Sharks are deserting coral reefs. Here’s why that matters

As ocean temperatures have soared in the past year, new research shows that some sharks are abandoning coral reefs — a troubling sign for both the cold-blooded creatures and the delicate ecosystems they help sustain.

The study found that as coral reefs heat up, grey reef sharks are spending significantly less time around them, The Guardian reported. Even worse, some sharks don’t return to these reefs for more than 16 months after a major heatwave.

“If it gets too hot, they’re going to need to move,” David Jacoby, a lecturer in zoology at Lancaster University who led the research project, told The Guardian’s Damian Carrington. “We think many are choosing to move into offshore, deeper and cooler waters, which is concerning. Some of the sharks were disappearing entirely from the reef for long periods of time.”

Between 2013 and 2020, researchers tracked more than 120 grey reef sharks in the Indian Ocean’s remote Chagos archipelago. They found that while it took months for the sharks to return to most of the reefs, sharks also spent more time sheltering in healthier and more resilient reefs.

Sharks play an essential role in maintaining the biodiversity and health of coral reef ecosystems by keeping fish populations in check. Without them, that delicate balance could fall apart.

Yet reef sharks have already disappeared from nearly a fifth of coral reefs globally, due to overfishing and other threats.

Reef sharks are vital for healthy reefs, but overfishing and climate change threaten that delicate balance. © Keith A. Ellenbogen

The good news: Protecting areas of the ocean can bring them back.

Two decades ago, for example, the coral reefs of Indonesia’s Raja Ampat archipelago were nearly destroyed by overfishing. But initiatives supported by Conservation International, including the creation of an expansive network of interconnected marine protected areas, gradually brought the ecosystem back from the brink — sharks, manta rays and whales have returned, and coral reefs are recovering. 

That now-thriving ecosystem is the backdrop of an audacious plan to reintroduce zebra sharks, a type of reef shark that has nearly disappeared from the region due to overfishing. Scientists are breeding the sharks in captivity and releasing them into the wild — it’s the first time endangered sharks have been bred in captivity to restore struggling populations. Last year, the first three zebra shark pups were released into Raja Ampat’s waters, said Mark Erdmann, the Conservation International marine biologist who came up with the idea.

“Sharks are some of the most misunderstood, and threatened, species on the planet,” Erdmann said. “We have an opportunity to give them a fighting chance.”

Further reading: How an extraordinary new effort is giving sharks ‘a fighting chance’

Mary Kate McCoy is a staff writer at Conservation International. Want to read more stories like this? Sign up for email updates. Also, please consider supporting our critical work.