SHARK WEEK

http://www.youtube.com/watch?v=UruXWui1EG8

Discovery Channel Shark Week

• http://dsc.discovery.com/sharks/shark-o-nator

• Resource site

Shark Myths

• http://www.mote.org/index.php?engine_id=&src=search&search_id=search_new&search_this=shark+myth

• Resource site

• http://www.sharks-world.com/facts_about_sharks.html

#1

• Sharks prefer human blood.• False! Most sharks don't appear to be

especially interested in the blood of mammals as opposed to fish blood

#2

• Sharks have peanut-sized brains and are incapable of learning.

• Sharks' relatively large and complex brains are comparable in size to those of supposedly more advanced animals like mammals and birds. Sharks also can be trained

#3

• All sharks have to swim constantly• Misconceived! Some sharks can respire by

pumping water over their gills through opening and closing their mouths while at rest on the bottom.

#4

• Sharks have poor vision.• Erroneous! Sharks' eyes, which are equipped

to distinguish colors, employ a lens up to seven times as powerful as a human's.

#5

• Sharks are not found in freshwater.• Forget it! A specialized osmoregulatory system

enables the bull shark to cope with dramatic changes in salinity -- from the freshwaters of some rivers to the highly saline waters of the ocean.

#6

• Whale sharks, the largest species of shark, are voracious predators

• Whale sharks, which are the largest fish that have ever lived, are plankton feeders like the great whales, thus the name.

Seaworld: sharks

• http://www.seaworld.org/infobooks/Sharks&Rays/home.html

What are Sharks?

• Vertebrates• Cartilage skeletons• 350 species• Can live for 20-30 years• Five gill openings on each side of head• Scales called “denticles” make skin feel rough• Scales do not grow larger. Shark grows more of

them. Scales cannot be used to tell the age of the shark

Denticles of a great white shark

Cont……

• Some are solitary hunters. Others, hunt in groups

• Found in all oceans at all depths- most prevalent in tropical, coastal waters

• Primarily marine, but do travel up the mouths of rivers into freshwater in some species

• Many are carnivorous, some planktonic• Most powerful jaws on the planet

Ancient Sharks

• The most common shark fossils are teeth because sharks, unlike most other animals, can lose many thousands of teeth during their lives

• Shark skeletons are not made of bone- therefore, whole skeletons are only found where the animal was quickly covered with mud and remained undisturbed

• Oldest shark fossil-More than 400 million years old. 150 million years since evidence of evolution

megalodon

• http://www.youtube.com/watch?v=Spo8vkrJFRo

Taxonomy

• 460 different species• 8 orders• Hexanchiformes-six gilled and seven gilled sharks• Squaliformes- dogfish sharks• Pristiophoriformes- sawsharks• Squatiniformes- angel sharks• Heterodontiformes- bullhead sharks• Orectolobiformes- carpetsharks• Lamniformes- mackerel sharks• Carcharinoformes- hammerhead and requiem sharks

• 25 species of sharks reside in the gulf of Mexico

Let’s get acquainted: Shark Anatomy

• Sharks typically have a fusiform body (rounded and tapering at both ends). This body shape reduces drag and requires a minimum of energy to swim

• No swim bladder. Tends to sink. Has oil in liver to increase buoyancy

• 5 gill slits• Caudal fin is well developed and powerful• Tail is heterocercal- upper lobe is longer than the

lower lobe• Powerful jaws with sharp teeth

fins

• Sharks have five different types of fins. • a. Paired pectoral fins lift the shark as it swims. • b. Paired pelvic fins stabilize the shark. • c. One or two dorsal fins stabilize the shark. In

some species, dorsal fins have spines. • d. A single anal fin provides stability in species

where it is present; not all sharks have an anal fin.

• e. The caudal fin propels the shark.

fins

Tails/Swimming

• The ability to pump water over gills (buccal pumping) varies between shark species

• Less active sharks have an increased ability for buccal pumping

• More active pelagic sharks use ram ventilation, meaning they ventilate the gills by holding the mouth open while swimming

• Some sharks are obligate ram ventilators, meaning they have to keep constant forward motion in order to continue respiration

Teeth

• Each type has a different shaped tooth• 20,000 teeth per lifetime• Arranged in parallel rows• Studies have shown that an average nurse

shark will replace each front row tooth every ten days to two weeks in summer when actively feeding and every one to two months when they are less active in the winter

• Sharks never run out of teeth. If one is lost, another spins forward from the rows and rows of backup teeth

Colors and Camouflage

• Countershading• Dorsal side is darker than the ventral side

Breathing

• Most sharks swim continuously because the opening and closing of the mouth forces water through the mouth, over the gills, and out through the gill slits

• When caught in fishing nets, sharks cannot swim to force the water in and therefore “drown”

• Not all sharks need to swim for gas exchange. Nurse sharks rest on the bottom because they force water over their gills by opening and closing their mouth

spiracles

• behind the eyes at the top of the head. These openings bring oxygen-carrying water into the gill chamber. Spiracles originate from rudimentary first gill slits and are reduced or absent in active, fast-swimming sharks.

Ramjet Principle

Shark Senses

• Sharks have six highly refined senses: smell, hearing, touch, taste, sight, and electromagnetism

Incredible Senses

• In addition to the lateral line, sharks have a sensory organ

called the Organ of Lorenzini; this organ is used to detect electrical currents when sharks are close to an object (the movement of muscles – even those used in respiration – emit a small electrical charge) – this allows sharks to detect living prey even it is hidden from their view if they can get within a few feet of the organism

• “built in compass”

Incredible Senses

• Lateral Line• The lateral line, together with the ampullae of Lorenzini

comprise the electrosensory component of the sharks sensory system. The lateral line allows the shark to orient to particle movement or sound. It consists of structures called neuromasts which are located in canals that lie just below the surface of the skin or the scales. Similar to the ampullae of Lorenzini there are pores that open to the outside and movement caused by prey can be detcted by the neuromasts.

Shark lateral line

Incredible Senses Cont…..

• Hearing-• Ears are internal, not external• Ears: 3 semi-circular canals that resemble

those in the ears of other vertebrates• Sharks can hear noises from over 700 feet

away• Vibrations in the water are heard as sound

Incredible Senses• Eyes • Sharks have a nearly 360-degree visual field• Some sharks have a third eyelid, called the nicitating membrane, which

protects the exposed portion of the eye during feeding or object contact• The great white shark does not have a nicitating membrane, and instead

rolls the eye back into its orbit to protect it during feeding• Most sharks have a reflective layer in the back of the eye called a

tapetum lucidum which boosts the sensitivity of the eye in dim light• A juvenile lemon shark has a lens with 7 times the optical power of a

human lens• Humans focus by changing the shape of the lens; sharks focus by

changing the position of the lens by moving it toward or away from the retina

Incredible Senses

• Nostrils- used only for smelling. NOT breathing• Seawater flows over the nostrils bringing

chemical clues as to what’s nearby• Sharks can detect tiny amounts of blood from

more than 1 mile away. • The hungrier the shark gets, the sharper its

sense of smell. Scent makes them aggressive- “feeding frenzy”

Shark Senses

• http://www.youtube.com/watch?v=h1XYa93Rz_Q

osmoregulation

• Shark Osmoregulation Facts:• Sharks use high concentrations of body urea to help

osmoregulate• Sharks living in salt water must balance the influx of NaCl (salt)

into the body by excretory mechanisms in the rectal gland, kidney and gills

• Sharks living in dilute salinity or freshwater conditions must balance the influx of water into the body by increasing urinary water excretion and increasing salt uptake through the gills

• 90% of the secretion of body acids/bases into the water in order to balance internal pH is done by the gills

• http://www.youtube.com/watch?v=LxYgsyKXQVg

Reproduction

• Sexually dimorphic: visible differences between males and females

• Externally, males have claspers which are modified pelvic fins used for sperm delivery

• Testes and ovaries are internal• Mating is vicious. Therefore, female skin is twice as thick

as males because males will bite the females while mating• Sexes often segregate and only come together to mate• Females can store sperm for a year until the eggs are

ready for fertilization

Reproduction

• Sharks have young in three different ways. After internal fertilization, some species lay a thick egg case that encloses the shark embryo (seen in the photo here). Most species are ovoviviparous, which means that the shark hatches and develops within the female shark and is born live. A third way (viviparous) is similar to human development, where the young shark grows within the female and gets nutrients from a placental link to the mother

embryo

• 70% of the sharks living today have developed a method to care for their brood inside the female’s body (viviparity or ovoviviparity)

• 30% of all sharks lay eggs (oviparity)• Gestation 6-22 months• New borns called “pups”

Shark embryo in egg case

Shark Reproduction

• “mermaid’s purse” – egg case• Several months-one year to hatch. Hatch faster in warmer

water• Example: Lesser-spotted Dogfish

• A January 2013 study in the journal PLoS ONE shows that embryonic bamboo sharks in egg cases can react to predation signals. The embryos in this study were exposed to electric fields that simulate the shark's predators and, in response, the sharks stop all gill movement and hold still so as not to alert the predator of their existence

Intrauterine Cannibalism in Sharks

• Adelphophagy- shark embryos eating each other

• Two forms of within-the-womb cannibalism are known in sharks. The most extreme form of intrauterine cannibalism — in which the largest and strongest embryo actually consumes its lesser womb-mates — is termed "embryophagy" or, more colorfully, "adelphophagy" — literally "eating one's brother". To date, adelphophagy is known only in the Sandtiger.

Sandtiger shark

• The less extreme and by far more common form of intrauterine cannibalism — in which developing embryos feed on a steady supply of tiny, unfertilized eggs — is termed "oophagy" (sometimes called "oviphagy") — meaning "egg-eating".

parthenogenesis

• Parthenogenesis, from the Greek meaning “virgin birth” is an odd quirk of embryonic development that allows female animals of some species to give rise to offspring without a male genetic contribution - usually by a doubling of the egg genome to generate a new embryo with the proper number of chromosomes. Parthenogenesis is common in insects, and among vertebrates it occurs in some species of fish and reptiles, and strangely enough, in turkeys.

• a white-spotted bamboo shark female gave rise to parthenogenetic offspring that have survived for several years. Parthenogenetic sharks are therefore not inherently less viable - normal sharks can be produced using only female-contributed chromosomes.

• occurred among animals in the controlled environment of aquaria, where the female was isolated from males for a long period of time.

White spotted bamboo shark

Feeding

Finding Nemo: Bruce “feeding frenzy”

• http://www.youtube.com/watch?v=LYmsVWmHI78

How common are shark attacks?

• Attacks are quite rare, averaging only 25 per year worldwide, and only ¼ of these are fatal

• More people die from wasp and bee stings• Even pigs kill more people annually than

sharks

What is shark prey?

• It depends on the type of shark as various species have different habits

• Shark feeding also depends on where they live

Diet evolution

• Shark diet needs to evolve based on what is offered so they can survive. sharks easily adapt to their habitat, therefore the number and variety of food selection will determine what will a shark eat in such location. Sharks may prefer certain types of foods but when they are scarce they will adjust their eating habits to compensate for it.

Carnivores

• Most sharks are meat eaters and so they feed on other fish and even other sharks. Larger sharks aren’t afraid to go after a huge meal such as a dolphin or a sea lion.

Jaws

jaws

• Sharks have very powerful jaws (most powerful on the planet) and teeth so they can rip through meat and bones without any trouble at all.

• Since many sharks are thrashing from side to side as they eat it may give the impression that they are having difficulties but that isn’t the case at all.

Attacks at Seal Island

• http://www.youtube.com/watch?v=XCWT-tBLnD8

• http://www.youtube.com/watch?v=T1r3FixM5wY

Other meals…..

• Sharks also eat crab, squid, and lobster in areas where it is available. Due to the amount of commercial fishing ships though gathering such items for humans to consume though it isn’t always a source of food that they have available.

Small invertebrates are meals too

• Other shark species live off of small aquatic life including mollusks and clams. These types of sharks often live at the bottom of the ocean where there is an abundance of such food sources. They blend in well so they aren’t spotted by their prey very easily. These are often the smaller species of sharks that don’t need a huge volume of food to live on.

Planktonic Sharks

• Whale shark; basking shark• gill rakers are bristlelike and are used to catch

plankton as water filters through the mouth and over the gills.

The Perfect Predator:Why sharks attack

• 1. attacking for food• 2. Mistaken identity- ex. Surfboards or

people• 3. Rogue Sharks- random where sharks

normally are not found• 4. Defending territory• 5. Provoked attacks

Taste Test

• Shark attack begins with a “test bite”. They will gently wound their prey to taste flesh and blood. The shark will shift its behavior into killing mode if it likes the prey

• research has shown that most sharks will bite and then let a person go as they realize it isn’t their normal food source. Of course that will make great damage in the person bitten, but the truth is that sharks do not eat humans

• People who are bitten usually die from loss of blood or from the injury caused by the bite

Sharks can’t……..??????

• Sharks can’t chew. • Must gulp food down throat. Can swallow

small prey whole

How much do sharks eat???

• The amount of food that a shark eats each day depends on the type of shark it is. Generally they consume about 2% of their total body weight. This is surprising to many people as it would appear that these large animals should eat much more

How often do sharks eat?

• Some Shark species will eat huge meals and then not eat again for weeks, months, or even a year in some cases.

• Most eat every 2-4 days• They are able to survive on the oil that is stored

in the liver when they do eat. When that gets low they will have the instinct to eat again.

Why don’t sharks need to eat more often???

• The reason sharks don’t have to eat as much as people think is because they are cold blooded. This means their circulation is slowed down and they burn energy at a slower rate.

Shark attacks around the world

• Where do most shark attacks occur?• Before the beaches of eastern AUSTRALIA

were protected with nets, Australia had the world’s worst record for shark attacks. 300 attacks. ¼ of all the attacks recorded

• More Australians are killed as a result of automobile accidents every MONTH than have died in 100 years from attacks by sharks

Shark net

Shark net…..

• Protects swimmers• Each end of the net is secured by an anchor

and its position marked by floats• 46 South African beaches are protected by

nets

Shark “cables”

• Another way of protecting swimmers • Cables are laid around beaches and pulses of

electric current are sent through the cables• Current is strong enough to turn sharks away

2nd most dangerous area

• #2 SOUTH AFRICA• Beaches of Natal

USA Sharks Attacks

• Americans have 50 times more chance of being struck by lightening than of being attacked by a shark.

• In the whole USA, there are fewer than 12 attacks per year

Shark repellent

• 1960’s Eugene Clark discovered a small flatfish that would stop sharks in mid-bite

• This fish (the Moses sole) exuded a white milky fluid over its upper surface when threatened

• Unfortunately this material breaks down rapidly and is easily dispersed in water

Time and Season of shark attacks

• Middle of the afternoon • Summer season• Depth of 5-10 feet

Shark proof material

• http://soldiersystems.net/2011/04/11/neptunic-technologies-protective-materials/

South America Shark Attack: Discovery Channel

• http://dsc.discovery.com/tv-shows/shark-week/videos/south-america-shark-attack.htm

Great White Attack

• http://dsc.discovery.com/tv-shows/shark-week/videos/great-whites-death-strike.htm

National Geographic shark attacks

• Shark Attack! - YouTube

• SHARK ID ACTIVITY

Nova Sharks Activity Site

• http://www.pbs.org/wgbh/nova/sharks/

1. Great White Shark• Great White Sharks are the largest predatory (aggressive) fish in the sea• 3,000 serrated teeth• Great White Shark meat is not recommended for human consumption because it

has very high mercury levels• Eat blubbery animals:• Seals, sea lions, tuna, etc.• Great White Sharks breed late in life. They do not start breeding until they’re at least

twenty years old.• OCRAS have been known to kill Great White Sharks

• http://www.youtube.com/watch?v=d-1xU0VfJ-g• http://www.youtube.com/watch?v=qRaJ9p4CWwU

Great White Shark

Great White Shark Video

• http://www.youtube.com/watch?v=d-1xU0VfJ-g

• http://www.youtube.com/watch?v=ao-PZCIGKpQ

Killer Sharks vs Killer Whales

• http://www.youtube.com/watch?v=6zOrUT0smV8

1. Octonauts: Great White Shark

• http://www.youtube.com/watch?v=Upvc0fZdNIE

2. Tiger Shark

• named for the dark, vertical stripes found mainly on juveniles. As these sharks mature, the lines begin to fade and almost disappear

• One of nature’s most successful predators• One of the world’s most common sharks• “garbage can of the sea”• A tiger shark that was caught off South Africa was

found to contain the front half of a crocodile, the hind leg of a sheep, three gulls, and two cans of peas

2. Tiger Shark

• They are second only to great whites in attacking people. But because they have a near completely undiscerning palate, they are not likely to swim away after biting a human, as great whites frequently do.

• Used for shark fin soup

Tiger Shark

3. Hammerhead Shark

• Solitary • Night hunters• School during the day• Hammerheads are aggressive hunters, feeding on smaller

fish, octopuses, squid, and crustaceans. They do not actively seek out human prey, but are very defensive and will attack when provoked.

• Likes to eat sting rays• Uses head like a shovel to dig up the ray• Immune to the venom of the rays’ tail barb• http://www.youtube.com/watch?v=s6Djl_inVQE

3. Hammerhead

Hammerhead Video

• http://www.youtube.com/watch?v=hgCKBTv03vc

4. Nurse Shark

• Nurse sharks prefer to dwell near the sea floor in the warm, shallow waters of the western Atlantic and eastern Pacific oceans

• Nurse sharks are slow-moving bottom-dwellers and are, for the most part, harmless to humans

• Feed mostly on bottom invertebrates- lobster and sea urchin

• They use their strong jaws to crush and eat shellfish and even coral, but prefer to dine on fish, shrimp, and squid

4. Nurse Shark

5. Whale Sharks

• More Whale Shark Facts: • Whale sharks can grow to be more than 14 meters

(~45 feet) long!• Whale sharks can be found in tropical and warm-

temperate oceans.• Whale sharks do have teeth--in fact, they have more

than 300 rows of them in either jaw, but they are only 1/12-of-an-inch long.

• The pattern of stripes and dots are unique for each shark- like a fingerprint

5. Fish and whale sharks

• Remoras and the Pilot fish• “Suckerfish”

Why do the fish follow the shark?

• The small fish follow the shark because it protects them from the larger fish that would otherwise eat them

Remora

• Both of these fish form a symbiotic relationship with the shark. The Remora is a Commensalism relationship where the Remora gains basically all of the benefits such as protection from other predators and free transport as the Remora attaches itself directly to the shark by means of a sucker on the top of it's head. The shark gains no real benefit from this relationship as they tend not to feed on ectoparasites on the shark etc, but neither is the shark directly harmed, as the Remora's sucker does not cut into the flesh or damage the skin to any noticeable extent

Remora

Pilot Fish• The Pilot fish on the other hand, shares a Mutualism relationship

where the benefits are to both the Pilot fish and the shark. Pilot fish do not attach themselves to the shark but instead swim in an almost perfect harmony and favour such species as the Oceanic Whitetip Shark. They again gain a great source of protection from other predators and also a regular food supply from left over scraps from the sharks meals, but also more importantly feed on the ectoparasites on the sharks skin. It is this last part that makes this relationship mutualist, as the sharks can enjoy a virtually ectoparasite free life. Small juvenile Pilot fish also serve as good dentists, and will happily swim into the obliging shark's open mouth to clean food particles from between the teeth with virtually no fear of becoming a meal themselves.

Pilot Fish

5. Whale Shark

Whale shark video

• http://www.youtube.com/watch?v=hgCKBTv03vc

• http://www.youtube.com/watch?v=uQrBwN39LJI

• http://www.youtube.com/watch?v=_B8qiqeDrI0

Basking Shark

• Gill slits encircle its enormous mouth• Very slow swimmers• Only one species exists• Social animals. Live in groups up to 100• Can filter 2,500 tons of water every hour

Basking Shark

Basking shark video

• http://www.youtube.com/watch?v=UbeXqgTC7g8

6. Bull Shark

• Can live in freshwater• Solitary• many experts consider bull sharks to be the

most dangerous sharks in the world

6. Bull Shark

7. Reef Shark

• There are 5 types of Reef Sharks:• Blacktip Reef Sharks• Gray Reef Sharks• Caribbean Reef Sharks• Whitetip Reef Sharks• Silvertip Reef Shark

8. Lemon Shark

• This shark is yellow in color which is where the name derives from.

• Lemon sharks are mainly found along the Southeastern coast in the United States. The Gulf of Mexico is also a prime location for them

• feed on various types of fish that are found in the waters. Mainly they stick to small prey that aren’t able to put up much of a fight.

• http://www.youtube.com/watch?v=f6UNSij65BA

• http://www.youtube.com/watch?v=LfQgRCg1bNA

• http://www.youtube.com/watch?v=-l6JgnBq88s

“sea dogs”

• Pygmy shark, piked dogfish, prickly dogfish, velvet belly shark

• Can life up to 5,000ft deep• “lantern sharks” because they produce a slimy

mucus that glows in the dark

“cow sharks”

• Sharpnose sevengill shark• Bluntnose sixgill shark• Crocodile shark• Cookiecutter shark• Leopard shark• Tope shark• Atlantic weasel shark

“weird and wonderful” sharks

• Angel shark• Filled shark• Bramble shark- covered with sharp spines and

a foul smelling mucus covers the shark’s body

• Goblin Shark- odd shaped head and unusually long beak like snout. Teeth at the front of their mouths look like fangs

• Sawshark-• Aren’t aggressive• Saw can grow to be 3 ft• Barbels on saw poke around for prey hiding on

the seafloor

carpetsharks

• Epaulette shark• Brownbanded bambooshark• Tasselled wobbegong• Nurse shark• Zebra shark

• Blacktip reef shark• Whitetip shark• Spinner shark• Blue shark• Silky shark• Lemon shark

Sandtiger shark

• “Ragged tooth shark”• “Gray nurse shark”• They can stay afloat while not moving. They

come to the surface and gulp in air. They keep some of it in their stomachs and either release it as gas. They can control the amount of air n their bellies and hover in the water where they want

White tip shark

Thresher shark

• Most famous for its tail• Upper lobe of caudal fin is very large• Hunt in groups• Can jump out of the water like dolphins. Called

breaching• Have enormous black eyes

Mako Shark

• Fastest swimmer• speed up to 20 mph• Can leap 20 ft out of the water as well

Cookie cutter shark

• Small, deep water sharks that attack larger fishes and dolphins and cut out chunks of flesh with their razor sharp teeth and sucking lips

• Even the rubber sonar domes of nuclear submarines have not escaped their bites

• http://www.youtube.com/watch?v=U3M7wWpX9qI octonauts

“How do you save a shark you know nothing about” TED talk

• http://www.ted.com/talks/simon_berrow_how_do_you_save_a_shark_you_know_nothing_about.html

Why Sharks need our help: discovery channel

• http://dsc.discovery.com/tv-shows/shark-week/videos/why-sharks-need-our-help.htm

Sharks and humans

• http://www.sharks-world.com/sharks_and_humans.html

Sharks and Humans

• What is a shark’s biggest threat??• humans because of hunting, pollution, global

warming, and taking over their natural habitat

• “Sharks have no place else to go but in the water. Humans have the choice though of where they are going to be. Therefore it really isn’t fair at all to blame sharks when humans end up in their territory.”

Using Sharks

• For thousands of years, sharks have provided people with a valuable source of food

• Ex. Chinese cooking shark fin soup

Shark fin soup

• Sharks fins are currently one of the most valuable and sought after marine products in the world

Using sharks: Shark oil

• The livers of sharks are rich in oil and this oil has been used for many purposes. In some isolated communities where other resources were not available, it has been used as a fuel for heating and lighting

Shark oil….cont….

• Because shark oil contains large amounts of Vitamin A, which is important for human sight, scientists are investigating the possibility of using shark’s liver oil for human consumption

• A chemical called squalene, which is present in the liver, has several commercial uses: leather, cosmetics, skin creams, medicines and drugs

Using sharks: Shark skin

• Because sharks are covered with DENTICLES, it was only recently that their skins were widely used as a source of leather

• Stronger than cattle hide• Denticles can be removed to produce smooth

leather. Touch leather, “baroso” contains denticles

Using sharks: medicine

• The liver oils of some sharks, especially the deep sea dogfishes, are thought to contain ingredients that can lower blood cholesterol and help prevent blood clotting

• Used to treat heart disease

Saving Sharks:Conservation

• The population numbers in many species of sharks are declining due to harvesting sharks for meat, oil, skin, fins, leather (shagreen), and for sandpaper (skin)

• Some believe that shark cartilage is a “joint nutrient” that may help in the treatment of arthritis

Why are shark populations depleting?

• most sharks have slow rates of growth, mature late and give birth to a small numbers of well-developed young after a long gestation period.

• For example, Basking sharks take at least 15 years to mature, have a gestation period of 2-3 years and produce only 4-6 pups.

• Sharks life history strategy is typical of top predators with few natural enemies; therefore their populations usually decline rapidly when threatened. Hence, if given the opportunity to recover they would do so very slowly, if at all.

Threats:

• #1: Commercial and incidental overfishing• Today, the increasing average wealth of people

(especially in East Asia) together with well-developed fishing methods have led to a vast over-exploitation of many shark populations.

• an estimated 50% of all sharks are caught unintentionally or as 'by-catch' in other fisheries

• #2: Habitat degradation • Besides geographically defined, habitat also

has physical (such as temperature), chemical (such as salinity) and biotic (such as prey availability) aspects

• “habitat destruction “

The importance of shark conservation

• We have no idea what the environmental impact of removing a very large number of sharks from the ocean ecosystems would lead to. Most sharks are top predators and scientists believe it is likely that sharks play a 'keystone' role in marine ecosystems. Predatory sharks assist in their prey's evolution by culling genetically defective and diseased animals and keeping their populations in check. Removal of this control due to extinction is liable to have a detrimental effect on marine ecosystems. Sharks are distributed worldwide and the consequences of their decline will also be widespread.

Important economic resource

• Although sharks contribute to economic growth through directed fisheries and trading of by-products, live sharks can also be economically valuable. Shark predation on weaker and diseased fish creates a stable, healthy and quality supply of fisheries. Besides that, shark populations in their natural habitats are used as the main attraction in sustainable trades such as ecotourism

Medical research

• There are several aspects of shark physiology that can be used to further our knowledge in medicine such as the ability of shark wounds to heal within 24 hours without treatment, the rapid healing and functioning of lacerated shark corneas whereas blindness ensues in other species, and resistance of sharks towards cancer tumours

Intrinsic scientific value

• Shark exhibits many unique and puzzling life history traits and behaviours. For example, there are species of predatory sharks that can detect blood in very low concentrations (Lemon shark). Some species of sharks can osmoregulate their body fluids in both freshwater and marine environments (Bull shark and Ganges shark). Other behaviour such as navigation is thought to be influenced by magnetic and electric fields, lunar movements, chemical stimuli and geographical topography. Besides that, unique forms of nourishment include interuterine cannibalism in reproduction (Sandtiger shark). Scientists have also yet to understand fully other physiology and behaviour such as attack, mating, schooling and use of nursery grounds.

Shark conservation societies

• http://www.bite-back.com/• Pewsharks.com

Top 10 shark conservation projects

• http://dsc.discovery.com/tv-shows/shark-week/lists/top-10-shark-conservation-projects.htm

Sharks and global warming

• http://www.sharks-world.com/sharks_and_global_warming.html

Dogfish Dissection