Running Hot: The Surprising New Threat Facing Great White Sharks

17 June 2026 | White Shark Ocean

For millions of years, the great white shark has been the ocean's most formidable predator. Built for speed, power and endurance, it has outlasted ice ages, mass extinctions and the rise and fall of entire civilisations. But a new study published in the journal Science this April reveals an unexpected vulnerability baked into the very biology that made it so successful — and warming oceans are now exploiting it.

The Hidden Cost of Running Warm

Great white sharks are what scientists call mesothermic — meaning they keep their bodies significantly warmer than the surrounding water. This isn't just a quirk of biology. It's the secret weapon behind their explosive speed, sharp senses and ability to hunt across vast ocean distances. By running warm, great whites can react faster, swim harder and track prey over thousands of kilometres of open ocean.

But that warmth comes at an enormous metabolic cost. Researchers at Trinity College Dublin and the University of Pretoria found that warm-bodied fish like great whites burn nearly four times more energy than cold-blooded species of similar size. They are, in effect, running a high-performance engine that constantly needs fuel.

Now picture that engine in an ocean that's getting steadily hotter.

A Double Jeopardy

As sea temperatures rise, great white sharks face what the researchers describe as a "double jeopardy." First, warmer water makes it harder for them to shed excess body heat — a one-tonne warm-bodied shark may struggle to remain in waters above 17°C without risking overheating. Second, the very food sources they depend on to fuel their energy-hungry bodies are declining, largely due to decades of overfishing and bycatch.

"If you're a shark, you can't just pop down to the supermarket and buy more food," said Professor Nick Payne, the study's lead author. "We're seeing animals move with climate change in every biome on land and in the sea; this is just another example of that mechanism."

The consequences reach far beyond the sharks themselves. Great whites are apex predators — keystone species whose presence shapes the entire food web beneath them. As their habitats shrink and their ranges shift, the effects ripple through entire marine ecosystems.

Why This Matters in Mossel Bay

Here in South Africa, the implications hit close to home. The study specifically highlights the decline of great white shark sightings in South African waters — including False Bay, Gansbaai and Mossel Bay — as an early signal of this thermal shift in action. Stephanie Nicolaides, a marine conservation researcher at the University of the Western Cape, describes the great white as a sentinel species: when their patterns change, it signals a deeper transformation in the marine environment.

The good news is that conservation science and eco-tourism are increasingly working hand in hand to reframe the great white's story. No longer cast as the ocean's villain, it is now understood as a keystone species essential to ocean health — and a powerful symbol of what we stand to lose if we fail to act.

The Ghost in the Mediterranean

The overheating story isn't the only major great white news of 2026. In March, researchers revealed the discovery of a juvenile great white shark caught by fishermen in the Mediterranean — reigniting a 160-year scientific mystery about a so-called "ghost population" that may still be quietly reproducing in the region. The find offers a rare glimmer of hope: that in some corners of the ocean, great whites are hanging on against the odds.

What We Can Do

The researchers are clear on the most urgent priority: tackling the fishing crisis. Bycatch — sharks and other marine life caught unintentionally in commercial fishing operations — remains the single greatest acute threat to great white populations worldwide. Climate change compounds this pressure, but overfishing is the lever we can pull right now.

For those of us fortunate enough to share the ocean with these extraordinary animals — whether in the water, on a cage boat, or simply from the shore — this research is both a warning and a call to action. The great white shark has survived 45 million years. Whether it survives the next 50 depends largely on the choices we make today.

Want to see great white sharks in their natural habitat and support shark conservation? Find out more at whitesharkocean.com.

Frequently Asked Questions

What does mesothermic mean in sharks?

Mesothermic means an animal can maintain its body temperature warmer than the surrounding water, without being fully warm-blooded like mammals. Great white sharks are mesothermic — they use metabolic heat to keep their muscles, eyes and brain warmer than the ocean, giving them a significant advantage in speed, reaction time and sensory ability. However, this comes at a high energy cost, burning nearly four times more energy than cold-blooded fish of the same size.

How does climate change affect great white sharks?

Rising ocean temperatures create a "double jeopardy" for great white sharks. Warmer water makes it harder for them to shed excess body heat, pushing them towards the edges of their thermal tolerance. At the same time, the prey fish they depend on are declining due to overfishing and ecosystem disruption. This combination of overheating risk and food shortage is forcing great whites to shift their ranges, with some populations already showing dramatic declines in their traditional habitats.

Are great white shark numbers declining in South Africa?

Yes. Great white shark sightings have dropped significantly across multiple South African locations including Mossel Bay, False Bay, Gansbaai and Plettenberg Bay. The causes are complex — including predation by orcas, mortality from shark nets and drum lines, overfishing of prey species, and increasingly, the effects of ocean warming. South Africa was once the global heartland of great white shark abundance, making these declines particularly alarming for the species as a whole.

What is bycatch and why does it threaten great white sharks?

Bycatch refers to marine animals accidentally caught in commercial fishing nets and lines that are targeting other species. Great white sharks are frequently caught as bycatch in longline fisheries, gill nets and trawl operations worldwide. Because great whites reproduce slowly — reaching maturity at around 15 years of age and producing small litters — even modest levels of bycatch mortality can have a serious long-term impact on population numbers.

Can I still see great white sharks in Mossel Bay?

Yes — Mossel Bay remains one of the best places in the world to see great white sharks in the wild. White Shark Ocean operates cage diving and surface viewing expeditions in Mossel Bay, giving visitors the chance to encounter these remarkable animals up close while directly supporting local shark conservation efforts. Visit whitesharkocean.com to book.