Presentation on theme: "What is a shark? Sharks are amazing fish that have been around since long before the dinosaurs existed. They live in waters all over the world, in every."— Presentation transcript:
What is a shark? Sharks are amazing fish that have been around since long before the dinosaurs existed. They live in waters all over the world, in every ocean, and even in some rivers and lakes. Unlike bony fish, sharks have no bones; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. Sharks also have no swim bladder (unlike bony fish). Sharks belong to the group of cartilagenous fish, that includes the sharks and rays.
The Evolution of Sharks Sharks have existed for over 350 million years. They evolved over 100 million years before the dinosaurs did. The earliest-known primitive shark remains are fossil "scales" that date from about 420 million years ago.
MAJOR DIFFERENCES BETWEEN SHARKS AND BONY FISH ATTRIBUTESHARKSBONY FISH SkeletonCartilage onlyBones and cartilage SwimmingCan only swim forward. Can swim forwards and backwards Buoyancy (floating)Large oily liverGas-filled swim bladder GillsGill slits but no gill cover Covered gill slits ReproductionEggs fertilized in female's body. Eggs usually fertilized in the water. SkinRough, sandpaper-like placoid scales Slippery, overlapping scales
TEETH Sharks may have up to 3,000 teeth at one time. Most sharks do not chew their food, but gulp it down whole it in large pieces. The teeth are arranged in rows; when one tooth is damaged or lost, it is replaced by another. Most sharks have about 5 rows of teeth at any time. The front set is the largest and does most of the work.
DIET Sharks vary greatly in their diets, but they are all carnivores (meat eaters). Sometimes they even take a bite out of us
DO SHARKS SLEEP? Fish don't sleep in the same way that we do, but they have active and inactive periods. Some sharks (like the nurse shark) have been observed resting motionless on the sea floor. Others have to keep moving in order to breathe.nurse shark
SHARK BUOYANCY 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. The oil in the liver is lighter than water and gives the shark some buoyancy, but it is still heavier than water and will sink if it dos not actively swim. Some sharks livers are up to 25% of the animal's body weight.
THE SHARK'S SIXTH SENSE Their sixth sense can detect very weak electrical fields that can detect electrical "vibes" as weak half a billionth of a volt. Struggling or scared animal creates a strong electrical current, which flows through the water which sharks can pick up. A shark can find animals under the sand, and at night, and at the last moment of the attack the eyes are rolled back and it cannot see. Large number of hammerheads can be found near underwater volcanoes which attract them from miles away with their electrical fields.
HEARING The shark has an excellent sense of hearing and can hear the low pulsing sounds made by animals swimming, splashing, and struggling. These sounds are too low for humans to hear, however sharks can hear them from a thousand miles away. Sharks do not have external ear flaps, but instead have ears inside their heads on both sides of the brain case. Each ear leads to a small pore on the sharks head. A shark's inner ear can also detect acceleration, and gravity.
SIGHT It was once thought that sharks had very bad eyesight, and were nearly blind. It is know known that sharks have very good eyesight, some better then ours. Some sharks roll their eyes back during attack for protection.
SHARK REPRODUCTION Unlike most bony fish, shark's eggs are fertilized inside the female's body. Baby sharks (called pups) are born with a full set of teeth and are fully ready to take care of themselves. They quickly swim away, even from their mothers who might eat them. Litter size ranges from one to fifteen for the Oceanic White Tip.
SHARK LIFE SPAN Great White Shark - No one knows the life span of the great white shark. Some people estimate it to be about 100 years, but this has not been proven.Great White Shark Whale shark - It has been estimated that whale sharks may live up to 100 - 150 years.Whale shark
Oceanic White Tip Shark (Carcharhinus longimanus) Habitat: Open Ocean. May cruise close to isolated islets but is not a common inshore visitor. To at least 180m depth. Abundance and distribution: Circumtropical and temperate. Recorded in the Western Atlantic from New York to Uruguay. Commonly seen at the Red Sea. Size: Maximum length 3.95m. Usually under 3m.
Oceanic White Tip Shark (Carcharhinus longimanus) Identification: Long, broadly rounded pectoral and first dorsal fins. Blotchy white colouration on tips of pectoral, first dorsal, pelvic, and lower caudal fins. Second dorsal and anal fin tipped in black. Dorsal colouration olive brown to bronze. Ventral surface pale.
Oceanic White Tip Shark (Carcharhinus longimanus) Cruises over deep reefs and through open oceanic regions in search of oceanic bony fishes such as tuna. Sometimes follows pods of pilot whales probably due to their ability to find squid and may feed on injured individuals. Oceanic whitetips can lift their noses out of the water and sniff the air to find prey over greater distances than by following water borne scent trails.
Pictures by Marlies Lang Red Sea, South Safari 09/2006
Sharks in danger SHARK FINNING Humans kill at least 100 million sharks every year, and probably many millions more. Half or more of sharks killed are "bycatch," snagged while fishermen are targeting other species on longlines or in enormous trawl nets. Although global populations are unknown, scientists agree that the numbers of many species are plummeting.
Marine Ecosystem Balance Sharks, like all top predators, play a critical role in keeping the marine food web in balance. Without them, numbers of mid-sized and smaller fish can quickly boom and then crash when their own food supply runs out. Yet despite their importance to the marine ecosystem, and by extension to commercial fisheries, surprisingly little is known about the life history, habits and numbers of the worlds sharks, and surprisingly few efforts have been made to reduce catches.
Human predators Sensational media coverage, movies and myths have contributed to sharks fearsome reputation. But no number of razor- sharp teeth or super- efficient swimming technique can protect them from the newest and greatest predator of all time humans.
WHAT YOU CAN DO Never eat sharkfin soup and refuse to patronize restaurants that do. Avoid any medicines or supplements that profess to utilizing the healing power of shark cartilage or any other part of a shark. Don't buy shark teeth (unless fossilized), shark jaws, or any items made with shark skin. Do not join shark cage diving. Do not go shark fishing.
Special thanks to Tota Dance Bar www.dahab-info.com On-line Internet Café (at Aladdin)