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Shark Population Decline Creates Major Changes in the Oceanic Ecosystem - June 11, 2017

Shark Population Decline Creates Major Changes in the Oceanic Ecosystem

We have all grown to know and love the glamorous Mary Lee, the celebrity great white shark that made her debut a few years ago. But besides the sightings and horror stories on the news how much do you really know about sharks?

The most common sharks found here on the eastern shore are the common hammerhead, Atlantic mako, sand shark, smooth dogfish, spiny dogfish, and the sandbar shark.

Sharks are considered an apex predator species, meaning they have very few natural predators.  They tend to be more active in the evening because that is when they feed. Sharks also have the ability to swim across entire ocean basins. They mature very slowly and cannot reproduce until they are at least twelve years old, which is about half their life span. When they are able to reproduce, they can only spawn one to two pups at a time. Because of this slow growth process, sharks have a hard time recovering from population decline.

Two major causes of the decline in shark populations are shark finning and bycatch issues. Shark finning is when fishermen slice off the shark’s fins and discard the rest of the living body into the ocean. Without their fins, sharks cannot swim properly and therefore drown or bleed to death.  The fins only make up 1-5% of the body, whereas the rest of the carcass is wasted. These fins are sold for up to five hundred dollars per pound and are used in shark fin soup, which is sold in China. To the Chinese, this soup serves as a delicacy and as a status symbol within their culture.  

Bycatch is a term used when non-targeted organisms are unintentionally caught as fisherman are looking to land specified fish, crustaceans, etc. Once the non-targeted organisms are caught, they are often thrown back into the water injured or dead.  One main contributor to this is the use of longlines.  Longlines are fishing lines that can stretch up to 60 miles off the back of a ship and have secondary lines attached to them. These secondary lines are filled with hundreds of baited and barbed hooks. Longlines are usually used for catching tuna, swordfish, and Patagonian toothfish; however, sharks are unintentionally caught as well.        

Sharks are not only being captured for fins, but also for the shark’s liver. Shark liver oil, also known as Squalene, is used in various cosmetics, lotions, and health supplements. However, the health supplements have inconclusive benefits. Is it worth killing more sharks for something that may not even work? Deep-water sharks are the primary targets for liver oil harvesting. This is because their liver makes up thirty percent of their body weight.

Coastal development is another major threat to the shark population. Development has led to a decrease of inshore habitat, which means less space for sharks to feed and give birth. Tied in with this, human impacts usually increase pollution in the water. Shark’s prey is being contaminated from toxins that they ingest from the water, which then the shark digests. Another human impact is the use of sharks as souvenirs. Many sharks are killed for only certain parts of their body, such as the jaw, and the rest of the shark is wasted. Lastly, in some areas shark nets are used to keep them away from beaches so that the bathers can swim safely. However, as the net does its job, sharks get caught and will eventually die if not released.       

As the shark population decreases, the mesopredator population increases. These mesopredators include smaller sharks, rays, and other marine mammals. As mesopredator populations increase, they consume a greater number of smaller fish, crustaceans, and shellfish, which includes some commercially important species.

Sharks are quite important for the oceanic ecosystem; They feed on the old, sick, or slower fish. Because of this, fish species become healthier over time. This helps prevent outbreaks and spread of disease throughout the fish population. The healthier fishes are the ones that survive to reproduce, which creates a stronger population.    

Having a healthy shark population is crucial to having a healthy oceanic ecosystem. Sharks are considered a keystone species; without them the structure of the ecosystem would change remarkably for the worse. Sharks have been able to survive for 450 million years without any major threats, but now due to human impact they could be extinct within the next few decades. Should we be afraid of sharks, or should they be afraid of us?   

Karley LeCompte is a ShoreCorps/PALS Americorps Volunteer with the Maryland Coastal Bays Program. 



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