Feeds mainly on plankton
Harmless to humans
* Not certain which shark is the smallest in the world,
among them is the Midwater Shark which is 22-25 cm
(8-10 in.)
Take notes in Red
Characteristics & Facts
• Sharks are believed to have developed approximately
350 million years ago.
• Due to their advanced evolutionary state, they have
remained virtually unchanged for the past 70 million
years.
• Large sharks generally cruise at a speed of 1.5 mph.
• Great White sharks are believed to swim at a top speed
between 40-50 mph.
• The Shortfin Mako is thought to be the fastest shark,
calculated top speeds have ranged anywhere from 30
mph to around 70 mph.
Characteristics & Facts
• Sharks typically have what is called a ‘fusiform’ body
shape (cylindrical / rounded with tapering at each end),
which makes swimming easier by reducing drag and
minimizing effort.
• Usually sharks have different colors on their dorsal and ventral sides.
When a shark is darker on the dorsal side and lighter on the ventral side it
is termed ‘countershading’, which makes it more difficult to see from above
and below.
Physiology
• Skeletons are made of cartilage, a fibrous tissue,
which is lighter and ½ as dense as bone tissue– Lighter structure makes it easier for shark to
move and support its weight
– Sharks have no ribs, not needed because
much of their weight is supported by the water
– Muscles are attached directly to the collagen
matrix which makes up the skin and outer
shell of body, allows skin to act as an external
skeleton making swimming motions much
more efficient for the shark
Physiology
• Sharks have an S-shaped heart that consists of two chambers.
• Blood is pumped from the heart to the gills, where it is oxygenated,
then flows throughout the body.
• The liver of a shark may account for up 25% of its body weight
because of stored oils and fatty acids which provide energy and
increased buoyancy.
• Two muscle types– Red- for slow, cruising actions (slow twitch)
– White- for faster, rapid swimming, speed bursts (fast twitch)
• Sharks are cold blooded which results in a significantly lower
metabolism than warm blooded animals. Therefore– They typically eat less than animals of their size
– Eat between 1% and 10% of their own body weight weekly
– Capable of going several weeks without food
Shark Sensory
•
•
•
•
•
•
Taste
Electric
Sight
Touch
Smell
Sound
Shark Sensory
Taste
• Direct touch when they bite something Theory - can detect energy content of prey
with first bite.
Smell
• External nares - organs for scent
(olfaction) located near front of the snout.
• Nostrils shaped for continuous water flow
– Odorants in water stimulate nerve cells in
scent organs
– Sharks are super sensitive to odorants
produced by predators, prey or mates and
most receptive to body fluids produced by
injured prey.
Smell
•
•
•
•
Smell 1 ppb - part per billion
Fish oil - 1 ppb in 10 billion
Large percent of brain is use for olfaction
The source can be 100’s of meters away
Touch
• Sense of touch in sharks is highly
developed
• Mainly used to detect:
– Large changes in temperature
– Presence of noxious chemicals
– Physical damage or trauma
Touch
• The lateral line is a tiny canal just under
the skin which detects movements on the
outside
– They also react to variations in water currents
around the shark and pressure waves from
underwater sound
– Allow for the detection of current flows or the
swishing of a fishes tail
– Similar to our ability to detect wind
– up to 100 meters away
Sight
• 15 meters - same as Humans. Nictitating
membrane - Extra protection for eye when
feeding.
Electro-Sensors
• Sharks can detect electrical fields emitted by
animals with the Ampullae of Lorenzini
–
–
–
–
Tiny pours in skin around the head and rostrum
Nerve cells in the pours react to electrical stimuli
Contiguous with lateral line
up to 18 cm away
Electro-Sensors
• This sense is relied upon more than any
other when sharks are hunting and close
to the prey
– Salts and minerals in leaking body fluids of
injured animals create certain types of
electrical signals
– This explains why sharks will repeatedly
attack a victim during rescue and ignore the
rescuer
Sound
• Use lateral line and ear to detect ripple of
water pressure
• Receptor cells in the ear are very similar to
those of humans
– Two tiny holes located behind eyes
– Hear better at lower frequencies, especially
irregular noises like those generated by
injured animal. Can hear 100’s of kilometers
away. Sound travels 4x faster in water.
Threat of Sharks
• About 80% of shark
attack victims survive
• Most often the shark
carries out an
exploratory attack
• Globally, people are
almost 1,000 times
more likely to drown
than be attacked
When, Where and Why They Attack
• Most attacks occur in warm and shallow waters
near resorts.
• Statistics are only recorded in affluent countries
• A lot of sharks feed of bigger prey such as sea
lions; a human on a surf board or floating at the
surface of the water can be mistaken for one.
• Most attacks are “hit and run” attacks