Transcript 1. dia - DAHAB INFO

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
ATTRIBUTE
SHARKS
BONY FISH
Skeleton
Cartilage only
Bones and cartilage
Swimming
Can only swim
forward.
Can swim forwards
and backwards
Buoyancy (floating)
Large oily liver
Gas-filled swim
bladder
Gills
Gill slits but no gill
cover
Covered gill slits
Reproduction
Eggs fertilized in
female's body.
Eggs usually fertilized
in the water.
Skin
Rough, sandpaper-like Slippery, overlapping
placoid scales
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.
White Tip Shark Tooth
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.
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.
• Whale shark - It has been estimated that
whale sharks may live up to 100 - 150
years.
OCEANIC WHITE TIP
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 world’s 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 razorsharp teeth or superefficient swimming
technique can protect
them from the newest
and greatest predator of
all time — humans.
Jaws (1975)
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)