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

• 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

Touch

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

• 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

Electro-Sensors

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