What happens when great white sharks disappear? Hint - it's not good

Great white sharks are top predators in ocean ecosystems and are known for their raw power and hunting prowess. They often launch themselves out of the water in pursuit of prey.

But in South Africa’s False Bay, these apex predators have all but vanished – and scientists are sounding the alarm about what that means for the rest of the ecosystem.

A new study from the University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science reveals what happens when a top predator is suddenly removed from the food chain.

After more than two decades of research in False Bay, the team found significant shifts in the marine food web that are consistent with long-held ecological theories.

Understanding great white sharks – the basics

To state the obvious, great white sharks are the rock stars of the ocean – massive, powerful, and a little bit mysterious. They can grow over 20 feet long and weigh a couple tons, cruising through the water like it’s nothing.

These sharks hang out in coastal waters all over the world, but they especially love cooler regions like the coasts of California, South Africa, and Australia.

With those rows of razor-sharp teeth and an uncanny ability to sense the tiniest movements, they’re built to hunt.

Seals, sea lions, and fish are usually on the menu, and when they strike, it’s fast and fierce – like a torpedo with teeth.

Despite their scary rep, great whites aren’t the mindless man-eaters movies make them out to be. They’re actually pretty curious creatures.

Sometimes, they’ll take a “test bite” out of something unfamiliar just to figure out what it is – which, unfortunately, can include surfboards.

In order to save them from the brink of extinction, scientists have been tagging and tracking them to learn more about their behavior, migration patterns, and even social lives.

Disappearance of great white sharks

False Bay was once home to large numbers of great white sharks (Carcharodon carcharias), but sightings have plummeted in recent years, indicating that the population may have crashed.

The study points to two major reasons for this decline: the long-term impact of capture in protective nets near swimming areas, and more recent predation by orcas.

Ripple effects in the food web

The absence of white sharks is reshaping the ecosystem. Without these predators, Cape fur seal (Arctocephalus pusillus) populations have increased.

So have the numbers of sevengill sharks (Notorynchus cepedianus), which are now more dominant in the area.

These changes, however, have consequences. The seals are depleting the local fish populations they feed on. Meanwhile, the sevengill sharks are preying on smaller shark species, and reducing their numbers.

These shifts demonstrate how the removal of a single species at the top of the food chain can have wide-reaching effects across multiple levels.

Documenting the ecosystem changes

The researchers used a combination of methods to document these changes. They conducted long-term boat-based surveys, gathered citizen science reports of Cape fur seals, and analyzed data from Baited Remote Underwater Video Surveys (BRUVS).

“The loss of this iconic apex predator has led to an increase in sightings of Cape fur seals and sevengill sharks, which in turn has coincided with a decline in the species that they rely on for food,” said Dr. Neil Hammerschlag, the study’s lead author.

“These changes align with long established ecological theories that predict the removal of a top predator leads to cascading effects on the marine food web.”

Video footage was a key source of information. It helped researchers see not just which species were present, but how they behaved.

“The use of underwater video surveys conducted more than a decade apart provided us with a snapshot of the food web both before and after the disappearance of white sharks from False Bay,” said Yakira Herskowitz, a co-author of the study.

“The number of individuals of a given species recorded on the videos not only informs us about their numerical abundance, but also their behavior, as species under increased predation risk often become more elusive and are thus less likely to be detected on our cameras.”

Sharks matter more than you think

These findings offer clear evidence that losing a top predator affects far more than just one species. It sends a shockwave through the entire ecosystem.

“Without these apex predators to regulate populations, we are seeing measurable changes that could have long-term effects on ocean health,” said Hammerschlag.

As ocean systems continue to face threats from climate change, pollution, and overfishing, the study makes one thing clear: protecting sharks isn’t just about saving one species – it’s about preserving balance in marine ecosystems.

With so much of the world relying on healthy oceans for food, recreation, and natural services, the role of large sharks is too important to ignore.

A warning for other ecosystems

False Bay may be the focus of this study, but it’s far from the only place where shark populations are under pressure.

Similar patterns of disruption could be unfolding in other coastal ecosystems around the world where large predators are disappearing.

This study serves as a warning: the health of marine environments depends on keeping their food webs intact.

Efforts to protect sharks – through conservation policies, public awareness, and improved fishing practices – are vital not just for the species themselves, but for the oceans they help keep in balance.

The full study was published in the journal Frontiers in Marine Science.

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