Why great white sharks are overheating—and what it means

If you’re wondering whether great white sharks can overheat in warming oceans, the short answer is yes. Their bodies are designed to hold onto heat so they can hunt in cold water, but that same system makes them less able to dump excess heat when the sea gets too warm. During marine heatwaves or in warm surface layers, the shark’s internal temperature can climb to levels that stress the heart, muscles, and brain.

This matters because great whites sit at the top of the marine food web. Thermal stress can alter where and when they feed, push them to new coastlines, and compress their safe habitat into deeper, cooler layers. The result is a reshuffling of ecosystems, new bycatch risks for fisheries, and shifting patterns of human–shark encounters near coasts.

What “overheating” means for a shark

Most fish are ectotherms—they match the temperature of the water. Great whites (Carcharodon carcharias) are different. They are regionally endothermic: certain body regions run warmer than the surrounding sea thanks to specialized heat exchangers called retia mirabilia. This trait evolved in several fast, active fish lineages (including tunas) and in lamnid sharks such as makos, porbeagles, and salmon sharks.

• Heat is generated by red swimming muscles, and by digestion after a large meal.
• Retia mirabilia—dense networks of blood vessels—recycle that heat, keeping the red muscles, stomach, and sensitive organs (eyes and brain) warmer than ambient water.
• A warmer core lets great whites sprint, digest efficiently, and see better in cold, dark water, opening up hunting grounds that are too chilly for many predators.

A built‑in radiator that can backfire

Like any warm machine, a shark must get rid of extra heat. It does so mainly by:

• Moving cooler water across the gills and skin
• Shunting warm blood toward the body surface, where heat diffuses out
• Seeking cooler layers or latitudes to increase the heat gradient between body and water

As surface waters warm, the temperature gap between the shark’s interior and the environment shrinks. That reduces the rate of heat loss. After a burst of activity (chasing prey, evading a threat) or after a big meal (which raises stomach temperature during digestion), the shark may not shed heat fast enough. Internal temperatures can climb into a zone that compromises performance—this is “overheating” in a physiological sense.

Two other physics‑of-life facts stack the deck:

• Metabolic Q10: As water warms, metabolic reactions speed up (often ~2–3× for a 10°C increase). Warmer seas make sharks burn more oxygen even while their ability to cool off is reduced.
• Oxygen solubility: Warm water holds less dissolved oxygen. So just when a shark needs more oxygen to power a higher metabolism and pump heat out across the gills, there is less oxygen available.

Together, these forces raise internal heat and push the cardiovascular system harder, a combination that elevates stress and narrows the safe operating window.

Why great whites may be more vulnerable than other sharks

Not all sharks retain heat. The very system that supercharges great whites also limits their ability to cool off.

• Highly efficient heat retention: Retia mirabilia and a large, insulated body make heat loss slower. That’s great in 10–15°C water. It’s a problem in 22–28°C water after a sustained chase.
• Cardiac constraints: In many warm‑bodied fishes, the heart itself stays relatively close to ambient temperature. At the upper end of their thermal range, electrical signaling and calcium cycling in heart muscle can misfire, limiting cardiac output and, therefore, oxygen delivery.
• Size and scaling: Large, thick‑bodied predators shed heat more slowly (lower surface‑area‑to‑volume ratio). Juveniles can sometimes cool faster than big adults, but juveniles also spend time in shallow nursery grounds—the places most affected by heatwaves.
• Daily heat spikes: Great whites experience large post‑prandial (after eating) heat loads as digestion ramps up. Add a marine heatwave on top and safe temperatures can be exceeded sooner and for longer.

Other sharks that don’t have strong heat‑retaining systems can dump heat more easily and may tolerate short warm spells better. But lamnids—the fast, warm‑bodied group that includes great whites, shortfin makos, porbeagles, and salmon sharks—share similar risks in hot water.

What changed in the ocean

The underlying ocean has shifted in ways that increase “overheating” risk for warm‑bodied sharks:

• More frequent, intense marine heatwaves: These are multi‑day to multi‑month events when sea surface temperatures spike well above normal. They are happening more often and lasting longer.
• Stronger stratification: Warm layers cap the ocean and reduce mixing with cooler, oxygen‑rich waters below. The cool refuge can sit deeper, farther from the surface zone where many coastal predators feed.
• Deoxygenation: Global ocean oxygen levels are trending downward. Even modest drops matter to large, active animals with high oxygen demand.
• Shifting prey: Many prey species are moving poleward or deeper to track their preferred temperatures, forcing predators to follow and sometimes trapping them in warmer, low‑oxygen layers.

What overheating looks like in behavior and range

Researchers tracking great whites with satellite and archival tags report several heat‑avoidance behaviors that become more common or more extreme during warm spells:

• Deeper daytime diving: Individuals spend more time below the warm surface layer (thermocline) where water is cooler and oxygen may be higher.
• Nighttime surfacing: Surface waters can cool at night, briefly improving the heat gradient for shedding excess heat.
• Habitat compression: When the surface warms and the cool layer shoals or deepens beyond a comfortable oxygen zone, sharks are squeezed into a narrower band of depths and temperatures, making them more predictable—and more vulnerable to fishing gear.
• Poleward or seasonal shifts: Observations and catch records show changes consistent with white sharks appearing farther from historical hot spots during very warm years, and showing up more often in higher‑latitude coasts that used to be too cold for consistent use.

None of these patterns are caused by temperature alone; prey availability, predators (including orcas), and human activity also play roles. But temperature sets the backdrop that frames those choices, and heatwaves are tilting the stage.

Implications for people, ecosystems, and management

• Ecosystems: Great whites shape prey behavior and population structure. If thermal stress reduces their hunting efficiency or pushes them away from core foraging grounds, mid‑level predators can surge, and cascading effects ripple down to forage fish and invertebrates.
• Fisheries: Habitat compression and range shifts can increase bycatch when sharks crowd into places and seasons with intense fishing. Conversely, sharks may vacate areas where fisheries traditionally avoided them, creating surprise interactions elsewhere.
• Coastal communities: Warmer summers can temporarily drive sharks offshore or deeper, then bring them inshore when upwelling or cold eddies form. Communities may see unusual spikes or lulls in local sightings. Heatwaves do not automatically mean more bites, but they can change when and where sharks and people overlap.
• Management: Static protected areas aren’t enough when habitat edges move week to week. Dynamic ocean management—using real‑time temperature, oxygen, and animal tracking—can help time closures, route vessels, and guide fishers to reduce bycatch while maintaining catches.

How scientists study shark temperature and stress

Directly measuring a free‑swimming great white’s internal state isn’t easy, but several tools now make it possible to piece together the picture:

• Pop‑up archival tags (PATs): Record depth, temperature, and light. They detach and transmit summarized data, revealing how sharks respond to heat in three dimensions.
• Acoustics and satellite telemetry: Real‑time movements tied to temperature maps help identify heat‑avoidance thresholds and preferred isotherms (temperature bands).
• Stomach‑temperature pills and gastric sensors: Show post‑feeding heat spikes and digestion timing in the wild.
• Inertial sensors (accelerometers): Quantify bursts of activity that generate heat and oxygen demand.
• Comparative physiology: Lab studies on closely related lamnids and tunas illuminate how warm‑bodied fish hearts, muscles, and nerves cope—or fail—at high temperatures and low oxygen.
• Bioenergetic and habitat models: Combine shark physiology with ocean forecasts to map when and where overheating risk is highest, including during marine heatwaves.

What we still don’t know

• Precise upper thermal limits: We know great whites avoid very warm layers, but the exact temperatures and durations that cause cardiac or neurological failure in the wild are still being narrowed.
• Acclimation capacity: Some fishes adjust their proteins and membranes over weeks to function better at new temperatures. How much thermal plasticity great whites have—especially across life stages—is unclear.
• Generational adaptation: Evolution can shift thermal tolerance, but large, slow‑reproducing apex predators adapt far more slowly than the rate of current ocean warming.
• Interactions with oxygen and prey: Temperature alone tells only part of the story. How heat, oxygen, and prey availability combine to shape real‑world risk is an active area of research.

What you can do

• Support dynamic ocean management: Back policies and tools that use live data to reduce bycatch and protect critical habitat when and where sharks actually use it.
• Choose seafood wisely: Favor fisheries certified for low bycatch and strong monitoring.
• Reduce emissions: Ocean warming and deoxygenation are driven by greenhouse gases. Individual and policy‑level actions both matter.
• Back tagging and citizen‑science programs: Data from responsibly designed tagging efforts and verified sighting networks improves forecasts and management.
• Respect wildlife closures and advisories: Give room to areas set aside during heatwaves or upwelling events—those may be temporary lifelines for heat‑stressed animals.

Key takeaways

• Great whites are regionally endothermic; they retain heat to hunt in cold water.
• In warm seas, their ability to shed heat drops just as metabolic and oxygen demands rise.
• Marine heatwaves, stronger stratification, and deoxygenation intensify overheating risk.
• Behavioral responses include diving deeper, shifting range, and compressing into cooler layers.
• Lamnid sharks (makos, porbeagles, salmon sharks) share similar vulnerabilities.
• Dynamic, temperature‑aware management can reduce bycatch and protect shifting habitat.

FAQ

• Are great white sharks “warm‑blooded”?
  They’re regionally endothermic, not fully warm‑blooded like mammals. Key muscles and organs are warmed above ambient water using specialized blood‑vessel networks.

• What temperatures are dangerous for great whites?
  They generally avoid very warm surface waters, but exact danger thresholds vary with activity, oxygen, and individual size. Risk rises during heatwaves, after intense activity, and post‑feeding.

• Does warming water mean more shark attacks?
  Not necessarily. Warming changes where and when sharks and people overlap. Local spikes or lulls in sightings can occur, but bites depend on many factors, including prey, water clarity, and human behavior.

• Are other sharks affected the same way?
  Sharks without strong heat‑retention systems may dissipate heat more easily. Lamnids—great whites, makos, porbeagles, and salmon sharks—face similar overheating constraints.

• Can great whites adapt to warmer oceans?
  Short‑term acclimation may help a little, but long‑term genetic adaptation is slow for large, late‑maturing predators. Management that reduces other stresses (bycatch, habitat loss) can buy time.

• How do scientists know sharks are overheating?
  Telemetry and archival tags track how sharks change depth and temperature use during warm events. Stomach and muscle temperature sensors, plus insights from related species, show how internal heat and cardiac performance shift with warming.

• What helps reduce risk right now?
  Heatwave forecasting, dynamic fishing closures, better bycatch mitigation, and protecting cool‑water refuges along migratory routes.

Source & original reading: https://arstechnica.com/science/2026/04/great-white-sharks-are-overheating/