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How many sharks are endangered?

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By Blaise Jones

Sharks have survived every major extinction event that has hit this planet since their species first evolved. However, past performance does not necessarily ensure future survival. More than 25 percent of all shark, rays, and skates are endangered or threatened, according to the International Union for the Conservation of Nature. The majority of the 80-plus species of sharks and rays that are threatened live in the open ocean where they fall are susceptible to fishing lines, nets, and other manmade perils.

Hammerhead shark. Credit Bryan Scott.
Hammerhead shark. Credit Bryan Scott.

In 2014, the scalloped hammerhead shark became the first shark species listed on the U.S. Endangered Species list. The hammerhead joins great white sharks, whale sharks, basking sharks and dusky sharks as some of the most threatened shark species in the world.

Agent of Extinction?
Despite their ferocious nature, there has been no record of any sharks driving another species into extinction. The same, however, cannot be said for their close cousins. Sharks, rays, and skates are members of the Elasmobranchii subclass of Chondrichthyes; and the cownose ray is known to do more economic and ecological impact on an environment than any shark species. Cownose rays can swim in schools so large that they strip the ocean bottoms bare in their hunt for prey. Shellfish industries along the east coast of the United States, particularly in Virginia and Maryland, have seen crab, scallop, mussel, oyster and clam populations devastated by massive schools cownose rays feeding.

Due to their slow maturation and low fecundity (rate of successful reproduction), sharks simply lack the numbers to put a dent into populations of their prey.

Please Don’t “Go Fish”
However, there’s plenty for sharks to be concerned about. Sharks face several major threats to their populations, all of them due to humans. Fishing is the biggest concern for the future of shark populations. Sharks are fished commercially for their meat, cartilage, and fins. Some are harvested for the oil that their livers produce, which is used in many forms of traditional medicine.

Many sharks are fished exclusively for their fins in order to make shark fin soup, which is considered a delicacy and status symbol in many Asian countries. Because sharks reproduce in small numbers and take so long to mature it is difficult for populations to rebound after being heavily fished.

Shark Bycatch
The nets the fishing industry use to catch fish also catch many other species including sharks, turtles, dolphins and whales. Complicating the issue is that sharks are attracted to the manmade danger because of the struggling fish caught in the nets. The dying fish bloody the water and emit electrical signals in their fight, both of which attract sharks, luring them to the lethal nets. Though the nets were designed to catch fish, not sharks, the manmade webs end up being the manner of death for millions of both each year.

Pollution And Sharks
The third threat sharks face is habitat degradation. This is when the habitats sharks use to hunt and reproduce are either damaged via pollution or destroyed to make way for construction projects. Even when habitats are not fully destroyed, the pollution and waste from these projects can harm sharks. If the water is too dirty or filled with too much debris, sharks cannot properly filter the water and suffocate.

Pollution doesn’t even have to directly affect sharks in order to harm them. Pollution and habitat degradation weaken and kill the species that sharks prey upon. If the prey population of an ecosystem dies, then predators, such as sharks, die with them.

The fish sharks feed upon do not even have to die for sharks to be affected. Smaller fish can become contaminated and rendered poisonous by pollution, making them dangerous for consumption. As sharks eat more and more of the contaminated fish, poison accumulates in the shark’s body in a process known as “bioamplification.”

Out-Competed
On top of all those dangers, sharks are now facing competition from the most lethal predator on the planet: humans. Industrialized fishing fleets have become so efficient that they can wipe out the populations of dozens of fish species in an area seemingly overnight. With such ecosystem devastation, sharks are left with nothing to eat and face starving to extinction.

The End?

All of these factors have led to a huge decrease in the populations of shark species. Of the estimated 495 known shark species, 201 are endangered to some degree, and this number includes only the species that have had population surveys performed upon them. As researchers learn about the long-term health of more shark species, the number of endangered sharks is likely to rise. Which guarantees only one thing for sharks: no guarantees.

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SOURCES:
http://www.shark.ch/Preservation/EndangeredSharks/index.html?lim=8&slang=2

http://www.seethewild.org/shark-threats/

“The Encyclopedia of Sharks” by Steve Parker

“Sharks: The Animal Answer Guide” by Gene Helfman and George H. Burgess

http://www.iucn.org/?14311/A-quarter-sharks-and-rays-threatened-with-extinction

http://www.discovery.com/tv-shows/shark-week/bios/endangered-sharks/

 
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