The largest shark, and also the largest fish
in the ocean is the Whale Shark, which can grow to be 15 m long.
The second biggest fish and shark is the Basking shark (12m).
The Great White shark grows to 6.4 m.
Fossil records indicate that ancestors of modern sharks swam
the seas over 400 million years ago, making them older than dinosaurs!
Throughout time sharks have changed very little.
The smallest shark is a deepwater Dogfish shark. This species
which is found in the Caribbean Sea is mature at under 20cm.
The fastest swimming sharks are the Mako sharks and Blue sharks,
which can leap out of the water. They might also be the fastest
fish. Estimates of their speed vary between 97 kph and 35 kph.
The Blue shark has been known to migrate from 2,000 to 3,000
km in a seasonal journey from New York State to Brazil.
Sharks that swim in open water have a colour pattern called “countershading.” The
upper portion of the shark is dark in colour to make it difficult
to see the shark from above against the dark ocean water. The
underside of the shark is light in colour so it blends well with
the lighter water near the surface when viewed from below. Countershading
makes it difficult for predators and prey to see sharks.
Sharks have an excellent sense of hearing with ears located
inside their heads on both sides rather than external ears like
humans. Sharks can hear best at frequencies below 1,000 Hertz
which is the range of most natural aquatic sounds. This sense
of hearing helps shark locate potential prey swimming and splashing
in the water. Sharks also use their lateral line system to pick
up vibrations and sounds.
Sharks have lots of teeth arranged in layers so if any break
off, new sharp teeth can immediately take their place. Sharks
can lose thousands of teeth during their life. Sharks’ teeth
can be found washed onto beaches. |
