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Monday, August 01, 2011

Treehugger Tuesday

In recognition of "Shark Week" I've decided to post a piece about the importance of sharks in the marine environment.


Sharks are more important to us alive

We have already discussed that sharks are being exterminated at an alarming rate, mostly for their fins. But, isn’t it good that sharks are being exterminated? Aren’t sharks dangerous to man?

No, sharks are generally not dangerous to man.

Many people believe sharks to be dangerous because they are often depicted that way in the media. The media magnifies the very rare incidents where a shark bites a human as if these are common and fearsome occurrences. The fact is only 5 people in the entire world will die from a shark wound in an average year, whereas many millions of people swim in the oceans where sharks live. Can you think of any way to die that is as rare than that? Death from bicycle accidents, dog bites, snake bites, or other accidents are many times more common.

The real story of sharks is how vital they are to the health of the oceans.

Sharks play a very important role in the oceans in a way that an average fish does not. Sharks are at the top of the food chain in virtually every part of every ocean. In that role, they keep populations of other fish healthy and in proper proportion for their ecosystem.

Sharks have evolved in a tight inter-dependency with their ecosystem. They tend to eat very efficiently, going after the old, sick, or slower fish in a population that they prey upon, keeping that population healthier. Sharks groom many populations of marine life to the right size so that those prey species don’t cause harm to the ecosystem by becoming too populous.

Where sharks are eliminated, the marine ecosystem loses its balance.

In the parts of the ocean where sharks have been fished out of existence, we can see the dangerous result of removing the top predator from an ecosystem.

In one scientific study1 of the mid-Atlantic part of the United States, 11 species of sharks were virtually eliminated. Of the 14 species of marine life that those sharks used to eat, 12 became more plentiful and caused great damage to the ecosystem.

For example, the cownose ray population was no longer kept limited by sharks and grew out of control. As a result, the rays destroyed the population of bay scallops, their favored food.

But, people like bay scallops, too! The scallop fishery, which had been thriving for over 100 years, was virtually gone, with scallop catch dropping to only 13% of its high point2. And, scallops were also no longer there to perform their function of filtering and cleaning the ocean water.

The lesson is important. Sharks are being killed for their fins for shark fin soup, a food that has cultural value but is not important for human survival or health. However, removing the sharks can result in the loss of important foods that we do depend upon for survival.

Sharks have survived for 450 million years, but may be gone within 10 years.

Life within the oceans, covering 2/3rds of our planet, has enjoyed a relationship with sharks for about 450 million years. Our growing demand for shark fin soup has increased the slaughter of sharks to such a great extent that many shark species are already nearing extinction. They may be all gone within only 10 or 20 years.

What will the health of oceans be like when such an important group of animals have been destroyed? Do we want the destruction of sharks and the oceans to be the legacy we leave for our children?

1. Ransom A. Myers, Julia K. Baum, Travis D. Shepherd, Sean P. Powers, Charles H. Peterson;
Cascading Effects of the Loss of Apex Predatory Sharks from a Coastal Ocean; SCIENCE, MARCH 2007

2. Clyde L. MacKenzie, Jr., The Bay Scallop, Argopecten irradians, Massachusetts Through North Carolina: Its Biology and the History of Its Habitats and Fisheries, Marine Fisheries Review, US National Marine Fisheries Service, June, 2008

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