Shark conservation must extend beyond merely protecting shark populations to prioritize safeguarding their ecological roles, according to research published in Science.

“The loss of sharks from ecosystems could have catastrophic consequences for our oceans,” said Mike Heithaus, co-author of the study and executive dean of Florida International University’s College of Arts, Sciences & Education. “When we look around the world, we see that sharks can play lots of different roles in ecosystems – and some of them are really important. That means we need to maintain a diversity of sharks in our oceans as well as a wide range of sizes of sharks. It also means we need to be rebuilding heavily depleted populations and managing for how sharks will function in oceans that are changing due to human uses and climate change.”

Sharks occupy a wide variety of niches and come in a range of sizes and shapes. But exactly what are the ecological roles that sharks play in their habitats? And what is a shark’s importance in terms of how they affect their ecosystems? That’s what the international team set out to prove once and for all.

It’s a well-known fact that big animals have big impacts on their surroundings. So, it’s no surprise that they confirmed that big sharks are crucial in maintaining oceanic balance through their feeding habits and sheer presence. “This study verifies what we’ve long suspected – sharks are critical to ocean health,” said Lee Crockett, executive director of the Shark Conservation Fund which funded the study. Their predatory behavior and size can deter prey from over-consuming vital marine vegetation like seagrass, essential for the ecosystem’s health. Sharks also contribute to ocean health in various ways beyond predation. They transport nutrients across ecosystems by feeding in offshore waters and returning to reefs. Some species facilitate nutrient cycling at the base of the food chain. Sharks can even serve as food for other marine animals and even act as cleaning stations, where fish remove parasites from their bodies by rubbing against the sharks.

And that means all sharks, not just the iconic ones like great white sharks or tiger sharks. “We’re not saying big sharks are the only ones that matter. There’s a lot more that sharks of all kinds are doing to shape entire ecosystems,” said Simon Dedman, FIU marine scientist and co-lead author of the study. “But what we do know is that big sharks of some species are playing an oversized role in ocean health and need better protection. It’s time to have a conversation about everything sharks are doing to maintain ocean health so we can better prioritize conservation efforts and have the biggest impact.”

Their important roles are under threat due to… well, us. From overfishing, climate change, habitat loss, energy mining, and increased shipping activities, anthropogenic threats have made it so that oceanic shark species have seen a 71 percent decline over the past 50 years, 43 percent of shark species are threatened with extinction, the top five reef shark species have been depleted by 63 percent, and 20 percent of reefs no longer have viable shark populations. It’s an alarming trend that is set to get more dire if conservation strategies aren’t put into place as soon as possible.

But what these policies put into place do also matters. The diversity of the threats, the team argue, highlights the need for a more nuanced approach to shark conservation. “This landmark study serves as confirmation that marine conservationists, philanthropists, policymakers, and the public alike need to recognize that sharks are keystone species that have a now-proven significant effect on marine environments,” says Crockett.

Heithaus agrees: “National and international policy must focus on actions that rebuild populations and restore sharks’ functional roles. That requires action to increase both spatial measures like Marine Protected Areas and fisheries management measures like catch/size limits and gear limitations. If people want healthy oceans, we need healthy shark populations.”