How about one specific type of fish, like the shark? Surely we could get an accurate count of just the sharks, right? Actually, probably not!
There happen to be so many different types of sharks that it would be impossible to count them all. There could be a billion or more sharks in all the oceans around the world.
Up until the 16th century, mariners called sharks “sea dogs.” Today, scientists believe there are more than 400 different species of sharks in the world.
The smallest of these — the dwarf lanternshark — is less than seven inches long. The largest — the whale shark — can grow as long as 60 feet, making it the largest fish in the world. (Remember: Whales are mammals, not fish!)
Scientists believe that sharks are older than dinosaurs. The earliest known sharks existed more than 450 million years ago.
Unfortunately, it is rare to find complete fossil remains of sharks. This is because sharks don’t really have bones.
Instead, they have skeletons made of cartilage, which is a kind of connective tissue strong enough to give support but softer than bone. Humans have cartilage in their ears and noses.
Sharks can be found in all seas around the world. Most sharks live in saltwater, but a couple of species — bull sharks and river sharks — can live in freshwater or saltwater.
Unfortunately, many shark species are under attack and are decreasing in numbers every year. Experts estimate that 100 million sharks are killed by people each year.
Sharks are eaten as seafood in many areas, including Japan and Australia. Commercial and recreational fishers are believed to be responsible for the reduced populations of some shark species.