"Sharks have unfortunately fallen victim to the man-hungry stereotype society has created for them," writes international ocean preservation society Oceana. "However, what the world should really fear is a world without sharks."
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Biodiversity
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Sharks are known as apex predators because they are at the tops of their food chains. Their position at the top means they directly affect the populations of their prey. Sharks limit certain species' numbers, which leads to more diversity in ecosystems. When one population grows too large, it can overconsume plant life or other species.
Oceana cited a study, conducted offshore at low-population Hawaiian islands, that showed that areas with more apex predators, including sharks, also had more herbivores.
Natural Selection
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Apex predators such as sharks can influence natural selection, Charles Darwin's theory of survival of the fittest, in other species in their ecosystems. Predators often feed on the weakest and sickest in a species, leaving the strongest to survive and reproduce.
Plant Life
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A Florida International University study indicates that sharks--tiger sharks, specifically--have a correlation with plant life in their ecosystems. The presence of tiger sharks determined the feeding habits of their prey--sea turtles, dugongs and some smaller herbivores. The sharks kept grazing in check by intimidating their prey into grazing on lower-quality sea grasses, a base of many ocean food chains.
Coral Reefs
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Many sharks feed on rays and groupers, which feed on smaller fish that eat algae in coral reefs, according to Oceana. Without sharks, rays and groupers overeat shellfish, causing algae to bloom out of control. The blooms can block out sunlight, which supports coral.
Industry
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Sharks' effects on their ecosystems--or their removal from them--have carried onshore to the economy. According to The New York Times, a 2007 study from Dalhousie University in Halifax, Nova Scotia, showed that the removal of sharks from ecosystems caused increases in cownose rays. The rays in turn overate scallops and other shellfish.
A 2008 Virginian-Pilot report stated that the scallop boomed until about 2000, which was about the same time researchers started noticing sharks' absence.
Killers
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Sharks kill between five and 15 people most years, according to Oceana. People kill more than 100 million sharks. Populations of large predatory fish, including sharks, have decreased by as much as 90 percent in the last 50 to 100 years, according to the conservation society.
On top of hunting sharks out fear, many commercial fisheries reel them in. Some do so by mistake, often throwing them back and leaving them for dead. But others fish sharks intentionally. In China, for example, shark fin soup is a delicacy. Some fishermen ignore laws to hunt the sharks fins, which can sell for as much as $500 per pound, according to a CNN report.
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