How sharks benefit the ocean's health, ecosystems

Although sharks have a negative reputation resulting from the fear surrounding potential attacks on humans swimming in the ocean, their presence is hugely beneficial to the health of the world’s oceans and ecosystems.

“The way media portrays sharks has caused a lot of unjustified fear,” said Dr. Guy Harvey, a marine artist and scientist with Nova Southeastern University's Guy Harvey Research Institute.

“There are over 500 species of sharks, and given the amount of people that swim in the water on a daily basis, there are very few human-shark interactions,” Harvey said. “Few result in significant injury.”

Sharks maintain balance, health of food web

These top predators play an essential role of keeping other fish populations healthy and in proper proportion, helping to maintain the balance of marine life, according to experts with the WildAid program, SharkSavers.

Most sharks primarily feed on smaller fish and invertebrates, while some of the larger species consume seals, sea lions or other marine mammals, according to the National Oceanic and Atmospheric Administration’s (NOAA) National Ocean Service.

Across reefs, kelp forests, mangrove estuaries, open and deep ocean habitats, the diversity within ecosystems is maintained and supported by top predators like sharks, said Mike Price, assistant curator of zoo operations at SeaWorld San Diego.

“Sharks’ role in the balancing act is to maintain top-down population control of smaller fishes and other marine life,” Price said. “They keep prey densities within levels that allow for a diversity of species to thrive within the myriad ocean ecosystems.”

Sharks regulate the behavior of prey species through intimidation, which keeps them from overgrazing on important habitats, according to SharkSavers experts, and this intimidation factor is believed by scientists to have a significant impact on the marine ecosystem.

In Hawaii, scientists found that turtles would primarily graze on the most nutritious sea grass in the absence of tiger sharks, which eat turtles. This destroyed these habitats. However, when tiger sharks were around, turtles did not overgraze one area, and instead grazed over a broader section of sea grass, according to SharkSavers.

Sharks also remove the sick and dying fish from the ecosystem to help prevent the spread of disease and keep prey populations healthy, according to Harvey.

This also benefits the prey population by strengthening the gene pool, as it means that the largest, healthiest and strongest fish will likely reproduce in greater numbers, resulting in a greater abundance of healthy fish.

Beyond the myriad of benefits that sharks have for the ocean’s health, they may also positively impact the health of humans.

“Researchers at the Guy Harvey Research Institute are studying the shark genome to determine if sharks’ low incidences of cancer and extremely fast healing rates could be applicable to humans,” Harvey said. “The world needs healthy shark populations.”

What would the ocean be like without sharks?

The absence of a top predator like a shark can throw a marine ecosystem out of balance. Such chaos can result in an unpredictable range of undesirable side effects from damaging marine ecosystem functions to depleting fisheries, according to Price.

Some research has demonstrated the negative impacts of the elimination of shark populations. One such study showed that the shellfish industry was destroyed due to shark fishing in waters off the United States’ mid-Atlantic coast.

Canadian researchers examined 17 marine surveys carried out along the U.S. East Coast between 1970 and 2005, concluding that “scalloped hammerhead sharks and tiger sharks may have declined by more than 97 percent, while bull, dusky and smooth hammerhead sharks may have declined by more than 99 percent,” the New Scientist reported.

“Imagine a coral reef with only one type of fish; a kelp forest devoid of diversity; a mangrove estuary that no longer functions as a nursery for juvenile fishes,” Price said. “These are the types of side effects that occur by removing sharks from ecosystems.”

“Healthy robust shark populations support vibrant marine ecosystems, which, in turn, can support sustainable fisheries for coastal communities,” he added.

If sharks were completely absent from Earth’s oceans, the mid-level predators and herbivorous fish would have less control over their populations and would over-consume their food source, according to Harvey.

“Once that resource is depleted, there would be nothing left to sustain the population of grazers and their populations could collapse, and so on down the food chain,” Harvey said.

“Billions of people around the world depend on the oceans as their primary source of protein, so if sharks were removed and the marine food web collapsed, we would be facing a dramatic food shortage and potential humanitarian crisis,” he added.

Report a Typo