KOROR STATE GOVERNMENT MARINE TOUR GUIDE ... - C3

3.8.3 Sharks
A lot of bad publicity (and movies!) have made many people fear sharks. Although some
of the sharks encountered on the reef have the potential to be dangerous, most sharks
are shy and will not bother divers if they are not fed and are left alone.
Characteristics
Skeleton made of cartilage
5-7 gills (usually 5)
no swim bladder
renewable teeth
skin covered with small teeth called denticles
have an electrical sense to detect prey
Role on the Reef
Like the lions of the African savanna, sharks play a vital role in the reef system, being
top predator. They remove the sick, injured and old and help control animals whose
populations are booming. By removing sick or injured animals from the fish populations,
mostly the healthiest fish are left to breed; therefore sharks play an important role in
maintaining healthy fish population that we depend on for food.
For millions of years, sharks have been top of the food chain, but now this has changed.
The removal of millions of sharks each year is upsetting the balance in the oceans.
Types of sharks
Sharks can be divided into two categories:
1. Bottom-dwellers – usually found resting on the sea floor. Easily recognized by an
opening behind their eye known as a ‘spiracle’. Water is pumped in through this
opening and out through the gills. (i.e. Leopard shark, Epaulette shark, and the
Wobbegong.
2. Mid-water sharks – do not possess a spiracle and most rely on a constant flow of
water through their mouth and across their gills as they swim. However, some
species, such as the white tip reef shark, are able to lie motionless and pump
water by opening and closing their mouths.
Senses
Sharks sense of smell is of great importance in sensing prey. Blacktip reef sharks have
been found to be able to sense one part grouper in 10 billion parts of water. Sharks also
possess a sixth sense. (i.e. the ability to sense minute electric fields generated by all
living organisms. This is detected through the small black pores located on the snout of
sharks. Sharks can detect voltages as low as a hundred millionth of a volt!
Reproduction
Males can be easily identified by the presence of two-finger like reproductive organs
called claspers, located in the pelvic region, on their underside. Females often have
mating scars on their backs, from when males grip them with their teeth. The male
inserts one of his claspers into the female in order to fertilize her eggs. Most reef sharks
give birth to live young, which quickly swim away from the mother when born.
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