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Are any sharks endangered?

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Slaughtered sharks on display at a market in Indonesia.

By Blaise Jones

Yes. Chondrichthyes (sharks, stingrays, and chimera) are one of the most endangered groups of vertebrate animals on the planet. According to the International Union for the Conservation of Nature (IUCN), all chondrichthyes are on the extinction watch list, and only 23 percent of all of them are listed as “Least Concern.” Some species of shark have seen their populations decrease by up to 99 percent in the past 30 years (bull shark, shortfin mako, others).

“Bycatch” is the term for animals killed accidentally by fishing nets that were not intended to catch other animals.

Sharks appeared on earth more than 200 million years before dinosaurs, but are now facing extinction due to many reasons.

All ecosystems in the world are tied together via subtle similarities not immediately apparent to the casual observer. One such similarity is the balance between predator and prey. While some ecosystems have found unique exceptions, prey species almost always outnumber predator species.

The ideal ratio between predator and prey has been crafted over eons of natural selection. The evolutionary fight for survival of both parties has led them to adapting both biologically and behaviorally. Sharks are no different.

Reproductive Woes

Sharks reproduce at a very slow rate. While the average age of maturity in sharks is between 15-16 years, it can vary. Some shark species take only two years to reach sexual maturity, others take close to 30. Evidence in recent studies leads many researchers to claim the Greenland shark doesn’t reach sexual maturity until at least it 70 years old.

Sharks have a low reproductive turnover rate. They can’t afford to have offspring too often, because overlapping generations would create unsustainable competition and could lead to a trophic cascade, which harms the entire environment.

Additionally, sharks, unlike bony fish, produce very few offspring. While some sharks, such as a the whale shark, can produce hundreds of offspring a year, most sharks are like the sand tiger, who only has one or two pups per year. All of these factors naturally keep shark populations lower than other fishes.

In Hot Water

Ecosystems of the world are changing at a faster pace than they ever have before. The most pressing of these is global climate change. The global climate has always been fluid, changing from periods of higher temperatures to lower temperatures. However, this process takes millions of years to naturally occur, giving the ecosystems time to slowly adapt. Times where the global climate has shifted radically, like in now, have always resulted in mass extinctions.

Right now we’re already seeing the effects of climate change on the oceans of the world. The massive amount of carbon being cycled into our oceans is increasing the acidity of the water. This is killing off hundreds of microorganism species, which are the basis for most marine food chains. Acidification is also killing coral reefs, which provide homes for 25 percent of all marine life on the planet.

The warming temperatures are causing many fish species to migrate into areas they’ve never been found before, leaving their traditional habitats barren. Sharks are forced to follow their prey into unfamiliar waters, making eons of instinctive behavior obsolete in just a few years.

However, sharks have been around for a long time. They’ve lived through four and possibly five major extinction events that have happened throughout Earth’s history. Why are they suffering this time?

As Dangerous as Humanly Possible

Never before in the history of this planet have sharks been the target of direct mass predation. Humans have hunted sharks for hundreds if not thousands of years for their teeth, skin, liver oil, skeletons, and meat. However, now more than ever before sharks are targeted by many fisheries specifically for their fins in order to make shark fin soup, a delicacy in many Asian countries. In fact, the most critically endangered sharks, including the blue shark, thresher shark, and oceanic whitetip shark, are classified as threatened because of their value to shark finners. The fins of these animals can fetch prices of up to $20,000 per fin. Unfortunately, the price only rises as the species become more rare.

It’s not only direct fishing that’s affecting sharks. According to the United Nations Food and Agriculture Organization more than a billion humans rely on fish as their primary food source, with as many as 4.3 billion relying on fish for 15 percent of their diet. The oceans are rapidly being depleted of fish and shellfish that sharks need in order to survive.

Bycatch

The nets and fishing lines intended for other species unintentionally kill sharks as well. This is called bycatch, and if affects everything from sea turtles to dolphins. It’s impossible to know the exact numbers of sharks humans kill each year, but estimates range from 100 million to more than 270 million sharks killed each year by humans. To put that in perspective, the conservative estimate of 100 million sharks killed by humans each averages out to be 11,417 sharks killed every hour. Only 10-15 people die worldwide from shark attacks each year on average.

So, yes, sharks are endangered.

SOURCES:

  1. “The Encyclopedia of Sharks” by Steve Parker
  2. “Sharks: The Animal Answer Guide” by Gene Helfman and George H. Burgess
  3. https://www.iucn.org/content/quarter-sharks-and-rays-threatened-extinction
  4. http://www.sharktrust.org/en/conservation_status
  5. http://www.sharktrust.org/en/shark_teeth_and_jaws
  6. http://www.sharktrust.org/en/shark_liver_oil
  7. http://www.sharktrust.org/en/shark_cartilage
  8. http://www.sharks-world.com/sharks_endangered/
  9. http://www.sharksavers.org/en/education/biology/shark-and-ray-reproduction/
  10. http://www.fao.org/docrep/003/X2352E/x2352e06.htm
  11. http://www.sciencedirect.com/science/article/pii/S016578361400085X
  12. http://www.globalchange.umich.edu/globalchange1/current/lectures/predation/predation.html
  13. http://www.iflscience.com/plants-and-animals/universal-pattern-governs-ratio-predators-prey/
  14. http://www.techtimes.com/articles/82432/20150906/new-law-nature-determines-predator-prey-ratio-systematic-way-study.htm
  15. https://www.skepticalscience.com/Can-animals-and-plants-adapt-to-global-warming.htm
  16. https://www.skepticalscience.com/climate-change-little-ice-age-medieval-warm-period.htm
  17. http://voices.nationalgeographic.com/2016/11/30/marine-scientist-follows-hot-fish-as-they-move-to-cooler-waters/?hd&utm_campaign=2016-12-13+SFN&utm_medium=email&utm_source=Pew
  18. http://www.bbc.co.uk/nature/extinction_events
  19. https://www.skepticalscience.com/ocean-acidification-global-warming.htm
  20. http://smallplanet.org/content/one-billion-people-depend-seafood-their-primary-protein-source
  21. http://www.sharkproject.org/haiothek/index_e.php?site=gefahr_5
  22. http://www.iflscience.com/plants-and-animals/how-many-sharks-do-humans-kill-hour/

-TSF-

#sharks #endangered #IUCN #threatened #TSF

 
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