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Did you know that some sharks are herbivores? That there's a much bigger chance of being killed by a cow than by a shark? And that sharks have been keeping our oceans healthy for hundreds of millions of years?
It's time to change the “Jaws” narrative and properly value sharks for their amazing contributions.
Sharks are vital to ocean health—without them, marine ecosystems can collapse. But shark populations are quickly declining. In fact, humans are the main culprit, killing an estimated 100 million sharks every year by overfishing. And that massive loss of sharks is harming the underwater ecosystems that rely so heavily on them.
Many sharks are top predators, ruling the oceans they live in. But because of this mighty role, their loss can have ripple effects through the food chain that throw entire ecosystems off kilter.
When larger sharks are overfished, populations of mesopredators—smaller predators that these sharks feed on—spiral out of control. An increase in the number of mesopredators may then lead to a depletion of other resources, harming their environments. For example, if snapper and grouper become too numerous on coral reefs because of limited reef shark populations to prey on them, these mesopredator fish will overconsume their food source: algae-eating fish. Without adequate populations of algae-eating fish in the ecosystem, algae may take over, smothering and killing the coral.
Another way that sharks help ocean ecosystems is by supplying them with vital nutrients. The ocean’s shallow waters tend to lack nutrients. Sharks help nourish these areas by diving to feed on deep-water organisms, swimming to shallow waters and pooping. By shuttling between the deep and shallow waters, sharks enrich the latter with essential nutrients.
For example, grey reef sharks serve as nitrogen couriers, transferring this key nutrient from the deep ocean where they eat, to shallow, nutrient-poor coral reefs via their excrement. The nitrogen acts as a fertilizer for the thousands of species that live in the reef environment. Without sharks around to transport nitrogen, the biodiversity in coral reef ecosystems would struggle.
Did you know that sharks can help combat global warming? Scientists have discovered that just by existing, they have a role in keeping greenhouse gases out of the atmosphere and in the oceans.
Tiger sharks in Australia, for instance, scare sea turtles away from underwater seagrass meadows. In doing so, the sharks prevent the turtles from overgrazing on the seagrasses. Seagrasses are an important holder of blue carbon—the carbon captured by the world’s oceans. They form dense underwater meadows that suck carbon dioxide (a greenhouse gas) out of the atmosphere. Plummeting shark numbers means more sea turtles around to deplete the seagrasses which, once destroyed, release their blue carbon stores and contribute to global warming.
A shark’s body is another source of blue carbon—the carbon captured by the world's ocean and coastal ecosystems. Sharks are made up of 10–15% carbon. When they die naturally, their bodies sink—along with that carbon—to the depths of the ocean. They become deep-sea carbon reservoirs for thousands or even millions of years. But overfishing of sharks means much of that carbon rises out of the ocean and into our atmosphere.
The sad reality is that sharks now need our help to carry on performing their vital ecosystem services.
Sharks are declining at a staggering rate. More than one third of shark species are currently threatened with extinction. There are 71% percent fewer sharks on the open ocean today than there were 50 years ago.
Global demand for shark meat and fins is the biggest culprit. But sharks are also quickly losing their habitats, especially those that reside in coastal areas that are being developed without proper regulations.
All of the threats sharks face are amplified by the fact that most sharks live their lives in the slow lane. They are slow to mature and have babies, and humans are fishing out many species faster than they’re able to reproduce.
Having more sharks around to perform their critical ecosystem functions keeps the oceans healthy and reduces the impacts of global climate change. That means efforts to conserve sharks benefit more than just the sharks themselves; they help the entire planet.