Four Hundred And Seventy

There are over 470 species of sharks and they have been living on Planet Earth for 420 million years.

The smallest shark - the dwarf lantern shark - is only 17 centimeters (6.7 inches) in length, while the whale shark is the largest specie in the world, with approximately 12 meters (39 feet).

Sharks live in all oceans down to depths of 2,000 meters (6,600 feet). Usually, they do not live in freshwater with the exception of the bull shark and river shark.

Teeth and jaws of sharks are deadly, but only the great white, oceanic white tip, tiger and bull sharks are responsible for fatal attacks on humans. The International Shark Attack File reveals that between 1580 and 2012, up to 2569 people lost their lives due to shark attacks.

USA and Australia are the most sharks infested countries in the world. From year 1580, a total of 510 shark attacks killed 144 people in Australia. In the United States, 1022 attacks have already caused 36 deaths.

Florida and California have been suffering more than any other US state. With a total of 772 attacks, both territories have claimed 21 lives. Maui, Oahu and Kauai record all fatalities (8) ever in the Hawaiian Islands.

Cartilage

Chondrichthyes are called cartilaginous fish. You can see the clear difference from their cartilage frame. Sharks, skates and rays are the main examples of Chondrichthyes fish. This type of fish usually does not have a connection between the upper jaw and skull. It gives them great difficulty as well to move it independently. The main structure of Chondrichthyes fish is comprised of ten cartilage parts. Chondrichthyes fish also have eyelids to protect their eyes and at the same time, Chondrichthyes fish usually do not have ribs and bone marrow. The dermal dental structure is also slightly different than Osteichthyes fish. Chondrichthyes fish and their red blood cells produced in the spleen as the two lobes of the fin are not equal in size. The size of the two lobes of the fin is important as they give them sharp mobility in the water. The fin is parallel to the longitudinal axis of the main body in Chondrichthyes fish. Chondrichthyes' fins that are parallel to the longitudinal axis of the main body basically helps them to balance and move fast in the water. Chondrichthyes are often called living fossils while many scientists believe that their evolution is in progress for the past 420 million years

Read more at: Difference between Chondrichthyes and Osteichthyes http://www.stepbystep.com/difference-between-chondrichthyes-and-osteichthyes-101533/

Sharksafe

Stellenbosch University scientists have developed an eco-friendly shark barrier which can be used as an alternative to a shark net.

The barrier is called Sharksafe.

Shark nets were introduced to reduce the number of shark attacks on swimmers but they have resulted in the death of other sea animals including dolphins and turtles.

Countries including Australia, Japan and the US are looking at alternatives to shark nets while in Cape Town new shark exclusion nets which can be removed daily have also been developed.

Professor Conrad Matthee, head of the Department of Botany and Zoology, said shark numbers had decreased by up to 90 percent over the past 20 years, “particularly the number of great white sharks”.

“Sharks are top predators and if they were to be taken out of the ecosystem, the latter will be disrupted. 

Mya

The megalodon was the largest shark of all time. Its scientific name is Carcharodon megalodon. It lived from 20 to 1.5 million years ago (mya). This giant of a shark was a huge version of the current great white shark (Carcharodon carcharias). Megalodon had teeth, which are among the largest ever found, over 18 cm (7 inches) long. Fossil remains suggest that this giant shark reached a maximum length of 15.9–20.3 metres (52–67 ft) and weigh over 60 tons.