Shark

General information
The earliest known species of shark dates to more than 420 million years ago. Since, 440 species have diversified with many different sizes and appearances. The largest known fish is the Whale shark, Rhincodon typus, which can reach a length of 12 metres and feeds on plankton, squid, and small fish. The smallest known shark is the Dwarf lanternshark, Etmopterus perryi, which can reach a length of only 17 centimeters. Sharks are most commonly found within 2,000 metres of the surface and generally do not live in freshwater, which exceptions such as the Bull shark and the River shark which can live in both freshwater and seawater. Sharks are covered in dermal denticles that protect their skin from parasites and damage that as well improve their fluid dynamics allowing them to move faster in water. Sharks have five to seven gills through which they breathe. They also have several sets of replaceable teeth. Sharks are usually at the top of the underwater food chain, but their survival is threatened by fishing and other human activities.

Fishing
Due to commercial and recreational fishing, humans kill about 100 million sharks a year. Sharks are commonly eaten in many places, including Australia and Japan. In Victoria, Australia, shark is most commonly eaten in fish and chips, when it is called "flake." Small sharks or baby sharks are sold in local markets in India. As the flesh isn't developed in baby sharks, cooking it breaks it down into a powder which is then fried in oil and used for spices. The soft, chewable bones are a delicacy in some parts of India.

Sharks are frequently killed for shark fin soup. Fishermen capture live sharks and use a hot metal blade to remove the fin and dump the rest of the animal back into the sea. The shark is left immobile and quickly dies from suffocation or predators. As a result, shark fin is a major trade in black markets around the world. Shark fins can sell for about $300 per pound. Because few governments enforce the laws that protect sharks from finning, poachers illegally fin millions of sharks a year.

Shark fin soup is considered healthy and full of nutrients as well as a status symbol in some Asian countries. Sharks are also fished for their meat. In Europe, dogfishes, smoothhounds, catsharks, makos, porbeagles, skates, and rays are consumed in the common diner. The U.S. FDA declares sharks as one of four fish that has a mercury content hazardous to children and pregnant women.

Sharks produce few offspring compared to other harvested fish and reach the age of sexual maturity after many years. Fishing sharks before they are able to reproduce has a strong impact on future popluations. Most shark fisheries lack monitoring or management. Due to recent increase in demand for shark products, many species are experiencing high amounts of depletion. While at the extreme, some species are experiencing 90% depletion, it is not uncommon for others to face 70% depletion. Some governments and the U.N. have recognized the need for protection of sharks but little effort has been made towards their protection due to their poor public image and low economic value.